Sure , Art - the only two issues are that 1) Navy found an increased
chance of toxing after multiday elevated ppo2 exposures ( like nitrox
diving every day or deco diving every day ) with the MK16 divers, and 2)
the lung damage and such are obvious and cumulative. The lungs tend to
scar and build "callusses" , decreasing vital capacity.

Art , I do not know what I said about anything  being bullshit unless it
is what the agencies teach, and that is solid bullshit, but I take
oxygen exposure very, very seriously, and to me it is the biggest risk
in tech diving outside of violating Rule Number One.


Paltz, Art wrote:
> 
> George,
> 
> Can you elaborate on Oxygen Exposure?  I remember you saying many times that
> OTU's and CNS clock's are BS.  How do you track this?  What about repetitive
> dives?
> 
> If you covered this before in the thread I apologize, I must have been
> snoozing...
> 
> Thanks,
> Art.
> 
>         -----Original Message-----
>         From:   kirvine@sa*.ne* [SMTP:kirvine@sa*.ne*]
>         Sent:   Wednesday, December 29, 1999 2:26 PM
>         To:     Shimell, David (shimell)
>         Cc:     QUEST@GU*.CO*; techdiver
>         Subject:        Re: SAMPLE DECO DIVE - 220 FOR 25
> 
>         I ignore the first dive - in this case you have mushed the bubbles
>         anyway. After enough time, I ignore any first dive other than as
> regards
>         the oxygen exposure - that is where the risk lies.
> 
>         Shimell, David (shimell) wrote:
>         >
>         > 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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> 
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