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Flame spread over kerosene soaked sand in a quiescent atmosphere and an opposed air stream has been examined, and the effects of the air stream on the flame spread mechanisms are discussed. The aspects of spreading flames, the flame spread rate, and the temperature distributions near leading flame edges were examined for various initial temperatures Ti of kerosene soaked sand and free stream velocities U of the opposed air stream. As U increases, the flame near its leading edge approaches the sand surface. The flame spread rate Vf at U=O increases considerably with T . . As U increases, Vf decreases rapidly and then gradually 1 decreases until U becomes 275 cm/s in the limits of present experiments. When U exceeds 275 cm/s, the flame spread becomes unstable and Vf decreases rapidly. In the case of U=O, the heat transfer from the flame zone to the unburned region ahead of the leading flame edge seems to depend largely on the flame radiation. On the other hand in the case of U 0, the heat transfer to the unburned region seems to depend largely on the heat conduction through the sand layer. The stabilization of the leading flame edge associated with the aerodynamic structure of the reverse flow region is found to be necessary for the stable flame spread.