Labor & Employment Law Daily Wrap Up, AGENCY NEWS—Chemical Safety Board issues report on fatal U.S. Steel Clairton Coke Works explosion, (Aug 17, 2026)

By Jason Albright, J.D.

“The U.S. Steel Clairton Coke Works facility was built in 1901 and is the largest coke manufacturing facility in the Western Hemisphere.”

The U.S. Chemical Safety and Hazard Investigation Board (CSB) has released a final report on a fatal explosion at the U.S. Steel Clairton Coke Works facility in Clairton, Pennsylvania, in August 2025. The incident occurred when “toxic flammable coke oven gas,” according to the agency, was released and exploded. The explosion fatally injured two people and injured 11 others, five of them seriously, causing an estimated $52.5 million in property damage.

Battery 13. The August 11, 2025 fatal explosion occurred during a maintenance operation in which U.S. Steel employees and contractors from MPW Industrial Services (MPW) were attempting to fully close and reopen a double disc gate isolation valve in the piping that supplied coke oven gas to one of U.S. Steel’s coke oven units, called Battery 13.

“Exercising” procedure. The CSB found that U.S. Steel maintained an operating procedure for “exercising” Battery 13’s cast iron double gate isolation valve, as well as other valves at the facility. Exercising a valve included closing it and then reopening it, to ensure that the valve could successfully operate through its full range. U.S. Steel employees told the CSB that they occasionally had difficulty fully closing a valve when exercising it due to the coke oven residue that accumulated in the valve seat over time.

Ad hoc cleaning. The CSB also found that U.S. Steel had a practice of injecting steam or high-pressure water into a valve’s cleanout port, in an attempt to remove residue, when the valve would not close fully. The company’s exercising procedure, however, did not mention the use of water, and the company had no formal procedure for washing valves with water. Despite this lack of a formal procedure for using water, U.S. Steel employees had used pressurized water to clean valves on an ad hoc basis for at least three years prior to the incident.

Catastrophic failure. On the day of the incident, a U.S. Steel supervisor decided to exercise the Battery 13 isolation valve, to confirm that the valve operated correctly. The supervisor arranged for contractors from MPW, a company that provides industrial cleaning services, to use a pump truck to apply pressurized water to the valve. While applying pressurized water to the valve’s seats, the workers closed, or nearly fully closed, the valve’s double gates, which created an enclosed space between the two gates. The pressurized water filled this space inside the valve and caused the pressure inside the valve to increase beyond the valve’s ability to contain it. The valve then failed catastrophically, releasing “toxic flammable coke oven gas,” according to the agency, into the surrounding area. Within minutes, the released gas ignited and exploded.

70-plus-year-old cast iron valve. The failed valve was made from cast iron and was over 70 years old. The valve was originally manufactured in 1953 and had been refurbished in 2013. Cast iron is widely recognized as a brittle material, and numerous safety publications either prohibit or warn against using cast iron equipment in certain hazardous applications, “including for flammable substances like coke oven gas,” noted the CSB.

“[T]ransfer area.” The explosion occurred in an area located between Batteries 13 and 14 called the “transfer area,” where there were multiple buildings routinely occupied by employees. The buildings were located less than 20 feet directly above the coke oven gas piping that was the source of the release. None of those buildings were designed or constructed to withstand an explosion, and all of them were catastrophically damaged.

Two fatal injuries. At the time of the explosion, the two fatally injured workers were each in or near separate control rooms directly above the coke oven gas piping, and two of the five seriously injured workers were inside a break room, also directly above the coke oven gas piping. One of the fatally injured employees was propelled by the force of the explosion and was found under rubble on the ground level adjacent to the coke batteries. The other fatally injured worker was buried in debris and found by a search and rescue team roughly nine hours after the explosion.

Key safety issues. The CSB identified three key safety issues that led to the severity of the incident: (1) procedures and hazard analysis; (2) facility siting; and (3) process safety management systems. As a result of its investigation, the CSB made a number of recommendations to U.S. Steel, MPW, and Nippon Steel North America (NSNA), which acquired U.S. Steel in June 2025.

Recommendations. The CSB recommended that U.S. Steel conduct a siting evaluation for all occupied and potentially occupied buildings at the Clairton Coke Works and mitigate all facility siting hazards that are identified. It also recommended that U.S. Steel develop a written procedure for washing valve seats with pressurized water to minimize the hazards of the operation and develop a comprehensive process safety management system for all coke oven gas processes at the Clairton facility.

Additionally, the CSB recommended that NSNA develop a corporate process safety governance program that will implement process safety management at its facilities, as well as conduct regular audits of facilities throughout the company’s organization and promptly correct process safety deficiencies. The CSB recommended that MPW develop written policies and procedures for cleaning piping systems containing “flammable or toxic gas” and ensure that all workers involved in such operations are trained on the policies and procedures.

Clairton Coke Works. Located near Pittsburgh, the U.S. Steel Clairton Coke Works plant was built in 1901. It is the largest coke manufacturing facility in the Western Hemisphere, according to the CSB. The plant processes coke inside coke ovens, which are connected by common walls and operated as one unit, a “coke battery.” U.S. Steel Clairton currently operates six such coke batteries, with a total of 455 ovens.

Process and gas release. The process of producing coke, the CSB noted, involves heating raw metallurgical coal to approximately 2,000 degrees Fahrenheit for a minimum of 18 hours. The nearly pure carbon that remains in the oven, the “coke,” is often used as fuel in blast furnaces for iron and steel production. During the production process, gases, known collectively as “coke oven gas,” are released and driven off into an off-gas piping system. Coke oven gas is highly flammable, toxic, and colorless, with a sulfurous odor. After tar, ammonia, light oil, and elemental sulfur is removed, the remaining coke oven gas is a mixture of hydrogen, methane, nitrogen and carbon monoxide, which is used, in part, to burn as fuel to heat the coke ovens.

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