How to tell how much of your scrubber you used after a dive

[davehicks]

So many words responding to this thread that were needlessly wasted.

The only answer is "No".

Useless snark. Of course you can. The canister is done of course once opened, but this is how you learn the real world characteristics of your CCR.

 

[Searcaigh]

The US Navy used a brand of Barium Hydroxide as an CO2 absorbent before the mid-1970s. It changed from a pink color to purple when it converted into Barium Carbonate. I'm not recommending it as a superior absorbent but I wonder if the feature is available on some modern absorbents.

The Calcium Hydroxide that we used for Sat Chambers on the DSVs I worked on back in the 80s also had a colour change from white to blue.

 

[Snusmumrik]

As my profiles, workloads and oxygen consumption are basically similar, i count only scrubber used time, based on practical testing results showing for me that 1 kg of Sofnolime works for relatively 2 hours.
When I use same scrubber repeatedly - i assume safety margin and reduce accounted next dive time to 2/3 of calculated time.
Remember - sorb is cheap, your life is priceless...

The absorber of carbon dioxide undergoes a chemical reaction when it picks up the exhaled carbon dioxide. The color changes when the absorber is exhausted.

Being somewhat educated in chemistry, i want to spend my 5 cents and clarify some info.

1. Medical absorbents are not often colored with usage indicator.
2. Reaction that produce colorisation is related NOT to CO2 amount absorbed directly, BUT to amount of water produced
during reaction of CO2 absorbtion by lime. Like CO2+Ca(OH)2 -> CaCO3 + H2O + Q
In basic, reaction was similar to colorisation of cuprum sulphate to blue vitriol, white CuSO4 absorbs some water
and forms a blue-colored complex CuSO4*5H2O
3. As related to water absorbtion, this reaction can be reversible, when water evaporates - colorant agent changes color backward.

 

[1c3d1v3r]

Why is it that deeper you go the easier the scrubber can break though especially when over breathing?
So is it because the co2 is denser and can't get into the pores of the sorb?

Kinda thinking about the Dave shaw..

The amount of co2 produced is very close in relation to the amount of o2 used form what I remember reading...
is that still used as away to track scrubber life?

Temperature is the most affecting factor. Other gas molecules is not the answer. Non-CO2 molecules do not block the CO2 molecule from reaching the sorb.
Why depth has an effect on sorb capability to scrub CO2

 

[kensuf]

I estimate the usage and repack using the following basic rules:

1 pound = 1 hour. This is an average estimate.
Anytime I'm at the "half-way" point on the stack, it gets tossed and repacked. For a 6# scrubber that means I'm tossing it anytime I've got more then 3 hours on it.
Anytime I'm planning a dive that will use more than half the theoretical limit, I start with a fresh stack.
Anytime I'm planning a dive where I'll be going deeper than 200', I start with a fresh stack.
Anytime I've done a dive where I worked hard, I toss it.

Could I push further than that? Probably, but the goal of every dive is to have fun and come home at the end of the day and when it comes to my scrubber, I want to be conservative rather than penny foolish.

 

[tbone1004]

Well scrubber breakthrough that seemed to be the conclusion of some videos I saw, but that maybe arm chair theory...

If you breath fast enough,and not enough dwelltime, should cause some break though,
couldn't it...?

I will have to rewatch the video but I do not believe that was the conclusion. He succumbed to hypercapnia, no doubt, but it was residual in his lungs that he was unable to expel because the gas density was far too high.

His rebreather, while heavily modified, would still be able to pass the WoB tests and scrubber tests. Check the article below which while applying to the O2ptima goes through the testing itself.
Please not in particular the description for 75lpm/2.6cfm RMV "A diver athlete in superb physical condition, doing severe work,
can sustain an RMV of 75 lpm for one or two minutes." Note that a "diver athlete" is a Navy SEAL or equivalent.
The tests are done with at 40lpm/1.4cfm which is 10% more than "A physically fit diver, taking slow deep breaths while swimming hard,
can sustain an RMV of 37.5 lpm for a few minutes.". If you want to confirm this and have air integration, go try to sustain it on an open circuit dive. If you don't, then work as hard as you can for as long as you can and calculate your SAC rate and see. He was most definitely not working anywhere near 40lpm/1.4cfm when he died, but did have a very high gas density and he overbreathed his lungs, not the rebreather. Please keep your gas density at no more than 5ata equivalent which is what the units are tested against but ideally no more than 4 if you have to work. While he had conducted the dive successfully the day prior, it was a bounce dive with near 0 effort involved at the bottom and you can get away with a lot of things if you aren't moving. Once you are moving it is a different ball game and you need to take extra precautions.

This article from @DiveGearExpress is also useful for @LFMarm as it shows scrubber duration under same breathing conditions but different temperates.

Dive Rite O2ptima Rebreather Scrubber Duration Test Results | Dive Gear Express®

Dive Rite O2ptima Rebreather CO2 Test Results

www.divegearexpress.com

 

[Doby45]

I estimate the usage and repack using the following basic rules:

1 pound = 1 hour. This is an average estimate.
Anytime I'm at the "half-way" point on the stack, it gets tossed and repacked. For a 6# scrubber that means I'm tossing it anytime I've got more then 3 hours on it.
Anytime I'm planning a dive that will use more than half the theoretical limit, I start with a fresh stack.
Anytime I'm planning a dive where I'll be going deeper than 200', I start with a fresh stack.
Anytime I've done a dive where I worked hard, I toss it.

Could I push further than that? Probably, but the goal of every dive is to have fun and come home at the end of the day and when it comes to my scrubber, I want to be conservative rather than penny foolish.

Thats crazy that you are saying EXACTLY what my CCR instructor taught me!!

 

[LFMarm]

This article from @DiveGearExpress is also useful for @LFMarm as it shows scrubber duration under same breathing conditions but different temperates.

Dive Rite O2ptima Rebreather Scrubber Duration Test Results | Dive Gear Express®

Dive Rite O2ptima Rebreather CO2 Test Results

www.divegearexpress.com

Great reference! I am very impressed by the users of this forum.

The article says “The recommended O2ptima rebreather scrubber duration for sport diving depths is 240 liters of CO2, if the diver is monitoring their oxygen consumption.”

Does this mean that if I monitor O2 consumption with pressure gauges, I can infer CO2 production and know how much of the total scrubber capacity (in this case 240 L) has been used?

 

[flymolo]

Great reference! I am very impressed by the users of this forum.

The article says “The recommended O2ptima rebreather scrubber duration for sport diving depths is 240 liters of CO2, if the diver is monitoring their oxygen consumption.”

Does this mean that if I monitor O2 consumption with pressure gauges, I can infer CO2 production and know how much of the total scrubber capacity (in this case 240 L) has been used?

that is the theory, but in reality you are probably better off just sticking to what your manufacturer says the scrubber duration is and applying sensible rules like @kensuf suggested

 

[tbone1004]

Great reference! I am very impressed by the users of this forum.

The article says “The recommended O2ptima rebreather scrubber duration for sport diving depths is 240 liters of CO2, if the diver is monitoring their oxygen consumption.”

Does this mean that if I monitor O2 consumption with pressure gauges, I can infer CO2 production and know how much of the total scrubber capacity (in this case 240 L) has been used?

Yes, that was what was being discussed above. You can safely assume a 1:1 ratio of O2 consumed to CO2 generated and is also the reason that many of us use Bar gauges on our O2 bottles *that is if you actually use gauges on your O2....*, so if you have 2L bottles and start the dive at 200bar, then you have 400L of O2 on board and once you consume 120L of O2 then you can assume the scrubber is done. As I did say in post #18, you can track this way however it is slightly conservative given O2 flushes once you get to deco and any inefficiencies you have in your diving. Those inefficiencies are primarily tied to really lean diluent mixtures and/or sawtooth profiles where you are adding a lot of oxygen in manually to compensate for lean diluent. You can go down rabbit holes to try to optimize gas mixes and all that nonsense but I wouldn't personally bother trying to get that close and for "normal" conditions I use 1lb/hr and call it a day. Slightly less if I know I'm going to be huffing and puffing, and I'll stretch it a little bit if I'm doing really deep stuff where most of the time is spend essentially napping on decompression, but those are extenuating circumstances.