CHICAGO (CBS) — A 58-year-old woman was found dead in a burning apartment Wednesday night in the South Shore neighborhood.

The fire started around 8 p.m. in a 3-story apartment building near 76th and Essex.

READ MORE: Former Chicago Park District Supervisor Mauricio Ramirez Charged With Sexually Assaulting 16-Year-Old Lifeguard

During their initial search of the building, firefighters found the woman unresponsive in her bed.

Fire officials said the woman was using an oxygen tank. Although the fire started in her bed, it was not immediately clear if she was smoking at the time.

READ MORE: Joel Quenneville Meets With NHL Commissioner Gary Bettman Over Handling Of Blackhawks Sexual Assault Scandal

The Cook County Medical Examiner’s office identified the victim as Therese Chenault.

The fire was contained to the bedroom, and the cause was under investigation.

A Fire Department spokesman said it was the third fatal fire this year in which the victim was using an oxygen tank.

MORE NEWS: 'Survivor' Contestant Michelle Yi Describes Frightening Santa Monica Assault

Smoke detectors in the building were working.