Question Different denominations for gas blends ?

[yodawarrior92]

Hi there, I recently got certified for Nitrox, and I have a few questions about gas blends :
- During my course, I was taught that Nitrox was a gas blend with a %O2 higher than 21% (%O2 in the air)
- From what I've read online and here on SB, I learned that other gas blends exist, e.g Trimix, which contains Helium.
AFAIK, Trimix can be either normoxic (min 18% O2) or hypoxic (under 18% O2).
Then here is the question : I've seen people using "Helitrox" gas blends and "Triox" blends, what are these mixes and what is the fundamental difference between these and Trimix ?

 

[huwporter]

'Air' - the gas mix the atmosphere contains, containing approximately 20.9% oxygen, 78% nitrogen, 0.9% argon plus a few trace gasses.

'Nitrox' - any mix of oxygen and nitrogen. In diving, almost always refers to a mix with a higher percentage of oxygen than air ("hyperoxic").

'Trimix' - any mix of oxygen, nitrogen and helium. In diving, can be normoxic (around the same percentage of oxygen as air), hypoxic (less oxygen than air, in diving this generally means less than about 18% oxygen) or hyperoxic (more oxygen than air).

'Heliox' - any mix of oxygen and helium. Not common in sport diving.

'Heliair' - what you get if you put some helium in a tank and then top up with air. Always hypoxic due to the way it is made. Sometimes referred to as 'poor mans trimix'.

'Triox' - an agency marketing name for hyperoxic trimix.

'Helitrox' - an agency marketing name for normoxic or hyperoxic trimix with a moderate to low percentage of helium.

The top four have pretty standard definitions, the following three are just (more or less common) useage names for types of trimix. I'd guess most people mostly stick to the top three when describing the mixes in their tanks.

(For completeness, in practice, all mixes also contain trace gases, particularly argon, as it is too difficult to remove it.)

 

[Wibble]

Worth mentioning "Standard Mixes". These are commonly available and tend to be relatively easy to mix with rules of thumb.

Nitrox 32% (MOD** 32m) is mixed using 30 bar of 100% oxygen and topping off with air to 230 bar.

Trimix 21/35 (MOD 57m) containing 21% oxygen, 35% helium is made using nitrox 32% and adding helium. (although generally mixed from scratch!)

Trimix 18/45 (MOD 67m) containing 18% oxygen, 45% helium is mixed by adding more helium to 21/35.


If you use MultiDeco, there's some mixing tools available which tell you what to add for the mix for any target mixture. Lots of other gas mixing applications available.


** MOD = Maximum Operating Depth for a maximum oxygen pressure of 1.4 bar

 

[yodawarrior92]

'Air' - the gas mix the atmosphere contains, containing approximately 20.9% oxygen, 78% nitrogen, 0.9% argon plus a few trace gasses.

'Nitrox' - any mix of oxygen and nitrogen. In diving, almost always refers to a mix with a higher percentage of oxygen than air ("hyperoxic").

'Trimix' - any mix of oxygen, nitrogen and helium. Can be normoxic (around the same percentage of oxygen as air), hypoxic (less oxygen than air, in diving this generally means less than about 18% oxygen) or hyperoxic (more oxygen than air).

'Heliox' - any mix of oxygen and helium. Not common in sport diving.

'Heliair' - what you get if you put some helium in a tank and then top up with air. Always hypoxic due to the way it is made. Sometimes referred to as 'poor mans trimix'.

'Triox' - an agency marketing name for hyperoxic trimix.

'Helitrox' - an agency marketing name for normoxic or hyperoxic trimix with a moderate to low percentage of helium.

The top four have pretty standard definitions, the following three are just (more or less common) useage names for types of trimix. I'd guess most people stick to the top three when describing the mixes in their tanks.
In practice, all mixes contain trace gases, particularly argon, as it is too difficult to remove it.

Thank you very much ! You clarified it

 

[100days-a-year]

Denominations as in religions, because the dogma sure seems similar at times.

 

[Manatee Diver]

(although generally mixed from scratch!)

I kind of question anyone that isn't using mixing sticks. Helium is expensive you would think that they want to get every bit of helium that the can out of a supply bottle.

 

[Manatee Diver]

@mdwalter Even using a booster you can only get a supply bottle to so low around 300psi. While with a mixing stick you can run a supply bottle almost empty.

You can see it at higher volume tech diving shop like we have in cave country. Supply bottles are used boosted to fill deco tanks until they reach whatever pressure is the limit for their setup. it is then wheeled over to mix nitrox using a mixing stick until it reaches the cut off pressure for the mixing stick's reg which is often a couple of dozen psi. And with the price of supply bottles these days, that could be a substantial savings.

 

[Tracy]

I kind of question anyone that isn't using mixing sticks. Helium is expensive you would think that they want to get every bit of helium that the can out of a supply bottle.

Because that isn't the way we have always done it.

You would be amazed how many people I talk to that blend nitrox everyday through their compressor, but hesitate to pump an inert gas into it.

 

[Manatee Diver]

Because that isn't the way we have always done it.

You would be amazed how many people I talk to that blend nitrox everyday through their compressor, but hesitate to pump an inert gas into it.

We also used to use calculators now there are apps.

I guess I am so used to cave country home of 3,000psi oxygen fills and banked 10/70ish nearly everywhere (which you can use to blend most standard mixes). I know others have argued "But we don't use standard mixes" I do wonder how much is the difference from PP blending both in lost helium and labor? Could volume even improve enough to maybe get prices to parity?

 

[Tracy]

We also used to use calculators now there are apps.

I guess I am so used to cave country home of 3,000psi oxygen fills and banked 10/70ish nearly everywhere (which you can use to blend most standard mixes). I know others have argued "But we don't use standard mixes" I do wonder how much is the difference from PP blending both in lost helium and labor? Could volume even improve enough to maybe get prices to parity?

Yes, volume can make up for waste, but outside of cave country, who does that volume?
I have no proof, but I would guess I sell more helium that anybody else in my area, and even that is maybe 4-5 bottles per week for three months. Not exactly high volume.
I want every one of those bottles going back empty.