belaying off harness/belay loop clarification
Clyde Soles
NNTP-Posting-Host: blkdia.bdel.com on 5/12/95, Chris Harmston <chr...@bdel.com>
wrote:
> Due to the recent splattering of comments from various people regarding
> the use (or not) of a belay loop I have asked Black Diamond Harness
> Designer Tom Jones to write this summary/history of belay loops.
It's worth noting that before he jumped ship, Tom started a company some of you
may have heard of: JRAT -- Jones Radical Applied Technology (at least that's one
version I've heard of the acronym)
Chris Harmston
the use (or not) of a belay loop I have asked Black Diamond Harness
that his comments answer most all questions I have seen to date. If any
of you have specific questions about this or specific test data you want
to see then e-mail me and I will try to answer them for you.
From a design and Quality (read liability) standpoint, we design our
harnesses to exceed the CEN (prEN 136.005.02) standards for harnesses.
This standard states that the harness tie in should hold at least 15 kN
(3372 lbs) over a period of time without damage. The ultimate strength of
the belay loop on NEW Black Diamond harnesses on average 22.1 kN (4983
lbs). When we apply the usual 3 sigma rating (i.e. average minus 3
standard deviations) the rating is 18.6 kN (4182). That is to say the
belay loop is 1.24 times stronger than the specified CEN strength (99.87%
confidence). Now please note, I said this was for new harnesses. We have
seen used BD harness belay loops break near 3000 lbs. With more wear
they will be even weaker. You should retire your harness when it has
excessive wear. Chris.
From Tom Jones:
Here is the spew for your review and posting.
Spew on Harness Belay Loops
There has been a lot of chat recently about the use and limitations of
harness belay loops. I would like to lay out the thoughts behind and uses
for belay loops as we have found through use and testing.
History
Belay loops were invented about 10 years ago to solve the problem of
having no obvious place to clip into a harness for belaying and
rappelling. Some bright guy thought of making a stout webbing runner,
that the structural parts of the harness would pass through, that
would then stick out in front and be easy to use. The idea caught on
because many people found it convenient. Some harnesses do not allow for
the use of a belay loop due to geometric constraints.
Design Constraints
A harness is designed to catch falls either as the faller or as the
belayer. The maximum loads felt by a faller are suspected to be at most
15 kN ( 3372 lbs ). This is the load at which other parts of the
system start breaking, such as the rope at the tie in knot, the top biner
through the protection, and the faller's body being broken by the forces
of de-acceleration. Thankfully, very few falls reach forces anywhere
near this high, but we can view it as an upper limit.
Can this force be felt by a belayer too ? You bet. The worst
case fall is where the leader does not get any pieces in, then pitches
off and falls directly on the belay. Climbers are usually smart enough
to clip the lead rope into a draw on the anchors, so that the belayer
experiences an upward force, but this is not always the case. The leader
could fall directly on the belayer with no intervening pieces so the
belay loop system must be able to hold that 3372 lbs of force.
This brings up why it is important to clip your belay device into
both your belay loop and the loop of the rope on multi pitch climbs. The
lead rope should be your primary anchor - your primary link from your
harness to the anchor - because it is dynamic and flexible. Your belay
biner should connect directly to the rope tie in loop so that the forces
of the belay can link directly to the anchor. Otherwise, the forces from
a severe fall would run from your belay biner to the belay loop,
to the harness, to the rope loop to the anchor. This would tend to rip
the harness apart and the results are very unpredictable. It is much
better to have the forces transfer as directly as possible to the strong
point in the system - your fully equalized, three bomber pieces anchor.
Wear and Tear
So if the belay loop is so strong, why don't I tie into it?
Because you would wear it out very fast. The established tie in points
on harnesses are usually covered with a durable cloth or webbing to take
the brunt of the abrasion from the rope being tied in. Falls, hanging
and hangdogging tend to move the rope slightly, under load, against the
harness, and this results in a lot of abrasive wear. If you subjected
the belay loop to this wear, it's unprotected webbing would wear out
pretty quickly.
In belaying, the situation is a little different. The belay
biner has a lot less friction so it slides to the top of the loop right
away. There is very little webbing on webbing sliding. Belay loops do
fuzz up a little from the forces of the biner, but not very fast. It
helps that belay forces are usually much less than falling forces.
No Belay Loop Harnesses
Many harnesses do not have a belay loop, usually because of
geometric constraints. Is it safe to belay off a carabiner clipped
through both the waistbelt and leg loop?
On first look, you might think this is a classic
case of triaxial loading of a carabiner - a definite no-no. At some modest
load, however, the belayer's body will change position and the harness
webbing will stretch so that the bottom of the belay carabiner gets
loaded correctly. The load required to do this is pretty low, probably
lower than the 6 kN side loading strength of a weak 'biner.
The greater danger is that the carabiner will get stuck on
something or that the gate will get stuck open by webbing or a piece of
clothing. We have all experienced the locking sleeve getting stuck on
something while belaying, and this could be dangerous. I got my finger
pinched once when I was straightening out my belay biner at the point of
impact. Ouch!
I have seen returns from where the locking belay biner was not
fully closed when loaded. I think they got stuck in the climber's
clothing, but the climber insists that the gate was closed and locked.
Maybe the first instance of a gate pin tunneling out the end of the biner.
Without a belay loop, it is VERY IMPORTANT to have the belay
forces transfer directly to the anchor, on a multi-pitch climb. I usually
belay off my tie in loop, essentially using that as a belay loop.
Summary
The belay loop is designed for rappelling and belaying only. Use it
if you find it convenient. If you tie the rope directly into it, you
will wear it out very quickly. On multi-pitch climbs, it is important
to have the forces of the belay link directly through to the anchor,
usually by clipping the belay biner into both the belay loop and the tie
in loop of the webbing.
Understanding the forces involved in climbing is helpful in climbing
safely. Understanding the limitations of your gear is essential.
Tom Jones (t...@bdel.com)
Black Diamond Equipment Ltd.
2084 East 3900 South, SLC, UT 84124 phone: 801-278-5552
DISCLAIMER: Unless otherwise indicated, this correspondence is personal
opinion and NOT an official statement of Black Diamond Equipment Ltd.
Chris Harmston (chr...@bdel.com)
Black Diamond Equipment Ltd.
2084 East 3900 South, SLC, UT 84124 phone: 801-278-5552
DISCLAIMER: Unless otherwise indicated, this correspondence is personal
opinion and NOT an official statement of Black Diamond Equipment Ltd.
This is official. Chris