Electric and magnetic fields
Elia acknowledges the concern about the potential health risks of electromagnetic fields, informs the public and supports scientific research.
Electric and magnetic fields are all around us. Technological innovations such as mobile phones, microwaves and WiFi mean that our exposure to electromagnetic fields has steadily increased. This has led to some concern among a section of the population about the potential health risks of these technologies. In the case of magnetic fields from high-voltage lines, a statistical relationship has been found between exposure to magnetic fields and childhood leukaemia, but no causal link has been demonstrated.
Elia acknowledges the concern about the potential health risks of electromagnetic fields and strives to keep the public as well informed as possible.
We do this with a brochure (in French) and by offering free field measurements. Elia also wants to make an active contribution to broadening scientific knowledge.
What are electric and magnetic fields?
An electric field is created naturally by electrical charges high up in the atmosphere. At ground level such fields are generally weak but in storms they become considerably stronger. Everybody is familiar with the magnetic field of the Earth thanks to compasses, in which a magnet points to the north under the influence of the geomagnetic field.
The term ‘field’ is used in physics to describe the impact of an object on its environment. An electric field is the force of attraction or repulsion that is exercised by electrical charges on each other. A magnetic field is the force exercised by a moving electrical charge.
When a light is connected to the power grid, there is always an electric field, even when the light switch is off and so no power is being supplied to the light. When the light is on, i.e. when power is flowing through the cable, this generates a magnetic field as well as an electric field.
The geomagnetic field changes very slowly and so is considered a constant field. However most electric and magnetic fields, including natural ones, fluctuate quickly and on a regular basis. They are known as alternating fields and have a specific field strength and a frequency.
The power grid, from the high-voltage and distribution networks to the low voltage in our homes, generates fields with a frequency of 50 Hz (50 cycles per second) and is classified as ‘extremely low-frequency’ (ELF). By way of comparison, mobile-phone frequencies range between 900 MHz and 1,900 MHz (million hertz).
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Electrical and magnetic field strength through the high-voltage grid
The electric field changes with the voltage (V). The higher the voltage, the stronger the electric field it generates. The electric field strength is expressed in volts per metre (V/m).
The magnetic field changes with the current (A). The greater the current, the stronger the magnetic field that is generated with it. The units for measuring magnetic fields are amperes per metre (A/m) but we generally use teslas (T), i.e. the unit for expressing magnetic flux density. The magnetic fields we usually measure are expressed in microteslas (μT). A microtesla is one millionth of a tesla.
The strength of the electric field along a high-voltage line depends on the voltage and the distance from the line. Under a 380,000 V line the average electric field 1.5 metres above the ground will be 4 kV/m. This field quickly weakens as you move away from the line. At a distance of 20 metres the field is approximately one tenth of this. For lines with a lower voltage (220, 150 and 70 kV), the electric field will be considerably weaker.
Underground cables do not generate any electric fields because they are shielded off by the metal sheath around the conductors.
The magnetic field generated by a high-voltage line is linked to the level of power flowing through it. Since the magnetic field is not dependent on the voltage, a line with a higher voltage does not necessarily generate a stronger magnetic field. However, in practice the strongest magnetic fields are measured along 380-KV lines. This is because the higher the voltage, the greater the transmission capacity and therefore also the power passing through the lines. In most cases the average strength of the magnetic field under the lines is not greater than 3 µT and quickly decreases as you move away from the line. Magnetic fields are not shielded off when conductors are laid underground. Underground cables generate magnetic fields that may even be stronger above the cable than under an overhead line, but the field strengths tail off more quickly as you move away from the cables.
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Health
After more than 30 years’ research, a possible health risk caused by exposure to low-frequency magnetic fields has still not been clearly demonstrated; however, researchers have not managed to completely rule out this risk either. As a result, the disquiet and confusion among the public is increasing. Furthermore, most people do not consistently make a distinction between fields having different frequencies – electrical facilities, mobile phones, radar, etc. – although they clearly have different characteristics and effects.
As far back as 1979, an epidemiological study (statistical comparisons between populations facing different levels of exposure) found a potential link between living in the vicinity of high-voltage lines and an increased risk of leukaemia in children. Since then, many studies have been carried out into the health effects of magnetic fields.
However, to date, researchers’ follow-up work has been balanced in its results. Not one experimental study (animal and cell-culture testing) has been able to establish a definite causal link between exposure to magnetic fields and certain illnesses. But at the same time no study has managed to completely rule out this risk either. In fact, it is almost impossible to do so. The result is continued confusion, especially with regard to children.
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International assessments
In June 2001 the International Agency for Research on Cancer (IARC) classified low-frequency magnetic fields as “possibly carcinogenic” (Group 2B). This classification was based on epidemiological analyses that showed a statistical relationship between leukaemia in children and exposure to high average magnetic-field strengths.
The International Commission on Non-Ionising Radiation Protection (ICNIRP) is an internationally recognised body that draws up recommendations to protect workers and the public from the harmful effects of non-ionising radiation. In 1998 the ICNIRP published its guidelines on electric and magnetic fields, which – based on proven acute effects – introduced a maximum of 100 µT for public exposure to low-frequency magnetic fields. When these recommendations were updated in 2010, the relevant reference level was increased to 200 µT. As far as chronic effects such as childhood leukaemia are concerned, the ICNIRP states that in spite of the statistical relationships that have been established they are not included in the recommendations because no experimental studies had as yet corroborated this link or shown any causal relationship.
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Standardisation and recommendations
In 1999 the European Union published a Recommendation on the limitation of exposure of the general public to electromagnetic fields. Like the ICNIRP, it recommended a limit of 100 μT for public exposure. Following the IARC classification of low-frequency magnetic fields as possibly carcinogenic in 2001, the scientific state of the art was assessed on the basis of the most recent studies. However, no reason was found to revise the 1999 recommendations.
Belgium has no federal (i.e. national) legislation on very low-frequency magnetic fields. This means that the benchmark is provided by the EU Recommendation, i.e. a maximum exposure limit of 100 μT. For electric fields the General Regulations on Electrical Equipment (AREI/RGIE) sets maximum levels between 5 kV/m (residential areas) and 10 kV/m.
Based on the sectoral conditions in the Walloon and Brussels-Capital Regions, the same 100 µT limit applies when operating power transformers.
In the Flemish Region, the Decree establishing measures to combat the health risks caused by pollution of building interiors has been in force since 2004. Under the Decree all those who are responsible for building, maintaining or fitting out homes or buildings that are open to the public must do everything they can to minimise the health risks affecting the interior of these buildings for the sake of the residents or users. To this end, target values and intervention values are given for 26 chemical and physical factors, including low-frequency magnetic fields. In the case of magnetic fields, the target value is 0.2 µT and the intervention value 10 µT, but no indication is given whether these are peak or average values.
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Elia’s policy
For a number of years now, Elia has been making an active contribution to broadening scientific knowledge. Elia supports a range of research centres and universities that are part of the Belgian BioElectroMagnetic Group (BBEMG), with a cooperation agreement guaranteeing their complete scientific independence. Elia also has a research contract with the Electric Power Research Institute (EPRI). This contract gives Elia access to the results of top international research in this field.
Elia aims for transparency and at the request of local residents conducts free measurements for electric and magnetic fields. You can ask for measurements to be made in the vicinity of our facilities by sending an e mail to etienne.vanvlassenrode@elia.be (Dutch-speakers) / michel.caers@elia.be (French-speakers).
Elia also has a brochure available entitled Champs électriques, magnétiques, et liaisons à haute tension / Elektrische velden, magnetische velden, en hoogspanningslijnen (Electric and magnetic fields and high-voltage lines) download it here (in French) or request it by filling in the form.
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