The designs of in vivo, in vitro and in silico studies do not adequately reflect the characteristics of long-term occupational EMF exposure; the higher exposure levels permitted for employees are nevertheless extrapolated on this basis. Epidemiological studies consider occupational exposure only in a very general way, if at all. There is a lack of detailed descriptive data on long-term occupational exposure over the duration of the working life. Most studies reflect exposure characteristics of the general population, exposures which are long-term, but at a comparably low level. Occupational exposure is often intermittent with high peak power followed by periods with no exposure. Furthermore, the EU EMF-Directive 2013/35/EU states a demand for occupational health surveillance, the outcome of which would be of great help to epidemiologists studying the health effects of EMF exposure. This paper thus aims to outline and specify differences between public and occupational exposure and to increase the understanding of specific aspects of occupational exposure which are important for long-term health considerations. This could lead to a future protection concept against possible hazards based on adequate descriptions of long-term exposures and also include supplementary descriptive features such as a “reset time” of biological systems and accurate dose quantities.

An exposure assessment study was performed within a sample of apartment buildings with built-in transformer rooms located throughout the Sofia city. This study was a part of the International project TRANSEXPO which goal was to find the epidemiologic association between extremely low frequency magnetic fields (ELF-MF) and childhood leukemia. The exposure assessment part was directed to estimation of magnetic field exposures in residences that are both near to and distant from the transformer room, based upon their location relative to the transformer station. Measurements of 50 Hz magnetic field (MF) were performed in 65 apartments, 21 buildings, with built-in transformer stations. In each building, measurements were made in the following types of apartments: 1. apartments that have rooms directly above and next to the transformer; 2. apartments selected on the same floor as the one directly above and next to the transformer; 3. apartments on the upper floors randomly selected among all the other apartments of the building; The measurement results show clear difference among the magnetic field values measured of the three categories of apartments, respectively 0,4 µT for the “exposed” apartments 0,23 µT on the same floor, and 0,1 µT on other floors. These results confirm that classification of magnetic field exposure based on apartment location is possible with specificity 0,91 and sensitivity 0,95 for cut-off point 0,4 µT. Values of 0,4 µT and above were measured in 18 out of 19 apartments that have rooms directly above and next to the transformer. The exposure assessment in the buildings with built-in transformer station shows that the apartments can be reliably categorized as an exposed, low exposed or unexposed based on their location to the transformer stations.