A woman was killed in a Garfield Ridge residential fire Sunday morning, Chicago fire officials said.

Chicago firefighters responded to calls of a residential fire in the 5400 block of South Mulligan Avenue shortly before 11 a.m. and found a woman in her 70s dead at the scene, Chicago Fire Department spokesman Larry Langford said. No other injuries were reported.

Langford said the fire had been “burning for a while” and was “pretty much out” when firefighters arrived on the scene. Investigators believe a family member discovered the fire.

He also said that although the home had working smoke detectors, there were also vacant lots on either side, and the alarms would’ve been hard to hear outside.

Fire investigators determined the fire was caused by the use of “smoking materials” near supplemental medical oxygen.

Langford said it was the second time this month that fire crews had responded to a fire caused by smoking near supplemental oxygen, though the other wasn’t fatal.

“It is definitely a problem, people need to stop smoking when they have oxygen on,” Langford said. “This is what can happen.”