In a plant producing ice creams, yoghurts and fruit juices, 2 ammonia (NH3) refrigeration leaks were detected by the automated monitoring system in september, one on the 6th and the other on the 8th. These leaks led to placing the facilities in safe operating mode and activating the internal emergency plan twice.

The 6 september leak was detected in the machine room around 9:40 pm. The safety devices servo-controlled to detectors functioned properly: sirens sounded, the electrical circuit tripped and valves closed. During his final round at 8 pm, the security agent encountered no anomalies. First responders, notified by neighbours around 9:45 pm, set up a safety perimeter and surveyed the site with an on-duty employee. The measured ammonia concentration was near zero. The plant operator located the leak near the joint on a low-pressure bottle filling filter, adjacent to an NH3 detector. The joint was replaced and the circuit re-pressurised at about 7 am the next morning. The facility was restarted around 9:30 am. The quick detection of this leak, owing to proximity of the detector, limited the quantity of NH3 released to 1 or 2 kg.

At 1:20 am on 8 september, the automated monitoring system detected another leak in the machine room. While making his final round at midnight, the security agent had found nothing abnormal. He called first responders and the on-call supervisor. Then, feeling ill, he left his post in making his way to a nearby service station without taking his protective mask. At 1:30 am, first responders measured 8 ppm of NH3 2 km from the site (i.e. a concentration below the toxicity threshold). The on-call supervisor arrived at 1:40 am, followed by the site director 5 min later. First responders, at the scene by 2 am, installed a safety perimeter. The ammonia concentrations at 2:15 were: 2 ppm at the site periphery, 5 ppm at the entrance, 13 ppm in front of the machine room, and above 200 ppm (device saturation point) near the staircase leading to the roof, where the relief valve responsible for the discharge was located. This valve was repaired and its operations verified from 2 am to 4 am, at which time the facility was restarted. First responders left the site at 4:50 am. Rounds conducted by a technician were scheduled every 4 hours until the morning of Monday the 10, in order to counter any new outbreak. This second leak occurred on the roof yet was detected by 2 detectors inside the machine room. No detector had been located on the roof, hence the leak, which could not be stopped earlier, amounted to 40 kg according to operator evaluation.

Inspectors of classified facilities visited the scene at 9 am and reminded the operator of the need to be alerted as soon as possible whenever an incident or accident occurred on-site. The operator had failed to notify the inspectorate for the first leak. Inspection authorities also requested that the operator identify ways to strengthen NH3 detection “outside the machine room”, around the relief valves and at the site boundary. Moreover, the defective valve was to be analysed in order to learn the cause of its malfunction. The next day, the operator shipped this valve to the manufacturer and agreed to forward to the authorities the expert’s report, due back within 3 weeks. While researching the 1st leak, the maintenance manager had spotted a white streak, characteristic of an NH3 leak, on the roof beneath one of the relief valves. This recording was not followed up by any valve inspections. Inspectors assumed that preventive maintenance should have been scheduled upon noticing this streak.

On 10 september, the operator replaced 4 of the 6 relief valves, namely the defective one plus 3 others, while awaiting receipt of other valves to replace the two remaining ones. Inspection authorities had expressed concerns over safety conditions when restarting installations on 8 september. The operator indicated that the valves had been installed in pairs on parallel lines and thus anticipated that the circuit was still protected against pressure surges. Inspectors asked the operator to confirm this point by justifying the number of relief valves required to discharge all of the flow to be removed. Moreover, no special training had ever been provided to either internal or external agents regarding NH3-related risks. This point, which needed to be corrected immediately, explained the watchman’s response of seeking shelter in a service station without wearing his protective mask. The operator’s safety procedures had not been updated or circulated to employees. Such procedures were to be updated and made available to the personnel.

Analysis of these 2 leaks led inspection authorities to request the local government authority issue a formal notice pertaining to the various points cited.