More than "Advanced", but not really "Technical"

[maniago]

To supplement Andy's great assistance here, I suggest reading Powell's "Deco for Divers".....

Thanks! Just bought it seconds ago. Now what a I need is a massive winter storm, a fire in the fireplace and some hot chocolate to keep me inside to read it! haha

(though massive winter storm would have me out playing with the snowblower, but that's off track for this thread!)

 

[boulderjohn]

How much improvement is 50%, which requires an advanced nitrox certification, over 40%, which does not?

 

[DevonDiver]

How much improvement is 50%, which requires an advanced nitrox certification, over 40%, which does not?

We're talking about gas switching from a bottom-gas to a deco gas. That requires training in gas switching procedures. I, personally, think that makes the issue of 40%, as means to circumvent training, a moot point. The issues and consequences pertaining to flawed gas switching and deco cylinder management are well known - they account for a significant number of fatalities in technical diving.

So... using 40% doesn't require training. But using 40% as a deco/ascent gas does require training. That's where AN or Tec40 come into play.

In respect to the deco efficiency of 40%, the same dive profile:

Runtime is 36 minutes. The ascent profile doesn't make great use of high PPO2 for off-gassing, because stops aren't conducted until a much shallower depth - the efficiency diminishes very quickly after the gas switch. By the time stops are undertaken, the PPO2 has dropped significantly.

That's on VPM+2. On ZHL16-B (GF 20-80) the ascent times for 40% and 50% are near identical. 40% = 33min RT and 50% = 32min RT. 100% gives a 31min RT.

 

[lowviz]

...//... the ascent times for 40% and 50% are near identical. 40% = 33min RT and 50% = 32min RT. 100% gives a 31min RT.

There is the problem with staged deco and a light obligation, there just isn't enough benefit from staging to counter the increased risk of carrying a hot mix underwater.

So now that we've chased each other around the barn quite a few times, I'm still supporting a course such as Tech 40 for backgas deco and gas management and Advanced Nitrox for a cylinder of 100% O2 to be left topside.

 

[tursiops]

There is the problem with staged deco and a light obligation, there just isn't enough benefit from staging to counter the increased risk of carrying a hot mix underwater.

So now that we've chased each other around the barn quite a few times, I'm still supporting a course such as Tech 40 for backgas deco and gas management and Advanced Nitrox for a cylinder of 100% O2 to be left topside.

Another advantage of that strategy is, should you decide to go further, both TDI Deco Procedures and PADI Tec45 are immediately available to you.....if you took the earlier class in tec gear. If you did it in modified rec gear, you may need some remedial material/time/dives.

 

[victorzamora]

Tech40 for backgas deco training and AN just to have a bottle up top makes sense, and I could totally support that.

Two things, though: 1) That is a little on the pricey side for the convenience of having surface-oxygen. It seems like medical/aviator oxygen would be easier/cheaper to get, especially if you don't need scuba tanks filled with it (because you won't be diving with it). 2) It seems like the temptation to dive with your O2 would be very strong, and that could be an issue considering it's beyond the spirit of your training....and if you include O2 in your run schedule it would be violating the letter of your certs as well.

 

[lowviz]

...//... It seems like medical/aviator oxygen would be easier/cheaper to get, especially if you don't need scuba tanks filled with it (because you won't be diving with it). ...//...

DAN's Oxygen Provider would also work. But I've taken AN and it is a worthwhile course -the material should also provide a great deal of reinforcement to Tech 40. As for diving with oxygen, that just requires self discipline on the diver's part. There are a few ways to get around it, I won't go into that...

 

[victorzamora]

DAN's Oxygen Provider would also work. But I've taken AN and it is a worthwhile course -the material should also provide a great deal of reinforcement to Tech 40. As for diving with oxygen, that just requires self discipline on the diver's part. There are a few ways to get around it, I won't go into that...

I agree with all of the above, I just meant it's a bit of a (HUGE) temptation. I don't know if I could help myself, and I really try. Like I said, I agree with your statement....but only in a perfect world where that temptation wouldn't get so many divers.

Also, yes, there are PLENTY of ways around it. I'd be willing to bet most shops that can pump O2 would be willing to fill an AL40 of O2 if it "looked" like it belonged to a Tech diver.

 

[ianr33]

We're talking about gas switching from a bottom-gas to a deco gas. That requires training in gas switching procedures.

Yet another reason not to use 32% in a pony when diving air. You are not trained to switch unless deco trained

 

[Lorenzoid]

I've been wondering, as a practical matter, if you show up at, say, one of the mid-Atlantic dive ops that caters to mainly experienced but not solely tec divers, and you want to go do one of their typical wreck dives in the manner being discussed here, what kind of reaction are you likely to get with the various combinations of certs being discussed here? Are you likely going to have to do some explaining when they see you with (or you ask them to fill) that EAN50 or whatever?