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Re: [PSUBS-MAILIST] ExtendAir scrubber cartridge
No doubt that lithium is nasty stuff and the cost probably trumps it's
increased effectiveness of CO2 absorption. In my opinion, the primary
issue that the ExtendAir cartridges solve is consistency. Soda lime
products in small subs suffer from the same problems that packing a
rebreather suffer from, primarily dust and absorption efficiency related
to the packing of the material. Pack it too tight, or too loose, and
the efficiency of absorption is reduced. By how much? Well, only your
CO2 meter will tell. This doesn't mean your life is in danger, but it
could certainly mean you use more soda lime than necessary (which
arguably is not a huge issue because of the lower overall cost of soda
lime).
The other consistency issue resolved by the Micropore canisters is
associated with scrubber design. Not all home-built scrubbers are
created equal. I think we've had some folks suggest stuffing a sock
full of chemicals is good enough, and in an emergency situation they are
correct. However, for general use you probably want to have a bit more
elegant design that incorporates some of the known parameters for good
CO2 absorption. In this respect, Micropore's solution is "turn-key" for
rebreathing, and nearly so for modifications necessary for small sub
use. The consistency of cartridge manufacturing provided consistency in
calculating chemical exhaustion and could result in better dive planning.
In regards to wastefulness due to unused portions, it would seem both
products suffer from the same issue since I don't think trying to
preserve soda lime from a partial dive is considered healthy either.
Given the lower cost of the soda lime, it likely isn't worth the risk
anyway. And, of course, wasting soda lime is not as much of a hit in
your wallet.
For short dive durations, it probably is hard to beat soda lime due to
cost advantages. For long dives on the order of 4 hours, it is
arguable that pre-loaded canisters win out. Some subs leave the pilot
only elbow-room and it would be much easier to swap out a cartridge than
loose material. Even if it is pre-measured.
Ultimately, sounds like personal preference to me. Like Dan Lance said
in Maine, use soda lime for your day to day diving, and carry some
micropore canisters with you in case of emergency. (at least I think it
was Dan who said that) That's going to be the route I take.
I don't think anyone questioned whether flammability was an issue in a
sub. The context was whether lithium hydroxide is flammable in contact
with water. Jay corrected himself on that and meant to say oil, not water.
Jon
vbra676539@aol.com wrote:
Aside from ops warnings from Jay and yours truly (LiOH is expensive
and nasty in the sinuses) you might think about the biggest user of
submersibles after Atlantis. That would be Professor Doctor Mister
Phil Nuytton. His folks use Soda Sorb or equivelant. They don't use
cartridges (which will ultimately be wasteful as it's hard to preserve
the unused portion once the sealing tape is pulled. They buy that
stuff in buckets. For us small time users, you can buy it in
small sealed bags which store nicely and last for a long time on the
shelf. That said, if you plan to do what Dan H. is doing, carrying
scrubbers for emergency use only, then the cartridges might pay for
themselves in convenience. None of us are building space stations or
shuttles or 50 passenger submarines, so the higher efficiency probably
won't be worth the cost. And who asked if flammability was really an
issue? I've done a couple of fires underwater, sports fans, and I'm
here to tell you that flammability IS an issue. Especially chemical
fires that you can't do a lot about except hope the viewports don't
melt before you can get your momma's favorite boy back to the surface.
Fires underwater SUCK. End of discussion. Avoid them whenever you can.
Always, for instance.
Vance
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