Tech Tips: Anchors Away

Published August 17, 2011 09:54AM

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.

A 2007 incident on the Grand Capucin near Chamonix, France, exemplifies the danger: A climber fell less than two feet onto the Dyneema sling attaching him to his anchor; the resulting impact broke the anchor sling, and the climber fell to his death. Ledges break, climbers slip—and the result can be dynamic loading of an anchor.

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.

These are aid climbers’ tools, used to link one’s harness to aiders or ascenders, but they’re commonly and improperly used as personal anchor tethers. Daisy chains should not be used as anchoring systems, for two important reasons. First, the best-case scenario for a climber dynamically loading a daisy chain is a perilously harsh impact that could break the daisy, rip the anchor, or injure the climber. Second, it is extremely easy to clip a daisy chain in such a way that you are clipped through loops that only are designed to hold body weight. Watch the Black Diamond video illustrating these points at climbing.com/print/techtips.

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.

If you use an anchor system, be aware of the risks and how to minimize them. Except for daisy chains, which were never designed to be used as personal anchors, tethers are safe, but only if they are never placed in a situation where dynamic loads could occur—the kind of load that could happen in the illustration at left. Keep the attachment weighted at all times! Even a short fall onto an anchor tether, especially if it is made of Spectra or Dyneema, can generate huge forces.

I have found that it is impractical to always keep the anchor weighted, and I now use the old-school Purcell, a prusik-based lanyard that offers excellent adjustability and energy-absorption potential, with just a bit more weight and bulk than daisies. The Purcell can be purchased (from Sterling Rope) or easily tied from 6mm nylon cord; see how in a video at climbing.com/print/techtips. The prusik knot will slip under high load, avoiding the extreme impact forces of falls on more static tethers. At any belay stance, you can always back up your tether with the tried-and-true method of tying into at least one anchor directly with the climbing rope.