Deco stops

[Saturation]

Dr Paul Thomas once bubbled...
I entirely agree with you, Saturation, and it frustrates me that many instructors and dive marshalls here treat the CNS oxygen clock as gospel.

As an aside, as you know, any healthy individual can have a surface fit, more than two fits points to a possible diagnosis of epilepsy. These rare events you report may have been in sub-clinical epileptic subjects with a higher than normal tendency towards fitting. (No pre-dive test for that.)

I am convinced CO2 is the major factor as I have posted elsewhere on this site. I am going away for a day or two but will PM you with the reference when I get back as I would greatly value your comments.

I'm taking this opportunity to comment issues raised in this thread without addressing anyone specifically, to keep peace.

The USN had an Oxygen Tolerance Test to determine a diver's inherent tolerance to high pp02. Besides genetics and c02, suspected modifiers to convulsion thresholds included drugs and vitamins, but data is scanty and did not undergo further verification.

I have tried not to call 02 convulsions seizures, as its likely two separate biological issues, there are no EEG findings to suggests epileptic foci in 02 convulsions. In the 2 2002 cases posted here, no information suggests they were epileptic prior to their 02 convulsions.

No short term harm has yet been recorded for recreational divers following the CNS clock within 132' depth limits of nitrox diving keeping pp02 < 1.4, however the lower one is from 1.4, the safer you are.

"Technical" implies they delve deeper into aspects of diving, and it was technical divers who first brought to my attention the controversies of recreational curricula.

I would read "technical" literature and give their comments thought and consideration, most of the information is on the Internet, as printed texts are quickly obsolete.

Technical diving is the future of sport diving today. They push the envelope and provide subjects to refine decompression theory, equipment, and procedures that are of little interest to traditional funding sources [USN, NASA, DoD]. It requires a different strategy to address reliable data collection but the numbers of divers, large in comparison to subjects in controlled studies, offers great promise to the researcher who can work with them and find alternative funding sources.

Technical diving has a dark side, and their good messages are at times drowned by poor diplomacy, hubris and machismo. They too may take a procedure as gospel, like in recreational diving. Scuba training suffers from a huge variation in quality control, and that includes technical diving.

A young technical agency is at the vanguard in re-examining and applying knowledge of diving. FAD within hours of a trimix dive and 02 decompression is one such insight, it is physiologically sound but unstudied in the classical medical sense. Dr. Vann's recent paper reinforces FAD potential:
http://www.scuba-doc.com/MFFAD.pdf

Time will tell whether they persevere in maintaining exceptional quality standards or yield to the sins of general humanity as has afflicted DAN.

Technology and knowledge moves ahead constantly, so why not in diving per se? Thus, its unlikely there is but one way, but a standard way helps coordinate and identify like minded individuals. After all, in diving the real opponents are not each other, but nature, the oceans and its depths.

 

[Dr Deco]

Dear Readers:

Technical Diving

One of the benefits of working on this FORUM is the opportunity to receive information on diving techniques that are somewhat out of the main stream. Just as amateur astronomers discover comets, so can “amateur” divers discover phenomena not yet recognized by professional researchers. Professional science is driven by a need to seek a solution to a specific problem. It is not a “let us just go into the lab and see what happens if we do this.” Money is not available to satisfy your personal curiosity.

Likewise, technical divers will “tinker” with a problem and often find a solution that is different than what may appear to be a variance with classical techniques. Very seldom have the laws of physics changed for the benefit of these individuals. Rather we are seeing a set of conditions that are different for the ordinary.

0-g Decompression

When I came to NASA, there was considerable interest into why the astronauts did not acquire DSC when they decompressed for space walks (extravehicular activity or EVA). There were many, many explanations, all of which were classical in their origin. I on the other hand approached it with the attitude of “suppose it is real, what would cause it?” This attitude provoked great shock and surprise and I was virtually alone in my assertion that DCS was the result of microbubbles whose in vivo concentration could be varied in short time intervals by physical activity. Activity as mild as simply walking.

Subsequent research at NASA demonstrated that there could be a five to ten fold (not 10%) difference between ground and space simulated decompressions.

Problem

So many of these things are very interesting, I believe, but will not be investigated in the near future for lack of money or a commercial purpose. Certainly the question of FAD is of great interest. The old standards could use a closer inspection

One thing I seldom discuss on this BOARD is the lack of testing in decompression computers. There are so many on the market today and most vary in but minor ways. [Some computers for decompression with deep stops are a different category.] They will present themselves as something different but I will tell you that they are all minor variations on the same theme. If you really wished to test something different in a laboratory, it would take money and the manufacturers will not put up the cash.

Possible it should be done from a fund established by DEMA, but it does not exist at present. DAN has some test programs, but something needs to be expanded.

Much good information exists but it is not easily available. My Decompression Physiology class covers some of this, but, until I retire, it is not offered in many places. Additionally it is at a faster pace than I might really like.

Until then, one must bear in mind that some individuals can do amazing things in a physiological sense. This is true in so much where human variability is concerned. Can many do these things with impunity? That is seldom true. We must learn to winnow the results and separate the wheat from the chaff.

These are but a few comments added to what Saturation had to say.

Dr Deco :doctor:

 

[Genesis]

Until then, one must bear in mind that some individuals can do amazing things in a physiological sense. This is true in so much where human variability is concerned. Can many do these things with impunity? That is seldom true. We must learn to winnow the results and separate the wheat from the chaff.

This is the "bottom line", really.

There are a lot of people who "get away" with things that others would find completely amazing or flatly unacceptable.

That is reality. Whether they do because they just have rolled lots of good dice, or whether its an individual physiology issue is unknown.

That it happens, however, IS known.

The problem is extrapolating that success to others - you, for instance. The model may not hold for you, and if it does not, bad things can happen....

 

[MikeFerrara]

Details on the Ginnie incedent can be found on the IUCRR web site. I have mentioned this incedent before and posted numbers in past threads. If I remember right the max ppo2 was more like 1.3something. A freind of the victem also posted that there was significant doubt that the cause of convulsion was ox tox. If I remember he didn't say why. Also if I remember correctly it was known that the diver had been using medication and decongentines (sp?) were found in the divers posession. I think in this case there are a number of interesting factors 1) Ginnie is high flow so hard work and CO2 retention may have been a contributing factor 2) the possible use of medication.

 

[Saturation]

Sorry folks, I've had problems with posting images but got it fixed.

Here's a rough draft of a curve of 02 toxicity versus pp02 and time. The "vertical line" is pp02 and "horizontal line" is time.

There are two 'asymptotes', that's were the curve has roughly no endpoint, at pp02 of 1 and after 4. As the curve is 'smooth' drawing a line where symptoms occur or not is almost arbitrary.

Lambertsen drew the line at pp02 above 3 were CNS toxicity was a certainty, and at below 2, were it was very unlikely, and thus below pp02 of 2, the main issues is whole body toxicity.

 

[wazza]

So how can some one go deeper
Than 60 MSW?
Some time u jump in the water and
U feel that today u are able to go to
80 or 85MSW and some time u feel
as well that u cant, though u did it
before. I do this as solo diving most
of the time, last week I did 70m dive
and I wasn’t been diving for 4 or 5months
and I had a extreme nice dive.
And I have friends they even go to
100m and even 120 MSW on air.
All these dives I am talking about is
On air.
But of course I would never teach some
Student To do something like this. And I
know its A very bad thing to do, but I don’t
enjoy diving if I was shallower, that is all.

So where is the toxicity and where is the
CNC clock and all the things we learned about?
Some time I believe that these are only books
Nothing much to learn from.

One more thing I heard that if u had orange juice
Before the dive is better for the CNS toxicity,
It will be less or would never happen.
And some time we take dehydration powder with
Water the one for kids from the pharmacy before
The dive as well. And I am still alive until now

 

[O-ring]

You are pushing a 1.67 ppo2 at 70M and on those 120M dives a 2.72!!!!

We try to maintain a working ppo2 of 1.2-1.3 on anything deep and max ppo2 in deco of 1.6 (o2 at 20'). I don't know anything about orange juice or dehydration powder, but remember that someone recently died at Ginnie at less than 1.4 and I have read of deaths (Ed Sollner) in the 2.0 range. The guy that toxed in the GUE DIRF/Tech 1 in Croatia was said to be breathing EAN50 at around 100'...that is right around a 2.0 ppo2. Only the quick thinking of an instructor saved his life..

One thing we know is that physiology is different among different people. Additionally, one person varies from day to day...there were some tests done (can't remember by who...I think the Navy or DAN) where somebody could take up to 2.0 or 3.0 ppo2 on one day and then would tox on 1.6 the next. There's too much we don't know to be pushing the envelope with ppo2, IMHO.

It seems to me a reckless chance to take, but it's your choice.

 

[Doppler]

Just spent 20 minutes or so reading through this thread... some useful information contained here... also nice to read some scientific arguments on the topic for a change.

One further question... andibk, does that answer your question? I am surprised you didn't ask whether or not the time on "air break" is added to or becomes part of total deco time...

DD =-)

 

[The Iceni]

wazza once bubbled...
. . . And I am still alive until now

Wazza!

I just read your thread in more detail.

Apart form oxygen toxicity the most worrying feature of deep diving on air is the effects of nitrogen narcosis. Like alcohol, you feel absolutely wonderful and from what you say it would appear that you and your friends may be in that group of divers who get a buzz from narcosis.

Take care! Even if you feel fine your performance will be impaired at those sort of depths. I would like to think you have posted 70 meters when you meant to post 70 feet.

Are you still alive?

I may decide to cross the road each time without looking and claim it is perfectly safe while I remain alive but is only be one person I would be fooling, and that would be myself.:boom:

 

[Saturation]

Dr Paul Thomas once bubbled...
Wazza!

I just read your thread in more detail.

Apart form oxygen toxicity the most worrying feature of deep diving on air is the effects of nitrogen narcosis. Like alcohol, you feel absolutely wonderful and from what you say it would appear that you and your friends may be in that group of divers who get a buzz from narcosis.

Take care! Even if you feel fine your performance will be impaired at those sort of depths. I would like to think you have posted 70 meters when you meant to post 70 feet.

Are you still alive?

I may decide to cross the road each time without looking and claim it is perfectly safe while I remain alive but is only be one person I would be fooling, and that would be myself.:boom:

I strongly second Dr. Thomas' position.

As a rule of thumb, one should know the human body has a range of performance, and while it varies per person, at some point its beyond even the most exceptional individual. These characteristics can vary daily for the same person, and declines with age. You can run that mile like you did everyday for ten years, then one day your Achilles tendon snaps. You've always had that knee pain from an old sport injury that did well on a two aspirins, and today it doesn't seem to be working, but works next day. Finally, the asprin stops working altogether.

In diving, you can do deep air during your youth, and following the same trend continue to do so ... until the close call or the final dive occurs as you age. Deep air is still possible and its effects managed to an extent, but its old technology and not the ideal gas to decompress from, given alternatives.

Even a professional gambler plays to win, with odds stacked in one's favor, and different games have different odds.

"Fortune favors the prepared mind" -- Pasteur.