Key facts
- A federal safety agency issued a final report on a 2025 blast at U.S. Steel's Clairton Coke Works plant.
- The blast killed two workers and injured 11 others.
- The U.S. Chemical Safety and Hazard Investigation Board recommended U.S. Steel develop written procedures for flushing gas valves.
- The Occupational Safety and Health Administration had previously fined U.S. Steel for inadequate safety procedures.
- The report noted the valve that failed was over 70 years old and made of brittle cast iron.
- A similar explosion occurred at the plant in 2010, injuring 20 people.
A federal safety agency has issued a final report detailing the cause of a 2025 blast at a U.S. Steel plant near Pittsburgh that resulted in two fatalities and 11 injuries. The U.S. Chemical Safety and Hazard Investigation Board recommended that U.S. Steel develop written policies and procedures for flushing gas valves and cleaning piping systems containing flammable or toxic gas.
The explosion occurred in August 2025 at the Clairton Coke Works facility when workers were flushing a gas valve with pressurized water in preparation for routine maintenance. The valve ruptured under intense pressure, releasing combustible coke oven gas. The Occupational Safety and Health Administration had previously fined U.S. Steel $118,214 and issued 10 citations, citing incomplete, outdated, or inadequate written procedures, practices, and training for equipment maintenance and valve flushing.
The Chemical Safety Board's report highlighted that U.S. Steel employees had utilized pressurized water to clean valve seats on an ad hoc basis for at least three years prior to the incident, despite the lack of a formal procedure. Board member Sylvia Johnson stated the blast was the result of workers routinely performing a task incorrectly over years. The failed valve was over 70 years old and made of cast iron, a brittle material widely recognized as unsuitable for hazardous applications involving flammable substances like coke oven gas.
Investigator Drew Sahli noted that the location of the workers directly above the coke oven gas piping contributed to the severity of the incident. The Clairton plant has a history of accidents, with previous reports of poor management and underinvestment impacting safety and air pollution. A similar gas oven explosion at the plant in July 2010 injured 14 U.S. Steel employees and six contractors. The report criticized U.S. Steel for not conducting a facility siting evaluation after that earlier incident.