Use a gag strap?

[Dusty123]

One benefit to the mouthpiece with the gag strap is its good for scootering or hanging on the line in heavy current. I have been using cbite style mouthpieces and had one get torn pretty bad hanging on the line in bad current. The revo one or draeger, whatever, kinda helps stabilize things when the current gets bad.

 

[Brad_Horn]

Performance of cartridge and granular carbon dioxide absorbents in a closed-circuit diving rebreather. - PubMed - NCBI
The EAC is more efficient than a granular canister of the same weight by a margin that varies from 0% to 20% depending on the exercise simulation protocol and CO2 breakthrough end point chosen. Whether 0 - 20% difference represents "quite some margin" is in the eye of the beholder, but it is certainly not the "outlasts a granular system by two times or more" that has previously been claimed.

G’Day Simon, Merry Christmas and a Happy New year to you.

Upfront I’m surprised that you got as much as a 20% efficiency out of an EAC at 1ATA in a DiveRite Optima over granular absorbent but that certainly bodes well for those scrubbers in rebreathers actually designed to get a good duration out of a Micropore 5” ExtendAir Cartridge. As testing by everyone other than you appears to confirm.

Noting the pre-existing independent peer reviewed study published by DUKE/DAN flagged at least an additional 43% efficiency comparing the EAC over granular absorbent in a rebreather during comparable human trials at 1ATA. As unlike your study of course, the focus of this was on an actual scientific comparative performance of the scrubber media in isolation without any impedance due to a specific rebreathers lack of design validation. And that EAC trial they cut short at 8 hrs….
https://www.diversalertnetwork.org/training/instructors/REMOReport.pdf

Jiang et al (July 2018) in their rather more extensive than yours “In vitro efficiency of 16 different Ca(OH)2 based CO2 absorbent brands” also found that the Micropore EAC “outlasts a granular system by two times” based on the evidence they have published in Table 2 and at least one of your co-authors has been aware of since July 2019; when they were formally advised of it in letter by Micropore.

Data directly comparing CO2 absorbents tested in identical and clinically relevant conditions are scarce or non-existent. We therefore tested and compared the efficiency of 16 different brands of Ca(OH)2 based CO2 absorbents used as loose fill or a cartridge in a refillable canister under identical low flow conditions. Efficiency ranged from 50 to 100 min per 100 mL of product, and increased with increasing NaOH content (a catalyst), the exception being SpiraLith Ca® cartridge with color indicator (performing as well as the most efficient granular products) and the SpiraLith Ca® cartridge without color indicator (outperforming all others)

Yan Jiang · Mohammed K. Bashraheel · Hongliang Liu · Jan Poelaert · Marc Van de Velde · Geert Vandenbroucke · Rik Carette · Andre M. De Wolf · Jan F. A. Hendrickx (25 July 2018) ‘In vitro efficiency of 16 different Ca(OH)2 based CO2 absorbent brands’, Journal of Clinical Monitoring and Computing https://doi.org/10.1007/s10877-018-00248-x

I note that while DiveRite marketing material does make the claim Micropore EAC "outlasts a granular system by two times or more” they reference this as coming from Micropore, and while DiveRite even copy the MicroPore hyperlink in their printed manual; they don’t include the conditions under which this is valid and publish no proof of testing that it even applies to the Optima…. A perhaps classic example of caveat emptor!

Thus irrelevant of your ‘testing’, the Micropore claim that it applies to an EAC is then still perfectly scientifically valid and makes your ‘study’ somewhat irrelevant in its overall conclusion; though very relevant as to the reduced performance of the EAC in the Optima. Leading to the very obvious question of why this might be the case…
Readers will note that DiveRite make no actual claim, that the EACs feature of “outlasts a granular system by two times or more”, actually applies to the Optima when breathed at the surface (like you consider sufficient for tests of diving equipment) or dived. Which as DiveRite have now introduced a granular adapter as the default for the Optima, post Skiles and other fatalities accident analysis, makes it seem that you have made a lot of noise about nothing. Unless it is just notification that those diving an Optima with granular sorb (in lieu of an EAC) need to reduce their scrubber duration and therefore planned dive-time on an Optima, by a further 20% for safety!

Only DiveRite appear to have copied verbatim this valid Micropore claim without any link to any design verification or testing of it in their rebreather. And as such the fact that you couldn’t replicate it in an Optima won’t be of any surprise to anyone, bar obviously yourself, as DiveRite certainly never tried to.

The combination of Micropore’s ExtendAir® adsorbent
manufacturing process, along with the parallel flow cartridge design, turns out to be extremely efficient. As the gas flow rate increases, Micropore’s ExtendAir® cartridge duration can out last a granular system by 2 times or more.

https://www.diverite.com/wp-content...ma-User-Manual-2016-Rev-A-July-2016-final.pdf

You just seem to have been so hot under the collar to come up with anything to disprove the Micropore claim that you failed to consider/research under what conditions it might be applicable. And in what diving rebreathers… Which doesn’t say much about your papers scientific validity and the publications supposed peer review process either…. 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.

 

[Brad_Horn]

In addition your ‘testing’ appears to go directly against what NEDU have professionally studied with significantly greater funding and approved for USN/SOCOM etc etc usage:
Whilst the testing report itself is probably ITAR’d, the results aren’t, per US SPECIAL FORCES GTA 31-02-003
@4.4C in a MK 25 MOD 2
Granular Carbon Dioxide Scrubber 4-8 Mesh without insulator sleeve gives a DIVED scrubber duration of 80min.
Micropore ExtendAir Double Cartridges without insulator sleeve gives a DIVED scrubber duration of 180min.
Under identical conditions….
Pg22 https://rdl.train.army.mil/catalog-ws/view/100.ATSC/6198AC6C-D50E-4ACC-B053-D641AA6207A2-1300758191561/gta31_02_003.pdf
Noting that the oxygen rebreather MK25 MOD2 double EACs are itty bitty ones and not the 5” one you ‘tested’ in an Optima but the core material performance and safety benefits are the same. LAR V/MK25 ExtendAir® CO2 Absorbent Canister Kit
And yeah, sure with DiveSorb Pro and insulator sleeve you can get an additional hours scrubber out of the MK25 MOD2 but then equally neither did Micropore specify against exactly what specific type of granular system they get twice the performance of. Marketing speak perhaps, but still honest marketing speak that’s backed up by evidence and a I’m sure considerable amount of manned dived high workload testing by NEDU et al. Though I’m sure John Clarke et al can educate you further on this…. especially interesting is the granular variation with depth and temp between units that he reports and you haven't considered.
How Does Your Rebreather Scrubber Handle the Deep?

And that’s not even considering that the MK25 MOD2 loop as a whole wasn’t optimised for the EAC; so (like you have ‘discovered’ with the Optima) will have a considerable amount of impedance to its performance. As a number of navies are noting when they trial the Incursion-CMR in comparison with LARs etc.

Of note, while the US Special Forces etc etc make use of the fact that the EAC can out last a granular system by 2 times of more (@4.4’C without insulator sleeve in a Drager MK25 MOD2 where 4-8 Mesh granular gives 80min duration and double EACs give 180min duration in comparable size scrubber); they also give the full spectrum of the scrubber duration under varying dive temperatures. Something certainly NOT available for the Inspiration or Optima. But something I’ll get OSEL to replicate in that easily readable table format, as we get an even better scrubber durations out of the military Incursion-CMR under the same conditions, due to significantly lower WOB and much better design; with significantly lower operating cost.
Though contrary to all other recreational mixed-gas rebreathers, and of significant benefit in the real world quite a wide spectrum of scrubber durations under differing conditions and depths, are already openly published for the Apoc Type IV CCR!

Most of the other rebreather manufacturers, whom (unlike DiveRite) have actually conducted test and evaluation of their own product, certainly don’t feel the need to use this in their marketing material as the (quite variable in their individual product) EACs performance speaks for itself in outperforming granular options for end user safety.
http://microporeusa.com/media/docs/ExtendAir_SCUBA_Datasheet.pdf
http://www.aqualung.com/militaryandprofessional/product_information/2014_Extandair4Frogs_LRes.pdf
https://www.sonistics.com/wp-content/uploads/Micropore.pdf
https://www.opensafety.eu/manuals/OR_Apocalypse_User_Manual_110505.pdf
Micropore Brochure
JFD | COBRA (Compact bailout rebreathing apparatus)
Micropore ExtendAir CO2 Absorbent
http://spiralithusa.com/wp-content/uploads/2013/10/ICES-Paper-2007-01-3278.pdf
TP Group to manage carbon dioxide contamination on submarines in UK
Evaluation of Micropore"s SpiraLith Absorbents - Full Text View - ClinicalTrials.gov
https://www.stahq.org/userfiles/files/51_Abstract_Poler(243).pdf
Low Flow and CO2 Absorbents - Anesthesia Patient Safety Foundation
http://archive.rubicon-foundation.org/xmlui/bitstream/handle/123456789/4992/ADA432680.pdf?sequence=1

 

[Brad_Horn]

A 2.6 kg scrubber out-performs a EAC {WHEN THE EAC IS FITTED TO A HIGH WOB REBREATHER SUCH AS A DIVERITE OPTIMA; WHICH HAS POOR GAS FLOW THROUGH THE EAC; DUE TO THE O2 CELLS BLOCKING THE EAC GAS FLOW PATH AND POOR FLOW CONE SHAPING/DESIGN WHICH CREATE A NON-LINEAR GAS FLOW}. The average duration of an EAC ventilated at surface pressure in a protocol simulating 6 MET of exercise in our experiments was 158 minutes (EAC in an Optima rebreather), whereas a 2.64 kg scrubber (in an Inspiration EVP) lasted on average 202 minutes.

Simon, I’ve just CORRECTED your statement to remove the accidental obfuscation you’re unfortunately introduced into the comparison. As while all Micropore 5” EACs are equal in performance; their resultant CO2 scrubbing performance is not equal in all rebreathers ‘at the mouth’…. Not something exactly hard to fact check!

Specifically as DiveRite note, but don’t enable with the Optima, you actually need to provide a uniform gas flow through the EAC for full utilization of the absorbent in the cartridge…

An important concept to understand with ExtendAir® cartridge technology is that the gas flow distribution through the cartridge must be uniform in order for the system to perform optimally. For example, one way to visualize flow through an ExtendAir® cartridge system is to take a bunch of soda straws in your hand (50 or so). What would happen if you blew air down through just a group of 5 straws? All of the air would flow down those five straws, and none of the air would flow through the other 45. The same thing would happen if you blew air into just one side of an ExtendAir® cartridge canister: all of the air would flow through that side only. The end result of this uniform flow is full utilization of the adsorbent in the cartridge.

https://www.diverite.com/wp-content...ma-User-Manual-2016-Rev-A-July-2016-final.pdf

 

[Brad_Horn]

I'm not entirely sure what Brad means by "minimal caustic cocktail risk" but we found no significant difference in the pH of water eluted from either granular sorb or an EAC after a 5 minute flood (12.7 vs 12.8 respectively).

This is interesting considering that the Micropore primary focus is on military rebreather systems and their value proposition of lower work of breathing, less variability in duration, less particulation (dusting) and less causticity after a flood has been recognized by the US military amongst quite a few other major players in the dive industry.
Doug McKenna's Micropore clears the air - DBT

I’m also aware that Micropore wrote directly to your colleague Hanna back in July 2019 asking how you achieved this comparison, noting you don’t appear to describe your test methodology? As it differs in result quite considerably from the scientific method that Micropore themselves use. And every other tester. They even explained in detail to you why it was the case amongst a few other corrections…..

Simon, further if it has taken you 5min to notice your loop has flooded sufficiently, to fill the scrubber and you haven’t yet purged it out so you can fault find or continue with the dive! It is probably time to bail out to your lower WOB BOV and a known safe gas. If you have an ALVBOV fitted of course, as otherwise as you know, you will be bailing out to a higher (and certainly in your case unknown) WOB….. or introducing the risk of drowning through having to swap to a 2nd stage off the loop.
Of course if you have flooded a granular scrubber your loop is now instantly caustic; which certainly offers an alternative and not minimal caustic cocktail risk you get on an Apoc with an EAC scrubber, no matter how you try and spin it Rebreathers: The Caustic Cocktail - Underwater Journal

Your ‘test’ for whatever reason, appears to contrast with the fact that after a couple of minutes the pH change of an EAC submerged in water is negligible

Looking at another independent third party, even AquaLung report that the EAC is 70% less Caustic after 5min http://www.aqualung.com/militaryandprofessional/product_information/2014_Extandair4Frogs_LRes.pdf

And it would be interesting if this is again a rebreather generic issue that you failed to properly allow for in your ‘testing’ as I’m unsure how you recovered either the Optima or Inspiration from a flooded scrubber whilst submerged and where you then sampled the water from on surfacing? Of course with OSELs Apoc, Incursion-BMR and Umbilical Commie rebreather you can sample direct from the Inhale CL OPV, then get back in the water and continue the dive! As for the Incursion-CMR, you can purge and recover from a flood direct from the scrubber OPV, with an EAC fitted.
http://www.deeplife.co.uk/or_files/Effect_of_flooding_with_granules_061027.pdf

It would also be interesting to see if the difference you got was due to the EAC in the Optima getting excessively wet prior to your caustic comparison, for the same reasons that DL and DAN have now implicated the Optima utter lack of any design validation, in two rebreather fatalities due to water blocked cells:

Case 1-10: Death due to CCR failure in a cave dive
• Cause of death: Drowning
• Disabling injury: Loss of consciousness
• Mechanism: Hypoxia
• Trigger: Equipment problem
• BMI = 20.5 kg/m2
An experienced male cave diver who had been diving with a closed circuit rebreather (CCR) for over a year began to act erratically during a cave dive with a buddy. According to the buddy, the victim was not able to continue using his scooter, his trim was off, his fine motor control was off, and his buoyancy was off. He was seen starting to swim in circles and bounce off the ceiling and the floor of the cave, so other divers started assisting him out of the cave. At some point, he lost consciousness and no longer had his regulator in his mouth. The other divers clipped him to the cave line and started a body recovery procedure after surfacing and calling local emergency services. The initial finding was that he had suffered a heart attack and that all his gear was functioning properly. A later examination found that water in his unit may have led to water-blocked oxygen cells and thus a hypoxic mix. The witnesses’ description of the diver’s behaviour suggests a loss of consciousness due to hypoxia rather than a heart-related cause of death.]/QUOTE] DIVING FATALITIES - DAN Annual Diving Report 2018 Edition - NCBI Bookshelf

 

[Brad_Horn]

identical breakthrough kinetics, whereas on a staged exercise protocol (6 MET for half of the expected scrubber life then 2 MET until breakthrough to either 0.5 or 1 kPa inspired CO2) the granular cartridge exhibited a more gradual breakthrough. This was the reason for a duration difference between the two canisters on this protocol where a breakthrough endpoint of 0.5 kPa inspired CO2 was chosen. Because the granular sorb broke through more gradually, it reached 0.5 kPa inspired CO2 more quickly than the EAC whereas the two scrubbers reached 1.0 kPa inspired CO2 at identical times (on average).[/QUOTE]
Simon, at what depth and water temp did you conduct this test?

As you know the specific depth and temp (as well as workload) introduces quite some variation in EAC (as well as granular) scrubber duration as DL quite extensively demonstrate http://www.deeplife.co.uk/or_files/DV_OR_ScrubberEndurance_Retest_SRB_101215.pdf
It would be great to directly compare your testing against DLs for those conducting 100m and deeper rebreather dives. Especially for the Inspiration, as even after 20 years of use of the same scrubber, there appears to be a real dearth of reporting on its scrubber duration at that depth… Maybe due to how quickly it breaks through deeper that 40m in 4’C water at only 40RMV but that’s just a guess. Conversely DL have testing of their EAC scrubber systems down to 350m under real world diving conditions….

Did your testing exhibit the same hump in inspired CO2 as DL showcased on their testing of the EAC at 100m for CE with the inspired CO2 measurement taken at the mouth?

Figure 5-7. Mouth CO2 in the breathing loop against time. Scrubber endurance (5 mbar PPCO2) = 105 min or 1 hour 45 min; Scrubber endurance (10 mbar PPCO2) = 136 min or 2 hour 16 min; Scrubber endurance (20mbar PPCO2) = 167 min or 2 hours 47 min; VWAI reaches the limit of 20 mbar at 161 min. The intervals are mass spectrometer calibration checks. The hump in the scrubber endurance around 35 minutes is a known phenomena, due to the time taken for the moisture balance to even out. In the worst cases, this can breach the CE ceiling, so is given as an endurance limit in manuals. As can be seen from the plot, the real endurance is over 2 hours at this depth. This is an extremely high performance scrubber.

http://www.deeplife.co.uk/or_files/DV_OR_ScrubberEndurance_Retest_SRB_101215.pdf

 

[Brad_Horn]

Brad will no doubt claim that these results are confounded by the testing of the EAC in a "poorly designed rebreather". Whether this is true or not, and whether the poor design features somehow selectively disadvantage the EAC and not the granular cartridge remain to be seen (I would certainly not take his word for it). But if so, such sensitivity to rebreather design could, of itself, be interpreted as a disadvantage for the EAC. Perhaps more importantly, unlike Deeplife's flagship "iCCR" (deposits taken 10 years ago, still not released) the Optima is a real rebreather being used by real divers. Thus the comparison of its CO2 scrubbing modalities is of real world relevance.

Simon, despite the fact that you know it is true. You would appear to be insinuating that the Optima had ‘any’ design optimisation applied to it and specifically its scrubber prior to public sale…
I certainly can’t find any evidence of this, bar a couple of scrubber tests done by Micropore, though most happy to be publically corrected…. Dive Rite O2ptima Rebreather Scrubber Duration Test Results | Dive Gear Express®

However, I’m sure DiveRite would be quite happy providing you the historical evidence of all of their test and evaluation, of the Optima’s ‘design’ verification, highlighting how they optimised its performance prior to sale! If it existed….

As you allude to, Micropore’s EAC is obviously extremely sensitive to scrubber canister design. This is not a surprise; though apparently it is to you. Just compare Leon’s testing in his ISC Meg fitted with an EAC to your Optima testing… Or APD. Or VR. Or what NEDU have likely done for USN/SOCOM albeit that’s under probably ITAR’d. Or JFDs. And then the results that apparently everyone else but you can read about in truly impartial academic studies of EAC absorbent performance in rebreathers.
Then compare it to the EAC scrubber duration results DL designed rebreathers get ‘at the mouth’….

Contrary to your insinuation that this sensitivity is a disadvantage, I’d argue it’s actually a significant advantage to the end user, if not manufacturer. Because with professional engineering (as you’d expect off a professional use rebreather that has actually been designed from the ground up for underwater life support) process you’ll have had the resources spent up front on validation and verification as part of a considered test and evaluation procedure to optimise the units design; well before any customer gets their hands on a unit.
If you get poor duration results in a diving rebreather, as the academic papers above show, it is NOT the EAC at fault….

How does this help the diver in the real world. They now expect to get a plethora of scrubber durations based on actual depth, water temp and workload to enable thorough and actual pre-dive planning for viable duration as a default. If as broad a set of results isn’t published for any specific rebreather, the prospective diver/buyer instantly know that no (or highly limited) test and evaluation has been done on that rebreather by the manufacturer. Which for those who are informed, will always trump glossy marketing…

The EAC being a solid state component, exhibits a known scientifically repeatable scrubber duration (in the same design of rebreather) utterly independent of any: packing variation, dust, channelling or caustic cocktail risk as evident by granular scrubber usage. And offers quite significantly greater functional safety to the end user out of the box before they even get wet.

Eliminating this variability will directly translate into longer minimum duration, and a +/-5% variation in duration at any test condition (granules can vary up to +/-30%).

https://www.diverite.com/wp-content...ma-User-Manual-2016-Rev-A-July-2016-final.pdf

Interesting that you claim “DLs flagship” CCR is their purpose designed mixed gas recreational use CE certified iCCR, which is in reality, only a lightweight spin-off, of their CE certified military use Incursion-BMR deep MCM CCR; itself a spin-off of their CE certified Umbilical Commercial rebreather. That flagship product being the ONLY CE and NORSOK certified primary Commercial eCCR on the market!
See pg126 http://www.edtc.org/MINUTES/Minutes...bers Meeting.pdf&bcsi_scan_5e8320feade9cba2=1 BUT just order from OSEL if you want this actually delivered…. OSEL having always owned the IP and tooling!!!

Of course, you didn’t need an iCCR for your test for scrubber comparison purposes, the US$995 Apoc Type IV CCR that OSEL shipped to every single customer whom paid for it and OSEL continues to manufacture for new customers, would have worked perfectly well. Nothing else on the market offering even close to the same low WOB for mixed gas use or general breathing performance or as good scrubber duration ‘at the mouth’ with an EAC.

When OSEL ships the iCCR to EAs, it will be sold for the same price it was ordered for; at least for those with outstanding deposits. OSEL still being the only supplier for rebreathers with end-tidal CO2 monitoring and at this time the iCCR looks like it will be the only unit for recreational use on the market; that will have CE certification for integrated solid-state PPO2 monitoring.

 

[Brad_Horn]

What we are "anti" is misleading claims. There have been many claims made around EACs which we wished to investigate, and as a step in this direction we conducted a comparison with granular sorb in a setting that we considered ecologically valid and fair - a rebreather manufactured to take either.

Simon, it is interesting you say “manufactured to take either”, and not as you imply above, designed to. A subtle but critical difference, as your limited study has found.

The only “misleading claim” would appear to be your conclusions when applied to the EAC itself and its use in rebreathers other than the Optima….

AFAIK, the aftermarket TECME et al granular scrubber adapter as machined to physically swap with an EAC scrubber was quite the afterthought in order to enable those who didn’t want to pay for the EACs additional performance or safety (nil dust/channelling, low WOB, low Caustic Cocktail risk (in certain units, but not apparently the Optima)) benefits etc etc. And therefore no rebreather on the market has actually been “designed for both”; not Kevin’s original VR Sentinal, the ISC Meg and even the MK25 MOD2 whose scrubber was specifically designed to firstly fit in the LAR and secondly take a EAC. As none of these units were actually designed from a clean sheet of paper and optimised for the EAC through any Test and Evaluation process. Part of that T&E being validation and verification of the design through an extensive and quite costly R&D process. And not just a single published test of the scrubber duration, without review and refinement until optimised, as tends to be the unfortunate norm for recreational rebreathers….
Could you get a better scrubber duration out of an EAC in an Inspo, Meg, Optima or any other recreational rebreather? Sure just start with an OSEL scrubber Open Safety Equipment Ltd and work from there BUTs its scrubber duration will always be less ‘at the mouth’ than an Apoc Type IV CCR….

Conversely as their quite extensive testing shows OSELs Umbilical Commie unit, Incursion and Apoc were purposely designed by DL to offer optimised performance with Micropore EAC; however, will offer the same scrubber duration with a 2.6kg fill of granular scrubber albeit with a greater requirement for increased hazard risk acceptance by the user. This isn’t an academic feature, rather reality.
And no, sorry, that 2.6kg granular scrubber fill option isn’t available for sale for recreational use ATT and is only supplied by OSEL where military operational use requires and outweighs it as a riskier option.

OSEL can even help you measure scrubber duration more accurately, as we are the only company selling the equipment to efficiently conduct deep high workload hyperbaric testing of diving rebreathers under real world conditions in the comfort of your own lab. The webshop needs an update but I’ll send you privately the details of the MKIV breathing simulator that OSEL are now supplying a host of the more serious rebreather manufacturers and test agencies. Open Safety Equipment Ltd

Unfortunately it is not possible to test an EAC against a greater mass of sofnolime in the same rebreather.

Simon, why not?
Works fine in OSELs Incursions! Albeit at a higher beneficence during manned testing/use but certainly no greater than the ethical risk of any other rebreather that was designed or even lower than those just manufactured to use granular absorbent.

When the Optima scrubber canister is filled with sofnolime 797 it occupies the same volume as the EAC canister and weighs ~2.1 Kg (about the same weight as the EAC)

Sure. And so what!
If you are at all interested in accuracy, you will have noted that my comment is relevant when an EAC is directly replaced by granular absorbent in a DL designed rebreather; when you need a fill of ~2.6kg…. Not exactly hard for folk to independently check this themselves, as an EAC measures 195 mm (5 inches) in diameter and 125 mm (7.7 inches) in length and then you have quite a lot of space in addition when you remove both the flow cones that are supplied as standard for EAC use in OSEL rebreathers. Granular absorbent obviously not requiring either flow cones or a core to wrap an EAC around during manufacture…..

Simon, what is the variation in CO2 scrubbing performance between the Optima and Inspiration that you have identified at say reasonable dive depths of 40m and 100m? If you are unaware of this, as your ‘testing’ to date would appear to indicate, might not the actual real world relevance of your testing, be that the safest place to dive an Inspiration or Optima is at the surface. Especially when neither is supplied by either manufacturer fitted with a gag strap….

Kind regards
Brad

 

[KenGordon]

When OSEL ships the iCCR to EAs, it will be sold for the same price it was ordered for; at least for those with outstanding deposits. OSEL still being the only supplier for rebreathers with end-tidal CO2 monitoring and at this time the iCCR looks like it will be the only unit for recreational use on the market; that will have CE certification for integrated solid-state PPO2 monitoring.

Hmm, a lot of future tense in here for a product at Eurotec 2008.

I read a couple of Brad’s links so (and all his posts above) to save SB’ers the pain. I have also previously paid up to EUBS so I got to read Simon’s paper too.

The DAN 8hrs (actually one broke through just before) thing is for human testing in lab conditions (at approximately sea level pressure) with gas temperatures of about 30C. So RMV rates in the 10 to 20l/minute range I would guess. The paper does not say that the humans had to do exercise and lists resting RMVs averaging 11.6l/m. Compare that to 45l/m in 18C and then deco at 17 l/min done with a machine. The simulated exercise looks to me to start off double that of the humans, although then a bit lower for the deco.

I would guess that running similar parameters might lead to similar outcomes, so maybe the Optima is not so non optimal as Brad would have us think.

I am off to read The duration of two carbon dioxide absorbents in a closed-circuit rebreather diving system. - PubMed - NCBI which uses a very similar method to compare two types or sorb.

 

[Dr Simon Mitchell]

Hello Brad,

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

Noting the pre-existing independent peer reviewed study published by DUKE/DAN flagged at least an additional 43% efficiency comparing the EAC over granular absorbent in a rebreather during comparable human trials at 1ATA. As unlike your study of course, the focus of this was on an actual scientific comparative performance of the scrubber media in isolation without any impedance due to a specific rebreathers lack of design validation. And that EAC trial they cut short at 8 hrs….
https://www.diversalertnetwork.org/training/instructors/REMOReport.pdf

Jiang et al (July 2018) in their rather more extensive than yours “In vitro efficiency of 16 different Ca(OH)2 based CO2 absorbent brands” also found that the Micropore EAC “outlasts a granular system by two times” based on the evidence they have published in Table 2 and at least one of your co-authors has been aware of since July 2019; when they were formally advised of it in letter by Micropore.

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 what 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. Based on their results the only granular product which 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​