Systems Analysis: When does 1=4.5
Updated and revised by Grant Prattley, OTE Rescue 2014.
Based on original work by SARINZ Trust 2010.
Article for Tomo Times, NZ Speleological Society, Waitomo, New Zealand.
It seems to happen you strike the trickiest part of rescue rigging around 4am in the morning, in the wettest part of the cave at the end of a long 20-hour day. So it was on a deep cave SAREX in Summit Tomo, Takaka hill, 2010. I found myself standing at the bottom of a 5m pitch looking at some rigging at the top 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 was the short length of the pitch (5m), the minimal amount of exposure to the patient and that there was a large thread that was being used as a backup belay.
So what did I see that concerned me to stand waist deep in water scratching my head at 4am in the morning? Well at first glance it looked OK. There was only a single person load on the mainline of the stretcher. On further inspection, I saw this single person load (or 1kN) going through a 90 degree redirect pulley. A 90 degree redirect will increase the load by about 1.5 times…
