Two workers died and at least 10 people were injured after multiple explosions at the U.S. Steel Clairton plant.

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.

Multiple people have been injured in Pennsylvania, and several medical helicopters have been dispatched to the area.