Method Exit Bag + Custom Mask

[Hollie]

I found I had a pack of three dust masks. Each one had a plastic and rubber valve that allows air flow one way but not the other. That got me to thinking about the main problem with the exit bag from my point of view - getting rid of CO2. My intent was to make a mask I could wear inside the exit bag, that would allow me to breathe in the inert gas from the bag, but have the exhaled gas leave the bag through a pipe.

I took the dust mask and took off the valve (it was a snap-together sort), and made a second hole for another valve. I then took a piece of plastic sheeting and lined the mask, cutting holes in the plastic to correspond to the mask. It was a bit tricky but I was able to make some folds that made it sit well inside the mask. I was then able to snap the valves in place, facing in opposite directions such that one valve would let air in and the other would let air out. On the outside of the mask, I glued an "out" pipe (a small section of plumbing pipe that I happened to have) to the out valve which was easy. Connecting it to a smaller pipe was easy enough to do with a tube made from a finger from a rubber glove which I was able to stretch over the pipe.



The plastic makes for a really good seal to my face, but I would probably secure the mask to my head with a few wraps of clingfilm to be sure it's going nowhere.

My method is to put on this mask, and pretty much use an exit bag as normal. One thing I can do is "breathe out" the air from the bag before I start the flow of gas. I'm thinking at this point a better seal at the neck would be good, such that I can't over-pressure the exit bag...

I would love to hear your thoughts on this :)

 

[TiredHorse]

So would the discharge tube be somehow arranged to exhale the CO2 beyond the eb, thus leaving the supply of ig in the eb uncontaminated by CO2?

 

[Hollie]

So would the discharge tube be somehow arranged to exhale the CO2 beyond the eb, thus leaving the supply of ig in the eb uncontaminated by CO2?

Yeah. I sort of picture like piping coming out and down my neck and exiting a distance below where the bag would be round my neck

 

[TiredHorse]

Yeah. I sort of picture like piping coming out and down my neck and exiting a distance below where the bag would be round my neck

You might have difficulty with creating and maintaining the necessary flexible neck-band seal around that piping.

 

[Hollie]

You might have difficulty with creating and maintaining the necessary flexible neck-band seal around that piping.

Thank you, that's definitely something I need to make sure of

I'm going to try it with 5mm (3/16 inch) plastic piping like the stuff they use in hospitals as this is about the narrowest thing I'd feel comfortable breathing through. Perhaps I need something like clingfilm to wrap around my neck to depress the pipe into my flesh a bit without cutting off my breathing and whatnot...

 

[TiredHorse]

If you're using thin tubing for the exhale piping, you might consider taping it to the tubing that's supplying the N2, since that will need to be entering the eb anyway. That way there'll only be the one gap in the elastic band.

Be careful not to use tubing that's too small, though. The last thing you want to do is restrict the removal of CO2.

At the risk of sounding negative, however, I think you might be overthinking this. The volume of N2 in an eb is reliably adequate to dilute the CO2 without the need for any sort of isolation mask, and a 15Lpm flow is pretty well proven to flush the CO2-laden N2. It's an interesting theoretical exercise, but I don't think you actually need the mask.

 

[Hollie]

At the risk of sounding negative

Not at all, it's entirely possible it is overthinking on my part

 

[Alysia]

I think it's perfectly understandable and something to respect that you want to minimize the chances of anything going wrong, in this case, having concerns about CO2. You know, measure twice and cut once, or, what's well-planned is halfway done. :) However, I really do think you have nothing to worry about in terms of CO2.

The 15 liters per minute flow rate comes from testing that Exit did using air.

Essentially, 15 liters of air into the exit bag per minute was enough to keep the CO2 levels inside the bag at more or less zero. Using air meant that the body's natural respiration was able to continue and the subject kept producing CO2 as normal. This is not the case, however, when the bag is at practically a 0 % oxygen level (when air is replaced with an inert gas) and you enter the bag with fully exhaled lungs. While I'm certainly no expert on human physiology, I wouldn't think it's too unreasonable to assume that after a few deep breaths in an out of inert gas (and starting with fully exhaled lungs) the body will likely very soon be exhaling only trace amounts of CO2. Furthermore, if 15 liters per minute of air (which allows CO2 production to continue as normal) was able to keep CO2 levels from rising, then 15 liters per minute of inert gas certainly will, and so should, in fact, a much smaller amount as well.

Provided you do the recommended 1 to 2 minute hyperventilation,

exhale your lungs fully and then hold your breath until you're inside the exit bag, I really think the chances are practically zero that you will have CO2 causing any problems. I'm afraid trying to build something to eliminate CO2 even further just complicates things unnecessarily and a more complicated system/setup tends to often be more prone to failure than a simpler one. Hope this is helpful to you. :)