Developing a predictive model for cook-off is a difficult task. Recent experiments with PBX 9501 have shown that under certain heating and confinement conditions it is possible to generate large regions of almost uniform temperature in an explosive. Such regions react violently in a coherent fashion and may have the potential to produce unusually symmetric detonation waves in certain geometries. These results were unexpected before the experiments and have generated considerable additional activity both experimentally and in model building. At this time, there is no unambiguous explanation for the observed behavior, and therefore, there is a considerable number of fledgling models in existence. These models suggest varying and possibly contradictory mechanisms to explain the thermal profiles and wave behavior data. In this paper, we present an approach to model development for cook-off of PBX 9501 based on logic models called process trees. Process trees are well-suited to the task of describing causal sequences and delineating alternative descriptions of observed phenomenology. Therefore, they provide a valuable basis for constructing physical models and integrating them.
