"Gary" wrote in message
news:EKwLf.66510$H%4.31397@pd7tw2no...
Dave wrote:
On Fri, 24 Feb 2006 01:39:46 GMT, Gary
said:


My experience is different. When free diving you can't
equalize because you don't have an air feed at ambient
pressure. (Your last breath was at the surface) Unless I am
not understanding the term "free diving" which I believe means
diving without tanks. I that case the air inside your body
gets compressed as you descend and you can't equalize by taking
in more air.


You are misunderstanding. An ear squeeze is caused, not by the
difference in
pressure between surface pressure and inner ear pressure, but
by low
pressure in the inner ear (which may or may not equal what the
pressure was
at the surface) compared to the pressure being exerted by the
water pressing
on ear drum from the outside. Since your Eustachian tubes where
they join
the throat are flat like the opening of a balloon, the
increased air
pressure in your throat doesn't get passed through to the inner
ear,
creating a relative vacuum, so the ear drum gets "sucked in".
Equalizing
consists, not of adding air from the surface, but of opening
the path from
your inner ear to your throat (where the air is, as you say,
compressed), so
the higher pressure air there can get into the inner ear and
eliminate the
relative vacuum.
I understand clearly. What I am saying is that you can't
equalize your internal air pressure without breathing air a
ambient pressure except at very shallow depths. You need to
take in air at the ambient pressure to equalize properly.

You've forgotten that your whole body is compressed at depth, such
that lung pressure is the same as the ambient pressure (give or
take an inch). Thus you can always equalise from lung/throat/
eustachian air. Otherwise all free divers going below 10 metres of
so would be deaf!

JimB