The Swiss Research Foundation for Electricity and Mobile Communication (FSM) at ETH Zurich has published a technical report on the electromagnetic fields generated by power technologies (EMF). The report was commissioned by the Swiss Federal Office of Energy (SFOE) and summarises more than 800 scientific papers on the topic. The report was written by the FSM in association with authors from the University of Applied Sciences Graubünden, the High Voltage Testing and Engineering Commission (FKH), Fields at Work GmbH, Swiss TPH and the University of Basel. Some of the findings of the report are presented here.
Where do electric and magnetic fields occur when electricity is supplied?
The various systems required to supply electricity generate electric and magnetic fields of varying strength in their immediate vicinity, depending on their function, construction and voltage level. This is due to physics and is nothing unusual. An electric field is also produced when a household appliance is plugged into the power outlet. As soon as the device is switched on, current flows through the connecting cable and a magnetic field is created in addition to the electric field. Electric fields only occur in the surrounding area of overhead lines and high-voltage installations if they use air for insulation (as is the case for certain switchgear in substations, for instance). Other high-voltage installations, such as underground cables, usually have a metallic shield or encapsulation that does not allow the electric field to pass through. Magnetic fields, on the other hand, occur in varying strengths in the vicinity of all installations, including cable lines laid underground and in the area around substations and transformer stations. The strength of the electric field depends on the voltage of the line. Since the voltage is usually kept constant, the electric field also remains constant. The strength of the magnetic field, on the other hand, is variable and depends on the intensity of current, which changes according to the load on the line. When the current or load is low, the magnetic field is also small. The electric and magnetic fields of extra-high-voltage lines like those operated by Swissgrid decrease rapidly as the distance from the line increases.
Unlike electric fields, magnetic fields are not weakened by the walls of houses, and can therefore pass from the outside into the rooms inside. This means that it is more important to investigate the impact of magnetic fields on the environment and on people than that of electric fields.
How strong are the magnetic fields that occur in everyday life?
Since 2021, an annual record of the magnetic fields in our environment has been kept on behalf of the Federal Office for the Environment (FOEN). The main sources of these fields are the supply of electricity and overhead contact lines for trains. The limit set for magnetic fields from extra-high-voltage lines in Switzerland is 100 microtesla (μT). This maximum immission value protects against all scientifically recognised adverse health effects. The values measured in the FOEN study in publicly accessible areas were far below this limit, with mean values of between 0.02 and 1.15 µT. These results are comparable to measurements carried out previously.
Can we perceive electric and magnetic fields?
When we talk about the effects of fields from power lines on humans, a distinction must be made between biological effects and possible health risks. A biological effect refers to the threshold above which we actually start to feel the electric and magnetic fields from power lines, e.g. in the form of a tingling sensation on the skin. The most recent research on the perception of electric fields from power lines was carried out in a laboratory in Germany. Perception thresholds vary a great deal from one person to another. It is unclear what causes these differences. According to this study, the average threshold at which the test subjects were able to perceive the electric field was a field strength of around 14,000 volts per metre (V/m). The strength of an electric field is measured in volts per metre. By way of comparison, a maximum immission value of 5,000 V/m applies to these fields in Switzerland. For us to perceive a magnetic field, it must have a strength of 5 to 10 millitesla (mT). This is 50 to 100 times higher than the applicable maximum immission value for power supply installations in Switzerland.
Are magnetic fields from extra-high-voltage lines responsible for negative effects on our health?
Scientific research has so far not proven any harmful effects on health from the weak magnetic fields that occur in everyday life and that remain below the set limits. One question for which there is not yet a conclusive answer concerns the possible increased incidence of childhood leukaemia in the vicinity of extra-high-voltage power lines. Statistical correlations have been found in epidemiological studies, but they do not necessarily indicate that childhood leukaemia is caused by these magnetic fields. There is great uncertainty surrounding the increased risk estimates derived from these epidemiological studies. On the one hand, many studies have investigated possible sources of methodological error, such as the inaccurate recording of the magnetic field strengths that the affected children are exposed to throughout their daily lives. On the other hand, it is also conceivable that factors other than magnetic fields could be responsible for the occurrence of childhood leukaemia. The greatest shortcoming of the assessment, however, is that to date, no scientifically sound concept has been established that could explain the development of childhood leukaemia through exposure to weak magnetic fields. But even assuming that magnetic fields from power lines are indeed responsible for an increased risk of childhood leukaemia, the risk would be small compared to that associated with other childhood diseases. This could perhaps explain a maximum of one percent of the total number of new cases of childhood cancer that arise each year. In general, it can be said that cancers in children are rare.
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