In a coin and medal factory, a mix of incompatible used acids caused a release of sulphurous-nitrous vapours. In order to periodically eliminate the site’s effluents and used liquid products, the operator would first transfer them into a 150-litre container; pumping would then convey the effluent and product to tanks at the physicochemical treatment plant. During the accident, the operator transferred 25 litres of a stripping compound (containing sulphuric acid and chloroacetic acid) into the intermediate container still filled with 60 litres of nitric and sulphuric acids. An exothermic reaction ensued within a few seconds inside the container and spread to the treatment plant tank, with the transfer pump remaining on for several minutes. Given this sulphurous-nitrous vapour release, a safety perimeter was set up to surround the company, whose 76 employees were evacuated. Some 40 members of the chemical emergency squad arrived on-site. Normal operations could be resumed after a half-day interruption. No one felt ill effects from the vapours and no contamination was observed outside the facility.