Shortly before midnight Friday, a fire broke out in a Northwest mobile home community, killing two residents.
The blaze, in Swan Lakes Estate Mobile Home Park near Flowing Wells and Wetmore roads, killed 94-year-old Edna Mayer and her 66-year-old daughter, Susan R. Weiner.
"We know that we have the connection with oxygen being used and smoking," said Capt. Adam Goldberg of the Northwest Fire District.
Goldberg said investigators ruled out all but three possibilities for the cause of the fire: lighting a cigarette while oxygen was in use, falling asleep while smoking, or improper disposal of a cigarette.
Weiner used an oxygen concentrator, a machine that collects oxygen from ambient air and delivers it to the user. She also smoked heavily.
"We spoke with witnesses, in relation to the patient, who said that she was a chain smoker," Goldberg said.
He also noted a caretaker said Weiner had in the past fallen asleep while smoking and taking oxygen.
As many as 23 firefighters were on the scene battling the blaze.
"A very quick and aggressive search and rescue attempt was made," Goldberg said.
Firefighters pulled Mayer from the burning mobile home minutes after firefighters arrived, but she died shortly after.
Attempts were made to rescue Weiner, who was still trapped inside the home. She too was pronounced dead at the scene.
A neighboring mobile home was slightly damaged during the fire.