Sorry about that, thread now open for questions. Actually I have a question. If you put a force of around 450 kg on a pair of jumars on a dynamic rope, the sheath of the rope will be ripped to shreads. I witnessed this last week under test conditions at Plas y Brenin. Are there any climbing situations where that could happen?

Hi Mick, you're absolutely right, most toothed ascenders will strip the sheath at about 450 kg. If ascending a rope using jammers, good technique maintains a position below or level the ascender at all times - never above. SRT cavers know more about this, through plenty of experience. So, avoid being clipped into a jammer with a sling and climbing up above it. Of course, with a damaged sheath already present, say on a fixed rope, the sheath might break much more easily. An old trick here is to have a knot tied in the bottom of the rope, so if the sheath breaks it slides down until it bunches up rather than sliding off the end of the rope. It's pretty scary looking, but at least the rope is functional enough to enable you to escape. Finally, any kind of hauling system which uses mechanical advantage to help hoist a heavy load might end up loading a jammer enough to strip the rope sheath - especially if the load gets stuck and you try to free it by cranking as hard as you can.

Thanks Dan. A recent death in Zion here. http://www.supertopo.com/climbing/thread.html?topic_id=808440

Hi Dan I have asked this question to a few people, but never had a accurate/reasonable response. If a cam had 100kg hanging on it, what force is being pushed outwards by the cams to counteract that 100kg. I have had answers from 100kg to 300kg. My guess is that more force has to push out, to prevent it slipping. Basically the argument is not to use cams behind flakes that might be levered off by the force being multiplied in the event of a fall.