U.S. Steel Clairton Blast Final Report Cites Years of Ad Hoc Valve Cleaning

A federal investigation into the August 2025 explosion at U.S. Steel's Clairton Coke Works near Pittsburgh has concluded that the fatal incident stemmed from a long-standing, informal practice of cleaning gas valves with pressurized water, a task performed without any formal written procedure.

The U.S. Chemical Safety and Hazard Investigation Board released its final report, which found that for at least three years prior to the blast, employees had used pressurized water to clean valve seats on an ad hoc basis. The explosion, which killed two workers and injured 11 others including contractors, occurred while workers were flushing a gas valve in preparation for routine maintenance. The valve ruptured under intense pressure, releasing combustible coke oven gas.

The report highlighted that the failed valve was over 70 years old and made of cast iron, a material widely recognized as brittle and often banned or warned against for use with flammable substances. It also noted that the two workers who died and two of the five seriously injured were in buildings directly above the gas piping. The investigator in charge, Drew Sahli, stated that if those buildings had been located elsewhere, the incident could have been far less severe.

Chemical Safety Board member Sylvia Johnson said the blast was the result of workers routinely performing a task incorrectly over a period of years until it led to a catastrophic explosion. The board recommended that U.S. Steel develop a written procedure for washing valves with pressurized water. It also urged the industrial cleaning contractor involved to create written policies for cleaning piping systems containing flammable or toxic gas and to train workers accordingly.

The report also criticized U.S. Steel for failing to conduct a facility siting evaluation after a similar gas oven explosion at the plant in July 2010 that injured 20 people. The Clairton facility has a history of accidents and legal disputes with county regulators over environmental compliance. The Occupational Safety and Health Administration previously fined the company $118,214 and issued 10 citations, stating that written procedures and training were incomplete, outdated, or inadequate.