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Personal Anchor Tethers for Climbing Safely
by Lee Lang
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Traditionally, climbers have anchored to the belay by tying in directly with the rope. Now, many prefer the convenience of personal anchor tethers specifically designed for this purpose for belays, as well as for cleaning the top anchor on a sport climb or anchoring during multi-pitch rappels. When used properly, these systems can be safe and strong, but when used improperly, they can lead to fatal accidents.
All climbing cord and webbing was once made from nylon, which stretches slightly, absorbing energy. Stronger materials such as Spectra and Dyneema now allow climbers to save weight, but lack the ability to absorb energy through stretch. When used in systems with an energyabsorbing component—such as in quickdraws, where the dynamic rope clipped to the draws absorbs energy—these materials excel. When they’re used in a system with no energy-absorbing component, any dynamic event results in extremely high impact forces.
Drop tests demonstrate the danger. DMM tested an assorted batch of Dyneema and nylon slings, using a 176-pound weight in fall-factor 1 (120cm drop on 120cm sling) and fall-factor 2 (240cm drop on 120cm sling) scenarios (www.dmmclimbing.com/video.asp?id=5). Even when the Dyneema slings did not fail, the impact force (18–22+ kN) delivered to the climber likely would have resulted in massive or fatal injury.
Rigging for Rescue also tested a variety of personal lanyards and anchors, using 176-pound and 220-pound loads (riggingforrescue.com/relanyards1.html). Spectra daisy chains began to fail at a fall factor of 0.25: a 220-pound weight dropped nine inches on a 36-inch daisy chain. At a fall factor of 0.5 (18-inch drop on a 36-inch daisy), virtually every daisy chain failed.
Consider the personal anchor systems that climbers are using today:
Specially designed tethers—such as the Metolius PAS, Blue Water Titan, and Sterling Chain Reactor—overcome a key weakness with daisy chains: the potential for improper clipping through loops. Still, most are made partly with Spectra or Dyneema (the Chain Reactor is 100 percent nylon), and none is intended to absorb much energy or withstand dynamic loading. During Rigging For Rescue’s drop tests, the PAS withstood a factor-1 fall with a 220-pound weight, but the resulting impact force was 19 kN. The potential for a factor-1 fall occurs when your waist is at the same height as the anchor and the system is completely slack.
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