Shiver Me Timbers!
Everyone knows blizzards, ice storms and other violent winter weather can kill you, but, under ordinary conditions, few of us think of cold as lethal. Most of us scurry from our homes to our cars and then right into another warm building where we spend the day marveling at how cold it is outside without really taking it seriously. Many of us donít bother to wear heavy coats, gloves or scarves in cold weather, but it doesnít take much to get us out of our comfort zone; maybe a minor accident that puts us on foot, or just a longer wait than usual for a train or bus. Cold can take you out with little warning and no one is immune from it. All it takes is a little inattention and a little time to get into big trouble, but sometimes, cold comes to get you in unexpected ways.
January 1982: A winter storm brought snow and ice to the Eastern Seaboard and airports struggled to de-ice aircraft before departure. As temperatures plummeted, icing both on the ground and in the cloud cover got worse. The combination proved fatal for Air Florida Flight 90. The jetliner crashed into the ice-clogged Potomac River and a female survivor clung to the tail of the nearly submerged plane. A helicopter hovered above her and attempted to rescue her with a lifeline but she lost her grip and fell into the icy water. Dressed in a light skirt and blouse, the woman tried to help herself but her limbs were not functioning at all well.
Once in the water, her condition worsened quickly and, as she struggled to swim to shore, her efforts grew more and more feeble. The helicopter tried again and again to get her to take a life ring the dropped to her but she could not hold on to it. Within minutes, her head sank below the surface and onlookers feared it was all over for her. Lenny Skutnik, a passing stranger, leapt into the water, grabbed her, and towed her to the shore where rescuers waited. She recovered from her ordeal, but few other victims of the crash survived.
What happened that made it impossible for her to help herself? She was too cold; she was suffering from hypothermia. Hypothermia occurs when your body temperature is lowered more quickly than your system can produce heat. It can happen at any time of the year, but winter is when most people are most vulnerable. She was already too cold before she hit the water but once she went in, she began losing body heat 25 times faster than when exposed to the cold open air.
There are four basic ways to lose heat: radiation, evaporation, conduction and convection. Radiation is your bodyís normal emission of heat as blood circulates around your system from the heart to the limbs and back again. Evaporation occurs when your sweat dries from your skin into the surrounding air. This goes on regardless of the air temperature and, ironically, is one of the ways your body avoids getting too hot. Cooling through conduction occurs when you are in contact with a surface colder than you are, whether you sit, lie or just lean on it doesnít matter. The more of you in contact with the colder object, the quicker you cool.
Water is an extremely efficient conduction cooler and when you are fully immersed in it, water can kill you with amazing speed. In 50F (10C) water, a person can be shivering uncontrollably in just 15 minutes and unconscious in 30 minutes. The table below gives you an idea of how quickly cold water can kill you.
|Water Temperature||Exhausted or Unconscious in||Expected Survival Time|
|70-80F (21-28C)||3-12 hours||3 hours to indefinitely|
|60-70F (16-21C)||2-7 hours||2-40 hours|
|50-60F (10-16C)||1-2 hours||1-6 hours|
|40-50F (4-10C)||30-60 minutes||1-3 hours|
|32-40F (0-4C)||15-30 minutes||30-90 minutes|
|under 32F (0C)||under 15 minutes||under 15-45 minutes|
|Note: Survival time depends in part on the physical condition of the person in the water.|
Convection, the fourth way to lose body heat, removes heat under windy circumstances. Heat is carried away from your near-body envelope of air by the wind and the harder the wind blows, the more heat convection removes. Radiation is usually the biggest cause of heat loss but, depending on circumstances, any of the others can also be significant. On a normal wintry day, all these heat robbers can be in action at the same time. Radiation and evaporation are always occurring just because youíre alive. The slightest breeze will convect heat away from you and just sit on a cold bench; conduction will kick in too.
The first thing that happens when your core (torso interior) temperature falls below normal is shivering. Uncontrollable shivering starts when the core temperature drops to about 96F (35.5C) and is the bodyís attempt to restore a normal temperature by generating heat in the muscles. Visible shivering can increase surface heat production by an amazing 500 percent but can only be sustained for a few hours. Muscles eventually become exhausted and then you are even more vulnerable to heat loss. Other early symptoms of hypothermia include increasing clumsiness as motor coordination begins to fail and an increased need to urinate. (The vascular system restricts, which is interpreted by the body as increased blood pressure, and the autonomic response is to increase urine production. Go figure.) Acting on these hints that you are too cold at this stage will save you a lot of trouble later. From here on, it only gets worse.
Between 95 and 90F, your thinking gets progressively more sluggish and irrational, on occasion, belligerent. You may suddenly feel rather warm. Hypothermia victims in this stage have been known to strip off their clothing because they feel hot. Your hands get uncooperative as fine motor control disappears, walking becomes all but impossible, and often, you get very sleepy. Speech is slurred and gradually, as your core temperature approaches 91F, shivering first becomes convulsive as the body makes a last ditch effort to warm itself, and then stops when the muscles are exhausted. Death is now close.
Between 90 and 86F, you are severely hypothermic. Arms and legs become rigid, blood flow to the limbs is sharply reduced, and the pulse slows. Your body is attempting to hibernate by shutting down the blood flow and slowing breathing and heart rate. The body is sacrificing the limbs to conserve the core heat. Around 86F, awareness and consciousness go and the heart begins to beat erratically. When the core temperature falls to 78.8F, respiratory failure and cardiac arrest both occur. At a core temperature somewhere between 78.8 and 77F, death is nearly certain even if you get help.
Brr! Sounds awful, doesnít it? Whatís the best way to treat cold-related injury or illness? It seems obvious, but the best way is to prevent it is to keep if from occurring in the first place. Pay attention to the weather forecast and wear clothing appropriate for the temperature. Multiple layers are better than single thick layers, and a hat and gloves are definitely important too. Put emergency gear in your vehicle to use if you get stranded in cold conditions and have emergency strategies all worked out beforehand.
If you are going to be outside, pay attention to your physical condition. Take shelter from the wind, drink warm beverages and watch for signs you are getting too cold. Warm your hands against your body and warm your ears with your hands. Move your hands and feet as much as you can to keep blood circulating to them. Exercise helps keep your temperature up, so keep moving.
A loss of feeling in your hands and feet is a sign of frostbite. If you have lost feeling for just a short time, the frostbite is probably light and you can safely rewarm the affected areas. If itís been a while, though, frostbite could be deep and rewarming the injury should be left to medical professionals. To treat a hypothermia victim, handle them very gently, rewarm the entire body slowly and watch them for possible after drop. After drop occurs when blood circulation out to the limbs is restored and the cold blood that stagnated out there is suddenly reintroduced into the core. The core temperature drops again and can result in cardiac failure. If someone is anything more than slightly hypothermic (anything more than a controllable shiver that stops quickly), they should get medical attention as soon as possible.
Cold is a dangerous condition but manageable if the appropriate actions are taken. As a weather forecaster, you are part of your customerís first line of defense in the war for survival. Accurate forecasts disseminated in a timely manner are important tools for them to have at their disposal. You have those same tools and a much greater understanding of the implications of any forecast you make or see. Pay attention to the forecast, your surroundings, and your personal gear. Keep warm and live!
Written by Melody L. Higdon, 14 WS/DOPA (Jun 2003)