deep stops or not

[Ste Wart]

Good morning
I have a question that I can't solve related to deep stops.
During my training I have been tought about the rule for deep stops: (depth+6m)/2, meaning if you dive at 30m, your first deep stop is at 18m for 1mn, then (18+6)/2 second stop at 12m for another mn, then 3mn safety at 6m.

What was the training? PADI, IANTD, TDI etc?

All that is without decco.
Unfortunatly sometimes applying this rule led me to reach decco during the deep stops -as if starting the ascent with 1 or 2mn before decco- that I, may be, wouldn't had if I went directly to the safety 6m.
So my question is: what is the best? Deep stops as it allow more off-gasing but some tissues continue to saturate, or going directly to 6m?
The framework of this question is recreational dives around 25/30m (air or nitrox).

Not sure where this plus 6 rule has come from, really a new one on me.

For a 30m dive on Nitrox 32%:

I would make 9mpm acsent to 15m
The slow to 6mpm or 30 sec stop 30 sec slides for each 3m increment.
At 6m take as long as possible to ascend to the surface.


I tend no to do physical deep stops for dives deeper than 30m rather change the acent rate at a certain depth. But this is the basic forum, so I'll not go into detail

 

[jh_MacLeod]

Each successive level on a multi-level dive is above the off-gassing ceiling of the previous depth... In a true multi-level dive.
you are doing it wrong! Your "deep" stops are arbitrary... Stop doing that.

I've been using deep stops on quasi-recreational dives for the last 5 years, and my perceived results have been positive with them, so I plan on continuing to use them. But I definitely agree that they should not be arbitrary. I was never comfortable with the simple rule-of-thumb calculations based on half the deepest depth, so I bought a computer which adapted the algorithm and calculated stops based on my actual profile (Luna). One of the first things I noticed is that the computer sometimes did not give me a deep stop at all (when I would have done one based on depth alone), and it regularly gave me shallower stops than I would have calculated using the typical formulas people quote.

One of the reasons that I wanted to start using deep stops is that when I dive with other people (like a dive master and a group), I will typically dive a little deeper that the others (2 or meters). Sometimes it's to look under the ledge, into a hole, or whatever; but by halfway through the dive, I may be pushing closer to my NDL than the others who are just following the dive master for the normal reef tour. The group are not using deep stops, of course, so FWIW here is how I use the deep-stop function when diving in such a situation.

Once I have stayed deep enough that a projected deep stop is displayed (at 12 meters, for example), I will look at my remaining bottom time and NDL and determine when to move up. Once I start moving up, I will move up to my deep stop (my off-gassing ceiling) and clear the obligation. This will usually take me past and above the group, who are typically still lingering at an in-between depth. By the time we all reach safety stop depth, all my deep stop or level stop obligations are cleared and I am in sync with the rest. At safety stop level, I linger, and am usually the last to surface.

The only other comment I have is that I am sometimes amazed just how close to the (nitrogen loading) limits that some dive masters in some locations will push recreational dives with relatively inexperienced tourists.

 

[Scubagolf]

DAN's discussion group on this subject for NDL divers indicates deep stops are not recommended.
DAN | Mobile

 

[lowviz]

Does anybody have a solid reference to all of the details concerning the offgassing ceiling (OGC)? I would guess that there is some agreed upon distance from the M-value line that sets the OGC. M-value being the maximum Inert gas tissue tension vs. ambient pressure that is allowed.

The ceiling also changes with bottom time, as bottom time affects your saturation. However, for all but big deco dives (with no preload), the OGC appears to not change much with bottom time. It does change with depth.

Taking my DC's first microbubble stops as my OGC (valid ?):

60 ft no OGC
70 ft no OGC
80 ft 48'
90 ft 53'
100 ft 57'
110 ft 71'
120 ft 75'
130 ft 80'

-again, any solid references? I would like to compare what my DC tells me to the literature.

 

[Ayisha]

DAN's discussion group on this subject for NDL divers indicates deep stops are not recommended.
DAN | Mobile

That's not entirely true. They each say different things.

 

[tursiops]

I've been using deep stops on quasi-recreational dives for the last 5 years, and my perceived results have been positive with them, so I plan on continuing to use them. But I definitely agree that they should not be arbitrary. I was never comfortable with the simple rule-of-thumb calculations based on half the deepest depth, so I bought a computer which adapted the algorithm and calculated stops based on my actual profile (Luna). One of the first things I noticed is that the computer sometimes did not give me a deep stop at all (when I would have done one based on depth alone), and it regularly gave me shallower stops than I would have calculated using the typical formulas people quote.

One of the reasons that I wanted to start using deep stops is that when I dive with other people (like a dive master and a group), I will typically dive a little deeper that the others (2 or meters). Sometimes it's to look under the ledge, into a hole, or whatever; but by halfway through the dive, I may be pushing closer to my NDL than the others who are just following the dive master for the normal reef tour. The group are not using deep stops, of course, so FWIW here is how I use the deep-stop function when diving in such a situation.

Once I have stayed deep enough that a projected deep stop is displayed (at 12 meters, for example), I will look at my remaining bottom time and NDL and determine when to move up. Once I start moving up, I will move up to my deep stop (my off-gassing ceiling) and clear the obligation. This will usually take me past and above the group, who are typically still lingering at an in-between depth. By the time we all reach safety stop depth, all my deep stop or level stop obligations are cleared and I am in sync with the rest. At safety stop level, I linger, and am usually the last to surface.

The only other comment I have is that I am sometimes amazed just how close to the (nitrogen loading) limits that some dive masters in some locations will push recreational dives with relatively inexperienced tourists.

I've been reading the manual for your computer, and I'm a bit confused as to what you are doing. Have you set your conservatism to something other than L0? Are you actually doing no-deco dives, or are you describing mandatory level stops due to being in deco? I see nothing in your manual about deeps stops for no-deco diving, just for deco diving.

 

[Glenlivet]

I've been reading the manual for your computer, and I'm a bit confused as to what you are doing. Have you set your conservatism to something other than L0? Are you actually doing no-deco dives, or are you describing mandatory level stops due to being in deco? I see nothing in your manual about deeps stops for no-deco diving, just for deco diving.

It's called PDIS (profile dependent intermediate stops) in Uwatec speak. It is documented here: http://www.scubapro.com/media/176944/galileo_pdis_multilanguage.pdf

 

[Basking Ridge Diver]

I have an Oceanic Veo 2.0 - It is interesting that for No Deco they recommend or at least give you the option but for Deco they do not recommend deep stops...

No Deco Deep Stops - Morroni, Bennet
Deco Deep Stops (not recommended) - Blatteau, Gerth, Gutvik

Personally, I stay in NDL so I turned it off on my preferences but this conversation got me interested in my PDC - I get close at times and would use my PDC as designed if I did cross over to Deco - but I do not turn on any conservative features.

 

[DiveNav]

Does anybody have a solid reference to all of the details concerning the offgassing ceiling (OGC)? .......

As I indicated in one of my posts on decompression theory a while ago, in my opinion there is no clear formula on how to determine OGCs, but they seem to me rather empirical constructs determined by trial and error and experience.
Basically, the question is: how much overpressure gradient (by compartment) are you willing to accept? 2 ATM for the fastest compartment? And what about the slowest one?

You can use divePAL Tech to see how each compartment begins to offgas based on a given dive profile / gas mix.

Of course this is just theory......

 

[tursiops]

It's called PDIS (profile dependent intermediate stops) in Uwatec speak. It is documented here: http://www.scubapro.com/media/176944/galileo_pdis_multilanguage.pdf

Thanks, now I understand. Not sure I agree it is a good idea, but now I know what it is. I will say it is better than the "half the max depth" deep stop, for which there is little justification and lots of things wrong with it.