I understand that sweat increases the chances of hypothermia but I am curious as to exactly why. If I understand exactly why this is, then I am more like to be able to correct a situation if/when it has already occured.

My assumption is basically that you get hot and sweat, then when you eventually cool down you now are not just cold, but cold and wet? Not very scientific... I know. I'm no medic. Fortunately however, there are plenty of medical proffessionals in this forum. I thought maybe they could explain this to me as well as anyone else who may be curious.

As Cody Emphasizes in his book, we are ideally maintaining a temperature of 98.6 in that thin microclimate on the skin's surface. The failure is when to much sweat remains without transpiring off. Remember that water has zero insulating value and will rapidly fall to the surrounding temperatures. This is when hypothermia is accelerated by our own system. A glaring example is the strategy of Vapor Barrior Clothing. The theory here is warm sweat is trapped by non permeable materials and makes for a warm, if wet and smelly cocoon. The failure is when the clothing is eventually removed or vented. Then all that warm sweat rapidly becomes very cold and the body actually loses a greater reserve of internal heat very quickly.

Brian,
From your signature it looks like you read Cody's book. His explanations about the risks of exposure are the best I have seen.
If you over exert and get real sweaty in cool / cold weather you do run the risk of rapid heat loss due to evaporation.

There are some highly noteworthy exceptions to your statement. You might want to google the "Three Hundred Degree Club" to learn about some of the superb insulating properties of water.

Unfortunately (or fortunately, depending on your point of view), you'll have to winter at the South Pole station to join. Very exclusive membership in this club... <img src="/images/graemlins/grin.gif" alt="" /> (No, I'm not a member, but I certainly would wear a sock if I were joining.)

I am a member. You get to join some pretty exclusive clubs in the Coast Guard.

Now, that claim needs some explaining.

The Coast Guard does visit McMurdo, but until everything melts, they're not getting near South Pole station. (It's serviced by the NY Air National Guard these days.)

And outside of a tiny group of scientists, support personnel, and in the past few years construction workers building the new base, no one winters over at South Pole. The Three Hundred Degree club requires -100F outside, which outside of South Pole and Vostok in the winter, doesn't exist at other bases on the continent.

So, how on earth did you join it?? Or should I have had taken that claim with a grain of salt? (Or maybe the whole shaker? <img src="/images/graemlins/grin.gif" alt="" />)

You can't shut down insensible perspiration. It's involuntary. And that is why you collect wetness in a VBL.

A southpat on your resume looks good for other adventures AFTER service. <img src="/images/graemlins/wink.gif" alt="" />

Sweat is the human body's method of preventing overheating. Hypothermia is caused by heat being lost from the body faster than the body can produce it. Normal cause of hypothermia is an external force transfering heat from the body faster than it can be generated. i.e. Wind or water etc. Prevention is relativily easy. Correcting a hypothermic situation is dramaticly more difficult. Requires shelter and effective rewarming. Prevention is facillitated by wearing the proper clothing including a warm hat and by thermostating and regulating your level of exertion. Thermostating is the art of adding or removing clothing, opening or closing sleeves and zips according to your level of exertion. In cold conditions, as in very warm, you should be deliberate in your movements so as to avoid generating too much heat and thus sweat. Vapour barrier waterproof garments are at their most effective in temperate -10° to 25°c temperature ranges. For very cold weather, layers of natural wool and a windproof outer layer are the most effective methods of protection.

Thanks guys. That is very helpful. You are also correct in that I have read and own a copy of 98.6 Degrees and after reading the replies in this thread I re-read chapter 9 (it's probably been almost 2 years since I first read it). <img src="/images/graemlins/smile.gif" alt="" /> I also noticed that it's been a loooong time since I changed my signature. I guess I'll get on that too. <img src="/images/graemlins/grin.gif" alt="" />