Simulations of hazardous material releases attempt to model and evaluate the dispersion of various kinds of materials including chemical, biological, nuclear, and radiological agents into the atmosphere, HVAC systems within buildings and other enclosed spaces, watershed systems, and the soil. Releases may be accidental (e.g., a ruptured tank car from a train derailment), intentional (e.g., a terrorist attack), or natural (e.g., a wildfire or volcanic eruption). Examples of release sources include nuclear power plant accidents, leaks or spills from tanks or industrial plants, use of chemical and biological sprayers, fires, smokestack emissions, nuclear detonation clouds, and other explosive blasts.