We are all exposed, but some are more exposed than others

Abstract

This paper defines functional cold exposure zones that illustrate whether a person is at risk of developing physical performance loss or cold weather injuries. Individual variation in body characteristics, activity level, clothing and protective equipment all contribute to variation in the effective exposure. Nevertheless, with the right education, training, and cold-adapted behaviours the exposure differences might not necessarily lead to increased risk for cold injury. To support the preparation process for cold weather operations, this paper presents a biophysical analysis explaining how much cold exposure risk can vary between individuals in the same environment. The results suggest that smaller persons are prone to be underdressed for moderate activity levels and larger persons are prone to be overdressed. The consequences of these discrepancies place people at different risks for performance loss or cold weather injuries. Nonetheless, even if all are well-dressed at the whole-body level, variation in hand morphology is also expected to influence hand skin temperatures that can be maintained; with smaller hands being more prone to reach skin temperatures associated with dexterity loss or cold weather injuries. In conclusion, this work focusses on bringing cold science to the Arctic warrior, establishing that combating cold stress is not a one size fits all approach.

Keywords: Individual variation; cold weather operations; modelling; thermoregulation.

Figure 1.

A) set of soldiers (n=2189) with varying body size (height and weight) for which the required clothing insulation analyses have been performed. B) calculated metabolic rate of the set of soldiers for a 4km/h walking activity on a small slope (2%) road, carrying a 20kg load.

Figure 2.

Calculated required clothing insulation for a varying set of body sizes. Relative to the average required clothing level (2.8±0.1 clo) 18% is underdressed, 28% is overdressed and 54% is well-dressed. The calculations have been performed using the metabolic rates shown in Figure 1b.

Figure 3.

Bare hands functional hand temperature zones vs air temperature for three levels of dress state (1 km/h wind). Top: a female hand. Bottom: a male hand. The lines indicate heat balance and hand temperature will not change. Points on the right side of a line coincide with positive heat balance and hands will warm up. Points on the left side of a line coincide with negative heat balance and the hands will cool down.

Figure 4.

Common mitten hands functional hand temperature zones vs air temperature for three levels of dress state (5 km/h wind). Top: a female hand. Bottom: male hand. The line indicates heat balance and hand temperature will not change. Points on the right side of a line coincide with positive heat balance and hands will warm up. Points on the left side of a line coincide with negative heat balance and the hands will cool down. The letters in the bottom panel are supportive of three thought experiments: (A) starting from the solid line, if the hand accidentally warms up, it will cool down again until settling on the solid line. (B) If the hand accidentally cools down and ends on the left side of the solid line, it will continue to cool down. (C) In case the hand temperature drops from the solid line and ends up at the right side of the solid line, the hands will be in positive heat balance and automatically warm up again.