Extreme but effective condensation prevention in a bivy or single wall shelter?

[John Carter]

Okay, so it's raining outside, or freezing, or windy. You've completely zipped up your bivy or single wall tent and are breathing out of a tiny air hole. Or, you've got an overhead vent like the ID Unishelter or Crysallis, or a completely enclosed Nemo GoGo bivy. But you toss and turn at night. You wake up with your mouth away from the opening and condensation all over the torso area.

Now consider using one of these medical face masks that contour to your face with adjustable inflation:

Picture this attached to a lightweight tube that exits the bivy/tent and a rubber band holding the mask to your face. This would send all the moisture from your breath to the outside, would allow you to breath in fresh air, and would allow you sleep in positions that are further from the vent, such as on your stomach.

Great idea or crazy? The tube opening looks small to me, like one could feel a little suffocated, yet this is a medical device used for assisted breathing, so it must allow enough air volume to pass easily in and out. Plus, it has multiple use potential, such as a CPR mask, gravity filter system components, or a small cup with the right cap. Now, where to buy one of these and test it out…

[paul johnson]

Interesting idea.

In warm weather don't forget to put some bug mesh over the tube opening.

In very cold weather, something like the Psolar face mask might be better as your body won't need to use as many calories to warm the cold outside air. Furthermore, the Psolar traps exhaled moisture and uses that to produce heat to warm the next breath of inhaled air.

Still, an interesting idea for other than cold conditions. Many thanks for sharing.

[Douglas Frick]

Right out of "Blue Velvet"…

There is a problem: rebreathing. There isn't an air valve and tubes to separate your outgoing breath from your incoming breath, so the volume of air that does not exit the tube when you exhale will be the first air in when you inhale. (Same problem as shallow-breathing with a snorkel.) For example, for a 2cm tube 50cm long the volume of stale air would be about [corrected] 0.15 liters. A typical resting breath is about 1/2 liter so…a reduction in fresh air.

>Now, where to buy one of these and test it out…

Easy test: get some cheap tubing of about the right diameter (garden hose), cut it to the right length, and use it to breath through your mouth. Breath shallowly and slowly, as you would when you sleep. Most likely you'll just get a slight headache or be unable to maintain slow shallow breathing, but you should have an observer who knows CPR.

[paul johnson]

Douglas,

Three questions:
1) are the tubes that come off of those mask really that large of a diameter?
2) is the volume of stale air really 600cc?
3) does the tube have to be 50cm in all cases?

[John Carter]

Wow, good point. I've both snorkeled and am a certified SCUBA diver, so I should have thought of that one. I suppose getting a mask with a rebreathing apparaus would be prohibitively heavy. And you'd look really, really funny to any passers by.

I'd thought of the PSolar mask, but like PJ imagine it would only be comfortable in really cold conditions. Anyone know what the upper level of remerature range the PSolar mask is cofortable to use in?

One other method I might try out is the Condensation Curtain used in some of the Nemo tents. Here's Nemo's description:

"A classic problem with sleeping in your tent in brutally cold conditions is waking up to find the inside of the tent lined with frost. Highly breathable fabrics will only go so far towards solving this problem. Even a tent made entirely out of mesh would still be lined with frost in the morning! To deal with this issue, NEMO created the Condensation Curtain™ to partition the area in which you breathe. The curtain attaches to the walls and ceiling of the tent and lightly drapes over your body around the chest area, trapping most of the vapor from your breathing in a small portion of the tent. In the morning, you simply pull the curtain aside and get dressed in the dry area of the tent! The Condensation Curtain™ is easily removed, shaken out and replaced."

I'm not sure I agree about frost even on mesh, but I might try an rig some mesh or light fabric over my upper chest to see if that prevents condensation from heading lower down my bag.

[Douglas Frick]

>Three questions:
1) are the tubes that come off of those mask really that large of a diameter?

As best I can tell. CPAP tubing is 22 F ISO (can't find a definition) and my guess is the "22" is mm. Some products mention 2cm inside diameter tubing, which is consistent. (I also initially guessed ~2cm by eyeballing the photo.)

2) is the volume of stale air really 600cc?

Did I make a math error? [Yup.] You know as well as I that the volume of a solid cylinder is pi * r^2 * h.

3) does the tube have to be 50cm in all cases?

Of course not. I figured 20 inches was about right to keep from pulling the hose inside when tossing and turning in a bivy shelter as mentioned above, or to stomach sleep (think snorkel length). Generally, the static air volume in a tube of useful length with sufficient diameter to offer low breathing resistance is still going to be problematic for a sleeper (IMHO anything over 100cc of static air). Rebuttals welcome.

[paul johnson]

Douglas, many thanks for the reply.

You said the diameter was rougly 2cm which negates my first question about the tubing being that large. I was thinking that you meant that it was ~4cm in diameter.

What radius did you use in your calculation?

Good observation on your part regarding the static air volume. Glad you had your "thinking cap" on!

100cc – good to know! Using your #'s, even my calcs are 50% larger than the 100cc figure.

[Douglas Frick]

>I suppose getting a mask with a rebreathing apparaus would be prohibitively heavy.

Yes, but you could use a Y-connector, two simple 1-way valves (one on each side facing opposite directions), and a tube on the exhaust valve that goes outside (no tube needed on the intake side unless you fart a lot). Then your exhalations would go outside and you'd have almost no inhalation resistance. (The slight exhalation resistance might even help you sleep at altitude by increasing the partial pressure of oxygen in the lungs for part of the breath cycle–just guessing, though.)

>Anyone know what the upper level of remerature range the PSolar mask is cofortable to use in?

It's +66F in my office and I'm not noticing any problem with it. According to Psolar, "the module captures the water vapor and returns it to the air you breathe." That should decrease total exhaled moisture because less moisture will need to be added to the inhaled air by the mouth, throat and lungs. Should help a bit with dehydration, although I'm not sure how much.

>I'm not sure I agree about frost even on mesh, but I might try an rig some mesh or light fabric over my upper chest to see if that prevents condensation from heading lower down my bag.

I sleep in a hammock. At -15F outside, my internal hammock temp was about +1F (near the mesh) and I had quite a bit of frost condensed on the mesh by morning, as well as frost riming my quilt top near my mouth. I think the mesh or light fabric idea would be useful. (A silnylon bib might be a good idea in my hammock.)

[Douglas Frick]

PJ wrote:

>>2) is the volume of stale air really 600cc?
>What radius did you use in your calculation?

Yup, math error; thanks. I know that when you ask obvious questions like that that you already know the answer is wrong, but I didn't see it on my own (duh).

The (correct) volume of stale air in the example tube is about 0.15l/150cc.

>100cc – good to know! Using your #'s, even my calcs are 50% larger than the 100cc figure.

That's just my guess. I started playing with infinite series calculations to find the stale volume that would end up causing suffocation, but I had work to do :) I figured that breathing (mixed) 20% oxygen would be about the limit that I would consider to be harmless; the body will adjust its breathing to make up for the deficit, but you're probably not going to sleep as well.

[paul johnson]

Douglas, you know, after reading your replies, i wish i had thought to PM you. i often forget that feature exists. my apologies to you – i didn't think.

[Jay McCombs]

how you gonna make it stay put. To get a good seal w/one of those you have to use the "c-clamp" method (not even going to try and explain w/words) and apply a fair amount of pressure. I guess you could put a head band on it but not sure how well it would keep the seal.

[John Carter]

C-clamp method? Maybe I've watched too many fake medical dramas, but my understanding it that these things are attached to the head with simple elastic bands, such as those that hold up a surgical or dust mask.

I'm intrigued by the Y-splitter idea, but yes, you would need to avoid any beans for dinner (that made me laugh out loud at work and almost get in trouble!). I suppose you could have an intake tube sticking out of the shelter as well, but that's going to start looking REALLY weird! I can just see some campmate coming over to chat and seeing me all tubed up like I've got the bird flu! Reminds me of some old coot who I was trying to sell cherries to at a farmers market. He said he was allergic to people and had to place a kleenex between their lips when he and his girlfriend would kiss. I sure felt sorry for that 'girlfriend!'

But alas, us lightweight hikers had to long ago forego our notions of style in favor of lightest and smartest. I'll have to go down to my local diving shop to see what I can find. But I've got a hunch that the draped curtain will be the lighter and simpler method.

[Roger Caffin]

> Great idea or crazy? The tube opening looks small to me, like one could feel a little suffocated, yet this is a medical device used for assisted breathing, so it must allow enough air volume to pass easily in and out.

Ah … small problem. I will assume you have solved the rebreathing bit (simple flap valve) and are now lying there with 1 metre of tubing (say) and the outside is at -10 F. Where will the moisture go? I suspect that it is going to start freezing onto the inside of the tube about half-way along. By morning you might have a very small hole at the outlet – very small.

Why won't the warmth of your breath keep it melted? It will, for some distance down the tube, but it will cool as it goes.

Might it work with a very short bit of tube and your head close to the door? Hum … maybe.
Be icicles hanging off the end of the tube though by morning! :-)

[paul johnson]

Roger, good thinking. This is perhaps(???) just another example of why this idea, which sounds really good initially, hasn't been implemented before. Don't you just love "brainstorming"?!

The Psolar facemask might be the best idea to date for cold weather breathing.

[Einstein X]

UUUHM,

I think sometimes you (we) can take this ultralight a bit too far. Replacing a 16 oz SB with a 14 oz SB a year after buying the 16 oz? OK. Carrying eight pieces of TP a day? OK. Not carrying water treatment on a JMT record attempt figuring you'll be home by the time your stomach starts to hurt. Already a bit overboard for me but OK.

But using a home made "snorkel" in your bivi so you don't get condensation is where i draw the line.

Wanna sleep in a bivi? You'll get some condensation every now and again. Period. Don't want the condensation problem? Buy a two walled tent.

Just my Eins

[John S.]

If I was using a standalone bivy, I would want an oversized piece of fabric with shock cord in the neck area so I could close off the body area from the head area (of the bivy). Hoodless sleeping bags would be better for this setup. Even then I may still pull my fleece balaclava up over my nose for warmth.

[paul johnson]

when i use a bivy sack (with or w/o overhead wire), my nose is placed close to the opening, thus minimizing condensation due to exhaled water vapor. when i use a hooped bivy sack, my nose is too far away from the opening to make this not practical. if there's a breeze during the night, then condensation is minimized. if not, one must just live with it. however, in many conditions there's less condensation in my eVENT UNI, than in other similarly shaped PTFE bivies.

[mark henley]

But you lose the dual functionallity of having a back country beer bong along on your trip ….

Of course ….. The Keg isn't exactly SUL, but then again … after the first hour, do you really care anymore?

[Michael Mangold]

John: I like your creativity. Talk with your local ambulance crew and see if they will give you one. My experience (and I collect used medical equipment for my non-profit group) is that there will be some extra masks, especially those beginning to show wear.
When you get one, just try it at home for a night and see if it works. Let me know.
Mike

[Mireille Halley]

CPAP masks attach with velcro or neoprene type straps,,,
Your local respiratory therapist or overweight people might kick down a used one too- Don't think I'd strap that to my face, but you might ;)

[John Nestler]

I've been looking for a solution for condensation as well as emergency situations to seal up a bivy during a rainstorm. Using a light 3M respirator and some vinyl tubing I built a "Bivy Breathing Mask." It's quite comfortable although it seems rather bulky to bring on a trip, but it could save bringing along a tarp.

Read more about the "Bivy Breathing Mask" and go here for directions:http://fluidglass.com/outdoor-living/how-to-make-a-bivy-breathing-mask/

This is my first post in the forums, and I'm sure I'll find a lot of interesting advice and projects here in the future.

See you guys around!

– Nessles
http://fluidglass.com

[David Thomas]

As a HX, mass-flow, psychometric weenie (Chemical Engineering / Berkeley), I have a number of thoughts.

1) absolutely, this will reduce condensation in your bivy,
2) it may take a while to adjust to sleeping with the mask on, but users of CPAP machines (my wife is an MD boarded in, among other fields, sleep medicine) have to deal with much more and they adjust.
3) you definitely took the right approach by using check valves close to one's face. You could share the tubing to reduce weight/bulk, but shared (in = out) tubing inceases the "tidal volume" and while reducing condensation in the bivy just as much, it would increase your uptake of CO2.
4) the reduced CO2 in the bivy may be the biggest benefit. I find I react (unfavorably) to the CO2 when I tuck my head inside my sleeping bag then I do to the humidity build-up.
5) the vinyl tubing you used is cheap and widely available. But HPDE tubing (as used in a radiant slap floor) is tougher and slightly lighter in the same diameter. Readily available in 100- to 300-foot rolls, Home Depot will sell it by the foot. There's 1/2", 5/8" and 3/4" available for residential appilcations and larger sizes for commercial use.
6) the length of tubing is a trade-off. Shorter is obviously lighter and offers less restricted flow. But longer gives you more flexibility in sleeping positions.
7) I strongly recommend you wrap some duct tape around your water bottle so you have some repair supplies handy. Even better is the 2" wide, red plastic tape used to seal vapor barriers in homes – it is stickier, stronger, and lasts for years instead of months.
8) **advanced concept** if you consider a tube-in-tube configuration for greater heat exchange or reduced number of tubes, here's the punchline: for X diameter in the inner tubing, you'll get equivalent pressure drop in a length of 2X diameter for the outer tube. e.g. if 5/8" ID works, you'll need 1-1/4" ID for the outer tubing with 5/8" inside of it. That seems really big with a lot more cross section but it is because of the increased "wetted area" of all those tubing sides exposed to the air flow. Probably better to tape two 5/8" diameters together an forego the HX. Maybe with a stick or lightweight plate taped to the end so it stays outside the bivy
8.1) There are HX masks with two check valves built in sold for aspiring avalanche victims so they can breath in and out of a chest-worn diffuser even when buried in snow. You've achieved something similar at a lower cost and weight, but you might look at those units for inspiration and/or parts. For high-altitude work, I like the how such a rig can capture heat from out-going breath and potentially recapture some moisture as well.

[James Klein]

Neat thread, and nice manifestation of the idea John. Thanks for posting.

I have considered making something like this before, this is nicer than what I was putting together in my head…:)

One thing I have used in a similar vein is, dust mask with light fleece pulled over. It took a few tries to find a dust mask comfortable enough for sleeping and I had to punch holes in it b/c I felt like I wasn't getting enough air. The fleece helps hold it in place and acts like a little HTX and captures some of my exhauled moister.

I have wondered if fleece would be more effective directly over my mouth and nose.

[Jim Colten]

interesting project.

I wonder how it'd work for piping exhaled air away from a sleeping bag or balaclava to reduce frost buildup near the breathing hole. Also taking intake air from inside the bag/quilt?

[James holden]

the UL way of course is to use reed tubes found by the rivers … ninjas use em to hide underwater ;)

of course with that mask you can hide from bears in the river … or from polar bears under the snow =O

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