Ten people were hurt in an explosion that caused a building collapse Thursday morning at a water reclamation plant on the Far South Side, with two getting trapped in the rubble, but emergency workers eventually extricated them.

Fire Commissioner Jose Santiago said the department received a call about the explosion around 10:50 a.m. at the sludge concentration building at the Calumet Water Reclamation Plant at 400 E. 130th St. The roof caved straight down in a pancake explosion, sending hundreds of thousands of pounds of concrete to the ground.

Eight of the ten people trapped were easily located and sent to the hospital, Santiago said, but the other two were trapped in the rubble. While the first individual took around 20 minutes to remove, the second required a 2 hour excavation.

The second victim was entombed, causing rescue workers to dig six feet down and tunnel through roughly 40 feet of concrete to reach the victim. Officials were initially worried that one of the man’s legs would have to be amputated, but they got him out safely. That man had a broken leg and jaw.

The other victims likely suffered minor injuries as well, Chief Tim Walsh said.

Five of the workers hurt had been treated and released from hospitals by 4:30 p.m., according to Allison Fore, a spokeswoman for the Metropolitan Water Reclamation District. None of the the others appeared to have life-threatening injuries, Fore said.

Two patients were brought to Christ Medical Center in Oak Lawn, according to fire officials. A spokeswoman for University of Chicago Medical Center said four other patients were brought in for treatment. By Friday morning, one of them remained in serious condition, another remained in fair condition and the two others had been released.

The explosion was likely due to a methane explosion from methane naturally occurring from the sewage process, Walsh said.

Alicia Tate-Nadeau, executive director for the Office of Emergency Management and Communications, praised the rescue effort.

“There’s been great coordination going on,” she said. “I would certainly like to commend all the firemen that are here today. They did a phenomenal job in this rescue. This doesn’t happen by chance. There is a lot of hard work that goes into making sure they’re ready at a moment’s notice to respond.”

Earlier Thursday, a small crowd of people who heard the explosion as far as five blocks away had gathered outside the entrance of the plant.

Many residents said they had smelled a strong methane-like odor for the last week.

Dorothy Barr and Mike Foulks both live in the area. Barr said the smell was so strong it was making residents sick. She complained of exacerbated asthma, nausea and headaches

The explosion only affected a small part of the plant, which is expected to continue normal operations with no effect to the city, Tate-Nadeau said.