Firefighters snuffed out a small fire Saturday morning at Arroyo Grande High School.
Five Cities Fire Authority received a report at around 5:40 a.m. of a fire alarm at the high school.
When firefighters entered the school’s student health building near Valley Road, they found light smoke coming from an unknown source, the agency said.
After accessing an interior roof panel and shutting off utilities, firefighters discovered that a smoldering heating unit in the attic had ignited a duct joint, the agency said. Crews then used thermal imaging to locate another hot spot in the attic's plywood decking where flames had burned completely through the decking and insulation.
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According to the Five Cities Fire Agency, had the small fire gone undetected, it could have led to a larger, more damaging blaze.
Three engines, nine firefighters and a battalion chief spent just over an hour at the site.
Although a damage estimate was not immediately available, officials said repairs may take several days.
No Arroyo Grande High students or faculty were present at the time of the fire.