Changing 02 Cells

[Major Clanger]

I was advised on Mod 1 to change them all at the same time. On Mod 2 my instructor recently gave good reasons for changing them out at different times, but also mentioned he flip flops between which of the two he thinks best. Sorry if this has been done to near-death elsewhere but interested in view points.

[Ian_6301]

Good question, don't know.

What does the manufacturer reccommend?

[SoggyBottoms]

a thread better suited to CCRX Clanger. just muppets here

moi y compris

[Zero-Viz]

I was advised on Mod 1 to change them all at the same time. On Mod 2 my instructor recently gave good reasons for changing them out at different times, but also mentioned he flip flops between which of the two he thinks best. Sorry if this has been done to near-death elsewhere but interested in view points.

I was taught seperately at around roughly 6 monthly intervals (ideally), replacing the oldest each time but there are lots of different opinions.

I just replace all of mine at the same time every 12 months or so.

[Zero-Viz]

...

[jturner]

I was advised on Mod 1 to change them all at the same time. On Mod 2 my instructor recently gave good reasons for changing them out at different times, but also mentioned he flip flops between which of the two he thinks best. Sorry if this has been done to near-death elsewhere but interested in view points.

I think I'd tend towards the latter option (staggered changing) mainly so that the odds of all 3 going belly-up at the same time (ie new duds or 3 at premature end-of-life) was reduced... however, since I'm still on APD's new cells, they die after a few hours so I've not ever had to change one due to old age yet! :(

[SilentDiver]

I was taught seperately at around roughly 6 monthly intervals (ideally), replacing the oldest each time but there are lots of different opinions.

I just replace all of mine at the same time every 12 months or so.


+1

I got a N@90 mini cell checker when they first came out. So I just replace them all at the same time and regularly check them, usually once a month.

[Glos-Tech]

When I change mine I normally change them between 3-4 weeks apart with Teledynes now quite regularly with the new cells as JT mentioned

[Major Clanger]

however, since I'm still on APD's new cells, they die after a few hours so I've not ever had to change one due to old age yet! :(

A common theme among Inspiration users I dived with last year.

[Mr Flibble]

Are AP cells still failing? I had one go a few months back and they replaced all 3. So far, touch wood, they've been fine. Haven't heard of many failures recently. This could be down to them getting it right or people just accepting that there failing and get them replaced as routine without posting about it. As for the original post. I think I'll start replacing them near end of life but perhaps a month apart (assuming they reach end of life).:D

[Stonybonytony]

Paul Raymakers did some very interesting simulations here http://www.revo-rebreathers.com/uploads/downloadsitems/Understanding_oxygen_sensors.pdf of the different strategies, and I think makes a convincing case for staggered swapping to minimise the risk of simultaneous cell failure. I have the n@90 cell checker and use this to determine which cell is the weakest, and to verify all cells are readin linearly and not current limited before each trip, and I err on the side of caution. It's always painful getting rid of perfectly good cells but, given the other thread re ox tox, am happy to spend money to reduce theoretical risks as far as I can.

I read recently, and I imagine it was on here or the other place, of a 3 cell rebreather where 2 cells failed simultaneously, and the two that failed were closest to each other and hence out voted the third good cell.

[Mark Chase]

Personaly I have in the past changed cells on a 6 month rotation swaping one and then two.

So 6 months in I replace cell 2 and six months later replace cells 1 & 3 then repet replacing cell 2 6 months later again.

The reasion behind this was I was keeping at least one tried and tested cell and not replacing all three with cells which could have a batch fault.

However since the great cell disaster of 2011 I have changed stratagy to replaceing one cell at a time. And yes this meens a cel will get to 18months old. And i have done this because prior to the launch of the reliable Narked @ 90 cells I was using my old BUD cells from AP and waiting wating for new cells.

In the end i discoverd two things.

1: Cells last 18months + no problem

2: When an old cell fails its no diferent to when a new APD rubbish cell fails.


As a result I have begun to question the logic of just arbitrerialy changing cells at 12 months. I have for the last two years just swaped out cells which start to run hot or have failed.

I have had more troubble putting in new cells than i have ever had with old cells failing.

ATB

Mark

[iamyourgasman]

I also use the staggered method as I have 5 cells in the rEvo, replacing them at once is not a viable option. I just changed a perfectly good one last week (it went in 07/2011! so had a good few hours out of it). As a result currently all my cells are <12months for a few more days until the oldest will celebrate its first birthday ;) and 3 are <6 months. My next scheduled change will be in August/September. If any of the five will fail, I'd be quite happy just to run the unit on 4 cells, but I can still put the perfectly good old one back (and probably watch it dying on the first dive!) if I wish,until I got a replacement cell from Paul.

[Major Clanger]

Paul Raymakers did some very interesting simulations here http://www.revo-rebreathers.com/uploads/downloadsitems/Understanding_oxygen_sensors.pdf of the different strategies, and I think makes a convincing case for staggered swapping to cell.

My OP was made after reading that article elsewhere and my views about deep tox hits and maximising avoidance. To me, the staggered approach has merit so will be changing my replacement procedure to try to minimise the impact of insidious cell behaviour. Was interested in what others do.

[Mark Chase]

My OP was made after reading that article elsewhere and my views about deep tox hits and maximising avoidance. To me, the staggered approach has merit so will be changing my replacement procedure to try to minimise the impact of insidious cell behaviour. Was interested in what others do.




To be honest the easiest thing to do is just buy Narked @ 90 cells and go diving :D

And this isnt because i hate APD. I used APD cells exclusivly right up untill Alex Dias screwed it all up for us. I did that because the old APD cells were very reliable. The new ones are a disaster and i wont dive them till they sort it all out.

Only good thing about the new APD cells is it teaching us all how to cope with cell failure and making us much more vigulent :D

[Major Clanger]

To be honest the easiest thing to do is just buy Narked @ 90 cells and go diving :D

I would do if I didn't have a meg and buy direct from ISC :) Good cells so far, barely dropped a mV in a year.

[Stonybonytony]

What struck me about Paul's paper, is that the risk of 3 of 5 cells failing in the simulation was 6 in a million. I can cope with 1 cell fail, no problem, and 2 is probably ok, though complicated in they were both on the shearwater and hence would affect automatic oxygen injection, but 3 and I wouldn't even have a trustable majority, and would effectively have no idea what the ppo2 was. At this point I would of course bail or at least go to scr mode depending where it was/ what I was doing. Though Sod's law it would happen right in the middle of some other crisis when brain is already busy dealing with something else.

Anyhow, 6 in a million, 1 in 166,000, doesn't sound bad. But if I do 50 dives a year, then it's a 1 in 3,000 risk in any year. And if I dive for the next 25 years, then there's a 1 in 133 chance of experiencing a 3 cell failure at some point. Which to me starts too look much too much like "something that could happen".

There is an apocryphal story about a Boeing executive who only flew on 4 engined planes. When asked why, he replied "because we don't make 6 engined planes"

[Stonybonytony]

...though I'm thinking of cell failure as "giving an incorrect reading" rather than reading zero, which I think may be Paul's definition of failure. If 3 cells fail and read zero, at least it is obvious to ignore them, and rely on the two remaining cells.

[Mark Chase]

...though I'm thinking of cell failure as "giving an incorrect reading" rather than reading zero, which I think may be Paul's definition of failure. If 3 cells fail and read zero, at least it is obvious to ignore them, and rely on the two remaining cells.




Thats more the point.

I have had cells read zero but usualy pre dive. i have never had a cell fail to zero which i properly tested during the set up and during the dive its self.

I have had cells drift out of acepted parity with other cells, I have had slow reacting cells and i have had cells which wouldent read higher than X PP02.


None of thease events caused me to go off loop during a dive. I meerly did the necessary testing to find out which cell was relaible and ended the dive on that cel or cells. I have had cells that wouldent read above 1.5pp02 so i just did the dive on 1.3 and regularly checked i could get 1.4 if i needed too.

WHen i first started diving CCR I was most feerfull of 02 levels and cell issues.

Now they hardly bother me at all and I only have one feer of CCR, and that is C02.

Cell issues can be checked difinitivly, even mid dive and the results can be worked arround, even if the work arround results in the decision to go OC and go home.


ATB

Mark

[notdeadyet]

I used to stagger the cells on my KISS. The Mk15 cells are made to order from AII (not worth keeping inventory of) and I can't decide if that makes them more or less likely to suffer from bad batch syndrome as the more common cells seem to. They have been very steady and reliable unlike the AII KISS cells I tried. That said, I still stagger them.

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[JPTaylor]

I change mine all in one go, think APD recommend this (and same batch). That said, I order three new cells, install one dive it & if OK repeat with next cell until all 3 replaced. That said, with the APD cells only lasting 4 - 6 months it's not really an issue at the moment.

New units come with 3 new cells often from same batch!

[JPTaylor]

Dupe

[Major Clanger]

What struck me about Paul's paper, is that the risk of 3 of 5 cells failing in the simulation was 6 in a million. I can cope with 1 cell fail, no problem, and 2 is probably ok, though complicated in they were both on the shearwater and hence would affect automatic oxygen injection, but 3 and I wouldn't even have a trustable majority, and would effectively have no idea what the ppo2 was. At this point I would of course bail or at least go to scr mode depending where it was/ what I was doing. Though Sod's law it would happen right in the middle of some other crisis when brain is already busy dealing with something else.

Anyhow, 6 in a million, 1 in 166,000, doesn't sound bad. But if I do 50 dives a year, then it's a 1 in 3,000 risk in any year. And if I dive for the next 25 years, then there's a 1 in 133 chance of experiencing a 3 cell failure at some point. Which to me starts too look much too much like "something that could happen".

There is an apocryphal story about a Boeing executive who only flew on 4 engined planes. When asked why, he replied "because we don't make 6 engined planes"

I'm not sure the likelihood of multiple cell failure increases the more years you dive, all things being equal and changes made within guidelines.

As an aside, though with possibly some relevance to failure statistics, I read somewhere that the likelihood of a spitfire pilot getting shot down during WW2 was the same each flight no matter how often they'd flown.

[Zero-Viz]

I read recently, and I imagine it was on here or the other place, of a 3 cell rebreather where 2 cells failed simultaneously, and the two that failed were closest to each other and hence out voted the third good cell.

I've seen this happen to a Sentinel on a dive. The dil flush showed that it was two bad cells outvoting the one good one so they had to disable the two bad cells.

[Zero-Viz]

...

[SoggyBottoms]

on the Vision:

In the Dive Mode - Underwater Menu, when deeper than 1.2m, there is a useful “Cell Check” display which calculates what the ppO2 will be if you flush effectively at your current depth.
The display on the left is the ppO2 should you flush with diluent and the display on the right is the ppO2 should you flush with oxygen.

I thought this useful for quick checks on cells

[nickb]

on the Vision:

In the Dive Mode - Underwater Menu, when deeper than 1.2m, there is a useful “Cell Check” display which calculates what the ppO2 will be if you flush effectively at your current depth.
The display on the left is the ppO2 should you flush with diluent and the display on the right is the ppO2 should you flush with oxygen.

I thought this useful for quick checks on cellsThe Predator also has a diluent F02 output available with a few presses on the right-hand button.

[nickb]

on the Vision:

In the Dive Mode - Underwater Menu, when deeper than 1.2m, there is a useful “Cell Check” display which calculates what the ppO2 will be if you flush effectively at your current depth.
The display on the left is the ppO2 should you flush with diluent and the display on the right is the ppO2 should you flush with oxygen.

I thought this useful for quick checks on cellsThe Shearwater Predator also has a diluent F02 output available with a few presses of the right-hand button.

[Neil Brock]

The day will come when as you get to 6msw to do a bubble check, the depth sensor twig's where you are, and instructs the solenoids to fire (oop's wrong word :giggle:) O2 across the cells and cross check that they read 1.6, all in the blink of an eye !
If it passes this linearity check it automatically makes the set point 1.3, but if it fails this check, drops the set point to 1.2.

Oh, it already does on the Mk6 :middlefinger:

[GLOC]

Neil, I do believe that there are some great innovations on MkIV and when the O2 cell presentation was given at RF3.0 there were certainly a few people asking why isn't cell/gas/depth sensor validation taking place using dil and or O2.

Regards

[Neil Brock]

Gareth, I do believe your right :nod:

It's all to do with what looks like squigley string, licorice allsorts, and dead beetles inside, that I know very little about, but it works quite well, I'am still here !

[GLOC]

I know that some of the recording of the lectures have made their way into the public domain but when I asked Petar Denoble when the conference proceedings were going to be released (should have been out by Dec 12), he said that some presentation papers hadn't even been received by DAN :(

Regards

[Baron015]

I've never changed a cell.

Actually that's not quite right - I had to change all 3 cells in my Sentinel after I flooded it.

Also I chucked one cell when I was in Bikini since it seemed to be working fine around 0.21 but very slow at around 1.3.

Although I've had the JJ about 16 months now, I ought to think about changing the other 2 ....

TB.

[notdeadyet]

The Shearwater Predator also has a diluent F02 output available with a few presses of the right-hand button.

Hammerhead has it too. Must admit I've never used it, I find it easier just to do it mentally. In eCCR mode there's enough button pushes to switch the solenoid off before flushing that I cant be arsed with the additional ones.

I find the mV display quite useful for the 6m ppo2 check though.

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[DiverMike]

Mine failed nicely out of sync so the replacement was staggered until cell gate and when I got my head serviced last April all 3 cells failed the tests at APD and they were replaced under warranty for free :-) My cell checking regime is to try and remember to do a linearity check when I hit the bottom pushing it to a bit beyond 1.4. At the end of my dive before leaving 6m I will occasionally get the loop as close to 1.6 as I can and then drop to 7/8 or 9m and see if the pO2 spikes to 1.9 and then review the traces in log viewer. If I am concerned about a cell and it is old I'll swap it out, if it is under a year I'll post it to AP with a nice note asking them to check it.

[Mark Chase]

Neil, I do believe that there are some great innovations on MkIV and when the O2 cell presentation was given at RF3.0 there were certainly a few people asking why isn't cell/gas/depth sensor validation taking place using dil and or O2.

Regards


It is

I do it all the time

Its very simple to acheive and i dont reely see the need for complex automation


ATB

Mark

[Neil Brock]

It is

I do it all the time

Its very simple to acheive and i dont reely see the need for complex automation


ATB

Mark

Hi Mark,

I kind of agree with your view. I used to do it manually in my head, that way you knew it was done, i.e. you can depend on yourself, but I find that having it done for me is one less small task to do that allows me to just go diving.

I suppose it's similar to them that have mccr as opposed to eccr, them that work primarily with tables, not computers, them that insist that the pilot fly the plane, not the auto-pilot, them that drive manual gearbox cars, not auto's, them that light the cooker with matches, those that don't bother with central heating and still light the fire in the morning, even those that use "instant" coffee, and not a Netspresso !

DINOSAURS :D

[Mark Chase]

Hi Mark,

I kind of agree with your view. I used to do it manually in my head, that way you knew it was done, i.e. you can depend on yourself, but I find that having it done for me is one less small task to do that allows me to just go diving.

I suppose it's similar to them that have mccr as opposed to eccr, them that work primarily with tables, not computers, them that insist that the pilot fly the plane, not the auto-pilot, them that drive manual gearbox cars, not auto's, them that light the cooker with matches, those that don't bother with central heating and still light the fire in the morning, even those that use "instant" coffee, and not a Netspresso !

DINOSAURS :D


Back up dive computer with Ratio deco Check

Never flown a plain with auto pilot :D Check

I have two cars I mainly drive both manual Check

No the cooker is a spark lit Fail

I have no central heating down stairs except 1 Rad in the kitchen and utility. I have background heating under floor and have a log fire to heat the house in the winter. Check

I drink instant coffee Check


Yep by your standards, defo a Dinosaur :D



In truth most of the things your offering up have been with us quite a while and are pretty reliable. My issue with complex automated CCR is X ATMs of water and miniscule R&D budgets which leave us in the water as crash test dummies.

My most automated CCR (Hammer Head) was so bloody unreliable I couldn’t stand it. Its advanced "safety" features tried to kill me a couple of times. My least advanced unit KISS was 100% reliable (total missed dives one flood due to a split mouthpiece)

If an when they bring out a reliable fully automated ECCR Ill consider buying one, but to date they have not. I have heard so many stories about failed boot up routines on Poseidon’s it doesn’t give me a great deal of faith in the system. There has also bee two deaths on Poseidon’s despite all its electronic support and that’s on a unit I have yet to see anywhere outside a dive show.


Volvo spent £23,000,000 on an automated anti collision system for their S60 car. This was designed to stop rear end crashes by automatically applying the breaks in time to stop the car.

Hear they demonstrated it to a public audience so one assumes they had got all the bugs out.

I wonder if Poseidon spent £23,000,000 on R&D for their safety features?

Volvo Collision Protection system tested on Truck - Crash. - YouTube (http://www.youtube.com/watch?v=0eChAKm1t3U)

[Neil Brock]

In a nutshell, your spot on, none of the current breed of RBs are 100% safe !

And if it makes you chuckle, and brightens up your day, I just bought er indoors a Volvo !
And if I had a £ for every time in the early years that the Mk6 failed its pre dive checks, I would be writing this from my Caribbean branch, not me Cardiff one, couple that with a £ for every promise that Posiedon make, I would be minted :giggle:


Re two deaths, for what its worth, the woodentop experts reckon the result of this one was human error.............

http://mkvi.poseidon.com/downloads/Accident_Report_IR-2010-05-31-1.pdf

It makes you wonder if some users might be killed crossing the road. You even need a licence to fish !

[notdeadyet]

Have there been many/any rebreather accidents where the unit was found to be at fault?

I don't put a lot of faith in bells and whistles as the vast majority of accidents appear to be human factors. Human error is only half the story, that kind of assumes we have no learned behaviour. When a system does x then it is human nature to react by doing y.

It's pretty common in industry where a system is either too complicated or too prone to shutting you out that the users find ways of working round it. Is that the fault of the user or the designer? Similarly, the more you remove the user from playing a part in his own safety the more accidents that happen.

The only dives I missed on my KISS were when a cell died. Other than that it never missed a beat. Automation is not a bad thing as long as you can still work it without it and know enough to spot when it has fallen over. The danger with a lot of the more complex rebreathers is that they increasingly stop either of these happening and turn the diver into a passenger.

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[Mark Chase]

In a nutshell, your spot on, none of the current breed of RBs are 100% safe !

And if it makes you chuckle, and brightens up your day, I just bought er indoors a Volvo !
And if I had a £ for every time in the early years that the Mk6 failed its pre dive checks, I would be writing this from my Caribbean branch, not me Cardiff one, couple that with a £ for every promise that Posiedon make, I would be minted :giggle:


Re two deaths, for what its worth, the woodentop experts reckon the result of this one was human error.............

http://mkvi.poseidon.com/downloads/Accident_Report_IR-2010-05-31-1.pdf

It makes you wonder if some users might be killed crossing the road. You even need a licence to fish !




To the best of my knowladge ALL CCR deaths were either human error or pre existing medical condition, reguardless of which unit they were on.


My only point is, if your going to make a system fully automated and remove all human input, it has to be very very reliable.

ABS springs to mind as a very reliable system which makes us all drive far too fast in the wet.

Traction control makes me floor the throttle with wild abandon on my 2012 BMW M Sport where as id be taking the same corner like a granny on valium in my 1994 MR2 Turbo (which I prefer driving :D)

If my ABS or traction control failed unexpectedly on the BMW I would undoubtably crash as I have put too much reliance on them.

My ABS on the Jeep Cherokee I had in 1996 was rubbish. Id never trust it to work properly. Rust on he sensor wheel would cause the car to keep on roling long after the breaks should have stoped it.

But these days the ABS systems all seem to be very reliable so i put my faith in them and relax when driving a modern car.

Not so with CCR. The "safety systems" on modern CCR are still in the 1996 Jeep bracket of crap

I have to admit the Sheerwater electronics package seems very impressive in terms of its reliabuility, but 02 cell technolagy is still the week link in the chain.


For me when diving an automated system I feel like I actualy have to put greater effort into checking the automation is working corectly than i do just flying a manual unit. Often its quite hard to work arround the automatied systems in order to do the proper manual checks.

ATB

Mark

[Neil Brock]

Morning Mark,

You were up early, or, in late :snooze:


To the best of my knowladge ALL CCR deaths were either human error or pre existing medical condition, reguardless of which unit they were on.

It's certainly looking that way, but only for those that have been recovered, remember that not all have been investigated because they were never found, so personally I keep an open mind on that ALL CCR deaths were human error stuff until proven otherwise.

I think your ABS analogy is a reasonable view and a good example, but you could also use it both ways.

If, and its a big if, all deaths on CCR are human error, might it not be argued that by removing the human input, you reduce the Deaths. I am firmly of the view though that all we can do is reduce, not remove !

Your ABS analogy shows that second and third generation ABS units from say Bosch, are better than the first generation ABS systems, and likewise it could be said by some that for instance the Vision software is better than the Classic version, just evolution. Not perfected, but getting there ?
Mind you, your right, its gone the other way with cells ! :D

Jeep, Ha, Jeep, you bought that on yourself, a f**king Jeep, I knew someone must have bought one Ha :rofl::rofl:


For me when diving an automated system I feel like I actually have to put greater effort into checking the automation is working correctly than i do just flying a manual unit. Often its quite hard to work around the automated systems in order to do the proper manual checks.

Again, a valid point, but I would argue that there is nothing wrong with say a unit doing it's own positive pressure test, and that an automated test that you watch as opposed to do, is no less safe than doing it manually ?.

I don't think we will ever remove the incidents caused by people swimming round ignoring warnings or alarms, no bail out etc etc they are just Darwins way !

Cheers

[Airburnr]

If only we could help Darwin, sometimes the bubbles should stop. Had a woman ignore, interrupt the dive breifing, just blow off everything being said, because she had 20 yrs experience, what a waste of her time, blah blah. She jumped in, oh yeah, didnt turn her air on. Yet we had, ok mayb not had to, but fish her out before she drowned. SOMETIMES THE BUBBLES SHOULD STOP . IMHO. Yea i know, wrong attitude.


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