A boiler was put out of service on 11/6 for repairs and the gas supply pipes of the blast furnace and coking plant drained. Each of the pipes was insulated with a sliding gate valve. The first pipe was insulated. During operations on the second valve, and after moving the seats aside, the escaping gas ignited when the gate was sliding. The leak was stopped by closing the anti-rolling compressor valve of the hydraulic insulation penetration seal of the station. The fire was extinguished after four hours and thirty minutes. The significant damage (piping, valves, and building) was estimated at 2.5 MF. Since the accident, the procedure requires operations on the sliding gate valve with gas supply cut off.