Quite a few years back we did an inspection on a nineteenth century chimney that was part of an old brewery here in Basel. The chimney had rather disconcertingly started spitting bricks and its condition was… questionable. I will spare you the gory details of the story, but put it this way, it was quite an adventure getting up there and moving around the chimney.
What struck me, as is often the case with old buildings, is how sometimes they only seem to be holding together out of habit. In this case the mortar between the bricks was being washed out, climbing up the inside of the chimney you could see chinks of light in many places where there was simply no mortar left. Give me a tree any day!
The parallel that struck me was to the wear you can sometimes find when inspecting equipment. Friction hitch cordage, for instance. Oftentimes you will look at the eye to eye sling, think it looks a bit weary but otherwise fine, for the mantle to then fall apart soon after. What is going on here? Well, in the Ocean Polyester eye to eye slings, for instance, the mantle is braided, made up of Aramid and Polyester, the core is braided Polyester (PES). You cannot die Aramid, so that is the yellow-ish part of the mantle, the PES is the green.
I have written this before, but what seems to give you the ability to dose the exact degree of friction in friction hitch cordage is the PES. High-modulus cordage on the other hand tends to be much more on/ off and less easy to dose. The reason for having Aramid in a friction hitch cord is heat resistance. The combination of PES and Aramid gives you the characteristics you are looking for, responsive handling as well as heat-resistance. By and by in use, the PES part of the mantel will be melted away, leaving you with Aramid, at which point in time the hitch starts to run less nicely on the line, you start to lose function – whilst still retaining the full strength of the core!
The link to the chimney above is how cordage can also apparently be intact, but that once you start plucking apart the mantle of a friction hitch cord which seems well-used but otherwise ok, the whole thing will simply disintegrate. This shows how Aramid – besides all its strengths – is a brittle fibre, which that has the tendency break when bent frequently. Yet that is acceptable in a wear part that will be replaced on a regular basis, the same is true of its low UV tolerance. Before this becomes an issue the hitch will be due to be replaced. Conversely, the same cannot be said of a device or assembly with a longer intended life-span, such as a lanyard or a false crotch.
Then there was the bridge below, which I came across during a gear inspection of a treeMOTION, it had been in use about one and a half years. I take every opportunity I get to pull apart old bridges to try to gain a better understanding of the variables which are in play when it comes to how they age. In this instance, the mantle was quite worn and distinctly flattened. The intermediate cover also showed quite a bit of wear, though no material was lost on either of them. The core showed similar wear.
I would suggest that this is quite a long time to wait before replacing a bridge, yet was positively surprised by the condition of the cordage.
When it comes to assessing wear parts in your PPE, I would strongly encourage you to identify and understand them, to heed manufacturer recommendations, inspect and maintain them diligently – and to replace them sooner rather than later – after all, the cost of the replacement parts is not that high, especially considering the potential risks that not doing so could entail.
Do not use as an indicator the fact that a component looks ok to draw the conclusion that it is ok. Do not be shy to dig a bit deeper and to look closer.