By Bruce R. Wienke, PhD

and Timothy R. O'Leary

Excerpt from ADM Issue 5, 2001
Since NAUI Technical Operation's release of the ranged trimix RGBM full-up phase model tables, by Dr. Wienke at DEMA, we have been barraged with requests concerning origin, validation, and purchase from all points of the globe. Phase modeling is rapidly gaining worldwide acceptance as an alternative to the dissolved gas models such as Haldane. In the past we have been left with a smorgasbord of Haldane dynamics and discretionary stop insertions that are no longer applicable. This has been evidenced by the collective comments of a very vocal, competent, and experienced technical diving community.

This year will usher in a new era regarding the manner in which we think about compression/decompression and the availability of full up RGBM phase tables, including nitrox, heliox, trimix, and air over the net crossing the alphabet soup of training agencies.

Phase mechanics and bubble dissolution time scales first came to light with the Hawaiian fisherman divers and the Australian pearl divers. Pearling fleets, operating in the deep waters off Australia, employed Okinawan divers who regularly made dives to depths of 300 fsw for as long as one hour, two times a day, six days per week, and 10 months per year. Driven by economics, Le Messurier and Hills observed that these divers developed their own decompression schedules with deeper stops but shorter times than would be called for with the dissolved gas theory. These profiles were entirely consistent with minimizing bubble growth and the excitation of nuclei through the application of increased pressure.

According to Farm and Hayashi, similar schedules and procedures evolved in Hawaii among diving fisherman. Hawaiian divers made between eight and 12 dives a day to depths beyond 350 fsw, making up to three repetitive dives a day. Consistent with bubble and nucleation theory, these divers made their first dive deepest with following excursions shallower. A typical profile might start with the first dive 220 fsw, the next two dives to 120-fsw, and dives 3 band 4 to 60 fsw. Obviously, these profiles literally clobber conventional tables, but when examined within the framework of bubble and phase mechanics, they acquire some credibility.

As Bruce Wienke stated, "Real pioneers very often go without proper recognition. Those of us who follow, reap the benefits of their insight and perspectives, and our benefits of hindsight and modern diving developments. RGBM was built upon the work of Brian Hills and David Yount, skillful work performed on phase mechanics, bubbles, and ultimately, the first translations of their findings to the diving arena and particularly diver staging. They didn't have all the answers (who does), but they underlined the basics. Both applied computer studies and simulations to diving profiles, though much has not been recognized until recently. True warriors, they labored in difficult times, and under enemy fire, so to speak. Hats off to you Brian and David and all your co-workers."

The following information represents important facts about RGBM validation and testing:

1. Counterterror and Countermeasures (LANL) exercises have used the RGBM (full up interative deep stop version) for a number of years, logging some 327 dives on mixed gases (trimix, heliox, nitrox) without incidence of DCI. Thirty-five per cent of these were decompression dives, and 25% were repetitive dives without decompression with at least two-hour surface intervals.

2. NAUI Technical Diving has been diving the full up deep stop version for the past two years, some estimated 200 dives, on mixed gases down to 250 fsw without a single DCI hit. This includes a solid week of aggressive diving by NAUI Technical Instructors in Cavailare, France while diving six straight days in cold water and rough seas.

3. Modified RGBM recreational algorithms (Haldane imbedded with bubble reduction factors limiting reverse dive profiles, repetitive, and multiday diving), as coded into SUUNTO, ABYSS, Cochrane decometers lower an already low DCI incidence rate of approximately 1/10,000 or less.

4. A cadre of divers and instructors in the mountainous New Mexico, Utah, and Colorado have been diving the modified (Haldane imbedded again) RGBM at altitude, an estimated 350 dives, without incidence. Again, not suprising since the altitude RGBM is slightly more conservative than the usual Cross correction used routinely up to about 8,000 feet elevation and with estimated DCI incidence less than 1/10,000.

5. Within deco implementations of the RGBM, not a single hit has been reported in the multidiving category. Up to now this encompasses 1000 or more dives.

6. Extreme chamber tests (300 fsw and beyond) for mixed gas RGBM are in the present works. Less stressful exposures will be addressed in the near future.

7. Probabilistic decompression analysis of some selected RGBM profiles calibrated against similar calculations of the same profiles by Duke, help validate the RGBM on a computational basis. This suggests that the RGBM has no more theoretical risk than other bubble or dissolved gas models (ala Weathersby, Vann, and Gerth methodology at USN/Duke). This will be reported in a very technical paper/journal.

8. All divers and instructors using RGBM decometers, tables, NET software are being advised to report all their profiles to DAN Project Dive Exploration (Vann and Gerth and many others).
The NAUI Nitrox and Trimix tables contained within this article are full-blown RGBM calculations yielding deeper stops but shorter overall decompression times as compared to Haldane type staging. Ascent maximum ascent rate is 33 fsw/minute (10 msw/minute) and maximum descent rate is 75 fsw/minute (23 msw/minute). These tables are for illustrative purposes only and should not be used without training from a qualified technical diving instructor.

The ranged trimix table is for 16% oxygen and 24% to 40% helium, with a switch on ascent to pure oxygen at 20 fsw (6 msw) to the surface. Should oxygen supply be lost the diver need only double the 20 fsw (6 msw) and 10 fsw (3msw) decompression times and continues decompression on trimix. One repetitive dive is allowed (shallower and shorter) with a minimum of three hours of surface interval. Minimum time to fly surface interval is 24 hours or 36 hours after a repetitive dive.

The EAN 32 tables are based on 32% oxygen (plus or minus 1%) and 68% nitrogen. Minimum surface interval between dives is at least two hours for up to 3 dives.

Minimum time to fly or ascend to altitude is 12 hours after one dive, 18 hours after two dives and 24 hours after three dives.

When cutting-edge technology and ideas can be transmitted to minimize risk in such a high-risk arena, these become very exciting times for both divers and agencies (regardless of alphabet soup politics). It seems like only yesterday that nitrox was discussed in Key Largo. Today phase modeling will revolutionize the way we look at decompression physiology regardless of gas mixture.

For more information on phase modeling you may contact NAUI Technical Training Operations