How Far Do You Push Your Scrubber?

decoweenie

Fil,

Have you ever ran our of gas (petrol if you drive on the wrong side) in the middle of the desert in the Summer ?

Then you won't think it is a simple problem any more...

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"...after a while you get bored offering advice to a bull that like to keep butting the fence with its head rather than walking through the open gate..."

- Rebreather World PM

CCR900

I still think pushing the scrubber is like russian roulette, you just need to get it wrong once.

F

decoweenie

Girly-man...

__________________
"...after a while you get bored offering advice to a bull that like to keep butting the fence with its head rather than walking through the open gate..."

- Rebreather World PM

Drmike

Your analogy - isnt

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Cave diving is a sport
Wreck diving is a sport
Diving in general is a sport

'Rebreather diving' is not a sport
its the delusional obsession with a highly dangerous and often inappropriate piece of equipment

leadking

I was down in Panama City Beach and visited with Mike Ward from Dive Lab, DSI's East coast operation. I was watching tests being conducted on USN submarine escape rebreathers and has some interesting discussions. The end result of which was: That despite all scrubber canisters being packed identically, there was a large variance in scrubber life. It showed me in that the life of a scrubber is variable and cannot be reliably predicted, so that for safety considerations you cannot take the longest duration and apply it across the board.

CCR900

True I do like the girlies, as for you well a pictures paints a thousand words .

Now go buy some lime....

F

nigelh

** shrug **
I push my classic YBOD to about 60%.
That is: if I've done two hours and I have a keg of lime to hand I change it.

100%??? More than 100%???

Cowards live longer.

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nigelh

Pierre Farrugia

Hello all,

I voted for the 25% over, that is less then 4hrs! That means that I will use it for dives shallow than 35m. If I have a 45min shallow dives and on scrubber I have 2 1/2 hrs, I just don't trough the lime and just go over the 3hrs limit. At then end this is down to what a diver what is accepted risk for him, I was also tough that I should not push above 80% of CNS clock but many do dives with 150% CNS! Just a tough, why people do 20min - 30min bottom times and go over the CNS and scrubber when they can do the dive tomorrow ? Not everyone takes same risks and what is acceptable to one is not acceptable for others! I also add that if you are just stating to CCR dive I would first do it as it should and then think about these thngs later!

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Pierre Farrugia

My wife told me " If you don't quit diving I'm going to leave you"
My reply " God, I'll miss you"

www.atlam.org www.divemed.com

grahamsp

You do me a disservice. Trust me, I'm not in any hurry to kill myself which is why I initiated this poll. Quite the opposite in fact. All I wanted to do was to find out what people actually do in practice. The related thread on the factors affecting scrubber duration was just an attempt to better understand something that I know all too well could kill me if I took it for granted. So no deathwish here.

Turning to the broader issues, all I can say is what I have already said elsewhere. If APD's scrubber limits are to be exceeded (as, anecdotally at least, many divers appear to do) then let us at least understand the risks being taken. To do that means knowing how scrubber performance is affected by all the variables at work - depth, water temperature, dwell time, work rate, absorbent type/size etc.; only then can an individual diver make an informed decision on the risks of extending scrubber time past the limits given by APD.

Graham

Sutty

Since I have a Kiss not an inspo I can't push "AP's limits", but stay within what I was taught were safe limits. I probably would be prepared to exceed the slightly in some circumstances (minimal exertion/anxiety, used less O2 than usual, etc). I doubt I'll ever want to do a single dive that will be longer than recomended duration either.

BUT the point I wanted to make was that the recommended limits are admittedly conservative, however there is also a huge difference in CO2 production and scrubber efficiency. It is possible that for some people, in certain circumstances, even the recomended durations may be "pushing the scrubber".

I don't believe that 2hrs59 is "safe" and 3hrs01 is "unsafe", there is a progressively increasing likelyhood that you are nearing significant CO2 breakthrough as time passes. Exactly what constitutes an acceptable risk of that happening is up to the individual user.

On a personal note I have spent many, many, many hours watching the indicator change colour in soda-lime in very small (by our standards) clear scrubbers, with CO2 monitoring attached, admittedly at 1atm and with the "user" producing much less CO2 than usual. (I work as an anaesthetist & we do this all the time). I accept that this does NOT translate directly to rebreather diving and accept that pressure and gas density has profound effects on scrubber function.
However my experience as an anaesthetist does give me a certain degree of confidence in the indicators in some brands of soda-lime, with the proviso that it must be examined immediately after (or during) use as there is a "re-generation effect). It is also interesting to note how much or little lime needs to be present beyond the reaction "front" for breakthrough not to occur (remember at 1atm).
This does mean that when I empty my scrubber after 3 hrs of use in cold water with moderate exertion, and find a large portion of it "unused" it gives me a high degree of confidence that 3 hrs is very conservative (for me, using my soda-lime, in my scrubber, packed the way I do, etc). It therefore makes me pretty confident that as long as the unit is working OK the scrubber should cope easily with what I ask it.
It does NOT mean I would advise anyone to exceed recommended durations!

Just my thoughts

Neil