are related by the velocity of light, c, as λ = c/f. The full range of frequencies (or wavelengths) of natural and anthropogenic electromagnetic fields is described as the electromagnetic "spectrum." The electromagnetic spectrum, described in detail in textbooks on radiation, ranges from extremely low frequencies (ELF),3 which are associated with common household electric current (50-60 Hz),4 to radio waves (106-1010 Hz), microwaves (1010-1012 Hz), infrared radiation (1012-1014 Hz), visible light (1014 Hz), ultraviolet radiation (1015 Hz), and very high frequencies and very short wavelengths of X-rays and gamma rays (> 1017 Hz). In this list, which represents a hierarchy of increasing electromagnetic (or photon) energy, only the radiation with frequencies greater than about 1015 Hz is capable of ionizing atoms and molecules (i.e., producing charged particles from the atoms and molecules with which it interacts). Ionizing radiation (e.g., X-rays and gamma rays) is a well-understood source of damage to biologic systems through the reactions of the products of ionization with critical cellular components. ELF radiation, on the other hand, is nonionizing; it does not have sufficient quantal (photon) energy to produce ionization in the manner of high-frequency radiation, and its mode of interaction, if any, with molecules and biologic systems at low field strengths is speculative. Most equipment used for the generation, transmission, and distribution of electric power in the United States generates ELF (60-Hz) electric and magnetic fields. The components of the electric utility system that generate such fields include power plants (generating stations), which produce the electricity; high-voltage transmissions lines, which carry the electricity to major population centers; substations and their transformers, which reduce the voltage to levels suitable for distribution within a population center; distribution lines (distribution primaries), which commonly carry power along residential streets; distribution transformers, which reduce the voltage to amounts suitable for use in homes; and distribution secondaries (service drops), which carry electricity to individual residences. Transmission and distribution lines are commonly called "power lines," but the term can also include service drops.

Electric power that is used to operate devices in the home and workplace is also associated with the production of electric and magnetic fields. As electric charges move to produce a current, magnetic fields are created. An electric appliance connected to a source of electricity might have an electric field present even when it is turned off. When turned on and operating, a magnetic field is also present.

The exposures of interest in this report are limited to ELF electric fields (expressed in volts per meter) and magnetic fields (expressed in tesla (T) or gauss (G), where 1 T = 104 G) associated with household use of electricity. Because

3  

 The extremely-low-frequency designation is generally reserved for frequencies that range from 3 Hz to 3 kHz.

4  

 Electric power in the United States is produced at 60 Hz, whereas power in Europe and other countries is generally produced at 50 Hz.



The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement