An escape of diesel oil has been confirmed as the cause of the Sleipner A platform fire on Sunday 18 October.
The leak resulted from an unfortunate technical solution and faulty adjustment of valves in the diesel supply system, according to operator Statoil's internal inquiry.
This investigation has been headed by Finn Strand, manager for the health, environment and safety sector in Oil Operations.
His team's findings indicate that diesel oil escaped through an air vent leading to the roof of a generator module from a 1,000-litre tank inside.
The leak lasted for almost 30 minutes, with 5-6,000 litres of oil flowing off the module and down between this structure and the living quarters to the generator exhaust channel.
Since the channel's expansion bellows is not insulated at one point, surface temperatures there reach around 300 degrees C - high enough to ignite diesel oil.
The leak became possible because a valve had not been re-set to the open position after another operation had been completed.
When diesel then was to be pumped into a supply ship on Sunday, oil entered the 1,000-litre tank as well and quickly filled it to overflowing.
The overfill prevention system in the tank has been poorly designed because the metering device may show too low a level when the contents are actually overflowing.
Combining this with a source of ignition in the neighbourhood sparked Sunday's fire.