Safety Assessment for Electric Utility Workers Exposed to ELF-EMF: Literature Review Tarek K Abdel-Galil Ibrahim O Habiballah 27 Nov. 2005

Outlines ELF-EMF ELF-EMF Safety Assessment Issues Safety Assessment Issues External/Internal Evaluation External/Internal Evaluation International Standards International Standards Mitigation Measures Mitigation Measures Case Study Case Study Conclusions Conclusions

ELF-EMF There is a growing concern among electric utilities workers regarding possible health hazards due to the exposure to power frequency electromagnetic field (ELF-EMF) There is a growing concern among electric utilities workers regarding possible health hazards due to the exposure to power frequency electromagnetic field (ELF-EMF) Failure to comply with the safety assessment standards may lead to possible health hazard on electric utility workers Failure to comply with the safety assessment standards may lead to possible health hazard on electric utility workers

ELF-EMF Aim of this paper is to assess and evaluate the existing scientific effort which aims to improve safety levels for electric utility workers Aim of this paper is to assess and evaluate the existing scientific effort which aims to improve safety levels for electric utility workers Discuss possible mitigation techniques in order to help electrical utilities complying with the existing international standards and guidelines Discuss possible mitigation techniques in order to help electrical utilities complying with the existing international standards and guidelines

Safety Assessment Issues Collect data regarding transmission lines, substations, loading conditions,...etc Collect data regarding transmission lines, substations, loading conditions,...etc Identify exposure scenarios of electrical line worker Identify exposure scenarios of electrical line worker Calculate the external magnetic and electric field for the different exposure scenarios Calculate the external magnetic and electric field for the different exposure scenarios

Safety Assessment Issues Calculate the internal electric field and average induced current density inside different part of the human body Calculate the internal electric field and average induced current density inside different part of the human body Compare the values of exposure for different scenarios with maximum permissible limits recognized by international standards and guidelines Compare the values of exposure for different scenarios with maximum permissible limits recognized by international standards and guidelines

Safety Assessment Issues Take necessary mitigation measures for the failed scenarios in order to comply with the existing international limits Take necessary mitigation measures for the failed scenarios in order to comply with the existing international limits

Safety Assessment Issues

External/Internal Evaluation At extremely low frequency (50/60 Hz) quasi- static conditions are met At extremely low frequency (50/60 Hz) quasi- static conditions are met This means that the exposure of electric field can be dealt with separately from exposure to magnetic field. This means that the exposure of electric field can be dealt with separately from exposure to magnetic field. Evaluation of external magnetic field and electric field requires the solution of Laplace equation. Evaluation of external magnetic field and electric field requires the solution of Laplace equation.

External/Internal Evaluation There are many numerical methods that can be used to calculate the external electromagnetic field due to transmission lines and substations: There are many numerical methods that can be used to calculate the external electromagnetic field due to transmission lines and substations: –Charge simulation method –Finite element method –Finite difference method –Boundary element method –Nodal method

External/Internal Evaluation Electric fields external to the body induce a surface charge on the body external surface; which produces induced electric field and currents in the body Electric fields external to the body induce a surface charge on the body external surface; which produces induced electric field and currents in the body The distribution of induced current depends on exposure conditions, on the size and shape of the body, and on the body ’ s position in the field. The distribution of induced current depends on exposure conditions, on the size and shape of the body, and on the body ’ s position in the field.

External/Internal Evaluation The interaction of extremely low frequency (ELF) magnetic fields with the human body will also result in induced electric fields and circulating electric currents. The interaction of extremely low frequency (ELF) magnetic fields with the human body will also result in induced electric fields and circulating electric currents. The magnitudes of the induced field and the current density due to magnetic field depends on the electrical conductivity of the body tissue, the rate of change and magnitude of the magnetic flux density, and the radius of the loop. The magnitudes of the induced field and the current density due to magnetic field depends on the electrical conductivity of the body tissue, the rate of change and magnitude of the magnetic flux density, and the radius of the loop.

External/Internal Evaluation There are different numerical techniques to solve the internal induced electric field and average induced current densities inside body organs: There are different numerical techniques to solve the internal induced electric field and average induced current densities inside body organs: –Finite Element Method –Moment Method –Finite Differences Method –Impedance Method –Finite Difference Time Domain Method –Space Potential Finite Difference –Hybrid methods

External/Internal Evaluation Different research groups used different human body models depending on the availability of updated information from Computerized Tomography (CT) and Magnetic Resonance Imaging (MRI) Different research groups used different human body models depending on the availability of updated information from Computerized Tomography (CT) and Magnetic Resonance Imaging (MRI) A summary of basic data of the human body models used in the computation and the conductivity values utilized by each research groups are shown A summary of basic data of the human body models used in the computation and the conductivity values utilized by each research groups are shown

External/Internal Evaluation

International Standards International standards deals with the subject of ELF-EMF identify limits for the Maximum Permissible Exposure (MPE) and the basic restrictions International standards deals with the subject of ELF-EMF identify limits for the Maximum Permissible Exposure (MPE) and the basic restrictions MPE is also named as reference level MPE is also named as reference level

International Standards Maximum Permissible Exposure (reference level) is identified for the external electric field (Eext) and magnetic field (Bext) Maximum Permissible Exposure (reference level) is identified for the external electric field (Eext) and magnetic field (Bext) Basic restrictions are the limitation on the induced electric field (Eind) and average current densities (Javg) over 1 cm2 inside the human body organs Basic restrictions are the limitation on the induced electric field (Eind) and average current densities (Javg) over 1 cm2 inside the human body organs

International Standards Compliance with the MPE will ensure fulfillment with the relevant basic restrictions Compliance with the MPE will ensure fulfillment with the relevant basic restrictions However, if the measured or calculated Eext and Bext exceed the MPE, this will not prove that the basic restrictions will be exceeded However, if the measured or calculated Eext and Bext exceed the MPE, this will not prove that the basic restrictions will be exceeded

International Standards Therefore, whenever a reference level is exceeded it is necessary to test compliance with the relevant basic restriction and to determine whether additional actions are required to fulfill basic restrictions Therefore, whenever a reference level is exceeded it is necessary to test compliance with the relevant basic restriction and to determine whether additional actions are required to fulfill basic restrictions

International Standards

International Commission on Non-Ionizing Radiation Protection (ICNIRP) International Commission on Non-Ionizing Radiation Protection (ICNIRP) American Conference of Governmental Industrial Hygienists (ACGIH) American Conference of Governmental Industrial Hygienists (ACGIH) National Radiological Protection Board National Radiological Protection Board

International Standards It can be observed from the table, that the values reported from different guidelines and standards are having large variability basically because of the variation of the safety factors recommended within each standard It can be observed from the table, that the values reported from different guidelines and standards are having large variability basically because of the variation of the safety factors recommended within each standard

International Standards It is very important to affirm that both the basic restrictions and MPE limits identified by international standards and guidelines are based on short term effects of the interaction of electric field with human It is very important to affirm that both the basic restrictions and MPE limits identified by international standards and guidelines are based on short term effects of the interaction of electric field with human The long term interaction of electric field with human body mechanism is still unclear and research done in this direction leads to conflicting results The long term interaction of electric field with human body mechanism is still unclear and research done in this direction leads to conflicting results

Mitigation Measures In situation where the ELF-EMF exposure fails to satisfy the recommended limits identified by international standards administrative actions followed by engineering actions should be taken to reduce the risk of exposure to ELF-EMF. In situation where the ELF-EMF exposure fails to satisfy the recommended limits identified by international standards administrative actions followed by engineering actions should be taken to reduce the risk of exposure to ELF-EMF.

Mitigation Measures Administrative actions include Administrative actions include –Putting warning signs in locations where ELF- EMF limits are exceeded –Educate the workers regarding health hazard associated with ELF-EMF exposure –Forming committees to study possible engineering actions to alleviate the problem

Mitigation Measures Engineering actions include Engineering actions include –Providing shielding to electric and magnetic field –Changing work practices –Reviewing design of new projects –Shielding from an E-field is simple; buildings, walls, and clothes may provide the necessary protection

Mitigation Measures Options available to utility engineers to reduce ELF magnetic fields from power equipment at design stage Options available to utility engineers to reduce ELF magnetic fields from power equipment at design stage Avoid putting large transformers, substations, or switchgear near areas or workplaces that are occupied continuously Avoid putting large transformers, substations, or switchgear near areas or workplaces that are occupied continuously

Mitigation Measures Arrange the T.L. phasing to cancel a major part of the field Arrange the T.L. phasing to cancel a major part of the field Reduce the separation distances between the conductors. This will increase the magnetic coupling between the conductors and reduce the field strength at a distance Reduce the separation distances between the conductors. This will increase the magnetic coupling between the conductors and reduce the field strength at a distance Use three-phase cable or twist and closely couple single-phase cables Use three-phase cable or twist and closely couple single-phase cables

Mitigation Measures Options available to utility engineers to reduce ELF magnetic fields from power equipment at operation stage Options available to utility engineers to reduce ELF magnetic fields from power equipment at operation stage Balance the currents in the phases Balance the currents in the phases Change maintenance practices to avoid working when the T.L. is fully loaded Change maintenance practices to avoid working when the T.L. is fully loaded

CASE STUDY Maximum flux density is equal to 0.44 milli-Tesla 500 KV, 1500 A transmission line configuration

CASE STUDY NRPB ACGIH-2000ICNIRP-1998IEEE 2002 Occupational Electric field KV/m Magnetic field, milli-Tesla General Public 12NA4.25Electric field KV/m 1.3NA Magnetic field, milli-Tesla This scenario comply with the limits identified by IEEE 2002, ACGIH- 2000, NRPB This scenario does not comply with the limits identified by ICNIRP-1998 since the calculated induced magnetic field is slightly higher the limit based on this standard. This scenario does not comply with the limits identified by ICNIRP-1998 since the calculated induced magnetic field is slightly higher the limit based on this standard.

Conclusions This paper has shed the light on the practices which should be followed by electric utilities to insure the safety of their employers against health risk associated with exposure to Extremely Low Frequency ElectroMagnetic Field (ELF- EMF) This paper has shed the light on the practices which should be followed by electric utilities to insure the safety of their employers against health risk associated with exposure to Extremely Low Frequency ElectroMagnetic Field (ELF- EMF)

Conclusions Different methods which are utilized in literature for calculating and measuring the electric and magnetic field produced by power equipment are surveyed Different methods which are utilized in literature for calculating and measuring the electric and magnetic field produced by power equipment are surveyed The existing international basic restriction levels and maximum permissible exposure of the existing standards are compared The existing international basic restriction levels and maximum permissible exposure of the existing standards are compared

Conclusions Some mitigation measures which can be utilized to minimize the risk of exposure to electromagnetic field are presented Some mitigation measures which can be utilized to minimize the risk of exposure to electromagnetic field are presented