Scrubber life when partially used?

[Brass Monkey]

I’m thinking this one must have been brought up before but here goes. How long is it safe to keep a partially used scrubber and what is the best method of storage? It’s not that I’m tight or owt like that it’s just scrubber is a bitch to get hold of in these parts and by the time everyone’s added there little bit to the price it’s working out at around 8 quid a kilo. That said I don’t want to start pushing the recommended 3hr life it’s just I want to get the full three hours. I completed a 90 min dive and had to leave for work the following day, not knowing how long I was going to be gone I stripped the unit down and sealed up the scrubber canister in a plastic bag. It’s only been 5 days now so I’m pretty sure it should be OK but how long would it be safe to use after being stored and is this method of storage a wise one?



Dave.

[nigelH]

Originally Posted by Brass Monkey

I completed a 90 min dive and had to leave for work the following day, not knowing how long I was going to be gone I stripped the unit down and sealed up the scrubber canister in a plastic bag. It’s only been 5 days now so I’m pretty sure it should be OK but how long would it be safe to use after being stored and is this method of storage a wise one?

This was done on the drogon Inspiration remailer and Martin Parker laid down the rules. It's going to be perfectly OK but it would have been better to leave it in the housing and not disturb it. If you stick to the time rules it keeps virtual as long as it does in the keg and closing the mouthpiece seals it better than taking the cannister out and messing it about with bags because you tested the seals on that.
However he was very careful to point out that once you pour part used granules out of the cannister it's trashed.

nigelH

[narked at 90]

i'll keep mine for upto two weeks as long as i've drained any liuqid and capped the can but my friend just keeps it some times for mounths i cant see to much growing in there as its a little bit caustic! but
i could be wrong.
best regards john routley

[Brass Monkey]

Thanks guys, I'll leave in toghether next time Nigel.


Dave.

[Padowan]

Originally Posted by nigelH

However he was very careful to point out that once you pour part used granules out of the cannister it's trashed.

Does anyone know why this is?

Extreme case scanario: you pack the scrubber, do a few minutes diving on the canister, why would the material not be usable if it was removed and repacked?

I can understand if it was heavily used, as the expired product would all get mixed up with the fresh stuff and change the dynamics of the reaction front.

I have a sealed container which has the contents from my scrubber that I emptied out before I took the box on holiday - it had done about 30 shallow minutes, and was completely dry when I tipped it out. Should I bin this, or could I perhaps use it for a shallow skills session, perhaps in the pool?

[beanie]

I take the scrubber out and dry the unit leaving the srubber on the side as is (if no gas flows through it no Co2 flows through it) then when the unit is dry i put it back in and seal it up either in the unit or the scrubber case with the hose back onto its self

[nigelH]

Originally Posted by Padowan

I have a sealed container which has the contents from my scrubber that I emptied out before I took the box on holiday - it had done about 30 shallow minutes, and was completely dry when I tipped it out.

Lets say it is 15% used. Let's assume you remix it evenly. Since you used it shallow the reaction front would have been very narrow and that is going to be effectively 15% totally used up granules mixed in with good ones. Diving deeper the front is wider. Gordon Henderson explained why in
Planet Zorg better than I ever could.

It is not just a case that the reaction front will be 15% wider but "is there a stepping path from used granule to used granule" so it will channel sooner than you expect. My guess is that rather than giving you the normal case of no CO2 until the reaction front touches the top when it breaks through it will give you some CO2 (ppm to start with) increasing with time as CO2 takes paths through the used up bits. You have gone to a statistical model for CO2 not a brick wall. This is a whole different take on scrubber duration and I wouldn't want to pioneer this one.

It's what? 8 quid a fill? You're throwing away 6 pounds. CO2 breakthrough seems to be the worst thing that can happen to us because nothing goes beep and at depth it doesn't seem to feel obvious. For example see Alasdair Allan's report recently.

I bid chuck it out.

nigelH

[Padowan]

is there a stepping path from used granule to used granule

This is a very interesting concept that I'd not thought about - due to the porousity of the material a "dead" granule is effectively a non-absorbing channel, and if they're orientated such, could provide a channel all the way through.

I was still toying with the idea of a Hyperfcapnia hit in the lounge to see what it feels like until a diving doctor mate (ChrisP) made the analogy of this and a Hypoxia simulation to the film Flatliners, and since then, I've been not so keen to try!

At the end of the day I'll put fresh stuff in, but I'm the kind of person who likes to know all the why's and wherefore, and try to understand exactly what's happening.

[NotDeadYet]

The DCIEM did a study into this for the Canadian Forces, you should be able to download it from their website. Basically, naval divers were using the RBs intermittently and when they were needed it was usually in a hurry so they wanted to keep them prepped and ready. The study looked at the feasibility and safety of it.

IIRC Canadian Forces rules based on the results are seven days storage allowed between dives (either unused or partially used scrubber) without maintenance as long as the unit had maintained positive pressure without leaking. From memory they were using Carlton SIVAs. Obviously there would have to be enough life left in the scrubber to make it worthwhile.

[Duncan Price]

Originally Posted by Brass Monkey

I’m thinking this one must have been brought up before but here goes. How long is it safe to keep a partially used scrubber and what is the best method of storage?

I've left mine partially used for weeks at a time. I also have more scrubbers than rebreathers so can plug the ports on a partially used scrubber and swop in a new unused one if necessary.

I save partially spent lime and use it for pool tests (after mixing it around) - or give it to Digger. I have also filled the scrubber with new stuff and then added used stuff as a packing to save filling the scrubber (takes 4 kg a shot) with good lime even though I pay £25/20kg for it.

Am planning to do some performance tests on the scrubber in a controlled environment to see how long it really will last - this involves hooking it up to a spectrometer and fitting thermocouples in the stack but should keep me out of mischief one evening.

Duncan