Pollution
Humain
Environnement
Economique

Around 7:30 pm, 5 or 6 vapour explosions in less than 60 seconds damaged the furnace (operating at 1,550°C) of a plant engaged in reprocessing industrial waste by means of pyrometallurgy techniques. The accident was caused by sudden contact between cooling water and molten metal and slag after perforation of the furnace sidewall due to refractory material wear; some 2 to 3 tonnes of molten metal and 35 tonnes of slag spread within the building. Three employees had to be hospitalised for hearing tests; one of them positioned 20 m from the point of explosion was diagnosed with a lesion on an eardrum, yet the condition was not found to be irreversible. Material damage was also observed: the 17-mm thick window pane on the facility’s control room located 11 m from the explosion was destroyed, walls shaken without any collapse, broken glass and small-scale damage within a 40-m radius, melting of a portion of the collectors, damaged pipes, etc. The inoperable installations were secured. The inspectorate for hazardous facilities performed an investigation, and the expert appraisal evaluated the source term of the explosion to be 200 g of TNT, which corresponds to the abrupt pressure expansion from 55 to 1 bar of slightly more than 1 l of water at its maximum superheat temperature (270°C). Following piercing of the furnace (an opening 66 cm long by 15 cm high above the casting zone), the first explosion would have been generated from contact between a small quantity of water and molten material near the casting zone. The second blast erupted once this material arrived into the cooling water collector pipe from the furnace casing (producing a thin liquid film inside the collector). The third explosion, which occurred 10 seconds after the first and according to witnesses was the most violent of the three, resulted from trapped water that had accumulated locally due to molten material flowing into pipe discharge zones. The other explosions were of much smaller magnitude and attributed to random water / melted material contact. The refractory materials refurbished in January 2004 were inspected; early abrasion subsequent to micro-fracturing following an assembly defect was cited for having prevented the creation of a sufficient dilatation space. Several measurements were taken: backup temperature measurements and their interpretation in the aim of preventing furnace perforation, confinement of potential water accumulation zones to avoid contact with molten material, issuance of guidelines laying out the set of operator actions and means for ensuring operator protection during accidental situations.