Bioelectromagnetics 35:245^250 (2014)
Occupational Exposure to Intermediate Frequency and Extremely Low Frequency Magnetic Fields Among Personnel Working Near Electronic Article Surveillance Systems Pivi Roivainen,1* Tuomo Eskelinen,1,2 Kari Jokela,3 and Jukka Juutilainen1 1
Department of Environmental Science, University of Eastern Finland, Kuopio, Finland 2 Savonia University of Applied Sciences, Kuopio, Finland 3 Radiation and Nuclear SafetyAuthority, Helsinki, Finland
Cashiers are potentially exposed to intermediate frequency (IF) magnetic fields at their workplaces because of the electronic article surveillance (EAS) systems used in stores to protect merchandise against theft. This study aimed at investigating occupational exposure of cashiers to IF magnetic fields in Finnish stores. Exposure to extremely low frequency (ELF) magnetic fields was also evaluated because cashiers work near various devices operating with 50 Hz electric power. The peak magnetic flux density was measured for IF magnetic fields, and was found to vary from 0.2 to 4 mT at the cashier’s seat. ELF magnetic fields from 0.03 to 4.5 mT were found at the cashier’s seat. These values are much lower than exposure limits. However, according to the International Commission on Non-Ionizing Radiation Protection (ICNIRP) occupational reference levels for IF magnetic fields (141 mT for the peak field) were exceeded in some cases (maximum 189 mT) for short periods of time when cashiers walked through the EAS gates. As the ICNIRP reference levels do not define any minimum time for exposure, additional investigations are recommended to determine compliance with basic restrictions. Even if the basic restrictions are not exceeded, persons working near EAS devices represent an exceptional group of workers with respect to exposure to electromagnetic fields. This group could serve as a basis for epidemiological studies addressing possible health effects of IF magnetic fields. Compliance with the reference levels for IF fields was evaluated using both broadband measurement of peak fields and the ICNIRP summation rule for multiple frequencies. The latter was generally more conservative, and the difference between the two methods was large (>10-fold) for EAS systems using a 58 kHz signal with complex waveform. This indicates that the ICNIRP multiple frequency rule can be unnecessarily conservative when measuring complex waveforms. Bioelectromagnetics. 35:245–250, 2014. © 2014 Wiley Periodicals, Inc. Key words: anti-theft systems; exposure assessment; magnetic flux density; intermediate frequency; electronic article surveillance
INTRODUCTION Electronic article surveillance (EAS) systems are used in supermarkets and other stores to protect merchandise against theft. These systems use electromagnetic fields of different frequencies to detect or communicate over short distances. Electromagnetic (EM) systems operating at frequencies from 20 Hz to 18 kHz and acousto-magnetic (AM) systems operating at frequencies from 58 to 60 kHz are two common examples of EAS technologies [ICNIRP, 2004]. Both technologies are composed of tags attached to merchandise, activators/deactivators of these tags and detectors that create the surveillance zone. The EM type systems detect harmonics resulting from nonlinear magnetization of the magnetically soft tag in the detection field. The AM type systems detect the 2014 Wiley Periodicals, Inc.
emissions of the tag’s magnetostrictive element that resonates in the presence of a specific frequency Grant sponsors: Finnish Work Environment Fund, grant number: 99268; Checkpoint-Meto. P. Roivainen and T. Eskelinen contributed equally to this work and therefore should be considered as equal first authors. *Correspondence to: Päivi Roivainen, Department of Environmental Science, University of Eastern Finland, P.O. Box 1627, 70211 Kuopio, Finland. E-mail: [email protected] Received for review 25 February 2013; Accepted 28 January 2014 DOI: 10.1002/bem.21850 Published online 24 February 2014 in Wiley Online Library (wileyonlinelibrary.com).
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pulsed magnetic field. The general public is exposed to intermediate frequency (IF) magnetic fields (300 Hz to 100 kHz) from EAS systems only for very short times, but occupational exposure of cashiers working close to these devices can include both high levels and long duration of exposure. Cashiers can also be exposed to extremely low frequency (ELF) magnetic fields (
Occupational Exposure to Intermediate Frequency and Extremely Low Frequency Magnetic Fields Among Personnel Working Near Electronic Article Surveillance Systems Pivi Roivainen,1* Tuomo Eskelinen,1,2 Kari Jokela,3 and Jukka Juutilainen1 1
Department of Environmental Science, University of Eastern Finland, Kuopio, Finland 2 Savonia University of Applied Sciences, Kuopio, Finland 3 Radiation and Nuclear SafetyAuthority, Helsinki, Finland
Cashiers are potentially exposed to intermediate frequency (IF) magnetic fields at their workplaces because of the electronic article surveillance (EAS) systems used in stores to protect merchandise against theft. This study aimed at investigating occupational exposure of cashiers to IF magnetic fields in Finnish stores. Exposure to extremely low frequency (ELF) magnetic fields was also evaluated because cashiers work near various devices operating with 50 Hz electric power. The peak magnetic flux density was measured for IF magnetic fields, and was found to vary from 0.2 to 4 mT at the cashier’s seat. ELF magnetic fields from 0.03 to 4.5 mT were found at the cashier’s seat. These values are much lower than exposure limits. However, according to the International Commission on Non-Ionizing Radiation Protection (ICNIRP) occupational reference levels for IF magnetic fields (141 mT for the peak field) were exceeded in some cases (maximum 189 mT) for short periods of time when cashiers walked through the EAS gates. As the ICNIRP reference levels do not define any minimum time for exposure, additional investigations are recommended to determine compliance with basic restrictions. Even if the basic restrictions are not exceeded, persons working near EAS devices represent an exceptional group of workers with respect to exposure to electromagnetic fields. This group could serve as a basis for epidemiological studies addressing possible health effects of IF magnetic fields. Compliance with the reference levels for IF fields was evaluated using both broadband measurement of peak fields and the ICNIRP summation rule for multiple frequencies. The latter was generally more conservative, and the difference between the two methods was large (>10-fold) for EAS systems using a 58 kHz signal with complex waveform. This indicates that the ICNIRP multiple frequency rule can be unnecessarily conservative when measuring complex waveforms. Bioelectromagnetics. 35:245–250, 2014. © 2014 Wiley Periodicals, Inc. Key words: anti-theft systems; exposure assessment; magnetic flux density; intermediate frequency; electronic article surveillance
INTRODUCTION Electronic article surveillance (EAS) systems are used in supermarkets and other stores to protect merchandise against theft. These systems use electromagnetic fields of different frequencies to detect or communicate over short distances. Electromagnetic (EM) systems operating at frequencies from 20 Hz to 18 kHz and acousto-magnetic (AM) systems operating at frequencies from 58 to 60 kHz are two common examples of EAS technologies [ICNIRP, 2004]. Both technologies are composed of tags attached to merchandise, activators/deactivators of these tags and detectors that create the surveillance zone. The EM type systems detect harmonics resulting from nonlinear magnetization of the magnetically soft tag in the detection field. The AM type systems detect the 2014 Wiley Periodicals, Inc.
emissions of the tag’s magnetostrictive element that resonates in the presence of a specific frequency Grant sponsors: Finnish Work Environment Fund, grant number: 99268; Checkpoint-Meto. P. Roivainen and T. Eskelinen contributed equally to this work and therefore should be considered as equal first authors. *Correspondence to: Päivi Roivainen, Department of Environmental Science, University of Eastern Finland, P.O. Box 1627, 70211 Kuopio, Finland. E-mail: [email protected] Received for review 25 February 2013; Accepted 28 January 2014 DOI: 10.1002/bem.21850 Published online 24 February 2014 in Wiley Online Library (wileyonlinelibrary.com).
246
Roivainen et al.
pulsed magnetic field. The general public is exposed to intermediate frequency (IF) magnetic fields (300 Hz to 100 kHz) from EAS systems only for very short times, but occupational exposure of cashiers working close to these devices can include both high levels and long duration of exposure. Cashiers can also be exposed to extremely low frequency (ELF) magnetic fields (
