This is an excerpt from Get-Outside Guide to Winter Activities, The by Andrew Foran,Kevin Redmond & TA Loeffler.
Being exposed to cold with proper preparation, dress, monitoring, and maintenance can be a comfortable, enjoyable, and rewarding experience. Failure to monitor and address the hazards of exposure to cold can kill. Conditions that contribute to and often accompany hypothermia are low temperatures, dehydration, improper clothing or equipment, poor food intake, wet or damp clothes or skin, alcohol intake, fatigue, and exhaustion.
The section on hypothermia is adapted, by permission, from K. Redmond, 2003, A guide to sea kayaking Newfoundland & Labrador. By permission of Kevin Redmond.
Hypothermia is a decrease in the core body temperature to a level at which normal muscle and brain functions are impaired. Hypothermia is a leading cause of death related to outdoor activities. Exposure to cold, wind, and snow without adequate clothing can lead to hypothermia. Extreme cold is not a prerequisite to hypothermia; in fact, most hypothermia occurs in cool weather. There is a real risk of hypothermia anytime you spend time outdoors in cool or cold weather. Of note is that hypothermia can occur at any temperature below body temperature - 37⁰ C (98.6⁰ F). Never let yourself or a member of your group reach even the early stages of hypothermia. Always monitor each other.
To minimize the risk of hypothermia and prevent or reduce heat loss, wear warm, dry clothing and wear warm-when-wet clothing such as pile or wool and dress in layers with a wicking layer adjacent to the skin, followed by insulation layers and an outer shell to minimize the effect of wind and keep heat inside. To increase heat production, increase activity or eat sufficient amounts of carbohydrate before and during activity.
You and your participants have an equal role in reducing the risk of hypothermia. Your job is to ensure that participants are aware of cold weather activity protocols that mitigate risk, as well as to create a mood and social culture in which participants feel empowered to address cold-related concerns. Once participants are aware of hazards and how to avoid or minimize risks, they should be personally responsible for themselves and communicate with their peers and leaders when there is a concern beyond their ability or control. You must encourage open communication in addition to constantly monitoring participants' conditions, especially temperature, hydration, energy level, and mood or demeanor. Everyone should also understand the ways we lose heat so you can all take steps to reduce the effect of cold when engaged in outdoor activity.
How Cold Can Cold Get?
The lowest temperature ever recorded was - 89.2 degrees Celsius in 1983 in Soviet Vostok Station, Antarctica.
Understanding how a person loses heat to the environment is the first step in the prevention of hypothermia. The four ways our bodies lose heat are radiation, conduction, convection, and evaporation.
- Radiation. Radiant heat loss occurs only when the surrounding temperature is below 37⁰ C (98.6⁰ F). Factors important in radiant heat loss are the surface area and the temperature difference between you and your environment. Dressing appropriately reduces heat loss through radiation.
- Conduction. Conduction is heat loss through direct contact between objects. Heat travels from a warmer object to a colder one. Water conducts heat away from the body 25 times faster than air. Generally, conductive heat loss accounts for only about 2 percent of overall loss. However, with wet clothes, the loss is increased five times. Conductive heat loss may be minimized by using a barrier between warm body parts (e.g., insulated boots) and snow or ice.
- Convection. Heat is lost when air or water molecules against the surface are heated, moved away, and replaced by new molecules that are also heated. The rate of convective heat loss depends on the substance (water convection occurs more quickly than air convection) and the speed of the moving substance. Wind chill is an example of the effects of air convection. In modern clothing systems, convection occurs when warm air escapes from the layers (e.g., through vents, cuffs, or collars) and is replaced by cooler air.
- Evaporation. Evaporation results from the conversion of water from a liquid to a gas. Heat loss through evaporation occurs through sweating, which is the body's response to excess heat. The body sweats to maintain a humidity level of 70 percent next to the skin; in a cold, dry environment, you can lose a great deal of moisture this way. During respiration, air is heated as it enters the lungs and is exhaled with an extremely high moisture content. Recognizing the strong connections between fluid levels, fluid loss, and heat loss is important. As body moisture is lost through evaporative processes, the overall circulating volume is reduced, which can lead to dehydration. This decrease in fluid level makes the body more susceptible to hypothermia.
Signs and Symptoms
When monitoring someone (or yourself) for signs and symptoms of hypothermia, watch for the umbles (stumbles, mumbles, fumbles, and grumbles) that show changes in motor coordination and levels of consciousness. Following are signs and symptoms of various stages of hypothermia:
Mild: Core temperature of 37-35⁰ C (98-95⁰ F)
- Inability to do complex functions but can still walk and talk
Moderate: Core temperature 35-33°C (95-92⁰ F)
- Dazed consciousness
- Loss of fine motor coordination, particularly in hands (e.g., cannot zip up a jacket)
- Slurred speech
- Violent shivering
- Irrational behavior
- "I don't care" attitude
Severe: Core temperature 33-30° C (92-86⁰ F) and below (immediately life threatening)
- Shivering in violent waves followed by pauses
- Pauses get longer until shivering finally ceases
The basic principle behind treating someone with hypothermia is to rewarm the person to conserve the heat he has and replace the body fuel he is burning up to generate heat. Reduce heat loss by replacing wet clothing with dry, adding additional layers of clothing, providing shelter, and adding fuel and fluids to help the body generate heat from within. Increased physical activity can help in mild stages. External heat can be from fire or another heat source such as another body.
Learn more about The Get Outside Guide to Winter Activities.