Nitrox tables going too?

[Charlie99]

a. What does Pressure Group "P" mean? (Or obviously, any other letter). When I've had to teach "The Tables" (PADI's RDP) I ask the question and to date, no student has provided me with an answer.

I'll wager that there is no longer anybody at PADI that could give you the answer to that question.

According to my calculations and reverse engineering of the PADI RDP, PG P corresponds to dissolved ppN2 in the 60 minute compartment of 42.12fsw (absolute), or 65% of the way from sea level saturation of 24.81fsw and the 51.44fsw DSAT M value for the 60 minute compartment. Pressure groups C to Z are 25% to 95% of the M value, in steps of 3%.

I figured this out because I wanted to understand what my Oceanic computer was telling me, and also wanted to see how it related to the PADI RDP since both are based upon the DSAT deco model.

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Along the lines of "teaching tables isn't the same as teaching deco theory", I find that another useful question is "Why do you only reach PG R when you hit the NDL limit at 80' ? " This leads into the concept of "controlling compartments" and how they vary with depth.

 

[Peter Guy]

Charlie, Thank you! I'm going to have to think and play with all this.

 

[explorer08]

b. Since teaching time is a precious and limited resource (in most teaching situations -- limited both from the standpoint of "How much time do I have" and "How much time will the student be paying attention") why waste it on something as frivolous as tables at the basic level? For the PADI OW Student, isn't the information contained in Knowledge Review 1, Question 5 much more important to actually, fully, understand in all of its ramifications? And for the Nitrox student, isn't MOD and testing much more important? Not to mention, of course, for ALL student divers, the notion that THEY WILL PROBABLY BE GAS LIMITED rather than NDL limited -- isn't "air supply management" a topic that needs the limited time for discussion?

I absolutely agree with you. It's not only nonsense to continue teaching tables while PDC's are in use for several decades. It is also nonsense to go deep into decompression theory with OW students. Because most of decompression theory is based on assumptions and theories every discussion about decompression is an academic one and that is far beyond the needs of OW students. And for everybody who is really interested in decompression theory I always recommend "Deco for Divers" by Mark Powell.

 

[Kingpatzer]

They are not difficult or time consuming to learn, having them in a class does not extend the class by large amounts of time.

What is "not difficult" for one person is often quite difficult for another. And regardless of how difficult they are, it does take time to teach them. What should I drop or shorten from my class in order to include them? Should I spend less time on deco theory? Perhaps I should skip teaching about how to ensure a tank is properly inspected and filled? Maybe I can just gloss over proper dive planning and air management to make room for tables, since they're so critical?

*oops, I see Peter beat me too it*

 

[beertiki]

In my Nitrox/Decompression Theory course, we learned at least seven sets of tables. Only part of one class was spent on computers. Now 99% of that class is never ever going to look at the German, Canadian, or British tables again, but all dive with a computer. New students need be taught how to use a computer to the extent that they are taught the tables. One guy on the boat today did not know how to use his computer to plan his next dive. Students should know how to plan dives, access the log feature, and understand the various alarms. All students are taught how to use a BCD and all the features on it, the computer is now standard equiptment for most divers and should be taught accordingly.

 

[TMHeimer]

In my Nitrox/Decompression Theory course, we learned at least seven sets of tables. Only part of one class was spent on computers. Now 99% of that class is never ever going to look at the German, Canadian, or British tables again, but all dive with a computer. New students need be taught how to use a computer to the extent that they are taught the tables. One guy on the boat today did not know how to use his computer to plan his next dive. Students should know how to plan dives, access the log feature, and understand the various alarms. All students are taught how to use a BCD and all the features on it, the computer is now standard equiptment for most divers and should be taught accordingly.

Yeah, that makes sense for sure.

Re my question of how did divers plan dives 15-20 years ago-- I assumed that before the late 80s they probably used the US Navy tables, then the rec tables (RDP). Would you guys that dived back then agree with those that said many of them did not in fact use any tables? Depended on the J Valve, did what the DM told them, etc.? That sounds like a scary time. I can say that of the 6 of us in OW class in '05 none immediately bought a computer or, to recollection, even thought of it. Of course nothing in class was taught about computers--that wasn't 15-20 years ago. Logic would say that there wasn't a big % of divers in 1985 that had computers, but I don't know.

 

[The Chairman]

My two cents, in math class before the student is handed a calculator they are taught how to actually work the math.

Tables aren't math at all. If anything, they are like learning how to use a slide rule. Last I checked, slide rules aren't taught at all in High School Chemistry. My Chemistry teacher wouldn't let us use our "TI-10"s in her class for many of the same reasons as posited here for learning tables.

Lest I be taken out of context: Tables are not evil. I have no problem teaching them as long as the student is interested in learning them. They do not increase situational awareness or otherwise provide an ounce of extra safety for my students. I would rather spend my time schooling them on why I do 2 minute half stops and a full five minute safety stop then trying to force feed them something they may never use. In my class you'll learn about different tissue groups and how they will affect your diving. You'll be able to work out halftimes for those tissue groups and see how time, depth and temperature will affect how you absorb Nitrogen.

 

[The Chairman]

They are not difficult or time consuming to learn, having them in a class does not extend the class by large amounts of time.

They can be intimidating and they can extend the time of a class almost indefinitely if the student has convinced themselves that they can't learn them.

But the very fact that tables aren't "hard" is the reason I really don't feel a need to teach them to the point that a student can use them. In a pinch, they'll figure them out.

Unfortunately, and you can see by the number who have mentioned it already, traditional methods somehow equate learning tables to learning deco theory. THAT'S NUTS! That's like saying that learning E=MC² teaches you quantum physics. In fact, it's worse, because while tables rely on deco theory, deco theory does not rely on tables.

 

[explorer08]

Re my question of how did divers plan dives 15-20 years ago-- I assumed that before the late 80s they probably used the US Navy tables, then the rec tables (RDP). Would you guys that dived back then agree with those that said many of them did not in fact use any tables? Depended on the J Valve, did what the DM told them, etc.? That sounds like a scary time. I can say that of the 6 of us in OW class in '05 none immediately bought a computer or, to recollection, even thought of it. Of course nothing in class was taught about computers--that wasn't 15-20 years ago. Logic would say that there wasn't a big % of divers in 1985 that had computers, but I don't know.

Of course it was a minority only that had computers in 1985. Whenever I appeared on a dive site or a dive boat with my Decobrain, it was a little sensation. And for some it was "infernal stuff". These guys, it had been infernal stuff for have been the same breed than one diving instructor I remember very well. For many years he declined using a low pressure inflator on his horsecollar BCD. He insisted in inflating it orally, because in his opinion the low pressure inflator would waste the air from his tank.

In fact the situation was not much different from today. How many divers own a PDC today? And what's about the rest, have you ever seen them using tables instead?

In the old days there has been a minority of ambitious divers who did well organized dives and they used their tables to plan them. The vast majority simply followed some guide (that may have been an Instructor or DM, as well as some more experienced friend) and they trusted in that nothing ever happend before to them.

Today the ambitious minority owns a PDC and they use it. The vast majority does as their ancestors. And what is worse than not using a PDC, a big number within this group even would not know how much air is remaining in their tanks, if their guide would not frequently ask them or check it himself!

 

[The Chairman]

Today the ambitious minority owns a PDC and they use it.

I don't think they are in the minority any more. PDCs have come WAY down in price and have made huge strides in terms of reliability and ease of use. It's pretty normal to see almost every diver on the boat having (or sharing) a PDC.