26 February 2012

Do ropes need to rest between falls?

Black Diamond carried out some tests to find out if letting your rope rest between falls would help to reduce the peak forces experienced in a fall. They did tests where the rope was left to rest for 30 mins, 2 hours and 24 hours. They also checked to see if loosening the knot after a fall helped to reduce peak forces.

The graph shows successive falls from 1-10, with peak force on the vertical axis (using antique lbf as units, 1000 lbf = roughly 4.4 kN).

Their conclusions were:

"As expected, progressive drops resulted in increasing forces

The largest increase was from the 1st to the 2nd drop as expected

 Loosening the knot after each fall reduced the load a bit, but not much

Letting the rope rest 30 min between drops had a bigger effect at lowering loads than loosening the knot, but still not much

Allowing the rope to rest for 2 hours and 24 hours had an even greater effect at reducing the loads on the 2nd drop, as expected

Allowing the rope to rest 24 hours still resulted in a 2nd drop load of 11% greater than the first drop"

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