SKOKIE, Ill. (CBS) — Thirteen people were sent to the hospital early Thursday, after they became sick because of a carbon monoxide leak at a Skokie apartment building.

CBS 2’s Mike Puccinelli reports investigators blamed the leak on a faulty furnace at the apartment building in the 8000 block of Keating Avenue.

A resident at that building called 911 around 2:30 a.m. after several people became ill. When emergency crews arrived, they discovered a carbon monoxide leak, and evacuated the building.

Thirteen people were taken to hospitals, though everyone was expected to recover.

Skokie Deputy Fire Chief Barry Liss said 11 of those people were living in a single apartment. Had one of those people not awakened due to feeling sick, all of them could have succumbed to carbon monoxide poisoning.

“Absolutely. No question about that; as well as the other residents of the building, as the carbon monoxide developed throughout the entire facility,” he said.

Two adults were treated at NorthShore University HealthSystem Skokie Hospital and released later in the day. Four children were treated and released at NorthShore University HealthSystem Evanston Hospital. Six people were treated and released at St. Francis Hospital in Evanston. One person was treated and released at Advocate Lutheran General Hospital in Park Ridge.

Police provided vehicles to keep other residents warm until they could find somewhere else to stay.

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