A standby condensate pump for reinjecting gas condensate into an oil export line on the Piper (Alpha) platform had been de-energised for maintenance. Its discharge pressure safety valve (PSV) was also removed and blind flange assemblies were fitted to the open PSV pipe connections. Meanwhile, the running condensate pump failed and would not restart. Liquid levels in the gas/liquid separation system were rising and would eventually trigger a total shutdown of the platform if not reversed. Night shift operators were aware the standby pump had been taken out of service for maintenance by the day shift but believed the work had not yet begun, so they decided to re-energise and start the standby pump. Gas condensate leaked from a PSV blind flange assembly; it found an ignition source and exploded. The explosion was soon followed by an oil pipe rupture and pool fire. The incident escalated rapidly as 3 high pressure gas lines ruptured after 20, 50 and 80 mins, respectively, creating a towering inferno. Smoke and flames outside the accommodation module made evacuation by helicopter or lifeboat impossible.

Basic Cause:
Loss of primary containment (LOPC) of hydrocarbon condensate due to overpressure of a temporary blind flange assembly after a pump undergoing maintenance was started in error.