U.S. Chemical Safety Board provides update in probe of fatal Clairton Coke Works explosion
The U.S. Chemical Safety and Hazard Investigation Board has released an update on its investigation into the fatal August 11, 2025, explosion at U.S. Steel’s Clairton Coke Works in Clairton, Pennsylvania. The incident resulted in the deaths of two U.S. Steel employees and injuries to 11 other workers, including personnel from Veolia Water North America Operating Services and MPW Industrial Services.
According to the Safety Board, the explosion occurred during maintenance work on a gas isolation valve in the basement of the facility’s Battery 13/14 transfer area. U.S. Steel employees, assisted by contractor staff, were attempting to exercise (close and reopen) the valve when gas monitors began alarming. Less than a minute after an evacuation call, the explosion occurred, causing severe structural damage and extended rescue operations.
The valve involved was a cast iron, 18-inch, double-disc gate valve manufactured in 1953 and refurbished in 2013. Post-incident examination revealed the valve body had split along a circumferential crack. Other valves collected from the site also showed evidence of damage.
The Chemical Safety Board is focusing its investigation on several areas, including the cause of the gas release, metallurgical analysis of the valve, U.S. Steel’s use of cast iron materials in its coke oven gas systems, maintenance procedures, and broader safety management practices. Board members emphasized the importance of identifying systemic issues to prevent future tragedies.
The agency will release a final report with findings and safety recommendations at the conclusion of its investigation. The Chemical Safety Board is an independent federal agency that investigates chemical incidents but does not issue fines or citations, instead providing recommendations to companies, industry groups, and regulators such as the Occupational Safety and Health Administration and the Environmental Protection Agency.
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