There is a very instructive video on the effects of fall
factor, knots and type of webbing on breaking slings at
<http://www.dmmclimbing.com/video.asp?id=5>. The short answer is
that if your sling is static, you only have to fall about a meter to
generate 4000 pounds. That's not an unrealistic distance to fall, so
careful attention to anchors and type of attachment is
paramount. Similar results showing the difference between webbing
and rope for cows tails is at
<www.caves.org/section/vertical/nh/53/lanyard_tests_v6.pdf>.
Although many people use Petzl Spelegyca cows tails, they really
aren't very safe if you fall on them. Lots more good test results
related to vertical work are
here: <www.hse.gov.uk/research/crr_pdf/2001/crr01364.pdf>.
Mark Minton
At 12:08 AM 2/4/2011, David wrote:
How far would you have to fall to generate 4,000 plus pounds of pull
like that on a biner?
I doubt your webbing or your body would survive the jolt.
Nevertheless,
I was impressed with the results of the Petzl Vertigo.
Although the gate latch broke early, it looked like had you been
hanging in it,
and had a gate failure like that, then it appeared that your webbing
might have
not slipped out.
All the carabiners first failed at the latch end of the gate, and not
at the pin end that
the gate pivots on, so maybe there is room for improvement there.
And the threads on the 4mm maillon seemed stronger than the bend in the link.
I did this test once on a used piece of 5 mm Kevlar cord that had
Figure-8 knots in it and
it broke at 5,000 pounds. I had been caving ( I used to do that )
with the rope tied
to a Jumar on a Mitchell System, and used it on several 100 foot plus ascents.
David Locklear
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