Town of Markham


AutoCAD work stations typically use computers connected to larger than average high resolution monitors to display detailed graphic information. The sheer size of such monitors often gives rise to the concern that, if there might hazards associated with the use of computers, they would be correspondingly greater with such equipment. Recurring media coverage suggesting a variety of adverse effects from using computers and recent reports about a possible connection between 60 Hz electric and magnetic fields and leukaemia coupled with some recent medical problems experienced by the operator of the AutoCAD system led to concerns being expressed about the magnetic field levels in the area.

RHSC carried out measurements of ELF and VLF magnetic fields in the vicinity of and AutoCAD work station to establish whether or not levels there might result in worker exposures in excess of recommended limits. RHSC reported on the measurement results discussing the significance of the observed levels comparing them to levels in other occupational, commercial and residential environments.


Difficulties had been experienced with the use of a computer monitor in the Theatre Manager's office. Noticeable colour distortion had been observed on numerous occasions although it was found to vary in severity from time to time. It was generally found to be minimal just after the system had been turned on but became progressively worse while the system was being used. Several substitute monitors had been tried to no avail. Some improvement had been achieved by moving the monitor to the other (south) end of the desk (user's left) but some abnormalities were still apparent.

The Theatre Manager's office is situated on the lower level of the theatre and the Development Coordinator's office is directly above on the second level. The main electrical room of the theatre is situated on the third level, above the two offices in question. Because the electrical feed for the building comes underground from a vault in a neighbouring building and passes up to the electrical room in the vicinity (possibly through the exterior walls) of the two offices it was suspected that it might be the source of the interference.

RHSC carried out measurements which showed that the power frequency magnetic field levels were lower than the levels commonly found to cause display jitter. Neither was there any indication of a significant spatial non-uniformity in the power frequency magnetic field. The variations observed at various locations throughout the office were small and the overall levels were within the range normally encountered in urban and office environments (as stated above). The computer monitor colour distortion problems observed in the Theatre Manager's office were ultimately traced to the influence of permanent magnets which are part of high power speakers stored in an adjacent area. Moving the speakers to a location at a greater distance from the monitor rendered the colour distortion negligible.

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