Workers were heating coal and preparing for routine maintenance when an explosion rocked a U.S. Steel plant outside Pittsburgh

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

An explosion at a U.S. Steel plant south of Pittsburgh killed two people and injured more than 10 others. The CEO has vowed to find out what caused Monday’s blast while the workers’ union says it will make sure there’s a thorough investigation.