From what I've read on the site, it seems like very slow final ascents are better. For recreational, non-technical dives on air, would the risk of DCS be reduced if the final ascent is made as slow as possible? Would a standard OW ascent benefit if the ascent from the safety stop is reduced to 10 fpm? Does the answer change if a deep stop has been added to the standard OW ascent?
Are very slow final ascents better?
- Thread starter BigTuna
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ronbeau
Contributor
BigTuna:
In my Advanced Open Water course it was mentioned that the latest thinking is to do a one minute safety stop at half the depth of the deepest depth of your dive. Followed by a 2 minute safety stop at 15 feet.
The recommended ascent rate is 30 feet per minute. To put this in perspective think about taking 20 seconds to go from the bottom of a 10 foot pool to the surface. This is really slow. I couldn't even picture me being able to consistently do a 10 foot per minute ascent.
ShakaZulu
Contributor
Try it, you'll even feel better........if you are feeling tired after diving, you are ascending too fast.
H2Andy
Contributor
BigTuna:
yes... basically, any time spent above 33 feet is good, giving your body a chance
to offgas at leisure
what i do is a 3 minute stop at half my max depth, then slowly to 30 feet,
then do a minute there, then REALLY SLOWLY to 20 feet, and spend as much
time as i feel like it there, then REALLY SLOWLY to 10 feet and again spend
as much time as i feel like there, and then REALLY SLOWLY ascend to surface
keep an eye on your computer. you will see that your "max time" continues to increase. this means that you are not incurring any additional nitrogen loading.
quite the contrary, you are reducing your surface interval.
ronbeau:
i think this is cheating, but it's what i do. i will go up two feet and stop,
then wait five seconds, then go up two feet and wait five seconds, and
so on.... it's start, stop, start, stop all the way up.
i guess it's cheating, but it works for me!
Latest Scuba magazine has a great article about ascents from the final 15 feet. You might want to go very slow.
The Chairman
Chairman of the Board
It's not unusual for that last 10 ft to take a minute! It's also not unusual for that cautionary stop to last 5 minutes or more (after the 1 minute deep stop).
BigTuna:
Research has been done by IDAN and they have been working with an Italian research team as well as NAUI who has been doing research in deco for technical diving. There are two different types of tissues; "compartments" in the body...slow and fast. The fast tissues will disolve inert gas much more quickly than the slow tissues. I takes 6 half times to fill a given tissue with dissolved inert gas. It takes 30 minutes to fill the fast tissues...brain, blood,spinal cord...and it takes 360 minutes to fill the slow tissues. If you look at the deeper recreational dives with a dive time of 25 to 30 the fast tissues will be almost filled while the slow tissues are not even close. So the focus related to DCS was on the fast tissues. The fast tissues also off-gas more quickly, but the recommended ascent rates...even 33 ft per min. did not give enough time for gas elimination to occur. IDAN came up with a profile of an ascent rate of 33 ft/min with a 45 ft stop and a 9 ft stop. NAUI favored a one minute stop at 1/2 depth and a 2 minute (instead of 3 minute) hang at 15 ft. DAN is also studying ascent rates specifically. Changes are being considered at this time but I don't think they have actually been incorporated. As I am aware it's still don't ascend faster than your bubbles and do a 3 min stop at 15 ft.
nauidiver2004
Guest
Well, it's all already been said but yes, the slower the better, esp the last 15 feet. This is where the greatest relative pressure change on you body is.
Of course those bubbles are flying up a bit faster than 33 feet per minuterawls:
The Chairman
Chairman of the Board
NAUI was the first agency to teach deep stops in ADDITION to your normal stop in their Open Water Class, and they DON'T teach chasing bubbles any more.rawls:
If deeper than 40 ft add a one minute stop at half of your deepest depth and then do a 3-5 minute precautionary stop at 15-20 fsw. If you are diving a computer, you should do a FIVE minute safety stop.
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