1936; Alistair et al. 2000; Penney 2000). Again, the incidence of these effects and the conditions necessary for their occurrence are not known. It is also not known whether these effects have occurred or may occur under the conditions of interest to this study.

CO and HCN are the major toxic gases considered in this report; however, the committee recognizes that other gases, such as oxides of nitrogen and sulfur dioxide, are produced during the combustion process and from other sources within armored vehicles. Both CO₂ and HCN are known to affect respiratory rates (Peterson and Stewart 1975; Purser et al. 1984), and the presence of these agents could result in an increased uptake of CO and other toxic gases. Data on such complex mixtures are insufficient to ascertain whether any such effects are functionally relevant to the questions the committee has been asked to address.

Recommendation The Army should consider close and systematic surveillance of vehicle crews with the intent of identifying any increased risk of sudden death, myocardial infarction, or other significant medical problems.