Smoldering is based on the slow, low-temperature, flameless combustion of a condensed fuel. The propagation velocity of downward smoldering is dominated by the rate of transfer of oxygen to the reaction zone. Regarding as this point, Kinbara et al. (1976) have revealed that the smoldering velocity of rod fuel; Vsml [mm/s], clearly increased as the diameter of the rod was reduced. The purpose of this study is to reveal the characteristics of smoldering in small-scale. We examined the smoldering characteristics of the rod-shaped solid combustibles whose width is ds [mm] under various conditions (ds=0.3~3.0 mm, porosity Φ=0.41~0.65). Based on the consideration that oxygen supply is dominated by diffusion, a theoretical smoldering velocity is found to be inversely correlated to the scale parameter ;ds(1-Φ) [mm]. The theoretical smoldering velocity is in good agreement with available experimental data especially in small-scale, where the previous works has never been examined.
