Many people are worried about potential health effects of electric and magnetic fields in the vicinity of high-voltage power lines.

Observing the limit values ensures protection against adverse health effects caused by low-frequency electric and magnetic fields according to the present state of scientific knowledge. Due to existing scientific uncertainties, however, (see “Biological and Health Effects of Low Frequency Electric and Magnetic Fields”) the exposure to low-frequency magnetic fields, such as those produced by high-voltage power lines, should as a precaution be kept as low as possible – even if they are well below the limit values. Nevertheless, the fact that only in very rare cases do high-voltage power lines represent the essential part of the fields people are exposed to in every day life must be considered. The predominant sources are electric appliances and domestic installations. This is also valid for dwellings in the vicinity of high-voltage power lines (see below "Is there a link between cancer and low-frequency magnetic fields in the vicinity of high-voltage power lines?".

It is difficult to evaluate the electric field intensity and the magnetic flux density in a particular case without performing on-site measurements since the actual exposure at a given place depends on voltage and current of the power line but also on buildings and plant cover in the surroundings. The distance from a high-voltage power line in itself is not a reliable measure for the assessment of the field strength (see also “Static / Low Frequency Fields Occurrence in Everyday Life”).

Electric and magnetic fields decrease rapidly with increasing distance to high-voltage power lines. For example, on average a magnetic flux density of 1.5 µT was measured at a distance of 20 meters from the middle of the route of a 380 kV power line. This is far below the limit (of 100 µT) permissible according to the 26th Ordinance on the Implementation of the Federal Immission Control Law (26. BImSchV). The electric field intensity values were also below the permissible limits (see " Limit Values and Precautionary Measures").

The BfS recommendation to restrain from construction under high-voltage power lines is a precaution to minimise field exposure. Right from the start this helps to avoid both long-term exposure and annoying perceptions electric shocks (see “Biological and Health Effects of Low Frequency Electric and Magnetic Fields”) caused by charging effects of conductive objects, which may in some cases occur even if electric field intensities are below the limit values.

Electric and magnetic fields directly below a high-voltage power line may possibly be hazardous to people with pacemakers. They might cause de-synchronization, mainly depending on the type of pacemaker and the mode of implantation. Since there are many different types of pacemakers, particular hazards need to be assessed in consultation with the attending physician.

Potential health risks of low-frequency magnetic fields of domestic electricity (50 Hz) and electrified transport systems (16 ½ Hz) have been a controversial issue for years. In the US, the first epidemiological evidence on a potential connection between cancer and the residential proximity to high-voltage power lines was published in 1979. Numerous studies have since tried to illuminate similar issues.

A great number of study results have been assessed by scientists in many countries. Internationally recognised radiation protection committees such as the International Commission on Non-Ionizing Radiation Protection (ICNIRP), the British Health Protection Agency (HPA) or the German Commission on Radiological Protection (SSK) and the Federal Office for Radiation Protection (BfS) concluded that there is no proof of a connection between every day life exposure to magnetic fields and an increased incidence of cancer in adults. This was recently confirmed by the WHO in the fact sheet “Electromagnetic fields and public health – exposure to extremely low frequency fields (see also “WHO Updates Risk Assessment of Low Frequency Fields”).

Several recent epidemiological studies show, however, a relationship between childhood leukaemia and low-frequency magnetic fields below limit values. One of these studies was carried out on behalf of BfS (so called Michaelis-Studie). The low frequency magnetic fields in the domestic environment of 514 children with leukaemia were measured. There was a control group of 1.301 healthy children.

The results of the measurements are in agreement with those of an extensive investigation previously performed by the BfS. They show that the fields in dwellings – as measured over a 24-hour period – amount to 0.05 microtesla (µT) on average. Dwellings are referred to as exposed if they present an average exposure of more than 0.2 µT. However, this group only consisted of very few participants. High-voltage power lines were responsible for magnetic field exposures above 0.2µT in only one third of the cases. Other relevant field sources were, e.g., rising mains and out-dated electric installations in the houses investigated.

A connection between field intensity and childhood leukaemia can be established for values exceeding 0.4 µT. As for all epidemiological studies a causal relationship is not proven by this statistical correlation. A biological mechanism explaining the development of leukaemia or the facilitation of growth of leukaemia cells by low-frequency magnetic fields could not be detected up to now. The authors of the study state that 1 % of leukaemia cases in children at the most could be explained by an increased exposure to low-frequency magnetic fields if there were in fact a causal relationship (see “Biological and Health Effects of Low Frequency Electric and Magnetic Fields”.

It is not known how exposure to low-frequency magnetic fields in a very low range of intensity can lead to an increased risk of leukaemia. Other unknown risk factors for childhood leukaemia might possibly also play a part. In 2001, after an expert scientific review the International Agency for Research on Cancer (IARC) of the World Health Organization classified low-frequency magnetic fields as possibly carcinogenic to humans based on epidemiological studies of childhood leukaemia. WHO reviewed the issue again in 2007 and confirmed the classification.

Although epidemiological studies cannot reveal a causal relationship, the results of these studies demonstrate the necessity of precautionary measures.

Transformer stations may contribute to the magnetic field exposure in dwellings in their immediate vicinity. The height of exposure is linked to the total electricity volume of such installations. At night the exposure is usually lower than at peak times.

The magnetic flux densities observed in the immediate vicinity of low-voltage transformers generally amount to 30 to 100 microtesla (µT), depending on the current electric power consumption. These field intensities are reduced to values between 1 and 5 microtesla at a distance of 1 or 2 meters, so that not even a fraction of the limit value for power supply installations is reached. For each individual case, however, the situation can only be specifically assessed if concrete measurements of the electric and magnetic fields are available.

No evidence of health risks caused by low-frequency electric and magnetic fields has been found so far. Nevertheless as a precaution, exposure can be minimised e.g., by ensuring that frequently used rooms such as bedrooms are not in the immediate vicinity of such transformer stations and by not putting the bed next to the wall nearest to the transformer station.

Electric currents in the body are the crucial factors for health effects of low-frequency electric and magnetic fields. If currents above a certain threshold value are induced in the body health hazards may occur (see “Biological and Health Effects of Low Frequency Electric and Magnetic Fields”). In order to obviate these health hazards  current density in the body (reported as milliampere per square meter (mA/m²)) is restricted. The International Commission on Non-Ionizing Radiation Protection (ICNIRP) and the German Commission on Radiological Protection (SSK) recommend a basic limit for the field induced current density of 2 mA/m². This basic limit was defined according to the available scientific knowledge on established health effects of those fields.

Since current densities in the body are difficult to determine easily measurable physical quantities were derived from the basic limit: the electric field strength (reported as kilovolt per meter (kV/m)) and the magnetic flux density (reported as microtesla (µT)). Limit values for the electric field strength and the magnetic flux density are defined in the 26^th Ordinance on the Implementation of the Federal Pollution Control Act (26. BImSchV). The limit value for the electric field strength at a frequency of 50 Hz (electrical power supply) is 5 kV/m and at a frequency of 16.7 Hz (electrified traffic systems) it is 10 kV/m. The magnetic flux density is restricted to 100 µT at 50 Hz and to 300 µT at 16.7 Hz. As long as these limit values are complied with, a compliance with the basic limit value is also guaranteed.