Effect of Depth on Scrubber

Marc T

Draeger-Kiss in englishmode, LOL or in french MDR ( mort de rire for who dont speak French ). Same production of CO2 watether the depth is, so PPCO2 in the loop decrease with depth so yeah some possible problem with scrubber.
But O2 manually or electronicaly added to the loop so constant PO2.
Am I wrong ( dont speak about my poor english )?

Stephane

OK Paul, the PpO2 is maintained constant during the dive, but what about the partial pressure of the inert gas (He or N2), it does increase whith depth no?
As the human body produces the same amount of CO2 (if we consider that the efforts done are the same wathever depth), the PpCO2 can only decrease with depth.
Or is it to late for me?

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Stéphane
Hammer-rEvo powered!

paulraymaekers

bonjour marc, hello,

I think you're wrong :-)

basic phisics and definition of partial pressure

same production of CO2, independant of dept, so SAME PPCO2 in the mix, whatever depth you are at the moment

remember simply: partial pressure= pressure that gas would have if it would be alone in that volume, so at the same metabolic rate, you produce the same amount of CO2 molecules, this wil give the same partial pressure of CO2

regards
paul

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.... the earth is flat, Elvis is alive, and radial scrubbers give longer dwell time than axials...

paulraymaekers

yes stéphan, it's getting late :-)

indeed, for a given PPO2, the PP of the other gasses will be higher the deeper you are (because the sum of the partial pressures of all the gasses equals the total pressure..)
but this has nothing to do with the PPCO2: this is gas that is produced at a certain rate, at a certain depth, this is not predicted by the gas you are INspiring
(continue: see mail for marc)

regards
paul

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.... the earth is flat, Elvis is alive, and radial scrubbers give longer dwell time than axials...

Marc T

Hey Tino C,I think we are thinking right, dont worry its certainly a PPCO2 Hit because of CO2 beer- bubbles ethering will become clear for everybody tomrorrow morning.
The real problem concerning Scrubber and depth efficiency is: is the CO2 dilution in more diluent the only problem?
To have a response you need to try and compare scrubber efficiency for different CO2 dilution ( percentage) at 1 ATA and different dilution for say 4 or 5 ATA.

Anyway I think somehone somewhere thought about that several years ago and tried it no?

J. V.

Try to dive with an empty canister, and you'll see if PpCO2 decrease .
Before the canister, in our lung, PpCO2 stay more or less the same and (normally) acceptable. After the canister, it is (more or less) equal to 0 cause the sorb capt it. If there is no sorb, each breath put a small amount of CO2 in the loop (around 0.6 L per min), and the PpCO2 rise.
Body act like a CO2 kiss valve, fortunatly there is sorb.
At each depth, CO2 production (and O2 consumtion) depend of work. Sometime we notice a low O2 consumtion at depth, it's cause sometime the deepest part of the dive is the less active part of the dive.

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Jacques
NPSFQQA-EDS IT # 007
(remué non agité)

Marc T

OK the last one for the night road (mdr )
IF you mean PPO2 in blood i agree, its always the same watether the depth is.
But IN A (exhale ) COUNTERLUNG for example 10 molecules of CO2 diluated in 1000 molecules at 1 ATA givE you a PPO2 of 100 the same diluated in 10 000 molecules because you in 10 ATA gives you a PPCO2 of 1
And the real question is is there a real diffrence scrubber efficiency ( same or diffrent number of CO2 molecule in the inhale counterlung ) or isnt it a problem of tolerance because of higher ppCO2 in the BLOOD but not IN the COUNTERLUNG??
So scrubber efficiency could be the same but you simply need a better scrubber at depth.
Am I dead?

Stephane

One good night of rest and tomorrow you will understand your mistake Jacques !!!

Bonne nuit les petits ... (good night kids ...)

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Stéphane
Hammer-rEvo powered!

paulraymaekers

I'm afraid you're dead :-)

altough partial pressure looks evident for every-one, (and actually it IS evident) , practice always seems difficult

basics: whatever pressure you have in a certain volume with many gasses in it, if you have the same numbers of molecules of gas X in that volume, you always have the same partial pressure of that gas X, because that is the definition of partial pressure (the pressure the gas would have if it were alone in that volume)

example, you have a volume at 1 bar, in total there are 1000 molecules in that gas. now there are 20 molecules CO2 in that volume, this means the partial pressure of the CO2 is 1 bar times 20/1000 so PPCO2= 0,02 bar

ok, now we have that same volume at 10 bar, this means in total there are 10.000 molecules in that volume. Again we have 20 molecules in that volume, so the partial pressure of the CO2 is 10 bar times 20/10000 so PPCO2 = 0,02 bar...

I agree that the FRACTION of CO2 decreases when depth increases, but the partial pressure is constant, (assuming the same metabolic rate)

regards
paul

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.... the earth is flat, Elvis is alive, and radial scrubbers give longer dwell time than axials...

divelermentov

hi there

it is tru that the co2 production is the same however hence the loop is at ambiant pressure the ppco2 will increase with depth if not all Co2 is removed by the scrubber.
In regards to the scrubber life a relevant factor is the mass of gas which is flowing through the scrubber not volume, with increase loop pressure (depth) you will start to push a greater gas mass through the scrubber.
(denser gas)
Due to the scrubber reaction is time as well as heat dependant, and the time in the sorb is in contact with Co2 molecules is reduced with depth (you push a graeter gas mass per time - so the relative flow will increase). You will therefore need a graeter scrubber surface at depth, hence your scruuber size is fixed this means the scrubber duration is reduced at depth.

The O2 cells are a different issue, basically it ias a galvanic element where O2 is the electron donor. Galvanis elemsnts produce a current depending on a concentration gradient and not due to mass. Therefore the cell reading is only influenced by the O2 concnetration (ppo2) in the loop.

If I am wrong please feel free to tell me off

But regardless I will always start a deep dive with a fresh scrubber, because Co2 breakthrough realy stinks
(and so does OC )

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