I occasionally lead rappelling (above ground) trips with a few friends with some vertical experience, but not enough to make me feel comfortable leaving them on their own. In the past, I would rappel first a provide a "fireman's" belay while another experienced person verified each rappeller's equipment was connected properly before going over the edge. I am interested in trying a running belay on a second rope with the Petzl ASAP or a similar fall arrestor. Does anyone have experience with the ASAP or any similar product? At what speed does the ASAP "lock"? Would there be a possibility of the device locking at normal rappelling speeds? The primary use would be above ground, so I'm not concerned about potential problems with a muddy rope or muddy device. As long as folks need a belay, we won't be going in cave.
Of course I would need to consider how to lower the belay line when the ASAP does lock. That is something I'm already familliar with and I'm not looking for advice on that topic.
Thanks in advance for any input.