Duration on the new EP Extendair cartridges?

n2diving

I'm told by people who are close to such matters that the EP cartridge in the various units you mentioned have exhibited significant differences in performance. This is apparently because various differences in housings, orientation, hose lengths, etc affect the flow of gas through the cartridge. Even the same canister housing retrofitted to different rebreather breathing loops should not be assumed to produce identical results.

It's an interesting point of view that you don't consider the Dive Rite recommendation of 3 hours for the O2ptima scrubber to be conservative enough. How do you feel about Molecular Products statement of >140 liters / kg for Sofnolime or APD recommendation of 3 hours for the Inspiration scrubber? In your opinion are they conservative, liberal or about right?

It occurs to me to ask... do you, when referring to the recommendation values, mean conservative in relation to your personal use or mean conservative in relation to a value for the entire population of rebreather divers?

I may have a different view of 'safety' than you do based on your comment 'the main concern should be safe diving'. I perceive 'safe', particularly as it applies to diving, as not having a binary state. To adopt the most 'safe' recommendation for duration on the cartridge then I think the majority of the non-diving and much of the diving population would set that value as ZERO, i.e. don't dive using CO2 absorbent or anything else for that matter. Once we allow the value to be something other than zero, what constitutes 'safe' introduces a lot of variables. I do not expect everyone will have the same risk/reward considerations when determining a 'safe' scrubber duration. I know of one diver who considers 'safe' to mean he begins each dive with fresh absorbent. I know divers (some of whom I consider to be quite reckless) for whom 'safe' means they can exceed the manufacturer recommended values by enourmous margins.

Genesis

Agreed with this for the most part.

I think that its reasonable to assume that "Safe", from a standpoint of CO2, is that the level in the inhale hose cannot exceed 0.5% SEV.

The problem is that right now we can't measure that in real-time with current units on the market.

As such anyone diving a xCR is by definition diving unsafely, since we have a parameter that, if it is exceeded, is quite likely to kill you, and we have no means to verify whether that parameter is currently within safe limits or not. This is somewhat like diving without a PO2 meter - you have bailout, but you're trusting that you will detect hypoxia and bail before you pass out, or hyperoxia and bail before you have a full-blown grand mal.

To a significant extent this is all playing canary in the coal mine. Exactly how each diver balances the scales of safety for themselves is an exercise that is ultimately their choice - and the more information available to the diver, the better.

__________________
"A venturesome minority will always be eager to get off on their own, and no obstacles should be placed in their path; let them take risks for Godsake, let them get lost, sunburnt, stranded, drowned, eaten by bears, buried alive under avalanches - that is the right and privilege of any free American."
http://www.denninger.net
http://www.diversunion.org/liability.htm - Fix the Diving Cert racket

paulraymaekers

hello, what is the weight of the micropore scrubber, and the diameter/length ??

just to compare with granular scrubbers

thanks and regards
paul

__________________
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.... the earth is flat, Elvis is alive, and radial scrubbers give longer dwell time than axials...

caveseeker7

I can see how for example gas velocity/dwell time through the scrubber can net different durations for the same cann/cartridge combo in different units. Still, a 50% increase in duration and 150% increase in MOD is quite a jump from the initial rating. And EP is misleading, I thought they changed the cartridge. TP would be more appropriate: Tested Performance.

I neither said nor believe that. Asuming that the few published graphs are just part of the tests of the cartridge I don't really know just how much of a safety margin is in the rating. But if performance was consistent, which is a safe assumption given that it's a cartridge rather than loose granules, I would probably have rated it close to the test numbers.

From the data I've seen even granular scrubbers properly packed get quite repeatable results, and ratings are not far off those.

That is the maximum absorbing capacity of the material in the lab.
All it really tells you is that if someone claims his breather absorbs 190 liters/kg he's blowing smoke up your ass and CO2 down your throat.

That number is really the only number Micropore as a manufacturer should be realeasing: The maximum absorbtion that the cartridge has under ideal conditions. That's for the cartridge.

If they then build and sell replacement canns and adapters to go with it, they should test and publish the relevant numbers and give each combo its appropriate rating.

You kinda answered that question in my initial quote of yours. Outside factors influence duration. A lot of them. At it's 3 hr rating, the YBOD absorbs 288 liters of CO2, or about 53 lts/hr. That is far below the maximum capacity of the absorbant and due to the outside factors (primarily) and scrubber design (secondarily).

Obviously I haven't seen AP's test data, but I'm pretty sure that for the test done the numbers are quite right.

I mean conservative in relation to the test results.

Say you're running tests on a scrubber and get results between 3 hrs 8 mins and 3 hrs 22 mins, averaging 3 hrs 14 mins. Rating that scrubber at 3 hrs seems like a sound idea. Rating it a 2 1/3 hrs would be overly conservative.

The test protocol also plays into it, of course. CE requires 40 lpm RMV, around 4 deg C and 1.6 lpm CO2 addition.

RMV is pretty average I guess, but it is well know that during high excertion, panic or hypercapnia that can go up considerably, so there isn't much of a safety margin there I guess. This may well be the likeliest place where divers have experienced problems, moving gas through the scrubber at almost twice the RMV, reducing dwell time to the point of being insufficient (me thinks).

I wish there was hight RMV/high CO2 addition (which I think are likely to go hand in hand unless someone hyperventilates and doesn't vent the lungs ... dive docs chime in that one, please) testing to the point the scrubber fails.

Temperature seems okay, plenty of places in the world that are cold, so that needs to be the standard. Additional tests are welcome though for lucky gits in Florida and Tahiti.

CO2 addition is probably a compromise. Few people if any will generate 1.6 lpm CO2 for hours at a time. Somewhere between 0.8 and 1.2 lpm is probably realistic, judging by the O2 addition flow rates the mCCR divers use. So the Navy's 1.35 lpm only pads little (indeed, it's a mean value for CO2 production between 1 lpm and 1.5 lpm). CE ups the ante with 1.6 lpm. While this seems to add some padding, it only does so as a sustained rate. Divers don't. I would be much more intrested in a test protocol that varies the flow. If the actual sustained CO2 production rate averages in the 1 lpm neigborhood or slightly lower, then the periodic peaks considered to elevate the average to 1.6 lpm are the intresting part. How long does the scrubber last at 2 lpm or 3 lpm CO2 a minute? It ties in with the high RMVs I mentioned above.

Some independent testing done suggests that this is where CO2 breakthrough can occur.

I don't know what having a binary state means.

With "safe diving" I meant no CO2 in the inhalation side, or at least below a level accepted as safe (said 0.5% SEV ... I hope).

That's why the manufacturer of the absorbant should publish a number for the max absorbtion capacity of their material/media, and the Rebreather (or scrubber) manufacturer the data for the rebreather(s).

__________________
Cheers
Stefan



"Political Correctness is a doctrine, fostered by a delusional, illogical minority,
and rabidly promoted by an unscrupulous mainstream media,
which holds forth the proposition that it is entirely possible
to pick up a turd by the clean end.'!"

Toren

I'm really enjoying this, guys, and learning a lot. Just so you know!
For the avg 60' bimble/reef tourist diving I had planned on the Dolphin for Cayman Brac, I was figuring 3.5 hours (probably in two 105 minute dives) per canister. With my avg SAC of 0.4 (as determined by years of diving a Cobra) that seemed pretty safe.
But now I'll sit down and do some more number crunching.

ScubaDadMiami

Just as an added "trivia" note, in my Rebreather class, my instructor informs me that there can be as much as 20 percent variation in the ability to absorb CO2 in any given batch of CO2 absorbant. So, even if you have "pushed" the duration many times, that does not mean that this will be reliable on a consistent basis.

This includes the Extend Air Cartridges. Micropore just takes the same absorbant, and then it molecularly bonds it to the plastic.

I was pretty shocked to find this out.

__________________
Howard Packer
IANTD CCR Instructor
Miami Beach, Florida
CCRDiveTraining.com

n2diving

As I read that statement in context... I assumed the meaning was you did not think the O2ptima manufacturer duration rating was conservative enough. I stand corrected.

The 'binary state' reference comes from my computer background... sorry... it refers to safe not being a 'black or white' condition... meaning for some activities such as diving it may not be useful to consider as either 'safe' or 'unsafe'.... but rather evaluate safety as having a range of shades of gray.

Regarding the information from Micropore and Dive Rite... I recall that almost a year ago Micropore provided the data that the 4.4 pound cartridge duration in the O2ptima was 4 hours at 1 ATA, 40 lpm RMV, 1.35 lpm CO2, and 50F to reach 0.5% concentration... i.e. CO2 capacity is 162 liters CO2 / kg. (Consider that Molecular Products states simply the CO2 capacity of Sofnolime 812 is >140 liters CO2/kg with no further information about conditions under which that capacity was determined.) Upon delivery of the O2ptima to customers, Dive Rite published recommended scrubber duration values and a good bit of test data under a variety of conditions to support their recommendations.

I think that Dive Rite and Micropore have provided enough information for me to make reasonable evaluation of the O2ptima scrubber duration for my diving and my biometrics. This allows me to conclude that their recommendations are a little bit conservative but reasonable... for me personally. Each diver must make their own judgement as to the recommendations. Dive Rite and Micropore seem to have done pretty well in providing enough information to make that judgement... instead they could have said something like "scrubber duration is 3 hours -- no further information is provided." They could have said "We don't provide a duration recommendation -- here is some test data, you decide how it applies"... or they could have said "we don't have a recommendation and we don't have any test data -- use at your own risk".... I think there are other Rebreather designs in wide spread use that fit those descriptions and more.

Would consumers like MORE testing under more conditions? Of course, we always want more. Will it be forthcoming? Only, if the marketplace perceives a need great enough to be willing to pay for it. So far, that does not seem to be the case.

n2diving

If I am intrepreting these statements correctly, you are saying that duration should be stated as something close to failure point. I will disagree and an analogy may illustrate why I disagree.

Suppose we pressure test aluminum cylinders rated at 3,000 psi and after 10 tests find they very consistently explode at between 11,000 and 12,000 psi. Your logic for absorbent duration would suggest that the cylinder's 3000 psi rating is overly conservative and a rating of say 10,000 psi would seem like a sound idea.... the DOT and ASME would seem to disagree with you.

Keep in mind, failure of the scrubber is what the engineers call a "low-probability, high-consequence event". Perhaps someone reading this thread can better explain the mathematics involved in deriving usage recommendations from failure testing.

Genesis

One thing that I find missing from these recommendations is an uncertainty.

The scientist in me wants to see that on critical measurements. I don't want to see "2 hours in cold water at 130'"; I want to see "X grams of CO2 absorbed +/- 5% with a 95% certainty, and +/- 10% at 100% certainty."

I realize this is an unrealistic expectation on many levels, but that sort of statement allows one to plan their own margins of safety, rather than believing that whatever is offered as a margin is sufficient (or not!)

__________________
"A venturesome minority will always be eager to get off on their own, and no obstacles should be placed in their path; let them take risks for Godsake, let them get lost, sunburnt, stranded, drowned, eaten by bears, buried alive under avalanches - that is the right and privilege of any free American."
http://www.denninger.net
http://www.diversunion.org/liability.htm - Fix the Diving Cert racket

caveseeker7

Thanks for the 'binary' explaination, I knew the computer term just not how it applied here. You're right, many shades of grey here.

I remember that, too.

As well as the initial 2 hr duration and 40 m max depth rating on the original Dolphin cartridge and the first test graph for that combo shown below.

I think they brought the distrust in their product on themselves, at least my distrust.
The first time I read about the cartridges I was excited due to the simple use and reduced chances of a caustic cocktail. But I was aware that earlier tries with such media had very mixed results, working better than some scrubbers but not others. Hopes that the cartridge would improve Dräger's duration were shattered when the exremely limited duration was announced. Even more so after Dräger ammended their scrubber ratings a few years back (they did that for Europe and the Middle East two or so years before including the US). To make things worse, not only was the duration only two thirds, but the protocol useless for divers. Ambient pressure is the single largest outside factor, and they tested at 1 ata ... my conclusion back then was No good, that stuff.

By the time they handed out the graphs in '04 their train had left the station, and while the duration was better the test protocol wasn't. To make it worse, it gave the appearance that they peddled the $350 scrubber and cartridges without much testing before and with dumb testing then. Something I just don't appreciate for life support.

When Farallon's Phil Eng gave me his spiel about the O2ptima and all the testing that had been done, and all the plans they had for publication (full range of depth in warm and cold water, not just 1 run at 300 feet where the rest of the protocol differs from the shallow stuff) I was very excited. When he didn't send out any of the promised data that excited went quickly.

The data they published eventually is okay, and ahead of most manufacturers. I don't know if they were bound by test protocol requirements or not, but they picked one that doesn't comply (and compare) to either CE or USN protocol. If I had my pick I would have chosen the CE protocol, as that is what most RBs are tested and rated to. Inspiration, Evolution, Ouroboros, Ray, Dolphin, Submatix and Voyager. That would also show how the cartridge performs in the Drägers, Azi and Inspo compared to their stock scrubbers. If someone purposely avoids that comparison I don't give them the benefit of the doubt, not in life support system.

The USN protocol would have been the second choice, even though the PRISM is the only civilian Rebreather tested to it with published results. Might be helpful selling the technology to militaries, there should be a decent LAR V market.

Since they have that huge testing setup, they could have well done both.
Or at least a good run for the combos they sell to CE protocol and different depths. 20 m, 40 m (SCRs & CCRs), 75 m and 100m if they want to stay within manufacturers' limits. The facility is there, might as well use it.

Maybe that would even get manufacturers of their collective a$$es and have them supply the same data.

You do that math just after I write something about blowing smoke ...
I doubt the cartridges plastic weights much, but is it included in the 4.4 lbs?
Do they use Sofnolime or another absorbant?

The form is probably the culprint, 4-8 and 8-12 are the same material, just different granule sizes with different absorbing capacities.

Yes, they have. More than most manufacturers, which doesn't say much but is commendable. Kudos to DR and Farallon to get Micropore to finally run some tests. They could have done better (testing, not results), but it's a start. I wouldn't be uncomfortable using the O2ptima in that respect, at least within rec depths.

__________________
Cheers
Stefan



"Political Correctness is a doctrine, fostered by a delusional, illogical minority,
and rabidly promoted by an unscrupulous mainstream media,
which holds forth the proposition that it is entirely possible
to pick up a turd by the clean end.'!"