Wilderness Skills - Olympia Mountaineers

In the outdoors, a person feels comfortable when the air temperature is approximately 70°, although that is a
difference of 30° between the outside temperature and the core. At this temperature, a person is able to
effectively heat the air around the body and needs very little clothing. At higher ambient temperatures, clothing
isn’t really needed. As the air temperature rises, the body protects the core temperature by eliminating heat
through increasing perspiration and respiration. When the air temperature decreases, the body also reacts to
maintain the core temperature by producing more heat through involuntary shivering and other responses.
With the air temperature drops below 70° F, more clothing is needed to maintain comfort and the critical core
temperature. In the mountains, when the air temperature drops, a person unable to add thermal protection
(more clothes) will eventually experience a decrease in core temperature. As the core temperature drops to 96
° the body responds by spontaneously shivering and forming goose pimples on the surface of the skin. When
the core temperature reaches 93 ° the body reduces the blood flow to the extremities as the body works to
preserve the core at the expense of the arms and legs, which loose heat much faster. The result is a loss of
dexterity and performance. As the core temperature continues to drop a person experiences progressive loss
of mental acuity, unconsciousness, and eventually will die. Survival in a cold environment requires proper
clothing to insulate the core temperature of the body (temperatures are approximate).
Heat Loss
The body looses heat in several ways. Convection is the loss of heat as the warmed air surrounding the body
rises and escapes through the openings in the clothing and is replaced by cooler air. It’s referred to as the
chimney effect. Conduction is the exchange of heat from a warmer object to a cooler object through physical
contact. Radiation is the transmission of thermal energy, primarily through infrared radiation waves.
Evaporation of perspiration from the skin results in the loss of heat energy. Respiration results in heat loss
when warm air is exhaled and cooler air is inhaled. The amount of heat lost to each of these factors will vary
depending on the weather conditions, clothing, exertion, and the ability to stay dry.
During the strenuous hike, a person with high quality clothing looses heat mainly through conduction, contact
with cooler air. A smaller amount of heat is lost through radiation and perspiration and a small amount yet
through convection and respiration. Factors that shape the heat loss include: the kind and amount of clothing,
the amount of wind and water in the environment and the hikers level of exertion.
OK, We understanding heat loss is important, but what really matters is the way we can use this information to
vent excess heat in hot weather and reduce heat loss in cold, wet weather.
By understand that through convection, the warm air inside clothes will rise and flow out of openings in clothes
only to be replaced by cooler air, allows the informed hiker to cinch down openings and billowing clothes to
better contain warmth. By understanding that by reducing exertion rather than rushing through the bush with
poor clothing, could help the lost hiker stay warm because it will help conserve body heat by reducing
perspiration and respiration. By understanding that conduction, contact with cooler air, is often the greatest
cause of heat loss, the informed back country traveler can take control of this loss by better insulating high
heat loss areas from contact with cooler air.
The body has a few high heat loss areas where there is high arterial blood flow and little or no muscle mass
to shield these areas. These high heat loss areas include the head, the neck, under the arms, down the sides
of the torso, and through the groin area. Protecting these areas with greater insulation can significantly reduce
heat loss and help the entire body stay warm. The old saying, “if your feet are cold put on a hat”, is very
true.
This information could be useful to the hiker who reaches the summit on a cloudy, wet day. After a 20-minute
rest at the summit, a hiker begin to descend and notices the temperature is dropping. As exertion decreases
on the decent, heat production decreases. Unprotected heat loss areas will eventually give up lots of body
heat. Without a hat and an open collar, the hiker will loose heat rapidly, much faster than it’s produced. After a
shivering spell, the hiker will notice her hands and feet become not only cold, but stiff. The body has begun to
restrict blood flow to the extremities. At this point, it is too late to simple protect heat loss areas. The hiker must
quickly add heat.
Wilderness Skills Module Page 22 of 73
Olympia Mountaineers - Hiking, Alpine Scrambling and Basic Climbing