EVALUATION OF LETHALITY ESTIMATES FOR COMBUSTION GASES IN MILITARY SCENARIOS

To meet the military objective of determining criteria for incapacitat ion and lethality from toxic gas exposures, a series of small animal t ests and data analyses were conducted. Carbon monoxide (GO), a narcoti c gas and nitrogen dioxide (NO2), an irritant gas, along with carbon d ioxide (CO2) were tested individually and in the following mixtures: ( CO + CO2), (NO2 + CO2) and (NO2 + CO + CO2). A group of six animals wa s exposed to each of the gases and their combinations, lethality and b iophysical data were collected. We conclude that our observations of l ethality from single toxic gases can be correlated with a fractional e ffective dose (FED) description, in which external concentrations are corrected for minute volume changes. Multiple gas exposures clearly de monstrate synergistic effects because lethality rates greatly exceed t hose expected from statistically independent causes. Simple addition o f the FED values, however, overstates the effect and implies a competi tion between the narcotic and irritant gas effects. The N-Gas model, w hile being an additive FED model, does not appear to be in a form that could guide the setting of military exposure standards.