Use a gag strap?

[uwxplorer]

Hello Brad,

You’ll have to excuse me for not addressing all the points you raise in your classic gish gallop.


Given that these two studies are virtually the only material you cite that is independent and not simply repetition of your own commercially conflicted claims, I will deal with this in a little detail. Especially since you claim that they disprove our work.

These studies are only relevant if you are interested in CO2 scrubbing on a breathing circuit connected to an unconscious or resting / completely immobile subject. They were both conducted in the context of managing either anaesthetised patients or sick patients requiring surface oxygen.

The four things that provide a challenge to a CO2 scrubbing system are high gas flow rate, high CO2 delivery rate, low temperature and high gas density. Our study simulated the gas flow rate and CO2 delivery rates of exercise relevant to diving and had the rebreather immersed in temperate water. It therefore provided relevant challenges on three of these four fronts. The two studies you cite as proof that ours was wrong provided none of the relevant challenges.

Jiang et al ventilated the circuit at 5 L/min gas flow, and introduced CO2 at 160 ml/min – parameters relevant only to a deeply unconscious anaesthetised subject.

Pollock et al used spontaneously breathing resting subjects with an average minute volume (the equivalent of circuit ventilation) of 11 L/min and an average CO2 production (equivalent to the CO2 introduction rate) of 350 ml/min. Effectively resting conscious subjects receiving oxygen first aid via a circle circuit system.

Our experiment ventilated a real rebreather circuit at 45 L/min gas flow, and introduced CO2 at 2000 ml/min in the simulations of (moderate) exercise that a published consensus equates to expectations of sustained work output in diving, and 17 L/min gas flow and CO2 at 670 ml/min in the simulations designed to approximate work during the decompression phase of a dive. Compare those numbers to the Jiang and Pollock studies above.

If you cannot understand the potential implications of these vastly different experimental paradigms on the outcome of a CO2 scrubber study then you have no right commentating authoritatively on the matter on a public forum. I note that you even explicitly state: “Noting the two above pre-existing peer reviewed and published academic papers disproving your papers claims and conclusions about the performance of the Micropore EAC in rebreathers weren’t hard to find” thus revealing a profound lack of knowledge about is or is not relevant to “in rebreathers". These studies are not relevant to diving rebreathers or the use to which they are put; they are relevant only to medical use of CO2 absorbent.

Your defence of the claim that an EAC outlasts a granular system by two times or more based on the Jiang study is typically disingenuous. The only granular product where Jiang's results would justify this characterisation is called “LoFloSorb” which is presented as spheres. Its product information states “LoFloSorb is a unique zero caustic medical carbon dioxide absorbent designed by Intersurgical specifically for clinical use during anaesthesia…” Are you suggesting the comparison with a product of this nature is relevant to diving? Or is it that you are indulging in ‘technicality speak’ where its OK to state that an EAC lasts twice as long as granular sorb so long as there is one granular product completely unsuited to diving where this is true?

In fact, the result of Jiang’s comparison between sofnolime (a diving sorb used in our study) and the EAC is actually quite similar to ours in our decompression simulation experiment (where, because the Granular canister breaks through more gradually and reaches 0.5 kPa inspired CO2 first, the EAC was 20% more efficient where 0.5 is used as the end point). If Jiang had carried on to an end point of 1 kPa inspired CO2 they may have found the same thing we did (essentially identical break through times).

The rest of your commentary is a mix of misrepresented facts (eg trying to present comparisons of double EACs with smaller granular canisters as relevant), gratuitous advertising, and your usual attempts to score points off a competing manufacturer’s product from the extraordinary position of not having a credible product of your own. It includes allusions to alleged design flaws in the Optima that you proposed in the Skyles court case, and everyone knows how that ended for you. While on that subject, you cite the DAN fatality report mentioning “water blocked cells” in a 2016 Optima death as though this was a determination made by DAN. What you fail to disclose is that the DAN authors were silly enough to simply cut and paste this determination from your database of rebreather accidents, so it was your determination - not theirs. I doubt they will make that mistake again.

Simon M​

Scientific literature is not written to be necessarily comprehensible by the layman. It is construed by some that this is proof of a desire of obfuscation (sometimes followed by the argument that this is to protect a caste-like profession from interference by the public). I do not believe so, even though there are many uncreative scientists working 9-5 jobs.
The more benign truth of the matter is that some science requires special vocabulary because concepts need to refer to very precise facts. Some common words may be used which do not have the same vague meaning as in the common language.
Then you have math, yet another language, dealing with numbers and how one is related to the others, according to this or that physical, chemical or physiological model. If the reader is challenged by either (which is perfectly fine), chances are that even more of the fundamental signification and significance of the article will be lost to them.
And finally, throw in open access of this literature (*).
You are bound to have some very confused readers, and some others who will not realize they are not trained to read this type of literature and pick apart a perfectly fine work and transform it into a statement that has very little to do with the original.
Again, saying that is not belittling the casual reader (I feel exactly that way when I try to read something that is not within my fields of expertise)...

You have done a pretty fine job of illustrating the above in this special case. Thank you for that.

PS: Interestingly, Micropore also claims up to twice longer duration in their commercial blurb:
Micropore ExtendAir CO2 Absorbent
I couldn't figure out their source. Maybe it's one of the OSEL "publications"?

(*) I am not mentioning the garbage that is increasingly making its way in the scientific literature thanks to overwhelmed and lax reviewers or an abundance of pseudoscientific (aka predatory) journals. Now that would give a varnish of respectability to all the commercial claims of many of the rebreather manufacturers (not just OSEL)...

 

[Dr Simon Mitchell]

Thanks Uwxplorer.

On the comprehensibility thing, on reading back through this morning I do realise that no matter how carefully something is described in words it may still be hard to understand. Our EAC vs granular paper is embargoed for a year but I am going to invoke editor privilege and post the key results figure here because at the end of the day the work was done to inform divers and the figure is much easier to understand than a bunch of words.

Each line is the breakthrough curve for an individual test with a new scrubber. You can see we did 5 tests of each scubber type in each condition. The curve shows inspired CO2 (what the diver would be inhaling) on the vertical axis against time on the horizontal axis. The first two sets of curves to the left are the continuous exercise protocol (ventilation of the circuit at 45 L/min and addition of CO2 at 2000ml/min to simulate continuous 6 MET exercise). The second two sets to the right are the staged exercise protocol in which the rebreather was operated at the 6 MET level for 90 minutes followed by parameters designed to simulate the exercise of typical decompression (2 MET - ventilation of the circuit at 17L/min and addition of CO2 at 650 ml/min). This staged exercise protocol was intended to be more typical of a rebreather decompression dive (with moderate exercise at the start and a longer period of comparative 'rest' later). I know its obvious, but just for clarity, the scrubbers last a lot longer on the staged exercise protocol because for much of it they are ventilated less 'hard' and have a lot less CO2 pushed through them.

The two dotted lines represent two potential end points (0.5 kPa inspired CO2 and 1 kPa inspired CO2). You can see that the more gradual breakthrough in the granular canister on the staged exercise protocol results in it reaching the 0.5 kPa end point more quickly than the EAC, but on that protocol they reach 1 kPa at identical times. On the continuous 6 MET exercise protocol the EAC takes a little longer to reach both end points.

On the basis of these results we have concluded that the EAC is indeed superior to an equivalent weight and volume of granular sorb operated in a diving rebreather manufactured to take both, but not by nearly as much as often insinuated in claims like 'lasts twice as long as a granular system'. Brad claims that the EAC is being selectively disadvantaged by poor design of the Optima rebreather. It is not immediately obvious to me how poor design would selectively disadvantage one type of canister that occupies exactly the same volume, space and flow path occupied by another, but we did not investigate that and I cannot comment definitively. If Brad wants to loan us one of his oxygen units we might be able to shed some light. The trouble with assessing Brad's claims is that he interminably claims flaws in just about every aspect of the design of every rebreather other than his own, whilst ignoring the fact that (like his commercial bailout rebreather) his promised iCCR has never made it to market, despite deposits being taken 10 years ago.

I am not mentioning the garbage that is increasingly making its way in the scientific literature thanks to overwhelmed and lax reviewers or an abundance of pseudoscientific (aka predatory) journals.

Unfortunately, so true. The most depressing aspect of my role as editor of Diving and Hyperbaric Medicine (a non-predatory, peer reviewed journal which does not charge a publication fee, and which belongs to two academic societies) is that the papers we reject almost invariably turn up in other journals, often unchanged.

Simon

 

[uwxplorer]

Thanks for the advanced preview of the curves. This is very useful and eye opening information, especially the variability from one run to the next (including in the case of EAC).
Any comment on the connection with the study on temp sticks, related to this inter-run variability?

PS: I am curious as to what the "glitches" every ~25 min correspond to...

PPS: that thread has diverged significantly from the initial poll on gag strap and might deserved some splitting, as it contains important info that one might not necessarily associate with that topic.

 

[silent running]

Thanks Uwxplorer.

On the comprehensibility thing, on reading back through this morning I do realise that no matter how carefully something is described in words it may still be hard to understand. Our EAC vs granular paper is embargoed for a year but I am going to invoke editor privilege and post the key results figure here because at the end of the day the work was done to inform divers and the figure is much easier to understand than a bunch of words.

View attachment 558527
Each line is the breakthrough curve for an individual test with a new scrubber. You can see we did 5 tests of each scubber type in each condition. The curve shows inspired CO2 (what the diver would be inhaling) on the vertical axis against time on the horizontal axis. The first two sets of curves to the left are the continuous exercise protocol (ventilation of the circuit at 45 L/min and addition of CO2 at 2000ml/min to simulate continuous 6 MET exercise). The second two sets to the right are the staged exercise protocol in which the rebreather was operated at the 6 MET level for 90 minutes followed by parameters designed to simulate the exercise of typical decompression (2 MET - ventilation of the circuit at 17L/min and addition of CO2 at 650 ml/min). This staged exercise protocol was intended to be more typical of a rebreather decompression dive (with moderate exercise at the start and a longer period of comparative 'rest' later). I know its obvious, but just for clarity, the scrubbers last a lot longer on the staged exercise protocol because for much of it they are ventilated less 'hard' and have a lot less CO2 pushed through them.

The two dotted lines represent two potential end points (0.5 kPa inspired CO2 and 1 kPa inspired CO2). You can see that the more gradual breakthrough in the granular canister on the staged exercise protocol results in it reaching the 0.5 kPa end point more quickly than the EAC, but on that protocol they reach 1 kPa at identical times. On the continuous 6 MET exercise protocol the EAC takes a little longer to reach both end points.

On the basis of these results we have concluded that the EAC is indeed superior to an equivalent weight and volume of granular sorb operated in a diving rebreather manufactured to take both, but not by nearly as much as often insinuated in claims like 'lasts twice as long as a granular system'. Brad claims that the EAC is being selectively disadvantaged by poor design of the Optima rebreather. It is not immediately obvious to me how poor design would selectively disadvantage one type of canister that occupies exactly the same volume, space and flow path occupied by another, but we did not investigate that and I cannot comment definitively. If Brad wants to loan us one of his oxygen units we might be able to shed some light. The trouble with assessing Brad's claims is that he interminably claims flaws in just about every aspect of the design of every rebreather other than his own, whilst ignoring the fact that (like his commercial bailout rebreather) his promised iCCR has never made it to market, despite deposits being taken 10 years ago.



Unfortunately, so true. The most depressing aspect of my role as editor of Diving and Hyperbaric Medicine (a non-predatory, peer reviewed journal which does not charge a publication fee, and which belongs to two academic societies) is that the papers we reject almost invariably turn up in other journals, often unchanged.

Simon

Hi Simon, thanks again for posting the data and taking the time to respond to Brad.

Given your above results, do you have an opinion on why some divers anecdotally report CO2 bypass with the EACs during temporary periods of high workload? Is it as simple as a granular scrubber’s greater density than an EAC slowing gas flow/dwell time enough to prevent over breathing? It would be interesting to see at what MET level this could be observed and how that correlated with real world exertion levels, like swimming into a current during a live drop to avoid getting blown off your target wreck or sea mount.

 

[Dr Simon Mitchell]

Hello again,

Any comment on the connection with the study on temp sticks, related to this inter-run variability?

The variability between runs is interesting given the very controlled / standardized nature of the conditions in our experiments from run to run. We can't explain it. The inherent variability of things. We saw the same thing in the temp stick study, but the temp sticks seemed to cope with it and still gave sufficiently accurate predictions. That study (published in March) will become freely available on 31 March at this link:

The performance of 'temperature stick' carbon dioxide absorbent monitors in diving rebreathers. - PubMed - NCBI

The abstract is there now, but you will see that the PMC link (at the bottom) to the full paper goes live on 31 March 2020.

PS: I am curious as to what the "glitches" every ~25 min correspond to...

Well spotted. Because of the criticality of accurate ventilation rate and CO2 addition (particularly the latter) to the validity of the experiment, we briefly stopped ventilating the circuit every 30 minutes to recalibrate the flow sensors to ensure accuracy, although we stopped doing it once the scrubber started breaking through quickly. These pauses appear as those little ticks on the traces.

Had I reviewed the Jiang study this would have been an important criticism. They used a rotameter system for CO2 addition (we used a precision electronic pump); the rotameter really is bucket chemistry when accuracy is crucial, and although they describe mitigations I remained uncertain about whether they actually worked or not. In any event, the study is not relevant to diving.

Given your above results, do you have an opinion on why some divers anecdotally report CO2 bypass with the EACs during temporary periods of high workload? Is it as simple as a granular scrubber’s greater density than an EAC slowing gas flow/dwell time enough to prevent over breathing? It would be interesting to see at what MET level this could be observed and how that correlated with real world exertion levels, like swimming into a current during a live drop to avoid getting blown off your target wreck or sea mount.

Yes, good question, the answer to which goes back to my response to Brad where I point out the stupidity of extrapolating from medical device tests to diving situations where the gas flow rates, CO2 addition rates, gas density, and temperature conditions can be vastly different - by an order of magnitude or more.

Our study showed the EAC performed fairly well (just not as well as sometimes claimed) in a limited set of conditions, albeit of undoubted relevance to diving, when compared in the same rebreather to a small (but equivalent size) granular scrubber canister containing sorb designed for diving. There are conditions that can definitely occur in diving that are even more challenging (greater than 6 MET exercise and thus higher ventilation and CO2 addition, colder, dense gas). Our results do not predict the performance of EACs in such conditions; that would be extrapolating beyond the conditions of the study.

It is possible that in these more challenging conditions EACs might break through more quickly which would explain the anecdote you mention. I have discussed this with several rebreather engineers who say that their own tests of EACs in high exercise, very cold, high pressure (dense gas) scenarios suggest that their performance is more compromised by such conditions than granular scrubbers. But I have no experience of such testing myself. One must always bear in mind that most rebreathers take a granular scrubber that is larger / heavier than an EAC, which will give them a natural advantage not apparent in our study.

Simon

 

[Brad_Horn]

Simon, you’ll note I’m not questioning your research as the more done on scrubber durations the better. But in your abstract you claim that there was NO published research comparing granular systems and the EAC design. Which isn’t the case as demonstrated. That the pre-existing peer reviewed published research comparing granular systems and EACs isn’t for diving comparison use is irrelevant, as it is research comparing both and like your research is done on the surface using a rebreather system.

What rebreather you have used to question Micropores claim as far as diving systems go is where your trial was flawed from the start. It’s insufficient to pick any rebreather that simply takes an EAC, as no one claims a twice over scrubber duration, for the “Diverite Optima”. At best you could ping Diverite for false advertising in their user manual by dint of their NOT informing their users that that capability of the EAC doesn’t apply to their unit by design (lack of). But then anyone diving an Optima isn’t likely going to question anything DiveRite says.

I understand at best that you’ll have gotten maybe 60% efficiency out of the EAC in the Optima in your testing and this is what your results reflect. It is the reason why if you repeat your trials with a different rebreather system that utilises the exact same size of EAC that you will get a different result… either better or worse, but probably better,

Micropore also you will note don’t claim that the EAC has twice the duration of the highest performance diving granular absorbent, just that it has twice the duration of granular systems. As proven correct for diving with the published durations of the Mk25 Mod2…
Again, something that your abstract and research published to date fails to take into account. Plenty of divers and militaries make use of low grade diving granular absorbent on a daily basis….

Our experiment ventilated a real rebreather circuit at 45 L/min gas flow, and introduced CO2 at 2000 ml/min in the simulations of (moderate) exercise that a published consensus equates to expectations of sustained work output in diving, and 17 L/min gas flow and CO2 at 670 ml/min in the simulations designed to approximate work during the decompression phase of a dive. Compare those numbers to the Jiang and Pollock studies above.

Interestingly also absolutely non-comparable with the norm of rebreathers CE or even USN testing regimes that extant dived scrubber duration data exists for.

It will be interesting to know how your unique regime compares with the dived exercise workloads done on the Mk25 Mod2 with EAC and granular scrubber systems?

These studies are not relevant to diving rebreathers or the use to which they are put; they are relevant only to medical use of CO2 absorbent.

They may not be directly relevant to diving use but it is relevant to the performance of the EAC and therein Micropores claim.

Your defence of the claim that an EAC outlasts a granular system by two times or more based on the Jiang study is typically disingenuous.

Actually, that was just to point out the error of your claim of “to our knowledge there are no published data that supports these claims”.
Is there published data = yes!
Does it support the claim = yes!
Is it still relevant compared to your study, yes, because it also compares the EAC to granular absorbent and also is like your study conducted at the surface.

present comparisons of double EACs with smaller granular canisters as relevant)

Simon, you’re going to ignore it because it doesn’t suit your agenda and bias but the Mk25 Mod2 data published and obviously in use by the US Military amongst others IS directly relevant to Micropores claim of EAC durations of twice that of granular systems and wholly supports it. https://rdl.train.army.mil/catalog-...3-D641AA6207A2-1300758191561/gta31_02_003.pdf

The LAR granular scrubber isn’t exactly small either….

You would have trialled this if you had actually wanted to test/disprove Micropores claim.

While on that subject, you cite the DAN fatality report mentioning “water blocked cells” in a 2016 Optima death as though this was a determination made by DAN. What you fail to disclose is that the DAN authors were silly enough to simply cut and paste this determination from your database of rebreather accidents, so it was your determination - not theirs. I doubt they will make that mistake again.

Interesting claim Simon…. Especially as DAN in their report, make no reference to using DeepLife as a source?

Based on my vague recollection of the details that DeepLife listed for that Optima fatality at around the time the 2018 DAN report of 2016 incidents was published, it said nothing about water blocked cells…..
I’m sure someone keeps date stamped versions of the DL list can readily correct my recollection….

 

[Brad_Horn]

Interestingly, Micropore also claims up to twice longer duration in their commercial blurb:
Micropore ExtendAir CO2 Absorbent
I couldn't figure out their source.

Which is what DiveRite copied chapter and verse without advising that it didn’t apply to the Optima….. And what Simon has taken offence to and now has the cognitive bias that it applies to all rebreathers using EACs (strangely inclusive of the Optima). Without actually testing any rebreathers for comparison purposes or discussing it with Micropore or any other authorities on it.

As far as a source, for when this does apply to the EACs when dived, again see scrubber durations at https://rdl.train.army.mil/catalog-ws/view/100.ATSC/6198AC6C-D50E-4ACC-B053-D641AA6207A2-1300758191561/gta31_02_003.pdf Which prove that you can get twice the duration off an EAC fitted rebreather over granular systems given the right conditions and granular media.

You can see that the more gradual breakthrough in the granular canister on the staged exercise protocol results in it reaching the 0.5 kPa end point more quickly than the EAC, but on that protocol they reach 1 kPa at identical times. On the continuous 6 MET exercise protocol the EAC takes a little longer to reach both end points.

Thanks for disclosing this data early Simon, whilst not safely usable as a scrubber duration datapoint for dived rebreathers noting the potential for variation with depth as covered below, it is still interesting.

Dr. Cunningham’s analytical approach (using Ansys CFX) showed that ambient pressure (depth) could reduce the effectiveness of scrubber canisters. In support of that finding were the words from the Dive Gear Express web site regarding the Diverite O2ptima using the ExtendAir scrubber cartridge.
“As pressure increases the total number of molecules, the relative concentration of CO2 molecules in the loop is reduced, slowing the chemical absorption process. Thus as depth increases, scrubber efficiency will decrease.” The U.S. Navy has no experience with the Diverite O2ptima, but they have information on other rebreathers using granular absorbent. That experience shows that there is no reliable depth effect across all rebreathers and all absorbents.
For example, in one rebreather there was indeed a 17% decrease in endurance using large grain absorbent (Sofnolime 408) at 50°F in descending from 190 fsw to 300 fsw (58 to 92 msw) breathing air. However, there was no decrease in duration when using fine grain absorbent (Sofnolime 812) under the same conditions. (On an actual dive, air would never be used at 300 fsw, but air was used in this study for scientific reasons.)
In another rebreather using Sofnolime 812, for a change in depth from 99 fsw to 300 fsw (30.3 to 92 msw) there was a 29% increase in duration at 75°F, a 10% increase at 55°F, and a 15% decrease at 40°F. Although air diluent was used at 99 fsw, 88/12 heliox diluent was used at 300 fsw.
From another manufacturer I obtained information on two of their rebreathers. At 4°C, 1.6 L/min CO2 injection rate (corresponding to a fairly heavy work rate), 40 L/min ventilation rate using air diluent, there was a 27% decrease in one rebreather in going from 15 to 40 msw (50 fsw to 132 fsw), and a 11% decrease in another of their rebreathers in dropping from 40 msw to 100 msw.
In another rebreather tested under the same conditions except depth, the canister duration dropped 39% between 15 and 40 msw.

How Does Your Rebreather Scrubber Handle the Deep?

 

[Brad_Horn]

On the basis of these results we have concluded that the EAC is indeed superior to an equivalent weight and volume of granular sorb operated in a diving rebreather manufactured to take both, but not by nearly as much as often insinuated in claims like 'lasts twice as long as a granular system'.

Again Simon that’s great but there is NO published claim by any party that the EAC lasts twice as long as granular systems in a “DiveRite Optima”…..
If you had wanted to actually challenge Micropores claim you would have been better off testing it in a rebreather that it IS claimed for https://rdl.train.army.mil/catalog-ws/view/100.ATSC/6198AC6C-D50E-4ACC-B053-D641AA6207A2-1300758191561/gta31_02_003.pdf

Brad claims that the EAC is being selectively disadvantaged by poor design of the Optima rebreather. It is not immediately obvious to me how poor design would selectively disadvantage one type of canister that occupies exactly the same volume, space and flow path occupied by another, but we did not investigate that and I cannot comment definitively. If Brad wants to loan us one of his oxygen units we might be able to shed some light. The trouble with assessing Brad's claims is that he interminably claims flaws in just about every aspect of the design of every rebreather other than his own, whilst ignoring the fact that (like his commercial bailout rebreather) his promised iCCR has never made it to market, despite deposits being taken 10 years ago.

Which just means Simon that you have never visually let alone scientifically compared the various scrubbers capable of taking EACs nor considered how their individual design may impact the performance of an EAC in that specific rebreather and scrubber design… Nor discussed this with Micropore; whom back in July 2019 happily pointed out to you that their twice granular system duration claim didn’t apply to the Diverite Optima.

Did you note in your testing that the straight edged EAC you put into the Optima likely came out with the sides slightly corrugated? This is caused from it pushing hard up against the cell retainer as there isn’t a flow cone at that end. As a result there is reduced flow through the EAC.
Which contrasts quite significantly with the flow cones in the OSEL units scrubbers; which are on either end of the EAC and have custom silicon seals in addition to the centre locating pin Open Safety Equipment Ltd
Also see Figure 8-13 https://www.opensafety.eu/manuals/OR_Apocalypse_User_Manual_110505.pdf

You have also failed to consider other aspects of the rebreathers design that will impact the scrubber duration. What’s the WOB of an Optima compared to an Apoc, at least twice its 1.44J/L at 40m at 75lpm on air!
http://www.deeplife.co.uk/or_files/DV_OR_WOB_Respiratory_C1_101111.pdf

The demand for OSELs Incursion Oxygen units is too high for me to think there will be any appetite to loan you one of them for surface only testing. OSEL wet test each one on their hyperbaric breathing simulator before it leaves the factory. Unless of course you’ll actually generate some dived scrubber duration comparison data that is commercially useful to OSEL and can be provided to OSELs clients for their use?

But I’d certainly recommend you take Micropore up on their written offer of help with your trials, as OSEL would happily support any testing they conduct, as it will be free of the bias that is in your abstract and I presume paper. Unlike your academic surface only setup, Micropore like QinetiQ, NEDU, JFD, Aqualung and OSEL/DeepLife amongst a few others, also have the capability to conduct practical dived testing of rebreathers with EAC and granular systems at varying exercise rates….

Or alternatively you could do what Paul Raymeakers did when he published comparative testing of the EAC and granular absorbent duration in the Apoc and borrow one of the many mixed gas Apoc CCRs that are out in the wild being actively dived or stripped down in other manufacturers sheds.

Simon, again hate to correct you but it’s JFD whom offer a bailout commercial rebreather that uses the EAC in preference over granular absorbent. OSELs is a dual EAC primary commercial life support rebreather system that the client was quite happy with Open Safety Equipment Ltd

And Simon, no need to claim design flaws in various rebreathers, when you can simply read about them https://www.hollisrebreathers.com/wp-content/uploads/2019/08/QQ-1900385-HollisPrism-v1-1.pdf

If the manufacturer hasn’t bothered publishing testing to this standard Deep Life Design Team: Functional Safety Design Services then either the units are still functionally untested or likely have unidentified critical underwater life support design issues. This isn’t rocket science, just engineering 101.

I’d love to buy another make of rebreather for comparison use and fun. I just have a real simple and easily achievable purchase criteria. All it needs is published testing for >30% of the ratified CE standard EN14143 with testing calibration data and no obvious safety/visual failings against this standard. Examples of visual/safety failings are a lack of a gag strap is therefore a real simple no go, as is lack of a BOV with known CC and OC WOB. Cash on hand to purchase….

[QUOTE="Dr Simon Mitchell]One must always bear in mind that most rebreathers take a granular scrubber that is larger / heavier than an EAC, which will give them a natural advantage not apparent in our study.[/QUOTE]
One day there will be such a plethora of data from sufficient rebreather manufacturers all comparing the results of their rebreather ‘at the mouth’ under identical dived conditions (depth, water temp, Co2 flow rate, RMV etc etc) to make this a known (either way) rather than assumption.

Until then, it is interesting considering just how good the dived scrubber duration results ‘at the mouth’ for EACs in rebreathers, that are designed and optimised for EAC use and underwater life support, at depth and under high workload, can be,
http://www.deeplife.co.uk/or_files/DV_OR_ScrubberEndurance_Retest_SRB_101215.pdf

 

[JohnnyC]

I know another use for a gag strap, but I bet it would get me banned.

 

[Dr Simon Mitchell]

That the pre-existing peer reviewed published research comparing granular systems and EACs isn’t for diving comparison use is irrelevant, as it is research comparing both and like your research is done on the surface using a rebreather system.

...using in vitro non immersed circle circuits (not a rebreather) at gas flow and CO2 addition rates relevant only to anaesthetised patients. If you think that has any relevance at all to testing scrubbers for use by exercising divers using diving rebreathers then, well, I can't help you.

What rebreather you have used to question Micropores claim as far as diving systems go is where your trial was flawed from the start.

Why? You may consider it poorly designed but unlike your iCCR the Optima is a real rebreather being used by real divers, and the results of the study are of relevance to those divers. Our study may even encourage them to use EACs which did exhibit slightly better duration / efficiency.

It never ceases to amaze me how you appear to think that you have a solid platform for your interminable criticisms of other manufacturer's equipment. How about the next time you decide to criticize someone else's rebreather, you just pause for a minute and consider the credibility problem you have after saying this about the iCCR in 2009 and never delivering. Its only 11 years ago....

iCCR shipping soon

No one claims a twice over scrubber duration, for the “Diverite Optima”.

Well, UWxplorer pointed out that Micropore talk about twice the duration for an EAC over granular sorb, to which you replied "Which is what DiveRite copied chapter and verse without advising that it didn’t apply to the Optima". That sounds like someone claiming twice the scrubber duration to me.

Micropore also you will note don’t claim that the EAC has twice the duration of the highest performance diving granular absorbent, just that it has twice the duration of granular systems.

Do you read what you write before posting? Draw yourself a Venn diagram.

Plenty of divers and militaries make use of low grade diving granular absorbent on a daily basis….

The use of low grade granular absorbent by divers is something we addressed in an earlier paper [1] - see uploaded file. Can you cite the source of your information on use of low grade sorb by military dive teams?

It will be interesting to know how your unique regime compares with the dived exercise workloads done on the Mk25 Mod2 with EAC and granular scrubber systems?

Why would you find that interesting? Your opening comments make it perfectly clear that you think comparative testing at zero exercise workloads (indeed, CO2 addition and gas flow rates relevant to a deeply unconscious patient) is a legitimate investigation. Also, our "unique regime" has a physiological provenance; being based on an international consensus on expectations for sustainable exercise in typical diving conditions. [2]

Simon, you’re going to ignore it because it doesn’t suit your agenda and bias but the Mk25 Mod2 data published and obviously in use by the US Military amongst others IS directly relevant to Micropores claim of EAC durations of twice that of granular systems and wholly supports it. https://rdl.train.army.mil/catalog-...3-D641AA6207A2-1300758191561/gta31_02_003.pdf

This is a very simplistic interpretation. The document presents no "data" - just a series of durations for various configurations of equipment. There is no indication of how the numbers were derived, or what (if any) comparisons were performed. It is impossible to tell whether longer or shorter durations are simply due to bigger or smaller scrubbers, single or dual EACs or design efficiency etc. In other words the document provides no useful information in a discussion about efficiency of different types of scrubber.

Which prove that you can get twice the duration off an EAC fitted rebreather over granular systems given the right conditions and granular media.

Yes, of course you can, but you are drifting ridiculously far away from the purpose of our study which was to test granular and cartridge sorbs of equal volume and mass in a rebreather manufactured to take both.

Thanks for disclosing this data early Simon, whilst not safely usable as a scrubber duration datapoint for dived rebreathers noting the potential for variation with depth as covered below, it is still interesting.

Thank you for the John Clark education piece Brad, but all you needed to do was quote the paper where we say:

The scrubber canisters were operated at surface pressure and in temperate water. Operation of scrubbers at greater
pressures (and with denser gases) and at lower temperatures is known to affect duration (typically adversely). It must
therefore be explicitly understood that the purpose of the study was not to define expected durations, but rather
to compare two different scrubber types under a set of standardised conditions.

But I’d certainly recommend you take Micropore up on their written offer of help with your trials, as OSEL would happily support any testing they conduct, as it will be free of the bias that is in your abstract and I presume paper.

There is a certain irony in a commercially conflicted commentator suggesting involvement of another commercially interested group to reduce bias in research performed by an independent academic department.

Simon M

1. HARVEY D, POLLOCK NW, GANT N, HART J, MESLEY P, MITCHELL SJ. Comparison of duration of two CO2 absorbents in a diving closed-circuit rebreather system. Diving Hyperbaric Med 46, 92-7, 2016

2. MITCHELL SJ, BOVE AA. Medical screening of recreational divers for cardiovascular disease: Consensus discussion at the Divers Alert Network Fatality Workshop. Undersea Hyperb Med 38, 289-296, 2011