Heat Loss Mechanisms
By John D. McCann
There are five ways that the heat from your body can be transferred to the environment, and they are called Heat Loss Mechanisms. In a cold environment, they can all be detrimental, but in a hot climate, some of these mechanisms can be to your advantage.
This is the primary cause of heat loss. Our body radiates heat to the environment, much like the sun radiates heat to the earth, or a campfire radiates heat to keep us warm. At 50°F, 50 percent of the body's heat can be transferred to the environment through an exposed head and neck. We can also lose heat from our wrists, hands, and feet. Have you ever had your mother or father tell you if you want warm feet to cover your head? This is the concept it is based on. Wearing a hat, scarf, wrist-over's or gloves, can help eliminate loss of heat through radiation, from your head, neck, and wrists. A shelter can help you from losing your body heat to the environment, by trapping your heat inside the shelter.
Conduction is the process by which we lose heat through direct contact between objects. This can occur when sitting on a cold or snow covered stump or rock. This can also occur when wet clothes come in contact with your body, by touching cold objects with bare hands, or kneeling on the snow to build a shelter. These situations should be avoided in order to prevent the transfer of heat from the body to other objects. This is another reason why you must insulate yourself from the ground in a shelter, in order to prevent transferring heat from your body to the ground. In the winter, I carry a small closed cell foam pad, cut from an old military sleeping pad, which I carry in the back of my pack. I use it to insulate myself from a cold object when sitting down
This is loss of body heat due to the movement of air or liquid across your skin. An example of Convection is Wind Chill. Through radiation, the human body is always warming a thin layer of air next to the skin. The temperature of that layer of air is usually equal to that of the skin. When this layer of warm air stays close to the body, the body stays warm. However, if this warm layer is removed by convection, the body quickly cools down. In cooler environments, your clothes are your first line of defense, as it helps protect that thin layer of warm air.
Evaporation is a process whereby liquid changes to vapor, and as this process occurs, heat within the liquid escapes to the environment. In a cold environment, it is essential that you wear fabrics that breath. If water vapor from you perspiring cannot evaporate through your clothing, it will condense, freeze, and reduce the insulation value of your clothing. This will cause your body temperature to go down. However, in a warm environment evaporation can be used to your advantage. Have you ever, on a hot day, worn a wet T-shirt or a wet bandana around your neck. This is also evaporation at work, because as the water is evaporated it pulls heat from the body, cooling you. It is called evaporative cooling. At our camp, we use this method in the summer by placing wet towels on our water containers, in order to keep the water cool.
We can lose heat through our normal breathing process. You can observe this when you see a person's breath on a cold day. This is heat from the body, lost to the environment. It is also difficult to prevent this loss, as we have to breath.
WHY ARE THE HEAT LOSS MECHANISMS IMPORTANT?
By understanding the ways in which our body losses heat we can utilize that information to protect ourselves from the elements. The two major threats from the elements are Hypothermia and Hyperthermia.
Often called "The killer of the unprepared", Hypothermia is a real threat to a survivor. The three main elements leading to hypothermia are cold, wind, and wetness. Keep in mind, it isn't necessary
for the temperatures to be at or below freezing for Hypothermia to take place. Many instances of hypothermic death have taken place in temperatures over 50°F. Hypothermia is heat loss at the body core, and it results from exposure to cold with the addition of other heat-loss mechanisms or nature's elements.
Hyperthermia is an elevated body temperature which occurs when the body fails at thermoregulation, and the body's temperature control system becomes overloaded. The body is normally able to cool itself through sweating, but under some conditions sweating is not enough and a person's body temperature can rise rapidly. If the temperature continues to rise it can damage the brain, other vital organs, and result in death.
As you can see, when we know how our body losses heat, we can either cover our body to prevent the loss of heat when it is cold, or we can uncover those areas to release unwanted heat when it is hot. Adjusting your body temperature when needed can keep you alive in a survival situation.
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Note: The above article is an excerpt from my book Stay Alive! Survival Skills You Need. For more information on that book, Click Here.