Piper Alpha oil platform disaster

 BBCThe Piper Alpha platform ablaze. Source: BBCPiper Alpha was a North Sea oil production platform operated by Occidental Petroleum (Caledonia) Ltd. The platform began production in 1976, 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 both of lives lost and impact to industry. At the time of the disaster the platform accounted for around ten percent of the oil and gas production from the North Sea.

Background

The Piper Field was discovered by Occidental in January 1973, with the Piper Alpha platform becoming operational in 1976. Located about 120 miles north-east of Aberdeen, the platform initally produced crude oil. In late 1980, gas conversion equipment was installed allowing the facility to produce gas as well as oil. A sub-sea pipeline, shared with the Claymore platform, connected Piper Alpha to the Flotta oil terminal on the Orkney Islands. Piper Alpha also had gas pipelines connecting it to both the Tartan platform and to the separate MCP-O1 gas processing platform. In total, Piper Alpha had four main transport risers: an oil export riser, the Claymore gas riser, the Tartan gas riser and the MCP-01 gas riser.

Explosion and Fire

On 06 July 1988, work began on one of two condensate-injection pumps, designated A and B, which were used to compress gas on the platform prior to transport of the gas to Flotta. A pressure safety valve was removed from compressor A for recalibration and re-certification and two blind flanges were fitted onto the open pipework. The dayshift crew then finished for the day.

During the evening of 06 July, pump B tripped and the nightshift crew decided that pump A should be brought back into service. Once the pump was operational, gas condensate leaked from the two blind flanges and, at around 2200 hours, the gas ignited and exploded, causing fires and damage to other areas with the further release of gas and oil. Some twenty minutes later, the Tartan gas riser failed and a second major explosion occurred followed by widespread fire. Fifty minutes later, at around 2250 hours, the MCP-01 gas riser failed resulting in a third major explosion. Further explosions then ensued, followed by the eventual structural collapse of a significant proportion of the installation.

167 men died as a result of the explosions and fire on board the Piper Alpha, including two operators of a Fast Rescue Craft. 62 men survived, mostly by jumping into the sea from the high decks of the platform. Between 1988 and 1990, the two-part Cullen Inquiry established the causes of the tragedy and made recommendations for future safety regimes offshore. 106 recommendations were made which were subsequently accepted and implemented by the offshore operators.

Most of those who died on Piper Alpha did so in the galley, waiting for helicopters that were prevented from landing by flames and thick smoke. Around 100 men gathered there amid growing panic and chaos. After 15 minutes, the emergency lighting went off and the room was dark except for the glow from fires licking the windows. One survivor described the galley as being "like a pot sitting on top of a gas stove". It was so hot that people cooled themselves with water from the fish tanks or squeezed tomatoes over their skin.

When smoke began to smother the room, men were forced to crawl along the floor, seeking an inch or two of clear air, wet towels wrapped around their faces as protective masks. In late 1988, after this part of Piper Alpha was recovered from the sea bed, the bodies of 87 men were found inside.

Timeline of Events

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 centre 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 were designed to suck in large amounts of sea water in order to extinguish any fires. These pumps had an automatic control which would start them in case of fire. However, the fire-fighting system was under manual control on the evening of July 6. Piper Alpha procedures required manual control of the pumps whenever divers were in the water (as they were approximately 12 hours per day during summer) regardless of their location, to prevent divers from being sucked in with the sea water. (Fire pumps on other platforms were switched to manual control only if the divers were close to the inlet.)

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 was 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.

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 attempt to reach the diesel pumping machinery below decks and activate the firefighting system. They are never seen again.

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 140 to 146 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 are released instantaneously and immediately ignite. A massive fireball of 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 22:50.

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 200 ft (61 m) into the cold, rough 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.

Trauma

Professor David Alexander, director of the Aberdeen Centre for Trauma Research at Robert Gordon University, led the psychiatric team that investigated the long-term psychological effects of Piper Alpha. Thirty-six survivors agreed to give interviews or complete questionnaires. Of this group, almost all reported psychological problems. Twenty-eight said they had difficulty in finding employment following the disaster; one reason seems to be that some offshore employers regarded Piper Alpha survivors as Jonahs – bringers of bad luck who would not be welcome on other rigs and platforms. More than 70% of those interviewed said they had feelings of acute guilt; many felt they should not have survived when equally or more deserving workmates perished. Some of these people went on to play what Alexander describes as "Russian roulette" with their lives – driving fast and recklessly, taking up dangerous jobs or sports. "Unconsciously, they may be looking for ways to be punished for the fact that they came through relatively unharmed while their loved ones died."

Sources

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