This paper uses the thermochemical behaviour of reacting species to differentiate between the combustion of gas phase and condensed phase detonation products in the fireball of an explosion. Experiments were carried out involving the detonation 15 g charges of C-4 and Detasheet-C explosives in a closed vessel. The initial partial pressure of oxygen in the vessel was varied in order to control the extent of the secondary afterburn reactions, and the total heat release was measured using the calorimeter that contained the closed vessel. A simple model that independently describes the evolution of heat from the gas phase and condensed phase detonation products as a function of oxygen consumption was developed, and was used to show that condensed phase products react much more effectively in the fireball than gas phase reactions, because the transport properties of particulates entrained in a turbulent flow gives them an advantage when it comes to the manner in which they mix with the surrounding air. An additional set of trials employing the entrainment of an external combustible material further confirms the importance of particle combustion in explosive fireballs. Crown Copyright (C) 2013 Published by Elsevier Inc. on behalf of The Combustion Institute. All rights reserved.