In a paint and varnish factory, a slow decomposition reaction occurred within a 1,500-litre tank containing a mix of nitrocellulose and ethanol. The tank underwent a rise in temperature above that of the reaction process. This excessive temperature led to the release of nitrous vapours. First responders cooled the tank with fire hoses, and a safety perimeter was installed. All 40 employees were evacuated, with 9 of them suffering from slight intoxication due to the nitrous fumes. The tank cooling regime was maintained for 4 hours until ambient physicochemical conditions had returned to normal. The cooling water blocked access to the retention basin and moreover overflowed a portion of the courtyard, yet without flowing away from the site. No pollution was detected. The personnel kept a monitoring system in place. The operator was required to set forth a strategy for controlling temperature when storing mixes and for raising retention efficiency.