FALLS CHURCH, Va. (AP) -- Fairfax County fire officials say a house fire that killed a Gallaudet professor and her daughter has been ruled accidental.

Officials announced Thursday that the blaze that killed the pair at their Falls Church home in January was traced to a wall-mounted natural gas heater, but the exact point of failure couldn't be determined.

The Washington Post reports (http://wapo.st/18ND1wA ) that the medical examiner determined that smoke inhalation was the cause of death for 48-year-old Laura Snyder-Gardner and her 16-year-old daughter, Mary Ann. Snyder-Gardner was a math professor at Gallaudet University and her daughter was a student at the Model Secondary School for the Deaf.

Officials say there were smoke alarms in the home, but the damage was so extensive they could not determine if they were visual alarms.

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Information from: The Washington Post, http://www.washingtonpost.com