Piper Alpha

The Piper Alpha was a North Sea oil production platform operated by Occidental Petroleum (Caledonia) Ltd.^[1] It produced around 10 percent of the then oil and gas production from the North Sea. The platform began production in 1976^[2], 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. To date it is the world's worst offshore oil disaster.

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 58° 28’ N 0° 15’ E, 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.^[3] 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.^[4] 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 62 crewmembers survived out of 229 on board that day, 167 perished ^[5]

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.

1800 hours

As he found the on-duty custodian busy, the engineer omitts to inform him of the condition of compressor A. Instead he places the worksheet in the control center and leaves. This sheet disappeared and was not found. Coincidentally there was another worksheet for the general overhaul of compressor A that had not yet begun.

1900

Like 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.

2145

Compressor B stops suddenly and cannot 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.

2152

The worksheet for the overhaul is 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.

2157

Compressor A is switched on. Gas flowed into the compressor, and due to the missing relief valve produced an overpressure which the blanking plate did not withstand.^[6]

Gas audibly leaks out at high pressure, drawing the attention of several men, but before anyone can act, the gas ignites and explodes, probably killing two men immediately and blowing through the firewalls. The custodian presses the emergency stop button; closing huge valves in the sea lines and ceasing all oil and gas production.

Theoretically, the platform would now have been isolated from the flow of oil and gas and the fire relatively contained. However, since the platform was originally built for oil, the firewalls were not designed to suppress explosions. The fire spreads through damaged firewalls and destroys some oil lines.

2204

The control room is abandoned. Piper Alpha's design did not anticipate the possibility of the destruction of the control room and the platform's organisation disintegrates. No attempt was made to use loudspeakers or to order an evacuation.

Personnel were trained to collect at lifeboat stations, but the fire prevented them from doing so. Instead men muster in the fireproofed accommodation block beneath the helicopter deck and await further instructions. Wind, fire and smoke prevented landings. No further instructions are given and smoke slowly begins to fill the personnel block.

As the crisis mounts, two brave men don protective gear and try to reach the diesel pumping machinery below decks and activate the firefighting system. They do not make it and are never seen again.

The fire would have burnt out were it not being fed new oil from both the Tartan and Claymore platforms, the resulting backpressure forcing fresh fuel out of ruptured pipework on Piper, directly into the heart of the fire. 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 fueled by them. Although the management admitted how devastating a gas explosion would be, Claymore and Tartan were not switched off with the first emergency call.

2220

Tartan's gas line melts and bursts. From this moment on, the platform's destruction is assured. Three tonnes of gas pump out each second and immediately ignite. Huge fireballs roll into the sky from Piper's deck.

2230

The Tharos, a large fire fighting and rescue platform, draws alongside Piper Alpha. Attempts are made to extend its rescue walkway the 30 metres to the deck. A woeful design flaw in Tharos becomes appartent as the walkway extends too slowly to be able to reach the platform before 2250.

2250

The second gas line ruptures, spilling millions of litres of gas into the conflagration. Huge flames shoot over three hundred feet in the air. The Tharos is driven off due to the fearsome heat, which begins to melt the surrounding machinery and steelwork. It was after this second explosion that the Claymore stopped pumping oil. Personnel still left alive are either desperately sheltering in the scorched, smoke-filled accommodation block or leaping from the deck some 200ft into the rough, undulating North Sea.

2350

The generation and utilities Module (D), which includes the fireproofed accommodation block, slips into the sea. The largest part of the platform follows it.

Aftermath

There is controversy about whether there was sufficient time for more effective emergency 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 claims he had to battle 80 mph winds and 70-foot waves.[7]

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.

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

1. ^ 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
2. ^ by the end of 1976 and Claymore by the end of 1977, CAPLAN 1.2
3. ^ 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
4. ^ were not designed as blast protection walls and their function was to localise fire CAPLAN 2.6.1
5. ^ leakage of condensate from a blind flange assembly at the site of a pressure safety valve CAPLAN volume 2 chapter 5 Causation 1
6. ^ see dti's Brown Book 1998 pipeline dimensions and map of oil fields Pf

External links

• Caplan. "Appendix to Opinions (Lord Caplan) pgs 560-739 0/1261/5/1990". Retrieved 2005-12-18.
• Caplan. "Appendix to Opinions (Lord Caplan) volume 2 chapter 5 Causation 1". Retrieved 2005-12-18.
• UKOOA. "Piper Alpha - A Briefing". Retrieved 2005-12-18.
• Department of Trade and Industry (dti). "Oil and Gas Resources of the United Kingdom Volume 2 1998". Retrieved 2005-12-18.
• Department of Trade and Industry (dti). "Piper". Retrieved 2005-12-18.
• BBC News. "On This Day". Retrieved 2006-07-06.