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.

The explosion, followed by several smaller blasts, could be felt in the nearby community and prompted county officials to warn residents to stay away from the scene so emergency workers could respond.

After an explosion rocked a steel plant outside Pittsburgh on Monday, workers scrambled into the wreckage alongside firefighters. A cloud of black smoke rose above a charred pickup truck as rescuers sprayed the scene with streams of water.

U.S. Steel says preparations for a routine maintenance task may have led to an explosion at a U.S. Steel coal-processing plant near Pittsburgh that left two dead, sent 10 to hospitals and damaged part