A federal workplace safety agency is calling for clearer written rules on how gas valves are flushed, one year after a deadly explosion at a U.S. Steel facility near Pittsburgh claimed the lives of two employees.
The U.S. Chemical Safety and Hazard Investigation Board released its final findings on the August 2025 explosion at Clairton Coke Works, where 11 additional people, including contractors, were hurt.
According to U.S. Steel, the blast occurred as workers were using pressurized water to flush a gas valve ahead of scheduled routine maintenance at the massive riverside plant, described as the largest coke-making operation of its kind in the Western Hemisphere. Under extreme pressure, the valve failed and released flammable coke oven gas.
The Occupational Safety and Health Administration had earlier issued 10 citations against the company and proposed fines totaling $118,214. OSHA said U.S. Steel’s written instructions, safety practices and employee training for maintaining equipment and flushing the gas valve were either incomplete, outdated or otherwise insufficient.
In its report, the Chemical Safety Board urged U.S. Steel to create a formal written process for cleaning valves with pressurized water to better control the risks tied to that work. The board also recommended that the industrial cleaning contractor, which used a pump truck to force pressurized water into the valve, establish its own written policies for cleaning piping systems that contain flammable or toxic gas and ensure workers are properly trained for those jobs.
Investigators found that when a valve failed to shut completely, U.S. Steel workers had been using steam or high-pressure water through a cleanout port in an effort to clear away built-up material.
“U.S. Steel had no procedure for how to safely conduct this operation, but for at least three years before the incident, U.S. Steel employees had utilized pressurized water to clean valve seats on an ad hoc basis despite the lack of a formal procedure prescribing it,” the report’s executive summary stated.
Chemical Safety Board member Sylvia Johnson said the explosion “was the result of workers routinely performing a task incorrectly over a period of years until it ultimately led to a catastrophic explosion.”
The valve that failed was more than 70 years old and made from cast iron, which the report said is widely recognized as a brittle material. Numerous safety publications either ban or warn against using cast iron equipment in certain hazardous applications, including for flammable substances such as coke oven gas.
The report also said the two workers who died and two of the five seriously injured workers were located around buildings directly above the coke oven gas piping. If these buildings were located in a different area of the facility away from coke ovens, “this incident could have been far less severe,” said Drew Sahli, the Chemical Safety Board investigator in charge.
Before the blast, Clairton Coke Works had a history of accidents and explosions, and some current and former workers there say poor management and underinvestment have exacerbated air pollution and undermined workplace safety, Pittsburgh’s Public Source and The Associated Press have found.
The blast came on top of a string of other accidents at the Clairton plant over time, as well as a long history of legal battles between U.S. Steel and Allegheny County regulators, who regularly accuse the company of flouting environmental rules at the facility.
The report noted that a similar gas oven explosion occurred at the Clairton plant in July 2010, injuring 14 U.S. Steel employees and six contractors. The report criticized U.S. Steel for failing to conduct a subsequent facility siting evaluation after that incident.
