Urban Shield is a building protection system that provides emergency response support in case of an accidental or intentional release of hazardous material into the atmosphere. We have developed and deployed systems that analyze the state of the atmosphere, predict the path of toxic plumes, and provide that information to security personnel in order for them to take actions that will protect the building's inhabitants. The system is especially complex as it continually combines data in real time from four meteorological models, ranging from a mesoscale model down to a model that accounts for the effects on the wind of individual buildings. This provides Pentagon officials with detailed information about local wind conditions. Sensors constantly monitor for any signs of a toxic release, and the system can initiate a plume prediction, if required.