In a food processing plant, liquid ammonia (NH3) spilled at night into a river via the stormwater drainage network. The following morning at 6 am, staff at a neighbouring distribution company detected an NH3 smell on their premises and notified emergency services. One person suffered a malaise and had to be hospitalised for observation, and all 86 employees were sent home. Moreover, production was stopped for the day at the company sounding the alarm.

The day before, a specialised firm had conducted works on the plant’s refrigeration installation. To conduct these works, which focused on a heat exchanger containing gaseous NH3, all of the liquid ammonia was transferred into special containers. The circuits were then degassed in order to eliminate residual gaseous NH3; the gas was injected into a 200-litre drum filled with water. According to the operator, the circuits still contained liquid NH3 as this stage was unfolding, and technicians had forgotten to close a valve. The liquid NH3 had been conveyed into the 200-litre drum that eventually spilled subsequent to contact with water. Since the drum had been placed just above a grating providing access to the stormwater network, ammonia water contaminated the stormwater network.

The next day, the environmental services and classified facilities inspectorate observed high death rates among amphibians within a few hundred metres of the network contamination source, yet without any discovery of fish remains. Several pH measurements were performed on the day of the accident at various points in the stormwater network; a maximum pH value of 11.5 was recorded.

A subcontractor then pumped and rinsed the sewers around noon. The water pH had returned to 7 by the morning of 20th April.