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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