PADI Dive Tables

[ifukuda]

Is the PADI dive table based on some sort of algorithm, or, is it basically a database of test Navy test results? If there is an algorithm, can anyone tell me what it is?

 

[terrydarc]

Good question! I got the impression that the tables were derived empirically by the Navy and PADI sort of took them over. It would be interesting to know what the various dive computers use - table lookup or some sort of formula?
Terry

 

[Iguana Don]

Hey guys, listen up!

Just so happens that our very own Dr.Deco aka Dr. Micheal Powell is one of the developers of the PADI RDP.

I'm gonna move this thread over to "Ask Dr Deco" and he will give you the full poop.

ID

 

[Dr Deco]

Dear ifukuda:

The PADI table (or the DSAT table) is derived from a variety of sources. First, there are the US Navy tables that were tested by the Navy with young men. To formulate these tables, the No Decompression Limits (NDLs), that is the longest permitted time at a given depth, were determined. These form the basis for recreational divers’ tables for which in-water decompression stops are not used.

In addition to these, Dr Ray Rogers also used some diving information based on Doppler ultrasound bubble detection by Dr Merrill Spencer at the Institute of Applied Physiology and Medicine (IAPM) in Seattle, Washington. His work indicated that the Navy NDLs were perhaps more liberal that were in the best interests of recreational divers. Dr Rogers reduced the NDLs in a systematic fashion, and this form the basis of the PADI Table and The Wheel .

These tables were then tested by a small group of individuals at the IAPM, and a schedule was developed for a large-scale test. Requests went out to northwest area dive clubs to solicit volunteers to participate in full-scale tests of the new tables. These were performed first in a hyperbaric chamber at IAPM, and the diver test subjects were monitored with a Doppler ultrasound device several times post dive. These dives were multiple dives and multilevel dives. I was the lead scientist for these and the other studies.

Following these chamber trials, a series of open water dives were performed from a boat in the Puget Sound. Doppler monitoring was also done on the divers after reboarding the boat.

The next set of studies was a six-day series on twenty divers in a hyperbaric chamber, again at IAPM. This consisted of four dives per day for six days. Doppler monitoring was conducted also.

In all dives, Doppler “Grades” were low and most divers did not show any bubbles at all. The age span of the divers was 21 (youngest accepted) and the oldest was 63. Some were thin, some were heavy, and 28% were women. All together, there were approximately 1,200 dives. There were no cases of DCS on the version of the tables that was released.

For those that desire more information, you can write to PADI and purchase the report.

[sp]Hamilton, RW, RE Rodgers, MR Powell, and RD Vann. Development and Validation of No-stop Decompression Procedures for Recreational Diving. Diving Science and Technology. (Pp. 78 + appendix). February 28, (1994).

These are (along with tables from DCIEM) the most tested today. It is my understanding that the Oceanic dive computers employ the table characteristics from the DSAT test program. Tests such as these are seldom performed because of the cost.

I hope that helps.

Dr Deco

 

[ifukuda]

Thanks for the first information Dr. Deco. I'm honored to be educated by the person who was in charge of these studies. And thanks I.D. for moving my thread where Dr. Deco would reply.

Terrydarc, it's always nice to hear from another fellow software engineer (and diver).

 

[terrydarc]

Thanks, Doc...as always, your answers are a marvel of completeness!

ikfukuda,
Yeah nice to know it's not all professional diver and dive shop people here - real people here after all.

I still wonder why with all the money divers throw at the sport that there's no activity AFAIK toward real-time measurements of N2 bubbles. Doc suggests that doppler was used to measure gas uptake and previously he noted that surface activity was a 10x predisposition toward DCS. Seems like someone could invent or at least work on a dive computer tied to physiological monitoring.

Now THAT would be a cool job - test engineer for next generation scuba computers that would measure N2 or gas uptake or whatever! Preferably testing in warm waters somewhere. Anyone want to form a company? I'm available for that test engineer slot.
Terry

 

[Dr Deco]

Dear Tarrydarc:

The next generation of decompression technology is not yet ready for the recreational diver. The monitoring of activity is very straightforward where astronauts are concerned. All the measurements are made in advance and the whole activity is choreographed so that we are aware of the metabolic loads. This is because we know in detail that they will not perform any walking on “spacewalks.” Thus, lower body work is removed from the equation. (In addition, the spacesuits are stiff, and astronauts seldom do much movement of their legs.)

There was some attempt Dr Max Hahn to adjust the algorithm of the UWATEC Aladdin when large gas bubble loads might be suspect to modify off gassing. This is based only on a “guestimate” and not an actual measurement. The “adaptive model” is an a priori one and is not actually connected to the diver or his/her activities.

There does not exist any quantitative system for routine field use that could be used for recreational divers to adjust their surface intervals. Assuming that such a system had been tested, an algorithm would require the measurement of oxygen uptake to determine the diver’s topside activity level. This would need to be correlated to both the upper and lower extremities.

We are in a similar position with Doppler bubble detection. These are not good systems for real-time monitoring of decompression. This is because there are many “false positives” that is, many bubbles are detected but the dive does not end with DCS. As a research tool, they allow us to judge the response of a group but they fail on individual cases. Prediction of group outcome is easier than individual outcome. This is why insurance companies make more money than fortunetellers do.

Dr Deco
:doctor:

 

[Lost Yooper]

Hey Doc, by "any bubbles" do you mean no micro bubbles were detected?

Also, somewhere I read that the US Navy tables had a DCI rate of like 5% (something like that). Can you substantiate or elaborate on that?

Just curious.

Mike

 

[Dr Deco]

Dear Lost Yooper:

The Doppler ultrasound system needs a certain size gas bubble to be detected, although clouds of very small bubbles can be found. It has been found over the past three decades that a few bubbles in the venous blood steam are without particular significance with respect to risk of DCS. Therefore, a few small ones do not really matter.

As far as the US Navy tables are concerned, there is a few percent of divers that will get DCS. Much of the risk is very diver-activity dependent, and remember that these tables are for decompression diving . US Navy divers are WORKING DIVERS.

The no-decompression limits (NDL) are the only portion of the US Navy tables that are used by recreational divers. To further reduce the probability of DCS, the NDLs were systematically reduced for the PADI tables in accordance with early Doppler research by Dr Merrill Spencer.

As far as DCS is concerned, do recall that the decompression is not over when you reach the surface. You are still off gassing and DCS events occur upon surfacing. Generally, 90% of DCS events arise during the first hour post surfacing.


Dr Deco

 

[Lost Yooper]

Ok Doc, here's another one for ya -- just to keep things moving on the subject.

Why does PADI still use a 60FPM ascent rate? Most agencies seem to be using a 30FPM rate. We use, on average, a slower than 30FPM rate.

Mike