Low frequency magnetic field induction factors for exposure assessment in the human hand

According to European Union (EU) Directive 2013/35/EU, occupational low frequency magnetic field exposure of the hands is assessed by comparing the maximum magnetic induction with the corresponding action level for the limbs (AL_Limb). If AL_Limbis exceeded, it must be demonstrated that the exposure limit values (ELVs) defined by the 2 × 2 × 2 mm³averaged<i>in situ</i>electric field strength (<i>Ê_i,</i>_avg) are not exceeded. However, there is no solid scientific evidence for the currently used AL_Limb. Assuming that AL_Limbensures compliance with the ELV in all limb regions, including areas with larger cross-sections like the lap, questions arise about its conservatism for exposure assessment of localized hand exposure. Therefore, we derived reasonable worst-case induction factors (IFs) for the hand using systematic numerical computations on 16 different MRI-based high-resolution anatomical hand models. Two simplified hand models were also included for comparison. The simulations yielded a robust IF of 0.6 (V m^-1) T^-1Hz^-1for a hand size representing the 95th percentile of adult males. This corresponds to a 33% relaxation of the magnetic induction limit compared to the current AL_Limb, which may reduce unnecessary restrictions in many workplaces with localized hand exposure. However, these relaxed limits must not be applied to other limb regions without proper verification. Furthermore, the study shows that oversimplified hand models, as proposed in the European standard EN 62369-1:2009, tend to significantly underestimate exposure and should therefore no longer be used for dosimetric exposure assessment. Finally, the data obtained confirm that in the case of localized exposure of body parts, comparing the 99th percentile of<i>Ê_i,</i>_avginstead of the (reasonably evaluated) peak spatial<i>Ê_i,</i>_avgwith the ELV leads to a significant underestimation of exposure, because real 'hot spots' of<i>Ê_i,</i>_avgare excluded from the evaluation, although they should be taken into account to avoid localized effects on the nervous system.