RDP M-Values and NDL limits

[likedonuts]

Dear Dr.Deco

I'm writing a program for graphically comparing different deco algorithms and different halftimes and M-Values.

I found some discrepancies when implementing the RDP/DSAT M-Values; they just don't add upp compared to the PADI RDP max bottom times. Did Dr. Michael R. Powell adjust the bottom times after establishing the M-Values?

This is what i got (using M-Values from Deep Ocean Diving - Science, technology and medicine related to scuba diving):


Depth__My_____RDP
(m)____MDL____NDL
10_____281____219 128%
12_____154____147 105%
14_____103_____98 105%
16______75_____72 104%
18______57_____56 102%
20______46_____45 102%
22______37_____37 100%
25______29_____29 100%
30______19_____20 95%
35______12_____14 86%
40_______8______9 89%
42_______8______8 100%



As can be seen, the errors are non-linear, which is disturbing.

Any ideas?

Thanks!

/Mike

 

[Gene_Hobbs]

No time to look at the numbers now but here are THE references on development of the RDP. Thanks to Dr. Deco for his hard work creating them and DSAT/ PADI for allowing us to add them to the repository.

Doppler ultrasound monitoring of gas phase formation following decompression in repetitive dives. [S.l.] : Diving Science & Technology Corp., c1988. RRR ID: 4229

Development and validation of no-stop decompression procedures for recreational diving : the DSAT recreational dive planner / by R.W. Hamilton ... [et al. ] ; with Richard Dunford, Merrill P. Spencer, Drew Richardson. Tarrytown, NY : Hamilton Research, c1994. RRR ID: 4228

 

[Dr Deco]

Hello likedonuts:

References

A good first step in this question is to access the book listed by Gene Hobbs on the DSAT Table development. (4228). [There is also an earlier edition, 4229.] It will require some time to acquire these, as there are large. Additionally, I am Dr Michael Powell - but the modifications were made by Dr Ray Rogers.

Short Answer - NDLs

For those interested, but not desiring to red through the booklets, all decompression tables start with the No Decompression Limits, NDLs. These are acquired from laboratory studies with actual human divining subjects. Laboratories will have different criteria for what constitutes DCS, and they have different dive subjects. This will result in variability.

Most current table designers in the US will start with the US Navy tables and their NDLs. These are modified according to studies by Dr Merrill Spencer with regard to Doppler-detectable gas bubbles following a decompression. To reduce bubbling, the NDLs are reduced to allow shorter times at each depth.

Some will reduce these NDLs even more, e.g., recreational dive tables, to allow additional safety margins. If one makes a plot of US Navy NDLs, they will see that it is not a smooth curve. This results from a limited number of test subjects and random “noise” the degree of “smoothing” will influence the final result.

M_o Values

One uses the NDLs to calculate a “limiting” halftime for each of the se depths. This is then the controlling compartment [in a Haldane =-type of analysis]. Virtually all decompression schemes today use fixed compartments. The exception is the NASA altitude decompression model [for exercise prebreathe] that I developed for EVA. The M_o-values will depend on the smoothed NDL curve.

Dr Deco :doctor:

 

[likedonuts]

Additionally, I am Dr Michael Powell - but the modifications were made by Dr Ray Rogers.
doctor:

Excuse my negligence; i did note notice that you actually are Dr Michael Powell. Know when i know, let me pay my respect and thank you for your great work in providing a safer world to dive in!

You mention that "modifications were made by Dr Ray Rogers". Are you hinting at the "non linearities" that i discovered?

As i hardly will be able to obtain the papers (I'm living in the Philippines), any references to on-line material would be most welcome.

FYI: My intention with the software is to show students graphically how a specific dive (i.e. depth samples imported from a dive computer) would be interpreted with different deco models/halftimes/NDL. I'm pretty much done except for the RDP which, of course, is the most essential one.

The software IS NOT meant to be a dive planner, but should be resonable accurate to give students an idea of the differences. I would be happy to send anyone contributing a copy for personal use (it's not a commercial product at this point).

Thanks and best wishes,
Mike

 

[Dr Deco]

Hi likedonuts:

The material from Gene Hobbs [his reply is in this forum] should be accessible. It is a complete description of the process undertaken by the table designers under contract to DSAT/PADI.
I actually do not recall what Dr Rogers did - it was 1985. I suspect that it was only smoothing the curve.