The U.S. Chemical Safety and Hazard Investigation Board issued its initial report Monday on the fatal explosion at U.S. Steel's Clairton Coke Works, which supplies coke to its Northwest Indiana mills.

The board is investigating the fatal Aug. 11 explosion that killed two U.S. Steel employees and seriously injured four U.S. Steel workers and one Veolia Water worker. Five U.S. Steel workers and a MPW Industrial Services contractor also were hurt in the blast.

The investigation found workers were flushing a valve at the coke oven battery, and the alarms went off shortly before the explosion.

The coke battery, the largest manufacturing facility of coke in the Western Hemisphere, employs about 1,300 workers who turn coal into coke to burn in blast furnaces, including those at Gary Works. The

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