Tech through PADI or TDI?

[Dan_P]

I never understood the industry's logic behind the use of lean deco gas earliest in the training progression... I mean, rubbish bouyancy is a problem, full stop, but particularly with a deco obligation, and:

1) it's not about the FO2 but the ppO2. 1,6 is 1,6 regardless if you're on Nx50 at 21m or 100% at 6m.
2) you're not going to tox out for pumping the ppO2 up to 1,7 for ten seconds.
If you did, how do breather divers check that their sensors can go above ppO2 1,6?

In my opinion, the only reason to use a leaner deco gas, is deeper application because of gas logistics. That's a problem that increases with diver progression, not the other way around.
In my opinion, using 50% shallow is a (yet another) good example of a procedural solution to sub-par training paradigms.

 

[stuartv]

1) it's not about the FO2 but the ppO2. 1,6 is 1,6 regardless if you're on Nx50 at 21m or 100% at 6m.

This is just speculation on my part, but I suspect the reason is that if you lose your buoyancy and drop 10', the effect on your ppO2 is much smaller when at 70' on 50% than when at 20' on 100%. Plus, it's harder to control your buoyancy when shallow, so the chance of dropping 10' by accident is greater at 20' than at 70'. Ditto for the chance of corking and totally blowing your deco ceiling.

However, I agree that it seems like the first tech course in any progression that certifies divers for accelerated deco should be ensuring that the divers have solid buoyancy control before they are certified.

 

[RayfromTX]

If I plan 3 dives to 100 within NDL using 32% would the reduction of residual nitrogen from using a hang tank of 70% at the safety stop be significant enough to justify training for it’s use even though I’m not exceeding NDL?

 

[stuartv]

If I plan 3 dives to 100 within NDL using 32% would the reduction of residual nitrogen from using a hang tank of 70% at the safety stop be significant enough to justify training for it’s use even though I’m not exceeding NDL?

Download and install Subsurface (free, with versions for Windows, Mac OS, and Linux). Use the Dive Planner feature to put in the dives and add a gas switch to 70% to see what it does. Only you can decide if the increase in NDL on repetitive dives is worth it.

Subsurface

I am curious, though. If you don't have an Advanced Nitrox certification, where/how are you going to get a tank filled with 70%? I think any dive pro would be committing a fairly serious breach of standards to give you a tank of 70% if you don't have Adv Nitrox (or equivalent) certification.

 

[decompression]

Not to mention 70% is a weird request.

 

[RayfromTX]

My instructor provided a 70% hang tank at the safety stop in this scenario. There is no breach of standards for an instructor to instruct and supervise in the process of training a student. Preparing a student for the next class while teaching the current one is a progressive approach to teaching. 70% at 5 meters is inherently safe. One of the things that we were learning is how the dive profile and accelerated deco gasses can dramatically reduce your nitrogen loading. It was surprising to me just how effective it was based on checking the tissue loading graph on my Perdix.

My question is meant to raise an example of an instance where AN could logically precede DP. There are dive planning strategies that help to minimize residual tissue loading. This is one that would require advanced nitrox training in the absence of a requirement for decompression dive training. I am guessing that there are a number of people here that would consider that silly. Others would not.

Of course there is no scuba cop out there and we survive or not on the judgements we make, not on authorization of an agency. Padi's progression seems logical. I'd actually like to get training in trimix for recreational limits but I'm only aware of one agency that teaches that. Fortunately my instructor can teach that agency among others.

 

[Dan_P]

@stuartv that's exactly what I mean.

I think that shy of gas logistics, the leaner deco mix only brings about an advantage if the student is doing deco diving without 'reasonable' bouyancy control.

What I mean is, why should the entry level tech course be about an entry level rec skill, if not because the training paradigm is off - here, we're seeing an example of adjusting standards (FO2) for a course to pad a problem, instead of acknowledging the problem (lacking bouyancy control even at the higher levels of rec) and taking the consequence of it - adjusting the way earlier courses are taught.

Not relying on individual instructors to go an extra mile, but rather assuring that all instructors/students 'meet the mark'.

Hence, my personal take on it is that agencies and indeed the industry, is at the heart of any relevant large-scale quality assurance issues.
That said, hats off to those instructors who do take it on themselves - particularly if they're assuming personal risk to increase their students' skills and safety - but I think that's not a reasonable offer to make customers/divers OR instructors on the industry's part.

 

[stevensamler]

This is just speculation on my part, but I suspect the reason is that if you lose your buoyancy and drop 10', the effect on your ppO2 is much smaller when at 70' on 50% than when at 20' on 100%. Plus, it's harder to control your buoyancy when shallow, so the chance of dropping 10' by accident is greater at 20' than at 70'. Ditto for the chance of corking and totally blowing your deco ceiling.

However, I agree that it seems like the first tech course in any progression that certifies divers for accelerated deco should be ensuring that the divers have solid buoyancy control before they are certified.

GUE=Bouyancy control,Trim, Balance, and stable platform before moving on.When task loaded all four go to crap now add the dive environment.

 

[Compressor]

While my comments does not add much to the discussion, this thread is a very useful thread for those contemplating going Tech. I'd also like to remind many Tech wanna bees that you can still enjoy diving without going tech. I am one of them. Now the thread can go on.

 

[stuartv]

My instructor provided a 70% hang tank at the safety stop in this scenario. There is no breach of standards for an instructor to instruct and supervise in the process of training a student.

I'm not an instructor (yet), but I still have a suspicion that with SDI, TDI, or PADI, it is a violation of standards to give a diver 70% unless they are either certified for Adv Nitrox (or equivalent) or currently enrolled as a student in an Adv Nitrox class.

There is no actual requirement in the training process to actually breathe a rich gas. If your instructor wants you to see how fast a rich mix cleans you up, by having you switch and watch the graph on your computer, he could do that by having you do the switch on your computer. You would not need to actually breathe the rich mix. And as long as you did it on your last dive of the last day, no problem with getting out with your computer having incorrect tissue loading info.

But like I said, that's just a suspicion as far as standards go. I'm curious for an instructor to weigh in on it.