Deep-stops vs shallow-stops: an interesting read.

[Ripley]

Gradient Factors in a Post-Deep Stops World

 

[AfterDark]

I've had suspicions about deep stops since I started reading about the subject. Seems the more I read the more those suspicions grow.

 

[markmud]

Hi Ripley,

The article you linked is a few months old. I am sure there are threads on SB about this information already. @boulderjohn has referenced his article on SB already. Dr. Doolette used John as a reference for the article you linked.

Nothing like real studies with evidence of DCS and VGE to give credence to the lack of efficacy of deep stops (however, I do understand there is a definitional problem with the term "deep stops" as John explained).

I enjoyed reading the articles again. The money quotes are posted below as far as I am concerned.

My computer uses ZH-L16 GF. So this is what I zeroed in on:

"With this information in mind, I set my GF low to roughly counteract the ZH-L16 “b” parameters (I have been using Shearwater dive computers with ZH-L16 GF in conjunction with my tried and true decompression tables for about three years). In ZH-L16, the average of “b” parameters is 0.83. I choose my GF low to be about 83% of the GF high, for instance GF 70/85. Although the algebra is not exact, this roughly counteracts the slope of the “b” values. This approach allows me to believe I have chosen my GF rationally, is not so large a GF low as I am unable to convince my buddies to use it, and satisfies my preference to follow a relatively shallow stops schedule."

"This article was prepared by Assoc. Professor Doolette in his personal capacity. The opinions expressed in this article are the author’s own and do not reflect the view of the Department of the Navy or the United States government."

@boulderjohn wrote:

"For Bühlmann ZHL-16C, GF low settings lower than 55 led to first stops that were considered to be too deep. The study mentioned that a GF Low of 70 was also acceptable, so it explicitly approved of a range of 55-70 but did not specify an upper limit. It also said a GF high of 70 or below was within the preferred US Navy limits."

Gradient Factors in a Post-Deep Stops World
Evolving Thought on Deep Decompression Stops

I enjoyed it,

m

 

[scubadada]

Most of my diving is no stop, about 5% light deco, less than 15 minutes, I have chosen to dive 80/95. After my SS, my SurfGF is about 85 or lower.

 

[markmud]

Most of my diving is no stop, about 5% light deco, less than 15 minutes, I have chosen to dive 80/95. After my SS, my SurfGF is about 85 or lower.

Hi Doc,

What computer do you use? Does it have a rec mode? If it does, do you dive it in Rec or Tec mode for your light deco diving?

cheers,
m

 

[scubadada]

Teric, rec mode, custom GF

 

[rick00001967]

 

[boulderjohn]

Just to make sure no one misunderstands, my article and Dr. Doolette's article are strictly related to deep stops on decompression diving and do not examine the practice in NDL diving.

Many people have trouble understanding the difference. When I was done with my article on decompression diving, I fully intended to write a similar one for NDL diving. When I finished my research, though, I did not know what to write. Although it is certainly true that decompression must occur on all dives, I decided there really is a difference between dives where decompression stops are required and where divers can ascend directly to the surface, with a gray area where safety stops are strongly recommended for the one and decompression stops are of minimal length and time for the other. There is very little research on deep stops for NDL diving--very little--and it is, IMO, inconclusive.

Dr. Doolette's article here--which I find persuasive and which has affected my decompression diving practices--is really not of much use for NDL diving because the GF low decision is not really important.

 

[d^2b]

Dr. Doolette's article here--which I find persuasive and which has affected my decompression diving practices--is really not of much use for NDL diving because the GF low decision is not really important.

Thanks for posting. I had exactly the question ("but what about NDL diving?") when I read Dr. Doolette's article.

 

[boulderjohn]

To help understand the complexity of the problem, think about 3 divers, each of whom leave the deepest portion of their NDL dive with 3 minutes of NDL on their identical computers. Draw you own conclusions.

1. Diver #1, a deep stops enthusiast, does a 2 minute deep stop at half the maximum depth before heading toward the surface, with a 3 minute safety stop.
2. Diver #2, a multi-level diver, extends the dive for 15 minutes at half the maximum depth, which does not exceed NDL on the computer, before heading to the surface, with a 3-minute safety stop.
3. Diver #3, a multi-level diver, extends the dive for 15 minutes at half the maximum depth, which does not exceed NDL on the computer, and then ascends to 30 feet, where the dive is extended for another 10 minutes before heading to the surface, with a 3-minute safety stop.

The one NDL deep stops practice that I can comfortably say is questionable at best is a rare one--doing a deep stop for a few minutes and then shortening or eliminating the shallow safety stop on the belief that the deep stop makes a full safety stop unnecessary.