Two Carabiners Break on Leaning Tower

At about noon on April 28, 2013, Shern Kier and Anthony Ho, both Bay Area climbers, began the seventh pitch of the West Face on Yosemite’s Leaning Tower. Ho took the lead, clipped a bolt and placed two nuts and a cam, equipping all of the pieces with “trad draws,” tripled shoulder-length slings that he extended.

Approximately 30 feet above the belay he placed a nut. As he eased onto his aider, the nut blew and Ho plunged 60 feet. All four pieces had failed. The cam and nut pulled. The two rope-end carabiners (on the first nut and the bolt) were gone. Later, climbers approaching the tower found one of the missing carabiners, which was broken at the top of its major axis (spine). The second carabiner was not found. Presumably it, too, broke. Both Ho and Kier suffered scrapes and bruises, but were otherwise OK.

Analysis

>Carabiners are strong, with most testing to roughly 4,500 pounds. This rated strength only applies when the carabiner is weighted with a closed gate.

If a carabiner is loaded with an open gate, all bets are off. According to Kolin Powick, Black Diamond’s Director of Global Quality, an open-gate carabiner can fail at 1,500 pounds, a force easily generated in short, high-impact falls. If the carabiner is loaded with its gate open and off its major axis, it’s even weaker. Powick (who has tested hundreds of carabiners in various scenarios) blogged that an open-gate, off-axis-loaded carabiner can fail at just 550 pounds, a force exceeded in most common climbing falls. In this accident, the break high on the major axis is consistent with an open-gate failure—but how could two carabiners in a row fail?

Here are five possible scenarios to explain the double failure. 1) Defective gear: Unlikely because the manufacturer (Mammut) uses stringent testing protocol including CE certification and 3 Sigma rating. The company also pulled the records on the seven-year-old batch and found no other failures. 2) Sticky gates: Sometimes the gates on older carabiners stick open because they get dirty or the springs fatigue. Yet Kier reported that his carabiners were still in good working order. 3) Gate flutter: Gate flutter happens when the rope passes through a carabiner at high speed and creates vibrations that judder the gate open and closed. This phenomenon has been observed using a slow-motion video camera, but is reportedly difficult to duplicate. 4) Whiplash: When a carabiner is suddenly loaded or smacks against an object (like the wall), the abrupt deceleration can open the gate. In this case, the wall was overhanging and the draws hung free. The double failure makes whiplash an unlikely sole cause for this accident.

5) Looped carabiner: It’s quite common when extending a “trad draw” for an extra wrap of sling to remain looped around the carabiner. If the climber continues without clearing this loop, it can slip and seat against the gate or nose of the biner. Under force, this loop could unclip the carabiner, or produce an off-axis and open-gate loading, the worst possible scenario.

Of course, it’s impossible to know exactly how two carabiners in a row broke. Likely it was a combination of the above examples … and a big dose of bad luck.

Prevention

>What makes this accident chilling is the fact that Ho and Kier really didn’t do anything wrong. Nevertheless, here are a few tips for preventing open-gate failure.

1) Retire any carabiners with sticky gates.

2) Use wire-gate rope-end carabiners. The lighter gate is less prone to whiplash and gate flutter.

3) When extending trad draws, remove any loops that develop.

4) Rack your long slings fully extended and fix the lower carabiners to prevent crossloading.

5) Use locking carabiners on critical pieces.

This article was published as an Accident Report in Rock and Ice No. 212