Inside a deep-freezing facility, 30 kg of gaseous ammonia (NH3) were released at 10:08 am for a 10-min period via the safety valve at a refrigeration installation containing 4 tonnes of refrigerant. Slightly intoxicated, 2 subcontractors working onsite had to be hospitalised as a precaution; moreover, 10 plant employees were examined at the scene and another 30 individuals were evacuated. The rescue intervention mobilised 49 fire-fighters and some 15 emergency vehicles. The Classified Facilities Inspectorate undertook an investigation. The Labour Inspector’s Office also visited the site at the request of the local Prosecutor’s Office. Specialised units conducted air quality sampling and analyses, which did not yield any alarming toxic concentration levels outside the facility, especially given the location of a forest in the same sector downwind of the release. First responders completed their mission at 2:23 pm. The plant was shut down for the time needed to determine the causes of this incident and implement remedial measures.

In seeking to accelerate an equipment de-icing phase, an employee who had completed the refrigeration specialist training module and was certified to work on this type of installation decided to shift into manual mode to turn off the condenser cooling fans supplying the installation’s high-pressure tank. Though de-icing took place more quickly, it nonetheless did so on an installation operating in an unstable regime: drop in compressor cooling, followed by an increases in temperature and in pressure in the high-pressure tank until exceeding the set valve pressure.

Several remedial measures were adopted: the set point on high pressure switches was lowered in order to increase the pressure differential relative to the valve set pressure; a new pressure switch was installed at the level of the high-pressure bottle; access to the machine room was restricted to maintenance technicians and site operators assigned to oversee equipment; a procedural guideline was drafted prohibiting the acceleration of hot gas production; mandatory scheduled risk-related training was provided to all subcontracted personnel with regular site presence (including instruction in the various sound alarm tones); a gas sensor was installed above the machine room and adjacent to the valves; and gaseous discharges were collected in the valve outlet with placement of an NH3 detector inside the outlet.