Comprehensive list of all accidents

**Dave Sutton** · 1st June 2008, 12:42

Quote: (Originally Posted by silent running)

I'm sorry about your suffering and fatigue, Dave. But exactly how much suffering and fatigue would you say you endured during these years?

Just a skepticism of snake oil, that's all, and eye muscles that are still sore after needing to roll them every time I read things published by SM. There's far more industrial history here than you seem to recognize. Back to the point: No test has establshed that the Prism has a WOB that's any better or worse than any other set, as the tests that are ballyhooed are not comparable in any metric against the others. There are no workable safety statistics for the rig due to low production numbers.

The germane part of the discussion here is to question your belief that the Prism has a WOB that is any better than any of the mainstream rigs. I am not convinced one way or the other, and as others have pointed out, the much flaunted "testing" is not comparable to others so cannot be compared. That's all the point that is being made. I have little confidence in the cred of the manufacturer, but look forward to any test that Alex does. It'll be interesting to see, as a few hours on the breathing machine there will have more value for comparison than "three years of EDU test"...

. Maybe it'll test great, maybe not. In the big picture, knowing this wil have little value as there are not enough of them in service for them to be of statistical interest. Heck, I'd love to see how my CIS Mk-5P tests too, but again: Why bother? With only 60 in service, who really cares? It's a failed design as well, similarly for economic reasons. The Prism is in good company here.

I'm glad you are happy with your rig: Don't take my lack of enthusiasm for the cred of SM personally. It's not about you and it's not about your rig. It's about my lack of confidence (and I must point out, a general lack of confidence by many others in the industry) regarding cred of the manufacturer. The purchasing public apparently agreed, voted with their wallets, and the result is that the design is essentially moribund. Anyone can see that.

Smile and go diving. We had a good day yesterday. Today ought to be better.

Dave

.

**Dave Sutton** · 1st June 2008, 13:00

Quote: (Originally Posted by jradomski)

not realy a hard thing to do.. the setup to read the code takes longer than to pull it.. but still less than 15minutes... turning it into usable soiurce code for modification is a small job as the code is very small..

And is apparently easier to do than to write your *own* code...

(not that any reputable manufacturer would take such a shortcut....)

Dave

.

***jradomski*** · 1st June 2008, 16:11

Quote: (Originally Posted by Dave Sutton)

And is apparently easier to do than to write your *own* code...

(not that any reputable manufacturer would take such a shortcut....)

Dave

.

Anyone that could create good source code, should be able to right new code even faster..

I have some code that was pulled out of a prism in nov 2002, and there is a big bug in the voting logic.. I dont remember how I originally obtained access to get the code.. that was along time ago..

**Gill Envy** · 1st June 2008, 16:47

with all this talk of WOB and skepticism, I have to ask Alex and Dave, when a test is done for WOB, is it on a machine or a human. there are so many variables to actual human performance which could be missed by a machine. for instance, what I've noticed is a huge variance of mouth piece thickness. the stock version that comes with the meg is super thin (my front teeth actually come together), the one that comes with the Evo is quite thick (holding my front teeth a good 1/2 inch apart) and I've seen everthing in between on other rigs. I can imagine that you could make a very capable rebreather in terms of WOB then make the mistake of putting a thin mouth piece on it that simply makes the teeth a barrier that add significantly to WOB in high respiration. I swapped out my mouth piece on the meg from the get go with a thicker one. Further, I've noticed that in the worst moment, we tend to bight down extra hard in current, potentially reducing the size of the air way. Are any of the WOB test taking this dynamic into account.

AD_ward9 · 1st June 2008, 17:16

Quote: (Originally Posted by Gill Envy)

with all this talk of WOB and skepticism, I have to ask Alex and Dave, when a test is done for WOB, is it on a machine or a human. there are so many variables to actual human performance which could be missed by a machine. for instance, what I've noticed is a huge variance of mouth piece thickness. the stock version that comes with the meg is super thin (my front teeth actually come together), the one that comes with the Evo is quite thick (holding my front teeth a good 1/2 inch apart) and I've seen everthing in between on other rigs. I can imagine that you could make a very capable rebreather in terms of WOB then make the mistake of putting a thin mouth piece on it that simply makes the teeth a barrier that add significantly to WOB in high respiration. I swapped out my mouth piece on the meg from the get go with a thicker one. Further, I've noticed that in the worst moment, we tend to bight down extra hard in current, potentially reducing the size of the air way. Are any of the WOB test taking this dynamic into account.

WOB is measured on a breathing machine with the equipment in salt water in a pressure chamber. This gives a result that can be reproduced at any time, that is objective and allows for direct comparisons.

In looking at the mouthpiece bite, we check the cross section is at least as large as the opening in the mouthpiece itself and record a problem in the results if it is smaller, and that we have had to change out the mouthpiece.

Humans are very poor at measuring WOB, but manned underwater tests do have a key roll in testing.

Human testing can check things like the ADV fires when the CLs are bottomed out in all positions, they feel they get a big enough breath or not, how the CLs affect trim, how water dumps work or interplay with the OPV and other ergonomic issues. Of course, if any changes are made, one has to repeat the machine testing all over again.

Alex

NB: Just one note on the recent divergence of this thread - the results of the under-funding complained about, are systemic in sports rebreathers. A new eCCR done completely properly costs vastly more than one would imagine. If there are 5000 rebreather users, who buy a Euro 3,500 rebreather once every 7 years, then that is just Euro 2.5mn of sales a year. Even if one spent every penny of it on R&D, it would take 5 years global sales to fund one new rebreather development properly. Given that revenue from sales has to be used to produce and support units, then there is simply not enough revenue potential in the sports market to fund a proper job. Some companies are better than other in avoiding the worst results of under-funding, and some have had larger budgets than others, but the result is still defects in products that would not be there in a commercial or military product, where the market is larger. The most expensive part is always that last 10%, and it is the most under-estimated.

One thing the accident list is for, and the Open Revolution initiative, is to enable some core information needed by everyone to be published, so each company does not have to reinvent the wheel. Lets return to that objective, to put the accidents here, and analysis on another thread. The WOB issue is a good point to debate, as its role in accidents is unclear, but saying unit A or B has underfunding problems is a statement that could be repeated many times on different units. There have been more than 30 companies try and make sports rebreathers.

**Dave Sutton** · 1st June 2008, 17:17

Quote: (Originally Posted by Gill Envy)

with all this talk of WOB and skepticism, I have to ask Alex and Dave, when a test is done for WOB, is it on a machine or a human.

Alex can answer for diving tests, all of the recent stuff I have been doing is test for a mine escape rebreather on which I am doing design consulting.
(And as a segue, there are 1000 mine rebreathers built for every diving one, so go see "Suttons Law")

Willie Sutton rule definition

In any case, having gone for the high-reward rebreather, all of our testing is machine driven and is done using a protocol that is duplicable by any other test center so that results may be validated. We are testing with the mouthpiece removed as the interface to the breathing machine does not accept a bite-bit.

Alex?

Photos of the unit under test as a teaser. And yes, with repackaging and use of lime rather than the Lithium scrubber it'll be modifiable to work as a bail out rebreather: Carried in an aluminum case sealed at 1 ATMA and being able to be deployed at depth and placed into service in about 30 seconds from the sealed state. It's a disposable rig (factory serviced after use) and is designed to be carried for 5 years between inspections, and has been tested to 2+ hours using Lithium scrubber. We need to get it finished as a mine escape system before putting attention to the diving market. What is shown is just a very rough prototype: NDA prevents posting the further developments.

But WTF do I know...

As Alex properly suggests, back to the thread topic and we can start a testing thread elsewhere if there is adequate interest.

Dave

.

AM · 8th June 2008, 12:58

This thread is going wildly off topic now, undermining the original objective to document, discuss and analyse accident data, not to discuss the semantics of rebreather strategic business directions.

Returning to WOB and test protocols - it is becoming increasingly evident that the CE rating process and indeed other rating protocols for sport rebreathers is unacceptable in that it contains too many variables and doesnt factor in some of the critical variables needed to draw effective conclusions.

The fact that every sports rebreather under the CE jurisdiction is not tested in the same methodology, i.e. under both prone and vertical positioning, is somewhat worrying. Equally it is concerning that there is a distinctive lack of data relating to how hydrostatic lung loading is factored into the testing. It is a classic feature of some BMCL rebreathers that if the lung(s) are not positioned correctly in alignment with the divers lungs, that the WOB is significantly altered.

Quote: (Originally Posted by paulraymaekers)

you start designing to meet the limits, and mostly as a consequence the unit becomes 'bigger': bigger hoses, bigger mouthpiece, larger volumes. Al this means you get a heavier unit, with often more drag under water.

now here comes a 50kg, 1.55m female diver who want to start diving CCR, and wants do buy a unit that meets the safety limits....

?? how many small female boris divers are around?

It is a valid point that there is a trade off between a bigger unit and more drag, therefore rendering WOB more difficult against the drag. The lack of small female boris divers is nothing to do with the weight of the unit, I am a small female and quite often I am carrying over 100% of my body weight in gear for some dives. The weight is not the issue, there is just an endemic lack of active female deep rebreather divers around, full stop. A real pity. I have tried tirelessly to encourage other female divers into rebreathers but the conversion rate is not high! As to wanting to buy a unit that meets the safety limits, well, in realistic terms, safety limits are a very subjective matter at this point in time.

Quote: (Originally Posted by Drmike)

yes but big bore doesnt necessarily have to mean heavy unit

The Sentinel (which apears to have the lowest wob (in upright position) is lighter than some mainstream units.

Putting a bigger bore dsv, good check valves and big hoses on a unit isnt going to make any real difference from a diveability or weight viewpoint at all but can in some cases significantly improve wob

Yes, that is the real key.

Quote: (Originally Posted by jradomski)

ANDY,
actually we can not be sure of that.. The test data indicates breathing resistance in the prone position.. All the other rebreathers are tested in the upright position.. This can be a tremendous difference.. ALso for WOB, traditionally the nedu tests were not calibrated to add in the WOB of the "diver" whereas ce test must add this in.. this will raise the WOB numbers for all CE units.. Until the prism is tested under CE parameters none of its test data is comparible.. Its apples to oranges..

The PRISM is being tested in the optimal position while most of the other rebreathers are being tested in one of the worse positions for many units..

Absolutely agreed. If the test conditions are not identical for all sports rebreathers, then the test outcomes cannot be used as a valid blueprint from which to draw COMPARATIVE conclusions across the board. Effectively at the present moment, we have subjective results which cannot be viewed with any relativity to other/all sports rebreathers.

Quote: (Originally Posted by jradomski)

actualyy wob tests were done at various levels.. 40m was one of them.. so at that level it wasnt deeper... The Nedu had a TARGET dept ofr operational performance at 150, so that had to be tested, but others were tested as well..

I personally dont agree with testing in the vertical position nor the prone position alone.. both need to be tested as the both have times they will be used.. for most rbs the verticle test will be worse (not just above the prone position), on some designs it will actually be quite acceptable.. if you are going to specify a single test for limits the one thats the hardest to pass makes senes, but neither should be used alone.. I personally beliver 3 positions should be tested 0, 45 and 90.. most CCR divers normal swimming position probably falls in the range of +20 or so from prone..

I am actually surprised to see NEDU just tested prone because many jobs the normal position is verticle and the most important position..

Mark 15 breaths well vertical sinceits design was for a working diver.. The classic Kiss breaths best somewhere in the middle, but still ok verticle, the sport breaths very poorly verticle but ok a few degrees up....

how well a unit will breathe in either position depends specifically on where the c-l are positioned.. units where the inhale or exhale lung will be below the lung centroid will breath bad verticle.. units that can spread them to keep them close to the lung centroid will be less effected..

our lungs are efficient at blowing against pressure but poor at sucking.. so a position where wh can inhale easily but work a bit exhaling is the best compromise.. OTS lungs work really well in the prone positin for 2 reasons.. the distance to the lung centroid is generally small, and it meets the above criteria.. we exhale to slightly higher pressure and gas from the inhale lung is at a greater pressure than our lung centroid so its forced into our lungs..

something like the rEvo does well becuase of the way he has the lungs positioned if you are slightly head up.. the inhale c-l is at a pressure slightly greater than the lung centroid and the exhale c-l is at a slightly higher pressure.. if you are fully head up.. no so good but MUCH better the fully head down where everything is the opposit of where we want..

Again good points. I still believe the hydrostatic lung loading is a key component and introduces a big variable to the test conditions conducted universally within the parameters of CE and other testing. The rEvo for example has a considerable variance in the breathing effort depending on where the lungs are positioned, this is classic for all BMCL rebreathers of course but if the rebreather lung is not accurately positioned in alignment with the diver's lung, it makes a HUGE difference to WOB.

Quote: (Originally Posted by AD_ward9)

WOB is measured on a breathing machine with the equipment in salt water in a pressure chamber. This gives a result that can be reproduced at any time, that is objective and allows for direct comparisons.

In looking at the mouthpiece bite, we check the cross section is at least as large as the opening in the mouthpiece itself and record a problem in the results if it is smaller, and that we have had to change out the mouthpiece.

Humans are very poor at measuring WOB, but manned underwater tests do have a key roll in testing.

Human testing can check things like the ADV fires when the CLs are bottomed out in all positions, they feel they get a big enough breath or not, how the CLs affect trim, how water dumps work or interplay with the OPV and other ergonomic issues. Of course, if any changes are made, one has to repeat the machine testing all over again.

Alex

NB: Just one note on the recent divergence of this thread - the results of the under-funding complained about, are systemic in sports rebreathers. A new eCCR done completely properly costs vastly more than one would imagine. If there are 5000 rebreather users, who buy a Euro 3,500 rebreather once every 7 years, then that is just Euro 2.5mn of sales a year. Even if one spent every penny of it on R&D, it would take 5 years global sales to fund one new rebreather development properly. Given that revenue from sales has to be used to produce and support units, then there is simply not enough revenue potential in the sports market to fund a proper job. Some companies are better than other in avoiding the worst results of under-funding, and some have had larger budgets than others, but the result is still defects in products that would not be there in a commercial or military product, where the market is larger. The most expensive part is always that last 10%, and it is the most under-estimated.

One thing the accident list is for, and the Open Revolution initiative, is to enable some core information needed by everyone to be published, so each company does not have to reinvent the wheel. Lets return to that objective, to put the accidents here, and analysis on another thread. The WOB issue is a good point to debate, as its role in accidents is unclear, but saying unit A or B has underfunding problems is a statement that could be repeated many times on different units. There have been more than 30 companies try and make sports rebreathers.

Alex, good point on the mouthpiece, this is something that many divers modify and appear to be unaware that it can create a significant alteration in WOB if the bore size is altered.

I second the points about the critical nature of this thread and the requirement for renewed focus upon the thread's primary objective which is accident data discussion, not dissemination of rebreather manufacturers' business decisions.

Regards

AnneMarie

AD_ward9 · 8th June 2008, 14:15

Quote: (Originally Posted by am)

Returning to WOB and test protocols - it is becoming increasingly evident that the CE rating process and indeed other rating protocols for sport rebreathers is unacceptable in that it contains too many variables and doesnt factor in some of the critical variables needed to draw effective conclusions.

You are right in that it should be much more explicit, with a diagram showing exactly how it is measured, stating clearly that the scrubber actually is filled, and setting down the precise test protocol.

Just on little point though, we go about testing WOB using the NEDU protocol with the EN14143 test depths etc. It defines WOB as the area enclosed by the Breathing resistance - volume Lissajou. I don't think the NEDU and CE definitions are right.

For example, take a Lissajou where the entire loop is positive pressure. Breathing in just involves opening one's mouth as the loop is positive pressure, but breathing out is harder. There is hardly any actual work in breathing in, but there is a pressure change from the mouthpiece to the suprasternal notch or lung centroid. That pressure change gets integrated and included as WOB. However, as it is positive pressure, all the pressure change is, is the effect of taking a gas volume out of the loop and putting it into the lungs.

Of course, going back the other way during the exhale cycle, the diver has to work against the pressure in the breathing loop to empty his lungs. The Work Of Breathing has nothing to do with the enclosed area of the Lissajou, but has everything to do with the integral of the exhale curve and the Y axis at 0mbar.

What I suggest we need is a better definition for WOB, which is the integral of the breathing resistance curve relative to the 0mbar axis, where negative values are treated as 0. That is real work of breathing. What everyone measures right now, has only a poor relationship with this real WOB figure.

Alex

**UWSojourner** · 8th June 2008, 16:34

While interesting, perhaps the WOB discussion also belongs elsewhere (maybe Rebreather design thread).

If it does belong here, then the implication seems to be that WOB in current RBs is causing accidents. Actually, the implication more likely is that the delta (actual WOB - CEApprovedWOB) is causing accidents. Is this true?

If we believe it is true, then I again ask why we haven't seen proportional WOB accidents in mCCRs? The only theory advanced so far (that I've seen) is that mCCR divers are more in tune with their rig so they don't overbreathe. Is this, then, not a training/diver issue? Or are we saying that RBs must be designed for the most out of shape, non-self-aware diver to enter the water? And is there evidence that these divers would not also overbreathe a CE-approved-WOB rig?

Again, while truly interesting in the rebreather design thread, I'm not seeing the direct relevance of WOB to the accident thread until WOB is shown to be the cause of these accidents.

silent running · 8th June 2008, 19:39

Quote: (Originally Posted by UWSojourner)

Again, while truly interesting in the rebreather design thread, I'm not seeing the direct relavance of WOB to the accident thread until WOB is shown to be the cause of these accidents.

As we don't know the full chain of events in most CCR accidents, all we can do is to speculate and then try to improve whatever can be improved in CCR design. By the above criteria, we shouldn't be discussing any cause which is not certain to have led to an accident, which wouldn't be very proactive, which I presume is a major reason for this thread.

High WOB is something that, unless it came from a badly kinked hose or severely over packed scrubber, is not likely to be noticed by an investigator as the beginning of a panic that could send someone bolting to the surface or into unconsciousness. The cause of death might then be listed as drowning or pulmonary embolism and DCS, when what started the chain of events was CO2 retention from too high a WOB.

As somebody who regularly finds himself working hard, sometimes at depth, WOB is always an important consideration in the type of diving I do, as is the size/drag profile of my unit or anything which could put me at a disadvantage in high workload situations.

1st June 2008, 12:42	#581 (permalink)
Dave Sutton Diveshop of Horrors Current Rebreather/s: Sport Kiss MK 15.X rEvo Other CCR Azimuth Home Build Other Rebreather/s: Classic Kiss rEvo Other CCR Azimuth Home Build Join Date: Jun 2006 Location: Narragansett, Rhode Island and Hackettstown, New Jersey Posts: 2,674	Re: Comprehensive list of all accidents Quote: (Originally Posted by silent running) I'm sorry about your suffering and fatigue, Dave. But exactly how much suffering and fatigue would you say you endured during these years? Just a skepticism of snake oil, that's all, and eye muscles that are still sore after needing to roll them every time I read things published by SM. There's far more industrial history here than you seem to recognize. Back to the point: No test has establshed that the Prism has a WOB that's any better or worse than any other set, as the tests that are ballyhooed are not comparable in any metric against the others. There are no workable safety statistics for the rig due to low production numbers. The germane part of the discussion here is to question your belief that the Prism has a WOB that is any better than any of the mainstream rigs. I am not convinced one way or the other, and as others have pointed out, the much flaunted "testing" is not comparable to others so cannot be compared. That's all the point that is being made. I have little confidence in the cred of the manufacturer, but look forward to any test that Alex does. It'll be interesting to see, as a few hours on the breathing machine there will have more value for comparison than "three years of EDU test"... . Maybe it'll test great, maybe not. In the big picture, knowing this wil have little value as there are not enough of them in service for them to be of statistical interest. Heck, I'd love to see how my CIS Mk-5P tests too, but again: Why bother? With only 60 in service, who really cares? It's a failed design as well, similarly for economic reasons. The Prism is in good company here. I'm glad you are happy with your rig: Don't take my lack of enthusiasm for the cred of SM personally. It's not about you and it's not about your rig. It's about my lack of confidence (and I must point out, a general lack of confidence by many others in the industry) regarding cred of the manufacturer. The purchasing public apparently agreed, voted with their wallets, and the result is that the design is essentially moribund. Anyone can see that. Smile and go diving. We had a good day yesterday. Today ought to be better. Dave . __________________ "Silent Diving with No Bubbles and No Politics".... www.nobubblediving.com Last edited by Dave Sutton : 1st June 2008 at 12:55.
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1st June 2008, 13:00	#582 (permalink)
Dave Sutton Diveshop of Horrors Current Rebreather/s: Sport Kiss MK 15.X rEvo Other CCR Azimuth Home Build Other Rebreather/s: Classic Kiss rEvo Other CCR Azimuth Home Build Join Date: Jun 2006 Location: Narragansett, Rhode Island and Hackettstown, New Jersey Posts: 2,674	Re: Comprehensive list of all accidents Quote: (Originally Posted by jradomski) not realy a hard thing to do.. the setup to read the code takes longer than to pull it.. but still less than 15minutes... turning it into usable soiurce code for modification is a small job as the code is very small.. And is apparently easier to do than to write your own code... (not that any reputable manufacturer would take such a shortcut....) Dave . __________________ "Silent Diving with No Bubbles and No Politics".... www.nobubblediving.com
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1st June 2008, 16:11	#583 (permalink)
*jradomski* Moderator Current Rebreather/s: Inspiration Classic Sport Kiss Optima rEvo Other CCR Home Build Other Rebreather/s: Inspiration Vision Evolution Megalodon Classic Kiss rEvo Other CCR Home Build Join Date: Mar 2005 Location: "Da" Bronx Posts: 3,015	Re: Comprehensive list of all accidents Quote: (Originally Posted by Dave Sutton) And is apparently easier to do than to write your own code... (not that any reputable manufacturer would take such a shortcut....) Dave . Anyone that could create good source code, should be able to right new code even faster.. I have some code that was pulled out of a prism in nov 2002, and there is a big bug in the voting logic.. I dont remember how I originally obtained access to get the code.. that was along time ago.. __________________ Joe Radomski CCR Trimix Instructor Trainer ANDI Instructor Trainer Director #10 All posts are personal opinions and DO NOT reflect any affiliated agency unless specifically stated.
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1st June 2008, 16:47	#584 (permalink)
Gill Envy Shearwater Copis Divers Current Rebreather/s: Other CCR Other Rebreather/s: Evolution Other CCR Join Date: Nov 2005 Location: seattle Posts: 1,316	Re: Comprehensive list of all accidents with all this talk of WOB and skepticism, I have to ask Alex and Dave, when a test is done for WOB, is it on a machine or a human. there are so many variables to actual human performance which could be missed by a machine. for instance, what I've noticed is a huge variance of mouth piece thickness. the stock version that comes with the meg is super thin (my front teeth actually come together), the one that comes with the Evo is quite thick (holding my front teeth a good 1/2 inch apart) and I've seen everthing in between on other rigs. I can imagine that you could make a very capable rebreather in terms of WOB then make the mistake of putting a thin mouth piece on it that simply makes the teeth a barrier that add significantly to WOB in high respiration. I swapped out my mouth piece on the meg from the get go with a thicker one. Further, I've noticed that in the worst moment, we tend to bight down extra hard in current, potentially reducing the size of the air way. Are any of the WOB test taking this dynamic into account. __________________ Gill Envy ...Because I wasn't born with gills! ><(°>><(°>><(°>><(°>><(°>><(°>><(°>><(°>
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1st June 2008, 17:16	#585 (permalink)
AD_ward9 So much more to learn Current Rebreather/s: Other CCR Other Rebreather/s: Other CCR Join Date: Jun 2005 Location: Scotland Posts: 1,868	Re: Comprehensive list of all accidents Quote: (Originally Posted by Gill Envy) with all this talk of WOB and skepticism, I have to ask Alex and Dave, when a test is done for WOB, is it on a machine or a human. there are so many variables to actual human performance which could be missed by a machine. for instance, what I've noticed is a huge variance of mouth piece thickness. the stock version that comes with the meg is super thin (my front teeth actually come together), the one that comes with the Evo is quite thick (holding my front teeth a good 1/2 inch apart) and I've seen everthing in between on other rigs. I can imagine that you could make a very capable rebreather in terms of WOB then make the mistake of putting a thin mouth piece on it that simply makes the teeth a barrier that add significantly to WOB in high respiration. I swapped out my mouth piece on the meg from the get go with a thicker one. Further, I've noticed that in the worst moment, we tend to bight down extra hard in current, potentially reducing the size of the air way. Are any of the WOB test taking this dynamic into account. WOB is measured on a breathing machine with the equipment in salt water in a pressure chamber. This gives a result that can be reproduced at any time, that is objective and allows for direct comparisons. In looking at the mouthpiece bite, we check the cross section is at least as large as the opening in the mouthpiece itself and record a problem in the results if it is smaller, and that we have had to change out the mouthpiece. Humans are very poor at measuring WOB, but manned underwater tests do have a key roll in testing. Human testing can check things like the ADV fires when the CLs are bottomed out in all positions, they feel they get a big enough breath or not, how the CLs affect trim, how water dumps work or interplay with the OPV and other ergonomic issues. Of course, if any changes are made, one has to repeat the machine testing all over again. Alex NB: Just one note on the recent divergence of this thread - the results of the under-funding complained about, are systemic in sports rebreathers. A new eCCR done completely properly costs vastly more than one would imagine. If there are 5000 rebreather users, who buy a Euro 3,500 rebreather once every 7 years, then that is just Euro 2.5mn of sales a year. Even if one spent every penny of it on R&D, it would take 5 years global sales to fund one new rebreather development properly. Given that revenue from sales has to be used to produce and support units, then there is simply not enough revenue potential in the sports market to fund a proper job. Some companies are better than other in avoiding the worst results of under-funding, and some have had larger budgets than others, but the result is still defects in products that would not be there in a commercial or military product, where the market is larger. The most expensive part is always that last 10%, and it is the most under-estimated. One thing the accident list is for, and the Open Revolution initiative, is to enable some core information needed by everyone to be published, so each company does not have to reinvent the wheel. Lets return to that objective, to put the accidents here, and analysis on another thread. The WOB issue is a good point to debate, as its role in accidents is unclear, but saying unit A or B has underfunding problems is a statement that could be repeated many times on different units. There have been more than 30 companies try and make sports rebreathers. Last edited by AD_ward9 : 1st June 2008 at 17:24.
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8th June 2008, 12:58	#587 (permalink)
AM In love with the big blue Current Rebreather/s: Other CCR Other Rebreather/s: Other CCR Join Date: Feb 2005 Location: Earth. Posts: 625	Re: Comprehensive list of all accidents This thread is going wildly off topic now, undermining the original objective to document, discuss and analyse accident data, not to discuss the semantics of rebreather strategic business directions. Returning to WOB and test protocols - it is becoming increasingly evident that the CE rating process and indeed other rating protocols for sport rebreathers is unacceptable in that it contains too many variables and doesnt factor in some of the critical variables needed to draw effective conclusions. The fact that every sports rebreather under the CE jurisdiction is not tested in the same methodology, i.e. under both prone and vertical positioning, is somewhat worrying. Equally it is concerning that there is a distinctive lack of data relating to how hydrostatic lung loading is factored into the testing. It is a classic feature of some BMCL rebreathers that if the lung(s) are not positioned correctly in alignment with the divers lungs, that the WOB is significantly altered. Quote: (Originally Posted by paulraymaekers) you start designing to meet the limits, and mostly as a consequence the unit becomes 'bigger': bigger hoses, bigger mouthpiece, larger volumes. Al this means you get a heavier unit, with often more drag under water. now here comes a 50kg, 1.55m female diver who want to start diving CCR, and wants do buy a unit that meets the safety limits.... ?? how many small female boris divers are around? It is a valid point that there is a trade off between a bigger unit and more drag, therefore rendering WOB more difficult against the drag. The lack of small female boris divers is nothing to do with the weight of the unit, I am a small female and quite often I am carrying over 100% of my body weight in gear for some dives. The weight is not the issue, there is just an endemic lack of active female deep rebreather divers around, full stop. A real pity. I have tried tirelessly to encourage other female divers into rebreathers but the conversion rate is not high! As to wanting to buy a unit that meets the safety limits, well, in realistic terms, safety limits are a very subjective matter at this point in time. Quote: (Originally Posted by Drmike) yes but big bore doesnt necessarily have to mean heavy unit The Sentinel (which apears to have the lowest wob (in upright position) is lighter than some mainstream units. Putting a bigger bore dsv, good check valves and big hoses on a unit isnt going to make any real difference from a diveability or weight viewpoint at all but can in some cases significantly improve wob Yes, that is the real key. Quote: (Originally Posted by jradomski) ANDY, actually we can not be sure of that.. The test data indicates breathing resistance in the prone position.. All the other rebreathers are tested in the upright position.. This can be a tremendous difference.. ALso for WOB, traditionally the nedu tests were not calibrated to add in the WOB of the "diver" whereas ce test must add this in.. this will raise the WOB numbers for all CE units.. Until the prism is tested under CE parameters none of its test data is comparible.. Its apples to oranges.. The PRISM is being tested in the optimal position while most of the other rebreathers are being tested in one of the worse positions for many units.. Absolutely agreed. If the test conditions are not identical for all sports rebreathers, then the test outcomes cannot be used as a valid blueprint from which to draw COMPARATIVE conclusions across the board. Effectively at the present moment, we have subjective results which cannot be viewed with any relativity to other/all sports rebreathers. Quote: (Originally Posted by jradomski) actualyy wob tests were done at various levels.. 40m was one of them.. so at that level it wasnt deeper... The Nedu had a TARGET dept ofr operational performance at 150, so that had to be tested, but others were tested as well.. I personally dont agree with testing in the vertical position nor the prone position alone.. both need to be tested as the both have times they will be used.. for most rbs the verticle test will be worse (not just above the prone position), on some designs it will actually be quite acceptable.. if you are going to specify a single test for limits the one thats the hardest to pass makes senes, but neither should be used alone.. I personally beliver 3 positions should be tested 0, 45 and 90.. most CCR divers normal swimming position probably falls in the range of +20 or so from prone.. I am actually surprised to see NEDU just tested prone because many jobs the normal position is verticle and the most important position.. Mark 15 breaths well vertical sinceits design was for a working diver.. The classic Kiss breaths best somewhere in the middle, but still ok verticle, the sport breaths very poorly verticle but ok a few degrees up.... how well a unit will breathe in either position depends specifically on where the c-l are positioned.. units where the inhale or exhale lung will be below the lung centroid will breath bad verticle.. units that can spread them to keep them close to the lung centroid will be less effected.. our lungs are efficient at blowing against pressure but poor at sucking.. so a position where wh can inhale easily but work a bit exhaling is the best compromise.. OTS lungs work really well in the prone positin for 2 reasons.. the distance to the lung centroid is generally small, and it meets the above criteria.. we exhale to slightly higher pressure and gas from the inhale lung is at a greater pressure than our lung centroid so its forced into our lungs.. something like the rEvo does well becuase of the way he has the lungs positioned if you are slightly head up.. the inhale c-l is at a pressure slightly greater than the lung centroid and the exhale c-l is at a slightly higher pressure.. if you are fully head up.. no so good but MUCH better the fully head down where everything is the opposit of where we want.. Again good points. I still believe the hydrostatic lung loading is a key component and introduces a big variable to the test conditions conducted universally within the parameters of CE and other testing. The rEvo for example has a considerable variance in the breathing effort depending on where the lungs are positioned, this is classic for all BMCL rebreathers of course but if the rebreather lung is not accurately positioned in alignment with the diver's lung, it makes a HUGE difference to WOB. Quote: (Originally Posted by AD_ward9) WOB is measured on a breathing machine with the equipment in salt water in a pressure chamber. This gives a result that can be reproduced at any time, that is objective and allows for direct comparisons. In looking at the mouthpiece bite, we check the cross section is at least as large as the opening in the mouthpiece itself and record a problem in the results if it is smaller, and that we have had to change out the mouthpiece. Humans are very poor at measuring WOB, but manned underwater tests do have a key roll in testing. Human testing can check things like the ADV fires when the CLs are bottomed out in all positions, they feel they get a big enough breath or not, how the CLs affect trim, how water dumps work or interplay with the OPV and other ergonomic issues. Of course, if any changes are made, one has to repeat the machine testing all over again. Alex NB: Just one note on the recent divergence of this thread - the results of the under-funding complained about, are systemic in sports rebreathers. A new eCCR done completely properly costs vastly more than one would imagine. If there are 5000 rebreather users, who buy a Euro 3,500 rebreather once every 7 years, then that is just Euro 2.5mn of sales a year. Even if one spent every penny of it on R&D, it would take 5 years global sales to fund one new rebreather development properly. Given that revenue from sales has to be used to produce and support units, then there is simply not enough revenue potential in the sports market to fund a proper job. Some companies are better than other in avoiding the worst results of under-funding, and some have had larger budgets than others, but the result is still defects in products that would not be there in a commercial or military product, where the market is larger. The most expensive part is always that last 10%, and it is the most under-estimated. One thing the accident list is for, and the Open Revolution initiative, is to enable some core information needed by everyone to be published, so each company does not have to reinvent the wheel. Lets return to that objective, to put the accidents here, and analysis on another thread. The WOB issue is a good point to debate, as its role in accidents is unclear, but saying unit A or B has underfunding problems is a statement that could be repeated many times on different units. There have been more than 30 companies try and make sports rebreathers. Alex, good point on the mouthpiece, this is something that many divers modify and appear to be unaware that it can create a significant alteration in WOB if the bore size is altered. I second the points about the critical nature of this thread and the requirement for renewed focus upon the thread's primary objective which is accident data discussion, not dissemination of rebreather manufacturers' business decisions. Regards AnneMarie __________________ Attitude keeps you alive Last edited by AM : 8th June 2008 at 13:08.
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8th June 2008, 14:15	#588 (permalink)
AD_ward9 So much more to learn Current Rebreather/s: Other CCR Other Rebreather/s: Other CCR Join Date: Jun 2005 Location: Scotland Posts: 1,868	Re: Comprehensive list of all accidents Quote: (Originally Posted by am) Returning to WOB and test protocols - it is becoming increasingly evident that the CE rating process and indeed other rating protocols for sport rebreathers is unacceptable in that it contains too many variables and doesnt factor in some of the critical variables needed to draw effective conclusions. You are right in that it should be much more explicit, with a diagram showing exactly how it is measured, stating clearly that the scrubber actually is filled, and setting down the precise test protocol. Just on little point though, we go about testing WOB using the NEDU protocol with the EN14143 test depths etc. It defines WOB as the area enclosed by the Breathing resistance - volume Lissajou. I don't think the NEDU and CE definitions are right. For example, take a Lissajou where the entire loop is positive pressure. Breathing in just involves opening one's mouth as the loop is positive pressure, but breathing out is harder. There is hardly any actual work in breathing in, but there is a pressure change from the mouthpiece to the suprasternal notch or lung centroid. That pressure change gets integrated and included as WOB. However, as it is positive pressure, all the pressure change is, is the effect of taking a gas volume out of the loop and putting it into the lungs. Of course, going back the other way during the exhale cycle, the diver has to work against the pressure in the breathing loop to empty his lungs. The Work Of Breathing has nothing to do with the enclosed area of the Lissajou, but has everything to do with the integral of the exhale curve and the Y axis at 0mbar. What I suggest we need is a better definition for WOB, which is the integral of the breathing resistance curve relative to the 0mbar axis, where negative values are treated as 0. That is real work of breathing. What everyone measures right now, has only a poor relationship with this real WOB figure. Alex
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8th June 2008, 16:34	#589 (permalink)
UWSojourner Pacific Northwest Current Rebreather/s: Megalodon Other Rebreather/s: Join Date: Feb 2005 Location: Portland Oregon Posts: 556	Re: Comprehensive list of all accidents While interesting, perhaps the WOB discussion also belongs elsewhere (maybe Rebreather design thread). If it does belong here, then the implication seems to be that WOB in current RBs is causing accidents. Actually, the implication more likely is that the delta (actual WOB - CEApprovedWOB) is causing accidents. Is this true? If we believe it is true, then I again ask why we haven't seen proportional WOB accidents in mCCRs? The only theory advanced so far (that I've seen) is that mCCR divers are more in tune with their rig so they don't overbreathe. Is this, then, not a training/diver issue? Or are we saying that RBs must be designed for the most out of shape, non-self-aware diver to enter the water? And is there evidence that these divers would not also overbreathe a CE-approved-WOB rig? Again, while truly interesting in the rebreather design thread, I'm not seeing the direct relevance of WOB to the accident thread until WOB is shown to be the cause of these accidents. Last edited by UWSojourner : 8th June 2008 at 19:09.
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8th June 2008, 19:39	#590 (permalink)
silent running Mature mouth breather Current Rebreather/s: Prism Topaz Other Rebreather/s: Join Date: Jun 2005 Location: U.S.A. Brooklyn, New York Posts: 1,832	Re: Comprehensive list of all accidents Quote: (Originally Posted by UWSojourner) Again, while truly interesting in the rebreather design thread, I'm not seeing the direct relavance of WOB to the accident thread until WOB is shown to be the cause of these accidents. As we don't know the full chain of events in most CCR accidents, all we can do is to speculate and then try to improve whatever can be improved in CCR design. By the above criteria, we shouldn't be discussing any cause which is not certain to have led to an accident, which wouldn't be very proactive, which I presume is a major reason for this thread. High WOB is something that, unless it came from a badly kinked hose or severely over packed scrubber, is not likely to be noticed by an investigator as the beginning of a panic that could send someone bolting to the surface or into unconsciousness. The cause of death might then be listed as drowning or pulmonary embolism and DCS, when what started the chain of events was CO2 retention from too high a WOB. As somebody who regularly finds himself working hard, sometimes at depth, WOB is always an important consideration in the type of diving I do, as is the size/drag profile of my unit or anything which could put me at a disadvantage in high workload situations.
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