Six months after an August 2025 explosion at U.S. Steel’s Clairton Coke Works outside Pittsburgh killed two workers and injured 11 others, the questions raised by the crash have merged with longer-running disputes over air pollution and day-to-day plant safety. A report by The Associated Press and Pittsburgh’s Public Source revisited the Chemical Safety Board’s findings on how the blast happened and tied them to concerns workers and regulators have raised for years. In the aftermath, workers said they remain unsettled, and residents have pushed for clearer answers about the plant’s safety practices and pollution controls.
The Clairton facility turns coal into coke at high temperatures inside industrial ovens that have operated for more than a century. That process produces a flammable byproduct, coke oven gas. The Chemical Safety Board has been investigating the incident’s cause, and the board has described the August blast as occurring during a specific sequence of work involving valves and gas isolation.
According to the Chemical Safety Board, the explosion happened while workers were closing and opening a gas isolation valve in a basement after pumping water into the valve. The agency said U.S. Steel’s written procedure did not mention the use of water and that a U.S. Steel supervisor directed workers to pump the water, and the valve then cracked, allowing gas into the area. In an October presentation to residents, U.S. Steel vice president Kurt Barshick described workers as trapped “3,000 PSI water inside of a valve that’s rated for 50 PSI,” and said the valve cracked and gas filled the area.
The Chemical Safety Board investigator in charge, Drew Sahli, described the incident as a “release of coke oven gas” that “contacted an ignition source” and exploded. Sahli also said the agency was still investigating how the gas was released and what mechanisms led to the ignition during the valve work. U.S. Steel, in a statement, emphasized its commitment to safety and said it has “strengthened several safety protocols” based on its ongoing investigation, including prohibiting the use of high-pressure water for valve cleaning.
Workers and some former employees who were interviewed for the report said they believed management decisions contributed to both operational problems and safety risk at the aging plant. They pointed to difficulties obtaining replacement parts for coke oven doors that can leak emissions, and they also raised concerns about maintenance and upkeep after other incidents. One example cited was a fire at the plant on Christmas Eve in 2018 that shut down pollution control equipment and led to repeated air pollution releases, according to a lawsuit filed by environmental groups after the incident.
In that 2018 case, an engineer hired by the plaintiffs wrote in a filed report that he found “no indication” that U.S. Steel “has an effective, comprehensive maintenance program for the Clairton plant.” The engineer also wrote that the 2018 accident “preventable by a robust inspection and preventive maintenance program and by better plant design.” The lawsuit later resulted in a 2024 consent decree in which U.S. Steel agreed to measures that included investing close to $20 million in facility upgrades, while admitting no liability. In its own statement for the AP/Public Source report, U.S. Steel said its “overall transformation efforts have improved our company’s performance, created a robust maintenance program, and improved employee safety over time.”
The plant’s record has also fueled scrutiny from local environmental regulators, with frequent clashes between U.S. Steel and Allegheny County regulators over the company’s permit compliance. The Allegheny County Health Department has said it is the largest local source of air pollution in recent years, and in 2023 the department fined U.S. Steel more than $2 million for violations at Clairton. In response to questions, the health department said air monitoring stations near the plant have measured a 15-25% reduction in annual average particle pollution concentrations compared with ten years ago.
On a broader scale, Public Source and The Associated Press analyzed federal Clean Air Act compliance data for about 14,000 facilities and concluded that Clairton’s national record stands out. Their analysis said the EPA classifies the plant as a “high-priority violator” and that only about 11% of major emitters fall into that category. The analysis further found that Clairton was among just 11 facilities nationwide that faced $10 million in penalties or more in the last five years.
U.S. Steel, in a statement, said it spends “$100 million annually on environmental compliance at Clairton alone” and reported an environmental compliance rate exceeding 99% for regulated activities each year at the Clairton plant. The company’s statements also appeared alongside the safety and maintenance disagreements raised in the wake of the August blast, as residents and workers weigh what changes U.S. Steel has already made and what still needs to be addressed.
The timing of the scrutiny also intersects with a corporate transition. In June 2025, Nippon Steel completed a $15 billion acquisition of U.S. Steel, and Nippon Steel pledged to invest $14 billion in domestic steelmaking operations. In public comments in November, U.S. Steel said the Clairton Coke Plant is an “important part” of its North American flat-rolled integrated operations and that “steady coke supply remains critical,” adding that the “Clairton Coke Plant will be maintained for the next generation of steelmaking.” The AP/Public Source reporting said U.S. Steel had not publicly committed to spending money at the Clairton plant to expand production, extend its life, improve efficiency, upgrade safety, or reduce its polluting air emissions, and it said that of the $14 billion pledged, U.S. Steel has said $2.4 billion would go toward plants in the Pittsburgh area.
As questions about the explosion and the plant’s long-term operating record continue, workers’ accounts and regulators’ data have sharpened pressure on U.S. Steel’s successor owners to clarify maintenance priorities and safety practices. MSI previously reported that hope and nerves in Clairton have continued as residents and workers process six months after the mill explosion outside Pittsburgh developing coverage.