Gas valve failure during routine maintenance work may have led to fatal
explosion, US Steel says
[August 16, 2025]
By MARC LEVY
HARRISBURG, Pa. (AP) — Preparations for a routine maintenance task may
have led to an explosion at a U.S. Steel coal-processing plant near
Pittsburgh that left two dead and sent 10 to hospitals, the company said
Friday.
U.S. Steel said it developed the information, along with other
investigators, from reviewing video footage and interviewing employees.
That has suggested to them that the explosion happened when workers were
flushing a gas valve in preparation for a routine planned maintenance
task, the company said.
The explosion, which heavily damaged part of the sprawling facility,
started around a set of ovens where coal is baked to 1,200 degrees
Fahrenheit (648.89 Celsius) into a more efficient carbon fuel called
coke, a key component in steelmaking. A byproduct of processing the coal
is a combustible gas called coke oven gas, made up of a lethal mix of
methane, carbon dioxide and carbon monoxide.
“Pressure built inside the valve, leading to valve failure and coke oven
gas filling the area and ultimately exploding when finding an ignition
source,” U.S. Steel said.
U.S. Steel didn't say why pressure built inside the valve or what was
the ignition source. It said the investigation is in the early stages
and that it will provide more information when it can. The United
Steelworkers union Local 1557, which represents workers killed and
injured in the explosion, had no immediate comment.
The top United Steelworkers representative in Pennsylvania, District 10
Director Bernie Hall, said it is working to seek answers about the
explosion.
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A portion of the Clairton Coke Works, a U.S. Steel plant, is seen
Monday, Aug. 11, 2025 in Clairton, Pa. (AP Photo/Gene J. Puskar
“It remains very early in the investigation, so we need to learn
more before speculating further,” Hall said.
The massive plant along the Monongahela River in Clairton is
considered the largest coking operation in North America and, along
with a blast furnace and finishing mill up the river, is one of a
handful of integrated steelmaking operations left in the U.S.
The blast was so powerful that it sent a plume of black smoke into
the sky, shook the ground and was heard by some people a mile or
more away. It took hours to find two missing workers, one dead and
one alive, beneath charred wreckage and rubble.
The Clairton plant is nearly 110 years old. Japan-based Nippon Steel
finalized its acquisition of U.S. Steel in June, winning President
Donald Trump's approval after he reversed then-President Joe Biden's
decision to block it.
To change Trump's mind, Nippon Steel boosted its commitment to
invest money into U.S. Steel's aging plants and gave the federal
government a say over some matters involving domestic steel
production.
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