A - B

AC or alternating current Electrical circuits where the voltage and current alternate direction, in the UK at 50 times per second (50 herz or Hz) and in the USA at 60 Hz

ACGIH American Conference of Governmental and Industrial Hygienists. An American body which has produced advisory occupational exposure guidelines.

AGNIR The NRPB’s Advisory Group on Non-Ionising Radiation, formerly chaired by Sir Richard Doll

ALL Acute Lymphoblastic Leukaemia (sometimes alternatively called Acute Lymphocytic Leukaemia), the commonest type of childhood leukaemia

ALS Amyotrophic Lateral Sclerosis, a form of neurodegenerative disease. Known in the USA as Lou Gehrig’s disease.

Amps (or amperes) The unit of electrical current, symbol A

Athermal Strictly speaking, effects which do not stem from the heating effect of a field, because the field is too low to cause significant heating. At power frequencies heating is usually not important, and athermal is often used to refer to effects below the level at which induced-current effects are recognised as significant.

B Usual symbol for the magnetic flux density or more generally the magnetic field

Bioinitiative A report written on EMFs in 2007

Bradford-Hill criteria A widely accepted set of pointers to help decide whether epidemiological results have established a causal effect or not

BSI British Standards Institute




Case-control study One type of epidemiological study. Two groups, the cases (those with the disease being studied) and the controls (a comparison group) are compared to each other. Often used to investigate comparatively rare diseases.

CCRG see Childhood Cancer Research Group

CENELEC European electrical standards organisation

Childhood Cancer Research Group A research group in Oxford University, currently performing and epidemiological study of power lines and cancer for the Department of Health

Circuit A set of wires along which current flows and returns. It is necessary to have a complete circuit for current to flow.

Circular polarisation The extreme case of elliptical polarisation, where the field traces out a circle

CNS Central Nervous System, the brain and spinal cord

Cohort study One type of epidemiological study. A group of people (the cohort) are examined over time to see which of them develop the disease under study.

Confidence interval A measure of the statistical confidence in a result.  The narrower the confidence interval, the more confident we can be in the value given.

Confounder, confounding In epidemiology, where an association between the agent being investigated and the disease is not caused by the agent at all, but a different factor, the confounder, which happens to be associated with the agent being investigated.

Corona Breakdown of the air , e.g. on the surface of a high-voltage conductor, to produce air ions

CSF Cerebro-spinal fluid. A fluid surrounding the spinal cord

CSTEE A Committee of the European Commission (Scientific Committee on Toxicity, Ecotoxicity and the Environment), now replaced by SCENIHR.

Current is the flow of electricity. A voltage will always try to drive a current. The size current that is driven depends on the resistance of the circuit.

D - F

DC or direct current Electrical circuits where the electricity flows in the same direction all the time (a battery produces DC)

Distribution In electric power systems, used to describe the lower voltages, used for distributing electricity locally, including into homes

E Usual abbreviation for the electric field

EA Electricity Association, the former trade association in the UK representing most electricity companies, now replaced by the Energy Networks Association ENA (EA can also stand for the Environment Agency)

Electric fields are produced by voltages, irrespective of how much current is flowing and indeed whether any current is flowing at all. The electric field is the region around a conductor where a force will be experienced by a charge.

Electrons. Fundamental particles carrying one negative charge each, which carry current in metals and many other materials

ELF. Acronym for Extremely Low Frequency, the scientific term for the power frequencies - 50 or 60 Hz - of the fields produced by the power system.

Elliptical polarisation If we have more than one source, e.g. a three-phase circuit, the field no longer has to oscillate along a straight line. It actually traces out an ellipse. This is known as “elliptical polarisation”.

Emdex name of a family of magnetic field instruments, available from Enertech Consultants in America.

EMFs Electric and magnetic fields. Sometimes also defined as electromagnetic fields, which usually means the same thing

Epidemiology The study of the patterns of diseases in a population, to try to determine their causes and to identify risk factors

EPRI Electric Power Research Institute, a research organisation in America. Many USA utilities subscribe to EPRI rather than perform their own research

Extremely Low Frequency.  Defined as the range of frequencies from 30 to 300 Hz and therefore including the power frequencies of 50 or 60 Hz.

Far field The situation where you are far away from a source of fields. The electric and magnetic fields are coupled together to form radiation. Often the case at radiofrequencies but not at power frequencies

Field A very general concept in physics for a region of space where a quantity exists with a specific value at each point in the region. You can have a field of almost anything that varies over space: temperature, for instance, as well as the more common gravitational and electric and magnetic fields. The term “field” is, however, only in common use for things which are capable of exerting a force.

Fluxgate magnetometer A way of measuring magnetic fields. A magnetic core is deliberately driven into saturation in alternate directions at a high frequency. An external magnetic field introduces asymmetries which are detected.

Free radicals Highly reactive chemical species (part of a molecule) with an unpaired electron. The number of free radicals can sometimes be affected by magnetic fields.

G - J

Gauss A unit of magnetic field still used in the USA. 10,000 G = 1T

H Usual abbreviation for the magnetic field strength

Hall effect A way of measuring magnetic fields. A current in a suitable semiconductor experiences a sideways force, in turn creating a measurable voltage, proportional to the magnetic field.

Harmonics. Multiples of the basic frequency. If the power frequency is 50 Hz, second harmonic is 100 Hz, third harmonic is 150 Hz, etc.

Herz (symbol Hz) The unit of frequency, 1 Hz = 1 cycle per second

HSE The Health and Safety Executive

Human Radiation Effects Group A former research group in the Physics Department at Bristol University, led by Professor Henshaw, active on EMFs

IARC International Agency for Research on Cancer. An agency of the WHO based at Lyon. One of their activities is to classify agents as to whether they are a cause of cancer

ICNIRP International Committee on Non-Ionizing Radiation Protection. Among other activities, they publish recommended exposure guidelines.

IEC International Electrotechnical Commission, an international standards organisation

IEE formerly Institution of Electrical Engineers, now IET, Institution of Engineering and Technology (UK based)

IEEE Institution of Electrical and Electronics Engineers (USA based)

IET Institution of Engineering and Technology (UK based)

Induction The process whereby an alternating field (either electric or magnetic) creates a current in a conducting object

Institute of Occupational Health A research group at Birmingham University who are active on EMFs

Inverse square, inverse cube Ways of describing how rapidly fields fall with distance from the source

IOH see Institute of Occupational Health

Ions Molecules that have had electrons stripped off them or added to them, so have a charge. Ions are usually either air ions or ions in solution such as in cells.

IRPA International Radiation Protection Association, predecessor body to ICNIRP (IRPA still exists but created ICNIRP as a separate body)

j symbol often used for current density

K - M

Kilovolt per metre 1000 volts per metre. Unit of electric field used sometimes where it is more convenient than volts per metre. Symbol kV/m or kV m-1

Latent period The period between the event or exposure which is thought to cause the disease, and the disease being detected

Leukaemia (USA spelling leukemia) A type of cancer of the blood; a malignant proliferation of blood cells

Linear polarisation If we have a single ac source or a single-phase circuit, the field at any point simply oscillates backwards and forwards along a straight line. This is known as linear polarisation.

Lou Gehrig’s Disease American name for ALS

LRF Leukaemia Research Fund, one of the major UK cancer research charities, heavily involved in the UKCCS.

Magnetic fields are produced by currents, irrespective of the voltage. The magnetic field is the region around a current where a moving charge will experience a force.

Magnetic field strength One of the two closely related characteristics of a magnetic field (the other is the magnetic flux density). For EMFs, it is normal just to refer the magnetic field without worrying about the distinction.

Magnetic flux density One of the two characteristics of a magnetic field (the other is the magnetic field strength). For EMFs, it is normal just to refer the magnetic field without worrying about the distinction.

Magnetite A magnetic material (an iron oxide) found in small particles in some biological material, which features in one proposed mechanism for the effect of magnetic fields.

Magnetophosphenes A flickering sensation round the periphery of vision produced by induced currents in the retina at high magnetic fields

Maxwell’s equations Four equations which describe how electric and magnetic fields interact with each other

Melatonin A naturally occurring hormone, involved in the body’s circadian rhythms and also in certain types of cancer, suggested by some studies to be affected by magnetic fields

Meta-analysis Combining the results from several different epidemiological studies into a single result

mG milligauss. 1/1000 of a gauss, a unit of magnetic field

µT Symbol for microtesla

Microshocks Small discharges sometimes experienced when touching a metal object in an electric field, similar to touching a filing cabinet or door knob after walking across a nylon carpet

Microtesla 1/1,000,000 of a tesla. A unit of magnetic field more commonly used than the tesla because it is more convenient. Symbol µT

Millitesla 1/1000 of a tesla. A unit of magnetic field more commonly used than the tesla because it is more convenient. Symbol mT

mT see millitesla

N - P

NCI National Cancer Institute in the USA, which performed a major epidemiological study on EMFs published in 1997

NGC, NGT Historical references to National Grid Company, which in 2002 became part of National Grid Transco and then National Grid plc in July 2005. The company which operates the England and Wales high-voltage transmission network - now known as National Grid Electricity Transmission plc

NIEHS National Institute of Environmental Health Sciences, a USA government organisation

NRPB National Radiological Protection Board. Created by Act of Parliament to advise on radiation issues including EMFs.  In 2004 became part of the Health Protection Agency (HPA).

Near field The situation where you are close to the source of the field. Electric and magnetic fields are not coupled to each other and radiation is small; the two fields exist separately. Nearly always the case at 50 Hz

Net current Created in a circuit when the live and neutral currents are not equal, usually because some of the neutral current has diverted out of the cable.

Odds Ratio The usual way of expressing the result of a case-control epidemiological study, often nearly the same as the relative risk or risk ratio. An odds ratio of 1 means there is no association between exposure and disease. Odds ratio greater than 1 mean the exposure is associated with the disease.

OMS the French name for WHO. Organisation Mondiale de la Sante

Phasing The way in which the two circuits of a power line are wired relative to each other, which affects the magnetic field produced

Pooled analysis An epidemiological analysis where the data from a number of individual studies are pooled to allow a single analysis to be made of the combined data set.

Possibly carcinogenic One of the categories used by IARC to classify agents. The middle of five categories, below “established” and “probably”.

Potential difference. The same thing as voltage. This term arises because the voltage is the potential to do work.

Power The rate at which work is done, measured in watts. In electrical circuits it is the product of voltage and current.

Power frequencies In the UK the frequency of the mains (and the rest of the electricity system) is 50 Hz. “Power frequencies” is often used to cover both 50 Hz and the first few harmonics.

Powerwatch A UK EMF interest group

R - S

Radiation the situation at high frequencies, where electric and magnetic fields are coupled together in a specific relationship so that they propagate through space carrying energy. Usually negligible at power frequencies

Radio frequencies Frequencies much higher than power frequencies, where radio and TV broadcasts and mobile phones operate

Radon A naturally occurring radioactive gas found in the air

Relative Risk How the result of an epidemiological study is often expressed. The ratio of the risk in the exposed group to the risk in the non-exposed group. An relative risk of 1 means there is no association between exposure and disease. Relative risk greater than 1 means the exposure is associated with the disease.

Revolt A UK campaign group with a strong interest in EMFs (Rural England Versus Overhead Line Transmission)

Right of Way (ROW) In the USA, the strip of land that a power line runs along.  The power company usually have rights over the land to restrict certain sorts of use.

Risk Ratio Alternative term for relative risk

RMS or root mean square A measure used for AC quantities which allows them to be expressed as a single number. For practical purposes in the electricity industry, it is just a constant fraction of the amplitude: rms = 0.71 x amplitude, amplitude = 1.41 x rms. (The factor 1.41 is the square root of 2.) Rms is used because an alternating current usually has the same effect as a direct current when its rms values is the same as the direct current.

Root mean square see rms

ROW see Right of Way

Search coil The commonest way of measuring magnetic fields at power frequencies. A coil of wire has a voltage induced in it by an alternating magnetic field.

Single phase electricity The electrical engineering term for a normal simple circuit, with one live wire and one return wire or neutral. Used to distinguish it from three phase circuits.

SMR Standardised Mortality Ratio. A way of expressing the result of an epidemiological study. The ratio of the mortality in the population examined to that in the whole population, after taking account (“standardising”) of any differences in ages

Statistical significance How likely a given result (in, e.g., an epidemiological study) was to have come about just by random chance. Conventionally, if the likelihood of it coming about by chance, in the absence of any actual causal risk is 5% or less, the result is said to be statistically significant

Substation One or more transformers plus their associated switchgear etc.

T - Z

Tesla The unit of magnetic field

Three phase electricity A system often used in power systems. A circuit has three “live” wires or phases instead of one, and can carry more electricity for the same amount of wire as single-phase circuits.

Transformer Device used to change the voltage of electrical circuits

Transmission In electric power systems, used to describe the highest voltages, used for transmitting power long distances

UKCCCR United Kingdom Coordinating Committee for Cancer Research, the body which set up the UKCCS

UKCCS United Kingdom Childhood Cancer Study, a major epidemiological study of childhood cancer which looked at EMFs among other possible factors.

Voltages can be pictured as electrical pressure. The analogy is often used with water in a pipe; voltage is analogous to the pressure of the water.

Volts The unit of electrical voltage, symbol V

Volt per metre the unit of electric field, symbol V/m or V m-1

Watts The unit of power, symbol W

Wavelength. The distance between two successive cycles of a wave – 6000 km for 50 Hz

WHO World Health Organization