Friday, 25 March 2011

Safety alert on abseiling with prussik on leg loops

Safety alert on abseiling with prussik back up on leg loops
This came to me from Pat Littlejohn in the British Mountain Guides newsletter and makes interesting reading:
Summary - Using a prussik loop back up on your leg loop can open the buckles which are 'cinched' tight (by pulling), now increasingly found on modern harnesses, with dangerous results.
" Last summer on a Technical Alpinism course I taught clients how to protect an abseil with a French prusik clipped into the harness leg loop, a standard technique used almost universally. While using this later abseiling from a gendarme, one client allowed the prussik to bite whereupon the harness leg loop opened and he was left dangling from his waist belt with the prussik jammed against his belay plate. Luckily he was nearly at the end of the abseil and other clients helped him to unweight and free himself.
Wanting to see how this had happened I tried it using his harness and the leg loop undid every time. We then tried other harnesses in the team (which were not identical but similar construction) and again this happened.
All were new harnesses which had leg loops with buckles which 'cinched' tight (by pulling) rather than being back-threaded in the old style (as the leg loop buckles on the harness I was wearing). What happens is that the karabiner of the prussik lodges at the buckle, which then opens because it is being pulled at an angle which 'cinching' buckles won't take, i.e. a force from behind the buckle. This is much easier to demonstrate than to explain!
So many modern harnesses now use 'cinching' buckles on the leg loops, or are in the “Bod” style, that we may have to revert to the method of protecting an abseil with a prussik by clipping the prussik into the belay loop of the harness (usually with a quickdraw or cow’s tail to extend either the prussik or the belay plate), I have always thought this was a safer method anyway, but a bit less convenient and involving more gear.
What worries me is the number of people out there who have been taught to abseil with a French prussik clipped into leg loops with 'cinching' buckles - a lot of people I suspect. "
I've tried to get this to happen on a new Wild Country harness without success - see pictures below. Climbers and instructors should, however, be aware of this possibility.

1 comment:

  1. A friend suggests clipping the krab from the prussik to the "inside" of the leg-loop. Haven't tried it, but it sounds like a good solution.