Electricity and health
Introduction
As soon as an electrical device is connected to the grid, as soon as the plug is in the outlet, there is an electric field present around the wires. When electricity flows through the wires, when electricity is being used (when a lamp is on or a vacuum cleaner is running, for example), there is also a magnetic field around the wire and the device. The electricity grid current is alternating current, with a frequency of 50 hertz in Europe (50 cycles per second, 50Hz). The electric and magnetic fields generated are alternating fields, which alternate with the same frequency as the electrical current: 50 Hz. This means that the fields belong to the category of fields with extremely low frequencies (ELF): from 0 Hz to 300 Hz.
Alternating fields with extremely low frequencies generate an electric current in the body. This effect appears as soon as an alternating field is present. If the field is strong enough, the current generated in the body can disturb the working of nerves and muscles or cause flashes of light to be seen. There are limits specified in order to prevent such effects. For the electric field, the limit is 5 kilovolts per metre (5,000 V/m or 5 kV/m), for the magnetic field, the limit is 100 microteslas (100 µT). The fields that surround us in our everyday lives are usually not this strong.
Limit values are established to prevent immediate harmful effects on the nervous system. Scientists are less certain as to whether other effects are possible in the long term.
In this section we take a closer look at the various sources of 50 Hz electrical and magnetic fields, the results of scientific research into the possible effects on health of long-lasting exposure and the recommendations resulting from this.
Electric and magnetic fields in everyday life
Electric field
Live wiring and appliances are surrounded by an electrical field. The strength of an electric field depends on the voltage in a wire. The strongest electric fields are found under overhead transmission lines: just beneath the wires, this field can reach a few kilovolts per metre. Only under a 380 kV transmission line can the limit of 5 kV/m be exceeded. Electrical appliances and machinery can never cause an electrical field above the limit value.
The electrical field decreases sharply with distance and is also resisted by barriers such as walls. As a result, the electrical field in homes is minimal, even in homes right next to a high voltage line.
The magnetic field also significantly decreases with distance, but is only slightly weakened by walls. There are magnetic fields around us originating from a whole range of sources both outside and inside. This is what the next section covers.
Magnetic field
The strength of a magnetic field depends on the electric current in a wire. The strongest magnetic fields occur in magnetic resonance imaging machines (MRI), used for medical imaging (a few teslas). Fairly strong fields occur nearby motors and other electrical devices (between a few microteslas and several hundred microteslas). The electricity grid generates relatively weak magnetic fields (at most in the tens of microteslas). The magnetic field always decreases sharply with distance from the source.
The electricity grid
On the electricity network the strongest magnetic fields occur near high voltage cables because they carry the strongest electrical current.
At ground level, the magnetic field is strongest a few metres from an overhead transmission line, and can reach a few tens of microteslas. Along underground transmission cables, the field weakens much faster than along an overhead line with the same voltage: this is because the underground lines lie close to one another, three lines together. They carry the electricity in three different phases, allowing the alternating magnetic fields generated to partially cancel each other out (see the “General concepts” ).
Note: not every cable hanging from a pylon is a high voltage line. High-voltage usually refers to a voltage of 30kV of higher. The voltage must be this high in order to efficiently transport large amounts of energy. This is what actually happens in high-voltage transmission lines: they transmit electricity over very large distances from the power plant to the users. In order to use the electric energy, the voltage must be reduced: this is done in substations. From there, the electricity is brought via the distribution grid (at medium voltage, up to 15 kV) to our homes (at low voltage, 230V) (see figure 2). The high-voltage transmission lines may be laid above ground or below ground.
(Fig. 2: the magnetic field in relation to the distance to an overhead line and an underground high voltage cable, source: Elia)
Substations produce a negligible magnetic field outside of the safety zone. The largest fields in zones accessible to the public are caused by the power lines that run in and out of the substation.
The magnetic fields around distribution lines and the wiring at home are even weaker, a few microteslas in the immediate surroundings.
Household electrical devices
As soon as an electrical device is switched on, there is a magnetic field present. Sometimes the field is unintentional, it is just a by-product of the electric current. But sometimes a magnetic field must be specially created because this is necessary for the working of e.g. electrical motors or adapters. In these cases the manufacturer ensures than the field outside of the device remains at a minimum. Yet this is not always possible, particularly when a device should be light-weight and compact. An electric razor or a hair dryer, for example can generate a magnetic field in the range of 5 - 200 µT. In other devices, those that have no motor or adapter, the magnetic field is usually weak. The exceptions to this are devices in which the electricity runs in large loops (electric kettles, electric blankets, convection radiators). Generally the power of the device plays no role.
The magnetic field decreases sharply as the distance from the source is increased. At a distance of 30 cm, the magnetic field around most household appliances is much lower than the current guideline of 100 µT at 50 Hz for the general public. At a distance of one metre, the magnetic field is already negligibly small.
A short exposure to a magnetic field larger than 100 µT does not necessarily constitute a risk. By setting the limit at 100 µT, a large safety margin has been included. Most devices are also not used close to the body. For occupational situations, the safety limit is set at 500 µT.
Normally, there is only a magnetic field present if a device is switched on. Devices that run on a lower voltage than the grid (halogen lamps and dimmers, for example) need an adapter (transformer). This adapter always uses electricity (and therefore also creates a magnetic field) whenever it is plugged in, regardless of whether the device is on or off.
Other devices and machines
There are also alternating magnetic fields present in the following situations:
- Near machines that run on a light petrol engine, lawnmowers and chainsaws, for example
A rotating magnetic field must ensure that the spark plugs are ignited.
- Around the battery of a mobile phone
This is because the battery of a mobile phone uses pulsed electricity, related to the radiation pattern of the mobile phone.
- In a car
These fields originate in the battery, the wiring and the magnetised steel belts of the tyres. When the tyres rotate, while driving, there is a rotating magnetic field. Car tyres can be demagnetised in a garage.
- In a train
Trains are driven by electricity.
Legislation and control
Het electrical power network
The Belgian legislation (General Regulations for Electric Installations (RGIE/AREI) limits the strength of the electric field that is generated by the 50 Hz electricity grid to:
- 5 kV/m in residential areas or residential expansion areas;
- 7 kV/m along roads;
- 10 kV/m in other places.
So far there is no federal Belgian legislation for the limitation of public exposure to magnetic fields of 50 Hz. Belgium has adopted the European recommendation of 100 µT. This is the limit for preventing strong currents in the body.
Independent research teams that are specialised in the measurement of transmission line magnetic fields include VITO (Vlaams Instituut voor Technologisch Onderzoek, Flemish Institute for Technological Research), the ISSeP (Institut Scientifique de Service Public) and the University of Liege (ULG, Transport and Distribution of Electrical Energy).
Elia, the operator of the Belgian transmission grid, is responsible for technical supervision. Elia measures the electric and magnetic field in homes free of charge.
Electrical household appliances
All these appliances such as washing machines, hair-dryers, electric blankets and microwave ovens may only be put on the market if they are safe and pose no danger to health. This also applies for electric and magnetic radiation that may be caused by these appliances. This requirement is established in the European low voltage directive (2006/95/EC). You can find more information about the regulations and control at the website of the FPS Economy
SMEs, Self-employed and Energy.
Research and recommendations
Electricity and child leukaemia
A short exposure to an electric or magnetic field under the recommended limits is not hazardous to your health. However, scientists have not yet come to a conclusion regarding the possible effects of long-term exposure to extremely low frequency magnetic fields.
There are indications from epidemiological research that long-term exposure may be associated with a mildly elevated risk of leukaemia in children. For that reason, the International Agency for Research on Cancer (IARC) has classified low-frequency magnetic fields (originating from the electric power grid) as ‘possibly carcinogenic to humans.’ ‘Long-term exposure’ refers to a long-term stay in places where the average magnetic field over 24 hours is higher than 0.3 – 0.4 µT, which could be the case near high-voltage power transmission lines.
The classification ‘possibly carcinogenic to humans’ is assigned to environmental factors and substances that show ‘limited epidemiological evidence’ in connection with cancer. According to IARC, coffee and car exhaust fumes also belong to this group.
How great is the risk?
Childhood Leukaemia appears in 3 children in 100,000 each year. There are various risk factors that can increase the chance of developing childhood leukaemia, for example, ionising radiation (such as x-rays), genetic factors, household use of pesticides and certain solvents in paint, smoking and possibly alcohol use by the mother during the pregnancy.
If it should emerge from further investigation that ELF magnetic fields also belong on the list of risk factors, this factor would be responsible for less than 1% of the childhood leukaemia cases each year (in the Flemish region), according to VITO (the Flemish Institute for Technological Research).
Recommendations
Although there is still much uncertainty regarding the precise role of magnetic fields in increasing the risk of childhood leukaemia, the Superior Health Council recommends that children under the age of 15 not exceed the exposure limit of 0.4 µT (averaged over a long period). This means that the home and in particular the bedroom should ideally be at a sufficient distance from electrical installations such as high-voltage power lines, distribution lines and substations. In addition, the bedroom and particularly the child’s bed should be placed at a sufficient distance from the home’s electrical installations (distribution board and wires, electric under-floor heating) and continuously operating devices (electric blankets, electric alarm clocks). You can find concrete recommendations in the advisory report of the Superior Health Council.
USEFUL ADDRESSES
• Elia: Keizerslaan 20, 1000 Brussels. Tel.: 02 546 70 11, Fax: 02 546 70 10. www.elia.be
• VITO (Vlaamse Instelling voor Technologisch Onderzoek), Integrale Milieustudies, Boeretang 200, B-2400 Mol. Tel.: 014 33 59 41, Fax: 014 32 11 85. www.vito.be
• ISSeP (l’Institut Scientifique de Service Public), Cellule “champs électromagnétiques”, Direction des risques chroniques, Rue du Chéra 200, B 4000 Liege. Tel.: 04 229 83 11. www.issep.be
• University of Liege, Transport et Distribution de L’Energie Electrique, 10 Grande Traverse, Sart Tilman (B28), B-4000 Liege. Tel.: 04 366 26 33, Fax: 04 366 29 98. www.tdee.ulg.ac.be
MORE INFORMATION
www.bbemg.ulg.ac.be (Belgian BioElectroMagnetic Group)
www.milieurapport.be (research reports about the high-voltage grid)
www.who.int/peh-emf/en (World Health Organisation – electromagnetic fields)
www.health.fgov.be/CSS_HGR (advice and recommendations of the Superior Health Council)
Federal Public Service (FPS) Health, Food Chain Safety and Environment
Eurostation II
Place Victor Horta, 40 box 10
1060 Brussels
Belgium
Contact Center: +32 (0)2 524.97.97
Published on 24/05/2011 – Page last updated on 24/05/2011
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