Assessment of Pulsed Magnetic Fields

Status:

completed 02/2022

Aims:

Low-frequency magnetic fields emitted by certain plants can potentially cause electrical stimulation of the nervous system of employees. The specifications in the Occupational Safety and Health Ordinance on Electromagnetic Fields (EMF Ordinance) from the Federal Ministry of Labour and Social Affairs (BMAS) represent a protection concept that prevents this type of stimulation. For the assessment of pulsed fields, the EMF Ordinance lists methods such as the weighted peak method (WPM) or other relevant state-of-the-art methods. In Germany, the time-domain assessment method (TDA) has been in use in the field of occupational safety and health for many years. Both methods, WPM and TDA, are based on slightly different assumptions regarding the underlying physiology behind nerve stimulation and deliver different results in some cases. As a result, it can be difficult to come to a sound and reliable decision when using these methods in certain situations. This problem was tackled as part of a collaboration between the Institute for Occupational Safety and Health of the German Social Accident Insurance (IFA) and the German Social Accident Insurance Institution for the Woodworking and Metalworking Industries (BGHM). The aim of this collaboration was to develop a software that provides support when using both methods of assessment. The results of the project are to be incorporated directly into the revised version of DGUV informative publication 203-038 on the assessment of pulsed fields.

Activities/Methods:

During the project, the physiological principles of the two methods of assessment were researched using scientific publications. Measurements of pulsed magnetic fields were performed directly on site at a business, utilizing a new measurement technique. This technique uses an add-on module developed in-house at the IFA, in order to effectively compare the two methods with a high temporal resolution. After the measurements were performed, the results of the two methods of assessment were analysed and compared against each other. At the same time, a software tool was developed in-house that makes it easier to assess the measured fields and enables direct comparison of the analysed methods. The tool was developed and documented in collaboration with users, in order to ensure that it was suitable for practical use. The findings from the project were incorporated directly into the revised version of DGUV informative publication 203-038, which focuses on the assessment of pulsed magnetic fields.

Results:

At the start of the project, the physiological principles of the two methods of assessment (WPM and TDA) were investigated. Both methods of assessment were evaluated using the SENN (Spatially Extended Nonlinear Node) neurostimulation model, and the WPM evaluation was presented at the BioEM 2021 international conference. The evaluation of the methods of assessment demonstrated that, in its current form, the TDA method is not compatible with some areas of the new Occupational Safety and Health Ordinance on Electromagnetic Fields (EMF Ordinance). While considering several factors during the process of revising DGUV informative publication 203-038 – "Assessment of Non-Sinusoidal Magnetic Fields", a decision was made that the WPM method will be recommended in future.

Later in the project, IFA worked with the BGHM to develop a user-friendly software for the assessment of magnetic fields using the WPM. The name of the software is BEMF, which stands for "Bewertung magnetischer Felder" – German for "Assessment of magnetic fields". This software can now be downloaded from the IFA website free of charge. The software is taken into account in the revised version of DGUV informative publication 203-038, which means that, in the future, a sound description will be available along with the software to ensure reliable assessment of non-sinusoidal magnetic fields in accordance with the EMF Ordinance. The BEMF software is already being used in training sessions at the German Social Accident Insurance Institution for the Energy, Textile, Electrical and Media Products Sectors.

To evaluate the software, current measurements and magnetic field measurements were carried out on coils which magnetised workpieces. The measured values were assessed using the BEMF software and compared with the WPM results from a commercially available measurement device. The assessments made using the BEMF software were correct, meaning that the software successfully completed the evaluation. A WPM implementation was also newly developed in the project "Reference system for the assessment of magnetic fields in resistance welding" from the German Welding Society (Deutscher Verband für Schweißen und verwandte Verfahren). This WPM implementation from the research centre for electromagnetic compatibility (FEMU) was compared with the BEMF implementation from the IFA and delivers comparable results. Furthermore, the experts from the German Social Accident Insurance Institution for the Woodworking and Metalworking Industries (BGHM) tested the BEMF software by using old datasets and comparing the assessments from the software with the previous assessments. The results demonstrated that the BEMF software meets expectations. For this reason, BEMF is now used in the BGHM and the IFA, which means that the assessment can be carried out much more easily and quickly.

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