Abstract
The aim of this study was to characterize 60-Hz magnetic field levels in 79 schools managed by the Carleton Board of Education. Using a Field StarTM 1000 magnetometer, 43,009 60-Hz magnetic field measurements were taken in June 1993. The average magnetic field levels in schools (AM =9 0.082 µT, GM = 0.033 µT) were lower than in many other occupational environments. Typing rooms exhibited the highest level with an AM of 0.226 µT. There was a trend for stronger fields in secondary schools, with a GM of 0.072 µT, than those in elementary and intermediate schools, whose fields had a GM of 0.065 and 0.061 µT, respectively. High energy consumption (more than 50,000 kW hr) correlated with the 1 percentile (L1%) of magnetic field levels (r = 0.615).The geometric mean (GM) of the average magnetic field levels of two-story buildings (0.080 µT) was found to be significantly higher than that for one-story buildings (GM = 0.056 µT, p = 0.024). The sources accounting for the largest number of hot spots were wires in the floor with a GM of 0.418 µT (n = 26) in the unmovable source category and electric typewriters with a magnetic field of 1.84 µT (n = 127) in the movable source category. The relationship between interior magnetic field levels and nearness to high voltage power lines (HVPL) did not reach the conventional statistical significance (p = 0.13), possibly because of the small sample size of schools near high voltage lines. Only 6 of the 350 identifiable hot spots above 0.2 µT were attributable to nearby HVPL. Attenuation of exterior magnetic fields from HVPL by building structures was found. The coefficient of attenuation ranged from 1.0 to 9.0. A high correlation (r = 0.922) was found between interior magnetic fields and exterior magnetic field levels within the group of schools near HVPL. The results show that magnetic fields in schools may be manageable to below 0.1µT.