The U.S. Chemical Safety and Hazard Investigation Board issued a final report Tuesday into the August 2025 explosion at the Clairton Coke Works that killed two workers and injured 11 others, finding the blast resulted from long-standing, informal practices for cleaning and flushing gas valves and urging written procedures and contractor training to prevent a repeat.
Board pins cause on ad hoc valve-cleaning practice
The CSB’s final analysis says the explosion occurred when workers were flushing a gas valve with pressurized water in advance of planned maintenance. According to the report, the valve ruptured under the intense pressure and released combustible coke oven gas, which subsequently ignited.
The facility, operated by U.S. Steel, is the largest coke-making complex of its kind in the Western Hemisphere and sits along the Monongahela River near Pittsburgh. Company statements cited by the report indicate the water wash was performed while preparing the valve for routine maintenance.
Board recommends written procedures and contractor safeguards
Investigators concluded the company had used steam or high-pressure water injected into a valve cleanout port when a valve would not fully close. That approach, the report says, was used on an informal, ad hoc basis for at least three years before the accident.
- CSB recommendation: U.S. Steel should develop a written procedure for washing valves with pressurized water to reduce hazards associated with the task.
- Contractor guidance: The industrial cleaning contractor that applied pressurized water with a pump truck should establish written policies for cleaning piping that contains flammable or toxic gas and provide training for workers performing those operations.
“The blast was the result of workers routinely performing a task incorrectly over a period of years until it ultimately led to a catastrophic explosion.” — CSB member Sylvia Johnson
Regulatory context and prior OSHA action
The Occupational Safety and Health Administration previously cited U.S. Steel after the incident, issuing 10 violations and proposing a total of $118,214 in penalties. OSHA found that written procedures, practices and training related to safely maintaining equipment and flushing the valve were incomplete, outdated or inadequate.
| Item | Figure |
|---|---|
| Deaths | 2 |
| Injuries | 11 |
| OSHA proposed penalties | $118,214 |
Local impact and implications
For Clairton and surrounding communities, the CSB’s final report highlights hazards at an operation that has a significant footprint in the region’s economy and environment. The board’s recommendations focus on preventing the kind of informal, routine workarounds that investigators said led to the release of flammable gas.
By urging both company-written procedures and contractor policies and training, the CSB emphasizes that responsibility spans the plant operator and third-party firms hired to perform specialized cleaning tasks. The board did not assign a monetary penalty but submitted safety recommendations intended to reduce the risk of future catastrophic releases.
What comes next
The report leaves open how U.S. Steel and the named contractor will implement the CSB’s recommendations. Federal safety boards like the CSB can issue findings and recommendations but generally do not have enforcement authority; OSHA and other agencies may decide on follow-up inspections or enforcement actions based on the findings.
Community groups and labor advocates often press for both immediate changes on the shop floor and broader oversight of high-hazard operations. The CSB’s report provides a basis for regulators and the company to review practices, update procedures, and institute training to better protect workers and surrounding communities.
Investigators noted that the practice of injecting steam or high-pressure water to clear valve seats had been used intermittently for years despite a lack of a formal procedure prescribing it. The board concluded that the absence of clear, documented methods allowed unsafe practices to become routine, ultimately culminating in the deadly 2025 explosion.
As the plant and regulators consider next steps, the families of the victims, former and current employees, and local officials will be watching whether the CSB’s recommendations are adopted and whether additional regulatory or legal measures follow.
