Tensioning Highlines w/ Camming Rope Grabs: Force Limiting vs. Breaking Ropes

What should the safety factor really be based on? The weakest link in the chain, right? So therefore if using a Capto, there really isn’t a failure mode and thus a safety factor is a moot point. For the new Rescucenders, the weakest link in the chain is not any MBS of any component, but rather the manner of function/interface of components w/ the rope…. So therefore weak link being the interface of the rope & rescucender at about 2,000 lbf. Therefore it doesn’t matter if the rope termination has a knot in it….. a tied off knot w/a bowline is just as effective as a tensionless hitch. Basically a tensionless hitch/HSTO is therefore irrelevant & unnecessary…. Thanks Jake Turnbull for pointing that out.


Capto: Force limits/slips rope @ 6 kN (1,350 lbf)... Is it really 'G' rated?
Pre-2016 Rescucender: Force limits/slips rope @ 8 kN (1,800 lbf).
Post-2016 Rescucender: Does not force limit/slip, rather de-sheaths the rope @ 10 kN (2,200 lbf).

8.6 Manner of Function Tensile Test
8.6.1.1 This test shall apply to ascending devices, rope grab devices, descent control devices, and belay devices.
8.6.3.3 Each specimen shall be tested to both Procedure A and Procedure B.
8.6.4 Procedure.
8.6.4.1 Testing shall be conducted in the “manner of function” for the item being tested.
8.6.4.2.3 The device shall be attached to the rope according to the manufacturer's instructions.
8.6.4.3 Procedure A.
8.6.4.3.1 One end of the rope shall be anchored on to a tensile testing machine and the device shall be anchored to the other end of the rope. The specified deformation force shall be applied to the device at the normal attachment point at a rate of 25 mm/min ± 5 mm/min (1 in./min ± 1∕4 in./min).
8.6.4.3.2 The specified deformation force shall be held for 30 seconds +1/−0 second, and then the tension shall be completely released over a maximum of 1 minute.
8.6.4.3.3 The device shall then be inspected for damage to the device or to the rope used for testing.
8.6.4.4 Procedure B.
8.6.4.4.1 Using the same item and test set up as in Procedure A, the load shall then be re-applied to the device until the breaking point of the device.
8.6.4.4.3* In the case of items that are designed to slip under high load, the rope shall be knotted or the device otherwise blocked to prevent slippage.
8.6.7 Specific Requirements for Testing Ascent Devices and Rope Grab Devices.
8.6.7.1* Technical-use ascent devices and rope grab devices shall be tested at a load of 5 kN (1124 lbf) for Procedure A.
8.6.7.2 General-use ascent devices and rope grab devices shall be tested at a load of 11 kN (2500 lbf) for Procedure A.