Staying Warm

Hypothermia
Hypothermia occurs when a person's core body temperature lowers causing decreased performance, discomfort and distress. People are more susceptible to hypothermia if they are: lean with low body fat, very young, have consumed alcohol or drugs, have become injured, or are fatigued or dehydrated. Hypothermia can occur at anytime of the year but is

obviously more common and severe on the coldest days.

Signs and Symptoms of Hypothermia:
-sensation of being cold -intense shivering (later, no shivering)
-fumbling hands, frequent stumbling
-slow, slurred speech
-drowsiness
-slow and shallow breathing
-exhaustion
Severe Hypothermia may lead to coma and even death. Frost Bite occurs from subfreezing cold. Frostnip is the superficial injury that people recover from quickly while frostbite injuries may be permanent. Chilbain (or Trenchfoot) occur when skin is damaged by a constant wet but above freezing temperature.Both chilblain and frostbite will cause damage to the skin and underlying tissues. Hypothermia, Frost Bite and Chilblain, may all coexist. It is much easier to prevent these conditions than to begin treating them, particularly if you are alone or with no nearby help. It requires less energy to stay warm and comfortable that it does to stay warm!

General Rules for Staying Warm
Blocking Conduction of heat away from the body.
Remember: Thickness = Warmth. This is only true if the insulative layer of clothing is dry. It is the air spaces in the insulation that prevents the loss of heat.

Block Convection or the loss of the layer of warmed air that is always next to your body. An outer 'shell' should be wind-proof and a drawstring at the waist will also prevent the 'chimney effect', which occurs when warm air escapes from the neck or head and cool air rushes in at the waist to replace it. A hat also blocks a significant amount of lost heat.
Stopping Evaporation. Much heat loss occurs through evaporation of sweat. During winter activities, vented clothing can bring down body temperature avoiding unnecessary perspiration. A water vapour, Slowing Heat Loss From Respiration. Exhaled breath contains warm humidified air. Breathing through a neck warmer, scarf, or air-warming mask, will create a warm vestibule reservoir so that you rebreath the same humidified air and decrease warm air loss.

Other Hints
Avoid extreme winds that will accelerate convection heat loss, wet clothing, or water that will drop insulation values down to zero. Wearing multiple layers of clothing is helpful since you can adjust the thickness of insulation by adding or subtracting layers of clothing.

Winter clothing can be divided into different types of beneficial clothing systems:

1) Breathable: consists of 3 levels- a thin, underwear (transport layer), middle insulative layers, and outer-shell fabric. The outer shell allows protection against wind but is still breathable.

2) Waterproof/barrier system; is the same as above except the shell layer is selectively permeable, since water vapour can escape from inside, but is waterproof from the outer. Gore-tex brand is an example. (Gore-Tex can fail if water freezes on it becomes a layer of frost)

3) The Vapour-Barrier system consists of 4 layers: The layer next to the skin is a thin layer of polyester or polypropylene. The next layer is the vapour barrier used to control perspiration and should be waterproof. (Usually a coated nylon or polyethylene). This vapour barrier prevents sweating into the layers of insulation. The following layer is the insulative layer and lastly the shell is Gore-tex.

This system thereby prevents contamination of the insulative material from inner and outer moisture. This system reduces insensible perspiration.

Most heat loss occurs from the head so be sure to remember the old mountaineer saying: "If your feet are cold, put on a hat, and if they are still cold........ put on another hat."

For your reference a downloadable version of this text can be found at these links.
Front Page - Back Page

References:
1) Secrets of Warmth, 2nd edition. Hal Weins, Rocky Mountain Books, *1992, Calgary, AB
2) Manitoba Lifesaving Society, 2001. 3) Wilderness Medical Society Guidelines on Hypothermia and Frostbite Injury 2001.