not a tech diver, but a gas question just out of interest

[h90]

I am just a normal AOW diver, but as I just read about the history of trimix. Just out of interest, if I would mix even more gases it would bring additional benefits, or? Less partial pressure for every gas, less decompression.

I don't know if other gases beside helium can be used, maybe argon?? hydrogen can be used but might a bit dangerous.

Is it possible to use more gases, like 4 or 5 gases and if which?


thanks
Michael

 

[Dive-aholic]

Each gas has its own benefits and risks. Helium helps lessen the effect of nitrogen narcosis, but still has its own decompression requirements. Argon is too heavy a gas and would work for breathing at depths. Hydrogen is an option, but cannot be mixed with oxygen percentages over 4%. Mixing 4 or 5 gasses together just makes the whole decompression model way to difficult to try to figure out. Helium use is failure new as a commonly used gas. Divers were doing decompression for several years based on homemade tables or tables obtained from others, but not scientifically tested or proven. We now have models for helium. I don't think there are many people out there that would want to bother formulating a model for a 4-5 gas mix.

 

[MikeFerrara]

The primary advantage of helium is that it isn't very narcotic. there are those who think that there are some decompression advantages but you still have to decompress. The point is that the primary objective of using helium is to reduce narcosis.

Argon is very narcotic.

 

[Charlie99]

IIs it possible to use more gases, like 4 or 5 gases and if which?

It is possible to use multiple gases, as is done in the O2, N2, He mixture of trimix, but you don't gain much, if any, advantage by adding additional gases.

The ongassing/offgassing of each gas is relatively independent of each other, and depends almost exclusively on the difference between the pressure/tension of each gas in the tissues and the pressure of each gas in the gas being breathed.

The big catch, however, is that bubble formation is driven by the difference between the SUM of all of the inert gas pressures/tensions in the tissues vs the ambient pressure. Since bubble formation is driven by the SUM of all the dissolved gases, you don't get any dramatic improvements as you add more gases.

 

[h90]

Charlie99: I did not know that!
Did I understand right: if I have 1 gas dissolved in a liquid and reduce the pressure I'll get the same bubbles as if I have 2 different gases (say with the same properties in dissolving)?

I never understood that, I always thought it is up to the partial pressure, and therefore as more gases as better.

Together with MikeFerrara post about the narcotic, it brings me to a complete new understanding of that.....

 

[espenskogen]

Charlie99: I did not know that!
Did I understand right: if I have 1 gas dissolved in a liquid and reduce the pressure I'll get the same bubbles as if I have 2 different gases (say with the same properties in dissolving)?

I never understood that, I always thought it is up to the partial pressure, and therefore as more gases as better.

Together with MikeFerrara post about the narcotic, it brings me to a complete new understanding of that.....

H90 - It depends on the gas - Generally, if you use heavier gases, they saturate slower, but create more narcosis. Either way, the decompression penalties are going to be incurred anyway, as long as the gasses you use are inert (As in they're not metabolized by the body)

The purpose of mixes is more to do with reducing narcosis than reducing deco penalties. To speed up deco, you just increase the oxygen fraction on the way up.
It's a lot easier than working with loads of exotic gasses.

In trimix, one leaves the nitrogen in to offset a side-effect of heliox diving called High Pressure Nervous Syndrome, and the helium is there to offset nitrogen narcosis.

There has been experiments using Neon in the mix, but it's a very expensive gas to be using, so it's not really that widespread.

E

 

[scububa]

Just recently did my AdvEANx and no trimix experience and meager book knowledge...but some relavent points

but, all inert gasses are believed to be narcotic (to various degrees, many not well understood, but then basic narcosis isn't, either)


other gasses, dependent on density, have thermal considerations, also

 

[Doc Intrepid]

One reference, although older, which offers a review of the history of development of mixed gas diving at an easily accessible and understood level is "Deep Diving" by Brett Gilliam et. al. (1995) The authors discuss research regarding gasses such as neon and xenon, among others.

It is available through Watersport Books, here:
http://scubadivingbooks.com/divetraininginstruction/0922769311.htm

Doc

 

[MikeFerrara]

H90 - It depends on the gas - Generally, if you use heavier

In trimix, one leaves the nitrogen in to offset a side-effect of heliox diving called High Pressure Nervous Syndrome, and the helium is there to offset nitrogen narcosis.


E

Most of us will never go deep enough for HPNS to be a factor. I leave some N2 in the mix because by topping with air of nitrox, I can usually get by without needing a booster. At the depths I dive (all my diving has been above 300 ft), I don't see an advantage to the N2 other than cost and the mechanics of getting a set of tanks "full".

 

[espenskogen]

Most of us will never go deep enough for HPNS to be a factor. I leave some N2 in the mix because by topping with air of nitrox, I can usually get by without needing a booster. At the depths I dive (all my diving has been above 300 ft), I don't see an advantage to the N2 other than cost and the mechanics of getting a set of tanks "full".

Which is another good point - A twinset full of 4/96 heliox is gonna cost a bleedin' fortune

E