When All Hell Breaks Loose (20 page)

If elevated core temperatures remain constant or continue to rise, the Grim Reaper will take you out to lunch.

How Your Body Loses and Gains Heat

Humans are incredibly vulnerable to temperature extremes. Like a motor vehicle, the body has very limited temperature parameters in which it will "run." If these limits are breached, the vehicle runs worse and worse until it finally stops running altogether. Regardless of where you live on this planet, you are susceptible to certain physical laws that dictate how your body loses and gains heat from the environment. It matters not if your environment is the deep woods of Alaska or an apartment in downtown Tokyo, the laws of nature described below will be enacted. By recognizing and understanding the following general physics involved in heat loss and gain, the survivor can intelligently assess virtually any situation placed before them and, one by one, manage the problems. Knowing these simple laws in advance allows the wise person to prepare accordingly and mitigate potential breaches to thermoregulation before they happen.

Conduction

Conduction is the transfer of heat (energy) through direct contact with an object, including hot or cold air against the skin. The direction of heat flow is always from a warmer to a cooler temperature. If you touch a surface that's less than 92 degrees F (33 degrees C), you will lose heat through conduction. If the object touched is warmer than 92 degrees F, your body gains heat. Substances vary in their thermal conductivity quite radically. Water has twenty-five times the conductivity of air while muscles possess nearly twice the tissue conductivity of fat. Under normal conditions, conduction accounts for approximately 2 percent of the body's heat loss for a standing person.

Convection

Convection is the transfer of heat (energy) through currents in air and liquids and can be either forced or natural. Convection has within it many variables including density, surface shape and temperature profiles, flow dynamics, conductivity, and specific heat. An example of forced convection would be rolling down the windows of a moving car or sitting in front of a fan. Natural convection happens when density changes in heating or cooling molecules next to the body cause them to move away from the body itself. This "boundary layer" effect is caused by slower-moving molecules directly against the skin produced by radiant heat given off by the body. This layer is only a few millimeters thick and is the equivalent of a constant, three-mile-per-hour wind.

Classic convection experienced by everyone is the "wind chill factor," which causes existing outside air temperatures to feel much colder then they actually are. The effects of wind chill are directly responsible for thousands of deaths all over the world. In contrast, hot desert winds can feel like a hair dryer on the skin, and suck away evaporating sweat so quickly you might not think it's hot because you're "not sweating." Sweat evaporating from the skin at such an accelerated rate does little to help cool the body.

Researchers have found that under neutral conditions as much as 40 percent of the heat loss from a naked human body stems from convection! Add wet clothing and/or strong winds to the scenario and the percentage climbs dramatically.

Radiation

Radiation is the act of losing or gaining heat (energy) through, well, radiation. There are two types of radiation we're concerned with. Terrestrial, or
long-wave
radiation, emanates from fire, a human body, or just about anything else on the planet having a temperature greater than absolute zero or minus 460 degrees F (minus 273 degrees C). Radiated body heat is truly the emission of electromagnetic energy in infrared wavelengths of which the body is both emitting and receiving. Curling up in the fetal position reduces your radiant heat loss by 35 percent when compared to a person standing with arms away from their sides. Radiant heat loss is a force to be reckoned with as it accounts for around 45 percent of the total heat loss from a nude body in neutral conditions. Surfaces that are good at absorbing radiation are also good at giving it off.

Shortwave
radiation emanates from the sun and varies in its intensity according to the time of day, altitude, latitude, surface reflection, atmospheric pollution, ozone levels, and season. Most ultraviolet radiation bathes the Earth at midday, 80 percent between the hours of 9 a.m. and 3 p.m. and 65 percent between 10 a.m. and 2 p.m. Radiation from sunlight can heat a person in three ways, directly on the skin, reflected off particulate matter in the atmosphere, and reflected off the ground, and, unlike long-wave radiation, it is absorbed to a greater extent by darker-colored clothing and skin pigmentation. In hot climates, all can lead to dehydration and hyperthermia if not properly managed.

HOW Your Body GAINS Heat
DESTITUTE DON
BODY TYPE
: Larger surface-area-to-volume ratio superior at eliminating excess heat

A: Direct Solar Gain [Radiation]

B: Breathing through Nose Limits Water Loss [Respiration]

C: Hot Wind [Convection]

D: Reflected Particulate Matter Solar Gain [Radiation]

E: Nicotine: Diuretic, Constricts Blood Vessels, Increases BMR

F: Insulation from Hot ground [Conduction]

G: Ground Reflected Solar Gain [Radiation]

H: Alcohol: Diuretic, Impaired Judgment, Increased Blood Viscosity

Destitute Don loses heat through: I: Increased Heat Loss through Wet Clothing [Evaporation]

HOW Your Body LOSES Heat
TED THE TRANSIENT
BODY TYPE
: Larger volume-to-surface-area ratio superior at minimizing heat loss

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.