Page 74 - Rappelling

Notes on Redundancy spacecraft all critical systems have backups when-
ever possible, and life support systems have two
By itself, redundancy does not guarantee safety— backups. NASA calculates that if the chances of a
you could be rappelling off a bunch of old weath- system failing are one in a thousand, then a backup
ered slings or a couple of old rusty chain links, on the same system (also with a one in a thousand
for example—but redundancy in anchor systems chance of failing) decreases the chances of failure to
is something to always strive for, a baseline and a one in a million.
starting point for evaluation. In rock climbing, a Is it safe to rappel off an anchor you’ve just built
nonredundant anchor is considered marginal. Many using two properly installed ⁄8-inch-diameter bolts
3
canyoneering enthusiasts argue that redundancy and a brand-new 1-inch nylon sling that you’ve
at the anchor system is superfluous, as there will properly tied with a water knot, equalized with a
be a point in the rappel system where redundancy magic X, and fitted with a brand-new CE-certified
can no longer be maintained—you rappel on only quick link? Sure. The strength of this anchor system
one rope, with one rappel device, on one locking far exceeds the load you’ll place on it, with a safety
carabiner. This is absolutely true, and it’s also true margin greater than 10:1. But not every anchor is
that climbing and rappelling equipment is manu- perfect. What about an anchor that has several slings
factured to strict standards, thoroughly tested, and of unknown vintage with a rusty old quick link to
certified to minimum specifications, with a built-in thread your rope through? This is where judgment
safety margin. After all, an airplane has only one tail and your ability to assess an anchor’s components is
section, and if it structurally fails, the result is cata- critical.
strophic. In aviation and in climbing, the built-in Redundancy by itself is simply not enough of
safety margin allows use of nonredundant equip- a guideline to ensure a safe anchor, but it’s a good
ment in critical applications. starting point. An anchor system with reliable com-
But in aviation, like climbing, critical systems ponents and redundancy is what I strive for. I’ll bet
have backups whenever practical. We don’t rappel against one in a million odds anytime.
off a single bolt anchor, even though it’s twenty-five
times stronger than the load we’re placing on it. In

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