ST. CLOUD -- The St. Cloud Fire Department says they were not able to determine the cause of the house fire that killed a family dog last Tuesday morning.

Firefighters determined that the fire started on or near a mattress in the basement of the home at 2216 10th Avenue South in St. Cloud. The house's electrical and mechanical systems and appliances were all eliminated as potential causes.

An investigation reveals that a reasonable ignition source was not identified based on the physical evidence and fire patterns. Authorities say they believe the fire was accidental.

A smoke alarm woke the two residents and their grandson who managed to get out safely and call 9-1-1. Their dog Mocha died in the fire. The blaze caused an estimated $50,000 in damage.