A deliberately set fire damaged a duplex on Olive Street in Santa Rosa on Saturday afternoon, Santa Rosa Fire battalion chief Mark Basque said.

The property at 507 Olive St. has been condemned for about a year and is at times occupied by transients. Basque said a transient likely deliberately started the fire around 2:40 p.m.

Fire investigators are treating the case as an arson. There are no suspects. No one was on the property when firefighters arrived.

Basque said firefighters from three companies and two ladder trucks encountered hazards in the building from months of vandalism. The floor was littered with garbage, needles and human waste, he said. There were holes in the walls and floor.

"The fire was difficult to fight because of the hazards," he said.

The fire was controlled in 20 minutes and and damaged the floor and some of the rooms, Basque said.