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.

Two people were killed and 10 others were injured in an explosion at the U.S. Steel Clairton Coke Works plant on Monday.

Don Furko is a mechanical maintenance planner who this week reached his 25th anniversary at the plant. He was working in a different area with the blast took place.