I told Michael that - when I got a few minutes - I'd transcribe the notes
that Olivier Isler handed out at OZTEk and his views on rebreathers.  What
follows are Olivier's thoughts - not mine.


"In the last few years, rebreathers have been generating an ever increasing
interest in the diving public.
Users' motivations are very varied:   For most, fun is the main motivator,
hence the success of the Dolphin or the Ray from Draeger.  Dives are limited
in duration and depth and usually don't require decompression stops.
Others, such as the wreck divers, cave divers and scientific divers, are
mostly interested in the autonomy provided by the units.  Those long and
deep dives require stops several hours long and safety in autonomy must be
looked at in a very different way.
No (scuba or other) system can be considered 100% safe.  One must therefore
be able to react to any failure.  In normal OC diving, a certain and
variable amount of redundant systems is the norm: tanks, regulator ... and
buddies.
What about rebreathers.
First, sharing a rebreather mouthpiece is much more difficult than on OC and
must be attempt only as a last resort.  That leaves only two possibilities:
redundant circuits, closed or open.  A redundant open circuit is the
solution of choice for most rebreathers on the market today.  There is even
a complicated and bulky mouthpiece system available which allows switching
from CC to OC without removing it.  Is OC bailout a good solution?
First let's compare the respective performances of CC vs OC. For the same
tank capacity there is a minimum ratio of 10 : 1 in favour of the least
efficient rebreathers.  In order to provide an equivalent OC redundancy, a
great number of tanks exclusively dedicated to safety must be used.  This
means that they must be carried along or staged.  What a waste of energy and
resources!
Further, from a "philosophical" point of view, isn't the reliance on OC for
safety a confession of weakness, the glaring proof that if rebreathers are
very efficient systems (which we have known for the last 50 years!), they
suffer from a chronic safety deficit?  To use a comparison which is not that
farfetched, what would airlines think of a plane with a single jet engine
needing to tow 2 or 3 zeppelins for safety?
The fact is, CC redundancy is possible, even though to my knowledge only two
systems can offer it:  the CIS-LUNAR in the USA and my own R.I. 2000 in
Europe, which is still a prototype.
If we take a hard look at the potential problems of deep wreck dives, double
closed CC circuits are not a luxury.
As for cave dives, my experience has convinced me that three independent
circuits are an absolute minimum to undertake such dives with a minimum of
serenity.
But what about the bulk of redundant CC systems?
With the limited means at my disposal, I was able to design, build and use a
redundant unit perfectly suitable for extreme diving, and i am convinced
that a professional approach could lead to further miniaturization of a CC
unit specifically designed for emergency use.
In conclusion: either in a future that I hope is near, rebreathers will
reach their maturity and offer for the safety of their users a minimum
redundancy of 2 units, or divers wishing to make full use of their
rebreather will need to practice some form of hybrid diving which will only
tarnish the reputation of CC system."

Strike