Honolulu firefighters responded to a small fire at a portable classroom at Maili Elementary School today that was determined to be intentionally set, according to a spokesman. Four units with 13 firefighters responded to the fire just before 4:10 p.m. Honolulu Fire Spokeman Scot Seguirant said the blaze occurred on the stairway of the portable classroom. When firefighters arrived, they observed smoldering smoke after the fire was apparently extinguished. No injuries were reported. Damage to the building was estimated at $500. Seguirant said the case has been passed to police.