How long will you let the scrubber sit

matthewoutram said:
Personally, in cold water, I wouldn't stray much from <50m 100 mins, <20m 140 mins, 180 mins max. regardless of any storage conditions.

Matt.
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Total in water time there is three hours... diving with those pesky OC divers ;)

For me it is still about practising the ascents and stops and I have to say I am getting most comfortable with both, my weight seems right which helps no end.

It could be said I am settling in nicely....
 
Bythesea said:
Total in water time there is three hours... diving with those pesky OC divers ;)

For me it is still about practising the ascents and stops and I have to say I am getting most comfortable with both, my weight seems right which helps no end.

It could be said I am settling in nicely....
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Nice. Good to see you moving forwards...I hated mine for ages, weight makes the difference.

Matt.
 
Comments from Gavin Anthony at RF3.

Canadian Study on Rubicon (Effects on Scrubber Endurance of Storing Soda Lime in CF Rebreathers) showed 1 week. (Google, first hit)

Gavin Anthony also said that if your scrubber had, say, a duration of 3 hours, then you could use it for 30mins over 6 success days without an issue.

He also said that some military users liked to store their units after a swim in and pick it up later, and had done so without ill effects, but there was no formal evidence to this effect. no-one at the conference could provide anything formal other than the Canadian study.

Regards
 
GLOC said:
Comments from Gavin Anthony at RF3.

Canadian Study on Rubicon (Effects on Scrubber Endurance of Storing Soda Lime in CF Rebreathers) showed 1 week. (Google, first hit)

Gavin Anthony also said that if your scrubber had, say, a duration of 3 hours, then you could use it for 30mins over 6 success days without an issue.

He also said that some military users liked to store their units after a swim in and pick it up later, and had done so without ill effects, but there was no formal evidence to this effect. no-one at the conference could provide anything formal other than the Canadian study.

Regards
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That's right, it's just not tested. Even if it was what combinations would you test?...there's no solution it's just too hard.

All I can say is when I see someone who says they out-breathed the scrubber a large number of them are with a second-hand scrubber...the rest are perhaps retainers.

Matt.
 
matthewoutram said:
That's right, it's just not tested. Even if it was what combinations would you test?...there's no solution it's just too hard.

All I can say is when I see someone who says they out-breathed the scrubber a large number of them are with a second-hand scrubber...the rest are perhaps retainers.

Matt.
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Yes, perhaps that is due to the fact that 99% of ccr dives are shorter than the stated duration of a scrubber. And people push them beyound the stated duration!

Btw, i have rarely read about some overbreathing rEvo, Jj or inspo within normal duration. Only the optima.
 
Hanssing said:
Yes, perhaps that is due to the fact that 99% of ccr dives are shorter than the stated duration of a scrubber. And people push them beyound the stated duration!

Btw, i have rarely read about some overbreathing rEvo, Jj or inspo within normal duration. Only the optima.
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I hear people say they out breathed their scrubber. But I also hear that with fresh and properly packed material it's not possible.

I don't doubt that the symptoms of CO2 are there for those people making the report - but asking about the scrubber you normally find it was a second-hand one. I would think the same is true for all types (especially those with CE). At least forum users are now better aware of retained-CO2, and I'd guess that's the other explanation.

Matt.
 
I wonder if outbreathing the scrubber is really what happens. I tried a pSCR clone a few years and got the feeling described as outbreathing it, same on my KISS in a current.

Looking back, I think I was outbreathing the loop as a whole i.e. I was breathing faster than the complete unit would allow gas to flow round it. I dont doubt the scrubber worked fine, I just couldnt push/suck gas round the loop quickly enough.

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lizardland said:
I wonder if outbreathing the scrubber is really what happens. I tried a pSCR clone a few years and got the feeling described as outbreathing it, same on my KISS in a current.

Looking back, I think I was outbreathing the loop as a whole i.e. I was breathing faster than the complete unit would allow gas to flow round it. I dont doubt the scrubber worked fine, I just couldnt push/suck gas round the loop quickly enough.

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Is that the definition of inadequate WOB?
 
matthewoutram said:
Is that the definition of inadequate WOB?
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Might well be. Which if it is makes me think WOB is a lot more important than I think we give it credit for. Both units felt like they had a WOB that was perfectly fine... Until I needed to breathe hard from them. Easy to forget that the test of a rebreather isnt how well it does in normal conditions.

Anyway, the way I've seen overbreathing the scrubber described sounds like what I experienced. However, being a pedant (some would say argumentative twat), it seems more like overbreathing the entire unit.

It would be nice if there was a more relevant unit for work of breathing. Joules doesnt real mean much, how hard would it be to come up with a "standard" diver model and test rebreathers to how many litres a min that diver could pump through it without retaining any co2.

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lizardland said:
It would be nice if there was a more relevant unit for work of breathing. Joules doesnt real mean much, how hard would it be to come up with a "standard" diver model and test rebreathers to how many litres a min that diver could pump through it without retaining any co2.
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It would help the WOB figures immensly if we had some sort of comparison. 'Sucking a maccy d's milkshake through a straw' to 'smoked 20 bensons' or 'walking in a pleasant pine woodland'
 
:offtopic:

I agree WOB is both important and opaque to the diver. IMHO there is no way to know what's what on this important topic - some figures are published, some not, and the threshold for which I am unclear about. I like the idea of some simple scale - low/medium/high etc for both CCR and OC allowing at least relative comparisons to be made (and someone clever could then set those thresholds).

Matt.
 
Breathing Effort

This is a worthy discussion you're having in this thread but possibly these comments of mine might need to be moved to a new thread..I'll leave that to one of you more experienced forumistas.

Work of breathing is not so straight forward... I liked the comment made about using a different way to measure work of breathing other than joules per litre.

Really that needs to be changed to have a new way of showing Breathing Effort.

As I and Oskar Franberg tried to point out during the closing statements session of RF3, the work of breathing or resistive flow is only part of the story. ( the forum proceedings will become public record when they are all compiled, but that probably won't be until the end of the year as it's a big job)

Breathing effort is generally measured in three ways:
Work of breathing, hydrostatic imbalance and elastance.

All three combine to give a varying " Breathing Effort".

E.g.
You can have a low work of breathing but it feels like a dog to breathe because the counterlungs are in the wrong place.

Quoting one without the others is a waste of time.

Breathing effort is what needs to be known and you'll need to know for each position ... And therein lies another problem..there is no international consensus on how to combine the effects and no units of measure, that I am aware of.

Dan Warkander was going to get involved but he left it up to Oskar at RF3 but Dan along with Buffalo University has published a paper on combining the three parameters..maybe someone here can find it.. If not I can dig it out when I get home.

I'll also dig out the work of breathing figures at the start and end of a CO2 endurance to give you some idea of the difference.
 
Sounds like we need one of these for Breathing Effort:

appliance-efficiency-rating%20crop.jpg
 
How long will you let the scrubber sit?

Thanks for that Gareth - I have another report at home which I am working through but basically -that's the gist of it.


The question was raised: how does the work of breathing vary on a new canister compared to a used one?

During a canister duration test we take snap-shot breathing loops, which gives us a backup timer and proof of depth, breathing rate and water temperature, amongst other things.

No effort is made to optimise the loop and as it's a canister duration, it's done only at 40 RMV.

Rather than quote joules/litre - I quote here as a % of maximum allowed.

At the start, the WOB on an Inspiration canister is 63% of that allowed in the EN14143:2003.

At the end of a canister run ( in this case, with 10mbar PCO2), the WOB is 78% of that allowed.
 
I am confused by some of the numbers quoted, but it is interesting how the longer the scrubber is used, based on manufacturer tests, the greater becomes the WOB.

This confirms my hypothesis that clumping increases WOB. We also know that clumping reduces Sofnolime ability to absorb CO2. I suspect clumping may also cause channelling and CO2 to bypass the scrubber.

It would be prudent until manufacturers actually test in a scientific and documented way not to store a used scrubber for any significant period of time, and then re-use it.

To put some numbers and documented facts (not opinion) behind my hypothesis:

1. Under EN14143, the max. WOB is 2.75 j/l. This based on 75 RMV, which is what is required under EN14143 (and not 40 or 25 RMV as others appear to suggest).
2. EN14143 is not science, but a "minimum" requirement (an unscientific politically acceptable consensus), and according to the best science, the max. WOB should not be 2.75 j/l, but it should be a lot lower - 1.5 to 2.0 j/l in the ventilation range 30 to 75 l/m (Warkander 1992).
3. As an example, from the NEDU research (WORK OF BREATHING LIMITS
FOR HELIOX BREATHING, Nov. 2010) few rebreathers meet the EN14143 and/or the Warkander limits (some exceed both, the higher the WOB, the more risky the rebreather):

CIS Lunar has a 2.66 j/l WOB at 300 feet and 75 RMV
AP Diving Inspiration has a 2.98 j/l WOB at 300 feet and 75 RMV
MK16 has a 1.85 j/l at 300 feet and 75 RMV
MK16 Mod 2 has a 2.08 j/l at 300 feet and 75 RMV
Stealth MOD has a 1.71 j/l at 300 feet and 75 RMV
Viper E Stealth MOD has a 1.82 j/l at 300 feet and 75 RMV

So, considering the already very high WOB (above "best science" limits and in some cases also EN14143 limits), and that clumping increases WOB (or to the least that as the scrubber gets used the WOB increases as shown by manufacturer tests), it would be very very unwise to reuse, store, and extend scrubber duration over multiple dives, until manufacturers provide some hard data to support that such use is safe.

Of course, as a Homebuilder I am not suggesting people should not be free to experiment at their own risk, but the available evidence already suggest it would not be prudent to do so over multiple dives and over multiple days after extended storage of a used scrubber.

I would welcome the opinion and comments to the above from the "experts" (as I am not one).
 
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Martin Parker said:
CIS Lunar has a 2.66 j/l WOB at 300 feet and 75 RMV
AP Diving Inspiration has a 2.98 j/l WOB at 300 feet and 75 RMV
MK16 has a 1.85 j/l at 300 feet and 75 RMV
MK16 Mod 2 has a 2.08 j/l at 300 feet and 75 RMV
Stealth MOD has a 1.71 j/l at 300 feet and 75 RMV
Viper E Stealth MOD has a 1.82 j/l at 300 feet and 75 RMV
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Interesting, do you have a reference for that data, Gian?

Matt.
 
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