• Military Menu                       

• Introduction
• Systems
• Facilities
• Agencies
• Industry
• Operations
• Countries
• Hot Documents
• News
• Reports
• Policy
• Budget
• Congress
• Links

• WMD
• Intelligence
• Homeland Security
• Space

SECTION II

COMBATING THE COLD

The body regulates the temperature of vital organs needed for survival (heart, brain, lungs, liver, kidneys) by varying the flow of blood to the extremities. As our body temperature rises, blood volume shifts and carries heat to the outer layers of the skin. As we cool, less blood flows to the periphery, preserving heat for the vital organs. When we are resting, only a small percentage of blood flows directly to the skin. During heat stress, the blood vessels open up and blood flow to the skin may increase a hundredfold. During cold stress, however, blood is shunted from the periphery to the core, reducing the heat lost to the environment. Constricted blood vessels can reduce blood flow to the skin by 99 percent. In this way, the body strives to preserve the functioning of the vital organs -- even at the expense or sacrifice of the extremities.

Humans are designed to live in tropical climates, so our heat loss mechanisms are highly developed. Our insulation mechanisms, however, are less efficient. To adapt structurally to cold weather environments, we would have to grow a thick insulating coat of hair all over and develop reserves of fat. We would also need to develop an increased ability to convert stored fat into heat production through more efficient metabolism, and chemicals that could act like antifreeze in our cells. In reality, we must take conscious measures to sustain body temperature in cold weather through the application of proper clothing, equipment, and training.

Heat Production 2

The body's three main physiological means for producing heat are metabolism, exercise, and shivering.

• Metabolism. Biochemical reactions which keep us alive produce heat as a by-product. Our basal metabolic rate is a constant internal furnace. However, when we are exposed to cold, wintry conditions for long periods, metabolism by itself does not produce enough heat to satisfy our body's entire heat requirements.

• Exercise. Exercise is an important method of heat production. Muscles, which make up 50 percent of our body weight, produce most of our heat during work. Short bursts of hard, physical effort generate tremendous amounts of heat. Moderate levels of exercise can be sustained for relatively longer periods. There are limitations, however. Physical conditioning, strength, stamina, and fuel in the form of food and water are necessary to sustain activity.

• Shivering. Shivering is a random, inefficient quivering of our muscles. It produces heat at a rate five times greater than our basal metabolic rate. It is our first defense against cold. Shivering occurs when temperature receptors in the skin and brain sense a decrease in body temperature and trigger the shivering response.

As with work and exercise, the price of shivering is fuel. How long and how effectively we shiver is limited by the amount of carbohydrates stored in muscles and by the amount of water and oxygen available.

To shiver, we have to pump blood into our muscles. Warm blood flowing close to the surfaces reduces our natural insulation and increases heat loss.

Shivering hinders our ability to perform the tasks necessary to reduce heat loss and increase heat production. It is difficult to zip up your parka, start your stove, or operate equipment while shivering violently. Conversely, vigorous physical activity can override the shivering response, causing a person to cool past the point of shivering without experiencing the response.

Heat Loss

There are five mechanisms by which our bodies lose heat. The primary means of heat loss is through the skin.

• Conduction 3is the transfer of heat through direct contact between a relatively hot and a relatively cold object. Heat moves from the warmer to the colder object. We lose heat when we lie on snow, ice, and cold or wet frozen ground (foxholes) -- or sit or lean against floors and bulkheads in unheated interiors of armored, mechanized, or wheeled vehicles.

• Convection 4is the transfer of heat by the circulation or movement of relatively colder ambient environment (air or water) around the body. Relatively colder moving air (wind chill) or water, besides cooling the body directly, also strips us of the microclimate of air heated by the body. The loss of this insulating layer next to the body further accelerates heat loss. (See Appendix A, Windchill Chart.)

• Evaporation 5is heat loss in the form of vapor. Heat is necessary to the evaporation of perspiration from the skin's surface. Evaporative heat loss accounts for 20 percent of the body's normal total heat loss. When we become overheated through physical exertion, evaporation becomes our major mechanism for heat loss. Sweating accounts for roughly two thirds of our evaporative heat loss; the remaining one third is lost through breathing.

• Respiration 6also cools the body. As a soldier breathes in cold dry air, it is warmed and humidified in the lungs. As it is exhaled, as much as 25 percent of the body's heat can be lost. Placing a wool scarf or mask over the mouth and nose warms inhaled air and assists in keeping the body warm.

• Radiation 7is the emission of heat energy in the form of particles or waves. Energy is emitted by one body, transmitted through an intervening medium, and absorbed by another body. Infrared, or heat radiation, is transferred from a relatively hot to a relatively cold object. In winter, we lose heat to the environment through radiation. We can receive radiative heat input from fires, from the sun, or from reflection off snow, water or light-colored rocks.

When exposed to the environment, the skin serves as a radiator. Unlike in the rest of the body, the blood vessels in the head do not constrict and reduce the blood supply flowing to the scalp. The head is, therefore, an excellent radiator of heat, eliminating from 35 to 50 percent of our total heat production. In cold weather operations, dry insulation, especially on the head, is essential in minimizing heat loss.

PSYCHOLOGICAL EFFECTS OF COLD ON SOLDIERS AND OPERATIONS 8

Cold has a profound numbing effect on the human body. Essential tasks take longer to perform and require relatively more effort than in temperate climates. In extreme cold, a soldier can easily become numb and indifferent to nonessential tasks. Experience shows that at temperatures lower than -10F, all other problems and requirements consistently lose significance in the personal battle for survival.

When the temperature falls below -25F, the problem of survival becomes even more significant. Soldiers tend to withdraw into themselves and adopt a cocoon-like existence, bundled in successive layers of clothing or wrapped in the warmth of a sleeping bag. These personal symptoms are also reflected in group behavior. The tent becomes a haven; soldiers become reluctant to leave its relative comfort.

To remain functional, the body must be protected from the effects of cold. Soldiers must keep their bodies clean, and commanders must emphasize good hygiene. The body must also be kept dry and sufficiently warm to keep normal body processes working properly. Soldiers must have adequate amounts of food and water to fuel heat production and prevent dehydration. Soldiers also need regular periods of rest. If these support factors are not available, soldiers become psychologically defeated by the first enemy, the cold. Eventually, they become physiologically defeated -- casualties to cold injuries. If widespread, the mission is threatened.

The right approach to winning in the winter keeps soldiers healthy and focused on the mission. There are four basic rules to remember:

• Keep soldiers in shape. Cold weather clothing is heavy and presents an additional burden to a soldier's normal equipment. The additional equipment, coupled with the difficulty of trudging through the snow, causes soldiers to expend extra energy. The importance of maintaining a high level of physical conditioning cannot be overemphasized.

• Eat to keep fit. Regular, satisfying hot food is essential for sustained performance. Even if soldiers are not hungry, they must eat or they will lose physical conditioning. They will also lower their threshold of resistance to cold stress -- because their bodies will not have the fuel it needs to sustain heat production and protect against lowering of the core body temperature.

• Drink plenty of water. Normally, in cold climates, soldiers drink only when they are thirsty. This will not give them the water needed to avoid dehydration. Drinking plenty of water avoids dehydration and the fatigue that comes with it. Irritability is often an early sign of dehydration. Soldiers should not eat snow as a water substitute; the moisture content of snow is relatively low, and eating it will lower the body's core temperature. Also, there is a danger of illness from bacteria. However, melted snow can be consumed after treatment with water purification tablets.

• Maintain a positive attitude. In cold weather operations, soldiers will face many new challenges -- but none that they cannot overcome. Leadership will be reflected in soldier's attitudes and performance. Tasks may take longer, but they do not become impossible. Leaders must watch for early signs of cold stress in their soldiers such as fatigue, lethargy, apathy, irritability, withdrawal, loss of dexterity or decisionmaking ability, decreased group cooperation, disorientation, or slurred speech.

_________________

1 Tod Schimelpfenig and Linda Lindsey, NOLS Wilderness First Aid, 2d edition (1993), published by the National Outdoor Leadership School and Stackpole Books, p. 154.

2Ibid., p. 155.

3Ibid., p. 158.

4Ibid., p. 159.

5Ibid., p. 160.

6TC 90-6-1, Military Moutaineering, April 1989, p. 1-39.

7 Schimelpfenig and Lindsey, p. 1549.

8 Adapted from Winter Operations Manual, pp. 3-2 to 3-4.

Section I: Sustaining the Soldier's Capability to Fight

Section III: Cold Weather Injuries