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Since 1962. US military researchers have engaged in a concerted effort to improve the thermal comfort of chemical and biological (CB) protective clothing ensembles. Although current-issue CB protective ensembles have benefited from this work, full encapsulation within these multi-layered, low-permeability garments still severely limits human tolerance, especially in the heat. This chapter will describe testing methods, research findings, and improved CB ensembles that have been developed for the US military services. Early CB ensembles were virtually impermeable and presented a serious health hazard to the wearer. In the early 1960s, protective textiles were evaluated for thermal and water vapor resistance using a guarded, heated flat-plate apparatus. Prototype overgarments employing improved activated carbon foam layers were then tested on thermal manikins outfitted with wettable cotton skins. In the late 1960s, biophysical data from the manikins were integrated with human volunteer trial data to make simple predictions of core temperature and heart rate. These predictive models further evolved to accurately describe sweat rates, hydration requirements, and safe work/rest cycles in a range of exercise intensities and environmental conditions. Carbon foam absorption remained the method of CB protection until 1995 when testing began to focus on thinner materials using microencapsulated carbon spheres. Current testing is being conducted on extremely thin, selectively permeable membranes (SPM) as the basis for lighter, highly breathable CB overgarments. This active testing program has allowed military textile technologists to produce prototype CB protective clothing that has gradually increased wearer thermal comfort. 25 years of prototype improvements were adopted to maximize the limited evaporative cooling potential of the carbon foam-based US Army Standard Battle Dress Overgarment (BDO). Extensive multi-service testing replaced the BDO with the lighter, more comfortable Joint Service Lightweight Integrated Suit, offering longer human tolerance times for an expanded military population. Initial manikin testing of SPM technology shows that evaporative resistance is markedly reduced, along with lower thermal resistance, thereby improving overall evaporative potential and improving user performance in hot environments. Biophysical analyses, predictive modeling, and physiological wear trials have been instrumental in improving the thermal comfort capabilities of military CB protective clothing systems. |
