Thermal properties of handwear at varying altitudes

Background: Total handwear insulation (IT) 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 de crease in air pressure reduces convective heat loss. As convective heat los ses decline, IT, which ii inversely related to the rate of heat loss, shoul d increase. Increasing air velocity also reduces the insulation (la) provid ed by the boundary layer. Methods: The military issue test handwear, Light- duty glove (LD), Trigger-ringer mitten (TF), and Arctic mitten (AM), were f itted over a biophysical hand model. Model surface temperatures were 25 deg reesC, and air temperature was 10 degreesC. The handwear was tested at simu lated altitudes of sea level (101 kPa), 2500 m (75 kPa) and 5000 m (54 kPa) in still air and at 5 m . s(-1). Results: Overall, the effects of wind and altitude on IT were significant. Differences for IT between 0 and 5000 m w ere significant Tor LD and TF. increases in IT greater than 10% are conside red of sufficient magnitude to alter comfort sensation. Conclusions: Differ ences or that magnitude occurred most frequently between 0 and 5000 m. The present results are consistent with an increase in IT with increasing altit ude. Changes in IT were greater in still air and for less insulated handwea r where the contribution of la to IT was more important.