Published Scrubber Research

Mark Chase said:
So basicly 30% reduction in scrubber duration with Spherasorb with a 10% improvement in WOB
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Hello Mark,

Just for clarity, what we measured was not work of breathing per se. We just measured the difference in peak to peak (or peak to trough - whichever way you want to look at it) pressures required to move a standard tidal volume (breath size) around the loop. The fact that we showed these were less for spherasorb does suggest the actual work of breathing is lower (and possibly by a proportional amount as you have assumed) but we can't be 100% sure of that.

Simon
 
I've been watching your video's, and have read this report as well as the first one. Glad you're doing this.
 
Simon Mitchell said:
Hello Mark,

Just for clarity, what we measured was not work of breathing per se. We just measured the difference in peak to peak (or peak to trough - whichever way you want to look at it) pressures required to move a standard tidal volume (breath size) around the loop. The fact that we showed these were less for spherasorb does suggest the actual work of breathing is lower (and possibly by a proportional amount as you have assumed) but we can't be 100% sure of that.

Simon
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Understood


Again I point out many KISS owners tried or switched to Spherasorb in order to improve the WOB on that unit.

I did the same and found it helped.

My main point was i thaught it would be significantly more than 10%? because it apeared noticable without an ANSTI macheen to tell me so

which is why I felt it likley there was a bit of Plecebo effect on my conclusion.

That said the biggest improvment on the KISS was running diferent loop hoses (cooper) and a Golum BOV with Drager Mushroom valves as aposed to the origional KISS Paragon one which i beleive used reclaimed inertubes off Mac trucks :D .
 
Simon

If its a big ask say so but could you comment on the calculation of scrubber duration using a test like this as a base line and altering the duration based on reduced C02 production.


IE if this test is based on co2 production of 2lpm how mad would it be to double the figure based on a C02 production of 1lpm?

It is obvious there would be a difference as I have run 180 to 240min run times (longest was an hour at 65m + deco) without incident in apx. 15c water and 360mins over multiple dives in shallow (14m max) 20c water (Mexico Caves) and Haven't had any adverse C02 incidents to date


By shear coincidence taking the 360min run time as an example, that is 2.66 X the duration you achieved with your testing and if you divide the RMV by 2.66 you get 16.5 RMV?

My RMV on average for the working phase of the dive is 13-15lpm (based on actual OC dive gas usage calculations)

SO I can explain to myself why I didnt suffer a C02 hit on those dives by the fact I pushed it to the limit with virtually no margin of error but didn't go past it.

I have always been under the impression water temperature had an impact on scrubber duration and as my base line tests were at 4C I was leaving a further margin of error by ignoring the benefit of 15-20c water in my calculations.

Am I self-deluding (bearing in mind I have already decided 6 hours is never happening again and 4 is my new max) or is there some method in my madness.
 
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Mark Chase said:
Simon

If its a big ask say so but could you comment on the calculation of scrubber duration using a test like this as a base line and altering the duration based on reduced C02 production.


IE if this test is based on co2 production of 2lpm how mad would it be to double the figure based on a C02 production of 1lpm?

It is obvious there would be a difference as I have run 180 to 240min run times (longest was an hour at 65m + deco) without incident in apx. 15c water and 360mins over multiple dives in shallow (14m max) 20c water (Mexico Caves) and Haven't had any adverse C02 incidents to date


By shear coincidence taking the 360min run time as an example, that is 2.66 X the duration you achieved with your testing and if you divide the RMV by 2.66 you get 16.5 RMV?

My RMV on average for the working phase of the dive is 13-15lpm (based on actual OC dive gas usage calculations)

SO I can explain to myself why I didnt suffer a C02 hit on those dives by the fact I pushed it to the limit with virtually no margin of error but didn't go past it.

I have always been under the impression water temperature had an impact on scrubber duration and as my base line tests were at 4C I was leaving a further margin of error by ignoring the benefit of 15-20c water in my calculations.

Am I self-deluding (bearing in mind I have already decided 6 hours is never happening again and 4 is my new max) or is there some method in my madness.
Click to expand...

Here is the all-important question: what CO2 production rate do you think you have based on your RMV of 13-15lpm? Or to pose the wider question: what is the relationship between minute ventilation on OC (RMV as you put it) and CO2 production on a CCR in an experienced diver?

I am not an expert but I believe the relationship between these parameters is not at all straightforward, if in fact one exists.

Andy
 
I believe that the published Sorb specs (for example 100L CO2/ KG 4-6 grade sorb) are pretty accurate as long as you are not way overbreathing your sorb, which might not be all that important anyway since everbody seems to prefer radial sorb cannesters which have a much shorter dwell time of gas in the sorb as compared to axial sorb cannesters.
If you are producing 0.5L of CO2 per minute and have 2.5Kg of 4-6 grade Sorb in a well working sorb cannester you should have a sorb lifetime approaching 500 minutes. changing to 797 would yield a sorb lifetime under identical conditions of 700 to 750 minutes.
Of course if you are fighting for your life and producing 2.5L of CO2 per minute the lifetime of 4-6 grad sorb becomes 100 minutes instead of the 500 minutes that you planned on for a relaxed dive.

How well flooded sorb works is something that I don't have any idea about, but I do know that I have dived over an hour with flooded sorb and several liters of water in the RB without ill effects - loading to my conclusion that flooded sorb will continue to work for an unknown but not insignificant amout of time.
The couple of times that I have deliberately dived my sorb to the point where CO2 was breaking through, I slowly noticed that the number of breaths per minute was slowly increasing without any other changes in my dive. Bailing out wasn't a problem nor was switching back to the used up sorb 20M higher up. Maybe I'm lucky that I notice CO2 buildup pretty early, but others should also be able to notice when they are slowly breathing 15 breaths per minute instead of 6-8 breaths per minute.

Michael
 
apitkin said:
Here is the all-important question: what CO2 production rate do you think you have based on your RMV of 13-15lpm? Or to pose the wider question: what is the relationship between minute ventilation on OC (RMV as you put it) and CO2 production on a CCR in an experienced diver?

I am not an expert but I believe the relationship between these parameters is not at all straightforward, if in fact one exists.

Andy
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Its a simple mathmatical calculation

C02 = 85% V02

V02 = 4% RMV

RMV of 14lpm = V02 of 056

C02 Production = 85% of VO2 so 85% of 0.56 = 0.476ltrs C02 produced per Min

ATB

Mark
 
michael_fisch said:
I believe that the published Sorb specs (for example 100L CO2/ KG 4-6 grade sorb) are pretty accurate as long as you are not way overbreathing your sorb, which might not be all that important anyway since everbody seems to prefer radial sorb cannesters which have a much shorter dwell time of gas in the sorb as compared to axial sorb cannesters.
If you are producing 0.5L of CO2 per minute and have 2.5Kg of 4-6 grade Sorb in a well working sorb cannester you should have a sorb lifetime approaching 500 minutes. changing to 797 would yield a sorb lifetime under identical conditions of 700 to 750 minutes.
Of course if you are fighting for your life and producing 2.5L of CO2 per minute the lifetime of 4-6 grad sorb becomes 100 minutes instead of the 500 minutes that you planned on for a relaxed dive.

How well flooded sorb works is something that I don't have any idea about, but I do know that I have dived over an hour with flooded sorb and several liters of water in the RB without ill effects - loading to my conclusion that flooded sorb will continue to work for an unknown but not insignificant amout of time.
The couple of times that I have deliberately dived my sorb to the point where CO2 was breaking through, I slowly noticed that the number of breaths per minute was slowly increasing without any other changes in my dive. Bailing out wasn't a problem nor was switching back to the used up sorb 20M higher up. Maybe I'm lucky that I notice CO2 buildup pretty early, but others should also be able to notice when they are slowly breathing 15 breaths per minute instead of 6-8 breaths per minute.

Michael
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Obviously I am in full agreeent, but its like planning a big OC dive on a emergancy RMV of X and then you masivly exceed that RMV so your origional gas volume calculations are no longer relevent

New divers planning 50SAC redundancy gas levels is all great but lets be honist you cant do a big cave push on those numbers so bigger dives are working with far smaller margins of error.

IF I were in a situation where RMV was extreemly high for a sustained period due to work load then I would hope to have the sense to bailout on to OC after a depth dependent time (probably 2 hours max) and not return to the CCR untill I was back under control or ran out of gas and had too
 
michael_fisch said:
everbody seems to prefer radial sorb cannesters which have a much shorter dwell time of gas in the sorb as compared to axial sorb cannesters.
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For the same volume of scrubber material the dwell time will be the same.
The velocity is lower through a larger cross sectional area in a radial scrubber.
 
Mark Chase said:
Its a simple mathmatical calculation

C02 = 85% V02

V02 = 4% RMV

RMV of 14lpm = V02 of 056

C02 Production = 85% of VO2 so 85% of 0.56 = 0.476ltrs C02 produced per Min

ATB

Mark
Click to expand...

VO2 = 4% RMV - this is the problematic assumption. Oxygen consumption is just not always tied to alveolar ventilation like that, especially under conditions of increased pressure and exercise.

It is better to look at CO2 alone. Arterial PCO2 is proportional to metabolic CO2 production and inversely proportional to alveolar ventilation (approximates to RMV). Therefore, if you double your workload, you have to double your alveolar ventilation to keep arterial PCO2 constant. Unfortunately we know that often divers will not keep arterial CO2 constant (they retain CO2) and therefore their alveolar ventilation must be less. Their RMV is lower at the expense of retained CO2. Under these conditions VO2 will be more than 4% of RMV, as you put it.

All I am trying to say is that you cannot reliably predict your CO2 production from your RMV because your assumption is that RMV remains proportional to metabolic CO2 production, and there is good evidence that it doesn't, especially in experienced OC divers.

So yes, the calculation is a simple one, but its underlying assumptions do not necessarily hold true under the conditions we are interested in.
 
Mark Chase said:
Its a simple mathmatical calculation
C02 = 85% V02
V02 = 4% RMV
Click to expand...

No, it's not.

Your respiratory quotient VCO2ex/VO2in can vary between 0.6 and 1.3 depending on exertion levels, diet (both long term and immediately prior to measurement) and general fitness. It varies widely from person to person and for an individual too. It can swing that full range during a single dive, for example. VO2in can also vary massively, as described by apitkin above.

Trying to calculate CO2 production rather than measuring it in anything other than a rough order-of-magnitude guesstimate is bloody dangerous. Which is why no course I've seen now will teach students how to pack a canister for a certain length dive, or how to guess at the life expectancy of the canister (and diver attached) based on that diver's details. Manufacturers will give a worst case tested limit and, without a temp stick, any pseudo calculations you make to guess at how hard you push at it are guesses only.
 
apitkin said:
VO2 = 4% RMV - this is the problematic assumption. Oxygen consumption is just not always tied to alveolar ventilation like that, especially under conditions of increased pressure and exercise.

It is better to look at CO2 alone. Arterial PCO2 is proportional to metabolic CO2 production and inversely proportional to alveolar ventilation (approximates to RMV). Therefore, if you double your workload, you have to double your alveolar ventilation to keep arterial PCO2 constant. Unfortunately we know that often divers will not keep arterial CO2 constant (they retain CO2) and therefore their alveolar ventilation must be less. Their RMV is lower at the expense of retained CO2. Under these conditions VO2 will be more than 4% of RMV, as you put it.

All I am trying to say is that you cannot reliably predict your CO2 production from your RMV because your assumption is that RMV remains proportional to metabolic CO2 production, and there is good evidence that it doesn't, especially in experienced OC divers.

So yes, the calculation is a simple one, but its underlying assumptions do not necessarily hold true under the conditions we are interested in.
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I dive a KISS which has a fixed 02 feed to match the metobolic rate of 02 consumption.

In my experiance theres no saignificant variation in 02 consumption with a regular RMV.

Increased exercise = increased RMV and greater consumption relative to RMV?

That goes without saying but I supose the question in my mind would be, whats the variable upper limits asuming a constant RMV of 15 and taking 4% RMV V02 as a base line?

ATB

Mark
 
Captain Starfish said:
No, it's not.

Your respiratory quotient VCO2ex/VO2in can vary between 0.6 and 1.3 depending on exertion levels, diet (both long term and immediately prior to measurement) and general fitness. It varies widely from person to person and for an individual too. It can swing that full range during a single dive, for example. VO2in can also vary massively, as described by apitkin above.

Trying to calculate CO2 production rather than measuring it in anything other than a rough order-of-magnitude guesstimate is bloody dangerous. Which is why no course I've seen now will teach students how to pack a canister for a certain length dive, or how to guess at the life expectancy of the canister (and diver attached) based on that diver's details. Manufacturers will give a worst case tested limit and, without a temp stick, any pseudo calculations you make to guess at how hard you push at it are guesses only.
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Do you have any peramiters for the upper limit?

Your numbers would make more sense to the lay person if you outlined the upper limit as a % V02


IE if a moderatly fit person enguaged in heavy exercise his % Vo2 would increase from 4% to X? %

Then I could clearley see the disparity
 
Mark Chase said:
Do you have any peramiters for the upper limit?

Your numbers would make more sense to the lay person if you outlined the upper limit as a % V02


IE if a moderatly fit person enguaged in heavy exercise his % Vo2 would increase from 4% to X? %

Then I could clearley see the disparity
Click to expand...

I was more looking at the "0.85" ratio of CO2 production to O2 consumption. Spent a lot of time looking at respiratory calorimetry about 15 years ago.

I watched RQ head down over three weeks from 1.0 of a western normal "occasional burger but really I normally eat healthy" diet down to 0.6 on an Atkins style zero carb diet. I've watched it then smash up to 1.3 ten minutes after the same person drank a can of coke as their body went "WTF is all this sugar doing here, roll out the insulin and make fat mofo!" Incidentally, I've watched it do exactly the same thing with diet sodas too, but that's a whole other can of coke zero. I've watched it swing from 0.7 up to 0.9 as a fit person started gentle exercise then jump to 1.2 as soon as they got into aerobic.

As far as VO2 consumption I wasn't really looking at that data from test to test - our main focus was on changes to RQ. If I wasn't so lazy :) I would rebirth one of the calorimeter machines I made for the job and start playing but it'd be a fairly mammoth task to wake all that up again.
 
Captain Starfish said:
I was more looking at the "0.85" ratio of CO2 production to O2 consumption. Spent a lot of time looking at respiratory calorimetry about 15 years ago.

I watched RQ head down over three weeks from 1.0 of a western normal "occasional burger but really I normally eat healthy" diet down to 0.6 on an Atkins style zero carb diet. I've watched it then smash up to 1.3 ten minutes after the same person drank a can of coke as their body went "WTF is all this sugar doing here, roll out the insulin and make fat mofo!" Incidentally, I've watched it do exactly the same thing with diet sodas too, but that's a whole other can of coke zero. I've watched it swing from 0.7 up to 0.9 as a fit person started gentle exercise then jump to 1.2 as soon as they got into aerobic.

As far as VO2 consumption I wasn't really looking at that data from test to test - our main focus was on changes to RQ. If I wasn't so lazy :) I would rebirth one of the calorimeter machines I made for the job and start playing but it'd be a fairly mammoth task to wake all that up again.
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Do people drink a lot of cola whilst diveing in Oz? Its not big over here
 
Mark Chase said:
Do people drink a lot of cola whilst diveing in Oz? Its not big over here
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:)

Funny. The point was more that you can't assume 0.85 is anywhere near the actual ratio of CO2 to O2 because it vary significantly and fast. So when I see guys rip out calculations based on various assumptions that they've somehow decided mean they can run this sorb change for a 3l O2 cylinder however long that takes, I shudder at the wrongness of it all.
 
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