Ascent rates. Why do you choose to do it the way you do it.

[nwbobber]

I learned to dive a long time a go. I took a long break ( 25+ years). Took another open water class. Things changed. What they taught was 60 ft/min., then 30 ft/min from your safety stop at 5M to the surface. In practice I have found divers who take at least 10 min to ascend from their safety stop to the surface. What do you do? Is this a precaution, or do you notice a difference in how you feel after a dive? I'm 50 now, and I want to be conservative, so I can keep doing this for maybe another 50 yrs or so..
Bob
PS I'm diving in the puget sound area, so relatively cold water.

 

[Papa_Bear]

I too was trained as you were! It is who can be safer in the on going organization battle to be the safest! DAN and others have done studies that indicate that slower is better and the safety stop is just that, a safety stop not a mandatory Deco stop! We were also taught 25min at 100ft using the Navy Tables..... Again safer to minimize liability among agencies wins out! If your going to error better on the safe side and there are always exceptions to the rule and profiles that are just as safe as the hang type safety stop! It is always a personal choice and your own safety in the balance..... I had a lot of dives over a thousand under the old rules and had no problems, but thats the point we are all different and every dive to depth is a calculated risk!

No you don't feel any better from being more conservative in your diving unless you count not getting DCS or an embolism?!!!

 

[Cacia]

Search Charlie99's posts on this and you'll have a great start and a good set of Cliff note gems.

He has never posted anything incorrect that I know, and he distills it down to a solid working knowledge better than almost anyone.

I do a half depth stop and then about a minute every ten feet to 15-20 feet, depending on the herd and conditions, where I do at least three minutes but usually more because I use most of my remaining air (down to 200-300 psi)there because all the other people thrash around getting on the boat during that time and I like hanging out there relaxing as opposed to being on the boat.

I strive to never exert myself on deep dives, in current. Plan to never fight the current. I advise you to get a SMB and befriend it.

was 60 ft/min.,

I'd say that is too fast for me to feel prudent.

 

[TSandM]

The teaching you originally got was based on a pure dissolved gas model of decompression. Using those models, you decompress most efficiently if you drive the gradient for offgassing as hard as is safe. That means getting as shallow as possible, and doing any in-water decompression at shallow depths. (You do recognize that all dives require decompression, of course? Just because something is a "no-deco" dive, doesn't mean you don't have to decompress and offgas. It just means you're unlikely to get bent if you go directly -- at a controlled rate -- to the surface.)

More recent work is focused on the production and behavior of microbubbles in the circulation and the tissues. Getting shallow fast promotes the formation and growth of bubbles. Although the lungs can filter a fair amount of microbubbles, they have a limit; and diffusion out of bubbles is slower than diffusion of dissolved gas. So many decompression strategies today are aimed at spending more decompression time deeper, to control the formation and growth of bubbles. This idea, for example, is the basis for the Suunto RGBM algorithm.

So some people slow their ascent rate at half their maximum depth, allowing time to offgas the fast compartments and control bubble growth. They then use a progressive stop system to control ascent rate and permit controlled offgassing. A stop every ten feet from half maximal depth gives you, in effect, a 10 fpm ascent rate -- although there are a couple of provocative studies that say that a more rapid ascent punctuated by stops is better than a steady 10 fpm ascent. At any rate, the last piece of this strategy is to slow the ascent rate even more in the last 20 feet, because the proportional pressure changes are so great there.

I use this strategy, and I'm very convinced that the post-dive fatigue I thought was normal really went away when I started to do my ascents like this. Like you, I'm no spring chicken, and I'm really eager to do anything that improves my safety, but improved safety is hard to prove for recreational diving because the bends rate is so slow to begin with. But the benefit in fatigue at the end of the day, when you're dragging the gear out of the car to wash it and hang it up, is not to be sneezed at.

 

[fisherdvm]

A widely reported study have shown that over 1/3 of recreational divers exceed the minimum recommended ascent rate of 60 ft/min. My guess is that this number should be much smaller if they were trained to use a computer consistantly with each ascent. It is too much task loading for a new diver to remember the check list for ascent, and half did not learn proper ascent procedure after they get their certification.

I tend to stay on the green zone of my dive computer's ascent rate - which is about 30 ft/min. Eventhough you don't need a safety stop at 30 ft or less, I still require my son to do it. Partly to teach him to be aware of the surface environment, part for buoyancy control, and part to make sure he is properly weighted. I also teach him not to be the first to break the surface.... It is better to let your buddy or another person get hit by boat traffic, than yourself... It is sad that many OW instructors don't force a new student to do a 15 ft safety stop, as "you don't need it because our dive was in less than 30 ft of water". Because these divers were never exposed to the concept in real life, they tend to forget to do it when they really need to.

 

[spectrum]

nwbobber,

First let me say that the few times that I found myself exhausted after diving were times when the outing included one or a few less than slow ascents. Sub clinical DCS was a real possibility here. Slow is good, especially as you approach the surface.

As long as you are deep you are on gassing. If you start up from 100 feet and ascend very slowly you are still spending time at a depth that is loading you at a significant rate. By making your way expeditiously to to a mid stop at something approaching 30 FPM you have cut the on-gassing rate significantly and the tide can begin to reverse.

As you slowly make you way to a safety stop the progression continues through the stop. Traveling the last 15 feet in a slow controlled manner gets you to the surface in a way that is least disruptive to your body. Once you break the surface extend the mentality. Try to bob on the surface or stand in the shallows for a bit where the water can support your rig before climbing on to the boat or hiking up the beach head. In a very real way our bodies are disrupted every time we dive and we need to respect that.

Age and cold are 2 significant DCS risk factors and a gentle ascent will help mitigate the risk.

Pete

 

[amajamar]

I don't mean to sidetrack the OP's question but as far as on-gassing vs. off gassing is concerned, if you begin a multi-level dive at 100' you are obviously on-gassing at a rate proportional for the depth.

Now, as you continue the dive and are ascending as you do so, are you off-gassing as you go or just on-gassing at a slower rate?

At what point does on-gassing become off-gassing?

Does anyone have any recommendations for good books that explain decompression theory in layman's terms?

 

[raymond phule]

Now, as you continue the dive and are ascending as you do so, are you off-gassing as you go or just on-gassing at a slower rate?

At what point does on-gassing become off-gassing?

This depends on which compartment you look at and how long you have been on depth.

Baker, Understanding M-values is a good article and can be found at many places on the internet. He has also written other good articles.

Deep Ocean Diving - Science, technology and medicine related to scuba diving is also good.

If the articles are good or not for a layman probably depends alot on the background of the layman...

 

[fisherdvm]

I don't mean to sidetrack the OP's question but as far as on-gassing vs. off gassing is concerned, if you begin a multi-level dive at 100' you are obviously on-gassing at a rate proportional for the depth.

Now, as you continue the dive and are ascending as you do so, are you off-gassing as you go or just on-gassing at a slower rate?

At what point does on-gassing become off-gassing?

Does anyone have any recommendations for good books that explain decompression theory in layman's terms?

I think it is a continous process. You are likely off gassing from fast compartments, and on gassing from slow compartments. I think the slow compartments are controlled by shallower depths, and the fast compartments are controlled by deeper depths. As some models have 6, and some have 100 compartments ... It is a continuum. My guess is, at less than 20 ft.... You probably are relatively safe, even for a 10 hour dive. But the standard dive tables make you assume it is a 35 ft dive with any dives less than 35 ft. Now if you dove at 20 ft for 10 hours each day, and 10 days straight.. Certainly you can be filling some very slow compartments, and run into risks of DCS. Fortunately, most of us do not dive for 10 hours every day.

I would google decompression models, and read about the concepts.

 

[grazie42]

I see people "hurry" to their safetystop so that they can spend time there and be "extra safe" which seems counter-productive...

what I do on recdives is that I make sure that my ascent rate stays constant and below 30ft/min thruout the ascent, I think it´s important to avoid "jumps" in your ascent-rate...my experience is that adding a few minutes to slow down my ascent(and doing a standard SS) is far more beneficial than going 30ft/min and adding those minutes to the SS...since I started "taking it slow" I´ve been feeling more alert and less sleepy after a days worth of recreational diving...