Deco stops

[wazza]

Dear Dr Paul Thomas
First let me thank u for your concern and to tell u the truth I cant agree with u more.
But just like u to know that I am a tek Instructor and Advanced Trimix diver and I have been diving for a long time, and what I am trying to say that by now I know my body very well and I know what u mean concerning Nitrogen narcosis and when I do feel or not. For 4 years when I started diving I could not go deeper then 60msw on air cos I felt the narcosis at 60 and I pushed my self to 65 or 67m but I could not go deeper, but few years ago and out of nowhere and in one year I could go to 85msw (solo) and I am in control and aware of what I am doing clear and relaxed, and every time I go deeper my breathing rate will go slower until I reached the 10 to 11 l/m
And as I said before that before the dive u can feel if u are able to go really on deep air or not, u have to listen to your body that is all.
And don’t forget there is dive agencies teach the deep air diving ( going deeper than 65msw) thought in each page of the book there is a big sign says (its not recommended ).
One more thing I don’t recommend any one to go deeper than 50msw on air ( even tek divers ) and when I do a deep dive I don’t tell any one with me on the boat how deep I went, cos I don’t want any one to think that its a peace of cake and any one can do it with out a proper training and years of experience.
Thanks again for all the help, useful info and concern.

 

[TwoBitTxn]

I just wanted to post a note of thanks to our medical regulators for some fascinating information.

Saturation I missed your addition to the board. Welcome. You are clearly a very valuable addition to a great group of people.

Thanks again,

TwoBit

 

[Saturation]

TwoBitTxn once bubbled...
I just wanted to post a note of thanks to our medical regulators for some fascinating information.

Saturation I missed your addition to the board. Welcome. You are clearly a very valuable addition to a great group of people.

Thanks again,

TwoBit

Thank you TwoBit, its a pleasure to be here.

This eboard has a wonderful collection of folks, and the technology it uses makes it very easy to post and search archives.

Vital for me, I can edit my posts that contained errors or omissions that in most eboards, you can't retract or correct.

 

[The Iceni]

wazza once bubbled...
Dear Dr Paul,

1) But just like u to know that I am a tek Instructor and Advanced Trimix diver and I have been diving for a long time, and what I am trying to say that by now I know my body very well and I know what u mean concerning Nitrogen narcosis and when I do feel or not

2) Thanks again for all the help, useful info and concern.

Hi Wazza,

1) Glad to hear you know about Trimix. IHPO that's the gas to use for such deep dives but take care. I note from your profile pics you use a rebreather. Take extra care, their technology is far from perfect.

2) You are very welcome. I think language differences added to my perceived worries.

 

[andibk]

Doppler,
Alot of good information has past. I could not believe the response to the thread. That is a good question you brought up, are people taking adding the airbreak time to there deco?

Bruce

 

[The Iceni]

Hi Bruce,

This is not the sort of diving I have ever done so never got into greatly extended deco stops using oxygen although that was my deco gas of choice, so do not take this post as gospel.

Needless say, I would strongly recommend you take the appropriate course with a good instructor before you even attempt the sort of diving that requires such extended decompression, if you have not done so already. I have no doubt Saturation would agree.

If you think about what is actually happening to the diffusion pressures during oxygen deco at 3 M during an air break, it is obvious that the nitrogen offgasing counterpressure at the lungs has been increased from zero to 0.79 X 1.3 bar = 1.03 bar. For all intents and purposes one can safely assume that nitrogen offgassing ceases because of this. Indeed the slower compartments may even be ongassing during an air break.

So every air break must be added to the total stop time.

If your table shows 30 min deco at 3 M and you take a 5 min break after 20 minutes the total stop time must be increased to 35 minutes. I believe this is why the vanguard are constantly trying to reduce the number of air breaks they do, as it adds to the total time spent in the water.

I continued to breath oxygen for several minutes after leaving the water as a "hidden stop" particularly if I was expecting to dive again that day.

 

[Saturation]

From my first post I wrote:

" (Mr.) Irvine has included the breaks in calculating the total 02 time, thereby shortening the total 02 deco by 5:20 or 25%. One credible hypothesis is that it takes 1-3 minutes for blood gases to equilibrate with alveolar gas, so decompression time may be effectively reduced only say 5-15%."

Since there is variability in response to decompression, as the human body has variability to many things, the question of optimal decompression in a schedule for a diver has to be individualized. Its best to begin a schedule as conservative as possible.

If we take circulation time as a factor to reduce the total 02 time by only 5-15%, Mr. Irvine's recommendation is indeed practical, particularly if you add two other of his recommendations as part of the regimen: a _very_ slow ascent from 20', which could compensate partially for this reduced 02 time.

However, as mentioned in my previous post, in dives in the 200-300' range for 30min bottom time, seldom is there a need to breathe 02 past even 30 minutes, and with bubble models for decompression, long pp02 exposures are less an issue.

A true wonder provided by technology and the combined work of many, has been the bubble models. Its effect on shortening total decompression time for in-water dives is revolutionary to say the least, and thus, it effectively reduces prolonged exposure to high pp02. However, how this works among all divers remains to be seen. The difference is startling:

http://www.divetekadventures.com/Pictures/decoCurves_MAX_DECO.gif

Is the much celebrated 'Maximum Deco' of Mr. Irvine in graph form.

The pink line is a Buhlmann schedule.

The room for error is very small. The deep stops in time and depth are increasingly critical in long dives.

The deep stops component is for 'fast' tissue offgassing. The shallower stops are for "medium" and "slower" tissue offgassing.

In another profile two divers had neurologic symptoms in-water during the decompression segments of the dive. Their ascent was rapid. The green line is VPlanner, a VPM program by Ross Hemingway, which is considered by some as aggressive. I've dove Vplanner without issues but I'm a decoweenie

Take Home Message:

Take the 02 breaks, add the break time to your 02 time

 

[TwoBitTxn]

In a couple of the take home messages it is reccommended not to exceed a ppO2 of 1.4. In a deco situation where a person is using 100% O2 the max depth is 13FSW. If you go to 1.6ppO2 its 19FSW.

At 80% your limits are at 24 FSW and 33FSW resepectively. I understand the concern that with 80% your deco is not as effective due to the presence of N2 in the gas.

If you stick to the 1.4 rule on the bulk of the dive but switch to 1.6 to utilize 100% O2 is there a significant risk involved?

I am probably more confused than I think I am.

TwoBit

 

[WreckWriter]

Saturation once bubbled...
I've dove Vplanner without issues but I'm a decoweenie

I dive V-Planner regularly and am very happy with it. I am NOT a decoweenie

WW

 

[TwoBitTxn]

I found the answer to my question in an earlier post. Just not sure I understand it. I need to take time to read it over a couple more times and see what I can get out of it.

Thanks

TwoBIt