Check my math regarding partial pressure.

[DaleC]

Back to the OP for a second. ATA's at 100' are 4 not 3.

 

[Texasguy]

Back to the OP for a second. ATA's at 100' are 4 not 3.

Where do you see me using 3ATA at 100 feet?

 

[Lorenzoid]

Where do you see me using 3ATA at 100 feet?

I was confused by this at first, too. But looking at it some more, I realized what you meant:

"Say at 100feet ~ 3ATM, one breathing air is taking in 21% * 4ATA = 0.84 P02"

 

[rhwestfall]

....he properly identified and used ATM & ATA

 

[wedivebc]

Ran a couple numbers through MultiDeco just for giggles. First is normal air (30m/15m/21%), 100ft dive for 15 minutes, VPM +3. Second is the 6% hypoxic mix (30m/15m/6%). Red means the PO2 is too low to sustain life. As you can see, there's really no reason to dive with such a hypoxic mix. It quite literally gains you nothing other than an intellectual exercise in doing the math for PO2 calculations.

AIR
Dec to 30m (2) Air 15m/min descent.
Level 30m 13:00 (15) Air 0.84 ppO2, 30m ead
Asc to 6m (17) Air -9m/min ascent.
Stop at 6m 0:20 (18) Air 0.34 ppO2, 6m ead
Stop at 3m 2:00 (20) Air 0.27 ppO2, 3m ead
Surface (21) Air -3m/min ascent.

EAN6
Dec to 30m (2) Nitrox 6 15m/min descent.
Level 30m 13:00 (15) Nitrox 6 0.24 ppO2, 38m ead
Asc to 18m (16) Nitrox 6 -9m/min ascent.
Stop at 18m 0:40 (17) Nitrox 6 0.17 ppO2, 23m ead
Stop at 15m 3:00 (20) Nitrox 6 0.15 ppO2, 20m ead
Stop at 12m 4:00 (24) Nitrox 6 0.13 ppO2, 16m ead
Stop at 9m 5:00 (29) Nitrox 6 0.11 ppO2, 13m ead
Stop at 6m 9:00 (38) Nitrox 6 0.10 ppO2, 9m ead
Stop at 3m 18:00 (56) Nitrox 6 0.08 ppO2, 5m ead
Surface (57) Nitrox 6 -3m/min ascent.

So since you are just playing with numbers try converting your 6% O2 to an EAD and run your same dive using PADI air tables or better yet US Navy tables since PADI tables won't go deep enough (hint hint)

 

[boulderjohn]

So since you are just playing with numbers try converting your 6% O2 to an EAD and run your same dive using PADI air tables or better yet US Navy tables since PADI tables won't go deep enough (hint hint)

So in figuring out an EAD for a mix of 6% O2, what are we to assume the other 94% is?

 

[JohnnyC]

The reason for diving hypoxic mixes is to avoid high PO2s that can lead to oxygen toxicity. In that case, you are going much deeper than 100 feet. In order to get the lower level of O2, you need to be doing something like adding helium to the mix.

I'm quite aware of the reason for using hypoxic mixes, I use them myself. The specific statement of matching surface PO2 at 100ft is what I'm curious about. What is his intention, since EAN6 is sort of pointless at 100ft. There has to be a specific reason for him to want to dive that mix at that depth, I'm wondering what it is. Or, it's just math practice.

I assumed 94% was N2 for the plan. To point out the absurdity of using EAN6 for a 100ft dive.

 

[boulderjohn]

I'm quite aware of the reason for using hypoxic mixes, I use them myself. The specific statement of matching surface PO2 at 100ft is what I'm curious about. What is his intention, since EAN6 is sort of pointless at 100ft. There has to be a specific reason for him to want to dive that mix at that depth, I'm wondering what it is. Or, it's just math practice.

I assumed 94% was N2 for the plan. To point out the absurdity of using EAN6 for a 100ft dive.

I'm guessing math practice, or just understanding partial pressures. I have no idea how I would get a mix of 6% O2 and 94% N2. It would probably have to call for re-engineering a membrane system

 

[wedivebc]

So in figuring out an EAD for a mix of 6% O2, what are we to assume the other 94% is?

If using Navy air tables it would have to be nitrogen

---------- Post added August 13th, 2015 at 10:39 AM ----------

So since you are just playing with numbers try converting your 6% O2 to an EAD and run your same dive using PADI air tables or better yet US Navy tables since PADI tables won't go deep enough (hint hint)

Ooops yes PADI tables will go deep enough. Just ran the numbers.

 

[Storker]

II have no idea how I would get a mix of 6% O2 and 94% N2. It would probably have to call for re-engineering a membrane system

It's simple. Air to 66 bar / 960 psi, hook up the N2 tank, fill'er up to 230 bar / 3350 psi.

And as a bonus, PP blending with N2 doesn't require oxygen clean tanks & regs.




...what? Are you saying you don't have an N2 tank?



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