"Improper disposal of fireplace ashes" caused a Saturday, the Massachusetts Fire Marshal's office said today.
"In this case, the folks thought they had done everything right by dousing the embers with water, but did place them in a trash barrel with other materials placed next to the house," Public Information Officer Jennifer Mieth said.
"It is amazing that fireplace embers can stay hot for several days even when they seem cool. It's important to place ashes in a metal container with a lid (and only the ashes, nothing else that can catch fire) Store that container a safe distance away from the house - not in the garage, under the porch or next to the house."
Saturday's fire at 37 West Ridge Drive "started in the rear of the building" and caused "substantial fire damage to the rear rooms, and then heat and smoke throughout the rest" of the house, Sharon Fire Chief James Wright said at the scene.
The residents were not home at the time. A neighbor reported the fire at 2:55 p.m.
No injuries were reported from the fire. A Canton firefighter showed signs of heat-related issues and was taken by ambulance to Norwood Hospital in Norwood for observation, Wright said.
Sharon Police closed West Ridge to through traffic at Mallard Drive and Partridge Hill during the incident.
Walpole firefighters covered the Sharon fire station during the incident.
Walpole and Stoughton firefighters also responded to an accident on Bay Road in Sharon during this period.