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Natural and human-made electric and magnetic fields are,in fact,present everywhere in our environment. The Earth's natural static background electric field is approximately 120 to 150 volts per meter(V/m). Natural electric fields are also produced by the local build-up of electric charges in the atmosphere that are associated with thunderstorms. The Earth itself has a magnetic field that ranges from approximately 300 to 700 milligauss (mG),the field is a steady-state or static (zero hertz) magnetic field,but has similar characteristics to the magnetic fields emanating from human- made sources. Electric and magnetic fields created by humans include X-rays and magnetic resonance imaging (MRIs) machines,electric and magnetic passenger trains,electric cars,and cellular telephones. The general wiring and appliances located in a typical home can produce an average background magnetic field of 0.5 mG to 4 mG (EPA, 1992). Electric and magnetic fields arise from the voltage and the flow of electricity(current) through a conductor. The intensity of the electric field is related to the voltage of the line and the intensity of the magnetic field is related to the electric current. The electric field associated with high-voltage transmission lines "extend" from the energized conductors to other nearby objects whereas the magnetic field"surrounds" the conductor. Together,these fields are generally referred to electric and magnetic fields or EMF. A summary of electric and magnetic field properties is summarized in Table 8. Table 8: Summary of Electric and Magnetic Field Properties ' Electric Fields Magnetic Fields Electric fields arise from voltage. Magnetic fields arise from current flows. Their strength is measured in kilovolts per meter Their strength is measured in milligauss(mG)or microtesla (kV/m). An electric field can be present even when a device is Magnetic fields exist as soon as a device is switched on and switched off. current flows. Field strength decreases with distance from the Field strength decreases with distance from the source. source. Most building materials shield electric fields to some Magnetic fields are not attenuated by most materials. extent. Source: WHO,1999 This section of the EA specifically addresses electric and magnetic fields produced through transmission of electric power at 60 Hz or cycles per second. Electric Fields ' Electrical fields are created by voltage. Voltage can be described as the potential difference between two points and will always try to drive an electric current. The voltage on any conductor produces an electric field that extends from the wire in all directions. The intensity of electric fields is Environmental Assessment PUC Docket E002/TL-11-223 Page 30