Estimating magnetic field exposures of rail maintenance workers

A measurement survey was undertaken to estimate exposures to 25 hertz (Hz) magnetic fields of maintenance workers on electrified rail lines near Philadelphia, Pa. Because of the mix of frequencies expected, a strategy was developed using new instrument to capture magnetic field waveforms, which were then analyzed by fast Fourier transform for their frequency components. This instrument could only take spot measurements, so a personal monitor repeatedly measured magnetic fields in the ranges of 40-100 Hz. To power trains in the mid-Atlantic region, electrical current flows from the overhead catenary to the locomotive and returns through the rails in a loop up to 10 miles long. This flowing current was the primary source of the magnetic field exposures when a train was near the maintenance work site being measured. A total of 93 spot measurements was taken at five locations. Peak magnetic flux densities ranged from 34 to 185 milligauss (mG) near a transformer, while medians at the five locations ranged from 6.5 to 40 mG. Time-weighted average personal exposures were estimated by combining spot measurements at occupied locations, with estimates of how much time was spent at each location. These averages were estimated to lie between 3.0 and 18 mG, depending on the location of how often trains passed the work site. Comparisons between the spot measurements in the 40-100 Hz frequency range and summarises from the personal dosimeter showed reasonably good agreement. Further characterization of personal exposures in this region may be justified, since on-train workers and passengers may be more highly exposed.