U.S. Steel early findings pinpoint gas valve failure as cause of fatal Clairton Coke Works blast

U.S. Steel on Friday pinned blame for the deadly explosion Monday at the Clairton Coke Works on a valve failure that led to coke oven gas igniting, according to the company’s preliminary findings.

“Preliminary indications lead us to believe that the explosion happened when flushing a gas valve in preparation for planned maintenance,” the company announced Friday afternoon. “Pressure built inside the valve, leading to valve failure and coke oven gas filling the area and ultimately exploding when finding an ignition source.”

The statement from U.S. Steel marks the first time company officials have offered a theory of the explosion. They previously noted maintenance was being performed at the time.

U.S. Steel and the United Steelworkers union are coordinating to find the cause of the blast with federal agencies, including the Chemical Safety and Hazard Investigation Board, the Occupational Safety and Health Administration and the Allegheny County Fire Marshal.

U.S. Steel emphasized the investigation is in its early stages.

Two people were killed in the blast, both workers at the plant, and 10 were injured.

Significant portions of the facility were damaged, primarily the two batteries next to the explosion.

The plant is operating in a limited capacity.

The Clairton Coke Works has a history of explosions.

In September 2009, a maintenance worker was killed in a blast. And in July 2010, another explosion injured 14 employees and six contractors.

Pittsburgh attorney John Gismondi represented affected workers and their families following both explosions.

U.S. Steel’s early findings about the latest explosion made it sound most similar to the 2010 incident, he said, which investigators traced back to workers performing maintenance on pipes used to transport coke oven gas.

The gas is generated when coal is heated at nearly 2,000 degrees to burn off impurities and turn it into the crucial steelmaking ingredient coke.

The company was cited by OSHA after the 2010 explosion for failing to shut down the gas line before maintenance started.

U.S. Steel may have identified the mechanical cause of the blast Monday, but much work remains, in Gismondi’s view.

“Knowing the immediate cause is sort of different from knowing what’s the root cause,” Gismondi said. “Were people properly trained? Were there the procedures and redundancies that you typically have? Those are all things to be looked at.”

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