Is a long safety stop beneficial?

[dvleemin]

Hi,
I always do a safety stop around 20' on all my dives - usually around 5 minutes. I end up assending with 4-500 PSI left in my tank. Is there a benifit to staying down longer at 20'. I certainly would like to. Hovering at 20' is still a lot of fun. Is there a downside to staying at 20' for lets say 15 minutes?

Darryl

 

[TexasMike]

I don't have a good answer (still learning about these things myself), but I know of a guy who might be able to give you a good response. PM me your e-mail and I'll pass it along.

 

[Rick Murchison]

A down side? The short answer is "not usually."
But a long stay at 15-20 feet doesn't do anything to obviate the need for a slow, controlled ascent to the surface from that stop. I strive for 15 FPM or less myself.
And then there *is* the matter of the rest of the folks on the dive boat waiting for you....
Rick

 

[Uncle Pug]

Originally posted by dvleemin
Is there a downside to staying at 20' for lets say 15 minutes?

Hi Darryl,
Your profile doesn't include a location...

I would say that we try to minimize the exposure to the elements...

Far better that hanging at 20' in my opinion is to practice a nice slow ascent from 20' at 2 fpm... just to see if you can do it.

Of course 10 fpm is more realistic for most rec. dives and far better than hanging at 20' for any length of time and then popping to the surface.

 

[Ladydiver]

I am sure that Dr. Deco or one of our other learned members will be happy to give us a thorough explanation of any possible benefits or drawbacks of an extended stop.

Oh Doc...Can you give us a hand here?

 

[Walter]

Doc discussed this topic at http://www.scubaboard.com/t201/s.html

 

[Dr Deco]

Dear Readers:

Extended stops are surely beneficial although more would probably be gained by slowing the ascent. As discussed earlier in this FORUM, the effect of the slowed ascent is to prevent the growth of gas micronuclei. This has been discussed on earlier occasions. I see one of those occasions is listed with the web address (although the equations appear to have been lost - - even in the original).

The concept is a rather easy one. You wish as much nitrogen to stay dissolved and exit the tissues via the blood stream. This is only possible when tissue nuclei are small in number (concentration) and also can not grow. Small nuclei radius equates to a high internal pressure from surface tension. This means that the gradient is such that pressures in the nuclei are greater than the tissue. Nitrogen will not enter these bubbles.
Surface tension keeps bashing these microbubbles down.

The more rapid the ascent, the larger nuclei will grow by Boyle’s law expansion. When these are of a marginal size, some will be capable of growing, since their internal pressure is now lowered. This does not occur with a few bubbles but rather with a whole spectrum of nuclei radii.

The result of this is that a pause at 20 fsw is good and experimentally is found to be quite beneficial. Remember, however, that it is also of value not to produce undue muscular stress and strain when reboarding the boat and moving your scuba gear.

Dr Deco
:doctor:

 

[buff]

A computer is very nice to help monitor your acsent speed. After practicing you know how fast you are ascending.

I am always surprised to find that I am ascending much faster than I would think. It can be very decieving.

Longer safety stops are beneficial too.........but not too long, the time you spend under can result in a dangerous response from the divers waiting up top!

 

[Uncle Pug]

Originally posted by buff
A computer is very nice to help monitor your acsent speed. After practicing you know how fast you are ascending.

I find just the opposite...
monitoring the computer results in ascents that are punctuated at best and overly rapid at worst... by the time your computer shows you moving to fast you are... well, moving too fast!

Better to watch the little floaty things in the water column... they give a very good reference point to gauge your ascent... we can do a free ascent watching the floaty things and keep the rate at:
Slow
Slower
Very Slow
Extemely Slow
Almost stopped Slow

 

[Spectre]

Originally posted by Uncle Pug

I find just the opposite...
monitoring the computer results in ascents that are punctuated at best and overly rapid at worst... by the time your computer shows you moving to fast you are... well, moving too fast!

Completely agreed on computers that just have ascent alarms. However some computers have speed indicators... Mine happens to show 0-4 bars, where 0 is less than 13 ft/min [4m] 1 is 13-20 ft/min, 2 is 20-26 ft/min, 3 is 26-33 ft/min, 4 is 33-39 ft/min, and 4 while freaking out is > 39 ft/min or continuously greater than 33 ft/min....

Better to watch the little floaty things in the water column...

My method of choise as well... I'd rather spend my ascents looking around and where I'm going rather than staring at my computer