Twenty two minutes that changed history

02 June 2008

Twenty years ago this month, 167 people died in a North Sea platform fire making Piper Alpha the worst offshore disaster on record. Most of the victims suffocated in toxic fumes, which developed after a gas leak set off the blasts and sparked the fire. The whole accident took place in just 22 minutes – the time it took to change the way the hazardous area industry has treated potential incidents ever since.

Piper Alpha destroyed

It did, however, take two years for the inquiry into the disaster to complete its comprehensive investigation and in November 1990, Lord Cullen's inquiry published its report, which severely criticised safety procedures on the platform without laying blame at the door of any individuals involved. A civil action over insurance payments in 1997 found that two workers, who died in the disaster, had been negligent; although these findings have since been contested both by relatives of the men concerned and television documentary investigations.

The report prompted a complete safety review of offshore operations, which in turn led to a fundamental change in the way the hazardous area industry approaches safety matters. Much of the safety culture, which has developed since the Cullen Report, has been incorporated into health and safety legislation and European equipment directives including ATEX.

Serious incidents involving explosion and fire are usually the result of a series of erroneous coincidences, which when combined with an ageing and often unsafe design result in disaster. The Piper Alpha incident began with a routine maintenance procedure. On the morning of July 6th, a pressure safety valve on a backup propane condensate pump in the processing area was being checked. This work could not be completed by that evening and the maintenance crew received permission to complete the job the next day. With the valve removed, the open pipe was sealed with a plate.

During the next shift, the primary condensate pump failed. Operators present were unaware that the valve had been removed and decided to start the backup pump. Excess pressure burst the blanking plate and gases escaped through the hole left by the valve. Gas audibly leaked out at high pressure, ignited and exploded, blowing through the firewalls. The fire spread through the damaged firewalls, destroyed some oil lines and soon large quantities of stored oil were burning out of control. The automatic deluge system, which was designed to spray water on such a fire in order to contain it or put it out, was never activated because it had been switched to manual mode.

Divers had been working on the seabed near the deluge system’s intake so it was deemed unsafe to leave the system in automatic. Because of the failure of the firewalls, access to the deluge system control panel was cut off and operators could not manually start up the fire system.

The blaze soon became hot enough to weaken and then burst the 36in gas risers, which contained flammable gas products at 2000lb/in2. When these risers burst, the resulting jet of fuel dramatically increased the size of the fire.

Lack of operator training caused people repeatedly to open and shut doors on the accommodation modules, which worsened the smoke problem. Conditions got so bad in the accommodation area that some people realised that the only way to survive would be to escape the station immediately. They, however, found that smoke and flames blocked all routes to lifeboats, and in the lack of any other instructions, they made the jump into the sea hoping to be rescued by boat. Sixty-two men were saved in this fashion. Most of the fatalities, left on board, suffered carbon monoxide poisoning or suffocation from the fumes in the accommodation area.

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