Dennis Fire and Police responded to a reported structure at 11:19AM, Monday morning. The duplex style dwelling was located at 87 Center Street, South Dennis. Upon arrival smoke was seen coming from the second floor of the building. The occupants of the building were out of the house when firefighters arrived. They reported a mattress burning in the bedroom. A 1 ¾ handline line was stretched to the second floor and extinguished the fire. The mattress was then removed from the building with assistance from the Harwich Fire Department. The fire caused extensive damage to the bedroom. The cause of the fire is under investigation however it does not appear to be suspicious at this time. An electrician was working on some wiring problems in the building at the time of the fire. No one was injured during the incident.