The explosion, followed by several smaller blasts, could be felt in the nearby community and prompted county officials to warn residents to stay away from the scene so emergency workers could respond.

A fire Monday at the US Steel mill, 20 miles south of Pittsburgh, hurt 10. Residents within a mile are advised to stay indoors.

The U.S. Steel plant in Clairton, Pa., where an explosion killed two workers and injured 10 on Monday, has a history of maintenance issues, explosions and environmental violations.