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 Allegheny County Health Department announced that mobile air units provided by the state and Carnegie Mellon University will be stationed in the Mon Valley where the plant is Thursday and Friday. The county said these measures are part of its ongoing investigation into Monday’s explosion at Clairton Coke Works.

The county said the measures go “well beyond the normal and rigorous regulatory air quality monitoring” and will assess parts of the valley for different types of pollutants such as volatile organi

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