Why do people add a few minutes to their last deco stop?
- Thread starter dylanfromwinnipeg
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Yes, @ginti. I must not have had my coffee when I wrote that! Clearly, if a diver has been deep enough long enough (breathing tri-mix or nitrox or air), then when he/she has ascended to his 20 fsw stop, the amount of nitrogen in even his slowest tissues almost certainly still exceeds the PN2 in any rich nitrox deco gas he will switch to (e.g., EAN80, FN2 = 0.20, has PN2 = 0.32 ATA at 20 fsw) . So, he will still be off-gassing nitrogen, though not as quickly--and, eventually, theoretically, not as completely--as he would if he had switched to 100% oxygen.
rx7diver
Research on saturation divers shows that tissues saturated at a depth shallower than 20 feet can safely surface. That means that slow tissues on-gassing during a safety stop cannot reach an unsafe level of saturation.
This is all true, yet for decades we've *implemented* all kinds of bogus ideas, everything from milk truck pulling up to their oxygen windows, isobaric counter diffusion, and assumptions about bubble growth via deep stops. Some of these ideas persist today despite years of refutations.
You are right. It is an unfortunate part of the scientific process that hypotheses are sometimes accepted as fact, errors are made, and erroneous conclusions are drawn from data. In time, those get corrected, but, yes, those corrections take a while. With diving, I think it takes longer to get corrected for one simple reason: there is no clear and accepted source for information.
Take for example the issue of bubble growth and deep stops. If you follow the research, you know that for a while, the idea that deep stops helped control bubble growth was very popular, but that idea is no longer supported by the leaders of dive research. Here's the problem--how do you follow the research? How are people supposed to know this?
Several years ago I did a Google search on the topic of deep stops, and I found that in the first 10 pages of results (100 articles), there were only 2-3 articles that reflected current thinking. Some of those articles even had headlines stating they were the latest thinking, even though nothing in the articles was from the previous 15 years. That is why I got help from Dr. Simon MItchell and published the latest thinking on deep stops in decompression diving. Do a Google search today, though, and you will find roughly the same thing I did years ago--article after article extolling deep stops as the latest and greatest thing, with my article probably not even showing up.
The issue of deep stops is different in NDL diving, and there you have a different issue. There is really no good research on the topic. The only studies are flawed and not highly regarded. DAN Americas has an article saying not to do them, but it is a very old article. DAN Europe says to do them, citing the two flawed studies.
So, where do people go to find accurate information on these issues?
GUE. GUE always has the right answers. /s
Unfortunately dive shops and instructors are some of the worst propagators of outdated information. And folks with financial interests in now outdated algorithms
More likely to find a consistent and nuanced answer there than most other agencies.
Jarrod’s 4 part series is worth a read.
Decompression, Deep Stops and the Pursuit of Precision in a Complex World
In this first of a four-part series, Global Underwater Explorers’ (GUE) founder and president Jarrod Jablonski explores the historical development of GUE decompression protocols, with a focus on technical diving and the evolving trends in decompression research.
indepthmag.com
After my article was published, GUE printed an article with a title and introductory paragraph promising new research that supported using deep stops for decompression diving. The article went on to produce no new research whatsoever. The only research cited was the two roughly 20-year-old articles on NDL diving deep stops that I mentioned before as being discredited.More likely to find a consistent and nuanced answer there than most other agencies.
Jarrod’s 4 part series is worth a read.
Decompression, Deep Stops and the Pursuit of Precision in a Complex World
In this first of a four-part series, Global Underwater Explorers’ (GUE) founder and president Jarrod Jablonski explores the historical development of GUE decompression protocols, with a focus on technical diving and the evolving trends in decompression research.
Of course they are. No one else is propagating that sort of information, and once they get an idea in their heads and have nothing to refute it, why wouldn't they repeat it?
I heard over and over as a new instructor that dehydration was the number one cause of DCS, and I repeated that misinformation to many students before I found out 1) there is no research supporting it, and 2) there is a danger in overhydrating. On the dive boats I used in Florida this winter, the DMs made the need to drink as much water as possible a key part of their initial introductory speeches. I did not tell them otherwise.
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