Info Why are tables not taught in OW classes anymore?

[L13]

And if you had completed your mandatory 3-minute deco stop, you'd get out of the water considerably more not bent than Craig with his 3-minute optional safety stop. That's how gradient factors work in a model whose outcome is incidence of clinical DCS.

What? Why? Our tissue nitrogen levels would be identical all the way to the surface and after!

We would exit the water identically not bent (assuming we are identical twins, identically hydrated, rested, etc., which probably actually dominate for bent/not bent on a dive like this).

 

[scubadada]

And if you had completed your mandatory 3-minute deco stop, you'd get out of the water considerably more not bent than Craig with his 3-minute optional safety stop. That's how gradient factors work in a model whose outcome is incidence of clinical DCS.

Don't be so sure. I would have started my ascent with at least 4 min of NDL, not that close to surfacing at my GF high. Then, I did a routine 3 min safety stop, not counted in Shearwater's calculation. So, I would have been below my GF high, not sure by how much.

Hi @L13

The question was no stop vs. deco dive. Despite your 2nd opinion with Subsurface, my dive was no stop and yours was a deco dive. You had a ceiling and a mandatory stop on your computer.

Again, this is the Basic Forum. Most divers are not using computers running Buhlmann with GF. Regardless of how conservative their computer is, if they exceed NDL and go into deco, they need to follow the computer and clear decompression. If not, they risk violation and lockout for 24-48 hours. I see this a few times every year on charter boats out of SE Florida.

 

[dmaziuk]

What? Why? Our tissue nitrogen levels would be identical all the way to the surface and after!

We would exit the water identically not bent (assuming we are identical twins, identically hydrated, rested, etc., which probably actually dominate for bent/not bent on a dive like this).

Yeah, but you see: if this were the case, then there wouldn't be no point in lowering your GF high from 95 in the first place, so... why did you?

 

[inquis]

If we tweaked the dive parameters just right, we could get a dive with 45/95 that was NDL with a 3 min SS, but with 35/75 that was a "deco dive" with a 3min deco stop.

I doubt it, but that's immaterial. The point is on the way up, your tissues are loaded in excess of your desired safety margin and Craig is under (well under) his. A direct ascent in his case is *still* under his limit. In your case, skipping mandatory stop(s) leaves you (still) above yours and is therefore no bueno.

No argument that the tissue loading is the same, but presumably you set your margin where you did for reasons. Those reasons are precisely why you have to stop but he doesn't.

 

[L13]

I doubt it, but that's immaterial.

Why? the 40 min dive to 80ft using EAN32 is exactly that on the SubSurface planer (with my ascent rates, etc.). But all you have to do is set to 35/75 and adjust your dive time till it calls for a 3min deco stop. Voila! The same dive with 45/85 with a 3min SS will be identical physiologically.

The point is on the way up, your tissues are loaded in excess of your desired safety margin and Craig is under (well under) his. A direct ascent in his case is *still* under his limit. In your case, skipping mandatory stop(s) leaves you (still) above yours and is therefore no bueno.

The claim was that the dives were fundamentally different, not that they were above or below a particular persons desired limits.

No argument that the tissue loading is the same, but presumably you set your margin where you did for reasons. Those reasons are precisely why you have to stop but he doesn't.

Exactly! The dives are identical! The differences are my desired margins, not anything fundamental about the dive itself!

But, @scubadada is right, since this is the basic forum, the correct answer is to pick your settings and do what your computer says with regard to stops and NDL. Understand how and why settings are different and what their real effects are, should be reserved for advanced scuba.

 

[EFX]

Are you contending that the dives are fundamentally different(NDL vs. Deco)? or that our behavior on the dives are fundamentally different?

I 100% agree with the latter, and strongly dispute the former. It is very possible we are talking past each other, and agree more than you think.

NDL and deco dives are fundamentally different because one type of dive demands mandatory stops and the other type doesn't. Our behavior is fundamentally different because those dives being fundamentally different demand that our behavior is different assuming we want to be safe from DCS.

Edit: content removed due to irrelevance.

 

[L13]

NDL and deco dives are fundamentally different because one type of dive demands mandatory stops and the other type doesn't. Our behavior is fundamentally different because those dives being fundamentally different demand that our behavior is different assuming we want to be safe from DCS.

As you mentioned in a previous post there is a gray area in which DCS is a possibility should a particular controlling tissue compartment's pressure venture inside it. Since human beings don't like fuzzy limits we depend on well-defined limits that can be depicted as a line through this gray area. Since it is a gray area our algorithms can determine the position of that line by the conservative settings (among other settings) we enter in our dive computers.

From the standpoint of the algorithm (ex. Buhlmann with GF's) all dives are identical in that a ceiling is always calculated. That ceiling becomes a limit to avoid either tissues developing dangerously high pressures or to remain an NDL dive. The calculation is the same but depending on the dive type (deco or NDL) the result is interpreted differently. The dive begins as a NDL dive. For NDL dives the ceiling is negative (above the water). At any particular depth a loop is started with time equal to 0. That time is incremented in 1 minute intervals and the ceiling is calculated until it becomes zero (at the surface). The accumulated time at that point becomes the NDL time remaining.

Should the diver run the NDL time down to zero, the dive becomes a deco dive and mandatory stops are required. In this case a calculation is done to determine the first stop (which has a positive ceiling, i.e. below the water) according to GFLo. It gets rounded up to the next deepest multiple of 10 ft or 3 m. The same kind of loop is run by incrementing time in one minute intervals and the ceiling is calculated. When the ceiling equals or is less than the next shallower deco stop according to the stop interval set or fixed in the computer, the accumulated time becomes the stop time at the current stop depth. When the diver has stayed for the required stop time she may ascend to the next shallower stop and the cycle starts over until the diver reaches the surface.

A whole lot of noise that didn't even remotely address the question. At l first glance all of it is right, and none of it is relevant.

Say I dive with two computers, one set to GF 35/75 and one that is set to 45/85. They are both running Buhlmann GF's as represented by SubSurface's dive planer for their algorithm. I Use EAN32 and go to 80 feet for 40 min. Computer 1 says I am in deco and must do a 3 min stop. Computer 2 says I am within NDL and recommends a 3min safety stop. I do a 3 min stop. Both computers say I ended the dive with a GF Surface of 75%.

Did I do two fundamentally different dives at the same time? Does anything change in my body depending on which computer I look at? Does anything change in my risk of DCS?

Or did I fundamentally do one dive with two different views about what was? Just one set of physiological effects, and just one DCS risk?

 

[EFX]

I tried to present some information that shows how both deco and NDL dives can be treated the same and in another way differently, but you reacted to it by insulting me. Without noise my answer to those five questions you posted above are: no, no, no, yes, and yes.

 

[L13]

I tried to present some information that shows how both deco and NDL dives can be treated the same and in another way differently, but you reacted to it by insulting me. Without noise my answer to those five questions you posted above are: no, no, no, yes, and yes.

You are right. I was insulting. I apologize. I lost track of who I was talking to and thought we were repeating arguments that I had already acknowledged. I should have been more patient and observant.

My answers to those questions are exactly the same as yours.

My point is that there is nothing fundamentally different between an NDL dive and a "deco dive" as such. The fundamental difference between dives is how much compression and decompression happened, along with many other factors like rest, hydration, health, exertion level, etc. And the vast majority of those differences between dives exist on a continuum without the sharp NDL/Deco dividing line that some think exists.

Yes, our procedures change once we cross a threshold in that continuum. They change quite dramatically. But the underlying nature of the dives themselves don't change dramatically, just incrementally.

 

[jborg]

My point is that there is nothing fundamentally different between an NDL dive and a "deco dive" as such. The fundamental difference between dives is how much compression and decompression happened, along with many other factors like rest, hydration, health, exertion level, etc.

I think you may be missing the point of those who say they are fundamentally different. It's not about the borderline dive in the grey area which could be classified in either direction by choosing different GFs. It's about the difference between (f.ex) an NDL dive to 20m and a dive to 50m with significant deco. They are different in the sense that research on what works for one just doesn't apply to the other. For example, is doing a slow ascent from an NDL dive "riding the the NDL" equivalent to doing a slow ascent from a deco dive "riding the ceiling"? No, because what happens physiologically is different enough that research on one doesn't apply to the other, so they're fundamentally different.