Place of dive tables in modern diving (Split from the basic thread)

[scubadada]

My Citizen watch:

 

[dmaziuk]

For the "Basic" section:
...
3) Ratio Deco - Better than tables. Inexpensive, adaptive, but inaccurate.

There's an even better one: Read The Fine Manual. Mine says (IIRC) if you're 5 minutes into deco: stay at SS for at least 5 minutes, if you're over 5 minutes into deco: stay as long as you can. Everyone with basic PADI cert is supposed to know everything they need to know about ratio deco.

 

[Dan_P]

There's an even better one: Read The Fine Manual. Mine says (IIRC) if you're 5 minutes into deco: stay at SS for at least 5 minutes, if you're over 5 minutes into deco: stay as long as you can. Everyone with basic PADI cert is supposed to know everything they need to know about ratio deco.

Your quote above mixed up several parts of my post, which is not accurate representation of what I said.
What I said Is:

For the "Basic" section:
...
Ratio Deco/Min Deco (RD/MD) - Easy (particularly at entry-level) and adaptable, more training required than computer

But there is a difference between knowing what the guideline is if (dare I say, "accidentally") exceeding NDL, and knowing Ratio Deco/Min Deco.
The two do not have anything to do with one another.
It does take a bit more learning than computers do, in fairness, but it's certainly not by an aweful lot at Min Deco-level (recreational).

In Min Deco, you relate your depth and gas, to a time (NDL), and frame your whole ascend from there.

This is one way to dive, using a computer is another.
I think traditional dive tables will eventually disappear in favor of these two approaches, with the majority of divers opting for computers.

 

[boulderjohn]

There's an even better one: Read The Fine Manual. Mine says (IIRC) if you're 5 minutes into deco: stay at SS for at least 5 minutes, if you're over 5 minutes into deco: stay as long as you can. Everyone with basic PADI cert is supposed to know everything they need to know about ratio deco.

Which manual is this?

PADI does not teach Ratio Deco at all, so how are PADI divers supposed to know about it?

 

[dmaziuk]

Which manual is this?

PADI does not teach Ratio Deco at all, so how are PADI divers supposed to know about it?

PADI does not teach deco for the basic cert. The only thing a PADI basic diver needs to know about a deco strategy, ratio or otherwise, is the emergency deco procedure for when they exceeded their NDL. That is covered in my OW manual.

 

[dmaziuk]

But there is a difference between knowing what the guideline is if (dare I say, "accidentally") exceeding NDL, and knowing Ratio Deco/Min Deco.

Yes, and the difference is: the latter does not apply to basic OW cert. At all.

 

[Eric Sedletzky]

There's an even better one: Read The Fine Manual. Mine says (IIRC) if you're 5 minutes into deco: stay at SS for at least 5 minutes, if you're over 5 minutes into deco: stay as long as you can. Everyone with basic PADI cert is supposed to know everything they need to know about ratio deco.

Actually, I’m looking at my PADI RDP right now. For others who have never seen a PADI table, here goes:

1. An ascent rate of 60 fpm is the standard rate (1994 version)
2. A safety stop is required any time a diver comes with three pressure groups of a no-decompression limit, and or a dive to 100’ or greater.
3. Emergency decompression:
If a no deco limit is exceeded by no more than 5 minutes, an 8 minute safety stop at 15’ is mandatory. Upon surfacing the diver must remain out of the water for at least 6 hours prior to making another dive.
If a no-deco limit is exceeded by more than 5 minutes, a 15’ safety stop of no less than 15 minutes is urged (air supply permitting). Upon surfacing the diver must remain out of the water for at least 24 hours prior to making another dive.

There are other rules for multiple dives per day, and more challenging dives.

Another note on the RDP:
“Since little is presently known about the physiological effects of multiple dives over multiple days, divers are wise to make fewer dives and limit their exposure toward the end of a multi-day dive series”

At no time do they mention deep stops, or any thing else related to ratio deco. Therefore, mentioning ratio deco and PADI tables in the same sentence makes absolutely no sense.

 

[Dr Simon Mitchell]

Hello Dan,

So, are DAN wrong when they say that deep stops are benefitial in a recreational setting?

Possibly.

Personally, I have no strong feelings about this. It has little to do with discussion of deep stops in the decompression diving context. Nevertheless, I think i should probably point out the context in which the advice has arisen.

DAN Europe has been quoted as providing this advice. It comes from a single study which involved several senior DAN people, and in which they showed a single stop at 15m during ascent from a 25m no decompression dive reduce post dive venous bubbles.[1] However, the extra stop at 15m was extra ascent time which was not added to the ascent or the shallow safety stop in the comparison group that did not do a deep stop. Put succinctly, the ascent in the group with the added deep stop was longer.

In a second study in which dives of identical length were compared, adding a deep safety stop during ascent (and therefore reducing the length of the shallower safety stop) resulted in more post dive venous bubbles in comparison to a group that did all their safety stop time shallow [2]. I'm sure you can figure out the implications for yourself.

Simon M

References.

1. Marroni A et al. A deep stop during decompression from 82 fsw (25 m) significantly reduces bubbles and fast tissue gas tensions . Undersea Hyperb Med 2004;31:233 – 243.

2. Schellart N et al. Bubble formation after a 20m dive: deep stop versus shallow stop decompression profiles. Aviat Space Environ Med 2008; 79:488 – 94.

 

[Dan_P]

Yes, and the difference is: the latter does not apply to basic OW cert. At all.

Min Deco is effectively taught from entry-level.
It's simply a different approach to dive/ascend planning than using a computer.

Ratio Deco adds to the framework taught from entry-level (Min Deco), adding decompression for technical dives.

 

[Dan_P]

In a second study in which dives of identical length were compared, adding a deep safety stop during ascent (and therefore reducing the length of the shallower safety stop) resulted in more post dive venous bubbles in comparison to a group that did all their safety stop time shallow [2]. I'm sure you can figure out the implications for yourself.

Hi Simon,

Thanks for the references and background on DAN Europe. I had previously asked them for a reference, but without reply.

Possibly is right

Even going by the RDP, 7 minutes of "deco" is unwarranted for a 40 minute dive to 20m.
It would make sense that excessive hanging would be disadvantageous in either case, but
In fairness, I should say that in light of recent studies, I am satisfied that excessive hanging would be particularly disadvantageous at depth (too long deep stops).

I'm curious to see a trial framed more in lieu with Min Deco metodis operandi than "MDD was 20 msw, bottom time 40 min and total diving time 47 min. In DSD, the "deep" stop (10 msw) replaced 3 min of the 7 min stop at 4 msw of SSD" [1].
It might replicate the result, of course, but I think it'd still be interesting to test the actual application of the two approaches ("safety stop" and "Min Deco") against oneanother.


Best Regards,

Dan

1. Schellart N et al. Bubble formation after a 20m dive: deep stop versus shallow stop decompression profiles. Aviat Space Environ Med 2008; 79:488 – 94.