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George
Here's another question.
Say you do your 220' for 25 and then ascend to do a multi-level dive to say
90' for 25. How would you calculate the deco for this? I recall you once
talked about superimposing one table on another but I had it on my list of
things to look at.
David Shimell
Email: shimell@se*.co* <mailto:shimell@se*.co*>
Project Manager, IBM NUMA-Q, Sequent Computer Systems Limited,
Weybridge Business Park, Addlestone Road, Weybridge, Surrey, KT15 2UF, UK
registered in England and Wales under company number: 1999363, registered
office as above
-----Original Message-----
From: kirvine@sa*.ne* [SMTP:kirvine@sa*.ne*]
Sent: Friday, December 24, 1999 12:43 PM
To: QUEST@GU*.CO*
Cc: techdiver
Subject: SAMPLE DECO DIVE - 220 FOR 25
Let's run through a sample dive. I will throw out the parameters and
the standeard deco on one side, and my changes and why on the other ,and
then we can discuss it.
We can then build the dive into a longer dive, a deeper dive and we can
add more gasses and more stituations, and then the equipment to do it.
Let's start with this and get the discussion going that way. I need all
questions, no matter how sophisticated, so we can get out the rock.
***PROFILE 220 FOR 25 CHANGES
***GAS 16% OXYGEN 50% HELIUM 1.2 PPO2
85 AED
REASON FOR GAS CHOICE: the more heluim, the better . It is
easier to breathe at depth, and it is easier to decompress from,
contrary to what you have been told elsewhere. The reduced narc is
obvious. I chose the 50% heliuum for this , but the more the better. The
oxygen ppo2 should be kept intentionally low. The reason is that you do
not want to unnecessarily deplete brain chemistry to pick up "perceived"
deco advantage, expescially in light of the fact that we have boosted
the helium which reduces the nitrogen damage and loading, and thus the
deco requirement. While inert gas is inert gas for purposes of this
discussion ( or said another way, the oxygen window is the oxygen
window) the reality is that helium changes the physiological factors
that are as real in deco as the straight compartment loading and
unloading factors. Very important to us in our diving, and more so as
the dives get more severe or repetitive. We also do not want to burn the
shit out of our lungs with high PPO2's either, and keep in mind that
depending on the bottom time, we are going to be forced to expose
ourselves ot elevated oxygen to decompress.
It is critical in multiday exposure that you reduce the oxygen dose, and
we will show how to do that in each decompression.
STANDARD DECO FROM A PROGRAM REAL LIFE DECO
DEPTH TIME GAS DEPTH TIME GAS
160-120 1 MINUTE EACH ON BG
110 1 16/50 110 1
100 3 100 1
90 4 90 1
80 5 80 1
70 3 50/50 70 5 50/50
60 4 60 2
50 5 50 3
40 9 40 5
30 11 30 8
20 17 OXYGEN 20 13 OXYGEN
10 26 20-0 8
TOTAL 88 TOTAL 60
REASONS FOR CHANGES
1) we start our deco at 80% of the profile in atmospheres, or in this
case , around 160 feet. We are not changing gases yet, so no reason to
sit on these stops. The ascent rate is 30 fpm, or the equivalent of a 20
second stop every ten feet from the bottom, so we are really only adding
40 seconds per "stop" from 80% of the profile. This actually "maxes out"
at about 5 minutes per "deep stop" in anything approaching saturations,
which I call 150 minutes for the purposes of decomprssion reality as
opposed to trying to decompress a whale. In a long dive, we also use the
first deco gas at 80% of the profile . Not in play here.
2) moving up we do not extend these stops per Bulhmann, since we have
already moved the "ceiling" quite a long ways above us, and are not yet
really pressing the gradient ( in percentage or relative terms, ie the
ratio of the atmospheric change deep a opposed to shallow). We need to
get to a deco gas first and spend some time, so......
3) we "SIT" on the 70 foot stop for quite a bit longer than is suggested
by theory. The reason is we want to use that wide open oxygen window for
all it is worth down there to both clear the slate as much as possible,
and to move that ceiling again quite a bit so that we can abbreviate the
stops above as their ppo2 declines, rather than lengthening them as
either Bulhmann or bubble mechanics would indicate - real life says we
are correct. In fact, I have SKIPPED up to 100 minutes of our 40 foot
stops with no repercussions, and Lucy Ho can vouch for me on this ( and
the doppler says so). The other reason is that we want to give the blood
a chance to totally circulate with the new gas. While it hits the key
body parts immediately ( spine, heart, brain), it takes a couple of
minutes to get to everything properly. We do not want to hammer high
popo2's, we want to use them to our advanntage.
3) since we have done our deep stops and our high ppo2's, both moving
our ceiling and shortening our upper time, we can go ahead and press the
gradient as it condenses, and shorten the next few stops and get to that
oxygen.
4) the oxygen does not have to be hit too ahrd. I like 12-13 minute
stints with 6-8 minutes off. The reasons are that it takes almost no
time to saturate with oxygen at any ppo2 once the immediate offgassing
slows - a few minutes - and the damage starts to accrue after about
16-20 minutes in our experience, depending of course on the dosages
already taken on the way up to this point. The swelling of the lung
tissue picks up after a few minutes, and the gas transfer process is
severely hampered. Vasoconstriction gets worse, and you are pissing in
the wind honking on the oxygen. You need to break to back gas, or in
this case , just move up and get out.
5) slow final ascent - the last move up to the surface is one of the
most critical. No matter how long you sit on a stop with the window wide
open, there will still be gas that will not be displaced by this method.
When you increase the gradient by trying to surface, the last of the gas
comes out rapidly and does so in bubble form. You must do a slow ascent
to reduce the risk of this, and for long dive it is one foot per minute
to the surface, for this dive it is more like 2.5 - 3 fpm.
6) at the surface, sit still for a bit and try not to exert for about 30
minutes thereafter. Bubbles forming at this time will now grow as they
pick up offgassing nitrogen ( the helium is long gone) and will become
problematic later, and severely so if you have a shunt that can then be
opened by the in increasing pressure on the cappillary beds of the
lungs.
OK - let's take it from here and get the discusion going. Please do not
copy back the whole message or it will become a mail bonb - just cut and
paste the parts you want to discuss, and lets discuss one item per
email, SVP. When we expand this to a long dive, then I will cross copy
it to WKPP@eg*.co*, and we will bring in the big guns ( Rose, Mee
,et al).
Let's go .
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