What is Piper Alpha?

The Piper Alpha was a North Sea oil production platform operated by Occidental Petroleum (Caledonia) Ltd.^[1] It accounted for around ten per cent of the oil and gas production from the North Sea at the time. 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. Total insured loss was about ₤1.7 billion (US$ 3.4 billion). To date it is the world's worst offshore oil disaster in terms of lives lost and impact to industry.

Piper oilfield

Four companies that later transformed into the OPCAL joint venture obtained an oil exploration license in 1972 and discovered the Piper Field located at in early 1973 and commenced fabrication of 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 thirty 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 twenty 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.

Explosion

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 of the incident

A new gas pipeline was built in the weeks before the 6 July explosion, 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.

12:00 p.m.

Two Condensate pumps on the platform, designated A and B, compressed the gas for transport to the coast. On the morning of July 6, Pump A's pressure safety valve (PSV #504) was removed for routine maintenance. The pump's fortnightly overhaul was planned but had not started. The now open Condensate pipe was temporarily sealed with a flat metal disc. Because the work could not be completed by 6:00 p.m., the metal disc remained in place. The on-duty engineer filled out a permit which stated that Pump A was not ready and must not be switched on under any circumstances.

6:00 p.m.

The day shift ends and the night shift starts with 62 men running Piper Alpha. As he found the on-duty custodian busy, the engineer neglects to inform him of the condition of Pump A. Instead he places the permit in the control center and leaves. This permit disappeared and was not found. Coincidentally there was another permit issued for the general overhaul of Pump A that had not yet begun.

7:00 p.m.

Like many other offshore platforms, Piper Alpha had an automatic fire-fighting system, driven by both diesel and electric pumps (the latter of which were disabled by the initial explosions). The 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 in the water below the platform (approximately 12 hours per day during summer), the pumps 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.

9:45 p.m.

Condensate (LPG) Pump B stops suddenly and cannot be restarted.

The entire power supply of the offshore construction work depended on this pump. The manager had only a few minutes to bring the pump back online, otherwise the power supply would fail completely. A search was made through the documents to determine whether Condensate (LPG) Pump A could be started.

9:52 p.m.

The permit for the overhaul is found, but not the other permit stating that the pump must not be started under any circumstances due to the missing safety valve. The valve was in a different location from the pump and therefore the permits were stored in different boxes, 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 disc replacing the safety valve was located several metres above ground level and obscured by machinery.

9:55 p.m.

Condensate (LPG) Pump A is switched on. Gas flowed into the pump, and due to the missing safety valve produced an overpressure which the loosely fitted metal disc did not withstand.^[6]

Gas audibly leaks out at high pressure, drawing the attention of several men and triggering 6 gas alarms including the high level gas alarm, but before anyone can act, the gas ignites and explodes, blowing through the firewall made up of 2.5 x 1.5 metre panels bolted together, which were not designed to withstand explosions. 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, because the platform was originally built for oil, the firewalls were designed to resist fire rather than withstand explosions. The first explosion breaks up the firewall and dislodges panels around Module (B). One of the flying panels ruptures a small Condensate pipe, creating another fire.

10:04 p.m.

The control room is abandoned. Piper Alpha's design made no allowances for the destruction of the control room and the platform's organisation disintegrates. No attempt was made to use loudspeakers or to order an evacuation.

Emergency procedures instructed personnel to make their way to lifeboat stations, but the fire prevented them from doing so. Instead the men moved to the fireproofed accommodation block beneath the helicopter deck to await further instructions. Wind, fire and smoke prevented helicopter landings and no further instructions were given with smoke beginning to penetrate the personnel block.

As the crisis mounted, two men donned protective gear in an unsuccessful attempt to reach the diesel pumping machinery below decks and activate the firefighting system.

The fire would have burnt out were it not being fed new oil from both Tartan and the Claymore platforms, the resulting backpressure forcing fresh fuel out of ruptured pipework on Piper, directly into the heart of the fire. The Claymore continued pumping until the second explosion, because the manager had no permission from the Occidental control centre to shut down. Also the connecting pipeline to 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.

10:20 p.m.

Tartan's gas line (pressured to 120 Atmospheres) melts and bursts. From this moment on, the platform's destruction is assured. 15 - 30 tonnes of gas gets ejected out instantaneously and immediately ignites. Gas bursts out at ½ a tonne per second, equivalent to the entire domestic consumption of gas in the UK. A massive fireball at 150 metres in diameter engulfs Piper Alpha.

10:30 p.m.

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 apparent as the walkway extends too slowly to be able to reach the platform before 2250.

10:50 p.m.

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.

11:20 p.m.

The pipeline connecting Piper Alpha to the Claymore Platform bursts and the disaster claims its final victims.

11:50 p.m.

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

12:45 a.m., July 7

The entire platform has gone. Module (A) is all that remains of Piper Alpha.

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 main 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]

Legacy of Piper Alpha

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. Conversely, even on the company history page, the Occidental Petroleum website contains no reference to the Piper Alpha disaster.

Notes

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. ^  See The 40 most costly insurance losses - 1970-2005.
4. ^  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
5. ^  were not designed as blast protection walls and their function was to localise fire CAPLAN 2.6.1
6. ^  leakage of condensate from a blind flange assembly at the site of a pressure safety valve CAPLAN volume 2 chapter 5 Causation 1
7. ^  see dti's Brown Book 1998 pipeline dimensions and map of oil fields

References

External links

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