Limitations of TDI helitrox?

[rjack321]

No mention of other gases, but the spirit of the rules were you weren't to push it; just a twinset and a single deco gas.

Yeah sadly TDI has never really recognized that neither the helium nor the depth are the loaded gun, it's the deco gas and carrying two of them and/or a stage + deco gas with minimal training is asking for trouble

 

[Nick_Radov]

Remembering back to my ANDP+Helitrox, it was one deco bottle and limited to less than 35% helium.

As if adding more helium was dangerous or something. Some of this TDI nonsense would be hilarious if it didn't lead to people getting confused on the basics and having to unlearn misinformation later.
(No argument with limiting the number of deco bottles, which is where the real risk of a gas switching error lies.)

 

[Scuba_Sonya]

You’re correct; there’s generally no limit on the number of tanks under your TDI helitrox cert, as long as you stay within the depth and helium limits. Your proposed 4-tank dive seems acceptable, provided you manage your gas switches safely. It’s always good to confirm with your instructor for specific guidelines!

 

[Tracy]

As if adding more helium was dangerous or something. Some of this TDI nonsense would be hilarious if it didn't lead to people getting confused on the basics and having to unlearn misinformation later.
(No argument with limiting the number of deco bottles, which is where the real risk of a gas switching error lies.)

Helitrox cert is limited to 150'
Do you really need more than 35% He for a 150' dive?
Even a working dive in cold water is damned comfortable with 35%.

The course does not limit what deco gas you can use, but it only allows for one deco gas during the dive.

 

[crofrog]

What’s the rational for limiting he %.

 

[Tracy]

What’s the rational for limiting he %.

It is adequate for the depth limitation.
It used to be limited to 20%
When they added the rebreather curriculum, it was increased to 35% to deal with gas density on the loop.

 

[Nick_Radov]

Helitrox cert is limited to 150'
Do you really need more than 35% He for a 150' dive?
Even a working dive in cold water is damned comfortable with 35%.

You don't necessarily need more, but the notion of imposing an arbitrary upper limit on He content is just asinine. Why do that?
To give a practical example, there are circumstances where you can only bring one set of doubles on a boat and want to do two 150ft dives. One option is to mix with extra He, then use the boat's compressor to top with air for the second dive. That way you still have a reasonable mix for the second dive. I've done this a few times, works fine. (I am aware that there are other options like bringing a stage of bottom mix but that doesn't necessarily work any better.)

 

[LFMarm]

I think the limit is there to make sure you are not tempted to go deeper and get in trouble with longer deco.

 

[Nick_Radov]

I think the limit is there to make sure you are not tempted to go deeper and get in trouble with longer deco.

So now the agency which still teaches deep air to 180ft is concerned about divers getting in trouble by using too much helium? I'm not sure I follow the logic on that one, but then those guys were never known for logical thinking.

 

[DiveLikeAMuppet]

So now the agency which still teaches deep air to 180ft is concerned about divers getting in trouble by using too much helium? I'm not sure I follow the logic on that one, but then those guys were never known for logical thinking.

It’s an arbitrary limit on the card to prevent you from getting a richer mix to dive too deep, I think. It’s just ANDP with a bit less narcosis.

TDI has an element of self sufficiency, you have one deco stage, if it’s gone for some reason, you generally plan to clear on your back gas. A bit tricky to clear with a lot of helium in back gas and no teammates around.