Redirected butt block ( ground lift and lower )
There are several methods to redirect a ground-based lift and lower system such that a casualty can be lifted vertically despite a poor original rope angle .
The simplest method is to redirect the main line through a pulley or pulleys attached to parts of the tree ’ s structure above the casualty , such that the working end of the line drops vertically down onto the casualty . Ensure that low-friction pulleys are installed wherever the rope makes an angle . Rope redirected through the unions of tree branches incorporates very high friction , and will inhibit or prevent lifting of a heavy casualty .
An alternative method that eliminates the need for multiple redirect pulleys is to attach the top lifting pulley to the end of an anchor line as a floating anchor ( anchor line shown in orange in right hand image above ). Whilst this may seem more complicated , in large trees it can be significantly quicker and easier to install as the rescue climber does not need to visit each redirect site to install a pulley . Instead , the anchor line can be thrown through the redirect point to the ground , the floating anchor can be installed on the ground and then hauled into place . With good throwline use , it may be possible to install the whole system without accessing the tree .
It is important to understand the additional force that can be applied to the tree ’ s structure using floating anchors or similar methods . Please see Chapter 2.3.1 Evaluating forces in rescue rope systems for further details .
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