背景和目的：紀錄鄰近高壓(69/161 千伏) 輸電線住家內部極低頻磁場24 小時之強度與變異，並探討能夠預測磁場強度與變異性的因素。方法：於2001年的1至5月間，汐止鎮總共有249個距高壓輸電線100公尺內的家戶(為一方便樣本)接受24小時連續之磁場測量。本研究將EMDEX II 至於客廳中央約1公尺的高度，每5分鐘紀錄1 次量測值，如此每1 家戶共約得到288 個量測值。吾人計算幾何平均數與幾何標準差來代表每一個家戶內磁場的強度與變異性，並進行全體樣本家戶間磁場強度與變異之描述性統計。本研究也探討某些環境與測量因素對家戶磁場強度或變異性的預測能力。結果：家戶磁場強度介於0.017 T 至5.176 T 之間，幾何平均與標準差分別為0.255 T與0.419 T；家戶磁場標準差介於0.001 T至0.495 T 之間，幾何平均與標準差分別為0.036 T 與0.057 T。與高壓輸電線的距離以及1週中量測的時間是家戶磁場強度的顯著預測因子；而建築材料則與家戶磁場變異性間有顯著相關，其中位於鋼架建築內之家戶磁場變異性較高。結論：本研究所分析之環境與測量因素對解釋家戶磁場強度與變異性的能力很低。位於鋼架建築內家戶之磁場變異性較高可能表示這些家戶內脈衝磁場強度較強。未來研究可以比較鋼架高樓內居民與其他建材建築內居民之健康風險，以進一步了解脈衝磁場對人體不良健康效應的可能影響。

Background and Purpose: To document the intensities and variations of 24-h extremelylow frequency magnetic fields in residences near high-voltage (69 and 161 kV) transmissionlines (HVTLs) and to determine the predictors for the magnetic field intensity and variation.Methods: Twenty-four-hour on site measurements of 60-Hz magnetic fields were completedfor a convenience sample of 249 residences locatedwithin 100mofHVTLs in Hsi-Chih, Taiwanbetween January and May 2001. Measurements were carried out, using EMDEX II, at the centerof the living room with a sampling rate of every 5 min, which in turn gave rise to roughly 288readings for each study residence. The geometric mean (GM) and geometric standarddeviation (GSD) were calculated to represent summary indicators of the intensity and variationof the magnetic field in each home.We used descriptive statistics to depict the distributions ofin-home intensity and variation among the study residences. A number of environmental andmeasurement-related factors were also recorded to evaluate the extent to which these factorspredicted 24-h in-home magnetic field intensity or variation. Results: Among the selected residences, the in-home intensity ranged from 0.017 to 5.176 micro-Tesla ( T), with a GM andGSD of 0.255 and 0.419 T, respectively. The in-home variation, on the other hand, showed thelowest and highest values of 0.001 and 0.495 T, respectively with a GM and GSD of 0.036 and0.057 T, respectively. Distance to the nearest HVTL and day of the week on which themeasurement was taken were found to be significant predictors of magnetic field intensity,whereas the magnetic field variation was significantly higher in high-rise apartments with asteel structure than in reinforced-concrete buildings. Conclusion: The overall ability of theselected factors to predict either residentialmagnetic field intensity or variation was limited. Agreater variation in magnetic field was found in residences with a steel structure, which mightsuggest a stronger pulsed magnetic field in those residences. Future studies comparing healthrisks between residents of highrises with a steel structure and residents of homes made fromreinforced concrete may help clarify the role, if any, of pulsed magnetic fields in causingadverse health effects.