The application of a fire-engineering field model to the analysis of a polymer fuel sample ignited in a cone calorimeter is described. The field model solves the three-dimensional, full Navier-Stokes equations in a time-dependant fashion. Transient thermal conduction within the fuel sample is included, and degradation of the polymer is controlled by a temperature-dependant zero-order Arrhenius expression. Using PMMA as the polymer fuel sample, the predicted ignition times from the numerical model are compared to experimental data at various cone irradiation levels.