Oil platform destroyed by explosion and fire in 1988
Piper Alpha was an oil platform located in the North Sea about north-east of Aberdeen, Scotland. It was operated by Occidental Petroleum (Caledonia) Limited (OPCAL) and began production in December 1976, initially as an oil-only platform, but later converted to add gas production.
Piper Alpha exploded and collapsed under the effect of sustained gas jet fires in the night between 6 and 7 July 1988, killing 165 of the men on board (30 of whose bodies were never recovered), as well as a further two rescuers. Sixty-one workers escaped and survived. The total insured loss was about £1.7 billion (£ billion in 2023), making it one of the costliest man-made catastrophes ever. At the time of the disaster, the platform accounted for roughly 10% of North Sea oil and gas production and was the world’s single largest oil producer. The accident is the worst ever offshore oil and gas disaster in terms of lives lost, and comparable only to the "Deepwater Horizon" disaster in terms of industry impact. The inquiry blamed it on inadequate maintenance and safety procedures by Occidental, though no charges were brought. A separate civil suit resulted in a finding of negligence against two workers who were killed in the accident.
A memorial sculpture is located in the Rose Garden of Hazlehead Park in Aberdeen.
Piper oilfield.
Four companies (Occidental Petroleum (UK) Ltd, Getty Oil International (England) Ltd, Allied Chemical (Great Britain) Ltd, and Thomson Scottish Associates Ltd) formed a joint venture and obtained an oil-exploration licence in 1972. They discovered the Piper oilfield located at in January 1973, and began fabrication of the platform, pipelines, and onshore support structures. Oil production started in December 1976, less than four years after discovery (a record rarely beaten ever since), with about of oil per day, later increasing to . Production declined to by 1988.
A large, fixed platform, Piper Alpha was located in the Piper oilfield, around northeast of Aberdeen in of water. Piper Alpha produced crude oil and natural gas from 36 wells. OPCAL built the Flotta oil terminal in the Orkney Islands to receive and process oil from the Piper, Claymore (both operated by OPCAL), and Tartan (Texaco) oilfields, each with its own platform. One diameter main oil pipeline ran from Piper Alpha to Flotta.
The Piper platform was the hub of a network of pipelines connecting it to nearby platforms and to shore. The Tartan field fed oil to Claymore, with the co-mingled oil flowing from Claymore through a short pipeline to join the Piper-Flotta line some to the west of Piper.
Separate diameter gas pipelines were run from the Tartan platform to Piper, and from Piper to the Total-operated manifold compression platform MCP-01 some to the northwest. Another line connected Claymore to Piper, primarily to provide gas from Piper to the Claymore gas lift system. MCP-01 would receive the gas from Piper and Tartan, as well as from the Frigg gas field (through a separate pipeline), and send the resulting stream to St Fergus Gas Terminal through a , 2 × 32-inch pipeline.
The inventory of the pipelines was significant, with the main oil line to Flotta containing around 70,000 tonnes of oil and the three gas lines linking Piper to the surrounding platforms close to 2,000 tonnes of high-pressure gas. The pressure in the Tartan–Piper and Piper–MCP-01 pipelines was around 127 bar.
Construction and layout.
Piper Alpha's production facilities were designed by Bechtel in London. The supporting platform jacket, as well as the topside module structures and buildings, were designed by McDermott Hudson. The eight-legged jacket structure was constructed by J. Ray McDermott in Ardersier, Inverness-shire, and Union Industrielle et d'Entreprise in Le Havre, France, with the sections united in Ardersier before being towed out during 1975. The jacket weighed around 14,000 tonnes and was tall, of which a length of was permanently submerged. Four clusters of foundation piles extended a further below the seabed. Topside modules weighing about 10,000 tonnes in aggregate were lifted from a crane ship and installed over the jacket in late 1976.
Piper's hydrocarbon facilities and principal utilities were distributed in four main modules (A, B, C, and D) separated by firewalls and sitting atop the steel jacket. Above the main modules were a drilling derrick, various utilities, the living quarters, flare booms, two pedestal cranes, and the helideck.
For safety reasons, the modules were organized so that the most dangerous platform operations took place far from the personnel areas. However, the conversion from oil to gas broke this safety concept, with the result that sensitive areas were brought together; for example, the gas compression module was next to the control room. The close position of these two areas played a significant role in the accident.
The hydrocarbon inventory actually held within the platform was small in comparison with that contained in the pipelines, standing at around 80 tonnes of process fluids and 160 tonnes of diesel fuel (which was stored in tanks located above module C).
Upgrades and production modes.
In 1978, major works were carried out to enable the platform to meet British government gas-conservation requirements, and to avoid waste from the flaring of excess gas. A gas conservation module (GCM) was added, built on top of module B. After this work, Piper Alpha operated in what was known as "phase-2 mode", i.e., using the GCM facility. In phase-2 mode, the GCM would treat the gas obtained in the crude oil separation process, separate condensate (or natural gas liquids, NGL) from it, reinject the condensate in the oil export pipeline to Flotta, and compress the gas for export to the pipeline to MCP-01. From the end of 1980 until July 1988, phase-2 mode was its normal operating state.
In the late 1980s, major construction, maintenance, and upgrade works were planned by Occidental, and by July 1988, the rig was already well into major revamp, with six projects identified, including the change-out of the GCM unit. This meant that the rig was returned to its initial "phase-1 mode", i.e., operating without the GCM unit, only three days before the accident. Despite the complex and demanding work schedule, Occidental made the decision to continue operating the platform in phase-1 mode throughout this period and not to shut it down, as had been originally planned. The planning and controls that were put in place were thought to be adequate. At the time of the accident, Piper weighed around 34,000 tonnes. It continued to export oil at just under per day (or 10% of the entire production of the UK sector of the North Sea, which made it the world’s single largest oil producer) and to export Tartan gas at some per day at standard conditions during this period.
Events on 6 and 7 July 1988.
Because the platform was completely destroyed, and many of those involved died, analysis of events can only suggest a possible chain of events based on known facts. Some witnesses to the events question the official timeline.
Preliminary events.
At 07:45, 6 July 1988, the permit-to-work forms for the day shift were issued and signed. Of the two condensate pumps, both located in module C, pump B was operating to displace the platform's condensate for transport to the coast, while pump A was due for maintenance. Two permits were issued to that effect, one for a pump overhaul and another for the removal of the pump's pressure safety valve (PSV #504), which was due for recertification. During the day, pump A was electrically and mechanically isolated, but containment was not broken. The PSV, instead, was removed. The open condensate pipe upstream of the PSV was temporarily sealed with a disk cover (a flat metal disc also called a blind flange or blank flange). It was hand-tightened only. Because the work could not be completed by 18:00, the blind flange remained in place. The on-duty engineer filled in information on the PSV removal permit to the effect that pump A was not ready and must not be switched on under any circumstances. However, this information was not provided in the pump overhaul permit.
The night shift started at 18:00 with 62 men running Piper Alpha. As the on-duty custodian was busy, the engineer neglected to inform him of the condition of pump A. Instead, he placed the PSV permit in the control centre and left. This permit disappeared and was not found.
At 19:00 the diesel-driven fire pumps were put under manual control. Like many other offshore platforms, Piper Alpha had an automatic fire-fighting system, driven by both diesel and electric fire pumps. The pumps were designed to suck in large amounts of sea water for firefighting and had automatic controls to start them in case of fire. However, the Piper Alpha procedure adopted by the offshore installation manager (OIM) required manual control of the diesel pumps whenever divers were in the water (as they were for about 12 hours a day during summer) although in reality, the risk was not seen as significant, unless a diver was closer than from any of the four level caged intakes. A recommendation from an earlier audit had suggested that a procedure be developed to keep the pumps in automatic mode if divers were not working in the vicinity of the intakes, as was the practice on the Claymore platform, but this was never implemented.
At 21:45, condensate pump B stopped and could not be restarted. This was likely due to the formation of hydrates and the consequent blockage of gas compression pipework, following problems with the methanol system. The operators were anxious to reinstate condensate pumping capacity. Failure to do so would have meant needing to stop the gas compressors and venting to the flare all the gas that could not be processed.
Around 21:52 a search was made through the documents to determine whether condensate pump A could be started. The permit for pump A overhaul was found but that for its PSV removal was not. The valve was at a distance from the pump, so the permits were stored in different boxes, as they were sorted by location. Because the overhaul had just started on the day, with no equipment removed or containment broken, the operators were under the impression that the pump could be put back in operation quickly and safely. None of those present were aware that a vital part of the machine had been removed. The missing valve was not noticed by anyone, particularly as the blind flange replacing the safety valve was several metres above ground level and obstructed from view.
Explosion in module C and initial reactions.
At or shortly before 22:00, gas was reintroduced into pump A, filling it. The loosely fitted flange did not withstand the resulting pressure. Gas audibly leaked out at high pressure, drawing the attention of several men and triggering multiple gas alarms. Before anyone could act, the gas ignited and exploded. The source of ignition is unclear, with the later investigation pointing to hot work, hot surfaces, broken light fittings or an electrostatic spark as potential sources (electrical equipment in the surroundings were rated for hazardous areas). The platform, which originally was built for oil production only, was not of a blast-proof design, so the firewalls were not designed to withstand explosions. The blast blew through the firewalls separating module C from the adjoining modules B and D (the latter of which housed the control room), made up of variously sized panels bolted together. As a result, the control room was almost entirely destroyed. Panels around module B were also dislodged, with one of them rupturing a small condensate pipe, thus creating another fire.
Immediately after the explosion, control room operator Geoff Bollands, who had witnessed the alarms going off in the control room and subsequently survived the blast, activated the rig's emergency stop button before escaping. This closed isolation valves in the wells and sea riser lines and ceased all oil and gas production. Theoretically, the platform would then have been isolated from the flow of oil and gas and the fire contained. The gas pipelines connecting Piper to Tartan and Claymore could only be isolated using separate push buttons, which were not actuated; however, the riser isolation valves probably closed due to loss of power supply in the explosion. (At any rate, the flare continued to burn until 23:30, indicating a leak in the Claymore riser isolation valve.)
The control room of Piper Alpha was abandoned. The rig's design made no allowances for the destruction of