Hypothermia — bow to survive in cold water

Waimarino Bulletin, Volume 4, Issue 28, 16 December 1986, Page 24

Hypothermia — bow to survive in cold water

When boats overturn, or occupants are flung into very cold water they often suffer symptoms of "cold shock". Experiments have shown that the sudden change in temperature brings about physiological changes that can kill. The first reaction when plunged into cold water is to take a large involuntary gasp, then over the next few minutes begin to breathe deeply and about five times faster than normal. If a person's head is under water at the time of this first gasp immediate drowning results. When the cold hits, the heart rate increases too and takes about 15 minutes to return to a level that maintains shivering and the movement needed to stay afloat. So a person who is immersed suddenly is helpless for a time, no matter how strong a swimmer they are normally. Within a few seconds, the blood vessels in the skin shut down and reduce the flow of blood. Gne of the sideeffects of this is that the squeeze on the blood vessels shunts most of the blood back into the central core of the body. Water pressure around the body makes it worse. These effects combine to bring a sudden increase in blood pressure and the heart's output can go up by about 30 percent. This, along with the effects of anxiety and panic that even the most cool-headed would experience, can be fatal for anyone suffering a heart problem. Middle-aged and older people who may not even know there is anything wrong with their heart can suffer a heart attack or stroke that may not kill them, but will put them out of action long enough to drown. Younger, fitter people's bodies can cope with the physiological changes but the loss of voluntary control over their breathing is dangerous enough. Cold water also cuts the ability to hold the breath by about two-thirds. In some situations it is possible to allow the body to get used to the changed temperature slowly by taking a few minutes to slide into the water.

When falling from a boat the first instinct may be to strike out for shore as fast as possible. But you can swim furiously and get nowhere. Rqmember the advice — "go wtth the How" Any movement in cold water dramatically increases the rate of body-heat loss and increases the chances of hypothermia. Staying with the boat is advised — unless your boat is heading fora poundingon a rocky shore. But if it is not possible to climb onto the boat or some other floating object, assuming a "huddle" position and keeping as still as possible minimises heat loss. If a boat is known to be carrying distress flares, the search will often be started at night. A plane will carry out sweeps at about 1000 metres using track spacings of between ten and 20 miles, letting off a green light every two to five minutes depending on its speed. When clear of the glare, crew members keep a sharp lookout. The procedure is for the people in the distressed boat, when they see. the green lights, to fire a red flare once the plane is clear

of the glare, then wait at least a minute and fire a second red flare. The plane turns towards the first flare, and checks its course on the second. Unless the plane is going off "course, usually only two flares are needed. Once over the boat, the plane drops a marine marker that burns for up to two hours, or a small radio beacon to use as a homing marker. The marine markers burn with considerable heat and should not be handled or attached to a boat. The beacon can be tied to a boat but as it may be powered on immersion in water it should be left in the sea. Radar may also be used to locate a boat, but small craft — especially those of wood or fibreglass — do not return a strong signal. A radar reflector can strengthen this, and a makeshift reflector can be fashioned from tinfoil wrapped around an oar. or by hanging up pots, pans or other metal objects. Research has shown that death from hypothermia — or exposure — is likely after about three hours in cold lake or sea water.