Strike Rescue’s official stance on the use, and misuse, of 6mm Purcell Prusiks:
Marc Beverly was contracted in 2006 to provide the instrumentation and data collection for the group performing the original research on Purcell Prusiks. Marc had done some preliminary testing on the use of 6mm material while working at the Pararescue School at Kirtland AFB, Abq., NM.
Strike Rescue does not recommend the use of 6mm PPs based on actual research that has shown catastrophic failure and impact forces exceeding standard recommendations with unacceptably high frequency (2 out of 3 on FF2). Yes, they are convenient since they are indeed smaller. However, in a rescue or big wall situation, 6mm PPs have no place as a tie in point to an anchor if there is a possibility that the load could rise above that anchor. This would be considered dangerous and improper application of materials.
6mm PPs can be used for ascending on rope or integrated into a system where substantial impact forces may be absorbed by other components in a system, but that system should be tested before use of 6mm PPs. An inappropriate rope to use might be HTP since the stretch is <1%, rendering it an effectual sold anchor point.
Furthermore, work hardening of knotted perlon will contribute to more frequent failures as the modulus of the material increases dramatically after the first loading event. Sewn PPs have not been tested by independent sources outside of manufacturer origin or in real world application. Use at your own risk. Failures of PPs during testing have been noted at variable locations that include, but are not limited to, the figure 8 knot or the girth hitch attachment point.
In general, it is a good device for static loading such as hanging on or rope ascension progress capture.
One cannot make assumptions in rigging. Using 8mm perlon does not necessarily make things better since the perlon is too stiff and offers no give.
Perhaps the worst enemy is not knowing what you don’t know…and testing your hypothesis on yourself or others anyway.