At around 9:35 a.m., ammonia started leaking in the confined 1500 m² building of an abattoir containing 8.8 t of ammonia. A concentration of 1000 ppm was measured in it. A 300 m cordon was set up. The abattoir’s 320 workers were evacuated to a gymnasium in town. Four of them, who were mildly sickened by the ammonia fumes, were taken to hospital. The road passing in front of the abattoir was closed to traffic. The ORSEC emergency-response plan was initiated at 12:07 p.m. Firefighters stopped the leak by actuating a valve and then set up fans to draw in fresh air at a faster rate. At around 3:20 p.m., the concentration was measured at between 150 and 300 ppm. The 1400 pigs that were still alive were evacuated to another abattoir. Operations did not resume until two days later.
The operator stated that between 200 and 400 kg of ammonia had been released. The accident occurred on the valves station supplying the first part of a rapid-cooling tunnel. This station is located in a confined space in the attic. A gasket fitted between two flat flanges (station return valve) failed due to the pressure of the ammonia.
This excess ammonia pressure was caused by a fire in an electrical panel that cut the power to the PLC controlling the refrigeration plant. The loss of electricity caused the valves station’s solenoid valves to close, trapping the ammonia while the supply of heat was at maximum. The ammonia, contained in the tubes and coils, rose in pressure. As the valves station was not fitted with a discharge system, the excess pressure escaped via the seal on the station return valve. The operator plans to equip the valves station with a relief valve.
The inspection authorities for classified facilities subsequently went to the site on 11 January 2018 to verify whether regulations on monitoring pressure equipment inside refrigeration units were being followed. It found that the list of pressure equipment was incomplete, pressure equipment inside refrigeration units was not being inspected, and the ammonia line involved in the accident was not fitted with a protective device. A formal notification order requiring the operator to monitor its pressure equipment was proposed to the prefect.
