An explosion at a U.S. Steel plant south of Pittsburgh killed two people and injured more than 10 others. The CEO has vowed to find out what caused Monday’s blast while the workers’ union says it will make sure there’s a thorough investigation.

Repairing Clairton, however, could be expensive, an investigation into the explosion could turn up more problems, and an official from the United Steelworkers union said it’s a constant struggle to get U.S. Steel to invest in its plants.