Piper Alpha was a North Sea oil production platform operated by Occidental Petroleum (Caledonia) Ltd. The platform began production in 1976, first as an oil-only platform and later converted to add gas production. An explosion, and the resulting oil and gas fires, destroyed it on 6 July 1988, killing 167, including two crewmen of a rescue vessel; 61 survived. The total insured loss was about £1.7 billion (US$3.4 billion). At the time of the disaster, the platform accounted for approximately ten percent of North Sea oil and gas production, and the accident was the worst offshore oil disaster in terms of lives lost and industry impact.
Timeline of the incident
During the late 1970s, major works were carried out to enable the platform to meet UK Government gas export requirements and after this work had been completed, Piper Alpha was operating in what was known as phase 2 mode (operating with the Gas Conservation Module (GCM)) since the end of 1980 up until July 1988; phase 2 mode was its normal operating state. In the late 1980s, major construction, maintenance and upgrade works had been planned by Occidental and by July 1988, the rig was already well into major work activities, with six major projects identified including the change-out of the GCM unit which meant that the rig had been put back into its initial phase 1 mode (i.e. operating without a GCM unit). 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. Therefore, Piper continued to export oil at just under 120,000 barrels per day and to export Tartan gas at some 33 MMSCFD (million standard cubic feet per day) during this demanding period.
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.
12:00 noon Two condensate pumps, designated A and B, displaced the platform's condensate for transport to the coast. On the morning of 6 July, Pump A's pressure safety valve (PSV #504) was removed for routine maintenance. The pump's two-yearly overhaul was planned but had not started. The open condensate pipe was temporarily sealed with a disk cover (flat metal disc also called a blind flange or blank flange). Because the work could not be completed by 6:00 p.m., the disc cover remained in place. It was hand-tightened only. The on-duty engineer filled in 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 ended, and the night shift started with 62 men running Piper Alpha. As he found the on-duty custodian busy, the engineer neglected to inform him of the condition of Pump A. Instead he placed the permit in the control centre and left. 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 were disabled by the initial explosions). The diesel pumps were designed to suck in large amounts of sea water for fire fighting; the pumps had an automatic control to start them in case of fire (although they could not be remotely started from the control room in an emergency). However, the fire-fighting system was under manual control on the evening of 6 July: the Piper Alpha procedure adopted by the Offshore Installation Manager (OIM) required manual control of the pumps whenever divers were in the water (as they were for approximately 12 hours a day during summer) although in reality, the risk was not seen as significant for divers unless a diver was closer than 10–15 feet (3–5 m) from any of the four 120 feet (40 m) 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 developed or implemented.
9:45 p.m. Because of problems with the methanol system earlier in the day, methane clathrate (a flammable ice) had started to accumulate in the gas compression system pipework, causing a blockage. Due to this blockage, condensate (natural gas liquids NGL) Pump B stopped and could not be restarted. As 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 Pump A could be started.
9:52 p.m. The permit for the overhaul was 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 Pump A. The missing valve was not noticed by anyone, particularly as the metal disc replacing the safety valve was several metres above ground level and obscured by machinery.
9:55 p.m. First Explosion Condensate Pump A was switched on. Gas flowed into the pump, and because of the missing safety valve, produced an overpressure which the loosely fitted metal disc did not withstand.
Gas audibly leaked out at high pressure, drawing the attention of several men and triggering six gas alarms including the high level gas alarm. Before anyone could act, the gas ignited and exploded, blowing through the firewall made up of 2.5 by 1.5 m (8 by 5 ft) panels bolted together, which were not designed to withstand explosions. The custodian pressed the emergency stop button, closing huge valves in the sea lines and ceasing all oil and gas extraction.
Theoretically, the platform would then have been isolated from the flow of oil and gas and the fire contained. However, because the platform was originally built for oil, the firewalls were designed to resist fire rather than withstand explosions. The first explosion broke the firewall and dislodged panels around Module (B). One of the flying panels ruptured a small condensate pipe, creating another fire.
10:04 p.m. The control room of Piper Alpha was abandoned. "Mayday" was signalled via radio by radio operator David Kinrade. Piper Alpha's design made no allowances for the destruction of the control room, and the platform's organisation disintegrated. 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 many of 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 seep into the personnel block.
As the crisis mounted, two men donned protective gear and attempted to reach the diesel pumping machinery below decks and activate the firefighting system. They were never seen again.
The fire would have burnt out were it not being fed with oil from both Tartan and the Claymore platforms, the resulting back pressure forcing fresh fuel out of ruptured pipework on Piper, directly into the heart of the fire. The Claymore platform continued pumping oil until the second explosion because the manager had no permission from the Occidental control centre to shut down. Also, the connecting gas pipeline to Tartan continued to pump, as its manager had been directed by his superior. The reason for this procedure was the huge cost of such a shut down. It would have taken several days to restart production after a stop, with substantial financial consequences.
Gas pipelines of both 16 in (41 cm) and 18 in (46 cm) diameter ran to Piper Alpha. Two years earlier Occidental management ordered a study, the results of which warned of the dangers of these gas lines. Because of their length and diameter, it would have taken several hours to reduce their pressure, which meant fighting a fire fuelled by them would have been all but impossible. Although the management admitted how devastating a gas explosion would be, Claymore and Tartan were not switched off with the first emergency call.
10:05 p.m. The Search and Rescue station at RAF Lossiemouth receives the first call notifying them of the possibility of an emergency, and a No. 202 Sqn Sea King helicopter, "Rescue 138", takes off at the request of the Coastguard station at Aberdeen. The station at RAF Boulmer is also notified, and a Hawker Siddeley Nimrod from RAF Kinloss is sent to the area to act as "On-Scene Commander" and "Rescue Zero-One".
10:20 p.m. Tartan Gas Line Rupture Tartan's gas line (pressurised to 120 Atmospheres) melted and ruptured, releasing 15-30 tonnes of high pressure gas every second, which immediately ignited. From that moment on, the platform's destruction was assured.
10:30 p.m. The Tharos, a large semi-submersible fire fighting, rescue and accommodation vessel, drew alongside Piper Alpha. The Tharos used its water cannon where it could, but it was restricted, because the cannon was so powerful it would injure or kill anyone hit by the water.
10:50 p.m. MCP-01 Gas Line Rupture The second gas line ruptured (the riser for the MCP-01 platform), ejecting millions of cubic feet of gas into the conflagration and increased its intensity. Huge flames shot over 300 ft (90 m) in the air. The Tharos was driven off by the fearsome heat, which began to melt the surrounding machinery and steelwork. It was only after this explosion that the Claymore platform stopped pumping oil. Personnel still left alive were either desperately sheltering in the scorched, smoke-filled accommodation block or leaping from the various deck levels, including the helideck, 175 ft (50 m) into the North Sea. The explosion also killed two crewmen on a fast rescue boat launched from the standby vessel Sandhaven and the six Piper Alpha crewmen they had rescued from the water.
11:18 p.m. Claymore Gas Line Rupture The gas pipeline connecting Piper Alpha to the Claymore Platform ruptured, adding even more fuel to the already massive firestorm that engulfed Piper Alpha.
11:35 p.m. Helicopter "Rescue 138" from Lossiemouth arrives at the scene.
11:37 p.m. Tharos contacts Nimrod "Rescue Zero-One" to appraise him of the situation. A standby vessel has picked up 25 casualties, including three with serious burns, and one with an injury. Tharos requests the evacuation of its non-essential personnel to make room for incoming casualties. "Rescue 138" is requested to evacuate 12 non-essential personnel from Tharos to transfer to Ocean Victory, before returning with paramedics.
11:50 p.m. With critical support structures burned away, and with nothing to support the heavier structures on top, the platform began to collapse. One of the cranes collapsed, followed by the drilling derrick. The generation and utilities Module (D), which included the fireproofed accommodation block, slipped into the sea, taking the crewmen huddled inside with it. The largest part of the platform followed it. "Rescue 138" lands on Tharos and picks up the 12 non-essential personnel, before leaving for Ocean Victory.
11:55 p.m. "Rescue 138" arrives at Ocean Victory and lands the 12 passengers before returning to Tharos with 4 of Ocean Victory's paramedics.
00:07 a.m., 7 July "Rescue 138" lands paramedics on Ocean Victory.
00:17 a.m. "Rescue 138" winches up serious burns casualties picked up by the Standby Safety Vessel, MV Silver Pit.
00:25 a.m. First seriously-injured survivor of Piper Alpha is winched aboard "Rescue 138".
00:45 a.m. The entire platform had gone. Module (A) was all that remained of Piper Alpha.
00:48 a.m. "Rescue 138" lands on Tharos with three casualties picked up from MV Silver Pit.
00:58 a.m. Civilian Sikorsky S-61 helicopter of Bristow Helicopters arrives at Tharos from Aberdeen with Medical Emergency Team.
01:47 a.m. Coastguard helicopter land on Tharos with more casualties.
02:25 a.m. First helicopter leaves Tharos with casualties for Aberdeen Royal Infirmary.
03:27 a.m. "Rescue 138" lands on Tharos with the bodies of two fatalities. "Rescue 138" then leaves to refuel on the drilling rig Santa Fe 140.
05:15 a.m. "Rescue 137" arrives at Tharos and after landing, then leaves taking casualties to Aberdeen.
06:21 a.m. Uninjured survivors of Piper Alpha leave Tharos by civilian S-61 helicopter for Aberdeen.
07:25 a.m. "Rescue 138" picks up remaining survivors from Tharos for transfer to Aberdeen.
At the time of the disaster 226 people were on the platform; 165 died and 61 survived. Two men from the Standby Vessel Sandhaven were also killed.
There is controversy about whether there was sufficient time for more effective emergency evacuation. 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 the platform design, which did not include blast walls. Another contributing factor was that the nearby connected platforms Tartan and Claymore continued to pump gas and oil to Piper Alpha until its pipeline ruptured in the heat in the second explosion. Their operations crews did not believe they had authority to shut off production, even though they could see that Piper Alpha was burning.
The nearby diving support vessel Lowland Cavalier reported the initial explosion just before 10:00 pm, and the second explosion occurred twenty two minutes later. By the time civil and military rescue helicopters reached the scene, flames over 100 metres in height and visible as far away as 100 km (120 km from the Maersk Highlander) away prevented safe approach. The largest number of survivors (37 out of 59) were recovered by the Fast Rescue Boat of the Standby Safety Vessel, MV Silver Pit; coxswain James Clark later received the George Medal. Others awarded the George Medal were Charles Haffey from Methil , Andrew Kiloh from Aberdeen, and James McNeill from Oban.
The blazing remains of the platform were eventually extinguished three weeks later by a team led by firefighter Red Adair, despite reported conditions of 80 mph (130 km/h) winds and 70-foot (20 m) waves. The part of the platform which contained the galley where about 100 victims had taken refuge was recovered in late 1988 from the sea bed, and the bodies of 87 men were found inside.