United States Steel said on Friday a fatal blast that killed two and injured 10 others at its Clairton Coke Works plant near Pittsburgh happened when flushing a gas valve, ahead of scheduled maintenance.

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.

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.