At around 11:30 a.m., a flash in the presence of petrol fumes occurred inside the manhole of one of the three compartments (two containing SP95 and one containing E10) of a 60 m³ underground fuel tank at the petrol station of a hypermarket. The contractor in charge of cleaning the tank was seriously burnt and died of his injuries two months later. The firefighters put up a 20 m safety cordon around the storage tank. The petrol station, open at the time of the accident, was closed. A nearby auto repair shop was also closed. The firefighters inerted the compartment by filling it with water. They left at around 3:00 p.m. after testing the air with an explosimeter and finding nothing. The inspection authorities for classified facilities conducted an investigation. The explosion was limited to the volume of the manhole and did not damage the inside the tank or create excess pressure. Just before the accident occurred, the contractor had started pumping oil sludge out of the bottom of the compartment with a hose connected to a road tanker.

When the explosive atmosphere ignited, the contractor was on an aluminium ladder inside the tank’s manhole. As he removed the ladder from the manhole, an electric arc formed between the ladder and the road tanker, which was parked too closely nearby. The lack of an equipotential bonding connection between the vehicle, the tank, and the ladder is what caused the electrostatic spark that ignited the flammable cloud. The inspection authorities for classified facilities also noted that the road tanker was parked within the safety perimeter (3 m). Inadequate ‘degassing’ of the atmosphere in the manhole and failure to plug the fuel transfer pipes (unloading and distribution) may have allowed flammable fumes remaining in the tank to flow back. The contractor did not have an explosimeter on him to check for the presence of an explosive atmosphere (ATEX).

The prefect made the service station’s reopening contingent on checking the integrity of the tank and authorised the operator to use an acoustic method with vacuum pressure (instead of a hydrostatic test) to check this. The prefect also asked the operator to inform the inspection authorities for classified facilities about the measures implemented to improve the checking and monitoring of contractors working at the service station.

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