Best Safety Stop Depth

[nereas]

true - it is a recommended stop rather than mandatory, but if doing another dive after you will be penalized for missing the stop.

Not if the computer is working correctly.

 

[1_T_Submariner]

Great Answers and Info all.

I have gotten into a habit of not being in a big hurry to get on the boat when diving off a boat in the ocean. I got back from Fla a few weeks a go and we did some 6-8 minute stops at 20-15 feet. We were watching others get on the boat and hey why rush.

 

[NorthWoodsDiver]

This is an interesting subject to bring up after yesterday. I did 2 dives deep with very little surface interval and so did my 2 dive companions. We all have Suunto cobras but all had rather strange differences in what the computer wanted.

First dive was to 140' for 2 min while we worked back up slowly to 15' for the safety stop. I dont recall the exact times for that first dive cause it was to investigate something quickly.

The second dive was done within half an hour of the first against my beliefs but one of the other divers is much less experienced and in poor shape but was determined to go so I felt some obligation to go in just to make sure things went okay. This second dive was also a quickie to 138' but on the way up I went ahead and stopped at 70' while they slowwwwwly ascended to 15'. my stops where 1 min at 70, 60, 50, 30, 20, and than 3min at 15' but my computer cleared me of any deco obligations when I hit 25'. When the other 2 divers hit 15' they had a 14min!!! deco obligation according to the computer. What is really strange is I had far more air than those 2 did at the end and I actually had to donate my pony to that weaker diver cause he was at 180psi with 9min left on the computer. I hung on the line with them at 15' and 10' just for fun BTW.

I understand all the stupid things that happened and that I should have been more stern about us not diving deep again so soon or taking a weak diver that deep but like I said I followed just to make sure they were okay cause they were determined to do the dive. But what I wanted to point out is how the computers interpreted our different profiles and how much different the deco obligations were. Now I normally follow tables and keep the computer just cause I paid so freakin much for it but its always interesting to compare what tables recmmend and what the computer wants.

I followed a normal procedure that I follow on that dive site for any normal dive and expected the computer to want me to do some deco at 10' but I was clear. I also would not have expected them to have that much of an obligation with such a slow ascent. Just proves to me that its better to start off-gassing sooner.

 

[jscott099]

Check out the DAN web site for research. They will show a study that:

"the optimal method for reducing post-dive bubble production is the combination of an ascent rate of 10 m/min (30 fsw/min) with a deep stop at about half the depth of the dive and a stop at 15 fsw (5 m) for 3-5 minutes."

Most of my deco dives involve a 10 ft stop but this is not a safety stop, its a deco stop. 10 ft is tough to maintain where I dive (the NC coast) where swells and wave action can really bounce you.

 

[lamont]

really, in the recreational area, more deco probably won't hurt. probably doesn't matter a huge amount at what depth you do the deco... do 6-10 minutes instead of 3 and you'll probably do better... obsessing over the perfect deco curve for a recreational dive is probably missing the bigger picture...

 

[Gene_Hobbs]

The optimum depth varies with the profile of that particular dive.

Excellent post!

Check out the DAN web site for research. They will show a study that:

"the optimal method for reducing post-dive bubble production is the combination of an ascent rate of 10 m/min (30 fsw/min) with a deep stop at about half the depth of the dive and a stop at 15 fsw (5 m) for 3-5 minutes."

I would encourage folks to read the studies that went into this statement. Blanket statements without understanding experimental conditions can often be bad.

Some papers I think are worth a glace through are:

Doppler Detection of Silent Venous Gas Emboli in Non-Decompression Diving Involving Safety Stops.
Uguccioni 1994 MS Thesis
http://archive.rubicon-foundation.org/3430

A deep stop during decompression from 82 fsw (25 m) significantly reduces bubbles and fast tissue gas tensions. (Article)
Marroni et. al. Undersea Hyperb Med. 2004 Summer;31(2):233-43.
http://archive.rubicon-foundation.org/3804

and follow-up to that article:
http://archive.rubicon-foundation.org/3805

Lang and Egstrom (eds.). 1990. Proceedings of the AAUS Biomechanics of Safe Ascents Workshop. Woods Hole, MA. 220p
http://archive.rubicon-foundation.org/4241

There are more but no time to pull them. Enjoy!

 

[quietstorm]

Since you seem like a perceptive person QS, you may want to customize your own safety stops, to get more safety out of them.

Thankyou kindly, nereas! Not only is your answer helpful, but you are clearly also a fine judge of character.

 

[jscott099]

Thanks Gene, I have found the papers on Rubicon quite useful. Perhpas you know another one. Got a friend who suggests that Nitrox divers should continue to breath down their tanks for a while on the surface. I've seen some work on Rubicon concerning surface breathing 100% O2 after a dive. Know of anything that discusses surface breathing <40%?

 

[Gene_Hobbs]

Thanks Gene, I have found the papers on Rubicon quite useful.

Thanks! It has been a group effort, we could not do it without our volunteers!

Posted my reply in your thread.

Since you are in Raleigh, will you be attending the DAN Tech Conference in January? (the price goes up soon...)

 

[AbyssalPlains]

The greatest pressure change occurs between 10 m and the surface (pressure goes from 2 bar to 1 bar = 100% pressure change with regard to surface pressure). I guess that's why they recommend to stop halfway during that change, i.e. at 5 m. Am I missing something?