Although I usually let Dwight cover the catastrophic failure front, my visit to the Norwegian Petroleum Museum made me want to discuss something that wasn’t covered there (only mentioned in passing): the Piper Alpha disaster. Piper Alpha was not only the worst disaster to occur in the North Sea oil fields, it’s the worst oil-related disaster ever, with 167 men killed, and is an important lesson in cascading failure.
Also, it blew up real good:
That’s what happens when you start pumping 15-30 tons of natural gas into an existing fire every second.
Because the rig was completely destroyed, and most of the personnel on it killed, exactly how the disaster actually unfolded is unknown, but the official report reconstructs events.
Piper Alpha was originally an offshore oil rig that was converted to natural gas production. On July 6, 1988, technicians took one of two gas condensate pumps offline for routine safety valve maintenance, but weren’t able to complete repairs before a shift change, and thus left a temporary plate in place. Though they had filed paperwork to this effect, the information was not communicated properly to the next shift, and when the other pump failed, the crew activated the pump being repaired. This resulted in a high pressure gas leak when the temporary plate failed, and shortly thereafter by an ignition and explosion.
Though the rig had firewalls, because it was a former oil rig they were designed to contain fire, not explosions. Fire and smoke blocked access from the rig accommodations area to the lifeboats. The switch for the automated firefighting system was below deck and not activated, and the two crewman sent off to activate it were never seen again. The fire got so bad the control room was abandoned and no evacuation announcement was made over the rig’s loudspeakers. The fire would have gone out after the rig’s emergency shutdown switch was activated, except for the fact that Piper Alpha was being fed oil from two other nearby rigs. Worse still, Piper Alpha was still being fed pressured natural gas from two 24 to 36 inch pipes, which melted and burst in the fire, resulting in the huge fireball in the video above. (The gas feeds from the connected rigs hadn’t been shut off, but even if they had been, the lines were so pressurized that it would have taken hours for them to bleed off.) The explosion was so powerful it killed five rescued rig workers and two crewmen on the rescue ship, and guaranteed the complete destruction of Piper Alpha.
Time between the pump being switched on and the giant fireball: 25 minutes.
Only 59 rig workers survived.
Lots of factors contributed to Piper Alpha’s demise: multiple elements of poor design, an inadequate retrofit, inadequate lockout/tagout procedures, and insufficient safety and emergency training procedures. Together they resulted in a devastating series of cascading failures, creating a disaster far more deadly than any single one of them could have produced.