On Fri, 14 Jul 2000 David Strike <[log in to unmask]> wrote:

>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