Franconia Ridge Rescue Followup

[Maddy]

By space blankets, I assume you're talking about the foil-like 'emergency blankets' they sell? If I'm not mistaken, they're considered most effective when actually touching the skin.

Yes, those are the ones. We used them on our patients after surgery who were a little chilly but we really never saw any great results with them. Eventually, they were no longer part of our standard equipment.

 

[DougPaul]

Re space blankets:

IIRC, they are red on one side and silver on the other.

In line with Grayjay's original suggestion, IMO they are better than nothing, but as stated, IMO a bag (bivy sack) is better in the wind (and in general).

I wouldn't count on either a space blanket or a bivy sack alone to keep one toasty warm. They block the wind and water and provide a small amount of insulation. They are best when used as a wind/water blocking shell with insulation inside: eg sleeping bag, down jacket, fleece jackets, down pants, fleece pants, etc.


BTW, the silver side is intended to reduce radiational cooling amd is most effective when on the outside. Radiational cooling is not generally much of a factor unless you are under a clear night sky.

Doug

 

[Woody]

I wouldn't count on either a space blanket or a bivy sack alone to keep one toasty warm. They block the wind and water and provide a small amount of insulation. They are best when used as a wind/water block with insulation: eg sleeping bag, down jacket, fleece jackets, down pants, fleece pants, etc.

Doug

I have been bringing an Adventure Medical bivy bag with me for several years in all seasons on my day hikes. I even bring it when hiking around Mount Wachusett. As DougPaul points out above, I don't rely on it to really keep me warm, but to help stay dry. For warmth I have my down parka, and my gore-tex parka and pants in my pack and I ussually have fleece shirt in there as well. I don't ussually bring a stove but I have on occasion. I do carry plenty of water and food. A few times I have also carried my 20 degree down bag with me as well. It is pretty light.

 

[Kevin Rooney]

Re space blankets:

IIRC, they are red on one side and silver on the other.

Doug - I think the one you're referring to here is much stronger than a space blanket which tend to be rather flimsy. I've got one of these red & silver units, and it's really more of a tarp and even has grommets. I got the idea of carrying one when I assisted in a rescue and the EMT's used one as a final 'wrap' around the injured person. If it's the one I'm thinking of it's very strong, but the downside is it weighs several ounces.

 

[Lou Hale]

By space blankets, I assume you're talking about the foil-like 'emergency blankets' they sell? If I'm not mistaken, they're considered most effective when actually touching the skin.

Thats interesting to hear. what I know about radiant barriers is that they are only effective if there is an airspace otherwise they just conduct heat away from you.

 

[DougPaul]

Doug - I think the one you're referring to here is much stronger than a space blanket which tend to be rather flimsy. I've got one of these red & silver units, and it's really more of a tarp and even has grommets. I got the idea of carrying one when I assisted in a rescue and the EMT's used one as a final 'wrap' around the injured person. If it's the one I'm thinking of it's very strong, but the downside is it weighs several ounces.

I think they used to call the red and silver blankets with gromets "space blankets". Whatever they call them, they are more of a medium tarp weight. Something like http://www.rei.com/product/407106 (12oz).

Perhaps you are referring to the aluminized plastic (polyethlene?) sheets (similar to http://www.rei.com/product/407104 or the bag version http://www.rei.com/product/357005, both 3oz).

Looks like they are attaching the word "space" to a wide range of products.

Doug

 

[Kevin Rooney]

Doug -

I agree - 'space' gets applied to different products of varying durability.

The first link, the one to a 12 oz. tarp - is, IMHO, about the only one worth carrying. The thinner blanket/bag ($3.99, used to $.99) are quite flimsy, and tear easily. I suppose they're fine to carry in the glove compartment, but provide false security above treeline.

 

[nartreb]

Yep, the thin one is quite flimsy. I tore one to shreds trying to get a sleeping bag inside it one winter (just practicing inside my tent).
I actually used one in an unplanned bivy this summer; it kept the rain off and can't have hurt but it sure didn't keep me warm (temps around 50 degrees - I wore a fleece jacket, raincoat, rain pants, hat and gloves inside the bag).
It weighs nothing and it's tiny, but it's not winter gear.

 

[Kevin Rooney]

Yep, the thin one is quite flimsy. I tore one to shreds trying to get a sleeping bag inside it one winter (just practicing inside my tent).
I actually used one in an unplanned bivy this summer; it kept the rain off and can't have hurt but it sure didn't keep me warm (temps around 50 degrees - I wore a fleece jacket, raincoat, rain pants, hat and gloves inside the bag).
It weighs nothing and it's tiny, but it's not winter gear.

Yes - I think a better solution is one or two HD trash bags, the bigger the better.

 

[DougPaul]

By space blankets, I assume you're talking about the foil-like 'emergency blankets' they sell? If I'm not mistaken, they're considered most effective when actually touching the skin.

Sounds like an aluminized thin plastic sheet. Eg http://www.rei.com/product/407104.

Thats interesting to hear. what I know about radiant barriers is that they are only effective if there is an airspace otherwise they just conduct heat away from you.

If the sheet is in contact on both sides, it is little different from a plain plastic sheet--a moisture and wind barrier with only a tiny bit of insulation. The aluminum coating does not affect convection, conduction, or evaporative cooling (the plastic of course does affect these).

If a shiny side is exposed, the shiny coating will reduce the radiation both emitted* and received by the same amount. Radiation gives a net heat transfer from the warm side to the cool side, so reducing it can make a difference under a clear night sky (very cold) but only a smaller difference under trees, under heavy clouds, indoors, in a tent, or with a blanket on top. (all facing relatively warm objects).

* All objects at temps above absolute zero emit radiation--infrared at normal temps, visible at burning temps. The amount is multiplied by 1-reflectivity_of_the_surface. A shiny surface reduces this multiplier. See http://en.wikipedia.org/wiki/Thermal_radiation and http://en.wikipedia.org/wiki/Black_body (includes an estimate of the radiational heat losses from the human body).

My guess is that touching the skin with the aluminized plastic isn't the key issue in reducing the radiational cooling. (Touching the skin will, of course make a difference to conductive, convective, and evaporative cooling.) The best place for the aluminzed plastic from the standpoint of reducing the radiational cooling is on the outside, whether the inside contacts skin or clothing. (I should note that since the aluminized plastic is fundamentally a plastic sheet, all the issues of where to place a vapor barrier (VB) apply--and the best place for the VB is next to your skin. So, it would actually be best overall to place a plastic VB layer (aluminized or not) next to your skin, then your insulation, and then the aluminized plastic layer.)

Stated another way, if you have two insulation systems with plastic sheets and conventional insulation (eg fleece, down), the best plastic layer to aluminize would be the outside one.

If you have only one sheet of aluminized plastic--you have the choice of using it on the inside as a VBL or on the outside to reduce radiational cooling. Which is better probably depends upon the situation.

Caveat: I think the above is accurate--there is some guesswork involved.


A thermos bottle works by using a double shiny layer with a vacuum in between. The vacuum cannot transfer heat by convection, conduction, or evaporation and the shiny layers reduce the rate of radiational heat transfer.

Doug

 

[DougPaul]

Doug -

The first link, the one to a 12 oz. tarp - is, IMHO, about the only one worth carrying. The thinner blanket/bag ($3.99, used to $.99) are quite flimsy, and tear easily. I suppose they're fine to carry in the glove compartment, but provide false security above treeline.

I carry the Adventure Medical bivy (an earlier version of http://www.rei.com/product/750938) in winter (7oz). It is far more durable than the plastic sheets. Mine is repacked and ready for a second use.

I only carry the 3oz aluminized plastic bag in summer.

Doug

 

[sardog1]

You did us all a service by posting a link to those emergency bags - thanks.

Seems like an obvious question, but ... wouldn't an orange bag be the obvious choice? Unless perhaps you were planning on using it as a 'regular' bag?

Another question - I carry an emergency bivy (Adventure Medical). Do you think it's a good idea to carry both the bivy and the Blizzard bag, or do you think the Blizzard bag is sufficient?

I would have bought the orange version had I been thinking more of my welfare than my wallet. I'm only planning on using it in extremis.

Your bivy, plus the Blizzard bag, plus a foam pad, makes sense to me. You'd add insulating dead space between the bivy and the bag, plus reduce convective cooling, with only an additional 6.9 ounces from that bivy. (The Blizzard bag weighs 12.3 ounces or 350 grams.) I'd want to make sure that the bag will fit inside the bivy without compromising the former's effectiveness. I carry a lightweight tent fly for the same purpose.

 

[DrewKnight]

Solo travel -- itinerary looms large in my safety plan

Good points, Maddy. Many people take 6 walks in the woods (daily for dogs or exercise) to every 1 full-scale hike in the mountains, but don't consider what it would be like to lie on the ground for a few hours until someone realized they were over due...

In my case, it's frequent solo early-morning mountain bike rides, often in the shoulder seasons when there aren't many people on the trail. My first line of defense is a definitive route plan (which I try not to vary from, no matter how much fun I am having) and a slightly pessimistic return-time, left on the dining room table for my usually-sleeping family.

I have had a couple minor incidents well past the point where casual hikers and bikers are likely to happen by, and the thought of laying on the ground unconscious and cold does play across my mind. My riding pack always has an extra fleece layer, water, food, a light, and a first-aid kit -- but if you go ass over teakettle on the trail, it's not certain that any of those will be deployed in a timely manner. In the end, I have to hope that my wife will call the cavalry if I am significantly overdue, as I am usually irritatingly punctual.