Abstract In order to understand characteristics of large pool fires, behavior of intermittent luminous zones appearing on the smoky plumes has been analyzed using a recently developed image processing technique. The images of large pool fires analyzed in this study are of 30 and 50-m diameter pool fires of kerosene recorded on videotapes at the large-scale experiments performed in Japan, 1981. The results indicate that the probability of a luminous zone appearing is the maximum on the central point of the average plume width and at a distance from its base, and decreases with the distance from the maximum point. It can be inferred that the luminous zone on the smoky plume of a pool fire likely appears at its concave boundary (in a side view). It ascends at an almost constant velocity while changing it's area at the same frequency as that of the “breathing”.