T he use of calculated adiabatic flame temperatures (CAFT), along with a selected limit flame temperature for combustion propagation, has been shown to be effective in determining the flammability envelope for hydrocarbon gases. This paper discusses the use of this methodology to determine the flammability of gaseous fuel-oxidizer-inertant mixtures. The paper then proceeds to describe how this methodology can be modified into a predictive tool to determine the flammability of a solid fuel-inertant mixture in air. The modification proposed here is based upon previous work by Hertzberg et al. Their model proposes that in the homogeneous mechanism for combustion (which is predominant for most carbonaceous fuels and some metal dusts) not all the volatile matter present in the system can participate in the combustion process. Only a fraction (termed the beta fraction) can be devolatilized rapidly enough to take part in combustion. It is this fraction of fuel that is used for the adiabatic flame temperature calculations. The model presented here differs from that of Hertzberg et al. in that it has been modified to allow for comparisons between inerting levels determined in a 20 litre chamber and a 1 m(3) chamber. The results indicate that the 1 m(3) model can be used to predict the experimental inerting levels of the 1 m(3) chamber, with limitations. Additionally, the 20 litre CAFT model can be used to predict the experimental inerting levels in the 1 m(3) chamber (again, with limitations). Ultimately, the utility of this modified model as a predictive tool for inerting level and minimum inerting concentration determination has been demonstrated.