Trimix...

[DrSteve]

I've been wondering...
plain old compressed air - max depth of 210 feet due to O2 toxicity and let's say standard deco limits
EAN - shallower max depth due to pO2, but enhanced no-deco limits
Heliox (assuming 80%He and 20% O2) - max depth of 210 feet due to pO2 but much enhanced deco limits
Trimix...what is the point of trimix? Every % of He replaced with N2 will give you N2 absorption. I'm guessing if you were to dive at 210 feet and had 10% N2 you would be diving at your max depth of 210 with about 0.7 pO2.

So...what's the point of adding N2 to the mix?

 

[mrobinson]

costs... some people think it's worth it to save some pennies. (That and trimix been proven - I personally think that's old school thinking. But I'm not certified in either so I have a very ignorant p-o-v for now! )

 

[IceDiverInCA]

Heliox (assuming 80%He and 20% O2) - max depth of 210 feet due to pO2 but much enhanced deco limits

Heliox doesn't give you any edge on deco limits. Helium bends are usually more severe than nitrogen bends.

Trimix...what is the point of trimix? Every % of He replaced with N2 will give you N2 absorption. I'm guessing if you were to dive at 210 feet and had 10% N2 you would be diving at your max depth of 210 with about 0.7 pO2.?

Every % of He added will give you He absorption so no difference there, except He gets absorbed and offgasses much faster. Also, how did you get 0.7 PPO2?

So...what's the point of adding N2 to the mix?

HPNS and the cost of He.

What you didn't mention on your post is the narcosis level and the gas density.

 

[mrobinson]

Heliox doesn't give you any edge on deco limits. Helium bends are usually more severe than nitrogen bends.QUOTE]
Hey Icediver- do you have some information about helium bends? I guess we could start a different thread if too much of a hi-jack.

 

[IceDiverInCA]

Hey Icediver- do you have some information about helium bends? I guess we could start a different thread if too much of a hi-jack.

Try DAN and UHMS. Helium bends being more severe or its onset occurring much sooner is something I heard at a UHMS seminar I attended awhile back.

 

[DrSteve]

Every % of He added will give you He absorption so no difference there, except He gets absorbed and offgasses much faster. Also, how did you get 0.7 PPO2?

10% N2 at 1 atmosphere = 0.1atm partial pressure
At 210 feet (70m approx) = oops 8 atm = 0.8 atm partial pressure.

 

[mrobinson]

Sweet - thanks!

 

[DrSteve]

What you didn't mention on your post is the narcosis level and the gas density.

So the only real benefit is shorter (?) deco stops due to quicker off-gassing and no narcosis?

 

[IceDiverInCA]

10% N2 at 1 atmosphere = 0.1atm partial pressure
At 210 feet (70m approx) = oops 8 atm = 0.8 atm partial pressure.

Ah, you meant PPN2.

 

[mrobinson]

Try DAN and UHMS. Helium bends being more severe or its onset occurring much sooner is something I heard at a UHMS seminar I attended awhile back.

I'm reading that helium comes out of solution much quicker than nitrogen. Assumption -less time in the water then or is the profile conservative, like if you were on trimix?