Comprehensive list of all accidents

***jradomski*** · 29th May 2008, 22:40

Quote: (Originally Posted by silent running)

Hi Paul, no big changes are necessary. The Prism has a lower WOB than any other CCR on the CCRB chart except possibly Boris and weighs only 47 lbs/21.5 kilos, fully charged, is only 53.4 cm tall, 43.2 cm wide and at 23 cm front to back, thinner than all other CCRs in the CCRB chart, except the Kisses and rEvo.

A CCR can have very low WOB and still be compact with low hydro drag. I couldn't do the kind of diving in strong currents so easily without the low WOB and low profile of the Prism... -Andy

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..

silent running · 30th May 2008, 03:19

Hi Joe.

Quote: (Originally Posted by jradomski)

ANDY,
actually we can not be sure of that.. The test data indicates breathing resistance in the prone position..

Yes, which is the position it is most often dived in, no surprise there. The NEDU test also states that the unit met the goal of 1.0 kPa for the hydrostatic load in the upright and prone position in 3 tests. Also, the CE test listed on the chart was at 131ft/40m as opposed to the NEDU test depth of 150ft, both were conducted with a 75 rmv. So the NEDU WOB test is more difficult with respect to it being done 19ft deeper.

Quote: (Originally Posted by jradomski)

All the other rebreathers are tested in the upright position.. This can be a tremendous difference..

Given that the NEDU 1.0 kPa goal for hydrostatic load was met in both the prone and upright positions in for the Prism, it doesn't seem that the WOB would be significantly different in the upright position, which I presume is why they decided to test it in the prone, where the diver will spend the most time. To quote the Closed Circuit Research web site further on the subject of hydrostatic loading in different positions: "It would seem a perfect solution is an over-shoulder counter lung upon which any hydrostatic effects have little result."

If I'm not mistaken, don't most back mount counterlung units perform better in a more upright position? It certainly seemed that way to me when diving the Dolphin and KISS. The NEDU guy at BTS told me that the MK16-back mounted lungs-breathed best in the upright position, and breathed "terrible" in the prone position. Which shouldn't be a surprise as it was designed to breath best in the upright position for it's role in mine clearance, probably the only situation where a CCR diver ever spends most of their time in an upright position.

Quote: (Originally Posted by jradomski)

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..

If you actually read the exchanges between myself and Alex in the "ISC post's data" thread, you'll see that Alex brought up this same point and then added the human loading figure to the NEDU Prism figures, and adjusted for depth, then Mike put it in the chart. It was still very low, only bettered by Boris. Given that Boris probably breathes best in the upright position and that it had the lowest WOB on the chart, the Prism may actually breathe better than Boris in the prone position it's usually dived in.

Quote: (Originally Posted by jradomski)

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..

So exactly which units are disadvantaged in the upright position? And if prone is the "optimal position" for the Prism and NEDU test, and also happens to be the one in which we spend most of our time, what does this tell us about the validity of a test used for comparison of CCRs that supplies only data for a body position that CCRs won't be dived in most of the time?

It's not a surprise to me that my highest sustained work loads always occur when I'm finning against heavy current in the prone position, given that most of us spend most of our dives in that position. So I'm glad my unit and it's test protocol has been optimized for it. I've never seen a CCR diver finning their ass off while making an ascent and I hope I never do. -Andy

***jradomski*** · 30th May 2008, 04:27

Quote: (Originally Posted by silent running)

Hi Joe.

Yes, which is the position it is most often dived in, no surprise there. The NEDU test also states that the unit met the goal of 1.0 kPa for the hydrostatic load in the upright and prone position in 3 tests. Also, the CE test listed on the chart was at 131ft/40m as opposed to the NEDU test depth of 150ft, both were conducted with a 75 rmv. So the NEDU WOB test is more difficult with respect to it being done 19ft deeper.
-Andy

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..

Hydrostatic loading and WOB test two entirely different parameters...

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..

silent running · 30th May 2008, 07:00

Quote: (Originally Posted by jradomski)

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..

I think it's fine to test in multiple positions, and your suggestion about doing a range of testing over 0-90 degrees is a good one. But the test which should be given the most weight is the one that we spend most of our time nearest to and working hardest in-prone. In the case of some back mounted counterlung units, the WOB will be more in the prone position than in the upright, which means the CE test is at best inaccurate and at worst misleading as it would then give the impression a unit had low WOB when actually it had a high WOB in the normal dive position. If one design is radically worse in the upright position, then it should be noted, but it certainly shouldn't be the only tested position, especially given that I can't conceive of a situation where somebody would ever spend much time working hard in the upright position.

Quote: (Originally Posted by jradomski)

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

The Prism was submitted to the NEDU for use in the Seal underwater delivery vehicle program, which one would presume means the divers were expecting to have long swims, which if they are concerned with minimizing effort and drag, means in the prone position.

Having just come back from an 18 day trip with lots of hard swimming against the current, more than is normal, even for me, I'm very glad I switched to a side mount BO setup. Even on the most difficult dives, I barely noticed the tank was there and I was able to cope with some very challenging currents without any real difference in my drag profile from the shallow dives I did without BO.

Given the above posts in this thread about the possibility of a correlation btw elevated CO2 and risk of heart attack in CCR diving, I think minimizing WOB, and any excess physical effort which could elevate RMV, is of paramount importance to us all. Especially those like me who are over 40 and have already lost one friend to a heart attack while diving CCR... -Andy

AD_ward9 · 30th May 2008, 07:43

Does anyone have a PRISM in the UK or Scandinavia, that we can borrow for 3 weeks, so we can test the WOB under exactly the same conditions as for all the other units?

We are publishing the WOB figures along with the detailed plots of WOB vs loop volume etc for each unit, for units in the vertical position. Prone positions are almost always better, if the counterlung centroid is higher than the suprasternal notch in the prone position.

So far, the Boris holds the prize for the lowest Sports rebreather WOB. The Boris meets the CE WOB safety limits to well over 40msw using air, and over 300msw using heliox. As we confirmed CCRL's figures for the Boris, we would trust their figures also for the Sentinel. CCRL also stands out as being the only company whose claimed figures and our independently tested results match. I hope Steam Machines can join them, but we need a unit to test first.

No other sports unit tested so far met the CE limit of 2.75J/L using air, though the Meg should do with the new radial scrubber (the Meg with the Cis-Lunar scrubber is just slightly above the borderline at 2.8J/L). The PRISM should do, but lets test one and confirm.

As Joe has nicely pointed out, only by comparing units in the exact same test conditions can we get a sensible comparison. We can test in any position (we have a 2,000msw working depth rated test chamber on a gimbal). The importance of vertical position is that when the muck hits the fan, that is the position divers tend to go into.

Cheers

Alex

silent running · 30th May 2008, 09:45

Hi Alex, nice to have you back.

Quote: (Originally Posted by AD_ward9)

As we confirmed CCRL's figures for the Boris, we would trust their figures also for the Sentinel.

Did you also test Boris for it's prone WOB? And if not, why? I would be interested to know how it compares to it's upright WOB, given the BMCL design and it's differing hydrostatic load in different positions and the fact that most of us spend much more time swimming in the prone position or close to it, which is obviously a more common CCR behavior than outright panic.

Quote: (Originally Posted by AD_ward9)

The importance of vertical position is that when the muck hits the fan, that is the position divers tend to go into.

Thanks for sharing the thinking behind the emphasis on the upright position. But in terms of safety, isn't an once of prevention worth a pound of cure? Shouldn't we be at least as concerned with what happens in an outright panic as we are with the circumstances that lead to it? Short of an OGS, isn't a CO2 hit the most likely way to induce outright panic? If so, isn't a CO2 hit most likely precipitated by extended heavy exertion and high WOB?

Another precursor to outright panic could be hypoxia, but once the PO2 is low and dropping as the diver breaks for the surface, the WOB will also be lessening. So how could having a lower WOB in the upright position be of any real help in an OGS panic ascent to the surface? -Andy

AD_ward9 · 30th May 2008, 13:45

Quote: (Originally Posted by silent running)

Hi Alex, nice to have you back.

Did you also test Boris for it's prone WOB? And if not, why? I would be interested to know how it compares to it's upright WOB, given the BMCL design and it's differing hydrostatic load in different positions and the fact that most of us spend much more time swimming in the prone position or close to it, which is obviously a more common CCR behavior than outright panic.

Thanks.

The prone WOB is around 0.1J/L lower than the vertical WOB for the Boris. The reason is we can almost eliminate the movement of the counterlung centroid as it inflates and deflates by optimising the loop volume. In a vertical position this movement of the counterlung centroid is quite pronounced: NEDU call it Elastance, and in Europe it is called Compliance, but in fact it is neither: it simply the hydrostatic movement of the counterlung centroid as the counterlung inflates and deflates..

There is also a trick to get an artificially low figure in the prone position (as there is a positive loop pressure around the optimal point) by using a very high rate of loop volume adjustment (imagine, venting a loop as you breathe out), depending on where valves are placed. We use a slow rate of loop volume adjustment. In the vertical position the trick tends not to work because it drives the rebreather into negative loop pressure. For this reason, we like the vertical position as it removes another variable when we are comparing our results with those quoted by the manufacturer.

In a prone position, the CLs usually have a positive pressure, which makes inhale easier. This is better from the physiological standpoint, than a negative pressure which there is around the optimal loop volume of most rebreathers in the vertical position. So again, if the rebreather meets the standard in the vertical position, it will be safe in the prone position.

I hope the above description is sufficiently detailed answer to your question. It also explains why we don't plan publishing prone figures: we do not want to get into a mud slinging match with anyone, who can show some absurdly low figure by doing things such as the tricks I mentioned in the prone position simply because there is positive loop pressure at the lowest WOB point. The best apples for apples comparison is a vertical rebreather, filled with the same 8-12 mesh sodalime, used by the same amount (50% roughly), with genuine sinusoidal gas flow from the breathing machine.

Alex

Drmike · 30th May 2008, 13:56

Quote: (Originally Posted by AD_ward9)

Thanks.

The prone WOB is around 0.1J/L lower than the vertical WOB for the Boris. The reason is we can almost eliminate the movement of the counterlung centroid as it inflates and deflates by optimising the loop volume. In a vertical position this movement of the counterlung centroid is quite pronounced: NEDU call it Elastance, and in Europe it is called Compliance, but in fact it is neither: it simply the hydrostatic movement of the counterlung centroid as the counterlung inflates and deflates..

There is also a trick to get an artificially low figure in the prone position (as there is a positive loop pressure around the optimal point) by using a very high rate of loop volume adjustment (imagine, venting a loop as you breathe out), depending on where valves are placed. We use a slow rate of loop volume adjustment. In the vertical position the trick tends not to work because it drives the rebreather into negative loop pressure. For this reason, we like the vertical position as it removes another variable when we are comparing our results with those quoted by the manufacturer.

In a prone position, the CLs usually have a positive pressure, which makes inhale easier. This is better from the physiological standpoint, than a negative pressure which there is around the optimal loop volume of most rebreathers in the vertical position. So again, if the rebreather meets the standard in the vertical position, it will be safe in the prone position.

I hope the above description is sufficiently detailed answer to your question. It also explains why we don't plan publishing prone figures: we do not want to get into a mud slinging match with anyone, who can show some absurdly low figure by doing things such as the tricks I mentioned in the prone position simply because there is positive loop pressure at the lowest WOB point. The best apples for apples comparison is a vertical rebreather, filled with the same 8-12 mesh sodalime, used by the same amount (50% roughly), with genuine sinusoidal gas flow from the breathing machine.

Alex

good stuff - thanks alex

***Decodiver*** · 30th May 2008, 19:56

Quote: (Originally Posted by AD_ward9)

Thanks.

The prone WOB is around 0.1J/L lower than the vertical WOB for the Boris. The reason is we can almost eliminate the movement of the counterlung centroid as it inflates and deflates by optimising the loop volume. In a vertical position this movement of the counterlung centroid is quite pronounced: NEDU call it Elastance, and in Europe it is called Compliance, but in fact it is neither: it simply the hydrostatic movement of the counterlung centroid as the counterlung inflates and deflates..

There is also a trick to get an artificially low figure in the prone position (as there is a positive loop pressure around the optimal point) by using a very high rate of loop volume adjustment (imagine, venting a loop as you breathe out), depending on where valves are placed. We use a slow rate of loop volume adjustment. In the vertical position the trick tends not to work because it drives the rebreather into negative loop pressure. For this reason, we like the vertical position as it removes another variable when we are comparing our results with those quoted by the manufacturer.

In a prone position, the CLs usually have a positive pressure, which makes inhale easier. This is better from the physiological standpoint, than a negative pressure which there is around the optimal loop volume of most rebreathers in the vertical position. So again, if the rebreather meets the standard in the vertical position, it will be safe in the prone position.

I hope the above description is sufficiently detailed answer to your question. It also explains why we don't plan publishing prone figures: we do not want to get into a mud slinging match with anyone, who can show some absurdly low figure by doing things such as the tricks I mentioned in the prone position simply because there is positive loop pressure at the lowest WOB point. The best apples for apples comparison is a vertical rebreather, filled with the same 8-12 mesh sodalime, used by the same amount (50% roughly), with genuine sinusoidal gas flow from the breathing machine.

Alex

Thank you Alex, nice to have you back.

Cheers,

Dave.

silent running · 30th May 2008, 21:10

Quote: (Originally Posted by AD_ward9)

Thanks.

The prone WOB is around 0.1J/L lower than the vertical WOB for the Boris. The reason is we can almost eliminate the movement of the counterlung centroid as it inflates and deflates by optimising the loop volume. In a vertical position this movement of the counterlung centroid is quite pronounced: NEDU call it Elastance, and in Europe it is called Compliance, but in fact it is neither: it simply the hydrostatic movement of the counterlung centroid as the counterlung inflates and deflates..

There is also a trick to get an artificially low figure in the prone position (as there is a positive loop pressure around the optimal point) by using a very high rate of loop volume adjustment (imagine, venting a loop as you breathe out), depending on where valves are placed. We use a slow rate of loop volume adjustment. In the vertical position the trick tends not to work because it drives the rebreather into negative loop pressure. For this reason, we like the vertical position as it removes another variable when we are comparing our results with those quoted by the manufacturer.

In a prone position, the CLs usually have a positive pressure, which makes inhale easier. This is better from the physiological standpoint, than a negative pressure which there is around the optimal loop volume of most rebreathers in the vertical position. So again, if the rebreather meets the standard in the vertical position, it will be safe in the prone position.

I hope the above description is sufficiently detailed answer to your question. It also explains why we don't plan publishing prone figures: we do not want to get into a mud slinging match with anyone, who can show some absurdly low figure by doing things such as the tricks I mentioned in the prone position simply because there is positive loop pressure at the lowest WOB point. The best apples for apples comparison is a vertical rebreather, filled with the same 8-12 mesh sodalime, used by the same amount (50% roughly), with genuine sinusoidal gas flow from the breathing machine.

Alex

Thanks very much for the detailed answers and explanation Alex. I hope one of the 2 UK Prism owners will lend you a unit. Otherwise, we'll have to wait for Hollis to get a CE test done for the Prism 2, which could be a while. And I didn't know that a prone position test was easier to manipulate to get a better result.

In the meantime, what do you think of the NEDU's protocol to measure the hydrostatic load of the unit in both upright and prone and then test the Prism for WOB only in the prone position? It seems to me that they were testing it for it's intended use for long swims in the prone position. Is this your impression, and what do you make of the hydrostatic load figures listed in the report? Also, I didn't see any reference to the how much volume there was in the loop. Do you have any idea how they set this in NEDU tests? -Andy

29th May 2008, 22:40	#561 (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: 2,870	Re: Comprehensive list of all accidents Quote: (Originally Posted by silent running) Hi Paul, no big changes are necessary. The Prism has a lower WOB than any other CCR on the CCRB chart except possibly Boris and weighs only 47 lbs/21.5 kilos, fully charged, is only 53.4 cm tall, 43.2 cm wide and at 23 cm front to back, thinner than all other CCRs in the CCRB chart, except the Kisses and rEvo. A CCR can have very low WOB and still be compact with low hydro drag. I couldn't do the kind of diving in strong currents so easily without the low WOB and low profile of the Prism... -Andy 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.. __________________ 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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30th May 2008, 03:19	#562 (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: 1,810	Re: Comprehensive list of all accidents Hi Joe. Quote: (Originally Posted by jradomski) ANDY, actually we can not be sure of that.. The test data indicates breathing resistance in the prone position.. Yes, which is the position it is most often dived in, no surprise there. The NEDU test also states that the unit met the goal of 1.0 kPa for the hydrostatic load in the upright and prone position in 3 tests. Also, the CE test listed on the chart was at 131ft/40m as opposed to the NEDU test depth of 150ft, both were conducted with a 75 rmv. So the NEDU WOB test is more difficult with respect to it being done 19ft deeper. Quote: (Originally Posted by jradomski) All the other rebreathers are tested in the upright position.. This can be a tremendous difference.. Given that the NEDU 1.0 kPa goal for hydrostatic load was met in both the prone and upright positions in for the Prism, it doesn't seem that the WOB would be significantly different in the upright position, which I presume is why they decided to test it in the prone, where the diver will spend the most time. To quote the Closed Circuit Research web site further on the subject of hydrostatic loading in different positions: "It would seem a perfect solution is an over-shoulder counter lung upon which any hydrostatic effects have little result." If I'm not mistaken, don't most back mount counterlung units perform better in a more upright position? It certainly seemed that way to me when diving the Dolphin and KISS. The NEDU guy at BTS told me that the MK16-back mounted lungs-breathed best in the upright position, and breathed "terrible" in the prone position. Which shouldn't be a surprise as it was designed to breath best in the upright position for it's role in mine clearance, probably the only situation where a CCR diver ever spends most of their time in an upright position. Quote: (Originally Posted by jradomski) 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.. If you actually read the exchanges between myself and Alex in the "ISC post's data" thread, you'll see that Alex brought up this same point and then added the human loading figure to the NEDU Prism figures, and adjusted for depth, then Mike put it in the chart. It was still very low, only bettered by Boris. Given that Boris probably breathes best in the upright position and that it had the lowest WOB on the chart, the Prism may actually breathe better than Boris in the prone position it's usually dived in. Quote: (Originally Posted by jradomski) 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.. So exactly which units are disadvantaged in the upright position? And if prone is the "optimal position" for the Prism and NEDU test, and also happens to be the one in which we spend most of our time, what does this tell us about the validity of a test used for comparison of CCRs that supplies only data for a body position that CCRs won't be dived in most of the time? It's not a surprise to me that my highest sustained work loads always occur when I'm finning against heavy current in the prone position, given that most of us spend most of our dives in that position. So I'm glad my unit and it's test protocol has been optimized for it. I've never seen a CCR diver finning their ass off while making an ascent and I hope I never do. -Andy
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30th May 2008, 04:27	#563 (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: 2,870	Re: Comprehensive list of all accidents Quote: (Originally Posted by silent running) Hi Joe. Yes, which is the position it is most often dived in, no surprise there. The NEDU test also states that the unit met the goal of 1.0 kPa for the hydrostatic load in the upright and prone position in 3 tests. Also, the CE test listed on the chart was at 131ft/40m as opposed to the NEDU test depth of 150ft, both were conducted with a 75 rmv. So the NEDU WOB test is more difficult with respect to it being done 19ft deeper. -Andy 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.. Hydrostatic loading and WOB test two entirely different parameters... 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.. __________________ 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. Last edited by jradomski : 30th May 2008 at 04:46.
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30th May 2008, 07:00	#564 (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: 1,810	Re: Comprehensive list of all accidents Quote: (Originally Posted by jradomski) 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.. I think it's fine to test in multiple positions, and your suggestion about doing a range of testing over 0-90 degrees is a good one. But the test which should be given the most weight is the one that we spend most of our time nearest to and working hardest in-prone. In the case of some back mounted counterlung units, the WOB will be more in the prone position than in the upright, which means the CE test is at best inaccurate and at worst misleading as it would then give the impression a unit had low WOB when actually it had a high WOB in the normal dive position. If one design is radically worse in the upright position, then it should be noted, but it certainly shouldn't be the only tested position, especially given that I can't conceive of a situation where somebody would ever spend much time working hard in the upright position. Quote: (Originally Posted by jradomski) I am actually surprised to see NEDU just tested prone because many jobs the normal position is verticle and the most important position.. The Prism was submitted to the NEDU for use in the Seal underwater delivery vehicle program, which one would presume means the divers were expecting to have long swims, which if they are concerned with minimizing effort and drag, means in the prone position. Having just come back from an 18 day trip with lots of hard swimming against the current, more than is normal, even for me, I'm very glad I switched to a side mount BO setup. Even on the most difficult dives, I barely noticed the tank was there and I was able to cope with some very challenging currents without any real difference in my drag profile from the shallow dives I did without BO. Given the above posts in this thread about the possibility of a correlation btw elevated CO2 and risk of heart attack in CCR diving, I think minimizing WOB, and any excess physical effort which could elevate RMV, is of paramount importance to us all. Especially those like me who are over 40 and have already lost one friend to a heart attack while diving CCR... -Andy Last edited by silent running : 30th May 2008 at 07:02.
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30th May 2008, 07:43	#565 (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: 1,732	Re: Comprehensive list of all accidents Does anyone have a PRISM in the UK or Scandinavia, that we can borrow for 3 weeks, so we can test the WOB under exactly the same conditions as for all the other units? We are publishing the WOB figures along with the detailed plots of WOB vs loop volume etc for each unit, for units in the vertical position. Prone positions are almost always better, if the counterlung centroid is higher than the suprasternal notch in the prone position. So far, the Boris holds the prize for the lowest Sports rebreather WOB. The Boris meets the CE WOB safety limits to well over 40msw using air, and over 300msw using heliox. As we confirmed CCRL's figures for the Boris, we would trust their figures also for the Sentinel. CCRL also stands out as being the only company whose claimed figures and our independently tested results match. I hope Steam Machines can join them, but we need a unit to test first. No other sports unit tested so far met the CE limit of 2.75J/L using air, though the Meg should do with the new radial scrubber (the Meg with the Cis-Lunar scrubber is just slightly above the borderline at 2.8J/L). The PRISM should do, but lets test one and confirm. As Joe has nicely pointed out, only by comparing units in the exact same test conditions can we get a sensible comparison. We can test in any position (we have a 2,000msw working depth rated test chamber on a gimbal). The importance of vertical position is that when the muck hits the fan, that is the position divers tend to go into. Cheers Alex Last edited by AD_ward9 : 30th May 2008 at 07:52.
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30th May 2008, 09:45	#566 (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: 1,810	Re: Comprehensive list of all accidents Hi Alex, nice to have you back. Quote: (Originally Posted by AD_ward9) As we confirmed CCRL's figures for the Boris, we would trust their figures also for the Sentinel. Did you also test Boris for it's prone WOB? And if not, why? I would be interested to know how it compares to it's upright WOB, given the BMCL design and it's differing hydrostatic load in different positions and the fact that most of us spend much more time swimming in the prone position or close to it, which is obviously a more common CCR behavior than outright panic. Quote: (Originally Posted by AD_ward9) The importance of vertical position is that when the muck hits the fan, that is the position divers tend to go into. Thanks for sharing the thinking behind the emphasis on the upright position. But in terms of safety, isn't an once of prevention worth a pound of cure? Shouldn't we be at least as concerned with what happens in an outright panic as we are with the circumstances that lead to it? Short of an OGS, isn't a CO2 hit the most likely way to induce outright panic? If so, isn't a CO2 hit most likely precipitated by extended heavy exertion and high WOB? Another precursor to outright panic could be hypoxia, but once the PO2 is low and dropping as the diver breaks for the surface, the WOB will also be lessening. So how could having a lower WOB in the upright position be of any real help in an OGS panic ascent to the surface? -Andy Last edited by silent running : 30th May 2008 at 09:48.
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30th May 2008, 13:45	#567 (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: 1,732	Re: Comprehensive list of all accidents Quote: (Originally Posted by silent running) Hi Alex, nice to have you back. Did you also test Boris for it's prone WOB? And if not, why? I would be interested to know how it compares to it's upright WOB, given the BMCL design and it's differing hydrostatic load in different positions and the fact that most of us spend much more time swimming in the prone position or close to it, which is obviously a more common CCR behavior than outright panic. Thanks. The prone WOB is around 0.1J/L lower than the vertical WOB for the Boris. The reason is we can almost eliminate the movement of the counterlung centroid as it inflates and deflates by optimising the loop volume. In a vertical position this movement of the counterlung centroid is quite pronounced: NEDU call it Elastance, and in Europe it is called Compliance, but in fact it is neither: it simply the hydrostatic movement of the counterlung centroid as the counterlung inflates and deflates.. There is also a trick to get an artificially low figure in the prone position (as there is a positive loop pressure around the optimal point) by using a very high rate of loop volume adjustment (imagine, venting a loop as you breathe out), depending on where valves are placed. We use a slow rate of loop volume adjustment. In the vertical position the trick tends not to work because it drives the rebreather into negative loop pressure. For this reason, we like the vertical position as it removes another variable when we are comparing our results with those quoted by the manufacturer. In a prone position, the CLs usually have a positive pressure, which makes inhale easier. This is better from the physiological standpoint, than a negative pressure which there is around the optimal loop volume of most rebreathers in the vertical position. So again, if the rebreather meets the standard in the vertical position, it will be safe in the prone position. I hope the above description is sufficiently detailed answer to your question. It also explains why we don't plan publishing prone figures: we do not want to get into a mud slinging match with anyone, who can show some absurdly low figure by doing things such as the tricks I mentioned in the prone position simply because there is positive loop pressure at the lowest WOB point. The best apples for apples comparison is a vertical rebreather, filled with the same 8-12 mesh sodalime, used by the same amount (50% roughly), with genuine sinusoidal gas flow from the breathing machine. Alex Last edited by AD_ward9 : 30th May 2008 at 13:49.
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30th May 2008, 13:56	#568 (permalink)
Drmike Custom Title Allowed! Current Rebreather/s: MK 15.X Ouroboros Other CCR Home Build Other Rebreather/s: Inspiration Classic Other CCR Home Build Join Date: Feb 2005 Posts: 3,128	Re: Comprehensive list of all accidents Quote: (Originally Posted by AD_ward9) Thanks. The prone WOB is around 0.1J/L lower than the vertical WOB for the Boris. The reason is we can almost eliminate the movement of the counterlung centroid as it inflates and deflates by optimising the loop volume. In a vertical position this movement of the counterlung centroid is quite pronounced: NEDU call it Elastance, and in Europe it is called Compliance, but in fact it is neither: it simply the hydrostatic movement of the counterlung centroid as the counterlung inflates and deflates.. There is also a trick to get an artificially low figure in the prone position (as there is a positive loop pressure around the optimal point) by using a very high rate of loop volume adjustment (imagine, venting a loop as you breathe out), depending on where valves are placed. We use a slow rate of loop volume adjustment. In the vertical position the trick tends not to work because it drives the rebreather into negative loop pressure. For this reason, we like the vertical position as it removes another variable when we are comparing our results with those quoted by the manufacturer. In a prone position, the CLs usually have a positive pressure, which makes inhale easier. This is better from the physiological standpoint, than a negative pressure which there is around the optimal loop volume of most rebreathers in the vertical position. So again, if the rebreather meets the standard in the vertical position, it will be safe in the prone position. I hope the above description is sufficiently detailed answer to your question. It also explains why we don't plan publishing prone figures: we do not want to get into a mud slinging match with anyone, who can show some absurdly low figure by doing things such as the tricks I mentioned in the prone position simply because there is positive loop pressure at the lowest WOB point. The best apples for apples comparison is a vertical rebreather, filled with the same 8-12 mesh sodalime, used by the same amount (50% roughly), with genuine sinusoidal gas flow from the breathing machine. Alex good stuff - thanks alex __________________ Get a girlfriend you sad twat - a Rebreather is an unfaithful mistress - dont blind yourself to her faults just because she goes down on you
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30th May 2008, 19:56	#569 (permalink)
*Decodiver* Administrator Current Rebreather/s: Megalodon Ouroboros rEvo Other CCR Other Rebreather/s: Inspiration Classic Inspiration Vision Evolution Sport Kiss Classic Kiss rEvo Other CCR Join Date: Jan 2005 Location: Geneva Posts: 2,178	Re: Comprehensive list of all accidents Quote: (Originally Posted by AD_ward9) Thanks. The prone WOB is around 0.1J/L lower than the vertical WOB for the Boris. The reason is we can almost eliminate the movement of the counterlung centroid as it inflates and deflates by optimising the loop volume. In a vertical position this movement of the counterlung centroid is quite pronounced: NEDU call it Elastance, and in Europe it is called Compliance, but in fact it is neither: it simply the hydrostatic movement of the counterlung centroid as the counterlung inflates and deflates.. There is also a trick to get an artificially low figure in the prone position (as there is a positive loop pressure around the optimal point) by using a very high rate of loop volume adjustment (imagine, venting a loop as you breathe out), depending on where valves are placed. We use a slow rate of loop volume adjustment. In the vertical position the trick tends not to work because it drives the rebreather into negative loop pressure. For this reason, we like the vertical position as it removes another variable when we are comparing our results with those quoted by the manufacturer. In a prone position, the CLs usually have a positive pressure, which makes inhale easier. This is better from the physiological standpoint, than a negative pressure which there is around the optimal loop volume of most rebreathers in the vertical position. So again, if the rebreather meets the standard in the vertical position, it will be safe in the prone position. I hope the above description is sufficiently detailed answer to your question. It also explains why we don't plan publishing prone figures: we do not want to get into a mud slinging match with anyone, who can show some absurdly low figure by doing things such as the tricks I mentioned in the prone position simply because there is positive loop pressure at the lowest WOB point. The best apples for apples comparison is a vertical rebreather, filled with the same 8-12 mesh sodalime, used by the same amount (50% roughly), with genuine sinusoidal gas flow from the breathing machine. Alex Thank you Alex, nice to have you back. Cheers, Dave. __________________ CCR/OC Trimix Instructor Trainer CCR Training to Mixed Gas in Switzerland, France, UK & Germany on Megalodon/COPIS-Megalodon/KISS/Sport KISS/Ouroboros/rEvo/Inspiration/Evolution/Sentinel www.zerogravitydiving.com Rebreather World Terms & Conditions
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30th May 2008, 21:10	#570 (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: 1,810	Re: Comprehensive list of all accidents Quote: (Originally Posted by AD_ward9) Thanks. The prone WOB is around 0.1J/L lower than the vertical WOB for the Boris. The reason is we can almost eliminate the movement of the counterlung centroid as it inflates and deflates by optimising the loop volume. In a vertical position this movement of the counterlung centroid is quite pronounced: NEDU call it Elastance, and in Europe it is called Compliance, but in fact it is neither: it simply the hydrostatic movement of the counterlung centroid as the counterlung inflates and deflates.. There is also a trick to get an artificially low figure in the prone position (as there is a positive loop pressure around the optimal point) by using a very high rate of loop volume adjustment (imagine, venting a loop as you breathe out), depending on where valves are placed. We use a slow rate of loop volume adjustment. In the vertical position the trick tends not to work because it drives the rebreather into negative loop pressure. For this reason, we like the vertical position as it removes another variable when we are comparing our results with those quoted by the manufacturer. In a prone position, the CLs usually have a positive pressure, which makes inhale easier. This is better from the physiological standpoint, than a negative pressure which there is around the optimal loop volume of most rebreathers in the vertical position. So again, if the rebreather meets the standard in the vertical position, it will be safe in the prone position. I hope the above description is sufficiently detailed answer to your question. It also explains why we don't plan publishing prone figures: we do not want to get into a mud slinging match with anyone, who can show some absurdly low figure by doing things such as the tricks I mentioned in the prone position simply because there is positive loop pressure at the lowest WOB point. The best apples for apples comparison is a vertical rebreather, filled with the same 8-12 mesh sodalime, used by the same amount (50% roughly), with genuine sinusoidal gas flow from the breathing machine. Alex Thanks very much for the detailed answers and explanation Alex. I hope one of the 2 UK Prism owners will lend you a unit. Otherwise, we'll have to wait for Hollis to get a CE test done for the Prism 2, which could be a while. And I didn't know that a prone position test was easier to manipulate to get a better result. In the meantime, what do you think of the NEDU's protocol to measure the hydrostatic load of the unit in both upright and prone and then test the Prism for WOB only in the prone position? It seems to me that they were testing it for it's intended use for long swims in the prone position. Is this your impression, and what do you make of the hydrostatic load figures listed in the report? Also, I didn't see any reference to the how much volume there was in the loop. Do you have any idea how they set this in NEDU tests? -Andy
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