A smoldering piece of insulation tossed near an air duct filled a Fullerton medical office building with smoke Sunday afternoon, authorities said.
Four fire engines were summoned to a medical office building in the 1300 block of North Harbor Boulevard about 2:30 p.m., said Battalion Chief Jack Cooper of the Fullerton Fire Department.
After an hourlong search of the smoky building, firefighters determined that there were no flames.
"We don't know if it was a prank or not," Cooper said. "It generated enough smoke that we initially thought there was a fire."