At 2 pm, within an industrial zone, ammonia (NH3) fumes seriously inconvenienced 9 individuals walking in the corridor of a covered wholesale fruit and vegetable market. At 2:55, external responders arrived on the scene and removed the victims; the ocular irritations and rashes they had been suffering quickly subsided.

The classified facilities inspectorate, notified by local health services the following morning at 9:05, conducted an investigation 2 hours later in a curing facility adjoining the market and operating a refrigeration unit utilising 900 kg of NH3. The accident actually resulted from degassing an undetermined quantity of NH3 during a poorly supervised bleeding of non-condensable gases in the machine room. In noting abnormally high pressure in the unit’s high-pressure (HP) circuit on the day of the accident, the operator decided to manually stop and drain the non-condensable gases. This operation began at 2 pm and involved 2 technicians, one wearing a cartridge mask and positioned outside the machine room at the drainage point equipped with a manual valve, while the other machine room technician was monitoring the change in temperature at the level of the negative compressor. The untimely degassing occurred following this approx. 30-min drain period. The gas cloud that had formed drifted towards the vegetable market immediately adjacent to the machine room, without any special measurements recorded by the operator, prior to quickly dispersing once the drain had been completed.

The investigation revealed that the operator had not complied with the procedure entitled “regular monitoring of non-condensable gases and their drainage”, as recommended by the installer, given that drainage steps had only been performed when the refrigeration installation was operating in degraded mode. 48 hours prior to the accident, the NH3 pump underneath the low-pressure (LP) reservoir switched off, causing compressors in both the negative cold storage room and freezer to shut down, in addition to major maintenance work, i.e.: manual oil drain, removal and cleaning of a sensor, and forcing of the liquid valve in order to re-establish the HP and LP levels. Poor adjustment by the subcontractor of the “lower threshold” pressure on the LP circuit at 300 g below atmospheric pressure would subsequently be recorded. These inappropriate operations and adjustments favoured the formation of non-condensable gases.

The inspectorate requested that the operator file a report on the facts, along with a causal analysis, of the accident plus proposed preventive measures. This document, submitted at the end of November, called for: compliance with the drainage procedure recommended by the installer, regular monitoring of non-condensable gases, and replacement of the current bleeding device by end of December. A comprehensive inspection of the installation and these operating conditions was scheduled in the presence of the “industrial risk” targeted by the local inspectorate.