There's a great article at the Outdoor Action Guide
on Hypothermia And Cold Weather Injuries
by Rick Curtis.
Traveling in cold weather conditions can be life threatening. The information provided here is designed for educational use only and is not a substitute for specific training or experience. Princeton University and the author assume no liability for any individual's use of or reliance upon any material contained or referenced herein. Medical research on hypothermia and cold injuries is always changing knowledge and treatment. When going into cold conditions it is your responsibility to learn the latest information. The material contained in this workshop may not be the most current.
He then goes on to discuss:
How We Lose Heat to the Environment
- Radiation - loss of heat to the environment due to the temperature gradient (this occurs only as long as the ambient temperature is below 98.6). Factors important in radiant heat loss are the surface area and the temperature gradient.
- Conduction - through direct contact between objects, molecular transference of heat energy
- Water conducts heat away from the body 25 times faster than air because it has a greater density (therefore a greater heat capacity). Stay dry = stay alive!
- Steel conducts heat away faster than water
Example: Generally conductive heat loss accounts for only about 2% of overall loss. However, with wet clothes the loss is increased 5x.
- Convection - is a process of conduction where one of the objects is in motion. Molecules against the surface are heated, move away, and are replaced by new molecules which are also heated. The rate of convective heat loss depends on the density of the moving substance (water convection occurs more quickly than air convection) and the velocity of the moving substance.
- Wind Chill - is an example of the effects of air convection, the wind chill table gives a reading of the amount of heat lost to the environment relative to a still air temperature.
- Evaporation - heat loss from converting water from a liquid to a gas
- Perspiration - evaporation of water to remove excess heat
- Sweating - body response to remove excess heat
- Respiration - air is heated as it enters the lungs and is exhaled with an extremely high moisture content
- It is important to recognize the strong connection between fluid levels, fluid loss, and heat loss. As body moisture is lost through the various evaporative processes the overall circulating volume is reduced which can lead to dehydration. This decrease in fluid level makes the body more susceptible to hypothermia and other cold injuries.
It'd definitely worth a full read. See the rest of the article at: