A discharge of slightly polluted effluent occurred on a Sunday in a surface treatment workshop (60 m³ of metal and wood stripping baths) subsequent to the break of a flexible water pipe used for: cleaning tanks, rinsing, and supplying a pressurised cleaner. Since the pipe’s shutoff valve had remained open, water flowed into the building, filled the retention located beneath the workshop floor and the rinsing system settling tank; next, a small volume spread into the facility’s courtyard. Rinsing water and the bottom sludge of a scrubber were thus discharged; these effluents were either slightly acid or slightly base and could contain hydrofluoric ions along with a several residues from stripped paints. Fire-fighters arrived at the scene; since the discharge was only slightly polluted, consequences were minimal. Workshop activity was suspended for a few days to allow draining these retention basins.

Failure to close the pipe’s shutoff valve at noon Saturday, at the end of the work week, caused this accident; the pipe remained pressurised and burst at night or on Sunday. No protocol had required that the valve be closed; moreover, no pipe verification had been performed. The Classified Facilities Inspectorate’s investigation revealed that the retention capacity below the workshop floor, used as a retention for some of the treatment baths, had not been fitted with a liquid detector. The Inspectorate proposed that the Prefect issue an injunction. Following the accident, it was intended to install: a display with a reminder to close the water valve, and an alarm detection inside the retention zones.