by Cody Lundin
A: Cold Wind [Convection]
B: Alcohol: Diuretic, Impaired Judgment, Increased Blood Flow to Skin
C: Increased Heat Loss through Wet Clothing [Evaporation]
D: Insulation from Cold Ground [Conduction]
E: Reduced Insolation [Incoming Solar Radiation]
F: Water Loss through Breath Respiration]
Ted the Transient gains heat through:
G: Food [Metabolic Heat]
H: Fire [Radiation]
Evaporation
Evaporation is the act of losing heat (energy) through the conversion of a liquid to a gas. The principal way your body loses heat in a hot environment is the evaporation of water, in the form of sweat, from your skin, as well as a small amount of evaporative cooling gained from exhaled moisture. To get the job done humans have 2.6 million sweat glands, more than any other mammal. Staying in wet, sweaty clothing after overexerting in winter cold will place you one step closer to death through increased hypothermia.
Respiration
Respiration is the act of losing heat (energy) and water vapor through the respiratory surfaces of the lungs by breathing. The air you inhale must be humidified by the body to saturation in order to be used efficiently. When this vapor is exhaled, the resulting evaporative heat loss at high altitudes can rival sweat as a cooling factor. More typically, however, respiration heat loss is minor when compared to the others above. A tremendous amount of water can be lost through the breath, especially in extremely cold temperatures. Cold, dry air breathed into warm, moist lungs pulls out as much as two quarts of water daily in minus 40 degree F (minus 40 degrees C) temperatures. In some instances, the same conditions destroy the cells lining the respiratory tract.
Critical Clothing
In a cold weather situation, the simplest means of staying warm is to trap your body's metabolic heat by using insulation or dead air space in the form of clothing, adding or subtracting layers as changing temperatures dictate. In addition, physical exercise, fire craft, shelter, and calorie-rich foods all help to keep the body's core temperature at a lively 98.6 degrees F (37 degrees C). Cold muscles work more slowly and with less efficiency, greatly retarding the ability to perform seemingly simple tasks for survival.
Conversely, in a hot weather situation, indigenous peoples wear long, flowing woolen robes in extreme desert temperatures for a reason. Your skin is the largest organ of the body, and if you burn it, you severely compromise your body's ability to cool itself as even moderate sunburn causes a decrease in the responsiveness and capacity of the sweat glands. Clothing is the easiest method to use to protect your skin from direct solar radiation from the sun, as well as radiation reflected off particles in the atmosphere and the ground. The most important factor in determining how a fabric will repel ultraviolet radiation is the tightness of the weave, followed by its color and whether the fabric is wet or dry. Specialized, sun-protective clothing is becoming more common and manufacturers have developed various strategies to keep out the sun's rays including tightly woven nylon, chemically treated cotton, cotton/synthetic blends, clothing bonded with ultraviolet-radiation-absorbing devices, and chemical shields added to laundry detergents.
In hot weather, when ambient temperatures are near or above normal body temperatures, to limit heat loss through vasodilation, your body relies on one main mechanism to cool itself called sweating. Sweat is 99 percent water with a pinch of sodium chloride (salt) and potassium and is the only way your body cools itself when subjected to elevated external temperatures. The conversion of a liquid to a vapor requires a certain amount of energy or heat, called the heat of vaporization, and is directly responsible for wicking away the high temperatures that threaten to kill you from hyperthermia. Even though sweat contains only a paltry 1 percent sodium chloride, long-term sweating without the ability to replenish that salt poses serious physiological problems, which is a major reason to store salt as part of your food storage program. People acclimated to hot weather produce more sweat, but with a lower concentration of lost salts.
Sweat glands are found in the skin in concentrations from 650 to 4,000 per square inch and occur most abundantly on the forehead, scalp, face, neck, front and back portions of the trunk, and the top of the hands and forearms. The face and scalp alone account for 50 percent of the body's total sweat production! In fact, the only skin areas that don't have any sweat glands are the lips, nipples, and external genitals. Sweat via evaporation cools the skin and, with it, the blood flowing through it. The cooled blood returns to the body's core via the veins where it picks up more heated blood and returns it to the skin's surface for cooling. Any liquid evaporating from the skin will work to cool the body, so don't be shy about soaking your clothing in scummy, nonpotable water, although make sure it's free from chemicals, pesticides, and other skin irritants.
* * *
A TRIED-AND-TRUE ACRONYM FOR WEARING WINTER CLOTHING IN BOTH CITY AND COUNTRY!
C = keep yourself and clothes CLEAN
O = avoid OVERHEATING
L = wear clothes LOOSE and in LAYERS
D = keep DRY
* * *
High water-vapor pressure, more commonly referred to as humidity of 70 percent or higher, severely restricts the evaporation process. Regardless of how much water you have available, if your body can't rid itself of excess heat you risk dying of dehydration and hyperthermia. Personal humidity levels close to the body's surface may elevate by wearing poorly ventilated clothing, as it reduces airflow over the skin. High humidity levels cause sweat to simply drip off the skin instead of evaporating. People in humid environments commonly experience the need to towel off several times after a shower or bath due to these elevated humidity levels. Be forewarned! Hot temperatures combined with high humidity levels are voracious killers and are responsible for summer heat waves that wipe out hundreds of people. Not only does proper clothing insulate you from the heat and cold, it also allows the sweat upon your skin to evaporate slowly and efficiently, making maximal use of whatever water you already have within your body.
The Layering System
Using the layering system, clothing for both hot and cold environments can be categorized into three sections: base layer, insulation layer(s), and environmental layer(s). Base layers are used against the skin, trapping air close to the body. They should be made from a fabric that insulates while transporting (wicking) water vapor away from the body and should be nonirritating and nonconstricting. Insulation layers are added or subtracted as outside temperatures warrant between the base and environmental layers. The environmental layer protects against outdoor elements such as wind, rain, snow, sun, and brush and should be lightweight, durable, loose fitting, wind and water resistant, and able to easily vent excess moisture buildup. Water-resistant and waterproof fabrics are two different concepts, as the former "breathes" to a certain extent to let generated body moisture escape. The latter is a vapor barrier and, although useful in some applications, requires advanced thought and the right conditions to be used successfully. Telling the difference between the two fabrics is easy. Put your hand on the outside of the material. Put your lips to the fabric and blow on the fabric from the inside out. If you can feel the air from your breath on your hand, it is water-resistant material.
All clothing systems for any climate involve dead air space or insulation. Clothing insulation is measured in clo. Technically, one clo is equivalent to the amount of insulation needed to keep a seated person comfy in an air temperature of 70 degrees F (21 degrees C) with a relative humidity of less than 50 percent, and an air movement of .2 miles per hour. Simply put, a common business suit provides one clo of insulation. Insulation is much more effective when worn in several thin layers as opposed to one thick layer, as this allows you to adapt not only to changing temperatures by taking off or putting on clothing, but the air space between the layers of clothing insulates as well while adding no weight, bulk, or cost to the user. The layers should resist moisture accumulation, and increase in
size so as not to constrict the body when worn on top of one another. They also need to be easy to put on and take off and pack in case of a pending evacuation.
Your clothing, especially the extra clothing you pack in a bug-out kit (a portable emergency kit containing vital gear when needing to evacuate an area, Chapter 22), should be adaptable to all types of circumstances. Your clothing should block the sun's ultraviolet rays, keep you both warm and cool, and also be bug-resistant, quick drying, durable, and nonrestrictive. The layering method allows you to add or subtract layers of clothing at will in response to your increasing or decreasing metabolic output and the environmental temperatures at hand. This ability to fine-tune your wardrobe helps minimize sweating-out your clothing through overexertion. Insulation filled with frost and water does little to keep you alive, thus venting excess moisture in cold conditions is of paramount importance. Actively venting excess perspiration from clothing and moderating physical activity in the first place has several advantages. Your clothing insulation layers stay drier and warmer when activity ceases, clothes remain cleaner longer, and you achieve a lower metabolic rate, which conserves precious energy and water. The ideal scenario in the cold is to regulate clothing layers and activities to allow you to operate at peak performances without wasting water and energy to sweating or shivering.
In hot climates, clothing protects you from direct radiation from the sun, hot winds, and scorching ground temperatures. Loose layers of the appropriate material grant protection from the sun and increase airflow while slowing the evaporation of sweat for superior cooling. The ideal scenario in the heat is to regulate layers and physical activity to allow you to operate at peak performances without wasting energy while achieving protection from the sun and making maximal use of your sweat for cooling.
Properties of Clothing Materials
The type of material your clothing is made from can directly affect your ability to successfully thermoregulate your core body temperature. The following are brief descriptions of the more common fabrics that have withstood the test of time. The properties described below are just as applicable for blankets and sleeping bags.
Cotton
Cotton is hydrophilic, meaning it transfers sweat from your skin to the material itself, thus it's horrible at "wicking" wetness away from skin. In fact, cotton loves moisture and will become damp simply when exposed to humid air. Once wet, it feels cold, loses 90 percent of its insulating properties, is a drag to dry out, and wicks heat from your body twenty-five times faster than when it's dry. Because of this, wearing cotton clothing in the wintertime is a death wish. Yet, in scorching summer deserts, it's my fabric of choice for precisely the same reasons. Cotton also has decent abrasion resistance and blocks out a reasonable amount of UV radiation from the sun.
Polypropylene
Polypropylene resists absorbing moisture as it's hydrophobic, meaning it transfers moisture from the skin across the fabric itself to other clothes or the air so it actually dries from the inside out. This quality makes it great at wicking sweat away from the skin, thus it's popular as a base layer with outdoor recreationists. Polypropylene feels soft and is relatively cheap and easy to care for. Wear it for a few days in a row however, especially if you exercise, and you will reek something awful, especially in a confined shelter. Being synthetic, polypropylene easily melts to skin when exposed to heat so be careful around fires, candles, stoves, and other heat sources. Polypropylene's most insidious disadvantage, ironically enough, comes from its superior wicking abilities. It wicks moisture away from the skin so well that the wicking action uses more body energy (calories) from the survivor than other fabrics. Because of this, polypropylene should only be worn when there are ample food supplies and when energy losses are not critical.
Wool
As wool is animal hair composed of hollow cells that trap air, it's a poor conductor, thus an exceptional insulator. Its natural crimp and elasticity contribute to its superior insulating properties. Wool is hygroscopic, which means it readily absorbs moisture but suspends the water vapor within the fiber itself. While any moisture in wool or other fabrics decreases its insulation value, wool can absorb 35 to 55 percent of its weight in water before "feeling" cold and wet. Although it's tedious to dry out, wool retains more heat as it dries than synthetics. This fact, combined with a slower wicking rate, allows wool to use less body energy than polypropylene.
Various breeds of sheep produce various types of wool so not all wool is garment quality. A wool fiber under magnification looks like a heavily barbed spear tip. Aside from allergies, cheap wool and poor manufacturing techniques will cause wool to itch like crazy when in contact with your skin. Wool is inherently flame retardant and won't melt to your skin when exposed to heat sources so it's safer and more forgiving than synthetics if you are using fire to dry out damp clothing. A real boon to the urban survivor is the fact that wool is able to neutralize many types of acids and chemical bases, helping to prevent the buildup of germs. On the down side, wool is bulky when compared to synthetics, thus requiring more space in your shelter or bug-out pack.
Polyester
Polyester is by far the most widely used material in clothing. Polyester pile fabrics, common in backpacking and camping stores, are good insulators, can absorb a fair amount of water without feeling cold, and are hydrophobic. The fibers themselves can be woven into many different thicknesses providing both insulation and wind-stopping abilities in a product that is more compact than wool.
Nylon
Nylon, especially rip-stop nylon, is tough stuff and is commonly used in the design of environmental layers from coats to jackets of all kinds. Tight weaves work well at repelling wind and water and can be made waterproof through various coatings available at outdoor stores, albeit at the expense of breathability. Nylon is also extremely compact and lightweight and the little water it does absorb evaporates quickly. Your environmental layer is critical, as a wind of merely nine miles per hour can reduce the effectiveness of your clothing's insulation by 30 percent. In addition to the wind chill, mixing wet clothing along with the "bellows" effect produced by walking and your clothing insulation can be compromised an unbelievable 85 percent!
Down
Down's compressibility, loft, and weight-to-warmth ratio are legendary—when it remains dry. Unfortunately, down is hydrophilic and sucks even more than cotton in cold, wet environments, losing virtually all of its insulative properties, and it is a booger to dry out.
To summarize, the gross motor skill art of putting on and taking off layers of clothing to regulate body temperature is amazingly simple, requiring very little practice, calories, and water from the survivor. Knowing the virtues of clothing is truly a family-friendly survival skill in which all can participate, from the very young to the very old. In short-term cold-weather survival, the divine simplicity of layering correctly even eliminates the necessity of firebuilding, which is a fine and complex motor skill that requires plenty of physical dexterity and prior training, precious time, calories and water from the survivor, dry tinder and adequate fuel, an ignition source, a safe spot to build, and constant monitoring. In a pinch, it's possible to improvise insulation from nature depending upon the environment. Leaves, pine needles, dry grass, plant fibers, moss, and other material may be available. Urban landscapes as well will present several options for improvised insulation such as the stuffing in chairs, sofas, vehicle seats, carpeting and carpet pads, and others.
Alternative Shelters
Unfortunately, your home may be completely or partially destroyed after a major disaster. This would be everyone's worst nightmare, even during temperate weather, but imagine the destruction happening when it's very hot or very cold outside. Thus the need to have some kind of alternative shelter should rank very high on your survival list. Major earthquakes in other parts of the world have happened during the peak of winter. Many people who had initially survived the quake itself died from hypothermia due to a lack of shelter.
If yo
ur home experiences a disaster, check for structural damage before entering the home, if you choose to reenter it at all. Make sure it's not in danger of collapsing. Ultimately, this inspection will need to be done by a professional. Some members of the family, especially kids, might not want to go anywhere near the house if they have been traumatized by the disaster, for fear of the house collapsing or triggering some other kind of nightmare. If you do decide to reenter your home, make sure to turn off any outside gas lines and let the house air out for several minutes to remove potential escaping gas. When entering the home, don't use open flames as a light source. Instead, use a battery-operated flashlight or some other nonfuel-burning light source.
If you live in a hot or cold environment, the primary motive for your shelter should be the thermoregulation of your core body temperature. Even temperate locations get chilly after rains or in the evening hours. Now that you're hip to the physics of how your body loses and gains heat by convection, conduction, radiation, evaporation, and respiration, don't place your alternative shelter in a dumb spot. Consider your shelter as a "body" as well as it, too, will be subject to the same laws of physics. If you attempt to shelter your shelter, so to speak, you'll get more bang for your buck as you'll gain more comfort with less effort and save wear-and-tear on your shelter. It's very common in the Southwest to see amazingly intact Indian ruins that are hundreds of years old. Without exception, the better-preserved ruins were built under basalt overhangs or in caves, thus the native person's shelter was sheltered.