A. Radiation: is direct heat loss from the body to its surroundings. If the surroundings are colder than the body, the net result is heat loss. A nude man loses about 60% of his total body heat by radiation. Specifically, heat is lost in the form of infrared radiation. Infrared targeting devices work by detecting radiant heat loss.
B. Conduction: is the direct transfer of heat from one object in contact with a colder object.
(1) Most commonly conduction occurs when an individual sits or rests directly upon a cold object, such as snow, the ground, or a rock. Without an insulating layer between the Marine and the object (such as an isopor mat), one quickly begins to lose heat. This is why it's important to not sit or sleep directly on cold ground or snow without a mat or a pack acting as insulation.
C. Convection: is heat loss to the atmosphere or a liquid.
Air and water can both be thought of as "liquids" running over the surface of the body. Water or air, which is in contact with the body, attempts to absorb heat from the body until the body and air or water is both the same temperatures. However, if the air or water is continuously moving over the body, the temperatures can never equalize and the body keeps losing heat.
D. Evaporation . Heat loss from evaporation occurs when water (sweat) on the surface of the skin is turned into water vapor. This process requires energy in the form of heat and this heat comes from the body.
(1) This is the major method the body uses to cool itself down. This is why you sweat when you work hard or PT. One quart of sweat, which you can easily produce in an hour of hard PT, will take about 600 calories of heat away from the body when it evaporates.
E. Respiration. When you inhale, the air you breathe in is warmed by the body and saturated with water vapor. Then when you exhale, that heat is lost. That is why breath can be seen in cold air. Respiration is really a combination of convection (heat being transferred to moving air by the lungs) and evaporation, with both processes occurring inside the body.
3. PHYSICAL RESPONSES TO HEAT. When the body begins to create excess heat, it responds in several ways to rid itself of that heat.
A. Initially, the blood vessels in the skin expand, or dilate. This dilation allows more blood to the surface where the heat can more easily be transferred to the surroundings.
B. Soon afterwards, sweating begins. This contributes to heat loss through convection and evaporation.
4. PHYSICAL RESPONSES TO COLD. Almost the opposite occurs as with heat.
A. First, blood vessels at the skin surface close down, or constrict. This does two things:
(1) Less blood goes near the surface of the body so that less heat is lost to the outside.
(2) More blood goes to the "core" or the center of the body, to keep the brain, heart,lungs, liver, and kidneys warm. This means fingers and toes tend to get cold.
B. If that is not enough to keep the body warm, the next step is shivering. Shivering is reflexive regular muscular contractions, this muscular activity causes heat production. As mentioned before, shivering can only last for a short time before exhaustion occurs. With shivering you will either warm up, as usually occurs, or continue to get colder and start to become hypothermic. Hypothermia will be discussed later.
5. ENVIRONMENTAL INJURIES (MSVX.02.15b) Are cold weather injuries, dehydration, and altitude related illnesses.
A. COLD WEATHER INJURIES:
1) Hypothermia (MSVX.02.15c) is the state when the body's core temperature falls to 95 degrees Fahrenheit or less. It is the number one killer of people in a survival situation. A common belief that extremely cold temperatures are needed for hypothermia to occur is not true. Most cases occur when the temperature is between 30 and 50 degrees Fahrenheit. This is the normal temperature range at MWTC, except during the harshest of winter.
a) Causes of Hypothermia. The ways in which the body generates and loses heat has been discussed earlier. Quite simply, hypothermia occurs when heat loss from the body exceeds the body's ability to produce heat.
Contributing factors include:
• Ambient temperature. Outside air temperature.
• Wind chill. This only affects improperly clothed individuals.
• Cold water immersion.
• Improper clothing.
• Alcohol intoxication, nicotine and drugs such as barbiturates and tranquilizers.
• Injuries. Those causing immobility or major bleeding, major burn and head trauma.
b) Signs and symptoms of Hypothermia
• The number one sign to look for is altered mental status; that is, the brain is literally getting cold. These signs might include confusion, slurred speech, strange behavior, irritability, impaired judgment, hallucinations, or fatigue.
• As hypothermia worsens, victims will lose consciousness and eventually slip into a coma.
• Shivering. Remember that shivering is a major way the body tries to warm itself early on, as it first begins to get cold. Shivering stops for 2 reasons:
• The body has warmed back up to a normal temperature range.
• The body has continued to cool. Below 95°F shivering begins to decrease and by 90°F it ceases completely.
• Obviously, continued cooling is bad. So if a Marine with whom you are working, who was shivering, stops shivering, you must determine if that is because he has warmed up or continued to cool.
• A victim with severe hypothermia may actually appear to be quite dead, without breathing or a pulse. However, people who have been found this way have been successfully "brought back to life" with no permanent damage. So remember, you are not dead until you are warm and dead.
c) Prevention of Hypothermia
• Obviously, prevention is always better (and much easier) than treatment.
• Cold weather clothing must be properly warm and cared for.
• Keep your clothing as dry as possible.
• If your feet are cold, wear a hat. Up to 80% of the body's heat can escape from the head.
• Avoid dehydration. Drink 6 - 8 quarts per day.
• Avoid fatigue and exhaustion.
• Increase levels of activity as the temperature drops. Do not remain stationary when the temperature is very low. If the tactical situation does not permit moving about, perform isometric exercises of successive muscles.
• Use the buddy system to check each other for signs/symptoms of hypothermia.
d) Treatment of Hypothermia.
• Prevent further heat loss.
• Remove the victim from the environment (i.e., into a shelter or snow cave).
• Insulate the victim.
*Zip two sleeping bags together.
*Pre-warm the bag by a stripped Marine.
*Place the victim in the bag with 2 stripped Marines inside on both sides of the victim.
• Medevac if possible.
e) Other Points to Remember.
• Fluids. If the victim is mildly hypothermic, he may be given hot wets. Otherwise give him nothing by mouth.
• Avoid, if possible, excessive movement of the victim, as his heart may stop beating if it is jarred.
• Major Wounds. Apply first aid to major wounds first, before attempting to re-warm the victim. Re-warming a victim who has bled to death does little good.
• Never give alcohol to hypothermia victims.
• Even after you have started re-warming a victim, he must be constantly monitored. Don't forget about him.
2) FROSTBITE Frostbite is the actual freezing of tissues. When in a survival situation, rewarming a severe frostbitten area will not help. It is best to wait for rescue and medical attention.
a) Prevention of Frostbite. Frostbite is an entirely preventable injury.
• Dress in layers. Keep comfortably cool. If you begin to become uncomfortable, add layers.
• Keep clothes dry. If clothing (especially socks and gloves) become wet, change them. This may mean you have to change sock 4-5 times a day.
• Dress properly. If the wind is blowing, wear the correct protective layer.
• Avoid dehydration. When dehydrated, the amount of blood available to warm your fingers and toes goes down, increasing the risk of frostbite.
• Avoid Starvation. Remember - Food is Fuel - and the body uses that fuel to make heat.
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