Re: [PSUBS-MAILIST] oxygen use

[Phil Nuytten <pnuytten@compuserve.com>]

All:
        Quick weigh-in on O2 use - as Vance sort of pointed out, it doesn't
matter what the actual metabolic uptake of O2 is - it's the rate that the
certifying agencies (ABS/Lloyds/DNV/etc,) accept as 'standard' as far as
classed subs are concerned. From tests, .25 lpm is a tad skinny for the top
users (overweight/poor shape/birdlike metabolism/scared ****less, etc.) but
.5 lpm is more than ample. Most sunbbers don't worry about carrying 72
hours of O2 cuz it's easy to do and, unlike air SCUBA, the molecules aren't
going any where - that is, too much O2 will be reflected in a rise in cabin
pressure. That's the way it was done for many decades - set the flow rate
at an approximate number - if the cabin pressure goes up (as measured on a
barometer or sky-divers altitude meter) cut the flow down - if the pressure
starts down, crank it up a hair. You qiuckly find the setting that's right
for you and only requires occasional adjustment.Make sure you also have a
small constant-flow orifice system that will sustain life if you baff out
for some reasonl 
        Manual O2 is a pain in the ass, tho. That's why we (Nuytco) favor
the 'bellows-add' system I described in a conference paper (that 's on file
in Psubs archives design stuff).
Strongly suggest splitting the absorbent into 'dive' and 'emergency' with
separate cannisters. The dive cannister is something over your average
bottom time - say 6-8 hours- or whatever is average for you. The emergency
cannister is the balance, hermetically sealed. It can be a complete
in-the-line scrubber or a container used to refill your dive scrubber, Be
SURE to include means for passive breathing (oral/nasal mask,hose) off your
scrubber when the power is gone. We use emergency Lithium ion battery packs
that can run the scrubber for full duration - these are small packs, but we
still carry passive gear.
Phil




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