At around 6.30 pm, 5 t of ammonia (NH3) was released over a 15-minute period from 2 valves at a height of 8/10 m on equipment used to manufacture an ammonium nitrate solution. 4 persons located at 1,100 m to the north-east of the unit were effected by the pollution; one had to be hospitalised e few hours.
Ammonia condensation occurred following a shutdown of the steam tracing system prior to performing work on the unit itself. The pressure measurement was subsequently altered and caused a valve to open automatically. The NH3 overflowed via an evaporator through a gas line. The high-level security was not operating independently form the process.
The operator installed a second security (very high level / temperature measurement), independent of the first one (high level / pressure sensor). He will take the feedback from this accident into account when preparing the safety study of its ammonium manufacturing facilities he had to submit before 1 January 1994.