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Rebreathers for use during the hang (and available on the boat
for emergency use on the surface) is an attractive idea, however,
the expense of the carbon dioxide scubber material is such that
it quickly can exceed the cost of the oxygen.  If you are going to
be using oxygen for an hour or more per dive, it is very possible to
run the bill up to $4.00 or $5.00 per dive just for the absorbant.

One problem is that we do not have any affordable CO2 monitoring systems
that would let us reuse the unit and be assured of not suffering from
CO2 poisoning during the hang.  Thus, we either use pre-pack units
and use a stacked unit system, throw away each unit as it turns color
to indicate exhaustion.  Even so, price per dive could exceed that 
of the oxygen.

However, on small boats, the ability to administer high oxgyen concentrations
to divers suffering from DCS/DCI or AGE (if they are spontaneously breathing)
for several hours on a small cylinder of oxygen is a great idea.

Another consideration is that the oxygen rebreather (if a simple, constant
flow system) could/would allow accumulation of enough inert gas in the
circle to degrade the outgassing gradient that we all desire (ie, the
largest possible gradient is achieved by breathing 100% oxygen during
the 20 and 10ft hang).

Increasing the flow rate of oxygen into the system would minimize
the inert gas consideration, but would increase the amount of oxygen
utilized.  The ideal situation still is to breathe 100% for each breath
and this is easiest accomplished with open circuit scuba.

Just a few thoughts on the subject.

John
Submariner Research, Ltd.
(johncrea@de*.co*)

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