Joseph S. Pete

U.S. Steel has determined a preliminary cause of the deadly explosion at the Clairton Coke Plant that supplies coke to its Northwest Indiana steel mill.

The Pittsburgh-based steelmaker, the United Steelworkers union, outside experts and state and federal authorities have been investigating the blast that killed two and injured more than 10 workers. U.S. Steel says it has been "tirelessly investigating, reviewing video footage and interviewing employees."

Workers had been preparing for a maintenance project at the coke batteries, in which coal is turned into coke, a primary ingredient in steelmaking. Coke oven gas ignited, triggering the blast that required workers buried under rubble to be rescued.

"Preliminary indications lead us to believe that the explosion happened w

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