Sudden Cold Water Submersion


If you were suddenly immersed in 10°C cold water, how long do you think it takes for your body to go from its normal 37°C to a temperature of 35°C which in medical terms is mild hypothermia?

Over many years of running REC outdoor First Aid Courses in North 

Wales, not too many folks have asked about what happens when we fall into cold water. On courses we do cover Hypothermia in a mountain environment, but this article will explain what happens when we suddenly end up in cold water.

This article is all about how cold water affects us, what we need to remember is that we are all various shapes, sizes, ages and have different percentages of body fat, some of you will be used to being in cold water and you will have got used to it and you will be able to tolerate it’s effects better than others.

I want to explain what happens to someone when they are suddenly immersed in cold water. For the purposes of this information let’s assume cold water is 10°C.

When the body is first submerged in cold water the natural response to the sudden change of temperature to the skin causes cold shock, we will all have had this, it’s when you suddenly gasp for breath, what do you think happens when you end up going into water head first? That’s right you take a big inhale of water and that’s it, game over. If you go into water feet first then your head will be under for less time and you might just be able to hold that gasp for a slit second until you surface. Once you surface, you’ll take that big gasp and then start hyperventilating (very fast breathing which you cannot control very easily). You now need to take control of this rapid breathing within 1 minute. Hyperventilating does not allow all of the used breath to get out of our lungs to be replaced with new oxygen rich air, so we end up with a low oxygen content in our blood stream. When we end up with a lack of oxygen to the brain we faint, we stop treading water and sink. So take control of your breathing, concentrate, try and not panic, you’ll be okay.

Now for the next few minutes (between 5–15 minutes depending upon the individual) you can get on with doing something about getting out. During this time your nerves and muscle fibres will be getting colder but for these important minutes you can make some progress. After those precious minutes our nerves and muscle fibres will get too cold and the body ends up with cold incapacitation. That means you can no longer swim or even drag yourself out of the water. Before this happens, if you are not out of the water, you need to try and attach yourself to something to stop yourself sinking.

Hypothermia has not yet set in and it will not until you’ve been in the water for about 30 minutes and you will not lose consciousness for close to an hour, it then takes a lot longer before you perish. In fact, studies have shown that a tall lean male (14.3% body fat) will not perish from fatal hypothermia on average until they have been in the water for about 2 hours and a tall lean female (19.9% body fat) for about 2½  hours. For a short overweight male (28.1% body fat) that time increases to about 8 hours and for a short overweight female (32.3% body fat) that time is 9 hours on average.

You might be thinking, why has heart attack not being mentioned, well here it is; In that first 5 – 10 minutes, the body tries to preserve its core temperature by narrowing of blood vessels (vasoconstriction) that results in minimized blood flow to hands and feet. However the heart works hard, very very hard in an attempt to circulate the blood against this resistance, this massive and sudden extra load can trigger a heart attack.

Okay, so that’s all a bit grim, or is it? As long as we remember this simple ratio 1:10:1 then in a situation of ending up in cold water we shouldn’t panic. 1:10:1 is basically, for the first 1 minute get your breathing under control. The next 10 minutes do something about getting out. You’ve got 1 hour in the water before you become unconscious.

More about Hypothermia here.

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