In the surface treatment workshop of a lock factory, 380 litres of sodium hypochlorite (NaOCl) were accidentally mixed with hydrochloric acid (HCl) during a delivery around 9 am. The violent reaction between these incompatible products triggered a chlorine release (Cl2 and HCl), which spread both in and between 2 buildings via storage vents located near the awning between the buildings; 39 employees became intoxicated, 16 of whom required hospitalisation (with 7 placed in intensive care). The other 300 factory employees took shelter once the alarm had sounded. The 75 fire-fighters wearing diving suits entered and ventilated the building using a large fan. All risks were eliminated by the end of the morning and workshop activities could resume the next day. No risk was posed to the adjacent population.

The transfer station (set up subsequent to a 1994 accident) was composed of a lockbox containing 3 clearly identified flange couplings distinct for each substance (mistake-proof slots). The delivery person, whose vehicle contained a full set of “tinkered” adapters, mistook the flange and chose the wrong coupling. The error went undetected (checked?) by his fellow crew member.

The factory operator fitted the storage tanks with electrically controlled relief valves locked by pH measurements and moreover improved the distribution of individual protective gear at the transfer station.