U.S. Steel released preliminary findings about the potential cause of Monday's deadly explosion at U.S. Steel Clairton Coke Works. U.S. Steel spokeswoman Amanda Malkowski said in a statement on Friday that "preliminary indications lead us to believe" that the explosion happened when a gas valve was flushed in preparation for planned maintenance.

Authorities confirmed a second fatality after an explosion at the U.S. Steel Clairton Coke Works facility outside of Pittsburgh.

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.