Workers were pushing coke out of huge ovens and preparing for maintenance when an explosion rocked a US Steel plant outside Pittsburgh, a company executive said Tuesday, a day after the blast killed two workers.

An explosion at a U.S. Steel plant near Pittsburgh on Monday left two people dead and at least 10 others injured, Allegheny County officials said. The explosion erupted at Clairton Coke Works at 10:51 a.

Authorities said 10 other workers required hospital treatment — including five listed in critical but stable condition — after an explosion Monday morning at the U.S. Steel Clairton Coke Works. The cause of the blast has not been determined.