For field commanders to make informed choices between one course of action and another, arguably less dangerous one (within the context of an assortment of many types of risks), appropriate comparisons must be made. Two types of information in particular are needed to make such comparisons of estimated impacts on troop viability and vulnerability: (1) the severity of the immediate medical consequences during the course of the mission, and (2) the likely number of troops affected in the exposure scenario envisioned during the course of the specific mission.

The purpose of the exercise reported herein is to explore the feasibility of using an approach that relies in part on probit analysis to describe, for three levels of severity (mild, moderate, and severe), the expected exposureincidence response for the reasonably healthy young adults that comprise the deployed population. As discussed in Chapter 4, this is not a definitive protocol for how to develop CCEGs. Rather, it is an example of one possible approach. The subcommittee recommends that the U.S. Department of Defense (DOD) develop guidance for establishing CCEGs and have that methodology peer-reviewed before application (see Chapter 4).

This analysis focuses on inhalation as the dominant pathway of exposure for military personnel. Unlike military exposure guidelines (MEGs) and other methods to identify levels of exposure that are unlikely to cause injury, the CCEGs (as envisioned here) are media-specific chemical concentrations expected to cause health impairments sufficient to reduce unit strength and therefore pose what the Army calls a medical threat. They are designed to evaluate course-of-action options that are expected to involve chemical exposures. Combat situations can result in human casualties that, although undesired, must nevertheless be tolerated to achieve military objectives. With that in mind, CCEGs allow commanders to weigh chemical risks against other operational risks and decide which chemical risks should be avoided and which must be borne for the sake of the mission.

Note that the approach described herein is intended to produce information about potential health impacts in a form that would allow field commanders to compare the impacts on the achievability of mission objectives from an assortment of chemical and nonchemical hazards that could degrade mission effectiveness. That is accomplished by using an approach that estimates the percentage of troops likely to be incapacitated (and the nature and duration of that incapacitation) by exposures to toxic agents.