Around 11:00 am, the arrival of a major delivery of liquid hydrocarbons was recorded at the preliminary sedimentation basin of the refinery’s waste treatment plant.

A technician noted the presence of product on the floating roof of tank CU15 containing “FCC gasoline”, with a gravity runoff system passing via the stormwater collection drain on the roof in the direction of the oily water collection network. The drain was isolated and the tank was first drained then filled with water.

The personnel present near the treatment plant were evacuated from the site’s basin zone as a precautionary measure due to strong hydrocarbon odours, while measurements of both COV and benzene content in the atmosphere were conducted: results proved to be negative. After cleaning, the plant and collection basin were placed back into service.

The quantity of FCC gasoline released was calculated at 40 m³.

The operator had identified external corrosion on the upper shell of the double-deck floating roof. Rainwater had infiltrated into the central caisson and subsequently overflowed into two other caissons. The roof tilted and wound up being partially submerged (less than 10% of its surface area).

The operator has been studying the possibility of installing a hydrocarbon detector on the basin’s oily water drain in order to prevent any accidental inflow of hydrocarbons into the treatment plant.