An explosion at U.S. Steel's Clairton plant outside Pittsburgh killed one person, left at least two unaccounted for, and injured dozens more on Monday, prompting a large-scale emergency response and renewed concerns over the facility's safety record.
The blast, reported around 10:51 a.m., sent black smoke billowing over the Monongahela Valley. Allegheny County Emergency Services spokesperson Kasey Reigner confirmed one fatality and said multiple people were treated for injuries. "It felt like thunder," construction worker Zachary Buday told WTAE-TV. "Shook the scaffold, shook my chest, and shook the building."
County officials dispatched 15 ambulances in addition to local emergency units, with patients sent to several area hospitals, including UPMC Mercy, Allegheny General, and Jefferson Hospital. Residents within a one-mile radius were advised to stay indoors, close windows, and set air systems to recirculate. The Allegheny County Health Department said its monitors have not recorded soot or sulfur dioxide levels above federal standards.
Sources told KDKA-TV the explosion occurred in the "reversing room" of coke oven batteries 13 and 14, which regulate coal baking temperatures. U.S. Steel said in a statement, "Our top priority is the safety and wellbeing of our employees and the environment... We are working closely with relevant authorities to investigate the cause of the incident."
The Clairton plant, employing about 1,400 workers, is the largest coking operation in North America, producing 4.3 million tons of coke annually. The process involves heating coal to remove impurities, generating a mix of methane, carbon dioxide, and carbon monoxide.
The facility has a long history of accidents and environmental violations. In 2009, a maintenance worker was killed in an explosion; in 2010, another blast injured 20 people. Fires in 2018 and 2024 damaged pollution control systems, leading to lawsuits accusing U.S. Steel of thousands of Clean Air Act violations. In recent years, the company has agreed to more than $30 million in settlements and equipment upgrades.
Environmental groups renewed calls for oversight. There needs to be "a full, independent investigation into the causes of this latest catastrophe," said David Masur, executive director of PennEnvironment.
The incident comes two months after U.S. Steel finalized a $15 billion partnership with Japan's Nippon Steel, an agreement shaped by national security reviews and political scrutiny in Pennsylvania.
Clairton Mayor Richard Lattanzi called it "a sad day for Clairton," adding, "Some people are not going to see the same husband or son or somebody that's working the mill."
