On a Sunday inside the alkylation unit at a refinery (producing 175,000 barrels/day), a sulphuric acid leak occurred on a 350 m³ capacity tank. Between 4,000 and 8,000 l flowed from the top of the tank, yet according to the refinery operator, the majority could be recovered in the site’s effluent network and channelled to the water treatment plant and waste processing centre.

From initial findings, a pressure surge caused the upper part of this tank to open. The refinery temporarily scaled back its operations. One investigation was conducted by the operator and another by authorities in order to determine the cause of this accident. No information however was released on the resulting air pollution: this acid could actually react in contact with metals and organic matter to yield sulphur dioxides, hydrogen and miscellaneous pollutants.

The next day, teams were assigned to decontaminate the site, which had experienced a major pollution incident in July 2001 subsequent to the explosion of a tank containing acid mixed with residual hydrocarbons. Since that time, some storage vessels (including sulphuric acid, one of which leaked) had undergone special monitoring. The incriminated tank during the latest accident had been built in 1996, inspected in December 2002 and was not scheduled for another internal inspection until 2006.