Pandora's Box
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Not correct. See my recent post about this in the other thread titled "Rebreather as bailout for sat divers"
Use a gag strap?
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Not correct. See my recent post about this in the other thread titled "Rebreather as bailout for sat divers"
uwxplorer
Contributor
In response to the meandering bickering above, I think I'll speak for most rebreather divers (although I am really nothing close to an expert) by saying that Mitchell's data and abstract provides an interesting perspective on EAC's benefits vs self-packed scrubbers.
I had once considered the Titan and Poseidon 6, which were offering pre-packed scrubbers (EAC?) and later on extended their offer with self-packed options (it would be interesting to figure out why), so the EAC debate is of personal historical interest to me, as I recall the caustic cocktail argument, but not the duration one, let alone the WOB one (maybe because of memory "breakthrough" or because, as a novice, I didn't pay as much attention to this aspect as much as to the caustic cocktail menace, which I tended to focus on).
What I learned here, is that in a specific rebreather, a specific EAC does perform slightly better than a specific granular scrubber. I also learned (or re-learned), incidentally, although it could be argued that this is a very important piece of information that might be none unit specific, that there is a significant variability in duration. Is it due to mechanical ventilation variations (that gives pause when thinking what the data would look like if different divers had performed the test in realistic conditions!)? Or is it due to packing variability (hence user "error" for granular scrubber) or unit manufacturing variability (EAC)?
Regarding the argument that this test doesn't demonstrate that EAC are twice better than packed scrubber in any and all possible situation of rebreather/diving/trim/etc. conditions is well taken. Blaming the results on the WOB of the remainder of the rebreather might be a stretch. If that where the case, the machine would have had to apply the same pressure to flow the same amount of gas in both cases (EAC and packed scrubber) and thus would have compared them both fairly. Maybe not in the best of all rebreathers that we are all having wet dreams about, but in a real rebreather. This test would thus say: if the rebreather's WOB sucks due to everything but the scrubber canister layout, an EAC will not change things dramatically.
That was hypothesis 1. Now, if hypothesis 2 states that the remainder of the rebreather doesn't contribute zilch to the WOB, but instead this is the canister layout (cell location, flow path, whatnot) that kills it, then again, both canisters are on a par footing. If the machine did need to apply a larger pressure (not sure whether that was recorded during the experiment) in the case of the packed scrubber, then, the fact that it did provide close to the same duration as the EAC means that the latter (assuming that it does indeed require a lower pressure or WOB) to be applied, would seem to work less efficiently, not more, than the packed scrubber (if they were tested under the same WOB conditions).
We could play with hypothesis 3, where the EAC would offer a higher resistance than the packed scrubber, and chant its merits, considering that despite this higher WOB, it does offer a longer duration...
In any case, in the absence of WOB data, the only thing we can say indeed, is that an EAC offers moderate advantages in anO2ptima (and possibly disadvantages in some high work situations, if we take into account DSIX6's testimony).
I'll note that this won't change much to the diving of all of us who cannot pluck an EAC in our unit, but does contribute to our better grasping of the complexity of factors involved in survival under water.
If this discussion has helped, and the repeated reminders of the importance of considering WOB in any discussion of diving related matters, if muddled within distracting sophisms, cannot be underestimated, so much the better.
I had once considered the Titan and Poseidon 6, which were offering pre-packed scrubbers (EAC?) and later on extended their offer with self-packed options (it would be interesting to figure out why), so the EAC debate is of personal historical interest to me, as I recall the caustic cocktail argument, but not the duration one, let alone the WOB one (maybe because of memory "breakthrough" or because, as a novice, I didn't pay as much attention to this aspect as much as to the caustic cocktail menace, which I tended to focus on).
What I learned here, is that in a specific rebreather, a specific EAC does perform slightly better than a specific granular scrubber. I also learned (or re-learned), incidentally, although it could be argued that this is a very important piece of information that might be none unit specific, that there is a significant variability in duration. Is it due to mechanical ventilation variations (that gives pause when thinking what the data would look like if different divers had performed the test in realistic conditions!)? Or is it due to packing variability (hence user "error" for granular scrubber) or unit manufacturing variability (EAC)?
Regarding the argument that this test doesn't demonstrate that EAC are twice better than packed scrubber in any and all possible situation of rebreather/diving/trim/etc. conditions is well taken. Blaming the results on the WOB of the remainder of the rebreather might be a stretch. If that where the case, the machine would have had to apply the same pressure to flow the same amount of gas in both cases (EAC and packed scrubber) and thus would have compared them both fairly. Maybe not in the best of all rebreathers that we are all having wet dreams about, but in a real rebreather. This test would thus say: if the rebreather's WOB sucks due to everything but the scrubber canister layout, an EAC will not change things dramatically.
That was hypothesis 1. Now, if hypothesis 2 states that the remainder of the rebreather doesn't contribute zilch to the WOB, but instead this is the canister layout (cell location, flow path, whatnot) that kills it, then again, both canisters are on a par footing. If the machine did need to apply a larger pressure (not sure whether that was recorded during the experiment) in the case of the packed scrubber, then, the fact that it did provide close to the same duration as the EAC means that the latter (assuming that it does indeed require a lower pressure or WOB) to be applied, would seem to work less efficiently, not more, than the packed scrubber (if they were tested under the same WOB conditions).
We could play with hypothesis 3, where the EAC would offer a higher resistance than the packed scrubber, and chant its merits, considering that despite this higher WOB, it does offer a longer duration...
In any case, in the absence of WOB data, the only thing we can say indeed, is that an EAC offers moderate advantages in anO2ptima (and possibly disadvantages in some high work situations, if we take into account DSIX6's testimony).
I'll note that this won't change much to the diving of all of us who cannot pluck an EAC in our unit, but does contribute to our better grasping of the complexity of factors involved in survival under water.
If this discussion has helped, and the repeated reminders of the importance of considering WOB in any discussion of diving related matters, if muddled within distracting sophisms, cannot be underestimated, so much the better.
One of the design requirements for the "Type-R" rebreathers (recreational) was a method of scrubbing that eliminated the variables of packing (thinking of recreational divers who might not do a lot of diving on the units etc)
The way to do this was with the EAC (Optima) and the SofnoDive 797, which was a factory-packed canister designed by Poseidon and Molecular products together. The Sofno cartridge was conventional granular sorb, but packed by the factory. Obviously this added to the cost and shipping issues and since Poseidon was the only customer, the canisters ended up being quite expensive. Unfortunately, part of the contract between Poseidon and Molecular was that the canisters would only be produced as long as the Poseidon only used them, so no factory repackable option.
Most divers' first upgrade to the unit was to purchase the Tecme repack canister, which invalidated the CE approval but was essential to be able to guarantee being able to get sorb in more remote locations. Last year, Molecular announced they were discontinuing the prepack, due to sales volumes as well as the issue of single use plastics etc.
That freed Poseidon to produce their own user packed canister, which they did. All units now ship with the factory CE approved canister and it is available to buy for existing customers.
Diverite use of the EAC was mostly, I suspect, because they wanted to use an existing product that was available for other industries (medical etc) and that was then adapted to the unit. A standardised sorb canister is IMO a good idea, eliminating variables in packing technique vs older sorb vs all the other factors that affect sorb life allows some pretty reliable estimation of remaining sorb life etc.
The compromise is that you end up designing a CCR around a "non-diving" component, which can be challenging, or building your own which gets expensive.
uwxplorer
Contributor
Interesting clarification. I believe the EAC is designed for diving applications. There are other models for different applications if my memory of my visit to Millipore's website serves me well.
As for the reproducibility of the new Poseidon pre-packed scrubbers, I am willing to take their detailed tests report at face value (where can they be found?), but would not bet on no variability in scrubber duration...
As for the reproducibility of the new Poseidon pre-packed scrubbers, I am willing to take their detailed tests report at face value (where can they be found?), but would not bet on no variability in scrubber duration...
silent running
Contributor
If EACs can be overbreathed as Don related, then everything else is moot. Many of my favorite dives have involved periods of high workloads, and I’ve never overbreathed my Prism 1 in to out radial, even in the last hour of the scrubber.
Add to the potential for overbreathing an EAC the fact that there isn’t room enough in your luggage for a 2 week trip, and I have no use for them.
If you can’t pack a scrubber, what other life supporting tasks are you unable to do? I really don’t think making CCR diving easier is going to help anyone become a better CCR diver. And if I were a combat swimmer I definitely wouldn’t want a bad CO2 hit if I were swimming hard against a tidal current trying to get to my objective.
Add to the potential for overbreathing an EAC the fact that there isn’t room enough in your luggage for a 2 week trip, and I have no use for them.
If you can’t pack a scrubber, what other life supporting tasks are you unable to do? I really don’t think making CCR diving easier is going to help anyone become a better CCR diver. And if I were a combat swimmer I definitely wouldn’t want a bad CO2 hit if I were swimming hard against a tidal current trying to get to my objective.
To clarify, the Poseidon canisters are packed by the user, same as most other CCR.
Sofnodive797 Technical Datasheet v3 | Sodium Hydroxide | Carbon Dioxide
That is the data sheet from Molecular for the OLD prepacked scrubber cartridge
Of course, but consistency of packing is a big factor. So if a production process with suitable QA is implemented and the cartridges are packed in consistent environmental conditions etc by a machine, a lot of the variables are reduced.
I stand corrected, I honestly haven't paid much attention to the EAC other than seeing them at the local Optima centre.
Hello uwxplorer,
I was going to call Brad out on his inference that a higher WOB could somehow compromise scrubber efficiency but could not be bothered. However, since you have mentioned it, I completely agree. If you have an EAC in two different rebreathers where the only difference is that it takes more work to move the same volume of gas and added CO2 around the circuit in one rebreather than the other, I cannot understand how that, of itself, would affect the comparative efficiency of the EACs. Brad might like to explain that to us.
He has opined in previous posts that the Optima is somehow imperfectly designed to take advantage of the capabilities of an EAC. His whining about how the Optima is therefore not a suitable platform in which to compare an EAC to a granular scrubber implies that these design imperfections only affect the EAC and somehow don't affect a granular scrubber. He has provided no objective evidence that the Optima design somehow selectively disadvantages an EAC. I am not a rebreather engineer and cannot comment expertly on this, but based on extensive discussions with Brad on issues in which I am expert, I am extremely skeptical about anything he says. I would certainly not accept his assertions about the Optima at face value. In any event, if such a selective disadvantage does exist, it must be based on flow path issues through the scrubber; not work of breathing per se.
You asked about measurement of pressures to move gas around the loop in our study. We did measure this, and found no difference between the two scrubbers. One of the claimed advantages of an EAC is that it less pressure is required to move gas through it. We could not detect that difference (compared to a granular canister) in an Optima ventilated at surface pressure. However, as we point out in the paper, that result must be interpreted cautiously. Any advantage in this regard will be magnified at greater pressure with denser gas. It makes sense to me that the EAC may have a WOB advantage at greater pressures. As silent running implies, that would be of little benefit if there were also a greater tendency to break through at greater workloads and gas density. Again, that is not something I can comment on.
For completeness, there is of course, a physiological reason why increased work of breathing could affect scrubber performance: it will cause the diver to produce more CO2. But this is not an issue in the sort of mechanical testing that has been discussed in this thread.
Simon M
martincohn
Contributor
uwxplorer
Contributor
Interesting. I did not remember that they were selling pre-packed granular sorb... What a rip off.
Yeah, me too: it is of course Micropore, not Millipore... Professional deformation, I guess. The page is:
Micropore ExtendAir CO2 Absorbent
Check this page too for a good laugh:
Micropore ExtendAir CO2 Absorbent
The other page I linked to has this interesting blurb:
Yet another point of contrast with the data provided previously by Mitchell...
The EAC is like a pack of straws. Full of axial holes. Does it allow uneven flow across the cross section more easily than with a granular scrubber?
Maybe EAC works bad in units which have not been properly designed for EAC and even flow across the cross section.
Maybe EAC works bad in units which have not been properly designed for EAC and even flow across the cross section.
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