Environmental Engineering Reference
In-Depth Information
wildlife habitat can mitigate visual impacts of transmission lines. Aesthetics are to a great
extent based on individual perceptions. Siting, design, construction materials, and right-of-
way management can mitigate some adverse aesthetic effects of a line, but perhaps not others
(PSC Wisconsin 2011).
Electromagnetic Fields
Health concerns over exposure to electric and magnetic fields (EMF) are often raised when a
new transmission line is proposed. Exposure to electric and magnetic fields caused by transmis-
sion lines has been studied since the late 1970s. These fields occur whenever electricity is used.
A magnetic field is created when electric current flows through any device, including the electric
wiring in a home. Every day we are exposed to many small sources of EMF from vacuum cleaners,
microwaves, computers, and fluorescent lights. Research to date has uncovered only weak and
inconsistent associations between exposures and human health. Magnetic fields can be measured
with a gauss meter. The magnitude of the magnetic field is related to current flow, not line volt-
age. A 69 kV line can have a higher magnetic field than a 345 kV line. Magnetic fields quickly
dissipate with distance from transmission lines. A common method to reduce EMF is to bring
lines closer together. This causes the fields created by each of three conductors to interfere with
each other and produce a reduced total magnetic field. Consequently, magnetic fields generated by
double-circuit lines are less than those generated by single-circuit lines because they interact and
produce a lower total magnetic field. In addition, double circuit poles are often taller, resulting in
less of a magnetic field at ground level (PSC Wisconsin 2011).
Pacemakers and implantable cardioverter defibrillators (ICDs) have been associated with
problems arising from interference caused by EMF. This electromagnetic interference (EMI) can
cause inappropriate triggering of a device or inhibit a device from functioning properly. Sources
of EMI documented by medical personnel include radio-controlled model cars, car engines, digital
cellular phones, antitheft security systems, and high-voltage transmission lines (PSC Wisconsin
2011). ICD manufacturers' recommended thresholds for modulated magnetic fields are five to
ten times greater than the magnetic field likely to be produced by a high-voltage transmission
line. Research shows a wide range of responses for the threshold at which ICDs and pacemakers
responded to an external EMI source. The results for each unit depended on the make and model
of the device and the patient's height, build, and physical orientation with respect to the electric
field. Pacemaker and ICD patients are informed about potential problems associated with expo-
sure to EMI and must adjust their behavior accordingly. Avoiding sources of EMI is a standard
response; patients can shield themselves from EMI with a car, a building, or the enclosed cab of
a truck (PSC Wisconsin 2011).
In some areas of the United States, exposure of people to transmission lines is quite common.
Federal government approvals of right-of-ways for transmission lines across public lands often
comprised 35 percent of all permits required, in a study of twenty-four new electric generation
and transmission projects in the southwestern states. The average number of permits required per
project was thirty-two (Hamilton 1989; Hamilton and Wengert 1980, 74). This study was completed
before deregulation of the electric utility industry severed ownership of most generation facilities
from that of transmission facilities. It is unknown how many approvals may be required today
for construction of new transmission lines, which are now often built separately from generation
projects. Exposure to electromagnetic fields from electric transmission lines increases as new lines
are built. Securing transmission line right-of-ways remains a significant source of environmental
and dollar costs for transmission projects in the United States.
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