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

The Pennsylvania county where an explosion at a U.S. Steel plant south of Pittsburgh killed two people and injured more than 10 others announced Thursday that it is stepping up air quality monitoring in the area of the sprawling facility that has a troubled environmental record.

The body was discovered after a search operation which stretched into the evening at the US Steel Clairton site outside Pittsburgh. Local police earlier confirmed that one other person had died and 10 others were injured in a large explosion which destroyed part of the plant.