Nitrox - Trimix

[Vtach]

So how many folks on the board are diving blended gasses like Nitrox or Trimix?

Benefits and drawbacks??

Once again, more spark for the advanced discussions forum...

[Chris H]

I love advanced discussions.

Helium=

Air= ???

Any questions?

Oh yeah, if you don't agree you are a stroke!! ;D ;D >

[matt t.]

Last year I took the adv nitrox/deco class, and this spring went on to the tri-mix classes. I never really noticed any impairment during deeper dives (100-160 ft), at least not the pounding, tunnel vision type narcosis you hear about (though I did always feel relaxed, and like things were flowing along pretty smoothly. Slight buzz?) . However I DID notice how clear I was on the deep dives (120-200ft, END of about 65 ft.) during the tri-mix classes. My primary light went out at about 180 as we were descending through a black layer, and it was no big deal to shut it down, clip it off, and go to my back up light. I'm waiting to do some of the same dives on helium that I did last year on air, to see what I may have missed. No doubt about it, the helium does work. The biggest down side I see is the costs associated with nitrox and helium. Doing some of the deeper dives it can cost almost as much for fills as the charter costs. Is it safer? Undoubtedly. Only the individual diver can decide where their depth/narcosis comfort level is, and then determine if the fill costs are worth it to them.

[dofundive]

Here are several other factors to consider when making the Nitrox/Trimix decision:

Visibility
Water Temperature
If tasks need to be completed
How much of the dive you want to remember later...

(Just to help fuel the discussion...)

[Vtach]

Another thing to realize that might be missed with trimix is the reduced density of gas.  Somewhere around 6 ATA (165 ffw), the density of air is the limiting factor in your respiratory systems ability to exchange gas in and out.  Air becomes so dense at these depths that your anatomy is physically unable to exchange enough gas beyond the "relaxed" breathing state.  Combine this with a regulator that is reaching its physical limit to providing a dense gas on demand and you have a prescription for CO2 retention.  Add exertion to the equation and you've just filled that prescription. 

CO2 is 25 times more lipid soluble than nitrogen.  There is a strong correlation between lipid solubility and the narcotic potency of gas.  So you begin to increase your arterial PCO2 due to the inability to efficiently exchange oxygen and CO2.  Your normal PCO2 is 35-45 mmHg, at 70-75 mmHg PCO2 you have reduced awareness.  At 100-120 mmHg you become unresponsive.

So words to the wise, deep air can bite you in the ass hard.  You might get away with it when the dive is easy, but combine nitrogen narcosis, anxiety and a bit of physical work making an already bad situation much, much worse.  Can you say...Big O' Dang O' Ni-Night... :

Helium on the other hand, while being expensive, has a much lower density and breathing resistance than air along with a low narcotic potential.  This helps to reduce the physical limitations of regulators, upper and lower airways while being used at high ATA's.  Not to say that you can kill yourself on Trimix but it at least gives you the physical ability to handle a situation where it becomes necessary to breathe enough to fully inspire the necessary PO2 and eliminate the PCO2. The reasonable equivalent narcotic depths don't hurt either.  It's nice to remember the dive.

For me, depths over 100 feet, I prefer Trimix. 
Anything less and Nitrox or Highmix is fine ;D

[dofundive]

Another concern with the use of trimix is the need for a separate suit inflation gas and usually inflation system that goes along with that. Increased drag can result...

[Chris H]

You've got to be kidding....

It is indeed necessary to use a gas than the Trimix for inflation, but are you saying that we should be using air on deep dives because the 6cuft Argon bottle most of us use causes too much drag to be worth it?

I don't ever consider my Argon rig a "concern" unless it's empty and I want to dive.

Even if I'm using the 13cuft Argon bottle I'll take the extra drag and a clear head any day of the week.

[matt t.]

Diving with the big steel tanks and dragging along 2 deco bottles, I guess I wouldn't consider the argon bottle to be much more of a problem. You are correct though, in that it is another set of things to consider (cost of buying and maintaining argon fills, argon reg, argon bottle mounts). IMO the extra cost and  trouble of the argon rig outweigh NOT using the tri-mix.

[voodooconstant]

One doesn't have to use argon, right?  Air would be a fine substitute.

[matt t.]

No one doesn't "have" to use argon. Again cost and availability may be a factor to some. Here in Milwaukee it costs around $6-$7 for an air fill. Argon costs $1 per cu ft. If I'm filling both of my 6 cu ft argon bottles I pay $12. In this case argon and air cost roughly the same and it's available. YMMV. There's also the whole physiological reason why argon is supposed to be better than air. There are many who can better explain that better than I can  .