A drying number, Dr, which is in effect a Damkohler number, is derived to account for the separation of the drying and devolatilization processes of a solid fuel particle. This number is a qualitative measure of the relative times for drying and devolatilization. It is intended for fuels entering an environment that has a considerably higher temperature than its saturation temperature. The number relates the kinetic rate of devolatilization to the rate of evaporation, which is controlled by heat transfer to an evaporation front. The information given by the drying number is useful for choosing all appropriate model for the drying and the devolatilization of a fuel particle. For example, if the drying number is small, drying and devolatilization can be modeled separately if it is around unity, a more detailed description is needed: and if it is very high, simplifications can be introduced, because drying and devolatilization then follow each Other, and the rate of conversion of Moisture and volatiles in a moist particle is given by the rate of evaporation. Experiments confirm that the drying number provides this information. (C) 2004 The Combustion Institute. Published by Elsevier Inc. All rights reserved.