In reply to Snowdave:
Know what Snafu meant but can't remember, Fubar, Tarfun + fishmo... U lost me!
The problem is, many people are learning to climb at walls, or have got back into it there, and it seems everyone has to do a fig 8 with stopper.
Not many wall staff will ever go over to you and say that's a dangerous way to add a stopper, because of the gap you left, it should be snug up to your fig 8.
Some of these people adopt this as their must do tie in method, then go out to a crag or mountain and are at risk of clipping into this loop, and dying.
Appreciate you posting test data etc, probably not needed now, i have tried it out, (not on a test rig, no data!)...
there are two ways to load this "loop", but either way, the stopper knot can pop through the carabiner and load the other side instead.
When you clip a quickdraw / sling + carabiner to this loop and lean on it, The carabiner tends to sit right behind the stopper, and deceptively "looks snug and safe there, but can pop through the clipped biner to put load on the live or dead line.
If it pulls on the live line, depending on how tight the stopper was pulled, and how heavy the load force is, a tight stopper seems go be gripping the live rope a little, (it is, but still not safe! ), but with a loosish stopper, as many are, the live end, which if you just finished seconding starts to pull through and you fall backwards, and if your partner has taken you off belay, the rope will pull right through if you are high up, until you hit the ground or a ledge, if still on belay you fall upto half the length of the rope, both likely to be fatal. The single stopper can be seen to be slightly unravelling too, the double doesn't, but you still fall.
If you clipped the dead end side of the loop, in which you tied the stopper, then even a single stopper holds you leaning back, and a some bouncing on it, but a double stopper seems to hold quite stongly, however it only needs the stopper knot to push through the carabiner, load the live line, then you could well be fatally falling again.
If you use a stopper, (preferably a double barrelled stopper, but not actually necessary) put it right up against the tie in knot (Fig 8 / bowline etc), so there are no potentially fatal loops you can clip.
SWALK.
Post edited at 11:46