Where do electromagnetic fields occur?
There are electric and magnetic fields surrounding all live power lines and electrical equipment. The term electromagnetic fields is a common collective term for electric and magnetic fields. Magnetic fields occur when current passes through a power line or electrical appliance. The size of the magnetic field depends on the amperage in the line or facility, the distance from the facility and how the various power sources interact. Magnetic fields are measured in microtesla (µT). The power supply in Norway is based on 50 Hz alternating current. At this frequency, the fields change direction. However, the frequency is so low that energy is not emitted as radiation. Consequently, this is referred to as Extremely Low Frequency fields (ELF).
Electric fields depend on the voltage and are measured in kilovolt/metre (kV/m). An electric field occurs when the power line or appliance is energised. This can be effectively shielded by metal, earth, most building components and vegetation. Buried cables will therefore only generate magnetic fields. It is difficult to shield magnetic fields, but a field can be reduced through appropriate facility planning and design.
Potential health effects
Generally speaking, it cannot be ruled out that there is no potential connection between magnetic fields and adverse health effects. However, recent research indicates that any such effects are modest.
Decades of research into electromagnetic fields has produced inconclusive results. Although more recent research has provided more thorough knowledge, indicating that any potential adverse health effects are minor. A small potential connection between proximity to power lines and negative health effects cannot, however, be entirely excluded.
A cautious strategy
When planning new power lines and transformer substations, Statnett complies with the provisions in the Regulations on Radiation Protection and Use of Radiation and follows the Norwegian authorities’ precautionary advice. This means that Statnett will seek to avoid planning and constructing new installations close to housing areas, kindergartens and schools if the assessment level exceeds 0.4 microtesla.
As the long-term health effects from exposure to power line fields have not been consistently documented and are thus uncertain, research will continue to play a key role also in the future. Statnett has actively contributed to such research, by commissioning research itself and by funding other studies. We impose strict requirements on research projects funded by Statnett, to ensure they achieve the highest academic standards and a high level of integrity. To obtain credible and reliable results, we prefer that research into health effects from exposure to electromagnetic fields is financed by neutral sources.
Statnett has focused its research on helping to develop a new type of pylon with smaller electromagnetic fields. The result of this research is the Compact Plus pylon. We continue to evaluate the use of this and other measures as new knowledge is acquired.
Information from the Norwegian Radiation Protection Authority
On its web page, the Norwegian Radiation Protection Authority writes the following about high-voltage power lines and illness:
"Comprehensive international research into the field has provided more thorough knowledge about electromagnetic fields and health effects than previously. In June 2001, the International Agency for Research on Cancer (IARC) classified magnetic fields from high-voltage power lines as potentially carcinogenic for people, mainly based on an association between residential exposure and an increased risk of child leukaemia in population studies. Magnetic fields are measured in microtesla (µT).
The population studies generally indicated a potential double risk of developing childhood leukaemia where the average value for magnetic fields near households is above 0.4 µT. In Norway, this may result in one extra case of leukaemia every seven to eight years among children exposed to magnetic fields from high-voltage power lines. As regards other types of cancer in children and adults, there is no consistent evidence that exposure to magnetic fields at home or at work causes cancer. As regards a potential connection between exposure and other adverse health effects and symptoms, the available data is insufficient to draw a conclusion."
Facts about magnetic fields
- Magnetic fields are usually measured in the unit microtesla (µT).
- The size of the magnetic field depends on how much electricity passes through the line.
- The limit value for short-term exposure is 200 µT for the general public.
- For an assessment of long-term exposure, a level of 0.4 µT has been set.