The demand for and the consequent production of porous materials, such as wood, increase with industrial development and income. If a smoldering fire occurs in a porous material such as wood flour, it is difficult to find the fire location because of the development of a downward deep-seated fire. In this study, a down-scaled downward deep-seated fire model was adopted for wood flour to experimentally and theoretically elucidate the propagation phenomena of the downward velocity of deep-seated fires and subsequently predict their location. The experiment was performed on radiata pine wood flour with the density range of 0.2038 to 0.2343 g/cm3. Different tendencies were observed quantitatively in the downward temperature profiles with the changes in the volumetric mass density of the wood flour. Based on these results, it can be concluded that the deep-seated fire propagation speed is in the range of 0.0014 to 0.0018 cm/s. The practical applications of this result would be in effective extinguishing of fires in wood flour factories and silos by predicting the fire site based on the determination of the speed of propagation of the downward deep-seated fire.