Scrubber duration in warm water

[doctormike]

Here’s a question that came up recently. I’m a fairly new JJ diver, and I have taken it to warm water destinations twice. I know that the stock axial scrubber is rated to 180 minutes, in 40 meters of 4° c water. However, I understand that scrubber duration increases with water temperature. It would be good to have testing done on this scrubber in warmer water, since reproducible demonstration of increased duration could make a significant difference in terms of travel logistics (and cost, although that’s not the primary driver of my interest).

I emailed Jan Peterson, who very nicely replied right away. He told me that they haven’t done testing in any other conditions, so he couldn’t give a warm water scrubber time, which I understand. I suspect that doing testing is expensive, and if there isn’t a big market of warm water JJ divers then it wouldn’t be a good business decision to do that.

But at some point, as rebreathers become more widely used, I would think that some good benchmark data on this (unit specific, sorb specific, or otherwise) would be useful to the CCR community. Does anyone know of any projects to formally investigate this? I found a thread from about 7 years ago, but nothing more recent. I saw the DiveRite study but this was with the ExtendAir cartridge which eliminates variations in packing techniques. Maybe something to fund with crowdsourcing by tropical rebreather pilots?

 

[fsardone]

Hi DoctorMike,
I believe temperature and CO2 production rate which go into scrubber duration are certification parameters (I am sure they are for CE certification) and therefore manufacturer will not have interest to show how long the scrubber will last outside controlled parameters, otherwise ned you will see people asking to provide duration for normal CO2 production and not the max metabolic rate used in certification.

Bottom line: if you use the scrubber longer than certified you are on your own and the manufacturer has no responsibility whatsoever.

Cheers

 

[KevinNM]

This might be of interest:

http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA139508 Appendix G

Also
A Look Inside Rebreather Scrubber Canisters, Part 1
A Look Inside Rebreather Scrubber Canisters, Part 2

He's got a bunch of interesting content.

 

[doctormike]

Hi DoctorMike,
I believe temperature and CO2 production rate which go into scrubber duration are certification parameters (I am sure they are for CE certification) and therefore manufacturer will not have interest to show how long the scrubber will last outside controlled parameters, otherwise ned you will see people asking to provide duration for normal CO2 production and not the max metabolic rate used in certification.

Bottom line: if you use the scrubber longer than certified you are on your own and the manufacturer has no responsibility whatsoever.

Cheers

Right, of course, which is why I didn't expect Jan to give me a number outside of his test parameters. But my question is why just one (arbitrary) set of test parameters? Is it because CE specifically requires testing at 4° C only? I wasn't able to find that particular temperature specified anywhere, but maybe it's a CE thing that I don't know about. Or does CE just require testing, but as long as the parameters are published, that's OK too? If JJs were made in Costa Rica and not Denmark, would the manufacturer opt for publishing and getting CE certification at a temperature more likely to be used by it's target demographic?

On the Meg website, they publish scrubber durations at different temperatures - for example, the axial scrubber lasts 122 minutes at 40 meters, 4.7° C, 40 RMV, while they specify 5 hours on another test in 13° C water at the same depth with variable CO2 production mimicking a typical dive.

Now, I don't know much about Megs, but it looks like they provide a CE and a non-CE version. So even if CE required testing at only 4°C, it doesn't look like generating and publishing data for other types of diving means that the manufacturer can't sell a CE version. My JJ, for example, is the international version (non-CE certified, missing the dil shutoff and the different O2 and dil tank valves). So I'm assuming that it's a business decision - if suddenly JJ had the opportunity to sell a lot of units in the Caribbean, they might decide that publishing specs for warmer water would be good for sales.

My idea isn't a safety shortcut - we all assume that a well packed scrubber is good for 3 hours if the temperature is above 4°C and the depth is above 40 meters based on the test data. All I would like is more test data for other conditions, but I recognize that someone has to pay for that.

Having actual data for the type of diving a diver is likely to do would be safer and better than the what many diver do now - use some sort of "fudge factor" for warmer water and push the scrubber. A manufacturer who provides that data is likely to have a leg up on their competitors in sales to divers in warmer locations.

 

[doctormike]

This might be of interest:

http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA139508 Appendix G

Also
A Look Inside Rebreather Scrubber Canisters, Part 1
A Look Inside Rebreather Scrubber Canisters, Part 2

He's got a bunch of interesting content.

That is cool, thanks!

 

[RainPilot]

If you do the calculations of total CO2 removal capacity, then convert that into metabolized oxygen, then convert that into the capacity of the O2 cylinder, you should get a number.

How useful, depends. Poseidon stipulates that the 3L O2 be filled to 135 bar. Reason? thats the amount of O2-CO2-scrubber that their scrubber can handle. Ive noticed that in colder water when working hard, I get a little over 180 min. Warm water, relaxed dive I get closer to 220 min.

When I change the O2 its time to change the scrubber. FWIW the Poseidon is also rated CE for 180 min.

 

[doctormike]

If you do the calculations of total CO2 removal capacity, then convert that into metabolized oxygen, then convert that into the capacity of the O2 cylinder, you should get a number.

How useful, depends. Poseidon stipulates that the 3L O2 be filled to 135 bar. Reason? thats the amount of O2-CO2-scrubber that their scrubber can handle. Ive noticed that in colder water when working hard, I get a little over 180 min. Warm water, relaxed dive I get closer to 220 min.

When I change the O2 its time to change the scrubber. FWIW the Poseidon is also rated CE for 180 min.

Yeah, but isn't that a lot of assumptions for a system with such variability - including variations in the relationship between O2 consumption and CO2 production, which must vary between individuals based on differences in metabolism, circulatory reserve and lung function.

Also, it would be good from a logistics point of view to be able to disassociate O2 fills from scrubber changes. I can throw some extra sorb in a truck and refill my scrubber in the field, but I won't have an O2 fill station with me.

 

[northernone]

Safety margins and liability.

One scrubber design is rated for 4hrs with 8/12 sorb, I personally know people warm water diving them 8, 9 and even 11 hours without break through.

That said I have had a suspected partial breakthrough from a hard working dive after only 2hrs in warm water for a scrubber rated 3hrs in cold.

Workload, personal metabolism and packing consistency all are variable so I appreciate why few manufacturers publish test results with the fear people will accept them without personalization.

Regards,
Cameron

 

[RainPilot]

As far as I know, the amount of CO2 produced is directly related to O2 consumption. Those O2 have to come from somewhere.... IIRC it's 0.7 to 1.0 with 0.9 used as a median. (L of CO2 per L of O2 metabolised)
This is known as respiratory quotient and is fairly stable in individuals but varies by fitness, metabolism etc in different individuals.

I definitely don't think you should adopt the same idea as Poseidon, I'm saying that they are so convinced that O2 consumption is linked to scrubber duration that they have written their manual that way. If you can get the numbers for your unit you may have a data based method of figuring out safe scrubber duration on your dives.

 

[doctormike]

As far as I know, the amount of CO2 produced is directly related to O2 consumption. Those O2 have to come from somewhere.... IIRC it's 0.7 to 1.0 with 0.9 used as a median. (L of CO2 per L of O2 metabolised)
This is known as respiratory quotient and is fairly stable in individuals but varies by fitness, metabolism etc in different individuals.

I definitely don't think you should adopt the same idea as Poseidon, I'm saying that they are so convinced that O2 consumption is linked to scrubber duration that they have written their manual that way. If you can get the numbers for your unit you may have a data based method of figuring out safe scrubber duration on your dives.

Right, exactly - it's directly related, but I agree with you that this doesn't mean that you can calculate your personal CO2 production knowing your O2 consumption. There might be an algorithm, but there are definitely going to be constants that very between individuals.

I guess if you limit your O2 supply enough, you will eventually get to a point where even an outlier individual woudn't produce enough CO2 to break through a new scrubber. But as I mentioned, that really changes the logistics of your consumables.