Desert survival

[Hoodoo]

In order for it to be more effective than white clothing, you have to be in a situation where the ambient temperature is greater than the body temperature AND there is a lot of convective wind. Also, the clothing has to be loose, with usually white clothing worn underneath a black robe.

The nomadic Bedouin typify this. They are always exposed to the open desert, unlike city dwellers.

Anyway you look at it, when the ambient temp is greater than body temp, you are going to be hot and miserable. But as long as you have water, you can keep your body cool by sweating.




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Hoodoo

And so, to all outdoor folks, the knife is the most important item of equipment.

Ellsworth Jaeger - Wildwood Wisdom

 

[Hoodoo]

Here's an interesting story that illustrates just how effective sweating is for cooling humans (and panting is for dogs):

About 200 years ago, Charles Blagden, then the Secretary of the Royal Society of London, managed to talk two friends into joining him in a small room in which the temperature had been raised to 126 C which is equivalent to 260 F. Now everyone knows that water boils at 100 C so naturally his friends were a little reluctant to join him. But Blagden convinced them and the men, along with a small dog and a steak, entered the room.

They emerged 45 minutes later not only still alive but in pretty good shape. The dog was fine too but the steak was cooked!

Source: Biology: The Science of Life. 4th Edition. Wallace, Sanders, and Ferl. 1996.

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Hoodoo

And so, to all outdoor folks, the knife is the most important item of equipment.

Ellsworth Jaeger - Wildwood Wisdom

 

[TLM]

A remark to the idea of spending 45 min in a sauna heated to 126 C. Yes it can maybe be done but I would not recommend it. As a finn I have been in this hot saunas every now and then and without throwing water you might survive, 15 mins would be easy 45 difficult and not very healthy.

TLM

 

[Hoodoo]

Originally posted by TLM:
A remark to the idea of spending 45 min in a sauna heated to 126 C. Yes it can maybe be done but I would not recommend it. As a finn I have been in this hot saunas every now and then and without throwing water you might survive, 15 mins would be easy 45 difficult and not very healthy.

TLM

It's hard for me to believe a Finn would say the sauna is too hot.

Good point, though. I wasn't recommending that people actually try this. The only point I was trying to make is that it COULD be done and it's a testament to our physiological thermoregulatory abilities (and actually more than sweating is involved here, but that's another story).

Also, I want to make another comment on the clothing color issue. If you wear black clothing next to the skin and compare it to white clothing next to the skin, if the clothing is thin, it would not be an appropriate comparison. A thin black t-shirt, for instance, worn next to the skin, would not only absorb heat, but since it directly contacts the skin, heat transfer to the body would be immediate. The key to the successful use of black clothing in the desert is in keeping the black surface at a distance from the body so that the absorbed heat doesn't penetrate to the skin, but is removed by convective winds (and radiation). For instance, the pelage on camels can be at least 5-6 cm thick and the plummage on ostriches can be 10 cm thick when erected. This reduces heat flow into the body and keeps the bulk of it out on the surface where it can be lost. The temperature of the outer surface is much higher than the temperature at the body. For instance, for a camel and desert sheep, the surface of the dorsal pelage can become as hot as 70-85 C. And again, most of this solar radiant heat is lost passively, not by evaporation but by convection and reradiation, before it can reach living tissues. Thus you save a lot of water. If you have lots of water to drink, though, you can cool yourself all day long by sweating. You just have to avoid sunburn and sunstroke.

One more point: black is not only a good absorber but also a good radiator. So more heat is radiated away from the body more quickly than for white clothing.

 

[TLM]

The discussion has been partly on the differences between different colors and their order in clothing. White is generally a good reflector but in hot conditions I believe for example Ray Jardine has utilized the MLI type metallized film as reflector. And If he is to be believed (in this case not very difficult) with good results. So use your "space blanket" also to keep the heet out not only in.

TLM

 

[Hoodoo]

"....clothing that interferes with evaporation is a disadvantage. Therefore, the ideal would be a type of clothing that does not impede evaporation from the skin, but still yield a maximum of insulating protection against conduction and radiation from the environment. Loose fitting garments are better than tight clothing commonly used by western man, for they permit circulation of air so that sweat can evaporate from the skin, rather than soak through the clothing and evaporate from its surface. White clothing reflects more radiation in the visible spectrum, but its effect is not as great as may be supposed, for in the infra-red range, which contains about one-half of the total energy of solar radiation, even the whitest cloth acts as a perfect black body. The radiation of heat from the ground is in the far infra-red, and here again the whiteness of the clothing is insignificant, for all kinds of fabric (excpet metal surfaces) are black bodies."

from "Desert Animals, Physiological Problems of Heat and Water", Knut Schmidt-Nielsen, 1979, (still in print)

 

[TLM]

HooDoo's quote makes a lot of sense physically. It is somawhat difficult though to make a fabric with metallized surface and keep it breathing. Might be possible with metallized yarn, I dont know. In foundries they use metallized suits against radiative heat, they are propably not very air permeable. It would be an interesting engineering exercise to design a good light weight desert suit. a still suit if possible or at least somehow water preserving.

TLM

 

[Jeff Clark]

I would not wear a non permeable film such as plastic, foil, or metal coated foil (rescue blanket material) in hot weather. The most critical problem is air circulation. I once wore aluminum foil leggings as part of a halloween costume and almost stewed in my juices. Foil and metalized plastic also don't let you radiate away your own body heat. It is a rule of electromagnetism and optics that if a surface reflects certain wavelengths of light it will also not radiate that wavelength well. Metalic surfaces reflect almost all wavelengths and radiate very few.

White is the optimum color for keeping cool in solar radiation, that is why they paint spacecraft white. The sun is a high temperature black body and radiates a lot of energy in the ultra violet, visible, and short infrared wavelengths. White reflects well in the ultra violet and visible wavelengths and moderately in the shorter infrared wavelengths. The result is that white reflects sunlight and reflected sunlight well. Hot terrain is essentially a lower temperature black body and radiates long wavelength infrared that is easily absorbed by white surfaces. Your body is a similar low temperature black body that can radiate its own heat well through a white surface.

Years ago I was tasked with painting a radio telescope that was to be installed at the Owens Valley Radio Observatory, a high desert location. After studying the reflection spectrums of several paints I selected a white urethaine for my coating. I painted struts by dipping them in the paint and then running them through a home made infrared oven to quick dry. At first I used bathroom IR bulbs with a comparitively high color temperature (they gave off a whitish color indicative of a lot of visible and short wavelength IR). These didn't do a very good job of transfering heat into the white surfaces. Next I switched to red colored IR bulbs (indicative of cooler, larger filiments that put out longer wavelengths). These bulbs worked 50% better. It was still too slow so I switched to using bare nichrome glow coils, much larger and cooler, puting out minimal visible light and lots of long wavelength IR. These worked about twice as well. My point is that white light (like sunlight) is reflected well by white surfaces, long wavelength IR (coming from surfaces that at most only glow with heat) is not.

PS. I guess that I should mention that the struts heated up 2 or 3 times faster if I left them with their original black finishes.




[This message has been edited by Jeff Clark (edited 08-17-2000).]

 

[logansan]

Recently after conducting water survival training in 90 degree heat with lots of humidity, a friend remarked about how we wore long-sleeved shirts with a turtleneck. I informed him they actually kept us cool instead of just a black t-shirt. Granted we were in a humid environment but the concept is the same. If you use clothing that covers the body and you have perspiration that cools you, you can be more comfortable. Also your mindset can help or hinder you. Most people(Americans) think, get clothes off not put more on. In the military we only use one layer(BDU's) that doesn't breathe very well and is not extremely light, so people take them off. I have not been to SWA but I would try to use clohting more native in style. I also find covering your head with a light colored material that extends over your neck helps out a lot. Just my dos centavos. Take care.

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Yol bolsun,
Jamie