www.arborage.com Arbor Age / September 2014 19
All images provided by Unitil Corporation
value change from ring to ring that can occur when someone
takes a step on energized ground (see page 20). Once a worker
has his or her feet in two different voltage zones, he or she is
facing a "step potential hazard" and can receive a powerful or
deadly electric shock as the body becomes the path of least re-
sistance for the fl ow of electricity. Voltage values that equal one
another (two feet next to each other on the same "ring") are
of the same potential and put a worker in the same position as
a bird on the wire — safe. Workers near potentially energized
ground should always keep their feet at the same step potential
by hopping or shuffl ing to safety.
Assume every wire is energized
Just because a wire is down or sits innocently on the
ground, it does not mean it is safe. A downed wire is often still
energized, especially if the other end remains connected to the
source of power. Wires are not insulated like the cords attached
to lights, appliances, and other electric devices in our homes.
They may have a protective coating, but this will not protect
an object or person that comes in contact with the wire.
Workers can come in contact with electric lines through
direct or indirect contact. Direct contact means that the
worker's body touches the wires. Indirect contact is when a
conductive object (such as an uninsulated tool, rope, tree limb,
or branch) that is touching the wires then touches the worker.
In both cases, the worker becomes part of the electricity's path
to ground.
Avoid accidents
While no single practice or piece of safety equipment can
fully protect against an incident, tree workers can reduce their
risk of injury by taking several precautions on the job site.
First, workers should assess each site by looking for electric
wires. They can follow wires from a known location (such as
where they attach to a house) out to the road or sometimes to
where they disappear into foliage. It is important to identify
the path of the wire and keep it in mind when considering
the risks of working in a tree (including whether it is safe to
climb and work in).
Once in the tree or working aloft, a worker should always
Street after vegetation management: Distribution vegetation
management is systematic removal of vegetation growth and
damaged or defective limbs along distribution circuits, along
roadways and driveways.
Street before vegetation management: Trees growing near
power lines can be dangerous. Trees near power lines are
the single greatest cause of power outages on most electric
systems.
