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

[Compressor]

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.

It seems like it would as useful on an anesthesiology machine as a rebreather.

Ping @rsingler and @Compressor

Thank you @Akimbo; during general anesthesia, a semi circuit system is typically used. Gas given to the patient typically consists of oxygen mixed with air and the anesthetic vapor. To preserve resources, the air is recirculated and similar to a rebreather, the carbon dioxide is scrubbed out. The carbon dioxide concentration is monitored closely (both when it enters the lungs and when it is exhaled). 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. A good byproduct of this chemical reaction is generation of heat which albeit low helps prevent some heat loss in the anesthetized patient.

Hopefully the questions are answered appropriately.

Photo Source: AMSORB® Plus - Armstrong Medical

 

[tbone1004]

Question. Is there a way to tell how much of your scrubber you used when opening the canister at the end of a dive?

Context. I am not trying to find this out to reuse or save on scrubber but rather to have a feedback loop on the assumption made on scrubber duration. I would love to be able to check after a dive if the manufacturer rated scrubber duration is conservative enough for my specific diving (RMV, ambient temperature, etc.) by checking if at the end of a 2h dive in >70F the scrubber has still 45% of life left

I can promise you that it is more than conservative enough unless you are doing high exertion dives under the ice, and even then it's probably good enough.

There is no real way to tell in most rebreathers. You can use color indicating sorb and if you have a clear scrubber then you can sort of get a hint of where the reaction front is, same with temp sticks in things like the APD, but that is only "close enough" as mentioned above.

Since you are concerned about running in warmer water, the reaction will be more efficient. I am not going to say that you should extend your scrubber duration beyond manufacturer specifications, but I'm also not going to say that I personally abide by the manufacturers recommended durations in my personal diving....

 

[rsingler]

Yes, we still have color change in anesthesia as the absorbent is exhausted. Don't know why they say not to use the color-changing type in my JJ, except perhaps for granule size and moisture content compared with operating room specs.

 

[Gone for diving]

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?

 

[rsingler]

For any given amount of work, the same number of CO2 molecules are produced, independent of depth. Those exhaled CO2 molecules are diluted with larger and larger numbers of breathing gas molecules, the deeper you go.
Under workload, with high RMV, there is less dwell time in the scrubber as you breathe hard. It is therefore more likely that the CO2 molecule won't diffuse to the edge of the gas pathway and bump up against a scrubber granule, since there are so many other gas molecules in the stream.

 

[Doby45]

It's easy, I look at my stack timer. That's how I tell how much of my scubber has been used after a dive.

 

[broncobowsher]

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?

Another bit to that is the distance between grains of sorb is fixed. Gasses are compressed. As you go deeper there are more molecules of gas between grains of sorb. Sorb only works when it comes into contact with a CO2 molecule. If the CO2 is insulated from the grains with extra gas molecules it has to go deeper through the bed before it comes in contact with a sorb grain.

 

[tbone1004]

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?

what makes you think Shaws scrubber broke through?

Shaw had a gas density issue and overbreathed his lungs, it is practically impossible to over-breathe a scrubber when following commonly accepted gas density guidelines.


O2 consumption can be used to track CO2 production though you have to understand that there is O2 wasted during the O2 flushes at the beginning of dive, at the start of deco, etc etc. so it's not really a precise way to measure it in practicality.

 

[Gone for diving]

Under workload, with high RMV, there is less dwell time in the scrubber as you breathe hard

I understand the dwell time problem...

If the CO2 is insulated from the grains with extra gas molecules

This makes lots of sense,
the co2 gets kinda lost in the thick gas..

Shaw had a gas density issue and overbreathed his lungs, it is practically impossible to over-breathe a scrubber when following commonly accepted gas density guidelines.

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...?

 

[nadwidny]

Question. Is there a way to tell how much of your scrubber you used when opening the canister at the end of a dive?

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

The only answer is "No".