The extinction characteristics of multi-species char clouds in pulverised fuel combustors were theoretically investigated using an adaptation of Semenov's thermal explosion theory. The critical sizes of char particles in the cloud were found to be strongly affected by the particle. temperature, shape, and reactivity, as well as the mass fraction of each species, and ambient conditions. The cloud shape, cloud particle number density, fuel mass fraction, and char reactivity were identified as the major parameters impacting upon the cloud extinction potential. Our analysis indicate that blending of a base fuel with a less reactive fuel generally increases the extinction potential of the cloud (i.e. likelihood of extinction) while addition of a more reactive secondary fuel to the base fuel minimises the probability of cloud extinction. (C) 2004 Elsevier Ltd. All rights reserved.