3 or 5 minute Safety Stop?

[tracydr]

Reference was made to a 3 and 5 minute safety stop in the thread on draining your tank dry. I'd like to discuss the pros/cons of each. Also, any actual papers or research done on the benefits of a longer safety stop would be great.
Finally, I'm wondering if doing several stops or pauses would be an even better way to perform ascents.
What's the safest way to perform ascents and what exactly are we trying to do? Prevent silent bubbles, prevent DCS, prevent what?
How do you ascend? Are you considering making changes?

 

[lowviz]

...//...What's the safest way to perform ascents ...//...

There are two extremes in terms of ascent, Haldane and RGBM. I'm sure that these will be discussed in great detail in this thread. I would like to start by saying that ascent rate is important and may not be getting the same attention as "stops". For ascents in general, leave the bottom rapidly and hit the surface very slowly.

 

[uncfnp]

Tracydr.

I'll let others more knowledge do the analysis but you might find this study interesting regarding deep stops. After reading this, I decided to add a 2 to 2.5 "deep stop" at half the depth for dives deeper than 60 and more than 20 minutes.

Effect of varying deep stop times and shallow stop times on precordial bubbles after dives to 25 msw (82 fsw).

There is another study that found 30 feet per minute was the optimal ascent rate, still looking for that one...

 

[Bopper]

In the book "Deco For Divers" IIRC there's actually a graph that illustrates a dramatic decrease in "silent bubbles" when doing 5 minute safety stops vs. 3 minute safety stops vs doing no stop at all. Maybe someone who has the book readily available can see if there is a specific study referenced. It would be in Ch 2 I believe.

EDIT: The graph is Figure 21 on pg 51. A little different from what I described (2 min vs 5 minute safety stops). It doesn't seem to reference a study.

 

[lowviz]

-found it (ascent rates vs. depth) : http://www.scubaboard.com/forums/ad...3-dive-computer-ascent-rates.html#post5404259

 

[Bopper]

Finally, I'm wondering if doing several stops or pauses would be an even better way to perform ascents.

This is controversial as when you do your "several stops" you are typically on-gassing as well as off-gassing.

Here's a DAN discussion about it.

 

[denisegg]

I just got back from a trip to Bonaire where we did several boat dives which I know is not what Bonaire is known for. What is interesting is how the DM's planned the dive. We were on either air or nitrox depending on your skill level. We started the dive on the wall by descending as deep as you would like to go, from about 60ft to 110ft, some went deeper. We were asked to turn at either 30 minutes or 1500 psi and then we began to ascend up the wall and finish the last several minutes of the dive at 15 to 20ft. By the time the max time of one hour was achieved you had completed a safety stop and then some.
I was not crazy about the 1500 psi turn pressure because I have gotten use to diving 1/3rds and thought people should be turning at 2000. But by following the general pattern of the dives and turning at their 30 minute limit I was still getting back on the boat with about 1/2 of my gas. I just can't envision that rule of getting back on a boat with only 800 psi anymore. I want about 1200 to 1300 psi on the boat after a one hour dive, no matter what the depth. Of course toward the end to do that I had to quit playing out at depths beyond 90ft the first half of the dive.
My point is, a gradual slow ascent while you are still enjoying the view but by planning this strategy ahead of time made for some pretty awesome dives with several minutes of safety stop zone diving while still completely enjoying the whole experience.
What is the golden rule after all, planning.

---------- Post added July 5th, 2013 at 07:25 PM ----------

This is controversial as when you do your "several stops" you are typically on-gassing as well as off-gassing.

Here's a DAN discussion about it.

If you have ever dove with someone who is using a suunto computer believe me, it doesn't like those deep stops. It will continue to rack up deco until you wind up doing a 15 minute deco stop at 15ft deep on a dive where you went with someone else who had one after only a 60ft dive and less than an hour.

 

[uncfnp]

...


If you have ever dove with someone who is using a suunto computer believe me, it doesn't like those deep stops. It will continue to rack up deco until you wind up doing a 15 minute deco stop at 15ft deep on a dive where you went with someone else who had one after only a 60ft dive and less than an hour.

That's odd since I understand that the Suunto's are based on RBGM and several models have an optional deep stop function.

 

[denisegg]

That's odd since I understand that the Suunto's are based on RBGM and several models have an optional deep stop function.

What year is your computer or model? I have 2 that are > 7 years old and a friend of mine has a newer model. I don't recall that option. I surmise we were diving approximately the same profile, she maybe even shallower than I. Our first year in Cozumel, I was using the predator and as we ascended mine compensated for the ascension as hers continued to obligate her to more deco until we hit the safety stop zone. We would wind up hanging at 15ft for several minutes longer to clear her ceiling. I am not an expert algorithmist but there are also warnings in the manuals on certain computers ( I own 4 different ones) that say they are only for recreation, not technical diving as the predator is designed for.

---------- Post added July 5th, 2013 at 08:15 PM ----------

That's odd since I understand that the Suunto's are based on RBGM and several models have an optional deep stop function.

Gas mixes also play a role in ascension rate as anyone who dives trimix could tell you.

---------- Post added July 5th, 2013 at 08:38 PM ----------

Forgive me for digressing... As for the original post, if you have the air left, take a longer safety stop. It is never bad to err on the safe side.

 

[Rhone Man]

When reading articles on different theories, just remember that they all agree on one thing: at the moment the causal nexus is poorly understood and so beyond a few definitive baselines (longer and deeper = more gas absorption for example) there are very few definite answers in terms of ascent profile.