Thanks for doing the testing Rob.
I would never choke a krab in the way you tested on such a small limb. That was cross loading, but didn't little krabby do well!
Its too easy to choke a sling in that situation. Oooh..no wait...doesn't that reduce the Breaking Strength?! Of course it does! Is that a problem in light of likely forces? Of course not! (come on guys - keep it real!).
As for Titan as a prusik cord - I think I'm right in stating its spectra/dyneema core. The cover is gone and the core is exposed to fuse failure. Seems no-one wants to acknowledge the research results I posted about high mod fibres and the flex fatigue flaws. They ALSO don't offer an alternative to choking the way I do it and why. Frank1's post is up my street.
As for the gate opening, thats as a direct result of the cross loading, again which I never do.
The point is, the way I use a choked krab is for improved security reasons as an arms reach supplementary anchor in all but one example (TLHamels). In this instance I'll clip in two krabs (no issues there); but again, there is no reason for the gate to be activated in this scenario.
There is no alternative technique that allows the same effect. The risks of not doing it in certain situations is certainly way greater than choking correctly. I'll explain it if I ever get round to publishing a book.
As for MA in the way various people have implied - thats not accurate - because of the inefficiencies of friction over the krab, the anchor force will be increased by a factor of only 1.5 at best, not 2. The further round it is set, the more it is isolated by friction and so reduced to low loads. Even so, as Rob's testing showed in a very worse case scenario, the krab has plenty of strength reserves for 6kN doubled.
As for building a system strength that can withstand 5000# forces - don't kid yourself that by having equipment this strong you may survive - its just for ensuring durable safety and less than ideal situations (even correct choking : )
If you really think you may incur forces to your PPE system over 6kN you should use energy absorbers. The activation of these have their own problems in contacting other hazards such as boughs and powerlines. If you think you may become part of your rigging system by mistake - again, kiss your [censored] goodbye.
Be sensible, recognise fall arrest situations and avoid them, and plan your system never to tangle with the rigging; surviving such situations is only possible through nothing more than luck and divine intervention : )
There are short stubby round section krabs that are suitable for correct choking. But if a manufacturer wants to make one specifically, then I'd use them for sure, and it would improve secure operations.
Oh, and for the record, a manufacturer once told me that their krabs were rated to 30,000 CTF with a WLL factored at 4:1 of MBS. And that most krabs will proof load to 50% of MBS without any problem but reduced CTF - they weren't sure how much, which is why they cut this in half for a 4:1 factored WLL.
I'm glad you like the site Norm - thanks for checking it out. Its due and upgrade soon.
I've got to leave it at that I'm afraid - its good to discuss these awkward areas of our work. Extreme tasks often call for extreme measures - Choking krabs of course isn't an optimum situation, just as habitual use of high mod. micro prusiks isn't - don't be seduced by high breaking strengths without establishing the potentially serious draw backs.
Bon voyage!
