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At 11:33 PM 4/9/98 -0400, you wrote:
>True/False.
>
>OK first, "or" makes this two statements, making the entire question
>false if either individual statement is false. What we
>get is:
No, that's AND.
OR Truth Table
A B Result
------------------
F F F
T F T
F T T
T T T
Where did you get your Computer science training? :P
>
>[1] "Oxygen can be employed to increase safety regarding DCS"
>
>Clearly, this is true.
>
>[2] "it can be used to shorten decompression time by permitting the diver to
>conduct the 10fsw stop at 20fsw."
>
>The statement "it can be used to shorten decompression time"
>is also obviously true, which is what I think you were
>getting at with your deco examples. Again, nobody is
>going to argue with that part - obviously O2 can be
>used for accellerated decompression.
>
>The problem comes with the next part; "by permitting the diver to
>conduct the 10fsw stop at 20fsw" which describes HOW it is
>that it can be used to shorten deco.
>
>IANTD uses Bulhmann tables in the manuals, and promotes
>Buhlmann-based deco software packages.
>I assume TDI does as well.
>
>The simple fact is that if you are using Buhlmann,
>and you are breathing pure O2, conducting the 10fsw stop
>at 20fsw will not make one second of difference in
>your hang time.
>
>And that makes the second part false, which makes
>the entire statement false - which makes the answer "FALSE".
>
>If somebody doesn't believe this, I suggest they
>*try* it. Run a profile with 100% 02 for deco
>starting at 20ft, using Voyager, Decom, ZPlan,
>or whatever, which are all Buhlmann ZHL16-based
>software packages. Most of these can combine
>your 10 and 20ft stops into one long stop.
>
>Run it both ways - you'll see there's virtually no
>deco difference.
>
>And to address the minless wanderings of this thread,
>let me once again repeat:
>
>This has nothing to do with whether or not Buhlmann
>ZHL16 is correct in this regard. It is the model
>used to instruct students, and the model used
>by 99% of recreational "technical" divers, and is
>therefore the basis with which we must answer this
>exam question.
>
>And to further repeat: while there is some evidence
>that higher PO2 by itself can be useful
>in shortening deco times, there aren't any models
>that explain why or exactly how.
>
>Even the stuff about "oxygen window", (a very misused
>term) does not explain it. Oxygen Window refers
>to a theory called "zero supersaturation ascent", which
>is basically a play on total tissue saturation
>that relies on the fact that due to metabolic
>consumption, you always have an O2 pressure
>deficit in the deeper tissues, which is
>normally 8-13% below ambient. Your body
>relies on this pressure differential to move the O2 from
>blood to tissues.
>
>You can pack this extra "room" below saturation with
>excess N2 or He. But it's not that simple,
>as the saturation deficit increases linearly
>with depth, and if you *use* that extra room,
>you've got to vent off the N2 overload
>in a conventional way before ascending, which
>ultimately gets back to tissue half-times
>and off-gassing gradients (recently modified
>by the bubble theorists).
>
>Anyway, the upshot is that "zero supersaturation"
>and "oxygen windos" were popular themes with
>commercial dive theorists in the seventies, but
>it does not by itself get around the problem
>that an off-gassing gradient can't go higher
>than 100%, which is the core of the theoretical snag
>when it comes to explaining how pure o2 is more
>effective at depth, when it should be depth-independant,
>since once you get on pure O2, your off-gassing gradient
>is maxed, no matter how deep you are.
>
>So the mystery is unexplained.
>
>-Will
>
>
>
>> -----Original Message-----
>> From: RMC <brownies@ne*.ne*>
>> To: Tom Mount <TOM.MOUNT@wo*.at*.ne*>
>> Cc: William M. Smithers <will@tr*.co*>; Jesse Armantrout
>> <armantrout@wo*.at*.ne*>; Tech Diver <techdiver@aquanaut.com>;
>> cavers@ww*.ge*.co* <cavers@ww*.ge*.co*>
>> Date: Thursday, April 09, 1998 11:18 AM
>> Subject: Re: Lovely
>>
>>
>> >Tom,
>> >
>> >You could just do it our way and run a fixed gas (30/30) for the 100/100
>> >bottom time and hit O2 for 15 minutes at 20 feet with a ascent time in
>> >excess of 8 minutes to get to 20 feet from the bottom. As you know this
>> >is one of our favorite weekly Fort Lauderdale dives during the summer
>> >and we routinely utilize the triple reef lines to make our deco more
>> >enjoyable. The most effective runs to date have been scootering accross
>> >the 60-80 reef for 10 minutes on the way to the shallower reefs where we
>> >grab our last few lobster's in 30 feet and get out. We have even done
>> >this on bottom mix with slightly longer shallow times.
>> >
>> >You should join us this summer and see how simple our "tek" dives have
>> >become. I have three spare Gavins charged at all times in addition to my
>> >old Gavin. I really think this is the most fun you can have in single
>> >Saturday dive.
>> >
>> >Have a good weekend,
>> >
>> >RMC
>> >
>> >Tom Mount wrote:
>> >>
>> >
>> >> 5 run a constant po2 of 1.2 and deco on 1.4 the runtime is 134 minutes
>> >> Tom
>> >
>> >
>> >> -----Original Message-----
>> >> From: William M. Smithers <will@tr*.co*>
>> >> To: Jesse Armantrout <armantrout@wo*.at*.ne*>
>> >> Cc: Tech Diver <techdiver@aquanaut.com>; cavers@ww*.ge*.co*
>> >> <cavers@ww*.ge*.co*>
>> >> Date: Wednesday, April 08, 1998 11:30 PM
>> >> Subject: Re: Lovely
>> >>
>> >> >
>> >> >On Tue, 7 Apr 1998, Jesse Armantrout wrote:
>> >> >> >From the 1996-1997 TDI Exams Book - Decompression Procedures Exam -
>> page
>> >> >> 1 - question 7:
>> >> >>
>> >> >> 7. Oxygen can be employed to increase safety regarding DCS or it
>> can
>> >> >> be used to shorten decompression time by permitting the diver to
>> conduct
>> >> >> the 10fsw stop at 20fsw.
>> >> >> True/False.
>> >> >>
>> >> >> TDI Answer: False
>> >> >>
>> >> >> The track record speaks for itself.
>> >> >
>> >> >I didn't do my tech training with TDI, so I can't
>> >> >speak for their record or training first hand,
>> >> >but actually, the answer to the above question
>> >> >is "False" according to most deco models, including
>> >> >Bulhmann, which is the predominant deco model
>> >> >used for decompression today (WKPP secret funky homebrew aside).
>> >> >
>> >> >According to the Buhlmann model, there is
>> >> >absolutely no deco difference between
>> >> >breathing O2 at 20, 10, or 60ft - depth won't
>> >> >shorten your hang time.
>> >> >
>> >> >Why? Well, under Buhlmann, the only thing
>> >> >that makes a difference in your deco time
>> >> >is the partial pressure of N2 and/or He in your
>> >> >deco mix, as this affects the relative
>> >> >gradient between the gas dissolved in your tissues
>> >> >and the partial pressure of the gas it is
>> >> >working against (what you are breathing). And *that*
>> >> >affects your off-gassing rate.
>> >> >
>> >> >Your PN2 will vary with depth, so as long as you are
>> >> >breathing a mix that contains *any* N2 or He, depth
>> >> >matters, but as soon as you go onto 100% O2, there is no
>> >> >diluent in the mix, so depth makes absolutely no
>> >> >difference - you are at your maximum off-gassing gradient, and
>> >> >because there's no He or N2 in the mix, the
>> >> >partial pressure of these gasses can't increase.
>> >> >
>> >> >-Will
>> >> >
>> >> >
>> >> >
>> >
>> >--
>> >Robert M. Carmichael
>> >
>> >http://www.browniedive.com SSA, Mixed Gas & Tank Fill Compressors
>> >http://www.halcyon.net Rebreathers, Harness Backplate & Wings
>> >http://www.selfrescue.com Responsible Diver Self Rescue P.S.A.
>> >
>> >"Simplify diving and restore the ADVENTURE.................Do it Right"
>>
>>
>
>
--------------------------------------------------
Kevin Connell <kevin@nw*.co*>
Northwest Labor Systems
http://www.nwls.com
Bellingham, WA
--------------------------------------------------
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