At 10:06 PM 1/4/00 -0500, Rich Lesperance wrote:
>>>I think that what everyone is looking for here is more
>quantitative/mechanical information on how to calculate profiles the way the
>WKPP/GUE guys do.  <<
>>
Sure, I understand and that is what we are trying to do with a combination
program and discussion list. The process of decompression is, in my
opinion, not half as precise as people are led to believe. For better or
worse, what we are doing in our diving is outside any conventional
mathematical guidelines, making the precision guide you ask for more
difficult. You should also bear in mind that the profile many of us follow
would clearly elevate your statistical DCS likelihood. It is common for us
to surface well above the m-values (ie over 100% of the m-value) for
several leading compartments. Studies indicate that the 85% range provides
much better DCS protection. Personally I do believe that the shape of the
deco is crucial to an effective deco and that is the area that we are
striving to refine especially in a way that can be reported and
consistently reproduced. This was the large motivator for developing
software with a consistent safety factor and a deep stop process that gave
everyone a good starting point. We are now testing a host of processes for
implementation into Decoplan based upon their success and the profiles we
generate. For example, modeling with VPM and bubble mechanics along with
max stop depth and gradient factor seem to be closing the gap on a more
efficient profile. However, there is no doubt that there is risk to any
diving and experimenting with deco is true guinea pig processing.

As for the mechanics of the deco, George covered a good bulk of the
philosophy. For my part here is a quantitative method relative to our
discussion. I use Decoplan to calculate the deepest possible stop. This is
often very similar to the rule that we used for some time ie 80% of max in
atmospheres. The ad hoc rule can be used with good success and is nearly
uncanny in its frequent similarity. Decoplan actually calculates the
ambient and compartment pressure break even point (ie the steady point
where these are essential equal). Deeper than this will produce ongassing
and shallower will produce offgassing. The farther you go beyond this
ambient pressure line the greater the gradient. Going too far will approach
the M-value and increase the risk of bubbling. Bubbles in the deeper phase
of the profile can grow interfering with the rest of the deco. Based on
this assumption, I start at the calculated deepest possible stop and do
approximately 10'/min ascent up to my first real stop. In Decoplan the
first "real" stop is based upon the deep gradient that you set. For
example, if you set a very low gradient factor the first stop will be right
at this deepest possible stop depth but the gradient will be pretty low and
the calculated deco a tad bit longer overall (a matter of a couple
minutes). In this situation if you set the deep factor at 5 and the shallow
at 100 (I do this often but DO NOT RECOMMEND IT) you will see a very
similar profile to the one that George released. If one were set on
reproducing this profile then it would easiest to run high gradient factors
deep and shallow and add the 10'/min ascent from the calculated max
possible stop. We are reviewing the safety of algorithms that would allow a
convenient calculation of this particular system. For most people the few
minutes are not very relevant and before you jump into heavy
experimentation be sure that you understand what you are doing and that you
are willing to take the risk.

Safe diving everyone,
JJ





--
Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'.
Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.

Navigate by Author: [Previous] [Next] [Author Search Index]
Navigate by Subject: [Previous] [Next] [Subject Search Index]

[Send Reply] [Send Message with New Topic]

[Search Selection] [Mailing List Home] [Home]