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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.

The reason for switching to nitrogen at shallow depths is not to 
conserve helium but that it provides a decompression advantage.  
In theory tissues approach saturation slower with nitrogen than with 
helium so tissue loading will be reduced, and in practice it has been 
found that air deco after heliox is safer than heliox deco.

regards

David Doolette
ddoolett@me*.ad*.ed*.au*

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