At 6 am. in an ammonia cooling unit, liquid and gaseous ammonia leaked into the insulation of a pipe due to pitting corrosion. The ammonia dripped from the pipe insulation on a roof covered with snow and ice.

Although the damaged pipe section was rapidly found (due to the intensive ammonia smell) and substituted, nobody noticed that ammonia had dripped on the ice. Ice melting released ammonia in the drainage system during the following days. A contractor noticed the ammonia smell on the 15/12. The municipal sewer concerned was flushed. The operator took the following measures :

1. Complete refurbishing of the ammonia pipe involved in the incident

2. Random sampling of the insulation on similar old pipes

3. Installation of an ammonia sensor in the rainwater sewer.