Objective To investigate the distributions of the level of electromagnetic fields in residence of Shanghai.
Methods Power frequency electromagnetic fields of five different types of power line supply in 125 residences were assessed by conducting spot measurements with KombiTEST. Electromagnetic field levels with electricity appliances turned off were compared to that with electricity appliances turned on through paired-sample Wilcoxon signed rank test. Power frequency electromagnetic fields of 5 different types of power lines supply in residences were analyzed by nonparametric chi-square test.
Results Average power-frequency electric field level was 3.100 V/m and power-frequency magnetic field level was 0.057 μT with all electricity appliances off, while average electric field level was 7.340 V/m and magnetic field level was 0.081 μT with all appliances on. Nine of the residences, approximately 7.2%, had one room there average magnetic field level with all appliances off was greater than 0.4μT. The average electric field level with appliances on was significantly higher than that with appliances off (Z=24.791, P < 0.001), meanwhile the average magnetic field level with appliances on was also dramatically greater than that with appliances off(Z=28.137, P<0.001). Power frequency magnetic field level in suburban residences near high-voltage transmission line was highest among 5 different types of power line supply. No matter that appliances were on or off, the difference of power frequency magnetic field level was significant among these five different types of power line supply(appliances off χ2=421.565, P < 0.001; appliances on χ2=265.575, P < 0.001).
Conclusion High-voltage transmission lines, outdoor distribution lines, indoor power distribution wiring, grounding systems and appliances are main electromagnetic field sources. High-voltage transmission lines and outdoor distribution lines mainly influenc power frequency electromagnetic field level in the residences of Shanghai, while indoor power distribution wiring, grounding systems and appliances have a relatively limited impact on local areas.
DownLoad: