CFD said a man went to work with symptoms of carbon monoxide poisoning, and, when his boss took him home, other members of the man's family were found unresponsive.
"Another hour and we may have had multiple deaths," CFD said.
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The incident took place in the 1600-block of North Keystone Avenue, near North Pulaski Road.
Two of the individuals taken to the hospital are in fair condition, and three are in good condition.
CFD urged Chicago residents to get carbon monoxide detectors, and praised the man's employer for helping him and his family.