A fire broke out in a treatment bath in a pen manufacturing plant. Flames were detected by an alarm at 3:03 a.m., triggering the automatic fire extinguishing system (foam). The rainwater and wastewater systems are blocked off. Having noted that the fire was extinguished, the fire brigade requested that the system be shut down at 3:55 a.m.

A treatment tank had overflowed. The foams, loaded with different products, contaminated the workshop floor and the retention basin.

The structure of a 475 l polypropylene tank, used to rinse parts containing cyanides, was slightly altered. The production line had to be stopped for a week while the premises were cleaned up, and the operator had to transfer 38.5 m³ of effluent to a specialised treatment centre.

It was determined that the fire started due to the overheating of an electrical resistor in the treatment bath. This element, normally submerged, was partially emerged, causing it to overheat. The low-level probes in the tanks, which normally are designed to cut off the power, did not work due to the presence of residual liquid.

In order to avoid this type of event, the operator installed the following technical and organisational measures:

• installation of a mechanical stop on each resistor to prevent any unintentional ascent;
• disconnection of the power supply used to heat the baths over the weekends.

In addition, the containment barriers that had been installed on all the openings of the workshop, installed in 2013/2014, limited the potential consequences of the incident. The reactiveness of the security guards allowed the situation to be managed effectively.

A similar event had already occurred in the company in 2008 (35257): a tank on an electroplating line had overflowed following activation of the automatic fire extinguishing system. The Inspection authorities for classified facilities thus requested additional information from the operator on the risk of mixing dangerous products in the event the fire suppression system was activated. The operator had to justify that there is no chemical risk and that appropriate measures will prevent it.