DAN article on ascent stops

[NJMike]

The article says, in part...

"What is interesting, and not necessarily intuitive, is that an in-water stop with a relatively rapid ascent rate appears to be more effective at eliminating inert gas than a very slow ascent rate."

I am new to diving (for the second time) and will be full swing next summer. For the winter, I will be getting to know my new gear (see the Christmas thread), reading, researching and learning.

I have been through the rock bottom pressure planning and plan to use that in my diving. But now I am considering adding another safety stop at half the deepest depth, per that article.

I haven't figured out all the details yet...but I [think] the idea is to figure out how long an ascent time you need to offgas enough nitrogen to prevent bubbles from forming after reaching the surface.

According to the article, the relative tissue compartments are the short half-time ones...and the example they used of a 100' dive for 25 min and looking at the spinal column (which has a half-time of 12.5 min) was very enlightening.

I will be trying to figure out how to calculate the ascent time actually needed. For example, suppose you went to 100' but only stayed for 15 min instead of the 25 min the example used?

But the Advanced Diving book from NAUI...seems to disagree with this.

Who wants to take this one on? Here's the question...

If we are planning a dive to 99' (makes it easier?) for 20 min, how long a total ascent time should we PLAN?

 

[Doc Harry]

That was interesting article.

I have a colleague who was long-time navy diver a long time ago. He relates that they used to actively swim upwards as fast as they could between in-water stops during their ascent. No one ever got bent, and he was doing some deep diving.

It was interesting to hear how it used to be done. It ascent technique going full-circle?

 

[NJMike]

It sounds like your total ascent time should be LONGER than the half-time of the critical tissue compartments...I think.

But I had another thought last night...with my computer that shows how much nitrogen is theoretically in the most critical tissue compartment at any given time, then why not....

make an ascent without a safety stop, check the computer and see what the tissue loading graph says...

then repeat with a standard 15', 3 min stop, and then do the same dive one more time but add a stop in at half the deepest depth.

At the end of the 3 dives, at least according to the computer, you would get a pretty good idea of how much nitrogen is in the most critical tissue compartment for the 3 dives.

Sounds like a fun experiment for next year!

 

[Doc Intrepid]

I haven't figured out all the details yet...but I [think] the idea is to figure out how long an ascent time you need to offgas enough nitrogen to prevent bubbles from forming after reaching the surface

Accurate, but incomplete. As you ascend, the reduction of ambient pressure may cause seed bubbles to form as dissolved nitrogen comes out of solution. If you ascend slowly enough, these seed bubbles will be offgassed via the lungs. If you ascend too quickly, they may not be, or may only partially be, and/or may expand (or more of them form as more nitrogen comes out of solution) to a point where they begin collecting around joints and become problematic in numerous ways. Therefore, to pick nits, the idea is to figure out what ascent rate you need (e.g. distance ascended over time) to allow nitrogen coming out of solution to offgas properly rather than ascending too quickly and allowing bubbles to expand during your ascent (as opposed to after you surface).

......If we are planning a dive to 99' (makes it easier?) for 20 min, how long a total ascent time should we PLAN?

There is no reason that I can think of, aside from a diver who has gone unconscious or is convulsing underwater, to ever PLAN to execute an ascent faster than 30 fpm. So the answer would be about 6 minutes - three minutes to ascend from 99' (100') to 10', and then a safety stop of 3 minutes, followed by a slow drift to the surface.

That said, decompression is an inexact and controversial topic. Many divers perform decompression differently, using different gasses, etc. The bottom line is that when you "experiment" on dives to discover varying bubble formation rates - with yourself as the lab rat - you risk more than simply finding out that bubbles form at rates faster than you thought. There are recreational divers (and technical divers) in wheelchairs today, for the rest of their lives, as a consequence of chamber rides that failed to completely alleviate their physical maladies that resulted from their getting bent.

I strongly recommend you rethink doing 3 dives to 100' for 20-25 minutes each to see the variance in tissue loading presented by your computer.

Just plan your dives for a 30 fpm ascent rate, and execute a stop at a depth calculated as described in the article. If you want to see what happens to decompression requirements on such dives, use a reputable dive software package such as this one by Ross Hemingway, who is also a member of this board:
http://www.hhssoftware.com/v-planner/index.html

If this topic interests you, I also encourage you to get some additional training - the courses you would be looking for are the advanced nitrox and extended range courses offered by IANTD, TDI, or DSAT or the Fundamentals and Tech series of courses offered by GUE.

Dive safe,

Doc

 

[Doubles]

That was interesting article.

I have a colleague who was long-time navy diver a long time ago. He relates that they used to actively swim upwards as fast as they could between in-water stops during their ascent. No one ever got bent, and he was doing some deep diving.

It was interesting to hear how it used to be done. It ascent technique going full-circle?

Did you ask your friend if he went right into a chamber when he exited the water or was all deco done in-water. I believe that happens a lot in military diving.

Cheers

 

[boulderjohn]

It sounds like your total ascent time should be LONGER than the half-time of the critical tissue compartments...I think.

But I had another thought last night...with my computer that shows how much nitrogen is theoretically in the most critical tissue compartment at any given time, then why not....

make an ascent without a safety stop, check the computer and see what the tissue loading graph says...

then repeat with a standard 15', 3 min stop, and then do the same dive one more time but add a stop in at half the deepest depth.

At the end of the 3 dives, at least according to the computer, you would get a pretty good idea of how much nitrogen is in the most critical tissue compartment for the 3 dives.

Sounds like a fun experiment for next year!

That experiment will really only show you how the computer theorizes your nitrogen loading basd upon its programming. If it does not have a benefit for a deep stop programmed into it, you will not see any benefit.

I did a semi-version of that experiment on several deep dives last month. I watched to see how it was reacting during my deep stops, and it kept "penalizing" me as long as I there. Of course, its program was written before the DAN study.

 

[spankey]

now if you all took the Naui master diver coruce you would know this.

 

[wallacm]

anyoen have a link or copy of this article?

 

[mikerault]

Instead of risking yourself, why not get a 100 foot rope and tie the computer with a dive weight to it, then you lower it down, let it sit for 20 minutes and bring it up however fast you want with whatever stops you want. Much safer than using yourself as a guinea pig. The computer could care less if you are attached or not.

Mike

 

[victor]

But I had another thought last night...with my computer that shows how much nitrogen is theoretically in the most critical tissue compartment at any given time, then why not....

make an ascent without a safety stop, check the computer and see what the tissue loading graph says...

then repeat with a standard 15', 3 min stop, and then do the same dive one more time but add a stop in at half the deepest depth.

At the end of the 3 dives, at least according to the computer, you would get a pretty good idea of how much nitrogen is in the most critical tissue compartment for the 3 dives.

Sounds like a fun experiment for next year!

If you want to do this can I sugest that you sit in a boat and use a heavy sinker attached to your computer on a fishing line. Mark the line for depth and just reel it at what ever rate you need.

This will eliminate the time you will spend in a deco chamber and / or a hospital bed.