Spot model for evaluating safety zones around sources of electromagnetic radiation emitting in two or more frequency ranges and its application for health risk assessment

Summary form only given. According to the Law of Environmental Protection in force in the Republic of Bulgaria all sources emitting electromagnetic (EM) power over 100 W within the radiofrequency range (30 kHz-300 MHz) are object of risk assessment for the population. The sanitary control over the sources is exerted as follows: (i) by calculating the borders of the hygienic safety zone (HSZ) and comparing them with those of inhabited areas in the neighborhood of the source (at the stage of the working project); (ii) by practical measurements of the EM field from at least three sites on the borders or in the inhabited area and the comparison of results with the current standard limits of EM field radiation (at the stage of experimental operation). As these two procedures are labor-consuming and expensive a simplified procedure of hygienic assessment of EM sources, based on the calculation of maximized extent of HSZ (R_max) is discussed. The maximized size or the maximized radius R_max of HSZ refers to the most complicated "ecological" case because the single source or the measured group of sources is reduced to a model of one isotropic spot emitter. The isotropic source emits in all directions like the real source/sources, which is always directed and emits only in the direction of its maximal radiation. If within a radius of R_max round the emitter/emitters there is not any inhabited area, then it is reasonable to assert that the studied emitter does not create a health risk. Therefore, it should not be an object of the entire (hard and expensive) procedure of exposure and risk assessment, because it satisfies a higher range criterion, namely "most complicated ecological case". A simple analytical relation for calculating R_max using the "passport" data (technical specification) of sources is given. Any other case, in which there is an inhabited area within the borders of R_max round the isotropic source, will require the entire procedure of hygienic assessment to be followed, because in such a case exists the probability of health risk for the population. The practice shows that more than 90% of the sources in Bulgaria are assessed as "most complicated ecological cases". It is a good reason for the large-scale application of the proposed cost-effective simplified procedure