CHICAGO, AUG 31, 2018 -- Ten people were injured in an explosion and roof collapse at the Calumet Water Reclamation Plant in Chicago. ABC News reports workers were using a torch when they shouldnt have been, before an explosion occured.
The explosion occurred in a room that contains a large tank that is recessed into the ground and holds sludge and they were in the process of pumping the sludge to the next building where it is broken down, the news station said.
The Chicago Fire Department said a flame ignited methane, a byproduct of the sludge in the atmosphere; caused the roof to raise and come back down, where it collapsed.
Two workers remained hospitalized as of Friday.
OSHA is investigating the incident. A statement from the Calumet Water Reclamation Plant said it will "thoroughly investigate this incident and work to identify measures to prevent something like this from happening again."