In a prepared foods plant located in an industrial park and operating at below capacity, an employee informed the on-duty maintenance technician of a very strong NH3 smell upon opening, at 5:15 am, the deep-freeze room.
The personnel were evacuated to the meeting point. Notified at his home, the Head of Maintenance arrived by 6 am at the site and, equipped with a cartridge mask, and performed an inspection of the facility’s main cold storage room from 5 to 600 m³ as well as in the attic space. A 7 or 8-m floor leak was identified on one of the 3 cold storage room evaporators, which had been taken off the circuit by closing the NH3 supply / return sectional valves on the low-pressure circuit.
Contacted around 9 am, fire-fighters had a safety perimeter installed by 9:15, then proceeded by: confirming the diagnosis and measures adopted, performing tests with an explosimeter detector in potentially hazardous places, and ultimately leaving the site around 10:15 am.
A short-circuit on one of the power supply cables of the electrical resistances punctured one of the tubular brackets on the adjacent refrigerant circuit; 56 kg (80 litres) of NH3 out of the 900 kg introduced into the refrigeration installation escaped via a 2-mm perforation, with the liquid phase pouring into the 1.25-m³ retention basin fastened below the evaporator.
The classified facilities inspectors were informed at 9:30 am; onsite by 9:45, they remarked that although the personnel evacuation procedures had been respected, the plant was still short of NH3 detectors, especially in the attic space and other areas capable of containing an explosive or toxic atmosphere, given that the detectors in the machine room were inoperable and moreover that no procedure for maintaining and inspecting NH3 pipes had yet to be adopted.
The NH3 only diffused within the cold storage room and a few adjoining work areas via the attic space; none of the personnel were reported to have been adversely affected. The workforce was placed on a 1-day furlough. The refrigeration specialist subcontracted to repair the evaporator had to wait until the following day to continue work, after aeration of the premises. The stock was transferred to a logistics platform. A cold storage room decontamination procedure was defined, including: forced ventilation via an 18,000-m³/hr extractor fan hooked up to 355-mm diameter duct 20 m long; water cleaning on all floors; de-icing, collection and transfer of snow/residue into 200-kg hermetic containers to a certified contaminated waste treatment company. The NH3 concentrations were measured every 48 hours at various points inside the plant for a total of 15 days, considered as the time necessary for decontamination. While waiting for the situation to return to normal, the workstations were moved to non-contaminated zones.
An NH3 leak had already struck this site at the end of October 2009 (ARIA 39396). An injunction had imposed installing the NH3 detection systems prescribed by regulations, along with a programme for controlling all NH3 pipes and an audit conducted by a certified expert body.
