Equipment for Adv Nitrox and Deco Proc

[Meng_Tze]

I don't think agencies can or want to write this up as a rule. But it seems more and more divers want them to or are at least looking for some guidance. You are right it is about logic, but also emotions and risk assessment. Thinking divers who keep a cool head will make the right decision. Even if this decision may seem harsh to others.

 

[rongoodman]

On paper we all can plan things, in reality at that crucial moment when it can quickly become a matter of living or suffering severe results, you decide and move on with your decision.

But the author doesn't even attempt to illustrate how one might plan this out. Reasonable people might disagree as to what the plan should look like, or where in the educational sequence it should be taught, but he just throws up his hands and says "it's hard to say". Thinking through Minimum Gas requirements isn't rocket science. I think the underlying assumption, at least when those texts were written, was that tech diving is essentially solo diving. It will be interesting to see if this mindset is carried forth in the upcoming revisions.

 

[ucfdiver]

But the author doesn't even attempt to illustrate how one might plan this out. Reasonable people might disagree as to what the plan should look like, or where in the educational sequence it should be taught, but he just throws up his hands and says "it's hard to say". Thinking through Minimum Gas requirements isn't rocket science.

This book is made to compliment a course being taught by an instructor from what I understand, right? If so, they might leave it at that to allow the instructor to further explain it. If you're wreck diving, you need enough gas to get you and your buddy out and back to the boat, if you're cave diving, you need enough gas to get you and your buddy out of a cave, and if you're reef diving, just enough to let you and your buddy surface might be enough.

If I were to write it, I would say "You need enough gas to get you and your buddy safely back to a safe destination.", but I don't think that helps a whole lot more than what the author has already stated.

 

[Meng_Tze]

But the author doesn't even attempt to illustrate how one might plan this out. Reasonable people might disagree as to what the plan should look like, or where in the educational sequence it should be taught, but he just throws up his hands and says "it's hard to say". Thinking through Minimum Gas requirements isn't rocket science. I think the underlying assumption, at least when those texts were written, was that tech diving is essentially solo diving. It will be interesting to see if this mindset is carried forth in the upcoming revisions.

You are talking about the adv. Trimix manual right? I think it is fair to assume that when you get to that point, basics like gas planning should be known. My TDI adv. Trimix manual does cover gas planning however it is high level only for the reason above. It is the 2004 v 1.5.

 

[wedivebc]

Even the Extended Range/Trimix text has no mention of Rock Bottom/Minimum gas in the dive planning section and says that deciding if you have enough gas to rescue a buddy who is out of gas is "one HARD question to answer

Rock bottom is a concept that belongs to single tank diving not doubles which are used in extended range diving. Gas management is very much a part of TDIs extended range and trimix course but goes well beyond "rock bottom"

 

[TSandM]

Dave, excuse my ignorance (I'm not open water tech trained), but don't you still have to figure some kind of rock bottom type reserve for extended range diving? If you use your backgas as your bottom mix, don't you still have to make sure you have enough to get you and a buddy up to your first gas switch?

 

[wedivebc]

Dave, excuse my ignorance (I'm not open water tech trained), but don't you still have to figure some kind of rock bottom type reserve for extended range diving? If you use your backgas as your bottom mix, don't you still have to make sure you have enough to get you and a buddy up to your first gas switch?

Yes but we use gas volume matching just like you do in caves. Rock bottom allows you to use gas beyond 1/3rds. That is not appropriate for tech diving.

 

[TSandM]

Yes but we use gas volume matching just like you do in caves. Rock bottom allows you to use gas beyond 1/3rds. That is not appropriate for tech diving.

I'm confused. The idea of Rock Bottom ONLY refers to the gas reserves that have to be maintained to get you and a buddy to the surface (for NDL diving) or to the next gas switch (for staged decompression diving). The management of the usable gas is determined by the type and conditions of the proposed dive.

Doesn't every agency teach you to maintain enough gas to get you and one other diver to the gas switch?

 

[wedivebc]

I'm confused. The idea of Rock Bottom ONLY refers to the gas reserves that have to be maintained to get you and a buddy to the surface (for NDL diving) or to the next gas switch (for staged decompression diving). The management of the usable gas is determined by the type and conditions of the proposed dive.

Doesn't every agency teach you to maintain enough gas to get you and one other diver to the gas switch?

Yes it's rule of thirds. Gas matching assures you turn the dive when the 1st divers consumes an equivalent volume to 1/3 of the diver with the smallest gas supply. Rock bottom is not used in any technical diving applications that I am aware of.
I should also mention that for open water type dives gas management is planned before the dive, not on the fly during the dive.
Having said all that is anyone aware of any case of a doubles divers being rendered completely out of gas?

 

[ucfdiver]

Having said all that is anyone aware of any case of a doubles divers being rendered completely out of gas?

Surprisingly, no, I've yet to hear of that, but I find it hard to imagine that it doens't happen, there seem to be a LOT of people diving doubles that can't reach their valves.

Most all doubles OOA situations I read about are false alarms from the manifold being closed.