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.

An explosion Monday at a U.S. Steel plant near Pittsburgh has left people trapped under the rubble, with emergency workers on site trying to rescue them, an official

The plant, a massive industrial facility along the Monongahela River south of Pittsburgh, is considered the largest coking operation in North America and is one of four major US Steel plants in Pennsylvania.