Testing Damage From A Rope Grab

Rope grabs are used in rope rescue and rope access in order to create an attachment point onto a rope without the need to tie a knot. Although there are many different styles, most use a cam which exerts pressure on the rope to hold the device in place. The cam comes in two main varieties with either a ribbed design or tooth design which uses small spikes.

Cam face of the Climbing Technology Ascender Simple, ISC Wales Mini Rope Grab, Climbing Technology RollNLock, and Petzl Tibloc.

Because they look more dangerous, there are concerns over the use of cams with teeth that they will unexpectedly strip the sheath off a rope at a low force. According to NFPA 1983 Standard on Life Safety Rope and Equipment for Emergency Services, a rope grab must withstand a force of 5kN for a technical use rating. Our goal in conducting this test was to determine if a toothed rope grab will damage a rope at a lower value than a smooth or ribbed cam device.
For this test three models of rope grab were used. The Climbing Technology Simple Ascender, Climbing Technology Roll’n’Lock, and ISC Mini Rope Grab. Three pull tests were done with each rope grab. A single test was also done with an older version of the Petzl Tibloc.

A sample of Teufelberger Platinum PES/PA used during the testing. The mechanical connection between the sheath and core is easily seen

The tests were all performed on used Teufelberger Platinum PES/PA 10.5mm rope. This rope was taken from our training cache and represents the condition of rope we expect to find in common use. Teufelberger Platinum uses a special patented construction which interleaves the sheath and core creating a mechanical connection between the two sections of rope. Additional tests were performed with Teufelberger Patron Rope which uses a standard kernmantle construction. Failure occurred at similar force with both types of rope although the distance the sheath was stripped was much shorter with the Teufelberger Platinum.
Tests were conducted by slowly pulling the to failure at a constant rate. Dynamic shock loads were not tested at this time. Test measurements were recorded using a Rock Exotica Enforcer Load Cell. The following results were observed:

Climbing Technology Simple Ascender: 6.78 kN, 7.09 kN, 7.12 kN

ISC Mini Rope Grab: 7.43 kN, 7.64 kN, 7.81 kN

Climbing Technology Roll’N’Lock: 6.28 kN, 6.69 kN, 7.50 kN

Additionally a single test was done with an older version of the Petzl Tibloc which failed at 7.54 kN
In all cases the rope suffered a catastrophic failure resulting in the sheath being stripped from the core. Devices were inspected after each test and no damage to the hardware was noted.
Observations:

All tests performed on all devices exceeded the 5kN NFPA technical use requirement.
Devices functioned similarly during the test.
Observed rope damage was consistent between all devices and all tests.

While this test is not conclusive, it supports the idea that rope grabs with aggressive teeth are not more likely to strip a rope than those with a ribbed cam face.