Deco cleared "on the go"?

[johndiver999]

If your computer stays in NDL until you surface, it was a no stop dive, safety stop is optional. If your computer goes over into deco, no matter how short the time, no matter if it clears on the ascent, this was a deco dive. I believe it would be recorded that way, on computer, or downloaded.

Exactly and the basic recreational diver needs to know little else. As others have mentioned, if you want to do a science experiment with your spinal cord and genitalia, then you can probably come up a little slower than recommended and be ok. Go up too slow and the penalty increases, come up a little slower and it may disappear. Run out of gas and things get really interesting. Experiment all you want.

We don’t need a re-writing of terminology.

 

[doctormike]

Define "long enough". On the profile I posted I get a ceiling after 7-ish minutes at 90-ish fsw, that would be the "long enough" by your definition. By PADI RDP definition, it's 21 minutes before the "optional means mandatory" grey boxes, and 25 to NDL=0. That's ~300% difference.

Long enough: The time it takes to run your NDL to zero based on the dive computer that you have chosen, the algorithm it uses, the conservatism or GF modifications that you use, the profile that you are actually running, and the mix that you tell your computer that you are breathing.

The fact that LE is a different number if you use different variables is irrelevant. Why would you imply to a recreational diver that the NDL that his or her dive computer generates during a dive is somehow up for negotiation or analysis? Being "in deco" isn't some absolute quality that you can measure in a diver, the phrase only has meaning in the context of all of those variables.

And just to silt things up more for the recreational divers reading this, there are a whole bunch of other variables that the computer can't account for that can get you bent! You can get bent by staying within NDLs, and you can blow off deco and have no symptoms of DCS. It's simply not possible to model physiology that accurately, but your standard recreational dive computer will do a good job of making the risk of DCS acceptably low.

Here, 90 FSW for 20 minutes on air. Same dive repeated on two successive days.

Day 1, GF 30/70 -> 8 minutes of deco

Day 2, GF 99/99 -> NDL dive

So was I "in deco" on day 1? On day 2? Both? Neither?

What this means is that a diver is "in deco" if their computer tells them that they have gone past NDL=0, or if it generates a mandatory stop, or if it generates a ceiling. Even if it clears on ascent, or if the stop goes away. And if that diver has no technical training, they should avoid that condition by not staying underwater so long, based on their own chosen means of tracking N2 loading (i.e. their DC).

Does RDP's "optional safety stop required" mean it's a mandatory stop?

Just trying to get the terminology right so that further discussion will be clearer. And I appreciate your replies.

This kind of fuzzy language is not helpful, not sure what it means for something to be both optional and required. Maybe I need some context for that language, don't have an RDP.

 

[scubadada]

Long enough: The time it takes to run your NDL to zero based on the dive computer that you have chosen, the algorithm it uses, the conservatism or GF modifications that you use, the profile that you are actually running, and the mix that you tell your computer that you are breathing.

The fact that LE is a different number if you use different variables is irrelevant. Why would you imply to a recreational diver that the NDL that his or her dive computer generates during a dive is somehow up for negotiation or analysis? Being "in deco" isn't some absolute quality that you can measure in a diver, the phrase only has meaning in the context of all of those variables.

And just to silt things up more for the recreational divers reading this, there are a whole bunch of other variables that the computer can't account for that can get you bent! You can get bent by staying within NDLs, and you can blow off deco and have no symptoms of DCS. It's simply not possible to model physiology that accurately, but your standard recreational dive computer will do a good job of making the risk of DCS acceptably low.

Here, 90 FSW for 20 minutes on air. Same dive repeated on two successive days.

Day 1, GF 30/70 -> 8 minutes of deco

Day 2, GF 99/99 -> NDL dive

So was I "in deco" on day 1? YES On day 2? NO Both? NO Neither? NO

What this means is that a diver is "in deco" if their computer tells them that they have gone past NDL=0, or if it generates a mandatory stop, or if it generates a ceiling. Even if it clears on ascent, or if the stop goes away. And if that diver has no technical training, they should avoid that condition by not staying underwater so long, based on their own chosen means of tracking N2 loading (i.e. their DC).

See my responses in @doctormike text. You are in deco if the computer you are diving says you have exceeded NDL and are in deco. Everyone has their own choice of computer to use, deco algorithm to run, personal settings to use. Once you choose, you're stuck with it, choose carefully.

 

[dmaziuk]

Long enough: The time it takes to run your NDL to zero ...

Well that's the problem: on my dive with the ceiling my NDL was never down to 0 (and I strongly suspect neither was the OP's). I had a ceiling and an NDL greater than zero.

Chopped up to keep the copyright weasels off the Chairman's back (hopefully):

 

[Jay]

...I'm making the point that a new diver should be situationally aware and NOT exceed NDLs, and NOT let their dive computer generate a ceiling, no matter HOW that ceiling is calculated. Because if a non-technically trained diver gets a mandatory deco stop on the computer that they choose to use (with whatever algorithm or conservatism), that's a major failure of situational awareness. ...

Didn't this aspect of the conversation start because of the the discussion around the effect (if any) of GFLo in No-stop diving. (ref page 3)
It takes an absurdly low GFLo to have any effect, and if there is any, it so minimal that it doesn't exist if you have a regular rate of ascent. (please see the other thread linked to in post #27)
Given it doesn't exist, it's merely just an academic discussion then (or one using extreme double conditions)?
In which case 'we' can say GFLo effectively doesn't affect a NDL or Non-stop dive. Which was the upshot of the other thread, for all of the computers we looked at.

I agree terminology is important (and FWIW I agree re the term NDL etc) , but if you survey non SB rec divers on what a ceiling I'd be willing to bet they think of something flat and white.

Situational awareness is obviously important, but in this [EDIT to add] aspect of the discussion/ case ...:

To input and absurdly low GfLo into your computer, be clueless of what it means, and it's something that is radically different to any of the computer's presets, then this case is more about being an excessively clueless than anything else?

 

[atdotde]

There is no black-white distinction between a recreational NDL>0 and a decompression dive: In no dive to any significant depth you should pop to the surface just like a cork and in some other dives the ascent rate that you assume as "standard" (e.g. 30ft/min) is not slow enough in parts of the ascent. But it is gradual as in "which ascent rate is slow enough"? Of course dive operators and agencies want to draw a line somewhere but that is because they don't want to be dragged into endless discussions with customers or find themselves in court arguing what they should have done.

And for a dive table or dive computer during a dive it makes a lot of sense to display the information to the user if a 30ft/min ascent is fine or not (and if not where they should stop or actually: slow down) because that information is the most relevant to the diver in the water.

As far as subsurface (and possibly other dive log software) is concerned, it shows that information as well (it's in the info box stating the NDL or TTS at a given point in the dive). But that is _not_ the information that is displayed by the green area (hopefully) above the profile that lacking a better word we call "ceiling": As I said above, this information is about the tissue loadings translated into depth meaning "your decompression model does not allow you to be above that depth at this moment in time". This is independent of ascent rate or how deep you actually dive in the future of that point in time. It is not "if at this point I would start a 30ft/min ascent, at which point will I hit the ceiling", it's the actual ceiling right now. And it might go up during an ascent. And if you find it confusing, there is a button to turn it off.

Note that in this mode, Subsurface is a dive log, it is not used during the dive but to analyse your dive in retrospect. And the information that the ceiling gives you is how much safety margin you had during the dive (according to a model of course), how far you were away from the "no go zone". As long as you are much deeper than the ceiling everything is fine, just don't cross it.

Of course, there is the planner as well and in recreational mode it will plan you a dive that (using the configured ascent rate) tells you how long you can stay at depth such that with that ascent rate you will not hit the ceiling. And in actual deco planning mode it will plan stops for you to avoid hitting the ceiling.

 

[KenGordon]

As far as subsurface (and possibly other dive log software) is concerned, it shows that information as well (it's in the info box stating the NDL or TTS at a given point in the dive). But that is _not_ the information that is displayed by the green area (hopefully) above the profile that lacking a better word we call "ceiling": As I said above, this information is about the tissue loadings translated into depth meaning "your decompression model does not allow you to be above that depth at this moment in time". This is independent of ascent rate or how deep you actually dive in the future of that point in time. It is not "if at this point I would start a 30ft/min ascent, at which point will I hit the ceiling", it's the actual ceiling right now. And it might go up during an ascent. And if you find it confusing, there is a button to turn it off.

Given that many people learn deco theory by playing with your software (I know they should not) perhaps displaying both the actual ceiling you show now and the ceiling assuming a 10m/minute ascent would aid understanding.

 

[taimen]

Given that many people learn deco theory by playing with your software (I know they should not) perhaps displaying both the actual ceiling you show now and the ceiling assuming a 10m/minute ascent would aid understanding.

Disagreed. The Subsurface ceiling display is correct right now. I know these are opinions, but personally I don't find that "dynamic" ceiling with assumed ascent rates logical at all. NDL, TTS and to some extent SurfGF displays can be used to figure out how the ceiling effects your plan.
And in planner mode, Subsurface (like all planners) does it already. If you don't hit your ceiling with a sepcified ascent rate, you won't see a stop.
Also the UI is rather complex already so I would be very careful when adding new features into it.

 

[atdotde]

Given that many people learn deco theory by playing with your software (I know they should not) perhaps displaying both the actual ceiling you show now and the ceiling assuming a 10m/minute ascent would aid understanding.

Well, maybe. But you realise that in the log, this is counterfactual: If at any point in the dive, you will ascent (with that rate) you either hit the ceiling or don't and that you already see now. Why include information about an alternative universe? I don't think that should go into the profile graph as well (and it is already in the textual information as the first stop depth).

 

[doctormike]

Well that's the problem: on my dive with the ceiling my NDL was never down to 0 (and I strongly suspect neither was the OP's). I had a ceiling and an NDL greater than zero.

Go back and read the OP's posts and look at his screen shots. As he mentioned, he had exceeded NDL for the time that a ceiling was generated. And that's the point of this discussion.

The only way that most divers get information about their real time nitrogen loading during a dive is with a dive computer. The diver makes a set of choices (DC model, algorithm, conservatism or GFs), and once those choices are made, they should be aware of and take seriously the output of that DC. In this case, the DC told the diver that he was past NDL=0 and had a ceiling. So while, yeah, I suppose that some computers would let you say "huh, I don't want to be in deco, I'll just change my GFs to 99/99 and continue my 'NDL' dive" but that would be ridiculous.

I see your point that based on the definition of "ceiling" used, you could have your DC telling you that you had a ceiling before NDL=0. That's not how (for example) Shearwater does it, but I will believe you if you tell me that your DC does that.

The whole point is that the OP was told by his DC that he had exceeded NDLs, and his computer had generated a ceiling and a stop. Coming up with explanations about how this was anything other than a failure of situational awareness and potentially dangerous is not helpful.[/QUOTE]