Sorry Alec, somehow this post escaped my attention. I think that
for the time it takes, a quick analysis of your bottled oxygen is
worth doing, if you are purchasing industrial or welding grade gas
for which the purity level is not guaranteed by the supplier. 99%+
within the error of your analyzer does not take long to produce a
stable reading, and provides some peace of mind against major
screw-ups. This is life-support, after all. I got in the habit of
checking bottles when I inadvertently purchased some "industrial"
helium which was actually balloon gas which had been cut with oxygen
to prevent kids from asphyxiating themselves, which of course threw
my mix off. It was an error by the gas supplier - the balloon stuff
is supposed to be in pink bottles or something, and I was able to
call them up and exchange that cylinder for helium. Probably less
likely with oxygen, as I'm sure the handlers know enough to respect
the dangers of HP O2, but the point is that errors occur. As for
checking air, I don't think the white handkerchief method is
particularly enlightening - certainly, if your cylinder was filled
with lubricated shop air or otherwise heavily contaminated with oils
that coalesce into droplets, it might show something, but textiles
are simply filters with large and poorly controlled pore sizes.
Small-chain hydrocarbon vapours are unlikely to show up on a rag.
-Sean
On 2012-05-07 06:44, Smyth, Alec wrote:
Interesting
in-depth information, Sean. I just use welding oxygen, but
now I’m asking myself whether I should have a new checklist
item, testing the O2 bottle to make sure what is in there is
in fact oxygen. Would this just be a matter of sampling it
through my O2 meter? If I get a reading of 99.9% or 100% O2
concentration, then go ahead and put the bottle on the sub.
If I got something lower, I might not know what it was, but
I would know to skip that cylinder.
Back
when I learned to dive in 1980 Argentina we didn’t have any
gas monitors of any sort, but we did a quick test on every
SCUBA cylinder. You’d hold a handkerchief or some such white
thing in front of the tank valve and give it a quick squirt
of air. The theory was that if the tank was contaminated
with oil, you’d get a stain. I never got a contaminated
tank, so I’m not sure how good the method was.
Best,
Alec
Scott, I have been dealing with issues like
this with gas suppliers for years. The purity issue is
nonsense. The medical grade oxygen is filled from the same
bulk cryo storage as the industrial stuff. The difference is
that medical grade is periodically sampled and analyzed for
compliance with USP specs, which adds a cost overhead, and on
the medical grade, the filling procedure is slightly different
- vacuum is pulled, O2 is flushed at low pressure, vacuum is
pulled again and then the cylinder is filled. Industrial
cylinders either have one or no vacuum steps before filling.
The idea is to avoid any kind of hydrocarbon contamination,
but such risk is small. I have been using industrial helium
and oxygen (run through my own physical and chemical filters)
for years without issue. If you can do so, it will probably
be cheaper. If not, just explain your situation to your GP
and you can probably get a prescription. Another option to
look for is so-called aviator's oxygen, which is certified to
have minimal moisture content (prevents freeze-up issues), but
may not track other impurities and so may be cheaper than
medical. For submarine breathing media, industrial grade gas
is fine provided you confirm the analysis (make sure it's
actually O2 in the tank at 99.5+ %). The breathable
atmosphere in your sub is exposed to external contaminants
anyway from your body, clothing, equipment and any dirt you
may have tracked in. Since you are conditioning the air
anyway (via CO2 scrubbing), for peace of mind you could
include other media stages in your filter for scrubbing
hydrocarbons, CO, etc.
-Sean
On 2012-05-06 07:53, swaters@waters-ks.com
wrote:
I
was at my local welding and gas supply the other day and
they were asking me how my sub was doing and we got on the
conversation about the life support system and how it
works. They told me they could not sell me medical grade
oxygen with out a prescription from a doctor which I
thought was kind of weird. They said I might be able to
use oxygen that you use for welding, but it is not as
pure. Does anyone on psubs have any ideas on what to do?
Also
I had asked a question a while back about the tubing in
the K-350. I have decided to go with stainless steal, but
was still wondering what wall thickness to go with and how
do you connect them (flair fitting, compression fitting,
or something else?)
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