A conservative table carries less risk than a liberal one. The difference in risk may not be enough to really matter, but I choose to err on the side of caution. I will not use the RDP, it's too liberal for my tastes.
The RDP is strictly for no-decompression diving, and it was designed with that limitation in mind. It went through extensive research, with its research findings published in peer reviewed journals, with our own Michael Powell (Doc Deco) intimately involved.
You have stated your observation to it many times in the past, but I have never seen your reasons clearly delineated. Perhaps you could be more specific.
1. Research with Doppler bubble imaging led to the conclusion that the 40 minute compartment controlled ascent and surface intervals for recreational dives, except of a small subset related to repeated dives to that approached the NDL's. Do you disagree with this conclusion, and, if so, why?
2. In order to make the tables more conservative, they went with the 60 minute compartment as the basis for the RDP. Do you disagree with that decision? If so, why?
3. They also decided to make the limits on the first dive more conservative than the USN tables, giving divers less bottom time at any depth than the Navy tables. Do you disagree with that decision? If so, why?
4. They decided to add more pressure groups, roughly double the number of the USN tables, in order to minimize rounding errors. Do you disagree with that decision? If so, why?
5. When the USN made the tables in effect at the time the RDP was created, it took the 5 compartments Haldane had created more than 100 years before the current time, and they then arbitrarily added a 6th compartment, the 120 minute compartment. They made that the controlling compartment for their dives with no real research prior to that decision. Do you feel the 120 minute compartment is the better compartment to use for recreational dviving than the 60 minute compartment? If so, why?
6. The RDP has been used millions of times by recreational divers since its inception. It is the basis for some dive computers. Do you have statistics indicating that those divers have suffered as a result of this use? If so, what are those statistics?
7. Here is an explanation Doc Deco gave on ScubaBoard on October 30, 2001. Can you explain where it all went wrong for us (and him)?
he 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 Ũrades 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
