There is no absolute certainty about the health effects of power lines
Even directly below the power lines, electric and magnetic fields are rarely so strong as to cause immediate harm to people.
When the lowest conductors in a 400 kV power line are less than 10 metres from the ground, the strength of the electric field may be at maximum approximately 10 kV/m under the conductors. In such an intensive electric field, some people may feel skin sensations when the electric field makes the hairs of the skin vibrate. In addition, a spark discharge may occur when a person touches a metal object insulated from ground, such as a car’s metal body, under a transmission line. The spark discharge may cause pain at the discharge point, say, in a fingertip. Vibration of hairs of the skin and the spark discharge may feel uncomfortable, but they have not been found to be detrimental to health.
Magnetic fields do not cause immediate harm even under the largest transmission lines. Public exposure to the magnetic fields of transmission lines is much smaller than the action level of 200 µT set out in the Decree of the Ministry of Social Affairs and Health (1045/2018). The action level of the Decree protects from the immediate effects of a magnetic field. It is also suspected that long-term exposure to a power line magnetic field may cause health hazards. Over the past decades, some epidemiological studies have shown that children living near transmission lines have a slightly increased risk of leukaemia compared to the rest of the population. However, no causal connection has been established in the studies. The risk is estimated to increase slightly when children are exposed for a long time to a magnetic field with an average flux density of more than 0.4 μT.
Childhood leukaemia is a relatively rare disease, which means that studying it statistically is challenging. The explanatory mechanism for the phenomenon is unknown and the linkage to magnetic field exposure observed in epidemiological studies has not been confirmed by cell or animal tests. On the other hand, the result has been repeated in some independent studies since the late 1970s, and the finding has not been shown to be a statistical anomaly. On this basis, the International Agency for Research on Cancer (IARC) has classified low frequency magnetic fields as “possibly carcinogenic”. Exhaust gases, among other things, are classified in the same way. Other health hazards of long-term magnetic field exposure, such as adverse effects on adults, have not been observed in the studies. Long-term exposure to electric fields of power lines has not been identified as causing health hazards.
Comparing the 0.4 μT magnetic field to magnetic fields close to power lines and the population numbers in Finland, it can be estimated that less than one per cent of children’s leukaemia cases might be caused by the magnetic fields of transmission lines, if the leukaemia were a result of children's exposure to a magnetic field. This would mean about two additional cases in ten years.
Modern cardiac pacemakers do not probably become disturbed in the vicinity of power lines. However, it is advisable to be cautious with older cardiac pacemakers and ask instructions from the attending physician.