At around 11:40 a.m., a delivery driver spilt 300 l of formic acid into a partially buried storage tank containing 3000 l of sodium hydroxide at a plant that manufactures laundry cleaning products. When the temperature inside the tank rose to 50 °C, the building was evacuated, the power supplies were cut off and the firefighters were called in. No vapours were seen coming from the tank. The tank was cooled down and normal operations resumed at around 1:30 p.m. A specialist contractor drained and cleaned the tank at around 5:00 p.m.

Each partially buried storage tank has a padlocked unloading cabinet. After the sodium hydroxide had been transferred into the tank, the site employee accompanying the delivery driver closed the cabinet but did not close its padlock. He then opened the formic acid tank’s cabinet. Distracted by another delivery driver, the delivery driver left the unloading area. When he returned, he connected his lorry’s hose without checking the destination tank and began transferring formic acid without waiting for the employee’s green light. At around 11:50 a.m., the employee noticed that the level in the formic acid tank was not rising. He realised that the delivery driver had not connected his lorry’s pipe to the right discharge head.

Hydrochloric acid is also used at the plant. The same mistake with this acid would have released a toxic cloud of chlorine.

The following day, the inspection authorities for classified facilities saw that the accident was caused by a lack of staff training and failure to follow the safety protocol setting out the steps to be followed during unloading. They also noted failure to follow the site’s rules on the use and storage of chemicals.

The operator was given one month to:

• train his employees in chemical risks;
• install the necessary secondary containments around tanks containing substances that, if leaked, could result in pollution;
• repair the water treatment tank, which was leaking on the day of the inspection.

The operator was also given four months to update placards and labels regarding the storage of chemicals and renovate the formic acid room. Indeed, this room, poorly ventilated, gave off a pungent odour and many items of equipment in it were corroded. No checks of the tank, of the correct operation of the secondary containment’s detection system or of the relaying of information to the alarm panel were carried out. The operator:

• checked the outside surface of the tank’s walls;
• implemented a procedure for periodically checking the tank’s walls and for checking that this is indeed done;
• presented a technical and economic feasibility study on the proper ventilation of the room, which included the actions envisaged and the associated timetable.

As the risk of incompatible mixtures during unloading operations had not been taken into account in the safety report, the operator had six months to update it and include a scenario where hydrochloric acid is mixed with sodium hydroxide.