The Implications of Temporal and Spatial Averaging in Hazardous Airborne Material Dispersion Calculations for Human Impacts Modeling within a Hyperlocal Environment

Conducting injury and casualty assessments associated with human exposure to airborne hazardous materials is a critical function of emergency response modeling tools. This calculation is based on a combination of models that represent the material release, fate and transport, and human response to the exposure. The calculation becomes even more complex for urban and indoor areas where the presence of buildings and other structures affects wind fields and the corresponding outdoor contaminant transport, high population densities and highly variable distributions in population that complicate the accurate assessment of consequences.

To explore the implications of temporal and spatial averaging on this type of injury and casualty calculation we used a new microscale atmospheric and atmospheric transport and dispersion (AT&D) modeling capability called the Joint Outdoor-indoor Urban Large Eddy Simulation (JOULES) system. JOULES has been designed to provide high-fidelity simulations of urban airborne hazardous materials that can be used to the support the testing, evaluation, and validation of operational urban modeling tools, and the development of scientific enhancements to these systems. A key enabling technology within JOULES is a Large Eddy Simulation (LES) model that has been implemented on a Graphics Processing Unit (GPU) computing platform. The GPU-LES model provides a simulation platform that is significantly faster than the current generation of Central Processing Unit (CPU) based LES models and enables the development of ensembles of AT&D simulations. JOULES has been extensively validated against open terrain and urban laboratory experiments and field trials and is shown to be able to accurately reconstruct the these dispersion scenarios. Recently this system has been further augmented with an indoor model that can calculate the exchange of hazardous airborne materials across the building envelope and provide indoor concentrations.

In this presentation we will provide a description of the JOULES system and a brief summary of the validation studies that have been undertaken to demonstrate its accuracy. We will also present results from a study where JOULES was used to illustrate the relative inaccuracies associated with calculating human casualty and injury estimates from the ensemble averaged AT&D simulations available in the current generation of emergency response tools for open terrain, urban, and indoor environments. Results will be shown for a variety of idealized scenarios that illustrate the impact of making outdoor and indoor casualty estimates from an ensemble of human toxic load calculations vs. making a single human-effects estimate from an ensemble of AT&D solutions.