Federal Report Details Safety Failures Behind Deadly U.S. Steel Plant Explosion
A deadly explosion at U.S. Steel’s Clairton Coke Works in Pennsylvania that killed two workers and injured 11 others was caused by a series of safety and management failures that should have been prevented, according to a federal investigation released Monday.
The U.S. Chemical Safety and Hazard Investigation Board released its final report into the Aug. 11, 2025, explosion at the Clairton facility, nearly one year after workers Timothy Quinn and Steven Menefee were killed.
Five of the 11 other workers injured in the explosion suffered serious injuries. The blast also caused an estimated $52.5 million in property damage.
CSB Chairperson Steve Owens said the deadly incident resulted from an informal procedure, poor facility siting and an ineffective process safety management system.
“It should never have happened,” Owens said.
The explosion occurred as U.S. Steel employees and contractors from MPW Industrial Services were working on a double-disc gate isolation valve connected to piping supplying coke oven gas to Battery 13.
Workers at the plant periodically “exercised” the valve by closing and reopening it to ensure it could operate throughout its full range.
Employees told investigators that accumulated coke oven residue sometimes prevented valves from closing completely.
Workers had used steam or high-pressure water to remove the material when valves would not close properly, according to the investigation.
On the day of the explosion, a supervisor arranged for MPW contractors to use pressurized water on the Battery 13 valve.
As the water was applied, workers closed or nearly closed the valve’s two gates, creating an enclosed space between them.
Pressurized water filled that space, causing pressure inside the valve to increase beyond what it could withstand.
“The valve then failed catastrophically,” the CSB report said.
The failure released toxic and highly flammable coke oven gas into the surrounding area. Within minutes, the gas ignited and exploded.
Investigators found that U.S. Steel did not have an established procedure describing how workers should perform the cleaning operation that preceded the explosion.
The valve itself also drew scrutiny from investigators.
It was manufactured from cast iron in 1953, making it more than 70 years old when the explosion occurred. The valve had been refurbished in 2013.
The CSB noted that cast iron is considered a brittle material and that multiple safety publications warn against or prohibit its use in certain hazardous applications involving flammable substances such as coke oven gas.
The location of occupied buildings around the hazardous piping also contributed to the severity of the disaster, investigators found.
Several buildings regularly occupied by employees were located less than 20 feet directly above the coke oven gas piping involved in the explosion.
Those buildings were not designed to withstand an explosion.
Quinn and Menefee were in or near separate control rooms above the piping when the blast occurred. Two of the five seriously injured workers were inside a break room in the same area.
One worker trapped in the wreckage was able to free himself and crawl through the debris to seek assistance. Another was rescued by emergency personnel approximately four hours after the explosion.
Nine workers outside the building were also injured.
Investigators concluded that U.S. Steel had not conducted necessary facility siting evaluations in the years leading up to the disaster.
“When buildings are occupied by personnel, they must be adequately designed or located to protect the personnel or equipment from fires, explosions, or toxic releases,” CSB Investigator in Charge Drew Sahli said.
Sahli said the consequences could have been substantially less severe if the occupied buildings had been located farther from the coke batteries.
The investigation resulted in additional safety recommendations for U.S. Steel, including evaluating occupied and potentially occupied buildings at Clairton Coke Works and addressing hazards identified through those evaluations.
U.S. Steel said it would thoroughly review the CSB’s recommendations and had already strengthened several safety protocols following the explosion.
The company said multidisciplinary teams established standardized practices for industrial valve cleaning and that it improved its Management of Change program.
Employees have also received training on the new procedures, according to U.S. Steel.
“Safety is our core value and shapes every part of our business,” the company said.
U.S. Steel said employees across its Mon Valley Works operations would lower flags to half-staff and observe a moment of silence to honor the workers killed in the explosion.
The CSB’s final findings place significant emphasis on preventing similar disasters, concluding that a combination of unsafe practices, inadequate procedures and the location of workers near hazardous equipment contributed to the deadly blast.
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