Hi, thank you for bringing Google Answers your question.
I'm glad you emphasized "approximately" and the approximate answer is
that it will take about 20 minutes before hypothermia becomes
irreversible.
It should be obvious that a lot of factors are involved in this and
that a precise answer is impossible.
For example, the body fat and clothing of the individual as well as
the amount they move around exposing themselves to new cold water not
previously heated by their bodies, will all have a significant effect
on the rate of heat loss.
The metabolic rate will determine how much heat is generated internally.
Any alcohol consumption would greatly affect the blood flow to the
body?s surface which would also have a significant effect (which is
why you don?t give a chilled person any alcohol unless they are now in
warm conditions.)
That is why most studies appear to refer to the body core temperature
rather than the temperature of the water.
However, that said, there are many studies on this and a useful Web
site is the Canadian Coast Guard site, ?A Hypothermia Treatment
Technology Web Site,?
http://www.hypothermia-ca.com/mayday/mayday.html
Another site,
http://hypothermia.org/inwater.htm
or
http://hypothermia.org/Hypothermia_Ed_pdf/Hypothermia-Land-Water.pdf
includes a chart comparing probable death with immersion time in water
of various temperatures.
http://hypothermia.org/images/timegraph.gif
The chart has a wide variation between the times for those who cool
quickly and those who loose heat more slowly.
Since you cite the Titanic, I presume the 28 degree temperature you
refer to is Fahrenheit which would be below ice temperature if the
water weren?t salty.
That would translate to a few degrees below zero Celsius.
I couldn't find any data for that precise temperature but there would
be little difference for the time at a slightly higher temperature.
The chart I cite above shows a survival range for zero-degree C water
ranging from a few minutes for the most susceptible to nearly two
hours for those with the slowest heat loss.
The average survival time is just over 1 hour.
But bear in mind that these survival times are associated with rescue
by trained medical personel who are prepared to immediately treat the
individual. Survival times adrift in the North Atlantic 100 years ago
would be considerably shorter.
Swimming will increase heat loss by 35-50% according to the hypothermia.org site.
The U.S. Coast Guard has a hypothermia chart at
http://www.uscg.mil/hq/g-m/mse4/pfdcold.htm
The expected survival time listed there is 15 to 45 minutes for
unprotected immersion in 32.5 degree F water (0.3 degree C).
Unconsciousness is likely to occur in fewer than 15 minutes.
Salt water (ocean) will begin to ice up at about two degrees C below zero.
So the approximate survival time for Titanic swimmers would be less
than an hour and as little as 10 minutes - that is for short term
survival. Pneumonia and death from organ failure would be a delayed
effect and would not have been treatable at that time in history.
Thank you for asking the question. |
