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

A gas valve failure caused the explosion at Clairton Coke Works on Monday morning that killed two people, U.S. Steel said Friday. Why it matters: The massive Mon Valley facility — one of the largest coke plants in the world — has a long history of environmental and safety violations.

U.S. Steel says preparations for a routine maintenance task may have led to an explosion at a U.S. Steel coal-processing plant near Pittsburgh that left two dead, sent 10 to hospitals and damaged part of the sprawling facility.