I know this has all been done before but.. Here goes...

I agree that for hard core tech diving the isolator is the way to go. 

The isolator does however add some issues that the techical diver must
be aware off.  We have all heard about instances where dives have been
aborted etc, by inexperienced tech diver due to the isolator being
closed, only one tank being filled at the shop etc.  The isolator also
adds a common failure point should the actual isolator valve fail.
These "human factor" problems I would suggest have an equivalent risk
to the tank O-ring or burst disk.

A properly maintained burst disk and tank O ring in my mind have very
low failure potential during a dive (when the tank pressure is
dropping).  The most likely failure point is during the filling
process.  This failure mode I agree is not zero however. Not
overfilling your tanks goes a long way to minimizing this risk.  Of
course there is also the WKPP burst disk plug method although I'm not
sure of the legality of this especially here in Canada.

I think that all being said it is prudent to dive with a buddy if you
are not using an isolator.  As a matter of fact it is probably a good
idea even if you have an isolator.

Mat.   
---Mike Rodriguez <mikey@ma*.co*> wrote:
>
> At 09:03 AM 2/23/99 -0800, Sean T. Stevenson wrote:
> 
> >Robert, have you removed a valve knob and seen how large the stem
is? 
> >This is not, IMO, a non-existent problem.  In addition to that,
> >consider the possibility of tank neck o-ring extrusion... not common,
> >but it does happen, as has been attested to by several list members. 
> >The isolator solves both problems.
> 
> I once had a burst disk blow out during a dive.  The disk had
> become corroded from exposure to salt water and was weakened
> to the point where it failed during the dive.  Without an
> isolator, it would have been a very unpleasant dive.
> 
> As tech and cave divers, we go to such extremes with gear
> redundancy, that it doesn't make sense to dive without an
> isolator and run the risk of an extruded o-ring or failed
> burst disk defeating the gear redundancy.
> 
> -Mike
> 
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