About five hours later, shortly before 3:30 p.m. Sunday, firefighters were called again to the building in the 2500 block of West North Shore Avenue because another resident had become ill.
Officials then discovered dangerous levels of carbon monoxide in the building's basement. The two women from the first call, Rasheeda Akhter, 77, and her granddaughter Zanib Ahmed, 18, later died at Swedish Covenant Hospital. The Cook County medical examiner's office determined Monday the cause was carbon monoxide poisoning.
The woman whose illness prompted the second call was taken to St. Francis Hospital in Evanston. A relative said she was doing well.
There was a combination smoke and carbon monoxide detector in the building's basement, but the detector was placed near a window that had been cracked open, Assistant Deputy Commissioner Mark Nielsen said. It never went off, officials said.
"Keep in mind CO poisoning is cumulative and it adds up. You get a little here, a little there and it keeps adding up," Nielsen said. "We believe it to be low dose, long-term exposure."
Fire officials and workers from Peoples Gas found that the boilers of the building's furnace were not burning properly and that there was a leak in the exhaust system, said Fire Department spokesman Larry Langford.
"Fresh air was coming into the basement, but the bad air was going upstairs into the house," Langford said.
The building had no other working carbon monoxide detectors, though there were smoke detectors. City and state regulations require carbon monoxide detectors to be placed on every floor where there are bedrooms, Langford said.
Shabbir Ahmed, Akhter's son and Zanib Ahmed's uncle, said he knew of no problems with the building's heating system. "It was the same boiler we had, it was working perfectly, then all of a sudden like a car, cars break down," he said.
Fire officials said the women who died were in first- and second-floor rooms directly above the boiler.
Carbon monoxide is odorless and can be hard to notice without detectors, experts said.When the gas is inhaled in significant amounts it attaches to the body's hemoglobin, which is a protein that carries oxygen throughout the body and into the brain.
"It's insidious. People don't know they are being exposed to carbon monoxide," said Dr. Aasim Padela, an assistant professor of medicine at the University of Chicago.
The building was bought more than 20 years ago by a family member.
Zanib Ahmed, the oldest of three children, was a senior at St. Scholastica Academy and was considering going to Northwestern University, where she wanted to pursue premedical studies, Shabbir Ahmed said
St. Scholastica's Head of School Lynne Farmer described Ahmed as a bright and well-liked student at the tightknit school. She was participating in a mentoring program for middle-school students at a neighboring charter school, Farmer said.
Rasheeda Akhter was a "beautiful person" much loved by her grandchildren. They often called her "Dadyji," which is Urdu for grandmother, Ahmed said.
"All of the kids loved her and played with her all of the time. They are going to miss her very badly," Ahmed said.
Written by Chicago Tribune