Industrial Hygiene & Environmental Health Office
During cold weather, the environment can directly affect an individual's health and performance. Cold can lower body temperature, resulting in cold injuries and impaired performance. Moreover, cold weather is often accompanied by wind, rain, snow and ice, which can worsen the effects of cold, as well as contribute to injury and performance.
Operational problems often arise in cold weather, including restricted movement due to heavy clothing; equipment malfunctions; travel difficulties, etc.
While cold makes daily tasks more difficult, it does not make them impossible. The purpose of this information is to describe how the environmental conditions stress health and performance during cold weather operations, and to explain ways of overcoming that stress.
How does the body adjust to the cold?
Humans protect themselves from cold primarily by avoiding or reducing cold exposure using clothing and shelter. When this protection proves inadequate, the body has biological defense mechanisms to help maintain correct body temperature. The body's internal mechanisms to defend its temperature during cold exposure include vasoconstriction and shivering. When these responses are triggered, it is a signal that clothing and shelter are inadequate.
- Vasoconstriction is the tightening of blood vessels in the skin when it is exposed to cold. The reduced skin blood flow conserves body heat, but, it can lead to discomfort, numbness, loss of dexterity in hands and fingers, and eventually cold injuries.
- Cold triggers shivering. Shivering increases internal heat production which helps to offset the heat being lost. Internal heat production is also increased by physical activity, and the more vigorous the activity, the greater the heat production. In fact, heat production during intense exercise or strenuous work is usually sufficient to completely compensate for heat loss, even when it is extremely cold. However, high intensity exercise and hard physical work are fatiguing, can cause sweating and cannot be sustained indefinitely. Moreover, most daily occupational activities are less vigorous than high-intensity exercise, so internal heat production will probably not be adequate to offset heat loss.
- Susceptibility to cold injuries can be minimized by maintaining proper hydration and nutrition, avoiding alcohol, caffeine and nicotine, minimizing periods of inactivity in cold conditions.
Humans do not acclimatize to cold weather nearly as well as they can acclimatize to hot weather, although repeated cold exposure does produce what is referred to as habituation.
- Following habituation, shivering is much less vigorous. This is advantageous because shivering is inefficient, and most of the heat produced is lost. Also, shivering can interfere with sleep causing fatigue.
- With habituation to repeated cold exposure, humans adjust mentally and emotionally.
Types of Cold Injuries, Symptoms, and Treatment
Nonfreezing cold injuries occur when conditions are cold and wet (air temperature between 32°F and 55°F). The most prominent nonfreezing cold injuries are chilblain, trench foot and immersion foot.
- Chilblain- result from intermittent expose to temperatures above freezing in high humidity.
- Symptoms - red, swollen skin which is tender, hot to the touch and may itch. It can develop in only a few hours in skin exposed to the cold.
- Immersion foot - result from prolonged exposure, usually in excess of 12 hours, in water at temperatures usually below 50°F. It is not limited to the feet, but may involve others areas of the body following immersion.
- Symptoms - see trench foot.
- Trench foot - develops when skin of the feet is exposed to moisture and cold just above freezing to 50°F. The combination of moisture and cold soften skin, causing tissue loss and often infection. Untreated trench foot can eventually require amputation. The average duration of exposure resulting in trench foot is 3 days.
- Symptoms - itching, numbness or tingling pain; feet may appear swollen, and the skin mildly red, blue or black.
First Aid for Chilblain and Trench Foot
- 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 occur whenever air temperature is below freezing (32°F). Freezing limited to the skin surface is frost nip. When freezing extends deeper though the skin and flesh, the injury is frostbite.
- Frost nip - involves freezing of water on the skin surface - skin becomes reddened and possibly swollen; painful; usually no further damage after rewarming Frost nip should be taking seriously since it may be the first sign of impeding frostbite.
- 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, constricting clothing
- Rewarm gradually by direct skin-to-skin contact between injured area and non injured skin of the victim or a buddy
- Evacuate for medical treatment (foot injuries by litter)
- Do not allow injury to refreeze during evacuation
- Do not rewarm a frostbite injury if it could refreeze during evacuation
- Do not rewarm frostbitten feet if victim must walk for medical treatment
- Do not rewarm injury over open flame.
Hypothermia is a life threatening condition in which deep-body temperature falls below 95°F. Body temperature falls when the body cannot produce heat as fast as it is being lost.
- 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. If left untreated, it may result 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
Who is susceptible to cold injury?
Susceptibility to cold injury (non-freezing, freezing or hypothermia) is affected by many factors related to the environment (cold temperatures; wind; rain) and.
Individual Susceptibility Factors
- Poorly conditioned persons are more susceptible to cold injury. They tire more quickly and are unable to stay active to keep warm as long as persons that are physically fit.
- 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. Keep in mind that anybody is susceptible to a cold injury regardless of age.
- 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 judgment, 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.
- Being in places where movement is very restricted and individuals remain inactive for long periods of time will greatly increase the 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 individuals. These individuals 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.
- Geographic Origin: The geographic origin of the individual seems to be a significant factor in the incident of cold injury. Origin from warmer climates of the United States predispose cold injury.
- Activity: Too much or too little activity can contribute to cold injury. Over activity vs. Immobility.
Environmental Factors and Working Conditions
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 wind speed 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. The Wind Chill Chart 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 wind speed, 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 or rotor-generated wind can be subject to dangerous windchill, even when natural winds are low.
When assessing weather conditions for working/vacationing individuals 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, assume the 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 and there is less cover 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.
Also keep in mind that 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.
- 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.
Preventing Cold Injury
Cold-weather clothing systems are designed to change with the wearer's needs. Cold-weather clothing protection is based on the principles of insulation, layering and ventilation. By understanding these principles, we can vary the clothing to regulate protection and stay comfortable.
When Using Cold-Weather Clothing,
keep it --------Clean
avoid --------- Overheating
wear it --------Loose in layers
keep it --------Dry
- Insulation depends on the clothing thickness, properties of the garment material, and the amount of air trapped within the garment. When clothing is dirty, the material tends to be packed down, which compromises insulation.
- Wearing clothing ensembles in multiple layers allows the wearer to remove or add clothes to adjust the insulation to changes in environment or workload as well as to the individual's own needs and preferences.
- Physically active people can sweat even in extremely cold weather. Sweat will be able to evaporate if clothing allows ventilation. Proper clothing will be made of material that water vapor can pass through, and will allow the wearer to unzip and open the clothing periodically to increase ventilation. If sweat can not evaporate, it will accumulate, wet the clothing, compromising insulation. Sweat evaporation will be compromised when clothing is dirty.
Feet, hands and exposed skin must be kept dry. Feet are particularly vulnerable and extra foot care is required for cold-weather operations. Feet should be washed, dried and dusted with a dry, antifungal powder daily. Socks must be changed whenever they become wet from exposure to rain or snow, or from excess sweat. This may require changing into dry socks at least 2-3 times daily. Extra socks can be air dried and then carried in the jacket/coat to warm.
Use the Buddy System to take care of each other. Holding (not rubbing) a warm hand on the blanched area until it returns to normal color will rewarm a buddy's ear, nose, or cheek. Fingers, toes can be rewarmed placing them against a buddy's bare chest or abdomen.
- Wear or carry adequate clothing for the weather to be encountered. Remove excess of clothing before perspiration starts so that the clothing does not become wet.
- Wear clothing in loose layers to permit layers or air to provide good insulation and permit good circulation of blood to all parts of the body.
- Keep hands well protected: mittens are better than gloves. Cover your head, great amount of heat is loss if unprotected. Do not touch metal, snow, or other objects with bare hands.
- Avoid immobilization in the cold. If the situation permits, walk about and exercise to generate and maintain body heat. Move toes, feet, legs, fingers, and arms. Do not sit directly on the ground.
- Remove excess clothing when near a fire or in a warm enclosure, otherwise the body adjust to the warm temperature and excess clothing.
- Use the windchill chart.
Treatment for Shock
- Keep warm by placing in sleeping bag or substitute.
- Raise legs above head level, unless patient's head is injured.
- Loosen clothing without compromising protection form cold.
- If conscious, provide warm drinking fluids.
- Minimize discomfort and provide reassurance.
Must have items for winter weather driving:
- First aid kit
- A can a waterproof matches (to melt snow for water)
- Windshield scraper
- Booster cables
- Road map
- Tool kit
- Paper towels
- Bag of sand or course cat litter (for added traction)
- Tire chains (in areas with heavy snow) or snow tires
- Collapsible shovel
- High-calorie canned or dried food and a can opener
- Flashlight(s) and extra batteries
- Canned compressed air with sealant (for emergency tire repair)
- Brightly colored cloths
- A change of clean clothes, including socks