KISA shock absorber

[MSD]

Anybody have any references/experience about using the Kong KISA shock absorber (or similar) with static rope? Kong give a number of different threading patterns for different amounts of friction and make suggestions about which are suitable for different diameters of dynamic rope, but using static rope isn't mentioned in the technical data.

That's probably because anybody in their right mind would plan to take a shockload on dynamic rope! But if static rope is what you have (for example a cave resuce situation), then it would be useful to know how to use such a device to best effect.

Some actual test data would be great, but I guess that's being a bit optimistic

Mark

 

[AndyF]

I (amongst others) have always been dubious of the value of friction based "shock absorbers". Since they turn kinetic energy into heat, its pretty easy to work out how many joules of energy the thing can absorb. Knowing its mass, and assuming a teperature rise of, say 100 celcius, the heat capacity can be calculated.

Compared to the number of joules that a falling body has, the absorbtion capacity is a tiny percentage of the fallers kinetic energy. Thus, all the device may do is delay the shock for an extra meter or so.....

Someone technical may well shoot me to bits on this...!?!? :shock:

 

[MSD]

The energy is absorbed in the rope, not in the device. The way it works is not to absorb the energy itself, but lengthen the amount of time in which the energy is absorbed by the rope. The peak impact force is a factor of how fast the energy has to be absorbed.

Similarly, if you look at a rip-out tape, it's patently obvious that ripping a few threads can't in itself absorb much energy at all in itsef.

Take a piece of blu-tack and stretch it. If you stretch it slowly it will stretch for miles. If you stretch it fast it will break.

Lifee is full of these conundrums. You can easily stand on a window, but if you throw a dart at it, it will break.

Mark

 

[cavermark]

if static rope is what you have (for example a cave resuce situation), then it would be useful to know how to use such a device to best effect.

Why would you happen to have a KISA shock absorber in a cave and what rescue situation would require it?

If its on your cowstail or something then surely it will have the appropriate rope in it?

 

[MSD]

If you are in the unfortuante situation of having to perform a resuce on a expedition, the only rope you might have available could be static. If you are hauling a combined load of casualty+minder, then a lifeline and/or belays could take a big shock if something fails. Hence the idea of a KISA.

But this is digressing somewhat from the original question, which was pretty specific and to the point.