Medical Modeling of Particle Size Effects for CB Inhalation Hazards

Abstract : In this project, Applied Research Associates, Inc. (ARA) developed the Deposition And Response in the Respiratory Tract (DARRT) model; an improved medical model of particle size effects for inhalation hazards from chemical and biological (CB) agents. This project was initiated to improve modeling of the variation in human response caused by differences in particle sizes, in particular, for coarse particles that may be present near a dissemination source and may remain suspended long enough in an urban environment to expose large numbers of people. Plume dispersion calculations with the Defense Threat Reduction Agency's (DTRA's) Hazard Prediction and Assessment Capability (HPAC) show that, contrary to common beliefs, particles as large as 20 to 40 microns in diameter can be a significant hazard tens of kilometers downwind of a release. DARRT predicts the probability of infection or injury from inhalation exposure to aerosol hazards of CB agents with aerodynamic diameters between 0.01 and 100 microns and describes the resulting medical impact. Many current models assume that only the 1 to 5 micron respirable particles capable of reaching the pulmonary region of the respiratory system are of concern; however, we find that inclusion of coarse (greater than 5 micron) particle deposition is important, as well.