O2 cells falling apart - bad batch?

teksimple

AII certainly does NOT state that their sensors will perform to spec, two years on the shelf unopened.

I'll take a sensor that does work over one that should, any day.

I think it is a double-edge sword. If you buy an extra sensor and keep it around unopened thinking that you might need it when one of your main sensors fails, you are all the while making it more likely that your backup sensor itself will fail.

Personally, I replace all my sensors at the same time every year with the best, freshest sensors I can buy. That is exactly what you did when you bought your new rebreather, right? After all, how many people stage their initial sensor purchases on a new rig over a few months? Perhaps alternating sensor replacement is a good idea for some people who's sensors have failed them in the past (perhaps because they kept them on the shelf for two years?)

I suggest using your one year old sensors as backup. Don't buy a new one for that purpose. I keep my older ones--dated--in a plastic bag. I have yet to use one of them.

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AD_ward9

Shelf life is stated in different ways by different companies. For the AI sensors, it is 6 months shelf life then 60 months operational life. For diving operations, the 60 months is reduced to 12 months. Insovt quote a 60 month shelf life, and 60 month operational life, but they run simultaneously.

The "oxygen starvation" on those two sensors does not appear to be an issue within their stated shelf lives. Different sensors have different mechanics, so what shelf life applies to one should not be assumed to apply to all.

As regards replacing them all at the same time, here I disagree. Bad batches do occur, and it is better to stagger replacement: every 3 months if you have 4 sensors, every 4 months if you have 3 sensors, in an ideal world.

The main thing is to look after sensors properly. They do not like mechanical shock, or having differential pressures put on them. If a sensor falls off a bench onto the floor, it is damaged. It can survive only a small number of such drops. If it is on the bottom of a RIB driven at speed, it is essential the counterlungs protect the rebreather from the shock, otherwise the cells will fail very early.

Alex

teksimple

Thanks Alex. Yes, I agree in principle, but I would venture in recent years there have been more incidents caused by worn out sensors than by simultaneous, precipitant failures in batches of new sensors. You will have to agree that there is really no one who stages their sensor purchases when they get a new rebreather. I would be interested in even anecdotal evidence of such simultaneous, precipitant failures in new sensors even after testing and calibrating fine.

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schford

Unfortunately I know of one fatality where it is likely that is what happened.

But nothing stops you buying a batch of cells at a time (I do) - just change them one at a time to check all is ok and check they are not current limited at 6m at the start of your dive.

It might mean it is a 3 by 5 min job rather than 1 by 5min job but ......

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divetheworld

What are the changes that have been made?

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Drmike

Happened to me and a buddy a while ago with 2 new inspirations- Posted here somewhere (or on YBOD list) might need to do some searching, Resulted in buddy toxing

Nobody wanted to hear it ...... so they didnt

Since then I never change all 3 at once
But hey Im the suicidal one remember

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PacketSniffer

It's in the report. You should really read it. It's good stuff.

Oxygen Sensor Study

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divetheworld

I was hoping someone would save me from that

Its not in the report what the specific change was to make the mechanical strength better, just that there was one as far as I can find. Yawn.

Its a shame the data backing up the claim that the Teledynes were "found to be unsuitable for diving applications." is not present.
I'm none the wiser either way as a result of this at present.

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n2diving

I'm going to have to go strongly on the side of not replacing all of them at once either. The 'bad batch' problem occurs much too frequently, and it was a regular occurance with the Teledynes... and I've had one such occurance with the AI's. As for the situation of a new rebreather getting three new sensors, well the new guy who has never been on a rebreather didn't have a choice. As for myself, on my new O2ptima I shuffled sensors from inventory around so that I at least didn't have all with the same month of mfg, and stuck a used one from another unit in... same with my sisters new unit when she started diving CCR... I took two of her new ones (we use four) and swapped them into mine and gave her my used ones. I would do whatever I could to avoid replacing all four at the same time from the same batch. Recently I did a crossover course and the CCR experienced student expressed concern about this very issue, he was more than happy to swap some of his new sensors for some of my used ones. I don't have a concern about buying all three at the same time, but I wouldn't suggest installing them all at once... I rotate new ones in over time. When several of us were testing the AI sensors in the O2ptima, we were using a mixture of Teledynes and AI's... and if you are really paranoid about sensors (and as apparent from the posts here, plenty are ... with good reason) then a mixture of manufacturers does have a certain appeal...

teksimple

Good question. My web site opening was delayed because the newly re-worked PSR-11-39MD sensors were not out of the factory yet. I do not know the specific changes, but I assume they had to do with impact resistance?

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"I don't know the percentage of the Internet that's valid, do you? Jesus, it's scary." - Hunter S. Thompson