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 Allegheny County Health Department announced Thursday it’s deploying two air quality monitoring vans provided by the Pennsylvania Department of Environmental Protection and Carnegie Mellon University until the end of Friday.

These units will track the presence and concentration of various pollutants, including fine particulate matter, sulfur dioxide — known for worsening heart and lung conditions — and volatile organic compounds, such as formaldehyde.

The vans are being used out of an abundance of caution, according to county spokeswoman Abigail Gardner.

The county has said its sensors in Clairton, Liberty and North Braddock have not shown readings of fine particulate matter and sulfur dioxide that exceed federal standards since the explosion, which spewed a massive cloud of black dust toward the sky.

Two people died in the blast and 10 others were injured, including a county health department employee who was treated at the hospital and released. Multiple agencies are investigating the cause of the incident.

The county described the borrowed monitors as going well beyond its usual program to track air quality.

Mobile monitors will be placed based on a weather forecast developed by county and state staff.

Weather conditions can have a significant impact on air quality, according to the National Weather Service. Wind speed, for instance, can affect how pollutants disperse, while higher temperatures can speed up harmful chemical reactions.

The plant in Clairton takes coal and heats it at nearly 2,000 degrees to remove impurities. Coke is the result, and it’s used fuel blast furnaces in nearby Braddock.

It’s dirty work and has repeatedly landed U.S. Steel in trouble with the county. Since 2020, the health department has fined the plant around $64 million for air quality violations.

Environmental groups have pushed Nippon Steel, the Japanese company that recently bought U.S. Steel for nearly $15 billion, to clean up the Clairton facility and others in the Mon Valley.

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