Pollution
Humain
Environnement
Economique

At around 9:15 a.m., there was a noticeable odour of ammonia in the refrigeration room of a cheese factory. The room contains two ammonia systems and two cooling tanks. The first tank, which was located in the mechanical equipment room, was shut down and isolated from production at 10:30 a.m. The refrigeration technician was called at 12:00 p.m. to work on the tank. The facility and the two associated units were turned off at 3:00 p.m. At 8:30 a.m. the following day, the refrigeration technician saw that the facility’s compressor had failed and confirmed that ammonia was leaking from the evaporator coil assembly of the first tank. At 7:00 p.m., the shut-off valve was closed, isolating both tanks. The contents of the second tank, located outside, were transferred to an available tank to produce more chilled water. The emptying of the second tank was stopped at 9:45 p.m. because ammonia emanations and bubbling indicated a leak on one of the evaporator coil assemblies. The second tank was isolated. The ammonia in both facilities was emptied on 1 and 2 August and again on 9 and 10 August.

The ammonia solution that had formed in contact with water (167 t) was taken away by a specialist company for treatment. Out of a total of 3.4 t of ammonia in the facility, 1.47 t were discharged. A portion dissolved in the water in the tanks and formed an ammonia solution. The rest was ventilated out of the building by manually turning on the extractor fan in the mechanical equipment room.

The initial analyses seemed to rule out a problem of corrosion of the evaporator coil assemblies. A specialised laboratory performed a metallographic analysis of the assemblies. This analysis ruled out both galvanic corrosion of the assemblies and a build-up of deposits between the tubes and assemblies. The performance of the water treatment system was not at issue as the corrosion was localised. Metallurgical degradation was also ruled out as no mechanical deformation was observed. In the end, the analysis was unable to find the source of the leak.