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RE: Deputies try to raise doomed sub
Jon's information is essentially correct, but somewhat abbreviated. The
danger presented from an ascent of as little as four feet presumes that
before the ascent, the victim inhaled from an air source underwater
(ambient pressure sub, (or suddenly ambient pressure sub), scuba tank
regulator or bubble of air trapped in an underwater enclosure, etc.). If
you inhale at the surface, dive to depth and return to the surface, you
will not overpressure your lungs. If you dive to depth, inhale from some
air source and then ascend, you may injure your lungs and create an air
embolism, if you do not exhale the pressure buildup caused by expanding air
as you ascend. Usually breathing normally is sufficient, but in emergency
or panic situations, an overlearned exhalation habit can spell the
difference between successful self rescue and an uncontrolled embolizing
ascent.
I have been a diver since 1966 and a NAUI instructor since 1972. If your
diving class didn't include enough practice in all phases of "safe ascent",
"controlled ascent" and even "free ascent" to develop the overlearned
exhalation response, you should "practice, practice, practice" safely on
your own while snorkeling, or with a reliable buddy or an instructor while
on scuba. In the pool sessions of my courses, students practice a
simulated 90' free ascent by breathing on regulator, removing regualtor,
then swimming diagonally across the 75' lanes without changing depth. In
open water, on mask, fins and snorkel, they free dive to 15 to 20 feet,
simulate an out of air situation and exhale all the way up. When the
spaghetti hits the fan, it is unlikely there will be time to mentally
rehearse self-rescue ascent procedures. Overlearning, from lots of
practice, until you exhale normally every time without thinking about it is
the best insurance policy.
Like minded instructors and I have been criticized for being too demanding
or "wasting time" on critical overlearning tasks. I believe that there is
no safe alternative.
-----Original Message-----
From: David Buchner [SMTP:Buchner@wcta.net]
Sent: Monday, March 08, 1999 3:55 PM
To: personal_submersibles@psubs.org
Subject: Re: Deputies try to raise doomed sub
I've been occupied, and I don't know if I'll ever catch up on the sudden
burst of messages, but this one caught my eye:
Jon Shawl wrote:
>ADDED NOTE. From what I understand, it was not the bends one would get
>>from staying under pressure too long, but it was a possible air embolism
>that he was treated for. This can happen when you hold your breath on
>accent, as little as a 4' rise while holding your breath can damage your
>lungs and force air into your blood stream and cause something like a
>stroke. You learn about this in a dive course. Please take a dive course
>before building a sub....
Or swimming very much either, apparently.
4 feet, really? Spooky. Why isn't this more generally known?
---------
David
buchner@wcta.net
http://customer.wcta.net/buchner
Osage MN USA