After yet another Facebook post about a bridge failure with non-approved cordage (8mm Beeline) and people saying that the importance of using only the approved rope bridge is not common knowledge, I thought I’d re-post this blog entry from August 2014 (!).
Yes, a competent climber is able to make his or her own choices given proper guidance by the manufacturers. In this instance, the harness manufacturer offers very clear, concise guidance, which is: use the specified rope bridge only – and that statement right there strikes me as being about as unambiguous as it gets.
Use. The. Approved. Bridge. ONLY.
Part of the certification process of Personal Protective Equipment (PPE) is that the manufacturer is making a statement about the performance of a configured assembly or system, for example in regards to dynamic or static breaking strain, maximum load, correct use etc.
This obviously also is true of elements of an assembly, such as the rope bridge on a harness. People often ask, whether it is ok to replace the specified Globe rope bridge on the treeMOTION with a different rope – and the answer is always the same: If you do so, the statement the manufacturer makes in regards to the certification of the harness is no longer valid.
The FB post shows the risks involved, especially – but not only – when using high-modulus fibres. These are extraordinary at some things but perform poorly at others, so for instance, a fibre may be highly tolerant of heat, but very brittle and performing poorly at handling repeated bending. So this needs to be taken into careful consideration when assembling systems.
My recommendation for certified assemblies and systems is to simply go with what the manufacturer specifies, in the case of harness rope bridges, I do not really see what you gain in regards to function by switching to a different line. The line is cheaper, because you had it kicking around the workshop? Not a very strong argument when your life is on the line…
To quote Clifford W. Ashely’s The Ashley Book of Knots:
A knot is never “nearly right”; it is either exactly right or it is hopelessly wrong, one or the other; there is nothing in between. This is not the impossibly high standard of the idealist, it is a mere fact for the realist to face.
When working at height, get it right – and do not cut corners!