PADI Deep Diver course 12-metre safety/decompression/"long" stop

[RainPilot]

NAUI remains the only agency I know of that truly endorses deep stops on recreational dives.

The NAUI love affair with RGBM and the deep(er) stops that implies was quite passionate years ago, right now the RGBM exists as a "Supplement" and instructors are required to adhere to "current best practices" in deco theory. The supplements are all optional, existing to give teaching materials on topics but these can be left out on instructor discretion.

In practice, that means that a NAUI Instructor does not have to teach or advocate any bubble models if they don't want to. I expose my students to the controversy to prepare them to make educated decisions, as well as not being caught flatfooted when a dive buddy starts talking about deep stops etc.

It does take a fairly detailed reading of the standards etc to realise that they do not particularly advocate deep stops, at first glance there does seem to be a proliferation of RGBM materials.

As to the OP, there is a benefit to a "sanity stop" at some depth commensurate with the max depth of your dive. This allows the divers to stabilise ascents, get their heads together and reduces the average ascent rate (a potential issue with recreational students doing their first deeper dives).

On a 40m NDL dive, coming up to 12m, stopping for a few seconds to gather your wits and get your buoyancy stable, before ascending in increments to your safety stop, is not a bad practice. Doing any meaningful time at depth will in turn affect your saturation, which then in turn leads to a whole different risk/benefit analysis.

If I have Deep students who are planning to go into tech, I will stop (briefly) at 21m (70') on the ascent. From there, ascending and stopping at each 3m / 10' increment for a few seconds is helpful in getting tech procedures/muscle memory to begin to form. By "a few seconds" I mean enough time to stop, look at the other members of the team and signal ascent to the next "stop".

 

[Graeme Fraser]

I am soon to be doing my PADI Deep Diver certification to go down to 40-metres deep. The training manual says that a 12-metre safety/decompression/"long" stop for 1 to 3 minutes is sometimes done in addition to the 3 minute safety stop @ 5-metres. Up until reading the deep diver course book l had never been aware of this stop: is it generally done only for dives deeper than 30-metres or is it an optional stop? ("better safe than sorry"). Does the use of a dive computer possibly factor this stop out with a "slower than 18-metre/minute ascent rate" therefore nullifying its requirement? Thanks.

Do you know which site you're doing the course yet? We tend to run dives 1 and 2 at Vobster, then 3 and 4 at NDAC, to get a bit of depth. Technically you can hit 33m under the freediving platform at Vobster but you'll need a shovel.

Both have trapezes which are handy for your safety stops and a good place to do the 8 minute emergency decompression with AAS exercise, required for dive 3. If you do venture into tech in the future, it'll also give you an insight into the rigging of a typical deco station. Pretty common to see tech divers hanging out on the 9, 6 and 3 metre bars.

Good luck. G

 

[Bob DBF]

With regards to the maximum ascent rate, the majority of dive computers stipulate 10mpm rather than 18, but again this should be discussed during the dive brief.

My computer uses 60'/min ascent rate below 60', then 30fpm. I won't stop there unless I do not make a good transition in ascent rates or still have cobwebs from narcosis. I'm not advocating the higher ascent rate, but I have been using it from well before computers.

The key thing is to be familiar with your computer settings and layout, thus not surprised or confused by any information displayed during the dive.

I was supprised once by my new computer at the surface by it flashing deco. Told my buddy and we went back to the safety stop and everything looked normal, we ran our air out and surfaced. When we got back to the truck, I looked in the manual and found it was the indication it had been deco during the dive. When I downloaded to a computer I found that as I was following the bottom up during the ascent, it had flattened around 70' and I had gone into and out of deco for less than 30 seconds and missed it. The computer did not show any indication of this during the rest of the dive. I reread the manual a few more times, and I now go through it occasionally to refresh my mind about odd indications I never see.

Another reason I bring this up is that stopping your ascent before you reach the safety stop may have unintended concequences. If you have plenty of NDL or have the air for a deco obligation it's no big deal, if not it would be more prudent to go on to the shallow safety and/or deco stop to get the maximum time from your air.

 

[boulderjohn]

It does take a fairly detailed reading of the standards etc to realise that they do not particularly advocate deep stops

I contacted headquarters and asked for an official statement. They told me deep stops are part of their teaching, and they cited one of the studies from the mid 2000's.

 

[RainPilot]

I contacted headquarters and asked for an official statement. They told me deep stops are part of their teaching, and they cited one of the studies from the mid 2000's.

As I said, RGBM is still "part of their teaching" in that it exists as an optional supplement. I was just clarifying for readers here that it is not compulsory for a NAUI course to include deep stops in any way.

Hijack over, back to the regularly scheduled viewing.

 

[boulderjohn]

As I said, RGBM is still "part of their teaching" in that it exists as an optional supplement. I was just clarifying for readers here that it is not compulsory for a NAUI course to include deep stops in any way.

Hijack over, back to the regularly scheduled viewing.

When I asked NAUI what their current teaching was, I got two replies, the second being a minor correction to the first. The replies do not say "optional," but I guess that could have been a mistaken omission.

Here is what they said. Both replies arrived April 16, 2019.

Not sure how in depth you want me to go.. Half pressure stops were implemented in the NAUI recreational RGBM tables some twenty years ago. Ascent rate is 33 fpm. For ease of teaching we changed the term half pressure to half stop. If the diver goes to a depth of 100 fsw then the diver would stop at 50 fswt for 2 minutes then continue to 15 few where they would continue with the safety for a couple of minutes.A. Marrroni and P.Bennett confirmed through their doppler test with DAN Europe that in fact a deep stop/half stop reduces both bubbles and fast tissue tensions. RGBM with half stops have been used in both meters and tables safely since implementation.

I am sorry, it was a UHMS pub in 2007.
We did not implement because of Marroni, we increased the time at half stop from 1 minute to two minutes because of Bennett and Marroni’s work​

 

[boulderjohn]

More information:

Here is a NAUI Blog commemorating the passing of Bruce Wienke, the creator of RGBM and a NAUI instructor. It explains Wienke's role in creating the NAUI tables and his work with NAUI leadership since 1997. It explains that Wienke was invited to do this by NAUI's Tim O'Leary, who is the author of the explanations I quoted above. O'Leary is quoted extensively in this blog.

To the best of my knowledge, Wienke was an enthusiastic proponent of deep stops until he died a few months ago.

 

[dmaziuk]

If you go into decompression and begin an ascent, a dive computer will penalize you for ascending too slowly, forcing you to do longer and deeper decompression stops. If you do not go into decompression and ascend slowly, that same computer will reward you by giving you more NDL time, usually without changing a safety stop requirement. You could potentially be near NDL at depth and then do a 20 minute extension of your dive at a shallower depth without a problem. You will only be penalized if your slow ascent exceeds NDL limits.

If you're deep enough and ascending slowly enough to keep on-gassing, the computer will keep you on-gassing, NDL or not. If you on-gas enough to go over NDL, you'll be over NDL.

I suspect it's highly unlikely that you can on-gas a slower tissue compartment on a "too slow" ascent from a recreational no-stop dive, for that to actually happen. 12 msw is close enough to no-limit depth that a 1-3-minute stop there will not on-gas anything other than the slowest compartments that don't matter anyway; all other compartments should at the point be either off-gassing, or nowhere near their resp. M0-values.

RGBM's "Gradient Reduction" factors are basically fudge coefficients "on the side" of the base model described above, so they effectively only make it more conservative -- until you go into deco and start generating the actual deep stops. On a no-stop dive that "profile-dependent intermediate stop" may reduce your residual fudge factor for the next dive, but since nobody's really seen the code: who knows what it really does. It should not affect your "current" dive in any appreciable way.