Prevention of cold injury
Humans' responses to cold are to reduce heat loss, increase body heat production and seek external heat. The prevention of hypothermia focuses on ensuring these processes can operate effectively.
A key part of prevention is adequate trip planning, party preparation and sound leadership. Party members should be fit for the trip and should have adequate rest and nutrition. Dehydration should be avoided. It is preferable to drink cold water than ingest snow or ice, as the conversion of ice to water uses a large amount of body energy. Appropriate clothing is essential. There should be insulation worn over areas with large blood vessels close to the surface, such as the head and neck, which have a high heat loss potential. Wet inner garments should be changed, conditions permitting. Clothing should be varied according to the weather conditions and exertion levels to stay warm and dry. The effectiveness of clothing in the cold depends on its insulating properties, including when wet. Parties should be well equipped for shelter in cold or wet conditions. Over exertion should be avoided, as cold and exhaustion in combination predispose hypothermia.
Clothing should be layered to avoid both cooling and over-heating. Water conducts heat around 30 times faster than air at the same temperature, so wet clothes, including those wet from perspiration, must be avoided. Keeping clothes dry reduces heat loss by evaporation and conduction. Ventilation is important to allow evaporation of sweat and to keep clothing dry. Windproof outer shells reduce heat loss by evaporation and convection.
The cooling effect of wind combined with cold should be understood. Windchill charts demonstrate that the rate of cooling ('windchill') increases as the wind rises, as shown in Figure 21.1. This is not a linear relationship - an increase in wind chill approximates the square root of the wind speed. There is no change in actual temperature, but the effect of wind velocity on the rate of cooling for a given temperature is significant.