Срыв. Две нагруженные верёвки и одна нагруженная верёвка со страховочной ненагруженной

Rope Rescue Systems Testing - Main/Belay (Back-Up) Failures Test comparison between Two Tensioned Rope Rescue System and Dedicated Mainline with Un-Tensioned Belay (back-up) Rope Rescue Systems. Challenging the premise of requiring an un-tensioned belay line (back-up) as opposed to two-tensioned techniques. Is there any evidence to support the use of an un-tensioned belay (back-up) in rope rescue?