One person I regularly climb with uses a belay technique that I was taught to be unsafe, so I would like to know just how unsafe it really is. With a classic tube-style belay device, after taking in slack and bringing the brake hand back down, he simply slides his brake hand up the rope, opening it up just enough to allow the rope to stay in place.
Although it is obvious that PBUS (which is unfortunately not taught here at all) would be much safer, it is less obvious to me whether there is any real danger of him not catching a fall, given that he would probably hold tight as soon as he feels his other hand being pulled. So ideally I would like to know some hard facts such as:
- Have any accidents been attributed to this belay technique? (Or a similar technique -- holding the brake hand above the device does not count as similar though.)
- Does anyone know of any experiments to determine if people usually catch falls even if they were holding the rope loosely?