One Sunday morning, the former director who had retired from a surface treatment plant entered the plant’s shop to perform some work on an empty trichloroethylene tank; his body was found 4 hours later in the tank’s retention ditch, at a depth of 1.5 m. The shop was not open for business and ventilation had been turned off. Evidence of burns on the victim’s body indicated a rather extended period of contact with the brownish liquid that was lying stagnant at the ditch bottom and filling its low point. This liquid, for which an analysis revealed a 5 g/l concentration of sodium cyanide and a pH of 10, would have been generated from leaks or drippings formed during disconnection of ion-exchanging resins near the ditch that were not on the retention circuit. A judicial investigation was undertaken. The Labour Inspection Office verified whether the installations could be started up from the standpoint of ensuring workforce safety. The Hazardous Installations Inspectorate noted the presence of unauthorised treatment tanks located outside the retention zone as well as tanks positioned in the same zone yet containing products (acid/cyanide) of incompatible composition in the event of a leak. The Inspectorate’s report proposed that the local Prefect issue a formal notice for the plant operator to proceed with a thorough cleaning of the retention ditch containing the cyanide liquid and to have these contents removed by a certified contractor; in addition, the operator was ordered to identify the root causes of the presence of cyanide liquid within the ditch connected to the trichloroethylene tank, to reorganise all installations on the retention circuit to ensure correspondence with the type of liquid present, and lastly to plan on performing a control of seals on all existing retention basins.