Safety stops and deco

[Lost Yooper]

IMO, one of the bigger mistakes made by divers (and taught by most agencies) is their rate of ascent from the safety stop to the surface. A safety stop is fine and dandy, but that final ascent should really be less than 30FPM instead of the recommended straight 60FPM (or even a straight 30FPM). I believe this very slow final ascent can be more important than the safety stop itself, as far as helping alleviate sub DCI syptoms (i.e. fatigue, etc).

Just thought I'd throw that in.

Mike

 

[Butch103]

I have read, anywhere from 15 - 30 ft for a safety stop.

I personally try to do a safety stop anytime I exceed 30 ft as an average depth.

I guess it just pays to be safe and practice this habit.

Butch eace:

 

[Jonathan]

My 3 Yen (about $0.02!)

In the original post there was:

I have found that it is easier to hang between 15 and 20 feet than 10 and 15 feet due to wet suit compression. Is there a significant difference?

I think you will find this is more do do with pressure change. The biggest change in pressure is right before you get to the surface. Going from Surface to 10 m you are going from 1atm to 2atm from 10m - 20m 2atm - 3atm etc. That's why it's good to get your neutral buancy sussed in the swimming pool 'cause if you can do it there you can do it anywhere....

Wet suit compression could come into it a bit but I would not think significantly at those depths - I notice the same thing in a membrane dry suit even in the summer with only shorts and T -shirt underneath.

Jonathan

P.S. with this fancy new site I now understand how you all did the fancy fonts etc - now I too can join in!!

 

[scubatexastony]

My peso (you do the math)
Pressure is linear, .445 lbs/fsw, .432 lbs/ffs so the most likey answer to this poser is that at a depth less than 20 ft, one is in the no deco time limits, and as stated below 10 ft to assure enough pressure to prevent over expansion of tissue.

Gassing off,..... I usually just fart real good and surface VERY slowly. LOL

Dive save, live long

tony

 

[Rick Murchison]

That "greatest pressure change" thing drives me crazy too.. what *is* greater the closer to the surface you get is the ratio of the change in pressure per unit depth to the total pressure. The reason that's significant is that bubbles will expand more per unit of ascent (ft, meter, yard, whatever) the closer you get to the surface, and therefore ascent rates close to the surface are more critical.
The change in pressure, however, is the same per unit of depth regardless of depth, as Tony said.
Rick

 

[blacknet]

Hello,

Assuming that is true (about the greater pressure change) then why is deep stops important? Kinda blows that theory out of the water

Ed

 

[Green_Manelishi]

why are deep stops so important?

simply put, MANY tables, etc. "bend you" by bringing you
"close" to the surface and then "clearing" you during the
stops. the "deep" stop idea is to stay ahead of the curve
so to speak so your deco is more even and gradual.

does that make sense?

 

[Dr Deco]

Dear Readers:

Here is the concept with the deep stops.

[1] As the diver ascends, the micronuclei grow by a Boyle’s Law effect;
[2] The larger bubble has a lower internal pressure (Laplace pressure) contributed by surface tension;
[3] the Laplace pressure being less, the internal pressure of many of the bubbles in the distribution of bubbles (remember they come in all sizes with many small and only a few being large) is less that the dissolved inert gas pressure;
[4] more bubbles can now grow since the diver ascended quickly;
[5] the more bubbles are growing, the more free nitrogen makes its way into the bubbles and less dissolved nitrogen diffuses into the capillaries.

What a diver or astronaut wants to do is to try to retain as much nitrogen in the dissolved state and as little as possible in the gaseous state. In the final analysis, this is accomplished best by staying deeper for a bit longer.

Dr Deco
:doctor:

 

[blacknet]

Hello,

Perhaps I should clarify myself abit. I was not asking about the deep stops but interjecting the concept of deep stops into the current thread about the shallow 'safety' stops (technicaly nothing more than a voluntary deco stop) I was trying to get those who posted to view the concept as it is, just another stop.

Ed