Nitrox PPB

[SparticleBrane]

Not quite. Although I will preface this by saying that I haven't taken a trimix class either.

"Nitrox" is any mix of nitrogen and oxygen. Air is usually considered a mix of 21% nitrox.
Trimix is a blend of nitrogen, oxygen, and helium, but there is less oxygen than normal everyday air. Examples are: 18/45, 15/55, 12/60, and 10/70.
Helitrox is a mixture of nitrogen, oxygen, and helium, where there is equal to (I believe some people call this "normoxic trimix" ?) or more oxygen than we breathe in normal everyday air. Think of this as nitrox, but with helium added. Examples are 25/25, 21/35, 30/30...the list goes on.

Helitrox has both an EAD and an END. The EAD comes from having MORE oxygen than what we breathe, and and also having helium, which reduces narcosis.
Trimix only has the END, since the helium reduces narcosis. The oxygen is LESS than what we breathe in normal air, so there is no EAD.

If you check out the PDF link that I posted above, most of this is fairly self explanatory.

 

[Packhorse]

PM me about 4 or 5 examples, and I'll run it against my blending program.

-P

example 1 Helitrox (?) 26/17
added to a tank containing 40 bar air

Air required 125.9 bar
Helium req 39.1 bar
O2 req 24.9 bar

Example 2 16/40 trimix
added to a tank containing 80 bar nitrox 32

air req 85 bar
H reg 92 Bar
O2 req 2.9 bar (maybe not the best example)

Example 3 16/40 trimix
added to empty tank
Air req 128.1 Bar
H req 92 bar
O2 req 9.9 bar

How do these example look?
Thanks

Edit: As Perronford pointed out these are missing the final pressure which is 230bar

 

[SparticleBrane]

It looks like you need to start using PSI.

 

[Packhorse]

AndyNZ just emailed me another Nitrox speadsheet and mine was out by .2 bar & .3bar.
In that sheet they seem to have calculated the fill pressure of 230 bar and added 1 to it.
Not sure why, maybe 1bar atmosphere? Anyway so far it seems more accurite than my spelling.

 

[Packhorse]

It looks like you need to start using PSI.

Is that some sort of advanced gas mixing program?
Oh I get ya. Sorry I dont do vintage diving :lol:

 

[PerroneFord]

I'm sorry, but these examples make no sense.

In blending, we need three things

1. Starting pressure and mix
2. Desired pressure and mix
3. Available gases for blending

So a proper example might be (in psi)

Tank containing 800psi of 21/35
Final Mix 3500psi of 30/30

What do I need to add?

582.3 psi of Oxygen
784.4 psi of Helium
1333.3 psi of Air


-P

 

[SparticleBrane]

...how is using PSI vintage diving?

I don't see why the rest of the world uses BAR, especially if it isn't technically an accepted SI unit.

For me, PSI is much easier. I can imagine 3000 pounds per square inch sitting on the inside of a scuba tank. It's hard for me to imagine 1,000,000 dynes (the force needed to accelerate a mass of one gram at a rate of [1cm/sec]^2, or 10^-5 newtons) per square centimeter.


Of course, I can be trained to use either, that isn't the issue. I just wonder why the rest of the world, who prides itself on using SI units, is using a non-SI unit for pressure.

 

[Packhorse]

We stoped using PSI before I was born. So to me it is vintage.
As easily as you can imagin 3000PSI of pressure so can I imagine 207 times increase in atmospheric pressure on the inside of my tank.
It also make it a lot easier to calculate various things such as pressure at depth, MOD etc.
I think you will find the SI is not that widely accepted by everyday people. Most choose the metric system

 

[do it easy]

Of course, I can be trained to use either, that isn't the issue. I just wonder why the rest of the world, who prides itself on using SI units, is using a non-SI unit for pressure.

I think that it makes the volume calculations easier- as in remaining BAR times liquid capacity is the remaining gas volume in liters or is it quarts?

 

[Packhorse]

I'm sorry, but these examples make no sense.

In blending, we need three things

1. Starting pressure and mix
2. Desired pressure and mix
3. Available gases for blending

So a proper example might be (in psi)

Tank containing 800psi of 21/35
Final Mix 3500psi of 30/30

What do I need to add?

582.3 psi of Oxygen
784.4 psi of Helium
1333.3 psi of Air


-P

Ok well for you examp I get
Air needed 1326.582283
Helium needed 770
O2 needed 603.4177169

So there is some small descrepancy with my spead sheet.
I will have to see if I can work it out