Look Down, Not Up! - Heat Loss In Regards to Shelter by Joe Adkins
When talking about shelter in a survival situation, the rule of threes states that three hours in extreme temperatures can result in death from exposure; exposure being hypothermia (low body temperature) or hyperthermia (high body temperature). Depending upon the environment and other circumstances (adding in wind or dehydration), that three hours can be significantly reduced and so too can the idea that an extreme environment is necessary to succumb to exposure. By taking some of the following information in mind, you can not only improve your chances as a survivor but you can also make your typical “primitive” (in this instance meaning tent, tarp, hammock, etc.) camping trip more comfortable.
Certainly, in regards to heat loss clothing must be addressed; however, that will be covered in a future article. After clothing, we should look at our shelters. Before we do, first we must understand how heat is lost or transferred. With this knowledge, we can utilize clothing and sheltering systems to full advantage. It is worth pointing out that heat transference is not a process that can be stopped, only slowed. Heat is transferred from the body in five ways. They are: conduction, convection, radiation, evaporation and respiration.
Conduction is the transfer of heat from neighboring molecules, i.e. direct contact. This happens when, for example, a person lies directly on the ground. The human body is, at average, 98.6?F. When the body is directly touching a surface that is either higher or lower in temperature heat is transferred through conduction. In a desert, the much hotter sand can burn or heat the body; likewise, in the eastern woodlands on a cool October night, the ground can suck the heat from you.
Convection is the transfer of heat through air currents and/or liquids. When a person falls overboard into frigid waters, the heat is sapped from their body. In a high heat environment, wind is great to whisk the heat from you. Hammock campers know all to well that the wind can be a significant factor in their ability to stay warm or cool.
Radiation is infrared and ultra violet radiation trying to move from a warmer area to a cooler area. For our purposes, there are two types of radiation; long wave radiation, our bodies infrared radiation and short-wave radiation, the sun’s UV rays. Ever snuggle up to someone on a cold winter night to get a little warmer? That warmth is the body radiating infrared heat. It is important to know that the sun can heat in three ways: directly, indirectly by reflecting through particulate matter (think glass or plastic) or indirectly by reflection from the ground (water, snow, ice or sand).
Evaporation is heat loss by converting a liquid to a gas. When we sweat, we are trying to produce a cooling effect by evaporating that sweat away from our bodies. This is important to know. In some environments controlling this concept is important. We want to control our perspiration in cold weather to keep us from getting wet and ruining or degrading the insulation value of our clothing. In a very hot and dry environment, we want to slow this process to maintain moisture and to allow our perspiration to cool us over time. That is why most desert dwelling peoples wear light, lose clothing covering the majority of their skin.
Respiration causes us to lose heat. We humidify the air that we breathe in and out. This results in heat loss and moisture loss. In extremely cold and hot environments it is important to breathe through the nose and to keep your mouth closed as much as possible. Respiration accounts for more than a pint of water loss per day.
Now that we know how our body transfers and loses or gains heat we can begin to examine our shelters. Most people look to the sky when they consider sheltering options. That is understandable and important because, as we discussed earlier, moisture can aid in heat loss. However, most people don’t look down and there in lies the danger. When sleeping in the wild the first enemy is the ground. The ground will conduct heat either to or away from you. Get off the ground, you need a barrier. In a cold environment, this means insulation from the ground (could be necessary in a hot environment too if you can’t dig and don’t have a means of overhead cover). Depending upon how cold of an environment you are in will dictate how much insulation is required. In our classes, which are in the Eastern US woodlands, we teach a minimum of four inches of compressed material; however, if you can do more you will be warmer. In a desert environment, finding shade or an overhead cover from the sun is important. Once that is established if you can dig in the ground try to get at least 8 inches from the surface where the ground is cooler. If you are camping with a tent or tarpaulin, foam pads and an inflatable mattress are wonderful, you can even pile up debris under these to get warmer. Think outside the box. If you carry trash bags in your kit (you should, you know) fill these with debris to make a quite comfortable improvised mattress. Obviously, if you are camping, your sleeping system should be adequate for the environment that you are in. In an emergency, remember dead air space is your insulation, pack debris in your clothing or around you to stay warm.
Convection is the bane of those that like to hang in the winter. Hammock campers, if you are doing cold weather camping, invest in good quality under-quilts. Again, the sleep system that you bring should be sufficient for the environment. We recommend synthetic fill but if you can keep your down filled sleeping bags dry they are very warm. When camping or selecting a site for your shelter, remember to look for loose limbs or trees that may come down on you in the night. Try to get on the leeward side of the hill or mountain and if its cold avoid the ridgelines where wind is worse. In the summer, deeper in the valleys stay cooler as heat rises.
Radiation from the body is slowed by the dead air space of our clothing and to an extent, our shelters if they are small. In cool environments, a reflector wall of stone or wood can act as a heat reflector but mostly absorbs radiant heat from a fire and releases it slowly. The wall will also deflect wind. In warm environments, seek the shade where possible to avoid direct and the indirect radiation of the sun. Insulation can help cooling as well. A light loose layer that protects the skin and allows air flow will slow evaporation and allow your sweat to do a better job. Don’t forget sunblock if on the water, in the snow and obviously when in the sun!
Evaporative cooling is avoided in winter time by controlling perspiration and with moisture wicking materials in clothing. In warm environments, as mentioned above a loose layer can facilitate your evaporative cooling system. Additionally, cotton can be an aid to cooling in warmer environments for exactly the same reason as it is a poor choice in cold environments.
Loosing heat and moisture from respiration is controlled by trying to keep your mouth closed in both environments. Controlling your work/rest cycles can keep you from breathing harder and avoid more moisture loss; however, in cold in environments exercise can keep you warmer than the heat lost from respiration.
Now that you understand how our bodies lose heat, you can make better decisions in regards to your shelter set-up and make your camping trips more comfortable. Remember that you want to be off the ground. Make shelters small in cold environments. Avoid the wind to stay warm and take advantage of it to cool. Cotton can be advantageous in a hot weather environment and aid in evaporative cooling. One final trick to staying warm or cool is obvious but is sometimes overlooked. Our bodies have to warm cool fluids. In the cold, drink warm liquids to help warm the body and in hot environments drink cooler liquids to facilitate heat transfer. Have fun in the woods and prepare for even a short hike or trip in the wild lands. Prepare, Survive, Thrive!
The Mountaineer Institute for Self-Reliance is a school located in West Virginia. Its mission is to provide quality self-reliance education for individuals, businesses and organizations. They are known for their thorough and intensive curricula.
Joe Adkins is the founder of The Mountaineer Institute for Self-Reliance. He is a life-long outdoors man. Joe has over 13 years military experience as an ARMY combat medic & nurse. Additionally, he is a certified Level 1 Sigma III instructor, a WV Master Naturalist candidate and a certified Basic Man-Tracker by a local law enforcement agency. He lives in Wayne, Co., WV with his family and his two dogs.