Seems there have been several discussions on climbing lately, and since this
happens to be a subject that I have more then adequate experience in, I
thought I would share with everyone some of the same info we provide to our
technicians about the Rohn 25g/45g series towers and fall arrest.
First - Understanding the difference between fall protection and
positioning:
A fall protection/arrest system consists of the following:
A harness with a dorsal (center of back between shoulder blades) D-Ring, and
means of attachment that can limit the falling force to less than 1800lbs.
The human body can exert several thousand pounds during a fall arrest
situation. In order to protect the climber most fall arrest lanyards utilize
a dampener/shock pack to dissipate the fall force to less than 1800lbs. All
fall protection/arrest lanyards should be double legged/(Y) and be used to
maintain a 100% attachment to the tower at all times. They should NEVER
exceed 6' in length.
Positioning devices are used in conjunction with Fall arrest to create a
working position while on the tower. These are static lanyards and devices
that do no have shock packs. While in use, these devices should be
positioned so that a climber can not move more than 18" vertically. As a
rule of thumb, your primary connection to the tower should always be your
fall protection, and then your Positioning device.
Now the Numbers:
It is recommended that Fall Protection/Arrest lanyards be anchored to a
point on tower that can hold 5000 lbs. OSHA claims that the human body
should not be able to produce more than 5000lbs during a free fall arrest
with a 6' lanyard.
Positioning devices should be attached in fashion that can hold the weight
of the climber and rigging with a 10-1 safety factor. (300lbs climber - 3000
lbs attachment)
Here is the shocking sad truth:
Rohn 25g section shearing strength - 2500lbs (this is the strength of the
entire section, all three legs and lattice, not just that one leg you may be
attaching to.
So a Rohn 25g section could fail if a climber falls and the lanyard shock
pack does not activate, or the climber is using a lanyard without a shock
pack.
Sadly enough the Rohn 45g section is not that much stronger.
Solutions for the Climber:
First and foremost - Never attach to the Z lattice of these towers for any
reason.
Second - Try to use a 3' shock absorbing lanyard for fall protection. The
reasoning behind this goes back to the numbers. OSHA claims that the human
body should not be able to produce more than 5000lbs during a free fall
arrest with a 6' lanyard... so if we limit the fall distance by 1/2 (3'
instead of 6') the arresting force is also reduced by half. (2500lbs) The
shorter 3' lanyard also allows you to position the lanyard an arms length
overhead. By doing this the fall distance is greatly reduced, in many cases
(depending on body size) to less then 12-18 inches, thusly greatly reducing
the force to a safe limit for the 25g towers strength. Something to also
consider, when positioning your fall protection overhead, is the swing zone.
Should you fall with you lanyard positioned directly overhead (same tower
face), your dorsal D Ring will pull you forward and swing your upper body
and head into the tower. For those who do wear hardhats (as you should) this
should not be a big deal. If however you would like not to have this
problem, position your lanyard hook overhead and around to another face (to
your strong side) so that during a fall arrest situation, your shoulder will
roll onto the tower first and your lead arm either grab the tower or cover
your face and head.
Third- Never rely on one point of attachment for positioning. On the 25g
and 45g tower, it is recommended that the climber choke at least 2 legs with
a positioning lanyard, to create a solid point of attachment. Another
recommended procedure is to use two large hooks, one on each side, to
connect to two different points on the tower. This actually works very well
and is known as the "gunslinger method" since a climber can attach and
detach very quickly with this setup.
Working up top - Working on the very top of a 25G/45G tower can provide some
challenging issues, one of which is positioning. If your harness has a seat,
do yourself a favor and don't try to use it while at the very top. While
sitting in the saddle is comfortable, it does not provide enough upper body
leverage to position or stab a large antenna. Instead use the side D rings
so that your upper body and arms can be used freely above the tower. When
attached to the top of this tower, a fall arrest anchorage point also
becomes an issue. If your work could take some time, use a 4' long choker
sling to create an attachment point by wrapping it around and choking all
three legs independently. When used in conjunction with your 3' fall arrest
lanyard, this setup will create a suitable anchorage point. Also something
to consider, whenever possible, use a ginpole to help position and hold
large items over the top of the tower. While it is possible to stack a large
antenna or even another tower section without a gin pole, using a gin pole
makes it much easier and safer for the climber.
Richard Elizondo
Senior Consultant
Ionos Communications
361-887-6700
relizondo@ionoscom.com
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