Oxygen consumption ?

Michel2711

Hi, I am new to CCR and this week end, I was reviewing my past dives on the Evolution to see if my O2 consumption had improved since the first drills (that were quite awful in that respect BTW) . I had written down the O2 tank pressure before / after and as I was doing my calculations, I was wondering what it means to consume "1.5 liter / mn". By that, does one mean "1.5 liter of O2 per mn under 1 ATM "?
That seems to be the logical answer if the O2 consumption is not to depend on the depth. Can someone explain ?

Thanks,
Michel

mortenkjerulff

Hi Michel.

Dependent on your diving depth, you will loose more og less oxygen on your accent, as the rebreather will try to maintain setpoint while you purge gas from the expanding loop and the surrounding pressure drops.
Thus your oxygen consumption seems higher than it really is.

"1.5 liter / mn" means that you have used 1.5 liters of oxygen per minut in average.

Morten

ScubaDadMiami

Remember, there is no change in metabolizm at depth.

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Howard Packer
IANTD CCR Instructor
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CCRDiveTraining.com

Michel2711

Yes, thanks

dteubner

1.5 litres O2 does in fact mean 1.5 litres at 1ATA. It is a useful concept if you think about the amount of oxygen in the tank in terms of litres at 1ATA.

It would be more strictly logical to say that you used 2.1 grams of oxygen a minute instead of 1.5 litres (2.1=32*1.5/22.4) but it doesn't seem as intuitive - given that grams do not change with pressure but litres do

Dave T

ccr_ada

cuckcooooooo go back do your nitrox again !!!! grams you having a laugh? back to ccr school we go

Gill Envy

hugh!

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Gill Envy

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Mixaddict

Is it possible to obtain a translation of this guy's emails? I think I am loosing something here!

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Randy Thornton (MixAddict)
Inspiration, Evolution,Hammerhead & Sentinel
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dteubner

If you don't like grams would you prefer 4,030,000,000,000,000,000,000 molecules?

Dave T

fubari

Grams aren't so bad. Not part of the nitrox curriculum, but
perhaps the physics is sound? We both may need to go back
to Chemistry 101, Ccr_Ada ( I am sure that I do ).

I say that because I decided to try following Dave's math.
2.1 grams of oxygen = 32*1.5/22.4
Huh? Now I'm feeling dumb.
Let's add some units:
32?? * 1.5 L / 22.4 ??
This ( Image:Mole.gif - Wikipedia, the free encyclopedia) tells me
that the 22.4 comes from the molar volume of a gas at 1 ata.

So 22.4L of Oxygen at 1ata equals 1 mole.
One mole of oxygen weighs 16gm (15.9994 grams), yes?
So 1L of Oxygen at 1ata weighs 16gm/22.4L --> 0.7143gm
So 1.5L of Oxygen at 1ata weighs 1.5 * .7143gm --> 1.07gm ??
Why not 2.1gm like Dave got?
Ah Hah! This is O2, not just O, so it is really 2*1.07 gm --> 2.14gm.

That is where the 32 in "(32gm/mol) * 1.5L / (22.4L/mol)" came from.
The atomic weight of 2 * one oxygen atom, since we're talking O2.
e.g. 2 * 16 gm.
I thought I was going to be up all night trying to work that one out.
Close enough for me.
I'm going to bed now.