In reply to Mark Collins:
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> If both krabs were clipped into a single middle ring I would expect a "by" rather than a "with" in the OP. However, let's assume for the moment that they are both secured to a single middle ring.
Well given thats how every single climbing wall I've been to does it I think it's a safe assumption...
> Now let's take the next link in the chain, the single climbing rope. A single climbing rope is made up of many strands and therefore redundancy is built into this.
You have to be kidding. So in your opinion slings are even more safe given they are made up of thousands of strands of dyneema/nylon.
> However, I do consider you have a point with a single person belaying. If they fail, there is no backup. I guess we're now getting into the realms of what is practical versus the amount of redundancy in a system, there is always a balance to be struck.
Yes and this is the point, backing up the 40kN steel krab is well into the realms of the mitigating a very tiny risk. Especially since the other end of the rope is going to be secured by means of a single alloy (24kn) screwgate which is in a much worse position with regards to the gate accidentally becoming undone.
And if you really are worried about the possibility of the climber "tampering" with the gate then the actual solution would be a maillon, not giving them an extra screwgate which they can also undo.