The fire was reported shortly before 4:15 a.m. in the 4000 block of 18th Street, police said.
A piece of plastic was burning in front of the doorway of a building. Firefighters responded but the fire was extinguished before they arrived, according to police.
Two second-alarm fires, one reported shortly after 5 a.m. Thursday at 3620 16th St. and the other at about 5:30 a.m. at 3943 17th St., also originated on the exterior of the buildings.
Investigators believe the fires were intentionally set, and are working to determine if they are related, fire Lt. Mindy Talmadge said Thursday.
“There are a lot of common factors,” Talmadge said. “The most obvious are the time and location, and both of those fires’ point of origin was on the exterior.”
The 16th Street fire displaced 13 people, while the 17th Street fire was at an unoccupied building under construction, Talmadge said.
A small trash fire was also reported earlier that morning in the 2200 block of Market Street. The fire was found in a locked area behind a building and was quickly extinguished.
Police will be increasing their attention on the Castro area after the series of fires, police Lt. Troy Dangerfield said this morning.
“Officers are on the lookout, and will pay more attention to this specific area,” Dangerfield said.
Police are also asking residents to be on the lookout. Anyone with information about the fires is asked to call the Police Department’s anonymous tip line at (415) 575-4444 or the fire department’s arson investigators at (415) 920-2937.
Dan McMenamin, Bay City News