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 at a US Steel plant near Pittsburgh, Pennsylvania, left two people dead and at least 10 injured on Monday, heavily damaging the sprawling facility, officials said. One worker was pulled from the wreckage hours after the explosion sent black smoke spiralling into the midday sky in the Mon Valley,

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