work for follow-up studies on combinations of the two agents to determine whether there are interactions involving any of those effects. Experiments on combined human exposures to CO and HCN, similar to those suggested in Chapter 3 for CO alone, would be ideal; however, the health risks posed to the subjects due to the high toxicity of HCN would likely be unacceptable. An alternative would be to design neuro-behavioral experiments in nonhuman primates to test the effect of HCN in combination with CO.

An additional or alternative approach considered viable by the committee is to conduct field studies in actual armored vehicles, where CO and HCN would be measured simultaneously along with crew performance (for example, reaction times). As stated in Chapter 4, however, such field experiments are unlikely to give definitive results because of multiple uncontrollable variables.

Recommendation The committee recommends that, as more data become available on the actual combined exposure concentrations of CO and HCN and durations of such exposures, the Army seeks to understand how exposures to additional chemicals might affect the interaction of CO and HCN. Examples of additional chemicals are ammonia, particulate matter (including combustion-derived nanoparticles), and other components of diesel exhaust. Furthermore, it recommends that information or experimental results related to such potential interactions be reviewed by an independent body to assist in setting priorities on such interactions, including those that might be synergistic.

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