[TowerTalk] Climbing belts/harnesses demonstration
K8RI on Tower talk
k8ri-tower at charter.net
Thu Jun 15 02:42:43 EDT 2006
> This past weekend at HamCom in Plano Texas; a representative of Pinkerton
> Sales; a manufacturing rep company for "Ultra-Safe", a climbing belt
> ("fall-arrest") company, gave an excellent demo outside of the convention
> hall on their demo-trailer. He would winch up a 220# weight and demo
> different situations. The message was that different lanyards ( position
> fall-arrest, whichever) exert dramatic differences in force to the user
> a fall occurs.
> As I recall (+/-)and briefly:
> 1. Six foot conventional lanyard: 2500# (ouch!)
At 2500# you are looking at a bit over 11 Gs and that is going to hurt even
with the best fall arresting equipment.
> 2. Six foot lanyard w/ sewn fold-out layers (shock absorbing): 700# (still
Not really. That's only a tad over 3 Gs which might make a person go
"Oofffffhhh". Even at my age I can tollerate a sustained 4 Gs relaxed. 4Gs
does not hurt and for that matter neither does 6. However it does make a
difference if that force is applied on a 2" wide belt or a full body
harness. It also makes a difference if you don't have the harness uniformly
snug and land upright with just the leg straps tight which could alter the
pitch of your voice. It doesn't matter how quick the G's are applied as G
is already an acelleration. The big difference is how quick you slow down
(applied G forces) as well as how uniformly the pressure is applied to the
These numbers are impressive and I believe they exist, (I know they exist)
but I'd ask how they are measured.
What you need are two figures. The instantaneous force in Gs as well as the
integrated, or total force. It's a whale of a lot easier to measure using
metric units though.
If you calculate the speed of the object based on the distance dropped you
can calculate the energy although the energy is slugs when using foot
pounds. Usually getting to the foot pounds is good enough, but effects on
the body are usually computed using G forces. Compare that energy to that
measured and you know how quickly the object is stopping and how much
distance it took to stop. Unfortunately that is not an effective number for
determining comfort, damage, or lack there of.
When you drop a weight, it depends on the distance it takes to stop that
weight so it makes a big difference whether a spring scale, or solid state
transducer is used to measure that force. Even then the time constant of the
measurement device needs to be taken into consideration. The old joke about
it isn't the fall that kills you, but the sudden stop at the end really
isn't a joke. The human body can withstand some suprising forces, but you
eventually reach a point where things inside start coming loose even with no
damage on the outside. Again it depends on the angle. Colonel John Stapp
survived over 45 Gs in the Airforce rocket sled experiments. OTOH that is
far more than you'd want to try applied to the long axis of the body even
sitting down. I never figured it out, but I stopped in about 4 or 5 feet
from 55 MPH.
The effect on the human body depends on many things up to a point. Of course
the magnitude is first, but almost as important is how much of the body is
subjected to that force and at what angle. THAT is one of the reasons why a
full body harness *CAN* be so much more effective than a narrow climbing
belt. Even a short fall can be bad if your gear whips you end for end and
beats your head against the tower. (Think of where your center of gravity
is located when using a hook on a climbing belt) Early linemen learned that
the wide 5 and 6 inch belts were far better than a single 2". I've climbed
a good many poles with a 2" leather climbing belt and climbers. I hasten to
add that was a long time and many splinters ago.
Another factor is that angle at which the stopping force is applied. That is
why the position of the D-Ring attach point is important. BUT and I
emphasize the "BUT" you are now playing the odds. The D-Ring is attached at
the point where it is "most likely" to do the most good. Depending on the
situation the best point may be either the front or the back. A good bit of
that depends on the design of the fall arrest gear and how it ataches to the
> 3. Six foot lanyard, now get this, WITH A KNOT IN IT: "0" force; it broke
> instantly! (Big ouch!)
It depends on the knot, but half and full, hard knots are quite capable of
reducing the strength of the rope to a fraction of its original breaking
strength. Even good knots reduce the strength, but I believe the so called
"hard knot" reduces it the most.
> At least on two of the ouch's, the user survived.
> He demonstrated, basically, two types of climbing harnesses:
> 1. Conventional, as we know, nylon straps.
> 2. A nylon harness, but the straps have some very slight stretch to them.
> liked that harness.
I don't like Nylon for one reason only. That is its suseptibility to
environmental deteoriation. It's sensitive to UV, Ozone, and many ordinary
Nylon is fine if it is replaced regularly, or properly tested. As I recall
from many years ago we used to be able to have the belts recertified. Where
I worked we just replaced them with new ones every year and cut up the old
> He added that any and all harnesses must be tightened "firmly"; not loose
> and, of course, not uncomfortably too-tight. Any extreme slack or
> can be harmful to ones health in the event of a fall.
When flying aerobatics if the belt or harness is loose enough to slide, or
rater *work* your hand, or even a finger under it, we figure it isn't tight
enough and yes, that is uncomfortable IOW if the 5 point harness isn't
uncomfortable it isn't tight enough<:-)) It's also a lot tighter than we'd
use for a climbing harness. OTOH we aren't trying to keep our butt down in
the seat while pulling 4 or 5 negative Gs.
> He also mentioned that always someone should be present while the climber
> working in the tower and have a plan in the event of a fall. He cautioned
> that even with the best fall-arrest full body harness, it is very
> to let the climber hang very long in the harness as the force of the leg
> straps in the groin area can shut-off blood circulation. It has been
> He demo'd one little gadget, like a reeled-up harness, that you hook ahead
> of your climb that catch's you immediately; with no drop at all; much, I
> think, as a vehicle safety belt does. Gradual movement around the tower
> climbing does not set it off; but a "instant thrust" (my words) does;
> much like a vehicle safety belt.
> He said that OSHA does not approve climbing gear; but does dis-approve
> climbing gear.
> As a climber of my own and others towers; it sure got me to thinking. If
> ever have the opportunity to view one of these demonstrations; I highly
> recommend it. Especially for those of us that need to be re-educated from
> using the old conventional belt-only climbing belt. Sure it worked and
> worked good; but it is full of weaknesses.
The weakest like is still the same though. The one wearing and using the
Roger Halstead (K8RI and ARRL 40 year Life Member)
N833R - World's oldest Debonair CD-2
> Mike, K5UO
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