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Very Low Frequency and Extremely Low Frequency

Various organizations divide electromagnetic waves into frequency bands or ranges. Frequency is expressed in terms of a unit called the hertz (Hz). One Hz equals one cycle per second. One kilohertz (kHz) equals one thousand cycles per second. The names of the frequency bands can cause confusion because different organizations may use the same band name for different frequency ranges. This site provides information on Very Low Frequency (VLF) and Extremely Low Frequency (ELF). For the purposes of this web site, ELF is defined as >0 Hz to 3 kHz, and VLF as from 3 kHz to roughly 300 kHz. Frequencies above this range are known as “radiofrequency” (RF). For information on RF waves, see the NC Radiation Protection RF page.

By far the most common and widespread source of ELF exposure is the electrical power grid, which operates at 60 Hz in the US and 50 Hz in most other countries. We are all exposed to electromagnetic fields from the earth itself and from human-made sources. Examples of human-made sources include power lines, household wiring, and electrical appliances. The Federal Communication Commission (FCC), in cooperation with other groups, allocates the electromagnetic spectrum for various applications. You can see a chart listing the types of ELF and VLF sources at each frequency here.

Scientific/Medical:

The health effects of exposure to high levels of ELF and VLF are well understood. Above a certain threshold level, these effects include reversible effects on excitable cells in the body such as a faint light flickering in the periphery of the visual field (phosphenes, at around 20 Hz); electric charge effects on the skin (similar to what is experienced when you comb your hair, causing your hair to rise); or a stimulation of nerves and muscles experienced as a tingling sensation. These effects occur at different thresholds depending on the frequency of the field. At even higher levels, ELF causes irreversible cardio-vascular effects or tissue burns. The much lower levels to which the public is exposed produce no known health effects, but the topic remains controversial.

General Health Effect Reviews:

· Low Frequency. Review of the Epidemiologic Literature on EMF and Health. International Commission on Nonionizing Radiation Protection (ICNIRP). These sites provide an overview of known health effects of exposure to ELF fields.

· Electromagnetic Fields. Extremely Low Frequency Fields. World Health Organization (WHO). Links to studies and publications.

· Electric & Magnetic Fields. National Institute of Environmental Health Sciences (NIEHS), National Institutes of Health (NIH).

· Electromagnetic Fields. Wisconsin Public Services Commission.

Leukemia and Other Cancers Electric & Magnetic Fields. National Institute of Environmental Health Sciences (NIEHS), National Institutes of Health (NIH). The International Agency for Research on Cancer states there is limited evidence in humans for the carcinogenicity of extremely low frequency magnetic fields in relation to childhood leukemia. Extremely low-frequency magnetic fields are possibly carcinogenic to humans (Group 2B). IARC Press Release; Monograph

Minimize Your Risk:

Although extremely low frequency (ELF) exposures occur everywhere, the potential hazard depends on the strength of the ELF fields at the source, the distance from the source, and the duration of exposure. If you worry about your exposure to even low levels of ELF fields, simple steps can reduce your exposure. The strength of these fields drops quickly with increasing distance from the source. Therefore, spending less time right next to large appliances and electric power lines will greatly reduce your exposure. Some people claim that a small percentage of the population can sense even low-level electromagnetic fields, but most of us cannot detect the presence of ELF fields with just our bodies.

If you are concerned about EMFs emitted by a power line or substation in your area, you can contact your local power company to schedule an on-site reading. You can also measure EMFs yourself with the use of a gaussmeter, which is available for purchase online through a number of retailers.

Exposure Limits:

Based on the known thresholds for biological effects, scientific consensus organizations have set “safe” exposure limits for ELF and VLF. No known harmful effects occur at levels below these limits. Organizations that have published these exposure limits include the International Commission on Nonionizing Radiation Protection (ICNRP), The Institute of Electrical and Electronics Engineers (IEEE), and the American Conference of Governmental Industrial Hygienists (ACGIH). One set of limits covers the general public. A higher set of limits applies to workers trained in the hazards and protective measures. Members of the general public will not exceed the public exposure limits under normal circumstances. Workplace exposures in some industries (for example, electric power utilities, foundries, and other sites the handle very large electrical loads) may exceed the public limits.

Additional information on workplace exposure to ELF appears at:

· Extremely Low Frequency (ELF) Fields. American Industrial Hygiene Association (AIHA) Position Statement.

· NIOSH Fact Sheet: EMFs in the Workplace NIOSH Publication No. 96-129.

· Extremely Low Frequency (ELF) Radiation. Occupational Safety and Health Administration (OSHA).

Radiation Protection Section, 1645 Mail Service Center, Raleigh, NC 27699-1645 919-814-2250 Disclaimer