New OSHA findings shed light on deadly U.S. Steel Clairton plant explosion
U.S. Steel is facing new fines levied by the Occupational Safety and Health Administration as a result of findings that shed new light on why a valve ruptured at its Clairton Coke Plant in August 2025, leading to an explosion that left two dead and a dozen injured.
The fines, which total nearly $120,000 for U.S. Steel, are also levied against contractor MPW Industrial Services, whose employees were working to clean the valve that eventually broke on the day of the explosion. It faces nearly $62,000 in fines.
The contractor failed to provide a relief valve for a high-pressure water system, according to a statement the U.S. Department of Labor, which includes OSHA, released on Wednesday. So, as pressure built, it couldn't escape before it was too late.
KDKA-TV was the first to report in the weeks after the explosion that, according to a local union vice president, contractors "significantly overpressurized" the valve that broke with water as they cleaned it.
U.S. Steel's Vice President told neighbors in October 2025 that workers trapped "3,000 PSI water inside of a valve that's rated for 50 PSI," according to a recent Associated Press report.
"Federal safety inspectors determined that United States Steel Corp. failed to use required safety management and energy control practices for hazardous work involving flammable gas," according to the Department of Labor's statement on Wednesday.
U.S. Steel's written procedures did not mention the use of water, saying a U.S. Steel supervisor directed workers to pump water, according to the U.S. Chemical Safety Board. Low-pressure steam had previously been used to clean valves, according to engineering and safety firm EDT.
"The department's Occupational Safety and Health Administration concluded United States Steel Corp. and MPW Industrial Services Inc. exposed workers at the Clairton Coke Works plant to unsafe working conditions including explosion, struck-by, and high-pressure injection hazards," according to the Department of Labor's statement.
OSHA also concluded MPW did not coordinate energy control practices for hazardous work involving flammable gas.
U.S. Steel was cited by OSHA with seven serious and one other-than-serious violations. MPW was cited by OSHA, with four serious and two other-than-serious violations.
Both U.S Steel and MPW have 15 days to either comply with the citations/findings, contest them, or request a conference with OSHA.
"We have received and are reviewing OSHA's citations related to the August 11 incident at our Clairton facility," said a statement from a U.S. Steel spokesperson on Wednesday. "We will continue our dialogue with OSHA and other agencies involved."
In the past, U.S. Steel has stressed how safety is a core value for them, adding that it anchors its responsibility to get all of its employees home each day.
In October 2025, U.S. Steel announced it would strengthen several safety protocols, including prohibiting the use of high-pressure water for cleaning valves as it reviews best practices. It also said it would review and restructure its management of change program, which assesses proposed changes in procedure and evaluates risk.
The high-pressure water was used to flush "accumulated deposits" in the valve, EDT's findings said.
When the valve ruptured, it released flammable coke oven gas, which then exploded when it reached an ignition source at battery 13/14. The gas had been accumulating in the transfer area's basement.
The U.S. Chemical Safety Board is still investigating the explosion.