Firefighters battled the bitter cold to put the fire out inside the building on the 3800-block of South Ellis.
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A 30-year-old victim suffered smoke inhalation according to the Fire Department.
The man was taken to the University of Chicago Medical Center in critical condition, fire officials said.
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The blaze was put out by about 3:40 a.m., according to fire officials.
The cause of the fire is now under investigation.
The Sun-Times Media Wire contributed to this report.