The tragedy has rocked the Mon Valley, and its congresswoman wants answers. Democratic Congresswoman Summer Lee is appreciative of U.S. Steel's efforts to get to the bottom of this, but she said this can never happen again.

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.

Rescuers were continuing to search for one missing worker at the Clairton Coke Works more than five hours after mid-morning explosions rocked the Mon Valley plant. The blasts killed one person and injured 10.