Environ Monit Assess (2015) 187:258 DOI 10.1007/s10661-015-4449-y
Hazard zoning around electric substations of petrochemical industries by stimulation of extremely low-frequency magnetic fields Monireh Hosseini & Mohammad Reza Monazzam & Laleh Farhang Matin & Hossein Khosroabadi
Received: 6 October 2014 / Accepted: 18 March 2015 # Springer International Publishing Switzerland 2015
Abstract Electromagnetic fields in recent years have been discussed as one of the occupational hazards at workplaces. Hence, control and assessment of these physical factors is very important to protect and promote the health of employees. The present study was conducted to determine hazard zones based on assessment of extremely low-frequency magnetic fields at electric substations of a petrochemical complex in southern Iran, using the single-axis HI-3604 device. In measurement of electromagnetic fields by the single-axis HI-3604 device, the sensor screen should be oriented in a way to be perpendicular to the field lines. Therefore, in places where power lines are located in different directions, it is required to keep the device towards three axes of x, y, and z. For further precision, the measurements should be repeated along each of the three axes. In this
M. Hosseini (*) : L. Farhang Matin Department of Physics, Faculty of Basic Sciences, Islamic Azad University–North Tehran Branch, Tehran, Iran e-mail: [email protected] M. Hosseini : M. R. Monazzam Center for Air Pollution Research (CAPR), Institute for Environmental Research (IER), Tehran University of Medical Sciences, Tehran, Iran M. R. Monazzam (*) Department of Occupational Hygiene, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran e-mail: [email protected] H. Khosroabadi National Petrochemical Company, Tehran, Iran
research, magnetic field was measured, for the first time, in three axes of x, y, and z whose resultant value was co nsid ere d as th e va lue o f mag net ic field . Measurements were done based on IEEE std 6441994. Further, the spatial changes of the magnetic field surrounding electric substations were stimulated using MATLAB software. The obtained results indicated that the maximum magnetic flux density was 49.90 μT recorded from boiler substation, while the minimum magnetic flux density of 0.02 μT was measured at the control room of the complex. As the stimulation results suggest, the spaces around incoming panels, transformers, and cables were recognized as hazardous zones of indoor electric substations. Considering the health effects of chronic exposure to magnetic fields, it would be possible to minimize exposure to these contaminants at workplaces by identification of risky zones and observation of protective considerations. Keywords Extremely low frequency . Magnetic field . Occupational exposure . Hazard zones . Electrical substations
Introduction The use of electricity has become an integral part of modern human life. Daily use of energy, despite numerous benefits, increases the number of individuals exposed to electromagnetic fields. Occupational and public exposure to this physical factor leads to concerns about its possible adverse effects on human health
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(Grellier et al. 2014; Monazzam et al. 2014; Li et al. 2007; Mangiacasale et al. 2001; Burdak-Rothkamm et al. 2009). Li et al. (2014) investigated the effects of chronic exposure (14 and 28 days) to a 50-Hz, 0.5 mT extremely low-frequency magnetic field (ELF-MF) on the NMDAR and AMPAR subunit expressions and rat spatial learning and memory. They reported that the dynamic and brain-region specific changes in ionotropic glutamate receptor expression induced by ELF-MF are insufficient to influence the rat spatial learning ability. In a study by Balassa et al. (2013), it was demonstrated that ELF magnetic fields have significant effects on basic neuronal functions and synaptic plasticity in brain slice preparations originating from rats exposed either in fetal or in newborn period. Pathogenic theory of electromagnetic fields on nearby residents and employees, especially their carcinogenic effects, has been studied in many studies worldwide. However, the results have not been conclusive, and there is still considerable controversy on the matter. In this case, the major concern is about the potential effects of magnetic fields. Unlike electric fields, magnetic fields can penetrate into buildings and the human skin (Habash 2001). Some epidemiologic studies have claimed an association between exposure to ELF magnetic fields and increased risk of cancer, including leukemia, brain tumors, and breast cancer, while other set of studies have not confirmed such a relationship. Turner et al. (2014) introduced occupational exposure to ELF magnetic fields as a suspected risk factor for brain tumors. Kheifets et al. (2010) confirmed an association between magnetic fields and childhood leukemia. Erdal et al. (2007) studied genotoxic and cytotoxic potential of ELF magnetic fields in Wistar rat tibial bone marrow cells using the chromosomal aberration and micronucleus test systems. They reported the in vivo susceptibility of mammals to the genotoxicity potential of ELF magnetic field. Stratton et al. (2013) showed that an alternating current, pulsed, extremely low-frequency electromagnetic field (0.3 μT at 10 Hz, 6 V AC) induced transient plasma membrane damage that allowed calcium influx. Moreover, in recent years, many studies have been done on noncarcinogenic effects of exposure to magnetic fields. These studies partially confirm the possible adverse effects of exposure to magnetic fields. Li et al. (2013) conducted a research on occupational exposure to magnetic fields and breast cancer among women textile workers in Shanghai, China. Their findings did
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not support the hypothesis that magnetic field exposure increases the risk of breast cancer. Sorahan (2014) investigated whether brain tumor risks are related to occupational exposure to low-frequency magnetic fields. They could find no evidence to support the hypothesis that exposure to magnetic fields is a risk factor for gliomas, and the findings are consistent with the hypotheses that both distant and recent magnetic field exposures are not causally related to gliomas. Chen et al. (2010) concluded that ELF electromagnetic field exposure has no association with the susceptibility of female breast cancer. Safety and health measures seem essential to reduce exposure to these contaminants in the environment. Substations are of risky workplaces whose personnel are exposed to a higher level of magnetic fields than others. Due to concerns about the health of employees at substations, measurement of magnetic fields at these workplaces is a research priority in most countries in order to reduce the exposure of people. Methner and Bowman 2000 designed a hazard surveillance study to measure the mean and peak magnetic field magnitudes at extremely low frequencies (ELFs) around 62 facilities from 13 Standard Industrial Classifications (SICs) with the highest monthly electric power usage. They found a weak relationship between the facility-specific monthly electric power consumption and the geometric mean of magnetic field magnitude. According to their findings, 89 % of the geometric mean values were at or below 0.4 μT. In another research by Bowman and Methner 2000, characteristics of magnetic field surveyed systematically in six factories with the Multiwave® II waveform capture instrument manufactured plastics, pharmaceuticals, cement, liquid air products, aluminum parts, and aluminum-framed filters. They indicated that the static magnetic field magnitudes had medians of 24.2– 46.2 μT, which is well below the geomagnetic reference field of 55.0 μT as a result of shielding from steel structures. Bowman et al. (2007) developed a population-based job exposure matrix (JEM) to assess personal exposure to power-frequency magnetic fields for epidemiologic studies. Improper architecture of substation buildings and incorrect layout of equipment expose employee to excessive magnetic fields or causes dysfunction of other equipment. As one of the strategies for reduction of workers’ exposure to a large extent is proper design of substation building and suitable layout of indoor equipment. For this, it is required to identify risky zones and
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generation sources of magnetic fields at each substation. Accordingly, designers would enhance safety at workplaces by proper layout designing. Obviously, increased safety of workplaces will enhance the health of personnel and the quality of the working environment. Accordingly, the present study was performed to measure magnetic flux density at indoor substations to stimulate spatial pattern of hazard zones. In this way, the safe points of the substation would be identified to avoid long-term presence of personnel in high-risk areas. Furthermore, by detecting the spatial propagation pattern of magnetic fields inside the substation, any possible interaction effects with other fields would be identified. Therefore, it would be possible to decline the synergetic effects where required.
Material and methods In this research, ELF magnetic field was measured at three indoor electrical substations (boiler, ethylene, and utility) at a petrochemical complex in southern Iran. In order to detect spatial variations in ELF magnetic fields, the map of under study sites was drawn. Measurement points were specified by gridding indoor space of the target sites. The number of grid points and the gap between them depend on the size and shape of each room as well as the layout of the equipment and boards at rooms. Characteristics of the target sites are presented in Table 1. Subsequently, operator measured ELF magnetic field values at each measurement point based on IEEE std 644-1994 (IEEE 1994), according to which the probe of the magnetic field meter was kept by the operator at a height of 1 m from the ground. The device was of HI-3604 type manufactured by Holaday Company, USA (Holaday Industries Inc. 2008). The magnetic field meter is a single-axis device. However, Table 1 Characteristics of the measurement sites
in order to accurately measure magnetic fields, measurements were done towards three axes of X, Y, and Z. Accordingly, at each node, ELF magnetic field values were measured along three axes of X, Y, and Z. The resultant of the measured values was announced as the final ELF magnetic field value of the node (Holaday Industries Inc. 2008; Hosseini et al. 2014). In order to further ensure of the accuracy of the obtained results, all of the measurements were done twice at each point towards each direction. The average of the measured values was considered as a final ELF magnetic field value at each direction. It should be mentioned that the complex was in its normal operational conditions during the measurement period. After measuring magnetic flux density at each site, the measurement data were stimulated by MATLAB to detect spatial variations in ELF magnetic field. It is worth noting that magnetic flux density values were generalized to places with data gap using interpolation method.
Result and discussion In this research, a total number of 1584 measurements were done at 264 measurement points distributed among 7 sites in the target complex. Monitoring results are provided here in separation of different measurement sites. The control building in the complex includes two rooms, namely, auxiliary room and control room. Total measurement point at this building was 64, of which 37 points belong to the auxiliary room and the rest (27 measurement points) were assigned to the control room. The map of the control building is demonstrated in Fig. 1 on which the measurement points are welldepicted. Equipment of auxiliary room includes a series of panels stacked neatly next to each other, on which there are measurement devices such as ammeters,
Workplace
Ethylen substation Utility substation
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Boiler substation Control building
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Fig. 1 Map of control building
voltmeters, etc. On the western auxiliary room, there is a control room where the operators are settled. The scope of operators’ table is illustrated in Fig. 1. A glass wall separates these two rooms. According to the results, the average magnetic flux density at the indoor auxiliary room was 0.13 μT. The minimum and maximum values of magnetic flux density were 0.03 and 0.93 μT (standard limit=1200 μT), respectively. The maximum magnetic flux was measured nearby the incoming panels. These panels are
the entry and distribution place of electricity at each room. Thus, the input power to each room is initially entered into these panels and, from there, is distributed among other panels. As mentioned earlier, the values of magnetic flux density at each room were stimulated using MATLAB. For a detailed stimulation of magnetic flux density at the auxiliary room, it was separated in two parts: north and south. Figure 2a (southern part) and b demonstrates spatial pattern of magnetic flux density at the auxiliary room. In these figures, X and Y are the
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At the control room, the average magnetic flux density was 0.04 μT. The minimum value was 0.02 μT. The maximum value of 0.14 μT (standard limit=1200 μT) was measured nearby the Emergency Shut Down (ESD) panel. The panel commands urgently power outage when electrical system of the complex cannot bear immediate overloading or loss of power. Red zone in Fig. 2c illustrates the location of the panel at the control room, which is near the southern wall of the room.
width and length of the room in meter, and B is the resultant value of the magnetic field in microtesla. In the figure, hazard zones, i.e., areas with maximum magnetic flux density, are depicted in red. Yellow and green colors indicate average values, and blue color shows minimum magnetic flux density values at the room. As the results suggest, hazard zone at the auxiliary room was found around the incoming panel where the maximum magnetic flux density was measured.
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Fig. 2 Distribution pattern of magnetic flux density at the southern auxiliary room (a), at the northern auxiliary room (b), and at the control room (c)
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At the utility post of the complex, a total number of 49 points were measured. There are LV switchgear room and MV switchgear room at this substation whose map is presented in Fig. 3. The number of measurement
Fig. 3 Map of utility substation
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points at the LV switchgear room was 34. The average magnetic field at these points was 1.36 μT. Minimum and maximum magnetic field values at this room were 0.10 and 11.69 μT, respectively. The maximum
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color on the figure represents measurement points with maximum magnetic field values, while green color refers to the an area in the west where there is the incoming panel (Fig. 4c), according to which it is concluded that magnetic field value around the voltage transformer is lower than that of incoming panel. Hazard zones at the MV switchgear room were found nearby tow incoming panels (Fig. 4c). Closeness of these panels can cause synergic effects
magnetic field value was measured adjacent to a 6 kV/ 400 V voltage transformer. A total number of 15 measurement points were considered at the MV switchgear room. Minimum, maximum, and average values of magnetic flux density were 0.08, 0.29, and 1.14 μT, respectively. Similar to the auxiliary room, the maximum value was measured nearby the incoming panels. Stimulation results of magnetic flux density of the LV switchgear room are presented in Fig. 4. Red
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Fig. 4 Distribution pattern of magnetic flux density at the southern LV switchgear room, utility substation (a), at the northern LV switchgear room, utility substation (b), and at the MV Switchgear Room, utility substation (c)
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resulting from interference between the magnetic fields. Thus, by displacement of the panels and placing them at a further distance from each other, it would be possible to avoid intensify of the magnetic fields and make the space between them as a safe environment for commuting of personnel. At boiler substation, 24 measurement points were considered. This substation has only one room that has a smaller area than other places. Indoor equipment of this substation includes electrical panels on the sidelines. Area in the middle of this substation is where the workers stay permanently during their work shift. Figure 5 presents a schema of boiler building. On the east side of the substation, with very little distance from its outer wall, there are two 20 kV to 400 V step-down transformers whose outputs, with the entrance to the basement of the substation, joins to the indoor panels. At the boiler substation, maximum magnetic field was 49.90 μT measured in areas close to the eastern wall of the building and in adjacent to the incoming panels. Average magnetic field at this Fig. 5 Map of boiler substation
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substation was 11.13 μT, which was higher than that of other rooms. Minimum magnetic field was 0.79 μT. Spatial pattern of magnetic flux density at the boiler substations is stimulated in Fig. 6. Ethylene substation includes of the LV and MV rooms. A total number of 112 points were measured at this substation: 88 points at the LV room and 24 points at the MV room. A schema of the ethylene substation is depicted in Fig. 7. Equipment of the LV room includes panels and transformers. It is worth noting that all of the transformers at the ethylene substation are of isolation type (1:1 transformer). In other words, the input 400-kV electric current leaves the transformers without increasing or decreasing. The MV room includes a series of panels located in the middle of the room (Fig. 7). In spite of transformers and incoming panels at the LV room, maximum magnetic field values were recorded at areas where there are electric buses as 400-V energy carriers. These buses are inside a closed compartment called bus duct. Distribution pattern of magnetic field released from the cables is demonstrated in
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Fig. 6 Spatial pattern of magnetic flux density at the boiler substations
Fig. 8a. Maximum and minimum values of magnetic flux density at this room were 40.43 and 0.48 μT, respectively. The average magnetic flux density was 1.39 μT. Figure 8b depicts magnetic field values measured at the east side of the room. At the other room of the ethylene substation, maximum magnetic flux density of 3.84 μT was measured nearby the incoming panels (Fig. 8c). Minimum magnetic field value at this room was 0.61 μT, while the average value was 7.46 μT. As was observed in this study, none of the magnetic flux density values exceed the standard limit recommended by ACGIH for occupational exposure. It should be mentioned that ACGIH recommends a value of 1.2 mT (1200 μT) as a permissible occupational exposure to magnetic fields in the frequency range of 50 Hz (ACGIH 2010). Similar studies have also been carried out in which the measured magnetic field values were much lower than the standard limit. As such, in a study by Joseph et al. (2008) on eight substations in Belgium, maximal magnetic field values for all the investigated substations were below 100 μT. Their results are consistent with that of this research. In a research by Fard et al. (2011), the measured magnetic field value did not exceed the standard limit at the target substations. They investigated a total number of 8 HV substations (230 kV) in Tehran City in 2010. Maximum field value measured by them was
0.69 μT at the control room and 9.15 μT at the switchgear. Korpinen et al. (2011) measured occupational exposure to electric and magnetic fields during various work tasks at switching and transforming stations of 110 kV. They reported maximum magnetic field value of 490 μT, which was below the standard limit. In a study by Teşneli and Teşneli in 2013 on uninterruptible power supply (UPS) factory, magnetic field value did not exceed 215.6 μT. Maximum magnetic field value of 7.6 μT was measured at production lines, while the minimum value was 65 μT measured nearby electrical substations. However, since the negative health effects of magnetic fields have been reported even when the magnetic field values were lower than the standard limit, it is necessary to assess magnetic flux density at human environment in order to adopt appropriate protective strategies. The present study was carried out to stimulate areas with maximum values of magnetic fields as well as their generation sources in order to avoid occupational exposure at the target substation. As the stimulation results suggest, spaces around incoming panels, transformers, and buses at indoor substations were recognized as hazard zones. In a study by Margallo (2009) on two 100-MVA substations in the Philippines, maximum magnetic values were measured nearby the transformers. In a study by Kandel et al. (2013), LV cables between transformers and LV switchgear were recognized as main sources of sever ELF magnetic fields. They measured ELF magnetic field around and above three stand-alone 22/0.4-kV transformer stations. Since improper design of substation can affect auxiliary equipments and endanger human health, it is necessary to allocate appropriately the equipment at indoor spaces, through which occupational exposure is reduced to the minimum possible extent. In the present circumstances, it is possible to protect the workers from potential adverse effects arising from these fields by displacing generation sources of maximum magnetic field (if applicable) and by providing the staff with health advices to keep a safe distance from these sources (Davanipour et al. 2007). Electromagnetic field density is influenced by the distance from generation sources so that field density decreases with increasing distance from the sources. The simulation results revealed that the field distribution follows a uniform and linear
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Fig. 7 Map of ethylene substation
pattern so that the field strength is reduced at further distances from the generation source. Distance between the generation sources helps avoiding interference of magnetic fields and prevents synergetic effects. Increased distance between generation sources is a simple and applicable strategy to protect workers from long-term exposure to magnetic fields.
Conclusion In recent years, the magnetic fields generated by electrical systems have been added to the list of
potential threats to human health. Preventive and corrective measures based on field measurements and recognition of hazard patterns can reduce occupational exposure of workers. In the present study, hazard zones at electrical substations were identified based on ELF magnetic field values measured. According to the obtained results, magnetic flux values were lower than the permissible limit for occupational exposure recommended by ACGIH. Although the magnetic field values measured in this study was lower than the recommended standard, but since the negative health effects of magnetic fields have been reported even in cases where their levels were less than the
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Fig. 8 Distribution pattern of magnetic flux density at western LV room (a), eastern LV room, and MV room (c)
standard limit, so any trace amount of magnetic field could be harmful and hazardous (Yousefi and Nasiri 2006; Davanipour et al. 2007). This turns out the need to analyze the status of magnetic fields in human environment in order to provide protective solutions against this risk factor. According to the research findings, incoming panels, transformers, and buses of indoor substation were identified as sources of the maximum magnetic flux. Since psychological effects of these
fields on the human body have been reported even in small quantities, therefore, it is recommended to reduce individuals’ exposure through different ways including identification of safe zones at workplaces, reduced shift hours, and training of exposed personnel. Due to the effect of aging on the quality and reliability of electrical equipment in the substations, it is strongly recommended to monitor changes in magnetic fields, after a period of time, within frequent intervals.
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Acknowledgments This study has been done with the financial support of Iranian National Petrochemical Company (NPC). We would like to thank Dr. Nassiri, Director of HSE Department, and Eng. Ahmad Hesami, Occupational health Expert at NPC. We would also like to express our sincere gratitude for the proofreading services rendered by Ravian Danesh Mohit Company.
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Page 13 of 13 258 Turner, M. C., Benke, G., Bowman, J. D., Figuerola, J., Fleming, S., Hours, M., et al. (2014). Occupational exposure to extremely low frequency magnetic fields and brain tumor risks in the INTEROCC study. Cancer Epidemioly Biomarkers and Prevention. doi:10.1158/1055-9965.EPI-14-0102. Teşneli, N. B., & Teşneli, A. Y. (2013). Occupational exposure to electromagnetic fields of uninterruptible power supply industry workers. Radiation Protection Dosimetry. doi:10.1093/ rpd/nct340. Yousefi, H. A., & Nasiri, P. (2006). Psychological effect of occupational exposure to electromagnetic fields. Journal of Research in Health Sciences, 6(1), 18–21.
Hazard zoning around electric substations of petrochemical industries by stimulation of extremely low-frequency magnetic fields Monireh Hosseini & Mohammad Reza Monazzam & Laleh Farhang Matin & Hossein Khosroabadi
Received: 6 October 2014 / Accepted: 18 March 2015 # Springer International Publishing Switzerland 2015
Abstract Electromagnetic fields in recent years have been discussed as one of the occupational hazards at workplaces. Hence, control and assessment of these physical factors is very important to protect and promote the health of employees. The present study was conducted to determine hazard zones based on assessment of extremely low-frequency magnetic fields at electric substations of a petrochemical complex in southern Iran, using the single-axis HI-3604 device. In measurement of electromagnetic fields by the single-axis HI-3604 device, the sensor screen should be oriented in a way to be perpendicular to the field lines. Therefore, in places where power lines are located in different directions, it is required to keep the device towards three axes of x, y, and z. For further precision, the measurements should be repeated along each of the three axes. In this
M. Hosseini (*) : L. Farhang Matin Department of Physics, Faculty of Basic Sciences, Islamic Azad University–North Tehran Branch, Tehran, Iran e-mail: [email protected] M. Hosseini : M. R. Monazzam Center for Air Pollution Research (CAPR), Institute for Environmental Research (IER), Tehran University of Medical Sciences, Tehran, Iran M. R. Monazzam (*) Department of Occupational Hygiene, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran e-mail: [email protected] H. Khosroabadi National Petrochemical Company, Tehran, Iran
research, magnetic field was measured, for the first time, in three axes of x, y, and z whose resultant value was co nsid ere d as th e va lue o f mag net ic field . Measurements were done based on IEEE std 6441994. Further, the spatial changes of the magnetic field surrounding electric substations were stimulated using MATLAB software. The obtained results indicated that the maximum magnetic flux density was 49.90 μT recorded from boiler substation, while the minimum magnetic flux density of 0.02 μT was measured at the control room of the complex. As the stimulation results suggest, the spaces around incoming panels, transformers, and cables were recognized as hazardous zones of indoor electric substations. Considering the health effects of chronic exposure to magnetic fields, it would be possible to minimize exposure to these contaminants at workplaces by identification of risky zones and observation of protective considerations. Keywords Extremely low frequency . Magnetic field . Occupational exposure . Hazard zones . Electrical substations
Introduction The use of electricity has become an integral part of modern human life. Daily use of energy, despite numerous benefits, increases the number of individuals exposed to electromagnetic fields. Occupational and public exposure to this physical factor leads to concerns about its possible adverse effects on human health
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(Grellier et al. 2014; Monazzam et al. 2014; Li et al. 2007; Mangiacasale et al. 2001; Burdak-Rothkamm et al. 2009). Li et al. (2014) investigated the effects of chronic exposure (14 and 28 days) to a 50-Hz, 0.5 mT extremely low-frequency magnetic field (ELF-MF) on the NMDAR and AMPAR subunit expressions and rat spatial learning and memory. They reported that the dynamic and brain-region specific changes in ionotropic glutamate receptor expression induced by ELF-MF are insufficient to influence the rat spatial learning ability. In a study by Balassa et al. (2013), it was demonstrated that ELF magnetic fields have significant effects on basic neuronal functions and synaptic plasticity in brain slice preparations originating from rats exposed either in fetal or in newborn period. Pathogenic theory of electromagnetic fields on nearby residents and employees, especially their carcinogenic effects, has been studied in many studies worldwide. However, the results have not been conclusive, and there is still considerable controversy on the matter. In this case, the major concern is about the potential effects of magnetic fields. Unlike electric fields, magnetic fields can penetrate into buildings and the human skin (Habash 2001). Some epidemiologic studies have claimed an association between exposure to ELF magnetic fields and increased risk of cancer, including leukemia, brain tumors, and breast cancer, while other set of studies have not confirmed such a relationship. Turner et al. (2014) introduced occupational exposure to ELF magnetic fields as a suspected risk factor for brain tumors. Kheifets et al. (2010) confirmed an association between magnetic fields and childhood leukemia. Erdal et al. (2007) studied genotoxic and cytotoxic potential of ELF magnetic fields in Wistar rat tibial bone marrow cells using the chromosomal aberration and micronucleus test systems. They reported the in vivo susceptibility of mammals to the genotoxicity potential of ELF magnetic field. Stratton et al. (2013) showed that an alternating current, pulsed, extremely low-frequency electromagnetic field (0.3 μT at 10 Hz, 6 V AC) induced transient plasma membrane damage that allowed calcium influx. Moreover, in recent years, many studies have been done on noncarcinogenic effects of exposure to magnetic fields. These studies partially confirm the possible adverse effects of exposure to magnetic fields. Li et al. (2013) conducted a research on occupational exposure to magnetic fields and breast cancer among women textile workers in Shanghai, China. Their findings did
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not support the hypothesis that magnetic field exposure increases the risk of breast cancer. Sorahan (2014) investigated whether brain tumor risks are related to occupational exposure to low-frequency magnetic fields. They could find no evidence to support the hypothesis that exposure to magnetic fields is a risk factor for gliomas, and the findings are consistent with the hypotheses that both distant and recent magnetic field exposures are not causally related to gliomas. Chen et al. (2010) concluded that ELF electromagnetic field exposure has no association with the susceptibility of female breast cancer. Safety and health measures seem essential to reduce exposure to these contaminants in the environment. Substations are of risky workplaces whose personnel are exposed to a higher level of magnetic fields than others. Due to concerns about the health of employees at substations, measurement of magnetic fields at these workplaces is a research priority in most countries in order to reduce the exposure of people. Methner and Bowman 2000 designed a hazard surveillance study to measure the mean and peak magnetic field magnitudes at extremely low frequencies (ELFs) around 62 facilities from 13 Standard Industrial Classifications (SICs) with the highest monthly electric power usage. They found a weak relationship between the facility-specific monthly electric power consumption and the geometric mean of magnetic field magnitude. According to their findings, 89 % of the geometric mean values were at or below 0.4 μT. In another research by Bowman and Methner 2000, characteristics of magnetic field surveyed systematically in six factories with the Multiwave® II waveform capture instrument manufactured plastics, pharmaceuticals, cement, liquid air products, aluminum parts, and aluminum-framed filters. They indicated that the static magnetic field magnitudes had medians of 24.2– 46.2 μT, which is well below the geomagnetic reference field of 55.0 μT as a result of shielding from steel structures. Bowman et al. (2007) developed a population-based job exposure matrix (JEM) to assess personal exposure to power-frequency magnetic fields for epidemiologic studies. Improper architecture of substation buildings and incorrect layout of equipment expose employee to excessive magnetic fields or causes dysfunction of other equipment. As one of the strategies for reduction of workers’ exposure to a large extent is proper design of substation building and suitable layout of indoor equipment. For this, it is required to identify risky zones and
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generation sources of magnetic fields at each substation. Accordingly, designers would enhance safety at workplaces by proper layout designing. Obviously, increased safety of workplaces will enhance the health of personnel and the quality of the working environment. Accordingly, the present study was performed to measure magnetic flux density at indoor substations to stimulate spatial pattern of hazard zones. In this way, the safe points of the substation would be identified to avoid long-term presence of personnel in high-risk areas. Furthermore, by detecting the spatial propagation pattern of magnetic fields inside the substation, any possible interaction effects with other fields would be identified. Therefore, it would be possible to decline the synergetic effects where required.
Material and methods In this research, ELF magnetic field was measured at three indoor electrical substations (boiler, ethylene, and utility) at a petrochemical complex in southern Iran. In order to detect spatial variations in ELF magnetic fields, the map of under study sites was drawn. Measurement points were specified by gridding indoor space of the target sites. The number of grid points and the gap between them depend on the size and shape of each room as well as the layout of the equipment and boards at rooms. Characteristics of the target sites are presented in Table 1. Subsequently, operator measured ELF magnetic field values at each measurement point based on IEEE std 644-1994 (IEEE 1994), according to which the probe of the magnetic field meter was kept by the operator at a height of 1 m from the ground. The device was of HI-3604 type manufactured by Holaday Company, USA (Holaday Industries Inc. 2008). The magnetic field meter is a single-axis device. However, Table 1 Characteristics of the measurement sites
in order to accurately measure magnetic fields, measurements were done towards three axes of X, Y, and Z. Accordingly, at each node, ELF magnetic field values were measured along three axes of X, Y, and Z. The resultant of the measured values was announced as the final ELF magnetic field value of the node (Holaday Industries Inc. 2008; Hosseini et al. 2014). In order to further ensure of the accuracy of the obtained results, all of the measurements were done twice at each point towards each direction. The average of the measured values was considered as a final ELF magnetic field value at each direction. It should be mentioned that the complex was in its normal operational conditions during the measurement period. After measuring magnetic flux density at each site, the measurement data were stimulated by MATLAB to detect spatial variations in ELF magnetic field. It is worth noting that magnetic flux density values were generalized to places with data gap using interpolation method.
Result and discussion In this research, a total number of 1584 measurements were done at 264 measurement points distributed among 7 sites in the target complex. Monitoring results are provided here in separation of different measurement sites. The control building in the complex includes two rooms, namely, auxiliary room and control room. Total measurement point at this building was 64, of which 37 points belong to the auxiliary room and the rest (27 measurement points) were assigned to the control room. The map of the control building is demonstrated in Fig. 1 on which the measurement points are welldepicted. Equipment of auxiliary room includes a series of panels stacked neatly next to each other, on which there are measurement devices such as ammeters,
Workplace
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Fig. 1 Map of control building
voltmeters, etc. On the western auxiliary room, there is a control room where the operators are settled. The scope of operators’ table is illustrated in Fig. 1. A glass wall separates these two rooms. According to the results, the average magnetic flux density at the indoor auxiliary room was 0.13 μT. The minimum and maximum values of magnetic flux density were 0.03 and 0.93 μT (standard limit=1200 μT), respectively. The maximum magnetic flux was measured nearby the incoming panels. These panels are
the entry and distribution place of electricity at each room. Thus, the input power to each room is initially entered into these panels and, from there, is distributed among other panels. As mentioned earlier, the values of magnetic flux density at each room were stimulated using MATLAB. For a detailed stimulation of magnetic flux density at the auxiliary room, it was separated in two parts: north and south. Figure 2a (southern part) and b demonstrates spatial pattern of magnetic flux density at the auxiliary room. In these figures, X and Y are the
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At the control room, the average magnetic flux density was 0.04 μT. The minimum value was 0.02 μT. The maximum value of 0.14 μT (standard limit=1200 μT) was measured nearby the Emergency Shut Down (ESD) panel. The panel commands urgently power outage when electrical system of the complex cannot bear immediate overloading or loss of power. Red zone in Fig. 2c illustrates the location of the panel at the control room, which is near the southern wall of the room.
width and length of the room in meter, and B is the resultant value of the magnetic field in microtesla. In the figure, hazard zones, i.e., areas with maximum magnetic flux density, are depicted in red. Yellow and green colors indicate average values, and blue color shows minimum magnetic flux density values at the room. As the results suggest, hazard zone at the auxiliary room was found around the incoming panel where the maximum magnetic flux density was measured.
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At the utility post of the complex, a total number of 49 points were measured. There are LV switchgear room and MV switchgear room at this substation whose map is presented in Fig. 3. The number of measurement
Fig. 3 Map of utility substation
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points at the LV switchgear room was 34. The average magnetic field at these points was 1.36 μT. Minimum and maximum magnetic field values at this room were 0.10 and 11.69 μT, respectively. The maximum
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color on the figure represents measurement points with maximum magnetic field values, while green color refers to the an area in the west where there is the incoming panel (Fig. 4c), according to which it is concluded that magnetic field value around the voltage transformer is lower than that of incoming panel. Hazard zones at the MV switchgear room were found nearby tow incoming panels (Fig. 4c). Closeness of these panels can cause synergic effects
magnetic field value was measured adjacent to a 6 kV/ 400 V voltage transformer. A total number of 15 measurement points were considered at the MV switchgear room. Minimum, maximum, and average values of magnetic flux density were 0.08, 0.29, and 1.14 μT, respectively. Similar to the auxiliary room, the maximum value was measured nearby the incoming panels. Stimulation results of magnetic flux density of the LV switchgear room are presented in Fig. 4. Red
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Fig. 4 Distribution pattern of magnetic flux density at the southern LV switchgear room, utility substation (a), at the northern LV switchgear room, utility substation (b), and at the MV Switchgear Room, utility substation (c)
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resulting from interference between the magnetic fields. Thus, by displacement of the panels and placing them at a further distance from each other, it would be possible to avoid intensify of the magnetic fields and make the space between them as a safe environment for commuting of personnel. At boiler substation, 24 measurement points were considered. This substation has only one room that has a smaller area than other places. Indoor equipment of this substation includes electrical panels on the sidelines. Area in the middle of this substation is where the workers stay permanently during their work shift. Figure 5 presents a schema of boiler building. On the east side of the substation, with very little distance from its outer wall, there are two 20 kV to 400 V step-down transformers whose outputs, with the entrance to the basement of the substation, joins to the indoor panels. At the boiler substation, maximum magnetic field was 49.90 μT measured in areas close to the eastern wall of the building and in adjacent to the incoming panels. Average magnetic field at this Fig. 5 Map of boiler substation
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substation was 11.13 μT, which was higher than that of other rooms. Minimum magnetic field was 0.79 μT. Spatial pattern of magnetic flux density at the boiler substations is stimulated in Fig. 6. Ethylene substation includes of the LV and MV rooms. A total number of 112 points were measured at this substation: 88 points at the LV room and 24 points at the MV room. A schema of the ethylene substation is depicted in Fig. 7. Equipment of the LV room includes panels and transformers. It is worth noting that all of the transformers at the ethylene substation are of isolation type (1:1 transformer). In other words, the input 400-kV electric current leaves the transformers without increasing or decreasing. The MV room includes a series of panels located in the middle of the room (Fig. 7). In spite of transformers and incoming panels at the LV room, maximum magnetic field values were recorded at areas where there are electric buses as 400-V energy carriers. These buses are inside a closed compartment called bus duct. Distribution pattern of magnetic field released from the cables is demonstrated in
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Fig. 6 Spatial pattern of magnetic flux density at the boiler substations
Fig. 8a. Maximum and minimum values of magnetic flux density at this room were 40.43 and 0.48 μT, respectively. The average magnetic flux density was 1.39 μT. Figure 8b depicts magnetic field values measured at the east side of the room. At the other room of the ethylene substation, maximum magnetic flux density of 3.84 μT was measured nearby the incoming panels (Fig. 8c). Minimum magnetic field value at this room was 0.61 μT, while the average value was 7.46 μT. As was observed in this study, none of the magnetic flux density values exceed the standard limit recommended by ACGIH for occupational exposure. It should be mentioned that ACGIH recommends a value of 1.2 mT (1200 μT) as a permissible occupational exposure to magnetic fields in the frequency range of 50 Hz (ACGIH 2010). Similar studies have also been carried out in which the measured magnetic field values were much lower than the standard limit. As such, in a study by Joseph et al. (2008) on eight substations in Belgium, maximal magnetic field values for all the investigated substations were below 100 μT. Their results are consistent with that of this research. In a research by Fard et al. (2011), the measured magnetic field value did not exceed the standard limit at the target substations. They investigated a total number of 8 HV substations (230 kV) in Tehran City in 2010. Maximum field value measured by them was
0.69 μT at the control room and 9.15 μT at the switchgear. Korpinen et al. (2011) measured occupational exposure to electric and magnetic fields during various work tasks at switching and transforming stations of 110 kV. They reported maximum magnetic field value of 490 μT, which was below the standard limit. In a study by Teşneli and Teşneli in 2013 on uninterruptible power supply (UPS) factory, magnetic field value did not exceed 215.6 μT. Maximum magnetic field value of 7.6 μT was measured at production lines, while the minimum value was 65 μT measured nearby electrical substations. However, since the negative health effects of magnetic fields have been reported even when the magnetic field values were lower than the standard limit, it is necessary to assess magnetic flux density at human environment in order to adopt appropriate protective strategies. The present study was carried out to stimulate areas with maximum values of magnetic fields as well as their generation sources in order to avoid occupational exposure at the target substation. As the stimulation results suggest, spaces around incoming panels, transformers, and buses at indoor substations were recognized as hazard zones. In a study by Margallo (2009) on two 100-MVA substations in the Philippines, maximum magnetic values were measured nearby the transformers. In a study by Kandel et al. (2013), LV cables between transformers and LV switchgear were recognized as main sources of sever ELF magnetic fields. They measured ELF magnetic field around and above three stand-alone 22/0.4-kV transformer stations. Since improper design of substation can affect auxiliary equipments and endanger human health, it is necessary to allocate appropriately the equipment at indoor spaces, through which occupational exposure is reduced to the minimum possible extent. In the present circumstances, it is possible to protect the workers from potential adverse effects arising from these fields by displacing generation sources of maximum magnetic field (if applicable) and by providing the staff with health advices to keep a safe distance from these sources (Davanipour et al. 2007). Electromagnetic field density is influenced by the distance from generation sources so that field density decreases with increasing distance from the sources. The simulation results revealed that the field distribution follows a uniform and linear
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Fig. 7 Map of ethylene substation
pattern so that the field strength is reduced at further distances from the generation source. Distance between the generation sources helps avoiding interference of magnetic fields and prevents synergetic effects. Increased distance between generation sources is a simple and applicable strategy to protect workers from long-term exposure to magnetic fields.
Conclusion In recent years, the magnetic fields generated by electrical systems have been added to the list of
potential threats to human health. Preventive and corrective measures based on field measurements and recognition of hazard patterns can reduce occupational exposure of workers. In the present study, hazard zones at electrical substations were identified based on ELF magnetic field values measured. According to the obtained results, magnetic flux values were lower than the permissible limit for occupational exposure recommended by ACGIH. Although the magnetic field values measured in this study was lower than the recommended standard, but since the negative health effects of magnetic fields have been reported even in cases where their levels were less than the
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Fig. 8 Distribution pattern of magnetic flux density at western LV room (a), eastern LV room, and MV room (c)
standard limit, so any trace amount of magnetic field could be harmful and hazardous (Yousefi and Nasiri 2006; Davanipour et al. 2007). This turns out the need to analyze the status of magnetic fields in human environment in order to provide protective solutions against this risk factor. According to the research findings, incoming panels, transformers, and buses of indoor substation were identified as sources of the maximum magnetic flux. Since psychological effects of these
fields on the human body have been reported even in small quantities, therefore, it is recommended to reduce individuals’ exposure through different ways including identification of safe zones at workplaces, reduced shift hours, and training of exposed personnel. Due to the effect of aging on the quality and reliability of electrical equipment in the substations, it is strongly recommended to monitor changes in magnetic fields, after a period of time, within frequent intervals.
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Acknowledgments This study has been done with the financial support of Iranian National Petrochemical Company (NPC). We would like to thank Dr. Nassiri, Director of HSE Department, and Eng. Ahmad Hesami, Occupational health Expert at NPC. We would also like to express our sincere gratitude for the proofreading services rendered by Ravian Danesh Mohit Company.
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