How long will you let the scrubber sit

Martin Parker said:
At 75 RMV the Inspiration is 1.84 j/l at 100.3m or 329ft
At 89.9m (295ft) it's 1.75 j/l

By interpolating, at 300 ft = 1.76 to 1.77 j/l

(All tests done at 4.3 C, all figures ATP, no BTPS adjustment. )

To put it into perspective, the limit is 2.75 j/l but with BTPS conversion. To find the 75 lpm BTPS level I'd have to test at 62.5 lpm and then convert both to BTPS and interpolate between the two. 75 RMV (ATP) was 82 (BTPS) from memory at 4.3C and 100.3m.

In 2002 when the NEDU test was done, the WOB limit was the one for OC regulators, 3.0 j/l. They tested one over this and one under, giving their average of 2.98. having seen much lower figures at QinetiQ I know there's an error in their testing.
All test houses are capable of making mistakes and I have challenged NEDU on their figures. We'll see whether they can be bothered to re-test

Since 2004, the Inspirations have been inside the EN14143:2003 limits and this has been proven by extra audits and external testing.

But, as I pointed out in my first post... A p*ssing contest on WOB is a waste of time, you need to take into account elastance and hydrostatic imbalance as well.

Humans are really good at feeling hydrostatic imbalance and often confuse that with work of breathing, elastance takes them a little longer to pick up but the pain arrives eventually, WOB or resistive flow historically isn't so easy to feel...look at the regulators produced in the 70s and 80s...there were probably only a couple of models that would meet today's EN250, (3 j/l limit at 50m (air) at 62.5 RMV.)

It's taken years to get agreement on how to even measure elastance and hydrostatic imbalance between both sides of the Atlantic and I'm not convinced the Hydrostatic imbalance test method is where it needs to be yet.

Dan Warkander's proposal is to add all three together, by adding the % of max. for each value, how valid that is I don't know but it would certainly give divers a better comparison tool. All figures would have to be gleaned in all positions which as Dave said is less onerous when you have your own machine and is something for the future but to have all those tests done and externally verified would be mega expensive and I can't see that getting through the standards committee without a lot of proof as to it's worth.

While I am writing about the European Standards Committee, Gian's comments about the makeup of the committee is wrong. As far as I am aware, explanations have been given to him as to why his claims for defective standards have been rejected. He claims commercial interest drove those decisions but my understanding is that the make up of the committee was provided which would make it clear that the make up is a balanced group comprised of physiologists, test houses, user group representatives as well as manufacturers and training organisations.
My understanding is that collectively and unanimously they rejected his claims.
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I have no problem with the truth, and it is not true that "explanations have been given to him [me] as to why his [my] claims for defective standards have been rejected."

I have repeatedly asked a "reasoned response" from the Committee as I believe it is under obligation to provide a "reasoned response" for its decisions, and the reply I received was that it has no such obligation.

I raised the issue, as I believe it was the morally right thing to do, that the current 2.75 j/l limit in EN14143:2003 was too high based on the best science available to date and provided a copy of Warkander 1992 research.

The response I received (from Resolution 88/2011 taken by CEN/TC 79/SC 7 on 2011-12-14) was:

"Man has evolved without the use of RPE. As soon as RPE is used risks are introduced; these have been assessed from those that are insignificant to those that may be considered unacceptable. The WOB levels agreed by a consensus in CEN/TC 79/SC 7 are considered by the experts involved, taking into account the best available scientific and engineering information, to be at an agreed level considering all aspects of diving equipment use and safety."

I do not consider that to be a "reasoned response" and look forward to receive a response as to exactly why the limit is not being lowered from 2.75 j/l to 2.0 j/l as advised by Warkander.

Until such time I receive a reasoned response, my belief is that commercial considerations have been placed ahead of safety (some CE rebreathers well exceed the 2.0 j/l limit), but I am prepared to change my view after having considered a reasoned response from the Committee if and when I receive it.

As to the Composition of the Committee, I have asked several times for a list, country by country, of the entities which represent the Consumer and the Consumer interest in the Committee.

To my knowledge there is none, and until such official list will be provided to me, none there is.

I maintain Warkander 1992 research should not be ignored, and if a better one exist we should go for it (but I have to date not been provided by any one alternative and better scientific research).

I can only agree that WOB alone is only part of the picture and there is other separate and independent factors and tests which have to satisfy the best science requirements, namely hydrostatic imbalance and elastance, but my Claim of Defective Standard was about only the WOB aspect (i.e. 2.75 j/l) being too high based on Warkander best science.

"Man has evolved without the use of RPE." - does not constitute a "reasoned response" to Warkander best science:

Physiologically and subjectively acceptable breathing resistance in divers' breathing gear, D. E. WARKANDER, W. T. NORFLEET, G. K. NAGASAWA, and C. E. G. LUNDGREN, Underwater Biomedical Research, Vol 19, No 6, 1992.
 
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Hi Martin,

I wanted to take a moment to personally welcome you, and to thank you for participating and for offering your expertise.

You wrote above:

Humans are really good at feeling hydrostatic imbalance and often confuse that with work of breathing, elastance takes them a little longer to pick up but the pain arrives eventually, WOB or resistive flow historically isn't so easy to feel...look at the regulators produced in the 70s and 80s...there were probably only a couple of models that would meet today's EN250, (3 j/l limit at 50m (air) at 62.5 RMV.)


This is dead on, and is an excellent point that RB divers especially ought to really think about. I think I could poll 1000 rebreather divers and perhaps get one that was able to parse out the differences, with what they think of as "WOB" really being hydrostatics at play. My guess is that the basic RB diver intellectually lumps all three together "in the field" and when reading published figures of WOB (resistive flow) thinks that this figure incorporates all of what they have modeleled internally as "WOB" when it's really not the case.



Excellent points, and something that I think I'll incorporate as an "added learning point" in courses.



Best,

Dave

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gianaameri said:
I accept I am critical of CE because it adopts an upper WOB limit which according to Warkander is unsafe.
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And according to many others is fine..... including the US Navy, NOAA, and CE... and I really don't think that the USN or NOAA are driven by commericial interests. Really... I doubt that CE is "corrupt" either.

The answer you received from CE was about what I would expect them to provide to any layman who writes them a letter. They are really under no obligation to expend a large amount of resources dealing with every consumer who writes them with a question. They politely told you that the majority of scientific opinion was on the side of the current limit. Factually... that's the truth. You have one paper, albeit one written by someone we all highly respect, *suggesting* that another limit be considered. That's one small minority opinion at present in the scientific literature. And... <sigh>... every scientific paper tries to generate enough interest in the subject so that more funding is given for more research, which is what keep researchers employed. I think we would be foolish to think that there is not some small level of "corruption" in that process... :chin: "suggestions" in the conclusions of scientific papers are the norm...

In any event, you have made your point, which is one that is appreciated. Now it's time to quit beating the dead horse. The CE standards for now are what they are. RB divers are not dropping like flies... which ought to mean something. Room for improvement? Always. Conspiracy theories? Uhh.... :sigh:


So.... move on please?

:deadhorse:



Best,

Dave

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Dave Sutton said:
And according to many others is fine..... including the US Navy, NOAA, and CE... and I really don't think that the USN or NOAA are driven by commericial interests. Really... I doubt that CE is "corrupt" either.

The answer you received from CE was about what I would expect them to provide to any layman who writes them a letter. They are really under no obligation to expend a large amount of resources dealing with every consumer who writes them with a question. They politely told you that the majority of scientific opinion was on the side of the current limit. Factually... that's the truth. You have one paper, albeit one written by someone we all highly respect, *suggesting* that another limit be considered. That's one small minority opinion at present in the scientific literature. And... <sigh>... every scientific paper tries to generate enough interest in the subject so that more funding is given for more research, which is what keep researchers employed. I think we would be foolish to think that there is not some small level of "corruption" in that process... :chin: "suggestions" in the conclusions of scientific papers are the norm...

In any event, you have made your point, which is one that is appreciated. Now it's time to quit beating the dead horse. The CE standards for now are what they are. RB divers are not dropping like flies... which ought to mean something. Room for improvement? Always. Conspiracy theories? Uhh.... :sigh:


So.... move on please?

:deadhorse:



Best,

Dave

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Indeed we should move on and I will not discuss CE unless statements are made about me by others which are not true, requiring my having to address them.

On your point about the USN, I am of the impression that according to NEDU 2.75 j/l is too high, and they prefer a different limit.

According to NEDU, the resistive effort (WOBNT, in kPa) should not exceed WOBNT = 2.49 - 0.016 * depth (with depth in msw) or WOBNT = 2.49 - 0.00485 depth (with depth in fsw). The elastance should not exceed 0.7 kPa/L independent of depth and ventilation. The maximum tolerable hydrostatic imbalances, measured relative to the suprasternal notch, should be in the range of +0.4 to +2.9 kPa for a vertical diver and in the range of -0.3 to +1.7 kPa for a horizontal diver.

Are you sure USN and NOAA are happy with 2.75 j/l upper limit?
 
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Martin Parker said:
At 75 RMV the Inspiration is 1.84 j/l at 100.3m or 329ft
At 89.9m (295ft) it's 1.75 j/l

By interpolating, at 300 ft = 1.76 to 1.77 j/l

(All tests done at 4.3 C, all figures ATP, no BTPS adjustment. )
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I've removed the error in my 2 previous posts to say 100m rather than 300ft (missed it, sorry).

At 300ft that's 64% (300ft/2.75) or 88% (300ft/2.0).

Matt.
 
matthewoutram said:
I've removed the error in my 2 previous posts to say 100m rather than 300ft (missed it, sorry).

At 300ft that's 64% (300ft/2.75) or 88% (300ft/2.0).

Matt.
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Can you do a table for air, say 40 meters 75 RMV (in percentage of course using 2.0 j/l as the upper limit)?
 
gianaameri said:
Until such time I receive a reasoned response, my belief is that commercial considerations have been placed ahead of safety...
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Did you ever discover who was on the committee? I asked CEN for the members list of CEN/TC 79/SC 7 and they said this:

CEN said:
Dear Dr Outram,

Thank you for your message.

Please note that lists of TC members are not made available to the public.

For any further information on this, please contact your National Standards Institution.
:: CEN - European Committee for Standardization :: United Kingdom

Best regards,

Anissa Azifi
Manager - Infodesk
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For me at least I'm pretty dubious that decisions are made for commercial interest reasons over safety. I'd say it's more likely a mix of both and that as with most things no utopia exists.

The list of names would help. I've no idea why it's a secret.

Matt.
 
:offtopic:
matthewoutram said:
Did you ever discover who was on the committee? I asked CEN for the members list of CEN/TC 79/SC 7 and they said this:



For me at least I'm pretty dubious that decisions are made for commercial interest reasons over safety. I'd say it's more likely a mix of both and that as with most things no utopia exists.

The list of names would help. I've no idea why it's a secret.

Matt.
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:nono::cussing:
 
matthewoutram said:
So you didn't want the table you just wanted to point this out about one unit - something you deny doing. What's your motivation?

Or 90% of EN14143:2003.

Let's take the assumption that the CE group are the experts and that the limit is 2.75 rather than trying to goad folks on the internet just because the experts disagree with you.

Thanks,
Matt.
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I prefer NEDU and Warkander insofar they have supplied some research to support their assertion.

Try also:

COMPREHENSIVE PERFORMANCE LIMITS FOR DIVERS' UNDERWATER BREATHING GEAR: CONSEQUENCES OF ADOPTING DIVER-FOCUSED LIMITS, TA05-12 NEDU TR 07-02 January 2007, D. E. Warkander, Ph.D.

in addition to:

WORK OF BREATHING LIMITS FOR HELIOX BREATHING, TA 10-06 NEDU TR 10-14 November 2010, D. Warkander, Ph.D.

in addition to:

Physiologically and subjectively acceptable breathing resistance in divers' breathing gear, D. E. WARKANDER, W. T. NORFLEET, G. K. NAGASAWA, and C. E. G. LUNDGREN, Underwater Biomedical Research, Vol 19, No 6, 1992.

I would have been corrected by Dr. Simon Mitchell by now if anything which I posted in his field of expertise were incorrect - so 125% for me.
 
gianaameri said:
I prefer NEDU and Warkander
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Good for you.

The number is 175% at 100BTPS. But ask yourself this - who the hell care about those numbers (75RMV on Air at 40m, really??)?

At 50BTPS (and if you were participating in a wider range of topics you'd see that figure a lot) then the figure is 75% (at 2) and 54% (at 2.75). That's a number I am interested in.

I'm less concerned with the theory and more with the practice.

I assume your regularly diving on Air to 40m and planning your bailout gas at 75lpm, and that's why this research is so useful to you.

Matt.
 
matthewoutram said:
Good for you.

The number is 175% at 100BTPS. But ask yourself this - who the hell care about those numbers (75RMV on Air at 40m, really??)?

At 50BTPS (and if you were participating in a wider range of topics you'd see that figure a lot) then the figure is 75% (at 2) and 54% (at 2.75). That's a number I am interested in.

I'm less concerned with the theory and more with the practice.

I assume your regularly diving on Air to 40m and planning your bailout gas at 75lpm, and that's why this research is so useful to you.

Matt.
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Matt,

you are just a little bit overly sensitive.

I do not make the research and publish the numbers.

The research is from NEDU and Warkander and the table came from the manufacturer website (APD published the table, so it is there because it wanted people to see it).

There are tests ("Testing" under InnerSpace Systems Corp ) done at lower RMV than 75 as well and the conclusion is:

"In comparison to the AP valve Inspiration that ISC contracted out the HSE/HSL to test on two different dates of 11/01/06 and 30/11/07 the WOB at a test depth of 50 meters using air diluent at a lower ventilation rate of 40 RMV, Tidal volume of 2.0 liters, and breathing rate of 20 bpm the outcome was 2.11 J/l, and 2.09 J/l respectively."

"ISC will post at a later date the 40 RMV test data for apples to apples comparison, but uses the data above for the reader to understand that the AP valve Inspiration would breathe considerably higher at the 75 RMV than the Megalodon system using any one of the 5 canisters."

"In comparison to Delta P's data posted comparing various rebreathers to each other the data is inaccurate in regards to the Megalodon. Delta P states on their comparison chart that the Meg exceeds the CE bench mark of 2.75 J/l. On the contrary, the Meg beats the Sentinel in WOB. According to Delta P, the sentinel has a 2.4 J/l WOB. 3 out of 5 canisters tested in the Meg beat the Sentinel."

So, quite frankly U.S. products and standards appear to be superior to EU products and standards based on available published test data and research.

I side with NEDU and Warkander wholeheartedly.
 
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I've no clue what you're now driving at. The limit is 2.75, all units seem to be under that figure from the numbers in those reports that you continuously quote.

Some units are lower, some higher, all are under.

Matt.

gianaameri said:
Matt,

you are just a little bit overly sensitive.

I do not make the research and publish the numbers.

The research is from NEDU and Warkander and the table came from the manufacturer website (APD published the table, so it is there because it wanted people to see it).

There are tests ("Testing" under InnerSpace Systems Corp ) done at lower RMV than 75 as well and the conclusion is:

"In comparison to the AP valve Inspiration that ISC contracted out the HSE/HSL to test on two different dates of 11/01/06 and 30/11/07 the WOB at a test depth of 50 meters using air diluent at a lower ventilation rate of 40 RMV, Tidal volume of 2.0 liters, and breathing rate of 20 bpm the outcome was 2.11 J/l, and 2.09 J/l respectively."

"ISC will post at a later date the 40 RMV test data for apples to apples comparison, but uses the data above for the reader to understand that the AP valve Inspiration would breathe considerably higher at the 75 RMV than the Megalodon system using any one of the 5 canisters."

"In comparison to Delta P's data posted comparing various rebreathers to each other the data is inaccurate in regards to the Megalodon. Delta P states on their comparison chart that the Meg exceeds the CE bench mark of 2.75 J/l. On the contrary, the Meg beats the Sentinel in WOB. According to Delta P, the sentinel has a 2.4 J/l WOB. 3 out of 5 canisters tested in the Meg beat the Sentinel."

So, quite frankly U.S. products and standards appear to be superior to EU products and standards based on available published test data and research.

I side with NEDU and Warkander wholeheartedly.
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matthewoutram said:
I've no clue what you're now driving at. The limit is 2.75, all units seem to be under that figure from the numbers in those reports that you continuously quote.

Some units are lower, some higher, all are under.

Matt.
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I side with the U.S. (Warkander and NEDU) because they have a better and safer approach (scientific and documented), and this seems to drive some manufacturers to strive for higher standards and safer products than other manufacturers - a lower WOB (2.0 j/l) being safer than a higher WOB (2.75 j/l).

It is not very difficult to understand.
 
They may have safer approach i am not qualified to know if its safer or not but I do know in the U.S they can be ignored. At least in europe the CE cannot be ignored
 
gianaameri said:
So, quite frankly U.S. products and standards appear to be superior to EU products and standards based on available published test data and research.
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Noting obviously that there is only *one* completely US Made rebreather in general use: The Megaladon. That's a "Product", not part of a set of "Products". I do not think there is anything magic about US "standards" (as there are none at all). This more speaks well of Leon and ISC.

We do have a non-CE but European manufactured rig that "fakes" as a US Unit, the Hammerhead, but... it's a Czech rebreather that has not undergone CE, and in fact as far as I know has not undergone any real testing at all.


Who's up for a thread split?


Dave

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ccrdave said:
They may have safer approach i am not qualified to know if its safer or not but I do know in the U.S they can be ignored. At least in europe the CE cannot be ignored
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They are ignored, but I believe this should the subject of a separate thread, so unless the Mods say otherwise here I will start a separate one.
 
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