At around 4:20 p.m., concentrated nitric acid began leaking from a pump at a chemical plant. Workers in the control room saw nitrous fumes on the CCTV screens. The internal emergency plan was implemented. A crew closed the bottom valves on all the tanks in the building. Calcium carbonate (180 kg) was spread to neutralise the acid that had spilt onto the ground. The acid ignited the vegetation along the edges of the storage area, near an embankment. The fire was contained at 4:50 p.m. The calcium carbonate-coated soil was removed and placed on plastic tarps to be treated offsite in early 2018.

An area measuring 500 m² was burnt; 150–200 l of concentrated nitric acid was spilt.

The following causes were identified:

• The pump’s manual discharge valve was left open following maintenance work performed the day before.
• The pump body suffered premature wear when the start-up phase was carried out a few hours earlier with this discharge valve closed. The stream of acid flowed directly onto the ground, not into the pump’s containment berm. It then continued on to the brush, starting the fire by chemical reaction.

The following actions were subsequently proposed:

• Creation of a pre-start checklist following maintenance work.
• Installation of a flowmeter with an interlock on the pump’s discharge to turn the pump off.
• Study of the best position of the single-pump unit to improve operating conditions and reduce the risk of spills spreading.
• Check of the equipment of the other pumps (already fitted with cut-outs, berms, and flowmeters).