The Defense Threat Reduction Agency (DTRA) has developed enhancements to its Hazard Prediction and Assessment Capability (HPAC) to enable it to provide dispersion calculations in urban areas, to include both building exterior and interior calculations.

The DTRA urban dispersion modeling program has several components. First, outdoor and indoor dispersion and wind models have been integrated into HPAC for operational use. Second, DTRA has an active project to acquire and archive the urban terrain data needed by urban models. Third, DTRA has supported laboratory (water channel and wind tunnel) experiments as well as several reduced-scale and full-scale field trials to study urban wind and dispersion phenomena. The data from these laboratory experiments and field trials are used in model development and validation projects. Finally, DTRA uses its urban dispersion modeling capability to support actual events, operational demonstrations, and planning functions, and some of this work will be described.