IS there an AIR rebreather?

[sitkadiver]

I've been following the thread about the new recreational rebreather and have also been eyeing the market for a while. Getting stuff to Sitka can be a pain though so that's the main reason I haven't made the plunge.... Shipping canisters can get expensive I imagine..

The big thing though, is that there is no Commercial Nitrox in town, everyone who dives nitrox is surface supplied/cascade or homebrew.

So my question is this:

Is it feasible to run an air rebreather? Or is that just not effective.

[eliseaboo]

You mean, keep the mix to air? From my limited knowledge it doesn't seem like that would be difficult. I know people who use air as their diluent for lots of dives. Provided you can get an O2 fill it shouldn't be an issue. But you would still need oxygen to add, otherwise you would just end up with an increasing amount of nitrogen in your gas. Where your problems come in would be the sorb, which is typically the limiting factor anyway (again, in my very limited experience)

[dlh]

Yes, check out the KISS GEM system. It is a Semi-Closed rebreather system that just attaches to a standard scuba tank running air or nitrox. Very little training required as well compared to a conventional CCR.

[Joshua Smith]

Yes, check out the KISS GEM system. It is a Semi-Closed rebreather system that just attaches to a standard scuba tank running air or nitrox. Very little training required as well compared to a conventional CCR.

The GEM is designed to work with Nitrox, not air, I'm pretty sure. At least, that's what the official brochure says. Since hypoxia, or not enough 02, is a big concern with Semi Closed rebreathers, you want a drive gas with a higher 02 content, generally speaking. Which is why there really isn't such a thing as an "air rebreather."

Eliseaboo is right- fully closed CCRs can use air as a dilluent, but you still need pure 02.

[LCF]

Sitkadiver, I don't know how much you know about rebreathers or lung physiology, so please forgive me if this is too simplified.

Your lungs are pretty simple gadgets. All they do is put what you breathe in close proximity to your blood, so gases can equilibrate between the two spaces. Venous blood coming back to the lungs is very low in oxygen, so oxygen diffuses out of the lungs and into the blood. The same blood is high in carbon dioxide, which isn't in the gas you breathe for the most part, so it diffuses out into the lung air spaces, and you exhale it. If you breathe into a paper bag, you are rebreathing the same gas, so each breath has a little less oxygen in it, and a little more carbon dioxide. We don't tolerate having our carbon dioxide levels go up very much at all, so you can't rebreathe the air in the bag for very long before you are quite uncomfortable.

The big thing a rebreather does is to remove the carbon dioxide. That way, you can continue to rebreathe the same gas without changing the CO2 levels in your blood. But there's still a problem -- you are using up oxygen, and that has to be replaced from somewhere.

In closed circuit rebreathers, there is usually a source of pure oxygen that either automatically bleeds or adds oxygen to the "loop" (the gas being rebreathed), or that you can manually add, as your monitors tell you the oxygen level is going down. But not all rebreathers recirculate all the gas -- some just recirculate some of it, and replace the gas that is allowed to leave with whatever is in your tank. As you can imagine, you're mixing the gas in the tank with gas that's been depleted of oxygen, and the end result is something in between.

So, if you start with 21% oxygen, you only have five percentage points to drop, before you cannot maintain consciousness. That doesn't allow for much rebreathing, since the gas you are adding is only a little bit better than the stuff you can't breathe any more. This is why semi-closed rebreathers use some kind of Nitrox, so that the oxygen can drop from whatever Nitrox percentage you have, to something you can breathe safely, and still allow enough reuse to make the machine efficient.

As you can see, with either type of rebreathing system, you can't just use air. You either have to have oxygen to add, or you have to start with a gas that's higher in oxygen than air is.

Hope that is helpful.

[sitkadiver]

LCF, Josh, dlh and ELisaboo,

That was pretty much what I expected, you still need O2. Thanks for answering my question.

[Joshua Smith]

Yeah, pretty much. (very good post by the way, Lynne! Super informative, but in plain language.)

Long story short, with your situation in Sitka, it might make more sense to invest in a compressor and some pp blending gear. Might cost about the same as a rebreather.

[camerone]

...or just figure out what a couple of welding bottles of o2 and a whip would cost. You use so litle oxygen with the rebreather system that you can dive on not a lot of oxygen. I get six months or more out of a T-sized oxygen cylinder with a Baby Booster.

'sorb is the PITA to ship around. Heavy and less common than the other supplies.

[Joshua Smith]

...or just figure out what a couple of welding bottles of o2 and a whip would cost. You use so litle oxygen with the rebreather system that you can dive on not a lot of oxygen. I get six months or more out of a T-sized oxygen cylinder with a Baby Booster.

'sorb is the PITA to ship around. Heavy and less common than the other supplies.

You forgot to factor in the baby booster cost!

[camerone]

...or just figure out what a couple of welding bottles of o2 and a whip would cost. You use so litle oxygen with the rebreather system that you can dive on not a lot of oxygen. I get six months or more out of a T-sized oxygen cylinder with a Baby Booster.

'sorb is the PITA to ship around. Heavy and less common than the other supplies.

You forgot to factor in the baby booster cost!

Not really. They pop up used all the time at very reasonable prices, and, if shopped for carefully and well treated, may be re-sold at cost...and maintenance is little more than a few O-rings and some Christolube. You just have to be willing to tie up the $1k or so until you decide you're no longer going to need the booster. You lose time value of money on it, but not really much more.

Actually, most boosters are that way. They somewhat defie the scuba pricing/value laws. Not sure quite why that is...

[CaptnJack]

Actually, most boosters are that way. They somewhat defie the scuba pricing/value laws. Not sure quite why that is...

Boosters, supply cylinders, and name brand compressors with a track record all hold a surprising fraction of their value.

In the boondocks I'd imagine a SCR/CCR taking bulk sorb is probably a better idea than one using proprietary canisters. Just a guess though, I don't have a rebreather.

[Dmitchell]

Getting sorb up here isn't a big deal, you just have to plan ahead cause it takes a little longer to get. Helium/O2 is the PIA shipping the bottles back n forth to Seattle takes weeks and isn't cheap.

[CaptnJack]

Getting sorb up here isn't a big deal, you just have to plan ahead cause it takes a little longer to get. Helium/O2 is the PIA shipping the bottles back n forth to Seattle takes weeks and isn't cheap.

Is sorb just regular "stuff"? Any special shipping restrictions? Can you fly with it? Just curious thanks.

[Dmitchell]

Yes sorb is the regular "kitty litter" stuff. No real restrictions, its perfectly safe to fly with and can be shipped by most any carrier.

MSDS - http://www.molecularproducts.com/pdf/so ... e%2012.pdf

[CaptnJack]

Cool since there are plenty of perfectly safe products you can't fly with (Costco sized toothpaste lol) I just figured I'd ask.

[camerone]

Interestingly enough, the last time I flew with one of the rebreathers, the TSA paged me and wanted me to prove the scrubber was empty. They don't seem to like the loose kitty litter for some reason, although it's relatively benign.

[loanwolf]

Interestingly enough, the last time I flew with one of the rebreathers, the TSA paged me and wanted me to prove the scrubber was empty. They don't seem to like the loose kitty litter for some reason, although it's relatively benign.

I got hung up a San Diego for sorb in the rig and had to dump it. wound up missing my flight then spent a few hours talking with the TSA manager and pulling the books out and looking at all the reg's that relate to dive gear, CCR's and sorb. And then taking a walk out and being shown how baggage is inspected and seeing why dive gear is not to be web checked in . it was a eye opener for me on that. But as long as it is in the original unsealed package and you have a MSDS you are fine.

You cannot fly like we used to at all today.