Introduction to EMF-EMI

Some projects produce an electromagnetic field (EMF) along with the prospect of electromagnetic interference (EMI) with sensitive equipment or instrumentation. An EMF consists of invisible lines of force that surround any electrical device, including power lines, electrical wiring and electrical equipment. EMI refers to the potentially disruptive effects on the operations of other electromagnetically sensitive devices. These can include televisions, radios, and other scientific instrumentation such as electron microscopes. TABLE 1 is a glossary of EMF-related Abbreviations and Acronyms.

Electromagnetic fields have both electric and magnetic field components. The strength of the electric and magnetic fields decreases rapidly with distance from the source. Electric fields are shielded or weakened by materials that conduct electricity including trees, buildings, and human skin. Magnetic fields pass through most materials and are more difficult to shield.

The electric field component is produced by the electrical voltage (V) and increases in strength as the voltage increases. Electric fields are measured in units of volts per meter (V/m). Electrical current through conductive wires or devices, reported in Amperes (A), produces a magnetic field that increases in strength as the current increases. Magnetic fields are measured in terms of their field flux density in units of Gauss (G) or Tesla (T). Most environmental EMF exposure levels involve magnetic field induction (B) that is a fraction of a Tesla or a Gauss and are commonly measured in units of microtesla (μT) or milligauss (mG). A milligauss is 1/1000 of a Gauss. A microtesla is 1/1,000,000 of a Tesla. To convert a measurement from microtesla (μT) to milligauss (mG), multiply by 10.

Electric and magnetic fields have characteristic wavelength, frequency and amplitude. Wavelength describes the distance between one peak on the wave and the next peak. The frequency describes how many wave peaks occur within 1 second of time. Electricity in North America is driven at a power frequency that alternates 60 times each second and thus has a frequency of 60 cycles per second, or 60 Hertz (Hz). In many other parts of the world, the frequency for electric power is 50 Hz, and some older transit systems in North America or Europe still utilize 16–2/3 Hz or 25 Hz supply systems as dictated by the power grid frequency at the time of their construction (see reference 1).

The EMF produced by alternating current (AC) is time varying in both magnitude and direction. The EMF produced by the direct electric current (DC) used in light rail traction power and electric trolley systems, for example, are static and so they do not show the variability in magnitude and/or directional characteristics of fields associated with AC systems. EMF can result in a variety of potential health impacts to humans. Certain EMF combinations can cause shock and burn injuries; others can also interfere with the operation of electrical and magnetic devices, including pacemakers. Additionally, facilities such as hospitals should also be considered as potentially sensitive receptors, due to the presence of medical equipment and/or patients under care.

Substantial research has attempted to determine whether prolonged exposure to EMF can result in other health effects. Concern regarding these potential health effects has focused primarily on AC fields, particularly the 50 Hz and 60 Hz fields associated with electrical transmission and distribution facilities, rather than static electric fields associated with direct currents. Extremely Low Frequency (ELF) exposure is commonly defined as being over a frequency range from 3 Hz to 3000 Hz. Static fields are correspondingly those within the lower 0 Hz to 3 Hz range. This research, which has been primarily epidemiological, is inconclusive thus far and medical opinions appear to be divided regarding the possible extent of these effects. Authoritative reviews have concluded that the association between exposure to ELF–EMF and health risk is weak, and no reproducible causal relationship has been identified using controlled laboratory studies. Further research into ELF magnetic field exposure was recommended (see reference 2) by this research program, the EMF RAPID program.

The Occupational Safety and Health Administration (OSHA) have provided Guidelines on EMF exposure that are derived from the International Commission on Non-Ionizing Radiation Protection (ICNIRP) and the American Conference of Governmental Industrial Hygienists (ACGIH). The OSHA synopsis of threshold limit values (TLV) for exposure to power frequency EMF is reproduced in TABLE 2. Distinct standards issued by state/provincial or local agencies have not been identified for evaluating these types of EMF impacts. The OSHA guidelines indicate a maximum recommended EMF exposure level of 1 Gauss (1,000 mG) for both the general public and workers with cardiac pacemakers. Further information can be found in (reference 3).

1.        Muc, A.M., “Electromagnetic Fields Associated with Transportation Systems”, prepared under contract for Health Canada, May 2001.

2.        EMF Research and Public Information Dissemination Program (RAPID), “Health Effects from Exposure to Power-Line Frequency Electric and Magnetic Fields”, National Institute and Environmental Health Sciences, 1999.

3.        California Electric and Magnetic Fields Program, “Electric and Magnetic Fields: Measurements and Possible Effects on Human Health — What we Know and What we Don’t Know in 2000”, California Department of Health Services and Public Health Institute, December 2000.