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During the management of exposures to high PO2's, we are all taught about
the need for air breaks (ie, 25 minutes on oxygen at depth, interspaced
with 5 minute intervals on air).

However, I have noticed that the major emphasis/focus is on the use
of airbreaks during the shallow decom stops (where 100% oxgyen is most
often used).  Since we are concerned about exposures to elevated PO2's,
it seems to me that we should be considering the use of "airbreaks"
during the deep decom stops (ie, take an "air break" prior to starting
onto nitrox during decompression).  

As to what to use for these "air breaks", it is essential that the 
inspired PO2 be less than 0.5 ATA, and the closer to 0.21ATA, the better.

So, what should we be using for these "air breaks" when at deeper stops??
Obviously, air is not going to give us a PO2 of less than 0.5ATA at depths of
greater than around 45.6fsw, so we have to consider another breathing mix
for this use.

The most obvious gas to use would be the trimix used, as long as it supplied
an oxygen PO2 of less than 0.5ATA.  However, we must consider the inert gas
uptake during these deeper "air breaks).  Ideally, a 90%N2/10%O2 mix would
be useable at stops down to 132 fsw.  

Any comments?????

John    

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