During a violent thunderstorm at the time of a shift change, an explosion occurred in a glyoxal synthesis unit. Two other explosions followed and the ensuing fire destroyed the entire unit. A 50-m³ tank was projected some 200 m. The Internal Response Plan (POI) was activated and 60 fire-fighters were called onsite and applied large quantities of water. The extinction water partially overflowed into the river. Radioactive sources were affected during the incident, although all radioactivity controls remained negative. NOx was released, yet no injuries were reported. The cost of the accident amounted to 170 million francs. Plant production was halted for 2 weeks. An expert appraisal revealed a flaw in the emergency electrical supply.