Joseph W, Verloock L, Tanghe E, and Martens L (2009) IN-SITU Measurement Procedures For Temporal RF Electromagnetic Field Exposure of the General Public. Health Phys. 96(5):529 –542.
There exists little measurement data concerning radiofrequency (RF) exposure from GSM and UMTS base stations over long periods, such as one day or one week. Typically, electromagnetic-field measurements are performed in an environment during short periods of less than 30 minutes, and from this the compliance with guidelines is tested. Measurements during longer periods are, in practice, difficult, time-consuming, and expensive, and so they are often extrapolated from short “worst-case” scenarios. With the development of a new standard for the in-situ measurement of electromagnetic field strength related to human exposure in the vicinity of base stations, this paper assesses the general public’s exposure to FM transmitters, and GSM and UMTS base stations, as well as all relevant signals in a frequency range of 80 MHz to 2,500 MHz, over seven days.
The purpose of the work is to investigate how short-period measurements can be representative for the actual maximal and average exposure during longer periods.
The study took measurements at different base station sites over several days in fall, winter, and spring in Brussels, Belgium. The fields were measured with both a tri-axial isotropic antenna and a broadband probe. The base station sites were subdivided into categories depending on the type of environment (e.g., rural, urban, etc.), population density, and the expected amount of mobile phone traffic (areas with a high or low possibility of phone calls). The authors defined several factors relating actual to estimated exposure. A factor X was defined as the ratio between the actual maximal value of the temporal measurements and the estimated maximal value from short-period data. A factor R was defined as the ratio between the median and maximal value of the momentary temporal field measurements, indicating the level of variation of a certain signal over time. Three different short-period methods were used to estimate X: CENELEC, max-hold measurement, and max-hold measurement at worst-case moment (where max-hold is defined as the maximum field values being retained by the measurement instruments over a period). These were compared to find an optimal in-situ measurement procedure.
About 352,800 temporal electric field measurements were performed in autumn, winter, and spring. When comparing the three methods, the authors note that: method 1 is only usable for GSM and UMTS signals (not FM), and it requires confidential operator information; method 2 depends on measurements at a particular instance and can lead to underestimation of the electric field strength; and method 3 is recommended because it is more practically usable. When using the recommended method (short-period max-hold), median values of X are 1.05, 0.47, and 0.96, for FM, GSM, and UMTS, respectively. Median values of R are 0.92, 0.66, and 0.71 for FM, GSM, and UMTS, respectively. Values of R close to one indicated little variation over time. For future epidemiologic studies, to calculate median values from maximal values, the authors advise using a value of R equal to 0.423 in sites where a lot of people use mobile communication and thus cause a high variation and amount of traffic, and equal to 0.66 for sites with less traffic.
The authors demonstrated methods that can be used to estimate long-term exposure. By combining the X and R factors, drawn from the appropriate exposure scenarios, one can reliably estimate the actual maximal and median exposure during longer periods from short-period measurements.