Time at Deepstop

[fisheyeview]

I was working a trade show a couple of years ago. The DAN booth was across from ours. On a slow day we taled about current research. They said they were going to come out recommending a 2.5 minute deep stop follwed by a 3 minute stop at 15'.

I'm curious if they were doing there own research, or using other studies for this.

 

[Pre BC]

AlbertVW:

Unfortunately your confusion is well earned... For two reasons!

First, by not providing detailed sources, Verna van Schaik has inadvertently denied you, me and anyone who reads her article of the opportunity to validate her conclusions or atleast understand the context of where they come from. Before making any changes based on the article, I would write or email the author and ask her to site her sources (both pro and con) and provide rationale why she believes her sources should be relied upon instead of the RGBM (Reduced Gradient Bubble Model) used by Suunto and others. We all know that "scientific fact" is a moving target and new technologies/testing techniques can cause us to redefine and find new "truths". If she is on to something, it would be good to know.

Second, while there is a body of evidence to support the 50% stop for tech diving (read the fascinating story of Dr. Bill Hamilton's deep water fish collecting experiences to understand the context), no one really at this point knows if extrapolating the idea from tech diving to recreational diving makes sense. Tech divers are routinely dealing with saturated tissues and decompression scenarios. Recreational divers should not be :cool2:. Therein lies the point yet to resolved with regard to the "nitrogen tissue absorption issue" (say that ten times fast!). For a fully saturated tech diver, the 50% stop prolongs/slows the offgasing process thereby redusing bubble formation. Given that bubbles -- once formed -- change the whole dynamic, the RGBM is most likely the best model for tech diving. Conversely, for a run of the mill recreational diver, chances are they are no where near saturated in most of their tissues and they are most likely going to continue ongasing while loitering at the 50% stop. However slightly, theory would suggest that continued nitrogen absorption is not a good thing and, as a result, the 50% stop actually makes things worse for recreational divers. As a result there are many bright minds out there reconsidering the RGBM for recreational diving and suggesting that recreational diving might be better modeled by a traditional or modified compartment model (Haldane).

But, here is the rub, the numbers we are dealing with are so small (1 incident per 100,000 dives) with either the RGBM or modified tissue compartment model that scientists may never be able to reach a statiscally significant conclusion. It will be a controversial largely non-issue until the experts reach a concensus.

The good news is, as long as you stay conservatively within recreational diving limits you are clearly both theoretically and practically in a safe zone whichever model you rely on and regardless of whether you do a 50% stop or not. The even better news is that multilevel dives (deep to shallow) solve the entire problem... None of the models suggest a 50% stop on a dive that goes from 100 feet to 70 feet to 40 feet to a 15 foot safety stop...

P

 

[ianr33]

AlbertVW:
(read the fascinating story of Dr. Bill Hamilton's deep water fish collecting experiences to understand the context), P

Do you mean Richard Pyle?

 

[Rhone Man]

I thought it was a very well analysed piece of research, although I agree it is difficult to tell how far one can extrapolate the data into diving practices for recreational divers.

The one thought that did occur to me is that it certainly lends support to the "flattening the curve" approach that DIR divers preach in their ratio deco.

 

[H2Andy]

says the article:

Dives with 2 1/2 min deep stops yielded the lowest PDDB scores--shorter or longer deep stops were less effective in reducing PDDB. The results confirm that a deep stop of 1 min is too short--it produced the highest PDDB scores of all the dives.

and it concludes:

While our findings cannot be extrapolated beyond these dive profiles without further study, we recommend a deep stop of at least 2 1/2 mins at 15 msw (50 fsw) in addition to the customary 6 msw (20 fsw) for 3-5 mins for 25 meter dives of 20 to 25 minutes to reduce PDDB.


what i get from this is that a longer deep stop is better, up to a point

that seems to be consistent with what we already know

Second, while there is a body of evidence to support the 50% stop for tech diving (read the fascinating story of Dr. Bill Hamilton's deep water fish collecting experiences to understand the context), no one really at this point knows if extrapolating the idea from tech diving to recreational diving makes sense.

i'm curious, why wouldn't it make sense?

it makes sense to me to stop your ascent before you hit two atmospheres and let your tissues catch up

for most rec dives, the "deep stop" will take place at three atmospheres (somewhere between 40-60 feet). combine that with a slow ascent past 33 feet and a long stop at 20, and you should be well served by deep stops no matter what kind of diving you do

 

[Pre BC]

IanR33 is right. I should have double checked my Who's Who of Diving! Richard Pyle was the scientist that observed the difference between dives where he relieved fish badders with those where he didn't catch any fish and went straight to his decompression stops... Ergo the nickname Pyle Stops...

Dr. Hamilton is the one who applied the annecdotal accounts and turned them into the science of the revised tables/formulas. Both are fascinating divers worth learning about! I have attached below the short bio of Dr. Hamilton published when he was awarded the Rolex Diver of the Year in 2001. There is a list of all the Rolex award recipients at the bottom... All are noteworthy and very interesting characters...




"Dr. Bill Hamilton Named 2001 DAN®/Rolex® Diver of the Year

Dr. Bill Hamilton has been named the DAN/Rolex 2001 Diver of the Year. The award was to be presented at Seaspace ceremonies in Houston on June 9, but flooding cancelled the event. The award will be given at an as-yet unscheduled date and location in the near future.

This distinguished award honors an individual with an excellent record of public service in scuba diving, and who is also a strong advocate of DAN and scuba diving safety. The award includes a plaque and a specially engraved Rolex Oyster Perpetual Submariner Date dive watch.

Walter Fischer, president and CEO of Rolex Watch USA, endorsed the selection. "Dr. Bill Hamilton is an outstanding addition to the men and women who have preceded him as the Rolex/Dan Diver of the Year," Fischer said. "For the bulk of more than 40 years, Dr. Hamilton has devoted his career as a physiologist to matters relating to making diving safer, more effective, and better understood by everyone."

Dr. Peter Bennett, founder, president and CEO of DAN, praised the choice of Dr. Hamilton for the honor. "Bill Hamilton’s long productive career since the 1960s in diving physiology and medicine and his unique role in computing safe decompression tables for technical divers makes him most deserving of the DAN Rolex Diver of the Year," he said.

After completing his Ph.D., Dr. Hamilton worked with a commercial diving laboratory where he helped define human performance during the first saturation exposures to continental shelf depths, and later he worked on extending this to the present operational depths (over 1,000 fsw). He helped develop commercial bounce, saturation, and excursion decompression tables, and worked to facilitate the transition from lab to sea.

He and colleagues in his lab produced and helped disseminate the fundamental data on hyperbaric chamber fire safety now universally applied by both the diving and hyperbaric medical communities. This work has saved many lives, and it has helped make hyperbaric medicine and underwater dry-chamber welding feasible and safe.

Dr. Hamilton and his colleagues have developed many types of decompression procedures for a wide variety of diving and exposures to pressure, ranging from submarine free ascent to space travel to deep commercial diving, including detailed instructions for treatment of decompression sickness. This work resulted in and has depended on a comprehensive computer program called DCAP, the first such computational program designed for use by individual researchers. For NASA he developed excursion and decompression procedures for use with a hyperbaric lock on a space station, and he assisted in the implementation of enriched air in the neutral buoyancy pools.

Always a strong proponent of safe diving practices, Dr. Hamilton applied his experience with decompression, physiological effects of gases, and methods of managing exposure to oxygen to help divers avoid narcosis when diving beyond the "recreational" range. Unique decompression and operational methods using oxygen-helium-nitrogen trimixes that he helped produce in cooperation with safety-conscious divers were instrumental in the origination and development of the new field of "technical diving." He has helped apply this to the problems of deep cave diving, specifically on several record-setting cave exploration dives with scuba over the depth range of 200 to beyond 870 fsw.

Dr. Hamilton has had a strong relationship with NOAA for many years. He was responsible for developing most of NOAA’s nitrox saturation-excursion procedures for "habitat diving," including NOAA OPS and NOAA’s Repex procedures for repetitive excursion diving, and he has worked on excursion procedures using helium mixtures. Repex also resulted in a widely applicable algorithm for managing long term exposure to oxygen. Dr. Hamilton also helped prepare the NOAA oxygen exposure limits. He has been consultant and advisor to NOAA's Aquarius habitat project since the design stage, and he has produced decompression tables for use in evacuating the habitat. He prepared trimix tables for NOAA’s research on the USS Monitor, and this led to his production of a set of trimix tables for the NOAA Diving Program. He contributed to earlier editions and co-authored two chapters in the 2001 NOAA Diving Manual.

He has worked on development of rebreathers, including especially rebreather decompression procedures and integrated computers, safety practices, and instruction materials, and he has carried out rebreather training and intensive manned testing. He has helped in the development and assessment of several diver-carried decompression computers and dive recorders. He designed and helped evaluate an effective breathing gas heat regenerator for use in a stranded diving bell.

He has been organizer, chairman, and/or editor of several specialized workshops; one on the validation of decompression tables that provides simplifying guidelines for bringing new tables into operational readiness may be the most important of these. He has served as editor of Pressure, the Undersea and Hyperbaric Medical Society’s newsletter. He worked on national standards for U.S. commercial diving; in that capacity he helped solve several challenging problems including eliminating some onerous and unworkable elements and establishing a uniform standard for effectiveness of decompression procedures. He conducted a worldwide survey for the U.S. Navy on air and oxygen-with-air diving practices.

Dr. Hamilton has received three different awards from the UHMS, and several from the diving community. He has been a strong supporter of DAN since its earliest days, including presenting at Divers Day symposiums. Major Hamilton served as a USAF fighter pilot in combat service in Vietnam, where he earned the Distinguished Flying Cross and other decorations. As Life Support Officer he helped solve an equipment problem that had caused unsuccessful bailouts. He has recently proposed a radical new idea for protection against very high G-forces in fighter aircraft.

Previous DAN/Rolex Divers of the Year are Walt "Butch" Hendrick (1989); Jim Corry (1990); Michael Lang (1991); Drew Richardson (1992); Karl Huggins (1993); Dr. Glen Egstrom (1994); Marjorie Bank (1995); Dick Long (1996); Dr. Lee Somers (1997); Richard Dunford (1998); Dr. Hillary Viders (1999); and Greg Mackay (2000)."

 

[AndyNZ]

I've read quite a few articles on deep stops, it seems that almost every study deals with a relatively limited scope. I think it's very hard to generalise at all on the basis of limited studies - you can almost guarantee that if you take any point of view that you can find a study that contradicts it......

 

[Soggy_Diver]

Hi,

There was a discussion of the 2.5 minute deep stop research last year in the thread below, in the Dr Decompression area. You might be interested in it. There were two studies that are mentioned in it--an initial study that did not seem to control for total ascent time, and a second study that did control for total ascent time--or that is as much as I understand of it. Hope this link works:

http://www.scubaboard.com/forums/ask-dr-decompression/234869-extend-deep-stops.html

 

[lmorin]

I read the article in question. It is poorly designed because the variable of interest, deep stop time, does not vary systematically while holding shallow stop time constant. The net result is that it is very difficult to determine the impact of 1 min vs 2 min vs 3 min vs 5 min deep stop and how they differ from a control with 0 min deep stop. It would have been nice to have had deep stops of 0,1,2,3,4,5 min all tested with 0 shallow stop time; then repeated at 1 min shallow stop time, then 2 min, etc. Then, a solid statistical analysis could have been done and would have yielded meaningful results.

So, I took their Bubble Score Index data and plotted it relative to a composite variable which is the simple sum of deep stop time and shallow stop time. The result is a statistically significant correlation coefficient (r = -0.59544, df=13, p<.02, 2-tailed). This means that a large proportion of the variance in the data is accounted for by simply taking more stop time, whether deep or shallow. In other words, the more time you spend at a safety stop, the lower (better) the Bubble Score Index.

More detailed data analysis is needed to determine whether one particular stop profile is better than another. The data, as presented in the article, do not allow such analysis. There is no indication of between- or within-diver variability or within group variability.

 

[Soggy_Diver]

I read the article in question. It is poorly designed because the variable of interest, deep stop time, does not vary systematically while holding shallow stop time constant. The net result is that it is very difficult to determine the impact of 1 min vs 2 min vs 3 min vs 5 min deep stop and how they differ from a control with 0 min deep stop. It would have been nice to have had deep stops of 0,1,2,3,4,5 min all tested with 0 shallow stop time; then repeated at 1 min shallow stop time, then 2 min, etc. Then, a solid statistical analysis could have been done and would have yielded meaningful results.

So, I took their Bubble Score Index data and plotted it relative to a composite variable which is the simple sum of deep stop time and shallow stop time. The result is a statistically significant correlation coefficient (r = -0.59544, df=13, p<.02, 2-tailed). This means that a large proportion of the variance in the data is accounted for by simply taking more stop time, whether deep or shallow. In other words, the more time you spend at a safety stop, the lower (better) the Bubble Score Index.

More detailed data analysis is needed to determine whether one particular stop profile is better than another. The data, as presented in the article, do not allow such analysis. There is no indication of between- or within-diver variability or within group variability.

I see what you're saying. I wonder if a way to get at the effect of deep stops statistically would be to do a multiple regression, with deep stop time as one predictor, shallow stop time as a second predictor, and BSI as the criteron variable. Then if deep stops are differentially helpful compared to shallow stops, then deep stop time should come out with a higher regression coefficient than shallow stop time; if shallow stop time and deep stop time are equally effective, their regression coefficients should be about the same. That kind of analysis would not be really proper, because each row in Table 1 is not one case, it is a bunch of cases. But it might give a hint of what is going on.