Measurements and Evaluation of Radio Frequency radiation at cellular base stations.
Mwaura, Ng' ang' a Francis
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The World Health Organization (WHO), International Commission on Non-ionizing Radiation Protection (ICNIRP) has stated that continuous exposure to Radio Frequency Radiation (RF) beyond certain levels could cause health consequences such as cancer, congenital anomalies, epilepsy, and persistent headache and may destroy reproductive organs etc. In this regard and following the proliferation of cellular base stations across Kenya this study was carried out to determine and evaluate the levels of RF radiation that a typical person would be exposed to in a given enviromnent in Kenya. This study measured radio frequency radiation levels at 16 selected cellular base station transmitters within Nairobi, Kenya. The results were evaluated against the recommended levels set by ICNIRP. Detailed measurements of power density of the radio frequency radiation were performed over the cellular frequency bands GSM 900, GSM 1800 and UMTS 2100, which are the frequency bands in which the cellular transmitters in Kenya operate. Measurements were taken at the point perceived to have high population density near the base stations paying more attention to the direction of maximum radiation of antennas used. The highest levels at each point of measurements were recorded and evaluated against the ICNIRP exposure guidelines. ICNIRP 1998 specifies a maximum non-occupational exposure limit of 4.5W/m2 at GSM 900 Band, 9W/m2 at GSM1800 frequency band and 10W/m2 at UMTS 2100 frequency band. Based on our measurements from 16 selected cellular base stations within Nairobi and its environs the worst case of RF exposure at GSM 900 was 0.080W/m2 from an indoor micro base station situated in Sarit Centre. This value is 1.7% of the ICNIRP maximum public exposure (MPE) limits at the frequency band. The highest level at Sarit Centre was attributed to the close proximity of the radiating antenna to the point of measurement and the electromagnetic waves may have been scattered by walls and other obstacles thus creating high radiation levels away from the base station antennas. At GSM 1800 band, the worst RF exposure recorded was 0.325W/m2 from the base station at Sarit Centre .This value is 3.6% of the ICNIRP MPE limits in this frequency band. The highest RF exposure at UMTS 2100 recorded was 7.06mW/m2 recorded at t"anindoor site 016 (Tuskys Supermarket) in Nairobi CBD. This value is only 0.07% of the' ICNIRP MPE limit at the frequency band in consideration. The study reveals that the radiation exposure levels in Nairobi and environs emitted by the four main mobile phones operators i.e. Safaricom, Airtel, Orange and Essar are several orders of magnitude below the maximum permitted limits.