Video display terminal very low frequency measurements: the need for protocols in assessing VDT user "dose".

It has been well established that video display terminals (VDTs) which employ the use of a cathode ray tube produce electric and magnetic fields of varying frequencies. Numerous studies have attempted to relate magnetic field exposure from VDTs in the extremely low frequency (ELF) and very low frequency (VLF) bands to adverse pregnancy outcome. Initial studies utilized VDT use time as a surrogate assessment of exposure, while later studies have obtained actual measurements. These measurements have been typically obtained at fixed distances from the screen. While VDT measurement criteria have been established for measuring VDT fields, criteria for the assessment of VDT user exposure has not. VLF magnetic and electric field measurements from approximately 140 and 40 different VDTs, respectively, were obtained over a 3-y period at the following positions: 0.50 m from the vertical centerline of the screen and at the approximate location of VDT user reproductive organs--0.30 m above the seat of the VDT operator in the working position. The measurement results of the two aforementioned locations were compared and demonstrate very little correlation. This lack of correlation indicates that VDT operator exposure assessment criteria are needed to determine any dose-response relationship between VDT electric and/or magnetic fields and adverse health implications.