Volume 2

Advances in military medicine, made by American investigators / edited by E.C. Andrus [and others].

  • United States. Office of Scientific Research and Development. Committee on Medical Research.
Date:
1948
Catalogue details

Licence: Public Domain Mark

Credit: Advances in military medicine, made by American investigators / edited by E.C. Andrus [and others]. Source: Wellcome Collection.

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    of the wool by environmental moisture and as a windbreak. When such an impermeable combination was tried in the field in Newfoundland, it was found impractical because of the moisture that collected within the inner glove. When the combination had to be removed in the cold this moisture sometimes froze in the glove, and in any event made its replacement on the hand a difficult and unpleasantly cold task. A similar system of impermeable layers was then tried on the foot. In this case a thin cotton sock was usually worn next to the skin, over this a rubber sock or one of some other material impermeable to both water and water vapor, over this again a heavy woolen sock, and over all a second rubber or plastic sock. Again the thick insulating sock was protected from wetting from both sides. When this assembly was tested in Newfoundland at near- freezing temperatures, it was found that the inner cotton sock became moist but that the collection of moisture was slight and negligible for exposures lasting a day or so. Such a combination provided excellent protection against wet cold and allowed men to walk through the snow and ice-water streams all day with impunity. Since the wet inner sock did not have to be removed and replaced, no trouble was experienced. Laboratory experiments demonstrated that a bare foot kept in practically still air at an ambient temperature slightly above freezing had a total effective protection against heat loss through all channels, including evaporation, equivalent to 0.52 Clo. Under these conditions foot cooling was rapid, aver- aging 0.01° C. per minute per degree of difference in temperature. When a foot was covered by a completely wet service boot and sock, effective insula- tion was no greater because evaporative heat loss was enormously increased, but the foot did not cool so rapidly because of the added effective heat capacity of the water in the assembly. A rubber sock inserted between the wool sock and the boot had little beneficial effect when all three were wet, because the water could still be evaporated at the skin and transmit heat as it condensed on the inside of the cooler rubber sock. On the other hand, the effective insulation obtained with the combination of a wet boot, rubber sock, and dry woolen sock was practically identical with that obtained with a completely dry assembly (about 1 Clo); the heat lost by vaporization of water from the boot was taken almost entirely from the surrounding air rather than from the foot itself. It was also shown that the insulating value of the woolen sock is little impaired by the moisture derived from the skin under cold conditions except after many hours. Since rate of cooling with a dry assembly was no slower than with a wet one (because of the extra heat capacity of the water), it was concluded that times of tolerance to cold can provide no real measure of relative insulation values unless the effective heat capacities of the assemblies being compared are the same.