At around 4 p.m. on a Saturday, a major change in the fuel oil level was detected in the dedicated tank of a cement plant. On the site, a technician noted the presence of fuel oil in the retention system. The alarm was raised. The fuel oil was spreading into the adjacent retention systems, revealing a defect in the waterproofing system. The operator established an ATEX area together with a safety perimeter. Electrical lockout was performed in the area. The fire department established a follow-up file. The retention units were pumped and then, after a compatibility test, the product was transferred into hazardous waste tanks. The leak stopped spontaneously two days later at around 9 a.m. The retention systems were cleaned by a specialised firm and the wastes were stored in a bin. The pipes’ heat insulating material was removed and replaced. This work was completed 13 days after the start of the event.

The leak is estimated to have started at 8.20 p.m. on the day before the event. The total leakage quantity was estimated at 290 tonnes, or 275m³. A 385m³ mixture of rainwater and fuel oil was pumped.

The cause of the leak was a valve whose body burst. The operator presumes that someone must have leaned on the pipe during work in the area. This valve had no support and was cantilevered. Given its thermal insulation it was not possible to inspect it. The incident occurred during annual technical inspection and maintenance on site with a large number of personnel present.

Following the event, the operator replaced the valve and installed a visual position indicator, a support under the pipe and a caisson allowing inspection of the valve under thermal insulation.