Question re easy to use Trimix

[Hatul]

The present Nitrox decreases nitrogen concentration at the expense in increasing oxygen concentration, with oxygen toxicity problems at depth.

So, I was wondering if instead of Nitrox we use a Trimix with the same O2 concentration as air (21%), and the nitrogen concentration of say Nitrox36 or 64% and the rest helium 15%. This would behave as air with respect to oxygen toxicity and as Nitrox with respect to nitrogen narcosis and may make a better substitute for air for the recreational diver than Nitrox.

Can someone with Trimix knowledge comment on this idea. Would this gas have similar decompression properties as Nitrox so a Nitrox computer could be used? Cost? Could it be used by someone without Trimix training, and if not why not?

Adam

 

[tbone1004]

this is normoxic trimix, and is used and taught at the basic nitrox level. you can't use a normal nitrox computer because it would get really upset once your PO2's got up. It still monitors your O2 tox risk.
The math for trimix is identical to that of nitrox as far as EAD's and MOD's go.
As far as cost, Trimix is based on mainly on the helium cost, which is quite expensive... Trimix courses also tend to be expensive because the charter costs to get out deep enough, especially on the east coast are rather expensive and the gas prices are rather high as well.

Big gripe with this training, and a large reason why a bunch of tech divers have their gas blender cards but not trimix cards. We'll mix our own in the garage instead of paying 2k-3k for a class that has no diving application whatsoever. Your deco obligations don't change, just adjusted depths. Your diving skill doesn't change, weighting MAY change slightly depending on helium content, but woopty doo. Most of us are diving heavy just from the gear alone. You do a dive to realize what it's like to be narc'd, then do the same dive with trimix to notice the difference, but most of us have been narc'd before.

so, yes you "should" have training, at least in decompression before you do that, and what you described is exactly "trimix 1" or "normoxic trimix" diving

 

[Lobzilla]

deleted ... question was answered while posting.

 

[MXGratefulDiver]

As far as cost, Trimix is based on mainly on the helium cost, which is quite expensive... Trimix courses also tend to be expensive because the charter costs to get out deep enough, especially on the east coast are rather expensive and the gas prices are rather high as well.

FWIW - I've done 200+ foot dives from shore where I live ... and there's places here you can get to from shore that go way deeper than I would ever want to go.

From a practical point of view ...

- 15% trimix won't do a whole lot to reduce your narcosis level ... it needs to be up in the 25+% level in order to make a noticeable difference.

- If you balk at paying extra for nitrox, you ain't gonna want to see what a trimix fill costs ... for a single tank of something like 25/25, you're probably going to be looking at $30-$50, depending on where you get it filled and the size of your cylinder.

- Helium goes into and comes out of your body much more easily than nitrogen. Therefore it's much easier to bend yourself on helium. If you're still working on buoyancy issues, breathing helium isn't a good idea. In fact, your buoyancy control should be pretty strong before you even consider it.

It does, however, put a whole new dimension of fun into testing your regs before the dive ...

... Bob (Grateful Diver)

 

[Crowley]

...not to mention it would be super-smegging expensive...

And divers don't like to spend money on stuff they can get for free...



C.

 

[ianr33]

this is normoxic trimix, and is used and taught at the basic nitrox level.

Huh? Guess they left trimix out of my nitrox course.

 

[Michael Kazma]

would just like to add on this.....The reason for adding higher O2% to nitrox is to increase NDL. This is done by decreasing the nitrogen (which causes the bends etc.) and replacing it with O2 which is metabolized (does not cause the bends etc.). However, when nitrogen is replaced with helium the helium has similar consequences as nitrogen (i.e. it causes the bends). The purpose of trimix is to keep the O2 at a level safe for the depth and lower the N2% to lower the effects of narcosis.

 

[tbone1004]

sorry, missworded. Was running back and forth from a loom that wouldn't stay running. Stupid yarn..
same basic principle as basic nitrox. I.e. no real new concepts or formulae to deal with. All of our decompression and NDL tables/models are based off of your nitrox percentage, so your decompression times don't care what the other gasses in your mix are. Only your oxtox percentages change, but that is still no different than calculating your best mix for nitrox.
Deal with O2 first, keep PO2 at or below 1.4
Deal with N2 second, keep PN2 at or below 3.2, or whatever other number you want
Finish mix with helium, but that doesn't change any of the basic formulae taught in your beginning nitrox course

 

[ianr33]

All of our decompression and NDL tables/models are based off of your nitrox percentage, so your decompression times don't care what the other gasses in your mix are. Only your oxtox percentages change, but that is still no different than calculating your best mix for nitrox.

That's not true.

NDL times and required deco stops will be different with helium in the mix. Larger the % of helium the larger the difference

 

[tbone1004]

how so? we were always taught to do our EAD's for decompression based off of the equivalent partial pressure of nitrogen.
If I have 60% nitrogen in the mix it doesn't matter if it's 40% oxygen or 15/25 at 110ft. It's still an EAD of 76fsw, which goes back to the tables.
Implying you're using Navy deco tables with air rates instead of premade deco tables.
The concept is still there though, that the helium isn't what effects your mix, it's the nitrogen percentages.