From: ps3p+@andrew.cmu.edu (Peter A. Simon)
Newsgroups: rec.scuba
Subject: Re: Terminology (and other things)
Date: 22 Nov 92 22:41:28 GMT
Organization: Carnegie Mellon, Pittsburgh, PA

Excerpts from netnews.rec.scuba: 20-Nov-92 Terminology (and other
things) by Erik van der Goot@jet.uk 
> With respect to Lee Vogt's posting I would like to say that:
> a: 
> carrying out dives with planned decompression stops has got nothing to
do with
>  
> professional diving or recreational diving. As a matter of fact, most
> professional divers would never do planned 'in water' decompression stops.
> they get hauled out of the water and plonked into a surface decompression
> facility. 

WRONG:  The US Navy Surface Decompression Tables using air and the US
Navy Surface Decompression Tables using oxygen both require in water
decompression stops depending on time/depth.  Sometimes a dive profile
is planned (as when working on a complex project at depth, the maximum
limits are used) but usually they are not.  The person running a dive is
paying very careful attention to the surface decompression tables to
make sure they are not exceeded, and by the time a diver leaves the
bottom this person knows exactly where the first stop is and for how
long.  Commercial divers get to know very generally what their stops
should be and, in my experience ALWAYS check the work of the person who
worked it out for them.  Unfortunately, this happens after the
decompression in over and accidents have happened!

Furthermore, in spite of what you may have heard, commercial divers
frequently use scuba, and, believe me, we are VERY careful to plan our
dives. Other than exceeding certain limits that recreational divers may
or may not have been taught and/or pay attention to, we are as careful
as any novice to watch our time and depth so as to be within the
PRE-PLANNED decompression stops.

If there is great uncertainty we may write two or three sets of stops on
our slates BEFORE THE DIVE and select the appropriate one when we leave
the bottom but we certainly don't carry the U.S. Navy tables with us. 
Exceptions to this are when decompression meters are used (but the diver
still has an excellent idea of what he is going to do where, including
his stops) and some French divers who I have seen using some very
simplified tables which they take along with them.
 
> b:
> Without looking at any tables here, I will not be far off by stating that the
> maximum time you could stay at 40m (130ft) without having to do a
> decompression stop is probably about 12-15 minutes. And this is when you 

It is 10 minutes so you are off by 20%-50%--enough to get you badly
bent.  Another thing about commercial divers (the ones who are alive,
anyway) is that they NEVER memorize the tables, nor make off-the-cuff
statmenets about them.

> 'professional diver'. Another reason for doing a staged decompression
dive >is
> that it actually gives you the opportunity to stay well within the tables,
> rather than dive them to the limits and fool yourself in thinking you are
> safe 'because I am not doing a decompression dive'!!

This is a good point.  It would be interesting to see the statistics on
bends with no-decompression dives vs.  bends gotten as a result of 
decompression dives.

Peter 
NAUI Inst. #1434