posted
Thought you guys that climb might find this interesting. There is a "Outdoor" oriented college here in Anchorage. The last few weeks, various students have presented some very interesting Senior Projects at our meetings for the Alaska Mountain Rescue Group (AMRG). Last nights presentation was a quantitative analysis of the effects of hard & soft cams when subject to a fall of various heights. Specifically what happens to the ropes these cam's are being used on if subject to a dynamic event (a fall), and is the rope usable after the event.
The hard cam's tested: Petzl TiBlock, the Petzl Ascension, and the Wildcountry Ropeman II
The soft cam's tested: A 3-wrap prusik using 6mm accesory cord. And a Kleimheist Prusik using a 9/16 spectra runner.
Results were a quite scary with regards to using hard cams as any form of safety if a fall is possible. The student wanted to test beyond the mfgs specs, to see what the max stress for each product was.
He tested each cam, by simulating a fall from 4 different heights (1.5ft, 3ft, 4.5ft, and 6ft), using 80kg/176lbs (approx= avg climber).
The Ropeman II, cant be used at all basically, at the 1.5ft fall it initially slipped a 1inch, then tore 3/4 of the way around the rope sheath exposing the kern, then slipped another 18 inches and cut the sheath again, finally stopping the drop there.
The TiBlock didn't damage the rope until a 4.5ft drop, but then it stripped about 18-24 inches of sheath straight down the rope before stopping.
The Acsension Acender didn't fail until the 6ft fall, but it completely stripped the ropes sheath, and severed one of the three Kern's within the sheath (inside of a climbing rope is made of three seperate strands called the Kern). Additionally there was enough force generated to actually bend the U-shaped Ropeguide part of the ascender a measurable distance outward.
The Kleimheist completely failed to clutch/stop the fall, and slid down the lenght of the rope. However many of use feel the results would be different if he used a 6mm accessory cord instead of a spectra runner. The actual results melted the runner into the shape of the Kleimheist even after taking it off the rope
And the WINNER. The Prusik. Did not fail under any circumstance tested, and slipped a max of 1.5 inches, and did not damage the main rope or the 6mm used to make the prusik.
not to mention that the prusic costs about $2.10 worth of accesory cord compared to the $50.00 Acsension, the $20.00 TiBlock, and the $32.00 RopemanII.
Posts: 2469 | From: Anchorage, AK | Registered: Oct 2001
| IP: Logged |
posted
I have a set of the Acsension but have not used them at any length. I guess I was always under the assumption that assenders/prusiks were not designed for any type of fall. They were for holding ropes and assending ropes, it's seems logical me that they would rip a rope apart if any great force was put on them. I certainly wouldn't trust my life to them.
Good to hear that in an emergency a prusik is the way to go. Good info.
Posts: 5484 | From: St. Paul, Mn | Registered: Apr 2002
| IP: Logged |
posted
The thing is, is some people, even experience climbers, may not realize that sometime, gripping A LOT is a bad thing under certain conditions. Well the hard cams are kinda designed just to be asenders (some more than others), this isn't necessarily true of softcams. In redundant systems, you end up using stuff like this to attach you into the two systems, along with using these to attach to safety lines at the top. The hard cams, particularly the petzle ascension is particularly convienient for this as opposed to the soft cam, just more handy. You wouldn't figure that a little 6 foot fall on the ascension could shred your rope (and granted these tests were worst case scenarios for a given height cause it was a unobstructed vertical fall, all the energy was transfered to the saftey system, as opposed to bouncing down a less-than-vertical incline would produce less force on the system). The big difference between the hard & soft cams that explains many aspects of these test results is that the hard cams grab, and GRAB TOO GOOD. The soft cams, particularly the prusik, have a "clutching" action as the load hits, and it distributes the load out to a wide area really well. The klemheist doesnt distribute quite as well, but I've used it and its easier to do (and works better IMNSHO) with same 6mm accessory cord, and is easier to tie with gloves on. The prusiks are actually a better brake than a human hand. If you read up on rigging a HIGHLINE traverse, a way of geting across a span (specifically diff. than a tirolian travers or zip line). They've done tests and in big dynamic events (such as a highline breaking) no matter what your using for a belay/break device (ATC, figure-8, Colorado Break Bar, 4-biner brake) the human hand is incapable of dealing with the force & friction. So in these systems they use a modified French prusik as a safety break, they're a really usefull rope trick for sure.
UBBFriend: Email this page to someone!
Printer-friendly view of this topic
![[shake]](graemlins/jpshakehead.gif)
![[beer]](graemlins/beer.gif)
