The Piper Alpha oil rig exploded and burned in the North Sea on July 6, 1988, killing 167 men. This accident highlighted many lapses in safety inspection, procedures, and attitudes prevalent at the time. It remains the world’s worst offshore oil disaster, both in terms of deaths and cost. The insured loss reached $3.4 billion.
The Piper Alpha oil rig was built in 1976 to exploit the Piper oilfield in the North Sea. It was a heavy rig, one of the largest of its kind. By 1980 the rig was modified to also recover and pump gas from the field. A 76 cm oil pipe extended from Piper Alpha 206 km to the Flotta terminal; 2 46 cm gas pipelines connected Piper Alpha to two other rigs in the area.
Piper Alpha had two pumps to compress gas. Pump A was undergoing maintenance on July 6, and a pressure safety valve was removed. The valve could not be replaced by day’s end, so the hole was covered with a metal disc. Paperwork on the pump’s out-of-service condition was deposited in the control room – not into the hands of the controller, who was busy. This paperwork disappeared.
At 9:45 pm the second pump failed; in order to avoid a costly shutdown Pump A needed to be started. The on-duty controllers could find no reason not to start Pump A, so they switched it on. The metal disc ruptured under the load, spewing gas, which immediately ignited.
The explosion ruptured firewalls which were designed to withstand oil fires, but not gas explosions, and were not retrofitted when the rig was modified to accept gas. The control room shut down the rig, but the explosion had sent a firewall into the next module, rupturing another line and starting another fire. The control room was abandoned. No evacuation order was given, and no other provision for order and authority existed.
Diesel firefighting equipment that sucked seawater onto the rig, usually automatically in case of fire, had been turned to manual control that day because of divers in the area. Lifeboats were inaccessible. Workers fled to the fireproofed accommodation room and locked themselves in to wait for orders that never came.
Controllers on the two rigs with connected pipelines to Piper Alpha saw the fire, but did not shut down their lines – shutdowns were costly, and they had received no orders to do so. The connecting gas fed the fire. A 140 cm undersea gas pipe which ran too close to the rig ruptured, creating a 150-meter diameter fireball which engulfed the rig.
Rescue efforts were sporadic. Helicopters could not reach the rig through the smoke and flames. The tharos rescue platform had to withdraw due to the intense heat. Several fast rescue boats managed to pull survivors from the North Sea, but one got too close and lost lives in an explosion.
By 11:50 pm the bulk of the rig, including the accommodation room, fell into the sea. Today the site of the wreck is marked by a buoy, close to the new rig, Piper Bravo.