Slow tissue on gas from stops

[Dan_P]

I see. Personally I think retiring RD is long overdue for similar reasons. Where we strongly agree is that students need to have a keen understanding of deco theory. Where we disagree is in the proposition that RD is the mechanism by which to teach that.

IN addition, teaching RD suggests to the student that they should (or could) USE it, which is highly inadvisable in any context. I personally believe that we should teach students skills in a course that they can apply after that course, not skills that they should avoid applying because they constitute a risk to their safety.

This is why I asked you if you would step back from RD. It is (a) a poor practice by any modern measure (b) inefficient at best and dangerous at worst if applied and (c) far FAR from being a best practice, which we (I believe) would agree should be the focus of training.

So why on earth should we be holding on to that?

R..

I agree with you that teaching students deco theory is very important. I agree that's every bit as well accomplished with algorithm or RD - where I personally think RD excels in the training, is in-water in relation to development of situational awareness.

That aside, and before we get to your actual question, what I'd like to share a thought on first, is an apparent premise to your conclusion, namely that [RD] "... is highly inadvisable in any context" and "constitutes a risk to their [the students'] safety".

I'd like to show the following, to illustrate the contrast to those quotes above:

My opinion? No its not "irresponsible". You have your reasons for using it. Fine. I also agree that we are not in a position to accurately define the absolute reduction in risk that would accrue from (for example) a GF approach with less emphasis on deep stops vs RD. It may be small, or it may be bigger than you think. But that too misses the point. Setting unresolvable arguments about the magnitude of differences in risk aside, if divers seek the "truth in the universe" about the most efficient approach to decompression (least risk in the same decompression time), all the current evidence suggests that approaches which emphasise deep stops are not it. I don't think you would disagree with that, and there is not much point in arguing about it ad infinitum.

If an individual diver (such as you Dan) has a reason to use RD based on its utility in specific situations I would not consider that irresponsible, and I could not put my hand on my heart and give you an evidence-based reason to call it unsafe (we have no data on DCS rates). But I would definitely be comfortable (based on existing evidence) to say that you are sacrificing decompression efficiency and therefore some degree of safety for whatever perceived utility exists for using it.

I feel it's prudent to mention that I'm not trying to conjure an equation between "proven safe" and "not proven unsafe", but I do think it's important to note how stark the contrast is between the quotes above about RD1.0 and the premises you've mentioned in your question.

These are science-based statements. For me to read them and decide to myself, "okay, I'll sacrifice some decompression efficiency for practical reasons", is not denouncing science. It's not religion, or kool-aid, or irresponsible. It's not living in a magic world where science doesn't matter - it's simply me making a choice that I want the practical utility I see enough that I can accept some reduction in deco efficiency.

So, is the next diver willing to make that same choice, is the question.
There is definitely a choice to be made there, and anyone making it should be made aware of that choice as well as given a fair base of knowledge so they can make the choice in an informed fashion, whether using RD or an algorithm.

To answer your question: "So why on earth should we be holding on to that [RD]?"

I personally find that its application offers me a very practical way to plan and execute dives, I feel that it's a very strong educational tool and I find that it's helpful during my progression.

That's all there's to it.

 

[Dan_P]

What I have an issue with is the UTD-RD(tm) version ignoring respected/tested algorithms and replacing computer-generated curves with whatever AG mandates. Having talked to UTD-RD(tm) trained folks, there's a right way of doing it and a wrong way. Having talked to GUE-RD trained folks, there's a generic way they're taught as "standard" but that's a baseline for divers to then adapt to their own preferences and needs.

Let me say I understand the sentiment you've posted.

I'll quote something from UTDs Student and Diver Procedures, page 194.:

"...we encourage you to start by using the set of Ratio Deco rules and strategy as outlined below, allowing you to both gain the experience and confidence in your deco schedules prior to deviating and developing your own set of rules or tweaks".

I think it's important for the position you've formed to consider that any impression of UTD having a doctrinary position against personal adaptation to RD, is not correct.

While RD is certainly not perfect, one thing that I personally appreciate, is that the organization puts up a solution model that divers can choose unless they prefer something else.

That said, I don't know how many other organizations actually take responsibility for showing a path, rather than print in their books the expectable "well, some divers like...and others prefer..., your instructor will show you how to....".
UTD has RD.
UTD instructors, students and divers can use that, or they can use something else if they prefer something else.

 

[boulderjohn]

"...we encourage you to start by using the set of Ratio Deco rules and strategy as outlined below, allowing you to both gain the experience and confidence in your deco schedules prior to deviating and developing your own set of rules or tweaks".

We were told the same thing when I was there, but to be more specific, it meant we could tweak Ratio Deco to match our perceived needs. It did not mean we could use dive computers or a desktop software program.

 

[Dan_P]

I'll be entirely clear:

At UTD, one is not bound to use RD.
Nowhere do the Standards and Procedures state that courses must be carried out using RD.

 

[Jack Hammer]

@Dan_P ,

Dan, I think may have figured out the difference in numbers. IIRC, we started our avg depth once we reached the bottom but time get there counted toward the total bottom time for the dive. That may account for the difference in calculated deco and average depth.

- Jeff

 

[Dan_P]

@Jack Hammer It accounts for a difference in avg. bottom times for sure - but it doesn't explain the extra time because the increments are at 48m and 51m and "by the book", you always round up (towards the surface, i.e. down to the smaller number).
Whether the avg. depth is (just under) 48m or 50m makes no difference.

 

[Patoux01]

but it doesn't explain the extra time because the increments are at 48m and 51m and "by the book", you always round up (towards the surface, i.e. down to the smaller number).
Whether the avg. depth is (just under) 48m or 50m makes no difference.

I sure hope that's not what the book says

 

[tursiops]

I sure hope that's not what the book says

Would it matter? He would still defend it.

 

[Dan_P]

I added the paranthesis to clarify if I meant a direction or a number

 

[Patoux01]

So let me get this straight, as I really hope it is just that you (or me) have (has) some kind of language issue.

You have increments at 48m and 51m. You are saying that if my average depth is 50m, then I use the values given from the 48m increment?