The results of measurements on a variety of electric and hybrid electric vehicles indicate that the most significant source of electromagnetic field exposure in such vehicles is associated with low frequency magnetic fields due to traction currents flowing in the high voltage power network and traction batteries. The highest exposures are often in the vicinity of the feet, due to power cables and/or traction batteries located under the floor of the passenger compartment, or the lower back for rear passengers in vehicles with traction batteries mounted in the rear luggage space. The most significant frequency content of these magnetic fields is generally below 3 kHz, and their spatial and temporal gradients are found to be of the order of 100 mT/m and 100 mT/s, respectively.
Limits on electromagnetic field exposure were defined by the International Commission for Non-Ionizing Radiation Protection (ICNIRP) in 1998, and guidance concerning low frequency fields was revised in 2010. Environmental field levels that should ensure compliance with the exposure limits have been derived assuming a standing human in an open environment exposure to a uniform field over the entire body. As these conditions are not representative of the in-vehicle exposure environment the use of these “field reference levels” may not be appropriate for assessing automotive electromagnetic field exposures. Numerical simulations of an anatomically detailed human model in a vehicle driver’s pose have therefore been used to estimate the induced internal electric field and current density in sample exposure scenarios that are representative of exposure to traction current transients in vehicles with electrical powertrain.
Measurements on electrical powertrains under laboratory conditions show that while magnetic field levels close to the electrical machine may be significantly above the ICNIRP 1998 field reference levels, values at distances in excess of 20 cm are compliant. The numerical models indicate that the basic restrictions on human exposure to electromagnetic fields of both ICNIRP 1998 and ICNIRP 2010 are not reached in the example exposure scenarios studied. Furthermore, the simulation results confirm that the ICNIRP 1998 field reference levels provide reliable safety factors for assessing compliance with the basic restrictions.
Nonetheless, the numerical models suggest that the ICNIRP 2010 field reference levels may not provide a reliable basis for assessing magnetic field exposure risks for exposure situations that are representative of those that may arise within vehicles. Based on the maximum magnetic field in the region occupied by the body, the magnetic flux density at which the restrictions on internal electric field would be reached is lower than the magnetic flux density reference level at some frequencies.
In addition, the immunity test levels specified for artificial implantable medical devices at low frequencies are largely based around the magnetic field reference levels of ICNIRP 1998 for general public exposure. At some frequencies, therefore, the immunity of these devices is not known in electromagnetic environments that may satisfy the general public magnetic field reference levels of ICNIRP 2010, but exceed those of ICNIRP 1998.
For these reasons it is therefore recommended that the field reference levels for general public exposure of ICNIRP 1998 should be used when assessing electromagnetic field exposure risks for the in-vehicle environment. Furthermore, it is recommended that exposure field levels should not be averaged over the body, as the spatial field gradients are so large that averaging is likely to erode the safety margins provided by the ICNIRP 1998 reference levels.