Triox, Trimix and Heliox question.

[ScoobaChef]

I'm currently reading DIR: Fundamentals of better diving and just wanted to get clarification on the definitions of the 3 gas mixes. (page 132 if anyone is wondering).

1. Triox - A helium based gas with 21% or greater oxygen content.
2. Trimix - Any combination of helium, oxygen and nitrogen
3. Heliox - Any combination of helium and oxygen.

-Is triox a version of heliox with a minimum o2 content restriction, or is there another inert gas added?

I'd appreciate any practical examples of the different uses of the terms.

 

[andrewy]

from wikipedia

Conventionally, the mix is named by its oxygen percentage, helium percentage and optionally the balance percentage, nitrogen. For example, a mix named "trimix 10/70" or trimix 10/70/20, consisting of 10% oxygen, 70% helium, 20% nitrogen is suitable for a 100-metre (330 ft) dive.

The ratio of gases in a particular mix is chosen to give a safe maximum operating depth and comfortable equivalent narcotic depth for the planned dive. Safe limits for mix of gases in trimix are generally accepted to be a maximum partial pressure of oxygen (ppO₂—see Dalton's law) of 1.0 to 1.6 bar and maximum equivalent narcotic depth of 30 to 50 m (100 to 160 ft). At 100 m (330 ft), "12/52" has a PPO₂ of 1.3 bar and an equivalent narcotic depth of 43 m (141 ft).

In open-circuit scuba, two classes of trimix are commonly used: normoxic trimix—with a minimum PO2 at the surface of 0.18 and hypoxic trimix—with a PO2 less than 0.18 at the surface.^[12] A normoxic mix such as "19/30" is used in the 30 to 60 m (100 to 200 ft) depth range; a hypoxic mix such as "10/50" is used for deeper diving, as a bottom gas only, and cannot safely be breathed at shallow depths where the ppO₂ is less than 0.18 bar.

In fully closed circuit rebreathers that use trimix diluents, the mix can be hyperoxic in shallow water because the rebreather automatically adds oxygen to maintain a specific ppO₂.^[13] Less commonly, hyperoxic trimix is sometimes used on open circuit scuba. Hyperoxic trimix is sometimes referred to as Helitrox or TriOx.

See breathing gas for more information on the composition and choice of gas blends.

 

[waterpirate]

The lines have been blured and lots of labels and names added. The post above says all that needs to be said, any other names or labels are just variations of the big 2.
Eric

 

[ScoobaChef]

The lines have been blured and lots of labels and names added. The post above says all that needs to be said, any other names or labels are just variations of the big 2.
Eric

Works for me. Thanks.

 

[waterpirate]

One final thought. The term triox, and heliox have been accepted to mean in effect " helium light ". It is commonly applied to mixes with 20% or less helium content for the purpose of adding sobriety to dives in the 100 to 150 fsw range without adding any more risk other than a deco obligation. For all intent a 20% mix could be dove on nitrox tables with no real advers effects.
Eric

 

[SeaCobra]

Heliox is just two gasses - helium and oxygen. Helitrox, is slightly different as it is oxygen, usually 21% to 26%, a light helium load such as 13% to 17% and the balance nitrogen. A nice gas in the 150fsw range.

 

[Dave1981]

Triox, or helitrox would be a gas like 25/25 or 30/30 to knock the END down a bit on relatively shallow dives.

Trimix has O2/nitrogen and helium in it, so the above is trimix, however I'd say that when people refer to trimix they usually mean hypoxic so less than 21% oxygen. Like say 18/45.

Heliox has no nitrogen in it at all so is not trimix, you could have say 8% O2, 92% Helium.

 

[ScoobaChef]

Ok so to sum it all up in "descending" order

-triox and helitrox refer to a hyperoxic trimix blend which gives you a shallower END than nitrox with an identical O2 content. (Though the MOD stays the same)

-trimix, while somewhat a catchall term, typically refers to normoxic or hypoxic blends of O2, helium and nitrogen used for deeper diving.

-heliox is O2 and helium only, mainly reserved for very deep dives to eliminate nitrogen narcosis.

Have I got it right?

Just out of curiosity, because I know it would be a huge waste of money and helium, but is there anybody out there who uses hyperoxic heliox for dives above 150 fsw? If so, why?

 

[PfcAJ]

I wouldn't get too caught up in the specifics. I never call anything triox or helitrox (and I don't really know anyone who does, either), regardless of o2 content. Its all just simply trimix to me

 

[Divin'Papaw]

Just out of curiosity, because I know it would be a huge waste of money and helium, but is there anybody out there who uses hyperoxic heliox for dives above 150 fsw? If so, why?

Yes. Same reason for trimix at deeper depths ... to control narcosis. GUE standard gas for 110-150' is 21/35.