A household heating oil spill was noticed around 7 am in a steel mill after scheduled shutdown of the hot rolling mill installation. The oil distribution circuit comprised 3 tanks placed in series. A 15-m³ above-ground tank was supplying by gravity a 3-m³ cistern, which itself was supplying via a motor-driven pump the 500-litre tank on a backup diesel-powered generator set. During the previous afternoon, technicians had observed that this 500-litre tank had been emptied upon unpriming the electric pump, yet they were unable to resolve the problem. The night shift overcame this operational deficiency by manipulating the 3-m³ tank’s “backup” valve. A fuel oil smell was detected but no correlation drawn with the pump restart; instead, technicians thought that the emanations had stemmed from a bin used during hot rolling mill maintenance works. The spill in the vicinity of the 3-m³ tank was in fact discovered by the morning shift after noticing that the 15-m³ tank had been emptied. Fearing a pollution incident in the installation’s cooling network, dams were set up on the water settling basins and valves discharging to the docks were closed; a monitoring programme was also implemented. The 6 m³ of spilled fuel oil routed to a retention basin were pumped and stored in 6 large bulk containers before reuse in the plant’s waste streams. No water or soil pollution was detected. The facility’s cooling water circuits were not affected and no consequences observed in the biocide treatments against Legionella.
Several deficiencies had caused this accident, namely: malfunction of the motor-driven pump, inability to close the backup valve between the 15-m³ and 3-m³ tanks after handling, technicians’ poor knowledge of the installations, inadequate valve references, and the lack of tank filling instructions. The mill operator proceeded by: updating the heating oil distribution plan, identifying the various valves, and scheduling personnel information sessions.