Posted by Kendall Raine on May 23, 2002 at 12:22:50:
Following the recent threads regarding alledged inherent flaws in the RDP, I corresponded with Mike Powell at NASA regarding his work on the RDP. He referred me to the report he and others prepared. I then asked PADI to send me the report, which they did promptly and at no charge. I sent a copy of the report to tecdiver so he can verify that what I say is correct.
The report is called The DSAT Recreational Dive Planner, Development and validation of no-stop decompression procedures for recreational diving. It is by Hamilton, Rogers, Powell and Vann. The report is dated February 28, 1994 and runs about 100 pages.
Without violating copyright laws, the report is comprehensive as to the history of why and how the model was developed, by whom and details the form and results of testing.
In summary, the model was developed to address the needs of recreational divers doing repetitive and multi-day multi-level no-stop diving on air. The testing was designed with this in mind.
The RDP was tested using both chamber and open water "dives." Most of the chamber dives involved excercise at moderate levels during compression to simulate work of diving.
Testing was divided into three phases. Phase I involved single exposures and repetitive exposures in the same day. 911 dives were done in Phase I. Doppler tests following these dives showed occasional bubbling, but most test subjects were clean. No incidents of DCI were reported during Phase I. Phase IIa was designed to test subjects doing six "dives" per day for six days. 51 dives were done in Phase IIa. Doppler testing showed a progressive increase in bubbling across days. On day 3 of the tests, one test subject developed pain in a knee diagnosed as a Type 1 DCI hit. The subject had injured the knee some years earlier in a motorcycle accident. The testing procedure called for termination of the series if DCI developed. Phase IIa was thereby discontinued. Nevertheless, a new series was initiated wherein four "dives" per day for six days were conducted. This was called Phase IIb. 471 dives were done in Phase IIb. Phase IIb again showed an increase in Doppler scores across dive days for some subjects. No DCI hits occured during this phase.
Open water testing was done in Washington in water about 52 degress. Open water divers dove both wet and dry. Test subjects ranged in age from early 20's to late 50's. Body fat calculations suggest a moderately unfit group with the average body fat of 25% for men and higher for women. A typical recreational cross sample.
The report concluded that the RDP posed no more risk to divers than "customary recreational diving practice" and that the there was no evidence that the repetitive and multi-level procedures of the RDP were not reliable. The conclusion goes on to recommend that dives per day be limited to 3, max 4 and that a reduction in repetitive dives be taken every 2 or 3 days.
Some of the criticisms of the model, including the use of the 60 minute half-time as controlling compartment and lack of adequate testing are discussed openly and counter arguments presented.
Those are the facts as presented in the report. What follows is my opinion:
1) The RDP did not "fail" after some period of time or some number of dives, either absolutely or in relation to other neo-Haldanian modles. One case of bends occured in 1433 test dives. Residual bubbles are progressive. That's a fact of physiology. If you don't like it, don't dive. If you don't like it but still want to dive, then dive conservatively, use longer SIT's, stop using air and, if you're not in shape, get in the gym. If you have preconditions, be even more conservative.
2) The argument that the RDP was not adequately tested seems vacant. More aggressive testing could have been done, but the purpose of testing wasn't to bend people, it was to see if the RDP performed up to its intended application. It did and the rest is BS.
3) There is no evidence that anything was covered up or that anyone was "silenced." The report appears to be comprehensive. While the report may have been commissioned by PADI/DSAT to correct misinformation or dispel criticism, the authors of the report, at least Hamilton, Powell and Vann, are highly respected researchers in the field and have no apparent ax to grind other than being paid to do research.
4) The allowable ascent rate of 60 fpm is too fast. The RDP does not specify that 60 fpm is correct, just that it is not to be exceeded.
5) The 60 minute half-time controlling tissue argument could have merit, but the argument needs to be better articulated. To me the issue is more one of symetrical on-gassing and off-gassing. Both Navy and RDP are symetric and this is probably wrong-see Bennett's editorials in Alert Diver. In this respect, the Navy's 120 minute half-time may be better in the context of repetitive diving, but for the wrong reasons. Bottom line, padding the repetitive group designation never hurt if you're going to do a lot of diving in a short period. Despite this, the multi-day testing did not turn people into potato chips. One guy, out of 500 dives, took a limb bend, but he was predisposed-see point 1 above.