This report describes efforts to develop models for predicting accidental thermal initiation of stored ammunition during fire. The models are supposed to be applicable in assessment of vulnerability and hazards of combat platforms and camps, which is attainable if the models can interact with vulnerability and lethality assessment software like AVAL. The software considers combat platforms at the system level, and is capable of simulating fire scenarios and consequences of initiation of stored ammunition. Available models for thermal initiation often involve detailed descriptions of the physical and chemical processes that underlie the phenomenon. The purpose of this work is to bridge the two model scales by investigating how the predictions from a physics-based model can be rationalized and efficiently employed with simulations at the system level. The report describes briefly how AVAL currently treats fire scenarios and thermal initiation, and gives a brief summary of available physics-based models for initiation. Then, a physics-based model for thermal initiation of a spherical TNT-charge, implemented in the multi-physics simulation software LS-DYNA, is studied. Different heating scenarios are considered, and the predicted time to explosion. Mechanical stresses in the charge and the casing are estimated post-simulation. In order to rationalize the predicted times to explosion, an empirical model is suggested. The model can be calibrated against LS-DYNA simulations and then implemented for efficient use at the system level.