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David Shimell (shimell) wrote:
> Drew
>
> Conventional wisdom is to use the richer gas last.
>
> Running the profile of a 30 m dive for 30 minutes, followed by a 60
> minute SI, followed by another 30 m dive for 30 minutes gives an
> in-water
> time of 100 minutes for 32 % followed by 21%. However, doing the
> air
> dive followed by the 32% gives an in-water time of 92 minutes.
>
> The richer gas allows better off gassing of the residual Nitrogen
> loading
> from the first dive even though there is initially a greater tissue
> loading. "Quality of deco is what counts, not quantity" - to quote
> George.
>
> (In the above, the gasses may not be ideal, just used by example.)
Dave,
I am no fundi, but I have used Buhlmann tables, decompression calculated
on Eq Air Depth, a CNS% loading/min of 1.3 for the 32% mix, a CNS%
loading/min of .25 for 21%, etc.
The results I got are as follows:
Air 1st;then Nitrox Nitrox
1st;then Air
Dive Number 1
Bottom time 25min 25min
Deco time 5min@3m** 1min@3m
Total dive time 33min 29min
%CNS at end of dive 8% 15%
Dive Number 2
Bottom time 25min 20min
Deco time 4min@3m* 2min@6m*
;7min@3m*
Total dive time 32min 32min
%CNS at end of dive 21% 19%
There we go, advantages and disadvantages - not really much of a
difference, but not as obvious at first glance. I would reckon one
should prioritize your preferences, but schucks, you have to have at
least 3500l per dive to dive within safety limits.
Any comments?
Regards,
Michael
(CMAS Diver)
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David Shimell (shimell) wrote:
<BLOCKQUOTE TYPE=CITE>Drew
<BR>
<BR>Conventional wisdom is to use the richer gas last.
<BR>
<BR>Running the profile of a 30 m dive for 30 minutes, followed by a 60
<BR>minute SI, followed by another 30 m dive for 30 minutes gives an in-water
<BR>time of 100 minutes for 32 % followed by 21%. However, doing the
air
<BR>dive followed by the 32% gives an in-water time of 92 minutes.
<BR>
<BR>The richer gas allows better off gassing of the residual Nitrogen loading
<BR>from the first dive even though there is initially a greater tissue
<BR>loading. "Quality of deco is what counts, not quantity" - to quote
<BR>George.
<BR>
<BR>(In the above, the gasses may not be ideal, just used by example.)
<BR>
</BLOCKQUOTE>
Dave,
<BR>
<BR>I am no fundi, but I have used Buhlmann tables, decompression calculated
on Eq Air Depth, a CNS% loading/min of 1.3 for the 32% mix, a CNS%
loading/min of .25 for 21%, etc.
<BR>
<BR>The results I got are as follows:
<BR>
<BR>
<BR> &
nbsp; &nb
sp;
<U>Air 1st;then Nitrox Nitrox 1st;then Air</U>
<BR><B><U>Dive Number 1</U></B>
<BR><U>Bottom
time &nbs
p;
<FONT
COLOR="#0000FF">25min</FONT> &
nbsp; &nb
sp;
<FONT COLOR="#FF6633">25min</FONT></U>
<BR><U>Deco
time &nbs
p;
5min@3m*
1min@3m*</U>
<BR><U>Total dive
time &nbs
p;
33min &nb
sp;
;
29min</U>
<BR><U>%CNS at end of dive
<FONT
COLOR="#DD0000">8%</FONT> &nbs
p;
&n
<FONT COLOR="#DD0000">15%</FONT></U>
<BR><U></U>
<BR><B><U>Dive Number 2</U></B>
<BR><U>Bottom
time &nbs
p;
<FONT
COLOR="#0000FF">25min</FONT> &
nbsp; &nb
sp;
<FONT COLOR="#FF6633">20min</FONT></U>
<BR><U>Deco
time &nbs
p;
4min@3m*
2min@6m* ;7min@3m*</U>
<BR><U>Total dive
time &nbs
p;
32min &nb
sp;
;
32min</U>
<BR><U>%CNS at end of dive
<FONT
COLOR="#DD0000">21%</FONT> &nb
sp;
; &
<FONT COLOR="#008000">19%</FONT></U>
<BR><U></U>
<BR>There we go, advantages and disadvantages - not really much of a
difference,
but not as obvious at first glance. I would reckon one should prioritize
your preferences, but schucks, you have to have at least 3500l per dive
to dive within safety limits.
<BR>
<BR>Any comments?
<BR>
<BR>Regards,
<BR>Michael
<BR>(CMAS Diver)
</BODY>
</HTML>
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