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While discussing the use of nitrox mixes EAN32,EAN36,EAN50 recently a friend
of mine made the joke that he was surprised that a mutual friend who had
been diving to approx. 235fsw wasn't using a 90/10 mix ( DAN10 - Depleted 
Air Nitrox ;-) ).

Continuing this line of thought leads me to the following suggestion which
( having seen what happened to other threads ) I am sure the list will rip
apart at it's leisure.

Add additional nitrogen to a standard scuba cylinder to produce a mix
with a ppO2 of .16 ( On the surface this is equivalent to being ventilated
with expired air from a someone attempting to resusctitate, i.e. you can
survive on it but its ideal.)

At 10fsw you now have a ppO2 of .21 ( shallowest stop depth )
At 300fsw you have a mix with pp02 of 1.6 ( maximum recommended ?)

Also at 300fsw you have an equivalent air depth of 315fsw.

So on the face of it for a ( .84/.79 = 1.06 ) 6 per cent increase in
ppN2 you get a ( .16/.21 = .76 ) 24 per cent decrease in ppO2.

There are some obvious issues raised by this propostion. Obviously deco
times will be extended by higher ppN2. Surely the use of 50/50 as a deco
mix could mitigate this. There has been mention on techdiver about 
micro-somethingorother damage caused by high ppN2 and so I guess that
this could be exacerbated. Other issues I am sure you will raise 
youselves.

The crux of the issue that I am interested in is what is the biggest
problem with deep air ( 200 - 300 fsw). Is it narcosis ( which although
the tolerance idea seems to be out of the window seems to be something
which can be 'coped' with given that the dive is planned to avoid 
complication, both with task and equipment ), or is it oxygen toxicity
which has the disturbing element of poor predictability ?

Cheers,

Andy.

Andrew.Hall@ma*.ac*.uk*

There are old divers, and bold divers, but there are no old,bold divers !
( Or at least they're a very rare breed ! ) 
 

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