Prebreathing Survey

[rjack321]

One minor point. If the JJ's designer told me that it was OK, that would be a completely different story. But Jan wont even let me update the controller with the new Shearwater firmware until he has tested it out, so I doubt that he is going to tell me to just wing it on scrubber duration!

Why does it have to be Jan?

There are a ton of scrubbers out there. They are all being tested with 797 sorb nowadays. Time per kg sorb really isn't a huge mystery, nor are there some unique flow paths that radically alter that CE time. Rated 150 L CO2 / kg is the same. There are far more dives done at non-CE conditions than there are CE test runs (some units have none, some have one or 2, "3" on the JJ is actually about the most CE data there is for any one unit. But they are all pretty congruent there's no mysterious outliers that are double or half the others. Making educated guesses about duration based on the universe of CE test data and corollary actual CCR dives is not really that big a deal (to me at least).

If you were my cave diving buddy and we went to FL, I would be pissed if our dives were limited to 3 hrs lol. 3 cave hours on that scrubber in 72F water is a modestly short dive.

 

[rjack321]

Something that occurs to me, especially with the results Simon posted, is that there is a really significant difference between doing 4 one hour dives on a scrubber and one 4 hour dive with a chunk of that being deco. Once you break those dives over multiple days, with all the variables in packing and storage, factoring in the low cost of sorb, I for one won’t be stretching my scrubber for the sake of more dives but I also am not too phased over going a few minutes over the CE numbers on a nice warm dive with no strenuous activity.

Simon's other study showed that storage can actually (by a very small not statistically relevant amount) increase duration.
But yes, doing repetitive deep dives that add up to 4 hrs is another variable that none of the machine tests account for. But 4x 1hr dives by definition couldn't have been all that deep.

 

[cathal]

I understand that you want something akin to a rigorous, scientific study. That doesn't exist (that we know of). The question I'm trying to ask is, at what point does the data that does exist (in the somewhat anecdotal form I described above) become sufficiently compelling to be considered "useful data" versus "insignificant anecdotes"? If your personal answer is "never", I certainly won't fault you for that.

Great post, but can I ask why as a community are we not accepting the scrubber duration data for each CCR that is produced during the course of the CE certification process to meet the EN 14143 norm?

Cathal

 

[doctormike]

Why does it have to be Jan?

Oh, I was just responding to Stuart's point about what I would do if the designer of my rebreather said that it was OK.

And I do get the point about this being an issue with longer dives. If I was doing dives of greater than three hours in duration, and I wanted to use a JJ, I would have to go outside of the CE testing range, and use a radial or expeditionary scrubber.

Again, look at my last response to Stuart. Don't think that I am categorically against ever exceeding the CE limit. I'm just saying that it's a complex analysis, involving balancing risks and benefits, and we simply don't have the data to quantify the risks. That doesn't mean we don't dive, but it does mean that for me, for the minimal benefit I would get from pushing a scrubber, I don't do it.

And I don't think that anyone should make categorical statements for general consumption by new CCR divers that aren't supported by data. Please don't take this the wrong way, I do respect your skills and training. But you wrote "In 25C water you would have at least 6 hrs on that scrubber and still be 3 sigma below the (tight) breakthrough distribution." Simon's experiment shows that isn't necessarily true. And some new rebreather diver might just take home from this discussion that a very experienced diver said that you have 6 hours at 25C.

 

[rjack321]

Whatever, I am done here. I get it you want authoritative statements. You like 3 CE test points that aren't even realistic dives. Simon's data are great and my statement about 6hrs in 25C is actually supported by that data, you just don't see it and all the words on the internet are not going to be the data or authority you seek. Exercising at 6 Mets for 3+ hours is a terrible way to vacation IMO, along with a great way to get horrendously bent.

 

[doctormike]

Simon's data are great and my statement about 6hrs in 25C is actually supported by that data...

Please understand that these tests were NOT designed to establish expected durations for this scrubber in real diving.

I thought that we were having an interesting conversation. I have been polite and complimented your skills and experience, and said that I appreciated your posts. I do object to generalizations about stuff that has potentially dangerous consequences, and I told you why.

If you want to respond like that, that's your choice, but it's possible to disagree without being dismissive.

 

[cathal]

Whatever, I am done here. I get it you want authoritative statements. You like 3 CE test points that aren't even realistic dives.

Authoritative statements? We just want scientifically validated data when it comes to the operation of a life safety system.

 

[Brad_Horn]

There are far more dives done at non-CE conditions than there are CE test runs (some units have none, some have one or 2, "3" on the JJ is actually about the most CE data there is for any one unit. But they are all pretty congruent there's no mysterious outliers that are double or half the others.

If you're interested in multi-run scrubber tests under a variety of conditions depth/temp/workload and in-depth scrubber duration testing there is more than just 3 tests out there done to the CE standard for at least one unit!
See http://www.deeplife.co.uk/or_files/DV_OR_ScrubberEndurance_Retest_SRB_101215.pdf
also some more scrubber duration runs covered on pg112-115 https://www.opensafety.eu/manuals/OR_Apocalypse_User_Manual_110505.pdf

However they have been done on Micropore EACs which are solid state so it takes the variability of scrubber packing out of the equation. The units tested were also optimised for EAC use as opposed to loose sorb and those published results were taken at the mouth (DSV/ALVBOV) as opposed to the inhale breathing tube; so factor in the deadspace of the DSV/BOV.

 

[lv2dive]

I would use the CE test results to inform my scrubber duration IF the tests were conducted in similar conditions to my dives. But the CE tests are intentionally conservative from both a temp and work perspective. The CE numbers are pretty worthless for someone who not exerting themselves (eg, is on a scooter) in warm water. I generally follow recommendations but I look at the CE test data for scrubbers as simply describing the scrubber duration in very specific set of circumstances... which are nowhere near my circumstances. I am going to give more credence to people who are diving the unit in similar conditions.

Great post, but can I ask why as a community are we not accepting the scrubber duration data for each CCR that is produced during the course of the CE certification process to meet the EN 14143 norm?

Cathal

 

[kensuf]

Y'all that are arguing how long you can push a scrubber need to go re-read Simon's post. Prebreathing Survey

Follow it up with Brendans post Prebreathing Survey

Then let it start to sink in. Scrubber duration is based on many factors, amount of sorb is just one of them. Water temperature is another. But most critically and importantly, it's workload.

I've done the pushing a 5# scrubber for 7 hours thing, with the majority of the dive basically being rest (either scootering or deco) and I've also done the 4x 60 minute swimming/working in high flow dives on a 5# scrubber thing and while the results of the first were "no problems, it's do-able" the results of the second set were quite hysterical (disastrous) on dive #4.

One dude may be able to get 6 hours out of 5.5 scrubber every day because all he's doing is drift dives in warm water. Another may try that same 6 hours on a scrubber, but be working hard the whole time. Guess what, it isn't going to work well.

It's really quite simple, the harder you work, the more oxygen you metabolize, the more CO2 you produce, the quicker your scrubber gets used up.