CSB Provides Update on Fatal Explosion at U.S. Steel Clairton Coke Works
The U.S. Chemical Safety and Hazard Investigation Board (CSB) released an update on its investigation into the August 11, 2025, fatal explosion at the U.S. Steel Clairton Coke Works in Pennsylvania. Two U.S. Steel employees were killed and five others seriously injured, the agency said. Six additional workers were treated for injuries but not hospitalized.
CSB chairperson Steve Owens said in a statement, “The focus of the CSB’s investigation is to understand what caused this terrible tragedy and identify actions that can be taken to prevent something like this from happening again.”
Board member Sylvia Johnson added, “Tragedies like this must lead to change. Our investigation will identify not just what went wrong, but what must be done to ensure workers across this country are protected from similar hazards.”
Preliminary information indicates the explosion occurred during maintenance of a gas isolation valve in the basement of the Battery 13/14 transfer area. U.S. Steel employees, assisted by personnel from MPW Industrial Services, reportedly attempted to flush the valve seat with water when gas monitors alarmed. Less than one minute after evacuation orders were given, an explosion occurred, the agency said. The explosion caused extensive structural damage and delayed recovery of one of the fatally injured employees for approximately nine hours.
According to the CSB’s investigation, the valve involved was an 18-inch, double disc gate valve made of cast iron in 1953 and refurbished in 2013. Post-incident examination revealed a circumferential split in the valve body, and additional valves recovered from the site showed signs of damage.
The CSB said its investigation continues to focus on the cause and source of the gas release, metallurgical analysis of cast iron components, U.S. Steel’s material selection and maintenance procedures, and overall safety management systems. The agency plans to issue a final report with detailed findings and recommendations once the investigation concludes.
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Amanda Joshi
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Amanda Joshi has more than 18 years of experience in business-to-business publishing for both print and digital content. Before joining Chemical Processing, she worked with Manufacturing.net and Electrical Contracting Products. She’s a versatile, award-winning editor with experience in writing and editing technical content, executing marketing strategy, developing new products, attending industry events and developing customer relationships.
Amanda graduated from Northern Illinois University in 2001 with a B.A. in English and has been an English teacher. She lives in the Chicago suburbs with her husband and daughter, and their mini Aussiedoodle, Riley. In her rare spare time, she enjoys reading, tackling DIY projects, and horseback riding.