Coke Works blast ‘should never have happened’

The U.S. Chemical Safety and Hazard Investigation Board has released its report on the 2025 explosion that killed two workers.

One year after an explosion at U.S. Steel’s Clairton Coke Works killed two employees, federal investigators say the disaster “should never have happened.”

U.S. Steel employees Steven Menefee and Timothy “TQ” Quinn were killed in the Aug. 11, 2025, blast. Eleven others were injured, five seriously.

On Monday, a day before the first anniversary of the explosion, the U.S. Chemical Safety and Hazard Investigation Board released its final report, concluding that an informal valve-cleaning practice, inadequate safeguards and occupied buildings located dangerously close to coke oven gas piping combined to turn a maintenance operation into a catastrophe.

The explosion caused an estimated $52.5 million in property damage.

“This deadly incident was the result of an ad hoc informal procedure, poor facility siting, and an ineffective process safety management system at the Clairton facility,” CSB Chairperson Steve Owens said. “It should never have happened.”

The CSB determined the direct cause was the overpressurization of a cast-iron double disc gate valve while U.S. Steel employees and contractors from MPW Industrial Services were attempting to wash the valve with high-pressure water.

But the board’s 86-page investigation goes considerably further, finding that a series of decisions and missed opportunities stretching back years contributed to the disaster and its severity.

Among the most significant findings, investigators said U.S. Steel had been using pressurized water to clean valves on an ad hoc basis for at least three years without developing a formal procedure for doing it safely.

The board also concluded that occupied buildings in the area of the explosion were located less than 20 feet directly above the coke oven gas piping that became the source of the release.

Those buildings were routinely occupied by employees, but none was designed or constructed to withstand an explosion.

The CSB identified three key safety issues: procedures and hazard analysis, facility siting and process safety management systems.

What happened

The explosion occurred at approximately 10:47 a.m. Aug. 11, 2025, between Batteries 13 and 14 at the sprawling Clairton plant.

The Coke Works, which dates to 1901 and sits along roughly three miles of the Monongahela River, is the largest coke manufacturing facility in the Western Hemisphere. At the time of the incident, the plant employed approximately 1,150 people and had about 350 resident contractors.

It currently operates six coke batteries containing a total of 455 ovens.

Coke is produced by heating metallurgical coal to about 2,000 degrees for at least 18 hours. The process releases coke oven gas, a highly flammable, toxic and colorless mixture containing hydrogen, methane, nitrogen and carbon monoxide.

Some of that processed gas is reused as fuel to heat the coke ovens, while the remainder is sent through pipelines to U.S. Steel’s Irvin and Edgar Thomson plants.

Five weeks before the fatal explosion, on July 8, 2025, a U.S. Steel employee discovered a coke oven gas leak from a valve downstream of the Battery 13 isolation valve.

The company found a hairline crack near one of the valve’s flanges and applied a metal repair composite as a temporary repair. Subsequent monitoring indicated the gas had stopped leaking.

The isolation valve involved in the eventual explosion was an 18-inch double disc gate valve manufactured in 1953. It was made of cast iron and rated for 50 pounds per square inch gauge. The valve had been refurbished in 2013 after both of its gates were found to be cracked and were replaced.

U.S. Steel had a procedure for periodically “exercising” valves, which meant closing and reopening them to make sure they could operate through their full range.

Workers told investigators that coke oven gas residue could accumulate around valve seats and sometimes prevent a valve from closing completely. When that happened, employees sometimes injected steam or water through a cleanout port to clear the material away.

There was an important difference between those practices.

U.S. Steel’s written valve-exercising procedure specified a maximum steam pressure of 10 psi. It did not mention using water to clean the valve seat.

Yet employees had been using pressurized water to clean valves on an ad hoc basis for at least three years before the explosion.

The company had no formal procedure telling workers how to safely perform that operation.

An ad hoc job

On the morning of the explosion, a U.S. Steel supervisor decided to exercise the Battery 13 isolation valve to make sure it was operating correctly. Contractors from MPW, which regularly provided industrial cleaning services at Clairton, were brought in with a pump truck to apply pressurized water to the valve.

According to the CSB, the U.S. Steel supervisor directing the work was described to investigators as the facility’s “water washing expert.”

But there was no formal written procedure for washing the valve with water.

Investigators found neither U.S. Steel nor MPW adequately identified or addressed the hazards created by applying pressurized water to the valve at a pressure greater than its design rating.

As workers applied the water, the valve’s two gates were closed or nearly fully closed. That created an enclosed space between the gates.

Pressurized water filled the space and caused the pressure inside the cast-iron valve to rise beyond what it could contain. The valve catastrophically failed, and approximately 19 pounds of toxic and highly flammable coke oven gas escaped into the surrounding area.

Workers began evacuating and warning others. Twenty-four seconds after an evacuation order was issued over the radio, the released gas ignited and exploded.

Workers directly above the danger

The location of workers became a central part of the CSB’s investigation. The explosion occurred in what U.S. Steel called the “transfer area” between Batteries 13 and 14.

Several buildings routinely occupied by employees were located there, including reversing rooms used to control and monitor the coke batteries, an electrical distribution center and a break room.

The buildings sat less than 20 feet directly above the coke oven gas piping, and none was designed or constructed to withstand an explosion.

All three occupied buildings involved in the incident suffered catastrophic damage.

Menefee and Quinn were each in or near separate control rooms directly above the gas piping when the explosion occurred.

According to the CSB, one of the fatally injured workers was propelled by the force of the explosion and found beneath rubble by emergency responders on the ground level adjacent to the coke batteries.

The other was buried in debris and located by a search-and-rescue team roughly nine hours after the explosion.

Two other workers were inside a break room directly above the gas piping. Both were seriously injured by debris from the room’s walls and ceiling. One suffered burns, broken ribs, broken vertebrae and a broken tibia. The other suffered shrapnel wounds to his face, burns and broken bones in his spine, ankle, lower legs, knees and hands.

One managed to free himself from the rubble, crawl from the debris and find help.

The other was trapped and unable to free himself. Emergency responders found him alive roughly four hours after the explosion.

Nine other people who were outside those buildings were also injured, three seriously.

CSB Investigator in Charge Drew Sahli said the placement of occupied buildings made the consequences of the explosion far worse.

Years without a formal procedure

Investigators found the water- washing practice that led to the explosion wasn’t new.

U.S. Steel workers told the CSB that when valves wouldn’t fully close because of accumulated residue, steam or water could be injected into the valve in an attempt to clear it.

But while the company’s valve-exercising procedure addressed the use of steam, it said nothing about using water.

Despite that, workers had used pressurized water for at least three years before the explosion.

The CSB found U.S. Steel never developed a formal procedure for water washing, even though the practice was used to prepare isolation valves for maintenance outages.

Investigators concluded U.S. Steel had multiple opportunities in the years before the explosion to evaluate and address hazards created by placing occupied buildings close to coke oven gas piping.

The company did not do so, the CSB said, because it believed it wasn’t required.

The CSB concluded that locating occupied buildings so close to the coke oven gas system “increased the severity of this incident.”

The report also notes that more than 20,000 people live in more than 10,000 housing units within approximately three miles of the Clairton facility.

Seven public schools are located within three miles of the plant.

Process safety questions

The investigation also examined U.S. Steel’s broader process safety management practices.

The federal Occupational Safety and Health Administration’s Process Safety Management standard establishes requirements intended to prevent or minimize catastrophic releases of toxic, reactive, flammable or explosive chemicals.

The standard applies to processes containing 10,000 pounds or more of certain flammable gases or liquids.

According to the CSB, U.S. Steel reported in its 2025 emergency-planning inventory that the Clairton facility handled an estimated maximum potential daily inventory of 2.5 million pounds of coke oven gas.

The CSB concluded U.S. Steel did not have sufficiently robust process safety management systems in place that could have prevented or reduced the severity of the explosion.

Recommendations for U.S. Steel

The CSB made five recommendations to U.S. Steel as a result of the investigation. Two were already issued on an interim basis in December. The board called on U.S. Steel to conduct a siting evaluation of all occupied and potentially occupied buildings at Clairton and mitigate hazards identified through that review.

The CSB is also recommending that U.S. Steel develop a written procedure for washing valve seats with pressurized water.

The board wants workers who perform or could perform the operation involved in developing the procedure and trained on it.

Its fifth recommendation calls for a comprehensive process safety management system covering all coke oven gas processes at Clairton.

Amanda Malkowski, a spokesperson for U.S. Steel, said in an statement emailed to TribLive the company will review the chemical safety board’s report and recommendations.

Because of the explosion, U.S. Steel has strengthened several safety protocols, established best practices for industrial valve cleaning and improved its Management of Change program to better assess procedural changes, Malkowski said.

Employees have been trained on the new program elements and procedural changes, she said.

“Safety is our core value and shapes every part of our business, influences how we lead and anchors our responsibility to ensure that every employee returns home safely, every single day,” she said. “This unwavering commitment is reflected across all of our operations, from the way our leaders model safety expectations to the meaningful engagement of our employees who drive continuous improvement at the frontline.

“We continue to hold in our thoughts the employees who were injured or lost during the Aug. 11 incident. We remain mindful of their families, colleagues and loved ones. Their memory guides our commitment to safety every day.”

In February, Quinn’s sister, Trisha Quinn, sued Nippon Steel, MPW and Valves Inc. of Pittsburgh, which in 2013 refurbished the valve where the explosion occurred. A week later Menefee’s wife, Danielle Menefee, filed a similar lawsuit.

Both cases, which began in Allegheny County Common Pleas Court, have moved to federal court.

Lupetin & Unatin LLC, the firm representing Trisha Quinn, said in a statement the explosions were caused by a lack of written rules, missed safety checks and poor safety management.

Quinn would have celebrated his 40th birthday last week, the statement said.

“The (chemical safety board) report makes clear that this tragedy was worse than it had to be. Workers like Tim were put in terrible danger because their breakrooms and work areas were placed too close to the hazard and weren’t built to survive a blast.”

Frischman & Rizza, the firm representing Danielle Menefee, could not be reached for comment Monday.

The chemical safety board is an independent federal agency. It does not issue citations or fines but makes safety recommendations to companies, industry organizations, labor groups and regulatory agencies — including OSHA.

Nippon Steel, contractor also face recommendations

The CSB also directed recommendations to Nippon Steel North America and MPW.

Nippon Steel North America acquired U.S. Steel in June 2025, about two months before the Clairton explosion.

The CSB wants Nippon Steel North America to develop and implement a corporate process safety governance program.

The CSB said all MPW workers who could participate in those operations should be trained on the procedures.

The board isn’t a regulatory or enforcement agency and doesn’t issue citations or fines.

Its role is to investigate major chemical incidents, determine their causes and issue safety recommendations intended to prevent similar disasters.