Errors in PADI's/DSAT's Imperial Version of the RDP

[Butt Ugly Toad]

Hello All,

I am new to the board and am not quite sure if this is the correct board to post this article to but since this board deals with situations surrounding the use of DSAT's Tables, I figured it was the best one to post to.

There are two errors in PADI's/DSAT's Imperial Version of the RDP:

L for 50 feet (39 on Table 1 & 38 on Table 3)

Q for 70 feet (35 on Table 1 & 34 on Table 3)


Table 3 is just the math from Table 1 (The "Residual Nitrogen Time" is subtracted from the "Maximum Allowable Bottom Time" giving the diver their remaining time left for that depth). The Metric Versions of the RDP completely match from Table 1 to Table 3, but the Imperial Version has 2 "numbers" out of 198 that do not match, but are off by only 1 minute on Table 3. I finally "got smart" and used the Wheel Version to figure out which Table was correct, since the Wheel is suppose to be identical to the Table Version (Table 1 is identical to the Wheel Version and Table 3 is 1 minute off). These errors, in Table 3, give divers 1 more minute bottom time than the planner allows for.

I have spent over 9 years arguing with people at PADI/DSAT to fix these errors, but to no avail. Their reasoning behind the errors have been ......

Rounding (Imagine rounding that leaves Table 1 & Table 3 with 99% of identical matches and 1% that do not match?)

The errors are within the safety limits that are built into the RDP (I do not believe the RDP should have any errors in it)


I am hoping that this board, and it's Moderator, can put some pressure on PADI & DSAT to finally correct these two errors!

Respectfully,
Butt Ugly Toad
AKA: George W. Shope
PADI OWSI 64259

 

[Dr Deco]

Dear George:

RDP

It certainly is correct to say that there should not be any errors in the tables or their derivatives. No doubt many, many of these tables have been printed up. I doubt they will be tossed out. It is probably true also that rounding off is a part of the story. This plays a big part in printed tables.

Nonetheless, you have sharp eyes.

Does It Matter?

Certainly accuracy matters if only for a philosophical reason. Does it matter, however, with respect to decompression sickness? No.

Why not? As has been mentioned in this FORUM, decompression sickness can appear at any time, especially during long decompressions (where divers are up and around in the chamber. Variations (lengthening the stops) would eventually correct the problem. The impression arose that table designers were treading on the fine edge of “DCS/no DCS.” It appeared to be so but was not so in reality (I believe). When this was coupled with the prevailing Haldane concept of the metastable state, we had a “knife edge” view of the decompression process.
:bonk:
Tables for recreational divers, however, are made with a view to the most susceptible diver. It is not clear to many, but DCS is not equally present in all individuals. A “dose” of nitrogen will not produce the same effect in all people. This is very clear to those who work with animals as test subjects, but most table designers do not.=-)

If you develop the no decompression limits (NDLs) for a group and then back off by quite a bit, you will really be quite safe. A minute is not a crucial amount. What is “crucial” (I believe) is what you do in addition to observing “table limits.” These are

• a slow ascent
• avoiding stress when climbing into the boat,
• moving about a bit during the surface interval (no big straining activities.

This will lead to safer dives.

Dr Deco :doctor:

 

[donacheson]

Dr. Deco, at least to me that was a clear, sensible and satisfactory explanation of the minor table discrepancies.

I'd guess that PADI's explanation to Butt Ugly Toad wouldn't have been, but I haven't seen it, of course.

 

[Butt Ugly Toad]

Thanks for the replies,

I guess I need to rephrase my question?

There should be only one answer to any question derived from the Table Version of the RDP (Metric, or Imperial versions). However, with the two sections I have mentioned, there are TWO answers and a minute off from each other. For those of you that do not know it, there are two ways to use the tables:

Table 1 & Table 2 method

Table 1 & Table 2 & Table 3 method

Nine years ago I gave a class of six students a dive profile to use to plan thier risidual nitrogen time and there were two answers. There CANNOT be two answers when planning using the Table Version of the RDP, yet there are 2 chances out of 198 that this can occur. Mathematically speaking (since Math is a PURE SCIENCE), there is something wrong but NO ONE has fixed it in the nine years I've been "bugging" them about it.

I think it is time for someone to fess up to the errors and fix them! The tables were created by humans and we all make mistakes, including myself, but an error that is allowed to remain an error, just because it is easier to not fix it, IS NOT RIGHT!

I have been left with only one alternative to teaching the Table Version of the RDP. I still teach both ways but I have to tell every student about the two errors (nine years is a long time for this). If the students/divers do not use Table 3 then the error will never be a factor, but since most Instructors teach the Table 1/Table 2/Table 3 method, the error can come into play for anyone who uses Table 3.

I do know that the 1 minute we are talking about, is not a significant factor, but that is not my point. The Table's have had 2 reprintings since I first brought this up and "someone" has decided these errors do not need correcting but other items were changed to reflect the new "standards".

How many years will it take, of my periodic complaining, to get this fixed?

Respectfully,
Toad

 

[Walter]

I agree it's not significant, but it should be fixed when reprinted. Nine years is a long time to ignore an error.

 

[blackwater]

I had only learned the three table method,
(find the pressure group on the first table (left side of front of RDP), move across for the surface interval on table 2 (right side of front), flip over and find RNT from table 3 (back side of RDP).


what is the two-table method?

GT

 

[Butt Ugly Toad]

Here's a little RDP lesson for those not aware of how Table 1 & Table 3 relate to one-another:

Take the number from any Pressure Group at any depth (corresponds to degrees of time in minutes), that number will correspond identically to the Residual Nitrogen Time on Table 3 for that Pressure Group & Depth (the "white box"). Take that same number and subtract it from the Maximum Allowable Bottom Time for that depth and the result will be identical to the Adjusted No Decompression Time on Table 3 (the "blue box"). Now you know how they made Table 3.

Secondly, if you add each two boxes in Table 3, "Residual Time" & "Adjusted No Decompression Time", you will find they add up to the Maximum Allowable Time for each depth. The only exceptions to this are after 18 meters or 80 feet. At the maximum limits, the RDP does not allow for 1 and/or 2 minute Adjusted No Decompression Times. That is easy to rationalize since it would be difficult and not feasible to make a 1 minute 100 foot dive or a 2 minute 130 foot dive, etc ......

The 2 errors (Table 3) are the only numbers out of over 400 numbers that do not "match" their counterparts on Table 1 (Imperial & Metric Version combined). I am quite sure that any analytically minded person at NASA (or anywhere), would come to the conclusion that rounding cannot be a factor when over 400 numbers match and 2 do not! To have less than 1/2% of over 400 numbers not match means that over 99.5% of the numbers do match. There HAS to be a correlation between Table 1 & Table 3. And the 2 numbers, that do not match, have to be in error!

Let's look even closer at the 2 numbers and let's do a dive profile for each of them using the Table 1 - Table 2 - Table 3 method:

You dive to 50 feet for 39 minutes, what's your maximum allowable bottom time for a second dive to 50 feet with no surface interval?

Answer - 42 minutes via Table 3 (39 + 42 = 81) which exceeds the Maximum Allowable Bottom Time by 1 minute (80 minutes is the Maximum Allowable Bottom Time for 50 feet).

You dive to 70 feet for 35 minutes, what's your maximum allowable bottom time for a second dive to 70 feet with no surface interval?

Answer - 6 minutes via Table 3 (35 + 6 = 41) which exceeds the Maximum Allowable Bottom Time by 1 minute (40 minutes is the Maximum Allowable Bottom Time for 70 feet).

These are the only two places where exceeding the MABT occurs and cannot be right!


Like I said earlier, the 1 minute timeframe is within the "built in" safety limits of the planner, but if you look at the Emergency Decompression rules, I can only assume that if I break any Maximum Allowable Bottom Time by only 1 minute, then I DO NOT need to make an Emergency Deco stop? I don't think this would be an acceptable stipulation by anyone at DSAT or PADI? But this is exactly what everyone has been saying for the past nine years, including within Dr. Deco's reply.

Newton said it best ..... for every action, there is an inverse reaction. If exceeding the Maximum Bottom Time, by only 1 minute, is within the safety limits built into the RDP then there is no need to do an Emergency Deco Stop if you exceed the limits by only 1 minute!

I think it would be easier to fix the two errors than to change the rules for Emergency Decompression Stops.

Respectfully,
Toad
AKA: Butt Ugly Toad

Ps: For Blackwater and anyone else that wants to know the Table 1 & Table 2 method, here are the instructions:

Find your Depth, go down to your Dive Time, go across to your Surface interval then down to your Ending Pressure Group (so far this is the same as the Table 1 - Table 2 - Table 3 method). Next, take and put your finger on the Pressure Group, in Table 1, you ended up after your Surface Interval. Follow that out to the depth of your next dive (the number in that block is your Residual Nitrogen Time). To find out the Maximum Allowable Bottom Time, just subtract the Residual Nitrogen Time from the Maximum Allowable Bottom Time for that depth.

I hope these instructions are understandable?

I find the Table 1 - Table 2 method to be less confusing for people cause they do not have to flip the RDP over and then flip it back. You get to stay on "side 1". Also, any RDP "problem" can be solved using the Table 1 - Table 2 method.

 

[Pez de Diablo]

I am going to see if my instructor will point this out!

 

[Dr Deco]

Dear BU Toad:

It sounds to me like there is more than a rounding off error here.

Dr D. :doctor:

 

[Butt Ugly Toad]

Hello all once again,

The RDP is about to get a new printing once again due to the new changes in the "Flying after Diving" recommendations. This will be at least the 3rd re-printing of the RDP since I first brought up the two mentioned errors and I believe the time is now for the errors to finally be corrected. I have shown where the errors are and the corrections are simple. However, I have gotten nowhere in 9 years by myself, so I would like everyone to send an email to the following persons at DSAT and express your feelings towards these matters:

bobw@padi.com
karls@padi.com
kenb@padi.com
aarona@padi.com
lorib@padi.com
toddm@padi.com

I have already sent emails to these people (I basically "copy-pasted" my ScubaBoard postings to an email). As of this posting, I have not had a reply from anyone?

I also CC'd the following people:

drewr@padi.com
johnk@padi.com
brads@padi.com

One voice is easy to ignore, but many voices can become impossible to ignore!

Respectfully,
Toad
AKA: George W. Shope
PADI OWSI 64259

Ps: Thanks to the creators of this BB and also, Thank You Dr. Deco for taking your time to help us weary divers!