bushcraft myths

[FerlasDave]

There seems to be no doubt that the huge claims about heat loss through the head are a bit exaggerated, but this is one where I would not throw the baby out with the bathwater. There is some physiological basis to this. When the body is cold, it begins to restrict blood flow to the extremeties. This is one of the reasons your fingers and toes get cold so quickly at low temps. However, because the brain needs oxygen, blood flow to the brain is not restricted. And with blood flow goes the heat from the core of the body. So, imo, cover up in the cold!

I agree! Some more common sense employed there!

 

[Hoodoo]

I do wonder how humans ever worked out food like cape gooseberry and tomatoes where edible,

Lots of children but low survivorship.

 

[Martyn]

There seems to be no doubt that the huge claims about heat loss through the head are a bit exaggerated, but this is one where I would not throw the baby out with the bathwater. There is some physiological basis to this. When the body is cold, it begins to restrict blood flow to the extremeties. This is one of the reasons your fingers and toes get cold so quickly at low temps. However, because the brain needs oxygen, blood flow to the brain is not restricted. And with blood flow goes the heat from the core of the body. So, imo, cover up in the cold!

Was going to say the same thing. The brain doesnt have the same sacrificial vasoconstriction as the extremities to ensure the brain is the last organ to be deprived of heat, that and the lack of insulation and comparatively huge blood flow, make the human head a very good radiator. I dunno about 80%, but it must be high - I've even seen steam coming off my own head after exerting and sweating in the cold.

The human thermal plume is an interesting image which seems to reinforce the point in a nice graphical way...

steaming head....

[video=youtube;g1y5k3H3me4]http://www.youtube.com/watch?v=g1y5k3H3me4[/video]

 

[cbr6fs]

Next time your out on a cold day try taking your upper body clothing off and see how quickly you get cold.
Then try it with just your legs uncovered.
Then your head.

If you lost THAT much heat from your head then you would not be able to survive for over 1 hour in temps lover than 5c without a hat.

The head is really no different to any other part of the body in hat respect, it's purely down to surface area rather than a certain part of the body.

 

[tamoko]

"1 hour in temps lover than 5c".

On the open air you will survive this time and temperature without any clothing.
In the water if you can’t get out in 5-15 minutes, you might not get out on your own power.

Onset of Hypothermia
(>30 minutes on)
• Cooling to UNCONSCIOUSNESS
• If head goes under,
Drowning (30-120 minutes).
• If head above water…
• Cooling to CARDIAC ARREST,
Death (90-180 minutes or more,
depending on water temp, body size, etc.)

http://www.uscg.mil/pvs/docs/coldwater1.pdf

So you can see the difference.

I have worked without gloves in -35C over one hour, but i will not try to do this without right hat.
In bad situation your feet and hands can be totally frozen but your body will not lose heat, but it is totally different if your head is frozen.

 

[Hoodoo]

The head is really no different to any other part of the body in hat respect, it's purely down to surface area rather than a certain part of the body.

Sounds good but I think it’s a bit more complex than that. The rate of heat transfer from the skin to the environment is going to depend on the temperature difference between the skin and the air. This is true for conduction, convection, and radiant transfer. If there is a layer of fat, then there is also the transfer by conduction across the fat layer to the surface of the skin to consider as well. Not much of a lipid layer in the skull to retard heat flux, although hair does (as does a hat). So basically the driving force per square inch of flesh depends on the temperature of the flesh, regardless of the surface area. Obviously the larger the surface area, the more area for heat to be lost, which is precisely why the body reduces blood flow to appendages. This reduces the temperatures of the appendages and reduces the driving force of heat loss by conduction, convection, and radiation. Additionally, rete mirabiles and the utilization of deep versus shallow venous return can be used in appendages to retain heat in the core and reduce heat flux to the appendages. For humans, no such rete exists in the head. Physiologists have tried to model heat exchange across the body as a function of spheres and cylinders but because body parts are living and not inanimate objects, such models can only give a rough approximation of what MIGHT happen. However, heat transfer is dynamic, not static.

 

[rik_uk3]

http://wildernessmedicinenewsletter...4/heat-loss-through-the-head-and-hypothermia/ An interesting article

 

[bushcraftmyway]

ok, since the things cooled down here, i feel like it's my job to wrap it up:
- i think criticism from you leads to better vids from me , so i welcome all your observations.
- i made these vids hoping to make people think about the "axioms" of bushcraft (maybe that would have been a better word - too bad it didn't cross my mind at that time ); i never intended to persuade people that i'm right (after all, "my way" and "right way" are not synonyms ), i just wanted to question things that are not questioned enough. considering your reaction, i reached my goal - you came up with pros&cons, shared your thoughts and even did a bit of research to back up your position - that's great and i thank you all for taking time to do it!
- i'm new on this forum, and this thread convinced me that i'll enjoy being a part of the bcuk community.

 

[winst0nsmith]

every now and then a known wild food is found to be just abit more toxic that we thought, it has happened with comfry and sweet woodruff. There is always more to know about plants.

Agreed, "just a bit" (a very little bit- you'd have to consume a shed load of it pretty much every day for a long time to actually harm yourself), 200 times more pyrrolizidine alkaloids in beer than comfrey and nobody is listing beer as unfit for human consumption so why comfrey?

What's the issue with sweet woodruff please? I aint heard about that and I'm always up for learning more about plants.

 

[xylaria]

Agreed, "just a bit" (a very little bit- you'd have to consume a shed load of it pretty much every day for a long time to actually harm yourself), 200 times more pyrrolizidine alkaloids in beer than comfrey and nobody is listing beer as unfit for human consumption so why comfrey?

What's the issue with sweet woodruff please? I aint heard about that and I'm always up for learning more about plants.

It was used in childrens drinks and sweets in germany, it does have a gentle saporific effect. There was problems with causing liver damage and nerve issues. All the children were under three. I cant find the original paper on google scolar, it was in german, and my friend who drank it as child translated it. Its use was banned in children foods but it seems to still turn up in alcaholic drinks. I can't find a single paper that backs up wikipedias claim to it causing coma, there is quite a few papers on woodruff being a strong antimicrobial esspiecailly in the gut against pathogenic bacteria. It might be becoming to useful so the "safety advice" is changing. I can imagine a saporific aimed at small children is open to been used in high quantities. Comfrey only looked dodgy when tablets that effectively contained a plateful of its active ingredients were marketed. There is a higher liver cancer rate in russia where it is commonly used as food, but then there is other cultural habits in rural russia that contribute to liver cancer as well.

 

[winst0nsmith]

Thanks for the info

but then there is other cultural habits in rural russia that contribute to liver cancer as well.

Very diplomaticaly put =)

 

[MattB]

I seem to recall that the 80% commonly bandied about was more a case that if you are in cold conditions, dressed to the nines and don't have a hat on, that you'll lose 80% of heat through the head - rather than 80% of body heat departing via the bonce under 'normal operation'.


As has been pointed out though, the proportion will rise as hypothermia sets in, as less heat will be lost from extremities due to vasoconstriction.

 

[Sappy]

To quote Mr T " take care of your head because that's where all the happy thoughts are made"

 

[udamiano]

Definitely a myth, skin temp is roughly about 35ºC at rest. Its just that most people cover-up everything but leave the head exposed, and you loose heat through radiation at a greater rate from exposed skin than you do from covered. when the body experiences severe cold and the core temp starts to drop then the blood is withdrawn from the extremities, the skin surface at these point becomes cold as they are no longer getting heat from the blood, but they do however start to radiate less as they cool, as the differences between themselves and the environment becomes less, but are now subject to freezing like any meat in a freezer will do (not a pleasant thought)

It should be noted though, that the same applies in hot environments as well. but in this case the heat is absorbed.

 

[Andy BB]

I may be wrong (nothing new there!), but I thought that the body doesn't treat the head as an extremity in cold weather (other than the extremities of the head - ears, nose etc)? It still keeps good blood supply going to the brain, and I thought to the scalp as well. And anyone who has had a head wound knows that even small scalp cuts bleed copiously, with substantial numbers of veins very close to the surface. So - in practical terms, the head - per square cm - will probably lose more heat than a similarly exposed arm or leg, or stomach. Its a bit like cooling yourself down quickly by holding your wrists under cold water - the closeness to the surface of the blood vessels in the wrists transfers that coolness very quickly to the rest of the body.

However, I think the "40-60% of heat loss through the head" statement only relates to when the rest of the body is covered.

 

[Filterhoose]

Is a myth a female moth?



Windy

 

[rik_uk3]

Urban myth, was on TV recently, broadly speaking heat loss from any exposed skin is the same, whether its your leg or your head.

 

[John Fenna]

If you do not wear a hat then naturally you will lose a huge proportion of the heat you lose from your body from your head.
If you went out with a hat on with your buttocks exposed you would lose the greatest proportion of the heat you lose from that part of your body (body part chosen to to represent a like amount of flesh - no scatological reason!)
The bloke who forgot to do up the fly of his windpants on the race to the North Pole lost a huge amount of heat forom the unprotected area, developed frostbite and needed an emergency circumcission!
If you leave a body part uncovered then that area, devoid of insulation, is where you will lose body heat as oposed to bits that are covered!