Numerical evaluation of 60 Hz magnetic induction in the human body in complex occupational environments

Abstract

Exposure to 60 Hz non-uniform magnetic fields is evaluated using realistic configurations of three-phase current-carrying conductors. Two specific scenarios are considered, one involving a seated worker performing cable maintenance in an underground vault with conductors carrying 500 A root-mean-square (rms) per phase, and the other involving a standing worker during inspection of a 700 MW generator with conductors carrying 20000 A (rms) per phase. Modelling is performed with a high-resolution (3.6 mm) voxel model of the human body using the scalar potential finite difference (SPFD) method. Very good correspondence is observed between various exposure-field measures, such as the maximum, average, rms and standard deviation values, and the associated induced field measures within the whole body and various organs. The exposure fields produced by the lower currents in the vault conductors result in correspondingly low current densities induced in human tissues. Average values are typically below 0.2 mA m(-2). On the other hand, the average exposure related to the inspection of the generator isophase buses is about 1.5 mT at a distance of 1.2 m from the conductors. This field induces organ average current densities in the range of 2-8 mA m(-2), and peak (maximum in voxel) values above 10 mA m(-2). A comparison with uniform field exposures indicates that induced fields in organs can be reasonably well estimated from the accurately computed exposure fields averaged over the organs and the organ dosimetric data for uniform magnetic fields. Furthermore, the non-uniform field exposures generally result in lower induced fields than those for the uniform fields of the same intensity.