At a facility producing carbonate and sodium bicarbonate, fire broke out at 7 am in an electrical cabinet containing transmission cables for the liquid part of the process.

The blaze caused a complete loss of control for 2 hours and a shutdown of the process responsible for :

• an emission of 2 to 8 kg of gaseous ammonia (NH3) into the atmosphere following the sudden stoppage of the gas scrubber, causing odour nuisance outside the site;
• an emission of ammonia water into the retention basin for accidental pollution at the plant following the backflow of a brine tank; this water was discharged into the MEURTHE due to the loss of control of the retention basin’s monitoring and piloting installations.

The quantity of NH3 released into the environment is estimated at between 100 and 300 kg. This discharge caused a mortality of 400 kg of fish.

According to the operator, heating of the electrical cables was the cause of the event. This overheating was due to a loss of insulation caused by wear. The control system, consisting of control stations, a link bus, and PLCs responsible for controlling the process, had a critical point in the form of a “node”, which has existed since the creation of the site’s first control system (26 years ago), through which the various PLC cables pass. While the power supplies for the electrical equipment are all redundant, all the control cables run in a single cable duct in the control cabinet.

In order to avoid the recurrence of such an incident, the operator proposes an action plan covering

• electrical protection, in particular the replacement of the 24 V distribution with a double supply for the PLCs and physical separation of the electrical supplies;
• the gas scrubber, by installing a redundant power supply for the salt water pumps
• the local relay cabinets in positive safety to ensure the operation of the scrubber and the closing of the basin autonomously;
• the monitoring facilities for the accidental pollution basin by installing a redundant power supply for the ammonia analyser sampling pump and the basin closure valve.

The operator issued a press release following the event.