Best Safety Stop Depth

[Cave Diver]

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.

 

[Cave Diver]

If your computer is yelping, you better have a good story because you will be interogated. (mine is usually that I freedived for the buoy and forgot to take it off)

Ackkkk!

 

[Cacia]

BEFORE the dives.

 

[Cave Diver]

Whewwww!

 

[Charlie99]

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?

IMO that 2 to 1 pressure change in the last 10m/33' is indeed the key factor, but for a slightly different reason.

The rule of thumb developed by Haldane in his original experiments with goats was that you can do a 2 to 1 pressure change after being completely saturated (and a higher pressure ratio change if you haven't stayed down so long that you are saturated).

Coming up from 100'/30m/4ata directly to the surface is a pressure ratio change of 4 to 1. Going from 100'/30m/4ata to 33'/10m/2ata is a pressure ratio change of only 2 to 1. Since you aren't fully saturated, you can ascend a bit more -- on into the 20'/6m/1.6ata range.

In other words, the 2 to 1 change in the last 10m is key, but because of how the relative pressure ratio between stop depth and bottom depth change dramatically depending upon where the safety stop is in that last 10m/33'.

Charlie Allen

 

[bracdiver]

I second the motion, but with a slight variation: I do at least a one minute stop at 1/2 maximum depth and then a 3-5 minute SS at 20', then another one minute stop at 10' and finally a very sloooow ascent the last 10' to the surface.

 

[keezdiver]

i've employed a more "staged" SS routine recently when doing deeper or repetative dives.

my typical deeper dives are about 20mins maxing out at 125ft

i'll come up the line slowly....do a minute at 25', a minute at 20, 2 at 15.

if i'm into deco (usually only a couple mins) on the dive, i'll extend that to 2 @25, 2 @ 20, 3 @ 15.
generally that gets me out of deco, and pretty much at the bottom of the caution zone on my old oceanic computer.

 

[quietstorm]

Well, it has been some time since I first posted this thread, and so I returned to see what I might learn anew.

I just came back from diving at Cozumel (with strange little red bumps and a rash on my hands again for the third time in a row I might add) and was curious to see what I might learn about safety stops/decompression stops.

Thank you for the input from all of your people (and yes, Nereas, this "QS" aspires to be as astute as possible).

Any new advice would be welcome. Thanks.

 

[DA Aquamaster]

Deco theory is just that - a theory. And on any given day you'll get x number of posters with x number of equally valid theories that seem to work for them.

And that is probably the point. Consider the various means people use to get out a little cleaner, find what works for you and stick with it.

- slow ascent rates
- 1 to 2 minute deep stops
- longer 3-4 minute deep stops
- a longer safety stop
- O2 at the 20 ft stop
- etc, etc, etc

Personally, I think a safety stop works anywhere from 10'-30' and I think the longer and deeper the dive the more sense it makes to start slowing your ascent and stopping deeper.

On a no deco dive, I find a deep stop for 2-4 minutes does wonders, as does a very slow ascent from there to the hang line at 20'. (Many NC rigged boats will have the line in the 20' range as sea state can make hanging at 10 ft impractical.) I tend to be close to the first off the boat and the last back on, I will often be the last one up the anchor line and even if not, I will hang out on the line at 20' until everyone else is out. It makes more sense to me to off gas there than rush back on the boat. Current permitting I will normally follow the last couple people up and take 2-3 minutes to come up the last 20' arriving at the ladder just as the last person goes aboard - a balance between maximizing the safety stop and not delaying the boat.

Of course if everyone did this, we'd all be waiting for someone else to go first until people started running out of gas. But since I usually have doubles I could wait a long time.

For deco dives in salt water, I plan the last stop at 20' as 10' makes little sense in 6' seas and will cut tables with DPlan where the stops are shorter but deeper.

After a cave dive, I will stay at the 20' stop for a few minutes, even after any deco is done and then will ascend very slowly from there to the surface - over a period of 5 minutes or so. If I am on O2 for the deco, I'll stay on O2 for the safety stop and slow ascent (with an air break if needed.)

Part of what got me here was training and theory, but a large part of it is just based on experience and adjusting the profiles so that I feel great after a dive without any fatigue or subclinical DCS symptoms.

 

[Mr. Nudi]

Hmmmmm.... my PADI skills book states, "To ascend, take a deep breath, hold it, and swim directly for the surface. You get 10 points for not blowing bubbles on the way up."


All your posts give me more understanding of off gassing while on my ascent back to the surface. Originally we were completing a 3 minute/ 20ft safety stop, but off gassing in stages keep us safer and help eliminate the chance of blowing the 20ft safety stop.