At around 5:15 a.m., in a poultry processing plant, employees in 2 workshops were evacuated after the smell of ammonia (NH3) was detected. A leak of 10 kg of liquid-phase ammonia was observed on a solenoid valve in the refrigeration installations located in the attic space above the workshops. Two maintenance technicians were able to isolate the leak after breaking the ice that had formed around the shut-off valves. The isolated section was purged at around 6 a.m. At around 6:45 a.m., the employees of a 3rd workshop were evacuated. A first aider called for help, and the premises were ventilated. At about 7:30 a.m., a maintenance technician used test strips to detect for the presence of ammonia. Workers from one of the 3 workshops returned to their workstations while the other 2 workshops were reopened after residual concentrations were measured by the fire brigade (3 ppm measured for a tolerated concentration of 10 ppm over 8 hours). The emergency rescue services had evacuated 183 employees. Thirty people were examined by paramedics and 6 were transferred to the hospital for further observation.

It turned out that the leak had been caused by an electrical arc on the solenoid valve coil, creating a hole in the hub. No signs of wear were found. The following aggravating factors were identified:

• inefficient evacuation planning (no alarms triggered, no instructions from managers) ;
• an inadequate operating procedure on how to deal with a liquid-phase NH3 leak (difficulty in accessing block valves trapped in ice, unsuitable protective equipment).

The operator plans to review the maintenance intervention and evacuation procedures, validate them through drills and acquire NH3 measuring equipment. In the long term, ammonia will be replaced by glycol in the work areas.