The Five Causes of Heat Loss

Hypothermia is the biggest threat to a person's survival in cold weather. However, this silent killer can be avoided if you learn to recognize and guard against the five major causes of heat loss.

Radiation
This is the transfer of heat from your body to the environment. The colder it is, the more heat is lost. The head, neck and hands are most at risk for heat loss from radiation. Wearing layers of protective clothing on these sensitive areas can significantly slow the process.

Conduction
Body heat is lost through conduction when the body comes in contact with cold objects. The colder the object is, the greater the heat loss. This poses a significant problem when a person's clothing is wet or one is submerged in cold water. When contact with a cold item is inevitable, use a foam pad or similar item to create a barrier between your body and the object. If clothes get wet, immediately remove and change them, if possible. If not, it is important to wring out as much of the moisture from your clothing as possible.

Convection
The body loses heat when air movement across the skin carries it away. This happens with any movement (walking, running, etc.) and when your body is exposed to wind. Convection heat loss can be eliminated by staying still and protecting yourself from the wind. Wearing loose layers with an outer nylon shell (like one made of Gore-Tex) helps trap warm air next to your body and decreases the impact of convection heat loss.

Evaporation
Body heat is lost through evaporation when moisture from your skin (perspiration) evaporates, so it's important to minimize sweating in a cold weather survival situation. If you start to sweat, slow down your movement or stop moving altogether. Add or remove clothing layers as needed to stay warm without sweating.

Respiration
The last type of heat loss occurs when you breathe, as the body warms inhaled cold air en route to the lungs. The colder the air is, the more heat that is lost. To decrease respiratory heat loss, cover (or encircle) your mouth with an insulating layer of clothing. This layer will trap air, allowing it to warm slightly before you breathe it in.