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Types of Heat Loss

We lose up to 65 per cent of our total heat through the combination shown above. Radiated body heat warms the cool air or moisture around our bodies, which is then stripped away by conduction or evaporation. Heat loss is greatest from exposed skin, particularly on areas of the body that have a large blood supply, such as the head and neck. The head alone accounts for 47% of the heat loss. 90% of the circulation in our hands is used to keep warm which is why our cold hands quickly lose dexterity. Therefore it is vitally important to reduce this danger by using high wicking base layers and covering up with hats, balaclavas, hoods and gloves.

Convection
The body heats the layer of air or moisture next to its surface. When this is taken away by cold air passing across the body, the wind or air caused by arm movement, convection takes place. This is substantially reduced by windproof clothes.

Conduction
Conduction is heat which is transferred by direct contact between objects. The rate of body loss is determined by the conductivity of the material with which we are in contact. Pay attention to the surfaces you are in contact with (sitting on or leaning against) as you will be losing heat through these materials. To help reduce this process use cut up foam sleeping mats for sitting on at rest stops.

Evaporation
To change from a liquid to a gas, water requires energy. So when we sweat, or when moisture in our clothes evaporates, the fluid draws energy warmth from our body to make the transformation. In hot weather, we sweat and this can keep us cool, however in a cold climate this works against you. Water conducts heat away from your body 25 times faster than air. As we sweat in cold weather we replace the warm air trapped between our clothing layers with sweat. Then as the wet clothing dries on your body, heat is lost by evaporation. It is for this reason high wicking base and mid layers are important as they keep moisture off your skin.

Respiration
We breathe in cold air, we warm it and then when we exhale our breath expels heat. This increases when in a cold atmosphere and is extreme in the dry cold artic, where more heat is lost as energy.

Metabolism
Every time we eat something your body is generating internal heat, which keeps us alive. We expend heat as we exercise and if we don’t replenish our internal supply we soon become exhausted. Exhaustion is a major contributor to hypothermia as well as creating a bad mental approach to our circumstances, anger, frustration and disappointment. Even if you are wearing the best gear, hypothermia is easily brought on by not eating and drinking regularly to stave off the effects of the cold.

The body heats the layer of air or moisture next to its surface. When this is taken away by cold air passing across the body, the wind or air caused by arm movement, convection takes place. This is substantially reduced by windproof clothes. 

 

Introduction

Part 2 - The Importance of Water

 

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