In cold temperatures the body burns extra calories to keep your body warm. Survival is all about energy expenditure, if you maintain a healthy internal temperature you conserve energy and you’ll be able to use that energy for more practical activities. Survivors must do their best to conserve as much energy as possible while still doing what’s necessary to survive. If you over exert yourself, you’ll lose calories (energy) and sweat which can eventually lead to chilling. If you become too cold, your body and mind will not function properly. In a cold weather environment you body temperature is every thing. Keep this in mind.
If your body is too hot, you’ll have to slow down to maintain a comfortable internal temperature, you’ll have to adjust parts of your clothing according to conditions. If the temperature falls, you’ll have to add layers of insulation to keep heat from escaping into the environment. The optimal temperature of the human body is 98.6 degrees F or 36.5 degrees C. The body is so fragile that being just two degrees below normal, you’ll be in a serious condition. If you go five degrees further then normal you can die.
The Physics of Heat Loss
There are several ways in which your body conserves or dissipates heat. Understanding the processes involved is vital if you want to minimize heat loss and preserve as much energy as possible. This knowledge could save your life.
Conduction is the transfer of heat from a warm object to a cooler one. The two objects must be in direct contact with one another and this serves to even out the energy (temperature) difference between them. If you were to lie on a cold floor, the heat from your warm body would transfer into the floor. Your body will become cooler as the floor becomes warmer. The rate at which the heat transfers depends upon several factors. This includes:
- Temperature Difference: The greater the temperature difference between two objects, the faster the heat is transferred. For example, if you were to place your hand on a glowing red hot stove top you would feel the heat immediately but if the stove top was only warm and just heating up, there would be less energy to transfer the heat to your hands. It would take a longer time for your hand to experience the heat.
- Amount of Connected Surface Area: The greater the connected surface area is between two objects, the faster heat is transferred between them. This concept can be best illustrated with this simple example: if you place the tip of your finger in a cold swimming pool, your finger would get cold but your body would be fine. Take of your clothing, strip naked and jump into the pool, your body heat would be quickly sucked out to reach equilibrium between you and the pool.
- Insulation: Insulation is any material that slows down the movement of heat between objects. This is usually achieved by using a material that has small pockets of dead air to prevent heat energy from transferring. A sponge or foam pad works great as an insulator because it’s full of air pockets. If you compress the insulator you remove the small pockets of dead air thereby making the insulator less efficient at stopping the transfer of heat.
Convection is almost like conduction, except the two objects in contact are also moving relative to each other. The amount of heat transferred is still dependent on the temperature difference and its still dependant on the amount of connected surface area but aside from those two, there is a third important component. The third component is the speed at which the cooler object is moving.
This is best demonstrated by the “wind chill” factor. If it’s a hot day, you’re really hot and you feel a cool breeze against your face, the speed of the air matters. If the air is moving slowly you probably won’t feel much but if the wind is traveling 60 mph you risk the possibility of frostbite within a matter of seconds.
Thermal radiation is the transfer of electromagnetic energy between objects. The warmer an object is the more it will radiate. We receive radiated heat from the sun, fires, and light reflected off of other objects. A good example of how thermal radiation works, is the effect of cloud cover on temperature. The earth radiates heat at night that was collected during a sunny day. The temperature will be cooler on a clear night then on a cloudy night because some of this radiation is reflected back by the cloud cover.
In order to prevent your body from losing heat, be sure to cover all exposed areas of you skin and wear plenty of layers. The clothing essentially works as cloud cover, bouncing energy back towards the body. Pay special attention to covering the face, neck, and head.
The process of evaporation (liquid to gas) requires a lot of energy and will actually lower the temperature of the surface on which it occurs. This is the process of evaporation.
In hot environments evaporation can be useful, getting your body wet will help cool you down. However, in cold environments, evaporation can freeze and kill as it consumes energy and warmth from your body and equalizes to the outside temperature. Insulation as we know works because of the dead air pockets it creates, when your clothing is wet the air pockets fill up with water and the insulation is diminished. Having wet clothing can expose you to the risk of hypothermia.
Pay close attention to the amount of perspiration you release during times of heavy exertion. Constantly adjust your clothing or level of exertion to prevent sweating; you want to keep sweating to an absolute minimum.
Evaporation not only occurs on your skin from sweating, it also happens when you’re breathing. Your breathing is actually the primary cause of heat loss in a cold weather environment. When you breathe in and out you are constantly exchanging heat by evaporation and the 3 other processes. When you breathe in cold air and breathing out your warmth, you’re putting yourself in bad situation. Breathe slowly (to prevent convectional heat loss) and cover your mouth with a scarf or cloth.
Preventing Heat Loss
Understanding the physics behind heat loss is invaluable and can be applied not only to clothing but also to shelter making. These concepts aren’t only important for cold weather environments but also hot dessert climates. Here are a few techniques to staying warm:
- Insert proper insulation between you and the object or environment to reduce the amount of heat you lose from conduction. The insulation should have dead air space built within its structure (sponge or foam) and it should be able to resist compression if you apply weight to it.
- Your clothing and shelter should have a windproof outer shell to prevent heat loss from convection. The windproof outer shell is always layered on top of the other layers to prevent wind from penetrating and removing the heat you have stored.
- To prevent heat loss by evaporation, you need to stay dry. Wet clothing loses its efficiency as an insulator. Aside from rain, snow and fog, sweat can also make you wet and will contribute to the amount of evaporation that occurs.
- Breathe slowly and don’t over work yourself, deep heavy breathing will remove large amounts of heat from your body, primarily via evaporation.
- Cover all the exposed areas of your skin to prevent heat loss through radiation. Pay special attention to your head, face and neck.
- Cool and Dry Stays Alive, remember this and survive another day.