Exposure of school employees to extremely low frequency magnetic fields

This study was initiated to determine and compare daily occupational exposure (OE) and non-occupational exposure (NOE) of three employee groups of teachers, maintenance workers and secretarial staff in a Canadian school district. The time-weighted average (TWA) individual OE for subjects ranged from 0.4-3.8 milligauss (mG), and the TWA NOE ranged from 0.2-7.1 mG. TWA OE and NOE were 1.2 mG and 1.5 mG for teachers, 1.8 mG and 1.2 mG for maintenance workers, and 2.9 mG and 2.1 mG for secretarial staff. The differences between TWA OE and NOE of each group and also among the three groups were not statistically significant. OE and NOE of secretarial staff exceeded 10 mG 9.0% and 6.4% of the time--significantly (p < 0.001) higher rates than those of OE and NOE of teachers (1.0% and 1.4%) and maintenance workers (2.8% and 0.1%). Exposures were well below recommended criteria.