Deep Stop Option

[nereas]

I'm not sure where you got amateur dive magazine. "Sources" is the NAUI dive professional magazine. The study in the magazine is not opinion, but a scientific study that includes information from the European Underwater Biomedical Society proceedings, "Undersea Hyperbaric Medicine 2004 and 2005", and "Aviation Pace Environment Medicine 2005". Bottom line, a 1 minute deep stop followed by a 3 minute normal safety stop resulted in a bubble score index (count of number and density) that was almost three times the score for a 2.5 min deep stop and a 1 min shallow stop.

There is much more to the study, but the bottom line is a deep stop of 2.5 min is more effective than a shallow stop of any length in prevention of bubbles. Hope you get a chance to look over it.

I know exactly what Sources is. I used to have a "free" subscription to it myself.

And if they are now recommending inverting the safety stop with more time at 1/2 MOD than at 15 ft, it smacks of amateurish. Go ahead and do it, if you trust everything you read.

From my own experience, 1 min at 1/2 MOD, followed by 1 min every 10 ft, and then finally 3 mins at 15 ft, represents the ideal egression from any NDL dive.

 

[dumpsterDiver]

It is a man-machine interface problem.

Right now, the dive computer controls your profile ONLY if you are into mandatory decompression. e.

That seems illogical. You seem to be arguing that it is desirable (or ok) to diverge from the computer profile for non deco dives, but NEED to follow it when doing deco?
Why???????????

I most definitely DO NOT follow my computer when doing deco dives, I will incorporate a few deep stops and sometimes my computer will penalize me for it by awarding more deco. I don't care, I do my deep stops and then clear the computer deco stops at the shallow depths like it wants.

 

[DA Aquamaster]

Many recreational divers do deco profiles based on a straight US navy table. Consequently it is a bend and treat type of profile with long shallow stops to accommodate the less efficient offgassing that occurs once small bubble already form.

Most serious techncial divers are using a variable permeability or bubble gradient model that uses much deeper stops that on a moderate run time deco dive are 1-4 minutes in lenght beginning at perhaps 70 ft followed by farily short 5 to 10 minute stops at 20 ft and 10 ft.

If I am doing deco on a recreational computer, I am going to adjust what it tells me to do based on a curve similar to what I'd get off a computer generated profile using a VPM or RGBM model. I know from experience that doing that leaves me feeling much better when I get out of the water.

You need to consider that most recreational computers are not designed for intentional deco and that the deco profile they suggest is more or less a not to be used too often when you screwed up kind of thing.

In my opinion, ascending at the max allowable rate to the celing depth on a recreational computer in deco mode, is not your best or safeest approach. I am not a Dr. or a deco expert but based on my experience and on the theories underlying most techncial decompresison models, a deep stop at 1/2 max depth followed by a slow ascent with a stop for aminute or so every 10 ft with a 3-5 minute safety stop at 20 ft with a slow ascent from there to the surface is far less liekly to get you into DCI trouble than blindly following your computers recommendation to ascend immediately to 10 ft and stay there for x number of minutes.

In my experience, doing the former when the computer is telling you to do the latter usually results in the computer clearing the longer 10 ft stop before you complete your safety stop at 20 ft and if not, you can go up to 10 ft and clear the computer normally.

 

[Charlie99]

]
It is a man-machine interface problem.

Right now, the dive computer controls your profile ONLY if you are into mandatory decompression.

That seems illogical. You seem to be arguing that it is desirable (or ok) to diverge from the computer profile for non deco dives, but NEED to follow it when doing deco?
Why???????????

I most definitely DO NOT follow my computer when doing deco dives, I will incorporate a few deep stops and sometimes my computer will penalize me for it by awarding more deco. I don't care, I do my deep stops and then clear the computer deco stops at the shallow depths like it wants.

This some miscommunicatons going on. Let me try and be clearer about it, by giving a couple examples.

If I dive down to 100' for 5 minutes, then head up to 80' for a couple of minutes to look at something, and then I'm heading on up towards 50', should me computer be showing a ceiling, or mandatory deco, or something like that as I come up from 100', or up from 80', or up from 50'. Right now, my computer just tells me how much NDL time I have left. It isn't giving me a ceiling or anything like that.

Now if I decided to end my dive and head for the surface at any one of those three depths, I'm going to do a couple of deep stops before my final/safety stop. Since I'm well within NDL limits, the computer won't be telling me anything about the optimum ascent profile. I will be the sole determiner of my profile.

----------------------

Now lets say I have a nice true RGBM or VPM-based computer. If I stay down at 100' for 20 or 25 minutes on air, I WILL have a deco obligation and the computer WILL be showing some short deep stops in the 30' range. In other words the computer will be controlling (or at least setting an upper limit) to my profile.

-----------------------

The two highlighted sentences above are what I mean in saying "the computer only controls your profile if you are in mandatory deco".

The problem, as I see it, is how to get the computer to generate deep stops for profiles that are well within NDL. One way would be to be able to press a button and say "I'm ascending, no give me some guidance and appropriate deep stops". Or maybe even let the diver pick a total-ascent-time and then the computer uses increasing conservatism on the VPM model to come up with an "optimum" ascent profile with that total-ascent-time.

Charlie Allen

 

[nereas]

...I do my deep stops and then clear the computer deco stops at the shallow depths like it wants.

That's what I do also, and that is what I also recommend for everyone else.

 

[nereas]

...
In my opinion, ascending at the max allowable rate to the celing depth on a recreational computer in deco mode, is not your best or safeest approach. I am not a Dr. or a deco expert but based on my experience and on the theories underlying most techncial decompresison models, a deep stop at 1/2 max depth followed by a slow ascent with a stop for aminute or so every 10 ft with a 3-5 minute safety stop at 20 ft with a slow ascent from there to the surface is far less liekly to get you into DCI trouble than blindly following your computers recommendation to ascend immediately to 10 ft and stay there for x number of minutes.
...

In my own experience, this is exactly right.

Therefore my first deep stop from any dive is always 1/2 of MOD (unless in extreme cases a computer program like V-Planner has told me to stop deeper, which is rare).

From this point, I stop for 1 min every 10 ft, for NDL diving.

The final stop is 15 ft for 3 mins, unless the computer tells me longer, for NDL diving.

This has worked perfectly so far for the last 8 years, since dive computers have started to incorporate sophisticated algorithms.

And even though the computer "says" its ok to ascend faster, there is no rush on my part, and the added safety factor of a slow ascent is well worth the effort.

The more time you spend at 15 fsw, the more safe you are going to be from DCS risk. So why rush the final stop? Enjoy it!

 

[yupito]

And it would be helpful if Oceanic added seconds to the Elapsed Dive Time or added a clock with current hour, minutes and seconds, to the main dive screen to be able to better measure the deep stops, whenever and whatever your plan is.

 

[mbwilliamn]

I know exactly what Sources is. I used to have a "free" subscription to it myself.

And if they are now recommending inverting the safety stop with more time at 1/2 MOD than at 15 ft, it smacks of amateurish. Go ahead and do it, if you trust everything you read.

From my own experience, 1 min at 1/2 MOD, followed by 1 min every 10 ft, and then finally 3 mins at 15 ft, represents the ideal egression from any NDL dive.

Effect of varying deep stop times and shallow stop...[Undersea Hyperb Med. 2007 Nov-Dec] - PubMed Result

Sorry to be away so long, but duty calls. Link is for the study excerpt. In case the link doesn't work:

Duke University Medical Center, USA.

In our previous research, a deep 5-min stop at 15 msw (50 fsw), in addition to the typical 3-5 min shallow stop, significantly reduced precordial Doppler detectable bubbles (PDDB) and "fast" tissue compartment gas tensions during decompression from a 25 msw (82 fsw) dive; the optimal ascent rate was 10 msw (30 fsw/min). Since publication of these results, several recreational diving agencies have recommended empirical stop times shorter than the 5 min stops that we used, stops of as little as 1 min (deep) and 2 min (shallow). In our present study, we clarified the optimal time for stops by measuring PDDB with several combinations of deep and shallow stop times following single and repetitive open-water dives to 25 msw (82 fsw) for 25 mins and 20 minutes respectively; ascent rate was 10 msw/min (33 fsw). Among 15 profiles, stop time ranged from 1 to 10 min for both the deep stops (15 msw/50 fsw) and the shallow stops (6 msw/20 fsw). Dives with 2 1/2 min deep stops yielded the lowest PDDB scores--shorter or longer deep stops were less effective in reducing PDDB. The results confirm that a deep stop of 1 min is too short--it produced the highest PDDB scores of all the dives. We also evaluated shallow stop times of 5, 4, 3, 2 and 1 min while keeping a fixed time of 2.5 min for the deep stop; increased times up to 10 min at the shallow stop did not further reduce PDDB. While our findings cannot be extrapolated beyond these dive profiles without further study, we recommend a deep stop of at least 2 1/2 mins at 15 msw (50 fsw) in addition to the customary 6 msw (20 fsw) for 3-5 mins for 25 meter dives of 20 to 25 minutes to reduce PDDB.


If you chose to use your experience, fine, but without facts all you have is an opinion.