Doolette's Alert Diver Interview

[boulderjohn]

The study to which I referred but was too lazy to look up was the Marroni study. It was summarized in an article in Alert Diver in 2004. It was republished by DAN about 5 years ago, but with a note saying that it does not reflect current thinking. You can see it here.

 

[stuartv]

I find it fascinating how many tech divers there are who swear by a specific algorithm (whether it's a computer algorithm or a mental algorithm), but then when you drill into their details it turns out they don't actually use that algorithm for their ascents. They just use it as a baseline for then adding their own customizations - generally along the lines of "I add a 1 minute stop at xzy depth before the algorithm calls for it", or "I pad my 6m stop by xxx minutes".

They tout some algorithm as being reliable and safe but then never actually dive it - instead diving a much more conservative version of it.

I'm also fascinated by the tech divers who use average depth for ANYTHING when it seems like all the science agrees that on- and off-gassing is not a linear process.

Example: 15:00 at 90 followed by 15:00 at 130 yields an average depth of 110. 15:00 at 130 followed by 15:00 at 90 yields the same average depth. And there are certified tech divers who, apparently, think the same ascent plan is appropriate in either case!

I do have to agree with the OP that intuition makes it SEEM like a "deep stop" followed by longer shallow stops would be safer. In fact, is that even a debated point? The OP makes it sound like this "intuitively obvious" answer is up for debate? Isn't the only real question "how much shallow time do we add to compensate for an extra deep stop"? If we don't add enough, the deep stop increases risk. If we add enough, the deep stop decreases risk. Right?

 

[RyanT]

Hey Stuart, it's really simple (tongue in cheek on the simple part). Get as shallow as you can without excessive bubbling and begin your decompression at that point. That is the most efficient way to off-gas. Of course, the problem is, what is the shallowest you can get without excessive bubbling? We still don't have a good answer for that. Your point is well taken, that safe deco procedures can vary quite a bit depending on the profile. For me, I like to dive a relatively conservative profile, and then usually add a couple of minutes on top of that, just because.

Of course, my profiles are what many would call "light deco." I never come close to a CNS clock of 100%, so my profiles give me a lot more wiggle room than folks who are doing really long hangs.

 

[beester]

No disrespect taken Simon, not at all. Just to clarify what I heard was just hearsay but it was from one of the test persons. Also hoping results and methodology will be published soon.

And thank you for clarifying a misunderstanding.

 

[Dr Simon Mitchell]

The study to which I referred but was too lazy to look up was the Marroni study. It was summarized in an article in Alert Diver in 2004. It was republished by DAN about 5 years ago, but with a note saying that it does not reflect current thinking. You can see it here.

Yes, that is the one.

Beester's one is different as I described.

Simon M

 

[atdotde]

For those of you who want to play around with them yourself, we have added the heat map diagram recently to Subsurface. You can use them both for logged dive as well as in the dive planner. You need to get the daily download for this feature to be present: Index of /downloads/daily

 

[DevonDiver]

... , it's really simple... Get as shallow as you can without excessive bubbling and begin your diffused inert gas decompression at that point. That is the most efficient way to off-gas not accounting for micro-bubble proliferation and their potential impact on DCS risk.

Fixed that for you.

There's more to it than accurately defining an M-value (which is what you seem to describe) and associated controlling compartment stop depth.

The deep stops issue is pretty fascinating. Some good theory, but the studies didn't deliver to expectations. Whether that was a 'simple' oversight in accounting for slow tissue saturation at stops . . . or a more fundamental misinterpretation of physiological issues will be revealing .

 

[David Doolette]

Hello John,

I think you and Beester are mixing up two studies. There was an Italian study of a single deep stop at ~half max depth on recreational air dives with venous gas emboli as the outcome measure. That study was published some time ago. I think that is the one you are referring to John.

There is a second study recently run in Italy in technical dives using ratio deco vs a GF approach with less deep stops. I think this is the one that Beester is citing. That study is complete but not published. Hopefully it will come out soon. No disrespect to Beester, but the claim that deep stops worked for some divers but not others is premature, and I would urge everyone to wait for the study to be properly described and published by the scientists who conducted it before discussing the results.

Simon M

Hi Simon,

There is actually a third study, as Beester described. I do not know much about it, but have also spoken to participants.

David

 

[PfcAJ]

I'm also fascinated by the tech divers who use average depth for ANYTHING when it seems like all the science agrees that on- and off-gassing is not a linear process.

Example: 15:00 at 90 followed by 15:00 at 130 yields an average depth of 110. 15:00 at 130 followed by 15:00 at 90 yields the same average depth. And there are certified tech divers who, apparently, think the same ascent plan is appropriate in either case!

That's because it *is* appropriate.

Your first depth/ time profile with 30/30 as a bottom gas and oxygen for deco, GF 40/85 produces a 7min oxygen stop.
Your second profile produces a 5min oxygen stop.
A 110ft avg depth produces a 6min oxygen stop. Literally within 1 minute of your example dives.

60 seconds dude. Come on.

 

[Michael Guerrero]

For those of you who want to play around with them yourself, we have added the heat map diagram recently to Subsurface. You can use them both for logged dive as well as in the dive planner. You need to get the daily download for this feature to be present: Index of /downloads/daily

Any idea when this will make it into the repositories? Fedora in particular?

Also, it's been forever since I looked at any of the deep stops threads. Anyone have a quick guide to reading the heat maps?