A survey of electric and magnetic fields among VDT operators in offices

The ambient electric and magnetic fields as well as the electromagnetic fields associated with video display terminals (VDTs) at 150 offices are measured. The aim of the study is to determine the general level of the various electromagnetic parameters in offices and establish a technical base for a case referent study of skin symptoms among VDT workers. The median value of the 50-Hz background field in the 150 offices is 0.07 μT. Seven of the offices have background levels higher than 0.5 μT, which is high enough to cause distortion of the picture on the screen. The dominant source for electric fields in the ELF range is electric equipment in the office, not the VDTs. The equivalent surface potential is less than 0.5 kV for 63% of the measured VDTs. The computer monitor is a major source of magnetic fields in the offices. The median value of the magnetic field in the ELF range in front of the VDT is 0.21 μT, and in the VLF range it is 0.03 μT