In an industrial zone, an ammonia (NH3) leak occurred around 4:15 am on one of the 10 refrigeration installation compressors at a food processing plant preparing meat-based products. The NH3 detection system, whose trigger threshold was set at 800 ppm, shut down and placed the refrigeration installation in safe mode when the explosive atmosphere fans automatically started up upon reaching the 1st alarm threshold set at 600 ppm.

The internal emergency plan was activated at 5:11 am, and the plant’s 230 employees onsite during the event were confined in the break room. Notified at 5:26, responders (fire-fighters) deployed significant intervention resources, in terms of both manpower and equipment.

This exclusively gaseous NH3 leak was caused by an oil return indicator light that had become unscrewed no doubt subsequent to vibrations. Located between the compression group’s ultra oil separator and the compressor, this indicator was most likely poorly tightened during a prior maintenance step.

A fire-fighter applied the guidelines of an “ETARE” plan, in conjunction with 2 refrigeration technicians from the plant: wearing self-breathing apparatuses and cartridge masks (K2 type, effective up to a concentration of 5,000 ppm), they stopped the leak at 5:58 am by manually closing the compressor’s suction and discharge valves. After verification of levels inside the installation, 50 kg of NH3 were evacuated via the explosive atmosphere fans positioned on the roof at a height of between 8 and 9 m.

The indicators on all other compressors were also verified, then the installation was placed back online the same morning at 10. Personnel were only authorised to return to their posts once the NH3 concentration in the corridor leading to the machine room had dropped below 10 ppm. This access corridor was separated from the machine room by an air-lock; however, during repair operations, a slight amount of NH3 dispersed into the corridor. On the other hand, no NH3 dispersion was reported in any of the plant workshops.

This incident caused no injuries and no environmental impact. Plant production was halted for 5 hours, and no redundancies were required.