Trimix

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I wasn't attempting to question that. I understood the OP to be calculating a mix based on given dive parameters that include a depth of 90m and a target max ppO2 of 1.4.

In that case, I would like to understand what model or assumptions tursiops is talking about that result in having an option for a calculated mix that has FO2 of 13%. As I said, I don't have training yet in trimix or special calculations for diving as deep as 90m. From what I know so far, I would have expected the answer on the mix to always have FO2 of 14% and the FN2 and FHe to be what is really being calculated.

Like I said, I'm just trying to learn more. Even just a keyword or two to search on or a link to something I can read would be appreciated.

Actually, the PPO2 for a 14% O2 at 195 ft is 1.0, per multideco, assuming an equivalent air depth of 100ft. It gives a 14/39 mix.

Having a target max PPO2 of 1.4 at depth could result in a problem if, for some reason, you go deeper. That should not be the plan.

I recommend the TDI Advanced Trimix book as a primer.
 
@stuartv, most trimix calculators and all hand calculations assume ideal gases. Under 10 ATM pressure Van der Waal gases are a better assumption, and give the 13/48 result. The VDW calculation drops the 14 to 13, and the END constraint thus causes the 47 to go to 48 so you still only have 39% N2.

Edit: Sorry, I said this backwards. The VDW calc moves the He 47 to 48, which drops the O2 14 to 13 to keep the END constraint. At least, I THINK that is what is going on.
 
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Why did that get deleted?
I was not the one who moderated the thread, but I assume it just got swept up with everything else. Your question was fine, and now that you have repeated it, it is back in place.
 
I assume you are a trimix student working your way through the academic portion of the course materials. Make sure to talk to your instructor about this issue. He or she might have a lot to say about the concept of best mix in addition to what those materials say--I know I would.
He (she?) asked this exact question on a whole bunch of other forums too. Hard to know exactly what the actual plan is and if this is even an OC dive. Or possibly just an academic question
 
14/40 1,4 ppO2 / 10 ATA (90 mt) = %14
5 ATA (40 mt) x 0,79 (%79N)=3,95 ppN
3,95/10 ATA= %39,5
 
14/40 1,4 ppO2 / 10 ATA (90 mt) = %14
5 ATA (40 mt) x 0,79 (%79N)=3,95 ppN
3,95/10 ATA= %39,5

Isn't the standard for the second number to be the He content?

And if you want END of 40m (or less), then wouldn't you round 39.5% down to 39%?

And if you have 14% O2 and 39% N2, then you'd have 47% He, right?

So, you'd write that as 14/47, right? I.e. what everyone else already said?
 
Isn't the standard for the second number to be the He content?

And if you want END of 40m (or less), then wouldn't you round 39.5% down to 39%?

And if you have 14% O2 and 39% N2, then you'd have 47% He, right?

So, you'd write that as 14/47, right? I.e. what everyone else already said?

Yes.
 
Isn't the standard for the second number to be the He content?

And if you want END of 40m (or less), then wouldn't you round 39.5% down to 39%?

And if you have 14% O2 and 39% N2, then you'd have 47% He, right?

So, you'd write that as 14/47, right? I.e. what everyone else already said?

Yes my bad, sorry

100-(14+39,5)=46,5 so, 14/47
 
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