Leading sport routes on a half-rope seems safe based on the fact that they are designed to take falls on trad routes where there is no guarantee that the other half-rope will take any load. Or am I misunderstanding something? What really worries me is that the UIAA fall test for a half-rope only uses a 55kg weight! Why so little? Do they only want featherweights to survive a high fall-factor fall of 5m? (see http://www.uiaa.ch/web.test/visual/Safety/UIAA101Pictorial.pdf) Someone help me out here, please!

Yeah I think you're suppose to have the other rope as a backup, but what if you fall on the first few pieces?

On the issue of 'half ropes' and fall factors. Experience, much much experience, has shown climbers over the decades that twin ropes are not only easier to climb with (reducing drag) on rough ground, but are also much safer. Say, you fall. Ok, at some point, say the rope comes taught over a sharp edge. If there is only one rope, this is going to bear the brunt, and may fail. If there are two ropes, the chance of *both* bearing exactly 50% of the weight (thus both coming taught over the edge) is negligible; one will always have more tension than the other. Hence the one may fail, the other holds. So, you live. Cool. Also, bear in mind that a trad belay is also much more dynamic than a sport belay; there are longer slings out as runners, usually more slack, the rope runs a more winding course usually and a sticht plate/ATC/bug style belay is more dynamic than the commonly used Grigri for single rope belay. So, all these points mean less force applied to your cord in a trad situation, under ideal conditions, hence the use of thinner double ropes in trad, and thicker single ropes in sport. Of course, there are always exceptions: a fall right onto the belay is always a bit of a no-no. One should always get a piece out soon after leaving the belay, no matter how easy the terrain. This will radically reduce your chances of scaring the crap out your belayer and stressing the system (and yourself). Note, dynamic belays (a good thing, duh) in sport belaying is why we don't anchor the belayer to anything. Even lightweight belayers taking short flights upwards is a very good thing for a system, giving the fallen climber a soft fall, and increasing the lifespan of your expensive rope. cheers

Thanks Brent. Just a short response: half-ropes and twin ropes are quite different things, but that's for another forum thread... I'd still like to ask others for comments on leading on just one half-rope rather than a full/single rope. PS: Half-ropes are also known as double ropes since you're supposed to use two of them, but not through the same protection as per twin ropes.

hi dave,
my understanding of a modern half rope is that it should take a factor 2 fall, ( granted it shouldn't take too many ) , and if you say they only test them with a 55kg weight, maybe that's because it's not designed to take a fall like that on it's own. usually it's used in a vertical situation with another half rope.
so if you were to fall directly onto the belay from 5 meters, your weight would be halved, because you would be falling onto 2 half ropes.
in a \" 'trad' situation were there is no guarantee the other rope will take any load \" , that's probably because you have used the rope through some protection or other ( nutt, camm, sling whatever ...), so therefore the force and shock load on the rope would be hugely reduced as the fall factor goes down, your belayer goes up, and the rope stretches.
As far as using a half rope for sport climbing, to my knowledge, half ropes stretch further than single ropes, ( hence you can use them like twins ). so when you fall on one half rope, you will fall further. which would be a bummer on a sport route. they are also thinner and harder to hold ( for belaying ), as well as the fact that some sport climbing devices are not made for them ( grigri ).
I can't recommend that anyone rock climbs with only one half rope, because single ropes are designed for that purpose, but if you absolutely have to, ( you dropped your other half rope and need to go on )...
i would recommend your partner belay you with a reversino, and to clip the anchor ( or highest piece of. ) before leaving the station.