🗞️ Deadly Blast, Deferred Action: OSHA Fines U.S. Steel and Contractor After Clairton Coke Works Explosion

On August 11 2025, an explosion tore through Battery 13 at the Clairton Coke Works, a sprawling 392-acre facility along the Monongahela River about 20 miles south of Pittsburgh, Pennsylvania. The blast — triggered when workers attempted to flush a cracked gas isolation valve using high-pressure water — caused a rupture that released combustible coke oven gas, which then ignited. Two U.S. Steel employees were killed, four others and a contractor were seriously injured, and six additional workers sustained non-hospitalization injuries.

The U.S. Chemical Safety Board (CSB), an independent federal agency, opened an investigation immediately and released a preliminary update in late September 2025 confirming the chain of events. By December 2025, the CSB had issued interim safety recommendations to U.S. Steel, including a call to conduct thorough evaluations of all personnel-occupied buildings near hazardous processes at the site — after finding that the buildings where the fatalities occurred were not capable of protecting occupants from explosion hazards. The CSB also noted that U.S. Steel had already rebuilt the damaged coke oven gas supply piping in nearly the same configuration as before the blast.

On February 18, 2026, the Department of Labor's Occupational Safety and Health Administration (OSHA) formally cited two employers following its own investigation. U.S. Steel received seven serious and one other-than-serious violation, with $118,214 in proposed penalties, for failing to apply required safety management and energy control practices for work involving flammable gas. Cleaning services contractor MPW Industrial Services Inc. received four serious and two other-than-serious violations and faces $61,473 in proposed penalties for failing to provide a pressure relief valve on its high-pressure water system and for not coordinating energy control practices with U.S. Steel. Both employers have 15 business days to comply, request an informal conference, or contest the findings.

The explosion did not occur in a vacuum. The Clairton Coke Works is the largest coking facility in North America, employing nearly 1,300 workers and producing 4.3 million tons of coke annually. It has a well-documented history of accidents and environmental violations — including a 2009 explosion that killed a worker, a 2010 blast that injured 20, and a 2018 Christmas Eve fire that knocked out pollution controls for three months and caused a dramatic spike in sulfur emissions linked to increased asthma cases in surrounding communities. Federal EPA data reviewed by PublicSource and the Associated Press identified the plant as a "high-priority violator" of the Clean Air Act — a designation held by only about 11% of major emitters.

The August 2025 explosion came just weeks after Japanese steelmaker Nippon Steel completed its approximately $15 billion acquisition of U.S. Steel following approval by President Trump. Nippon Steel had pledged to invest $2.4 billion in U.S. Steel's Mon Valley Works, which includes Clairton, though the blast raised immediate questions about the plant's future and the adequacy of safety protocols under new ownership. U.S. Steel stated after the incident that it had "strengthened several safety protocols," including prohibiting the use of high-pressure water for valve cleaning.

Key Points

• The explosion occurred on August 11, 2025, at U.S. Steel's Clairton Coke Works in Pennsylvania, killing 2 workers and injuring 12 when a cracked gas isolation valve ruptured during a high-pressure water flush, igniting coke oven gas.
• OSHA fined U.S. Steel $118,214 for seven serious violations related to inadequate safety management and energy control practices for flammable gas work.
• OSHA fined MPW Industrial Services $61,473 for four serious violations, including failure to provide a relief valve and failure to coordinate hazardous energy control with U.S. Steel.
• The CSB issued interim recommendations in December 2025 urging U.S. Steel to evaluate all occupied buildings near hazardous processes and reduce identified risks before resuming full operations.
• The plant has a long history of accidents, environmental violations, and regulatory conflicts with the Allegheny County Health Department, which has fined U.S. Steel millions over Clean Air Act violations in recent years.
• Nippon Steel acquired U.S. Steel in June 2025 with a pledge to invest in the Mon Valley Works; the explosion added uncertainty to those commitments.
• Both cited employers have 15 business days to comply, request an informal OSHA conference, or contest the findings before the Occupational Safety and Health Review Commission.

Primary Source Author: U.S. Department of Labor, Occupational Safety and Health Administration

Primary Source: US Department of Labor cites 2 Pennsylvania employers with serious safety violations following 2025 Clairton Coke Works explosion

Primary Source Link: https://www.dol.gov/newsroom/releases/osha/osha20260218

Supplemental Sources

• OSHA Fines U.S. Steel After Clairton Explosion — PublicSource / AP
• CSB Interim Safety Recommendations to U.S. Steel Clairton Coke Works — U.S. Chemical Safety Board
• CSB Preliminary Investigation Update — U.S. Chemical Safety Board
• Fatal Explosion Triggered During Valve Maintenance — WESA 90.5 Pittsburgh
• Clairton Coke Works History of Problems — The Allegheny Front
• CSB Calls for Safety Fixes as U.S. Steel Rebuilds — Insurance Journal
• Pollution, Safety Issues Plagued Coke Plant — Altoona Mirror / PublicSource / AP