Safety Assessment for Electric Utility Workers Exposed to ELFEMF: Literature Review

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Safety Assessment for Electric Utility Workers
Exposed to ELF-EMF Literature Review

• Tarek K Abdel-Galil
• Ibrahim O Habiballah
• 27 Nov. 2005

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Outlines

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

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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

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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
• Discuss possible mitigation techniques in order
  to help electrical utilities complying with the
  existing international standards and guidelines

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Safety Assessment Issues

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

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Safety Assessment Issues

• 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

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Safety Assessment Issues

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

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Safety Assessment Issues
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External/Internal Evaluation

• 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.
• Evaluation of external magnetic field and
  electric field requires the solution of Laplace
  equation.

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External/Internal Evaluation

• 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

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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
• The distribution of induced current depends on
  exposure conditions, on the size and shape of the
  body, and on the bodys position in the field.

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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 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.

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External/Internal Evaluation

• 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

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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)
• 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

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External/Internal Evaluation
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External/Internal Evaluation
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International Standards

• 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

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International Standards

• 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

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International Standards

• 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

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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

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International Standards
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International Standards

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

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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

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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
• The long term interaction of electric field with
  human body mechanism is still unclear and
  research done in this direction leads to
  conflicting results

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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.

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Mitigation Measures

• 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

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Mitigation Measures

• 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

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Mitigation Measures

• 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

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Mitigation Measures

• 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
• Use three-phase cable or twist and closely couple
  single-phase cables

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Mitigation Measures

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

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CASE STUDY
500 KV, 1500 A transmission line configuration
Maximum flux density is equal to 0.44 milli-Tesla
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CASE STUDY
This scenario comply with the limits identified
by IEEE 2002, ACGIH-2000, NRPB-1993. 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.
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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)

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Conclusions

• 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

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Conclusions

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