Diving with gradient factors for a new recreational diver

[BlueTrin]

I just look at it as a long safety stop if at GF70 vs GF85 or GF100.

were you replying specifically in the context of shallow depths in your previous post?

 

[scubadada]

How do you know? Do you actually know what the expected incidence of clinical DCS is at GF100, GF85, and GF70? Do you have a cite to show for it, or are you just saying it because you read it on The Internet So It Must Be True(tm)?

Yes, but if the expected incidence "is usually assumed to be one hit in a few thousand dives"(*) at GF100, and lowering it to GF70 results in one hit in a few thousand and one dive, then why bother. It maybe would matter if it's one hit in a few tens of thousands of dives, -- depending on one's personal take on risks, -- but we have no data to show it's one or the other, or anything in between.

*) The Theoretical Diver – Theorizing about scuba diving

The SAUL recreational dive planner is currently unavailable, or I would have run GF highs of 99, 85 and 70. Here is a previous example of diving to the NDL at 100 ft. on 32% with GF highs of 95, 85, and 75.

Conservatism

I had a dialog with a fellow diver on consevatism. He is an fierce advocate of eliminating risks, and consequently diving conservatively. He recommended to set my my Shearwater computer at high conservatism AND set max ppO2 at 1,2. This made me wonder afterwards, how does each of this impact...

scubaboard.com

Of course, these are not for an individual, but a population. The risk of DCS is increased with increased exposure and decreased with less exposure.

 

[dmaziuk]

Yes, the way the Buhlman model works, the lower the GF High the lower the incidence because you get out of the water with lower residual inert gas.

You get out of the water with lower residual inert gas if you're following the decompression schedule to the letter and surface at exactly the controlling M-value. Has Buhlmann ever modeled no-stop dives where most people never hit the M-value anyway, and then hang at the safety stop until their surfacing overspressure drops into low 50s? If not, then he didn't know how the model works in that scenario. But I'm sure you do.

 

[dmaziuk]

The SAUL recreational dive planner is currently unavailable, or I would have run GF highs of 99, 85 and 70. Here is a previous example of diving to the NDL at 100 ft. on 32% with GF highs of 95, 85, and 75.

Yeah, but what do his numbers actually mean to the user? If you don't know what the expected DCS incidence was on DSAT, how do you relate his predicted probabilities to your thousadns of DSAT dives?

 

[scubadada]

Yeah, but what do his numbers actually mean to the user? If you don't know what the expected DCS incidence was on DSAT, how do you relate his predicted probabilities to your thousadns of DSAT dives?

You can look up NDL times from DSAT just like you can for Buhlmann and run those in the SAUL planner. I've been running DSAT and Buhlmann together since 2016, a little over 1100 dives, and know that DSAT runs similarly to a GF high of 95.

In reality, most no stop dives are not to the NDL and carry a lesser risk of DCS. Since I bought my Teric in May 2019, my average surfacing GF has been in the 50s. For dives closer or to the NDL and my light deco dives, I have not surfaced with a GF greater than 80 by using SurfGF on my Teric. I have reduced my risk tolerance as I have gotten older.

 

[tursiops]

DSAT runs similarly to a GF high of 95.

For a first dive only, right?

 

[JoeTPhilly]

How does one see the SurGF on Shearwater? GF99 appears on the graph but I don't see anything for SurGF.

 

[Capt Jim Wyatt]

were you replying specifically in the context of shallow depths in your previous post?

I don't understand your question.

 

[BlueTrin]

I don't understand your question.

You said that GF would just make it similar to a long safety stop, I guess that’s because OP was asking about recreational dives and you are replying in this context?

For deeper dives that may involve a deeper stop so it would be less clear.

 

[steinbil]

How does one see the SurGF on Shearwater? GF99 appears on the graph but I don't see anything for SurGF.

You mean after the fact? Import it to subsurface. During the dive? You can customize the display to show it on the middle line in Tech mode.