There's
a lot of
inaccurate beliefs in the climbing
world. Is hardware
ruined after dropping it? Will a clove hitch slip?
Will the Euro Death Knot invert during a rappel?
How often do you accept what you
hear
without checking to see if the source is reliable?
This
page is dedicated to getting things straight. Most
of what
you'll read there is based on actual pull tests conducted by myself and
Jeff Fassett.
In other cases, we've directly contacted individuals who have
conducted controlled tests themselves.
How am I qualified to bust these myths?
Judge for
yourself. A lot of the time I've done research on
what seasoned, intelligent climbers have tested themselves.
As
for my
credentials: I'm an AMGA Certified Rock Instructor, I have
multiple degrees involving
research, thousands of days in the field, a really good head
on my shoulders, and lots of training from recognized experts.
Keep in mind a few things:
I've edited most of the anecdotes to keep
them succinct.
It's only necessary here to present the facts, not
lengthy periodical-like papers. But don't
assume that
hasn't crossed my
mind.
If you're questioning what you read below, good.
That's the point. Think critically
and test things yourself in a safe
environment.
Nothing is better for
building your confidence than your own experience.
If you'd like, submit your questions/suggestions/myths via
email by clicking
the contact link above. We'll see if we can test it out for
you.
For some of the testing I have built a station at my home.
It's 12 feet long and has three chains on each side secured
under
9 inches of concrete. I use an industrial dynamometer to
measure
the loads produced by a cable puller.
Myth 1: Carabiners are fragile
Myth: "Carabiners are susceptible to
hair-line fractures if they are dropped. These fractures cannot be seen
by the naked eye, but can drastically weaken a carabiner. So NEVER DROP
YOUR CARABINER. If you do, it is best to discard it immediately and
replace it with a new one." (source:
http://www.cbcnsw.org.au/docs/AbseilGuidelines.pdf)
Reality: This is not true of modern
carabiners. First, the "grain" of the aluminum runs parallel
to the
stock, not perpendicular, so undetectable hairline fractures
spontaneously causing carabiner failure just isn't true. Steve Nagode,
a quality assurance engineer with REI, conducted an experiment in which
carabiners were dropped six times from a distance of 10 meters onto a
concrete floor. The breaking strength of the carabiners was
then
determined with a 50-kN load cell. The results: no reduction in strength was
observed when comparing the dropped carabiners with carabiners that had
not been dropped.
Black Diamond's website says this: "It's best
to
inspect dropped gear for dings and significant trauma. If only light
scratching is visible and gate action is still good, there is a good
chance it is fit for usage."
Here's a more colorful test, this time done with a Petzl
Reverso: I call this "Reverso VS .357
Magnum". Shooting a small object with a snubnose .357 from a
safe
distance
is tricky, but yields thrilling results. This
is akin to throwing the Reverso into a rock surface at 67m/s,
which would
require dropping it 240m (790 feet).
And these calculations omit air resistance,
which limits the
terminal velocity of the Reverso free-falling to around 35m/s (the
terminal velocity of a baseball). In actuality, the piece of
gear
would not reach 68m/s even falling this far. The Reverso bent
various
ways, but it took 5 direct hits before it actually broke.
This seems to indicate that a single, short drop for a piece
of hardware does little to no damage.
Myth 2: Nonlockers and Reversos mix
On two recent occasions, I arrived at
belay stances and found that I was being belayed with a Reverso
directly off the anchor, but with a NON-locking carabiner on
the ropes. (see the photo below).
Reality: While the chances of the rope coming
unclipped
are low, I strongly discourage this practice. Any time a person's life is
dependant upon one carabiner, it's best to use a locking carabiner.
This includes rappelling, tying in to an anchor, and use in
a plaquette device. Consider this carefully:
in the event that the rope is
unclipped, the belay will
fail.
In a critical application such as this, use of a locking
carabiner will further reduce the chance of the rope escaping the
device.
Note, too, that the instructions for the device (shown below)
illustrate use of a locking carabiner.
Myth 3: Dyneema is a good material for
friction hitches
(Submission from Bill Holman, Pittsburgh, PA) - "Geir, I
have heard a rumor that dyneema is bad to use for an autobloc,
as the strong thin material can cut through ropes. Myth? "
Reality:
The dyneema will not cut through
the rope if used as an autobloc. I have tried this out on
multiple occasions. There are two big concerns that I have
heard when
using
Dyneema (or any other spectra sling) for an autobloc:
1) The biggest concern is that Spectra produces much less
friction than
nylon. In "Comparative Testing of High Strength Cord" by Tom
Moyer, Paul Tusting, and Chris Harmston, the authors found that the
autobloc grip strength of Mountain Tools Ultratape (a nylon/spectra
blend) was about 1/5-1/10 as strong as cords with a nylon cover.
The thin dyneema slings I have tested since Bill asked this
question are quite slick; I found them slipping under body weight
when
wrapped 5-6 times around a new rope. A 5.5 mm nylon cord
under the same conditions gripped very well. For this reason, it's
probably best NOT to use dyneema for an autobloc.
2) The second concern I have heard is the possiblity of melting the
Spectra. The melting point of spectra (297 F) is
significantly
lower than the
melting point of Nylon-6 (Perlon) at 428 F. Spectra rapidly
loses
strength above 257 degrees Farenheight. So there's a greater
chance of weakening your spectra slings for subsequent use if you use
it
for an autobloc. The question is, however, how hot does it
get under an autobloc sliding along a rope? Well, I checked
this
out, too. Using a meat
thermometer
I found that the temperature under an autobloc on a single-rope rappel
of about 100 feet does not go above 120 degrees F. So melting
does not appear to be an issue.
Based on these initial findings, however, it's probably best NOT to use
dyneema
for an autobloc.
Myth 4: You can make a clove hitch slip when
tied in with it
Many climbers use a clove hitch to tie in to the anchor during
multipitch climbs. One myth about the clove hitch is that a
climber can cause it to slip when tied in, and that both
strands
need to be loaded
for the
knot to be stable.
Myth: "Used as a traditional hitch, that is loading only one
end, the clove
hitch is liable to slip. It requires a load in each direction in order
to be effective, such as when being used as a crossing knot." (source:
http://en.wikipedia.org/wiki/Clove_hitch)
Myth: "The drawback of the clove hitch is that it can slip,
creep up the
carabiner, and open its gate ... if allowed to go unsupervised, the
knot is extremely dangerous." (source:
http://books.google.com/books?id=3Ohpsz6jP8cC&pg=PA40&lpg=PA40&dq
=clove+hitch+slip&source=web&ots=BbHlLZzmL3&sig=RgHr8P8uLxxksAyZ6dDu-o2-g7s)
Reality:
The clove hitch does not slip under body weight.
Jeff
Fassett and I pull tested a clove
hitch
tied around a carabiner with a heavily-used 9.6mm rope. After
tieing it on a carabiner, we tightened it by pulling it
to 1150
pounds.
Tightening the knot required one end of the clove hitch to be
pulled out about 5 inches. (Tape was used to mark the
starting
point on the load strand). The clove was then pull
tested to
failure. No
slip occurred as it was pulled to higher loads.
Ultimately, even when pulled to failure, the clove hitch did
not
allow rope to slide through. The rope broke at the clove
hitch at
2700 pounds.
"Before" photo: note that a piece of tape marks the load
strand prior to pull testing
Here is the video of the pull test:
"During" photo: note that 5" of rope crept through as the
clove
hitch was fully tightened down. The photo below was taken
after
the clove was pulled to 1150 pounds. No slip occurred when the clove
hitch
was pulled beyond this load.
"After" photo: the clove hitch ultimately failed at 2700 pounds.
The mechanism of failure is a familiar one: the
rope is severed at its entry point into the knot.
Myth 5: The Euro Death Knot can roll during a
rappel
The Euro Death Knot (flat overhand) is gaining wide acceptance
among the climbing community as a means of joining ropes for
double-rope rappels. However, I still run into
climbers who
believe
that it's prone to rolling under rappel loads.
I've found only one documented case in which a climbing party
claimed that a flat overhand "untied itself" during a rappel
(9/12/1997, Guide's Wall, Grand Teton NP). In this
case, the party had rappelled multiple pitches with the EDK, but just
before the accident, a beginner in the party untied the EDK and
then "retied" it. The newly tied "knot" untied
itself during
the next rappel.
Countless
pull
tests and probably a million rappels since then have failed to
replicate what
happened. More than likely, the retied "knot" was not a flat
overhand.
Quite a few tests, however, have demonstrated that the flat overhand is
quite strong.
In 2000, Burton Moomaw, an AMGA Certified Rock
Instructor, pull tested
the flat overhand tied in two single dynamic lines. He found
that the knot inverted at 1400 pounds, then did nothing further as it
was subjected to higher loads. (Source: direct
communication)
In 2005, Jeff Fassett (also a Certified Rock
Instructor), completed an unusual and
humorous test on the flat
overhand. After using a flat overhand to tie a dynamic line
in a continuous loop, he dragged a 6,000 pound van with it.
The van was in park with the emergency break on!
Based on the vehicle weight and the friction of the tires, he
calcluated the load on the knot to be 1500 pounds. The knot
did not invert or slip.
He repeated the test using the flat overhand to join an 8.5mm
rope and a 10.5 mm rope. Again, the knot neither failed nor
inverted. (Source: direct communication)
Tom Moyer performed a series of tests on the
flat
overhand. He found that properly
tied and set flat overhands did not roll until loads
of 1400-2400 pounds were applied.
If the ropes were soaked and of significantly different
diameters, he found that the knot could initially invert at a
load
of 950 pounds. However, subsequent inversions
required
1070-1400 pound loads. (Source:
http://www.xmission.com/~tmoyer/testing/EDK.html)
It is
difficult to produce loads of even 600 pounds on a rappel.
Jeff Fassett and I measured the force produced on an anchor
during a double-rope rappel using a dynamometer. Not
surprisingly, during normal rappelling the force on the anchor was
simply body weight (in our measurements, 150 pounds). In this
case, the load on the flat overhand is 75 pounds. Even with
rigorous
5-foot deadfalls close to the anchor, e
anchor, we were unable to produce a load greater
than 600 pounds on the anchor. In this case, the load on the
flat overhand
is only 300 pounds. (These tests were conducted with
a
heavily-used 10.2 mm Beal dynamic line and a 150 pound person.)
Based on these measurements, the following conclusions can be drawn:
The
flat overhand is about
18 times stronger than it needs to be for rappelling when using two
single, dry ropes, and rappelling normally.
Very agressive rappelling may cut this margin down to
a 5-fold difference.
Under the worst of conditions tested (two soaking wet
ropes of different diameter), the flat overhand is
still 12 times stronger than the anticipated load on the anchor.
Very agressive rappelling may cut this margin down to
a 3-fold difference.
Even if the "roll load" of the knot is exceeded, it
would
take repeated, increasing loads to cause additional knot inversions.
Myth 6: It's a good idea to use daisy chains
for attaching to an anchor
Over years of climbing, we have seen thousands of
climbers using a daisy chain (or a similar "personal anchor system") to
clip into anchors on multipitch climbs.
A daisy chain is usually made from nylon and/or spectra and
is around four feet long.
Daisy chains have limited usefulness if you are not
planning
to aid climb. They are bulky and are a poor substitute for
attaching to the anchor with your ROPE using a clove hitch.
Why?
1) The rope's there anyway.
Use of a daisy chain adds unnecessary bulk to the
items you carry on
route.
2) The rope is much more adjustable.
A clove hitch can be adjusted seamlessly to any length, while
most daisy chains are limited to 44 inches. Imagine your
frustration at a "hanging" belay if there is a comfortable stance four
feet below you.
3) The rope is much more resistant to
being cut.
4) Shortening the daisy chain has its own inherent
risks:
5) The rope
is better able to absorb
shock loads than a daisy chain. Some people
argue that this is incorrect over a short length of rope. We
decided to test this to find out.
Jeff Fassett and I conducted a simple test using a dynamometer attached
to a bolted anchor. In the first part of the test, I attached
to
the anchor using a daisy chain so that i hung freely two feet below it.
With a backup rope in place, i pulled myself up a few inches
and
let go so that I fell statically on to the anchor. The force
on
the anchor was shocking - the dynamometer measured a peak force of 900
pounds on the first drop. I subsequently took slightly
further
falls, and found that the
force on the anchor was over 2,000 pounds when falling just one foot.
I stopped at this point simply due to pain.
Similar tests conducted at BlueWater found that a two foot fall (with a
test weight) caused a two-foot sling to completely fail. This
is
consistant with the simple data we obtained; in sum, it
is likely that falling two feet statically on to a daisy chain will
cause (at the minimum) a failure of that loop. If you
happened to
be clipped into the last loop, it will fail completely.
On a personal note, I can confirm that if you did not cause
the
daisy chain to fail, you would almost certainly sustain injury.
The story changes significantly if you are attached to the anchor with
a climbing rope and a clove hitch. Jeff and I repeated the
test:
this time, however, I was attached to the anchor with my
climbing
rope tied at two feet long (the same length of daisy chain used above).
I immediately noticed that short, static falls on the anchor
were
far less jolting, and the dynamometer confirmed my suspicions.
When falling one foot on the climbing rope, the force was
about
400 pounds. On subsequent, longer falls, we
found that even falling two feet (the full length of the rope I had
tied) the force on the anchor was only 1,000 pounds.
This indicates that a short length of climbing rope
is far
better at absorbing shock loads than an equal length of static daisy
chain.
Myth 7: GriGris are good for belays in a
traditional climbing setting
Use of a GriGri for traditional climbing makes it more likely that your
gear will fail during a fall.
The reason for this is the static nature of the device. With
a GriGri, a fall is stopped abruptly when compared to a plate
device such as an ATC. The reason for this is the very
limited
amount of slipping that occurs when a GriGri arrests a fall.
An
ATC, however, allows the rope to slip through the device during a fall,
braking more slowly. This is similar to stopping a car:
when pressing the brake slowly, the car stops gradually.
When pushing the brakes more, the car jolts to a stop.
A breif internet seach provided no numbers to back up this idea in
climbing, so Jeff and I headed out once again. After
climbing up 40 feet on a sport climb with a heavy, clunky industial
dynamometer strapped to my back, I took repeated 10-foot falls
and
measured the maximum force on the bolt with each fall. After
five
falls were caught on the GriGri and five falls were caught using an
ATC, we repeated the test, this time falling from a bolt closer to the
ground (20 feet).
In both cases, the force
exerted on the top piece was significantly higher when using a GriGri
than with an ATC. When the 10 foot falls were
arrested in the first test (falling from 40 feet), the average maximum force on the
bolt was 820 pounds with the GriGri
as opposed to 435 pounds with the ATC. With less rope out
(falling from 20 feet), the force exerted on the top piece was higher,
although interestingly, the difference between the two devices was
smaller: the
average for the GriGri was 1030 pounds while the average
for the ATC was 900 pounds.
The significance of this for traditional climbing is that use of the
GriGri resulted in a higher force when arresting a fall. In
traditional climbing, the gear used is much weaker than a correctly
placed bolt. Moreover, the strength of a traditional
placement
also depends on the nature of the rock it is in, the shape of the
feature the climber is trying to protect, the type of gear that is
placed in the feature, and a host of subtleties that are dependant on
the skill and experience of the leader. So while a traditional placement
may be as strong as the gear is rated
(generally 5 to 16 kN, or more simply put 1100-3600 pounds), in
practice
most placements are weaker.
The small difference between the lower end of the gear's strength range
and the forces we measured make it clear that there is a narrow margin
between what the gear can sustain and the forces that will be placed on
if a fall occurs. Using a GriGri for a belay significantly
narrows this margin because of its design. For this reason, a
device which allows the rope to slip more easily through the device
(such as an ATC) is a safer choice for traditional climbing.
