In a deep-freezing tunnel of an ice cream manufacturing plant, 40 kg of ammonia (out of a total of 13 tonnes of NH3 in the facility) leaked at 6.30 am from a pipe in the cone production line. The refrigerationist onsite was immediately informed by a technician. At the same time, the workshop’s automatic detection system alarm was activated indicating a 300 ppm threshold and was deported to the control room triggering a siren.

At 6.40 am and in 10 minutes, an intervention team (refrigeration specialist + on-call refrigeration specialist + NH3 installation manager) locates the leak and closes manual shut-off valves to cut off the NH3 arrivals. The circuit is made safe by activating the emergency stop and the piping is purged. The process workers leave the workshop and production is stopped. The operator notifies the company responsible for the maintenance of the refrigeration systems at 8:00 am. The fire brigade alerted at 8:30 am intervenes 1 hour later to facilitate the extraction of NH3 in the leak area and in the production workshop, then the premises are ventilated. On arrival, the refrigeration service provider carries out NH3 concentration measurements in the freezing tunnel; they show a progressive dispersion of the NH3 emitted into the atmosphere. At 9 a.m., the operator decides to lay off its 122 employees for one day. The NH3 emitted in the workshop will be evacuated from the building using the extractors spread over the area; the concentration thus drops from 437 to 194 ppm in 2 hours. A favourable meteorology with average winds directs the NH3 towards the industrial zone where it is dispersed. With the concentration having become practically zero, the fire brigade’s intervention was completed at around 5 pm.

The damaged pipe was covered with polyurethane foam that in turn was protected by a steel coating. Significant external corrosion was detected below the heat insulator. The corrosion could not be detected upon mere visual inspection and was responsible for the rupture of the pipe that operated in rough conditions in a humid atmosphere. This possibility was not taken into account during the safety assessment studies. The emitted NH3 accumulated in the pipe between the closed valve and the point of leak. The operator had already taken steps to prevent corrosion especially when replacing pipes at regular intervals by systematically protecting them with petrolatum tapes to minimise the effects of humidity. A new round of inspection of all pipes in the deep-freezing tunnel was carried out to gradually replace the polyurethane-insulated pipes with petrolatum tape protected pipes as polyurethane speeds up corrosion.