WILLIAMSPORT, Pa. (AP) — A 66-year-old woman who was critically burned in her Pennsylvania hospital room had a cigarette lighter and using oxygen.

Williamsport Fire Chief Todd Heckman says both factors may have led to the Tuesday afternoon's fire at UPMC Susquehanna Williamsport Regional Medical Center.

Nursing staff found the woman's gown ablaze and a chair she had been sitting in also burning. They used sheets and, eventually, a fire extinguisher to put out the flames. Two nurses and a third employee were treated for minor burns.

Investigators and the hospital aren't identifying the woman who was being treated for medical and mental health issues. She remained in critical condition Thursday at the Lehigh Valley Health Network Regional Burn Center in Allentown.

The woman smoked, but that's prohibited in the hospital, where her cigarettes and another lighter were stored in a lockbox.