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.

Authorities confirmed a second fatality after an explosion at the U.S. Steel Clairton Coke Works facility outside of Pittsburgh.

• At least one person is dead, 10 injured and one unaccounted for in an explosion at the Clairton Coke Works in Pittsburgh, Pennsylvania. The cause of the explosion is unknown and officials are investigating, US Steel said.

Regulators are temporarily stepping up pollution monitoring in the Mon Valley after a deadly explosion at U.S. Steel’s Clairton Coke Works on Monday sparked worry about the release of toxic gases. The

The health department began deploying mobile air units Thursday provided by Pennsylvania’s Department of Environmental Protection and Carnegie Mellon University. The units will travel around Clairton to test for dozens of hazardous air pollutants.

Family members tell Pittsburgh's Action News 4 Steven Menefee, a father of two, was a loving man who would give you the shirt off his back.

An explosion at the U.S. Steel Clairton Coke Works about 15 miles southeast of Pittsburgh has left one dead and at least 10 injured, with some people still trapped under the rubble as emergency worker

Allegheny County Emergency Services said a fire at the plant in Clairton started late Monday morning. Officials said they had not isolated the cause of the blast.

Authorities said their investigation has shifted to the cause of the explosion after they accounted for everyone who was missing.

Allegheny County Executive Sara Innamorato joined ABC News Live with an update on the investigation of the explosion at a Pennsylvania steel plant and its impact on the local community.

The CEO of U.S. Steel pledged a transparent investigation into the Clairton Coke Works explosion that killed two and injured 10 Monday morning. CEO David Burritt was joined at a press conference Tuesday afternoon by Pennsylvania Gov.