A model for assessing occupational exposure to extremely low‐frequency magnetic fields in fabrication rooms in the semiconductor health study

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Abstract
A model was created to assess occupational exposure to extremely low-frequency MAgnetic fields (ELF-MF) among semiconductor fabrication-room (fab) workers. This model was based on the assumption that each subject's exposure arose from being near identifiable ELF-MF sources or being in areas with high ELF-MF levels. To assess ELF-MF exposures, the model superimposed subjects' time-activity patterns (patterns of how and where they spent their time) with measurements of MAgnetic-field levels from devices and work areas. This model, which was validated by personal dosimetry on 192 persons in three fabs, predicted actual time-weighted average exposures with a correlation coefficient of 0.62. The inability of the model to predict individual exposures more accurately was attributed to unforeseen sources of elevated ELF-MF (transformers, distribution panels, sources in adjacent rooms) or to errors in subjects' judgments of time spent near devices. These unpredictable errors are intrinsic to the method used to Estimate exposure.