no nitrogen breathing gas ?

[Woody88]

all right it makes sense. Then the main benefit to use heliox is to reduce nitrogen narcosis and allows greatest depths (as long as oxygen content is reduced).

This is true. But Helium is a fast loading gas and will actually require more decompression if a high amount of helium is used in the mix. The reason you would dive helium in your gas would be to reduce narcosis. The deeper you dive the more you would have to reduce the o2 content. You would not want to add more nitrogen because it would eventually become too narcotic for you too function, and give you a much greater risk of deep water black outs.

Most tech divers do not dive heliox either. The reasons are:
- Voice distortion if you are using a com system
- It sucks the heat out of you body and therefore can slow decompression
- HPNS; high amounts of helium can cause the shakes (similar to a mild seizure). Adding nitrogen back into the mix will counterbalance this effect.
- Helium is damn expensive compared to air.

 

[Woody88]

We all know about how nitrogen loading at depth limits our bottom time (more than our air consumption.

at recreational depth (say 120 feet), if we were to breath 21% oxygen, 79% helium (or any other inert gas, excluding nitrogen), asides from the problem of getting such a fill, would it eliminate NDL ?

Your NDL would be reduced on heliox at 120 fsw. If you were to do a 120 fsw for 15 minutes and were not gas switching for accelerated deco you would be hanging for 30 minutes. Helium loads in the tissues faster than nitrogen. The only way to get more NDL is to raise the amount of oxygen as close to a 1.4 ATA mix as possible.

 

[MonkSeal]

But Helium is a fast loading gas and will actually require more decompression if a high amount of helium is used in the mix.

This depends on exposure lenght. For short exposures this is true.

- Voice distortion if you are using a com system

You'll have voice distorsion if you use any He based mix not only when using heliox.

- It sucks the heat out of you body and therefore can slow decompression.

That's not true. Breathing He based mix will not cool you. Adding He based mix in your dry suit will.

- HPNS; high amounts of helium can cause the shakes (similar to a mild seizure).

Depends on depth.

- Helium is damn expensive compared to air.

Agree.

 

[MonkSeal]

- It sucks the heat out of you body and therefore can slow decompression.

That's not true. Breathing He based mix will not cool you. Adding He based mix in your dry suit will.

Just to add the explanation. He mix will be colder than air when entering the lungs due to heat loss from cylinder to lungs (lower molecular density of He - better heat transmition). But due to grater density air can conduct more heat over a relative volume of gas contributing more to core heat loss then He based mix. These two efects seem to counteract one another giving the similar termal loss for both air and trimix.

 

[Rick Murchison]

This is an interesting thread if only for the "almost right" stuff here.
Take a trimix course if you really want to learn about using helium.
As for helium's (or any other gas's) effect on narcosis, WOB, heat transfer and NDL, etc., TANSTAAFL applies.
Rick

 

[pickens_46929]

RumBum, sounds good to me. But I don't know anything. I like your avatar.

99 bottles of rum... take one down pass it around...

Couldn't resist! :05:

mmmm.... Brinley's Gold Vanilla Rum.... mmmmmm

 

[Woody88]

TANSTAAFL applies.

Huh???

 

[knotical]

Huh???

http://en.wikipedia.org/wiki/TANSTAAFL

 

[Woody88]

This depends on exposure lenght. For short exposures this is true

We are not talking about saturation or commercial diving. This is a discussion about rec/tech diving.

You'll have voice distorsion if you use any He based mix not only when using heliox.

Yes you will but the point was the more HE in the mix the more this will be an issue. Obviously a 30% mix will have less distortion than a 79% heliox mix.

That's not true. Breathing He based mix will not cool you. Adding He based mix in your dry suit will.

HE does have more of a cooling effect on the body. Take a look at this article.


http://www.scuba-doc.com/HPNS.html

 

[RumBum]

99 bottles of rum... take one down pass it around...

Couldn't resist! :05:

mmmm.... Brinley's Gold Vanilla Rum.... mmmmmm

Bacardi factory tour. The Wall-O-Rum was a floor to ceiling circular, about 4 feet radius. The gift shop was pretty cool too.

I am going to take Nitrox at some point before May. I don't expect to ever get into the other gas mixes; I do find them interesting though. I like to understand WHY things work.

Rick - if you see something incorrect, rather than just saying it is incorrect maybe you could enlighten us? We learn nothing by just being told that something somewhere in this thread is wrong. :05: