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on 9/7/01 10:31 PM, Don Hoover at Don.Hoover@da*.ne* wrote:
> George,
>
> That slow assent from 20 feet to the surface is that slower that 10ft/min?
> Also, do you incorporate a surface transition before getting out of the
> water...say 10 minutes of resting on the surface?
Hi Don, not sure if you saw these posts of Trey's on deco a while back ? The
last 5 paras of the first one in particular are specifically about
discarding the 10ft stop and time for the latter stages of deco.
Following that is follow up/clarification posted in answer to a question
from Doc G.
*************************************************************************
TREY's FIRST POST:
Let me first say I am not going to entertain any discussion or argument on
any of this with anyone who wants to read me ancient history. My stuff is
based on what works, and I have zero interest in what anyone else things,
other than JJ who does it with me and who's team of deco geeks keeps doing a
wonderful job of coming back to me with reasons why I am right. Getting past
that an moving on...
Decompression is a not linear event: twice the bottom time does not mean
twice the deco, and half the bottom time does not mean half the deco. This
is fairly intuitive, but for you Marines, the fact is that the fastest
movement of gas occurs where there is the greatest differential. When you
first go from one ATA to two for instance, there is a fast on gas rush, but
as you stay there a while it slows down since the gradient factor powering
the movement is lessening, like charging a battery.
On gassing is easy - you do not blow gas into the tissues in bubble form
by on gassing. Off gassing is more tricky, as you want to prevent bubble
formation in the tissues at all depths, and in the blood deep. Off gassing
in bubble form into the blood is extremely efficient time wise and allows
faster decompressions that avoid building in one tissue while eliminating in
another, but this is for non shunt people only. Unfortunately for the
shunts, the greatest incidence of bubbling into the venous blood occurs
after you get out of the water.
It takes a certain amount of time to circulate the blood, maybe about two
minutes, and it can take as much as five to get gas in solution to begin to
come out of solution in bubble form in the tissues or into the blood in
response to a reduction in pressure. Most of the short on/offs are handled
well by the body in terms of outright pain or obvious symptoms, but they may
cause the body's immune system to respond to the insult that is actually
occurring, and uneven off gassing from sensitive tendon attachment points
and live bone surfaces as well as certain dense muscle may not be able to
accommodate the super short cycles. Tissues that are hard to on gas are not
as much of an issue on minimum deco, only on longer exposures.
We have found that the short schedules under 30 minutes are inaccurate
predictors. What we do is set a shape for the deco as if it were a longer
dive, complete with starting the stops at 80% of the profile in ATA's, and
merely go to a minimum reading for each stop. The minimum deep stop is 20
seconds at each ten feet, which is effectively 30 feet per minute plus the
moving time. The max for these is five minutes for saturation ( or anything
within 85% of technical saturation, which I assume to occur at 150 minutes
bottom time ).The stops indicated by the shape of the deco curve higher up
need to be done to a minimum number, like 1 minute for the deeper ones and
then more when the gas switches come in. Give the gas a chance to work, then
go back to the curve with the 1-2 or 3 minute stops. As you get higher up,
the fact that you did the deeper part more meticulously will allow some
abbreviation in the shallower steps.
In any of these decompressions, do your calculation and then discard the
ten foot stop completely from the figures - throw it and its time out
completely - that is total bullshit. Then ask yourself how much time do I
need at 20. The answer is , enough to make it work if I did the deeper steps
correctly. Two minutes on oxygen is not doing anything, ten is more like it.
However, what you want to do is incorporate a slow ascent rate into the last
20 feet of the dive, so what was the 20 foot stop should be eased up from
20-6 in a steady motion after you have sat at 20 and allowed a full
circulation of the blood and the effects of the pressure change and the gas
to begin to work and a relative time based on you real bottom time where the
total of the 20 plus ascent to surface is at least equal to your bottom
time, again assuming you have done the other steps correctly. Do not waste a
bunch of pyramided time at steps where there is little partial pressure
advantage, use the gradient more in these cases, again assuming you have
conscientiously done the lower steps.
Don't be in any big hurry to get up from the bottom, and do not be in
any big hurry to get up from 30 feet to the surface. These two areas need
careful attention.
I think that if you discard the 10 foot silliness in any program and the
unnecessary time, then put some of that time back into the correct shape and
strategy, you will not only prevent the out right DCS, you will prevent the
sub clinical DCS and the immune responses.
If you execute deco correctly and are in good shape and have no
preconditions, you should be clean and ready for anything 30 minutes after
you get out of the water. You can tell if you have not done what I am saying
here, you will not feel so good. It will be subtle, but if you want to test
it, try going for a run. If you are immediately short of breath, you blew
the deco. If you can rock, you did it right. If you get bent trying this,
then tough luck, blame JJ. In reality, you will feel a little sluggish and
heavy just putting your gear away if you did an inadequate deco.
Now , if there are questions that can help with the understanding ,
bring them on. If anyone wants to argue with me, save your breath and be
ready to show me your logbook, and don't bother with the IANTD, TDI, PADI,
DAN or any other form of nonsense that is floating around out there. Nobody
understands this like I do, and nobody can execute it like I do, and nobody
has done it this way for as long as I have, not even my own team. I know for
a fact that this is not only correct, it is correct beyond a shadow of a
doubt. I remember getting Exley to get out of the water with me at Wakulla
one time on my schedule. That was easy to do with him because he responded
very well to peer pressure - I could get him to do anything I dreamed up. He
spent the next four hours in the lobby of the Lodge getting FSU to Doppler
him over and over just waiting for the big bends hit - never happened. That
was nine years ago. We have really perfected it now.
*************************************************************************
Then Doc asked:
-----Original Message-----
From: Wendell Grogan [mailto:wgrogan@dc*.ne*]
Sent: Sunday, June 03, 2001 10:27 PM
To: Trey
Subject: Re: MINIMUM DECOMPRESSION
>>
>> "a relative time based on your real bottom time where the total of the
>> 20 plus ascent to surface is at least equal to your bottom time..."
>
> I'm just writing back personally because I know I'm just missing
> something here and there's no reason to waste everyone else's time with
> explaining this to me. It seems like you're saying that the time from
> 20 to the surface should equal real bottom time. I can see where this
> makes sense on a significant dive- where your actual BT is going to be
> relatively short. Is it just that these rules don't really apply to
> long shallow dives like the one I was postulating?
and Trey replied:
Dr. G, this is a bit confusing, sorry. The text surrounding this explains
it, but to be more specific, the total of the 20 foot stop and ascent to the
surface is a function of bottom time and it maxes out at the saturation
point I mentioned - never need be more than 150 minutes, for deep short
dives will come out about equal to the bottom time, and for long shallow
dives will be quite a bit less but will be in the realm of what most deco
programs will give for a 20 foot stop. Remember we discard the 10 foot
completely and we do not ask the computer program to dive us a 20 foot only,
as this will not work past the time the window has done its job and the
gradient needs to be increased.
A good rule of thumb for long shallow dives, lets say 100 minutes at 150-190
is that the total deco in all forms will be about equal to the bottom tine.
Shallower depths will be quite a bit shorter since the steps to decompress
are so close to the profile, and as such not such a big deal.
Thanks for picking this up - I get so used to dealing with steeper profiles,
but I see from swimming in the ocean the last few days that it is diving
time here again, so I will be more balanced in my answers to these
questions. The big thing for most people is how to get a successful deco
from dives that the idiots tell them need some horrendous nonsense, and then
to show everyone how to decompress properly - what is taught at the agencies
is dead wrong, other than where some of Bruce's stuff is used, and then only
with the right gases, which again the idiots don't get at all.
*************************************************************************
hth
regards
***
dean laffan
real world productions
melbourne, australia
ph +613-9419-3966
Mobile - 0418-525-315
It said on the box: 'Requires Windows 95 or better' ... so I bought a Mac !
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