Simultaneous AC and DC magnetic field measurements in residential areas: implications for resonance theories of biological effects

The goal of this study was to obtain data that could be used to evaluate the applicability of “resonance” theories of biological effects in residential settings. We first describe a measurement system which allows the study of AC and DC magnetic fields simultaneously in space and in time. Sample measurements were taken near two power lines, two objects and in two residential homes. The results show that the Earth´s (DC) magnetic field was unaffected near power lines. The compass orientation of the power line influenced the relative values of the AC components parallel and perpendicular to the DC field. The electric heating system greatly affected the AC field levels in the home, causing the levels to increase from less than 1 mG to a maximum of 7.5 mG during heating. The magnitudes of the DC field in the two homes varied from about 380 to 650 mG, with the larger variations near metallic or magnetic objects such as the refrigerator or a metallic air duct. The Earth´s field was elevated above its natural level within a distance of 8 feet from a subcompact passenger car, e.g., the level changed from about 540 to 1100 mG beside the headlight. A steel chair changed the Earth´s field by up to 60 mG within a distance of one foot. These results suggest that some of the narrow “resonances” described in laboratory studies may be difficult to observe against the variations in DC field amplitude and direction resulting from the presence of everyday metallic objects