CHICAGO (CBS) – A community is mourning the loss of a 2-year-old girl and her 7-month-old sister in a fire.

Chicago firefighters are speaking out Monday hoping to prevent another such tragedy. CBS 2’s Mai Martinez has more.

The firefighters who put out the fire and helped to rescue a 6-year-old boy are also mourning the loss of those two little girls. They cautioned people not to use things like stones to heat their homes.

“Please make sure your smoke detectors are working,” said Chicago Fire Department District Chief Dan Cunningham.

It is a simple, but important message the Chicago Fire Department hopes people will remember following Saturday night’s fatal fire that claimed the lives of two sisters.

Three children and two women were in the apartment when the fire started, by the time firefighters arrived, the women had made it out, but the children were all still inside.

“Upon their arrival, it was very chaotic,” Chief Cunningham said. “People screaming that there were children in the basement.”

The first firefighter on the scene rescued a 6-year-old boy from a front room, but it was too late to save the sisters, 2-year-old Samari Grace and 7-month-old Ziya Grace. Their bodies were found together in the same bed.

The 6-year-old boy was transported to Comer’s Hospital in serious condition.

Investigators believe a gas stone, left on to heat the basement was the source of the fire. Clothing and other items near it fueled the flames.

Firefighters said there were no working smoke detectors, and that is why they are urging everyone to check their own.

“A little bit of smoke can activate that smoke detector,” Chief Cunningham said. “Heat also does the same thing, so that alerts everybody in the area, before things might get out of hand.”

The 6-year-old boy remains at Comer Children’s Hospital in critical condition. According the Chicago Fire Department, he was burned over 75 percent of his body.

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