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Ed Graves wrote:
>
> I'd never consider arguing with the C.A.R.L., but I do
> have a question.
 
Good move :^)
 
> I am seriously considering enriched air this Winter.
> I was in a scholarly discussion at the local dive shop
> yesterday and the conversation came around to enriched
> air.
> A couple of weekends ago I was diving with someone who
> keeps a 40% mix in his pony bottle and switches to it
> on all safety stops.  Sounds like a hell of a plan to
> me.
> One of the "experts", this weekend, said that if I
> wanted to do that, with that high a mix of O2, I
> should at least have my pony reg O2 cleaned.  It made
> sense, but I freely admit my ignorance.
> Was he right?  Is there a right answer?
> Ed
 
Virtually all the training agencies say that for mixes
of 40% or less you do not have to O2 clean the regs.
 
Did that "expert" per chance either own or work at
the dive shop that would do the work ??? :^)
 
As others have said, with a mix this hot, it's
MOD (maximum operating depth) is 82.5 feet -
80 feet for round numbers.  That is - at 82.5',
you are at a PPO2 of 1.4 ATA.  Now, others have
commented on the PPO2 of this mix at greater depth
(Art reported that at 45m, which is 147' we're at
a PPO2 of 2.2 ATA).  Breathing this mix at this
depth is a bad idea, however, in real life, it's
certainly not worse than drowning.
 
The point is that this is not a gas that one should keep
in reserve to breath at a depth greater than 80'.  Since
O2 Tox is related to PPO2, Time, and a whole host of
other factors one cannot say if one will tox with this
mix at 45m, but *I* certainly won't try it - that is
unless my only other chance is death.  Remember - a long
time ago a PPO2 of 3 ATA was the accepted limit - then
it went down to 2 ATA, now the (almost universally)
accepted limit for the working part of a dive is 1.4 PPO2
(1.6 PPO2 for deco).
 
Carl