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Precautions against exposure to low frequency fields
- Even if limit values are adhered to, exposure to low frequency fields can be reduced for reasons of precaution.
- This holds true for power lines as well as for personal precaution in everyday life and in the household.
- The Federal Office for Radiation Protection offers advice on precaution and supports further research in this field.
Limit values offer up-to-date protection from the established harmful effects of electric and magnetic fields. Precautionary measures enhance the limit values so as to accommodate scientific uncertainties in risk assessment.
Precautionary measures for power supplies
Basically, exposure to electric and magnetic fields should be as low as possible. Therefore, from the radiation protection point of view, new power lines should be planned in such a way that they do not lead to additional exposure of the population to electric or magnetic fields.
The amended 26th Federal Immission Control Ordinance (26. BImSchV, in German only) stipulates a minimisation requirement. In line with this, the construction and significant alteration of low-frequency installations and direct current installations should keep the field strengths emanating from these installations to a minimum.
The possibilities in each individual case depend on the state of technology and the conditions in the impact area of the respective installation. Details are regulated by the General Administrative Provision on the Implementation of the Ordinance on Electromagnetic Fields – 26. BImSchV (26. BImSchVVwV, in German only) as of 26 February 2016.
The field strengths in the surroundings of power supply installations (and therefore the exposure of the population) generally depend on the distance from the installation, on its technical design and on the operating mode of the installation.
Right from the planning stage, all opportunities should be taken to keep the exposure of the population as low as possible by maintaining distances between residences and power lines and other power supply installations. This means that new power lines, if possible, should not pass through residential areas.
For 50-Hz overhead power lines with a nominal voltage of 220 kilovolts or more that are erected within a new transmission route, the amended 26th Federal Immission Control Ordinance (26. BImSchV) sets out a spanning ban. This means that routes for new high-voltage lines for three-phase current transmission must for precautionary reasons be planned in such a way that the lines do not pass over buildings or parts of buildings that are intended for permanent residence.
- With increasing distance from residences, the contribution of a high-voltage line to human exposure to electric and magnetic fields gets lower. The overall exposure is then predominantly from the use of electric energy within the household. For alternating current power lines, the distance in question here is 100 to 400 metres. In individual cases, it depends on the design and the operating parameters of the power line.
- When constructing power lines, mains electricity suppliers should make full use of their technical possibilities for reducing electric and magnetic fields. This can be, for example, by improving the structural design of electricity pylons, by carefully selecting the circuit layout, the height of the pylons or the distance between the individual conductor ropes. Even if cables are laid underground, the distances and arrangement of the individual conductors can have an impacted on the emitted magnetic fields. The most suitable option depends, among others, on local conditions. Economic considerations also play a role here.
- With regards to electric installations within the household, supply and return conductors should, if possible, be kept closely together (in one cable). Cable strands that conduct high currents, for example rising mains that supply several residences, should be installed at the greatest possible distance from inhabited rooms (for example in the walls of corridors and storerooms). The use of energy-saving devices might also reduce field exposure.
To most people in Germany, it is not high-voltage lines but electric installations and devices in everyday life and the household that cause the greatest share of their exposure to low-frequency electric and magnetic fields. Therefore, each individual can contribute to the reduction of their personal exposure – the BfS offers tips on individual precautionary measures.
In order to resolve scientific uncertainties, the Federal Office for Radiation Protection supports further research on the subject of electric and magnetic fields.
State of 2016.06.06