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Low frequency

1 Hz - 100 kHz

Frequency range and LF use

Low Frequency (LF) is the abbreviation used for low frequency time-varying electric and magnetic fields, which describes that part of the electromagnetic spectrum comprising the frequency range from 1 Hz to 100 kHz. LF fields have two components: an electric field due to an electric charge, and a related magnetic field. Magnetic fields only occur when an electric current is flowing. The electric component is measured in volts per metre (V/m). The magnetic component is measured in amperes per metre (A/m) and expressed as a flux density in tesla (T) or in some countries in gauss (G).

LF fields are mainly related to the electric power supply, through the generation, distribution and use of alternating current (AC). The frequency used for this purpose is usually 50 or 60 Hz depending on the country in question. In daily life, people are exposed to LF fields around electric appliances and electronic devices mostly in the home and at work. Power lines are also a source of LF fields.

LF effects on the body and health implications

When people are exposed to LF fields, electric fields and currents are generated inside the body and they can interfere with the body’s own electric fields and current flows related to normal biological functioning. In addition, the LF electric field interacts with the surface charge of the body. At low levels, these interactions go mostly unnoticed, and do not compromise health.

However, above a certain level of exposure, referred to as threshold, the induced internal fields provoke reversible effects on excitable cells in the body such as a faint light flickering in the periphery of the visual field (phosphenes); 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 higher levels, LF causes irreversible cardio-vascular effects or tissue burns.

Potential health effects associated with long-term low-level exposure have been extensively studied over the last few decades.

Epidemiological studies have suggested that long-term low-level exposure to 50-60 Hz magnetic fields might be associated with an increased risk of childhood leukemia. However, a combination of selection bias, some degree of confounding and chance could possibly explain these results. In addition, no biophysical mechanism has been identified and results from animal and cellular laboratory studies do not support the notion that exposure to 50-60 Hz magnetic fields is a cause of childhood leukemia. Therefore, the currently existing scientific evidence does not lead to the conclusion that a prolonged exposure to LF is a cause of childhood leukemia. Evidence for cancer in adults from LF exposure is very weak. There is no substantial scientific evidence for an association between LF exposure and Parkinson’s disease, multiple sclerosis, developmental and reproductive effects, and cardiovascular diseases, while for Alzheimer´s disease and amyotrophic lateral sclerosis the evidence is inconclusive. Studies of symptoms, sleep quality, cognitive function have not provided consistent evidence of an effect from this type of exposure.

Overall research has not shown to date that long-term low-level LF exposure has detrimental effects on health.

Protection

To prevent health-relevant interactions with LF fields, ICNIRP recommends limiting exposure to LF fields so that the threshold at which the interactions between the body and the external electric and magnetic field causes adverse effects is never reached inside the body. The exposure limits, called basic restrictions, are related to the threshold showing adverse effects, with an additional reduction factor to consider scientific uncertainties pertaining to the determination of the threshold. They are expressed in terms of the induced internal electric field strength in V/m. The exposure limits outside the body, called reference levels, are derived from the basic restrictions using worst-case exposure assumptions, in such a way that remaining below the reference levels (in the air) implies that the basic restrictions will also be met (in the body). Refer to the ICNIRP Fact Sheet and ICNIRP Guidelines for all figures and more information.

ICNIRP follows up the scientific LF related research and new information relevant to health, in particular through its reviews of the scientific research or the organization of relevant workshops, such as the Workshop on Risk Factors for Childhood Leukemia.

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