# Radio Frequency Electromagnetic Fields Exposure Assessment in Indoor Environments: A Review
## 3 Results
### Educational Buildings  
Many studies focused on the RF-EMF exposure levels in buildings hosting educational activities, from kindergartens and nursery to universities. As an example, an extensive study of RF exposures from Wi-Fi access points and laptops used in schools in the UK was reported by [PERSON] and colleagues [49, 50]. In [49], the authors investigated the electric field strengths from 15 different laptops and 12 different access points, typical of those used in UK schools, during Wi-Fi transmission. The maximum electric field strength values recorded at 0.5 m around laptops and access points were 2.9 mV/m and 5.7 mV/m, respectively, indicating that the field strengths from access points were generally higher (almost double) compared to those from laptops. The results also demonstrated that the electric field strength reduced rapidly with distance for all Wi-Fi devices. The corresponding maximum power density values for the laptops and access points at 0.5 m were 22 mW/m\({}^{2}\) and 87 mW/m\({}^{2}\), respectively, decreasing to 4 mW/m\({}^{2}\) and 18 mW/m\({}^{2}\) at 1 m distance. In the second part of the study [50] the authors examined Wi-Fi devices in a small sample of schools in the UK, with measurements being performed in both primary and secondary schools during lessons in which a range of tasks were being performed. The tasks included internet based interactive learning, emails, web browsing, and downloads. In all the networks examined, the duty factors of individual laptops, ranging from 0.02 to 0.96%, were considerably lower than those of the access points, with a range from 0.06 to 11.67%. Applying these duty factors to the earlier laboratory measurements [49] resulted in maximal time-averaged exposure at 0.5 m distance of 220 \(\upmu\)W/m\({}^{2}\) (22 mW/m\({}^{2}\) with 1% duty factor) from individual laptops and 22 mW/m\({}^{2}\) (87 mW/m\({}^{2}\) with 12% duty factor) from access points. Even in the unlikely event that all 30 laptops in a classroom transmitted bursts simultaneously at the maximum 0.5 m distance power density, with the maximal duty factor of 1% measured in the present study, time-averaged exposure values from all laptops would only be 6.6 mW/m\({}^{2}\). This exposure, added to the maximum time-averaged exposure from an access point at 0.5 m would only give 16.6 mW/m\({}^{2}\). It has to be noticed that in these works [49; 50] the assessment was focused on the RF-EMF emitted by Wi-Fi access points and laptops, discarding all other sources, placed indoor or outdoor, that may be influence the levels of RF-exposure in schools. The study by [PERSON] et al. [18] focused on the assessment of the levels of RF-EMF exposure in schools due to the use of Wi-Fi systems, considering also the contribution due to mobile phones and external base stations. The assessment was carried out by measuring the teachers' RF exposure during their activity at school in order to approximate the children's exposure. Every teacher measured from 6 to 31 h, resulting in a total of 255 h of observations. The mean exposure to RF radiation ranged from 1.1 to 66.1 \(\upmu\)W/m\({}^{2}\) (0.02 V/m and 0.16 V/m, in terms of electric field, corresponding to 0.07% and 0.6% of the ICNIRP reference level), with higher levels during lessons when laptops or mobile phones were actively used. The maximum values were found to be higher when connecting to mobile phone base stations outside of the school building, up to 82.8 \(\upmu\)W/m\({}^{2}\) (0.18 V/m, in terms of electric field, corresponding to 0.45% of the ICNIRP reference level) from uplink from GSM 1800, 3G or 4G. The maximum level of exposure due to the downlink from the same base stations was 3.3 mW/m\({}^{2}\) (0.04 V/m, in terms of electric field, corresponding to 0.09% of the ICNIRP reference level).