Investigators have determined that a fire that badly damaged a garage and upstairs bedroom in Portland this morning was started when rags soaked in linseed oil spontaneously ignited.

Such rags need to be kept outside in a fireproof container, officials said.

2:49 p.m.

City officials are saying a garage smoke detector and firewall helped prevent injury and property damage from a fire in Portland early this morning.

Firefighters were called ot 17 Bartley St. for a fire in a garage at about 1:30 a.m. When they arrived, all the occupants had escaped safely, having been alerted to the fire by the smoke detector, said city spokeswoman Nicole Clegg.

The fire caused severe damage to the garage and the bedroom above it, which had been occupied, but fire-resistant walls prevented the fire from spreading to the adjacent house, she said. The house suffered only minor smoke damage.

The fire is not considered suspicious but the cause remains under investigation