What happened to the West Vanguard drilling rig?

On 6 October 1985 a drilling brake occurred - the operator pulled back the drill from some 15m below the seabed, resulting in a flow of gas.

Several attempts to block the hole failed and so a decision was made to divert the flow to a catchment system. This system was unable to contain the flow, resulting in the liberated gas exploding at around 23:30 pm, engulfing the rig into a fireball.

The resulting over-pressures and intense heat damaged the rig extensively. Tragically one man remained unaccounted for and is believed to have lost his life in the incident.

What can the industry learn from the West Vanguard drilling rig blowout?

Following the incident the rig was towed to Freifjorden near Kristiansund, Norway where a fire investigator discovered that gas initially leaked from the gasket between the riser and the slip-joint. This formed a gas cloud on the cellar deck level that then migrated into the shaker house via a poorly closed valve and travelled through an exhaust pipe, across the upper deck and into other rooms via air ducts before igniting.

Doors and hatches in and around the drilling module on the upper deck were knocked open in a pattern that gave indications to the course of explosions.

The failure of the diverter system was attributed to the extreme flow of gas, drilling mud and sand, which eroded holes in pipe bends of the diverter system. Spurts of sand against the metal of the rig were suggested as one of the possible ignition sources of the gas cloud.