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This question was prompted by PaulD's question about hypothermia prevention after a falling into icy water. A subsequent answer by Roddy stated that the immediate danger of cold water immersion is not hypothermia, as it takes quite long to lower the central body temperature. This statement caused some controversy on how fast this really happens and I feel like it is not what was asked by the OP. So here it is:

How long does it take after immersion into cold water to develop hypothermia?

I am interested in different water temperatures and without or with some kind of heat loss protection (relevant for diving/sailing?), just state for what conditions your information hold.

It is generally considered that the first stage of hypothermia begins below 35degC core temperature. Please reference studies, first hand experience or give any other sort of explanation, why your source is viable. I found many articles via google that claimed different things, mostly not well based (at least not declared).

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  • I encountered the same thing when searching on google. Hall of mirrors. There didn't seem to be consistency.
    – Citizen
    Commented Jan 6, 2016 at 3:00
  • You can get hypothermia in the middle of summer after falling into a creek, the temperature of the water has little to do with it, it's evaporative cooling that brings your body temperature down. Fully immersed in water there are many other factors that come into play, like what are you wearing? Is the water moving? Are you moving? You can stay warm in cold water for a long time if the water isn't flowing and you stay still, even longer if you're wearing thick layers and a life jacket. Your body will warm the water immediately around you, and as long as you don't flush it, you may stay warm.
    – ShemSeger
    Commented Jan 6, 2016 at 4:58
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    @ShemSeger "Your body will warm the water immediately around you" Yes, that's how partly how wet suits work. But I'm not aware if that effect makes any difference without something like a neoprene barrier layer. You'll be moving in the water anyway to stay afloat/swim/get out.
    – Roddy
    Commented Jan 6, 2016 at 9:01
  • @PaulD Do you have any links for those? Most of my google searches seem to back up the '30 minutes' figure, give or take.
    – Roddy
    Commented Jan 6, 2016 at 9:03
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    @Roddy if someone is wearing baselayer+mid layer+full waterproofs (which might be realisitic for winter hiking) this will be quite an effective barrier layer. Everything will get soaked almost instantly but once soaked the rate of water replacement will be quite slow, and a warm-water layer will build up.
    – Chris H
    Commented Jan 6, 2016 at 10:22

2 Answers 2

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Here's one study: http://www.eisberg.narod.ru/Ch17-ColdWaterImmersion.pdf

And a couple of snippets, the first showing how water cools faster than air. In this test with 10degC water, subject's core temperature was still over 36degC after approx 40 minutes.

enter image description here

...and the second showing effect of different clothing. In this test with 10degC water, subject (wearing 'street' clothes) had core temperature of 35.6degC after 30 minutes.

enter image description here

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Roddy's answer is great for study details, but in the nautical realms of boating safety and courses that include boat safety (safe boater, boatUS, USCG, ASA, USSailing,etc)

We are taught in New England that if you fall in the water in winter, you have to get yourself out as fast as you can. Any longer than 10 minutes in the water and you will no longer have the strength nor ability to hoist yourself out of the water, and may begin to loose awareness of the fact that your in trouble at all. After 45 minutes floating in winter seawater and the chances of survival are near to zero.

Of course there is always the freak incident of someone's body shutting down allowing survival past all comprehension, but that's a very rare exception to the general rule.

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    "Any longer than 10 minutes in the water and you will no longer have the strength nor ability to hoist yourself out of the water". Agreed, but that's not hypothermia, it's cold incapacitation. outdoorswimmingsociety.com/swimming_outdoors/embrace_cold/…
    – Roddy
    Commented Jan 6, 2016 at 8:57
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    @Roddy yes, but if I am incapacitated I don't really care that I don't have hypothermia yet.
    – njzk2
    Commented Jan 6, 2016 at 16:35
  • @njzk2 Indeed :) But the question body is specifically asking "How long does it take after immersion into cold water to develop hypothermia?". But you're right not care unduly about Hypothermia, as it almost certainly won't be what kills you.
    – Roddy
    Commented Jan 6, 2016 at 16:44
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    The question itself asks, "How fast do you lose heat in cold water immersion?". Hypothermia and death may be the end result, but the effective limit to be immersed in icy water is 10 minutes for the average person before they become essentially helpless.
    – Escoce
    Commented Jan 6, 2016 at 16:50
  • @Escoce The question text I quoted conflicts with question title that you've quoted :( Everythng you say is correct (so +1 from me) but I think you may be answering the wrong question.
    – Roddy
    Commented Jan 8, 2016 at 10:14

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