Forums: Climbing Information: Accident and Incident Analysis: Re: [billl7] Rappel accident, 60' fall: Edit Log


Dec 27, 2012, 9:18 AM

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Registered: Oct 13, 2005
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Re: [billl7] Rappel accident, 60' fall
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After a bit more testing (details below), here are some summary points about using the french-prusik as an autoblock below the rap device:

a) The author of the linked forum contended that clipping forward or aft of the girth made the difference. True - changing the number of wraps by half-a-wrap can indeed make a difference.

b) The length of the loop of cord matters with the french prusik. It affects the compactness of the hitch and so affects ability to grip.

c) Others in this thread have stressed testing the exact config as being important. That is good advice. Variables that can make a significant difference include one-stranded versus two-stranded rappels. The significance of wet versus dry conditions was not tested.

d) In situ testing should not include pre-tensioning the french prusik as this can hide the actual effectiveness in some surprise falls (assuming a surprise fall is what one hopes to back up).

Bill L

P.S. A little more detail from further testing that supports some points stated above ...

After scrutinizing the clearest image of the autoblock in this thread and after a little trial and error, the config chosen to best approximate the accident was a 13" loop with ~3 wraps of 5mm cord with a locking biner that was about 3 3/4" in longest length (BD Positron Screwgate, outside measurement).

Clipping rear-ward of the girth passed the drop test. Clipping front-ward of the girth failed the drop test (removes half a wrap bringing the total to ~2 1/2 wraps). In both cases, pre-tensioning the autoblock held the weight.

Note that all my testing was done dry.

(This post was edited by billl7 on Dec 27, 2012, 9:34 AM)

Edit Log:
Post edited by billl7 () on Dec 27, 2012, 9:30 AM
Post edited by billl7 () on Dec 27, 2012, 9:31 AM
Post edited by billl7 () on Dec 27, 2012, 9:33 AM
Post edited by billl7 () on Dec 27, 2012, 9:34 AM

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