Compliance with EU Basic Restrictions near induction furnaces used in precious metal industry: a 3D numerical dosimetric analysis using the Scalar Potential Finite difference (SPFD) technique and a posturable digital body model

Induction heating is widely used for metallurgic treatments on precious metals. A survey in a few plants located in the Tuscan province of Arezzo, one of the main Italian districts of gold industry, revealed that workers involved in these treatments are often exposed to intense magnetic fields, many tens of times higher than the maximum allowable levels specified by the 2004/40/EC Directive. A numerical approach has been developed and used to check compliance with the European Directive exposure limit values for the induced current density, as requested in these situations. This approach is based on a 3D implementation of the scalar potential finite difference method, in conjunction with an original articulation technique, able to put the digital model used to represent the exposed body in the typical posture assumed in the working practice. Thanks to the low frequency of operation and to other characteristics of induction furnaces, our approach takes great advantage of the application of the so called quasi-static approximation and of the possibility to disregard the electric component of the field. One of the main problems we had to deal with in setting up our methods, concerned the algorithm to be used to calculated the cross-section averaged current density in the tissue of the nervous central system, as requested by the Directive. Actually, the Directive specifications are somewhat ambiguous and there are quandaries on how they should be applied. Moreover, these specifications become completely inapplicable in the general case of elliptical field polarization. Under acceptable hypothesis, out results show that, with magnetic flux densities values exceeding up to 65 times the maximum allowed values, the averaged induced current density surpasses the exposure limit value by just a 10%, a fact that indirectly confirms the validity of the two-level approach of the Directive.