In an electric steel mill, once the furnace (capacity: 70 tonnes per casting) had been emptied into a ladle, an employee was called in to plug the drain hole, which represented the only operation still not automated. As the employee entered the “Dog House” (name given to the concrete enclosure surrounding the furnace), an explosion of vapourised water in contact with the molten steel occurred, killing him on the spot. The furnace was damaged: the cover became misaligned, and the vaulted chamber was projected several metres. A material defect (water leak on the cooling circuit) was the suspected origin. The premature entrance of the employee into the protective enclosure, even though the furnace had not returned to the normal position, would have been the fateful cause of the employee’s death. A judicial investigation was conducted.