Preference: Platform Presentation
Working Group: Chemical and Biological Defense Hazard Assessment
Abstract Predicting the dynamics of biological warfare agent dispersed as an aqueous slurry from a commercial-grade spraying system requires simulation of several complex processes. The resulting biological agent particles of interest are the respirable ones less than 10 microns in diameter; however, the initial slurry droplets are expected to range from 10 microns up to 500 microns in diameter. The droplet fall velocity must therefore be accounted for. The droplets will evaporate as they are carried by the wind and fall towards the ground. The rate of evaporation of a pure water droplet is a function of fall velocity, vapor pressure, and relative humidity. Biological warfare agent slurry droplets add the solution effects associated with the presence of organisms, insoluble growth media, and soluble growth media, all of which act to lower the droplet vapor pressure. The slurry droplets leading to respirable particles must be small to begin with and will evaporate within seconds under conditions of low humidity. Under moderate to high humidity conditions, though, complete evaporation will not occur. Finally, a fraction of droplets and particles reaching the ground will deposit. Only a small fraction of respirable particles reaching the ground will deposit; the rest will be carried by eddies back into the plume. This presentation discusses the methodology developed by the Naval Surface Warfare Center in Dahlgren, VA to address these processes.