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Thermal properties of handwear at varying altitudes
1Biophysics and Biomedical Modeling Division, US Army Research Institute of Environmental Medicine, Natick, MA 01760-5007, USA. william.santee@ns.amedd.army.mil
Background:
Total handwear insulation (I(T)) is dependent on the rate of heat transfer in air through the skin-handwear interface, handwear layers, and the surface boundary air layer. As altitude increases, the corresponding decrease in air pressure reduces convective heat loss. As convective heat losses decline, I(T), which is inversely related to the rate of heat loss, should increase. Increasing air velocity also reduces the insulation (Ia) provided by the boundary layer.
Methods:
The military issue test handwear, Light-duty glove (LD), Trigger-finger mitten (TF), and Arctic mitten (AM), were fitted over a biophysical hand model. Model surface temperatures were 25 degrees C, and air temperature was 10 degrees C. The handwear was tested at simulated altitudes of sea level (101 kPa), 2500 m (75 kPa) and 5000 m (54 kPa) in still air and at 5 m x s(-1).
Results:
Overall, the effects of wind and altitude on I(T) were significant. Differences for I(T) between 0 and 5000 m were significant for LD and TF. Increases in I(T) greater than 10% are considered of sufficient magnitude to alter comfort sensation.
Conclusions:
Differences of that magnitude occurred most frequently between 0 and 5000 m. The present results are consistent with an increase in I(T) with increasing altitude. Changes in I(T) were greater in still air and for less insulated handwear where the contribution of Ia to I(T) was more important.