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Comparison of Articulograph and VDT use

Epidemiological and laboratory studies suggest that the VLF magnetic fields produced by a video display terminal do not increase the risk of spontaneous abortion. It should be noted, however, that there are important differences between exposure to the VLF fields of a VDT and exposure to the fields generated by the Articulograph, which make comparison difficult.

First, the fields to which a subject is exposed in an Articulograph are several orders of magnitude higher than the VLF fields of a VDT. This is in part because the Articulograph transmitters produce stronger fields than any VDT, and in part because subjects are closer to the Articulograph transmitters than they would be to a VDT. At a distance of 50cm, a single Articulograph transmitter coil produces a field of 0.7-0.8uT. This is the equivalent of 7-8 worst-case VDTs (VDTs taken from the top of the range measured by Haes and Fitzgerald), or the equivalent of 50-60 typical VDTs (VDTs taken from the logarithmic midpoint of the Haes and Fitzgerald range). The field strength at 7.5cm distance is 44 times larger than the field strength at 50cm distance, for a total exposure similar to the level of 2200-2600 typical VDTs.

Second, exposure to the fields of an Articulograph is acute, while exposure to a VDT is chronic. Although neither acute nor chronic exposure to VLF fields has been linked to any health risk, the study of Lindbohm et al. (1992) suggests that exposure to ELF fields carries a risk which increases with the duration of exposure.

Mark Hasegawa-Johnson
Mon May 26 15:33:40 PDT 1997