An improved flame extinguishing criterion is implemented to the Fire Dynamics Simulator (FDS) for gaseous suppressants under the lumped species model with transport-limited combustion (infinitely fast chemistry). The criterion considers the total enthalpy of gas mixture as a function of temperature, and evaluates whether a limiting adiabatic flame temperature can be obtained due to combustion in a cell. The model is validated against a number of experiments in the cup burner apparatus, a standard means of obtaining the minimum flame-extinguishing concentrations (MEC) for a variety of fuel-suppressant combinations. The results indicate that the model can reproduce the MEC values for all common inert gas agents, as well as some of the fluorinated halocarbon agents. It is further demonstrated in the paper that the flame extinguishment criterion, although validated using grid cells on the order of 1 mm, is equally applicable to larger cell sizes more appropriate for full-scale simulations. This improves the capability of FDS to predict the performance of full-scale fire suppession systems.