Systems Analysis: How does 1kN become 4.5kN

Systems Analysis: How does 1kN become 4.5kN

So what did I see that made me stand waist-deep in water, scratching my head at 4 am?

It seems to happen that you strike the trickiest part of the rescue rigging around 4 am in the morning, in the wettest part of the cave at the end of a long 20-hour day. So it was in a deep cave, SAREX in Summit Tomo, Takaka hill, 2010. I found myself standing at the bottom of a 5m pitch, looking up at the rigging to see what was happening – undertaking a systems analysis.

At first glance, I had some concerns about the rigging. However, after a quick risk assessment, I thought we could get away with this setup. Things I considered were the short length of the pitch (5m), the minimal exposure to the patient, and the large thread being used as a backup belay.

Well, at first glance, it looked OK. There was only a single person on the mainline. On further inspection, I saw this single-person load (1 kN) passing through a 90-degree redirect pulley. A 90 degree redirect will increase the load by about 1.5 times…

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