Effectiveness of Radiofrequency Field Exposure Assessment for Vehicle Occupants Based on Empty Vehicle Field Data and Field Reference Levels

Electromagnetic field levels are widely used as a convenient metric for assessing non-localised human exposures, by comparing them with field reference levels derived for standing humans under uniform exposure in an open environment. In practice, however, people are more frequently seated in partially resonant cavities, such as buildings or vehicles. This paper outlines a simulation-based investigation of the possible effectiveness of such an approach for vehicle occupants, including the influence of occupancy variations, for frequencies in the range 0.4-2.4 GHz. The results indicate that limiting the average empty-vehicle fields to the field reference levels recommended by 1999/519/EC did not ensure compliance with the basic restrictions at the higher frequencies. However, different statistical field metrics or alternative reference levels could achieve a safety factor of two or more at the higher frequencies. These observations have implications for the development of related standards for assessing field exposure levels in cars and other human environments.