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Last weekend I spent a night in an igloo. The event was organised by professionals (it was a company retreat) and during the night there was always one of the guides awake making rounds and checking on the people in the igloos. They also made sure that the entrances stayed clear (there was some heavy snow fall).

For Oxygen the method the guides used was to put a small candle inside every igloo: their reasoning being that should the candle go out the people in the igloo would have to be evacuated because the Oxygen was getting low (so that was what they were checking on regularly).

I was wondering:

  • How real is the danger of suffocating in an igloo with an open entrance, but without air holes in the cupola?
  • How real is the danger of suffocating should the entrance (and any potential air holes) be covered by heavy snow fall in the night?

I'd be interested in an estimate of how much time can pass before you should start to be worried...

And maybe as a follow up:

  • How often would one have to check for clear entrance / air holes in case where there is no person staying up all night?

Let's assume an igloo for 3 people (maybe 2m diameter), built with a 'siphon' style entrance of maybe 50cm diameter (i.e. the entrance makes a bend that is the lowest point of the igloo, thus trapping the warm air inside).

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    I'm not an expert on chemistry, but it seems to me that the candle won't go out before CO2 buildup might become toxic... lack of oxygen won't happen as quickly in a confined space. – Gabriel C. Jan 17 at 18:15
  • It is pretty hard to accidentally suffocate from low 02 levels and high C02 levels as a healthy person will wake up gasping for air in a panicked state prior to being anywhere close to being in danger. – StrongBad Jan 18 at 21:11
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Not as real as the danger of death by exposure and hypothermia while outside the igloo.

Your risk of asphyxiation in a snow shelter depends largely on its size, and the number of people inside it. People have been living in igloos for hundreds if not thousands of years, and not just for one night or two at a time, but as permanent dwellings also. Igloos wouldn't make a very good home if you were at risk of asphyxiating in them every night.

I've seen figures claiming that at rest an average person can breath with 1m3 of air for 8-10 hours before all the oxygen is consumed. The average igloo is 3-4m across, which would give you about 7-16m3 of air, so even without ventilation you should technically be safe overnight, but things like elevation, snow density and even your V02 max will be a factor, so proper ventilation is always advised when constructing a snow shelter.

I've spent countless nights sleeping in snow shelters of all varieties, and I build my own igloos. The trick to building an adequate shelter is balancing the size of your shelter and the amount of ventilation. Smaller means warmer, larger shelters take longer to get warm. Too much ventilation and your shelter won't retain any heat either. I usually put the ventilation hole close to my head, and make it just big enough that I can feel the fresh air on my face, but not so big that it makes me cold.

Freshly fallen snow is a welcome addition to your snow shelter, as it provides excellent insulation. Your concern with the falling snow cutting off your air supply is minimal. It's common to block the entrance of your igloo for added insulation, and it's easy to poke your vent hole open again with your ski pole, If you're like me you wake up often enough in the night that you have plenty of opportunities to open your vent again if it's snowing and you're concerned about it. All in all you're going to be fine overnight in an igloo as long as it's built right and doesn't collapse on you.

  • It has been a while, but do you have sources to back this up? I'd be especially interested in how important the air holes are, given that your igloo has an entrance that is not 100% closed up. – fgysin Apr 15 at 6:55
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It's a real danger, especially as the night goes on. Snow has plenty of air in it, and is somewhat breathable, but the moisture from your breath and the heat you generate is going to starting melting the snow and then freezing, so that there is an ice shell on the walls and ceiling. This is especially a problem in snow caves.

However, so long as you have an unblocked entrance and clear air holes, you should be fine. The snow that is falling will be more breathable than the snow the igloo is made out of. Just make special care to build the entrance in such a way that it takes quite a bit of snow to fill in, and remember to keep your shovels inside, in case you need to dig your way out.

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    "It's a real danger" - this seems to contradict @ShemSeger's answer above. Do you have any data, accident reports, or anecdotes to back this up? I have no idea myself! – aucuparia Jan 21 at 12:20

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