Electromagnetic exposure assessment for welding workers (up to 10MHz)

Abstract

The work in the frame of this master thesis was carried out in the course of the project "Belastung von Schweißern durch elektromagnetische Felder am Arbeitsplatz" which was commissioned by the AUVA and realized by the business unit Mobile Communications Safety of the Smart Systems Division / Austrian Research Centers GmbH - ARC. This master thesis covers the work package "Methoden der numerischen Expositionsbeurteilung" which deals with feasibility, methods, realization and results of numerically determining the density of the electric current within the central nervous system (CNS) of a welding worker being exposed to an electromagnetic field typical for Spot-Welding, MIG/MAG welding and TIG welding. These three welding techniques were selected out of the multitude of different techniques, because they are commonly used in Austria and they deal with high welding currents, which can cause a high exposition of the welder. For the investigation of each single welding technique, a typical scenario has been determined which represents a realistic welding situation. International and national relevant standards and guidelines were evaluated. The standards showed that determination of the induced current densities within the welding worker's CNS is concluded to be the most meaningful restriction for the exposure of the worker. Studies concerning the feasibility of a numerical exposure evaluation employing the finite differences time-domain (FDTD) method lead to the conclusion that the method of frequency scaling needs to be applied for simulations in this frequency range. The method of frequency scaling is subsequently extended to an exciting current with a broad spectrum. The current density levels within the CNS for the three welding scenarios analyzed are 11.33% in the Spot-Welding scenario, 26.25% in the MIG/MAG welding scenario, and 11.6% in the TIG welding scenario, given relative to the basic restriction levels proposed in ICNIRP (1998). The ICNIRP reference level was compared to the magnetic field averaged over the volume of the absent body. Finally, the exposure relative to the basic restriction level is compared to the ICNIRP (1998) reference levels. It is shown that e.g. an exceeding of the reference levels by as much as 659.67% for Spot-Welding does apparently not lead to a violation of the basic restriction level concerning the current density within the CNS.