Investigators have determined that the cause of the fire that killed Mary Ann Margaret Gardner and Laura Jeanne Snyder-Gardner this winter was accidental.

A wall-mounted natural gas heater in the living room caused the fire, resulting in the death of the mother and daughter, according to a Fairfax County Fire and Rescue Department news release. The fire occurred in the early morning hours of Jan. 23 at their home on Manor Road in the Fairfax County area of Falls Church.

According to the news release, the specific mode of failure could not be identified; both victims were hearing impaired and, while firefighters located smoke alarms in the home, investigators were unable to determine if they were visual smoke alarms due to the extensive fire damage.

According to the medical examiner, the cause of death was smoke inhalation.