In the morning at an oil depot, crude oil was noticed flowing along the outer shell of a tank. A subcontractor working nearby raised the alarm and the release was stopped. It turned out that the tank was empty in anticipation of work to be performed. An estimated 10 m³ of hydrocarbons had been collected in a retention basin. A specialised company was able to skim off and recover the oil floating in the basin’s water puddles. Contaminated soil was removed.

Oil contamination of the fire system was identified as the cause of the event. Operations had been underway to replace a sleeve on a pipe at the outlet of a crude oil tank. The facility operator connected the fire system to the piping in an attempt to push the oil contained in the system back to its storage tank. However, the hydrostatic pressure exerted by the tank’s liquid was higher than the discharge pressure of the 2 fire network pumps used. Crude oil was then able to flow back into the fire system.

The operator became aware of this contamination before the release occurred. Not seeing the level in the oil tank rise, 10 minutes after the 2 fire pumps started, a technician opened a drain on the water network. Noting that crude oil was flowing out, he decided to use a third, more powerful fire network pump. When the pump started, oil from the fire network was directed to the sprinkling ring of the empty tank. With the inlet valve of the sprinkler column being open, crude oil was able to flow along the external wall.

Following the incident, the operator installed a non-return valve on the fire network to prevent contamination.