An analysis of the fire on board the drilling rig West Vanguard in 1985

Late in the evening on October 6 1985 an uncontrolled flammable gass blowout occurred with subsequent explosion and fire on board the drilling rig West Vanguard. The rig was in operation at Haltenbanken at the time, and the blowout happened when the bit entered a shallow gas pocket.

The crew, with exception of one, was evacuated in the foremost life boats in few minutes. One man was missing and was never found.

West Vanguard was later towed from Haltenbanken to Freifjorden outside of Kristiansund, where Nordmøre police headquarters took over the responsibility. The chief constable at Nordmøre police headquarters requested SINTEF for expert advice in connection with the investigations of the accident on board.
A group of 5 persons was established and the group was on board the drilling rig twice during November. The task was to find where the fire/explosion started, the ignition source and describe the fire development.

Possible course of events

Gas leakages from the gasket between the riser and the Slip-joint, together with the later Diverter System collapse, created a gas cloud on Cellar Deck level (Main Deck). Gas flowing into Shale Shaker Room through a poorly closed valve could diverge to other rooms through the exhaust pipe, across Upper Deck and into the other rooms through the air ducts.
Drilling mud had splashed into the Shale Shaker Room through a puncture in the bulkhead close to the Flow Line inlet. The flow of gas/mud/sand had made a hole through the steel pipe material in Flow Line. Punctures were also found close to two bends in the gas diversion system. The flow of gas/mud/sand had managed to make holes here as well. Spurt of sand may create sparks when sand strike steel, and can be a possible ignition source.
Doors and hatches in and around the drilling module abaft on Upper Deck were knocked open in a pattern that gave indications on the course of explosions.

Based on the possibility of gas diffusion, the damage, the corroborating calculations, the position of the doors and the testimonies, the investigators concluded with two possible alternative course of events.

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