The deadly explosion at Clairton Coke Works near Pittsburgh occurred when a gas valve was flushed before planned maintenance, U.S. Steel said in preliminary findings.

U.S. Steel says 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, sent 10 to hospitals and damaged part of the sprawling facility.

United States Steel Corp. said Friday the fatal blast that killed two workers at its Clairton Coke Works facility in Pennsylvania happened when flushing a gas valve in preparation for planned maintenance.