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.

A gas valve failure during maintenance work may have led to the fatal explosion at the U.S. Steel Clairton plant in Pennsylvania.