Updated: Two Dead, 10 Injured in Clairton, PA, Steel Plant Explosion

The century-old plant is the largest in the United States and sits on 400 acres.

Aug. 12, 2025

9 min read

Hallie Lauer

Pittsburgh Post-Gazette

(TNS)

Aug. 11—The Clairton Coke Works Plant in the Mon Valley plays an essential role in steelmaking in the United States.

The century-old plant was the site of an explosion Monday that killed two people and left at least 10 people injured.

Here's what you need to know about what happens inside and around the massive plant.

What is Clairton Coke Works?

The Clairton Coke Works plant is located about 20 miles south of Pittsburgh along the Monongahela River. The Clairton plant helps make up the Mon Valley Works division, along with the Edgar Thomson Plant and Irvin Plant along the Mon River and the Fairless Plant near Philadelphia, which puts finishing touches on Western Pennsylvania-created products. About 3,000 people work at the facilities, including 1,300 people at the Clairton Coke Works.

The Mon Valley Works were part of the recent acquisition by Japanese steelmaker Nippon Steel, which purchased the iconic Pittsburgh steelmaker in a $15 billion acquisition. Pittsburgh has been the headquarters for U.S. Steel since 1931.

How old is Clairton Coke Works?

The plant has been in operation 109 years.

Clairton Coke Works is the largest coke manufacturing facility in the United States, sitting on nearly 400 acres. The plant was built in 1916 and had an even larger footprint with about 1,500 ovens at the time. Now it has 10 coke ovens.

What happens at the plant?

The Clairton Coke Works is one part of the overall steelmaking process.

The plant is where workers process raw coal into coke via massive ovens. The plant produces about 4.3 million tons of coke annually, according to U.S. Steel's website.

Its 10 coke batteries digest more than 18,000 tons of coal daily, cooking it until it releases organic compounds like sulfur and nitrogen and concentrating the carbon left over into coke.

Coal is crushed and blended before being put in the ovens, where it will essentially bake at 1,800 degrees Fahrenheit for 18 hours. This removes impurities in the coal and what's left behind is the coke.

Once cooled, the coke is transported to a blast furnace. Oftentimes, it is transported to the nearby Edgar Thomson Works, which just marked its 150th year of operations. From there, the chemical reaction from blasting — blowing hot air into the furnace from the bottom — coke, iron ore and limestone creates molten iron. Other elements are added to the molten iron to create the steel.

Is the process dangerous?

The creation of coke is potentially dangerous for a number of reasons.

It can be dangerous to people's health because of the carbon emissions that come from the heating process, but the process itself is also dangerous.

During the heating process, the coal expands as it softens, leading to increased pressure inside the ovens. This pressure over time can lead to oven walls cracking or bending, which can shorten the lifespan of the ovens.

Workers also deal with extremely high temperatures during the coke-making process.

It's unclear at this point what led to the explosion at the Clairton Coke Works. At a news conference Monday afternoon, U.S. Steel officials said the investigation had only just begun and they did not yet know the cause.

Have there been other incidents at the plant?

There have not been other major explosions at the Clairton Coke Works. However, earlier this year, U.S. Steel halted production in one of the batteries after the release of excess gas caused an ignition and a loud boom.

Two employees were taken to the hospital after getting material in their eyes, although both were later released and returned to work.

U.S. Steel said that incident was a "rare occurrence" and that there was no risk to the community.

The Allegheny County Health Department attributed the incident to a hydraulic failure that led to a buildup of combustible material that then caught fire. Neighbors said the early-morning boom woke them up around 4:30 a.m.

In 2018, a massive fire on Christmas Eve caused about $40 million in damage and destroyed pollution control equipment causing sulfur dioxide to leak into the air. Residents in the area sued U.S. Steel over the pollution. The company settled and said it has since invested more than $750 million in improvement projects at the Mon Valley Works, including about $100 million annually in Clairton for environmental compliance.

What's next for the plant?

With the acquisition by Nippon Steel, significant modernization projects for the Mon Valley Works have been promised to the tune of $2.4 billion. The company also promised to not close any existing facilities for at least a decade.

Though Nippon promised to not fundamentally change how steel is made in the Mon Valley, plants owned by the company in Japan have set a goal to reduce carbon emissions by switching out some of the coke with hydrogen.

The company estimated it could reduce emissions by 50% by doing so. The company could also eliminate blast furnaces entirely in pursuit of a cleaner steelmaking process. Concerns regarding that option are what prompted members of the United Steelworkers to seek assurances that Nippon was not looking to close their blast furnaces, which could eliminate a significant number of jobs.

Has Clairton Coke Works recently been fined?

In February 2024, U.S. Steel was issued a $1.9 million fine over uncontrolled emissions at the Clairton Coke Works.

The enforcement order found that the plant was not capturing and ducting the emissions prior to pushing the coke out of an oven. The Allegheny County Health Department found that the plant did not use mandated pollution controlling equipment more than 350 times between March 2022 and December 2023.

The February fine came just one month after the county slapped a $2.2 million fine on the company over air-emission violations at the Clairton plant.

Two other times in 2023, U.S. Steel was fined for violations at Clairton Coke Works for air-emission violations, for about $300,000 each.

Environmentalists have long protested the plant and its impact on local air quality. They have been pushing for Nippon to implement cleaner operations.

“The steel way of life is sacred here, the union way of life is sacred here,” he said. “That’s why I fought for (the plant to reopen) as lieutenant governor and why I’m proud to be here today.”

He also said that support for steelworkers is why he “jammed up” the sale of U.S. Steel to Nippon Steel “and forced them to make the billions and billions of investment to upgrade this facility and all of the other facilities here in the Valley.”

Monday's explosion in Clairton shook Melanie Meade’s house, which overlooks the sprawling plant, but booms and bangs at the plant are nothing new, she said.

“It felt like the house shook,” she said. “It was really, really loud and then you saw large plumes of dark smoke.”

Meade has been an environmental activist since 2014 in a town where her family has lived since the early 1900s.

But smaller sounding explosions from the plant are fairly routine in the neighborhood, she added. There’ve been at least three other explosions at the plant this year alone.

“I could hear and feel earlier explosions,” she said. “I hear booms through the night. We could never find out what they were. And this would wake me up.”

No one from any government agency has been to Clairton to explain the noises, she said, “so we have to wonder what’s exploding and where.”

Her real concern is a ballfield directly across the street from the site of the explosion, where kids as young as 5 practice football. Nothing warns the children or parents about the air pollution risks of using the field, she said.

As of late afternoon, she said she hadn’t received any word from the county health department about unhealthy pollution levels in Clairton as a result of the explosion.

Trisha Quinn, 39, told the Pittsburgh Post-Gazette that she was told her brother Timothy was the person killed in the explosion. She said Timothy, a father of three, lived with their mother to help take care of her in South Huntingdon, Westmoreland County.

Quinn had told the Post-Gazette earlier in the day that her brother was on the battery at the time of the explosion.

She said she had been calling every hospital around Pittsburgh to try to locate her brother. As of mid-afternoon Monday, she hadn’t had any luck.

“There was a coworker that said my brother was loaded into the ambulance and wasn’t responsive at the time, that they thought he was deceased,” she said at the time.

Attempts to confirm the information with U.S. Steel and county officials were not successful.

Ms. Quinn said her brother has worked at the mill for 17 years, and her father worked at the same mill for 42.

Local and state officials during a news conference Monday afternoon said in addition to the one fatality, one of the two unaccounted-for people had been rescued and taken to a hospital. Another person remains missing.

The person who died in the incident died at the hospital, U.S. Steel Senior Vice President Scott Buckiso said.

Matt Brown, chief of Allegheny County Emergency Services, said about 20 EMS agencies and 14 fire departments responded to the scene, along with county resources. They are continuing to work at the scene to find the remaining person who is missing.

Ten people were injured, said Victor Joseph, assistant superintendent of Allegheny County Police.

PennEnvironment, a statewide environmental advocacy nonprofit, said its thoughts and prayers were with the people and families affected by the catastrophic accident, as well as the Clairton community.

The group also called for a full, independent investigation.

U.S. Steel CEO David B. Burritt in a statement Monday afternoon said “our top priority is the safety and well-being of our employees and the environment.”

He said the company was working closely with authorities to investigate the explosion at the plant, where nearly 1,300 people work.

“During times like this, U.S. Steel employees come together to extend their love, prayers, and support to everyone affected,” he said.

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