陰極射線映像管型電腦終端機電磁場暴露評估

Exposure Assessment of Electromagnetic Fields Emitted from Visual Display Terminals with Cathode Ray Tube

本研究選定桌上型個人電腦終端機（VDT）共29 台，測量VDT 所產生頻率為20-30 kHz 之電磁場強度以瞭解：1. VDT 之特徵是否會影響所產生之電磁場強度？以及2. VDT 螢幕前方與操作者座位上方兩處所量測到之電磁場強度是否有差異？本研究利用HOLADAY(TM) MODEL HI-3603 VDT/VLF RADIATION SURVEY METER進行電場與磁場之測量。至於測量方法則依1992 ANSI/IEEE（C95.1-1991）所規範之測量準則進行之。該準則包括，分別測量電場與磁場，使用前之校正，針對每一個測量點，測量時間為6 分鐘，電場或磁場強度則為6 分鐘時量平均值。測量結果發現：座位正上方30 公分處所量測到之電場與磁場強度平均值分別為0.49 V/m與8.63mA/m（或0.11 mG），而螢幕尺寸與此處之電場強度有顯著正相關。螢幕中心點正前方50 公分處所量測到之電場與磁場強度平均值則較高，分別為1.29 V/m 與38.4mA/m（或0.48 mG），而與此處電場強度有顯著相關之VDT 特徵則包括VDT 廠牌與VDT 之使用年數；本研究數據也顯示，有無使用護目鏡與兩處之電場強度並無顯著相關性，而VDT 之特徵也與兩處之磁場強度無顯著相關。本研究數據也顯示：兩處磁場測量值間之相關性高於電場測量值間之相關性（r＝0.558 vs r＝0.356），而無論是VDT 前方或座位上方所測量到電場與磁場值間之相關性均很低，相關係數分別為──0.252 與0.153。本研究建議，未來流行病學研究進行VDT 暴露評估時應分別測量電場與磁場之強度，此外，也應考慮VDT 之特徵對電場強度之影響，並在選擇測量點時，宜考慮此測量點之電磁場是否能反應暴露評估器官之位置。

This study seeks to measure potential exposure to very- low-frequency (20－ 30 kHz) electromagnetic fields (EMF) at visual display terminal (VDT). Two questions were addressed. The first question focussed on whether the EMF varies with the characteristics of VDT. The second issue determines whether the exposure to electric and magnetic fields varies with measuring locations at the terminal. We performed measurements at a distance of 30 cm above the seat of the VDT operator in the working position－an approximate location of VDT users’ reproductive organs (site A) and at a distance of 50 cm in front of the screen (site B). A convenient sample of 29 VDTs was selected for measurement. A HOLADAY™ MODEL HI－3603 VDT/VLF RADIATION SURVEY METER was used for measurement. The measurement procedure was based on the 1992 ANSI/IEEE（C95.1-1991）standard which requires separate measurement of electric and magnetic fields, calibration before use, and calculation of the 6-minute time-weighted-average for each site being measured. Results showed that the average electric and magnetic fields measured at site A were 0.49 V/m and 8.63 mA/m (or 0.11 mG), respectively. The corresponding figures for site B were higher at 1.29 V/m and 38.4 mA/m (or 0.48 mG), respectively. The electric fields were found to be positively associated with the size of VDT at site A; while at site B, both the brand and age of VDT were associated. It appeared that the use of filter is unrelated to electric fields and VDT characteristics posed no effect on magnetic fields. Results also indicated that the correlation for magnetic fields between site A and site B was stronger than that for electric fields (r＝0.558 vs r＝0.356). There was no significant correlation between electric and magnetic fields, irrespective of where they were measured. This study suggests that future epidemiological studies should separately assess electric and magnetic fields in exposure assessment. Additionally, exposure assessment of electric fields should take VDT characteristics into consideration, and the EF of VDT should be measured at approximate positions in studying its health implications.