Deflection forces in rescue
When considering any rescue strategy where a tensioned line is deflected by a load , it is critical to consider the additional force that will be applied due to deflection .
For example , in the image below , a rescue team are extracting a casualty by lifting them to a floating anchor suspended between two trees . Whilst this can be an effective technique for many possible scenarios , if used as pictured the potential consequences can be severe .
In the example shown , a 100kg casualty could apply up to approximately 5kN force to either anchor point . As the force is applied perpendicular to the lever arm of the tree structure , there is a high risk of branch failure or the tree tipping over .
The system can easily be improved . First , the included angle of the floating anchor ropes should be kept as acute as possible . The anchor line should be passed through a suitable fork of the tree and secured to a suitable anchor away from the tree in the same plane as the line . The resulting force on the tree will be reduced in magnitude and will act vertically downward as compression force .
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