This paper describes a probabilistic analysis of an unusual safety concern encountered during safety analysis of a closed system containing high explosive (HE). In this application, a pyrophoric material could be generated inside the system by corrosion of system components. This pyrophore may form extremely small particles that could be transported through a complex path to a high explosive component, where they could collect on exposed surfaces as a result of routine handling operations. A potentially serious accident could be initiated if the system is opened for maintenance and oxygen reaches the pyrophoric particles that are resting on the surface of the high explosive. The pyrophoric particles react vigorously in the presence of oxygen and will ignite the high explosive if there is a sufficient concentration of the particles in a localized area. This paper reports on models for estimating the probability of achieving hazardous concentrations of pyrophoric particles on the explosive surface. These probability estimates are based on occupancy likelihood and geometric models. The probability models provide a means for exploring the effects of material behavior, heat transfer, and material transport on the likelihood of achieving unwanted concentrations of pyrophoric particles on the explosive surface.