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.

Todd Barrett was with a crew of laborers at the Clairton coke works that morning when they all felt something. It was an explosion at batteries 13 and 14 at the plant. The batteries consist of dozens of tall,