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What Is Wrong
With Flexible Lifeline Style Fall Arrest Systems?
With flexible lifelines (also known as "safety cables"), secondary
falls are a serious concern A wire rope under load has an elastic
memory very similar to a bungee cord or a rubber band. All safety
cables, regardless of manufacturer (including ours!), "bounce" the
fall victim during a fall arrest, an effect known as a "Secondary
Fall". Studies of injury reports conducted by professionals have
proven that secondary falls may prove more damaging to a fall victim
that the initial fall arrest.
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Support Structures
for Safety Cable Fall Protection Systems must be
very strong to withstand the side loads required
by a fall arrest.
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To minimize cable deflection
and spring-back during fall arrests, safety cable systems
cannot safely span long distances without using several
intermediate attachments. One of our competitors actually
spans 200 feet between poles without any intermediate supports!
At FPS, we think this is totally irresponsible and very
dangerous!
Safety Cable type fall arrest systems
typically allow a falling worker to drop several feet before
his fall is totally arrested, creating a much higher likelihood
that the fall arrest victim will strike an impact hazard
below. For example, "slips and trips" on a cable system
are quite likely to cause a worker to strike his knees on
the walking surface he is traversing.
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All safety cable systems, regardless of manufacturer,
have a common generic problem with intermediate supports.
Intermediate attachments must support the cable to minimize fall
arrest deflection, however, the cable trolley must be able to pass
intermediate attachments without losing its hold on the cable. To
prevent excessive drag resistance on a walking worker’s harness
attachment, safety cable trolleys must pass smoothly over the intermediate
connections without hanging up on the attachment brackets.
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Although some cable systems are designed
to much higher standards than others, users of even the
most popular safety cable systems, including ours, complain
that their cable trolleys can get temporarily hung up as
they pull the trolley by the intermediate attachments. When
demonstrating the efficiency of a safety cable system trolley
crossing over an intermediate connection, it is essential
to run a real test that simulates the working conditions
anticipated for the system. To prevent the "slight of hand
demo" technique that makes these systems appear to be more
efficient than they are, we recommend that this test be
conducted under "real use" conditions:
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These installers are mounting a typical "Intermediate
Attachment Bracket" on a Horizontal Support Arm
for one of our Safety Cable Systems. The braided
stainless steel wire rope is typical of those used
throughout the industry.
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Use all of the exact same components
that will be included in the system (trolley, self-retracting
lifeline, carabiner, harness).
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Run the test with the self-retracting
lifeline extended from the approximate height at which
the system will be located when the user is working
with the system.
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Run the test under the same conditions
the system will see in service. For example, will the
user be bending over, or walking toward either side
of the protected vehicle as he passes the intermediate
connections, etc.
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Observe the droop in the cable between
columns.
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Observe carefully how the system
operates.
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Ask for several local references,
and go out and talk to the people who use these systems
every day.
Hang-ups cause the user’s self-retracting
lifeline to temporarily feed out additional slack as the
trolley is pulled past the resistance caused by the intermediate
attachment. If the worker is walking too fast, the lifeline
may be fooled into sensing a fall and may activate the brake
mechanism, potentially pulling the worker over backward.
This is a serious problem with virtually all safety cable
systems with intermediate attachments, and documented falls
have been caused by this problem.
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To minimize the effect of constant stress loading
on the safety cable, as well as to the structure to which it is
attached, most safety cable systems are installed with only 1200
lbs. of tension on the cables. Therefore, the cable will eventually
"droop" as the cable stretches over time. Shock absorbers may be
added to help minimize cable deflection, although their use delivers
minimal improvement at best. To minimize droop and traversing problems
past the intermediate connections, lanyards or lightweight self-retracting
lifelines (SRL’s), are used with most safety cable systems, since
heavier self-retracting lifeline systems tend to hang up on the
intermediate connections while traversing the system. Furthermore,
because there is no brake in the cable trolley system, when a worker
falls anywhere but in the center of the span between the overhead
cable attachments, he is likely to coast down hill toward the center
of equilibrium of the span between supporting attachments.
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Consider
The Advantages!
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(Click to enlarge.)
Cable Systems allow longer falls, dangerous secondary falls
(bounces) which can lead to potential injuries. |
(Click to enlarge.)
Our Trolley Beam System arrests falls in the shortest distance
possible with no secondary falls. Result: Eliminates injuries. |
Falls with safety cable systems always introduce
significant horizontal load stress on a building structure. Most
buildings are not designed to absorb such a severe horizontal load.
Unless the system is properly engineered, your building structure
may suffer costly structural damage due to the horizontal stresses
introduced by a fall arrest with a safety cable system.
 Regardless
of the manufacturer, all professionally engineered safety cable
systems must be quarantined after a fall is arrested, and a thorough
recertification inspection must be conducted by a competent person
before the system may be used again.
Falls are not covered under most manufacturer’s
warranties. After a fall, virtually every professionally engineered
safety cable system, including ours, must be taken out of service
temporarily until it has been repaired and recertified by a competent
person. Most safety cable system manufacturers' repair procedures
require temporary dismantling of the system while a factory-trained
professional replaces the costly damaged parts.
The apparent major advantage of safety cables
is lower initial cost, until you do a little research into our rigid
trolley rail systems, which address every one of these issues with
a logical solution!
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