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Re: [[PSUBS-MAILIST] Undersea Habitats]
I remember a no decompression profile with 25
divers, dives from a underwater habitat at saturation at 42 feet to 130 ft,
bottom time 33 minutes, as you can see it is beyond the navy tables, though no
symptomes occurred during any of these dives.
However there is abundant evidence that when the
excess of atmospheric pressure does not exceed about one and a quarter
atmospheres (10.1 m) there is complete immunity from symptomes due to bubbles,
however long the exposure to the compressed air may have been, and however rapid
the decompression.
Thus bubbles of nitrogen are not liberated within
the body unless the supersaturation corresponds to more than a decompression
from a total pressure of two and a quarter atmospheres to a total pressure of
one atmosphere.
(Davis 1962)
Besides other theories I would add that myself like 500 minimum other divers
experienced (French Navy) several days at 30 Ft at saturation under strict
monitoring without a single decompression sickness reported.
500 Navy divers that s a lot of divers who are no
goats, they may be healthier than the average population, but 0 incidents it is
more than a confirmation. it is a fact.
This is physics, like water boils at 100 deg C,
nitrogen bubbles just do not appear at such low partial pressure, but is
expelled in the lungs not in the blood.
The test you mentionned with goats by Dr Hadlane to
my knowledge was performed at 62 feet somewhere in 1960.
I would be very interested to see your litterature
about decompression sickness incidents which occured in less than 33 Ft.
However I find always interesting litterature that
contredicts facts and experience.
Take a chance and spend 1 week in the
underwater habitat of the Scott carpenter center in Florida Key Largo, it is
like a hotel room by 22 feet .
nothing to worry about the bends
though.
Herve John
----- Original Message -----
Sent: Friday, April 06, 2001 9:36
PM
Subject: Re: [[PSUBS-MAILIST] Undersea
Habitats]
John,
I have
written a number of programs that calculate decompression problems and
I
would not make the statement about 30 feet.
I believe that dates from
the turn of the century when a 50% reduction in
ambient pressure was
considered "Bend Proof" (pressure at 33 feet is two
atmospheres while the
surface it is 1 atmosphere). This was based largely on
tests made with
goats (Dr. Haldane). Unfortunately ( or perhaps fortunately)
humans are
not goats or perhaps not far removed from goats. (I'm not too sure
about
some of the people I've met.)
The math models usually assume various
tissue time constants which is a gross
oversimplification of the human
body. There does not appear to be a tissue
that corresponds to a fast
tissue such as the lungs as Haldane assumed. The
best that can be said is
that the models seem to fit what happens.
I found that a lot of
"common knowledge" was/is based on opinion and not
facts such as you
become more susceptible as you age. Or that the Navy dive
tables are based
on a 5% incident rate.
Exhaustive studies have not been done except
empirically by tech divers. Some
pearl/sponge divers blow the hell out of
the Navy dive tables and live to
tell about it. The Navy dive tables also
have errors in the Tables with very
little testing performed for the
various dive profiles, especially the 100
foot for 25 minutes.
I
do not claim absolute numbers as 30 feet as absolute criteria nor do I
think absolute numbers exist. The best I've seen is based on statistical
predictions for decompression sickness which suggest that any dive carries
a
risk of decompression sickness. It has been rumored that one of the test
subjects Dr. Spencer used in his testing program for silent bubbles (1976)
would experience the symptoms of decompression sickness when he took a
commercial air flight.
Anyway, for what it's worth, the reason I
have looked into the problem is
that I have been a witness and more to
several Decompression sickness
incidents. I have also written about these
incidents which I can send you,
but I don't think they are pertinent to
this website.
That's what neat about 1 ATM subs.
Have fun,
Ken Martindale
PS I've never been Bent, luck?