A simplified heat transfer model applicable for vapor-phase combustion of individual fine metal particles predicts existence of a critical particle diameter, below which the vapor-phase flame alone cannot be self-sustaining. Other heat generation mechanisms (i.e. surface oxidation) should complement the vapor-phase flame. The predicted Critical particle diameter is a function of the flame temperature and pressure. For single aluminum particles burning in atmospheric pressure air, CO2 and H2O, the predicted critical particle diameters are close to 6, 7, and 15 mu m, respectively. (C) 2009 The Combustion Institute. Published by Elsevier Inc. All rights reserved.