Undetected hot lime material from #6 kiln cooler system caught the stacked long tunnel conveyor belts on fire. Hand extinguishers could not control the fire. Local fire dept was called @ 12:35 pm and began applying foam suppression after 12:50 pm. Fire was controlled and out by 1:20 pm. MSHA called @ 12:56 pm (SR #1-48113790). There were no injuries involved.