Are electric lines and transformers dangerous?
Power lines
Electricity is transferred via high-voltage transmission lines long distances from power stations to end users. The voltages can range between 110 to 765 kV. The current produces a magnetic field around the lines, and the voltage produces an electric field, thus the former correlates with current (amperes), the latter with voltage (volts). The current varies with the load, but the voltage and electric field remain rather constant.
Exposure to electromagnetic fields is regulated by legislation in many countries. The established safety limits are based on the guidelines of the International Commission on Non-Ionizing Radiation Protection (ICNIRP) published in 1998, and recommendations of the Council of the European Union. The guidelines protect with a large safety margin (over 100-fold) the nervous system from any functional disturbance induced by currents.[1] In a strong magnetic field, disturbances occur in the functions of retina[2] seen by the individual as irregular flashes of light. It is thought that these phenomena are caused by small changes in the charges at nerve cell membranes evoked by the induced currents. This effect is reinforced in the synapses[3] between nerve cells.
An electric field is decreased by any solid structure (such as a wall) to a fraction in all indoor spaces. Magnetic fields are not attenuated by any building materials, thus there may be higher intensities than background in homes close to high voltage transmission lines. Only people who live in the immediate vicinity of the lines are exposed to the electromagnetic fields produced by the high voltage transmission lines; at 65 m the intensity is less than 1 μT[4] while the guideline value is 100 μT. The background is attributable to domestic appliances and electrical wires.
Experimental and population studies
The guideline values are based on the presence of biological effects that have been confirmed in scientific studies. The problem causing uncertainty is that there are over 25 population studies starting in the 1970s that imply that there is an increase in leukaemia in children living in the vicinity of power lines, if the magnetic field exceeds 0.4 μT. These findings have not been associated with electric fields. The International Agency for the Research on Cancer of the World Health Organisation has classified magnetic fields as possible carcinogens. A higher classification was not appropriate, because there was no support for the population studies from either animal or in vitro studies.[5] There is also no currently plausible mechanism to explain such an effect at field levels found around power lines.
Guidelines
Nonetheless people living close to power lines may be concerned because of the population studies. Therefore, the authorities in many countries have adopter stricter limits or now recommend that new housing should not be planned close to high voltage transmission lines. When new power lines are planned, it may be wise to ensure that they run nowhere near housing, day-care centres, playgrounds and schools.
Transformers in houses
The magnetic fields in homes and workplaces are typically 0.05 to 0.5 μT. In the ground floor of an apartment complex, a flat may be directly above a transformer. Since there may be a current of hundreds of amperes in a restricted area, the magnetic field may be up to 100 μT. This may be very local and extend only a few metres, but it clearly increases the field in a few rooms. One special problem is old transformers constructed in the 1970s or earlier. Rather simple technical solutions have been introduced in newer transformers to reduce the magnetic field.
Several population studies suggest that there might be an increased risk of children’s leukaemia in the vicinity of high voltage transmission lines. No biological mechanism has been detected and experimental evidence is inadequate. Therefore the safety recommendations are purely precautionary.
Notes and references
- ↑ Electromagnetic induction means that a change in magnetic or electric field induces a current in any electricity-conducting material within the field. Electric induction motors and transformers are based on this phenomenon. It means that electric currents may be induced in the organism even if one does not touch an electric wire.
- ↑ Retina is the layer of cells sensitive to light in the back wall of the eyeball.
- ↑ The synapse is a small area of contact between two nerve cells where electrical current propagating along the nerve cell membrane induces the release of chemical substances to transmit the message to the next cell.
- ↑ Tesla (T) is the unit of magnetic field intensity, μT is one millionth of T
- ↑ See chapter "Why are experts usually so sceptical?"
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