I'm not an arborist, but I'm interested in it and have been doing some studying. I'm curious about a couple things. 1. Why can a snap be double acting but a carabiner has to be triple acting? 2. I read occasionally about climbers needing an emergency descent plan, and carry along a figure 8 for that purpose. Why can they not just let go of their working lanyard and descend on their climbing line using their friction hitch? I'm just learning and have only climbed drt with a Blake's. Is the figure 8 needed for descent if you are climbing srt?