This post is sort of an extension of one that I posted a few months ago.
The Australians have written a basic guide to freediving sumps:
http://www.caves.org.au/s_freedive.htm
It does not put a limit to the timespan of the dive, nor the length of the
dive.
I didn't know about the baratrauma issue.
[ I have never dove the short sump at Carrizal, ( near Candela, Coahuila ), but
baratrauma would now be a concern I would have, if I did. ]
I have heard at least one experienced cave-diver post that a dry caver
should never free-dive a sump over 25 feet long.
I think a time limit is more important, like 90 seconds. That way if you get
in 90 seconds and start having problems, you should still be able to
turn around and get back.
So lets say the sumped passage is borehole size and that the diving
line is properly secured in dry passage on each end, but the passage
is 26 feet long. Do you resort to hauling a scuba tank?
I think I have asked this question before:
What could a caver do to safely negotiate a free-dive that is questionable
without hauling a scuba tank thru the sump? Meaning some kind of air hose?
For example:
http://snubagirl.files.wordpress.com/2010/01/kwd9019november-21-2009.jpg?w=700&h=581
Note the Australians, only recommend 2 sources of light for
freediving. I guess they
figure that your lights should not fail in the 2 or 3 minutes that you
would be underwater,
and since you are holding a hand-line, light isn't so important.
I think their tug signaling system is worth taking a look at. I
remember one time being
on the end of the rope waiting for the last caver to pass a sump and
he didn't show up for
a minute or 2. It seemed like 5 minutes, and the thought occurred
as to what should I
do if he doesn't come up soon. I think he was on the other end
worried that I still hadn't
completely negotiated the sump, and he was wondering if he needed to jump in and
rescue me. Fortunately it was just a few feet more than a duck-under.
I don't know how many duck-unders or free-diveable sumps there are in
Texas, but there
are probably nearly a hundred in Mexico.
So do the Aussie rules above apply to caving here?
I think 3 important things are a helmet, a waterproof headlamp, and a
facemask. You
should also try holding your breath in a swimming pool to see how many
seconds you
can safely be under a sump.
My memory of the duck-under in Honeycreek, is that the only reason it
is intimidating is that
you can't stand up on either side of it, because you are in swimming
passage on both sides.
Right? Is that the most dangerous spot in Honeycreek?
David Locklear
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