In a steel mill, explosion occurred while a disused blast furnace was being dismantled. According to the expert evaluation firm, initial elements indicated that maintenance crew were working in a room 6 meters below ground level, seriously limiting evacuation possibilities. They were disassembling a 25-cm diameter valve located on a blast-furnace coke gas supply pipe. Fuel still present in the pipe exploded and fire broke out. Among the 10 workers in the zone at the time, a mill employee and a member of the subcontractor’s staff died and another 4 were injured (from smoke intoxication), one of whom in serious condition. According to the procedure employed, coke gas (mix of methane, hydrogen and carbon monoxide) was produced from coal, by means of a chemical combustion process, similar to that producing charcoal from wood. The gas was used as fuel, and the coke (solid) introduced into the steelmaking operation. The Chemical Safety Board, an independent American federal agency assigned to carry out technical evaluations of the accident, sent a team to the site to determine the precise causes of the accident.