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  In this time of tragedy to a well-known diver who (from what I read so far)
seems to have worn three or more aqualung-type systems at once (heliox (for
deep), air or nitrox (for shallower), oxygen (for decompressing)) and chose
the wrong mouthpiece at depth: I apologize for yet again bringing out my usual
subject, but if he had used a large AMRB (= automatic mixture rebreather)
instead (with helium as diluent), could this tragedy have been avoided?
  (1) As the AMRB is closed circuit, much less diluent is used than with an
aqualung, and there would be no need to carry nitrogen also merely to avoid
using up expensive helium in shallower water.
  (2) If it could be switched to pure oxygen rebreather mode when near the
surface, for decompression, that would avoid the separate oxygen mouthpiece
and another risk of confusion, and also having to carry a big oxygen cylinder
as is needed to open-circuit breathe pure oxygen.
  Resulting in a lighter and simpler set-up for the same duration and depth
capability. To avoid this keep on happening, <<<PLEASE>>> can the AMRB
makers
bring a model out <SOON>, even if they have to leave out the BIDM (= built-in
decompression meter) to simplify development and manufacture. It seems to be
developing the BIDM that has so badly delayed matters. I can understand that
some developers treat developing a whole diving system including a BIDM, as a
challenge to prove their abilities; but it has delayed development so far and
expensively that I feel that they should try another route. As I wrote before:
merely keeping the ppO2 right seems to me to be an easy electronic design job,
and there are other advantages in the decomp meter being separate.
  And, a diver with a large AMRB all in a backpack box seems to be far more
agile and mobile, and able to go into small corners with much less risk of
getting fouled by trailing kit, than a diver trailing several large aqualung
cylinders from his waist as well as those on his back, all adding to the bulk
and mass and hydrodynamic drag.
  If AMRB's are too expensive due to being too complicated, many divers won't
buy them but will stick to the old system and its disadvantages and hazards.

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