ELF-magnetic flux densities measured in a city environment in summer and winter.

Epidemiological studies have indicated a connection between extremely low frequency magnetic flux densities above 0.4 microT (time weighted average) and childhood leukemia risks. This conclusion is based mainly on indoor exposure measurements. We therefore regarded it important to map outdoor magnetic flux densities in public areas in Trondheim, Norway. Because of seasonal power consumption variations, the fields were measured during both summer and winter. Magnetic flux density was mapped 1.0 m above the ground along 17 km of pavements in downtown Trondheim. The spectrum was measured at some spots and the magnetic flux density emanated mainly from the power frequency of 50 Hz. In summer less than 4% of the streets showed values exceeding 0.4 microT, increasing to 29% and 34% on cold and on snowy winter days, respectively. The average levels were 0.13 microT (summer), 0.85 microT (winter, cold), and 0.90 microT (winter, snow), with the highest recorded value of 37 microT. High spot measurements were usually encountered above underground transformer substations. In winter electric heating of pavements also gave rise to relatively high flux densities. There was no indication that the ICNIRP basic restriction was exceeded. It would be of interest to map the flux density situation in other cities and towns with a cold climate.