A ship discharged its cargo of SP95 petrol into a petrol station: tank 4 needed to take 1,100 m³ of the product with the remaining 800 m³ being channelled to tank 5. Unloading was in progress when the high level alarm indicated that the first tank was nearly full. The technicians responsible for the operation opened the valves of tank 5 and closed those of no.4 to initiate a tank-to-tank transfer and thus reduce the level of tank 4. They then noted that 500 litres of petrol overflowed through the inlets located at the top of the tank shell in retention tank no. 4. They activated the fire extinction system to: clean the pressure envelope polluted by water flowing from the cooling crown; keep the product on the surface of the sub-tank; and direct it quickly to the PED system and onto the decanter. The retention basin floor was polluted to a depth of 5 cm over a surface area of approximately 200 m² at the foot of tank no. 4. During the following days, staff stripped the contaminated topsoil and an expert took samples to characterise and map out the pollution. The soil contaminated deeper down was to be excavated. The monitoring of piezometers was reinforced in order to detect possible impacts on groundwater. The Classified Facilities Inspectorate was informed.

This accident resulted from several failures: the “stop pumping” safety mechanism was inactive following work carried out on the wharf; the level of probes were fixed by the surveyor without taking into account the tank inlets; poor risk assessment by staff (one of two plant technicians should have remained to monitor the manifold and tank).

The operator instructed specialised companies to correct the probe positioning, with support and supervision of the headquarters’ technical service, as well as to repair the “stop pumping” connection. The operator defined the following corrective measures: review and communicate specific instructions for receiving product at the depot, develop an awareness programme for technicians of the risks and required vigilance; set up an additional and direct link between the operations office and the ship by purchasing ATEX compliant mobile phones; and establishment of a VHF link between the depot and the control room of the ship’s pumps. Moreover, the operator transmitted the experience feedback of this accident to all staff and the group responsible for this depot.