Extremely low frequency magnetic field measurements in buildings with transformer stations in Switzerland

► There is a distinct ELF-MF exposure gradient in buildings with transformers. ► In apartments that were fully adjacent to a transformer room mean ELF-MF was 0.59 μT. ► The location of the apartment relative to the transformer room predicts ELF-MF exposure. ► Such an approach minimizes selection bias in a future epidemiologic study.