HARRISBURG, Pa. (AP) — The fatal explosion last week at U.S. Steel’s Pittsburgh-area coal-processing plant has revived debate about its future just as the iconic American company was emerging from a long period of uncertainty.

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 released preliminary findings about the potential cause of Monday's deadly explosion at U.S. Steel Clairton Coke Works.