Pollution
Humain
Environnement
Economique

At 1 p.m., an employee noticed a rather large oil spill in a thermal power plant. It was determined that a submersible pump had discharged the hydrocarbons into the rainwater system. The employee stopped the pump and raised the alarm. The release, estimated at 100 m³, spread under a photovoltaic panel installation located on the site. The spillage resulted from the overflow of a fuel oil tank.

The context of the incident was unusual. Operations at the plant had been severely disrupted by a strike that had been going on for ten days. The strikers were restricting access to only the requisitioned operating crews.

On the day before the event, in preparation of a ship unloading operation, alignment operations were performed on a fuel oil tank. A lockout system was set up, based solely on a visual position report. During the night, the position of several valves was modified. Two tanks were connected, leading to gravity filling of the fuel oil tank. This tank is equipped with a high-level and a very-high-level sensor. Both sensors activate visual and audible alarms. Only the visual alarms were activated in the control room; the audible alarms were out of service. The operators in the control room had not seen the visual alarms, and the tank overflowed.

The fuel oil flowed from the overflow into the holding tank which was not equipped with a hydrocarbon detector. The holding tank’s shut-off valve was open thus allowing the hydrocarbons to flow into the stormwater network. During normal operation, this network leads directly to a stormwater tank. At the time of the incident, the stormwater tank was being worked on and its inlet was blocked off. The stormwater system was purged using a submerged pump that discharged directly into the natural environment. Having overflowed from the tank, the fuel oil spilt into the retaining tank and then into the stormwater system before being discharged by the pump.

The Classified Facilities Inspection Authorities visited the site following the incident and recommended that the operator reinforce its technical and organisational safety barriers. It also called for the mechanical lockout of transfer control devices when a lockout system is implemented. A review of the danger study, including the Inspection Authorities’ demands as well as the assessment of the risks associated with social movements, is also requested.