Showing papers on "Clothing insulation published in 1996"

Clothing insulation in a hypobaric environment.

Abstract: Hypothesis: Clothing insulation is the result of complex interactions between heat transfer mechanisms and clothing material thermal resistances. Hypobaria changes the heat transfer processes therefore should have observable effects on the clothing insulation. Methods: The effect of hypobaria on the thermal insulative properties of U.S. Army fatigue uniform (BDU) and U.S. Army chemical protective overgarment (BDO) were examined. Barometric pressure of 429 mmHg, comparable to the condition at terrestrial elevation of 4570 m (15,000 ft) above sea level was created in a hypobaric chamber. The sea level environment was used as a baseline condition. Results: Our data support a diminished convective heat transfer and an enhanced evaporative heat transfer at higher altitude. We also found that hypobaria had only a small effect on the intrinsic clothing insulation values. For the less insulative BDU, hypobaria did not appreciably affect clothing insulation values. For the more insulative BDO, a maximum difference of 0.2 clo (clo = 0.155 m 2 .K.W -1 ) was found between hypobaric and normobaric environments. Conclusion: Heavy clothing insulation forced the heat transfer processes at the skin surface to operate almost independently from those at the clothing surface. At the skin surface, evaporation was the dominant process, while at the outer clothing surface, convection dominated. At higher altitude, enhanced evaporative heat transfer resulted in a lower skin temperature, while reduced convective heat transfer hampered heat dissipation from clothing surface to the ambient environment, hence elevating the clothing temperature. Therefore, in hypobaric environment, the skin temperature was found to be lower, but the clothing temperature higher than at sea level.

The effect of water leakage on the results obtained from human and thermal manikin tests of immersion protective clothing

Abstract: The effect of both the volume and location of water leakage on the protection provided by an uninsulated immersion suit was investigated using human subjects and, in corresponding experiments, an immersion thermal manikin. Three volumes of “leakage” to the torso (200, 500 and 1000 ml) were examined, as were two conditions in which no leakage was simulated and one condition in which a 500-ml leak to the limbs was simulated. All leakages were introduced in a standardised way before immersion. The measurements of clothing insulation obtained, both from the manikin and the humans, were in general agreement. The human experimentation provided some support for a 200-ml limit to water leakage in tests of immersion suits. Rectal and aural temperatures remained significantly (P < 0.05) higher when a 500-ml leak was applied to the limbs rather than the torso; this was primarily due to greater heat flow through and from the torso (back) during the immersions with torso wetting. The physiological responses and anthropometric characteristics which determine this response are not present in manikins; the implications of this for the application and design of immersion thermal manikins, as well as the protection of those at risk of immersion in cold water, are discussed. It is concluded that using immersion thermal manikins to provide a single overall measure of clothing insulation will not necessarily distinguish between suits which provide quite different levels of protection for humans.