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Non-evaporative effects of a wet mid layer on heat transfer through protective clothing

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Author: Bröde, P. · Havenith, G. · Wang, X. · Candas, V. · Hartog, E.A. den · Griefahn, B. · Holmér, I. · Kuklane, K. · Meinander, H. · Nocker, W. · Richards, M.
Type:article
Date:2008
Institution: TNO Defensie en Veiligheid
Source:European Journal of Applied Physiology, 104, 341-349
Identifier: 19205
doi: doi:10.1007/s00421-007-0629-y
Keywords: Clothing · Clothing insulation · Conduction · Moisture · Skin temperature · body position · cooling · evaporation · heart stress · skin temperature · sweating · thermoregulation · treadmill exercise · weight change · Adult · Body Temperature Regulation · Body Weight · Cotton Fiber · Heat · Humans · Humidity · Male · Manikins · Microclimate · Permeability · Polyvinyl Chloride · Protective Clothing · Sweating · Temperature · Thermal physiology

Abstract

In order to assess the non-evaporative components of the reduced thermal insulation of wet clothing, experiments were performed with a manikin and with human subjects in which two layers of underwear separated by an impermeable barrier were worn under an impermeable overgarment at 20°C, 80% RH and 0.5 ms-1 air velocity. By comparing manikin measurements with dry and wetted mid underwear layer, the increase in heat loss caused by a wet layer kept away from the skin was determined, which turned out to be small (5–6 W m-2), irrespective of the inner underwear layer being dry or wetted, and was only one third of the evaporative heat loss calculated from weight change, i.e. evaporative cooling efficiency was far below unity. In the experiments with eight males, each subject participated in two sessions with the mid underwear layer either dry or wetted, where they stood still for the first 30 min and then performed treadmill work for 60 min. Reduced heat strain due to lower insulation with the wetted mid layer was observed with decreased microclimate and skin temperatures, lowered sweat loss and cardiac strain. Accordingly, total clothing insulation calculated over the walking period from heat balance equations was reduced by 0.02 m2 °C W-1 (16%), while for the standing period the same decrease in insulation, representing 9% reduction only showed up after allowing for the lower evaporative cooling efficiency in the calculations. As evaporation to the environment and inside the clothing was restricted, the observed small alterations may be attributed to the wet mid layer’s increased conductivity, which, however, appears to be of minor importance compared to the evaporative effects in the assessment of the thermal properties of wet clothing. Electronic supplementary material The online version of this article (doi:10.1007/s00421-007-0629-y) contains supplementary material, which is available to authorized users. Keywords Moisture - Clothing insulation - Conduction - Skin temperature - Sweating The content of this manuscript was presented at the International Conference on Environmental Ergonomics 2007.