Cold-Weather Operations:
Sustaining Health & Performance in the Cold

Heat flows from places with high temperature to those with lower temperature. When a person is surrounded by air or water having a lower temperature than body temperature, heat will be lost from the body to the outside air. If heat escapes faster than the body produces heat, body temperature will fall. Normal body temperature is 98.6°F, and if body temperature falls much below this, performance decrements and cold injuries can result.

TOPICS IN THIS SECTION INCLUDE:

How Cold Affects the Body

   Chilblain & Trenchfoot

   Frostnip & Frostbite

   Hypothermia

   Cold Injury Risk Factors

Minimizing Effects of Cold on the Body

How Cold Affects the Body:

Severity of Temperature -- The colder the surrounding temperature is, the greater the potential for body heat to escape. When the skin is exposed to cold, the brain signals the blood vessels in the skin to tighten, and blood flow to the skin decreases. This is the body's attempt to prevent heat inside the body from being carried to the skin where it will be lost. However, due to reduced blood flow to the skin, the skin temperature falls.

Time of Exposure -- When cold exposure lasts for more than an hour, cooling of the skin and reduced blood flow to the hands leads to blunted sensations of touch and pain and loss of dexterity and agility. This can impair ability to perform manual tasks and lead to more severe cold injuries, since symptoms may go unnoticed.

Nonfreezing Cold Injuries -- Nonfreezing cold injuries can occur when conditions are cold and wet (air temperatures between 32°F and 55°F) and the hands and feet cannot be kept warm and dry. The most prominent nonfreezing cold injuries are chilblain and trenchfoot.

Chilblain is a nonfreezing cold injury which, while painful, causes little or no permanent impairment. It appears as red, swollen skin which is tender, hot to the touch and may itch. This can worsen to an aching, prickly ("pins and needles") sensation and then numbness. It can develop in only a few hours in skin exposed to cold.

Trenchfoot is a very serious nonfreezing cold injury which develops when skin of the feet is exposed to moisture and cold for prolonged periods (12 hours or longer). The combination of cold and moisture softens skin, causing tissue loss and, often, infection. Untreated, trenchfoot can eventually require amputation.

Often, the first sign of trenchfoot is itching, numbness or tingling pain. Later the feet may appear swollen, and the skin mildly red, blue or black. Commonly, trenchfoot shows a distinct "water-line" coinciding with the water level in the boot. Red or bluish blotches appear on the skin, sometimes with open weeping or bleeding. The risk of this potentially crippling injury is high during wet weather or when troops are deployed in wet areas. Soldiers wearing rubberized or tight-fitting boots are at risk for trenchfoot regardless of weather conditions, since sweat accumulates inside these boots and keeps the feet wet.

FIRST AID FOR CHILBLAIN AND TRENCHFOOT PREVENT FURTHER EXPOSURE. REMOVE WET, CONSTRICTIVE CLOTHING. WASH AND DRY INJURY GENTLY. ELEVATE, COVER WITH LAYERS OF LOOSE, WARM CLOTHING AND ALLOW TO REWARM (PAIN AND BLISTERS MAY DEVELOP). DO NOT POP BLISTERS, APPLY LOTIONS OR CREAMS, MASSAGE, EXPOSE TO EXTREME HEAT OR ALLOW VICTIM TO WALK ON INJURY. REFER FOR MEDICAL TREATMENT.

Freezing Cold Injuries -- Freezing cold injuries can occur whenever air temperature is below freezing (32°F). Freezing limited to the skin surface is frostnip. When freezing extends deeper through the skin and flesh, the injury is frostbite.

Frostnip involves freezing of water on the skin surface. The skin will become reddened and possibly swollen. Although painful, there is usually no further damage after rewarming. Repeated frostnip in the same spot can dry the skin, causing it to crack and become very sensitive. It is difficult to tell the difference between frostnip and frostbite. Frostnip should be taken seriously since it may be the first sign of impending frostbite.

Skin freezes at about 28°F. As frostbite develops, skin will become numb and turn to a gray or waxy-white color. The area will be cold to the touch and may feel stiff or woody. With frostbite, ice crystal formation and lack of blood flow to the frozen area damages the tissues. After thawing, swelling may occur, worsening the injury.

FIRST AID FOR FROSTBITE PREVENT FURTHER EXPOSURE. REMOVE WET, CONSTRICTIVE CLOTHING. REWARM GRADUALLY BY DIRECT SKIN-TO-SKIN CONTACT BETWEEN INJURED AREA AND NONINJURED SKIN OF THE VICTIM OR A BUDDY. EVACUATE FOR MEDICAL TREATMENT (FOOT INJURIES BY LITTER). DO NOT ALLOW INJURY TO REFREEZE DURING EVACUATION. NOTE: 1) DO NOT REWARM A FROSTBITE INJURY IF IT COULD REFREEZE DURING EVACUATION; 2) DO NOT REWARM FROSTBITTEN FEET IF VICTIM MUST WALK FOR MEDICAL TREATMENT; 3) DO NOT REWARM INJURY OVER OPEN FLAME

Hypothermia Cold Injury -- Body temperature falls when the body cannot produce heat as fast as it is being lost. Hypothermia is a life threatening condition in which deep-body temperature falls below 95°F.

Generally, deep-body temperature will not fall until after many hours of continuous exposure to cold air, if the individual is healthy, physically active and reasonably dressed. However, since wet skin and wind accelerate body heat loss, and the body produces less heat during inactive periods, body temperature can fall even when air temperatures are above freezing if conditions are windy, clothing is wet, and/or the individual is inactive.

Hypothermia can occur rapidly during cold-water immersion (one hour or less when water temperature is below 45°F). Because water has a tremendous capacity to drain heat from the body, immersion in water considered even slightly cool, say 60°F, can cause hypothermia, if the immersion is prolonged for several hours.

Hypothermia is a medical emergency. Untreated, it results in death. Hypothermia may be difficult to recognize in its early stages of development. Things to watch for include unusually withdrawn or bizarre behavior, irritability, confusion, slowed or slurred speech, altered vision, uncoordinated movements and unconsciousness. Even mild hypothermia can cause victims to make poor decisions or act drunk (e.g., removing clothing when it is clearly inappropriate).

Hypothermia victims may show no heart beat, breathing or response to touch or pain when in fact they are not really dead. Sometimes, the heart beat and breathing of hypothermia victims will be so faint that it can go undetected. If hypothermia has resulted from submersion in cold water, cardiopulmonary resuscitation (CPR) should be initiated without delay. However, when hypothermia victims are found on land, it is important to take a little extra time searching for vital signs to determine whether CPR is really required. Hypothermia victims should be treated as gently as possible during treatment and evacuation, since the function of the heart can be seriously impaired in hypothermia victims. Rough handling can cause life-threatening disruptions in heart rate. All hypothermia victims, even those who do not appear to be alive, must be evaluated by trained medical personnel.

FIRST AID FOR HYPOTHERMIA PREVENT FURTHER COLD EXPOSURE. REMOVE WET CLOTHING. INITIATE CPR, ONLY IF REQUIRED. REWARM BY COVERING WITH BLANKETS, SLEEPING BAGS AND WITH BODY-TO-BODY CONTACT. HANDLE GENTLY DURING TREATMENT AND EVACUATION.

Cold Injury Risk Factors -- Susceptibility to cold injury (non-freezing, freezing or hypothermia) is affected by many factors.

• Poorly conditioned Soldiers are more susceptible to cold injury. They tire more quickly and are unable to stay active to keep warm as long as fit Soldiers.

• Dehydration reduces skin blood flow. This increases susceptibility to cold injury.

• Fat is an excellent insulator against heat loss. Therefore, a very lean person may be susceptible to the effects of cold, if clothing is inadequate or wet and/or the individual is relatively inactive such as during sentry duty.

• Persons 45 years old or older may be less cold tolerant than younger persons, due to the decline in physical fitness that often occurs with aging. This emphasizes the importance of physical fitness training, particularly for older Soldiers.

• Alcohol, and to a lesser extent caffeine, cause the blood vessels in the skin to open which may accelerate body heat loss. Also, alcohol and caffeine both increase urine formation, leading to dehydration which can further degrade the body's defenses against cold. Most importantly, alcohol blunts the senses and impairs judgement, so the individual may not feel the signs and symptoms of developing cold injury.

• Nicotine decreases blood flow to the skin, therefore smoking or chewing tobacco can increase susceptibility to frostbite.

• Inadequate nutrition, illness and injury compromise the body's responses to cold and the ability to recognize and react appropriately to the symptoms of developing cold injury.

• In defensive fighting positions like foxholes or small vehicle crew compartments, movement is very restricted and Soldiers must often remain inactive inside them for long periods of time, which can greatly increase risk of cold injury.

• Individuals who have experienced a cold injury in the past are at greater risk of experiencing a cold injury than other Soldiers. These Soldiers may be more sensitive to the effects of cold, or they may not have learned how to properly protect themselves.

• When the face and other exposed skin areas are covered by camouflage paint, it is difficult to see the changes in skin color which signal the early development of frostbite.

COLD INJURY RISK FACTORS:
ENVIRONMENT RELATED: COLD TEMPERATURES WIND RAIN MISSION RELATED: SUSTAINED OPERATIONS INADEQUATE SHELTER INACTIVITY (e.g. SENTRY) WETLAND OPERATIONS	INDIVIDUAL: INADEQUATE TRAINING PRIOR COLD INJURY POOR CLOTHING & EQUIPMENT ILLNESS, INJURY, WOUNDS FATIGUE DEHYDRATION ALCOHOL POOR NUTRITION LOW BODY FAT CAMOUFLAGE PAINT ON SKIN

Wind Effects -- For any given air temperature, the potential for body-heat loss, skin cooling and decreased internal temperature is increased by wind.

Wind increases heat loss from skin exposed to cold air, in effect lowering the temperature. The wind-chill index integrates windspeed and air temperature to provide an estimate of the cooling power of the environment and the associated risk of cold injury. The wind-chill is the equivalent still-air (i.e., no wind) temperature at which the heat loss through bare skin would be the same as under the windy conditions. Appendix A depicts the Equivalent Chill Temperature for different wind speeds and air temperatures. To find the equivalent chill temperature in the table, find the row corresponding to the windspeed, and read across until reaching the column corresponding to the air temperature.

Wind-chill temperatures obtained from weather reports do not take into account man-made wind. Man-made winds worsen the wind-chill effect of natural wind. Individuals riding in open vehicles or exposed to propeller/rotor-generated wind can be subject to dangerous windchill, even when natural winds are low.

Altitude Effects -- When assessing weather conditions for troops operating in mountainous regions or for flight personnel in aircraft, altitude may need to be considered, if weather measurements are obtained from stations at low elevations. Temperatures, windchills and the risk of cold injury at high altitudes can differ considerably from those at low elevations.

• In general, it can be assumed that air temperature is 3.6°F lower with every 1000 feet above the site at which temperature was measured.

• Winds are usually more severe at high altitude.

• There is less shelter from wind above the tree line.

• Individuals are more susceptible to frostbite and other cold injuries at altitudes above 8,000 feet than at sea level, due to the lower temperatures, higher winds and lack of oxygen.

Effect of Water -- Water can conduct heat away from the body much faster than air of the same temperature.

• When clothing becomes wet due to snow, rain, splashing water, or accumulated sweat, the body's loss of heat accelerates. For example, when air temperature is 40°F, heat loss in wet clothing is double what it is in dry clothing.

• Swimmers and persons working or wading in water can lose a great deal of body heat even when water temperatures are only mildly cool.

• Individuals working in cold water should be closely watched while they enter the water, since sudden plunging into cold water can produce irregular heart beats, gasping and hyperventilation which could cause inhalation of water, heart failure and drowning.

Metals and Fuels in the Cold -- Metal objects and liquid fuels that have been left outdoors in the cold can pose a serious hazard. Both can conduct heat away from the skin very rapidly. Fuels and solvents remain liquid at very low temperatures. Skin contact with fuel or metal at below freezing temperatures can result in nearly instantaneous freezing. Fuel handlers should use great care not to allow exposed skin to come into contact with spilled fuel or the metal nozzles and valves of fuel delivery systems.

Source: SUSTAINING HEALTH & PERFORMANCE IN COLD WEATHER OPERATIONS