Proven effects of static and low-frequency fields

In the German power grid, alternating current flows at a frequency of 50 hertz (Hz). This creates so-called low-frequency electric and magnetic fields, which, like the alternating current in the line, change direction 100 times per second. This is why we speak of low-frequency alternating fields.

Effect of alternating magnetic fields on humans

Natural electric fields in the body

All living beings, including humans, contain many electrically charged particles. Their movement leads to electric fields and currents. In many metabolic processes, electrically charged particles are shifted and nerves transmit their signals in the form of electrical impulses. The heart is also electrically active.

Doctors can measure such endogenous processes in the electrocardiogram (ECG) or the electroencephalogram (EEG), for example.

Effects of low-frequency fields

Low-frequency fields generate additional electric fields and currents in the human body. As a result, nerve and muscle cells can become irritated. However, for this to happen, certain frequency-specific impact thresholds must be exceeded. For example, for the stimulation of nerve fibers located in the skin or muscles, electric field strengths of 4-6 volts per meter (V/m) are necessary.

The lowest proven efficacy threshold concerns the triggering of so-called "phosphenes". These are light perceptions that are caused by the irritation of sensitive cells in the retina of the eye. Although phosphenes do not have any adverse effects on health, they are considered to be a particularly sensitive model for irritation of electrically excitable cells.

The higher the field strengths that occur in the body, the more dangerous it can become. If the nerve conduction in the body gets confused, there is a risk of cardiac arrhythmias, for example.

Protection against health hazards

A pacemaker

Since the thresholds for the proven effects are known, recommendations for limiting low-frequency fields can be made on this basis. The International Commission on Non-Ionizing Radiation Protection (ICNIRP) recommends that the electric field strengths generated in the brain and retina should remain below 20 millivolts per meter (0.02 V/m) for frequencies of 50 hertz.

The limit values for stationary installations (e.g. high-voltage lines) set in Germany in the 26th Federal Immission Control Ordinance (26th BImSchV) are also based on this recommendation. The limit values for the immissions acting on the body from the outside protect against the proven health-relevant effects of low-frequency electric and magnetic fields.

Static electric and magnetic fields

No health hazards have been proven for static electric fields emitted by direct current lines, as they occur in normal exposure situations. The static magnetic fields emitted by direct current lines are also harmless in normal exposure situations.

With the amended 26th BImSchV, which has been in force since August 2013, limit values for direct current systems are legally defined in Germany for the first time. The limit of 500 microtesla (0.5 millitesla) is chosen in such a way that interference from pacemakers caused by static magnetic fields is excluded.

In the medical field, strong static magnetic fields of several tesla (i.e. several thousand millitesla) are used for imaging procedures. In this area, acute effects such as dizziness or nausea can occur for patients, but also for medical staff.

By the way: The effects of low-frequency fields are fundamentally different from those of high-frequency fields. The latter are used, for example, in mobile communications.