UKC

Just got back from a trip to Cairngorm where we dug and slept in a snow hole, it was fantastic fun and I wanted to share a few tips and ask a few questions for next time.

Tips

* Take a good shovel each so you can all dig, a saw for hard snow, and a probe for measuring the drift depth.
* We dug 2 doors, and dug towards each other so we were both working, then blocked up 1 door, this seemed to be a good system.
* Have a range of sites in mind, as the snow might not be deep enough or too hard at some sites.
* Construct a good shelf for all your clobber!
* Keep an axe and shovel inside so you can dig out of the frozen door block in the morning.
* Smooth the roof to keep drips to a minimum.
* It takes a long time - 2 hours in perfect snow to dig a 3 man hole, much longer in hard snow.
* Dig just wearing waterproofs, keep the base layers dry for night time.

Questions
* How much of a ventilation hole do we need to prevent suffocation? If it is snowing outside, do we need to keep opening up the vent or will we be ok for a night?
* How big can we make the hole without danger of a roof collapse?

Any other tips or quesions

In reply to ablackett: Good tips!

Not sure about size of ventilation hole, but worth considering that carbon monoxide sinks, so a low level vetilation hole might be a good idea.

Did you light a candle or two to keep the chill off?

BW

In reply to Baron Weasel:


No, as we were worried about Carbon Monoxide, as it turns out we left a big ventilation hole so I don't think it would have been a problem.

Our ventilation was so effective it never got above freezing in the hole so we didn't have to worry about drips either!

In reply to ablackett:
My tips...
Trangia lids are good for digging/scooping/scraping and
you will discover if you are claustrophobic but hadn't realised.

No real idea how thick the roof should be but we pogoed on the roof in the morning and it didn't budge.

In reply to ablackett:

You ideally want a flow of air through the hole so a door and a vent are probably best. It'll depent on how many bodies are in there. Carbon monoxide poisoning has happened before in snowholes.

If it's snowing and it's drifting into your snowhole you will have to get up regularly to dig it out. Keeping a shovel handy for this is more efficient than using and axe. Failure to do this will result in carbon monoxide build up.

The largest I've built was about 5 metres long by 2.5 deep and 2 high. The roof had slumped by about 20cm in the morning. This was in good conditions. In a thaw it would probably have collapsed.

It's worth carrying a transceiver and sticking it on send in the back of your hole so that if the worst happens your body can be found without too much effort.

Trailing a rope from the door can help relocating the site in a hooly after a piss. Or take a piss bottle.

In reply to Craig Mc:

I thought that Carbon monoxide was only a problem if a stove or candle are left on for an extended period. Carbon Dioxide would be the other problem from all the breathing, but I don't know how much of a problem.

In reply to ablackett: Aye you're right. Carbon dioxide will still harm you though. Something to do with not enough oxygen in the air so the body starves of it - not good.

In reply to ablackett:


No, it is potentially a real problem. A load of cavers died in the Dales a few years back when free diving a sump via an air bell. They had been to the air bell from the down stream side of the sump 1st before doing a through trip and didn't realise that the earlier visit had used most of the oxygen.

BW

In reply to ablackett:

I made a snow hole the other day above Idwal Stream, we forgot the snow probe and just had one shovel. Snow was quite soft so wasn't difficult to dig and the drift seemed to be about 3m deep, but we found that the rocks were closer than we thought! We ended up digging straight down 1m then into and diagonally along and upwards through the drift to try and get round the rocks! Ended up with a big cave for two, but had a sloping bottom which meant we were constantly sliding down in the night.

So make sure you build em with nice flat smoothed ledge for sleeping!!! Sounds obvious but after we'd dug a big hole and got our stuff in for a brew we couldn't be bothered to dig again and cover our stuff in snow.

I was planning to use my axe to dig another entrance but it seemed like a pointless effort with a tiny adze against a proper shovel, so we just took turns digging and clearing which seemed to work well. (Also snow seems to stick to my adze instead of falling off making it tricky to dig quickly).

I was wondering about the roof myself - as I discovered in the morning we had dug close enough that the light was shining through, I guess that means less weight for it to bear and less danger if it collapses? Rather than a thick roof that is heavy but stronger??

Personally I think if you make it as arched as possible it should be ok. I would be interested to know if anyone has had snow cave collapse without someone walking on it?

I would add Carbon Dioxide isn't a problem unless your snow cave becomes properly airtight due to snow or collapse and you then run out of oxygen to breath, CO2 is heavier than air and will drain out of your low entrance along with the cold! Carbon Monoxide however preferentially replaces oxygen in the blood and is very dangerous in confined spaces, requiring a much smaller amount to cause problems and has caused a number of deaths in the last year due to BBQ's, gas fires, generators etc. Basically don't ever leave anything bigger than a candle burning when you go to sleep - as you may not wake up and if you find yourself short of breath then get out quickly. It is caused by incomplete burning of carbon - basically a yellow flame produces Carbon Monoxide (very bad) and a blue flame produces Carbon Dioxide (better).

Poking some holes with the snow probe into the roof or sides is a good idea for some vents if you want.

In reply to ablackett:
Slept in a snow hole in Canada a few years ago. Brother-in-law dug whilst I shovelled all excess snow out. Things we learnt / did we're:
1. Put a kink in your entrance tunnel as it stops a lot of wind
2. Make sure you can sit up in your sleeping area
3. Dig an alcove for cooking with a few vents made with ava probe
4. Make floors and sleeping areas very level
5. Sleep with your transceiver on

In reply to ablackett:

Not so sure that 'extended period' is absolutely correct. There's a good article in the Alpine Journal 2012 about carbon monoxide poisoning and mountaineering.

In reply to ablackett:

cool post and neat ideas (2 digging towards each other is lateral).

thoughts on your Qs:
- not sure how big a hole other than big enough to not worry about it, which to my mind means a couple of holes big enough to poke an ice tool thru (handle first). even better, a door (keeps things cold to minimize dripping).

tips?
after 'avoid snow holes where possible' how about:
- dig just before dark when the temps are dropping, the snow is drying and you can jump into a sleeping bag with that hard earned warmth.
- for a door ive used a backpack left just outside it (in a dry bag if youre smarter than me) that i kicked occasionally then pulled back to clear.
- personally i rely on my s/bag for most of the warmth, the shelter is there to stop wind and cut the cold if its nasty. id rather a hole below freezing (just) than too warm.
- have an intentional gradient to the ceiling so it drips towards the door.
- again with a tarp: dump excavated snow onto it and drag away to despose of. beats double handling it

another snow shelter is the lazy mans igloo where you dump your gear in a pile (a tarp is nice here) and pile snow thick over it. smooth it off, dig out your gear thru a tunnel and dig downwards. can be long and narrow or traditional igloo shaped.