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There is a lot of discussions engaged about the Odyssey rebreather who is
announced as SAFE unit because using a passive addition method. Odyssey
rebreather principle is not something new, it has been using for years and I
do not believe that proportionnal purging principle which create a passive
addition is safer than other system.

What happens if you have a failure on the purging system? 

A complete failure (zero purge=zero gas addition) is probably easily
detectable due to lack of bubbles emission, but what about a partial failure
of the purging system? Let say that instead of purging 25% of every breath
you purge only 10%, then you are in big trouble? It will generate a partial
gas addition and the risk of hypoxia or DCI (%O2 below what is planned for
deco) will be a reality. Despite of what is said, the Odyssey has a single
point failure which makes it not safer than other system.

The only way for a semi-closed rebreather to be safe is to be fail safe. For
me, it means that any incident will result in a impossibilty to breath from
the system. On an open circuit, an incident will result in a free flow, no
gas or increased breathing resistance. 

Also, WWW pages claim that the odyssey can be used for cave diving, i am far
from being convinced. As a french cave diver, I dive with double independent
in solo (do not be Moron, i dive in France not in US) which is the standard
in France, so using a rebreather for cave diving means for me that I need a
total redundancy, probably two independent systems (2 rebreathers! What a
juicy market for a rebreather dealer). With the new semi-closed rebreathers
coming to the market, I do not see any that meet this criteria.

For info the WWW pointer of RBC is: http://www.gate.net/~dlv/odyssey/ 

I hope that my broken english will not obstruct to the understanding of my
view. 
Safe dives

Frederic

PS: I do not claim to be a rebreather specialist, just my "EURO"0.02
contribution ...

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