I'm allowed 1 silly question of the day and here's mine.

While on the WRT I used my Alpkit Hunka XL bivi and was tasty warm both nights.
But I did get a frost bite on my lip as my face was exposed, but don't worry (not that you do anyway) it's clearing up now.

On the last night I slepted next to Mick Knight who had the same set up, but he slept with his head completely inside the bivi bag.

What with breathing out CO2 and re breathing it in as well. Yes Mick survived I didn't leave his body there and we briefly chatted about it, but I'm not 100% sure if I'd feel safe with my head fully inside a closed bivi bag and what about the condensation.

My question is
Is it safe to sleep in a close up a breathable bivi bag for 8 hours at night?

Depends how much you fart I guess.

The air you exhale is only about 5% co2 and a bag like a hunka will never be that well sealed.

I had a rab Bivi bag that completely zipped shut with a 1" mesh strip alongside the zip. Not that I ever zipped it shut as it was awfully claustrophobic.

Don't know about a hunka but if I fully close the clamshell on my helium depending on out side temps the condensation can get quite bad

I'd say he's a daredevil or has some sort of ventilation going on... Probably a dare devil and I would have thought he'd probably have woken up a few times in the middle of the night when his co2 levels got dangerously high* and his body gave him the nudge...

But... Would you wanna take that risk!!

Thats just my twopence

*in general and for most people the drive to breathe is high CO2 in the body... respiratory centres (wherever the heck they are) in the body tell you, mate... you nweds to breathe**
** NB I'm not a doctor

From Alpkit https://www.alpkit.com/develop/bivvy-bag-development

Not sure about the lipping next to Mike!

That aside I can remember a company withdrawing from sale their tunnel bivi because when the door was closed the co2 levels became too high. Can't remember who they were though.

Seeing others wake up in what looks like a sauna I'd go for the ventilation option.

Perhaps have a buff over your face.

Are you sure it was frostnip? I didn't think it was that cold during the WRT. I've bivvied out around -8c and not suffered.

I'm a side-sleeper and would usually have a hat on and mibbe the hood of my jacket up if it's very cold. Can't say I've ever had such a problem.

Both my bivvy bags have mesh panels to aid "breathability" though I rarely do the bag up and use these(hence pulling 24 ticks out of me after one trip).

fatbikerbill wrote: ↑Sat May 11, 2019 5:55 pm Not sure about the lipping next to Mike!

Spelling error edited, cheers

CO2 aside. What you will end up with in a closed bivi bag is condensation. A well hydrated person will exhale a considerable amount of water vapour during a nights kip. In cool conditions that’s gonna turn to liquid water all over your bag. Not ideal.

On arriving home from the WRT I also chapped my nose and lips after waking up with my head out the bag something I wont be doin again May have something to do with Butty Bach too tho

By the... I'd like to add... Thats not a silly question john (climber)...

Good question and I'd go with what jonnystorm says.
I only know from own experience in Alpine tents like the old O.D. Summit (GTX Exchange) or Rab Latok Summit (eVent) and Locus Djedi (DCF-eVent) that two persons in them, completely closed, are absolutely okay for CO2 levels. Also in thin air, when you breathe more heavily.

Frostnip on the lip? My one silly question...

Having likely slept more than 100 nights at -10 °C or less (down to -40 °C) I never got frostnip, neither on nose, nor on lips. I often use a buff I pull over my nose, but that's because I've got a sensitive nose for dry air and after multiple nights in the cold with rocket snotting during the day, I easily get a light nose bleed.

Sounds more like dry lips or a burst of HSV.

Are you sure it wasn't just a chapped lip John? You didn't look particularly frostbitten on the Monday, just a bit startled.

Unless the bag is completely sealed CO2 won't build up to dangerous levels. The gas exchange across your lungs when you're asleep will be lower than the gas exchange between the inside of the bag and the outside world.

A wee bit of a follow-up on this...

I spent last night at the summit of Cairngorm. Anyone who has been there will know it's pretty barren, so I was sleeping on a big rock shelf. It turned pretty cold overnight and, though I had my head partially uncovered, the inside of my bivvy bag was wet this morning. Only on the bottom though, between the Exped mat (inside the bag) and the base of the bivvy bag itself. I don't mean just damp, I mean actually running with water. The bag is a RAB Ascent which has an Event upper and a fully waterproof lower. The upper was fine inside, as was my sleeping bag.

Thanks all for your replies.

I'll take a buff and keep my face exposed from the bivi bag

a wee bit of follow up

I don't mean just damp

Was there a yellowish colour to the 'water' and a smell of ammonia?

LOL, I was lying in a slightly foot-down position so I'd have expected that to accumulate at the other end of the bag.