A small fire broke out early Thursday morning in a modular building at the Santa Rosa City Schools district headquarters on Ridgway Avenue, though fire crews quickly doused the flames.

An maintenance worker used a fire extinguisher to attack the flames before fire crews arrived and put them out, Santa Rosa Fire Battalion Chief Matt Dahl said.

The 12:30 a.m. fire drew 16 firefighters who discovered smoke coming from a crawl space vent underneath the building and a spot in the floor where the fire had burned through, filling the structure with smoke, Dahl said. The blaze was under control in 15 minutes of their arrival.

Investigators were still trying Thursday to determine the cause of the fire, which caused $25,000 in damage. Assistant Fire Marshal Paul Lowenthal said there was no indication of anything suspicious.

You can reach Staff Writer Mary Callahan at 707-521-5249 or mary.callahan@pressdemocrat.com. On Twitter @MaryCallahanB.