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N. Vaiciunaite / Medical Physics in the Baltic States 7 (2009) 106 - 108 Table 2. Permissible levels of electromagnetic irradiation from industrial electromagnetic fields Country Inhabita Worker Inhabita Worker or nts s nts s organiz Electric Electric Magneti Magneti ation field, field, c field, c field, kV/m kV/m mT mT ICNIRP (1998) 4,16 6,33 0,0833 0,4166 ACGIH (1996) 25,0 1,0 CENEL 8,33 25,0 0,53 1,33 EC (1995) 3 3 3 NRPB 10,0 10,0 1,33 1,33 (1993) 3 3 NH&M RC (1989) 5,0 10,0 0,1 0,5 German y (1989) 20,6 20,6 5,0 5,0 Russia (1985) 5,0 1,76 Poland (1980) 15,0 Lithuani a (2001) 25-5,3* 0,7-4,0* * - depends on working hours ICNIRP – International Commission on Non – Ionizing Radiation Protection; ACGIH – Amerikan Conference of Governintel Industrial Hygienist; CENELEC – Comite Europeen de Normalization ELECtrotechnique; NRPB – National Radiological Protection Board; NH&MRC – National Health & Medical Research Council (Sante nationale et Conseil de recherches medicales). Permissible electric and magnetic field intensities were investigated using the results of experimental investigation, mathematical modelling and extrapolation. It was assumed that a human body has homogeneous and isotropic electrical conductivity. The sine equation of time and Faraday law was used for the evaluation of the induced current intensity: J = πRfσB , Where B is magnetic flux density; R is a radius of loop of the induced current.. Elliptic model was used for the estimation of the current density in the body. Assuming, that the homogeneous conductivity of the body is 0,2 S/m and the magnetic flux density is 100 μ T, the resulting current density of 0,2-2mA/m 2 in a human body was calculated [CRP 1997]. The highest values of current density were found in the head–neck region. If an electric field vector is parallel to the axis of human 107 body, the 5kV/m field induces 2mA/m 2 current at in the head and neck area of human’s body [ILO 1994]. 2. Measurement of electromagnetic radiation Measurements of electromagnetic radiation were performed using equipment and methodology of the Computer equipment testing laboratory (CETL) at Kaunas University of Technology (KTU). CETL is accredited at the Lithuanian National Accreditation Office as the electromagnetic radiation of computer displays exploring institution (www.kompirsveikata.lt). Electromagnetic radiation limits for video display units (VDUs) are set in „TN01:1998. Displays. Permissible levels of electromagnetic radiation“, which corresponds to international standard MPR II..These limits are presented in Table 3. Table 3. Permissible levels of electric field strengths and magnetic flux densities [4]. Field Frequence range Electric Magnetic MPR II, TN01:1998 TCO 0 Hz 500 V 500 V 5 – 2 kHz 25 V/m 10 V/m 2 – 400 kHz 2.5 V/m 1.0 V/m 5 – 2 kHz 250 nT 200 nT 2 – 400 kHz 25 nT 25 nT *according to MPR II, measuring device should be located in 50 cm in front of the VDU; according to TCO - in 30 cm in front of the VDU and at 50 cm around the VDU. Hygiene requirements for the computerized working place environment and equipment are regulated by Lithuanian Hygiene Norm HN-32:2004 „Working at video terminals. Safety and health requirements“. However the levels of electromagnetic radiation emitted by modern VDUs are lower than those from natural sources, and are not are not considered to be harmful to the human’s health [5]. 3. Results Measurements of VLF electric and magnetic fields at 124 workplaces in 42 rooms of Kaunas University of Technology have been performed. The results of measurements are presented in the Table 4. It was found that Hygiene Norm (HN) levels of electric field strength were exceeded at 13 places and were twice as high as recommended at 3 workplaces, when measurements were performed for the electric field frequency of 2 to 5Hz. Also, the magnetic field levels were higher than recommended at 19 workplaces and were twice as high as recommended at 7 places for the frequency range 2 - 5Hz.
N. Vaiciunaite / Medical Physics in the Baltic States 7 (2009) 106 - 108 Measurements performed in Student’s hostel No.2 (3 rooms, 7 workplaces) have shown twice enhanced level of the electric field strength as compared to the recommended level at all investigated work places. It is to point out, that in many cases the overexposure was registered for the 5Hz-2kHz frequency range of the measured electromagnetic fields. Table 4. Measured electric field strengths and magnetic flux densities Sub division No of rooms Central buillding of KTU Gymnasium o KTU IT Institute Hostel No.2 SC “Vibro Technika” Faculty of Informatics Faculty of Management Measurements were done in No of work places 5– 2 kHz Number of workplaces where HN levels were exceeded* Electric field 2 – 400 kHz Magnetic field 5 – 2 kHz 2 – 400 kHz 17 41 13 (3) 1 19 (7) 4 (1) 1 14 1 - - 5 5 16 3 (3) - 8 - 3 7 7 (7) - - - 5 6 3 (2) - - 1 3 23 - - - - 8 17 6 (2) - 2 - Total 42 124 33 (17) 1 29 (7) 10 (1) * Number in parenthesis indicates the number of workplaces where measured electromagnetic radiation 108 was more than twice higher as compared to the HN levels. 4. Conclusions Electromagnetic fields could be reduced by: • using proper installation of power network in room, • using computer equipment satisfying requirements of international standards, • moving part of computer equipment and various electric devices farther from work desk, • regular measurement of electromagnetic fields. This enables to decrease the negative and possibly dangerous influence of electromagnetic radiation in the case when it exceeds internationally recognized norms. Periodically performed measurement of electric field strength and magnetic flux density at the computerized workplaces should ensure that the recommended HN levels are not exceeded. 5. References 1. Electro-Magnetic Pollution and Health in the Workplace.http://www.powerdome.ie/research/The %20Facts/EM%20in%20the%20Workplace.htm 2. EMF Exposure Standards & Guidelines. http://www.lessemf.com/standard.html 3. WHO. Establishing a dialogue on risks from electromagnetic fields. WHO, 2002, 68 p 4. IEEE standards for safety levels. http://www.lessemf.com/book4.html#631 5. TCO’03 Displays. CRT Displays Ver. 3.0. TCO Development, 2005, 100 p. 6. TFT versus CRT: A comparison of advantages and disadvantages.http://www.necdisplaysolutions.com /coremedia/generator/index,realm=Monitorizing_ _BGArticle__Details,spec=x__uk__en,solutionId= ,docId=56396 7. 8. Wim van Eric. Electromagnetic radiation from Video Display Units: http://jya.com/emr.pdf 8. Marcus G. Kuhn. Electromagnetic eavesdropping risk of flat-plain displays http://www.cl.cam.ac.uk/~mgk25/pet2004-fpd.pdf 9. Electromagnetic Radiation Standards Committee http://www.sae.org/standardsdev/groundvehicle/e mr.htm
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2009 PROCEEDINGS OF THE 7 th INTERN
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