b) The safety of bottom belaying depends very much on how you do it. If you're just standing directly under the rope, holding it loosely with lowered hands, and paying occasional attention to the person above, you're asking for trouble.
If you're in a situation where almost any action you take will tighten the rope - standing a bit above pitch bottom, firmly holding rope high up, keeping absolute minimum slack, taking up slack as novice descends, mentally rehearsing the appropriate actions (pull down, sit down, jump off ledge, etc) - and paying attention, you're on much safer ground.
The *alternative* bottom belay technique can simply be to almost-tension the rope at a significant angle, standing some way off from the pitch bottom. Due to the geometry of the situation, as the caver descends, the total distance from pitchhead->novice->you increases, so you have to *pay out* rope to avoid them slowing down, rather than *taking up* minor slack as in the directly-below situation. If you have a decent safe stance, or there's a convenient hanger to attach a crab to run the rope through, it's a pretty safe setup - the more they descend, the tighter the rope gets, and it may be easier to see what's happening than may be the case with pitchhead lifelining. It's a little like the 'loop' method, though slightly 'unrolled', and with the option of more progressive braking.
Obviously, the relative weights of novice and belayer may come into the equation, but aren't terribly hard to allow for when just using bodyweight for the sideways pull. With a 20-stone novice, I'd probably try something else.
In practice, even a 'regular' bottom-belay may well be sideways enough to require paying out rope, rather than taking it in.
c) With a knot in the rope, the very worst-case scenario is an impact somewhere below fall factor 1, depending how much energy is lost to friction during the clutch and plummet, and how far down the descent starts to go wrong. In most conceivable cases that will be rather better than hitting the deck, *even* with the occasional minor complication of possibly having to instruct someone in doing a changeover, or climbing up to give them a short self-rescue if they are somehow rendered incapable. Hauling them up the pitch seems unlikely to be necessary except in pretty rare circumstances.
As a simple alternative to doing nothing for someone judged not to need actual lifelining, but still a partial novice, it makes a deal of sense to at least consider.
d) With the 'loop' method, I can't imagine anyone bothered enough about safety to lifeline someone down a pitch and yet standing at the top without clipping in their cowstails.
With the descender acting as a pulley (giving a 2:1 mechanical advantage), and also providing extra friction as soon as there was *any* tension on the 'lifeline' side of the loop, I'd assume that holding a caver would be fairly easy if you hadn't given them more than a small potential distance to fall.
Presumably the people who use that method could offer their experiences?
If *really* paranoid about letting the rope slip, it'd be possible to tie off the lifeline side of the loop so the novice would *still* be left dangling a couple of metres off the deck even if the lifeliner just let go, and/or use a stitch plate or similar.
We aren't the Marines, and *ultimately* we are training for competence and self-reliance, but the idea is how best to help people safely cover their first few steps. Once they can be seen to have mastered basic speed control, and not be so scared they clutch at anything and everything, or so foolhardy as to try descending at a speed they can't cope with, the stabilisers can come off the bicycle.
