Feedback on recent two-tank and dive limits

[ofg-1]

We just go doing multilevel NDL and Deco dives and not get DCS hits.
So if I have over 3500 dives and no DCS hit's hows that work out for your mathematical probablility of me getting a DCS hit?

You know, I've had over 3500 showers in my life and never fallen in the tub. That does not mean the probability is zero.

 

[Blackcrusader]

You know, I've had over 3500 showers in my life and never fallen in the tub. That does not mean the probability is zero.

I did not write my probability was zero did I? But for someone to claim there is a 3% probability I will get one I'd like to know based on what information that came from. If I get a DCS hit I will let you know.

 

[JMarc]

I don't know anyone that does square profile dives even on deco dives

Some are close. Last wreck dive I did, bottommed at 55m, ascent from 45m to the gaz switch depth then to the stops.

Another non-wreck dive. Bottommed at 40m, ascent starting from 30m, launch of at DBSM and stops...

Being able to ascent and doing stops along a reef for sure make that part more pleasant.

Still none of this is relevant to the OP"S post

The thread has drifted far from that. The thing which keeps it alive is the nonsense that nobody want to leave uncorrected fearing a lurker would think it is serious.

 

[inquis]

Probability is the mathematical potential of something happening, not that something is going to happen and I did include a + and -.

You did include a ±, but without any numbers, leaving it up to the reader to guess the interval of your estimate, as well as the confidence level of said interval. In other words, stop digging.

I also noticed you didn't comment on my observation that Buhlmann ZHL+GF at the common presets is LOWER average risk than DSAT. I'm not trying to throw DSAT under the bus. On the contrary, I feel it is extremely safe and am using it to refute your claim that ZHL+GF is a danger to NDL divers.

 

[crofrog]

I did not write my probability was zero did I? But for someone to claim there is a 3% probability I will get one I'd like to know based on what information that came from. If I get a DCS hit I will let you know.

The US Navy and the Swedes have both done manned validations of the USN tables both the older standair tables, and the newer Thalman based tables in rev6 and rev7. VVal-79 produced longer no-stop times than the older standair tables that resulted in the new tables in rev7 which used the older no-stop times.

All of these are built around a pDCS of 3% for type 1, and 0.1–0.2% for type 2.

It's important to read how those validations where conducted, and consider if you're dives are similar or not.

If you want some light reading...

Andrew, B. T., & Doolette, D. J. (2020). Manned validation of a US Navy Diving Manual, Revision 7, VVal-79 schedule for short bottom time, deep air decompression diving. Diving and hyperbaric medicine, 50(1), 43–48. Diving and Hyperbaric Medicine - Abstracts 2020 50 (1)

Fraedrich D. (2018). Validation of algorithms used in commercial off-the-shelf dive computers. Diving and hyperbaric medicine, 48(4), 252–258. Diving and Hyperbaric Medicine - Abstracts 2018 48 (4)

 

[crofrog]

also noticed you didn't comment on my observation that Buhlmann ZHL+GF at the common presets is LOWER average risk than DSAT. I'm not trying to throw DSAT under the bus. On the contrary, I feel it is extremely safe and am using it to refute your claim that ZHL+GF is a danger to NDL divers.

For no stop dives.

 

[scubadada]

The document describing the development and validation of the DSAT RDP is available on SB, courtesy of @tursiops It makes for good reading and is highly recommended

Info Thread 'The DSAT Recreational Dive Planner (RDP), 1994'

Feb 20, 2024

Document Name: Development and validation of no-stop decompression procedures for recreational diving: The DSAT Recreational Dive Planner
Authors: R.W. Hamilton, Raymond E. Rogers, Michael R. Powell, Richard D. Vann, with Richard Dunford, Merrill P. Spencer, Drew Richardson

Attached is the 1994 report from DSAT on the Development of the Recreational Dive Planner (RDP).
It used to be available on the Rubicon site, which is now defunct.

Filename: DSAT_1994_The_Recreational_Dive_Planner_OCR_opt
File Format: Adobe PDF
Size: 14,323 kB
Pages: 126

• tursiops
• Replies: 1
• Forum: ScubaBoard Download Library

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I have been diving an Oceanic computer running DSAT since 2002, over 2,400 dives. I have been diving a computer running Buhlmann ZH-L16C with GF since 2016, over 1,300 dives, first a Dive Rite Nitek Q and then a Shearwater Teric since 2019. Most of my diving has been no stop, much of it reasonably close to NDLs. A little less than 5% of my dives have been light back gas deco, generally less than 10 min, always less than 15 min.

My Oceanic computers have always run DSAT without conservatism. I did some experimentation with Buhlmann GF settings in the beginning but have run a GF high of 95 the vast majority of the time. DSAT and a Buhlmann GF high of 95 run similarly but are different on both first dive and repetitive dives. DSAT tends to be more liberal on first dive, particularly when deeper. Buhlmann tends to be more liberal on repetitive dives, particularly when shallower. I have posted some of this experience on SB, including these more extreme examples

Thread 'DSAT vs GF high 95, examples'

Sep 28, 2021

I have written previously about my experience diving DSAT and Buhlmann ZH-L16C with a GF high of 95. I have an example of what I have previously reported. This dive is a first dive of the day on the Castor in Boynton Beach. It was relatively deep with a max depth of 107 feet and an avg depth of 73 feet. DSAT gave me a minimum NDL of 6 minutes. A GF high of 95 on my Teric gave me 1 min of deco at 10 feet. My surfacing GF was 79.

This is a dive later in the week. It is the 4th dive of the day, following 3 moderately deep and long dives. This was a...

• scubadada

I have been fortunate to have never had signs or symptoms of decompression sickness. Many years ago, I began padding my safety stop when I was close to the NDL and adding additional time to my deco stop. Since having my Teric, I have used SurfGF to adjust my safety stop or deco stop to surface with the GF I desire.

Until a couple years ago, the SAUL decompression model, a probabilistic algorithm, was available. Unfortunately, it is no longer online. The recreational dive planner allowed for the calculation of the probability of DCS based on gas, depth, and time. Below is a screen shot of the RDP and a spreadsheet listing the probability of DCS for diving air at the DSAT NDLs. The highest probability, 0.41%, would be a risk of about 1/244 dives all the way to this limit. Obviously, this is far less than the 3%, 1/33, discussed above.

 

[Subcooled]

You make very good point about situational conditions. And on many occasions the dive you execute may turn out to be quite different to the dive you anticipated and planned.

This is how the frogman executes a NDL recreational dive. I use one of my dive computers which has a DSAT algorithm (no conservative settings). I complete the bottom time. Just before or during my ascent I decide which safety stop profile I adopt, based on the dive conditions I just experienced.

I may choose to do 3 min at 15 ft, or perhaps 5 min at 15 ft, or if it has been bit of a tough dive I may break up the safety stop into 2 x stages, that is, 2 min at 15 ft followed by 3 min at 10 ft. (just a few stop options in my bag of tricks). It's all about using the safety stop to keep the DCS risk value to about 3%.

If doing a stop at 10 ft, I may shoot a DSMB, go slightly negative buoyant and just hang relaxed on the SMB. Off gassing at 10 ft is enhanced.

No messing about trying to decide on what GF to select or changing the GF mid ascent because it is not adequate for the actually experienced dive conditions.

Simple, no expensive over the top dive computer required.

Less is more.

Some people think that the dive ends at 18 feet. It does not, however. The shallow stops can be great for many reasons:

1. Sunshine, finally. Plants and fish to be seen.
2. All the extra time spent at 15 or 9 feet is still diving.
3. Buoyancy control skill grows fastest in the shallows.
4. I feel much better after spending "too much" time at 15 feet and also some at 9 feet and then doing an excessively slow ascent. I do not know if this is due to physical or mental effects, but the relaxed and prolonged resurfacing feels really good.

 

[old frogman]

I'd like your source for the probabilistic modelling used for tables in use in the early and mid 80s. I'm just aware of probabilistic modeling done during the mid to late 80's and not aware of any table nor dive computer which used those models (although the probabilistic models were used in experiments and in the parameter determination and validation of other models).

BTW, I know of no used model which keep a constant DCS risk on the range of depth and time. Everything that I'm aware of indicates that the risk increase with the depth and time of the dive. US Navy table used in the 80's are not an exception.

"Deeper into diving" 1991 Edition 1, author John Lipman. Delves into the history of decompression diving from pre-Haldane to PADI RDP and BSAC 88 Tables. Contemporaneous record of the 1980s dive tables development. Goes into the US Navy Tables development, and its subsequent relationship to the development of the NAUI tables, Bassett tables and Huggins tables and eventually the PADI RDP tables.

"Deeper into diving" 2005 Edition 2, author John Lipman and Simon Mitchell. Review of Edition 1 with introduction to Bubble based, decompression theory, for example VPM, RGBM. Also covers Buhlmann with GF (dissolved gas, based decompression theory).

Incidentally, Erik Baker not only develop the Buhlmann GF decompression system but also developed the VPM-B decompression system. Both developed for technical diving.

VPM-B was based on bubble propagation theory.

Buhlmann GF was based on Haldane's original dissolved gas theory combined with a mathematical interpolation of low and high GF producing an ascent profile for deep decompression dives.

Although based on two different theories, that is, bubble propagation for VPM-B and dissolve gas for Buhlmann GF, both are an attempt to control microbubble propagation during ascent from deep technical dives.

 

[JMarc]

I'd like your source for the probabilistic modelling used for tables in use in the early and mid 80s

"Deeper into diving" 1991 Edition 1, author John Lipman.

I happen to own that one. I just reread the US Navy table chapter and there is no hint that the tables were based on a probabilistic modeling.

Could you provide me a page number where to check?