Radiation Protection Dosimetry Advance Access published December 22, 2013 Radiation Protection Dosimetry (2013), pp. 1–10
doi:10.1093/rpd/nct340
OCCUPATIONAL EXPOSURE TO ELECTROMAGNETIC FIELDS OF UNINTERRUPTIBLE POWER SUPPLY INDUSTRY WORKERS N. Berna Tes¸neli* and Ahmet Y. Tes¸neli Department of Electrical and Electronics Engineering, Sakarya University, Serdivan, Sakarya 54055, Turkey *Corresponding author: [email protected]
There is an increasing concern that exposure to extremely low-frequency (ELF) electromagnetic fields (EMFs) may cause or contribute to adverse health effects. To assess exposure to ELF EMFs, electric and magnetic field spot measurements were performed extensively at the workplace of a worldwide uninterruptible power supply (UPS) factory. The measurements were carried out in order to get the electric and magnetic field exposure results in real working situations in test areas, production lines and power substations. The electric and magnetic fields reached up to 992.0 V m21 and 215.6 mT in the test areas, respectively. The fields existed up to 26.7 V m21 and 7.6 mT in the production lines. The field levels in the vicinity of the power substations did not exceed 165.5 V m21 and 65 mT. The data presented are useful in determining the occupational exposure levels of UPS industry workers. The measurements are below the reference levels recommended by the guideline published in 2010 by the International Commission on Non-Ionizing Radiation Protection and action levels of the directive adopted in 2013 by European Parliament and Council.
INTRODUCTION Since the mid-twentieth century, electricity has been an essential part of our lives. In recent years, there has been concern that exposures to extremely low-frequency (ELF)-range electromagnetic fields (EMFs) produced by generation, transmission, distribution and use of electrical energy can potentially cause or contribute to various types of adverse health effects. ELF magnetic fields have been studied as a risk factor for childhood leukaemia since the late 1970s. The association between childhood leukaemia and residential ELF magnetic fields was first identified by Wertheimer and Leeper(1). Like childhood cancer, adult cancer was found to be associated with highcurrent electrical wiring configurations near the home(2). Two pooled analyses of epidemiologic studies showed 2-fold increase in leukaemia risk for children exposed to residential magnetic field levels of .0.3–0.4 mT(3, 4). Epidemiological studies and risk assessments in this area led to the classification of ELF magnetic fields as a ‘possible human carcinogen’ (group 2B) by the International Agency for Research on Cancer (IARC)(5). The IARC conclusion of 2002 is still valid but there is no known mechanism to explain how ELF magnetic field exposure may induce leukaemia, and adequate evidence has not been provided in animal studies(6 – 8). Besides exposure of the children themselves, parental exposures to ELF magnetic fields either preconceptional period or during pregnancy as a risk factor for adverse health effects are another cause of concern. A number of studies concerning parental exposure
have been presented in the IARC monograph(5). Several significant associations have been reported for paternal occupations with probable exposure to ELF magnetic fields, although some studies have suggested no link between parental exposures and childhood cancer(9 – 12). Overall, studies on parental occupational exposure to ELF EMFs are methodologically weak, and the results are not consistent (5, 7). Occupational exposures have been evaluated in a large number of studies, and variety of methods for exposure assessment have been devised and applied to epidemiological studies of the effects of EMF in occupational settings. A significant association has been reported between electrical jobs and leukaemia risk in epidemiological investigations of workplace exposure to EMF(13, 14). Some of the recent studies suggest that people employed in electrical occupations might have an increased risk for amyotrophic lateral sclerosis and Alzheimer’s disease(15 – 18). Most of these studies focused on electrical workers, persons working near machines with electric motors and welders. Because they tend to have the highest exposures to ELF EMFs which are determined in the range of 0.1–4.0 mT for time-weighted average magnetic field exposure levels(19). The average magnetic fields to which workers are exposed for various jobs in the electric power industry have been reported as follows: 0.18–1.72 mT for workers in power stations, 0.8–1.4 mT for workers in substations, 0.03–4.57 mT for workers on power lines and cables and 0.2–18.48 mT for electricians(20, 21). The maximum magnetic field exposures in the workplace that is invariably associated with the presence of
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Received 29 October 2013; revised 24 November 2013; accepted 27 November 2013
N. B. TES¸NELI AND A. Y. TES¸NELI
Europe, because of the EU Council Recommendations and Directives that are based on the guidelines. Long-term effects of chronic exposure have been reviewed but excluded from the scope of the guidelines because ICNIRP considers that the currently existing scientific evidence that prolonged exposure to low-frequency magnetic fields is causally related to an increased risk of childhood leukaemia is too weak. Thus, the perception of surface electric charge, the direct stimulation of nerve and muscle tissue and the induction of retinal phosphenes are the only wellestablished adverse effects and serve as the basis for the guidelines. However, risk management advice, including considerations on precautionary measures, has been given by WHO(7) and other entities(24). The ICNIRP guidelines specify ‘basic restrictions’ and ‘reference levels’. Basic restrictions are based on the physical quantity directly related to the established health effects. The physical quantity used to specify the basic restrictions are the induced internal electric field strengths that affect nerve cells and other electrically sensitive cells. Reference levels of exposure provided for practical exposure assessment purposes are derived from the basic restrictions using the data from computational simulations based on anatomically detailed human body models. ICNIRP recognises that the reference levels are given for the condition of maximum coupling of the field to the exposed individual, thereby providing maximum protection. Compliance with the reference levels is designed to ensure compliance with the relevant basic restriction. However, when the reference levels are exceeded, it does not necessarily follow that the basic restrictions will also be exceeded. They need to be determined by further investigations. Table 1 shows the reference levels for occupational exposure by a uniform field with respect to the spatial extension of the human body(24). According to Table 1, the reference levels for occupational exposure to time-varying electric and magnetic fields at 50 Hz frequency are 10 kV m21 and 1000 mT, respectively.
Table 1. Reference levels for occupational exposure to timevarying electric and magnetic fields (unperturbed RMS values)(24). Frequency range
ICNIRP GUIDELINES The ICNIRP develops internationally accepted sciencebased recommendations for protection against various non-ionising radiation (NIR) exposures. ICNIRP is the formally recognised non-governmental organisation in NIR for the World Health Organisation (WHO), the International Labour Office and the European Union (EU). The exposure guidelines published by the ICNIRP have a significance role in
1 –8 Hz 8 –25 Hz 25–300 Hz 300 Hz– 3 kHz 3 kHz–10 MHz
Electric field strength (E) [kV m21]
Magnetic flux density (B) [T]
20 20 5` 102/f 5` 102/f 1.7` 1021
0.2/f 2 2.5` 1022/f 1` 1023 0.3/f 1` 1024
f is the frequency expressed in Hertz.
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conductors carrying high currents can reach 10 mT, and workers may be exposed to electric fields up to 30 kV m21 in the electrical supply industry(7). Measurements of the field levels are very important for the verification of the results obtained using computational methods and the evaluation of the EMF exposure particularly at multiple source sites and complex working environments. Measurements often prove that more conclusive and computational methods are often not enough to assess compliance with safety limits. Measurements are also needed, when the calculated fields are close to the threshold for overexposure or when fields are likely to be distorted by reflection from various objects(22, 23). Although occupational exposure environments are studied in the context of specific industries and workplace, it is not so easy to find investigations particularly focused on uninterruptible power supply (UPS)-manufacturing facilities that are a part of the electric power utility industry. UPS industry workers represent one group of electrical workers who are exposed to highlevel ELF EMFs emanating from UPSs, transformers, resistances used loading of UPSs, power cables, printed circuit board (PCB) assembly lines, soldering machines and power systems supply energy for production. The present paper presents spot measurements of ELF EMFs obtained near a number of high-power on-line UPS models and at workplace in the visited UPS factory, which is a worldwide member of UPS industry. The factory has large closed facility, is able to produce every single part of its products, does final assembly and testing and exports products to 75 countries in 5 continents. The measured values have been compared with permissible exposure limits. The International Commission on Non-Ionizing Radiation Protection (ICNIRP) has published guidelines for limiting exposure to time-varying EMFs (1 Hz– 100 kHz), in which upper limits for occupational exposure have been presented(24). Based on the ICNIRP guidelines, European Parliament and Council has adopted a directive on the minimum health and safety requirements regarding the exposure of workers to the risks arising from physical agents (EMFs), in 2013(25). This directive repeals directive 2004/40/ EC(26). However, so far, there is no legislation for occupational exposure to EMFs in Turkey.
EXPOSURE TO EMF OF UPS INDUSTRY WORKERS
EUROPEAN DIRECTIVE (25)
Table 2. ALs for exposure to electric fields from 1 Hz to 10 MHz (RMS values)(25). Frequency range
1 f , 25 Hz 25 f , 50 Hz 50 Hz f , 1.64 kHz 1.64 f , 3 kHz 3 kHz f 10 MHz
Electric field strength low ALs (E) [V m21]
Electric field strength high ALs (E) [V m21]
2.0` 104 5.0` 105/f 5.0` 105/f 5.0` 105/f 1.7` 102
2.0` 104 2.0` 104 1.0` 106/f 6.1` 102 6.1` 102
f is the frequency expressed in Hertz.
MEASUREMENT METHOD The study was performed at different locations in the facility of a UPS manufacturer. The electric and
Table 3. ALs for exposure to magnetic fields from 1 Hz to 10 MHz (RMS values)(25). Frequency range
1 f , 8 Hz 8 f , 25 Hz 25 f , 300 Hz 300 f , 3 kHz 3 kHz f 10 MHz
Magnetic flux density low ALs (B) [mT]
Magnetic flux density high ALs (B) [mT]
Magnetic flux density ALs for exposure of limbs to a localised magnetic field (B) [mT]
2.0` 105/f 2 2.5` 104/f 1.0` 103 3.0` 105/f 1.0` 102
3.0` 105/f 3.0` 105/f 3.0` 105/f 3.0` 105/f 1.0` 102
9.0` 105/f 9.0` 105/f 9.0` 105/f 9.0` 105/f 3.0` 102
f is the frequency expressed in Hertz (Hz)
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for occupational European directive 2013/35/EU exposure to EMFs with frequencies up to 300 GHz is intended to protect the working population. The provisions of the directive, considered as minimal requirements against occupational risks due to exposure to EMFs, have to be transposed into national legislation by all EU member states by 1 July 2016. The European Commission shall make available practical guides to facilitate the implementation of the directive. The provisions of the directive are based on a similar philosophy and rationale with the ICNIRP guidelines. The directive is intended to address all known direct biophysical effects and indirect effects caused by EMFs, but it does not cover suggested long-term effects of exposure to EMFs since there is currently no well-established scientific evidence of a causal relationship. The ICNIRP basic restrictions and reference levels equate to exposure limit values (ELVs) and action levels (ALs), respectively, in the directive. ELVs means values established on the basis of biophysical and biological considerations. ‘Health effects ELVs’ and ‘sensory effects ELVs’ are additionally set out in the directive. Health effects ELVs for internal electric field strength from 1 Hz to 10 MHz are related to electric stimulation of all peripheral and central nervous system tissues in the body, including the head. Sensory
effects ELVs for internal electric field strength from 1 to 400 Hz are related to electric field effects on the central nervous system in the head, i.e. retinal phosphenes and minor transient changes in some brain functions. ALs means operational levels established for the purpose of simplifying the process of demonstrating the compliance with relevant ELVs. ALs correspond to calculated or measured electric and magnetic field values at the workplace in the absence of the worker. The AL terminology of the directive contains ‘low ALs’ and ‘high ALs’ terms. Low ALs for external electric field are based on limiting the internal electric field below the ELVs and limiting spark discharges in the working environment. Below high ALs for external electric field, the internal electric field does not exceed the ELVs and annoying spark discharges prevented, provided that the specific protection measures in accordance with the directive are taken. For exposure to magnetic fields, low ALs are derived from the sensory effects ELVs for frequencies of ,400 Hz, and from the health effects ELVs for frequencies of .400 Hz. High ALs for exposure to magnetic fields are derived from the health effects ELVs, and compliance with it ensures that health effects ELVs are not exceeded, but the effects related to retinal phosphenes and minor transient changes in brain activity are possible if the exposure of the head exceeds the low ALs for exposures up to 400 Hz. ALs for exposure to magnetic fields of limbs are derived from the health effects ELVs by taking into account that the magnetic field is coupled more weakly to the limbs than to the whole body(25). ALs for exposure to electric and magnetic fields from 1 Hz to 10 MHz are shown in Tables 2 and 3, respectively. The ALs calculated according to the tables for 50 Hz frequency are presented as follows. Electric field strength low and high ALs are 10 and 20 kV m21. Magnetic flux density low and high ALs are 1000 and 6000 mT, and ALs for exposure of limbs are 18 000 mT.
N. B. TES¸NELI AND A. Y. TES¸NELI
RESULTS AND DISCUSSION The electric and magnetic field spot measurements were performed at the same points, taking into
account the load situations, the workers’ natural movements and closeness to the source while performing the tasks. The fields were identified by manual scanning along the source enclosures and workers’ positions. To minimise field distortions, the measuring person stayed away from the investigated field source or position as far as possible holding the meter with his/her stretched arm. The measurement results are separately presented for the test areas, the production lines and the substations in the facilities of the UPS factory. The measured fields show spatial maximum values obtained scanning the height from floor to 1.8 m except measurements around both 250- and 300-kVA on-line UPS. Test areas The measurement of EMFs was made in four different UPS test areas, one transformer test area and one service test area. During the surveys, test equipment and units under test operated at normal running conditions. UPSs under test were fixed on the floor, whereas transformers under test were fixed on a table. UPSs under test operate as loaded or unloaded in accordance with its test procedures. So, the fields from the UPSs under test are separately measured for these load conditions. Description and horizontal distances to the enclosure of unit under test of the selected measurement positions are presented in Table 4 with load conditions and measured fields. According to the measurement results of the test areas, electric fields vary between 2.7 and 992.0 V m21 whereas magnetic fields are between 0.1 and 196.4 mT. Maximum fields were recorded in the transformer test area at operator position that is 0.15 m away from the transformer under test. Operator limbs have been exposed to electric fields of up to 742.6 V m21 and magnetic fields of up to 80.4 mT, because of the UPS feeders that lie on the floor. The maximum electric and magnetic fields from UPSs under test were 380.0 V m21 and 143.0 mT, respectively. The fields from the high-power UPSs were lower than the fields from the relatively low-power UPSs; the reason is that physical dimensions of high-power UPS enclosure are larger and current or voltage sources are away from the enclosure and measurement position. The UPS test operators reported that an UPS test takes 3 h (1 h loaded and 2 h unloaded) and maximum three UPSs are tested for a day. The transformer test operators said that transformer tests take a total of 3 h per working day. The EMFs were additionally measured around 250 and 300 kVA on-line UPS models, whereas they are under the test in the UPS test areas 1 and 2. Dimensions (W` D` H ) of the 250- and 300-kVA UPS models are 1.59`0.95` 1.90 m and 1.34`1.08` 1.95 m, respectively. The field distributions were measured along a plane 0.1 m apart and tangential to the UPS enclosures.
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magnetic field measurements were taken in the areas most occupied by the operators while production and testing in order to establish the typical exposure in the course of a day’s work. There are varieties of measurement methods that can be used to measure ELF EMFs. Spot measurement that is one of them was used in this study. However, data obtained from this method can only be used on that particular time. Magnetic fields emanating from the UPSs and the equipment in the workplace vary with current loadings. To determine the worst-case field exposure, the measurements were also performed at specific times when the UPSs and the equipment are under the maximum load that may be possible in the workplace. In general, time-averaging can be applied of .10 MHz and cannot be applied of ,100 kHz(27, 28). Reference levels have been determined for the exposure conditions where the variation of the electric or magnetic field over the space occupied by the body is relatively small. In most cases, however, the distance to the source of the field is so close that the distribution of the field is non-uniform or localised to a small part of the body. In these cases, the measurement of the maximum field strength in the position of space occupied by the body always gives safe results(24). ALs represent maximum calculated or measured values at the workers’ body position. This results in a conservative exposure assessment and automatic compliance with ELVs in all non-uniform exposure conditions(25). In this study, all measurement results present spatial maximum fields. The fields in the workplace were measured using Spectran NF-5035 EMF spectrum analyser, which is a hand-held commercial electric and magnetic field measuring instrument developed by Aaronia AG, Germany. The frequency range of the spectrum analyser is 1 Hz –20 MHz and allows frequency selective electric and magnetic field measurements. The electric and magnetic field ranges of the instrument are 0.1– 20 kV m21 and 1 pT–2 mT, respectively, with a typical accuracy at +3 %. The analyser features an integrated three-dimensional miniature sensor coil that allows isotropic measurement of magnetic fields in all three orthogonal axes. The analyser also has an internal sensor that enables electric fields measurements only in one-dimension (1D). The sweeps were performed from 45 Hz to 1 kHz, and the root-mean-square (RMS) detector is used in the electric and magnetic field measurements. Threedimensional magnetic field sensor and 1D electric field sensor were used. The measurements were recorded and analysed using the LCS Spectran analyser software developed by Aaronia AG.
Table 4. The measurement results of test areas. Description of the measurement location
UPS test area 1—Test desk 1 Between operator workstation and UPS Operator workstation
Load condition of unit under test [%]
Characteristics of unit under test
Distance (d ) [m]
Electric field strength (E) [V m21]
Magnetic flux density (B) [mT]
No load 100 No load 100
0.50 0.50 1.00 1.00
211.0 308.0 105.0 220.0
1.0 12.0 0.4 6.0
UPS test area 1—Test desk 4 Operator workstation
UPS (250 kVA, 3 phase –3 phase)a
No load 100
2.00 2.00
2.7 22.0
0.1 0.2
UPS test area 2—Test desk 1 Operator workstation
UPS (300 kVA, 3 phase –3 phase)b
No load 15 No load 15 15
1.00 1.00 0.05 0.05 0.15
13.2 16.0 685.0 742.6 420.0
0.9 2.6 54.0 80.4 6.1
UPS (20 kVA, 3 phase– 1 phase)a
No load 83 No load 83
0.20 0.20 0.60 0.60
250.0 282.5 94.0 116.0
36.4 65.2 1.9 4.7
UPS (10.5 kVA, 3 phase –3 phase)a
75
0.20
80.0
18.1
Transformer (20 kVA)
– – –
0.15 0.50 0.15
415.0 45.7 992.0
196.4 9.3 0.4
No load 90 No load No load (1 phase –1 phase) and 90 (3 phase –3 phase)
0.10 0.10 0.10 0.30
180.0 380.0 134.3 75.0
143.0 52.3 9.1 16.1
Above the UPS feeder lies on the floor
UPS test area 4—Test desk 1 Operator working position Transformer test area Operator working positions
Transformer (750 VA) under 3-kV isolation test Technical service test area Operator working positions
UPS (10 kVA, 3 phase– 3 phase)a UPS (10 kVA, 1 phase– 1 phase)a UPS (80 kVA, 3 phase– 3 phase) Two UPSs (10 kVA, 1 phase– 1 phase and 3 phase –3 phase)
d is the horizontal distance to source enclosure. a Side panels of UPS are demounted. b Three side panels are demounted and front panel at the operator side is mounted.
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In the vicinity of the load/resistance UPS test area 3—Test desk 1 Operator working positions
EXPOSURE TO EMF OF UPS INDUSTRY WORKERS
UPS (250 kVA, 3 phase –3 phase)a
N. B. TES¸NELI AND A. Y. TES¸NELI
Figure 2. Electric field strength measurement results for 250-kVA UPS.
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Figure 1. Measurement points in the vicinity of UPSs: (a) Top view and (b) front view (A, B and C represent the planes that have different height from the floor; all dimensions are in metres).
Measurements were made at three different heights from the floor, which are 0.5, 1.1 and 1.7 m. The measurement positions around the UPSs are shown in Figure 1, and the measured fields are graphically shown in Figures 2–5. Measurements were performed for both loaded and unloaded conditions. The fields in the graphics present spatial maximum value at relevant measurement position and its neighbouring points. For unloaded 250-kVA UPS, the electric fields are between 3.0 and 188.6 V m21 whereas the magnetic fields are between 1.0 and 142.5 mT. For 100 % loaded 250-kVA UPS, the electric fields are between 3.1 and 192.5 V m21 whereas the magnetic fields are between 4.1 and 215.6 mT. Similarly for unloaded 300-kVA UPS, the electric fields are between 2.4 and 150.0 V m21 whereas the magnetic fields are between 2.4 and 80.3 mT. For 15 % loaded 300-kVA UPS, the electric fields are between 2.5 and 167.3 V m21 whereas the magnetic fields are between 3.7 and 176.3 mT. When the UPSs are in loaded condition, the magnetic fields increased but the electric fields did not vary significantly. This result is not surprising because loading of a UPS increases current. Three hundred kilovolt-amperes UPS is loaded to 15 % during the tests, and the field measurements were performed considering normal working conditions in the factory. The field levels of 15 % loaded 300-kVA UPS provided sufficient knowledge to assess the exposure to ELF EMFs of the workers in the test area 2. When 300kVA UPS loads more than 15%, especially the
EXPOSURE TO EMF OF UPS INDUSTRY WORKERS
Figure 4. Electric field strength measurement results for 300-kVA UPS.
magnetic fields increase significantly and further measurements are needed for assessments. Production lines EMFs in the production lines were measured around automated PCB assembly lines and wave soldering machine where the operator spends 8 h a day. The
fields that were obtained during normal production process are represented in Table 5 as spatial maximum values. Electric fields vary between 5.5 and 24.0 V m21, whereas magnetic fields vary between 0.2 and 7.6 mT. The maximum magnetic field was recorded at the rear of the lead-free process line as during the wave solder process. Magnetic field was 0.2 mT at the operator position of the wave
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Figure 3. Magnetic flux density measurement results for 250-kVA UPS.
N. B. TES¸NELI AND A. Y. TES¸NELI
Table 5. The measurement results of production line. Description of the measurement location
Distance (d ) Electric field strength [m] (E) [V m21]
Automated PCB assembly lines In front of the soldering oven of the line 1 In front of the line 1, operator working positions In front of the soldering oven of the line 2 In front of the line 2, operator working positions In front of the line 3, operator working positions Rear of the line 3 Wave soldering machine In front of the lead-free process line, operator working positions Rear of the lead-free process line Marketing department In the vicinity of the office workstation contains four desks and four personal computers that are switched on
Magnetic flux density (B) [mT]
0.20 0.20 0.20 0.20 0.20 0.20
21.0 7.8 24.0 9.4 5.5 6.4
5.3 0.5 6.1 0.6 0.2 0.5
0.20
9.0
0.2
0.20
11.2
7.6
–
26.7
0.2
d is the horizontal distance to source enclosure.
soldering machine. The electric and magnetic fields in front of the soldering oven, which is a part of the automated PCB assembly lines, were measured up to 24.0 V m21 and 6.1 mT, respectively. The magnetic fields in front of the other parts of the PCB assembly lines did not exceed 0.6 mT. The measurements were also performed around the office workstation in the marketing department that is near the production areas, and the electric and magnetic fields were recorded as 26.7 V m21 and 0.2 mT, respectively.
Power substations The factory has one 630-kVA power substation and two 1000-kVA power substations that are placed in the garden and close to the factory building. EMFs measurements were performed at the positions where substation workers spend time during maintenance and repairs. Substation maintenance workers and repairers had not been exposed to the fields emanating from the substations all day. Table 6 shows the measured fields that are spatial maximum values in front of the power substations. The electric and
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Figure 5. Magnetic flux density measurement results for 300-kVA UPS.
EXPOSURE TO EMF OF UPS INDUSTRY WORKERS Table 6. The measurement results of power substations. Description of the measurement location
Electric field strength (E) [V m21]
Magnetic flux density (B) [mT]
0.20 0.30 0.20 –
65.5 21.8 28.6 6.7
0.6 0.9 14.7 1.3
0.20 0.20 0.30 0.30
9.7 41.0 91.7 165.5
3.5 43.1 7.2 65.0
0.30 0.20
8.6 21.4
6.7 8.3
d is the horizontal distance to source enclosure.
magnetic fields reach up to 165.5 V m21 and 65.0 mT, respectively. Workers have to open the panel doors during their tasks of maintenance and repair. When the panel doors are kept open, the exposed fields dramatically increase. There is an administrative office that shares a wall with 630-kVA power substation, and office workers are exposed during all working day. The fields did not exceed 6.7 V m21 and 1.3 mT in front of the shared wall and at workstations in this office. CONCLUSIONS The results of this study demonstrate the levels of ELF EMFs that can be encountered in UPS industries. Electric and magnetic field spot measurements were performed in test areas, production lines and the vicinity of power substations considering all working conditions. The measurement results show that the electric fields vary between 2.4 and 992.0 V m21, whereas the magnetic fields vary between 0.1 and 215.6 mT. Occupational exposure levels are relatively high in the test areas where the maximum fields are obtained. The measured fields were compared with ICNIRP reference levels and European directive ALs. All the measurements obtained for the described conditions are below the reference levels recommended by ICNIRP guidelines(24) and low ALs described by European directive(25). Further investigations should be performed for the working environments including higher power UPSs and different load conditions. FUNDING This work was supported by Sakarya University Scientific Research Foundation (Project number: 2012-01-00-005).
REFERENCES 1. Wertheimer, N. and Leeper, E. Electrical wiring configurations and childhood cancer. Am. J. Epidemiol. 109, 273–284 (1979). 2. Wertheimer, N. and Leeper, E. Adult cancer related to electrical wires near the home. Int. J. Epidemiol. 11, 345–355 (1982). 3. Ahlbom, A. et al. A pooled analysis of magnetic fields and childhood leukaemia. Br. J. Cancer 83, 692– 698 (2000). 4. Greenland, S., Sheppard, A. R., Kaune, W. T., Poole, C. and Kelsh, M. A. A pooled analysis of magnetic fields, wire codes, and childhood leukemia. Childhood LeukemiaEMF Study Group. Epidemiology 11, 624–634 (2000). 5. International Agency for Research on Cancer, IARC. Non-ionizing radiation, part 1: static and extremely lowfrequency (ELF) electric and magnetic fields. IARC Monographs on the Evaluation of Carcinogenic Risks to Humans. Vol. 80. (IARC Press) (2002). 6. Schu¨z, J. and Ahlbom, A. Exposure to electromagnetic fields and the risk of childhood leukaemia: a review. Radiat. Prot. Dosim. 132, 202– 211 (2008). 7. World Health Organization, WHO. Environmental Health Criteria 238. Extremely Low Frequency Fields. WHO (2007). 8. European Commission Scientific Committee on Emerging and Newly Identified Health Risks, SCENIHR. Health Effects of Exposure to EMF. SCENIHR (2009). 9. Feychting, M., Floderus, B. and Ahlbom, A. Parental occupational exposure to magnetic fields and childhood cancer (Sweden). Cancer Causes Control 11, 151–156 (2000). 10. Infante-Rivard, C. and Deadman, J. E. Maternal occupational exposure to extremely low frequency magnetic fields during pregnancy and childhood leukemia. Epidemiology 14, 437– 441 (2003). 11. Li, P., McLaughlin, J. and Infante-Rivard, C. Maternal occupational exposure to extremely low frequency magnetic fields and the risk of brain cancer in the offspring. Cancer Causes Control 20, 945– 955 (2009).
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Substation 1 (630 kVA) In front of the substation 1 In front of the circuit breaker 1 In front of the main distribution panel 1 Administrative office that has common wall with the substation 1 Substations 2 and 3 (1000 kVA) In front of the substations 2 and 3 In front of the transfer panel (panel door is open) In front of the main distribution panel 2 In front of the main distribution panel 2 (panel door is open) In front of the main distribution panel 3 In front of the shielded cable channel of the main distribution panel 3
Distance (d) [m]
N. B. TES¸NELI AND A. Y. TES¸NELI 21. National Institute of Environmental Health Sciences, NIEHS. Assessment of health effects from exposure to power line frequency electric and magnetic fields. (National Institute of Health) (NIH Publication No. 983981) (1998). 22. Habash, R. W. Y., Brodsky, L. M., Leiss, W., Krewski, D. and Repacholi, M. Health risks of electromagnetic fields. Part I: evaluation and assessment of electric and magnetic fields. Crit. Rev. Biomed. Eng. 31, 141–195 (2003). 23. Vulevic, B. and Osmokrovic, P. Evaluation of uncertainty in the measurement of environmental electromagnetic fields. Radiat. Prot. Dosim. 141, 173 –177 (2010). 24. International Commission on Non-Ionizing Radiation Protection, ICNIRP. Guidelines for limiting exposure to time-varying electric and magnetic fields (1 Hz to 100 kHz). Health Phys. 99, 818– 836 (2010). 25. EC. Directive 2013/35/EU of the European Parliament and of the Council of 26 June 2013 on the minimum health and safety requirements regarding the exposure of workers to the risks arising from physical agents (electromagnetic fields). Official J. Eur. Union L-179 (2013). 26. EC. Directive 2004/40/EC of the European Parliament and of the Council of 29 April 2004 on the minimum health and safety requirements regarding the exposure of workers to the risks arising from physical agents (electromagnetic fields). Official J. Eur. Union L-184 (2004). 27. European Committee for Electrotechnical Standardization (CENELEC). Procedure for the assessment of the exposure of workers to electromagnetic fields (Standard prEN 50499:2008). (CENELEC) (2008). 28. European Committee for Electrotechnical Standardization (CENELEC). Assessment of electronic and electrical equipment related to human exposure restrictions for electromagnetic fields (0 Hz–300 GHz) (Standard EN 62311:2008). (CENELEC) (2008).
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12. Hug, K., Grize, L., Seidler, A., Kaatsch, P. and Schu¨z, J. Parental occupational exposure to extremely low frequency magnetic fields and childhood cancer: a German case-control study. Am. J. Epidemiol. 171, 27–35 (2010). 13. Milham, S. Mortality from leukemia in workers exposed to electrical and magnetic fields. New Eng. J. Med. 307, 249 (1982). 14. Milham, S. Mortality in workers exposed to electromagnetic fields. Environ. Health Persp. 62, 297–300 (1985). 15. Ahlbom, A. Neurodegenerative diseases, suicide, and depressive symptoms in relation to EMF. Bioelectromagnetics 5, 132–143 (2001). 16. Sobel, E., Davanipour, Z., Sulkava, R., Erkinjuntti, T., Wikstrom, J., Henderson, V. W., Buckwalter, G., Bowman, J. D. and Lee, P. J. Occupations with exposure to electromagnetic fields: a possible risk factor for Alzheimer’s disease. Am. J. Epidemiol. 142, 515–524 (1995). 17. Garcia, A. M., Sisternas, A. and Hoyos, S. P. Occupational exposure to extremely low frequency electric and magnetic fields and Alzheimer disease: a metaanalysis. Int. J. Epidemiol. 37, 329– 340 (2008). 18. Kheifets, L., Bowman, J. D., Checkoway, H., Feychting, M., Harrington, J. M., Kavet, R., Marsh, G., Mezei, G., Renew, D. C. and van Wijngaarden, E. Future needs of occupational epidemiology of extremely low frequency electric and magnetic fields: review and recommendations. Occup. Environ. Med. 66, 72–80 (2009). 19. National Institute of Environmental Health Sciences, NIEHS. Report on health effects from exposure to powerline frequency electric and magnetic fields. (National Institute of Health) (NIH Publication No. 99-4493) (1999). 20. AGNIR. ELF electromagnetic fields and the risk of cancer. Report of an Advisory Group on Non-ionising Radiation. Doc NRPB 12, 1 –179 (2001).
doi:10.1093/rpd/nct340
OCCUPATIONAL EXPOSURE TO ELECTROMAGNETIC FIELDS OF UNINTERRUPTIBLE POWER SUPPLY INDUSTRY WORKERS N. Berna Tes¸neli* and Ahmet Y. Tes¸neli Department of Electrical and Electronics Engineering, Sakarya University, Serdivan, Sakarya 54055, Turkey *Corresponding author: [email protected]
There is an increasing concern that exposure to extremely low-frequency (ELF) electromagnetic fields (EMFs) may cause or contribute to adverse health effects. To assess exposure to ELF EMFs, electric and magnetic field spot measurements were performed extensively at the workplace of a worldwide uninterruptible power supply (UPS) factory. The measurements were carried out in order to get the electric and magnetic field exposure results in real working situations in test areas, production lines and power substations. The electric and magnetic fields reached up to 992.0 V m21 and 215.6 mT in the test areas, respectively. The fields existed up to 26.7 V m21 and 7.6 mT in the production lines. The field levels in the vicinity of the power substations did not exceed 165.5 V m21 and 65 mT. The data presented are useful in determining the occupational exposure levels of UPS industry workers. The measurements are below the reference levels recommended by the guideline published in 2010 by the International Commission on Non-Ionizing Radiation Protection and action levels of the directive adopted in 2013 by European Parliament and Council.
INTRODUCTION Since the mid-twentieth century, electricity has been an essential part of our lives. In recent years, there has been concern that exposures to extremely low-frequency (ELF)-range electromagnetic fields (EMFs) produced by generation, transmission, distribution and use of electrical energy can potentially cause or contribute to various types of adverse health effects. ELF magnetic fields have been studied as a risk factor for childhood leukaemia since the late 1970s. The association between childhood leukaemia and residential ELF magnetic fields was first identified by Wertheimer and Leeper(1). Like childhood cancer, adult cancer was found to be associated with highcurrent electrical wiring configurations near the home(2). Two pooled analyses of epidemiologic studies showed 2-fold increase in leukaemia risk for children exposed to residential magnetic field levels of .0.3–0.4 mT(3, 4). Epidemiological studies and risk assessments in this area led to the classification of ELF magnetic fields as a ‘possible human carcinogen’ (group 2B) by the International Agency for Research on Cancer (IARC)(5). The IARC conclusion of 2002 is still valid but there is no known mechanism to explain how ELF magnetic field exposure may induce leukaemia, and adequate evidence has not been provided in animal studies(6 – 8). Besides exposure of the children themselves, parental exposures to ELF magnetic fields either preconceptional period or during pregnancy as a risk factor for adverse health effects are another cause of concern. A number of studies concerning parental exposure
have been presented in the IARC monograph(5). Several significant associations have been reported for paternal occupations with probable exposure to ELF magnetic fields, although some studies have suggested no link between parental exposures and childhood cancer(9 – 12). Overall, studies on parental occupational exposure to ELF EMFs are methodologically weak, and the results are not consistent (5, 7). Occupational exposures have been evaluated in a large number of studies, and variety of methods for exposure assessment have been devised and applied to epidemiological studies of the effects of EMF in occupational settings. A significant association has been reported between electrical jobs and leukaemia risk in epidemiological investigations of workplace exposure to EMF(13, 14). Some of the recent studies suggest that people employed in electrical occupations might have an increased risk for amyotrophic lateral sclerosis and Alzheimer’s disease(15 – 18). Most of these studies focused on electrical workers, persons working near machines with electric motors and welders. Because they tend to have the highest exposures to ELF EMFs which are determined in the range of 0.1–4.0 mT for time-weighted average magnetic field exposure levels(19). The average magnetic fields to which workers are exposed for various jobs in the electric power industry have been reported as follows: 0.18–1.72 mT for workers in power stations, 0.8–1.4 mT for workers in substations, 0.03–4.57 mT for workers on power lines and cables and 0.2–18.48 mT for electricians(20, 21). The maximum magnetic field exposures in the workplace that is invariably associated with the presence of
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Received 29 October 2013; revised 24 November 2013; accepted 27 November 2013
N. B. TES¸NELI AND A. Y. TES¸NELI
Europe, because of the EU Council Recommendations and Directives that are based on the guidelines. Long-term effects of chronic exposure have been reviewed but excluded from the scope of the guidelines because ICNIRP considers that the currently existing scientific evidence that prolonged exposure to low-frequency magnetic fields is causally related to an increased risk of childhood leukaemia is too weak. Thus, the perception of surface electric charge, the direct stimulation of nerve and muscle tissue and the induction of retinal phosphenes are the only wellestablished adverse effects and serve as the basis for the guidelines. However, risk management advice, including considerations on precautionary measures, has been given by WHO(7) and other entities(24). The ICNIRP guidelines specify ‘basic restrictions’ and ‘reference levels’. Basic restrictions are based on the physical quantity directly related to the established health effects. The physical quantity used to specify the basic restrictions are the induced internal electric field strengths that affect nerve cells and other electrically sensitive cells. Reference levels of exposure provided for practical exposure assessment purposes are derived from the basic restrictions using the data from computational simulations based on anatomically detailed human body models. ICNIRP recognises that the reference levels are given for the condition of maximum coupling of the field to the exposed individual, thereby providing maximum protection. Compliance with the reference levels is designed to ensure compliance with the relevant basic restriction. However, when the reference levels are exceeded, it does not necessarily follow that the basic restrictions will also be exceeded. They need to be determined by further investigations. Table 1 shows the reference levels for occupational exposure by a uniform field with respect to the spatial extension of the human body(24). According to Table 1, the reference levels for occupational exposure to time-varying electric and magnetic fields at 50 Hz frequency are 10 kV m21 and 1000 mT, respectively.
Table 1. Reference levels for occupational exposure to timevarying electric and magnetic fields (unperturbed RMS values)(24). Frequency range
ICNIRP GUIDELINES The ICNIRP develops internationally accepted sciencebased recommendations for protection against various non-ionising radiation (NIR) exposures. ICNIRP is the formally recognised non-governmental organisation in NIR for the World Health Organisation (WHO), the International Labour Office and the European Union (EU). The exposure guidelines published by the ICNIRP have a significance role in
1 –8 Hz 8 –25 Hz 25–300 Hz 300 Hz– 3 kHz 3 kHz–10 MHz
Electric field strength (E) [kV m21]
Magnetic flux density (B) [T]
20 20 5` 102/f 5` 102/f 1.7` 1021
0.2/f 2 2.5` 1022/f 1` 1023 0.3/f 1` 1024
f is the frequency expressed in Hertz.
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conductors carrying high currents can reach 10 mT, and workers may be exposed to electric fields up to 30 kV m21 in the electrical supply industry(7). Measurements of the field levels are very important for the verification of the results obtained using computational methods and the evaluation of the EMF exposure particularly at multiple source sites and complex working environments. Measurements often prove that more conclusive and computational methods are often not enough to assess compliance with safety limits. Measurements are also needed, when the calculated fields are close to the threshold for overexposure or when fields are likely to be distorted by reflection from various objects(22, 23). Although occupational exposure environments are studied in the context of specific industries and workplace, it is not so easy to find investigations particularly focused on uninterruptible power supply (UPS)-manufacturing facilities that are a part of the electric power utility industry. UPS industry workers represent one group of electrical workers who are exposed to highlevel ELF EMFs emanating from UPSs, transformers, resistances used loading of UPSs, power cables, printed circuit board (PCB) assembly lines, soldering machines and power systems supply energy for production. The present paper presents spot measurements of ELF EMFs obtained near a number of high-power on-line UPS models and at workplace in the visited UPS factory, which is a worldwide member of UPS industry. The factory has large closed facility, is able to produce every single part of its products, does final assembly and testing and exports products to 75 countries in 5 continents. The measured values have been compared with permissible exposure limits. The International Commission on Non-Ionizing Radiation Protection (ICNIRP) has published guidelines for limiting exposure to time-varying EMFs (1 Hz– 100 kHz), in which upper limits for occupational exposure have been presented(24). Based on the ICNIRP guidelines, European Parliament and Council has adopted a directive on the minimum health and safety requirements regarding the exposure of workers to the risks arising from physical agents (EMFs), in 2013(25). This directive repeals directive 2004/40/ EC(26). However, so far, there is no legislation for occupational exposure to EMFs in Turkey.
EXPOSURE TO EMF OF UPS INDUSTRY WORKERS
EUROPEAN DIRECTIVE (25)
Table 2. ALs for exposure to electric fields from 1 Hz to 10 MHz (RMS values)(25). Frequency range
1 f , 25 Hz 25 f , 50 Hz 50 Hz f , 1.64 kHz 1.64 f , 3 kHz 3 kHz f 10 MHz
Electric field strength low ALs (E) [V m21]
Electric field strength high ALs (E) [V m21]
2.0` 104 5.0` 105/f 5.0` 105/f 5.0` 105/f 1.7` 102
2.0` 104 2.0` 104 1.0` 106/f 6.1` 102 6.1` 102
f is the frequency expressed in Hertz.
MEASUREMENT METHOD The study was performed at different locations in the facility of a UPS manufacturer. The electric and
Table 3. ALs for exposure to magnetic fields from 1 Hz to 10 MHz (RMS values)(25). Frequency range
1 f , 8 Hz 8 f , 25 Hz 25 f , 300 Hz 300 f , 3 kHz 3 kHz f 10 MHz
Magnetic flux density low ALs (B) [mT]
Magnetic flux density high ALs (B) [mT]
Magnetic flux density ALs for exposure of limbs to a localised magnetic field (B) [mT]
2.0` 105/f 2 2.5` 104/f 1.0` 103 3.0` 105/f 1.0` 102
3.0` 105/f 3.0` 105/f 3.0` 105/f 3.0` 105/f 1.0` 102
9.0` 105/f 9.0` 105/f 9.0` 105/f 9.0` 105/f 3.0` 102
f is the frequency expressed in Hertz (Hz)
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for occupational European directive 2013/35/EU exposure to EMFs with frequencies up to 300 GHz is intended to protect the working population. The provisions of the directive, considered as minimal requirements against occupational risks due to exposure to EMFs, have to be transposed into national legislation by all EU member states by 1 July 2016. The European Commission shall make available practical guides to facilitate the implementation of the directive. The provisions of the directive are based on a similar philosophy and rationale with the ICNIRP guidelines. The directive is intended to address all known direct biophysical effects and indirect effects caused by EMFs, but it does not cover suggested long-term effects of exposure to EMFs since there is currently no well-established scientific evidence of a causal relationship. The ICNIRP basic restrictions and reference levels equate to exposure limit values (ELVs) and action levels (ALs), respectively, in the directive. ELVs means values established on the basis of biophysical and biological considerations. ‘Health effects ELVs’ and ‘sensory effects ELVs’ are additionally set out in the directive. Health effects ELVs for internal electric field strength from 1 Hz to 10 MHz are related to electric stimulation of all peripheral and central nervous system tissues in the body, including the head. Sensory
effects ELVs for internal electric field strength from 1 to 400 Hz are related to electric field effects on the central nervous system in the head, i.e. retinal phosphenes and minor transient changes in some brain functions. ALs means operational levels established for the purpose of simplifying the process of demonstrating the compliance with relevant ELVs. ALs correspond to calculated or measured electric and magnetic field values at the workplace in the absence of the worker. The AL terminology of the directive contains ‘low ALs’ and ‘high ALs’ terms. Low ALs for external electric field are based on limiting the internal electric field below the ELVs and limiting spark discharges in the working environment. Below high ALs for external electric field, the internal electric field does not exceed the ELVs and annoying spark discharges prevented, provided that the specific protection measures in accordance with the directive are taken. For exposure to magnetic fields, low ALs are derived from the sensory effects ELVs for frequencies of ,400 Hz, and from the health effects ELVs for frequencies of .400 Hz. High ALs for exposure to magnetic fields are derived from the health effects ELVs, and compliance with it ensures that health effects ELVs are not exceeded, but the effects related to retinal phosphenes and minor transient changes in brain activity are possible if the exposure of the head exceeds the low ALs for exposures up to 400 Hz. ALs for exposure to magnetic fields of limbs are derived from the health effects ELVs by taking into account that the magnetic field is coupled more weakly to the limbs than to the whole body(25). ALs for exposure to electric and magnetic fields from 1 Hz to 10 MHz are shown in Tables 2 and 3, respectively. The ALs calculated according to the tables for 50 Hz frequency are presented as follows. Electric field strength low and high ALs are 10 and 20 kV m21. Magnetic flux density low and high ALs are 1000 and 6000 mT, and ALs for exposure of limbs are 18 000 mT.
N. B. TES¸NELI AND A. Y. TES¸NELI
RESULTS AND DISCUSSION The electric and magnetic field spot measurements were performed at the same points, taking into
account the load situations, the workers’ natural movements and closeness to the source while performing the tasks. The fields were identified by manual scanning along the source enclosures and workers’ positions. To minimise field distortions, the measuring person stayed away from the investigated field source or position as far as possible holding the meter with his/her stretched arm. The measurement results are separately presented for the test areas, the production lines and the substations in the facilities of the UPS factory. The measured fields show spatial maximum values obtained scanning the height from floor to 1.8 m except measurements around both 250- and 300-kVA on-line UPS. Test areas The measurement of EMFs was made in four different UPS test areas, one transformer test area and one service test area. During the surveys, test equipment and units under test operated at normal running conditions. UPSs under test were fixed on the floor, whereas transformers under test were fixed on a table. UPSs under test operate as loaded or unloaded in accordance with its test procedures. So, the fields from the UPSs under test are separately measured for these load conditions. Description and horizontal distances to the enclosure of unit under test of the selected measurement positions are presented in Table 4 with load conditions and measured fields. According to the measurement results of the test areas, electric fields vary between 2.7 and 992.0 V m21 whereas magnetic fields are between 0.1 and 196.4 mT. Maximum fields were recorded in the transformer test area at operator position that is 0.15 m away from the transformer under test. Operator limbs have been exposed to electric fields of up to 742.6 V m21 and magnetic fields of up to 80.4 mT, because of the UPS feeders that lie on the floor. The maximum electric and magnetic fields from UPSs under test were 380.0 V m21 and 143.0 mT, respectively. The fields from the high-power UPSs were lower than the fields from the relatively low-power UPSs; the reason is that physical dimensions of high-power UPS enclosure are larger and current or voltage sources are away from the enclosure and measurement position. The UPS test operators reported that an UPS test takes 3 h (1 h loaded and 2 h unloaded) and maximum three UPSs are tested for a day. The transformer test operators said that transformer tests take a total of 3 h per working day. The EMFs were additionally measured around 250 and 300 kVA on-line UPS models, whereas they are under the test in the UPS test areas 1 and 2. Dimensions (W` D` H ) of the 250- and 300-kVA UPS models are 1.59`0.95` 1.90 m and 1.34`1.08` 1.95 m, respectively. The field distributions were measured along a plane 0.1 m apart and tangential to the UPS enclosures.
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magnetic field measurements were taken in the areas most occupied by the operators while production and testing in order to establish the typical exposure in the course of a day’s work. There are varieties of measurement methods that can be used to measure ELF EMFs. Spot measurement that is one of them was used in this study. However, data obtained from this method can only be used on that particular time. Magnetic fields emanating from the UPSs and the equipment in the workplace vary with current loadings. To determine the worst-case field exposure, the measurements were also performed at specific times when the UPSs and the equipment are under the maximum load that may be possible in the workplace. In general, time-averaging can be applied of .10 MHz and cannot be applied of ,100 kHz(27, 28). Reference levels have been determined for the exposure conditions where the variation of the electric or magnetic field over the space occupied by the body is relatively small. In most cases, however, the distance to the source of the field is so close that the distribution of the field is non-uniform or localised to a small part of the body. In these cases, the measurement of the maximum field strength in the position of space occupied by the body always gives safe results(24). ALs represent maximum calculated or measured values at the workers’ body position. This results in a conservative exposure assessment and automatic compliance with ELVs in all non-uniform exposure conditions(25). In this study, all measurement results present spatial maximum fields. The fields in the workplace were measured using Spectran NF-5035 EMF spectrum analyser, which is a hand-held commercial electric and magnetic field measuring instrument developed by Aaronia AG, Germany. The frequency range of the spectrum analyser is 1 Hz –20 MHz and allows frequency selective electric and magnetic field measurements. The electric and magnetic field ranges of the instrument are 0.1– 20 kV m21 and 1 pT–2 mT, respectively, with a typical accuracy at +3 %. The analyser features an integrated three-dimensional miniature sensor coil that allows isotropic measurement of magnetic fields in all three orthogonal axes. The analyser also has an internal sensor that enables electric fields measurements only in one-dimension (1D). The sweeps were performed from 45 Hz to 1 kHz, and the root-mean-square (RMS) detector is used in the electric and magnetic field measurements. Threedimensional magnetic field sensor and 1D electric field sensor were used. The measurements were recorded and analysed using the LCS Spectran analyser software developed by Aaronia AG.
Table 4. The measurement results of test areas. Description of the measurement location
UPS test area 1—Test desk 1 Between operator workstation and UPS Operator workstation
Load condition of unit under test [%]
Characteristics of unit under test
Distance (d ) [m]
Electric field strength (E) [V m21]
Magnetic flux density (B) [mT]
No load 100 No load 100
0.50 0.50 1.00 1.00
211.0 308.0 105.0 220.0
1.0 12.0 0.4 6.0
UPS test area 1—Test desk 4 Operator workstation
UPS (250 kVA, 3 phase –3 phase)a
No load 100
2.00 2.00
2.7 22.0
0.1 0.2
UPS test area 2—Test desk 1 Operator workstation
UPS (300 kVA, 3 phase –3 phase)b
No load 15 No load 15 15
1.00 1.00 0.05 0.05 0.15
13.2 16.0 685.0 742.6 420.0
0.9 2.6 54.0 80.4 6.1
UPS (20 kVA, 3 phase– 1 phase)a
No load 83 No load 83
0.20 0.20 0.60 0.60
250.0 282.5 94.0 116.0
36.4 65.2 1.9 4.7
UPS (10.5 kVA, 3 phase –3 phase)a
75
0.20
80.0
18.1
Transformer (20 kVA)
– – –
0.15 0.50 0.15
415.0 45.7 992.0
196.4 9.3 0.4
No load 90 No load No load (1 phase –1 phase) and 90 (3 phase –3 phase)
0.10 0.10 0.10 0.30
180.0 380.0 134.3 75.0
143.0 52.3 9.1 16.1
Above the UPS feeder lies on the floor
UPS test area 4—Test desk 1 Operator working position Transformer test area Operator working positions
Transformer (750 VA) under 3-kV isolation test Technical service test area Operator working positions
UPS (10 kVA, 3 phase– 3 phase)a UPS (10 kVA, 1 phase– 1 phase)a UPS (80 kVA, 3 phase– 3 phase) Two UPSs (10 kVA, 1 phase– 1 phase and 3 phase –3 phase)
d is the horizontal distance to source enclosure. a Side panels of UPS are demounted. b Three side panels are demounted and front panel at the operator side is mounted.
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In the vicinity of the load/resistance UPS test area 3—Test desk 1 Operator working positions
EXPOSURE TO EMF OF UPS INDUSTRY WORKERS
UPS (250 kVA, 3 phase –3 phase)a
N. B. TES¸NELI AND A. Y. TES¸NELI
Figure 2. Electric field strength measurement results for 250-kVA UPS.
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Figure 1. Measurement points in the vicinity of UPSs: (a) Top view and (b) front view (A, B and C represent the planes that have different height from the floor; all dimensions are in metres).
Measurements were made at three different heights from the floor, which are 0.5, 1.1 and 1.7 m. The measurement positions around the UPSs are shown in Figure 1, and the measured fields are graphically shown in Figures 2–5. Measurements were performed for both loaded and unloaded conditions. The fields in the graphics present spatial maximum value at relevant measurement position and its neighbouring points. For unloaded 250-kVA UPS, the electric fields are between 3.0 and 188.6 V m21 whereas the magnetic fields are between 1.0 and 142.5 mT. For 100 % loaded 250-kVA UPS, the electric fields are between 3.1 and 192.5 V m21 whereas the magnetic fields are between 4.1 and 215.6 mT. Similarly for unloaded 300-kVA UPS, the electric fields are between 2.4 and 150.0 V m21 whereas the magnetic fields are between 2.4 and 80.3 mT. For 15 % loaded 300-kVA UPS, the electric fields are between 2.5 and 167.3 V m21 whereas the magnetic fields are between 3.7 and 176.3 mT. When the UPSs are in loaded condition, the magnetic fields increased but the electric fields did not vary significantly. This result is not surprising because loading of a UPS increases current. Three hundred kilovolt-amperes UPS is loaded to 15 % during the tests, and the field measurements were performed considering normal working conditions in the factory. The field levels of 15 % loaded 300-kVA UPS provided sufficient knowledge to assess the exposure to ELF EMFs of the workers in the test area 2. When 300kVA UPS loads more than 15%, especially the
EXPOSURE TO EMF OF UPS INDUSTRY WORKERS
Figure 4. Electric field strength measurement results for 300-kVA UPS.
magnetic fields increase significantly and further measurements are needed for assessments. Production lines EMFs in the production lines were measured around automated PCB assembly lines and wave soldering machine where the operator spends 8 h a day. The
fields that were obtained during normal production process are represented in Table 5 as spatial maximum values. Electric fields vary between 5.5 and 24.0 V m21, whereas magnetic fields vary between 0.2 and 7.6 mT. The maximum magnetic field was recorded at the rear of the lead-free process line as during the wave solder process. Magnetic field was 0.2 mT at the operator position of the wave
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Figure 3. Magnetic flux density measurement results for 250-kVA UPS.
N. B. TES¸NELI AND A. Y. TES¸NELI
Table 5. The measurement results of production line. Description of the measurement location
Distance (d ) Electric field strength [m] (E) [V m21]
Automated PCB assembly lines In front of the soldering oven of the line 1 In front of the line 1, operator working positions In front of the soldering oven of the line 2 In front of the line 2, operator working positions In front of the line 3, operator working positions Rear of the line 3 Wave soldering machine In front of the lead-free process line, operator working positions Rear of the lead-free process line Marketing department In the vicinity of the office workstation contains four desks and four personal computers that are switched on
Magnetic flux density (B) [mT]
0.20 0.20 0.20 0.20 0.20 0.20
21.0 7.8 24.0 9.4 5.5 6.4
5.3 0.5 6.1 0.6 0.2 0.5
0.20
9.0
0.2
0.20
11.2
7.6
–
26.7
0.2
d is the horizontal distance to source enclosure.
soldering machine. The electric and magnetic fields in front of the soldering oven, which is a part of the automated PCB assembly lines, were measured up to 24.0 V m21 and 6.1 mT, respectively. The magnetic fields in front of the other parts of the PCB assembly lines did not exceed 0.6 mT. The measurements were also performed around the office workstation in the marketing department that is near the production areas, and the electric and magnetic fields were recorded as 26.7 V m21 and 0.2 mT, respectively.
Power substations The factory has one 630-kVA power substation and two 1000-kVA power substations that are placed in the garden and close to the factory building. EMFs measurements were performed at the positions where substation workers spend time during maintenance and repairs. Substation maintenance workers and repairers had not been exposed to the fields emanating from the substations all day. Table 6 shows the measured fields that are spatial maximum values in front of the power substations. The electric and
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Figure 5. Magnetic flux density measurement results for 300-kVA UPS.
EXPOSURE TO EMF OF UPS INDUSTRY WORKERS Table 6. The measurement results of power substations. Description of the measurement location
Electric field strength (E) [V m21]
Magnetic flux density (B) [mT]
0.20 0.30 0.20 –
65.5 21.8 28.6 6.7
0.6 0.9 14.7 1.3
0.20 0.20 0.30 0.30
9.7 41.0 91.7 165.5
3.5 43.1 7.2 65.0
0.30 0.20
8.6 21.4
6.7 8.3
d is the horizontal distance to source enclosure.
magnetic fields reach up to 165.5 V m21 and 65.0 mT, respectively. Workers have to open the panel doors during their tasks of maintenance and repair. When the panel doors are kept open, the exposed fields dramatically increase. There is an administrative office that shares a wall with 630-kVA power substation, and office workers are exposed during all working day. The fields did not exceed 6.7 V m21 and 1.3 mT in front of the shared wall and at workstations in this office. CONCLUSIONS The results of this study demonstrate the levels of ELF EMFs that can be encountered in UPS industries. Electric and magnetic field spot measurements were performed in test areas, production lines and the vicinity of power substations considering all working conditions. The measurement results show that the electric fields vary between 2.4 and 992.0 V m21, whereas the magnetic fields vary between 0.1 and 215.6 mT. Occupational exposure levels are relatively high in the test areas where the maximum fields are obtained. The measured fields were compared with ICNIRP reference levels and European directive ALs. All the measurements obtained for the described conditions are below the reference levels recommended by ICNIRP guidelines(24) and low ALs described by European directive(25). Further investigations should be performed for the working environments including higher power UPSs and different load conditions. FUNDING This work was supported by Sakarya University Scientific Research Foundation (Project number: 2012-01-00-005).
REFERENCES 1. Wertheimer, N. and Leeper, E. Electrical wiring configurations and childhood cancer. Am. J. Epidemiol. 109, 273–284 (1979). 2. Wertheimer, N. and Leeper, E. Adult cancer related to electrical wires near the home. Int. J. Epidemiol. 11, 345–355 (1982). 3. Ahlbom, A. et al. A pooled analysis of magnetic fields and childhood leukaemia. Br. J. Cancer 83, 692– 698 (2000). 4. Greenland, S., Sheppard, A. R., Kaune, W. T., Poole, C. and Kelsh, M. A. A pooled analysis of magnetic fields, wire codes, and childhood leukemia. Childhood LeukemiaEMF Study Group. Epidemiology 11, 624–634 (2000). 5. International Agency for Research on Cancer, IARC. Non-ionizing radiation, part 1: static and extremely lowfrequency (ELF) electric and magnetic fields. IARC Monographs on the Evaluation of Carcinogenic Risks to Humans. Vol. 80. (IARC Press) (2002). 6. Schu¨z, J. and Ahlbom, A. Exposure to electromagnetic fields and the risk of childhood leukaemia: a review. Radiat. Prot. Dosim. 132, 202– 211 (2008). 7. World Health Organization, WHO. Environmental Health Criteria 238. Extremely Low Frequency Fields. WHO (2007). 8. European Commission Scientific Committee on Emerging and Newly Identified Health Risks, SCENIHR. Health Effects of Exposure to EMF. SCENIHR (2009). 9. Feychting, M., Floderus, B. and Ahlbom, A. Parental occupational exposure to magnetic fields and childhood cancer (Sweden). Cancer Causes Control 11, 151–156 (2000). 10. Infante-Rivard, C. and Deadman, J. E. Maternal occupational exposure to extremely low frequency magnetic fields during pregnancy and childhood leukemia. Epidemiology 14, 437– 441 (2003). 11. Li, P., McLaughlin, J. and Infante-Rivard, C. Maternal occupational exposure to extremely low frequency magnetic fields and the risk of brain cancer in the offspring. Cancer Causes Control 20, 945– 955 (2009).
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Substation 1 (630 kVA) In front of the substation 1 In front of the circuit breaker 1 In front of the main distribution panel 1 Administrative office that has common wall with the substation 1 Substations 2 and 3 (1000 kVA) In front of the substations 2 and 3 In front of the transfer panel (panel door is open) In front of the main distribution panel 2 In front of the main distribution panel 2 (panel door is open) In front of the main distribution panel 3 In front of the shielded cable channel of the main distribution panel 3
Distance (d) [m]
N. B. TES¸NELI AND A. Y. TES¸NELI 21. National Institute of Environmental Health Sciences, NIEHS. Assessment of health effects from exposure to power line frequency electric and magnetic fields. (National Institute of Health) (NIH Publication No. 983981) (1998). 22. Habash, R. W. Y., Brodsky, L. M., Leiss, W., Krewski, D. and Repacholi, M. Health risks of electromagnetic fields. Part I: evaluation and assessment of electric and magnetic fields. Crit. Rev. Biomed. Eng. 31, 141–195 (2003). 23. Vulevic, B. and Osmokrovic, P. Evaluation of uncertainty in the measurement of environmental electromagnetic fields. Radiat. Prot. Dosim. 141, 173 –177 (2010). 24. International Commission on Non-Ionizing Radiation Protection, ICNIRP. Guidelines for limiting exposure to time-varying electric and magnetic fields (1 Hz to 100 kHz). Health Phys. 99, 818– 836 (2010). 25. EC. Directive 2013/35/EU of the European Parliament and of the Council of 26 June 2013 on the minimum health and safety requirements regarding the exposure of workers to the risks arising from physical agents (electromagnetic fields). Official J. Eur. Union L-179 (2013). 26. EC. Directive 2004/40/EC of the European Parliament and of the Council of 29 April 2004 on the minimum health and safety requirements regarding the exposure of workers to the risks arising from physical agents (electromagnetic fields). Official J. Eur. Union L-184 (2004). 27. European Committee for Electrotechnical Standardization (CENELEC). Procedure for the assessment of the exposure of workers to electromagnetic fields (Standard prEN 50499:2008). (CENELEC) (2008). 28. European Committee for Electrotechnical Standardization (CENELEC). Assessment of electronic and electrical equipment related to human exposure restrictions for electromagnetic fields (0 Hz–300 GHz) (Standard EN 62311:2008). (CENELEC) (2008).
Page 10 of 10
Downloaded from http://rpd.oxfordjournals.org/ at Northwestern University Library on August 15, 2014
12. Hug, K., Grize, L., Seidler, A., Kaatsch, P. and Schu¨z, J. Parental occupational exposure to extremely low frequency magnetic fields and childhood cancer: a German case-control study. Am. J. Epidemiol. 171, 27–35 (2010). 13. Milham, S. Mortality from leukemia in workers exposed to electrical and magnetic fields. New Eng. J. Med. 307, 249 (1982). 14. Milham, S. Mortality in workers exposed to electromagnetic fields. Environ. Health Persp. 62, 297–300 (1985). 15. Ahlbom, A. Neurodegenerative diseases, suicide, and depressive symptoms in relation to EMF. Bioelectromagnetics 5, 132–143 (2001). 16. Sobel, E., Davanipour, Z., Sulkava, R., Erkinjuntti, T., Wikstrom, J., Henderson, V. W., Buckwalter, G., Bowman, J. D. and Lee, P. J. Occupations with exposure to electromagnetic fields: a possible risk factor for Alzheimer’s disease. Am. J. Epidemiol. 142, 515–524 (1995). 17. Garcia, A. M., Sisternas, A. and Hoyos, S. P. Occupational exposure to extremely low frequency electric and magnetic fields and Alzheimer disease: a metaanalysis. Int. J. Epidemiol. 37, 329– 340 (2008). 18. Kheifets, L., Bowman, J. D., Checkoway, H., Feychting, M., Harrington, J. M., Kavet, R., Marsh, G., Mezei, G., Renew, D. C. and van Wijngaarden, E. Future needs of occupational epidemiology of extremely low frequency electric and magnetic fields: review and recommendations. Occup. Environ. Med. 66, 72–80 (2009). 19. National Institute of Environmental Health Sciences, NIEHS. Report on health effects from exposure to powerline frequency electric and magnetic fields. (National Institute of Health) (NIH Publication No. 99-4493) (1999). 20. AGNIR. ELF electromagnetic fields and the risk of cancer. Report of an Advisory Group on Non-ionising Radiation. Doc NRPB 12, 1 –179 (2001).
