The deadly explosion at Clairton Coke Works near Pittsburgh occurred when a gas valve was flushed before planned maintenance, U.S. Steel said in preliminary findings.

U.S. Steel says it believes a gas valve failure led to the explosion Monday morning at its Clairton Coke Works, in which two workers died and 10 others were injured.

U.S. Steel has released new details on what investigators believe caused the explosion at the Clairton Coke Works plant that killed 2 people and injured 10 others.