Theoretical Gas Blends for Rec Diving

[Nomad]

Why doesn't anyone use Trimix at recreational depths?

It seems to me that a Trimix blend of 21-39-39 would have all the benefits of Nitrox, without the depth limitations. Is there something else here that I am not seeing?

Please respond only if you KNOW a reason. I can speculate like the best of them, and I am not interested in opinions about this, only science.

Thanks...

 

[Tamas]

Biggest reason is cost! Simple as that.

 

[NJScubaDoc]

One main reason is cost, second reason is the fact that helium is an excellent conductor of heat, so unless your toying with this stuff down south, up north you need a seperate gas for drysuit inflation (usually argon) after a while your spending mucho $$$ on gas.

I know you wanted scientific answers, figured I'd share what I knew about the economics of it.

 

[spectrum]

Why doesn't anyone use Trimix at recreational depths?

It seems to me that a Trimix blend of 21-39-39 would have all the benefits of Nitrox, without the depth limitations. Is there something else here that I am not seeing?

Please respond only if you KNOW a reason. I can speculate like the best of them, and I am not interested in opinions about this, only science.

Thanks...

I'm not mixed gas qualified but I'll take a stab at...

1. Cost
2. Helium promotes heat loss
3. General availability and turn around time for fills.
4. Exceeding the depth limitiation of appropriate nitrox blends is already taking you beyond recreational depths

I don't consider the above to be opinions, just practical issues. I belive you could dive that blend. If I'm wrong we'll both learn something. :10:

Pete

 

[Nomad]

... 4. Exceeding the depth limitiation of appropriate nitrox blends is already taking you beyond recreational depths

Nitrox should only be used above about 100 feet. Recreational diving includes dives up to 130 or 140 feet (depending on who you ask).

 

[Kim]

Why doesn't anyone use Trimix at recreational depths?

I believe that people are starting to do that. GUE has it's RecTriox class for instance. While there certainly doesn't appear to be anything wrong with the science of it, the cost will probably be the limiting factor. I suppose if you have the money and want to dive in the 32-40 meter range it would be a better mix than Nitrox. Shallower than that I think it would be hard to justify.

 

[Diesel298]

also
He has a whole different set of properties.
it absorbes into your system faster, and off gases faster...
you do deeper stope on He. mixtures...
basically its a whole new set of physics when goin to He.

plus all of the other reasond given are valid points

 

[MikeFerrara]

Who says that divers don't use trimix at recreational depths? I don't know any one who would mix any up for a 30 ft dive but absolutely for depths beyond 100 ft and some past 80 ft or so.

GUE has a rec triox class, IANTD has a recreational trimix and an advanced recreational trimix class and I forget what the NAUI version is called (helitrox or something) but they have one to. GUE's gas of choice for 100 - 120 is 30/30 I think, the IANTD courses are set up for an END of no more than 80 ft, if I recall, and I don't know about NAUI.

There isn't any reason to knock the O2 down as low as 21% unless you're going deeper. The recreational mixes are usually hyperoxic (like nitrox) with some helium to replace some of the N2. There's the science of it. LOL

Visit the web sites of the agencies I mentioned for more info.

 

[HowardE]

Nitrox should only be used above about 100 feet. Recreational diving includes dives up to 130 or 140 feet (depending on who you ask).

This statement is not true. Nitrox can be used at deeper depths. The MOD for 30% is 121 feet at 1.4 PPO2.

 

[Diesel298]

This statement is not true. Nitrox can be used at deeper depths. The MOD for 30% is 121 feet at 1.4 PPO2.

i think hes talkin about practical limits where its advantages are best bennifited from