The Pelagian Way

Rebreatherlab · 4th September 2007, 10:48

Quote: (Originally Posted by Steve)

I'm still not seeing how you are able to validate your loop composition with 2 sensors. If the displays are different you do a dil flush and presumably they agree given the lower pO2 (current limited cell being the most likely failure). When you try to bring them back up to your required pO2 how do you know which one is safe? The bad cell may have failed High or failed Low. With only 2 sensors you don't know which way. You still have 2 different outputs and no way of knowing which one is correct as far as I can tell.

A simple question. You are at 50m and your displays read 1.333 and 1.666. You flush with dil and the displays agree and both display 1.222. Which cell is the bad one?

In this case I would go deeper and validate again. If one cell is truly off high or low it must show at some mathematical point. Interesting. I have so far never seen a cell fail high during a dive. Only when they come out of the vacuum pack. Some give 140 mV in air at 1 ATA. These typically do not respond at all to varying PO2 and goes in the bin on day one.

It would be great if you or any other divers could provide more details regarding cells failing high during dives.

Best,

Andy

**Steve** · 4th September 2007, 11:02

Quote: (Originally Posted by dantheman)

Steve,

What is the failure mode of a sensor that causes it to read high?
Can you explain it, or do you have a reference for any investigation of this?

--dan

Hi Dan,

I hated chemistry at uni so will pass on the how. My basis for this is solely based on experience. I've had it happen a couple of times and know of several other divers that have had it happen. Where is Alex D when we need him?

Many years ago Tubby and I banged heads over this issue. He said 2 was enough and i said he needed 3. Many threads on DiveOz and NWDesigns. We decided to call it a truce and left it there. A year or so later he sought me out to tell me that he had had a sensor fail high on a dive whilst in PNG. Scared the hell out of him as he firmly believed that it couldn't happen. He changed the design of his stingray on the spot.

I still think it is a true measure of the bloke that he looked me up to pass the info on. Does anyone know what he is up to these days?

**Steve** · 4th September 2007, 11:05

Quote: (Originally Posted by Rebreatherlab)

It would be great if you or any other divers could provide more details regarding cells failing high during dives.

Best,

Andy

What do you mean by details? It happens just as often as low in my experience. I'm told it is rarer by others,

<edit> Make the display show 3 sensors simultaneously and I think you have a winner. Sure there are some other bits I'd change but this one is a real danger to you in my opinion. It is a simple change that I see no down side too. Happy to chat about it off line at length if you like.

Drmike · 4th September 2007, 12:14

One way for cells to fail high is if the cells temp compensation fails.

I have experienced temp comp boards failing (low rather than high but it can go either way)

Bottom line is simple - the more cells a unit has the safer that unit is. Cells are BY FAR the weakest and most dangerous part of an Rebreather

OceanOpportunity · 4th September 2007, 12:29

given the 2 vs 3 cell debate for mCCR, and the (in)ability to manually 'vote out' the bad sensor, it almost makes sense to dive one sensor as Andy described previously with very routine diluent checks. THe math will show instantly. If it's bad, bail semi-closed or bail to OC

Drmike · 4th September 2007, 12:52

Quote: (Originally Posted by OceanOpportunity)

given the 2 vs 3 cell debate for mCCR, and the (in)ability to manually 'vote out' the bad sensor, it almost makes sense to dive one sensor as Andy described previously with very routine diluent checks. THe math will show instantly. If it's bad, bail semi-closed or bail to OC

only makes sense if you have a death wish

OceanOpportunity · 4th September 2007, 13:02

if it is a 'death wish' so to speak, then so are all 2 sensor units. A 2 sensor system is basically a one sensor system with a means of redundancy in case of a failure..so you basically terminate the dive CC rather than bailout to a new mode as with one cell.

with a series of routine dil checks, I dont see how 2 cells vs 1 cell would serve you any better. If it craps out, bail out.

Drmike · 4th September 2007, 13:07

Quote: (Originally Posted by OceanOpportunity)

I dont see how 2 cells vs 1 cell would serve you any better. .

Because on a single cell unit if a cell craps out you may be dead before you realise if your not checking often enough (who wants to spend a dive flushing to test cells

)

on a two cell system a 2nd cell may give you a warning (by showing a variance) that the other cell is duff PROVIDED the 2nd cell doesnt have the same fault - so it got to be a different age, maybe even different mnf.) if it does have the same fault your probably dead.

IMO 1 is stupid, 2 is unwise, 3 is a good start and 4000 cells of different ages and different suppliers would be quite safe.

the more cells you have the safer you will be - and the fewer the less safe - sure you can put protocals in place to manage only having 1 or 2 cells but at the end of the day you wont change that basic fact.

Rebreatherlab · 4th September 2007, 13:15

Quote: (Originally Posted by Drmike)

only makes sense if you have a death wish

Seems you're missing the point. The point is that the ability to quickly and easily put some DIL across the cells is safer than not being able to do it. Sure it is better to have 3 than 2 cells and sure it is better to have 5 than 4 cells.
The Pelagian can use 3 cells, but they are split up in order to not share common ground or battery. The Pelagian is not sold with a third read out in its a basic package as many divers would prefer to run a live deco computer from one cell. If not an additional display can be added.

If one argues that simply adding a third cell would be a better solution and think that you are safe just because 2 cells read one thing and ONLY one cell reads another you are just trying to improve your luck.

the corner stones are checking cells in air (or any other known gas) at 1 ATA, then in pure O2 at 1 ATA, then pure O2 at 6m, then reference the readouts frequently with DIL during the dive.

Sorry I am tired...

Andy

OceanOpportunity · 4th September 2007, 13:15

not to split hairs or start a pissing match, BUT your electronics could fail and leave you not noticing until its too late as well. I'm not convinced that there is enough hard evidence on failure mode analysis to say one method is better than another. Yes, doing a dil check every few minutes may be distracting during a dive, but practically speaking it will work, which is my point. mCCR is constantly trickling O2 at or close to your metablic rate anyway, so it'd be next to impossible to go so long as to not notice the PO2 drop on a dead sensor...you'd notice right away. You should be looking at your display more often that that if you are manually adding O2 now and then.

4th September 2007, 10:48	#21 (permalink)
Rebreatherlab RebreatherWorld Sponsor Current Rebreather/s: Pelagian Other Rebreather/s: Not Bought Yet Classic Kiss Pelagian Join Date: Sep 2005 Location: Thailand Posts: 193	Re: The Pelagian Way Quote: (Originally Posted by Steve) I'm still not seeing how you are able to validate your loop composition with 2 sensors. If the displays are different you do a dil flush and presumably they agree given the lower pO2 (current limited cell being the most likely failure). When you try to bring them back up to your required pO2 how do you know which one is safe? The bad cell may have failed High or failed Low. With only 2 sensors you don't know which way. You still have 2 different outputs and no way of knowing which one is correct as far as I can tell. A simple question. You are at 50m and your displays read 1.333 and 1.666. You flush with dil and the displays agree and both display 1.222. Which cell is the bad one? In this case I would go deeper and validate again. If one cell is truly off high or low it must show at some mathematical point. Interesting. I have so far never seen a cell fail high during a dive. Only when they come out of the vacuum pack. Some give 140 mV in air at 1 ATA. These typically do not respond at all to varying PO2 and goes in the bin on day one. It would be great if you or any other divers could provide more details regarding cells failing high during dives. Best, Andy __________________ www.rebreatherlab.com
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4th September 2007, 11:02	#22 (permalink)
Steve Ladies bring a plate Current Rebreather/s: Megalodon Home Build Other Rebreather/s: Not Bought Yet Inspiration Classic Sport Kiss Classic Kiss MK 15.X Home Build Join Date: Feb 2005 Location: Perth - Australia Posts: 1,045	Re: The Pelagian Way Quote: (Originally Posted by dantheman) Steve, What is the failure mode of a sensor that causes it to read high? Can you explain it, or do you have a reference for any investigation of this? --dan Hi Dan, I hated chemistry at uni so will pass on the how. My basis for this is solely based on experience. I've had it happen a couple of times and know of several other divers that have had it happen. Where is Alex D when we need him? Many years ago Tubby and I banged heads over this issue. He said 2 was enough and i said he needed 3. Many threads on DiveOz and NWDesigns. We decided to call it a truce and left it there. A year or so later he sought me out to tell me that he had had a sensor fail high on a dive whilst in PNG. Scared the hell out of him as he firmly believed that it couldn't happen. He changed the design of his stingray on the spot. I still think it is a true measure of the bloke that he looked me up to pass the info on. Does anyone know what he is up to these days? __________________ WARNING: I contain occasional coarse language, extreme sexual references, nudity, and adult themes, which may offend some people - Usually churchy types.
(Online)

4th September 2007, 11:05	#23 (permalink)
Steve Ladies bring a plate Current Rebreather/s: Megalodon Home Build Other Rebreather/s: Not Bought Yet Inspiration Classic Sport Kiss Classic Kiss MK 15.X Home Build Join Date: Feb 2005 Location: Perth - Australia Posts: 1,045	Re: The Pelagian Way Quote: (Originally Posted by Rebreatherlab) It would be great if you or any other divers could provide more details regarding cells failing high during dives. Best, Andy What do you mean by details? It happens just as often as low in my experience. I'm told it is rarer by others, <edit> Make the display show 3 sensors simultaneously and I think you have a winner. Sure there are some other bits I'd change but this one is a real danger to you in my opinion. It is a simple change that I see no down side too. Happy to chat about it off line at length if you like. __________________ WARNING: I contain occasional coarse language, extreme sexual references, nudity, and adult themes, which may offend some people - Usually churchy types. Last edited by Steve : 4th September 2007 at 11:13.
(Online)

4th September 2007, 12:14	#24 (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: 3,104	Re: The Pelagian Way One way for cells to fail high is if the cells temp compensation fails. I have experienced temp comp boards failing (low rather than high but it can go either way) Bottom line is simple - the more cells a unit has the safer that unit is. Cells are BY FAR the weakest and most dangerous part of an Rebreather __________________ 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 Last edited by Drmike : 4th September 2007 at 12:17.
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4th September 2007, 12:29	#25 (permalink)
OceanOpportunity for a world of water Current Rebreather/s: Other CCR Dolphin Home Build Other Rebreather/s: Not Bought Yet Inspiration Classic Other CCR Dolphin Home Build Join Date: Nov 2006 Location: Providence, RI USA Posts: 465	Re: The Pelagian Way given the 2 vs 3 cell debate for mCCR, and the (in)ability to manually 'vote out' the bad sensor, it almost makes sense to dive one sensor as Andy described previously with very routine diluent checks. THe math will show instantly. If it's bad, bail semi-closed or bail to OC __________________ Michael Lombardi Oceans of Opportunity www.oceanopportunity.com Elected Director, Society for Human Performance in Extreme Environments MN'07, The Explorers Club Project Manager, Diving a Dream
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4th September 2007, 12:52	#26 (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: 3,104	Re: The Pelagian Way Quote: (Originally Posted by OceanOpportunity) given the 2 vs 3 cell debate for mCCR, and the (in)ability to manually 'vote out' the bad sensor, it almost makes sense to dive one sensor as Andy described previously with very routine diluent checks. THe math will show instantly. If it's bad, bail semi-closed or bail to OC only makes sense if you have a death wish __________________ 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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4th September 2007, 13:02	#27 (permalink)
OceanOpportunity for a world of water Current Rebreather/s: Other CCR Dolphin Home Build Other Rebreather/s: Not Bought Yet Inspiration Classic Other CCR Dolphin Home Build Join Date: Nov 2006 Location: Providence, RI USA Posts: 465	Re: The Pelagian Way if it is a 'death wish' so to speak, then so are all 2 sensor units. A 2 sensor system is basically a one sensor system with a means of redundancy in case of a failure..so you basically terminate the dive CC rather than bailout to a new mode as with one cell. with a series of routine dil checks, I dont see how 2 cells vs 1 cell would serve you any better. If it craps out, bail out. __________________ Michael Lombardi Oceans of Opportunity www.oceanopportunity.com Elected Director, Society for Human Performance in Extreme Environments MN'07, The Explorers Club Project Manager, Diving a Dream
(Offline)

4th September 2007, 13:07	#28 (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: 3,104	Re: The Pelagian Way Quote: (Originally Posted by OceanOpportunity) I dont see how 2 cells vs 1 cell would serve you any better. . Because on a single cell unit if a cell craps out you may be dead before you realise if your not checking often enough (who wants to spend a dive flushing to test cells ) on a two cell system a 2nd cell may give you a warning (by showing a variance) that the other cell is duff PROVIDED the 2nd cell doesnt have the same fault - so it got to be a different age, maybe even different mnf.) if it does have the same fault your probably dead. IMO 1 is stupid, 2 is unwise, 3 is a good start and 4000 cells of different ages and different suppliers would be quite safe. the more cells you have the safer you will be - and the fewer the less safe - sure you can put protocals in place to manage only having 1 or 2 cells but at the end of the day you wont change that basic fact. __________________ 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 Last edited by Drmike : 4th September 2007 at 13:14.
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4th September 2007, 13:15	#29 (permalink)
Rebreatherlab RebreatherWorld Sponsor Current Rebreather/s: Pelagian Other Rebreather/s: Not Bought Yet Classic Kiss Pelagian Join Date: Sep 2005 Location: Thailand Posts: 193	Re: The Pelagian Way Quote: (Originally Posted by Drmike) only makes sense if you have a death wish Seems you're missing the point. The point is that the ability to quickly and easily put some DIL across the cells is safer than not being able to do it. Sure it is better to have 3 than 2 cells and sure it is better to have 5 than 4 cells. The Pelagian can use 3 cells, but they are split up in order to not share common ground or battery. The Pelagian is not sold with a third read out in its a basic package as many divers would prefer to run a live deco computer from one cell. If not an additional display can be added. If one argues that simply adding a third cell would be a better solution and think that you are safe just because 2 cells read one thing and ONLY one cell reads another you are just trying to improve your luck. the corner stones are checking cells in air (or any other known gas) at 1 ATA, then in pure O2 at 1 ATA, then pure O2 at 6m, then reference the readouts frequently with DIL during the dive. Sorry I am tired... Andy __________________ www.rebreatherlab.com
(Offline)

4th September 2007, 13:15	#30 (permalink)
OceanOpportunity for a world of water Current Rebreather/s: Other CCR Dolphin Home Build Other Rebreather/s: Not Bought Yet Inspiration Classic Other CCR Dolphin Home Build Join Date: Nov 2006 Location: Providence, RI USA Posts: 465	Re: The Pelagian Way not to split hairs or start a pissing match, BUT your electronics could fail and leave you not noticing until its too late as well. I'm not convinced that there is enough hard evidence on failure mode analysis to say one method is better than another. Yes, doing a dil check every few minutes may be distracting during a dive, but practically speaking it will work, which is my point. mCCR is constantly trickling O2 at or close to your metablic rate anyway, so it'd be next to impossible to go so long as to not notice the PO2 drop on a dead sensor...you'd notice right away. You should be looking at your display more often that that if you are manually adding O2 now and then. __________________ Michael Lombardi Oceans of Opportunity www.oceanopportunity.com Elected Director, Society for Human Performance in Extreme Environments MN'07, The Explorers Club Project Manager, Diving a Dream
(Offline)

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