"Riding your Computer Up" vs. "Lite Deco"

[DevonDiver]

That's pretty obtuse and pedantic.

YOUR no-stop limit in the one shown by YOUR instrument.

Conservatism is good. Significantly large experience may prove you need less conservatism. Wise divers still want it though. Chamber rides may prove you need more conservatism. Unremarkable, conservative dives show you're doing something right.

Diving occasional weekends or only on annual vacations (or internet chattering) won't teach you squat about your current physiological tolerances to DCS. If you're not doing hundreds of dives per year, you're just fantasising.

 

[uncfnp]

While a diver may carry and refer to an array of NDLs (tables and computers), for a given dive they must end up choosing a subset that they follow and a subset that they violate. Subsequent dives should be conducted using only the subset that was followed on all active previous dives.

Most recreational divers conduct their dives with only a single NDL.

Not necessarily. Again, I am an outlier and I doubt many choose to dive this way. Both of my computers are set for conservative algorithms. Although they are similar there are some differences since algorithms are more then just length of bottom times, especially with repetitive dives. On all my dives I follow the most conservative computer. This can vary from dive to dive. It might be the Petrel on the first dive but often the Cressi on subsequent dives.

And I never "violate" either, unless placing one or both into deco is what you mean by violate.

 

[stuartv]

Think about what you just said...

No-decompression LIMIT

It's a very definitive line, dictated by the model that represents a very reasonable statistical assurance of DCS symptom free diving.

Pick a model (your term) and I will pick 3 different computers that are "based on" (because that's what they all say) that model that all produce different NDLs for the same dive.

Thus, "the model" does not "dictate" a "very definitive line".

As RonR posted here:

Cressi Leonardo- Too conservative?

The implementor of the algorithm in every computer makes many choices in their implementation that can produce different results, even when using the same model.

And that doesn't even factor in the fact that you can pick 3 identical computers and the user can choose different settings (Conservatism, GF, critical radius, whatever...) and get 3 different NDLs - even though all 3 computers are using the same model. So, even further from the model producing a very definitive line.

 

[DevonDiver]

While a diver may carry and refer to an array of NDLs (tables and computers), for a given dive they must end up choosing a subset that they follow and a subset that they violate. Subsequent dives should be conducted using only the subset that was followed on all active previous dives.

Most recreational divers conduct their dives with only a single NDL.

Again, harking back to agency teaching and guidelines.... the recommendation is to dive to the most conservative (i.e. shortest no-stop limit) instrument.

 

[Scuba J7]

There is still a line, what you describe is the manufacturer and end user moving the line. Maybe we should FORCE all manufacturers to use the same algorithm and then follow up with training agencies.

Pick a model (your term) and I will pick 3 different computers that are "based on" (because that's what they all say) that model that all produce different NDLs for the same dive.

Thus, "the model" does not "dictate" a "very definitive line".

As RonR posted here:

Cressi Leonardo- Too conservative?

The implementor of the algorithm in every computer makes many choices in their implementation that can produce different results, even when using the same model.

And that doesn't even factor in the fact that you can pick 3 identical computers and the user can choose different settings (Conservatism, GF, critical radius, whatever...) and get 3 different NDLs - even though all 3 computers are using the same model. So, even further from the model producing a very definitive line.

 

[stuartv]

There is still a line, what you describe is the manufacturer and end user moving the line.

Yep. "The model dictates a very definitive line" (as DevonDiver said) is simply incorrect. There are many more factors than just the model that go into setting where the line is. Including the diver's own choices. And when the diver's own choices are part of what dictates where the line is, it's hard to see how you can ever say that "the line" is "very definitive".

And that's the trouble. OW divers follow exactly all the training given them and get widely varying results. They get told to "dive conservatively" but don't get told what that actually means. If they are diving a DSAT computer with Conservatism 0 and they stay down until the NDL says 5 minutes remaining, DevonDiver says that is "diving conservatively". But, if they happened to also wear a second computer that is running PZ+ algorithm with a Conservatism Factor set to +1 and the exact same dive has that computer showing a deco obligation, then suddenly the diver is NOT diving conservatively. Just because they took a second computer in the water with them. And they get called gibbering morons by an instructor for being confused about what exactly constitutes "diving conservatively" in this context.

 

[scubadada]

Can you explain that? Can you provide any supporting data on the different risk levels?

This may illustrate what @KenGordon meant. The 2.3% DCS comes from the USN Equal Risk NDL studies. As you see, the current USN table NDLs for 60-90 feet are very close to or exceed these values. NDLs from 100 to 130 feet are shorter than the 2.3% DCS values. So, in the same table, USN 2016, shallower dives may have a different risk of DCS than deeper dives. The 1957 USN table exceeded the values at 70 and 80 feet by even more when the NDLs were 50 and 40 minutes, respectively. That was the major motivation for lowering them in the 2008 tables. This may be true of other tables and/or computer algorithms. NDLs at certain depths may carry more risk than other depths. In the table I included, the DSAT NDLs at all depths are all 7-8 minutes shorter than the USN 2.3% DCS values. For Buhlmann, the 60 foot dive is 5 minutes less, whereas, all the other depths are 10-12 minutes less. Due to the relative conservative nature of most dive computer decompression algorithms compared to USN tables, these differences may carry no importance, but it did make me pause to think about it.

 

[MXGratefulDiver]

Read: Alert Diver | Conservative Diving

See:

"Make all dives no decompression dives and allow a margin of safety"
PADI Statement of Understanding - Safe Diving Practices
​

Seriously...what gibbering moron wouldn't understand the general premise of diving conservatively within the limits specified by their agency?

In what dimension of lunacy would doing 'lite deco' beyond no-stop limits, that you'd be content to blow off if necessary, constitute diving conservatively as a no stop dive with a margin of safety and within the limits of your training?

I don't think calling people names in discussions like this adds anything constructive to the conversation, and only calls the credibility of the name-caller into question. When it's done by a dive professional, it undermines their professionalism.

You may have some valid points, but the manner in which you're making them is, at best, counter-productive to the discussion ...

... Bob (Grateful Diver)

 

[Scuba J7]

If an instructor cant explain why one computer is in deco and one isn't on the same dive, well they shouldn't be instructors. This thread has just turned into people that like to argue.

So if dsat is considered safe and everything else is more conservative (recreationally) then what the hell is the problem? You're not going to force one deco algorithm on every manufacturer and training agency, so what's your solution?

Yep. "The model dictates a very definitive line" (as DevonDiver said) is simply incorrect. There are many more factors than just the model that go into setting where the line is. Including the diver's own choices. And when the diver's own choices are part of what dictates where the line is, it's hard to see how you can ever say that "the line" is "very definitive".

And that's the trouble. OW divers follow exactly all the training given them and get widely varying results. They get told to "dive conservatively" but don't get told what that actually means. If they are diving a DSAT computer with Conservatism 0 and they stay down until the NDL says 5 minutes remaining, DevonDiver says that is "diving conservatively". But, if they happened to also wear a second computer that is running PZ+ algorithm with a Conservatism Factor set to +1 and the exact same dive has that computer showing a deco obligation, then suddenly the diver is NOT diving conservatively. Just because they took a second computer in the water with them. And they get called gibbering morons by an instructor for being confused about what exactly constitutes "diving conservatively" in this context.

 

[redacted]

Would a higher pressure group(on dive tables) mean more risk for DCS? Depending on depth differing NDLs put you into different pressure groups.

No, it would not.

For most recreational divers, the risk of DCS when they stay within their NDL and ascent rate limits is NEGLIGIBLE. When they exceed those limits, the risk of DCS are INCREASED.