DIR Pre-dive Planning?

[limeyx]

That's the NAUI Helitrox gas (26/17).

My team uses 28/15-20 or so down to 120'. Sometimes we just use 28% if we don't have a spent set of 21/35 to top off. Below that we switch to 21/35. I just don't have a lot of use for 30/30.

Stroke! You are going to Die if you don't use the standard gases in exactly the one holy prescribed manner

 

[Soggy]

Stroke! You are going to Die if you don't use the standard gases in exactly the one holy prescribed manner

Probably, but since I trained in NAUIDIR instead of GUEDIR, I have more freedom

 

[rjack321]

I do wonder about how 30/30 came to be a part of the standard gasses when not a single thing about it was similar to all the other standard gasses, or what its origins are. The best answers I've seen so far are, "GI3 refused to dive any trimix with less than 30% He" and "It was thought up in an airport terminal."

I thought 30/30 was ginned up based on max+average depths at Ginnie?? But I could be way off on that. I don't see much use for 30/30 myself, although I do end up with a little bit of a gap between gases. Personally, this is how I'd shake this out, given my filling capabilities.

0' - 100' : Nitrox 32
80 - 110 : Triox 30/30
90 - 120 : Triox 25/25
121 - 150: 21/35
151 - 200: 18/45

 

[Dan Gibson]

I agree. I think the minimum 30% is for dives most will never do. That's why I stated it's likely taken out of context. However, I don't mind the extra helium. I don't find it a bad thing.

btw, is it really 25/25 or is it 24/25?

Quite possibly -- my post was supposed to be a joke (Although I did read that quote somewhere). I am guessing he was meaning very different kind of diving than I am used to

From what I understand, GUE has "clarified" the use of bottom gases to make MOD be a PPO2 of 1.2 (so 21/35 is now 150 and not 190 -- if it ever was 190)
GUE (from my understanding) is saying that this is not a change, but a "clarification" of existing procedures.

Generally, I would try to average the PPo2 to about 1.2 and keep END max 100 feet.
So that means I would use 30/30 down to 110-120 for 1/2 the dive, and do the other 1/2 shallower. Same for 21/35 -- I would go 1/2 the dive at 160, the other half at 140 to average 1.2 @ 150 etc.

My understanding of 30/30 was that it was introduced for day 4 of tech1 (where you were about 100 feet anyway) to show the benefits of Helium without having to go into mandatory deco. It then snuck its way into Triox etc. etc.