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On Wed, 7 Sep 1994, Richard Pyle wrote:
> On Wed, 7 Sep 1994, Jason Rogers wrote:
snip
> > We are already making our first stop at 39 or 42 metres. Do you mean deeper
> > than that?
> > If you intended deeper than that, then for how long?
> My experience causes me to agree with David here. We've found that the
> most critical aspect of avoiding DCI or "pre-DCI" problems after deep
> dives is SLOWWWW ascent rate, and that includes extra deep stops. If your
> first stop is in the neighborhoo of 40 m, then you're obviously talking
> about some pretty hard-core exposures (90 m? 100 m?). If my tables call
> for the first stop to be 40m, then I usually hang out at 60-70 m for about
> a minute, then 50 m for a minute, then proceed with the schedule. Also,
> my ascent rate between stops is very slow (10m/min or less). The
> problem, of course, is that the tables assume you are going to be
hmmm......
well here is a different perspective.
When making extremely deep dives make a rapid ascent of 60 feet per minute
up to your first deco stop.
Why do this? It gets you out from underneath all that ongassing pressure.
If you think about it, what drives the mechanism and the accompanying dcs?
It's the pressure DIFFERENTIAL. In other words going from 363 feet to 165
feet in one minute is the same as going from 33 feet to the surface in terms
of pressure differential. Making a "rapid" ascent to your first stop is not
inherently dangerous (imho)! If you cut tables that assume you are
ascending at 30 fpm and you ascend 10 fpm then which way are you
"biasing" your dissolved gasses? Well I think you end up with MORE gas
than what the table "thinks" you have so that when you end up doing your
deco it MAY be inadequate.
I would post a little matrix showing what ascent depths involve in terms of
percentage of pressure redution per foot but I know we don't need that.
SO - minimize ongassing (less time at depth i.e. rapid ascent)
maximize gas pressure differentials on deco - high O2 low N2
do your deco as prescribed in the table (or use DECOM and ongass
the extra time you are going to spend at that depth so that you
totally account for all gas activity)
Well that's my .02$ worth!
Ronnie Bell
trying to never get bent!
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