5 Ways Your Body Loses Heat During Outdoor Activities

Staying warm in the great outdoors is an important bushcraft and survival skill. In cold conditions in the wilderness you can lose heat through a bunch of different processes - radiation, convection, conduction, evaporation and respiration (breathing).

Radiation: Whenever you lay by a good fire and feel its heat, you are absorbing heat radiated by the fire. Another way to look at this is that while you are gaining heat, the fire is losing heat to its environment. It’s the same for you when the surrounding environment is cold: You may radiate warmth and so be losing body warmth to your environment.

Many individuals think that heat loss from radiation occurs just from exposed skin. But even if you are clothed, heat radiates from your body to your garments, then from your attire to your local environment.

Convection: Convective heat loss occurs between a material surface and a moving fluid or gas that is moving over it. The air closest to your skin is heated by the body. If this warm air is allowed to move away from your body, chillier air will take its place and more body warmth will be given up in warming this cold air. Putting on insulating layers of clothing helps to hold warm air near to your body. It’s the air retained in your clothing that helps you to maintain body warmth, not the garments themselves.

Particular attention should be paid to insulating your core body area; the head, neck, trunk and groin. There is usually a good blood supply to your neck and head and there is certain to be a lot of warm blood passing just underneath the surface of your neck. Therefore , it is always sensible to have a warm hat with you, even in summer. It need not be heavy: A merino wool beanie is a great choice. In chillier conditions, you must also include a head-over or scarf to prevent heat loss from your neck. These items, despite being little, can make a massive difference to how warm you are on a cold day, if the weather conditions turns bad, or if you have to spend an unplanned night out of doors.

Strong winds and low temperatures can conspire to creat the right conditions for massive convective heat loss. Unless your outside clothing layer is windproof, cold air passing over your body will disturb the warm air and take body warmth away from you.

Conduction: Heat loss through conduction comes as a result of contact with cold surfaces or objects.

Aluminium is an extremely good conductor. Water is a good conductor of heat. Air is a poor conductor of heat. That’s why it’s so nice to have air captive in your clothing to insulate you. It’s good to insulate your body from cold surfaces with a poor conductor. A typical example of this is the use of a sleeping mat when camping out. If you sleep directly on the ground, you lose an awful lot of heat into the earth. If you are building a shelter, make sure you build a good bed, with acceptable insulation.

Avoid handling cold objects, especially metal, with your bare hands. Do not touch metal objects with your hands in temperatures much below 0 degrees Celsius (32 degrees Fahrenheit) as they can cause near-instant freezing of skin. Even if you’re using gloves, limit how much you handle metal objects in sub-zero (Celsius) temperatures.

Evaporation: To convert a liquid to a vapour or a gas requires energy. What this implies is when sweat on your skin or moisture in your clothing evaporates, this evaporation draws heat away from your body. This is named evaporative heat loss.

Evaporation is an especially effective mechanism for losing heat. It explains why sweating works so well at keeping you cool. The darker side of evaporation is that if you get wet in a cold environment, it’s possible to get extremely cold, extremely rapidly. Thus, it is vital that you do all that you can to remain dry while in the outdoors.

Your first line of defence agains this sort of heat loss is effective waterproof shell clothing to stop rain, and other water, getting into your clothing. But it is not only about stopping water getting in; you need to attempt to reduce the amount of sweat in your clothing. When you exert yourself, getting wet from the inside can be a more serious issue than water coming in from the exterior of your clothing. Breathable fabrics that allow perspiration to pass through and escape will really help to an extent but if you are working hard and producing lots of heat, you can still get sweaty and damp.

If you take notice of the environmental temperature and your level of exertion you may help to maintain an even body temperature and minimise sweat by adjusting layers, particularly taking layers off before starting exercising. Ventilation also helps - open up front zips, expose the neck, etc. Adjust your clothing as is needed during exercise. You can regulate our activity level; if you are still getting hot and sweaty in spite of the above measures then you need to likely slow down a bit and. Pace yourself.

Respiration (breathing) : As you breathe in cold air it is heated before it gets to your lungs. You then breathe out warm air and you are effectively losing heat every time you breathe. There isn’t anything we will be able to do about breathing. We’ve got to do it to stay alive! In comparison with the other mechanisms of heat loss , however, heat loss thru breathing is relatively insignificant.

Conclusion: So these are the five ways you lose heat to the environment in the wilderness: Radiation, convection, conduction, evaporation and respiration. If you understand these processes well and blend this knowledge with your expereience of the outside, it should assist you in staying safe and less likely to suffer from hypothermia.

Paul Kirtley teaches bushcraft and survival skills. Paul is passionate about nature, wilderness and remote travel. This is something that comes across exceedingly clearly on his bushcraft courses.