Equinor (EQNR) said Tuesday that it has completed its investigation into a well control incident on the Deepsea Bollsta at the Troll field.

The Norwegian energy company said the leak occurred while cutting a casing at 510 meters, releasing gas and fluids onto the drill floor and shaker room.

Equinor said one worker suffered minor injuries during evacuation, and part of the ventilation system was damaged.

Safety systems, including the blowout preventer and diverter, were properly activated, stopping the flow within 71 seconds, the company said, adding about 930 kilograms of gas escaped, but ignition was prevented.

The company said the leak was caused because the blowout preventer was left open when the casing was cut, allowing confined gas to enter behind the casing.

Equinor said it has introduced a new rule requiring the blowout preventer to be closed during shallow casing cuts to prevent similar incidents.