At approximately 9:45 p.m., strong hydrocarbon odours were detected emanating from an oil depot’s sewer system. It was determined that the odours were caused by a petrol leak. The employees identified a flow of 1000 l of fuel from a wastewater discharge outlet valve. As the valve was leaky, the fuel flowed into the port’s network. The odours were also detected outside the site. The emergency services evacuated 23 employees from a nearby company, stopped the leak and dispersed the hydrocarbons.

A maintenance operation conducted a few days earlier was responsible for the event. On 24/12, an electrician intervened on the electrical cabinet of the vapour recovery unit (VRU). He was tasked with adding an alarm relay on the depot’s general supervisory system. During the intervention, however, the electrician mixed up the wiring. When an operator cleared an error on the supervisor on 29/12 at 7:30 a.m., the consequences of the faulty wiring appeared. The result was an uncontrolled opening of all the unit’s operating valves. The tanks and piping filled abnormally and overflowed into the containment area. The containment area was equipped with a gas detector, but it had been out of order since 29/12 at 1:45 a.m. Upon noticing the spillage, an operator closed the motorised wastewater discharge outlet valve, isolating the containment area. The leakage of this valve was detected at 10:30 a.m. during the search for the origin of the petrol in the sewers.

Initially, the operator reviewed the supervisory system’s wiring and replaced the faulty gas detector and the leaky valve. The safety loops were reinforced. The operator took several technical measures to prevent this type of incident from recurring. A gas detector was installed in the VRU. The hydrocarbon separator was equipped with a second high-level detection system, and a hydrocarbon detector and motorised valve were installed in the containment area. The motorised valves are controlled by the detection systems.