Hypothermia: What Are The Details???

[renodesertfox]

The question is simple, show me the details of how much a normal body temperature drops from 98.6F before hypothermia becomes a factor to one's sleeping on an 18" queen-sized air-mattress for 6 hours. The outside temperature when entering the tent is 28 degrees Fahrenheit and through the course of the night drops to 10 degrees Fahrenheit and under the following circumstances?

When we pitch our tent, first the ground is cleared of,snow, ice, large rocks & stones and raked. Then we place a custom made ground-tarp thick 6mil. The Kodiak Cabin Wall 10x14 tent is pitched which has a thick vinyl floor. Next we spread 8-4x6' unrolled Army sleeping pads over the surface of the floor to give us separation from our feet coming into contact with the vinyl floor. The queen-sized air-mattress is a top-of-the-line insulated 18" high Aerobed. Once inflated it is covered first with a fitted-sheet, and two California King-sized wool blankets are placed on top. Anyone can see I'm a gear hog and proud of it! Next goes our winter-rated to -30 degree sleeping bags and on top of the sleeping bags is placed two additional fleece blankets. We each sleep in light-weight nylon insulated long-sleeved underwear. Just prior to retiring to our bed of air, I always turn off the Big Buddy 2 burner heater, zip up the open windows and settle down for our night's nap. Been doing this way for at least 10 years.

Please someone show me the details of how much my body temperature(98.6F) will drop using this system for winter camp sleeping? Also would like to see the details of how much a normal temperature of 98.6F would drop just using a sleeping pad; an insulated sleeping pad and also using no pad at all?

If there is a huge difference in the numbers(not generalities) then I might rethink our sleeping configuration.

[Phil_R]

Re: Hypothermia: What Are The Details???

Hypothermia becomes a factor when the body temperature drops below 95f/35c... if you can’t stop shivering, you’re in trouble. You are an experienced cold weather camper and know what works for you. Personally, I wouldn’t be afraid to camp under the conditions you describe with identical equipment.

In my experience, my 3” thick Thermarest pad provides much better insulation from cold ground, than my 4” air mattress, under identical conditions. But you insulate the tent floor and top of air mattress, conditions are no longer identical. Your sleep system has stood the test of time. If you are sleeping comfortable and warm, it doesn’t matter if (in scientific tests) air mattresses provide ground insulation.

Our canvas tents are a good indicator that comfort is primary...

[Mike]

Re: Hypothermia: What Are The Details???

I have been with a person who died of hypothermia when we were hiking in a storm above treeline in the Rockies. It was a bad scene. We went up three young guys and came down two (barely alive).

I will leave the science to the other folks on the forum, but I can tell you that when you are really freezing to death, you can't use your hands at all and you can feel the veins in the core of your body carrying cold blood to the center of your being.

Here is one thing I learned: We could not untie the double knots we had on our packs because we could not move our fingers or thumbs, so we could not get sleeping bags out. We could not get our hands in out pockets to get our knives to cut our packs open.

Now, I always have a tether for my knife; knife in my pocket with a string tied to the knife and to my belt loop. So, if I am ever in any kind of situation where I cannot use my fingers, I can pull the tether and get my knife out. HOPEFULLY in that kind of situation, I can open the knife with my teeth.

I suppose gear is better now with button releases and such. Also, these days I usually have a sheath knife on my belt. So the situation might be different today than it was then.

Being on the receiver end of severe hypothermia, what I can tell you is that the first symptoms are familiar to all of us; shivering, feeling cold, stiffness of fingers, etc. When you get beyond that, your whole body freezes up - even your mind. Your legs are like stumps up to your thighs. Your arms become paralyzed to your biceps or beyond. Your stomach muscles tighten and cramp. You have a dull headache, you have a hard time thinking clearly EXCEPT that you clearly know what is happening and have to think your way through the situation to survive.

Beyond that, you don't feel the pain of the cold. You feel encouraged to just lay down even for awhile because there is a calm almost warmth that comes over you. At that time, only that last bit of will power and clear thinking in your head will save you - convince you not to just lay down, not to stop; literally crawling to survive and get off the mountain.

For me, I was more afraid when I got beyond the cold and started to feel the calm warm when I knew I was literally freezing to death.

After experiencing extreme hypothermia, I am convinced THAT is the best way to go. After you get past the point of pain, just laying down and letting nature take over seems comfortable and inviting. That is just what one of the guys in our party did and when I watched him lay down and not get up and not respond to our shouts and saw the blowing snow piling up on him like a blanket, I knew what he was feeling and understood his inability to resist it. I confess to having the same urge.

[tplife]

Re: Hypothermia: What Are The Details???

if you're not shivering, likely your body temp is not dropping. The sleeping pads will provide a barrier to convection from the ground cold, that's solid transfer. You're insulating loss from above by your sleeping bag. The air temperature inside the tent is typically 10-degrees-F warmer than the outside due to natural insulating properties. By your example, 28-degrees F drops to 10-degrees F. Allow the average 10-degrees inside and you likely only drop to 20-degrees F. Your air mattress has hollow tubes inside that lack the cellular or glass-fiber insulation to create millions of cells like a closed or open-cell sleeping pad (like your mattress in an RV or at home) which slow heat transfer, just like sleeping inside a solid box would. As long as this mattress is in the tent, the air inside is seeking equilibrium with the ground, the air in the tent, and any solid objects (you, your sleeping bag, your pad between tent and ground, etc.) to all become exactly the same temperature. Solid transfer is slower than the air, which is slower than water (remember the cooler water example and ice experiment). When you awake in the morning, rather than being warm like you are from sleeping, the air inside the air mattress is cold, and has been working over 6 hours to become the same temperature inside as it is outside. While you slept, you were transferring heat to the air mattress to help it achieve equilibrium with you, but it cannot. It never stopped absorbing heat from you since the air around the mattress is considerably colder than you are. That's the definition of a heat sink. In extreme conditions, it's not good to sleep on a heat sink. In ideal conditions, you're basically sacrificing sleep quality or having to over-compensate with insulation for a good night's sleep. The point of avoiding a heat sink is simply to improve sleeping quality, or require less gear for the same quality of sleep. I'm not going to bore anybody here with the laws of thermodynamics and what particular laws govern the transfer of heat - anyone interested would already discover that in 60 seconds of Internet research.

[renodesertfox]

Re: Hypothermia: What Are The Details???

Thank you gentlemen for your input. Next winter I shall do a test and we will see for ourselves. I completely understand where everyone is coming from. For now the weather is warming except in the higher elevations and those campgrounds and dispersed areas are still imbedded with impassable snow. When we sleep as we have done for years we are never cold when we first wake up, we're quite pleasant really. I only get chilled for as long as it take me to climb out of my bag, unzip a window and fire up my Big Buddy Heater(about 30 seconds). Then back in the sack where it's still warm and wait for the tent to warm up some. But the heat sink thesis is interesting.lol

[Bigdog57]

Re: Hypothermia: What Are The Details???

Reno, your direct personal experience mirrors mine exactly, though our gear is a bit different. Me, I put the GI closed cell foam pad down, then the air matress atop it - this provides better insulation than the matress alone. Also some protection from wet ground getting through the tent floor. Next I place a folded GI wool blanket atop the air matress - again, added insulation, and it is easier to roll on than the no-slide flocked top the air matress has. I tend to be a 'toss & turn' sleeper even at home. Then a good sleeping bag or blanket, generally rated well lower than expected temps.
I have comfortable in 17 degree F. temps. There are times I even have to open the bag/blanket a bit to let out excess heat. And THIS is the thing the theorists always forget - the Human body is warm blooded, and is a heat generating machine. Properly fed, we keep producing heat as we sleep. Properly insulated, this heat keeps us comfortable.

Proper science comprises several steps:
1: Hypothesis - which is literally a 'best guess' based on available info and what one 'thinks' should be.
2: Theory - you gather more data, and refine your hypothesis. You define rules, and see if it fits the hypothesis. If not, refine the hypothesis further.
3: Test - do some real world testing to see if your theory holds water. If not, find out what DOES work, and refine your theory, as you missed something vital.
4: Proof - the testing and data are compiled into true real world FACTS that can be shown to others.

These last two steps are what I have never seen from certain parties........ best guesses don't tell me anything. We get out there and see what DOES work, for us. Nothing else is of any consequence.

[tplife]

Re: Hypothermia: What Are The Details???

The ice cube in the mesh bag over the water experiment in the "make your ice last longer by draining the water off" post is the same common experiment to demonstrate these particular thermodynamic laws of heat transfer, and are pretty easy to do in your own kitchen. As far as why you can't sleep as warmly on a cot or air mattress, your body heat is absorbed by the mattress, which is achieving equilibrium by becoming the same temperature as you. The outside and bottom of the air mattress are cold, and transferring heat (or cold) into the air mattress in order that they may achieve equilibrium and become the same temperature. The air mattress eventually becomes the same temperature inside as the outside air is, and will achieve equilibrium with you once you become the same temperature as the cold air inside. As long as you're "alive" and generating heat, it won't, but you give up your energy for no good reason, because the air mattress will continue to absorb heat off of your body until it becomes the same temperature. You'll sleep great, as long as the outside air is warm (summer). This is physics, and it's not a theory, hypothesis, hunch or belief. It's just the way things work, and what one learns in any first-year physics course.

[frank6160]

Re: Hypothermia: What Are The Details???

I insulate my air mattress in much the same way as Bigdog. I'm good with outside temps down to about 30. Much colder than that I want a campsite with electric and use a heater or I don't tent camp till warmer weather. Except for deer season and I have an old RV with power there.