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VOLUME 2
CHAPTER FIVE -CAUSATION 1
5.1The Parties’ Cases on Causation
5.1.1The 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, interalia, 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 PSV504. 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 164degrees true and the wind speed was south south-east3, 16.4knots. 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 pumpA 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 ModuleC 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 ModuleB and propagated through a breach in the wall between ModulesB and C. The defenders further averred that immediately after the initial explosion fire was seen to have broken out in ModuleB and that after the tripping of condensate injection pumpB, 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. MrMiller 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 MrClark (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 MrBollands 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 MrYoung 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 ModuleC 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 CaptainClegg 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