Question of the Day- which is better?

[Tad Englund]

Question of the Day:
Over the weekend I was in a discussion about hypothermia. We were discussing the "burrito wrap" and while wrapping the patient/victim in a Sleeping bag "burrito"; if a "thick" emergency blanket were available, should you place the em-blanket immediately next to the person or could/should it be placed on the outside of the sleeping bags as a sort of bivy?

The agreed upon theory that came up was the emergency blanket would act as a Vapor Blanket: but the "issue" was, being a VP, would the blanket accelerate or impede recovery if the VP was placed next to the skin?
Part of the discussion was, the blanket as a VP, could/would make the body, as it was heating up, misread the retained vapor and inadvertently "turns down" the heat production (similar to what the body does in a normal situation when the skins feels warm moisture). Or would it speed up recovery if paced next to the skin?

Which solution is better?

A. Next to skin

B. Bivy style

C. Don't use the emergency Blanket

D. None of the above

[Steven McAllister]

Maybe outside to reduce breeze.

Perspiration is not an issue when suffering from hypothermia, so the VB concept does not contribute.

I could be wrong though.

[Stephen Barber]

If by "thick emergency blanket" you mean the scrimmed mylar emergency blanket, I would say that the best use in this situation would be to use it as a reflector to a fire built next to the victim. The lightweight mylar sheet works just as well for this as the "thick" one (which has just about 0 insulative value).

YMMV.

[Tad Englund]

Steven, I think all parties would agree the perspiration might not be an issue in the moderate to severe cases; until the body starts warming up and then it could be an issue- that is what the question is all about. Can the VP at some point lessen the recovery?

Stephen, no not one of those cheesy thin Mylar sheets, it is a thick blanket like the thicknesses of 2 or more layers of a blue tarps with a Mylar coating on one side.
Far more insulating value than the cheap Mylar sheets but nothing like a sleeping bag or regular blanket or even a thin fleece blanket.

[James holden]

if your patient is now sweating … i dont think they are hypothermic anymore ;)

[Colin Krusor]

I don't know whether putting the mylar radiant/vapor barrier outside or inside a sleeping bag would be best. I suspect the conditions would influence that decision. If the hypothermic person is wet, it might be better to put the mylar blanket inside the sleeping bag to protect the insulation from becoming damp. On the other hand, if the sleeping bag has a very light and breathable shell fabric and it's very windy, it might be better to put the mylar on the outside.

In any case, I think there is one important detail that is often overlooked when people use radiant barriers (like space blankets, etc.). The aluminized surface has not only a high reflectivity to IR wavelengths emitted by a person (in the neighborhood of 10 microns), but also a low emissivity. If the mylar goes inside the sleeping bag, near the skin, the aluminized side of the blanket should face OUT. In this case the blanket itself is relatively warm and it's job is to reduce IR emission. If it were turned around, aluminized surface facing in, the blanket itself would be just as warm and IR emission from the non-aluminized surface would be much greater. IR emissivity of most plastics (including mylar) is nearly 1. Putting a radiant barrier against your skin with the aluminum surface facing you reduces evaporative heat loss but not emission of radiant heat. It would be about the same as one layer of clear cellophane (the aluminum surface does nothing for you in this case).

If the mylar blanket goes outside the sleeping bag, the aluminized surface should face IN. In this case, in contrast to the first example, the mylar blanket is cold. Its job in this case is to reflect radiant heat emitted by the person. If it were turned around, aluminum side out, the blanket would still be cold, so very little would be achieved by the low emissivity of the outward-facing aluminum surface, and the inner surface, facing the person, would have a much higher IR absorbance.

These guidelines hold for use of radiant barriers in any situation, emergency or no. Radiant barriers that are aluminized on both sides are ideal because they work in almost any configuration.

[Jerry Adams]

Same discussion at portlandhiker.org with no definitive conclusions

I think that if you had the alumized layer on the outside, then you would have no radiant heat loss which is maybe 25% of your heat loss. http://en.wikipedia.org/wiki/Thermal_radiation

If you have aluminum layers inside, then you get some benefit but not as much – there is radiative heat transfer happening inside insulation

All the emergency blanket manufacturers have pictures with the shiny side facing in and the colored side facing out. Color at visible wavelengths is different than reflection at IR wavelength (emissitivity). If the colored side has less emisitivty, then it would be better facing in and shiny side facing out.

A lot of people talking about the shiny saide reflecting heat back to you, but I think it's more like you want the shiny side out so you don't emit so much IR.

[Raymond Estrella]

Well really YOU spooning with the victim, wrapped in the E-blanket, with the insulation over you both.

But take yourself out of the equation if it is another big ugly dude I suppose… ;-)

The only reason to use the insulation first would be in a very stiff breeze in my opinion. You don't want the heat blowing away.

[Mike R]

As mentioned, the best way is to use another person's body heat for the rewarming phase. BUT given your question, I might say that using the e-blanket next to skin first with the sleeping bag over top might be faster initially. It can take a bit of time to warm-up a sleeping bag. Then, once the sleeping bag has warmed-up, I'd remove the e-blanket and put it on the outside to reduce the clammy VBL feeling.

[W I S N E R !]

The fastest way to warm someone up is to spoon inside a bag (or two), on a good pad, inside a tent. If you've got a third person, fire up the stove and start making hot water bottles. Hell, get a three-man spoon going…

Provided I had access to sleeping bags, jackets, shelters, etc., I wouldn't bother with space blankets at all.

If spooning a naked or half-naked partner in a real emergency is something someone wouldn't consider, then I don't think they should be a partner.

[Tad Englund]

Spooning wasn't discussed in the original question, but is addressed below.

Colin and Jerry,
What I hear you saying is that the aluminized surface should be facing out if next to the skin; almost like it is reflecting the colder air/wind outside away from the body. If not please explain.

Raymond,
I even have trouble getting my wife to spoon when I'm warm and healthy; I guess I'm doomed if I every get in a bad situation (nobody will want to).

Spooning- I am of the opinion that "spooning" being the right thing to do for a Hypothermic person is a myth- developed by a male co-ed to entice an uninformed victim into a compromising situation.
Spooning puts the rescuer into a situation where his/her health could suffer. It could cause the rescuer to become a liability, never something you want in a rescue situation.

[Jerry Adams]

The aluminized surface should be on the outer layer, facing out, so you emit less radiation

Or, less effective, anywhere inside

Or, maybe it's even better to suspend above you – http://en.wikipedia.org/wiki/Multi-layer_insulation

or, if you have a fire, it's probably better behind you refecting radiation from fire

I think it would warm you up more to be in a bag with hypothermic person, because they would be warmer than ambient. In bag with hyperthermic person is no danger to you. You can wear a base layer and you don't have to cuddle to get benefit.

[Roger Caffin]

> opinion that "spooning" being the right thing to do for a Hypothermic person is a myth
> Spooning puts the rescuer into a situation where his/her health could suffer.
No worries, to each his own.

But you can be very sure that if it is a cold night, my wife and I sleep 'very close together'. And we can put one quilt over the other when we are that close. Benefits:
* Heat loss from 2 sides rather than 3 sides
* Body temperature 'hot water bottle' on the 3rd side
* Double the amount of down insulation.

> entice an uninformed victim into a compromising situation.
When it is -10 C outside???? You jest!

Cheers

[Luke Schmidt]

Back in 08 I recall hearing in Wilderness First Aid that spooning was no longer recommended. I believe there were two reasons give but my notes aren't handy so I could be wrong
1. You don't want to create a second victim by getting another person in a sleeping bag with a cold and wet victim.
2. At some stages of hypothermia an extra body may not be that helpful.

If no one else comes up with more complete answers I'll try to get more info tomorrow but I gotta run soon.

[Jim Colten]

I take a short (16 hour) "wilderness first aid" refresher course at least once every three years (BSA rules for backcountry outings) and also occasionally attend winter camping lectures by NOLS and Outward Bound staff. Not only has "spooning as hypothermia first aid" not been taught during the 21st century, it has been discouraged.

[Ken Thompson]

Don't go and ruin it for everyone.

Just sayin'

[Jerry Adams]

If someone is hypothermic but alive, their skin temperature must be above 80 degrees F? Maybe 70 F?

If you put them in a sleeping bag, you would want to take all their wet clothes off.

If you got in with them, the fact that they're 70 F or 80 F would be no danger to you. Especially if you were both wearing some clothes.

I can see how organizations might not want to recommend because they're afraid of lawsuits.

My 1960 "Freedom of the Hills" suggests warming someone up by lieng next to them wrapped in a tarp or whatever.

[James holden]

a hawt nalgene wrapped in a fleece works better ….

like i said if they start to sweat, they arent hypothermic anymore … so either way will work

of course if shes (or he depending on yr tastes) is young, hawt and willing … spooning is ALWAYS an acceptable method in that case ;)

[Jerry Adams]

Maybe hypothermia treatment should be practiced ahead of time to make sure it's done correctly

[James holden]

Maybe hypothermia treatment should be practiced ahead of time to make sure it's done correctly

if shes hawt i volunteer to demonstrate the spooning technique ;)

[Tad Englund]

Ok, enough about spooning or the whole body thing-

Does the heavy Mylar emergency blanket have any real value? And of so how much?

[Colin Krusor]

Tad, I don't agree with Jerry's various suggestions.

If you put the space blanket where it's warm (inside the insulation), the aluminum side needs to face out. If you put the space blanket where it's cold (outside the insulation), the aluminum side needs to face in. In the first case you are taking advantage of the low emissivity of the aluminum surface, and in the second case you are taking advantage of the high reflectivity of the aluminum surface.

I don't know what your heavy emergency blanket is made of. If it is one of the common nonwoven fabric + film heavy emergency blankets (and not fleece), and there is other insulation available (like a dry sleeping bag), you will almost certainly be able to trap a lot more heat with four standard mylar space blankets than with one heavy emergency blanket. If the victim doesn't have to be carried out (just warmed up), fragile space blankets might be a more effective tool.

[Jerry Adams]

You may be right Colin

but, if the aluminum side faces in, then it will touch the surface that's closer, and will conduct heat well because it's aluminum, so you're not taking advantage of the emissitivity/reflectivity

but, there is a small air gap, so maybe that's enough

is there a difference between reflectivity and absorbtion? I don't think so because the Stefan-Boltzman equation doesn't have different terms for refectivity and absorbtion.

I agree, flimsy (light) aluminized mylar is more weight effective – the actual layer of aluminum that does the reflecting weighs practically nothing – the substrate is where the weight is – which makes it hold up better to abuse, but in an emergency maybe the light weight aluminized mylar is sufficiently robust

[Matt Dirksen]

Reflective barriers are more effective at reflecting heat, but rather ineffective at controlling heat loss.

Coming from the remodeling world, I am often asked about adding reflective materials up in an old attic to help with a houses r-value. The reality is that these materials are only effective when there is an unobstructed film of air between it and other surfaces. Even dust in an attic can degrade performance rather quickly.They can only help with reducing solar heat gain – not improving the warmth of a house in the winter.

Go to greenbuilding websites for more info on this: http://www.greenbuildingadvisor.com/community/forum/energy-efficiency-and-durability/18717/reflective-insulation-attic

[Jerry Adams]

or http://energy.gov/energysaver/articles/radiant-barriers

they say when installing radiant barrier to leave at least 1 inch air space between radiant barrier and hot inside of roof (they talk more about cooling than heating)

analog for space blanket – if the foil is facing inward, there's no air space at all so it wouldn't work so good. If the foil is facing outward on the outer layer, then there is an air space onext to the foil.

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