U.S. Steel last year settled a lawsuit brought by environmental groups over emissions that stemmed from the 2018 Clairton plant fire. The settlement with the groups and the county included $19.5 million in coke-oven upgrades and $17.5 million in other plant improvements.

The mill, which is part of the recent merger between U.S. Steel and Nippon Steel, has faced scrutiny from federal and local regulators.

Dozens of workers at a steel plant near Pittsburgh are trapped beneath rubble following an explosion, and police have confirmed at least one fatality. The incident unfolded Monday morning at Clairton Coke Works near Pittsburgh in Allegheny County.