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.

A fatal explosion that killed two steelworkers and injured more than 10 shut down four of the 10 coke batteries at U.S. Steel's Clairton Coke Works in Pennsylvania.