An explosion occurred around 12:30 pm on a cadmium vaporization column inside a unit devoted to refining zinc by means of fractional distillation. A cloud of zinc vapour and zinc oxide powder (?), combining to form an opaque white fog, spread within a few minutes throughout the workshop. The 11 employees and subcontractors working in the immediate vicinity were severely burned; a welder was killed on the spot, and 9 other people died in the following minutes, hours and days, with the lone survivor sustaining burns to 90% of his body. Property damage inside the workshop was limited. The 13-m high column, restored with a new stacking sequence of 59 silicon carbide plates and new flues, started running again on 25th May. The actual production phase was initiated on 24th June, as the operating regime had been maintained below its nominal capacity. Around 5 pm the day before, an abnormal rumbling sound had alarmed technicians, and a subsequent inspection exposed the temperature rise in the smoke-heat recovery system and its extremely filthy state. On the morning of the accident, technicians were required to intervene several times to resume normal operations.
Administrative surveys and third-party appraisals were conducted. Since the source of this accident was attributed to a break in the plates (potentially caused by a quality issue or thermal shocks during either preheating or the 1st column supply), the installation was rebuilt in taking special precaution during the steps of plate reception and preheating. Moreover, new control instruments were installed. Rebuilt in December 1993, the column resumed production on 17th January, 1994 at a reduced flow rate. On 24th January, another explosion occurred. A subcontractor driving around the installation in the zone placed off limits following the 1st accident (though the sector had not been physically barricaded) was killed. Upon completion of investigations and expert assessments of both explosions, the preferred hypothesis was a clogging of the column due to insufficient zinc racking flow at the column bottom (resulting from partial blockage of the liquid metal discharge siphon or from excessive zinc viscosity during the column start-up phase?). Given the rise in liquid zinc level within the column, the release of zinc vapour bubbles created vibrations that, in turn, caused breaking of the silicon carbide plates followed by the column, accompanied by releases of vapour and zinc aerosol that reacted explosively with air from the combustion chamber.
On 25th September 1997, the court sentenced the Plant Manager and Director of Technical Services to suspended prison terms and a 30,000-franc fine each; the company was found to be liable for civil damages. The various investigations revealed the absence of a feedback system to learn from other accidents in the world, coupled with blatant organisational malfunctions. The factory definitively suspended operations at the beginning of 2003.