Exposure & Hypothermia – 5 Things You Need to Know about Body Heat

Snowy Creek by Ken Kistler

Our body’s are amazing organisms with a remarkable sense of self-preservation, but they’re only able to manage heat transfer to a point. In a wilderness survival situation, understanding the 5 methods of heat transfer could prevent the very real possibility of experiencing problems related to exposure.

The 5 Methods of Heat Transfer

There are five ways body heat is transferred: Radiation, Conduction, Convection, Evaporation and Respiration.

Radiation

Our bodies radiate heat all the time as a way of regulating body temperature. Areas of exposed skin (particularly the head, neck, hands and feet) will quickly lose heat to the environment through radiation.

Snowy Creek by Ken Kistler
Photo by Ken Kistler

Protection from the Cold
In a cold environment, it’s important to keep as much of that radiant body heat as possible to prevent hypothermia. There are three basic ways to reduce, or even prevent, radiant heat loss to the environment: fire, insulate yourself and decrease skin exposure.

First and foremost, fire is your number one combatant against the chilling cold. I only mention it here because the warmth you feel from fire comes from radiation. If you have the means, then light it up. Fire will give you a sense of safety when you need it most, not to mention the ability to warm yourself, boil water and cook food, among other things.

Beyond fire, sleeping bags and insulating clothing, such as puffer jackets and mittens, work by using our body heat to warm the air trapped within the insulation. Other heat retaining clothing, like thermal underwear and warm beanies, can be worn to reduce the amount of exposed skin, thereby reducing the amount of heat loss.

Protection from Heat
In a hot environment, heat radiates from the environment to your body. You can reduce exposure by wearing loose-fitting, light-colored clothing, and try to avoid direct exposure to the sun as much as possible. Hike during morning or evening when it’s cooler, and try to find a shady spot to rest during the middle of the day when it’s the hottest.

Conduction

Conduction of heat to or from our body occurs when we come into direct contact with another object. If you’ve ever been burned by a hot stove or held an icecube for so long that it hurt, then you have a first-hand understanding of what it means to conduct heat.

Protection from the Cold
The first priority in preventing heat loss through conduction is to avoid cold water. Hypothermia can set in quickly when you’re exposed to even moderately cold water. If you find yourself in cold water, either by accident or necessity, and you’re capable of getting out, then get out right away! Once you’re out, remove any wet clothing, dry off and find a way to warm up as quickly as possible.

Aside from staying dry, it is important to insulate yourself from objects in the environment that are cold, such as snow, rocks and logs. Sleeping pads aren’t just for comfort, they’re also designed to insulate your body from the ground. If a sleeping pad isn’t available, try to find other ways of insulating yourself from the ground, like dry grass or leaves.

Protection from Heat
Anything affected by extreme cold is conductive and can also be affected by heat. Sand, rocks, and metal, just to name a few, can all get extremely hot in direct sunlight. In general, avoid touching anything with bare skin that can burn you.

Convection

Convection of heat from the body occurs when air moving past it pulls the layer of air it has warmed through radiation away from it.

Protecting from the Cold
In a cold, windy environment, heat loss through convection can quickly lead to hypothermia. To lower the risk of heat loss, find shelter or wear clothing that’s effective at blocking the wind. Look for high quality windbreakers that are breathable. They allow air to escape, which helps to keep you dry, but prevent wind from breaking through and sucking away valuable body heat.

Protecting from Heat
In a hot environment, convection is your friend (usually). As the heat passes over your skin, it will pull the heat away, helping you to stay cool. But in a survival situation where water is a scarce resource, it’s important to remember that retaining water is necessary to avoid dehydration. So don’t go pulling your clothes off just to get a dose of that cooling wind, because you don’t want to lose your valuable moisture too quickly. Instead, it’s best to wear loose fitting clothes that allow air to flow freely, while also acting as a barrier so that moisture doesn’t evaporate (see Evaporation) too quickly from your body.

Evaporation

When we sweat, moisture from our body move’s to the surface of the skin. When the moisture on our skin evaporates, it takes the heat trapped within it along for the ride.

Evaporation can be just what the doctor ordered when it’s hot out. When it’s cold, it can turn a perfectly enjoyable hike into a shivering cold nightmare in seconds. If you’ve ever experienced this, then you know exactly what I’m talking about.

Protection from the Cold
The number one thing you can do to protect yourself from heat loss through evaporation when it’s cold is to avoid activities that will make you sweat. Sweating when it’s cold is like taking an express train to hypothermia. If you’re hiking, open zippers and vents, or layer down to your comfort level. When you stop, you can add layers back on as your body begins to cool down. Wear moisture-wicking synthetics and wool blends that are breathable and fast drying. The key here is to stay dry so that evaporation of heat from your body doesn’t occur.

Water in the Desert by Ken Kistler
Photo by Ken Kistler

Protection from Heat
Much like convection, evaporation is generally a good thing to have when it’s hot. The cooling effect received when sweat evaporates from your skin can feel really good. But once again, in a survival situation where water is a scarce resource, don’t go pulling off your clothes. Take advantage of your clothing’s ability to keep some of the valuable moisture, and to slow the evaporation process to slow down dehydration. If water isn’t scarce, douse your shirt in water and wrap it around your head. As the water evaporates, it will help cool your skin, and could help reduce the risk of problems resulting from heat exposure.

Respiration

When we breathe, there is almost always a difference in temperature between the air we are breathing and the air in our lungs. Respiration is one of the body’s most efficient means of regulating temperature.

Protection from the Cold
When it’s cold outside, we expel body heat as we breathe out and take cold air in as we breathe in, which is then heated by the body before being expelled. To decrease heat loss through respiration, try to keep respiration low by avoiding strenuous activities that will raise your heart rate. You can also use a mask, bandanna or other piece of clothing to loosely cover your mouth and nose so you can take advantage of the warm air before it’s lost to the environment forever.

Protection from the Heat
I could be wrong on this, but I’m guessing that unless you’re standing next to a burning fire that’s radiating heat that could burn your lungs, there’s not much to be worried about here. In a hot environment you should be far less concerned with respiration, and far more concerned about radiation, convection and evaporation.

Conclusion

Our bodies are a remarkably efficient furnace, capable of regulating their temperatures with incredible accuracy, given normal circumstances. But things don’t always go as planned, especially in extreme environments.

Understanding how heat transfer occurs and knowing how to minimize heat loss when it’s cold, or maximize heat regulation when it’s hot could make the difference when the going gets tough.


There is a lot more to be said on this subject, I’ve really just touched the surface here. If you feel like I’ve missed something or gotten something wrong, or you’d just like to add to the conversation with suggestions of your own, please let me know in the comments. I’d love to hear about it.

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Robb Keele

Robb Keele

Robb is a native San Diegan and avid hiker, backpacker, picture taker and 52 Hike Challenger. He created Getgo Outdoors with the goal of giving back to the outdoor community and inspiring others to get outdoors.
Robb Keele

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