Electric and Magnetic Fields (EMF)
Environmental Issues
Electric and magnetic fields exist everywhere.
The generation, delivery, and use of electricity produce electric
and magnetic fields (EMF). Electric fields are produced by
voltage, the electrical “pressure” that causes current to flow in
a wire or cable; magnetic fields are produced by current, the
movement of electric charge. Electric and magnetic fields can
be imagined as invisible lines of force that weaken with
increasing distance from their source.
Electric and magnetic fields also occur naturally. An electric
field is present between the earth and the upper atmosphere;
this field can increase and discharge as lightning during
thunderstorms. The earth has a magnetic field that is the basis
for the magnetic compass. Because these natural fields
generally change little from one moment to the next, they are
referred to as static fields.
In the electric power system, voltage and current oscillate at a
frequency of 60 hertz, or 60 cycles per second, in the United
States and 50 hertz in Europe (the power frequency). Similarly,
the electric and magnetic fields created by the power system
oscillate at the power frequency. When people are exposed to
these electric and magnetic fields, imperceptible electric
currents are produced in their bodies. Although these currents
are weaker than those that result from natural electrical activity
in the heart and nervous system, scientists have investigated
whether they produce biological or health effects.
Possible health effects from exposure to EMF
have been studied for more than 30 years.
Questions about potential health risks from exposure to EMF
first arose in the 1960s and 1970s with the introduction of
higher voltages for electricity transmission in the United
States. During that period, research focused on electric fields
because near and beneath high-voltage transmission lines
they produce more current in the body than magnetic fields
do. Overall, studies of electric fields