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

"Pressure built inside the valve, leading to valve failure and coke oven gas filling the area and ultimately exploding when finding an ignition source," the company said. U.S. Steel added that the investigation into Monday's explosion is still in early stages and it will provide more information when possible.

The deadly blast at the U.S. Steel facility outside Pittsburgh was just the latest in a series of recent workplace accidents.