Piper Alpha
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The Piper Alpha was a North Sea oil production platform operated by Occidental Petroleum (Caledonia) Ltd.Template:Ref It produced around 10 percent of the then oil and gas production from the North Sea. The platform began production in 1976Template:Ref, first as an oil platform and then later converted to gas production. An explosion and resulting fire destroyed it on July 6, 1988, killing 167 men.
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Piper Oilfield
Four companies that later transformed into the OPCAL joint venture obtained an oil exploration license in 1972 and later that year or next discovered the Piper Field located at 0° 15’ E 58° 28’ N, and started building the platform, pipelines and onshore support structures. Oil production started in 1976 with about 250,000 barrels of oil per day increasing to 300,000 barrels, and a gas recovery module was installed by 1980. Production declined to 125,000 barrels by 1988. OPCAL built the Flotta oil terminal in the Orkney Islands to receive and process oil from the fields Piper, Claymore and Tartan, each with its own platform. One 30 inch (0.762 metres) diameter main oil pipeline ran 128 miles (206 kilometres) from Piper Alpha to Flotta, with a short oil pipeline from the Claymore platform joining it some 20 miles to the west. The Tartan field also fed oil to Claymore and then onto the main line to Flotta.Template:Ref Separate 46 cm diameter gas pipelines run from Piper to the Tartan platform, and from Piper to the gas compressing platform MCP-01 some 30 miles to the Northwest.
Construction
A large fixed platform, Piper Alpha was situated on the Piper Oilfield, approximately 120 miles (193 km) northeast of Aberdeen in 474 feet (144 m) of water, and comprised four modules separated by firewalls.Template:Ref For safety reasons the modules were organised so that the most dangerous operations were distant from the personnel areas. The conversion from oil to gas broke this safety concept, with the result that sensitive areas were brought together, for example the gas compression next to the control room, which played a role in the accident. It produced crude oil and natural gas from twenty four wells for delivery to the Flotta oil terminal on Orkney and to other installations by three separate pipelines. It hosted a complement of about 240 personnel.
Fire
On 6 July, 1988, a leakage of natural gas condensate, which had built up beneath the platform, ignited, causing a massive explosion. The explosion ignited secondary oil fires, melting the riser of an upstream gas pipeline. The released gas caused a second, larger explosion which engulfed the entire platform. Only sixty two crewmen survived out of 229 on board that day. Template:Ref
Timeline
A new gas pipeline was built in the weeks before the 6th of July, and while this work disrupted the normal routine, the platform was operated as normal. The discovery of a small gas leak was normal and no cause for concern.
Two large compressors on the platform, designated A and B, compressed the gas for transport to the coast. On the morning of July 6, compressor A's pressure relief valve was removed for overhaul. The compressor's fortnightly overhaul was planned but had not started. The now open pressure tube was temporarily sealed with a plate. Because the work could not be completed by 18:00, the plate remained in place. The on-duty engineer filled out a form which stated that compressor A was not ready and must not be switched on under any circumstances.
18:00
As he found the on-duty custodian busy, the engineer omitted to inform him of the condition of compressor A. Instead he placed the worksheet in the control center and left. This sheet disappeared and was not found. Coincidentally there was another worksheet for the general overhaul of compressor A that had not yet begun.
19:00
As many other offshore platforms, Piper Alpha had an automatic fire-fighting system. Diesel pumps sucked in large amounts of sea water in order to extinguish any fires. These pumps should automatically switch themselves on in case of fire. However, when divers were working on the pumps they were switched to manual and could be started only from one place. Fire pumps on other platforms were switched to manual only if the divers were close to the inlet, to prevent them being sucked in with the sea water. However, Piper Alpha procedures dictated that the pumps be manual whenever divers were in the water, regardless of their location. This meant that the fire-fighting system was on manual on the evening of July 6.
21:45
Compressor B stopped suddenly and could not be restarted.
The entire power supply of the offshore construction work depended on this compressor. If the platform lost power the drill would stick, and incur enormous costs. The manager had only a few minutes to bring the compressor back online, otherwise the power supply would fail completely. A search was made through the documents to determine whether compressor A could be started.
21:52
The worksheet for the overhaul was found, but not the other sheet stating that the compressor must not be started under any circumstances due to the missing relief valve. The valve was in a different location from the compressor and therefore the worksheets were also kept in different folders, as they were sorted by location. None of those present were aware that a vital part of the machine had been removed. The manager assumed from the existing documents that it would be safe to start compressor A. The missing valve was not noticed by anyone, particularly since the metal plate replacing the valve was located several metres high and obscured by machine parts.
21:57
Compressor A was switched on.
Gas flowed into the compressor, and due to the missing relief valve produced an overpressure which the blanking plate did not withstand.Template:Ref Gas leaked out, caught fire and produced an explosion which probably killed two men immediately. The custodian pressed the emergency stop button. Now the valves of the enormous lines in the sea were closed, and oil and gas production stopped immediately. Theoretically the platform would have been isolated from the flow of oil and gas. Since the platform was originally built for oil, the firewalls were not designed to suppress explosions. The fire spread down the firewalls and destroyed some oil lines.
22:04
The control room was abandoned. Piper Alpha's design did not anticipate the possibility of the destruction of the control room. The platform's organisation failed and no attempt was made to use loudspeakers or to evacuate.
Personnel were trained to collect at lifeboat stations, but the fire prevented them from doing so. Instead men collected under the helicopter deck and awaited rescue. Wind, fire and smoke prevented landings. No further instructions were given and smoke filled the personnel block.
Two men undertook to restart the firefighting system and were not seen again.
The fire would have burnt out were it not being fed new oil, but both the Tartan and Claymore platforms were pumping oil into the network. Claymore continued pumping until the second explosion, because the manager had no permission from the Occidental control centre to shut down. Also the Tartan continued to pump, as its manager had received this directive from his superior. The reason for this procedure was the exorbitant cost of such a shut down. It takes several days to restart production after a stop, with substantial financial consequences.
Gas lines of 40 to 46 cm in diameter ran close to Piper Alpha. Two years earlier Occidental management ordered a study, which warned of the dangers of these gas lines. Due to their length and diameter it would take several hours to reduce their pressure, so that it would not be possible to fight a fire on them. Although the management admitted how devastating a gas explosion would be, Claymore and Tartan were not switched off with the first emergency call.
22:20
Tartan's gas line melted and broke. Three tonnes of gas pumped out each second and burnt. From this moment on the catastrophe was unavoidable.
22:30
The Tharos, a large fire fighting and rescue platform, anchored near to Piper Alpha. Attempts were made to extend walkway 30 metres.
22:50
The second gas line burst and exploded. The Tharos retreated due to the immense heat. After this second explosion the Claymore stopped pumping oil.
23:50
The generation and utilities Module (D) slipped into the sea, the largest part of the platform following it.
Aftermath
There is controversy about whether there was sufficient time for more effective evacuation. People were still getting off the platform several hours after the initial fires and explosions. The proximal problem was that most of the personnel who had the authority to order evacuation had been killed when the first explosion destroyed the control room. This was a consequence of design of the platform, including the absence of blast walls. Another contributing factor was that a nearby platform (the Tartan) continued to pump gas into the heart of the fire until its pipeline ruptured in the heat. The operations crew on the Tartan did not have authority to shut off production even though they could see that Piper Alpha was burning.
The nearby support vessel Lowland Cavalier reported the initial explosion just before 22:00, and the second explosion occurred just twenty two minutes later. By the time civil and military rescue helicopters reached the scene, flames over one hundred metres in height and visible as far as one hundred km (120 km from the Maersk Highlander) away prevented safe approach. Tharos, a specialist firefighting vessel, was able to approach the platform, but could not prevent its destruction.
Two crewmen from the Lowland Cavalier were killed when an explosion on the platform destroyed their "Fast Rescue Craft", which had recovered several survivors from the water. Tharos could not pump sufficient water to approach the burning platform until after the rupture of the Tartan pipeline, about two hours after the start of the disaster. Only once Tartan stopped pumping gas into the fire could Tharos come alongside. Tharos recovered no one that night.
The fire was eventually put out by a team led by famed firefighter Red Adair in which he had to battle 80mph winds and 70-foot waves.
The Cullen Enquiry was set up in November 1988 to establish the cause of the disaster. In November 1990, it concluded that the initial condensate leak was the result of maintenance work being carried out simultaneously on a pump and related safety valve. Piper Alpha's operator, Occidental, was found guilty of having inadequate maintenance procedures. A second phase of the enquiry made far-reaching safety recommendations, all of which were accepted by industry.
Practically all offshore workers in the North Sea would dispute the sincerity of the industry in some of their responses to the Cullen Report. Certainly the oil companies' response to Cullen's recommendation for full, organised worker representation has been less than full-hearted.
The wreck buoy marking the remains of the Piper is approximately 120 metres from the south-east corner of the replacement Piper Bravo platform. A lasting effect of the Piper Alpha disaster was the establishment of Britain's first "post-Margaret Thatcher" trade union, the Offshore Industry Liaison Committee.
A memorial sculpture, showing three oil workers, can be found in the Rose Garden within Hazlehead Park in Aberdeen. The sculptor is Sue Jane Taylor.
References
- Template:Note OPCAL’s share 36.5%, Texaco’s share 23.5%, Union Texas Petroleum’s share 20%, and Thomson’s share 20%. CAPLAN, section 1.2
- Template:Note by the end of 1976 and Claymore by the end of 1977, CAPLAN 1.2
- Template:Note 167 lives lost, 159 were British, 1 American. 61 aboard the platform survived, CAPLAN section 1.1. 167 people died, 62 people survived according to UKOOA
- Template:Note were not designed as blast protection walls and their function was to localise fire CAPLAN 2.6.1
- Template:Note leakage of condensate from a blind flange assembly at the site of a pressure safety valve CAPLAN volume 2 chapter 5 Causation 1
- Template:Note see dti's Brown Book 1998 pipeline dimensions and map of oil fields
External links
- {{cite web
| author=Caplan | url=http://www.scotcourts.gov.uk/opinions/piperappealindex.html | title=Appendix to Opinions (Lord Caplan) pgs 560-739 0/1261/5/1990 | accessdate=2005-12-18
}}
- {{cite web
| author=Caplan | url=http://www.scotcourts.gov.uk/opinions/Pipervol2.html | title=Appendix to Opinions (Lord Caplan) volume 2 chapter 5 Causation 1 | accessdate=2005-12-18
}}
- {{cite web
| author=UKOOA | url=http://www.ukooa.co.uk/issues/piperalpha/v0000864.htm | title=Piper Alpha - A Briefing | accessdate=2005-12-18
}}
- {{cite web
| author=Department of Trade and Industry (dti) | url=http://www.dbd-data.co.uk/bb1998/index.htm | title=Oil and Gas Resources of the United Kingdom Volume 2 1998 | accessdate=2005-12-18
}}
- {{cite web
| author=Department of Trade and Industry (dti) | url=http://www.og.dti.gov.uk/information/bb_updates/appendices/fields/piper.htm | title=Piper | accessdate=2005-12-18