U.S. Steel plant explosion investigation released

The U.S. Chemical Safety and Hazard Investigation Board has released its final report regarding an August 2025 explosion at U.S. Steel’s Clairton Coke Works near Pittsburgh. The incident, which involved a series of three explosions, resulted in the deaths of two workers and injuries to 11 others, while causing approximately $52.5 million in facility damage.

The investigation determined that the blast occurred when workers attempted to clean a 72-year-old cast iron valve using pressurized water or steam to remove coke oven residue. This practice, which had been performed on an ad hoc basis for at least three years without formal written procedures, caused water to build up pressure between valve gates. This overpressurization led to a valve rupture and the subsequent release of combustible coke oven gas.

The Chemical Safety Board recommended that U.S. Steel and its industrial cleaning contractor develop formal written policies for flushing gas valves and cleaning piping systems containing flammable or toxic gases. The Occupational Safety and Health Administration (OSHA) previously issued 10 citations and $118,214 in fines to U.S. Steel, citing inadequate training and outdated safety procedures. Contractor MPW Industrial Services was also fined $61,000 for related violations.