On August 11, 2025, at 10:47 a.m., 19 pounds of coke oven gas, a toxic and flammable gas mixture, released at U.S. Steel Clairton Coke Works. Of the 11 hurt workers, five of them suffered serious injuries, and blast caused an estimated $52.5 million in property damage, according to the final report issued by the Chemical Safety and Hazard Investigation Board (CSB).
Killed in the explosion were Steven Menefee and Timothy “TQ” Quinn.
The release occurred during a maintenance operation in which U.S. Steel employees and contractors 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 batteries, called Battery 13.
During this maintenance operation, the workers also attempted to wash the valve’s seat using pressurized water from a contractor’s pump truck, as instructed by a U.S. Steel supervisor.
No Procedure
U.S. Steel had no procedure for how to safely conduct this operation, but for at least three years prior to the incident, employees utilized pressurized water to clean valve seats on an ad hoc basis despite the lack of a formal procedure prescribing it. While applying pressurized water to the valve’s seats, the workers closed or nearly fully closed the valve’s double gates, creating an enclosed space between the two gates.
The pressurized water filled this space inside the cast iron valve and caused the pressure inside the valve to increase beyond the valve’s ability to contain it. The valve then failed catastrophically, allowing toxic and flammable coke oven gas to release into the surrounding area.
After the valve failed, the workers evacuated the area of the release and over the next one to two minutes alerted other workers of the need to evacuate. Twenty-four seconds after an evacuation order went out via radio, the released coke oven gas ignited and exploded.
The area in which the explosion occurred, called the “transfer area,” was in between Batteries 13 and 14 and contained multiple buildings routinely occupied by workers.
At the time of the explosion, Menefee and Quinn were each in or near separate control rooms and two of the five seriously injured workers were inside a break room. All three buildings were in the transfer area, less than 20 feet directly above the coke oven gas piping system that was the source of the release.
Post-incident photo of the 13/14 transfer area. The break room was behind the EDC and the Battery 14 reversing room.
Source: CSB
As it turns out, none of the buildings ended up designed or constructed to withstand an explosion. All three buildings suffered catastrophic damage.
Safety Issues
As a result of its investigation, the CSB investigation identified the safety issues:
- Procedures and Hazard Analysis: On the day of the incident, the valve washing operation was performed in a way that directly caused the catastrophic failure of the Battery 13 coke oven gas isolation valve. U.S. Steel occasionally utilized water washing to address valves that could not otherwise fully close, but the company never developed a formal procedure for water washing valves despite relying on it to prepare isolation valves for maintenance outages. Additionally, neither U.S. Steel nor its contractor, MPW Industrial Services, Inc., (MPW), identified or addressed the hazards created by applying pressurized water to the valve at a pressure greater than the valve’s design rating.
- Facility Siting: The buildings in the Battery 13/14 transfer area were less than 20 feet directly above the coke oven gas piping system. The buildings ended up occupied by U.S. Steel personnel and not designed nor constructed to withstand an explosion. Prior to the explosion, four U.S. Steel employees were occupying three buildings in the transfer area. All three buildings ended up destroyed by the explosion, which caused the deaths of two employees and seriously injured two other workers who were in or near the buildings. In the years leading up to the explosion, U.S. Steel had multiple opportunities to evaluate and address the inherent hazards resulting from the co-location of occupied buildings and the hazardous coke oven gas piping. However, U.S. Steel affirmatively chose not to do so.
- Process Safety Management Systems: Effective process safety management systems are crucial for facilities where hazardous chemicals end up produced and handled. U.S. Steel did not have sufficiently robust process safety management systems that could have prevented or reduced the severity of this incident.
Beginning of Incident
The entire incident really started on July 8, 2025, five weeks before when a U.S. Steel employee identified a coke oven gas leak from a valve downstream of the Battery 13 isolation valve. The company found the valve had a hairline crack near one of its flanges. U.S. Steel applied a metal repair composite onto the crack as a temporary repair.
Subsequent monitoring by U.S. Steel determined that coke oven gas had stopped leaking from the temporarily repaired valve. As a precaution, U.S. Steel placed air movers near the valve, intended to exhaust air outside to prevent the accumulation of flammable gas in the basement.
As a result, U.S. Steel began developing a plan to remove and replace the cracked valve by isolating and purging Battery 13’s coke oven gas supply. In addition, U.S. Steel planned to opportunistically replace at least three other valves in the Battery 13 coke oven gas supply piping system while they isolated and purged gas from the piping to the battery.
On July 28, 2025, two weeks before the incident, U.S. Steel held a “Hazardous Job Meeting” (HJM) to review and plan the scope of work for replacing the cracked valve. The job was planned for August 19, 2025. The objective of the HJM was to have a team approve a “Hazardous Job Procedure” (HJP) developed to address hazards associated with isolating and purging the coke oven gas system at Battery 13.
Pre-incident photo of the 13/14 transfer area. The break room is not pictured, as it was behind the EDC and the Battery 14 reversing room.
Source: U.S. Steel, annotated by CSB
Moreover, the HJP was a step-by- step written procedure intended to safely accomplish the tasks required to isolate and purge the Battery 13 coke oven gas system.
Team Assembled
The team assembled for the HJM included nine U.S. Steel employees and supervisors familiar with Battery 13 operation, maintenance, and safety practices. Three contractors also attended the meeting. Two of the contractors were there to assist U.S. Steel if any asbestos abatement would be needed, and the other was from a mechanical contracting firm.
The team approved isolating Battery 13 from the coke oven gas supply using the double disc gate valve and subsequently purging the coke oven gas from the Battery 13 piping to allow for removing and replacing the cracked valve. The plans made during the meeting did not include exercising, steaming, or washing the Battery 13 isolation valve. None of the workers or contractors who exercised and washed the isolation valve on the day of the incident were present at the meeting.
On Monday August 11, 2025, the day of the incident, a U.S. Steel supervisor decided to exercise the Battery 13 gas isolation valve, to confirm the valve’s isolation capability, in preparation for the upcoming Battery 13 outage. The supervisor had arranged for MPW to provide a pump truck to flush the Battery 13 isolation valve, and specified the equipment for MPW to use to assist with the task.
The MPW pump truck arrived at the Battery 13/14 transfer area, and by approximately 8 a.m., two MPW employees had connected water from a nearby hydrant to the pump truck. At 10:35 a.m., a U.S. Steel employee and an MPW employee connected a hose from the pump truck to a cleanout port on the bottom of the isolation valve. At 10:39 a.m., U.S. Steel personnel shut off the flow of coke oven gas to the individual Battery 13 ovens.
Pumping Water
MPW then began pumping water into the valve body through the cleanout port. Once water was introduced into the valve, the U.S. Steel employees began to exercise it.
w/art: Post-incident photo of the isolation valve involved in the incident (left) and a diagram of the valve internals (right).
Source: CSB
At this time there were three U.S. Steel employees (two operators and one supervisor) and two MPW contractors present at the scene. Each of the workers had personal carbon monoxide monitors, and one of the MPW employees carried a four-gas monitor to detect oxygen, carbon monoxide, hydrogen sulfide, and flammable gas.
One worker told investigators, “And then we started the water pressure through, turned on the valve to the bottom, ran it down, ran the gate[s] down, and it gets to a certain point, and you raise it back up a little bit, lower it down, to just wash it out. Anyway, we got to a point where the valve wouldn’t turn anymore, and we were [almost fully closed], and the monitor started to go off, so we tried to raise it. We couldn’t raise it. There was three or four of us on the wrench trying to pull it back up to raise it.
Valve Leaking Water
One worker told the CSB they observed water leaking from the valve. Another worker described the moment the valve failed:
“We heard a pop. It sounded like when you overinflate a tire. It just went [“pop”], and in my mind, I felt like it was a breach. I ran, and everybody ran out with me. And [the supervisor] was like, ‘What…what was that?’ I said, ‘I don’t know if that was the hose or if that was the valve.’ And [the supervisor] stuck his head back in and he said, ‘I smell gas.’ He wanted me to shut it off from outside of the battery. There’s no shutoff outside of the battery for it.”
Because they could smell gas and their personal gas monitors began alarming, four of the workers quickly evacuated the basement to the ground level adjacent to the batteries. One of the U.S. Steel operators ran up the stairs from the basement to the bench level and informed another U.S. Steel employee located there that the workers needed to evacuate, then ran to the Battery 13 reversing room and informed an operator there of the situation.
A worker, located on the bench level at the time of the incident, told the CSB they could smell coke oven gas and could hear the audible alarm from their personal gas monitor, indicating the releasing coke oven gas had risen to the bench level. This worker then called for the evacuation of Batteries 13 and 14 by radio, addressing the call to another U.S. Steel employee located on the top of the batteries.
Workers Ran Wrong Way
On the top level of the battery, a group of three workers consisting of a U.S. Steel employee, the ACHD environmental inspector, and the Veolia contractor, heard the radio evacuation call and began evacuating, but ran toward the Battery 13/14 transfer area instead of away from it. Twenty-four seconds after the radio evacuation call, at 10:47 a.m., the released coke oven gas ignited and exploded.
Click here for more extensive details in the final report.