Stranger : I was under the impression that NASA space suits used reflective metal (Aluminum / Chromium) barriers - something they borrowed from the cryogenic industry. Also the radiation barriers need not be the top layer as we use them inside cryogenic pipe insulation.
I’ve seen sleeping bags which have a breathing tube. I think they were rated to -80 or so assume F. The breathing tubes get your breath through the very thick down and does help to mitigate the cold air somewhat. I’ve also seen some low temperature breath heat exchangers and have something, I think metal mesh, perhaps copper, to capture the heat in the exhale breath to preheat the next one. Though that was headgear designed for awake time not a sleeping bag.
I’ve spent considerable time outdoors in freezing weather, including overnight, wearing nothing but Stone Age clothing. Fur clothing is extremely warm (fur keeps Arctic animals alive & well without shelter or fire, after all), and many are also quite lightweight, unless made using chrome-tanned modern shite, or too thickly-furred winter-killed animals. I can function 100 % unencumbered wearing a braintanned September deer hide parka and leggings, while keeping as warm as with any modern store-bought winter wear. Same goes for footwear.
The downsides to fur clothing is they don’t fare well at all with water (hence gut and grass overcoats, or going naked in the rain), they aren’t very long-lived in hard use (although most modern clothing isn’t either), and numerous insect species use fur as food / kindergarten, rendering stored fur clothing kaputt in short order.
At some point, you’re not making clothing any more, but rather, building a house.
Much more.
With adequate clothing, cold isn’t a big issue until - for whatever reason - you become immobilized at high altitude. And a shortage of oxygen will contribute significantly to the problem, as it suppresses your metabolic rate and thus the heat that is a byproduct.
You have a definite bottom at -297F (-183C) when the oxygen in the air starts to liquify.
We got to set our own assumptions though, so if we start out with our cocoon at body temperature there are no limits*. If the heat loss is too high, add another layer.
*The bundle will eventually start compressing itself under its own weight and the flat part will be less insulating.
The insulating effect is only linear to the extent that the thickness is small compared to your overall dimensions. As you make your Maggie Simpson snow suit so big that you’re more of a dot in the middle of it, besides having their thickness the outer layers have larger overall dimensions, so their area is bigger. The thermal conductance is going to be proportional to the area as well as inversely proportional to their thickness.
The story is narrated by a ten-year-old boy living on Earth after it has become a rogue planet, having been torn away from the Sun by a passing “dark star”. The loss of solar heating has caused the Earth’s atmosphere to freeze into thick layers of “snow”. The boy’s father had worked with a group of other scientists to construct a large shelter, but the earthquakes accompanying the disaster had destroyed it and killed the others. He managed to construct a smaller, makeshift shelter called the “Nest” for his family, where they maintain a breathable atmosphere by periodically retrieving pails of frozen oxygen to thaw over a fire. They have survived in this way for a number of years.
Yeah, if I recall the kid had some sort of space suit he used - you’d need to keep a bubble of breathable oxygen around you somehow, and presumably you’d be in and out quick enough your body heat would keep it breathable long enough for you to grab your pail of air.
Somebody explained to me (I have no direct knowledge), that liquid oxygen was a waste product from liquefying Nitrogen (-320F), as well as being a dangerous oxidant, and you could get it for the price of storage and transport.
Please don’t cite that story as having any kind of scientific rigor about pretty much anything. It has an interesting concept, but has holes you could drive a rogue planet through.
Remember, top of Everest the main issue isnt cold (altho that is a issue) but the high Altitude. That’s the killer.
In the Arctic and Antarctic people can survive- for at least a short time- in the coldest temps on Earth.
Fun story for a cold winter day, but not really very plausible, on any level.
But, one thing to keep in mind would be the fact that in a vacuum, the cold isn’t as intense as if there is an atmosphere to carry away heat.
Some years ago there was a claim that in Antarctica, you couldn’t dress warm enough to stay outdoors (-60C) indefinitely because merely breathing would slowly cool you down. I showed that this was not true:
Assume absolutely dry air is inhaled at ambient temp, and that air is then exhaled at body temperature (37C) and 100% relative humidity. Heat is lost from the body due to the warming and humidification of that air.
Assume typical parameters for an adult male at rest: 16 breaths per minute, 1/2-liter tidal volume.
Assume ambient temp of -60C. I calculated heat loss via respiration to be 29 watts. For reference, heat loss (via respiration) when ambient temp is 0C is 19.2 watts, so the heat loss at -60 is only an additional ten watts on top of that. (humidification requires an impressive 13.2 watts, no matter the ambient temperature; this is why the total power requirement doesn’t drop that rapidly with increasing ambient temp.)
Various web references indicate that a normal human bean at rest produces 60-90 watts of heat. If your body is perfectly insulated, you’ll eventually overheat since you’ll only be dumping 29 watts through respiration.
So assuming my clothing is perfectly adiabatic, how cold would it have to be before merely breathing is enough to remove all 60 watts of the heat that my metabolism produces?
In the above scenario, respiration is removing 29 watts, so I need to find an ambient temp that will remove an additional 31 watts. At -60C if humidification takes 13.2 watts, then 15.8 watts is required for heating the air from -60C to +37C. If I want an additional 29 watts of cooling, then my ambient temperature needs to be:
37- (29+15.8)/15.8 * (37+60) = -238C
Not only is this cold enough to damage the respiratory tract, it’s below the condensation temperature of oxygen. So in theory, no matter how cold it is, it’ll always be possible dress warmly enough so that something else kills you before hypothermia does.
Although the assumption of adiabadicity is often made for the purpose of calculationg theoretical thermodynamic cycles and is a reasonable approximation for highly transient cycles where thermal energy lost through a barrier is negligble compared to heat transfer and state changes within a system, nothing like an adiabatic barrier does or ever can exist in the real world for heat transfer in or out of a system over an extended interval. In the case of a system that is a person wearing clothing in a cold environment, the body heat will warm the inner layers of the clothing by a combination of conduction and evaporative transfer (via perspiration and breathing vapor), and thence through the clothing layers to the outside world via conduction. A ‘puffy’ wool or fleece layer will retard heat transfer but cannot stop it. You would not even want a clothing system that is perfectly adiabatic because at any state above the minimum, system heat would inexorably increase until the temperature became uninhabitable.
To return to the comparison to EVA “space” suits, these are the best insulated ‘garments’ (they’re actually more a miniature space habitat) in existance which are totally sealed against the outside environment, and the biggest problem in terms of heat is keeping an astronaut from overheating rather than freezing. Of course, the o.p. is not referring to any kind of adibatic or active thermal control; just “bundling up” with normal clothing, and thus I think we have to assume conventional textile clothing with a very finite R-value.
Stranger
Well, almost anyone in the NE is going to have a combination of clothes that would keep them alive, indoors, pretty much indefinitely, at temperatures as cold as it ever gets (I admit, I don’t know how long it would take for an insulated house to reach sub-zero temperatures). No one there ever escapes occasionally having to go outside when it is hella cold. I have a Columbia coat that is downright hot at everything but the coldest temperatures, not to mention similarly insulated sleeping bags.
It would not surprise me if many people in, say, Texas, were not situated as such.
One thing this conversation is missing is the dramatic difference in heat production between someone resting (e.g. in a sleeping bag) and even just walking around at a moderate pace. A quick non-rigorous search shows one site saying about 60 cal/hr resting, and 300 cal/hr hiking. So the amount of insulation necessary is vastly different for sleeping and walking/working
For instance – and i can confirm this from experience – at -15 F a sleeping bag rated to -20 might be necessary for sleeping (with a tent or something as well), but hiking will probably only need an underlayer, a couple thickish fleeces and a windbreak jacket (with appropriate hat/gloves/insulated boots/etc), and even then after a long climb things will start being unzipped.
I don’t think there are any naturally occurring conditions where a well-clothed human can’t survive the cold for half an hour of activity. If you count a big Everest down-insulated parka as a ‘decent winter coat’ and allow a couple layers of hat, insulated boots, and multiple pants layers, then they might even fit into the OP.
That’s a fair point; a lot of those calories go to physical work but you’ll also produce significantly more waste heat during exertion. However, at sub-zero temperatures your sleeping bag is also almost certainly inside of a four season impermeable wall tent or shelter which will add 5–10 °C. I have been in temps below -20 °F (-29 °C) in this coat and some down bib pants, and the only thing that got really cold were my feet and eyes; I certainly got the sense that if I tried to exert myself I’d heat up really quick but taking off a layer would have been immediately uncomfortable and rapidly dangerous if I had any perspiration.
Stranger
Just a ray of sunshine, aren’t 'cha. 