VOLUME 2

 

CHAPTER FIVE -CAUSATION 1

 

5.1 The Parties’ Cases on Causation

5.1.1 The Closed Record

The pursuers’ case as pleaded is that the initial explosion and subsequent explosions and fires on the platform occurred as a result of a leakage of condensate from a blind flange assembly at the site of a pressure safety valve (hereinafter referred to as PSV 504) which was not leak tight. That pressure safety valve was normally connected to pipework in Module C of the installation. Module C was at the 84-foot level of the platform. PSV 504 serviced a pump known as pump A being one of two condensate-injection pumps situated at the 68-foot level of the installation . The other condensate-injection pump was situated close to pump A at the 68-foot level and was known as pump B. The two condensate-injection pumps were part of the production processing plant on the installation. On the date of the accident pump A had been taken out of service for maintenance and repair. Pump B was in operation. When taken out of service pump A and its associated pipework had been isolated and depressurised. Valves known as gas operated valves (hereinafter referred as GOV or GOVs) required for its operation had had their air supply disconnected. On the said date PSV 504 was removed by Alexander Rankin and Terence Sutton (now deceased), both employees of Score, then acting in the course of their employment. Terence Sutton died in the accident. PSV 504 was removed by the said Score employees for recalibration and re-certification. The intention was refit PSV504 to its site on the pipework that same day. Once PSV 504 had been removed it was the task of the said employees of Score to fit two blind flanges on to the pipework left open by the removal. In particular a class 900lb blind flange was to be fitted on the upstream side at the site of PS 504. On the said date two blind flanges were fitted to the pipework at the site of PSV by Terence Sutton although it is believed that he may have fitted a 1500lb blind flange to the upstream side. At the end of their working day (before 6pm) the re-calibration and re-certification work being carried out by said employees of Score on PSV 504 had been completed. They stopped work at about said time. The upstream blind flange remained in situ. PSV 504 was not replaced although the intention had been that it would be replaced during the working day. During the evening of said day pump B tripped. The running of the process plant on the installation at said time was under the control of Robert Vernon (now deceased) Lead Production Operator. Robert Vernon was then acting in the course of his employment with pursuers. Also directly involved in the running of the process plant at said time was Robert Richard (now deceased) the Phase 1 Operator. Both Robert Vernon and Robert Richard died in the accident. Robert Richard was also acting in the course of his employment with the pursuers. Following upon the tripping of pump B, Robert Vernon decided pump A should be brought back into service. To bring pump A into service, it was necessary, inter alia, to reconnect the air supply to the GOVs. It was then necessary to check that the air supply was correctly fitted and to begin re-pressurising pump A.

Re-pressurising was done by jagging open the GOV on the inlet side of the pump. Jagging was done by the operation of a push/pull button located near pump A. Said air supply was re-connected and said jagging took place. These operations allowed condensate to pass through pump A and to move through the line of pipework leading from the discharge side of pump A line to the upstream blind flange assembly at the site of PSV 504. Condensate thereafter escaped through an aperture or apertures between the pipework and the upstream blind flange, because the blind flange assembly was not leak- tight. The upstream blind flange had not been fitted securely to the pipework by the said employees of Score. After condensate escaped, it vaporised and ignited, causing the explosions and fires hereinbefore referred to. The initial explosion occurred at about 2200 hours on said date. At that time the wind direction was 164 degrees true and the wind speed was south south-east 3, 16.4 knots. The initial explosion was in Module C and it caused damage to said module and its firewall. Damage was also caused to the condensate line in Module B resulting in a release of condensate. Damage was also caused to Module B which resulted in a continuous release of oil.. Hereafter, a further major explosion occurred some twenty minutes after the initial explosion upon the failure of the Tartan Riser. This resulted in an even more substantial fire. A further major explosion occurred some 50 minutes after the initial explosion upon the failure of the MCP-01 Gas Riser. Other explosions also occurred and eventually there was a structural collapse of the installation. The pursuers tried to establish the foregoing version of the accident although they did not seem seriously concerned to prove that the wrong size of flange may have been fitted

The defenders replied in their pleadings by admitting that PSV 504 normally connected to the pipework in Module C which was at the 84-foot level, that the valve serviced one of the two condensate injection pumps at the 68-foot level, and that these pumps were part of the production processing plant. They further admitted that on the date of the accident pump A had been taken out of service for maintenance, that PSV 504 had been removed by Alexander Rankin and Terence Sutton (now deceased ) before they fitted the blind flange assembly, that these operatives were employees of Score acting in the course of their employment, and that the valve had been removed by these employees from the line of pipework leading from the discharge side of pump A for re-calibration and re-certification. It was admitted that once the pump had been removed it was Sutton’s task to fit blind flanges to the pipework left open by the removal, and that he had thus fitted them, that on the evening of the said day pump B tripped, that the running of the process plant was under the control of the Lead Production Operator, Robert Vernon, and that he was acting in the course of his employment with the pursuers. It was admitted that in order to bring pump A into operation it was necessary inter alia to re-connect the air supply to the GOVs and that there were a number of explosions on the installation beginning about 2200 hours on that date eventually leading to a structural collapse of the installation. Otherwise the pursuers’ averments as to the facts of the accident are denied. The defenders went on to aver that the pursuers’ hypothesis of the initial explosion in Module C is not consistent with noises heard on the platform shortly before the explosion, damage to the area of the dive skid, and the sequence of gas alarms which occurred immediately prior to the explosion, the first of which was a low level alarm. The damage to the platform was said to have been consistent with an explosion initiated in Module B and propagated through a breach in the wall between Modules B and C. The defenders further averred that immediately after the initial explosion fire was seen to have broken out in Module B and that after the tripping of condensate injection pump B, but before the explosion and immediately before the first gas alarms a centrifugal compressor tripped. This it was claimed was consistent with upset conditions in Module B in the process equipment located upstream of the compressors which would have brought about the discharge of flammable vapours. It was further claimed that there was a sudden and material drop in the flow of oil from Piper Alpha at least seven minutes before the initial explosion. The source of oil from the platform was the separation plant in Module B the module being open at the west and east ends to encourage a flow of air. At the time of the explosion air would have passed from west to east through the Module (a fact about which the parties were not in dispute). The suggestion averred is that gas and other vapours would have been discharged out of the open east end of Module B and thereafter ingested by the air intakes for the centrifugal compressors at the east end of Module C. The first low level gas alarms prior to the initial explosion were said to have been at the centrifugal compressor in Module C. The alarms which followed were said to have been at the east end of C and the high level alarm immediately preceding the initial explosion was at one of the centrifugal compressors. Moreover it was said that the status of fire and gas alarms in Module B at the time of the accident is not known and welding was being carried on in the Module on the day of the accident. This work was liable to set off fire or gas alarms which were not inhibited or isolated. It is averred that gas alarms in a particular zone may be inhibited during maintenance work by "pinning out" but this line of defence was not insisted upon at the proof.

The defenders further pleaded that planned maintenance of Fire and Gas Area B2 commenced on 29 June 1988. Blind flanges at the site of PSV 504 were fitted by Sutton. He was an experienced and conscientious worker. He would, as a matter of ordinary and usual practice, have tightened or "flogged up" the studs of the blind flanges. There was no reason for him not to have followed such ordinary and usual practice when fitting the blind flanges at the site of PSV 504. It is further averred that in any event an escape of condensate from the upstream blind flange assembly at the site of PSV504 would not have produced the vapour distribution for the initial explosion.

The pursuers for their part admit that the first gas alarm prior to the initial explosion was a low level alarm at the site of centrifugal compressor C and that after the tripping of pump B and before the explosion all three of the centrifugal compressors tripped. It is admitted that the further low level gas alarms which followed were at the east end of Module C although it is claimed that not all of the alarms related to the centrifugal compressor there. However it is admitted that the high level gas alarm immediately preceding the explosion was at one of the centrifugal compressors. The fact that Module B is open at the east end to encourage a flow of air is admitted as is the fact that at the time of the explosion the air flow would have been from west to east. It is also admitted that gas and other vapours discharged at the east end of Module B could have been discharged through the open end of the module. It is accepted that the air intakes of the centrifugal compressors in Module C were located at the east end of the module (although outside the module). There agreement in the pleadings on the relevant matters stops. However the pursuers go on to aver that any drop in the oil flow which occurred was as a result of the tripping of pump B and the actions consequently taken by the operators. The reciprocating compressors were unloaded and put on recycle, bringing a loss of gas lift and a reduction in production. It is said that no gas detectors or alarms in Module B would have required to be inhibited in order for welding work to be carried out and furthermore no maintenance work on the gas or fire detectors was being carried out on 6 July 1988. There were no Permits to Work relating to Module B extant on the installation at or about the time of the original explosion. No detection of gas or other flammable vapours was annunciated in Module B at or about the time of the original explosion. Any significant quantity of gas or other vapours discharged in Module B would have activated the gas detectors situated at high and low levels within the module and any such release would have been accompanied by a release of hydrocarbons. It is averred in addition that any major failure in process equipment located upstream of the centrifugal compressors in Module B which were liable to bring about a discharge of a sufficient quantity of flammable gas would have been annunciated in the control room or would have caused the plant or equipment concerned to trip. It is claimed that any significant quantity of gas or vapour in Module B that would have caused failure of the B/C firewall would also have caused failure of the A/B firewall. The said firewall is said not to have failed. As a separate matter it is averred by the pursuers that even if Module B had been completely filled with a stiochiometric mixture of gas and vapours resulting in an escape of gas from the east end of Module B so as to be ingested by the air intakes of the centrifugal compressors in Module C such a sequence of events would not have resulted in the pattern of gas alarms which in fact occurred in Module C. It is further said that any damage in the area of the Dive Skid was not inconsistent with an initial explosion in Module C. All the gas alarms which annunciated were related to the south-east part of Module C and were consistent with a leak of condensate in the said module. Nor was another gas alarm set-off in the installation in the period shortly prior to the explosion. The tripping of the centrifugal compressor is consistent with the tripping of condensate injection pump B especially in consequence of the actions taken to recycle and unload the former. In summation the pursuers aver that the general pattern of damage and lack of damage, the pattern of gas alarms , the double escape preceding the explosion, the actions of the process operators at or about the time of the initial explosion, the vapour and fireball seen from the 68-foot level immediately following the initial explosion, the blue flash seen at the initial explosion, the lack of hot gas or flame in the control room, the rush of cold air into the mechanical workshop immediately after the initial explosion and the damage to the condensate line in module B and resulting fireball, are all factors indicative of Module C being the location of a condensate leak and of the initial explosion.

Thus the parties set out their respective cases on causation and although the averments do not appear to be unduly expansive they proved to be capable of generating an immense volume of evidence. It should perhaps be observed that I was only informed shortly before the proof that the defenders by way of an amendment decided to challenge the pursuers’ hypothesis that the accident had resulted from a leak in Module C.

5.1.2 The Parties’ Contentions

The pursuers’ principal contention on causation as has been seen is that the explosion was caused initially by an escape of condensate in Module C as a result of a blind flange being inadequately attached to the pipework to the upstream of PSV 504 which had been removed from its location for maintenance. The pursuers accepted that their case on causation was entirely circumstantial. To bring themselves within the indemnity provisions attached to the contracts with the contractors they clearly had to prove that an accident had occurred that justified them in paying damages to the claimants and I think they accepted that this involved requiring to prove what had caused the accident. The parties’ respective cases of course, and sadly, were handicapped by the fact that so many persons on the platform when the accident occurred, and who very likely could have given important evidence, had perished. Moreover most of the relevant records and equipment lay for practical purposes irrecoverable at the bottom of the sea. The pursuers emphasised that they were relying heavily on the incidence of the gas alarms to pinpoint that the explosion had happened in Module C. It is claimed that there was a fully effective system of gas alarms in both Module B and Module C so that the absence of any prior alarm in B strongly militates against the possibility that the explosion originated in B. The pursuers also argued that the evidence from witnesses who were in vessels standing off the platform and who observed certain features of the accident supports the view of the pursuers that the accident originated in Module C. In this regard particular weight was attached to the evidence of the witness Captain Clegg who said in evidence that as the first explosion occurred he saw a blue flash emanating from Module C. Mr Miller who took photographs from the support vessel Tharos almost immediately after the explosion was able to produce prints which showed light grey smoke coming from the west face of Module C. Other witnesses were off the east face of the platform at the time of the explosion. Captain Morton was thus placed on the Maersk Cutter and he saw a substance like smoke which he pinpointed to the east face of module C. Mr Flaws was also on the Tharos and has first observation after hearing the bang was to see dark smoke rising from the east face of the platform. He also saw a ball of flame in module C which could have been the residual burning after an explosion there. In relation to witnesses who were survivors from the platform it was claimed that the witnesses Mr Bollands and Mr Clark (both of whom had been in the control room in Module D when the accident occurred) had each been moved by the blast in such a way as to suggest that the C/D firewall had collapsed. Indeed it is significant that Mr Bollands described the effect of the explosion as being " the wall coming in". This it was argued was more consistent with an explosion in C than B. Similarly witnesses who had been having tea in the same maintenance unit in Module D had experienced the blast in a way which suggested that the C/D firewall was not intact. A Mr Elliot working on the west face of the platform at the 68-foot level almost directly below Module C had described how he had been " beaten to the ground" by the explosion. A Mr Young who had descended to the 68-foot level just before the explosion, after it occurred, experienced a rush of hot air from the direction of the stairs behind him leading to Module C. It was said that the damage to such equipment as was available to be observed immediately following upon the explosion also pointed to Module C as being the source of the explosion. Thus the witness Mr McGregor spoke to main oil line pump panels being damaged and these had been located in Module C. Likewise the Chanter Riser Gantry had been damaged in a manner consistent with the blast having come from C. There was other damage to the mechanical workshop doors, the instrument workshop door, and the divers’ decompression chamber door that at least were consistent with Module C having been the explosion point. With regard to the photographs taken by Mr Miller, these showed that the fire had spread to the north face of the platform and that could only be consistent with the failure of the C/D firewall. It was of course accepted that immediately following upon the initial explosion a substantial degree of fire was seen in Module B but this was ascribed to the effects of an explosion in C which caused the B/C firewall to collapse thus causing a fire to break out in B. One feature of the fire observed in Module B was said by the pursuers to have been a fireball. It was said that the experts had agreed that this fireball was consistent with a high pressure release of condensate into an existing fire-ground. If an explosion in Module C had caused the firewall between Modules C and B to fail then this would have generated enough energy to cause projectiles capable of rupturing the condensate line in Module C bringing a release of condensate sufficient to cause the fire phenomena observed in B. Senior Counsel for the pursuers accepted that if the explosion can be shown to have occurred in Module C he is left with the need to prove just what caused that particular explosion. As a preliminary to this, the determination of the location within Module C where the explosion originated would be important. The two contentions which the pursuers particularly sought to rely upon in this regard are the submission that the explosion was from a source that produced a release of heavier than air hydrocarbon gas and that the release created a flammable cloud near the eastern end of Module C. These requirements it was said can be satisfied if the gas concentration originated from a leak from the blind flange attached to the pipework of PSV 504. This hypothesis is supported by the evidence of Captain Clegg who deponed that the blue flash he saw was at a low level suggesting that the fuel was a heavier than air fuel. The witness

Mr Grieve had seen a ball of flame burning near the ceiling of the 68-foot level which suggested that it was caused by heavy fuel penetrating down from Module C above. Mr Bollands and Mr Clark in the Control Room which was situated at the mezzanine level of Module D did not experience the in-rush of any hot combustion gases whereas Mr Young at the 68-foot level had felt a rush of hot air at the stairs leading to the 84-foot level. It was said that the contention that the fuel which caused the initial explosion was a fuel of the character of condensate was vouched by the expert, Dr Davies, who had carried out certain wind-tunnel experiments. He is claimed to have established that only condensate could cause the pattern of gas alarms observed before the explosion. If the explosion had been towards the west side of the platform the fire and smoke observed by witnesses off the platform would have been different. Given that the gas must have first gathered at the east end of Module B then it was claimed that the evidence proved that the likeliest source of this gas was an escape of condensate under pressure from the said blind flange. The evidence most suggestive of this fact was to be found in the operative activity going on at the time of the accident in the vicinity of the condensate injection pumps. A decision had been taken to put pipe A back into operation to compensate for the pipe which had failed and this meant that the pump had to be repressurised by the process called jagging which was intended to lead to the gradual re-introduction of condensate to the pump. It was not disputed that it would not be in accordance with proper practice to run the pump at a time when PSV 504 was missing. It was contended that looking to the evidence of Dr. Richardson, in the process of jagging, condensate would have been able to pass quickly through the pump A and to the site of PSV 504. The introduction of gas during the jagging process would have produced a small leak which would have caused the first gas alarm which was observed. A continuation of the jagging process would have produced a larger escape of gas which would have produced the flurry of alarms immediately before the explosion and the explosion itself. It was contended that the noise that was observed just before the explosion was consistent with the escaping of condensate through a small aperture under pressure. The scientific evidence led by the pursuers was said to support the pursuers’ hypothesis. Moreover the defenders it was claimed had not led any evidence - particularly expert evidence - giving specific support to any contrary explanation of the explosion and in particular relating it to Module B. Indeed the fact that no gas alarms had been noted in Module B prior to the explosion discounted the possibility that it had been the location of that explosion. Moreover there had been no indication by way of process alarms or otherwise that there had been any process upset in Module B. Everything which happened after the initial explosion in Module C was clearly a consequence of that explosion . Furthermore the evidence (and in particular evidence of recordings taken at the Flotta terminal), it was said, did not show any reduction of oil flow prior to the explosion as the defenders contend. Moreover the off-shore observations contradict any possibility that the explosion originated in Module B. The witnesses confirm that the A/B firewall was intact after the explosion.

The defenders did not attempt to argue that any particular explanation for the accident alternative to the pursuers’ explanation had been proved. Indeed in cross-examining the various experts they did not seek to bring out that any particular alternative to the pursuers’ case had probably caused the accident. Essentially their approach was to attack the reliability of the evidence which the pursuers claimed substantiated their case and also the inferences that the pursuers seek to draw from such of the evidence as might be accepted. The defenders would be quite content if the determination was simply that the cause of the accident had not been proved. The starting point of the defenders’ case is that most unfortunately most of the critical witnesses had been killed in the accident. This included persons whose evidence would have been of major importance such as Mr Vernon, the Lead Production Operator who is partly blamed for the accident, Mr Sutton, the Valve Fitter also blamed for the accident and Mr Richard the operator working with Mr Vernon when the accident occurred. Other witnesses who are dead and whose evidence might have been of importance included Mr Grant the Phase 1 Operator who was present at least during some of the time, Mr Sutton was carrying out his flange fitting duties and Mr Flook the Lead Production Operator who had handed over to Mr Vernon. Mr Rutherford another possible witness to the flange fitting procedure carried out by Mr Sutton was too ill to give evidence. Moreover the platform’s equipment all ended up at the bottom of the sea so that none is available for analysis. Thus, it was contended, on the limited and inconclusive evidence which remains available any decision ascribing a specific cause to the accident is essentially speculative and thus unjustified. The defenders are correct to the extent that there is less evidence about the accident than the Court would like to have seen and that is an unfortunate but inevitable consequence of the catastrophic nature of what happened. However there is some evidence and the question is what can be taken from it when it is pieced together. If more evidence had been available then no doubt it would not have been necessary to spend almost four years on the proof.

The defenders submitted that the pursuers’ case is based on coincidence such as the fact that Mr Vernon made some observation about starting the decommissioned Condensate Injection Pump. However they claim that there were many other coincidental facts that the pursuers have ignored. One of these is that a few days before the accident OPCAL had switched from Phase 2 operation to Phase 1. This meant that instead of coping with the burning of about 2.5 million cubic feet of gas the production system had to cope with about 15 to 25 million cubic feet. The transfer to Phase 1 operation had been completed on 4 July 1988. The actual transfer operation would have involved the opening of some lines and the blanking off of others. The equipment was much older than it had been during the last period when it had been exposed to Phase 1 operation. It had been years since the equipment had been exposed to Phase 1 Operation. On the other hand Mr Bollands the Control Room Operator said that before the explosion the whole plant had been normal. The relief valves PCV 1000 A and B which had to release the surplus gas had the reputation for not being entirely reliable and they have a reputation for hunting which means that they tend to open too far. These valves are located quite close to PSV 504. The witness Mr Henderson said that when the reciprocal compressors were ever re-cycled PCV 1000A would take a massive thump and I have no reason not to accept this particular evidence. Some minutes before the accident Captain Clegg noticed a substantial increase in flaring which would in itself suggest that the relief valves were performing their function. Moreover if the relief valve had leaked as a result of the unloading of the reciprocal compressors the delay between the unloading and the accident may be difficult to explain. The witness Dr Davies was not asked about this. Just before the accident the centrifugal compressors had tripped. This would have had the effect of re-routing gas through a series of pipes at the east end of Module C. This means that valves that had previously been closed required to open. PCV 50 1 and 2 were located at the north-east corner of Module B and when the centrifugal compressors trip they are going to see a large quantity of gas. However if these particular valves leaked there is a question as to how a sufficient quantity of gas would get from Module B to Module C without triggering alarms in the former. Minutes before the accident a substantial increase in flaring occurred and for what it is worth I accept the evidence to that effect. On the other hand the only relevance of the defenders’ reference to the Phase 1 situation would be to suggest that there may be an alternative to the pursuers’ version of the cause of the accident. However the defenders did not ask Mr Wottge, the main engineer on the platform, if the switch to Phase 1 operation or the implications of re-cycling the compressors could have caused a leak. This must render their submissions about the matter somewhat speculative.

Another factor which the defenders used in an attempt to discredit the pursuers’ arguments on coincidence was that Module B was rated a higher risk zone for hazards than Module C. Module B was in part zoned Zone 1 which indicated that an explosive atmosphere was likely to occur in normal operations. In Zone 2 (the rating for Module C) an explosive atmosphere was not likely to occur in normal operations and if it did it would exist only for a short time. On the other hand I must observe that if the evidence generally points to the explosion having occurred in Module C then that fact would suggest that there had been an abnormality. However the defenders sought to counter this by pointing to the evidence of Mr Wottge that in 1986 further gas detectors were introduced to Module C because of OPCAL’s experience of gas leaks that were not being picked up by the preceding detection system. It has to be noted that Mr Wottge was not questioned about the significance of such leaks and as to whether they were of a scale as could cause the explosion which occurred. In fact were it the operators’ experience that Module C generated dangerous gas leaks the existing zoning would have been inappropriate. The detection system was of course designed to ensure that a leak would set off a low level alarm before the gas cloud reached explosive limits. Moreover according to the expert Dr Davies if there was a release of less than about 4 kgs a minute there would be no alarm at all. It is plain that from time to time small quantities of gas escaped and indeed witnesses such as Mr McLeod, Mr Almeira, Mr Ferguson, Mr Ballantyne, and Mr Henderson all spoke to occasions when they had smelt gas but below alarm levels and without apparent consequences.

The defenders submitted an argument that the source of the leak may have been the centrifugal compressor discharge scrubbers. But these were sited at the north side of Module C and it may be difficult to explain how a leak there could have triggered the first alarm at C3. Dr Davies certainly did not consider that the alarm patterns was consistent with a leak at that source. It was further said that at the changeover between the phases a certain amount of gas under pressure would have been trapped in the pipework. However any such exposed pipework would have been protected by spading and pressure tested flanges. They had served for 3 or so days after the changeover without any trouble and there was no expert evidence as to how such a situation could have caused a 2 stage gas release.

Of course the defenders also submit that there was no evidence that would justify a conclusion that shortly before the accident Mr Vernon had actually introduced condensate to pump A. Indeed a sound analysis of the evidence would, so it was claimed, point in the opposite direction. There was also, it was said, no evidence that the blind flange protecting PSV 504 had been improperly fitted. Certainly nobody actually witnessed gas escaping from the blind flange.

Moreover it was submitted that there was evidence that shortly before the accident the Prover Loop had been removed from its site for maintenance. It is correct to say that this is what the evidence established. The defenders pointed out that the Prover Loop was situated quite close to where there was a door between Modules B and C. With the Prover Loop out of commission use was made of a temporary Loop which was connected and disconnected as required. The defenders contended that the Prover Loop arrangement could have been a source of leak. Moreover as I have already indicated there was evidence that during the shift preceding the accident the door on the B/C firewall had been seen to be open. It was suggested that this could have admitted gas from an escape in B to Module C. Indeed Dr Davies had said that in certain circumstances gas coming through this door could trigger gas detectors in Module C.

It would be mistaken, as the pursuers were said to have done, to elevate a possibility to a probability. The pursuers, it was maintained, had failed to prove the primary facts from which they sought to draw inferences. In other words the necessary links in the chain had not been proved.

The defenders contended that because of the nature of the gas detection system a proper analysis of the evidence would show that an escape from PSV 504 could not have caused the particular alarm patterns that Mr Bollands, the Control Room Operator observed. The point was made that it is not possible to make a circumstantial case if there are elements in the chain of circumstances which are doubtful or even contradict the inference that the pursuers seek to draw.

5.2 Defenders submissions on Requirements of Proof

5.2.1 Standard of Proof

The starting point for the defenders’ submissions on this matter was the trite proposition that the onus is on the pursuers to prove their case on a balance of probabilities. It was said that it is not enough for the pursuers to claim that their hypothesis of the cause of the accident is the only possibility that has been established. Nor would it suffice for the pursuers to argue that their hypothesis is the most likely of the possibilities that have been considered. They must fulfil the complete responsibility of proof and show that the cause of the accident which they espouse is the probable cause. I was referred to Rhesa Shipping Company v Edmunds and Fenton Insurance Company (1985) 1 WLR 948. In this case a motor vessel had sunk rather mysteriously in calm seas. The Owners claimed to recover insurance under a policy that insured them against ‘Perils of the Sea’. At the trial the Plaintiffs’ explanation for the accident eventually resolved itself to being that the accident was caused by a collision with an unidentified, submerged submarine. The trial judge held that although he regarded the plaintiffs’ case as being inherently improbable that nevertheless the plaintiffs’ submarine hypothesis had to be accepted as established on the balance of probabilities. When the case was appealed the Court did not like this and held that something is only inherently improbable if it is not probable. The trial judge’s approach had been based on a position where after hearing 15 experts he was left with two explanations. One was perhaps improbable but the other was even less likely and could not be justified by the evidence. What he then did in effect was to conclude that the accident must have been caused by the least improbable circumstance. It was observed when the case came to the Court of Appeal that it is always possible even after a prolonged inquiry to conclude that the cause of a loss remains in doubt and that the plaintiff’s case has therefore not been established. It was also observed that the fact that the ship had sunk and that it was therefore not possible to examine it weakened the proof. The defenders of course sought to make a parallel with the facts of the present case. Indeed they went somewhat further and suggested that where the whole structure of the platform had been lost all theories as to the cause of the accident could at best be a possible hypothesis rather than a proven cause. If there were two hypotheses suggested namely the Module B hypothesis and the Module C hypothesis then it was not sufficient as the pursuers seemed to suggest that I should hold the most likely established. Simply because one is more probable than the other does not make it a probable cause.

Another observation in the Court of Appeal in Rhesa Shipping Company which the defenders relied on was that although it is open to defendants to advance explanations different to that advanced by a plaintiff yet there is no obligation for them to do. Even in the absence of competing explanations the pursuers have to prove their case. If there are only two explanations for an incident which emerge at a proof there is always the third possibility to be considered namely that the case has not been proved.

The defenders contended that simply because some scientific evidence in the present cases was to lead to the conclusion that a particular hypothesis was well within the bounds of scientific possibility does not elevate the point into a probability.

The defenders also referred to the case of McWilliams v Arrol 1962 SC(HL) 7. In that case a workman was killed when he fell from a lattice tower and the pursuers alleged that the accident had happened because the defenders had not supplied a safety belt. There was evidence that for years he had been provided with a belt and never worn one. Viscount Simons observed that in a claim against a dead man inferences unfavourable to him should not be drawn except on a strong balance of probability. However it has to be noted that his Lordship then goes on to observe that there has to be justice to the living as well as the dead. The defenders submitted that the point of the observations I have just discussed is that if the critical circumstances proved are not straightforward clear and cogent the court has to consider what the material witnesses might have told the Court. Lord Reid in McWilliams observed that the court would not readily infer that a person had acted unreasonably but that in the case before the Court there was in fact evidence that the deceased had persistently acted unreasonably. However the Court would begin its enquiry from the presumption that those concerned did what was reasonable and prudent. The party wanting to displace the presumption would have to prove that there is occasion to do so. The defenders argued in this case that there is no evidence that Mr Sutton did not follow the normal practice and tighten the flange properly. Thus there would have to be compelling circumstantial evidence that he did not do so. In fact in so far as there was relevant direct evidence.

Mr McDonald had seen Mr Rankin attach blind flanges on certain occasions and he said that he always flogged them or tightened them with combination spanners. This differed from McWilliams where the deceased was shown to have been inclined to ignore the proper practice.

The defenders did accept that a case could be proved when a critical witness who is blamed is dead. This could hardly be otherwise because cases concerning deceased persons are proved every day. All that was maintained was that when a party is deceased and could possibly have exonerated himself this is a factor which heightens the need for alternative proof which is strong enough to overcome the presumption that the deceased had acted properly. Of course in this case the alleged cause of the accident requires successive acts of negligence by two witnesses who are deceased, Mr Vernon and Mr Sutton.

The defenders also made reference to the case of Woods v Duncan. I shall later refer to this case fully in relation to res ipsa loquitur but the interest at the present juncture rests in the observation of Lord Simonds in the House of Lords that:

" If it be thought remarkable that after so long and elaborate an investigation no-one should have been found liable for this loss of life, the answer is that in order to recover damages it is necessary to prove liability against one or other of the parties sued. The key to what is uncertain may have been lost among the ninety- nine who perished in the disaster"

I doubt if that observation casts any new light on the law but it is not difficult to see why the present defenders seek to draw comfort from it. Thus the defenders say the fact that there are intrinsic difficulties in a situation does not lessen the burden on the pursuers.

The defenders made the further point that if one is going to make a case against an individual then it is necessary to put the case to him. The pursuers had claimed that Mr Rankin had failed to check the blind flange and that is probably so but they had not asked Mr Rankin if it was his duty to check the blind flange. This is the case so that I was left with no evidence which would enable me to conclude that Rankin had failed in his duties by not inspecting the blind flange. We were not even told what such an inspection would have consisted of. For example if the flange had not been tightened properly would this have been obvious to the naked eye or was some more stringent test required.

I do not really find any difficulty with the points the defenders have been making in regard to standard of proof. If the main witnesses are lost or important real evidence is unavailable the case is obviously going to be much harder for the pursuer to prove. In arriving at conclusions about a person’s conduct then if the person is dead and unable to defend himself upon any evaluation of evidence the court will find it requires more care before arriving at adverse conclusions. Simply because an investigation is extensive does not lessen the burden of proof and the court must always be alert to the possibility that the case has not been proved. Some complex situations simply cannot be resolved particularly if the best evidence is not available. The Court must be careful to avoid deciding the case simply on the most attractive hypothesis if this does not amount to a clear probability. The problem does not reside in identifying the correct approach in law but rather in applying the principles to a specific situation.

5.2.2 Circumstantial Cases

The defenders maintained that in order for a pursuer to prove a circumstantial case one has to prove incidental or probative facts which when taken together can be held as pointing as a matter of probability to the essential facts in the case. I was referred to Dickson on The Law of Evidence Part II paragraphs 63 and 64. The author points out that evidence may be regarded as direct or indirect. Direct evidence is that which is expressly affirmative or negative of the issue and the only question is whether the evidence is to be believed. In relation to indirect evidence on the other hand ( and this included circumstantial and presumptive) evidence consists of a factum probatus of one kind from which a different fact, the factum probandum, has to be inferred. Consequently there are two inquiries. The first is whether there is proof of the probative facts. The second is whether the fact in issue is deducible from them by inference sufficiently strong to found a verdict. The author also defined a presumptive fact as being "an inference as to the existence of one fact from a knowledge of the existence of some other fact, drawn only solely by virtue of previous experience of the ordinary connection between the known and inferred facts, and independently of any process of reason in the particular case. In the circumstantial situation an inference from circumstantial evidence is arrived at as a result of reason being applied to the facts or reason and experience conjoined".

The defenders relied on that analysis and I accept that its authority is beyond question. Counsel accepted that even if the evidence of one witness may not be reliable enough to establish a probative fact a combination of witnesses speaking to the same fact may restore confidence in the direction of the evidence. Each probative fact must be proved on a balance of probability. Once you have decided what probative facts have been established one had to decide what state of affairs is deducible from the probative material. The defenders maintained that in the present cases it was very difficult to identify the probative facts upon which the pursuers erect their cases.

The defenders say that Mr Vernon’s state of mind is a probative fact that is critical in the present case. The pursuers, so it is claimed, are in some confusion about this matter saying on the one hand that on the evidence Vernon ought to have known that the PSV was not in position and on the other that he would not have attempted to start the pump in the knowledge that the PSV was missing. Since the views of Mr Vernon are unfortunately not available the pursuers have to rely on what the defenders consider to be conjecture to arrive at the state of Mr Vernon’s knowledge at particular points of time. In any event it was claimed that there was no direct evidence of the state of mind of Vernon so that it needs to be proved by circumstantial evidence including evidence of the normal practices on the platform. The second important and necessary fact would be that Mr Vernon re-pressurised the pump. In this respect the defenders claim that there was a direct witness Mr Grieve, who states that Mr Vernon did not pressurise the pump so that the pursuers require to rely on indirect evidence in the face of direct evidence. The third required factual influence is that Mr Sutton left the blind flange finger-tight. The defenders complained that the pursuers do not set out in the presentation of their case the facta probata that they rely on for the inferences needed if their case is to be established. The pursuers attempted to found their case on a broad consistency but that it was argued was meaningless unless the probative facts that are supposed to provided that consistency are indicated. I found a certain difficulty in the approach the defenders urged upon me. I think this stems from the suggestion that the probability of each fact should be considered in isolation. Where the facts are interrelated it may be that a fact which may not be proved if the evidence concerning it is considered on its own can be taken as proved when it is seen how it fits in with other facts. Of course care has to be taken in this connection to avoid circularity of reasoning and the defenders are right that care has also to be taken to differentiate between the established facts and the inferences that these may permit.

The defenders attack the pursuers’ approach to some of the expert evidence since the pursuers seem at times to say that a particular piece of evidence shows that the pursuers’ evidence is possible. If there was only evidence of such possibility then admittedly that would not be enough . However if there was general evidence that on its own pointed to a probability then it might be relevant for the pursuers to anticipate counter-attack by demonstrating that as far as the expert evidence goes it also shows that the inferences which the pursuers are relying upon are acceptable in scientific terms. Of course if the defenders in their extensive analysis were merely trying to say that if there are for example four facts essential to the pursuers’ case then the case cannot succeed unless each of these facts is proved on a balance of probability then of course I could not quarrel with that.

I was referred again to Dickson where at paragraph 108 (1) the learned author observes that "Every one of the circumstances essential to the conclusion should be established by its own independent proof; in other words, the superstructure of theory should only be raised on a foundation of undoubted facts". I can find nothing wrong with that. However Counsel for the defenders conceded that there could be circumstances in which one probative fact may not be enough but a series implying the same conclusion may be enough. As was pointed out Dickson also says " a circumstantial proof is like a chain, which cannot be stronger than its weakest link, and which becomes continually weaker as each new link is added until it breaks under its own weight". However there can be difficulties in the use of graphic analogies like the one used. Thus if there are an added number of strong links the chain may become stronger because the weight on it is better spread. However of course I accept that if a fact critical to the chain of reasoning is not established then the whole argument would fail. Thus taking the eyewitness evidence of Mr Grieve, which the defenders rely so heavily on, if I were satisfied that such evidence was totally reliable and necessarily excluded the possibility that Mr Vernon had jagged pump A then certainly that would eliminate any other circumstantial evidence that may have pointed to the fact that Mr Vernon completed the jagging operation.

Dickson also made other pertinent observations such as at sub-paragraph (7) where he says that " When the inconsistency between any of the probative facts and the hypothesis deductible from the rest of these facts is not absolute but probable, the conclusiveness of that hypothesis is diminished in proportion to the strength of the contrary probability".

5.2.3 Contradictory Witnesses

The defenders also argued that if two or more witnesses are led by the pursuers in support of a critical fact and they contradict one another then if the pursuer does not challenge any of them he is barred from seeking to rely on the witness whose account at the end of the day best serves his purposes.

I was referred to McGhee v The Glasgow Coal Company 1923 SC 293. This case came to the Inner House after a Jury Trial. The case was about an explosion at a pit and the widow of a victim sought to establish a case that there had been inadequate inspection. At the trial three witnesses were led to establish this case. Two of these witnesses said that they saw the fireman at the relevant location and that he failed to make an inspection. The third witness said that he saw the fireman go to the coalface for the purpose of making an inspection. It was held that the evidence as laid before the jury, being self -contradictory upon an essential part of the pursuers’ case was not such as to justify them in arriving at a verdict for the pursuer. Accordingly a new trial was granted. The Court categorised the case as being one where the inconsistency was not one of an accidental nature such as could be disregarded but rather a case of an irreconcilable and unexplained contradiction between witnesses adduced for no other purposes than to establish the point on which they contradict one another. To illustrate the point he was making Counsel referred to the discrepancies between the evidence of Mr Bollands and Mr Clark as to what happened in the Control Room in relation to the red tags. However it may be difficult in a case such as this for the pursuers to know just where the truth lay and they may be prepared to leave it to the Court to see which piece of evidence fits in best with other evidence. They may well have thought that each witness was doing his best to recall facts that occurred in circumstances which were at the end of the day very disturbing and that to suggest otherwise might not be justified. Essentially the pursuers at the end of the day would have to say that the specific evidence of these witnesses on the matters being considered could not be conclusive so that other evidence would have to be looked at to discover, if possible, where the truth lay. In any event the pursuers claimed that their case could be adapted to both versions. In a case such as this much of the evidence has to be decided not on impressions of the reliability of individual witnesses but upon analysis of how these impressions slot in with the weight of the evidence.

The defenders also referred to areas of the expert evidence where experts lead by the pursuers gave evidence which on important issues contradicted one another. This is certainly a difficulty for the pursuers which in specific instances may dilute the value of such evidence.

The defenders addressed me at length on the foregoing questions raised by this section of the chapter. The arguments were somewhat of a technical nature and cover material with which a judge is dealing day in, day out. On the other hand in a case as extraordinarily complex as this one I can understand why it was thought necessary to attempt to delineate the parameters governing my decision about the factual questions. However many of the cases and rules I was referred to are very general and really relevant to particular sets of facts. I find it easier to deal with any of these problems in the concrete as and when they arise.

5.2.4 Expert Evidence

As a preliminary to their detailed submissions on the facts the defenders also addressed me at length on the admissibility of expert evidence. The defenders submitted that it must be established that the witness is an expert and I think that again is pretty obvious. It was said however that questions arise because it is critical that the expert must be expert not only in a general sense but on the question he has been asked to address. It was said that if an expert is led by the pursuers and another expert is also led by the pursuers and he declares that the first expert is not a properly qualified expert at all then the Court is not in a position to know which of the experts to respect. Again I found this submission difficult to deal with in the abstract. It was suggested that Mr Cubbage and Dr Mitcheson were not experts in general engineering problems. However Dr Mitcheson was an engineer and both he and Mr Cubbage had many years of experience in investigating explosions. This would inevitably give them some general experience of the response of structures to an explosion. In relation to a specific issue their experience may not qualify them to express an opinion as well as it would in the case of a specialist structural engineer but this may resolve itself into a question of the weight to be accorded to their evidence. It would not follow automatically that their view necessarily had no value at all. Thus Dr Mitcheson may not have the detailed knowledge of structural engineering enjoyed by Dr Palmer but he could possibly have more direct experience of the response of structures to particular kind of explosion. As I say this kind of question is difficult to decide in the abstract. However the defenders made another point. The fire expert Dr Drysdale, while explaining the theory that the fireball he observed in Module B derived its fuel from a rupture of the 4-inch condensate line, was asked to explain why it had taken some seconds after the initial event before the fireball appeared. He gave a possible explanation by describing what might have happened to the condensate line after the explosion. It was contended that seeing that he was not a structural engineer he had no right to comment on mechanical evidence outside his expertise. Certainly it is true that on a question such as he answered he was at best expressing the opinion of a general fire engineer and his evidence on the matter in question would have to be considered under that caveat. It would also have to be considered that although the pursuers led a number of highly qualified structural engineers they did not ask them to address the issue about the pipe raised by Dr Drysdale. The defenders are right to suggest that the evidence of Dr Drysdale on the matter of what caused the delay in any rupture of the condensate pipe would have to be considered with special care.

The defenders made the second point that if expert evidence is to be admitted then the facts upon which the opinion is based must be made clear. This I think must be beyond dispute. However it was said that it is important that the expert should not be taking any account of an assumption not disclosed in the evidence or ignoring a fact without disclosing it in the evidence. If a witness does fail to disclose an important fact and it emerges in cross examination then one may wonder what weight if any can be placed on the rest of his examination in chief. Again I feel that one has to look at circumstances of particular cases before deciding such a question. Thus in a very complicated case it would not surprise me that cross-examination should throw up a consideration that the expert had not previously considered relevant or even thought about.

I was referred to Davie v the Magistrates of Edinburgh 1953 SC34. That case was decided in the First Division and the leading judgment was delivered by Lord President Cooper. The pursuer had led no expert evidence but the defenders had led three. Unfortunately for them their third expert contradicted the other two. The Lord Ordinary rejected the expert opinion evidence and the defenders reclaimed. They contended that as the pursuers had led no evidence to contradict their first expert his evidence should have been accepted. It was held inter alia that the court was not bound to accept the opinion of an expert even when uncontradicted. It was also held that the opinion of the Lord Ordinary should be affirmed. Lord Cooper observed that the value of expert evidence depends on the authority, experience and qualifications of the expert and above all upon the extent to which his evidence carries conviction. I am very happy to accept that. The Lord President held that the value of the first witnesses evidence would not have been affected if the contradicting third expert had not been led. Experts witnesses however skilled or eminent can give no more than evidence. They cannot usurp the function of the judge. They supply the necessary scientific criteria for testing the accuracy of their conclusion so as to enable the judge to form his own independent judgment by the application of these criteria to the facts proved in the evidence. If the scientific opinion evidence is intelligible, convincing and tested that would be an important factor for consideration. The Lord President points out that the issue in the case has been submitted to a judicial tribunal and not the oracular pronouncement of an expert. An observation which the defenders laid stress on was " if conflicting scientific expert evidence is adduced by a party, he cannot complain if on that account the whole of it is treated with more than suspicion". However in respect of the last point I do not take the Lord President to be laying down any inflexible rule nor to be contradicting the very helpful analysis of expert evidence which he had earlier given. As the Lord President had indicated the value of an expert must in the first instance be assessed in the light of the quality of what he has said. Of course if the experts contradict each other the judge may, depending on what is said, find it impossible to choose between the competing experts. The defenders argued that as a matter of public policy a party should not be in a position to lead expert after expert until he finds himself with one he considers may help his case. If this were done in my view it is unlikely that the opponent would allow the judge to ignore the earlier adverse evidence without there being a need to resort to notions of public policy. However as an illustration of the difficulties the Court can confront if faced with competing evidence the defenders referred to the witness Professor Fenner who had been asked by way of static analysis to calculate the over pressure for static failure pressure on the C/D firewall and he came up with a result of 0.011 bar. Professor Fenner had been led by the pursuers and they did not challenge his result. Later they led Dr Palmer and he calculated the same matter but came up with a result that was substantially greater than that of Professor Fenner namely 0.16 or 0.18 bar. The pursuers did not challenge that result either. The defenders suggested that both results would have to be ignored because it is impossible to adjudicate between them. However it has to be noted that these experts used a different methodology and obviously what they were trying to do posed an immensely difficult scientific problem. One expert arrived at his conclusion after a beam analysis whereas the other used plate theory. Thus for example it might be possible to say that the actual figure is likely to rest somewhere between their respective results or, as indeed I shall say, that one expert arrived at his conclusion by use of what was accepted to be a more refined method. On the other hand the evidence I mention has to be tested by reference to the evidence of Professor Reid who said that manual methods of calculating the matter in question are unreliable. Moreover the defenders make the point that rather than give Professor Fenner’s calculation to their witness Dr Bakke (who needed such material as a starting point for his own work) they led another witness Dr Palmer and arbitrarily gave his results to Dr Bakke because it brought out a better result for them. Certainly the defenders do not have difficulty in persuading me that the expert evidence in this case is extremely difficult to unravel.

The defenders argued that an expert who is privileged to address the court on matters of opinion has certain responsibilities. I was referred to The Ikarian Reefer (1993) 2 Lloyds Law Reports 68. This like the present case was an extensive proof (100 days in The Ikarian) and there were many experts adduced as witnesses. Lord Justice Cresswell made comments on the duties and responsibilities of expert witnesses. These he summarised as follows;

"The duties and responsibilities of expert witnesses in civil cases include the following:

1. Expert evidence presented to the Court should be, and be seen to be, the independent product of the expert uninfluenced as to form or content by the exigencies of the litigation.

2. An expert witness should provide independent assistance to the Court by way of objective unbiased opinion in relation to matters within his expertise . An expert witness in the High Court should never assume the role of an advocate.

3. An expert witness should state the facts or assumption upon which his opinion is based. He should not omit to consider material facts which could detract form his concluded opinion.

4. An expert witness should make it clear when a particular question or issue falls outside his expertise.

5 If an expert’s opinion is not properly researched because he considers that insufficient data is available, then this must be stated with an indication that the opinion is no more than a provisional one. In cases where an expert witness who has prepared a report could not assert that the report contains the truth, the whole truth and nothing but the truth without some qualification, that qualification should be stated in the report."

The analysis then deals with other matters of less relevance to these cases. There is no doubt that his Lordship’s formulation of an expert’s duties is helpful and correct. The question of expert evidence was also considered in John Pierce v Her Majesty’s Advocate 1981 SCLR 783. The case was not fully reported and the Opinion of the Court which was dated 19h June 1981 was made available to me. This was a case reviewed by the Court on a referral by the Secretary of State and the substance of the referral was the possible doubt about the evidence given at the trial by a forensic expert. The expert had made an assumption which was not a justified assumption and he had not disclosed the assumption to the Court. The Lord Justice General observed after considering the position that had arisen.

"This was in our judgment, conduct on the part of an expert witness which demonstrated a complete misunderstanding of the role of scientific witnesses in the Courts, and a lack of the essential qualities of accuracy and scientific objectivity which are normally to be taken for granted."

He concluded that the expert in question had been discredited not only as a scientist but as a witness upon the accuracy, fairness, and objectivity of whose evidence reliance could be placed. The defenders said that the two cases I have just quoted bear special relevancy to the position of Dr Mitcheson whose evidence I shall later consider.

A final point which the defenders made about expert evidence is by their own concession a trite one and is that where an expert opinion is based upon a particular version of the facts or on assumptions then the opinion is only going to be of value if these facts or assumptions are proved. Thus the expert in the course of his evidence should make clear the facts or assumptions central to his opinion. Further these facts or assumptions have each to be proved on a balance of probabilities. I think it has to be recognised that the proof which parties required to conduct was most exceptional. The proof lasted a number of years, the disaster on any view was exceptionally difficult to explore, there were many witnesses expert and non-expert, and the technical material was difficult and protracted. It was quite obvious that because of the scale of the proof, the parties’ cases were to a degree developing as the evidence itself developed. Thus is do not find it the least surprising that certain points may not have assumed the importance at the time when evidence was led that they assumed later. I do not think that Counsel are to be criticised if on occasions they omitted to ask a question which at a late stage of the case they may wish that they had asked. Moreover if a party is not expecting a particular matter to emerge this may be less important if many months of proof lie ahead during which the point may be investigated. Thus within the limits of the technical restraints I was generally inclined in this case to give considerable weight to the considerations of fairness to parties and risk of prejudice rather than any mechanical application of more specific principle. Moreover, again subject to the limits of fairness and technical restraints, considering all the effort that has gone into the case I think it is important that the case should be decided after as wide an exploration of issues as is necessary. It would be unfortunate if the factual issues in this case required to be determined on the basis of an artificial reality.

5.3 Background Scene.

The accident happened at 22.00 hours on 6 July 1988. At the time the weather was good and visibility was clear. There was a wind speed of 16.4 knots and this was from a direction of 164.4 degrees true. The wind speed is confirmed by a print-out taken on the Artemis system of dynamic positioning on the Lowland Cavalier. This was taken at 22.00 hours on the night of the accident. The platform itself was 43 degrees counter clockwise from true north so that in relation to the platform the wind was blowing at 207 degrees in relation to platform north. The Artemis system also records that it failed at 22.01 hours and 10 or 16 seconds the inference being that the system failed because of the explosion. The Tharos log spoken to by Mr Kondol records that the explosion and the procedures that were then put in train occurred at 22.02 hours. Given that the record is not only of the explosion but of consequential actions taken the log puts the time of the explosion as very close to 22.00 hours. The eyewitnesses put the accident at times which vary marginally but generally can be said to be about 22.00 hours and indeed there is no dispute about this time.

At the time of the accident there were a number of vessels in the vicinity of the Piper Alpha platform. One of these was MVS Tharos and as a result evidence was given by Mr. Flaws, Mr Murray and Mr Miller who were on that vessel at the relevant time and can speak to various observations connected with the accident The weight of the oral evidence is to the effect that Tharos was about 550 metres from the platform and its stern was facing the west face of the platform. That distance is consistent with entries in the log of Tharos. At the time of the accident Mr Flaws and Mr Murray were on the helideck lounge of Tharos. Mr Miller was on the helideck itself, towards the starboard side of the heli-reception and when the accident occurred he was about to take photographs for a school project. He was thus in a position to take photographs of the platform almost immediately after the accident occurred and this he did. His photographs were produced and clearly provide valuable and relatively reliable evidence of how the platform appeared to those on Tharos immediately following the accident. After he had photographed for about 15 seconds he changed his position and thereafter took photographs from the starboard side of the vessel before returning to his original position and taking further photographs. Quite detailed evidence was given of Mr Miller’s precise position as he was photographing but I doubt if anything turns on that. At the time of the accident the witness Mr Kondol was asleep in the upper deck of the accommodation beneath the helideck and his window looked out to the west face of the platform.

Another vessel off the platform was the Lowland Cavalier which had been engaged in trenching a pipeline under the seabed. There were three of the witnesses aboard this vessel namely Captain, Mr McDonald and Mr Ritchie. At the time of the accident the stern of Lowland Cavalier was about 25 metres from the west face of the platform. Captain Clegg and Mr McDonald concurred on this measurement. The boat was positioned between the legs of the platform B1 and B2 which are at the south-west corner of Piper Alpha. The photographs, number of process 12/358, give some additional confirmation of the position of the vessel and it was about 85 metres long and 17 metres wide. The aft bridge was 50 metres from the stern and Captain Clegg was on the aft- facing control room on the bridge when the accident occurred. This would have placed him at about 56 feet above sea level as compared with the height of 84 feet of the production modules. Captain Clegg’s own position when the accident happened was about 75 metres from the south-west corner of the platform and his line of vision would have been about 25 feet below the mouth of the Modules. He was accordingly well positioned to see the west face of the platform.

There was one witness from the Maersk Cutter and that was Captain Morton, the master. The vessel at the time of the accident was on standby one mile north-east of the platform. It was sitting side-on to the platform facing in a north-westerly direction. Captain Morton was on the bridge which had a 360 degree vision. He was looking out of the port side at the forward end of the vessel and his bridge was about 30 feet above sea level. Another vessel was the Maersk Leader. Mr Anderson was the witness from that ship and he produced a video which he had taken at the time of the accident The Maersk Leader was on standby for anchor handling and the vessel was two miles from the platform in a southerly direction away from the tip of the east flare boom. After the explosion the ship moved and ultimately ended up at the west side of the platform behind Tharos.

The position of the Silver Pit is perhaps the only ship whose position caused a degree of controversy. This is because the position of the ship had only become material when the defenders led the witness Mr Haffey who had been aboard that ship . In these circumstances the pursuers themselves had led no evidence on the matter such as log books. Mr Haffey was a deck hand on his first trip and had been on board the ship for two or three weeks. However he had had experience in the Royal Navy. As he was going to bed in his cabin shortly before the accident he had heard a double bang and after perhaps thirty seconds he looked out of his cabin window ( which was a starboard hatch ) at the platform. When he thus looked he claims to have seen what looked like a cloud of dirty white smoke emanating from the heat shield in the area between the two flare booms. That would have placed the smoke coming from the south side of the platform at an area which runs alongside Module A. He placed the Silver Pit off the south-west corner of the platform although he felt unable to venture a distance. However he did eventually say that he was within a mile of the platform. There was no other evidence to give his view support and because of the stage at which his evidence emerged it was not put to the pursuers’ experts. His placing of his vessel was not very confident and in cross-examination he accepted that Silver Pit could possibly have been off the north-west corner of the platform. The photographs number 12/358 of process 19 and 20 seem to place the Silver Pit in that vicinity. Mr Haffey identified the ship himself. He remembered seeing Tharos, the Maersk Cutter, possibly the Lowland Cavalier and other supply ships. His most confident recollection is of seeing the Tharos and the Maersk Cutter and this would be achievable if he were at the north-west corner which would place him between these two vessels. When asked he could not recollect where Tharos had been in relation to Silver Pit (although the former is a large vessel). If the Silver Pit had been off the south-west corner of the platform as the witness originally opined this would have placed it quite close to Tharos . He does not claim to have seen anything along the west face which is at variance with other witnesses and with photographs taken by Mr Ritchie from the Lowland Cavalier and by Mr Miller from the Tharos . Indeed in these photographs there does not appear to be any sight of Silver Pit in the area where Mr Haffey first claimed it to be. However photographs show it to be in a position consistent with it being at the North West corner of the platform (and with its bow facing south). The upshot of his evidence was that it became clear that Mr Haffey had an unclear memory of events and I would be hesitant to place much reliance on his evidence on matters of detail. Moreover he personally was involved in operations on a rescue craft, no doubt bravely, and this may have rendered his recollection of events more confused than in the case of others. Of course the Silver Pit may have moved position in the course of the evening but this is perhaps unlikely in the case of a ship acting as base for a rescue craft.

5.4 Gas Detection System

5.4.1 The Detectors

The pursuers rely heavily for their explanation of the accident on the pattern of gas detection alarms observed just before the accident so that an understanding of the alarm system is important.

The pursuers’ witnesses who dealt with the matter were mainly Mr Wottge, Mr Scothern and Mr Tea. Mr Wottge was I have said the pursuers’ Facilities Engineering Manager with knowledge and experience of the construction details of the platform over an 11 years period. Mr Scothern was aged 56 when he gave his evidence and now teaches and consults on fire and gas systems. He had started off his career as a mechanical technician in the Fleet Air Arm. In 1977 he was employed by the Wood Group as a Fire and Gas Technician and after completing a course with alarm manufacturers went offshore as a Product Engineer. In this capacity he commissioned a number of systems including the Piper system. In 1977 he was employed by OPCAL on Piper Alpha as a Instrument Technician but he was in practice the fire and gas technician. He left the employment of OPCAL about August 1987. When he left Piper he was replaced by Mr Wakefield who died during the disaster. After leaving Piper Mr Scothern transferred to Claymore but he made it his business to keep in touch with what was happening on the former because he was hopeful of returning there. The witness Mr Tea was employed on Piper at the date of the accident although fortunately he was off the platform at the time. At the time of the proof he was 47 years of age. His position was that of Instrument Technician and he was Mr Scothern’s back to back and worked under his wing. His job was to keep the gas and fire detection system in a good state of repair. The defenders urged me to regard Mr Tea as a much more reliable witness than Mr Scothern. This was not necessarily my impression at the time in respect of all evidence. Both witnesses were trying their best to remember matters of detail. Mr Scothern had been longer removed from a position on Piper Alpha than Tea. However he had at least some knowledge of developments in the alarm system after he left because he had kept in close contact with his successor Mr Wakefield. However both witnesses were speaking to events and situations that when they gave their evidence were some years in the past. It is a further point that just before the accident Mr Scothern had worked for almost a year on Claymore and this being similar to Piper Alpha there may have been some room for a confused recollection. Certainly I am prepared to accept that Mr Scothern maintained a genuine interest in the gas detection system on Piper Alpha until the accident. There was a dispute between Mr Scothern and Mr Tea as to whether the detector 103/1 faced upwards or down. In this respect Mr Tea may have had some advantage since he had been working on that particular detector shortly before the accident.

Detectors generally were placed in areas where it was thought that escapes were most likely to occur and also where the airflows were most likely to direct gas. The low placed detectors were aimed at detecting the heavier gases and the high placed detectors the lighter gases

With regard to Module C the location of the gas detectors is as shown in the drawing which is 12/112 of process (and 12/109 which is to scale). All the detectors pointed downwards. The areas where detectors were placed were zoned into areas C1, C2 , and C3 moving to the east from the west. Module C has 5 zones in all. C1 was west Module C, C2 was east module C, whereas C3, C4, and C5 were related to the centrifugal compressor compartments. Each zone would have a number of alarms common to that zone. There were audible and visual alarms for particular zones in particular Modules so that the Control Room Operator could identify the zone in which the alarm had annunciated. There was also a visual indication in the Control Room as to what was the cause of the alarm i.e. fire, gas, etc. Once the Control Room Operator had identified the zone where trouble appeared to be present he would communicate with the operator responsible for the zone so that the matter could be investigated. Thus there is a system to pinpoint the source of a possible difficulty. Moreover if there was an alarm certain beacons lit up in the Module itself to warn operators that there was a pending alert.

The alarms G100/1 and G100/2 are to the west of the module and would have gone off had there been a gas cloud in that area. As to the heights of these particular alarms there is some minor disagreement on that issue between Mr Scothern and MrTea but I do not regard this as significant. Indeed the assumptions as to the heights of alarms which were given to the pursuers’ expert Dr Davies were as is set out in the flip-chart 44/117 or process. The next detectors moving west to east are G22, G23, G24, and G25. Mr Scothern places these in the roof space at a height of between 20 and 24 feet and there was no conflict about this. I think that such alarms as were attached to roof beams were likely to be at a height of at least 20 feet. Those attached to angle irons would be some feet lower. Thus for example G101/3 was attached to an angle iron and was said to be at a height of about 15 feet. The detectors I have described so far were in zone C1. The next group of detectors were in zone C2, that is more towards the east of the module. Detector G101/1 is the first detector encountered to the east of the reciprocating compressors. There was some discrepancies in the evidence as to the height of this detector. Mr Scothern places this in the roof space at a height of about 20 feet whereas Mr Tea gives three figures varying between 15 and 20 feet. On this matter I preferred Mr Scothern because Mr Tea was rather uncertain in his recollection and it is also not clear how that detector would be attached at a height of 15 feet. Going again to the east and rather to the north the next detector is G 101/2. Mr Scothern had this located at a height of about 20 feet but Mr Tea had a clear recollection the he had relocated this device at a height of about two to three feet above deck level. Mr Tea seemed to be clear about this particular matter and gave detail which has prompted me to accept him on the question. One point worth noting is that if such condensate as flashes or gas which may escape at the relevant location tend to be lighter gas why was it thought necessary to relocate the detector at a lower level?. The detector G101/3 in zone C2 was above centrifugal compressor B and was at a height of 15 to 20 feet. Again there is a discrepancy between the witnesses but Mr Tea is in a position to be more specific with regard to his estimate of 15 feet. He claimed that he could get access to this detector by standing on the compressor. However there is an element of imprecision about the heights of the higher detectors.

Zones C3, C4, and C5 covered the detectors associated with the centrifugal compressors and in particular detectors G28, G31, and G34. C3 was at C centrifugal compressor, C4 at B, and C5 at A. G 103/1 is between compressors C and B, G103 /2 is between B and A and G103/3 is on the north side of A. These particular compressors monitor the fuel gas valve enclosures. The detectors G26, G29, and G32, all monitor the compartment ventilation air intakesand thus can monitor air coming from the exterior. They are located outside the module. Thus G26 is inside the air vent to the turbine compressor compartment. That is to say that the air taken in at that point ventilates the turbine compartment as distinct from the turbine machine. Then it exhausts from the louvre in Module C. The louvre however can only exhaust air not ingest it. In general it seems unlikely that G26 would detect gas from within the module. The defenders maintained however that the detector could detect gas coming from Module B. The defenders maintained that Dr Davies was proceeding on the false assumption that each compartment had two louvres. G27, G30, and G33 are located at the turbine compartments of the compressors. G27 had originally been located inside the cabinet but had been moved outside by Mr Scothern and connected inside by a tube. Thus it was capable of detecting gas inside the compartment itself. There was some controversy as to whether it was capable of detecting gas from outside the compartment. However Dr Davies eventually gave the considered view that if there was a relatively large cloud of gas outside the compartment it could find its way to G27. This was because of gas diffusion. On the other hand the cloud of gas would have to be relatively substantial to survive the effect of dilution by air. I think this view must be respected. On the other hand Dr Davies’ view was expressed on the basis that the compressor was running He accepted that the position might still be favourable to gas detection if the compressor was not running although he had not quantified that possibility. Later Mr Tea had also moved G30 and G33 outside their related compartments. These detectors were at a height of about 3 feet above the grating and all faced downwards. G28, G31, and G34 are each located at the west end of the respective compressor compartments and within them. It was not suggested that they could sense gas from outside the compartment itself. G1O2/1, G102/2, G102/3 and G102/4 are at the combustion air intakes for the gas turbines. The approximate arrangement of gas detectors within each compressor compartment is shown in the schematic 12/128 which relates to compressor C. In particular the approximate positions of detectors G103/1, G26, G27, G 28 and G102/2 are shown. G 02/2 was one of the common alarms (zone C3 and zone C4) and was about 8 feet up in the intake ducting . Another detector G102/1 is equivalent to G102/ 2 but on the opposite side of the compressor. This detector is linked only to C3. It has to be noted that detectors G102/3 and 102/3 are located in turbine intake compartments common to two machines. Each compressor took its air from two intakes and the ones in the middle of the series were covered by the same canopy. Thus if gas was detected by G 102/2 this could refer to both zone C3 and C4. On the other hand if a common detector goes off it will signal at two zones. But the existence of a common detector could explain why Mr Bollands saw gas alarms annunciating at zones C4 and C5 at the same time. In relation to compressor B there is G102/3 and G102/4. The detector G103/1 monitoring the fuel gas valve enclosure in compressor C was located below the walkway grating and was connected by a tube to the box arrangement around the fuel valve although the actual detector was outside the box. It could sense gas outside the box. The defenders contended that any gas which dropped below the walkway grating within the Module and then arrived at G103/1 would be within the upward airstream being drawn into turbine air intake. Since the Compressor did not trip until after the first gas alarm the air intake would still be operative when the detector would see gas It was claimed that there would have to be a considerable quantity of gas to withstand the dilution effect of the air. Dr Davies on the other hand thought that the matter was finely balanced and depended on the exact structuring of the relative walkway, the location of any solid plate gratings and the position of the actual head of the detector. When Dr Davies did his modelling exercises the relevant probe was outside the module. In general he seemed to consider that the plans and drawings leave some degree of doubt as to the exact location of the detector. Certainly since there had been various changes to the detectors from time to time it is difficult to locate the actual detector head precisely with confidence although if it was not actually outside the confines of the module it was close to being so. Moreover it was slightly to the east of the combustion intakes. During his cross-examination he was asked to assume that the quantity of air at the combustion intake was 1 to 2 metres per second. He was also asked to assume that the air being drawn up for combustion purposes flows past the detector head. The defenders never proved these assumptions. There were similar arrangements for G103/2 and 3. These detectors had originally faced upwards but not long before the accident had been altered to face downwards.

The point emphasised by the defenders is that since about 80% to 90% of the compressor air intake is drawn from the atmosphere and only about 10% to 20% from within the module then there was a possibility that the alarms were triggered by gas originating in Module B. The ventilation air intakes were substantially higher than the combustion air intakes. The ventilation air intakes in a general sense point south while the combustion air intakes point downwards.

In relation to Module B there was some controversy with regard to G99/4. Otherwise the general layout of the detectors is shown on the drawing 41/1 of process. In Module B we have zones B1 and B2 being approximately the west and east half of the module respectively. Detectors in B1, namely G13 through to G18 were located in the roof space. G13 and G14 were the furthest west. G15 was above the Prover Loop and this may be important since the defenders regarded the loop area as a possible source of the explosion. G16 was to the west of the MOL booster pumps. G17 was located close to the pig launcher. G17 was on the south side above the manifold. In relation to zone B2, G19, G20, and G21 were all at ceiling level as shown in 41/1 of process. G99/1, G99/2 , G99/3 and G99/4 were all in the area of the separators. These had been added sometime after the initial construction of the platform and were all placed in low positions just above the floor. Mr Scothern had a clear recollection of the height of these detectors. Mr Tea perhaps placed the detectors a little higher than Mr Scothern but the latter in this matter appeared to have a much more crisp memory of them and got a measure of support from the witness Henderson. Moreover these detectors had not been moved after Mr Scothern left the platform. The defenders had claimed in their pleadings that at the time of the accident the gas detectors in Module B may not have been operative because they were "pinned out" but they indicated during submissions that they were not insisting on this point.

The detectors at the 68 - foot level were as shown in the drawings 12/121 and 12/119 of process. There was again a measure of difference between Mr Tea and Mr Scothern with regard to the respective heights of G127, G128, and G129 but these are not material. What is material is that there were detectors at the open east end of the level beneath Modules B and C.

5. 4.2 The Gas Alarms

The gas detectors were linked to the Seiger 1400 series control modules within the Control Room by cabling via one or more junction boxes. These control modules were in racks behind the fire and gas panels If there had been any interruption of this connection it would have triggered off a fault panel on the alarm panel in the control room. Moreover if a gas detector failed or a fuse blew or if there was failure of power at the alarm, a light and buzzer alarm would go off in the Control Room. However a mere fault in the sensitivity of the detector would not register. If a detector were to register gas a signal was transmitted to the Control Room and the operator could identify the particular alarm which was registering (as distinct from the group of alarms) by recourse to the control modules. This would enable the relevant operator to be contacted and asked to inspect the situation at the alarm which has registered. The Control Room operator sits in front of the panels which register various alarms throughout the platform including the gas alarms.

The alarm panel was located between the production mimic and the fire and gas matrix and mimic. These arrangements are illustrated in the productions 12/203 (a photograph of the Control Room), 12/188, and 14/9 of process. The alarm panel provides an immediate signal in the event of a fault in the detection system or the triggering of a gas detector. Each alarm signal is by way of a flashing light and very loud buzzer. If a buzzer annunciates the operator having noticed it presses the mute button on the panel which silences the buzzer and converts the light to steady state. To acknowledge the visual indication of an alarm (which is by way of a light) the operator would press an accept button. On the alarm matrix panel itself the operator would only be shown the zoning of the alarm which had annunciated but not the precise alarm which is only shown at the control module. The alarm panel is the panel directly below the red rectangle to the right of the major board (the production process mimic) in the centre of the said photograph. The production 14/9 is a representation of the alarm panel. LED lights at the top of the panel shine continuously and will indicate that the electric supply is on. A back-up system provided power should the normal alarm supply fail. The fire and gas panel

(on which the flashing lights are situated) is on the right of the alarm panel. The Production Process Mimic mimics the production plant and alarms relating to specific pieces of production equipment (such as for example the compressors and condensate injection pumps) are specifically indicated. At the bottom of the panels are series of special switches such as the emergency shutdown buttons. At the very top is an alarm panel showing the lights for common alarms relating to the process system. That is where the high level alarm from the JT flash drum would enunciate. On the lower panel there was a button with test lamps and this would be pressed daily to make sure that all the lamps on the panel were working. The alarm panel system also incorporates other alarm systems which I am not concerned with.

The overall position is that the Control Room operator received an immediate indication of any alarms which went off indicating low or high levels of gas concentration and although he would not know before consulting the control module just what precise alarm had annunciated he could immediately ascribe it to a particular zone in a particular module. The drawing 12/202 of process gives the layout for the fire and gas matrix and mimic. In that drawing the production deck section shows the various zones represented and these include all the fire and gas zones in the A and B modules and each has a LED light which would indicate if one of the gas alarms went off. This would enable the operator to know in which zone the detector had detected gas. If an alarm had shown a certain level of gas in a certain zone then once it had been accepted and returned to a steady state it would flash again if a further detector in the same zone detected gas. Once a particular detector has given a signal it can not show again until it has been reset by an operator at the control module but an adjacent alarm could signal. At one point the defenders suggested that there may not have been an alarm to cover zone C2. However the possible discrepancies in the drawing were explained to my satisfaction and I am satisfied by reference to all the drawings as explained by the witnesses that there was at the time of the accident an alarm covering C2.

5.4.3 Gas and Equipment Alarms Annunciating at Accident

The only alarms which annunciated in the Control Room shortly before the accident related to detectors at the east end on Module C. The critical evidence of the alarm pattern before the accident came from Mr Bollands who was acting as the Control Room Operator at the time of the accident Mr Bollands was an experienced production operator who rotated through various duties as a production operator but he was working in the Control Room on the evening of the accident having begun his shift just before 6pm. The events immediately leading up to the explosion not only directly involved him but obviously produced a powerful impression on his mind. Insofar as he was talking about his experience at the control board I think his recollection is likely to be accurate. He also indicated that he was repeating the information which he had imparted shortly after the accident in 1988. In very broad outline he gets support in respect of certain events from Mr Clark (the Maintenance Lead Hand on duty at the time of the accident) who was also in the Control Room when it occurred.

The first untoward event that Mr Bollands noticed was that an alarm signalled that the condensate injection pump had tripped. This occurred shortly before 9.45pm. The time of the tripping can to an extent be derived from the fact that Mr Bollands left the control room to telephone his wife about 9.30pm. and then returned to the control room about 9.40pm.. I think the condensate pump must have tripped no later than about 9.40 because it was only after Mr Vernon’s return to the control room after a visit to the 68-foot level that he contacted Mr Clark. Mr Vernon was the Lead Production Operator who was on duty and in immediate control of production at the time Mr Clark said that he had received Mr Vernon’s message at 9.45pm and I think that is a time that is likely to be reasonably accurate because Mr Clark had looked at his watch when the message came. Mr Clark, as is perhaps understandable, seemed very anxious to deny any knowledge of the status of PSV 504 at the time of the accident but he would have no interest in distorting the time when he got a message to call Mr Vernon and his evidence on this gives a reliable point of reference. Mr Vernon certainly did not contact him until some minutes after the pump trip alarm had annunciated. Mr Vernon was in the Control Room at the time the alarm went off. Mr Bollands shouted over his radio to Mr Richard, who was the Phase 1 Operator on duty, to tell him that the pump had tripped and at the same time Mr Vernon left the Control Room to go and investigate the situation. Before this the alarm which had sounded had been accepted so as to mute the audible alarm and convert the lamp from a flashing state to a steady state. At this time Mr Clark was in the Maintenance Office. After Mr Vernon’s departure the next thing Mr Bollands was aware of was that the JCP panel alarm relating to the 68-foot level went off. He accepted it and told Mr Richard that there had been this alarm and that it probably related to the high level in the JT Flash Drum. In relation to the JCP panel alarms to know precisely which particular alarm had sounded as distinct from knowing the equipment area to which it related it was necessary (as with the gas alarms) to consult the control modules which were situated at the rear of the control panels and it was often not practicable to do this until the emergency signalled by an alarm had been dealt with. However with the condensate injection pump tripped it was expected that the level in the JT Flash Drum would rise since the pump would stop pumping away condensate coming from the production process. The matter of identifying an alarm with precision (as follows from what I have said earlier) also arises in relation to gas alarms since a particular alarm as I have explained above will only indicate the level of alarm and the gas zone in a particular Module which has triggered it. To identify the detector in the Zone which has responded to gas it would be necessary to consult the control modules. This factor gives rise to certain problems in this case because in relation to gas alarms which were triggered before the accident it is at best a matter of inference just what detectors in a zone caused the alarm to go off. Mr Bollands thought that the JCP panel alarm had sounded about 3 to 4 minutes after the injection pump had tripped. The witness Mr Grieve when he came to the 68-foot level three minutes or so before the explosion in fact noted that the liquid level of the JT Flash Drum was relatively high. When Mr Bollands contacted Mr Richard about the JCP alarm he asked him if he had unloaded the reciprocating compressors. To recycle and unload the reciprocating compressors would stop gas going forward into the JT valve and the consequent reduced production of condensate would limit the inflow to the JT Flash Drum. Accordingly he would have expected Mr Richard as the operator on duty to have unloaded the reciprocating compressors but he could not remember how Richard had responded to his query. However Bollands describes how Mr Vernon had returned to the control room about 5 minutes before the explosion . Given that Mr Vernon sent Mr Clark a message from the Control Room at about 9.45pm it seems likely that he returned to the Control Room rather earlier that Mr Bollands remembers. The estimates of times given by the witnesses are essentially approximate but if Mr Vernon had first left the Control Room about 9.40p.m. he must have been away at least 5 minutes if his return to the Control Room was at about 9.45pm. It is clear that the explosion occurred close to10pm. When Mr Vernon returned to the Control Room he told Mr Bollands categorically that he had unloaded the reciprocating compressors. This information would be consistent with the observations of other witnesses who had noted an increase in flaring shortly before the explosion. The unloading process would have caused an increase in the gas going to flare. We do not know whether it was Mr Richard or Mr Vernon personally who completed the unloading procedure (which would have just taken a minute or so) but Mr Vernon on proceeding from the Control Room to the 68-foot level (and also on returning there) would have passed through Module C close to the reciprocating compressors and may have taken advantage of the opportunity to unload them. It can be inferred that upon entering Module C Mr Vernon neither saw gas vapour nor smelt any unusual degree of gas. In any event since the condensate injection pump had first tripped at least 5 minutes or so had passed and at that stage no gas alarms had been noted.

The next event of significance in the Control Room was that there was a low gas alarm at the zone C3 (which is the zone attributed to the centrifugal compressor C). The pursuers accept in their pleading that there was such an alarm. First Mr Bollands heard the buzzer and then identified that the alarm came from zone C3. He describes this C3 alarm as occurring about two to three minutes before the explosion. The pursuers contend that this first gas alarm must have been due to an attempt by Mr Vernon to start condensate injection pump A by jagging it for the purpose of re-introducing pressure to it. It may be significant that Mr Grieve who was at the 68-foot level when the explosion occurred arrived there from the Phase 2 Gas Conservation Module some minutes before the explosion. When Mr Bollands heard the first gas alarm he silenced it by accepting it and then he contacted Mr Richard. I would have expected that he did this fairly quickly after the event. Mr Richards thereafter left the 68-foot level to investigate the gas leak as would be expected. The point is that Mr Grieve was present at the 68- foot level when Mr Richard went off to see about the leak although he himself did not know why Richard had left the 68-foot level at that time. In order to get from the Phase 2 Module to the 68-foot level Mr Grieve had descended stairs which are just outside Modules B and C at the point where they meet. He claims that he had noticed nothing unusual as he passed this point which would suggest that there was no massive flow of gas between the Modules just before the first gas alarm noted by Mr Bollands. Mr Vernon when he had returned to the Control Room had told Mr Bollands that his attempts to restart Pump B had failed and he expressed the intention of attempting to recover Pump A from maintenance and to start it. Apart from any other significance this information may have had it reinforces the view that Mr Vernon’s first visit to the 68-foot level must have lasted quite a few minutes. He would have required some time to get down to the 68-foot level and back while presumably any serious attempt to restart pump B would have taken at least a few minutes. Nor does it seem likely that he would have on the occasion of his first departure from the Control Room have begun to restart pump A. This is because pump A could not have been started without being electrically de-isolated and indeed it was to see if he could achieve this that Mr Vernon had contacted Mr Clark. Since Mr Vernon had contacted Mr Clark at 9.45pm he must have returned to the Control Room about that time. There is some division in the evidence as to what happened after Mr Vernon contacted Mr Clark. Mr Clark thought that after he got a Tannoy message to contact the Control Room he had telephoned there and presumably he did not waste any time in doing so. He is somewhat tentative as to what happened after he made the necessary call. He certainly claims that there was communication with Mr Vernon about the status of pump A and Mr Vernon’s intention to restart that pump were it practicable to do so. Mr Vernon wanted Mr Clark to sign the portions of the red tags which had originally been prepared to warrant the electrical isolation of the pump and which required to be signed by the designated and performing authorities so that the pump could be de-isolated. However he could not recollect if he had spoken directly to Mr Vernon or communicated through Mr Bollands as an intermediary. Mr Clark claims that he then descended to the Control Room to sign these tags. When he arrived there he claims that Mr Vernon had left the tags for him but was no longer present in the Control Room. Mr Bollands on the other hand said that Mr Vernon was still present in the Control Room when Mr Clark arrived. I find it difficult to come to a concluded view about this particular discrepancy in the evidence although Mr Clark might be supposed to have a better memory as to whether or not he had spoken to and seen Mr Vernon. However Mr Clark may have difficulty in accepting that he actually saw Mr Vernon to shield himself from any suggestion that he had discussed the position about the PSVs. In any event it is clear that he arrived in the Control Room only a few minutes before the explosion. Mr Bollands himself confirms this. After receiving Mr Vernon’s communication Mr Clark had required time to descend to the Control Room, to sign off the tags, and to seek to obtain an electrician . His first attempt to secure an electrician were not very successful since the electricians first contacted had gone off duty. All this happened before the explosion and the time needed would probably be consistent with Mr Clark’s assertion that he received the original message about 9 .45pm. He must have taken a few minutes. It seems clear that Mr Vernon had left the Control Room before the first low level alarm went off and the fact that Mr Vernon was present at the 68-foot level when Mr Grieve saw Mr Richard get the message about the gas alarm not only confirms this but suggests that Mr Vernon must have left the Control Room some minutes at least before the first gas alarm. Indeed given the time required to contact Mr Clark and communicate with him it would be surprising if Mr Vernon left the Control Room for a second time much before about 9.50pm. Mr Bollands thought that it had been about 9.55. Thus at best Mr Vernon had about 10 minutes for his return to the 68-foot level before the explosion and quite possibly less. If as the witnesses seem to agree there was a gap of about two to three minutes between the first gas alarm and the explosion Mr Vernon possibly had at best up to 7 minute or so between leaving the Control Room on the second occasion and the first gas alarm. Some of this time would have been spent in getting back to the pumps.. The pursuers suggest that Mr Vernon must have jagged condensate injection pump A at least once before Mr Grieve arrived at the 68-foot level and he would in fact have had time to do that even allowing for the fact that the air supply to the GOV system would have required reconnection and vents on the pump would have required adjustment. Indeed it would have been possible for Mr Richard to have performed some of the preparation work while Mr Vernon was returning to the Control Room. However Mr Vernon must have taken say a minute to get from the Control Room to the 68-foot level and Mr Grieve was present there for at least about a minute before the gas alarm during which time he did not see Mr Vernon jag pump A . It follows that the time available to Mr Vernon to jag the pump must have been a very narrow slot of about 5 minutes at the most. That of course would have been enough for the operation or operations being considered. In this chapter I am principally concerned about the sequence of alarms that was noted by Mr Bollands but the timing of these is finely related to what activities may have been taking place at the time of the explosion.

When gas alarms went off on the night of the accident Mr Bollands could have discovered which particular detector was alarming by referring to the control modules behind the alarm panels but he explained that such was the development of events that he did not have an opportunity to do this. The function of the control module is to amplify the signal so that it shows up on the alarm panels. To resort to the control module would take the Control Room Operator about 2 minutes. The implication of not going to the control module is that the same detector cannot send a second signal of the same type to the Mimic until it has been reset at the control module. There can only be one light for each zone on the Mimic until the zone light has been reset. However this not preclude a second audible alarm.

Mr Bollands describes how just after (perhaps a minute) the first gas alarm annunciated either centrifugal compressor A or C tripped . Shortly after that a further centrifugal compressor tripped and immediately before the explosion the third such compressor tripped. Thus by the explosion all three compressors had tripped. Mr Bollands then described how about two minutes or so before the explosion he got the detectors at A and B centrifugal compressors showing low level alarms (zones C4 and C5) and as fast as he would accept an alarm another would annunciate. He also got a low level gas alarm from zone C2. Thus C2 ,C3, C4, and C5 had all annunciated and he distinctly remembers an unbroken line of lights for these four alarms on the matrix. However he could not remember the precise sequence of this final flurry of low level alarms so that C2 may have annunciated before the compressor alarms. Eventually he received a high level gas alarm and the pursuers admit on the closed record what Mr Bollands confirmed namely that this alarm was in respect of a detector at one of the centrifugal compressors. The defenders argued that this admission bound the pursuers and that it does not fit into Dr Davies’ evidence. I think the defenders are perhaps trying to make rather much of this pleading point. The pursuers’ admission is in answer to an averment by the defenders that the high level alarm was "at" a centrifugal compressor. This is not quite the same as saying it was "within" or "on" such a compressor. Some of the C2 alarms were quite close to the compressors. However the point may not matter for Mr Bollands himself asserted that the high level alarm came off one of the compressors. This cluster of alarms were annunciating just seconds before the explosion and the high level alarm came immediately before the explosion. Mr Bollands related the high level alarm to one of the reciprocal compressors but he could not say which. The high level alarm had come in and Mr Bollands was trying to talk on the radio when the explosion occurred and blew him off his feet. The blast which toppled him came from his right. There were no alarms from Module B or the 68-foot level.

The alarm first noted by Mr Bollands was activated by one of G28, G27, or G103 /1 or 103/2. The alarm from the C2 zone could have been triggered by G101 /1, G101/2 or G101/3. These alarms are independent of the compressor enclosures although the other alarms which annunciated were associated with the centrifugal compressor area. However if the cloud of gas which triggered the alarm came from within Module C then the detector most likely to have triggered it was G103/1. PSV 504 which the pursuers nominate as the source of escaped gas is to the west of the detectors responsible for the said alarms and rather to the south of reciprocating compressor A. Thus an escape of gas from the PSV can readily be aligned with centrifugal compressor C. Because of the wind direction the air flow at the time of the accident was from west to east. If the escaped gas had entered Module C at the east end then this would probably only have been possible if gas had been sucked in through the compressor equipment and thus the alarms associated directly with the compressors might have been expected to annunciate first.

Taken at its broadest the defenders argued that it was odd that the pursuers postulated a leak from about the middle of the module but apart from one low level alarm at C2 the bulk of the alarms that annunciated were located at the centrifugal compressors at the east end of Module C.

5.4.4. Detector Types

The detectors on the platform at the time of the accident were manufactured by Messrs Sieger. However these manufacturers produced a number of different models of detectors and since these had different structures and capabilities it is important to know which models were on the relevant production modules at the time of the accident. I am satisfied that the model 910 was the model that was almost exclusively employed in modules A and B when the accident occurred. This model was a development from models 780 and 770 which had previously been used. Mr Tea had been the witness with the most up-to-date experience of the detector system on the platform . Certainly the records show that by 1986 or earlier if a detector was replaced it was replaced with a 910 model. Both Mr Scothern and Mr Tea gave evidence that for some time before the accident Mr Wakefield has been engaged in a programme of replacing on a routine basis older detectors with the 910 model. This was partly because the older type of detector was no longer available but also because the new detectors were easier to maintain. However Mr Scothern accepted that when he left the platform about 9 months before the accident some of the lower G numbers in Module C had still been older models. But he had kept in touch with Mr Wakefield and expressed the view that in all probability the detectors in Module B had been replaced by new models although his evidence on this aspect of matters was somewhat uncertain. Mr Tea whose direct knowledge was more up-to-date was more certain about the replacements. At best for the defenders it is clear that by the time of the accident there were a good number of the new detectors both in Module B and Module C. Indeed Mr Tea indicated that about a week prior to the accident new 910 detectors were installed in Module C in the positions associated with the fuel gas pumps

The witness Dr Balfour gave evidence as to how the detectors worked. He was 60 when he gave evidence and was a director and scientific consultant with Sieger Ltd. He held a B.Sc. with first class honours and also a Ph.D. I have no doubt that he was widely experienced in the technical aspects of his company’s products. He had also considerable experience of research, university teaching, and the production of technical literature. He held himself out as an expert in the design and operation of gas detectors and this claim was well justified. The pursuers produced a Report from Dr Balfour which was prepared in 1992 and was 13/65 of process.

The purpose of a gas detector system is to monitor gas concentrations by the deployment of a number of detectors at significant locations and these contain sensors which give an output signal if a pre-set level of gas concentration arises. The Seiger detectors I am concerned with are all what are known as catalytic detectors, that is the sensors contain a particular configuration of materials which will enable combustible gases to combine with oxygen and give rise to a signal that is proportional to the amount of combustible gas present. The catalyst substances themselves are rare earth materials such as platinum and iridium. A catalyst is a material which alters the rate at which a chemical reaction occurs but which is itself unchanged at the end of the process. The core part of the detector is a bead made up of a porous ceramic material, alumina. A further material is thoria ,a finely powdered catalytic ceramic material which is made up as a slurry and then spread over the bead and dried so as to provide an outer crust. For the combustible gases to react with oxygen the catalyst thus sits on the surface. However since the reaction requires a minimum temperature a current is passed through a wire to the bead to produce a temperature of about 450 degrees. The enclosure of the bead requires to be constructed so that the enclosure itself does not heat to become a source of ignition. When the combustible gas reacts with oxygen as a result of the catalyst heat is generated and this heat is the source of the measurement of gas concentration. Two beads (or elements) are positioned together, one with the catalyst (the sensitive element and one without (the compensating element). Comparison of the differences in the respective reactions of these two elements provides a basis for measurement. An electric circuit is created by means of what is known as a Wheatstone Bridge and of course the strength of this circuit is related to the gas concentration.

At Figure 2 of Dr Balfour’s report the 780 sensor is shown in schematic form. The feature there described as the sinter is in effect a sinterised element whose purpose is to prevent the combustion which takes place within the chamber from going outside of the sinter. Some filters are designed to prevent particles of material entering and clogging the sensor. The catalysts are vulnerable to certain elements known as poisons and these include sulphur, lead, chlorine, and silicon. The 780 type of detector can be fitted with filters which will react with and absorb these poisons so as to give a degree of protection. Another type of filter is hydrophobic and is designed for situations where the detector may be exposed to water. Dr Balfour indicated that there was much concern about the poison failures of earlier 780 models on Piper Alpha and as a result they would have been fitted with filters to remove the poisons. However because of vulnerability to poisons and other contaminants detectors should be checked and calibrated at three to four months intervals. Figure 3 of the report shows a schematic of the 910 type of detector. This model was not fitted with a filter since the construction was designed to have a bead which itself offered greater resistance to poisons. This was accomplished by spreading the catalyst not only over the surface but throughout the bead. Moreover in this model the detector could be dismantled and the bead replaced. The 780 detector which was supplied after about 1985 and thus was supplied in the period between the withdrawal of the 770 and introduction of the 910 models also contained the poison resistant bead.

The detectors take a certain finite time to respond to an increased concentration of combustible gas. The response time is the time it takes from the first concentration of gas at a particular level of concentration to be presented until the alarm signals. These times are set out in Dr Balfour’ report. Thus if a 780 sensor type is exposed to the lower explosive limit (LEL) of methane (namely 5% methane in air) the response time will be 19 seconds whereas with the 910 detector the response time is 22 seconds. With the LEL of butane the response times would be 24 and 27 seconds respectively. These times are within the accepted standard response time which is 30 seconds. The alarms are set to respond to set levels of concentration. Thus the alarms on Piper Alpha were set to respond as low level alarms if 15% of the LEL is presented and as high level alarms if 75 % of the LEL is reached. Methane was taken as the standard. Thus the LEL of methane if mixed with air requires a mixture of 5% methane in air. In his report number 13/65 of process Dr Balfour calculates the LEL for different gases. With information in Table 3 of that production and knowledge of the LEL of different constituents obtained from published literature the LEL of mixtures can be deduced. The results he obtains are not challenged. There is a degree of artificiality about his results because to obtain them he has to assume that the whole mixture is in vapour form. This assumption he claimed gave the worst case scenario. The detectors are more sensitive to the lighter ends than to the heavier. Thus if the detector is calibrated to give a LEL alarm at 15% of methane it would need a concentration of 23% of the vaporised mixture from the condensate line to give the same alarm. Likewise a low alarm set at 75% of methane requires 115% for the condensate mixture. If the sensor was exposed to a high concentration of gas then the low level alarm would go off very quickly. Indeed if the alarms are exposed to critical gas levels response times are to be measured in seconds. If the sensor is exposed to a gas cloud for a period of time which exceeds the short response times of the sensor then the sensor will react to it. This however means that the sensor could miss a very rapid transient exposure to gas. Nevertheless a 15 % LEL concentration level alarm could be triggered by a gas pulse of 100% LEL methane of 1.5 seconds duration and for higher concentrations by pulses of even shorter duration. However even when a 15% LEL alarm has been triggered a pulse of methane of concentration just exceeding 100% LEL could last for 12 seconds without generating an alarm at 75% LEL. It follows that the response of the detector is governed not only by the level of concentration of combustible gas but by the period of the exposure. Relating the position to the facts of the accident it does not necessarily follow that because the first alarm noted by Mr Bollands was a low level alarm that the gas concentration was not much higher than that level provided that the exposure time was sufficiently short. A higher alarm takes longer and may be say about 15 seconds.

A difference between response time and time to alarm must be noted. Response time is the time taken for a detector to give a valid indication of the concentration of gas to which it is suddenly exposed. It is commonly regarded as the time taken for the sensor signal to reach 90% of its equilibrium value after the sensor has been exposed suddenly to a fixed proportion of gas. It is essentially independent of the gas concentration and characterises the temporal behaviour of the sensor. Time to alarm is the time from exposure of the sensor to a sudden fixed concentration of gas to the activation of the alarm indicating a pre-determined level of gas concentration has been reached. In his Report at Table 1 Dr Balfour states the response times and times to alarm for 100% methane and 100% butane for 910 and 780 type sensors. The response times for the higher level alarms are more significant since they are longer. If only one high level alarm annunciated then the size of gas cloud and time of exposure would have to be within confined parameters.

If the gas which triggered the alarms in Module C originated in Module B and particularly at the west end of that module it would dilute by mixing with air as it travelled towards the mouths of B and C so that it is difficult to see how it could have avoided triggering alarms in B unless the alarms there were not functioning properly.

Because of the constituents of the condensate that would have been in the line of PSV 504 if a leak occurred at that point a higher concentration of gas would have been required to set-off the low level alarm than would have been the case with methane.

5.4.5 Maintenance

At the time of the accident there was no maintenance work in progress in relation to the detectors in Modules B or C. If there had been such work in progress Mr Bollands who was in charge of the alarm panels would have expected to have been told about it at handover. Generally the system was that detectors were maintained on a 4-monthly basis. The document 12/204 of process is dated 18 January 1989 and is material taken from the computer system of OPCAL relating to the planned maintenance of detectors in Module C. On the basis of these records the planned maintenance intervals were sometimes exceeded but Mr Todd (who was a Maintenance Superintendent with OPCAL and generally seemed quite a reliable witness) explained this not as a failure in maintenance but as a failure in keeping the computer records up-to-date. He indicated that there had been reporting failures identified after the accident due to some of the points mentioned in the actual logs being misinterpreted by maintenance controller. The computer records purport to show that a four-months planned maintenance was completed on 23 January 1988. However it is also recorded that a twelve- months planned maintenance (which would have incorporated calibration of detectors normally included in a four-months maintenance) was completed on 8 February 1988 and this gives some support to the view that the computer records were not entirely accurate. Moreover Mr Tea gave evidence that he had been replacing detectors during his last stint on the platform shortly before the accident and he describes this as being part of planned maintenance. He stated that the replaced detectors had in fact been in good condition but had been replaced because it was wanted to replace the cables. Mr Tea also said that Lloyds inspectors had inspected certain detectors some weeks before the accident. This inspection would not cover all the detectors on the platform but merely a selected area but the inspectors had not complained about the detectors although they had wanted some cabling replaced. Mr Tea gets further support from 15/6 (a schedule of unscheduled maintenance prepared by Mr Todd in conjunction with Department of Energy inspectors for an inquiry) and this shows that maintenance of detectors was proceeding in June 1988 as Mr Tea suggested. This document also reflects inaccuracy in the computer record. In all I have no reason not to accept the evidence of Mr Tea (who after all was doing the work) that the detectors were generally maintained on a four-monthly basis and Dr Balfour said that such a programme would have been adequate.

In 15/7 of process is a list of maintenance routines covering the period from the 22 June to 5 July 1988. This shows that a four-monthly planned maintenance routine was begun in 29 June 1988 and related to the detectors in area B2 in Module B. The time it would take to complete this work would depend on the number of men employed on it but in any event would take less than a shift. Since it would appear that other similar work was carried out after 29 June it is a fair inference that the work in B2 had been completed.

Mr Bollands indicated that there was a faulty gas head on a detector at centrifugal compressor C and that this tended to give false alarms. However Mr Bollands had been away from the platform and Control Room duties for some weeks prior to the accident date and during that period Mr Tea had replaced each of the fuel gas valve detectors. The detectors replaced seem to include the detector that Mr Bollands branded as faulty since this was said to have been difficult to work at because it was underneath the grating. Only one of the detectors at C was underneath the grating. In any event it would have been a bit of a coincidence if a detector went off about the time of other alarms simply because it was faulty.

5.4.6 Accessibility of Detectors to Gas

There was a suggestion raised in the evidence that underneath the centrifugal compressors at the east end of Module C there was not grating but rather solid steel deck. The result would be that walking between the compressors one would be walking not on grating but on solid deck. This could affect any view as to the precise location of G103/1. It gives rise to the possibility that the detector and associated fuel gas valve are not at the compressor but further to the east because immediately outside the east end of the module there was a walkway made up of grating. On the other hand Mr Scothern said in evidence that walking between the compressors one walked on grating and he was not challenged on this. The general arrangement within the production modules was to use grating as walkway. The schematic 12/128 shows the location of the fuel gas valve as being just to the right of the box inboard of the turbine compression air hood. In 12/107 of process which was spoken to by Mr Wottge grating is shown extending along the side of the compressor. On the other hand in the schematic 12/112 of process the position of the fuel gas valve is ambiguous. The defenders’ witness Mr Ferguson was a mechanical technician who had joined OPCAL on Piper Alpha about 1977 and worked on it until the accident which he had experienced and survived. In his evidence he refers to there being grating between the centrifugal compressors. The video 41/21 of process may show that the walkways between the compressors were grating but unfortunately none of the witnesses spoke to this particular feature of the video and the relevant pictures may in the circumstances be open to misinterpretation. When the pursuers’ witness

Dr Davies expressed the view that G103/1 was the likeliest candidate to have been the first alarm noted by Mr Bolland what was critical to his theory was not whether the detector was inside or just outside the module but rather whether there was a clear path for gas to travel between PSV 504 and the detector. However given the evidence of Mr Wottge, the clear and unchallenged evidence of Mr Scothern (who had worked in the relevant area), of Mr Ferguson, and the general arrangements for walkways then the likeliest situation is that the relevant walkways were comprised of grating. If the defenders had made it clear in time that they were challenging this point then no doubt it could have been settled emphatically by other witnesses who gave evidence before any challenge emerged and were familiar with the modules. Indeed when the defenders cross-examined Mr Tea they seemed to be suggesting to him that there was a labyrinth of grating between the compressors. If the grating extends inside the module then there is nothing to prevent gas within the module proceeding to the detector underneath the grating wherever the fuel gas valve is situated. What is important is that G103/1 although it may be outside the strict bounds of Module C is situated inboard of heavy equipment blocking the mouth of the module. It would thus appear to be more vulnerable to gas coming from within the module than to gas coming from outside it. It is gas coming from outside that would certainly have to pass the combustion air intake. In fact in my view assuming a single C3 low level alarm triggered by gas coming from within the module G103/1 would be the most likely detector to be affected. This was indeed the conclusion to be drawn for the tests carried out by Dr Davies. As to the indication by Dr Davies that he had assumed that the detector G103/1 was within the module the practical point of interest for him was that it should be exposed to the airflow coming from within the module. His interest in the limits of the module was not a technical matter but a practical matter.

The fuel valve gas detectors were able because of their construction to detect gas within C Module as well as from the valve itself. Mr Scothern’s evidence on this matter was not challenged. The position is the same in relation to the detectors outside the gas turbine compartments except that there was a challenge to the effect that positive pressure inside the compartment might affect the ability of the detector to detect gas from outside the enclosure. Dr Balfour accepted that there was a possibility that G27 might have been unable to respond other than rather slowly to gas from outside the turbine compartment. However Dr Davies was quite positive that in respect of G103/1, that detector would be capable of responding normally to gas coming from the outside of the compressor compartments.

5.4.7 Poisoning of Detectors

The question of the poisoning of the gas detectors is important because the defenders suggest that one reason why no detectors in Module B signalled alarms at the time of the accident may have been because these detectors had been immobilised by poisoning caused by H2S gas. In support of this possibility the defenders towards the end of their proof led an expert, Professor Johnson, and a number of eyewitnesses, particularly Mr Meanan and Mr Ballantyne, who spoke to the presence of H2S gas on the platform in the days preceding the explosion. This evidence was led under reservation in the face of an objection by the pursuers that the issue had only been raised at a late stage of the proof and had not been suggested to the pursuers’ witnesses. I certainly think that it unfortunate that the defenders did not develop the matter at an earlier stage of the proof and in particular at a time which would have permitted the pursuers to explore the matter with the witnesses who spoke on the question of gas detection. Moreover other witnesses such as Mr Bollands had opportunities to observe the factual position which could have proved highly significant. Shortly before the date of the accident Mr Bollands spent five shifts on duties which would have involved working in Module B and thus may have been in a good position to observe any intrusion of H2S (a gas with a strong and distinctive smell). Mr Clark (the Maintenance Lead Hand) would have walked about the module on the night of the disaster and the painter witnesses Dixon and Barron claim to have been working in Module B on the day of the accident. Indeed looking to the defenders’ pleadings until a late stage of this very lengthy proof the pursuers in my view were perfectly entitled to consider that the defenders’ explanation for the lack of alarm responses from Module B was that at the time of the accident the detectors in that module had been "pinned out" - that is to say temporarily decommissioned. Whereas I shall consider the evidence in question I should not be inclined to give much weight to it unless I was satisfied that the pursuers had not been prejudiced by its late and unheralded introduction. Certainly the witnesses McLeod and Henderson were asked some general question about the possible presence of H2S on the platform before the accident but this was not obviously linked to any possible effect on the efficiency of the detectors.

The defenders’ expert on gas detection, Professor Johnson, did not give his evidence until February 1995 but had not been approached by the defenders until January of that year. He was a chemist aged 56 and had recently been elected to a Chair in that subject at the University of Cambridge. Before that he had occupied a similar position at the University of Edinburgh. He was a B.Sc. and Ph.D. and indeed there is little doubt that he is a distinguished chemist. He was a fellow of a number of learned Societies and has more that 600 publications to his name. Professor Johnson confirmed that H2S contains sulphur elements which constitute a well recognised poison of catalysts. H2S would be capable of penetrating the Sieger detectors and affecting the catalysts so as to completely de-activate the detector by bonding with the catalyst and forming platinum sulphide. The professor claimed that the poisoning would take place quickly so that with 10 to 12 parts per million it could occur within seconds. The precise timing would depend on the number of catalytic sites. However he accepted that a concentration of 3 or 4 parts per million of H2S would have a notable smell and 15 parts per million would have a clear effect on health. It follows that since any escape of H2S would have to travel to reach a detector and could scarcely escape dilution it was likely at some stage of its journey to reach noxious limits. The gas is rather heavier than air. It also has to be noted that Professor Johnson had no practical experience of detectors and in particular Sieger detectors. Moreover the detectors were operating at higher temperatures than Professor Johnson had used in his experiments. Dr Balfour ‘s experience with the 910 model in the field was that poisoning was materially inhibited. The pellisters specially developed for the 910 models were designed significantly to increase the time resistance to poisoning. Moreover the 780 detectors had filters of a chemical nature designed to absorb poisons. The varieties of these were designed to give particular protection against specific gases. Professor Johnson’s calculations related to pure H2S without reference to the effect of filters. The pellister on the 910 model was thought by Dr Balfour to be so improved that it did not require a filter. Furthermore because of the way this evidence developed Professor Johnson’s views were never put to Dr Balfour. Indeed Dr Balfour’s opinion was that the Sieger 910 would respond well to concentrations in the field of 100 parts per million of H2S. His views on the effect of poisons on Sieger detectors were based on laboratory tests. On the other hand Professor Johnson considered that the fact that the catalyst was spread throughout the bead would fail to keep the gas out but the practical experiments carried out by Dr Balfour to compare the different types of beads do not bear this out.

The phase II Module on the platform had the capacity to produce limited amounts of H2S with the result that on the drilling rigs associated with that module there were H2S detectors. There was some concentration of H2S in the separators in Module B but any escape from the separators would release a quantity of hydrocarbon which would trigger an immediate gas alarm and would also be likely to trigger the pressure level warnings on the separators. Although the defenders did not explore with the pursuers’ experts the precise relationship between hydrocarbon and its content of H2S insofar as reacting on detectors it is not difficult to suppose that the hydrocarbon would cause the alarm to trigger before any H2S could affect it otherwise there would be little point in having detectors . This is essentially a practical question which Dr Balfour would have been well qualified to answer. Moreover the risk of gas escaping from the separators was not taken up with the pursuers’ witnesses like Mr Wottge. The H2S of the gases in the separators was of a concentration of about 41 parts in a million but no attempt was made to ask the experts what degree of dilution this would experience after escape and before it reached a detector. In the oil itself as it left the platform there was a concentration in it of about 2.2 parts of H2S per million. One implication of this is that if oil itself were to escape there the H2S in it should cause a smell which should be readily noticed.

The defenders led evidence designed to show that there had been escapes of H2S on the platform in the days immediately preceding the accident. Thus Mr McLeod, a pursuers’ witness gave evidence in cross-examination that some days before the accident there had been an intense smell of gas in the dive skid area. There was no indication where this gas (if it was H2S) came from. Mr Tea could not remember having had problems with poisoning of detectors accept in a specific area associated with silicon polish. There was no evidence that any escape of H2S from the Gas Conservation Module could have extended to the dive skid, the experts of flow patterns not having been asked about this. It however seem to be the case that in regard to the flushing out of the molecular sieve beds in the Gas Conservation Module going on about the time of the accident that a certain amount of H2S would have been generated. However it has to be noted that the relevant operations were being monitored by safety personnel and that this included testing for H2S

The defenders led three witnesses to speak to the presence of H2S on the platform just prior to the accident. Their witness Mr Fowler was 36 when he gave his evidence. He had been a survivor and had been a joiner with Wood Group. He had on occasions noted a smell of gas on the platform but attributed this largely to the flaring. He does not attempt to relate his experience of gas to any particular date and I did not consider that his evidence had much significance. Another witness Mr Meanen was aged 36 and had been working on the platform as a scaffolder at the date of the disaster. He had worked on the platform only since March 1988. He claimed that during the period of about three days prior to the accident he had noticed a strong smell of gas in the area of the Gas Conservation Module. He had been told to avoid the staircase coming down past the face of that module. He claims that there were a lot of OPCAL activity in the area involving men with safety meters. They were on the hatches above the gas module. Indeed he opines that on the day of the accident he could smell gas all over the platform. He was not certain if what he smelled was H2S. The problem is that earlier witnesses had not been asked about this by the defenders so that it is difficult to know what might have accounted for any such smell and what steps may have been taken to monitor for H2S. Mr Grieve who was the phase II operator and had an office in the Gas Conservation Module was not asked about it by the defenders. The evidence was led towards the very end of the defenders’ proof. Indeed the pursuers had objected to the evidence being led at all and I had reserved this objection. The defenders’ third witness on this topic was Mr Ballantyne. He was 52 at the time of giving evidence and was employed by Wood Group as an electrician. He was on the platform on 6 July 1988 and he had commenced working on about 4 July in the Utility Module which is above Module C. About 11am on the morning of 4 July he and a fellow employee had smelt gas. He reported the matter to OPCAL’s employees who were monitoring gas next door in the Gas Conservation Module. He had lifted some of the grating off the floor in the Utility Module. He was advised that it might make him a bit sick but otherwise would do him no harm. I think that the probability is that the gas he smelt was H2S. The smell continued through to 6 July. He explained that he had opened the door of the Utility Module to disperse the gas particularly as it has been very warm. Indeed he proceeded to say that when working on North Sea platforms the smell of gas is always present. On the other hand he accepted that the gas was always being monitored. Of course because the matter had been not raised earlier the pursuers’ witnesses were not asked about it and about the nature and effect of any monitoring. Nor were experts asked about possible flow patterns between the likely source of the gas and the Modules B and C. For example I could not know if any escape of gas from the Gas Conservation Module could have penetrated significantly into Module B. It must be noted that Professor Johnson indicated that H2S would only be noticed as a smell in low concentrations . This is because high concentrations would de-sensitise the nose. He had doubts as to whether a concentration of 10 parts per million would be detectable by smell. The implication is that if workmen were smelling gas on the platform the concentrations must have been relatively low.

In my view Dr Balfour raised the question of poisoning not in connection with any suggestion that the detectors in Module B might have been disabled by poisoning but rather to explain the evolution and attributes of the various models of detectors and also to explain the maintenance requirements affecting the detectors. He was never specifically asked to what degree if any the circumstances described by the defenders’ witnesses could have immobilised detectors in module B. However in his Report there is a graph which purports to demonstrate that exposure of the 910 detector to 100 parts in a million of the gas over a period of five hours would still leave the detector with a substantial degree of efficacy although it would suffer a 10% reduction in efficiency. To understand what Dr Balfour’s position would have been it certainly would have been essential to hear him on the implication of this graph for an assessment of Professor Johnson’s evidence. Moreover it is clear from the evidence that before an escape of H2S could arrive at a detector with a concentration of 100 parts in a million anyone who happened to encounter it on the way would be rather ill. The cross-examination of Dr Balfour seemed to be aimed to bring out the fact that it was the 770 filters that were vulnerable to poison. It would appear that some of Dr Balfour’s experiments were carried out using a substance known as HMDS which he describes as a strong poison although Professor Johnson suggested that perhaps this poison might have more difficulty in penetrating the beads than H2S. This would depend on the pore size of the beads in relation to the molecular size of the gas and the matter was not put to Dr Balfour. Moreover Dr Balfour’s tests were apparently carried out for practical reasons . It might seem odd that a person as well qualified and experienced with detectors as Dr Balfour would choose for tests a gas which was unsuitable for examining the efficiency of the detectors in respect of a gas which he well knew was commonly encountered on oil platforms. However, as I have said, he was not asked about this. Even Professor Johnson accepts as a general rule that the more catalyst is spread through the bead the longer it would take for a poison to de-activate it and he had no direct experience of the effect of H2S on platinum at temperatures of 450 degrees Centigrade (this was the temperature at which the sensors operated and it might feasibly cause burning off of the sulphur). However his general opinion was that the higher temperature would accelerate the poisoning process.

There was no evidence in the case that H2S might itself have caused the explosion.

The importance of the question of poisoning is that it is important to explore why at the time of the accident none of the 13 detectors in Module B went off whereas a number of detectors in Module C did register gas. However I am of the view on the limited evidence which was before me that it is unlikely that all or indeed any of the relevant detectors in Module B were incapacitated by gas. Certainly the detectors in Module C which were close to the open east end of the module do not appear to have been affected by gas and if there was indeed an escape of H2S there was no evidence to explain why this should be confined to Module B. The witnesses who spoke about H2S were not consistent as to the whereabouts of the gas. Moreover it is difficult in particular to understand why the whole length of Module B would be affected by poisoning of detectors without there being any effect on those detectors at the east end of Module C.

5.4.8 Incorrect Control Modules on the Detectors

Although it was not raised in their pleadings the defenders developed a case that the detectors in Module B would not have been working at the time of the accident because they had been fitted with the incorrect type of control modules. The function of the control module was to amplify the signal that was coming from the detector so that the alarm in the control room would respond to the signal being received from it. It also had the function of sending the correct electrical signal to the detector head to heat up the detection bead to the right temperature. The pursuers rely for their contentions on certain evidence from Dr Balfour although it was conceded that Dr Balfour was not called to develop the point that the defenders ultimately made but to give general evidence on the design and operation of the detectors. His company after all were the manufacturers and suppliers of the detector equipment. I accept that he was well qualified to give authoritative evidence on the matters he dealt with. Dr Balfour had explained how his company had supplied to the platform Operators at various times the detector types designated 770, 780, and 910. Because of changes in the configuration of the catalytic beads type 910 was distinctive from the 710. Dr Balfour explained that the later detector (910) required a different amplification of electrical signal to the 770. Thus the 1401 module or 1402 went with the 770 whereas the 1411 or 1412 module was required for the 770 and 910. The two later detectors were of course developed because of concern about poisoning which arose in relation to the earlier type of detector. When Mr Scothern was asked about the type of detector in Module B at the point of time when he left working on Piper Alpha in August 1987 he stated that all the low numbers that is G13, 14, up to G21 were 770 with the 1401 modules whereas the high numbers were the 910 series. The defenders accepted that in relation to Module C the high numbered detectors were of the 910 type and that they had the correct type of control modules. Indeed there is nothing in Mr Scothern’s evidence to suggest other than that the 910 detectors fitted in his time had the correct type of control modules. The modules required for the type 910 detectors required to be fitted to the control room as extensions to the original panels for the 1401 modules. This was because there was not room in the original panel racks for the replacement modules. The Operation Manual (number 12/3 of process) gives some detail of the layout and types of control module but the document was prepared about 1986 and the 910 detector only became available after about that time.

It is clear that in the period shortly before the accident Mr Wakefield , who was Mr Tea’s back-to -back, was replacing certain of the older type of detector heads with the 910 type. However Mr Tea himself did not seem to have participated in that particular programme and we do not know why Mr Wakefield had been nominated for this work. Unfortunately Mr Wakefield did not survive the accident so that all the evidence about his activities essentially comes from Mr Tea. The defenders suggest that the actions of Mr Wakefield were not planned or controlled but I find it hard to accept this especially since it was not taken up with the witnesses who were responsible for supervising Mr Wakefield such as Mr Todd. It is difficult to believe that he would not have required specific approval to withdraw the detector heads from supplies and to earn the overtime it was suggested that he was enjoying.

Mr Tea certainly suggested that by the date of the accident the detectors would all have been 910 models and that Mr Wakefield had done the replacement work. Mr Scothern also indicated that he was aware that Mr Wakefield had been engaged in replacing detectors and he thought that all in Module C would have been replaced with the newer detector. It seems clear that Mr Wakefield was doing the replacement work outside the formal maintenance programme (which meant in effect that he did the work in overtime) but that of course does not mean that the work he was doing was not approved or supervised. It should be noted that the replacement of detector heads appears to involve the replacement of cabling and it was never suggested that this could be done without a permit to work unless the work was to be regarded purely as routine work. The matter was never effectively explored in the evidence because the specific point that the defenders raised for the first time in their submission (namely that detectors with incompatible modules were fitted) was not really raised with any of the supervisory witnesses who should have been in a position to comment. Indeed the matter was not even raised unequivocally with Mr Tea. He declared that to replace the detector heads with the newer model the only additional work that had to be done was to replace the junction boxes but this answer may well have been intended to describe the work in the field and not replacing the modules which would have been carried out at a different location and possibly even at a different time. The evidence about the extent of the replacement of the earlier detector heads with the 910 model is somewhat vague and not always consistent. However older detectors had been replaced with the newer 910 detector over a period stretching from 1986. I should hesitate to find as the defenders asked me to do that all the detectors in Module B had been placed by 910 types but I think it likely that at least a material number of the detectors had been thus replaced. The defenders’ contentions were in the end that none of the detectors in Module B could have been regarded as reliable at the date of the accident because Mr Wakefield had replaced the heads without fitting the appropriate modules. I find it impossible to accept this submission. Firstly it would mean that the defenders had no effective gas detection system at all in Module B and although that it not impossible it is intrinsically unlikely for the pursuers certainly had in place quite elaborate arrangements for maintaining an effective gas detector system. The detectors at the east end of Module C which seem also at least to a large extent to have been fitted with the 910 detector heads seem to have been functioning on the occasion of the accident . The defenders’ maintenance system may not always have been recorded accurately but they clearly had such a system and Mr Todd explained the situation. Indeed even on Mr Tea’s evidence Mr Wakefield was normally employed on maintenance. The platform Operators had Lloyds inspectors auditing at least some of the gas detection system some months before the accident. The main objection to the defenders’ position is that they seek to construct a very material deficiency in the gas detection system on a basis that was not raised in the pleadings nor even with most of the relevant witnesses. The defenders are constructing their whole argument on the basis of certain observations by the witnesses Tea and Scothern and even that evidence was never focused on the specific issue I am asked to consider. In fact during the course of the case in respect of the matter of the gas detectors the defenders changed their attack from time to time. They began by relying on allegations that the detectors had been racked-out. During the evidence the gravamen of their attack appeared to change to the effect that the detectors may have been poisoned and not working for that reason. I must say that it must have seemed as big a surprise to the pursuers as it did to me when in late submissions the defenders argued that the detector types were not compatible with the control modules. When Dr Balfour was giving his illustrative evidence about detector types he did observe that the 910 detector was supplied with a specific module type and that other modules were inappropriate but just what would happen if the existing module was not replaced was never really raised with him. If the 910 detectors were supplied with the appropriate module (which is what one would expect) no-one explained what had happened toall the modules if they were not fitted as the detectors were replaced. In any event it may be that accuracy would be affected if the modules were not changed but the detector could still be expected to register. Alternatively the position may simply be that the alarm would require more time to produce a signal. Nor was Dr Balfour asked about Mr Scothern’s suggestion that the 910 detector could be adapted to work with the 770 module. He was never asked what instructions for fitting new detectors were supplied with the equipment. Since the new type detectors had been used since 1986 I find it highly unlikely that audits and calibrations since that time would not have thrown up problems if the detectors were not functioning properly. Thus I think it can be assumed that the platform operators were familiar with the requirements of the new detectors and there is no reason to suppose that Mr Wakefield who had been entrusted with the task of fitting further detectors was in any different position. I am not convinced that Mr Wakefield did not fit new modules. Mr Tea may have seemed to suggest that Mr Wakefield’s overtime activities did not include this but Mr Tea was not present when Mr Wakefield did his work. Moreover Mr Tea gave no indication that he personally was aware that to fit new detectors involved the replacement of the old modules and if he was ignorant on this point it may explain why he did not realise that Mr Wakefield may have been fitting modules. He may well have misunderstood the position. It may be that when new detectors and modules are supplied the modules are fitted first in preparation for the work on the detector heads. It was suggested that the regular calibration tests might not have shown that the wrong control modules were fitted but again this was never put to the witnesses who would have known. Even Mr Tea was never in fact asked if it was possible that the detectors in Module B were not working. If this matter had been put to him he might well have said that his maintenance and calibration tests would have disclosed this problem if it had existed. Indeed insofar as the evidence went it is clear that after a head had been replaced it would be calibrated by the fitter. There is not a great deal of evidence about the calibration procedure but the calibration routine is set out in Number 41/14 of process which was spoken to by the witness Mr Scothern . The procedure set out in this document indicates that when a calibrated mixture of gas is applied to the detector upon testing the Panel and Fire Alarms (as they were described) sound. In addition to calibration at the time a new head is fitted the detectors were calibrated during routine maintenance schedules. Moreover the alarms had a fault detecting alarm that might be expected to register any reduction in the electrical supply. Whether or not this fault alarm would annunciate if a detector was fitted to a module that transmitted an electrical supply that was too weak was not explored. Nor is it really clear whose job it would have been to fit replacement modules. Mr Scothern’s evidence on this was rather vague and in any event it may be that in Mr Wakefield’s time a different system was employed particularly of fitting the new modules requiring a more specialist technique. If Mr Wakefield had the experience and responsibility for fitting any replacement modules that were required then it would be difficult to explain why he did not do this since he would have known that to fit the detectors alone was worse than useless. If he did not know that different types of detector require different modules this may be because it was someone else’s job to attend to this. It was accepted that certain at least of the 910 detectors had been provided with the appropriate module. None of the surviving witnesses were asked about the matter. More significantly the senior personnel were not asked about the possibility that the defenders seek to rely on . Nor were they asked about the system for instructing work carried out for the replacement of detectors nor any supervision or checking that would have been applied. Detectors certainly registered in Module C and it would again be a striking co-incidence if any problems with the detectors only applied to B. The defenders’ submission really involves the implication that the pursuers had no proper system for the fitting of new detectors and I do not see how I could begin to suppose this when the appropriate witnesses were not even asked about it

It should also be noted that the witness Scothern said that he was able to adapt the new detectors to the old modules. Dr Balfour said that the 910 was not compatible with the earlier modules. However he was not asked about the possibility of adaptation.

In regard to the control modules (and also to poisoning) the main reason that the evidence did not cover so many matters which were important if these issues were to raise significant questions in the cases is that neither issue formed part of the defenders’ case as pled. The defenders have sought to construct defence points from evidence that emerged as incidental to quite different questions that were being explored. Looking to the whole position I have no reason to believe that the detector system in Module B was not functioning properly on the occasion of the catastrophe. Even on the basis that Mr Tea’s evidence bears the significance that the defenders seek to confer on it some of the detectors in Module B had been fitted with appropriate control modules and it is a curious co-incidence that none of these should have annunciated alarms if Module B produced a volume of gas which even when diluted by air proceeded to Module C in sufficient concentration to set off alarms there and cause an explosion.

It should be noted that there was evidence that the week before the accident new 910 detectors had been installed in Module C in connection with the Centrifugal Compressors.

The defenders asked me to note that Dr Balfour was present during the evidence which was given by Mr Scothern.

5.5. Observations of the Explosion and its Consequences

5.5.1 General

The pursuers led evidence from a number of witnesses who had seen or perceived aspects of the explosion or its consequences. The implications of this evidence was then spoken to by experts. In this regard the pursuers led as one of their principal experts Dr Mitcheson. He was at the time of giving evidence a partner in a firm of consultant scientists and engineers who specialised in fires and explosions and had become a partner in the firm in 1983. He was 43 years old and held a first class B.Sc. in mechanical engineering. He then won various scholarships and was eventually awarded a research scholarship with British Gas to undertake work on gas explosions. He also worked at the Midland Research Station of British Gas and there worked under the direction of the witness Cubbage. He gained a Ph.D. in 1977 on "The relief of pressures from containers with internal explosions". He was involved in the investigative and loss prevention work of his firm. He had investigated about 500 incidents involving fire and explosions. In particular he had been involved in incidents relating to the Petro-Chemical industry and investigated two explosions in the North Sea. He is a member of a number of distinguished engineering Institutes. He was instructed in the Piper Alpha case the day following upon the accident. He had been retained by Paull & Williamsons in relation to the present cases in about January 1993. I gained the impression that he had a wide range of experience and that he was practical and quite sensible. However he made one mistake which I am inclined to ascribe to error of judgment. As a preliminary to his evidence he was asked to assume that Captain Clegg (a witness whose evidence will be analysed later) had seen the initial explosion manifesting itself as a blue flash which, originating at the mouth of Module C, then travelled in both direction along the west face of the platform. Dr Mitcheson gave evidence on the assumption that this had happened. However when the question of the northward travel of the blue flash was raised in cross-examination he volunteered that he was not happy about the phenomenon of the blue flash spreading northwards from Module C. He explained that since he had been asked to assume that this had been seen and the matters he had been asked to comment on related to the possible source of the explosion he had felt no obligation to comment on the assumption he had not been asked about. However he freely admitted that he did not like the evidence about the extent of the spread of the flash and indeed he volunteered this information before he was being pressed about his evidence in any serious way. I think it would have been much better if Dr Mitcheson had said at the beginning that he did not see how the assumption which had been put to him could be justified. The defenders sought to make much of this matter and indeed suggested that since Dr Mitcheson had shown himself to be unreliable his value as an expert was totally discredited. They sought to extract support for this from Ikarian Reefer. It may have been an error of judgment not to draw my attention initially to his doubts about the pursuers’ assumptions but it is clear from the way he raised the matter later that he was not deliberately trying to mislead the Court. However apart from any possible criticism that may be levelled against him for the way he handled the matter of the perceived spread of the flash to the north it seemed to me that Dr Mitcheson was a very useful and reliable witness. In any event much of his evidence was supported by either Mr Cubbage or Dr Drysdale and there is simply no reason not to consider any of his evidence which seems to represent his professional view and to be supported by other well qualified experts.

The defenders also contended that Dr Mitcheson’s experience was inadequate in relation to the matter he opined about. He deponed that he had investigated about 500 incidents of Fire and Explosions. Of this number perhaps about 10% related to explosions. He thought that he may have investigated about 50 to 100 incidents relating to the petrochemical industry but he could not be precise about the number. The best figure he could give was between 30 and 50 incidents. Perhaps 10 of these involved explosions and of these two were on North Sea platforms (Glomar Artic II and Heather Alpha). He accepted that the two North Sea explosions had not involved breaches of firewalls. However one of the incidents involved leakage from a flange. There was some damage to internal dividing walls. The explosion injured but did not kill an operator who had been investigating the leak. It is perhaps interesting to note that this person reported having observed a swirling cloud of gas just before the explosion. Dr Mitcheson accepted that in relation to the incident he was discussing he did have available to him after the accident the process equipment. He accepted that he had never been involved in investigating an accident such as Piper Alpha where all the platform had been lost . It would be very unfortunate indeed if there were many opportunities for such an investigation. I do not think the defenders’ submission that Dr Mitcheson had limited experience of oil platform explosions is very significant. Nor do I think it is important to suggest as they do that he had no experience of investigating something as complicated as the Piper Alpha accident. He was only asked about such matters as it should have been within his competence to answer and as I have said on a number of important issues his views were supported. He was an experienced engineer and his experience although widely focused in relation to fire and gas accidents did have the advantages of such width. He seemed to me to be well versed in explosive theory and this no doubt originated from his experience. Investigating accidents involving fire and explosion was his work and the defenders had no equivalent general expert giving evidence.

The pursuers’ witness Mr Cubbage was 68 at the time he gave his evidence and was a retired engineer. At the time of his retirement he worked with the Midland Research Station of British Gas at Solihull this establishment being a leading centre for gas production research. He had done particular research into explosions in ovens used for paint drying processes. He had been involved with many explosions on an experimental basis and had also investigated a number of accidental explosions. His memory on the number of such investigations was rather inconclusive. The figure is likely to lie between 30 and 80. He had also worked for some years in experimenting with a device to prevent flames propagating through pipes. He had carried out a series of tests in connection with the investigative work that followed upon the Ronan Point explosion. He was manager of a unit researching into safety and hazards. He too had a B.Sc in his case being in General Sciences. He had considerable research experience and at the time of his retirement before the accident in July 1988 he was in charge of 50 to 60 staff. He was a member of various Institutes and was clearly well recognised in his field. He had been a member and Chairman of the United Kingdom Explosion Liaison Group and in 1987 had been awarded the MBE. His colleague at the research station, Dr Harris, had published a book on their experimental work which is used widely by academics in the field. He had given evidence at Lord Cullen’s Inquiry and had been instructed by Paull & Williamsons about the early summer of 1992.

Mr Cubbage was well versed in the theory of explosions. The defenders disputed this and claimed as they did with Dr Mitcheson that Mr Cubbage had little experience of investigating accidents where all the real evidence had been lost. I do not know how meaningful this is . Mr Cubbage said that he had investigated accidents where all that was left was a pile of rubble. In another case the damaged plant had been taken out and there was only witness evidence. He agreed that he had never investigated an explosion on an offshore production module and that such an incident would raise particular problems such as the effect of turbulence. Moreover his experience has generally been with town or natural gas rather than petrochemicals. He however has had experience with gas oil which is similar to the lighter types of crude oil. Mr Cubbage occasionally got a little confused about certain matters. Sometimes he accepted that he had changed certain views since the original Cullen Inquiry. He is retired and I got the impression that the odd episodes of hesitation and imprecision were due to his age rather than to any inadequacy in his experience. At the Cullen inquiry he had apparently suggested that the flashing phenomenon seen by Captain Clegg may have been caused by two explosions, one at each end of Module C. Not surprisingly he was not too happy about that position and he changed it after hearing Captain Clegg give evidence before me. Certainly like Dr Mitcheson he had a wide general experience of the theory of explosion. Again the defenders produced no witness of superior specialist knowledge in relation to the general investigation of explosions. When the evidence of Dr Mitcheson and Mr Cubbage coincided I had little difficulty in accepting it. Even on occasions when Dr Mitcheson stood alone in the evidence, on many matters his evidence was so obviously founded on experience and persuasive that I considered that I could pay regard to it. On the few matters where Dr Mitcheson and Mr Cubbage disagreed I generally found that Dr Mitcheson showed evidence of having greater depth of technical knowledge Where there was disagreement I was inclined to prefer Dr Mitcheson. However none of this is intended to be a departure from my view that Mr Cubbage was a witness who had wide and valuable practical experience of explosions

The pursuers’ specialist expert witness on the subject of fire was Dr Drysdale. He was 54 when he gave his evidence and was a Reader and Director of the Unit of Fire Safety Engineering at the University of Edinburgh. He had a first class honours degree in Chemistry and a Ph.D. from Cambridge University gained in 1966. He has held a research position at the University of Toronto. He has also held a post at the University of Leeds. He has been attached to the Fire Engineering Department at Edinburgh University since 1974. He is attached to the Center for Fire Safety in Massachusetts in the United States where he is a visiting professor. His experience encompasses the entire range of fire phenomena. He has produced 40 Research Papers and 32 Conference Papers. He has also published a number of books the main one being " The Introduction to Fire Dynamics". This book has international recognition and he declared that it was his understanding that every chief fire officer in Sweden has a copy of his book on his desk. He is the Editor of the Fire Safety Journal and European Editor of a series on Fire Science and Engineering. He also has had practical experience of investigating fires. To me Dr Drysdale seemed a witness of very wide experience in his subject and of sound judgment. He gave his evidence in a restrained and convincing manner. Just as they had attacked Dr Mitcheson and Mr Cubbage the defenders impugned Dr Drysdale’s experience. Certainly his experience did not lie principally in the field of Hydrocarbon fires and he had little direct experience of pool fires. Much of his investigative work had involved combustible solids. Against this must be placed the fact that as his curriculum vitae shows Dr Drysdale has a very wide general experience of fire propagation. Moreover he indicated in his evidence that the concerns of a fire engineer would include understanding petro-chemical fires. He was confident and balanced in his evidence. His logic and reasoning were much easier to follow than was the case with Dr Magnussen (the next witness I shall describe) although that may have been attributable to the fact that the latter was not always comfortable in expressing himself in English. It cannot be denied that Professor Magnussen is a well qualified witness and is no doubt highly respected in various areas of the petrochemical industry particularly in theoretical and experimental work. It must be noted however that Professor Magnussen had not personally investigated accidents. He was altogether more hesitant and less certain than Dr Drysdale about his views. This may partly have been a temperamental difference.

As I have said the defenders also led a witness on fire science namely Professor Magnussen. He was 61 when he gave his evidence . He was a Norwegian national and although his English was in the circumstances good I found that occasionally it let him down and he was not easy to follow. He is the Professor and Head of the Department of Applied Mechanics, Thermodynamics and Fluid Dynamics at the Norwegian Institute of Technology in Trondheim in Norway. This is the most important establishment of its kind in the country. He was also a Division Director for the Society for Technical and Industrial Research in Norway. which does consultancy work for outside bodies including industry. He holds a M.Sc.and a Ph.D. both gained in Norway. His doctorate involved studying combustion and turbulent jet flames. His working life before securing his present position included extensive practical engineering and research experience. In 1982 he was made a visiting professor at Keio University in Japan. He has extensive experience in all aspects of combustion including theoretical investigation into oil flames. He has investigated the turbulent interaction of flames and has a special interest in soot. It has to be observed that Professor Magnussen may not be particularly experienced in explosions as such. He had done work in connection with pool fires. He was first instructed by the defenders in June 1994. Some of his evidence may have incorporated specialist knowledge not available to Dr Drysdale. For example he may have had a more extensive knowledge of the quality of smoke likely to come off hydrocarbon. On the other hand he gave certain evidence which is difficult to reconcile with what actually happened

Gas may be specifically mixed with oxygen or instead of such pre-mixing the gas may be allowed to stream into the atmosphere and mix with oxygen as it will by diffusion. Thus the consequent flames will either be pre-mixed flames or diffusion flames. An explosion will involve a sudden or rapid release of energy released by combustion and the consequent manifestation of pressure. The pressure is the hallmark of the explosion. In a turbulent flow of gas the movement is somewhat random and chaotic. On the other hand in a laminar flow all components of the fluid (which includes gas) are moving in the same direction and at the same speed. A propagating flame is one which propagates into a flammable atmosphere ahead of it. The rate at which the flame propagates through the flammable material is the burning velocity of the flame. In most conditions this will be quite slow - perhaps 0.5 metres per second. The normal picture of a gas explosion is a flame propagating through a gas mixture. The flame causes a reaction which generates heat and this causes the gas to expand thus in turn causing the pressure particularly if there is an enclosure. For most gases the increase in the volume of the gas will be of the order of 7 or 8 times. This is the expansion ratio. If the commencing pressure was of the order of 1 bar the resultant pressure would be of the order of 7 or 8 bar. In a situation where there was no enclosure there would be an expanding ball of flame but no explosion. If a flame ignites a ball of gas at the centre of it the products of combustion are trapped behind the flame envelope and this pushes the flame ahead much quicker than would normally happen because of the expansion of the combustion products. The unburned gases themselves are also pushed ahead of the flame. The movement of gases will be towards an available vent such as the open end of a module. If an explosion were towards the east end of Module C there would be a rapid movement of gas towards the west end of the module with some, but less, venting out of the east end which because of equipment is much more confined than the west end. The early stages of the explosion will generate little pressure and it is not until the later stages that the pressure becomes highly significant. In the case of an idealised spherical cloud, at the point when the flame has penetrated halfway into the cloud, only about one-sixtieth of the combustible gases have been consumed. The time taken for the explosion to develop is short in absolute terms but nevertheless a finite time is required. The pressure generated would travel at the speed of sound. Thus the pressure disturbance travels at about one hundred times faster than the propagating flame and due to the disparity between the speed of the flame and the speed of the pressure disturbance this leaves sufficient time for the expansion to equalise throughout the bulk volume of the burned and unburned gases. Thus there is isobaric pressure. Because the pressure is acting equally throughout the container there will come a moment when it will overcome the weakest part of the container. In a real situation as the unburned gases are pushed ahead of the flame if it encounters an array of obstacles, such as would be created by equipment, the gas flow instead of remaining laminar will become turbulent. When the flame encounters a region of turbulence it will experience a very rapid combustion. The swirling that will occur behind an obstacle as the eddies take effect will assist the reaction of the flame with the unburned gas ahead of it and this will greatly accelerate combustion. The increase in burning velocity will accordingly also accelerate the development of pressure. The flame in fact generates its own turbulence ahead of itself and then feeds on it. The acceleration of the flame speed by turbulence can reduce the differential between that speed and the pressure pulse to the extent of disturbing the isobaric effect which there otherwise would be. However this effect will not be too great. Thus if the explosion took place in Module C the pressure effect for practical purposes could be considered to be isobaric. If the composition of the gas mixture is stiochiometric (that is to say if the composition of the gas mixture is that which gives the best chemical combination between the fuel which is being burned and the oxidant) then this will give the highest burning velocity and pressure. As the explosion vents unburned gas will be propelled out of the mouth of the module. The pressure difference between the enclosed gas and the external atmosphere will pull the flame quickly towards the vent and this will cause the flame to travel very quickly. Eventually as a result of the momentum one would be left with a slight degree of negative pressure within the enclosure in relation to the external atmosphere. This can result in material being sucked back into the enclosure. This is referred to as the rarefaction phase of the explosion. This effect could cause the kind of damage I shall refer to later in relation to the mechanical workshop door. The increased pressure within the enclosure would create an overpressure in relation to the external pressure and one effect of this could be to burst open the enclosure walls ( in this case the firewalls). Moreover light equipment such as panels could be damaged by the same phenomenon but it would be unusual for pieces of heavy equipment such as machinery or piping to be seriously damaged. These are generally strong enough to withstand an explosion such as is being considered. Furthermore the movement of gas caused by the explosion would have sufficient velocity to take quite heavy articles up and move them in the direction of the flow. The wind generated by the explosion would be quite hot. The propagating flame itself is unlikely to cause much thermal damage. If there is a continuing release of combustible gas after the explosion (which is not uncommon) then the flame may travel back to the original source and thereafter continue as a steady jet flame. When the flame reaches the open mouth of the module it slows down rapidly.

A witness some distance from the explosion would hear it before seeing it. Noise itself is quite a subjective matter and witnesses can find it difficult to describe it accurately. If the gases burst out of their enclosure then the sudden release of pressure would be likely to cause a bang as the enclosure bursts. In the present case none of the parties attempted to prove a precise ignition source for the gas which caused the explosion but any source of heat could have ignited an escape of gas. Indeed a gas escape under pressure could itself generate enough heat to provide its own ignition and an electrical spark is another common source. Indeed if there is an accumulation of flammable gas in a confined space such as a module there is a serious risk that an explosion may occur. A bang could also occur if heavy articles were displaced by the explosion or if the pressure waves were sufficiently fast in relation to the speed of sound. It should be noted that the explosion experts were not examined on the possibilities surrounding the explosive potential of a cloud of gas in an unconfined space.

The propagating flame itself would tend not to be particularly luminous and would also tend to have a blue hue. What can make a flame luminous are incandescent particles and such might well arise through the formation of soot. Such soot would be expected in a case where there is an excess of fuel such as in a pre-mixed fuel-rich mixture. Soot is carbon and this tends to burn with a luminous yellow flame . With a lean gas the flames will tend more to blue. Not much smoke will be produced and this will tend to be light coloured. A fuel rich in carbon will produce more smoke and this will tend to be blacker. I do not think these particular facts are in dispute.

5.5.2 Captain Clegg

The witness Captain Clegg, whom I have already mentioned, was the only witness who claims to have observed the explosion from its beginning and therefore must be regarded as a potentially important witness. As it happens he was looking towards the west face of the platform when the explosion occurred. Captain Clegg appeared to me to be a particularly careful and observant witness but of course even such a witness might have recollection difficulties with momentary events. He was the Master of the Lowland Cavalier, was aged 40 when he gave his evidence, and had spent his working life as a seaman. His ship had gone to its position off the south-west face of the platform early on the day of the accident and on the evening of that day was engaged in dynamic positioning trials. He was about 75 metres away from the platform and being at a height of 56 feet he would to some extent be looking up in relation to its’ 84-foot level. The first thing that attracted his attention was that about 10 minutes before 10 p.m. when he was looking at the platform in connection with a lining up exercise he noticed material increase in flaring. This in fact is likely to have been caused by the unloading and re-cycling of the reciprocating compressors. Shortly before 10 o’clock the flaring again increased and this would be consistent with the tripping of the centrifugal compressors. Then while he was looking at the crane pedestal he suddenly saw a blue flash which originated at the mouth of Module C and then spread in both directions along the west face of the platform . A blue flash is quite a distinctive phenomenon and indeed is consistent with an explosion. From an early date after the accident Captain Clegg has maintained that he saw a blue flash and I have little difficulty with this part of his evidence. There is however a question mark about his evidence as to the location and spread of the flash. On his own evidence he only saw this flash for a second or two at the most. Indeed he showed a certain degree of reservation about the precision of his observation and on a number of occasion talked about his "impression". When asked if he had seen the flash spread along the platform he replied "I saw something like that ". However before me he had no hesitation in locating the origin of the flash which he stated was at the mouth of Module C. The defenders argued that Captain Clegg had never stated specifically that the flash had come from within a module and this may literally be true however I think the implication of his evidence was that the flash had come from within Module C. After the flash had spread it retreated back to Module C It is difficult to see why it should have stopped just there unless there is some explanation such as Dr Mitcheson supplied to the effect that as the gas expelled was consumed the flame retreated to the fuel source. Mr Cubbage likewise confirmed that a flame after an explosion will tend to track back to where the fuel is coming from. Thus if the fuel was coming from Module B it would be expected that the flash would contract back to that module and not C. The defenders contended that Mr Cubbage had contradicted himself because after describing the flame as tracking back he had later talked about it fading back. I think the defenders are making too much of this and that Mr Cubbage was all along talking about the same phenomenon.

Once it became visible the flash appeared to extend southwards across the edge of the platform and across the heatshield without however extending beyond the platform. Northwards the flash he thought extended along the edge of the platform until the end of the west face. The witness claimed that the flash had then retreated to the mouth of Module C and disappeared. He described the flash as being like the effect noticed when a gas boiler is ignited.

After observing the flash he heard a bang or thump and more or less simultaneously felt a thump on his chest and pressure on his ears. At that time the only extraordinary phenomenon visible on the platform was a shimmering giving the appearance of smoke or dust although it could also have been the platform vibrating. In my view there is much to support the suggestion that there was at least a degree of vibration of the platform. Certainly some material was displaced and the fact that certain persons lost their footing may also have been due to vibration. The highly confined conditions at the mouth of Module C would cause vibration had the explosion occurred there. In any event there were then a few seconds of stillness. This was followed by what seemed to be an explosion and yellow flame and black smoke came out from Module B at the north side of the module opening. From his description it would appear that the fire from Module B originated as if with explosive force. Captain Clegg made it clear that he had observed two separate episodes. The first was the blue flame which he ascribed to Module C and the second ( from two to ten seconds later) the bright yellow flame and dark smoke which burst out of Module B. Captain Clegg at one stage mentioned " split seconds" and the defenders sought to take from this that the gap between the blue flash and the emergence of fire from Module B was "a split second". However it is perfectly clear from his own evidence and also from the events he spoke to that the gap was at least about two seconds It also has to be noted that his observation encompassed a period of vibration between the blue flash and the emergence from Module B of fire. He saw panelling "flying through the air" at either side of the crane pedestal. This if accurate suggests that the firewall between Module C and Module B was no longer in place since it would seem that the overpressure was able to penetrate from one module to another. The defenders pointed out that the flying debris was apparently associated with the fire explosion rather than the original flash but there was not explosive fire in Module C at that stage and debris seems to have been propelled from there. Moreover the suggestion that any linkage between the events in Module B and the events in Module C may be ascribed to the gap behind the crane pedestal does not convince in relation to the flying debris. Captain Clegg has this debris propelled for some distance away from the platform. He also noted some smoke emanating from Module C although less than he observed from B. The fire in Module B then began to increase in volume engulfing more and more of the crane pedestal and there was also increased flame from C. It may be significant that Captain Clegg saw the development of the fire as being like an explosion although he later modified this evidence to suggest that the sound he heard may have been the fire raging. In any event this development does not seem to have caused Captain Clegg any consciousness of pressure. The evidence of fire in the adjoining modules and an expulsion of materials from both modules may suggest an opening in the firewall. The time taken from the development of the flash until Captain Clegg stopped his observation was about 10 seconds. This estimate of time is given a certain credence by the fact that the witness Mr Miller describes how he began to take photographs about 10 or 15 seconds after he was drawn to the event and at that stage it is apparent that the fire is quite developed. It should be noticed that it cannot be totally clear that all the flame ascribed by witnesses to Module C was actually burning within that module since there was a gap at the rear of the crane pedestal which created some space between the mouths of the modules.

When Captain Clegg was asked at the Cullen Inquiry about the blue flame (and this happened in 1989 at a time much closer to the accident) he had said that it was difficult to remember if the flame had come from the right or left of the crane pedestal. He also had the extension of the flame across the face of the platform to the south more extensive than that to the north. He explained these discrepancies by saying that somehow his memory of the event now seems more clear. He accepted that his present recollection could be wrong but he now had a definite impression that the blue flame had come from the mouth of Module C. As I have indicated in general terms Captain Clegg was an impressive and seemingly honest witness. Moreover whereas the recollection of a witness is usually more reliable when it is fresher I cannot exclude the possibility that his memory had reacted as he described. Closer to the accident he may well have been more emotionally disturbed by the excitement of the accident and it is possible that with the passage of time he may have found that with rather more detachment he had a better recollection of what he had seen. Of course there is the possibility that pondering about his evidence may have distorted his memory. Without some support I should have found it difficult to accept Captain Clegg on any questions of detail connected with the flame. However his evidence has to be considered and, as I shall show, in some respects fits in well with the other evidence connecting the initial explosion with Module C. Moreover he has maintained all along that he saw a blue flame originating at the mouth of a module appearing to extend along the west face and that this was at a low level in relation to the 84-foot level - indeed even to a degree below it. These circumstances, which he has all along been quite certain about, also fit in reasonably well with the Module C theory. In any event his evidence can in no way be taken seriously to contradict the fact that the blue flame originated in Module C. Indeed his evidence confirms that first there was a blue flash of flame which was not likely to have been caused by a fuel rich mixture. It should also be noted that in order for the blue flash to be seen it could not have been travelling at a speed of more than about 10 metres per second. However although the flame will be travelling much faster through the Module Mr Cubbage for example considers that upon emerging from the module the flame could decelerate with sufficient rapidity to be visible.

The view expressed by Professor Magnussen that he had difficulty in seeing the explosion and evolution of fire as separate events is rather difficult to reconcile with what Captain Clegg actually reports.

The low level of the blue flash if correctly observed by Captain Clegg supports the view that the explosive gases were heavier than air. Again if this observation stood alone I would hesitate to be too confident about Captain Clegg’s recollection but this detail fits in very well with other evidence supporting the pursuers’ thesis.

Dr Mitcheson considered that what Captain Clegg saw when he saw a blue flame was the combustion of a pre-mixed gas-air mixture which was venting out of the module where the explosion had occurred. Flammable gas had been forced out of the mouth of the module and this was followed by a flame which propagated through it. A continuing expulsion of flammable material would allow the flame to flash back to the fuel source. However as far as he is concerned it has to be noted that without reference to where Captain Clegg located the origin of the blue flash he cannot ascribe it to C rather than B. Dr Mitcheson appeared clear and persuasive on this point . Moreover his opinion was based on his experience.

A major question arose in relation to Captain Clegg’s impression that the blue flame appeared to extend northwards to the north-west corner of the west face. As I have already indicated Dr Mitcheson found it difficult to explain how this could have happened. He had no problem with the spread of the blue flash southwards along the heat frame. This at least he thought was quite possible. His explanation proceeded on the basis that the collapse of the B/C firewall could have permitted an oblique expulsion of gas to the south of Module B. Professor Magnussen suggested that the blue flash may have been caused by the development of a vapour trail resulting from a spillage in B. However he also appeared to find it very difficult to offer an explanation for what Captain Clegg claimed to have observed. He had observed a blue flame during certain experiments in the South of France that came from a gas cloud which had formed in the atmosphere but his observations it would seem were also associated with the development of yellow flames. Professor Magnussen did not dispute that in order to produce a blue flame the combustible gas requires to be a lean mixture. However not only does account require to be taken of the fact that his general hypothesis was not put to Dr Drysdale nor Dr Mitcheson nor Mr Cubbage (so that it is impossible to know what the pursuers’ experts would have thought of the idea) but at first sight, one might have expected a spillage in Module B to set off gas or process alarms. Furthermore as I have said Dr Mitcheson took from the fact that the blue flame was at a low level the inference that the flash was caused by a high density fuel such as condensate. A gas such as methane which might come off oil would have drifted to the ceiling because of its low density. Obviously if the blue flash spread along the west face to the north there would either have to have been gas present along the face or it would have to be the consequence of gas expelled along the face by an explosion elsewhere. In this respect there is important evidence from the witness Mr Young. He was on the west face just before the explosion. He was travelling to the 68 foot level and had not even reached the pumps where Mr Vernon and Mr Grieve were working before the explosion took place. On this journey along the west face Mr Young did not claim to have noticed any gas. If a trail of gas had reached explosive concentrations moments later it is curious he did not notice it. Moreover this absence of gas coming from Module B along the west face is supported by all the other evidence such as the failure of any gas alarms to register in Module B and the fact that the oil and water operators did not report any gas leak. If there was a trail of gas along the west face then the source of this gas must also have provided the gas that set off alarms at the east end of Module C. If the oil and water operators were in Module B as I think is likely it is indeed curious if they did not note the alleged accumulation of gas within the module. Moreover with the wind blowing from the west if a trail of gas passed the mouth of Module C it might be odd if no gas entered the module and set off alarms there. I think it is fairly obvious that there was no trail of gas along the whole west face of the platform. Indeed the pursuers’ experts were not asked if such a trail of gas could have developed and caused the explosion particularly as the suggestion that the defenders seem to be putting is that the explosion may have originated outside the bounds of the modules, essentially in an unconfined area. In cross-examination Dr Mitcheson did venture the opinion that he did not see how a trail of gas could extend along the platform face but he was discouraged by the defenders from explaining this. Nor was the question of ignition in that kind of situation explored with the pursuers’ experts. This leaves Captain Clegg’s impression of the full extent of the blue flash somewhat difficult to explain. The explanation of course may be that his description of what happened is not wholly accurate. This would not be at all impossible even with the best witness because he was describing an event that occupied at best a few seconds. Mr Cubbage and Dr Mitcheson raised the possibility that given where Captain Clegg was located (to the south of Module C and at a substantially lower height) a flame expelled directly out of the module westwards may have seemed through perspective to stretch along the west face. Given the fleeting nature of the observation this in my view seems to be perfectly possible. Another possibility of course is that he was mistaken as to the extent of any spread of the flash along the platform face, which is also possible. He accepted that he had changed his evidence slightly on this point since the Cullen Inquiry. However what he seems all along to have been definite about was that the flame he saw was blue and was low. This fits in well with other evidence. The defenders argued strongly that Captain Clegg had not been challenged by the pursuers when he claimed that his impression was that the flash extended all the way along the west face. This is correct. The defenders proceeded to claim that in the interests of fairness and proper witness examination practice it has to be taken as proved that a flash occurred as Captain Clegg described it. Since such a flash cannot be reconciled by the experts with an explosion in Module C such as the pursuers rely on then the defenders contend that the whole structure of the pursuers’ hypothesis must fall. I do not know why Captain Clegg was not examined further assuming of course that this was really necessary. Since the experts’ problems with the flash only emerged sometime after he had given evidence this may have been the explanation. Moreover it was fairly obvious that the pursuers were not suggesting that at any time Captain Clegg was doing other than his best to detail his impressions as accurately as he could recollect them. It is difficult to see quite what a challenge would have achieved. The witness said that he thought this momentary flash extended along the whole of the platform face. This is what he remembered.. All the other evidence from experts and eyewitnesses indicates that this impression is very unlikely to be accurate on this narrow point. There are reasonable explanations for a mistaken impression such as distortion by perspective or simply faulty observation. The defenders did not want to challenge Captain Clegg’s quality as a witness and in this I think they were quite right. However the fact that he is mistaken in any detail in an observation such as he is describing in no way detracts from the quality of his evidence and in the circumstances if all the other evidence refutes the accuracy of such a detail this cannot be ignored. In cases as extraordinarily long as these it is inevitable that developments will arise in the evidence which perhaps were not anticipated at an earlier stage. This affected the defenders as well and many of their theories were not put to earlier witnesses who had given unchallenged evidence difficult to reconcile with what was said later. With the evidence there, the Court must try to assess it fairly giving weight to any material inadequacy in its presentation (particularly if this latter is truly prejudicial). It should also be noted that because of the difficulty of the cases I made it clear on a number of occasions that I would give very serious consideration to any reasonable request to recall a witness but of course with busy expert witnesses who had come quite long distances to Court this may not always have been a practical suggestion

In relation to the development of events during the incident I found it difficult to correlate the evolution of a pool fire as postulated by Professor Magnussen with the earlier observation of a blue flash. Indeed I formed the impression that Professor Magnussen himself was not too comfortable in his attempts to link these two aspects of the matter.

The defenders argued that the evidence of Dr Mitcheson to the effect that a cloud of unburned gas had been pushed through the exploding flame out of the mouth of Module C was based on a false assumption namely that Captain Clegg had described that flash as coming out of Module C whereas his evidence was that he had seen the flash at the mouth of the module. Even if it were right that Captain Clegg did not say specifically that the flash had come out of module C, as I have said before, his account of what he saw must signify that the flash came out of Module C and I have already discussed this.

Dr Mitcheson thought that the shimmering described by Captain Clegg could have been caused by a heat haze resulting from the heat generated by the explosion although vibration could also have caused it. . The yellow fire observed a second or two after the explosion was not to be associated with the initial explosion but rather with a later pool fire of flammable liquid. The gap between the explosion and the pool fire he considered to be significant because if the explosion had been caused by a pool of oil discharging gas in Module C he would have expected the pool fire to be simultaneous with the explosion. Even if the initial explosion had occurred in Module C as a result of a pool of oil in B generating gas which somehow had infiltrated into C, then one would have expected a different sort of fire at the mouth of Module B - namely a fire venting out of B under pressure and without a time gap. Dr Drysdale also thought that a blue flame would be consistent with a lean mixture but not with a fire caused by a spillage of crude oil near the west face. The crude oil would produce enough soot to cause a yellow luminosity. While Professor Magnussen has certain specialist experience concerning the development of soot in petrochemicals and though it was possible that a blue flame could emerge from a pool fire he did not claim that he had ever seen this happen in practice. He agreed that it was necessary to have a lean mixture to have a blue flame but thought that, with a fire originating in a pool, such a lean mixture could develop although he seemed to agree that there was also the likelihood of smoke and some yellow flame. For a blue flash to be seen according to Dr Drysdale it would be necessary to have a gas cloud with a pressure gradient leading to a stratum of lean gas. I am not sure that Professor Magnussen disagreed with that. Ignition would have to occur at the lean gas and Dr Drysdale could not envisage a mechanism for this. I formed the impression that Dr Drysdale’s observations on the kind of flame to be expected from a pool fire were related to flames in the immediate vicinity of the source. He was not necessarily saying that vapour spread out from a pool could not generate a blue flame. I think it is possible that in discussing the genesis of a blue flame Professor Magnussen and Dr Drysdale may not have been talking about the same situation. One was talking about the blue flame seen to spread along the platform whereas the other was discussing the origin of the fire that was seem emerging from Module B. Nevertheless if every other factor was favourable or at least neutral I would accept that it is possible that a trail of gas emanating for a pool of crude oil could cause a blue flash. However the preconditions do not apply in this case.

It is of course critical to Dr Mitcheson’s theory that the B/C firewall will have disintegrated venting products and smoke into B. If an explosion in Module C had ruptured the B/C firewall this could explain the later massive fire in B since the explosion may have had enough energy to project missiles into B which could have disrupted or severed small bore pipework causing an escape of flammable substance to fuel the fire in B. It would also explain the gap in time between the explosion and the incidence of fire in Module B although quite why there was a delay in the escape is not so clear. Thus the foregoing evidence gives support for locating the blue flash in C as Captain Clegg eventually believed he had observed. Mr Cubbage gave evidence which in general terms supported Dr Mitcheson as to what a blue flash as described by Captain Clegg might signify. The expert witnesses I have been discussing also agreed that the impression of Captain Clegg would have been consistent with an explosion and not a mere fire. Moreover it would be consistent with the evidence of the pursuers’ experts if in a situation where the B/C firewall was ruptured some of the gases causing the blue flame penetrated into, and was expelled out of, Module B albeit that the explosion itself had originated in C. The defenders sought to extract from certain pieces of evidence that the fire which developed within the firewall and which broke up the firewall would have been travelling too fast to appear outside the module as a visible blue flash. However Mr Cubbage thought that the flame would slow down rapidly when it emerged from the contained space. He did say that initially the question had given him some trouble. Dr Mitcheson did not see any difficulty. This however is based on an assumption that there is a relatively clear channel just to the north of the B/C firewall. He thought that turbulent inducing objects were relatively few there. There may be a doubt about this. On the other hand he was not asked to clarify what he meant by "just to the north of the B/C firewall". Certainly immediately to the north of the said firewall whereas there was equipment it did not have the massive character of much of the other equipment in the module. Thus the implications of the actual layout of the Module as it is shown in plans were not really investigated with him.

Combustible gas could be expelled through the firewall from C into B and then ignited by the blue flame emerging from C . This could explain why the blue flame was perceived to travel southward. The suggestions made to the experts that the gases that caused the blue flash may have been transported by the wind do not seem to me in the light of the evidence to be realistic since wind forces would be overwhelmed by the velocities resulting from the explosion. One reason that the flame speed would drop as the gases emerged from the module is the removal of the turbulence factor.

The defenders referred me to the detailed evidence of Professor Magnussen but I did not always find this easy to follow. He certainly seemed to say that a blue flash need not necessarily come off condensate although he accepts that it connotes a lean mixture. He accepts that crude oil burning causes a yellow flame but if gas flashes off crude oil it could cause a blue flame depending on the mixture. Essentially in relation to the probability that the blue flash came from an explosion of condensate he takes a seat on the fence position since he asserts that he does not know what actually happened. In fact his only firm conclusion is that the blue flash is gas burning. One observation he makes may be significant for he says that the movement of gas against the wind is very unlikely because it is not within an eddy structure. This may make it difficult to explain how gas could have spread to the south of the face of Module B before the explosion. He repeatedly says that to find an explanation for the spread of the blue flash is very complicated and doubts if there can be much disputeabout that. When asked about ignition sources he replies. "There is a lot to these accidents which many people don’t know about". Perhaps with his experience he is right about this and it demonstrates that great care must be taken when advancing premises that are too rigid on matters of detail. At the end of the day Professor Magnussen could give no satisfactory explanation as to why it could be postulated that a cloud of gas moved against the wind out of the mouth of Module B and then continued to move against the wind south along the platform face while at the same time some gas was drifting north with the wind. This hesitation in his evidence is not a matter of criticism. Of course with turbulent eddies the necessary propulsion of the gas may be scientifically possible but that there should have been the necessary combination of eddies seems improbable. Professor Magnussen did not seem very keen to adopt an opposite view

Of course the experts Dr Mitcheson and Mr Cubbage had at various stages agreed that if the location of the blue flame showed that it came out of Module B then that would be consistent with the explosion having originated in B. However at the very best for the defenders I would be quite unable on the basis of Captain Clegg’s evidence alone to find that the blue flash came from Module B. I should require to look at the whole evidence to see which of the possible locations for the origin of the flash is indicated by other evidence. On that approach the evidence supports the view that Module C was where the flash come from. The evidence of Captain Clegg although honestly and credibly given is not altogether free from difficulty but even pitching the evidence at its lowest it certainly in my view is not inconsistent with the type of explosion which the pursuers say must have occurred in Module C. The defenders argued that the evidence of Captain Clegg presents insuperable problems for the pursuers. However in relation to the difficulties they advance, as elsewhere, they seek to extrapolate from restricted observations among a mass of evidence coming from the various expert witnesses led by the pursuers, and none of the resultant hypotheses are spoken to by their own experts nor really examined in depth with the pursuers’ witnesses. Both parties laid great emphasis on the evidence of Captain Clegg and spent a lot of time discussing it but I do not see it as critical. Even although the pursuers did not challenge his narration of his recollection he cannot be taken as being precisely correct in respect of every detail he claims to have observed. In relation to the matters that took place in the space of a second or two it would violate common experience to regard him as infallible in every detail. If there are other indications that the explosion was caused by an accumulation of gas in Module C (and there are) then I do not think that Captain Clegg’s evidence when viewed against the other evidence can be taken as supporting the possibility that the explosion originated in Module B.

5.5.3 Mr C A Miller, Mr Ritchie, and Captain Morton

The witness Mr C. A Miller is also potentially a significant witness because he observed the incident from the deck of the Tharos and he took photographs of the platform at various stages of the accident. He was 45 years of age when he gave his evidence and his job on Tharos was to drive a small submarine. He had been working on Tharos for about 12 years before the accident. The first thing that Mr Miller noticed that drew his attention to the fact that something was wrong at the platform was that while he was standing at the rear deck of Tharos where he was hoping to take certain photographs for his family he heard a thump. He was facing towards the west face of the platform. At first he thought that the thump was caused by flaring . However when he looked up after hearing the thump he noticed some light grey smoke coming out of Module C. Mr Miller seemed to have a clear recollection of seeing smoke from Module C and this was followed by smoke from Module B. The appearance of smoke at the mouth of C is consistent with the expulsion of burned gas from that Module and also suggests that something had happened within that module. Moreover whatever else was happening in Module B there was no evidence apparent to Mr Miller of an immediate fire there. To that extent there is consistency between Mr Miller and Captain Clegg since although Captain Clegg for understandable reasons is not too positive about the gap between the explosion and some manifestation of abnormality in Module B I think there is no doubt that he speaks to some gap in time. The weather and the light were both quite good and this is confirmed by other witnesses . Indeed at the time he had his camera to his eye as he was on the point of taking his photographs. Almost immediately after his first observation of smoke (within two or three seconds) he noticed more smoke this time coming from Module B. His evidence is not totally consistent with Captain Clegg who saw fire in Module B at an early stage. However the witnesses were viewing from different angles and Mr Miller was substantially further away. Mr Cubbage observed that far from making his observations more difficult the distance may have given Mr Miller an advantage since he would have a better perspective and a better view of the whole of the west side of the platform. He began to take photographs about 10 to 15 seconds after the thump. He had not noticed any flames before he did that. On the other hand there is no doubt that his original photograph showed fire and it would be odd if the fire manifested itself first at the precise instant the photograph was taken. Because of the distance of the Tharos from the platform it would have taken about 1.5 seconds from the explosion before Mr Miller heard the thump. The description of the smoke as being light coloured would be consistent with what would produced by a pre - mixed gas cloud. Smoke from a large pool of oil would have been darker in colour. Mr Miller appeared to have a clear recollection of events and from what he saw the first manifestation of the explosion was in Module C and it was only a few seconds later that any irregularity was observed in Module B. Dr Mitcheson thought that the fact that the smoke observed by Mr Ritchie had spread out and was above and below the 84 foot level is likely to indicate that the smoke seen was the smoke originally seen from Module C and now drifting. The fact that the smoke had drifted to the south of Module C may show some propulsion by the explosion. What was observed would also be consistent with the burnt products of the combustion of gases in C venting into B. The defenders asked me to note that the evidence of Mr Miller was not cross- examined . The witness, Mr Ritchie, who was aboard the Lowland Cavalier, (and consequently much nearer to the platform) saw, when he first looked at the platform, light smoke which seemed to have come from a point beneath the mouth of Module B but the smoke he saw may have been forced out of a module some time before he made his observation and he may have begun his observation after that of Mr Miller since when he first heard a bang he was travelling towards the conference room on the ship . After the bang he heard he required to take a few steps before he could see the platform. The interesting thing is that neither Mr Miller nor Mr Ritchie saw flame in Module B when they first looked at the platform. Since light travels faster than sound Mr Miller certainly will not have looked until he heard the bang which must have been some time after the flash seen by Captain Clegg. It may just be significant that he claims also to have seen falling debris which he thought might have been lagging. In this respect there is some divergence from Captain Clegg who thought the debris he saw was panelling. Perhaps they were both right and it may not matter much. When Mr Ritchie returned to the bridge after say 30 seconds he observed flame on the platform. This does not contribute much information since by this time we have Mr Miller’s photographs. Mr Ritchie was a qualified civil engineer and indeed he and Mr Miller seemed to be attempting to give accurate narratives. Like Mr Miller Mr Ritchie was not cross-examined. As Dr Drysdale indicated the smoke described by Mr Miller and Mr Ritchie is consistent with the combustion of condensate in the rich part of the mixture above the stoichiometric value although the witnesses place the smoke in rather different locations. Dr Drysdale is not always consistent with what Mr Cubbage conceded in cross-examination but since he is a specialist fire expert I have no difficulty in preferring Dr Drysdale’s evidence on the relevant matters. He did not see this smoke as being consistent with the burning of crude oil/air mixture which would be very quickly masked by black smoke and he is very positive about this. This is also consistent with what Dr Mitcheson says. Professor Magnussen is not as certain as Dr Drysdale on this matter but I am afraid I was not too clear about the precise cause of his doubts. Dr Drysdale expresses himself in a much more intelligible and persuasive manner and on this point I definitely prefer his evidence. Professor Magnussen did appear to consider that what Mr Miller had observed may not have been smoke but dust or droplets. Even if the light material seen by Mr Miller was dust, account still has to be taken of the fact that it was first seen emerging from Module C. Professor Magnussen accepts that the smoke spoken to by Mr Miller was at least consistent with the explosion having originated in C.

Captain Morton was situated on the Maersk Cutter so that he was viewing the platform from the east of the platform. He was about a mile off it. The first he saw was what he thought may have been a cloud of cement dust at the east face of Module C. His surmise that he was seeing dust was prompted to a degree by the fact that the platform sometimes vented off cement dust. However his impression that he may have been seeing a cloud of dust altered when shortly afterwards the cloud darkened and became black. The wind appeared to drive it northwards and the platform was emitting smoke like a train. He was reasonably certain that the smoke or dust he had observed had not come out of the end of Module B. He was a ship’s captain and had been in the Merchant Navy since about 1973. At the time when he gave his evidence he was 38 years of age. He had been on the bridge of his vessel and just as the 10 o’clock News began he had felt a shudder on his vessel. He went to walk round his vessel to make sure all was well and it was then that he looked at the east face of the platform. Mr Cubbage explained the shuddering of the Maersk Cutter as having its likeliest cause in vibration on the platform caused when the expanding gas tried to force itself out of the heavily restricted east end of Module C. This movement would transmit a pressure pulse through the sea. According to Dr Mitcheson it would take about 4 seconds to register on the ship. The time that lapsed between Captain Morton perceiving the pressure pulse and looking towards the platform was less that ten seconds. From the time of the first shudder until the smoke turned black was he said about 2 or 3 minutes. The defenders claimed that Captain Morton must have been wrong in his timings since other witnesses saw smoke at an earlier stage. It may be that his timings are not entirely accurate but on the other hand the first thing he saw was what appeared like dust or smoke emerging from C and this became darker which suggests it was in fact smoke. This darker smoke was in all likelihood originating in Module B and would have been driven by the wind diagonally into Module C through a gap in the firewall. Soon after his observations of smoke he noted flame coming from the 68-foot level of the platform. He thought that he first saw flames about three minutes after he first noticed the shuddering. If the explosion had originated in Module B then one would have expected that the force of the explosion would have been sufficient to expel combustion products directly out of the mouth of that module. Again Professor Magnussen has a trace of scepticism about the meaning of what Captain Morton claims to have seen although he accepts that what was described would be at least consistent with an explosion in Module C. The defenders raised a query as to why if Captain Morton is correct he did not also see smoke emerging from Modules B and D. Nor did he mention seeing smoke at the north face. Of course once there was any material quantity of dark smoke there inevitably would be some masking. I do not think there is any question that these witnesses were honest and if there can be any doubt it must relate to their powers of observation in respect of events which occurred very quickly. Nevertheless the fact that the gas detectors signalled a concentration of gas at the east end of Module C just before the explosion must not be lost sight of when testing the eye-witness evidence. The defenders are probably right in saying that the greyness of the original smoke if this fact were looked at totally in isolation would not in itself tell us that the source of the fuel was condensate. Dr Mitcheson clearly thought that the emergence of light grey smoke from the mouth of Module C was consistent with an initial explosion of relatively lean gas having taken place at that end of the module although questions connected with time span were not exactly resolved. He would not have expected the explosion to be at the east end of Module B without a similar manifestation at that end of the module. Moreover the development of dark smoke at the end of Module C is consistent with a fuel rich fuel at the west end of Module B with a south east wind propelling it through the damaged firewall. However he also accepted that what Captain Morton saw could be consistent with the light and dark smoke generated from one source be it Module C or Module B. Dr Mitcheson states that in the circumstance where wind is being blown eastwards from the west of Module B he would have been expecting some smoke to emanate also from Module D. Mr Cubbage thought that the grey smoke must have resulted very early on in the explosion process but that of course is not entirely consistent with Captain Morton’s timescale. On the other hand Captain Morton had indicated that the light smoke hung in the air before moving away. The events being considered were on the lee side of the platform. He thinks that the explosion may have been making an impact on Captain Morton’s ship in one to one and a half seconds. This is in contradistinction to Dr Mitcheson’ 4 seconds or so. It all goes to confirm that it is dangerous to rely too much on the witnesses’ recollections of such short times. Dr Drysdale was very positive that the origin of the grey smoke must have been condensate. This presumably was because he could see no mechanism that would have generated such a lean mixture at the east end of Module C from crude oil. Professor Magnussen was less definite than Dr Drysdale about the possible origin of the grey smoke. He thinks one cannot take too much from colour since this depends on light . However Captain Morton was quite certain that the colour changed quickly from very light smoke to black smoke and it is not too easy to see how light change could have caused this. Insofar as I could understand what Professor Magnussen was trying to say I think his approach was to remain relatively uncommitted about this chapter of the case. There are certainly a lot of questions that have to be answered before the evidence of Captain Morton can be accepted as completely accurate. What he observed was seen from a distance off the platform. Like other witnesses he was describing events compressed into a very short period of time and with so much happening he may have been concentrating on certain aspects of the scene before him rather than others. If his evidence stood alone I should hesitate to take too much from it. He was very positive about his reference to the mouth of Module C and I am prepared to accept that he saw some substance issuing out of it and that the colour of this turned from light to dark. Whether his timings are right and whether he may have missed other important phenomena is more open to doubt. The fact is that other witnesses relate the initial events to Module C and Captain Morton would be consistent with this approach.

5.5.4 Mr Flaws

The witness Mr Flaws was aboard the Tharos when the accident occurred. He was aged 39 when he gave his evidence and was Deck Foreman. He was on the helideck when about 10 o’clock he heard a bang. The first thing Mr Flaws noticed after the explosion was a column of dark thick smoke but he attributed this to the east side of the platform and to the north east. It was travelling north-east. From his description the smoke was observed just above Module C so that this fits in with those witnesses who locate their first observation of abnormality with Module C. At about the same time he observed what he describes as an orangey flame appearing and he places this in Module C. If he is right about this what he saw is not consistent with it being an extension of a fireball originating from a pool of oil in B because this would have occasioned dense black smoke. After a few seconds he goes off to tend to his fire-fighting duties. The evidence of this witness is not entirely reconcilable with the evidence of other witnesses but of course minor differences as to the time of observation or to the point at which attention is focused could account for this. Mr Miller’s photographs are fairly objective accounts of what the platform looked like within say 10 seconds of the incident so that Mr Flaws can only be correct in the detail of his observations if he is talking about the period rather earlier than Mr Miller’s photographs. He thought that he had looked at the platform about 5 seconds after hearing the bang. Then he observed dark smoke from about the middle of the east face of the platform. However a salient feature of Mr Flaw’s evidence is that at the beginning he only watched events unfold for a few seconds. Dr Mitcheson expressed the view that once the original blue flame had come to the fuel source then it might continue to burn as a fireball while the pressured escape of condensate continued. This fits in well with evidence which we will see came from the witness Grieve which suggests that there was evidence of a fireball close to the ceiling at the 68-foot level. Of course the supply of condensate that could continue to emerge from the point of escape in Module C would be finite and the consequent fire might not have endured for long. In fact the evidence of Mr Flaw may be somewhat suspect in matters of fine detail but all the eye-witnesses I have been considering only had a restricted opportunity of observing the extremely brief initial features of the accident so that errors in detail must be possible in relation to any of these witnesses. The really significant test is how detailed evidence fits in with the picture painted by other witnesses and the likelihood described by the experts. Moreover Dr Mitcheson (like Mr Cubbage) was at pains to point out that even at the same point of time different witnesses could see different things because of their differing perspectives. It is a little difficult to conclude that Mr Flaws saw what he describes in Module C and that he did not confuse it with the fire that quickly emerged on Module B. On any view his location of the flame was not too precise. He may of course have seen fire in both B and C as to a degree the photographs may show. It has to be noted that after seeing that something was wrong Mr Flaws was very properly more concerned about carrying out his emergency duties than observing the detail of what was happening.

5.5.5 Witnesses on the platform

The witness Mr Elliot described how at the time of the explosion he had been standing on the north landing in the area of the Chanter Gantry at the 68-foot level on the west face of the platform (below the Chanter Riser Gantry which protrudes from the platform and which thus places it effectively below Module C) . He claims that he had no prior warning of the explosion but was suddenly knocked off his feet and "beaten to the ground". He was looking out and the force came from behind and above him. Dr Mitcheson could not exclude the possibility that what happened to Mr Elliot was consistent with an explosion either in Module B or C but he regarded C as the likelier candidate. Standing where he was equipment would have partly protected him against the force of a shock wave in B and certain damage to the Chanter Riser Gantry has also to be taken into account. Moreover if the blast had come from B Mr Elliot would have been more likely to have been thrown in a more northerly direction. Dr Mitcheson said that as compared with C it would have needed a larger explosion in B to have attained the same effect. The defenders contended that this was meaningless since it was not backed up by a quantitative analysis. The inferences that can be drawn from the experiences of Mr Elliot are rather slender but plainly his fall was consistent with an explosion in Module C and marginally less likely to have been as a result of an explosion in Module B.

The witness, Mr Young, had been at the 68-foot level at the time of the explosion. He had been in the Instrument Workshop and had been summoned to the 68-foot level to attend to a the problem with the condensate injection pumps. He had proceeded to Module C and entered it to descend to the 68- foot level by the staircase at the north-west wall of Module C. During his short traverse through the north-west corner of Module C he had noticed nothing irregular. Since this happened very shortly before the explosion it suggests that wherever the explosion originated it was not caused by an accumulation of gas at the north-west of Module C. As he arrived at the 68- foot level he noticed that Erland Grieve and Robert Vernon were near the condensate injection pumps. Then after having taken a few paces he heard what sounded like a quick escape of steam behind him that ended up in a dull thud. Then there was a rush of warm air and he lost his footing falling quite heavily. Mr Young was very certain that the blast of air that had hit him was quite hot. His hair and eyebrows were singed. The rush of air was followed by what he describes as an eerie silence. When he recovered his balance and proceeded to return to Module C he had only mounted about two steps of the stairway when it became clear that he could not proceed further because of swirling smoke in Module C. Thus from an early stage after the explosion there was heavy smoke in the module. Dr Mitcheson made the point that if the rush of air experienced by Mr Young had been caused by an explosion originating in Module B then it could only have affected him as it did if it had punctured the B/C firewall. In this eventuality the first sound heard by Mr Young was likely to have been the bang caused by the firewall rupturing. The hiss heard by Mr Young was probably the sound of rushing gas in Module C as it encountered obstacles. The bang in all likelihood would be the pressure waves catching up with one another. There was no appreciable gap in time between the different sounds that Mr Young heard and he makes the point that it was in any event normally very noisy in the area where he was. Moreover he had been wearing ear defenders until they had been knocked off by the explosion. Mr Young confirms that Mr Richard was not at the 68-foot level when he arrived there and as we shall see this may be significant in other respects. He also confirms that he had not passed Mr Richard. It is also significant that Mr Young does not appear to have noticed a trail of hydrocarbon vapour when he passed along a stretch of the west face such as Professor Magnussen said could have accounted for the blue flash. The fact that Mr Young noticed only hot gas and not flame suggested to Dr Mitcheson that the flammable accumulation that gave rise to the incident could not have been situated close to the top of the stairway. The witness Mr Cubbage was unable to venture any specific explanation for the hissing sound spoken to by Mr Young but I found that Dr Mitcheson’s view of the matter seemed quite acceptable particularly when considered along with the other evidence.

The witnesses Mr Bollands and Mr Clark also contribute to the evidence about the pressure occasioned by the explosion. Both were in the Control Room at the time of the explosion and were propelled in a northerly direction (about 15 feet in the case of Mr Bolland). Dr Mitcheson describes this phenomenon as being consistent with shock wave pressure whereas Mr Cubbage attributed the effect to dynamic wind. It may not matter which of these two explanations is selected since each would require the rupture of the C/D firewall and the control room wall. At the time there was smoke coming from the south of the control room and this too suggests the rupture of the C/D firewall. It has to be noted that neither Mr Bollands nor Mr Clark felt any particular heat when they were knocked down and this I was told suggests that the gas which had exploded was restricted in quantity.

5.5.6 Damage to Equipment

After the explosion damage was noted on the north-most part of the Chanter Riser Gantry. The damage was on the inboard side at the part of the gantry that faced the west end of module C. This gantry was a relatively new structure. At the time of the explosion the witness Mr Bradley was at the 20-foot level in the area of leg B4 of the platform. He heard a loud bang and after having prevented his workmate Mr Ralph from falling he looked up and saw bits of debris descending in an arc. This debris was coming from above and beyond the north landing area in a westerly direction. The defenders sought to argue that the debris was consistent with the panelling that Captain Clegg describes after what he called an explosion of fire in Module B. On the other hand Mr Ralph who was close to Mr Bradley ended up with oil on his face and this could I suppose have been connected with Captain Clegg’s fire explosion in Module B. However Mr Bradley does not mention having heard a second explosive noise between the initiation of the incident and seeing the debris. Dr Mitcheson said if the firewall had ruptured then an explosion in Module B could have vented into C and ejected debris out of that module. Thus the debris although suggestive of an explosion in C is not exclusive of an explosion in B. As Mr Bradley looked up he noticed the damage to the gantry. He described it as a small indentation. Dr Mitcheson took the view that this damage was more consistent with and explosion in C than B although he accepted that the fact that it had occurred in B could not be totally excluded as a possibility. He points out that the target area is to the north of Module B and that the impact point faces due east. Mr Cubbage for his part thought that it was just possible that the dent in the gantry was caused by an explosion in B but he thought that if this had happened it would have been surprising. It must be noted that the defenders did not bring any explosives expert to contradict the expert views of Dr Mitcheson and Mr Cubbage. The defenders argued that it had not been proved that the indentation had been caused by the accident. However the gantry was a new piece of equipment and the damage was first noted immediately after an accident that had showered the surrounding area with debris. I think the probability must be that the indentation was caused by the explosion and although the source of the damage is not perhaps conclusively proved the finger again points at Module C rather than B.

The Main Oil Line Panels were situated at the west end of Module C and

Mr MacGregor the witness described how after the explosion he had seen bits of these panels lying on the western catwalk. He had also noticed some small fires in the vicinity of the crane pedestal. However he had not approached the mouth of Module C. He was a maintenance technician and therefore was in a reasonably good position to identify this equipment. Dr Mitcheson had this factor consistent with an explosion in either C or B but only the latter if the B/C firewall had failed. However Mr Cubbage makes the point that if the panels had been blown out of C as a result of an explosion in B he would have expected there to be not only debris from the panels but also pieces from the firewall. Once again Module C is the area more consistent with what occurred.

There was a double door on runners on the westmost wall of the Mechanical Workshop and this too was damaged by the explosion. The door had been blown off its runners for a few inches in a westerly direction. This was a fairly substantial steel door. Dr Mitcheson indicated that the likeliest cause of this was that the explosion itself had caused rarefaction so that negative pressure arose with the pressure within the workshop being greater than the rarefied pressure outside. The Maintenance Workshop wall at the south had buckled but not failed. The fact that the Control Building wall had failed at the Control Room but not at the Maintenance Workshop would be consistent with an explosion originating at the east end having a pressure gradient which weakened as the explosive forces moved to the west. Dr Mitcheson said that he would have been surprised if an explosion venting out of Module B would have produced the rarefaction effect necessary to explain the damage to the workshop door.

The Instrument Workshop also had a door damaged by the explosion. The witness Mr Cassidy described that at the accident the inner door of this workshop (which was a hinged door) flew in and knocked him onto his back. Before this he had heard a very high pitched noise like metal grinding together. He was proceeding to investigate when the explosion occurred. The explosion had occurred immediately after the noise stopped. The door came off one of its hinges. A lot of instrumentation on the benches got knocked to the floor. The outer door of the workshop was kept permanently open but the door which struck Mr Cassidy had been shut.. This damage was ascribed by Dr Mitcheson to the shock wave which arose after the explosion and which affected Mr Elliot. Again he thinks that this is more consistent with the explosion having originated in Module C since the explosive forces would weaken as they travelled further from their source. If the damage had been caused by an explosion in B a much larger event would have been required. Thus it was easier for an explosion in Module C to have caused this than an explosion in B.

At the time of the explosion the witness Mr Thomson had been sitting in the Tea-room in the control building facing east and with his back to the emergency door. When the explosion occurred the door (which had been closed) was blown off its hinges, the ceiling collapsed, and the lights went out. The door was blown inwards (from west to east) and had knocked him off his seat. The cause of this damage was the same as with the Instrument Workshop and with the same implications.

5.5.7 Witnesses on State of the Firewalls.

The heatshield that surrounded Module A and extended partly across the east and west faces of Module B was undamaged by the explosion. Moreover so far as the eyewitness evidence is concerned this points to the fact that the A/B firewall was not ruptured by the explosion.

The witness Mr Gutteridge had entered Module A during his escape from the platform. At the time of the explosion he had been in the Bawden Workshop. Some minutes after the explosion Mr Gutteridge had seen heavy smoke to the north of the crane pedestal to the east and west sides of the platform. At that time although on the Pipe Deck he had seen no fire. About 20 minutes after the initial explosion and after a further explosion at the Tartan Riser he describes how there was black smoke and fire all across the Pipe deck which straddles A and B. He noted from there smoke coming out of the skid deck hatches. These are effectively the slots for the drilling rigs and they are directly above Module A. Some of the hatches had been dislodged presumably as a result of pressure from below. At that point of time (about eight minutes after the second explosion) there was no flame coming out of the hatches which is to say that there was no evidence of large flames in Module A. He then managed to get on to the drilling rig. As he surveyed the scene from there everything to the north of the cranes was engulfed in fire. He then proceeded to effect his escape by descending down the stairs from the skid deck to the production deck at the 84-foot level and entered Module A. As he descended he noticed smoke issuing from the skid deck like a kettle boiling. Before entering into Module A he paused at the half landing and had a good look into the module. In particular he looked at the wellheads to ensure that they were still intact. He saw small fires at flanges and there was one jet of flame which he associated with a leak at that point. At that particular point of time there was a large fire in Module B and if the A/B firewall had been ruptured it is likely that there would have been a large fire in A because flames from B would have entered A in search of oxygen. Thereafter he proceeded into A Module at a point close to the seawater pump and went towards the north to find a route to a lower level of the platform where the Navigation Aid Platform was situated. After penetrating about 15 feet towards the north wall of the module he had to stop because of the heat. He was proceeding diagonally and he got to a point at about the middle of the three rectangular marks below the water injection pumps as shown in the drawing 12/108 of process. He accordingly turned back and left the module. When Mr Gutteridge was proceeding towards the north wall of the module he felt radiated heat but saw no flames or other indication that the A/B firewall had been ruptured. Indeed the witness was quite definite that the wall was, at the west end of Module A, intact. His view was to a degree impeded by the Christmas Trees but he could see staggered areas amounting in all to about 60% of the firewall and if a fire had been raging behind the Christmas Trees it is difficult to believe that the witness would not have seen this. In fact he claims that he could see through the pipe runs which were spaced apart. Mr Gutteridge seemed to me to be a reasonably observant and reliable witness and of the various possible witnesses was best placed to note the actual condition of the A/B firewall. Mr Gutteridge gained valuable support from the witness, Mr J. M. McDonald. He had worked on the platform for some years as a rigger with the Wood Group and was familiar with the platform layout. He was in his cabin when he heard a bang and he noted that was followed by an unusual silence. This reference to a significant silence is consistent with other witnesses. He also confirms that the first explosion was followed by a second about 20 minutes later. Following the second explosion he was attempting to escape using the same route as Mr Gutteridge. As he descended the same stairs into Module A he looked into the module and all he noticed was that some of the Christmas Trees were on fire. He could not at that time see into Module B. Nor was there much smoke. When he went towards west alongside the open module he did not notice much fire. He too was proceeding towards the Navigation Aid Platform. He looked at the west section of the A/B firewall and did not notice any sign of rupture.

The witness Mr Swales was in the Mud Module when the accident occurred. About 10 pm he heard the flare die down significantly and this was followed by a tremendous thump. He was blown backwards off his feet so that he finished up with his head to the west. When he looked out from the east side of the Shaker House he saw flames licking up from the south west corner of the area of the heat shield to about the level of the skid deck. These could have been coming from the area of Module A because Module B would have been obscured. These flames seemed to be on either side of the heat shield. He first tried to make his way through the Sack Storage Module but found this to be full of light grey smoke. After an unsuccessful attempt to proceed to the north west of the platform he returned to the Shakers. At that point when he looked at the skid deck like other witnesses he noted that some of the drilling hatches had been displaced. He noted that there was at the time some fire in module A but this was not raging and not accompanied by black smoke. He then made various unsuccessful attempts to reach a safe place and eventually arrived back at the skid deck. He proceeded down to the A module level as had other witnesses and noted a lot of fire in the module. However he proceeds eastwards. He seemed to consider that at that time it would not have been possible to proceed to the west. He had arrived at Module A at a different time to Mr Gutteridge and Mr McDonald although it is not absolutely clear whether it was before or after. However Mr Swales refers to the crane boom coming crashing down on the heat shield of the south side and since neither Mr Gutteridge nor Mr McDonald refer to such an obstruction it may well be the case that Mr Swales arrived opposite Module A at some time significantly later than these two witnesses. He also speaks to a particularly large explosion followed by the platform splitting. Mr Swales proceeded east to the south-east corner of the platform and as he was unable to go north from there he then descended to the Navigation Aid Platform at that corner of the structure. He confirmed that the heat shield along the south of the platform from the centre to the east was certainly intact. When he was in the course of his journey he looked into Module A. There was quite a lot of fire but this seemed to be associated with burning Christmas Trees and there was not much smoke. He found the western half of the module to be afflicted with a worse degree of fire than the eastern. He declares that the burning he observed in Module A was not of the same degree of intensity as what is shown in the photographs taken by Mr McDonald and relating to Module B. However he could express no view as to the integrity of the A/B firewall. In assessing the value of the evidence of Mr Swales I require to take note of the uncertainty of his timings. Given the extreme strain he must have been under this is in no way surprising.

Another witness on this aspect of the case is Mr Rae. He was an electrician employed by Bawden Drilling and had only been on the platform for about three months prior to the explosion. He thought that between the time of the explosion and his leaving the platform was about 25 minutes although he had thought erroneously that the first explosion had taken place about 9.40pm. After various abortive steps to find a safe escape from the platform Mr Rae went back to the electrical workshop and there met Mr Swales. Mr Rae eventually went down the stairs leading to Module A which had been used by other witnesses and then went to the Navigation Aid Platform at the south-east of the platform. When he looked into the module he saw some slight smoke and small pool fires. He could see the A/B firewall quite clearly and confirmed that it was intact. It is not entirely possible to reconcile Mr Rae and Mr Swales as to the state of Module A but I prefer Mr Rae because his evidence seems to fit in better with the other witnesses. In any event because of the relationship the collapse of the crane boom bore to the explosion of the Tartan Riser it seems that these witnesses arrived at Module A sometime after Mr Gutteridge. Moreover Mr Swales declared that he had been reluctant to examine the interior of the module too closely in case he saw something he would rather not have seen. Another point in favour of Mr Rae is that he narrates that it was only when he arrived at the Navigational Aid Platform that he realised the full extent of the fire which may suggest that any exposure to fire as he walked past Module A was moderate. On the other hand Mr Rae was less certain about the state of the fire wall at the Cullen inquiry. He explained this by saying that since the inquiry he had had more time to try and place his memories together and he is now certain that from what he saw the firewall could not possibly have been ruptured. Moreover one clear recollection which he had at the Cullen Inquiry was that you could see the back of the module through the smoke. This does not seem to be consistent with a position where the thick dark smoke in Module B was free to move into A. Finally he observed that on the Navigational Aid Platform the heat had been much stronger than it had been as he passed Module A.

The defenders led two witnesses to speak to the condition of Module A. The first of these was Mr Barron who was a foreman painter with the Wood Group who was survivor of the accident. While escaping he had proceeded alongside the open side of Module A. He explains that at the time there were flames at the Christmas Trees. These he says were about 4 to 5 feet high. He describes the scene as being like a sea of flames. He hardly looked at the module and simply is describing what he saw as he passed the module and looked back. Unfortunately we do not know at what stage of the incident he passed the module or even where he was at the time. Certainly he did not enter the module. The second witness is Mr John Wood, a diving technician. He had been in the Dive Machinery Room at the time of the first explosion. He had heard a loud thump, a whooshing sound, and then noted an eerie silence. These observations fit in well with those of other witnesses. He proceeded out of the Dive Machinery Room to the west side of the platform below Module B. When he came out he described the scene as "dark". At this point there was a grating noise above his head. He looked up and saw red flames and black smoke coming from Module B in the area where that module meets the heat shield. He speaks specifically to the fact that the flames were on the north side of the firewall between Modules A and B. This observation was repeated some minutes later. This evidence of Mr Wood could be very important. The defenders contend that the theory that the fireball observed in Module B was caused by damage to the condensate line by a projectile was not easy to understand because there had a been an interval of some seconds between the initial explosion and the development of the fireball. Indeed the suggestion seemed to be that the fireball was part of a continuous event involving a pool fire. However it is clear from Mr Wood that there was a grating sound shortly before what appears to have been the fireball. This could have signalled delayed damage to equipment such as the condensate piping or the escape at that stage of hydrocarbon from a confined space such as a pipe. We know from the Nowsco experiments that the escape of gas from a flange can cause a noise and at or about the time that the gas which caused the first explosion must have been escaping witnesses on the platform heard a substantial noise perhaps not dissimilar to that described by Mr Wood.

I am prepared to conclude that immediately after the initial explosion the A/B firewall was generally intact. Of course I cannot completely exclude the possibility of some minor or local perforation of the firewall which could have promoted some of the limited fire in Module A. If there was such damage, and the witnesses do not actually speak to it, this must have been very much less than the damage suffered by the B/C firewall.

5.5.8 Photographic Evidence of the A/B Firewall

The balance of the eyewitness evidence in my view plainly favours the fact that after the first explosion the A/B firewall was intact. This approach is re-inforced when the photographs taken after the explosion are considered. The witness Mr Miller (referred to earlier) began to take photographs about 15 seconds after the initial explosion and thereafter he photographed at short intervals so that he estimated that he took print 14 (number 12/358 of process) about 14 seconds after the first photograph. After taking print 14 he changed his location to the north side of the helideck. The gap in his photographs at that point was 20 seconds. Dr Drysdale’s opinion is that the first series of photographs show the development of a fireball in Module B. Some fire is shown behind the heat shield but this according to Dr Drysdale is less intense than the fireball and is a jet of flame coming from the main combustion process in Module B which has been forced behind the heat shield. He sees it as being a transient flame. In prints 2 and 3 the flame behind the heat shield has disappeared. He therefore supposes that this is because the transient flame has burned out. Dr Drysdale considered that the development of a fire in Module C is only shown from about print 5 onwards. This print also shows flame behind the heat shield but again Dr Drysdale attributes this to transient flame. The fire there is caused by a quantity of burning vapour from the main fire which has come out of Module B and been deflected behind the heat shield. In photograph 5 in can be seen that the flames are above the level of Module A. The witness Mr Ritchie also took photographs after the explosion and these are 15/27 of process. The first which shows events relevant to the fire is print 13. This supports the view that the flame behind the heat shield is an extension of the fire in Module B because there is a tongue of flame in front of the heat shield. This flame diminishes in the subsequent two prints. Mr Ritchie began taking his photographs about 10 or 15 minutes after the explosion. Looking at print 22 Dr Drysdale can see substantial fire in Modules B and C. However there is no sign of equivalent fire in A so that he is able to conclude that the firewall between A and B is still intact. When in cross-examination it is suggested to Dr Drysdale that the photographs are consistent with fire extending from Module B to A through a gap in the firewall he strongly rejects this. He also places reliance on the fact that there was apparently very little smoke coming from A. Dr Mitcheson takes the same view as Dr Drysdale with regard to interpretation of the photographs and opines that they do not show any flame encroaching from B to A through a gap in the firewall. He points out that the photographs show that the fire in Module B was burning under sufficient pressure to be the probable source of the fire at the north of the platform which in all probability comes from gas being forced through Modules C and D. If there had been a breach of the A/B firewall the same pressure would have forced fire into A. In Mr Ritchie’s photographs Dr Mitcheson sees a sharp delineation between the fire in B and the area of darkness which is A. If there had been fire in Module A one would have expected to see flame curling around the upper part of the module. It should be noted that the heat shield was transparent. The said photographs do not show in relation to Module A any silhouettes of equipment within the module such as might be expected if there was fire within the module. Even after the transient flames within the heat shield have diminished the flame in Module B continues but the light behind the heat shield disappears.

Professor Magnussen’s evidence was based not only on the individual prints of Mr Miller’s photographs but also on 59/1 of process with shows these prints developed to different degrees. In the photographs which are numbers 2 and 3 of the series he sees no evidence of the A/B firewall although in number 4 he sees a trace of flame. It is to be noted that the flame seen in print 4 seems to tie in with the shape of the flame coming from B. Professor Magnussen sees in prints 5 and 6 a flame extending above the production deck level but this appears to be between the heat shield and the drilling tower and to be part of the flame coming out of B. Professor Magnussen’s views as to a possible connection between the flames in Module B and any flame co-extensive with A are unfortunately not very clear although he perhaps is agreeing with Dr Drysdale. Indeed in general he appears to agree with Dr Drysdale in relation to the photographs. However he claims to see some smoke coming out of Module A although no fire. Of course I know from other eyewitnesses that there were certain well-head fires in Module A . Even looking at the print number 12/239 of process which was taken by Mr Lindsay McDonald which was taken about 30 seconds into the incident Professor Magnussen cannot identify any fire in A. Mr Cubbage accepts that it would have been possible for the A/B firewall to be breached and the wind to have driven the flames away from A but this is not his own assessment of what happened. Moreover the possibility he refers to takes no account of the pressure factor mentioned by Dr Drysdale.

In the body of evidence I have been discussing there is no clear evidence that the A/B firewall was ruptured by the initial explosion. On the other hand there is much reliable evidence from which I can conclude that the explosion did not rupture this firewall. On the other hand there is evidence in the said photographs from which the experts were able to conclude that the state of the B/C firewall was such as to permit the spread of flame from B into C.

5.5.9 The C/D Firewall

This wall was breached after the explosion along its length. Mr Bollands gave evidence that just before the accident he had been in the Control Room. He was standing at the control panel muting an alarm and speaking on the radio when he was blown over by a blast coming from the south. He head had been facing east. He was moved about 15 feet to the north and because of that distance Dr Mitcheson considered that he must have been knocked down by a pressure force and not say by vibration. He was briefly unconscious and when he revived there was a lot of smoke at the top of the Control Room coming from the south. There was no natural passage for the smoke to come from outside the structure into the Control Room. The telephones had gone and there was a lot of loose debris that had been blown in the same direction as Mr Bollands. Mr Clark had also been thrown northwards across the Control Room and was lying injured with debris and equipment on top of him. Mr Clark himself gave evidence and described the effect the explosion had on him in much the same terms as Mr Bollands. In particular he indicated how he had been thrown northwards across the Control Room so as to be flung against the Well Status Board. He also described that one could not see in the Control Room because of a dense white dust (although elsewhere he describes this as smoke). He thought that this dust like substance had come from the south and that it looked like "the stuff the firewalls are made of". There was no suggestion put to him that it could have come from within the Control Room itself. Shortly after the explosion Mr Ian Ferguson, a mechanical technician, came up into the Control Room. This happened within minutes of the explosion. When he entered he noticed that the Control Room was dark and dusty as well as being in what he describes as a shambles. He confirms Mr Bollands and Mr Clark as to their positions. There is clearly some doubt as to whether the substance obscuring the Control Room after the explosion was dust or smoke or both. On this point the witnesses Cassidy and Thompson indicated that when they came up towards the Control Room after the explosion they each saw black smoke coming out of it. When Mr Thompson entered the Control Room one section of the inner doors was hanging off into the Control Room. The Control Room was devastated and there was smoke within although lighter than the smoke outside it. Mr Cassidy paints a rather starker picture for he says that the smoke coming out of the Control Room was fierce and choking him. The observations of Mr Cassidy and Mr Thompson were about three to five minutes after the explosion.

Mr Thompson, as I have already described, indicated that the explosion had damaged a door in the tea-room. He also spoke to the fact that after the explosion he had entered the Maintenance Workshop and found that the wall on the south side behind the lathe had buckled. The lathe itself had been damaged as had also the east wall. Another effect in the Maintenance Building was described by the witness Ferguson. He had at the time of the explosion been in the Tool Room facing west There was a loud bang and he was thrown forward. Shelves, manuals, and fittings were dislodged. Dr Mitcheson considered that the pressure wave which knocked Mr Bollands and Mr Clark so forcibly to the north indicated that the explosion had ruptured the sealed wall of the Control Room. For this to happen the C/D firewall would also have to be ruptured. The presence of the dust or smoke would also signify the bursting of the Control Room wall. Dr Mitcheson attributes the damage to the Maintenance Workshop walls to pressure difference caused by the breach of the firewall. The overpressure from Module C would decline gradually the more west the explosive forces moved. The evidence which Mr Cubbage gave on the matter of the Control Room was fundamentally the same as that of Dr Mitcheson. Indeed none of the experts in the proof suggested that if the eye-witnesses are accurate what was experienced in the Control Room could have been caused other than through failure of the C/D firewall.

The witness Thompson also testified that after the accident he had seen Mr Vernon and Mr Carroll (later to become casualties). They had been proceeding to the east end of Module D to get to the water pumps. They later came back saying that they could not get through because of the dense smoke. This would seem to suggest that there was a serious amount of smoke either at the east end of the module or at least in the area leading to it particularly as the men in question appear to have been wearing breathing apparatus.

Indeed there is evidence from which it can be concluded that the C/D firewall must have failed not only at the west end opposite the Maintenance Building but at the east end as well. This deduction is primarily available because of the emergence of fire at the north face and in addition operatives who tried to proceed to the east end of Module D to use firefighting equipment were forced back by smoke.

5.5.10 The B/C Firewall

I have no difficulty in concluding that the B/C firewall was ruptured by the initial explosion. In the first place once it is accepted that the C/D firewall was broken by the explosion it would be unlikely that the B/C firewall (a less sturdy construction) would not also be ruptured. The available evidence in any event supports that conclusion.

The witness Mr McGregor said that as he emerged after the explosion onto the external walkway on the west face he noticed debris which he thought included the MOL control panels. He also noted some small fires at the mouth of Module C. Mr Thomson in similar circumstances also noticed smoke and some flame in the area of Module C and Mr Young saw smoke there. The smoke seen was emerging from the module. Given that from the photographs it is perfectly obvious that there was serious fire and thick black smoke in Module B then that location is the likely source of the black smoke and yellow flame observed in C. This is only explicable if the firewall had been ruptured. From the expert evidence (and particularly Dr Mitcheson and Dr Drysdale) black smoke would have come from an oil fire and there was no oil inventory near the mouth of Module C. Mr Thomson could barely see the crane pedestal because of the smoke. Mr Ferguson had emerged from the Maintenance Workshop and when he looked south he saw smoke and flames but this was coming direct from Module B. The smoke was extending considerably beyond the platform and was drifting towards the witness. The differences between the witnesses may be explicable to the circumstance that Mr Ferguson emerged on to the walkway rather later than the other witnesses I have mentioned in this connection. It should be noted that because of the thick smoke Mr Ferguson was unable to approach the mouth of Module C. In fact anything he says about the situation along the west face has to be qualified by the fact that his vision was seriously impeded by smoke. However the fact remains that at no time did Mr Ferguson claim to have seen anything emerge from other than Module B. He did not claim to see flame pass through the opening at the rear of the crane pedestal. However the witnesses who describe seeing fire and smoke in Module C not only support one another but get support from the photographs. Moreover Mr Clark, who came down the Control Room steps at the same time as Mr Ferguson did see smoke coming out of Module C. Indeed he saw smoke and flames coming out of both modules. He claims to have seen flame at the back of the crane pedestal and it is not very clear whether he means by this flame coming through the space at the back of the pedestal or that he is saying that looking through that space he could see flame from Module B. The witness Cassidy came out of the Instrument Workshop and when he looked south along the west face he saw flames shoot out of C Module over the sea and he also saw black smoke and debris. The witness Grieve also indicates that when he came from the 68-foot level to the west face there was thick smoke around the crane pedestal which would perhaps be consistent with smoke emanating from Module B. He then descended again to the 68-foot level where he saw more smoke and flame emanating from under B module. When he had tried to approach Module C and look inside he did not see any flame although he saw smoke at that stage but it is obvious he did not have a complete view. Moreover the smoke in the module would have been capable of obscuring flame. He too did not claim to have seen flame coming through the space between the crane pedestal and the Modules. Of course it has to be acknowledged that all the witnesses were likely to have been in a state of confusion and excitement due to the terrible events which were unfolding around them so that it is very important to be able to test their evidence by relatively objective evidence such as the photographs. Some of the witnesses such as Mr Clark, Mr Cassidy and Mr Bollands had to an extent been injured. The defenders tried to persuade me that because Mr Ferguson does not seem to have been injured he should be regarded as a more reliable observer than those who were . However I think this would be a dangerous assumption. At best all the witnesses were likely to have been shocked and probably frightened for their lives. Just how an individual would react under such circumstances is difficult to know unless there is some pointer in the evidence. Indeed when one considers the evidence of the various survivors and the circumstances to which it related it is perhaps surprising what degree of consistency there is.

As to whether or not there was serious smoke in the Control Room the evidence on this is not consistent. On the other hand the light was poor. Witnesses may be speaking to different points in time. There may have been dust and other debris which confused the situation.

It is clear that shortly after the explosion fire and smoke was observed at the north face. Dr Drysdale explained that this smoke must have come from Module B and found its way to the north face through internal channels in Modules C and D. I found this evidence entirely convincing. Professor Magnussen suggested that the smoke may have travelled from B to the north externally over the top of the platform but had this happened it would have been noted by witnesses such as Mr Gutteridge who would then have been close to the path of the smoke. He was standing on the pipe deck not long after the explosion.

It is perhaps significant that none of the eye-witnesses speak to seeing extensive flame in C and this too is consistent with the photographs. However there was noticeable flame in C from at least about 20 seconds after the initial explosion.

On examining Mr Miller’s photographs Dr Drysdale can detect fire low down in Module C about 22 seconds into the explosion. Of course at that time it also clear that there is massive fire in B. He thinks that this in shape and form is consistent with the fire in B spilling into C through a ruptured firewall. His views are based on consideration of the whole series of photographs. Some of the photographs show silhouettes that are consistent with there being of equipment within C and thus suggest that the flame was behind this. It would not be consistent with a situation where the flame which appeared to come from Module C was simply flame from B passing behind the rear of the crane pedestal. Thus within the first minute after the explosion there was certainly flame in Module C and when Mr Grieve claims that he could not see this he is either mistaken or he had arrived rather later by which time the situation had changed because the flame had burned out or was obscured by smoke. Moreover Dr Drysdale looking to the colour of the flame in C opines that there is no obvious source of fuel at the west end of the module to produce a flame of that colour. He pointed out that in print 19 the flame emerging from Module B seems to have grown in intensity and the flames in Module C also seem to have intensified. If there had been an independent source of fire in Module C Dr Drysdale would have expected to see flames emerging under the ceiling in C as air was sucked in. He refuted the suggestion that the fire in C could have been caused by a diesel pump which is located just outside the module. If the fire had been located at the pump the obstructions shown in silhouette in some of the prints would not be shown. Diesel has a relatively high flash point and would have taken some time to ignite at all. There is no mechanism for rapid release and involvement.

Dr Drysdale also emphatically refutes the suggestion of Professor Magnussen that what is seen in the photographs could be small localised fires and I think the reasons he gives for this sound convincing. Professor Magnussen when his theory was tested found himself unable to identify a clear source for the supposed local fires and also seemed puzzled by their shape. He accepts that the flame in C could have been obscured to some extent by the black smoke. He maintains that if the fire in C had been coming from B he would have expected to see flames protruding into C with the same periodicity as those in B. The prints he lays great store by are numbers 20 and 21 but these were taken after the Tartan Riser explosion had caused extensive fire at the 68-foot level and the earlier fire in C cannot have been caused by this as Professor Magnussen suggested. Moreover if the fire in Module C was set back some distance into the module it would have the periodicity of the fire set into Module B (which we cannot see) rather than of the fire at or extending from the mouth of Module B which is what we do see.

Dr Drysdale was taken to the photographs 1 to 13 and commented on the fire at the north face which is shown by these. He comments that at some stages this fire is obscured by the thick black smoke. The fire at the north face occurred within about 15 seconds of the initial explosion and Dr Drysdale finds it difficult to attribute this to a separate fire. He thinks that the fire is attributable to a flow northwards of hot burning gases which started in Module B and which thereafter travelled horizontally through the broken fire barriers to the north face. The distance of about 30 metres would have been covered in about 8 to 10 seconds. The fireball in Module B would have created some overpressure which would have helped propel gases out of the module. Dr Drysdale testified that in a single space such as in the module nitrogen, oxygen, and combustion products accumulate near the ceiling and will eventually begin to burn. A flashover occurs but the burning is quite inefficient since the flames under the ceiling cannot easily entrain more air. It is possible under such conditions for the flow of flame to travel for some distance, the flames being on the underside of the layer. When the flow finally emerges into more space there is mixing with oxygen and thus substantial flaming. The photographs show that initially the flame on the north face seems to extend further than at a later stage and this is consistent with the effect of overpressure occasioned by the fireball. There seems to be no dispute that the Module B and north face fires are connected. If the flame had travelled along any of the external walkways or through the accommodation modules it would have been seen by other witnesses. Not only was the route that Professor Magnussen suggested not consistent with the actual observations of Mr Gutteridge and Mr Swales but his theory was not put to Dr Drysdale. Indeed there must in the circumstances be some doubt as to whether the process described by Dr Drysdale could have occurred if the route of the fire had been as Professor Magnussen postulates. Moreover if the flame had travelled the route prescribed by Professor Magnussen, Captain Morton might have expected to see it while observing the east side of the platform. Otherwise the observations of Captain Morton (smoke coming out of the east end of C) are further confirmation that smoke in Module B was able to penetrate into Module C. It also has to be noted that Mr Ferguson and Mr Clark looked at one point along the north face of the platform and saw smoke coming out from between the John Brown exhausts. Indeed Mr Ferguson could proceed no further than the north west corner of the platform because of thick black smoke along the north face. Looking down below the grating all he could see was thick black smoke coming out of the John Brown exhausts. Module D was of course unenclosed at the north side. Mr Clark describes the flame along the north face as coming from an open area between the switch room and the John Brown exhausts. It may also be noted that the evidence of Mr Gutteridge and Mr Swales had not been read by Professor Magnussen. Eventually in his evidence Professor Magnussen accepted that if there had been a route available through the firewalls Dr Drysdale’s explanation would be quite plausible.

Further evidence of the existence of dark smoke and orange /red flames on the north face is given by the witness Amaira, a diver, who got a view of the north face about 12 minutes after the explosion and described seeing these phenomena. Another witness Mr Murray who had been on the helideck did not notice any flame at first but about twenty minutes after the explosion he observed flame on the north face. It has to be noted that before that time he had been fairly well occupied. The significance of the evidence is that it demonstrates that the flames were persistent. Indeed a number of the eyewitnesses speak to there being dense black smoke in the area of the north face and when Mr Carroll and Mr Vernon (neither of whom survived) tried to activate the water pumps at the east end of Module D they were unable to accomplish this. Mr Clark located the thick black smoke as coming out of Module D at the gap between the switchroom and the John Brown generators. Mr Ferguson on the other hand speaks to seeing smoke come "over" the John Brown generators but I do not find any discrepancy about this significant.

Dr Mitcheson agreed with the views of Dr Drysdale regarding the fire at the north face.

Captain Morton noticed substantial flames on the east face below the production deck but this was about 10 minutes after the explosion. Dr Mitcheson was of the view that the smoke observed by Captain Morton coming out of C module was consistent with smoke originating in B which was blown eastwards by the wind and penetrated through the B/C firewall. Indeed when Mr Gutteridge explained how at one point he had seen smoke along the east face it may be material that he locates this to the north of the crane pedestal.

The defenders’ engineering witness Professor Reid accepted that the C/D firewall seemed to be of a stronger construction than the B/C. Moreover pressure within Module C would tend to push the B/C firewall (which is on the south side of the module’s trusses) away from these trusses consequently putting the clamp bolts through tension. The C/D firewall on the other hand would be pushed into its trusses. With isobaric pressure within Module C if the C/D firewall were to fail one would expect the B/C firewall also to fail. Dr Mitcheson and Mr Cubbage agreed with the same generality and for the same reasons. Indeed Dr Mitcheson’s opinion on this matter was the most positive of the experts because he was looking at the matter on the basis of his wide general experience as an explosives expert. Dr Bakke, (who carried out modelling experiments to study pressures within module C) agreed that if one considers that there is a further wall to be breached beyond the C/D firewall before smoke could enter the Maintenance Building then if that happened the probability is that the B/C firewall would also be breached. Some of the experts’ evidence on this is somewhat qualified and tentative because no calculations had been carried out but what lends it support is that it fits in so well with other evidence. There was certainly no evidence that the C/D firewall would go at pressures lower than those required to pierce the B/C firewall. It should perhaps be noted at this point that the A/B firewall seemed to have been of the same construction and strength as the B/C. Thus Dr Mitcheson is able to conclude that if the explosion had taken place in B then if the B/C firewall had gone the A/B wall must have gone as well. However some of the structural engineering evidence casts doubt on this.

The experts who gave evidence about the puncturing of the firewall made it clear that they were not saying that the firewalls had necessarily disintegrated along their whole lengths. This was particularly so in relation to the ends of the modules where the pressure gradients may well have been weaker. This could be important in relation to the witness Mr Grieve since the limited view he had into the mouth of Module C may well not have included an area of ruptured firewall.

5.5.11 The C/D Firewall

The defenders queried to what extent it had been proved that the C/D firewall had been ruptured. Dr Mitcheson had opined that as the flame travelled through the module he would not expect any significant difference between the pressure on the north wall and that at the south at any particular point in its east west travel. However that does not necessarily mean that the damage to each wall would be the same since the position of the walls in relation to wall trusses differs and the C/D wall was, I think it was agreed, a more solid construction than the other walls. Moreover in relation to the control building complex there was an additional steel construction between the C/D wall and the interior of the control building. Although on any south to north plane the north and south firewalls are under approximately the same pressure the response of the walls will be governed by the difference in pressure on either side of the wall. Thus if there is venting into Module B from C as the firewall collapses at certain points the pressure differential between B and C may reduce and this could affect the degree of damage at particular sections of the firewall. The point of this exercise was to support Dr Mitcheson’s suggestion that despite damage to the C/D firewall parts of the B/C firewall could have escaped damage. The defenders were of course concerned to have it established that on the basis of Mr Grieve’s evidence the B/C firewall was not damaged at the west end. However I have already commented that Mr Grieve’s evidence does not go so far as to prove that. On the other hand if the defenders were right it could (so they contend) have implications for the pursuers’ theory that a projectile destroyed the condensate line.

5.5.12 The Dive Complex

The Dive Complex was situated at the south west area of the 68-foot level approximately under Module B. The Main Oil Line comes down from Module B at the 84-foot level to the 68-foot level at a point near the Diver’s Launch Platform.

The witness Mr McLeod (who was the Stena Diving Manager) had his office inboard of the Machinery Room on the Diving Skid. He heard the bang of the explosion and the whole office was severely shaken. Chairs overturned, shelves emptied, and fittings and the ceiling fell down. He was knocked off his seat. About a minute and a half after the explosion he emerged from his office and saw some smoke coming from the south. Pieces of pipe lagging was strewn around the area and some of this was smouldering. He noted that oil was beginning to run down the structural bracings from the level above and some of this was beginning to ignite. He also saw oil run down the MOL. The penetration of the MOL through Module B deck left some space which would allow oil to pass. This leak of oil was caused by the explosion because the witness, Mr Niven, had been in the area at the time of the explosion and does not speak of seeing any leakage of oil then. The witness Mr Amaira had been in the same area within a minute of the explosion and on looking around had not noticed oil. None of that may be conclusive in itself but at least can be said to be consistent with a situation where damage to the oil pipes had been caused by the explosion rather than that a leak had preceded it. The volume of oil observed by Mr McLeod increased quite quickly. It took about 3 minutes to remove the diver from the water and during this time the situation was deteriorating rapidly. There was fire all around the Dive Skid and more fire was approaching rapidly from the east. Mr McLeod appeared to be a particularly alert and reliable witness and indeed appears to have acted with special gallantry after the events I have described. Dr Mitcheson considered that the damage Mr McLeod described was consistent with that expected from very severe vibration.

The witness Mr Almeira at the time of the explosion was in the small structure known as the Wendy Hut which is situated on the Dive Recovery Platform. About 10pm there was a tremendous bang followed by substantial vibration of the platform. He got the impression that the bang came from the north and the east. We were informed by the experts that witnesses attempts to locate sound can to be unreliable. Prior to proceeding to the Wendy Hut he had passed a point from which he would have had a good view of the MOL but did not notice anything extraordinary. He confirmed that on his journey he would have had a good glance around him. Moreover he did not notice any unusual smell. After the explosion he went to attend to the diver’s winch and then saw oil running down the MOL. This was about 20 seconds after the explosion. Thus whatever the position before the explosion it appears that there was a material quantity of free crude oil in Module B very shortly after the explosion.

Two decompression chambers are also on the Diving Skid. They each had a door consisting of a heavy gauge steel plate and they opened inward. The doors were connected to the chambers by a loose hinge which enabled the doors to swing freely against the "O" ring seals of the chambers. The hinges were not particularly robust. The doors would normally be kept closed but if there was a diver in the water (as was the case when the explosion occurred) the door of one chamber would be kept open to receive the diver when he emerged from the water. On the said occasion the door that had been left open was that of Decompression Chamber No. 2. This door was found to be damaged after the explosion. In particular the door was found to be off its hinge and lying inside the chamber. Dr Mitcheson thought that this could be attributable to vibration caused by the explosion. He accepted that had there been other evidence suggesting overpressure in the area then the damage to the door could also have been caused by that overpressure. Indeed Mr Cubbage thought that negative pressures generated by the shock waves resulting from the explosion could have caused the damage to the door. He also thought that rarefaction waves could also be responsible and he did not discount vibration. His evidence represents a degree of change of mind from the Cullen Inquiry where apparently he had difficulty in offering an explanation for the door damage. Mr Cubbage’s evidence about the cause of the damage to the compression chamber door is obviously somewhat hesitant and that may be because the problem like so many in this case is not a simple one

The witness Mr Niven was at the time of the explosion standing on a step two or three steps up from the Divers’ Launch Recovery Platform. He heard a loud bang and felt a blast which he thought came from the south west of where he was standing; that is to say the blast seemed to come from the sea. He felt a push on his face and chest. This is in itself not inconsistent with the effect of an explosion from Module C for the pressure waves from such an explosion would expand in all directions on emerging from the module and would enter the diving skid where this was possible. About 2 to 3 minutes after the accident while he was engaged in the task of retrieving the diver he noticed oil dripping in the area of the MOL and some of this was on fire, burning with a yellow flame. In particular there was flame at the point where the MOL penetrated the deck above him. At the time of the explosion Mr Niven had also felt the platform shake substantially. The witness Mr Wood was called by the defenders. He had at the time of the accident been working in the Machinery Room on the diving skid. He had heard a loud bang followed by what he describes as a whooshing noise. Then there was a dead silence. The lights were off. The fact that a number of witnesses refer to the explosion being followed by a profound silence suggests that the explosion caused the platform machinery to stop functioning. Normally this machinery creates a considerable noise throughout the platform. He came out of the Machinery Room through doors that had been forced open by the blast and their hinge points buckled. The doors were heavy duty doors held by three hinges. Before this he had noticed that most of the fixtures and fittings of the Machinery Room had been dislodged. This in itself suggests severe vibration. He was concerned about some oxygen pods that were stored at the dive complex in case they should explode. He then heard a grating noise above him and when he came out onto the landing platform to investigate he saw red flames and black smoke in the area of Module B towards the north side of that module. He only saw this as a result of a quick glance. The flames he saw were about 15 feet in diameter. Thus what he saw would have been consistent with the fireball described by other witnesses. Two or three minutes after the explosion at the south of the Dive Complex he saw a red substance running down the beams. He took this to be oil or possibly molten metal. He indicates that the flame he saw seemed to be coming from the lower part of the module and it was developed towards the south side of the module and at the lower part. He also saw flame inboard of the crane pedestal in the area of the mouth of module C. This he describes as being a 5 foot ball of red flame. It seemed to be contained in the area behind the crane pedestal. He thus describes two fires, one in Module B and a second (which he calls a contained fire) on the other side of the walkway. I am not sure that more can be taken from this evidence than that he saw what appeared to be two separate fires on either side of the walkway and possibly to an extent encroaching behind the crane pedestal. Just how precise his evidence was on the matters in question may to a degree have depended on his perspective. However the point the defenders attempted to make from this evidence was that any fire in Module B or C was not necessarily as a result of fire spreading through a shattered firewall. His look at the fires was quite brief and he retreated into the platform to attend to other duties. If the photographs were looked at in isolation then in the light of Mr Wood’s evidence this might have been so.

The damage to fittings, and the compression chamber door, within the dive complex is probably attributable to the consequences of severe vibration. In this connection the dislodging of lightweight material (as certainly occurred) is significant. Because the east end of module C was severely congested by heavy machinery, this factor would have constricted any rush of gases due to an explosion near that end. The easier venting at the west would have caused gases to rush to that end and this would have imparted a reactive force towards the east. These effects would have been likely to cause the platform to vibrate significantly. The compression effect was not so likely if the explosion had been in Module B since there was not the same pattern of obstruction at the ends. The localised damage in the Dive Area excludes the possibility that the explosion itself took place in that location. Dr Mitcheson indicated that the damage to the Machinery Room door was consistent with the sucking effect that would have resulted from rarefaction. Thus the damage to this door was probably caused by a combination of vibration and negative pressure. Mr Cubbage makes the point that if the explosion had been in Module B and not at the east end of C he would have expected the blast felt by Mr Niven to have been stronger than what would have been felt by the men in the Control Room in Module D. This was not the case. However barring other evidence the events in the diving complex would in themselves be relatively neutral.

5.6 The Fire

5.6.1 Mr Grieve

The pursuers’ claim that the fuel for the fire which developed on the platform after the explosion was condensate. In this connection they rely in the first place on the observation of the eye-witness Mr Grieve. At the time of the explosion Mr Grieve was standing just to the west of condensate injection pump B on the 68-foot level. He saw the witness Young arrive. As Mr Grieve was standing at the west side of the said pump there was an explosion which he felt was directly above where he was standing. He was perhaps close to being beneath the PSV 504. He fell to his knees because he felt as if someone had dropped something really heavy on the ceiling above his head. Despite what is acknowledged to be a difficulty in locating the whereabouts of a noise what Mr Grieve described so dramatically must have some significance because the noise was so close to him. He got up and made his way to the west side of the module but having taken a few steps he looked back. As he did so he noticed a ball of flame directly above the area of the injection pump and this seemed to be hanging in the roof void space. I doubt if Mr Grieve in the circumstance could expect to pinpoint the fire ball other than within general limits. Apart from other considerations it was dark . The fireball had no apparent force behind it. Generally the lights where he was had been extinguished by the explosion. The ball of flame seemed to have no obvious source and was relatively transparent. He describes it as having a "bluish sort of orangey hue to it". It was at a height of about 15 to 20 feet - in other words contiguous with the deck above. It had a diameter of six to three feet. Mr Grieve proceeded to the north west corner of the 68-foot level (where there was fire fighting equipment) but by the time he got there, which would have taken about ten seconds, when he looked back the fireball had vanished. Altogether it lasted about 10 seconds. I have no reason to doubt that the essence of Mr Grieve’s account of events is accurate. His evidence means that shortly after the explosion there was this ball of fire that was in the general area of the pipe penetrations that would lead to PSV 504. He noticed nothing at his own level which could account for the fireball.

Dr Mitcheson concluded that the fuel which gave rise to the fireball was temporary. The phenomenon was consistent with a quantity of lean or rich unburned fuel and air being forced through the pipe penetration point in which case it could be expected to burn as a fireball in an area close to the penetration. He was certain that a fireball at C deck level below C would be linked with a release of gas within that module. If the gas were being released under pressure the pressure itself might be sufficient to force the gas down. Since condensate is denser than air it would be at a lower level within the 68-foot level were it not descending from the module above. Once the gas was ignited the burning itself would cause a reduction in density which is why the fireball would remain close to the ceiling. The fireball suggests a residual burning in C after the explosion. Mr Cubbage made an observation which seemed to make sense. He indicated that the fireball seen by Mr Grieve could not have been caused by liquid fuel oil since this would have dripped on the deck of the 68 foot level and been noticed as burning droplets. He thought that we were dealing with gas which was pushed through or dropping under its own weight. He gives an explanation for the bluish tinge around the edge of the fireball as air diffusing into the mixture. Mr Cubbage proposes the interesting theory that gases may have been pushed through to the 68-foot level by the initial explosion. That would mean within a second or two of the explosion. This theory would mean that the gas would have had to be ignited within a very few seconds of the explosion or it would have dropped down. Of course Mr Grieve did not notice the fireball until a rather larger number of seconds after the explosion. However he had been knocked down and dazed so that he may not have noticed the fireball until some seconds after it manifested itself.

Dr Drysdale was also asked about the fireball seen by Mr Grieve. He thought that the colour of flame described by Mr Grieve would not be consistent with an escape of gas under pressure but equally the fireball was not consistent with what would be seen if crude oil were the fuel. However Dr Drysdale and Mr Cubbage are generally supportive of Dr Mitcheson on this matter. Mr Cubbage thought that the gases must have been ignited at the time they penetrated below the deck or at least very quickly thereafter and he thinks this would have resulted from afterburning from the explosion.

Professor Magnussen took the view that the fireball must have been caused by a gas lighter than the surrounding air. However he thought that a diffusion type of burning was being witnessed and there seems to be general agreement about that. He suggests that methane might be the fuel because it is a light gas. However he cannot offer any explanation as to the possible origin of this methane and in fact there was no evidence as to a source for an escape of methane at the relevant part of the 68-foot level. The operators who had been working near the condensate injection pumps did not note any escape of methane nor did the gas alarms go off. Under cross-examination he seemed to accept that burning could cause an increase of buoyancy in condensate to account for the fireball. As I have already said a certain difficulty with language sometimes rendered the Professor’s explanations less than clear. He seems at one point to suggest that if the gas had been ignited at the 84-foot level it would not have dropped down to the deck below but would have risen. On the other hand if it were not ignited and was heavy enough to penetrate it would have dropped to the deck of the 68-foot level. However another possibility spoken to by Dr Mitcheson and more likely is that the gas had dropped (or been forced) through a pipe penetration when it was outwith explosive limits and then when it entered the explosive limits upon dilution the flame from above followed it through. Dr Mitcheson did not exclude the possibility that the flame had been pushed through the penetration directly from Module C. Indeed if the fireball was in a general sense directly below the pipe penetration and there was a continuing leak under some pressure this is what would be expected to happen.

The defenders argued that the evidence was not conclusive that the pipe openings in the deck between Module C and the 68 foot level were unsealed. They may possibly have been sealed with Mandolite or foam glass. I do not consider this very critical. There was a great deal of vibration after the explosion. Dirt, dust, lagging and other materials were loosened. Even if the pipe openings had been sealed the sealant could very readily have been displaced by the explosion. After all this is an explosion that allegedly developed an over- pressure that penetrated firewalls. The defenders suggested that the phenomenon observed by Mr Grieve could have been caused by unconsumed gases driven into the 68 foot level by the burned gases originating with the explosion. This if it was light gas could have risen to the roof space and there ignited. This theory immediately presents another coincidence with the exploding gases travelling in every direction that unconsumed gas should just happen to accumulate and ignite in the general locality beneath the alleged site of the explosion. There was evidence that machinery or sparks could readily ignite an accumulation of gas but it would have been interesting to hear if the experts thought that this could happen in the roof void where there was no machinery and not likely to be many sparks. Counsel suggested that there could have been static electricity but I should have found that suggestion more interesting if it had come from one of the experts. The defenders suggested that there was a dearth of evidence about pipe penetrations but apart from anything else I think they eventually accepted that there must have been a penetration where the condensate injection relief pipe went up to PSV 504. Indeed this and other penetrations are illustrated in the Schematic 13/49 which may not be strictly to scale but shows the general position. It would appear from this that a leak at an angle to the PSV would lead down to the pipe penetration although it might have some distance to travel and we do not know the effect of this. More precise measurements can be derived from the ‘as built’ drawing 12/146 of process. The point at which the relief line goes through the floor is about 6 feet east of A pump and a little more than that from the PSV in an easterly direction in Module C. In the absence of this having been explored in the evidence the precise implications, if any, of these distances is not known. It should be noted that the isometric sketch shows a space round each pipe penetration although of course as I have mentioned these spaces may have been sealed. What the drawing suggests though is that on any view there was room for a space to develop at the penetrations. Moreover if there was an accumulation of gas near the PSV and it was ignited it might cause a degree of pressure

Mr Grieve was a witness who before the explosion had been standing more or less below the PSV. When the explosion happened he thought that it was directly above him. Materials are dislodged by the explosion and within seconds Mr Grieve observes a fire ball below the general area of the PSV which is being blamed for the accident. These are pretty powerful facts that seem at first glance to support the view that the PSV may well have been implicated in the explosion. The actual mechanism for the development of the fireball at the place where it was observed is difficult to isolate with scientific precision. The task of precisely explaining this fireball presents many problems. However the experts seemed agreed that the obvious source of the fireball was a leak from the floor above in the area above. They give a number of possible explanations and it would be unjustified to ascribe the event to a particular process. The one that most appeals to me is that suggested by Mr Cubbage that the gas was forced through by explosion and that Mr Grieve only observed it some seconds after it had developed. However the important feature of the evidence is that apart from Professor Magnussen who could offer no explanation for the incident the pursuers’ witnesses were all satisfied that the fireball was related to what had happened above. In the whole circumstances this is exactly what one would expect and I have no hesitation in adopting this view. None of the experts suggested a plausible provenance for the fireball that was independent of the circumstances in the floor above. The theory developed by Counsel was not put to witnesses. The other implication of gas coming down from the module above is that this suggests a gas heavier than air and not a light gas such as methane.

5.6.2 The Observations of other Eyewitnesses

Captain Clegg’s observation of a low blue flame emanating from Module C at the time of the explosion was, it was argued by the pursuers, also more consistent with an explosion caused by condensate. From this observation Dr Mitcheson concludes that the fuel which caused the flame had a density heavier than air. Condensate fits such a description. If the fuel leading to the explosion had been lighter than air it would have risen to the ceiling within the module and the flame emerging from it would have been at a higher level. It is possible of course to have a condensate cloud that contains lighter components that would rise, particularly as the upper layer is diluted, but it is not possible to have a lighter gas with heavier components. If the flame seen by Captain Clegg had indeed been emerging from B and say caused by the combustion of crude oil it is difficult to explain the apparent gap of some seconds between the first observation and the eruption of fire within the module. The events would have been continuous. The colour of the flame seen may also have been difficult to explain. As Dr Drysdale explained if the flame seen by Captain Clegg had been caused by crude oil he would have expected the flame to contain at least some yellow. When Professor Magnussen had seen an equivalent flame in the south of France he accepted that it contained yellow elements. Mr Cubbage supports the position taken by Dr Mitcheson. The evidence therefore supports the view that what was seen by Captain Clegg was caused by condensate gas.

When Mr Young was hit by a blast of combustion materials on the occasion of the explosion he described this as being warm or hot. He was at the 68-foot level and the blast seemed to come down the stairway leading up to Module C. It would therefore be reasonable to assume that the gases which hit Mr Young had come from a low level in the Module. On the other hand the blast which struck Mr Bollands in the Control Room appears to have been cold. Because of the height at which this gas must have been when it penetrated into Module D it could be assumed that the gas came from a relatively high level in Module C. The pursuers therefore sought to take this as confirmation that the main combustion when the explosion had occurred had been at a low level which of course is consistent with a condensate explosion. The gas which penetrated into the control room came from a higher and cooler layer of gas in Module C.

5.6.3 The Fire in Module B.

The pursuers’ contention is that after the explosion there was a localised fire in Module B and that this was soon overtaken by the generation of a massive fireball. Then thereafter there was a continuing crude oil fire in B. The first clear manifestation of the fireball is in the photograph of Mr Miller which was taken about 15 seconds after the first explosion. Thus at about the time of Mr Miller’s photograph there was a large area of flame emerging from Module B. Moreover this development must have been eminently noticeable to anyone watching at the time

A fire can be described as a pool fire when there is a manifestation of fire above the surface of a free liquid. The flame is caused by the reaction between fuel vapour and air mixing with the fuel vapour. The combustion process is exothermic. The heat released is mainly convected upwards by means of a buoyant plume but a significant proportion is returned to the surface of the liquid. This will maintain the evaporation of liquid from the surface. The heat released by the process raises the temperature of the combustion products including air and nitrogen trapped within the flame. Temperatures as high as 1200 degrees Centigrade can be generated. Because of the heat the density of the gas will be low. The main heat loss will be the upwards buoyant movement of the hot gases. However some of the heat will be transferred back to the liquid pool by a combination of radiation and convection. Some of the heat is also being radiated to the surroundings. The surface of the pool will reach boiling point and this will continue to drive the vapour out. This vapour will in turn burn off. To ignite the pool fire in the first place there must be enough vapour above the pool to create a flammable mixture. The fire hazard of a particular liquid fuel is often defined by its flashpoint which is the temperature at which you get a flammable vapour/air mixture at the surface. To provide an ignition source a number of possibilities may well be available such as an electrical connection or a spark from clashing metal. Indeed Dr Mitcheson indicated that the circumstances of a release may in itself provide an ignition point. In a confined space the flame would be likely to rise to hit the ceiling and at that point spread out to any space available. There will be a layer of hot combustion products which would contain soot or smoke and as the fire increases in size this layer will grow as more fuel becomes involved. The radiation of heat will become very high and cause an increased rate of burning. This mechanism is known as flashover. Petrol as such is a relatively stable liquid and unless released under pressure as a spray it will vaporise slowly. On the other hand a gas such as liquefied propane would if released from its liquid pressure be very unstable and would readily convert to vapour. This process is known a flashing. With the sudden release of pressure the liquid begins to boil through its volume. The liquid is likely to be released with the vapour in the form of a spray and the individual droplets will gain heat from the surrounding air and also evaporate. The flash fraction of a gas is a measure of the latent heat of the gas in liquid form and will reflect the heat required to allow vaporisation to take place. A stable liquid like petrol will largely just fall to the floor if it is released from a pressurised situation but in the case of a hydrocarbon liable to flash a relatively small amount would merely fall as liquid. Most of such liquid will be released as a spray and will evaporate on release. However a stable hydrocarbon such as petrol which is released into a flame would burn almost immediately and would contribute to the fire. If a liquid with a relatively high flash fraction were released into a fire one would experience a large volume of flammable liquid spray which would immediately burn and there will be a large volume of fuel which will burn very quickly and is known as a fireball or BLEVE. This last expression stands for Boiling Liquid Expanding Vapour Explosion.

During the first ten seconds or so after the fire (while he was watching the structure) Captain Clegg did not see the subsequent fireball but he did see a fire develop in Module B and quickly increase to extend into C. Dr Drysdale considered that the fire described by Captain Clegg was likely to be caused by a pool fire of restricted surface area. By the time Mr Miller takes his first photographs the development of the fire is consistent with the existence of a fireball such as I have described and indeed an event that is far less localised than what Captain Clegg originally saw. Dr Drysdale‘s view is that the initial explosion must have resulted in a localised pool of oil and the ignition of this gave rise to the fire which Captain Clegg saw. The initial pool fire gave rise to the development of a fireball and this would be consistent with damage having been caused to the condensate line which gives rise to the release of condensate under pressure. Such a release would represent a classic fireball situation. After the fireball had quite quickly exhausted itself the fire which remained in Module B was of the character of a much more extensive pool fire than had existed earlier. Dr Drysdale explains this by suggesting that the fireball had occasioned a much larger escape of crude oil than had occurred initially. The smoke observed by Mr Miller low down in Module B is also consistent with Dr Drysdale’s views. If there had been a very large spillage of crude oil at the time of the explosion one would have immediately seen the flashing-off of a lot of vapour which would have immediately produced large flames. Dr Mitcheson also supports this view. Moreover the rich mixture of a large crude oil pool would not have produced a blue flash such as was seen by Captain Clegg.

The defenders’ witness Mr Kondol was asleep in his cabin on the Tharos when he was awakened by a loud bang. He had a window in his cabin which faced onto the platform. A few seconds after the explosion he looked out of that window. It should however be noted that his observation of the incident could not have been simultaneous. Firstly he was asleep and had to wake up from the noise. Then as he says he had to get out of his bunk before he looked out of the cabin window. His own estimate of the time gap between the explosion and his observation was 3 or 4 seconds. The first thing he saw was a yellow/red glow in Module B. It is important to notice that some seconds after the explosion he did not see a substantial fire but rather a glow. The three leftwards box shapes at the face of the Module (the MOL pumps) were silhouetted by the fire. The fire was certainly inboard of these pumps but not as deep as the separators which would have obscured it further. It has to be noted that at the point of time described by Mr Kondol, Mr Miller had seen no flames but he did however notice smoke and this may have obscured his view. What was seen by Mr Kondol appears to me to be consistent with the effects of a localised pool fire as these are described by Dr Drysdale. Dr Drysdale considered that a likely cause of the fire was oil escaping from the small bore pipework at the metering skid. What Mr Kondol saw also seems to have occurred before the fireball captured in Mr Miller’s photographs. If the initial explosion had originated in a sufficiently large pool of crude oil in Module B then it would be difficult to relate the large immediate fire that might then have been expected with the limited fire described by Mr Kondol. Mr Kondol did not see the large bright flame apparent in Mr Miller’s early photographs but then he only maintained his observation for a few seconds. Mr Kondol also spoke to a helicopter report at the time 22.13 which records that a helicopter has reported that there are no flames at the east side of the platform. This confirms that the major fire was at the west side of the platform and also discounts Professor Magnussen’s theory that flame was sweeping round towards the east side of the platform to arrive eventually at the north of the platform.

The witness Mr Murray was also on the Tharos and was at the time of the explosion in the heli-reception area near Mr Flaws. Before the explosion he claims to have noticed a swirl of gaseous material which looked like a pink ribbon. This observation must be of doubtful relevance to the accident because Mr Murray places the phenomenon as being nearer to the Tharos than to the platform and to get to that position from the platform it would have to have defied the wind unless it came from the Tharos itself. None of the experts sought to attribute importance to it. It was also a minute or two before the explosion. When the explosion occurred he heard a bang and then saw smoke and flame developing in Module B. The flame was orange in colour. It would have taken about one and a half seconds for the sound of the explosion to have reached Mr Murray. The flames and smoke seen by Mr Murray were relatively limited in scope. The smoke extended above Module B. The time over which Mr Murray continued his observations cannot be quantified precisely but he described it as being a few moments. The likelihood is that Mr Murray had moved away to attend to his duties with the helicopter before the emergence of the fireball seen in Mr Miller’s photographs. Mr Murray thought that the wind blew the smoke he saw through the accommodation area. This is intrinsically likely since a number of the casualties appear to have been overcome by smoke in this area. However it contradicts Professor Magnussen who suggested that the smoke was carried to the north over the accommodation area rather than via the gap in the C/D firewall. Dr Drysdale thought that the orange flame observed by Mr Murray was likely to have been caused by a gentle diffusion flame.

Dr Drysdale having considered the composition of the condensate stream in the condensate pipes indicates that the greatest proportion would be made up of methane, ethane and propane and that this would give rise to a high flash fraction. He considers that as much as 50% of the condensate constituents would flash on being released from pressure although he was happy to accept a flash fraction of 40% for the whole stream. This also fits in with Mr Wottge’s evidence. The metering skid is inboard of the MOLs but to the west of the separators. They had a three-eighths inch bore sampling connection. In fact there was a maze of small bore pipework in the area of this skid so that this would have presented an obvious and vulnerable target in the event of projectiles ensuing from a collapsed firewall. Above the metering skid sat the Prover Loop but this had been removed for repair on or before 5 July 1988. The Prover Loop was a fairly heavy piece of equipment and was designed to prove the accuracy of the metering system. The Prover Loop connections would have required to be blanked off but if this had given rise to any leaks of hydrocarbons one would have expected this to have given rise to alarms in the area and in any event to have been noticed particularly as a result of smell, in the days before the accident by men working in Module B such as the Oil and Water Operators. Any leakage of material under pressure would have tended to flash and this would have helped to trigger the alarms. Moreover any oil which leaked would have been contained in bunded areas and would have been expected to drain off. The bunding resulted from the fact that the equipment in the module rested on large H-beams. There was a drainage system to permit any spilled liquid to drain away. Dr Drysdale calculated that the inventory of crude oil that would have been in Module B after any depressurisation of gas to flare would have been about 55.7 metric tonnes. He considers that such quantity of oil would have burned off in about 30 to 40 seconds so that for the continuation of the fire one would have to look for other sources of oil such as the MOLs. Indeed he considered that a backflow of oil from the MOLs after the initial explosion was a distinct possibility. With regard to the condensate line there was a length of about 78 feet 5 inches from the valve PCV 511 to the tie -in point with the MOLs. With a pool fire the flame will be about twice the effective diameter of the pool. Thus even with the kind of limited fire that Dr Drysdale postulates as being the initial fire there would be a fairly high flame within Module B. However he assumes that if the initial fire was due say to an escape of oil from the metering system the size of the consequent pool would be limited by the bunding. There would be an initial small fire which would gradually extend as the bunded area filled up with fuel.

The kind of fire that would have developed from a large pool of oil which existed before the explosion is not consistent with the degree of fire spoken to by witnesses such as Mr Murray and Mr Kondol. On the other hand Dr Drysdale thought that the fireball like image photographed by Mr Miller was what would be expected from an escape of condensate under pressure. He was moved to this view by the shape of the flame shown in the early photographs including the symmetry, and the uniformity of mixing and colour. Also the lack of smoke associated with this phase of the flame is consistent with intense burning. Dr Drysdale is quite positive that the flame associated with Mr Miller’s first photograph has all the characteristics of a fireball. This as I have indicated suggests a sudden release of flammable material which has immediately ignited. Condensate could supply the necessary amount of flashing liquid. By a scaling process Dr Drysdale works out the diameter of the fireball as being about an average of 28 metres. This would suggest about 100 kilograms of fuel released into the fireball. This figure coincides with what he was asked to assume was the inventory of condensate available in the 4 inch line. He arrives at his own figure by making use of an equation evolved by a Dr Allan Roberts. He confirms that this equation is well established as being appropriate for circumstances such as he was considering. He believes that what is seen in the photograph could not be caused by a pool fire. Such a fire would not have driven the vapour outwith the module in the manner observed in the photograph. Nor would the flame have had the shape and uniform combustion which is recorded. The intensity of the colour could only result from efficient mixing.

In estimating the amount of fuel likely to have been in the fireball Dr Drysdale availed himself of a mathematical expression developed in two research papers known as the first and second Robert’s papers respectively. Dr Drysdale calculated using this expression that the fuel required to create a fireball of the size he estimated the Piper Alpha fireball to be was 112.5 kilograms of fuel He accepted that his calculation was approximate since his measurement of the dimension of the fireball was only an estimate and in any event the use of the equation cannot be justified as being correct in absolute terms since it is based on correlating experimental data. Indeed he accepts that his calculations can only give a feel for the quantity of fuel that would be required and that the actual amount may vary say between 70 and 150 kilograms. It was suggested to him in cross-examination that on the basis of a paper by two Japanese research workers, Hasegawa and Sato, the proper figure should have been about 300 kilograms. Dr Drysdale also calculated that an amount of condensate consistent with the fuel requirement of 100 kilograms would have been in the relevant section of condensate line. His calculation in this respect is criticised. He calculates on the basis of a 4-inch line whereas the defenders contend that the actual internal diameter of the line would inevitably be less than 4 inches. This could reduce the inventory of the line to about 78 kilograms. Of course this would not matter if the calculated dimension of the fireball was marginally wrong. Professor Magnussen at times sought to suggest that vapour released from a crude oil explosion if affected by explosions could cause a flame which when pushed out would create what Mr Miller’s photographs show. However he also accepted that what was shown in the photographs was consistent with a release of condensate into an existing fireball. Professor Magnussen when he began his evidence had not seen or considered the two Robert’s papers and he had relied on two Russian research papers. Dr Drysdale indicated that the Robert’s equation is a tried and tested method of calculation accepted in the gas industry. He discounted the Japanese formulation because it had been evolved on the basis of small releases of about 40 kilograms. The Robert’s papers correlate with much larger releases and is based on a variety of experimental data. Even were it the case that Dr Drysdale’s calculations cannot be taken as exact the fact is that the condensate line contained just about the same quantity of fuel as he worked out as being necessary for the fireball. Because of the high flash fraction of the condensate a release of the material under pressure would have taken place rapidly creating the conditions for a fireball. If there was already an existing fire the released condensate would ignite quickly and as condensate continued to be released it would feed the fire and produce the effect of a large expanding cloud of burning gas. The lifespan of a fireball created by about 100 kilograms of fuel would only be about four seconds at the most so that the photographs show that there is a smaller fire burning intensely simultaneously, which would be a pool fire. The implication is that there has been a major spillage of oil which provides fuel for the continuing fire. The gap between the relevant photographs was about 1 second or thereabouts and Dr Drysdale considered that this would be consistent with what the photographs show. In photograph 2 not only is the fireball shown but there is signs of burning below the 84 foot level and Dr Drysdale links this to the fireball by suggesting that it was pushed down by it. The important consideration however is that Dr Drysdale is of the opinion as a result of his experience and for reasons which he gives in convincing fashion that the fireball effect could not be caused by a pool of crude oil. One of the factors considered by him is that there is no mechanism for getting from a pool fire the intense mixing which the photographs show. He also thought that if the fireball had been caused by gas flashing of a hydrocarbon pool he would not have expected the fireball to extend below the platform as obviously it did. There would be more combustion in the upper part of the flame. Moreover the combustion would not be as uniform as is seen in the photographs.

If Dr Drysdale had used the Japanese expression and if he has underestimated the dimensions of the fireball then a fuel requirement of about 340 kilograms can be derived but applying his considerable experience he did not use such an approach. Dr Drysdale begins by deciding that what the photographs portray looks like a condensate fireball and when he then does his calculations he gets confirmation that the conditions which would generate a condensate fireball could have been present.

In considering whether the phenomenon in Mr Miller’s photograph was a fireball Professor Magnussen did not seem nearly as positive as Dr Drysdale and as I have already observed he seemed to change his ground to some extent. At one point he seemed to accept that what appeared in Mr Miller’s photograph looked like a fireball but later he qualified that by suggesting that the phenomenon could have been caused by an eruption type release pushed out of the module by some localised overpressure. This view he attributes largely to the symmetry but it is symmetry which Dr Drysdale opines is characteristic of a fireball. Professor Magnussen considers that the fireball may have been pushed outwards by localised explosions. He suggests that if there is an escape of gas under pressure there will be no fireball but this is not only inconsistent with Dr Drysdale’s general evidence but is not consistent with the explanation of the fireball phenomenon given by Dr Roberts in his paper. In relation to the expression for calculating the mass of fuel in a fireball Professor Magnussen at times suggested that Dr Drysdale’s calculations of the amount of fuel that would be needed to create the fireball he describes had been materially undercalculated. In this regard he relied more on what may be referred to as the Russian papers but when he formed his opinion he had not seen the Roberts’ papers nor the Japanese paper and moreover did not appear to know much about the standing of the Russian authors. Professor Magnussen suggested that because Dr Roberts was concerned with standards he may have been concentrating on an idealised worst case scenario rather that on practical situations. For that reason he claims that Dr Roberts was basing his calculations on stoichiometric mixtures and an adiabatic situation. Unfortunately Dr Drysdale was not asked about these matters in cross-examination. However it is clear that whatever Roberts’ ultimate objectives he was basing his results not on idealisation but on experimental data. However the Russian papers take into account experimental results by a Dr High but this is of doubtful applicability because the experiments were carried out not merely with fuel but with a fuel and oxidiser. If allowance is made for the oxidiser there is little between the High and the Roberts’ results. Nevertheless in his evidence Professor Magnussen seems to take some account of the unadjusted Dr High data. Moreover in cross-examination he eventually agreed that if a condensate with a high flash fraction were suddenly released under pressure it would be liable to burn as a fireball. After cross-examination of Professor Magnussen it was not at all clear that at the end of the day there was much between him and Dr Drysdale in respect of conclusions. If one applied Dr Roberts’ expression one finds that 100 kilograms of fuel would produce a fireball of about 28 metres in diameter whereas applying the results of the second Russian paper (which was based on a wider range of data than the first paper) the same quantity of fuel would produce a fireball with a diameter of about 26 metres.

With regard to Dr Drysdale’s calculation of the likely quantity of fuel needed to cause the fireball said to be shown in Mr Miller’s photographs I found his evidence clear and convincing. He did not claim accuracy for his calculations beyond that they gave a feel for the quantity of fuel we are interested in and on this basis I think his calculations are valid and useful.

Professor Magnussen could not agree with Dr Drysdale that the photographs show a fireball that burnt out within a few seconds and that there was a separate pool fire burning behind it. For his part he thought the fires were connected and essentially the same conflagration. As he saw matters the residual fire we see in photograph 4 is merely the continuation of the earlier fireball or eruption. There was a second explosion which propelled the hydrocarbon vapour from the pool fire out of the module. However if Dr Drysdale is correct that the fireball is consistent with a release of condensate of about 100 kilograms then this would be consumed in about 4 seconds. Of course the implication of Professor Magnussen’s evidence is that the whole conflagration is the consequence of a pool fire but I find it difficult to reject the convincing evidence of Dr Drysdale that the features of the so-called fireball are more consistent with a release of gas under pressure such as condensate. He does not exclude the possibility that a cloud of hydrocarbon gas could explode during a fire and be thrust out of the module but he regards what is shown in the photographs to be more consistent with a fireball due to condensate escaping under pressure. The mass of gas calculated by him is very broadly consistent with the inventory of condensate available and that in turn is broadly consistent with the timescale for burning represented by the photographs. Even on the refined version of the Russian paper one would expect a fireball to burn for about 4 seconds. It would be a co-incidence if an eruption which had no connection with a fireball type phenomenon took the same time to burn out. It is true as Professor Magnussen professes that in photograph 2 there does not seem to be the same luminosity reflected off the legs of the platform and he regards that as an indication that the eruption quickly retreats back to the module. However the fireball is all along rising and moving and thus a change in perspective could account for variation in luminosity reflected off the legs of the platform. Indeed my own impression from the photographs based on the reflections is that the flame is still protruding from the platform as it moves to the north. Professor Magnussen did of course not think it possible that a fireball would have the buoyancy to move in this way. However he did not explain with any clarity why he considered that a fireball could not have had the movement shown in the photographs. He also thought that it was important that the photographs show images that are only two dimensional. Dr Drysdale on the other hand would have expected a spherical shape rather than a flat disc shape from the apparent nature of the fire shown. Professor Magnussen eventually came to accept that the fireball or disk seemed to project about 28 feet beyond the platform and he seemed to have difficulty in explaining how it could have retreated back into the module to explain his theory. Moreover if the so-called fireball was just an extension of the pool fire it is not clear how it came to run out of fuel so rapidly and was of relatively short duration.

It may be noted that Dr Micheson also thought that the phenomenon in Mr Miller’s photographs was consistent with a fireball. He thought the flame must have been a diffusion flame and not pre-mixed. His evidence in effect was that the fire showed itself to be more consistent with a sudden release of lighter material than of crude oil. Gas released under high pressure would entrain rapidly and on ignition would burn with a very intense bright light like that shown in the photograph. With a fire caused by crude oil there would be much more masking by smoke than is shown. Dr Cubbage also considers that there had been a fireball caused by condensate. Thus I have little difficulty in concluding that Mr Miller in his first photograph recorded a fireball caused by an escape of condensate under pressure.

One matter that requires to be explained in relation to Dr Drysdale’s fireball theory is that none of the witnesses noted the phenomenon until about 15 seconds from the explosion had passed. He advanced certain possibilities but was unable to suggest in certain terms exactly how the condensate line had failed. For example the condensate line may have been damaged by the explosion but not failed until the passage of a short period of time. Mr Wood on the Dive Skid spoke to hearing grating noises and the sound of items falling somewhere above him shortly after the explosion. One theory advanced by Dr Drysdale is that the ESV-208 failed affecting the pressure differential need to move the condensate into the MOL. It should be noted that this valve is a heavy piece of equipment and that it is provided with a number of safeguards intended to ensure that it always closed in an emergency. Its failure could have caused backflow and an increase in the pressure of the condensate causing the damaged condensate line finally to break. Another possibility is that the explosion caused vibrations which affected the damaged condensate line. If the explosion caused massive disruption and damage it is not difficult to conclude that any indication of a significant and sudden release of condensate at the west end of Module B had been caused by the violence of the explosion even if the precise cause of the final rupture is not certain.

The defenders submitted that Dr Drysdale’s opinions had been influenced by the assumption the pursuers gave to him that the condensate pipe had been damaged by the explosion leading to an escape of condensate under pressure. However Dr Drysdale sought to justify his view on the basis of factors other than the assumptions he was working on.

It has to be noted that the defenders argued that it is critical to the pursuers’ case that they prove that the initial explosion caused damage to the small bore condensate pipe thus explaining the so-called fireball.

With regard to the fire that developed in Module B after the fireball this in my view was caused by an escape of crude oil and there would have had to be a leakage of such oil to fuel the fire for the period it lasted (which would have exceeded the effect of the normal inventory of oil in the module). Dr Drysdale estimated that the complete inventory of fuel in Module B would have been exhausted after about 20 minutes but it is clear that the fire there burned for much longer than this. Dr Drysdale explains the possibility that if the condensate line is ruptured and emptied of condensate this may have caused a backflow of crude oil from the MOLs caused by the removal of the differential pressure at the tie-in point between the condensate line and the MOLs. This of course could only happen if the ESV-208 did not operate effectively. Certainly the violence of the explosion may have disrupted the power supply needed for the emergency shut-down valve (ESV) to have operated properly. Dr Drysdale’s evidence on this matter must be considered against the background that he is not a mechanical engineer. I can however accept Dr Drysdale’s main thesis that there was first a localised fire caused by a spillage of crude oil. This was followed 15 seconds later (or perhaps rather less) by a substantial fireball produced by condensate and then there was a massive fire which must have been fuelled by a considerable quantity of crude oil. That such oil escaped after the explosion can hardly be in doubt because witnesses in the Dive Complex saw oil freely running down the MOL pipes where they pass through the 64-foot level. The original source of spilled oil could have been the small bore piping associated with the metering skid which being a lighter pipe may have been vulnerable to damage from the initial explosion. It has to be noted that the removal of the Prover Loop could have affected the shielding which might otherwise have afforded some protection for the small-bore piping.

About 20 minutes after the original explosion there was a significant outburst of fire and Dr Drysdale considers that this could be associated with a release of the gas from the Tartan Riser which exploded about this time. The failure of the Tartan Riser was probably caused by the heat generated from the substantial fire on the platform which had developed by this time.

There was little or no crude oil in Module C which suggests that the limited fire seen burning there shortly after the explosion was coming from B through the ruptured firewall.

5.7 The Reciprocating and Centrifugal Compressors.

5.7.1 Effects of unloading and recycling

In the event of the reciprocating compressors being unloaded the gas cannot go forward and as a result some of this has to be directed to flare and this happens through PSV 1000 A and B. In normal Phase 1 operations this relief line will cope with 16.5 million standard cubic feet of gas in a day. This quantity is because in Phase 1 operation gas is not being exported so that such gas as is not exported is released to flare. Through Differential Pressure Valve (DPC) 723 a further 5.1 million standard cubic feet of gas is released to high pressure flare daily in Phase 1. Normally a total of about 21 million standard cubic feet of gas goes to flare daily. In normal Phase 1 production the flow of gas going daily from the centrifugal compressors to the first stage of the reciprocating compressors is about 67.9 million standard cubic feet. When the reciprocating compressor is unloaded this extra amount of gas requires to be flared off. Thus there is a four-fold increase in the amount of gas going to flare through PSVs 1000 A and B. This additional release to flare would occur very quickly after the unloading switches were thrown. Captain Clegg had noticed a considerable increase in the flare from the platform about 9.50p.m. on the occasion of the accident. This would be broadly consistent with the evidence that the reciprocating compressors had been recycled and unloaded just before Mr Vernon returned to the control room about 9.45pm although the timing given by Captain Clegg may be some minutes out. It is perhaps also interesting that Captain Clegg stated that the flare had increased in size by three or four times which is consistent with the change in the volume of gas going to flare. In the whole circumstances it is clear that the flaring change noted by Captain Clegg was in consequence of the fact that the reciprocating compressors had been unloaded and recycled. It also gives force to the hearsay evidence that Mr Vernon claimed to have recycled the pumps. Moreover some minutes before the accident and consistent with the time when centrifugal compressors were tripping Captain Clegg noted a further surge in the flare. This would be consistent with hydrocarbon being diverted to PSV 51/1 and 2

After the flow of hydrocarbon has been through the second stage of the reciprocating compressors it is directed to gas lift and in normal Phase 1 operation this will amount in quantity to about 53.5 million standard cubic feet per day. The quantities and nature of the constituents of the various flows is derived from a process flow chart (number 13/42 of process) prepared by Mr Martin Clark, the pursuers’ Process Engineer. This flow chart was itself prepared from the Daily Production Report for the platform for 5 July 1988. The lift gas is then sent back into the reservoir to assist in the extraction of more oil. Thus as an immediate effect of reloading and recycling there is a serious reduction in gas available for gas lift which is going to affect the quantity of oil produced by those wells which benefit from gas lift. Moreover there will be less gas coming back into the separators with the oil so the gas circulating in the production system will also reduce. In the event of loss of gas lift the effects would be seen in the fiscal meters from 3 to 5 minutes and the full effects would be felt in about 10 minutes. Thus although the initial effect of unloading the compressors is materially to increase the flaring, the flaring will within minutes drop as the loss of gas flow decreases the supply of new gas.

Upon unloading and recycling the first stage reciprocating compressor stops increasing the pressure of the gas from about 700 psia to 1400 psia.. The stream still flows through the scrubber, the first stage reciprocating compressor (with its pistons unloaded) and the cooler. However it does not go further forward but flows round the system by way of the bypass valve GOV 902 recycling through the system in a circle. It cannot go through the JT valve which only operates when the pressure reaches 1400 psia. If the centrifugal compressors are still operating gas is still coming forward but cannot find an unblocked route through the reciprocal compressor skid. To cope with this it goes off to flare by way of PCV 1000 A and B. So that the centrifugal compressors can keep working some of the gas coming into them will also recycle automatically. It has a line with PCV 201 A on it which is its own bypass. Some of the gas which is effectively being recycled at this stage through the centrifugal compressor system may also go to flare through PCV 51/1 and 2.

5.7.2 Tripping of Centrifugal Compressors

In regard to the tripping of the centrifugal compressors I got valuable help from the witness Thomas Henderson. At the time of the accident Mr Henderson was in post as a Lead Production Operator on the platform but was in fact working as Deputy Operations Superintendent on a 6 months temporary basis. He had at the time been working for about 8 years with OPCAL on production and he seemed to be a reasonably well informed witness. He confirmed that the centrifugal compressors were fairly sensitive machines and often gave trouble with tripping. The most common cause of tripping was upset downstream particularly with the reciprocating compressor or the PCVs 1000 A and B. The PCV 1000 B (which was the larger of the two valves) had to "hunt" about for the correct opening pressure because of high discharge scrubber levels (their boot had insufficient volume and in the event of certain GOVs closing the level of condensate would get too high and transmit a signal back to the compressors to trip) and power turbine over-speed could also generate tripping when the valve failed to respond to it appropriately. Sometimes trouble associated with the centrifugal compressor engine could cause a trip but generally trouble upstream was not a cause of tripping. If there was a sudden trip or stoppage of gas going forward from the centrifugal compressors to the reciprocating compressors then PCV 1000A and B were intended to help to keep the compressors running by admitting the obstructed gas flow to flare. Unfortunately the larger of these valves was unreliable and had a tendency to over-shoot its set-point. Essentially the problem with this valve was that it did not respond as quickly as it should to pressure variations. The valve accordingly had to " hunt" for its correct set-point. Valve A being smaller was more reliable but if the pressure were too much for it to cope with then valve B had to come into operation. If the valve PCV 1000 B failed to "hunt" effectively the system would receive a substantial jolt because there would not be the correct relief available for what could be a substantial quantity of additional gas. In order to obviate this problem sometimes operators would change the pressure setting of the valve to ensure that it opened more readily.

There were two obvious means of which ambient gas could be drawn into the centrifugal compressor or its associated compartment. Such gas could be drawn into the combustion part of the compressors (air was required to mix with gas to create the combustion necessary to drive the compressor turbines). The gas/air mixture would expand upon combustion and create the power to drive the shaft of the compression mechanism. Alternatively as a source for the ingestion of ambient gas air was drawn into the compression chambers for ventilation and cooling purposes. The gas intake and exhaust arrangements are properly illustrated in the schematic which is number 12/126 of process. To operate the centrifugal compressors in the optimum way the correct discharge pressures and discharge flow rates would be worked out and then that would be governed by seeking to achieve particular temperatures within the gas generator. Indeed the primary method in 1988 of controlling the speed of the centrifugal compressors was the turbine inlet temperature control for each machine. If the pressure on the discharge side of the machine increases the flow rate through the compressor will decrease (because the flow encounters more resistance). This can upset the balance of the machine and cause tripping. If the power turbine is working with less gas it will speed-up and this would trigger off automatic trips. If the pressure at the discharge side of the machine were to decrease this could also cause a trip since with the flow through the machine increasing there would be a requirement for more gas in the combustion process. Since all three machines are receiving their flows from the same separator source there was a common fuel gas suction pressure control for all these machines. This was done by way of valves. The centrifugal compressors also had their own recycling system designed to operate as an anti-surge valve and redirect gas back to the suction side of the compressors if this was necessary to maintain pressure in the compressors. This system could result in the machines being presented with competing signals (particularly fluctuating pressures) and thus provide a further cause of tripping. If the compressors tripped it would normally be one or two but it was not unknown for all three to trip. In essence however tripping of the centrifugal compressors was not generally associated with trouble upstream of the compressors. Thus the fact that on the night of the accident all three centrifugal compressors tripped just before the explosion is not in itself surprising given that the reciprocating compressors had been recycled. This of course would be an indirect consequence of the fact that the condensate injection pump had tripped.

If the centrifugal compressors trip then their GOVs close and no fresh supply of gas can go forward to them. This means that the flow of gas is relieved by PCV 51/1 and 2 which routes gas to flare and this would also result in transient increases in flaring. Indeed eventually these valves would send to flare the gas which in the first instance would have to be dealt with by PCVs 1000 A and B when the reciprocating compressors are unloaded. This could explain the fact that after first noting a surge in the flaring Captain Clegg later noted further surges.

In addition to Mr Henderson, Mr Wottge and Mr Grieve gave us views of the possible causes of the compressors tripping. The evidence was not all consistent in this respect and may well have reflected the differing experiences of the witnesses. What does seem clear however is that the tripping of the centrifugal compressors can be associated with the unloading and recycling of the reciprocating compressors especially if this is not done carefully. The defenders argued that a leak could cause tripping of the compressors. However if a leak was of sufficient dimension to trip all three machines I would have expected more trip or gas alarms to annunciate. Moreover if one compressor trips the excess gas relating to it goes to flare so that the tripping of one compressor should not in itself produce tripping or for that matter leaks in others. Moreover although Mr Henderson had never had direct experience of all three centrifugal compressors tripping he did say that it happened occasionally.

Looking at the whole question of the centrifugal compressors tripping on the night of the accident in my view it is not difficult to conclude that this was related to the condensate injection pump B having tripped. The tripping of the condensate injection pump would stop the condensate going forward and in the light of the evidence this is likely to have caused an upset upstream. The compressors tended to react sensitively to such a situation and tripped. When the machines tripped there was no indication in the evidence that this in itself caused special concern. However the defenders argue and it is perhaps their main point that although it may be a coincidence that shortly before the explosion Mr Vernon had shown his intention to put Pump A back into production it was even more of a coincidence that immediately before the explosion the tripped pumps and recycling were putting a substantial strain on the system which with the re-introduction of Phase1 it may not have been equipped to handle. Gas under considerable pressure was being re-routed and a series of valves required to shut or open. Countless flanges other than the blind flange on PSV 504 had to take this strain.

5.8 The J.T. Flash Drum

Mr Grieve explained that when he had descended to the 68-foot level just before the accident the first thing he did was to proceed to the J.T. flash drum and pass under it. He looked at the local control panel near this drum and noted that the injection pumps were not running, that the GOVs were closed and that there was a high level in the drum. The drum was registering as about 80% full. In respect of this drum it registered as full in practical terms when the drum was physically half full. When Phase 1 was operating normally with the whole system in operation it would take only a period of about 3.3 minutes from the normal operating level of the drum to its high level alarm and then a further 13 minutes from the high level alarm to the overflow condition (when the overflow would go to flare). Mr Wottge the Process Engineer considered that this was a contingency to be avoided if possible. This is of course with the compressors loaded and on the assumption that condensate is not being put forward from the drum. Thus with the condensate injection pumps tripped if no other action had been taken by the operator the drum would have filled in about 16 minutes. On the other hand if the reciprocating compressors are unloaded the position changes because a substantial proportion of the condensate production is not coming forward to the drum. Some limited quantity of condensate made in the centrifugal compressors would still be coming forward into the JT flash drum. If the reciprocating compressors were unloaded and recycled then it would have taken about 63 minutes before the JT flash drum reached the overflow level. That time presupposes that the centrifugal compressors are still working. Thus the tripping of the only condensate injection pump operating created a certain pressure to get a pump working quickly to avoid the prospect of a shutdown of process but the urgency was not desperate in that there was probably at least an hour available. Thus at the initial stages the main pressure on operators to get a pump working was to avoid loss of production.

5.9. The Oil and Water Operators.

Since one of the possibilities advanced by the defenders is that the initial explosion occurred in Module B the pursuers while advancing the contention that this would not be fatal to their case nevertheless were at pains to establish that the finger pointed at Module C. One submission was that if there had been an accumulation of gas in Module B this would have been noticed by operatives before the explosion. On the evening of the accident there were two Oil and Water Operators on duty namely Mr Sandy Bremner and Mr Gordon Rennie. Unfortunately both were killed in the accident. Generally their duties involved the plant in Modules A and B and they also had responsibilities in the produced water package which was at the 68-foot level. Among their duties were the care of the wellheads and seawater injection facilities in Module A and the separators, booster and MOL pumps, the metering, and the gas cooler in Module B. They sometimes worked in tandem and at other times they separated. When not directly on the floor of the platform they were to be found in the Control Room. The bulk of their duties had to be carried out in Module A. The evidence of Mr Murray, who seemed to me to be an acceptable witness on this matter was that in the event of the reciprocating compressors being unloaded he would expect to see the Oil and Water Operatives in Module B where they would concerned with the MOL pump suction pressures. Moreover since production would be lost the Oil and Water Operators would be concerned about the levels of the Separators in Module B and to make sure that the level control valves caught up and did not overshoot. Because the level of oil produced would fall it required care to ensure that the separator levels also did not fall to undesirable levels. They would also be concerned about the differential pressure across the hydrocyclone. They would also be concerned in shutting the lift gas to the wells in Module A but this would be done when things had quietened down a bit. I was told that the Oil and Water operators would become involved within minutes of the recycling of the compressors and what they had to do might take 15 minutes. They would know of the recycling because the flare would take-off and be deafening. Moreover the probability is that the Oil and Water Operators would hear the radio messages passing between Mr Bollands and Mr Richard and Mr Vernon. Indeed it was overhearing such a message that triggered Mr Grieve into action. All the operators had such radios and the practice was to keep them switched on all the time. It must however be noted that Mr Bollands claimed that he had no contact with the Oil and Water Operators. The implication that the pursuers ask me to take from all of this is that had there been an escape of gas in Module B or had there been the sort of process failure that the defenders claim was recorded at Flotta then this inevitably would have been noted and reported by the Oil and Water Operators. Indeed if the production loss had been as extreme as some of the Flotta witnesses claim then one might have expected them to have activated an alarm or even a general shutdown button. This of course did not happen. The first thing an Oil and Water Operator might have been expected to do after recycling was to check the suction pressure on the MOL pumps. The interesting thing is that these are situated at the west end of B and any evidence that may have pointed to a leakage of condensate in B having caused the explosion tended to focus on that very area. The next job would almost certainly be to check level controllers which were almost in the centre of Module B. Mr Murray indicates in his evidence that after the Oil and Water Operators had carried out their priority duties in Module B which would have taken about 15 minutes they had the further duty of isolating the gas lift valve which was also in that module and to which access was gained by a ladder. Indeed the valve is situated close to the metering skid in Module B. Mr Murray confirmed that the duties he was ascribing to the Oil and Water Operators did not require to be specially instructed because it was a well established drill which had to be followed from time to time. Although there may just be other possible reasons to account for the absence of other process and gas alarms the pursuers contend that the fact that there were no such alarms bears out the probability that the Oil and Water Operators saw nothing untoward. Certainly had there been any pool of crude oil forming as a result of a leak or otherwise or any material amount of hydrocarbon vapour anywhere near the west end of Module B I should have expected the Oil and Water Operators to notice this.

A further circumstance (albeit the inference from it is more speculative) is that both Oil and Water Operators did not survive the accident. It is clear that the explosion, however it originated, had a catastrophic effect on Module B. Thus it would not be at all surprising if the men would have been killed if they has been in B when the explosion took place. On the other hand if they had been in Module A it is unlikely that they would have survived the accident if the A/B firewall had not been punctured. Some witnesses were in the area of Module A shortly after the accident. Many were able to reach a platform from which they escaped. Mr Bremner and Mr Rennie if they were on duty would not have been in the accommodation modules where many of the casualties were. However none of the witnesses who came to the south side of the platform spoke to having seen either of them. Nor for that matter did the witnesses who were in or who looked into Module A speak to having seen casualties there. If the Oil and Water operators had been at the 68-foot level when the accident occurred then again they would have had a reasonable chance of escaping from the platform since we had a number of witnesses who were at that level and survived and none spoke to seeing casualties there. Mr Amaira and Mr Niven were in the region of the gas skid area at the 68-foot level at the time of the explosion. Not only do neither of these witnesses claim to have seen Mr Rennie or Mr Bremner before the accident but neither apparently noticed before the accident any spillage of oil dripping down to that level as might have been expected if oil was leaking from directly above. After the accident witnesses saw oil and flame on the MOL which passed through the 68-foot level near to the Dive skid. There were certainly deck penetrations in the area of the MOL. It would be expected that an escape of oil which was under pressure would spray out in all directions and overcome any collar around the deck penetrations. I think it is probable that the Oil and Water Operators were in Module B when the accident happened and that before the event they had noted nothing untoward.

5.10 Other Evidence that no Gas Escape in Module B

5.10.1 Mr Grieve’s journey

The pursuers argued that a further inference that the explosion was not caused by an escape of gas in Module B can be taken from the fact that shortly before the accident Mr Grieve who had been in the Gas Conservation Module when he heard a message between the Control Room and Mr Richard informing the latter that the condensate injection pump had failed. After some interval of time that he is not very precise about he decided to proceed to the 68-foot level to see if he could give them a hand. Since he arrived at the 68- foot level shortly before Mr Richard received a message about a gas leak in Module C I think that Mr Grieve must have made his way to the 68-foot level about 3 or 4 minutes before the explosion and certainly only a minute or two before the first gas alarm annunciated in the Control Room. He himself states that he was not at the 68-foot level for more than 2 to 3 minutes before the explosion. His route took him down stairs on the east face of the platform and close to the north-east end of Module B. He also passed close to the east end of Module C. The interesting fact is that Mr Grieve did not claim to have noticed any smell of gas as he descended past the east end of the modules. He might have been expected to notice the gas if there had at the time been a material quantity of gas passing from B to C. He was certainly at the said interface a few minutes before the first alarm, The platform gas contains a quantity of H2S which gives it a smell.

The defenders claimed that since in their calculation if Mr Grieve had been at the 68 foot level for about 2 minutes before Mr Richard got his message from Mr Bollands then given the likely short period between the first release and Mr Bollands’ call Mr Grieve would have required to be present during the alleged first jagging. In my view this supposes that Mr Bollands acted with optimum speed in contacting Mr Richard and also that the period of Grieve’s presence was as long as 2 minutes. I think that these times are so approximate that I do not think that too much can be read into them. Assuming that jagging caused the accident I think it is likely that the first jagging or jaggings took place before Grieve’s arrival or in any event before he had time to form a view as to what was happening.

5.10.2 Contention that explosion in Module B.

The defenders unlike the pursuers did not claim to know the actual cause of the explosion but they sought to extract evidence to support their pleadings to the effect that it was at least quite possible that the explosion had originated in Module B. The pursuers’ main answer to this hypothesis is the absence of any gas alarms relating to Module B. However there was at least some suggestion in the evidence that the gas detectors in B may not have been working properly if at all so the pursuers required to refer to other evidence that might refute the suggestion of an explosion in B. The defenders advance the notion that the circumstances of the accident may be explicable by the hypothesis of an explosion in B piercing the firewall B/C then generating a further explosion in C as a result of the process known as pressure piling. In essence if there are two chambers both filled with gas and one explodes then if there is an opening to the second room with more restricted venting not only will the gas in the second room explode but the explosion will be relatively bigger than that in the first room. There was no reference to pressure piling in the defenders’ pleadings. However they possibly considered that they required to introduce pressure piling in case I were to decide that the A/B firewall had not failed at the explosion. If that firewall did not fail then it may be difficult to explain how an explosion in B could have caused any penetrations that may be shown to have occurred in Module D. The defenders’ contention was that if an explosion in Module B had burst into Module C through the B/C firewall then pressure piling in C could have caused an intensification of the explosion which would explain any penetration of the explosion into D. However the defenders did not lead any of their own evidence on the matter and they depend on what they claim are inferences available to them from the pursuers’ experts. They did not even ask their own witness Professor Magnussen about pressure piling although one might have thought he would have been competent to contribute to the question. Moreover it must be noted that as far as the thrust of their evidence goes the pursuers’ experts discount pressure piling as a factor in the explosion. The first time pressure piling was raised was in relation to Dr Munday’s Report 42/7 of process. Dr Munday prepared his report on the defenders’ instructions but he was not called as a witness by them. The defenders’ whole case in the matter of pressure piling is weakened by the absence of evidence about the matter. The whole question of pressure piling is dependent on the venting situation and the presence of a gas accumulation in the second compartment. We had no evidence as to how an explosion in Module B might have penetrated into C and as to what concentration of gas and what location of gas and venting pattern would have been needed to produce pressure piling. Moreover it is difficult in the light of the evidence of Dr Davies to see how gas could have penetrated from B into C without triggering an alarm in the C1 zone. If any gas in Module C has come from B at the west end of the modules then again one would have expected alarms in C. Moreover both Mr Young and Mr Vernon had passed through Module C at the west end shortly before the explosion and neither had detected any sign of gas there. Dr Mitcheson referred to experiments about pressure piling but asserted that it was critical to the results that the two explosion compartments start off with a equivalent gas cloud. There is no quantification whatsoever as to what quantities of gas in the respective modules would have been required for pressure piling to take place and as to what precise venting conditions would have been required. Even Dr Munday in his report concedes that to arrive at any conclusion that pressure piling was possible it would be necessary to do calculations. Mr Cubbage, the pursuers’ expert thought that it was inconceivable that pressure piling would have occurred because the ends of the modules are so well ventilated. Mr Cubbage had himself been concerned with the investigation of the Ronan Point disaster where the matter of pressure piling arose. He indicated that his only experience of pressure piling was where there were two closed vessels connected by something equivalent to a pipe and both filled with a flammable mixture. Mr Cubbage went so far as to say that he found it totally incomprehensible that pressure piling could exist in the relevant modules. He did however accept that in theory if the second chamber had more restricted venting there were instances where the overpressure in that room could be higher than in the first chamber. On the other hand Mr Cubbage had not done any calculations of the circumstances which could possibly have produced pressure piling in the modules so I am left with his general evidence that the phenomenon would not occur in the circumstances of the accident. He was reluctant to place much emphasis on turbulence as a factor contributing to a pressure piling situation. As he said to have any pressure piling it would be necessary to have gas in both modules. Even giving the sketchy evidence about pressure piling the gloss most advantageous to the defenders I could not in the whole circumstances conclude other than that the development of pressure piling as a phenomenon affecting this accident was unlikely.

There was evidence that a day or so before the accident the Prover Loop at the west end of Module B had been removed for maintenance. We were not told just what arrangements were used to isolate this section of line but it would appear that they had functioned without incident for say 24 hours before the accident. Moreover there was no indication of any irregularity in the removal of the prover loop nor the arrangements to allow for this. Any leakage from the Prover Loop would have been oil and this should have been visible to any operatives in the area. Moreover there were witnesses involved with painting duties in the general area of the Prover Loop until about 3pm on the day of the accident and they did not speak to having seen any leakage of oil from it. If proper procedure was followed when the reciprocating compressors were unloaded and the gas lift line was isolated the valve that required to be operated was just 15 feet away from the metering skid where the Prover Loop was situated.

Any spillage of oil at the west end of Module B that was not released under pressure might have been expected to accumulate in the bunded area below the deck grating and drain off from there into the sump. However if the oil were released under pressure it could be expected to spray out and in that event at least some of it could have been sprayed onto the pipe penetrations leading down to the 68-foot level. If oil were sprayed onto the MOL it could be expected to run down that line to the level below the deck. As I have previously said in the period prior to the accident the men working at the Dive Skid did not report having seen such oil although some saw it after the accident. If there had been a leakage of oil accumulating in Module B this would have released hydrocarbon vapours that should have triggered gas detectors (assuming that these were operating). One presumes that if an escape of oil were sufficiently substantial then there could come a point when the drainage system could not cope with it and a pool of oil could build up. However this has to be viewed against a background where as we were told the drainage pipes were of 3 or 4 inch diameter. Indeed the creation of a pool fire in Module B after the accident and its development in consequence (which is the sort of scenario the pursuers advance for the period after the accident) may have required the scale of accumulation of oil I have been considering. However any escape of oil after the explosion could have been massive and there was no evidence of the scale of leak prior to the accident which would have been required to build up a pool of oil below the grating. It may be worth noting that the witness Henderson who gave some evidence of the physical arrangement of the drainage system did not think that it would be possible for a leakage at one end of the module to flow to drains at the other end and I accept this. This was essentially because of the bunding. Within the sump pile were two submersible pumps and their purpose was to pump back to the separators any reclaimable oil in the sump pile. If the level in the sump exceeded a certain level an alarm would go off. Thus the pursuers argued that if there had been a serious accumulation of oil on the deck prior to the accident the sump levels would have risen and an alarm would have annunciated.

5.11 Maintenance of PSV 504

5.11.1 General

If the pursuers were correct in suggesting that the explosion was caused by a leak through a blind flange following upon the removal of PSV 504 then the arrangements for maintaining the PSV and for fitting and securing the blind flange must be considered. The pursuers aver that the cause of the leak and the accident was that the flange was not leak tight. The pursuers further aver that once PSV 504 had been removed from its site for recalibration and re-certification it was the duty of the Score employees charged with the operation (Alexander Rankin and Terrence Sutton) to fit a blind flange to each of the opened-up ends of the relief pipework. Of course the flange which has significance for these cases is that on the end of the pipework still connected to the pump. The defenders admit that the person who actually fitted the blind flange was Terence Sutton, who unfortunately failed to survive the accident. Moreover the flange that should properly have been fitted was of the 900lb. category. The pursuers sought rather faintly to develop a case that the wrong flange, namely a 1500lb. flange, had been fitted but at the end of the day there was really no evidence to that effect. It is also beyond dispute that the PSV was removed in work starting in the early part of the day of the accident, that at the end of the day shift the valve had been removed and not put back and that accordingly the Score employees retired from work for the day, leaving the blind flange to cover the pipework from the pump. At the time when Sutton had secured the flange when the PSV had been removed in the late morning or early afternoon the intention had been that the PSV would be calibrated and replaced during the same day. The effective issue between the parties on this matter is in respect of the securing of the blind flange and as to whether its bolts had been fully tightened by Sutton by a procedure such as flogging or merely left finger tight. The pursuers’ case of fault is based on the averments that it was a requirement of the pursuers on Score in terms of their contract, work orders, and instructions issued thereunder, that blind flanges should be fitted securely to open-ended pipework after the removal of any PSV. The pursuers claim that one of the reasons for the requirement about blind flanges was to prevent a leakage in the event of any inadvertent admission of hydrocarbon to the system. The pursuers aver that in accordance with good established and proper practice that any blind flange fitted to open pipework should have its bolts flogged-up using a hammer and flogging spanner or at least pulled up by hand using combination spanners. The case of fault against the Score employees is that the flange bolts were not tightened in accordance with the proper practice with the result that the blind flange was not fitted securely but leaked so causing the accident. The pursuers seek to infer that Terence Sutton only made the bolts finger tight.

5.11.2 Fitting the Bolts

As Mr Todd, a Maintenance Superintendent, indicated he would expect that the requirement to fit blind flanges would be specified as a safety requirement in the permit to work issued to the valve fitters in respect of a valve calibration. I think this could not be seriously challenged. He was asked as to the purpose of the blind flange and he indicated that it was to prevent any seepage of fluid past the isolation valves and escaping to the atmosphere. However he later generalises this somewhat saying that the blind flange should be put in place and secured tightly as it was meant to be secured to prevent gas or fluids escaping from the open pipework. Evidence was also led from Mr Brian Reid who was 37 and was production manager of Wood Group Engineering Services of Peterhead. Before that he had been for some years a Quality Assessor Engineer with the same firm. He had been employed offshore as a valve technician and indeed had worked for about 9 years on valves. In particular he had experience of fitting flanges to open-ended pipework after the removal of pressure safety valves. He explained how he would have fitted the flange required after the removal of PSV 504. He explained that he had understood the flange to be an RTJ one (ring type joint). First he would have fitted the ring type joint into the ring groove and then put up the flange to match that ring groove. The ring would have helped to line the flange. Then he would have introduced the bolts and tightened them using combination spanners. He thought that he would probably begin by putting in the bolts round the bottom side of the flange and then drop in the sealing ring. Then he would put in the rest of the bolts and tighten them. Mr Reid’s explanation for the use of blind flanges is perhaps significant for he ventures the view that " Its the same on any line, you don’t want an escape of the medium into the module or whatever". Mr Reid seemed an experienced and reliable witness. Another witness Mr Barclay, aged 45, was a Maintenance Engineer in Fraserburgh but had previously worked offshore for 4 or 5 years with Wood Group as a valve technician dealing with the removal of PSVs. When asked how he would fit a blind flange he claims that he would tighten the bolts to hand tight and then would tighten beyond that using flogging if the valve was high rated and otherwise spanners. There was evidence from another employee of Wood Group who had worked offshore for them as a valve technician and had indeed worked regularly on Piper in that capacity. He testified that it was normal and established practice on Piper to fit blind flanges securely by flogging or by using combination spanners He had understood that the purpose of using blind flanges was to prevent the leakage of any contents that might pass. The witness Mr Bagnall was 53 years of age when he gave his evidence and was a Senior Mechanical Technician on the Piper Bravo platform. He had been a Lead Maintenance Technician on Piper Alpha. He claimed to have had a lot of experience in fitting blind flanges to open-ended pipework. In fact he had worked for twenty odd years in the petro-chemical industry. He had had personal experience of fitting blind flanges to PSV 504. He observed that it is quite a difficult job because it is a restricted area. In fact he would have two men doing the job. One man would hold the stud bolt whereas another would lift the flange onto the bolt. The nut would be placed on the other side and then you would spin the flange round until you had a further bolt into the top of the flange. Then he would put bolts in at alternate sides until all bolts were in place. He emphasised the sequence in which bolts were tightened so that you pull and tightened the flange parallel. Once the bolts had been tightened as much as possible with the combination spanner then he would flog the bolts with the flogging spanner. Mr Bagnall thought that flogging was the proper way to tighten the bolts and indeed he said that you would flog "until you got an appropriate scream from the bolt" . He made the further point that if the bolts are flogged it is possible to tell when they are sufficiently tight by the ring of the hammer. He describes that to use the combination spanners at the particular site of PSV 504 one would put the spanners on either side of the bolt and nuts and then pull in opposite directions.

I think the foregoing body of evidence can be taken as correctly reflecting the experience and views of these witnesses. All the witnesses seem to accept that something more than finger tightening was required to secure the flange although otherwise there may have been a measure of difference as to whether they flogged, used combination spanners or both methods. Clearly some care had to be taken to secure the flange parallel to the piping and there was a degree of problem with restricted space in relation to PSV 504. In my view it was certainly not proper practice on Piper Alpha to fit a blind flange merely by leaving the bolts finger tight.

5.11.3 The Nowsco Tests

Certain tests were carried out under the direction of the witness Mr Standen. These were initiated by Mr Wottge and were carried out by a firm called Nowsco. An attempt was made to construct a length of pipework with a configuration similar to that in the relief pump to PSV 504. There was suction and discharge pipework of about 5 metres on each side. Mr Bagnall assisted Mr Standen in the technical problems associated with the construction of the test pipework and in devising the necessary flange arrangements. This pipework was provided to Mr Standen for his tests. Mr Gray a Technical Contracts Controller with Belmar Engineering who provided pipework to the oil and gas industry had supplied the structure that was used in the test and gave perfectly satisfactory evidence about the matter. I was satisfied that the test pipework was a sufficient representation of the actual relief line to give a practicable basis for the tests that were then carried out on it. The tests were carried out on the basis of three standards of tightness namely " finger tight", "hand tight", and "flogging". "Hand tight" was as tight as a physically fit man could achieve using combination spanners pulled by hand. "Flogging" was as tight as a physically fit man could achieve using a flogging spanner and a 4 lb. hammer. The gas used in the tests was nitrogen and water and the pressure was as close as could be achieved to 650 psi. We were told that nitrogen will escape from a leak at a much faster rate than water. Likewise water is more liable to leak than condensate so that if there is no water leak it is unlikely there would be a condensate leak. The critical conclusion which can be derived from the test runs is that if the blind flange is properly fitted it should not leak. In fact it should not matter even if a 1500 lb. flange had been fitted to a 900lb. Neck flange provided that the bolts were flogged or pulled tight with combination spanners.

The witness Mr Standen, who directed the tests, was aged 44 at the time he gave evidence. He was head of technology at Nowsco Pipeline Services and he had a B.Sc. in applied physics. He had been employed by Edwards High Vacuum who were involved in all aspects of vacuum engineering including leak detection. He spent five years with that company in the Research and Development Section and as a lecturer. He took a particular interest in leak detection and was for a period in the Leak Detection Sales Department. He joined Nowsco in 1983 and this was in particular because of his interest in leak detection. He had made about 20 trips offshore half of them in connection with leak detection. His tests were carried out with 900 and 1500lb flanges and involved different combinations of ancillary materials and the different methods of tightening. The 900 and 1500lb. blind flanges have different thickness and weights and thus the heavier flange can accept higher pressures. The bolts for each size of flange differ. The flanges were applied to a 900 lb. flange neck which according to Mr Wottge corresponded with what was on the relief line to PSV 504. The results of the tests appear in Mr Standen’s Report (number 13/79 of process) and individual tests were spoken to in evidence. Table 8.2 lists the leak rates determined in these tests. The tests in the table were done with a 900 lb blind flange but if a 1500 lb flange had been used the results would not have been significantly different. It must be noted that even if the neck flange had been 1500 lb then with the correct blind flange and ring it would have given a secure blind with flogging or hand tightening. The defenders could not make too much of this because it would have been the fitter’s responsibility to choose the correct flange and materials for the needs of the job unless they were not available and there was no suggestion of this.

Where leaks occur with finger tight blind flanges the leakage rate thrown up by the tests extends from 7.1 to 106 kilograms per minute in respect of Nitrogen and from about 74.3 to an extrapolated 300 kilograms per minute in respect of water. These figures are of course not necessarily applicable to condensate in its liquid or gaseous state (condensate was not used in the tests because it was considered to be too dangerous). However it can be said that at least in certain situations failure to render the blind flange other than finger tight could lead to leaks of substantial amounts of material. The defenders argued that if Mr Standen’s tests for water were extrapolated for condensate and for a pressure of 654 psig they would show a leak rate of about 50 kilograms per minute. However it must be noted that the fingertight tests are based on the assumptions that the fitter tightened the flange as tightly as a reasonably strong man could make it with his fingers. If Mr Sutton failed to tighten up the flange properly there is no saying just how tight he would have made the flange. The defenders say that Mr Standen was not asked if higher rates of release such as 200 kilograms per minute could be released with a slack flange but it is difficult to see what Mr Standen could have contributed in that connection for there were no tests done to explore the matter. However the tests do show that if a 1500 lb blind flange is used with a 900 lb seal and with eight bolts finger tight then with water an escape rate equivalent to 275 kilograms per minute can be achieved with a pressure of 650 psig.

Mr Standen also carried out a number of accoustical tests and in this respect his conclusion is more interesting than helpful for he found that with leaks developing it was possible to produce a variety of sounds of different qualities. He found that where they were leaks they tended to fall into two types namely those with a leak rate generally below a value of 0.03 kilograms per minute and those with a much higher leak rate which he describes as gross leaks. He found that all combinations of blind, flange, and seal types gave gross leaks when the bolts were only finger tight. The opposite conclusion that when bolts were flogged tight or tightened with combination spanners they did not leak was not seriously challenged by the defenders. In fact the tests showed that in many combinations it only required four bolts hand tight (combination spanners) to make the flange leak tight. In normal conditions of quietness gross leaks would be easily audible.

Mr Standen indicated that whether there was a downward pointing leak or a leak in some other direction would depend on the sequence in which the bolts were tightened and the tightness of the various bolts. Obviously in these cases that is not known unless it can be implied from the circumstances. The defenders suggested that there was no evidence that if bolts were put on finger tight a leak could develop which was only downwards. In my view if the bolts were not properly tightened just what direction of leak occurred would inevitably depend on the particular facts.

It requires to be noted that the pursuers’ case while primarily that Mr Sutton only made the bolts finger tight is at the end of the day that in any event he did not make the flange effectively secure. There seemed to be little challenge to the fact that a fitter doing his job properly could render the flange secure.

5.12. Events on the Evening of the Accident

5.12.1 Operational Structure of the Platform

The organisational structure of the platform is set out in the Chart number 12/209 of process. In control of the platform is the Offshore Installation Manager (the OIM). At the time of the accident he was Mr Seaton and he did not survive. Directly beneath him was the Operations Superintendent, and on the day shift of the accident this was Mr Bernie Curtis. He was on duty during the day and for a large part of each evening. Normally he would work until at least 10pm. Thereafter he would remain on call. He did not survive the accident. He was responsible for the safe production of oil and gas on the platform. No one could apply for a permit to work without his approval (that is he was the approval authority). His function in this last respect was to take an overview for he did not grant the permit nor lay down specific safety requirements. However his function was not purely decision making and he would take an active part in the operation of the platform by conferring with those working under him. There was only one Operations Superintendent on the platform at one time but he had a Deputy. The Deputy Operations Superintendent had particular responsibility for the gas plant including trouble shooting. Thus he would have practical responsibility for the supervision of the gas production process. Thus as we shall see at the time of the accident although Mr Vernon was in immediate control of operations affecting the gas plant there were two persons senior to him who should have been available if required. Beneath the Deputy Operations Superintendent came the Lead Production Operators of which there were three. They are the designated authority for the permit to work system. They are essentially the foremen and supervisors on the floor of the platform. Mr Lynch was the Lead Production Operator on the morning of 6 July 1988. He was involved in the request for access to the condensate injection pump A by the Score representatives However he left the platform about 11am. and Mr Harry Flook took over from him. Mr Flook in fact only held the position of Operator but he was delegated to carry out temporary duties as a Lead Production Operator. Unfortunately Mr Flook also died in the accident. Mr Lynch claimed that he had given Mr Flook a comprehensive account of matters affected by the handover and I do not think that was challenged. Mr Flook handed over to the Lead Production Operator, Mr Vernon, sometime between 5 and 6 pm. Mr Vernon had a major part to play in the history leading up to the accident and he too failed to survive it. Like Mr Flook he was only acting as Lead Operator although about that time he seems to have been doing that fairly regularly. Mr Vernon was aged about 50 so that he was experienced. Mr Grieve thought that Mr Vernon was a very experienced and competent operator. No doubt he was but the various tributes which flowed from witnesses as to the competency and quality of their deceased comrades have to be considered carefully since one would expect that inevitably such observations could only be tinged with a measure of charity. On the other hand unless there are indications to the contrary effect I consider that it is appropriate that I should presume that particular workmen not available to give evidence would have and show the standard of competency which their position and experience would suggest. Moreover the witness Mr Henderson when he was asked about Mr Vernon went beyond what was required for courtesy to a deceased and said that once in discussion between three Lead Operators Mr Vernon had been unanimously nominated as the best candidate for a promotion. Mr Murray described him as being "fairly serious, very conscientious, quite industrious"

The Lead Production Operator, as described by the witness Henderson I think accurately, had the task of directly looking after production and in particular the ongoing efficiency and safety of production. He had the duty of liaison with Maintenance to ensure that equipment was available, to try and minimise production down-time, and to administer the permit to work system. He issued the permit to work after he was satisfied that the necessary safety precautions had been identified and carried out.

The actual operators on the day of the accident included Mr Bollands (who as part of his rota as operator was looking after the Control Room at the time of the accident), Mr Bob Richard, and Mr Peter Grant. Mr Richard was a contractor’s employee working on the production side of the platform. He had perhaps been on the platform for a year. Both Mr Grant and Mr Richard were described by their colleagues as good workmen. There were also on duty when the accident occurred Mr Bremner and Mr Rennie who were the Oil and Water Operators. Mr Grant had been the Phase 1 operator during the day shift and he was replaced by Mr Richard for the overnight shift. Mr Groves had been the day-shift Phase ll operator and he was replaced by Mr Grieve for the night-shift. Mr Bollands had taken over from a Mr Price (another casualty).

On the night of the accident Mr Grieve was the Phase II operator. This operator generally looked after the Gas Conservation Module. This module was shut down for overhaul so that Mr Grieve was looking after the work going on under the overhaul and also looking after the methanol injection which was required that night. Mr Richard as Phase I operator would have had the normal duties of such an operator and these would include looking after the centrifugal compressors, the operations at the 68-foot level which included the JT flashdrum, the booster pumps and the condensate injection pumps. The Control Room Operator would be in charge of alarms and if alarms went off he would be expected to direct operators to the source of the problem. He would be expected to observe the various control readings. He would be expected to observe the fire panels and the lock-outs. Mr Bollands considered that the Control Room Operator would be aware of the permits to work that were out. Occasionally he would leave the Control Room since he had certain checks to make outside it. He would only leave the Control Room when the Lead Operator was present and would expect him to stand in for him.

In the maintenance line of responsibility there was a Maintenance Superintendent. He was in charge of a team of tradesmen and was responsible for the maintenance of all production equipment. He also had to organise planned maintenance and deal with breakdowns. On the platform the Maintenance Superintendent was responsible directly to the OIM. He would also be in daily contact with the Maintenance Department on the Beach who directed on technical matters. On the day of the accident the Maintenance Department on the platform had been in touch with the witness Mr Seddon who was a Senior Maintenance Superintendent on the Beach. Two Maintenance Superintendents were employed on the platform in July 1988. Mr Todd was one and his back to back was Mr Barry Clark, who was on holiday at the date of the accident. Mr Todd had left the platform on 5 July 1988 so that at the date of the accident the Deputy Maintenance Superintendent was in charge of maintenance. He was in fact Mr Kevin White (who died in the accident). He too was described by witnesses as being competent and thorough. His office was on the north side of the platform opposite the Maintenance Department where maintenance records were kept. Below the Deputy Maintenance Superintendent was the Lead Maintenance Technician. At the date of the accident Mr William Smith was the day shift Lead Maintenance Technician on the day shift and Mr Alexander Clark had taken over from him for the nightshift. Mr Clark survived the accident and was a witness but unfortunately Mr Smith perished. Mr Todd described Mr Smith as being excellent and dedicated at his job. Indeed he described him as being one of the best Lead Hands on the platform. The Lead Maintenance Technician (or Hand) was in control of the maintenance tradesmen or technicians and directed their work. He was answerable to the Maintenance Superintendent.

In terms of the permit to work procedure the Maintenance Superintendent would normally be the Requesting Authority. If the tradesmen on the job were under the charge of the Lead Maintenance Hand then he would normally be the Performing Authority. Thus if maintenance work which involved a permit was required the Maintenance Lead Hand would normally request the work from the Maintenance Superintendent (the Requesting Authority). Then the permit application would have to go to the Operational Superintendent for approval (the Approval Authority). Once approval is available the permit is taken to the Designated Authority (usually the Lead Production Operator ) who would arrange for the necessary safety isolations and precautions. Once these were attended to the permit could be issued to the Performing Authority and this would be done when the work was about to be carried out. Specialist maintenance contractors like Score (the valve technicians) would arrange their permits without reference to the Lead Maintenance Hand because they were working independently of him. Score in fact were specialists in maintaining PSVs and they were brought on to the platform specifically for such work. If work involved a number of separate trades then the Maintenance Lead Hand would take over the permit formalities. However under the valve maintenance programme that Score were carrying out at the time of the accident they would be the Performing Authority under any permits. Score were in this respect responsible to the Maintenance Superintendent and reported to him (or Deputy if he was in effective control)

5.12.2 The Maintenance System

An Offshore Maintenance Controller was on the platform but did not survive the accident. His job was to be responsible for the computer based planned maintenance system and also for entering data from the Logs and Reports. In effect he compiled the platform history. He only worked during the day shift. All equipment was identified within the system and maintenance routines were devised for all equipment to be carried out at specified intervals. The computer would each month print out the maintenance work to be done that month and this was then given to the Maintenance Lead Hands. Pressure Safety Valves had to be re-certified about every 18 months. Thus when Mr Rankin and Mr Sutton came out to the platform towards the end of June 1988 there would be a certain number of valves which had to be attended to by them and these would be specified in the valve register. They would also be given a print-out to show the valves they had to recalibrate and refurbish. The Maintenance Controller would receive a log from tradesmen every day so that he could feed the state of maintenance work into his computer. The Beach could as a result keep control over the progress of maintenance work. PSV 504 was the last valve which Mr Rankin and Mr Sutton required to work on before their tour of duty was finished. On 6 July 1988 the Maintenance Controller had not reported to the Beach regarding operations on PSV 504 before he went off duty. However every morning the Maintenance Controller would compile a Report based on the logs kept by the various trades people and the would give the Maintenance Superintendent and the Maintenance Lead Hand a copy of the logs. It covered the various pieces of work particular trades had completed during the previous 24 hours. Moreover the Maintenance Superintendent or his Deputy would know when work was pending or in progress because of their involvement in the permit to work system. However they might not know the precise state of the work because they would not necessarily know if the permit to work had been issued only that in general approval had been given for it. Thus if the maintenance work to be done on a valve had been completed the Maintenance Superintendent would not know this until he received a report the following morning. The Maintenance Controller was essentially Clerical in background rather than Technical.

5.13. Condensate Injection Pumps

5.13.1 Handover to Maintenance

Since the pursuers’ case involves the allegation that the root cause of the accident resulted from an attempt to start a condensate injection pump in circumstances when the attempt should not have been made it is necessary to recount in specific terms the procedures that could have given rise to the situation. If a pump required to undergo a 24 month planned maintenance the first step would be to switch over to the standby pump (that is assuming that the pump to be maintained had been operational before the maintenance). It was practice then to run the standby pump for a period of about four hours to make sure that it was working properly before the pump to be maintained was switched off. Once it was clear that the standby pump was operating effectively the other pump would be switched off. When this was done the suction and discharge GOVs of the pump would close and the airlines to them would be disconnected. The Manual Isolation Valve on the relief line from the pump would also be closed. This valve in the case of pump A was situated in Module C at a height of 15 to 20 feet above the deck and quite close to PSV 504. This meant of course that if the pump was to be restarted the Manual Isolation Valve would first require to be opened. After the foregoing steps had been completed the pump had to be depressurised which would take about 15 minutes for the initial part but to take the pressure below about 20 psi would take about one and a half to two hours. After the pump had been depressurised the main motor and the lube oil motor were electrically isolated. It seems that the total time required to demobilise the pump took from 5 to 6 hours. At the stage that the demobilisation of the pump had been completed before any maintenance work could be carried out on the pump a hot work (pink) Permit to Work would require to be issued. Then the Maintenance men could move in and spade the pump. Under the system the approval authority is effectively saying the pump can be handed over to maintenance and the designated authority given the actual go-ahead to begin the maintenance work.

Thus on the morning of the accident when pump A was withdrawn from operation for maintenance Mr Smith the Performing Authority went to the Approval authority to get permission to begin the work on that date. After obtaining such approval he took the permit to Mr Lynch in the Control Room and as a preliminary step he set in motion the procedures for shutting-down the pump. However it is only after the permit is actually issued that the maintenance staff can move in to spade the pump and carry out any instrument work or other maintenance tasks. In the case being considered the designated authority would be the Lead Production Operator on duty when the permit had to be issued, the Requesting Authority would have been the Maintenance Superintendent and the Performing Authority would have been the Maintenance Lead Hand.

A Maintenance Superintendent would be alerted by computer records to the fact that a pump was due for its 24 month maintenance. This period is of course the period between maintenance routines. Before initiating a maintenance routine the Maintenance Superintendent would confer with Production to ensure that the pump could be made available and also inquire about the availability of the requisite spares. Then steps would be taken to shut-down the pump and get the necessary permit for the maintenance work

The witness Mr Todd (who was a Maintenance Superintendent) described how after the maintenance department took over a machine which had been isolated they would carry out spading. This involves further mechanical isolation of the machine by the fitting of blind flanges between two pipe flanges and is a procedure akin to the fitting of blind flanges. This would of course accompany the removal of components from the pump and would be necessary in the case of a 24 month maintenance since in that procedure the pump has to be opened up Thus if the flow of condensate were able to overcome the closed GOV it would then be held back by spading. One fact that seems clear is that on the night of the accident there is no suggestion that the maintenance of the pump had proceeded to spading. Indeed if the pump had been spaded Mr Vernon should have seen this when he approached the pump since it would be obvious and any attempt to start it in these circumstances is clearly unlikely. The Permit to Work should specify the spading that is required in connection with a particular operation. Mr Todd certainly thought that spading would normally be carried out shortly after the pump had been isolated.

The 24 month routine maintenance of a condensate injection pump would normally take about seven days if no problems were found but in certain cases the procedure could take several weeks.

On the occasion of the accident the maintenance routine was rather complicated by the fact that prior to that procedure trouble had been experienced with the Voith coupling on the motor so that repair was required to that component. If the work had purely been on the Voith coupling a cold work permit would have sufficed but if the repair of the coupling was to be incorporated into the routine maintenance it would be covered by the maintenance permit. Of course if the decision to repair the Voith coupling were taken after the maintenance permit had been issued than a further permit would be required. The work that had to be carried out on the Voith coupling on the occasion of the accident would not, viewed in isolation, have required the depressurisation but some operators preferred depressurisation to assist in the testing of the work. Otherwise only the electrical isolations would have been necessary because the work did not involve going into the pressure envelope.

The general evidence is that a permit to work would not normally be issued until just before the relevant work was to be carried out.

There was evidence from Mr Henderson that he personally would not have electrically isolated if the only work to be carried out was the maintenance of a PSV. However if this indeed was the practice followed by Mr Henderson it was not the usual practice of others. Mr Clark for example seemed in no doubt that PSV 504 would have been electrically isolated before any work was allowed on it. In a permit produced dated 23 March 1988 and relating to the PSV the electrical isolation on the check list is ticked although the authorised electrician has not completed the form. Clearly then the practice is not entirely free from doubt but the preponderance of the evidence is that in 1988 the practice was to isolate valves even on a cold work maintenance permit

5.13.2 Status of pumps at accident

There is little doubt that during 6 July 1988 the intention of the operators was to carry out a planned maintenance of condensate injection pump A. Indeed it is because of this that the maintenance of PSV 504 was allowed to proceed for the maintenance engineers were waiting until the connected pump became available before being allowed to do their work. Planned maintenance of the pumps could be deferred or advanced according to circumstances and in this case the work was advanced because of the trouble being experienced with the Voith coupling which had been vibrating unduly. There was also a connection with the change to Phase 1 operation since it was thought that this phase could be worked with only one condensate injection pump. The decision to carry out the work was only taken after extensive discussion. The actual date of 6 July was chosen for the commencement of the work because necessary spare parts were expected to be available by that date.

On 6 July the morning shift Lead Production Operator had been Mr Lynch who began work about 4am and who only worked a short shift because he left the platform about 11am. The Lead operator Harry Flook took over from him. Mr Flook could have been an important witness but unfortunately was killed in the accident. Mr Flook was doing the Lead Production Operator’s job on a temporary basis and although he was an experienced operator he was in a sense undergoing training for the position of Lead Operator. It was he who would eventually have handed over to Mr Vernon and although there is no evidence to suggest that Mr Flook did not perform that task to standard it has to be observed that the possibility always exists that he was not as experienced in the matter of a Lead Operator’s handover as some. Mr Lynch carried out his handover with Mr Flook at about 7am and it may cast some light on the handover process in general that he says going through the permits was carried on with constant interruption particularly constant telephones ringing and other jobs. Mr Lynch describes Mr Flook as a meticulous person and this may well be a fair judgment although it has to be noted that for understandable reasons all the survivors were inclined to ascribe excellent characters to the victims. However Mr Lynch gives the impression that if anyone wanted the handover to be exceptionally comprehensive it was Mr Flooks rather than himself. Mr Lynch got a telephone call from the production Superintendent, Mr Curtis, who told him that Mr Smith, the Maintenance Lead Hand wanted to do a planned maintenance on pump A and asking Mr Lynch to put pump B on line and to shut pump A down. Mr Lynch instructed the Phase 1Operator Peter Grant to do the job. I think it must have been the intention at that point of time to proceed immediately to the maintenance work or presumably the closed pump A would have been left on standby until the work was imminent. It is also noteworthy that at the time of his original instructions there would appear to have been no reference made to Mr Lynch of the valve maintenance. His instructions seem to have been based on a proposed planned maintenance which he described "as a big job". Mr Lynch had instructed Mr Grant to run the standby pump (pump B) for some hours to test it and he left the platform before that process was complete so Mr Lynch himself would not have had direct involvement in the depressurising procedures. However before he had left the platform he had been presented with an application for the planned maintenance permit which could of course not be issued until the isolations were effected. The permit application which was a pink permit application had been brought to Mr Lynch by Mr Smith just after 7am and left on Mr Lynch’s desk. He understood that all that had been left to him was to get the job ready. Mr Lynch seems to suggest that by the time he left the platform he was satisfied that the proposed alternative pump was working well. It is perhaps significant that Mr Lynch said that he had discussed the position with Mr Flooks and that the latter knew that the permit was there for him to deal with once it was clear that the standby pump was alright.

Mr Bollands the Control Room Operator said that when he came to the Control Room (which would have been shortly before the 6pm. shift) there was only one condensate injection pump running and that was not "the one with maintenance". He certainly implied that he thought that one pump was with maintenance. Mr Bollands recalls how Mr Vernon had after his first visit to the pump B when an alarm showed that it had tripped said that he could not get the other pump going and that he wanted to take the other pump "out of maintenance" . Thus there seems to have been little doubt that a number of operators including Mr Vernon considered pump A to be "with maintenance". This is not entirely consistent with a position where the pump has not been released from Production for Maintenance because no permit had been issued. Indeed Mr Bollands went further because he explained that his understanding was that instrument technicians had already been working on the pump doing maintenance. Mr Bollands would have required to have some knowledge of the pump during his shift since he was responsible for monitoring any applicable alarms. Indeed Mr Bollands claimed that he always checked the hot work permits for this reason. Mr Bollands indicated that he was not aware that PSV 504 was missing but of course that would be consistent with him not requiring to check cold work permits. Mr Bollands refers to the fact that after Mr Vernon had returned to the Control Room after failing to get pump B restarted he got a pink permit out of the box which contained live permits. This evidence if accurate is important in two respects. In the first place Mr Bollands seems to be in no doubt that what Mr Vernon extracted was a pink permit. Indeed he states that he had looked at the live permit box earlier that night and had seen a maintenance permit which he understood was for instrument technicians to use to work on the pump. Next he says that it came out of the tray of live permits. There can be little doubt that the permit for valve maintenance over-night would have been with suspended permits. Moreover the boxes had different compartments for permits relating to the various production levels. Thus any permit covering the maintenance of the pump would have been kept in the 68-foot level box whereas a permit relating to PSV 504 would be in the 84-foot level box. At the time Mr Vernon had extracted a permit Mr Clark, the Maintenance Lead Hand, was in his own office so that he was able to respond at once when Mr Bollands called him. Mr Bollands then gives an important piece of evidence. He claims that Mr Vernon spoke to Mr Clark and then told Mr Bollands that he wanted to get the pump back from maintenance and to get the permit signed off

Mr Clark then arrives in the Control Room and there is an issue as to whether or not he saw Mr Vernon before he returned to the pump. Then he telephoned for an electrician to reconnect the electrical supply to the pump. Mr Bollands’ position is that he handed the permit to Mr Clark but the latter said that he did not remember seeing the permit in the Control Room only the red electrical tags. In fact Mr Clark maintained categorically that the maintenance permit has not been issued. Mr Bollands has a clear recollection that Mr Vernon spoke to Mr Clark and asked if he could have the pump back from maintenance. There is I suppose some possibility that Mr Bollands is wrong in remembering a conversation between Mr Vernon and Mr Clark in the Control Room and that what he remembers is a conversation over the telephone but given that he remembers the content of the discussion I think it is unlikely that he did not at some stage hear a conversation in the approximate terms he remembers. As Mr Bollands remembers the conversation that took place he recalls that Mr Vernon made it clear that he was "withdrawing" the permit . Even Mr Clark appears to accept that the red tags he signed related to the permit for the pump. It should be noted that in general the evidence was that the electrical red tags were stapled to the permit. There seems to be little doubt that any instruction to the electricians to reinstate the connection to the pump had to come through the Maintenance Lead Hand and this no doubt is why Mr Vernon troubled to contact Mr Clark and left the question of electrical connection to him. In fact some difficulty was experienced in contacting electricians because Mr Savage the electrician was in the accommodation module and off shift. An attempt was made to contact the night shift.

Mr Seddon was aged 46 and was the Onshore Senior Maintenance Superintendent at the time of the accident. He also had extensive experience of working offshore as a Maintenance Superintendent. He confirmed that shortly before the accident there had been a partial shutdown of one of the production sections of Piper Alpha to accommodate the maintenance of the Gas Conservation Module. This was clearly a major maintenance task. Mr Seddon described it as the major maintenance activity. Just before the accident he had been on vacation. About 5 or 6pm on the day of the accident he had from onshore a telephone conversation with the offshore Maintenance Superintendent on Piper Alpha and the individual concerned was Kevin White. Generally he was discussing the maintenance work that was being done on the platform. He was told that there had been a history of difficulty with the Voith Coupling on Condensate Injection Pump A and in these circumstances his stand-in had taken a decision to go ahead with planned maintenance work on the pump although the work had not been due to start until August. Mr Seddon informed Mr White that he disagreed with the decision to proceed with the planned maintenance but that the Voith Coupling repair should proceed seeing that the pump had been shutdown. He thought that planned maintenance involved rather too lengthy a period for the immobilisation of the pump with other major work going on. Mr White made it clear to Mr Seddon that the pump had already been shut down but although Mr Seddon agreed that the Voith Coupling work should proceed he advised against continuing with the planned maintenance. However Mr Seddon states that he was only rendering advice and that the final decision was a platform decision and such a decision would have to be preceded by discussion.

The special significance of the evidence of Mr Clark, who fortunately was one of those who survived the accident, is that he categorically denies that a permit to work for the planned maintenance had actually been issued. He does say that when a planned maintenance was imminent the equipment would be taken out of production and then handed over to Maintenance. He confirms however that the maintenance would be covered by the permit to work system. He explains that when equipment is handed over to maintenance this means that Production no longer require its use and that Maintenance are free to work on it. When the maintenance work was finished the equipment was handed back to production who would pressure test it before putting it into production. He indicated that if a pump tripped then the Production team would try to restart it and if this could not be done maintenance would be called in to repair it.

On the night of the accident Mr Clark explains that he had working under him on the nightshift two electricians, two Instrument men, two mechanics and some kind of labour as well "like an Instrument man and a mechanic". He indicated that on 6 July 1988 the Voith Coupling on one of the Condensate Injection Pumps was causing trouble and the dayshift had decided to shut it down for repair. He said that would be an "as soon as possible" repair rather than a planned maintenance. However Mr Clark is certainly wrong about this since it is clear from Mr Lynch, Mr Bollands and Mr Seddon that the intention during the day had also been to carry out a planned maintenance and he later accepts this although he said that the maintenance programme was to be limited - perhaps 3 or 4 days. Of course Mr White did not survive so that we do not know what action, if any, was taken by him in response to Mr Seddon’s intervention between his telephone call with him and the accident. It is, I suppose, possible that a decision had been taken only to do a limited maintenance and that this had been communicated to Mr Clark as the Maintenance Lead Hand on duty. He was asked about his handover with Mr Smith and his recollection is that in relation to the work ongoing into his shift it was only the shutdown work. This is not very clear since it is obvious that before Mr Clark’s shift began all the shutdown work had been completed. The depressurising work was complete or the valve technicians would not have been allowed to go ahead and it is clear from events later that night that the electrical isolations had taken place. Mr Clark had said that he had told Mr Smith that if he could get other work finished in time then he would try to get the Voith Coupling out. There may be an area of uncertainty here. If the Voith Coupling repair was on a planned maintenance permit then Mr Smith may have expected that work on the coupling would proceed during the night and had the permit continued before he went off duty. This does not accord particularly well with Mr Clark’s recollection but then I am not entirely satisfied that Mr Clark is an accurate witness. Mr Clark was asked if any work had been carried on in terms of the planned maintenance and he declares that Mr Smith had told him that he had written out a permit application and done an electrical isolation on it but that they had not actually started any work because they did not have the men. This does not accord with Mr Bollands’ recollection that instrument men had worked on the pump during the previous shift but there was probably room for misunderstanding on this point. If the instrument technicians had only carried out technical work such as testing this may not have been the sort of work that Mr Smith would have considered would trouble Mr Clark. I am certainly prepared to accept Mr Clark insofar as it is obvious that Mr Clark had been told that no serious work had been done on the pump. Otherwise Mr Clark could not have accepted Mr Vernon’s suggestion that the pump be put back in production. In any event if the pressure envelope had been broken into, the pump would at that point have required spading. I think however that an important aspect of Mr Clark’s evidence is that he claims to have been told that the pump had been electrically isolated in connection with the proposed maintenance. If this were so it is to be expected that the isolation tags would be attached to the maintenance application. That was the procedure and the maintenance permit could never have been issued without these tags. The procedure was generally not to issue a permit until the work was about to commence but equally the procedure was to effect the electrical isolation just before the permit was issued. Certainly it can be seen that if the pump had been de-pressurised then there could be sound arguments for doing the electrical isolation at that point to complete the isolation of the de-pressurised pump.

A further interesting point is that Mr Clark claims that he had not been informed that the PSV work had been begun and not completed. I shall later consider the reliability of Mr Clark’ recollection on this point. The proper procedure was for Score employees (such as the valve technicians) to report to the Maintenance Superintendent and if there was any situation that might have affected maintenance work one might have expected that Mr Todd would have told the Maintenance Lead Hand. In fact however Mr Rankin reported at the end of his shift to Mr Smith who was already off duty. This could possibly account for a situation where Mr Clark was unaware of the valve maintenance work. In deciding whether or not as Mr Bollands says the permit for the planned maintenance had been issued an important point is that if it had not been issued the permit with its tags was probably lying on the Lead Operator’s desk ready to be issued when needed. However if that were the position Mr Vernon would have seen at a glance that no work could have been done on the pump and would not have required to ask Mr Clark about the status of the pump. It has to be noted that in multi-craft work such as planned maintenance the Maintenance Lead Hand would be the performing authority so that Mr Clark’s signature would have been required to de-isolate the electricity. Indeed to de-isolate signatures would have been required from both the designated authority and the performing authority.

At the end of the day I am not sure that it is truly significant whether the permit to work had been issued or was merely lying on Mr Vernon’s desk with its tags awaiting imminent issue. However if I had to make a decision of the matter I would favour the view that the permit had been issued . Either Mr Bollands or Mr Clark must have a faulty recollection of this matter. In general I found Mr Bollands to be an accurate witness. Of course even such a witness can be unreliable on a matter of detail. However Mr Bollands was very positive in his recollection that the Permit had been issued and he had no particular axes to grind about that matter. He remembered seeing Mr Vernon remove the permit from the live permit container. He remembered reading the permits when he came on duty and as the Control Room Operator he would have needed to know what was going on. He seemed to be clear that Instrument Personnel had been working on the pump earlier in the day. I am not quite sure how he would have known this but on the other hand it would be a curious detail to imagine if there was not some substance in it. Mr Clark is equally positive that the permit had not been issued and as Maintenance Lead Hand if his memory is accurate this is a matter one would have expected him to know. On the other hand I was not entirely convinced that Mr Clark remembered all points accurately. He had been very badly shaken by the accident. He seemed very concerned to minimise his knowledge of what might affect his own responsibilities and at times I thought that perhaps understandably he was being defensive. For example in describing his conversation with Mr Vernon he said " we decided we would put Pump A back on". This would mean that he could have been embarrassed if it were shown that he knew about the valve maintenance work (not that it was ever demonstrated that he did). He did say that he did not know if the pump had been depressurised which is a little strange if he had gone through the handover procedures with Mr Smith earlier and in any event if he was intending to tie the Voith Coupling work in with the planned maintenance permit (and it seems to have been on this form that the Voith Coupling work was to proceed) then Mr Clark could not have got a permit issued to begin work on the Voith Coupling (as he intended) without the pump having been depressurised. He also said that the unissued application for a permit had been put in the Safety Box but it is clearly the case that Mr Vernon had not had an opportunity to retrieve an application from the Safety Office. Thus although Mr Clark said that tags were always kept in the Safety Office if not attached to an issued permit this could not have happened on the occasion in question. Moreover other witnesses said that a pending permit awaiting issue was kept in the Control Room to be issued when needed. This might appear a more convenient arrangement. There seems to be little doubt that Mr Vernon asked Mr Clark what work had proceeded on the pump and if production could take it back. If Mr Vernon was merely asking that electrical isolation tags should be signed off and no permit had been issued it is perhaps odd that he did not simply ask Mr Clark to come and sign the tags. As I have already suggested it is odd that Mr Vernon should be interested in the state of the pump if no permit had been issued. Of course as was argued by the defenders it was the normal practice to issue the permit only when the work was about to commence. If Mr Bollands is right that some instrumentation work had been carried out on the pump then this may explain why the permit had been issued. In any event although it was practice only to electrically isolate just before the work it has to be noted that the electrical isolation had been effected earlier that day. As I have said this might be expected in the case of a pump which had been de-pressurised whatever the normal procedure in relation to other work. It may be that when the work is to be protracted as with a planned maintenance the point thought of as the commencement of the work is when the machine is taken out of production and handed over to Maintenance to get on with the work when they can. The work had not been spaded but that may mean that the work which would have required breaking into the pressure envelope had not at that point begun. Indeed Mr Clark said that it was not necessary to have the pump depressurised to do any repair work on the Voith Coupling. The carrying out of the maintenance work when linked as it was to the Voith Coupling and no doubt some work on instrumentation is likely to mean that different teams of men are beginning different jobs at different times. If the permit had been issued during the day shift then of course Mr Clark would not have a direct recollection of this. It may even be the case that the permit had not been re-validated for evening work and was waiting in the Control Room until it was seen if Mr Clark could proceed with further work that night. This could have muddied his recollection. However the main significance of the state of the permit is to cast light on what was the state of Mr Vernon’s knowledge when he indicated an intention to bring Pump A into use and as I shall later indicate I am not convinced that it matters materially whether there was a completed application for a permit with tags attached or an issued permit.

It is interesting that when Mr Clark reported to Mr White that the intention was to re-introduce Pump A to production Mr White did not demur. Of course it may well be that no-one had reported to him that PSV 504 had not been replaced. Also the fact that apparently Mr Clark said nothing to Mr White about the wisdom of starting the pump without the relief valve suggests that Mr Vernon said nothing to Mr Clark about that aspect of the matter. After receiving Mr Vernons’ call Mr Clark went to the control Room and signed off the red tags. He was about to go and instruct the electricians when the explosion occurred.

One detail where Mr Clark may well have a correct memory is when he is describing what happened when he was in Mr White’s office and received the telephone call from Mr Vernon. He said he looked at his watch, because the time at which one receives such calls is important, and it was 9.45pm. As I have indicated this may have an important bearing in the precise timing of events just before the accident.

One incidental but important view arises from Mr Clark’s evidence. He was asked if he would not have noticed the PSV Operation when making his round because of the presence of scaffolding at the valve. His response was that there was so much scaffolding in the modules that he would never take account of it unless it was causing an obstruction. Activities such as painting were going on from time to time and scaffolding was going up and down on a routine basis. However he does claim that in the evening of the accident he had earlier made an inspection round.