The Five Mechanisms of Heat Loss

When you're out-of-doors, there are five heat loss mechanisms you should be intimately familiar with. Understanding these mechanisms will help you mitigate their effects should you ever be placed into an emergency survival situation.

CONDUCTION

Conduction is the process by which heat is directly transmitted through a substance when there is a difference of temperature between the adjoining regions (hot to cold), without movement of the material. Put simply, conduction is the cold feeling on your butt when you sit on the ground; the heat from your warmer butt is transferred to the cooler ground through conduction.


CONVECTION

Convection is the movement caused within a fluid by the tendency of hotter and therefore less dense material to rise, and colder, denser material to sink under the influence of gravity, which consequently results in transfer of heat.


You'll notice convection occurring around your coat collar on a very cold, still day. As your body warms the air under your jacket, that warm air rises. If there's no neck warmer or a hood to stop it, the warm air heads right up and out, pulling cold outside air in through the bottom of your jacket. Many ski and mountaineering jackets have pull cords on the bottom to help inhibit this process.


RADIATION


Body heat is actually a form of electromagnetic radiation. The wavelengths are longer than visible light, but shorter than radio waves. Radiative heat loss, like conduction, occurs from your warmer body into the surrounding environment--especially into outer space on a clear night. You'll notice a cloud cover at night considerably dampens the effect of radiative heat loss from your body because it reflects a certain amount of infrared radiation back to earth.


RESPIRATION


Our bodies regulate heat levels partially through respiration--breathing. Every breath we take brings dry outside air into our lungs. When we exhale, our bodies have both heated and moistened that air. Each breath gets rid of just a little bit of heat and moisture. This isn't a problem in a controlled environment, but must be understood in a survival situation.


PERSPIRATION


Sweat is the body's natural heat regulation mechanism. When we exert ourselves, sweat uses the mechanisms of conduction and convection to efficiently carry off excess body heat. In a survival situation, sweat is one of our number one enemies--to be avoided at all costs.


Controlling Heat Loss Through Mitigation of the Five Heat Loss Mechanisms


Instead of reinventing the wheel, Backpackinglight.com has a wonderful article on how to avoid heat loss through our five mechanisms. Visit this link to read the article.