Exposure to Electromagnetic Fields

1
Exposure to Electromagnetic Fields

• London Health Safety Group

Simon Mann 21 January 2008
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Health Protection Agency

• Independent body that protects the health and
  well-being of the population.
• Plays a critical role in
• protecting people from infectious diseases, and
  in
• preventing harm when hazards involving chemicals,
  poisons or radiation occur.
• Prepares for new and emerging threats, such as a
  bio-terrorist attack or virulent new strain of
  disease.

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Simon Mann

• Acting Leader of EMF Dosimetry Group in
• HPAs Radiation Protection Division
• Secretary to Advisory Group on Non-ionising
  Radiation
• UK representative to CENELEC TC106X
• Member of ICNIRPs Dosimetry Standing Committee
• Project Leader for HPAs WiFi Assessment Work
• Telephone [phone]
• E-mail simon.mann_at_hpa.org.uk

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Role of HPA Radiation Protection Division

• Activities
• Research
• Advice
• Services
• Agents
• Ionising rad.
• Optical rad.
• EMF
• UVR
• Ultrasound

www.hpa.org.uk/radiation
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Todays Talk

• Five sections
• 1. International Exposure Guidelines
• 2. Basis of Guidelines
• 3. Implementation of Guidelines
• 4. Electromagnetic Modelling of the Body
• 5. Practical Exposure Assessment

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1) International Exposure Guidelines

• Who publishes the guidelines?
• What is their scope and purpose?
• What quantities do they restrict?

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International Commission on Non-Ionizing
Radiation Protection (ICNIRP)
SC - I Epidemiology
Main Commission
SC - II Biology
SC - IV Optical Radiation
SC - III Physics Eng.

• Independent international scientific organisation
• Officially recognised by WHO as its advisory body
  
• Members are elected - none from industry
• Publishes reviews, guidelines and statements

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International Recognition of the ICNIRP
Guidelines

• World Health Organization -
• International guidelines developed by ICNIRP
  are based on a careful analysis of all
  scientific literature (both thermal and
  non-thermal effects) and offer protection
  against all identified hazards of
  RF radiofrequency energy with large safety
  margins.
• The most recent exposure guidelines from ICNIRP
  on exposure to radiofrequency fields were
  published in 1998
• International EMF Project www.who.int/peh-emf

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NRPB Advice on Exposure Guidelines

• Updated its position in March 2004
• EMF Advice Document Docs NRPB 15(2)
• EMF Science Review Docs NRPB 15(3)
• The review of current scientific knowledge, the
  adoption of a cautious approach to the
  interpretation of these data, and a recognition
  of the benefits of international harmonisation,
  combine in a recommendation to adopt the ICNIRP
  exposure guidelines for occupational and general
  public exposure to electromagnetic fields between
  0 and 300 GHz.
• NRPB became HPAs Radiation Protection
  Division
• on 1 April 2005
• see www.hpa.org/radiation

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Protection Rationales

• Stochastic effects Ionising radiation, but not
  EMFs
• Risk of an effect increases with increasing dose,
  but a risk exists for all dose levels
• Limits are set based on an acceptable level of
  risk
• Deterministic effects EMFs and ionising
  radiation
• Effects occur above a threshold exposure level,
  which may vary to some extent from person to
  person
• Limits are set at the lower end of the expected
  range of thresholds in order to prevent effects

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Scope of Guidelines

• Cover exposure to EMFs from static E H fields
  to lower boundary of infra-red, 300 GHz
• Relate to the exposure of people, not the
  emissions from sources
• Intended to apply to workers and members of the
  public
• Do not apply to patients exposed for medical
  diagnostic and treatment purposes
• Do not cover electrical interference with or
  heating of medical implants
• Set out a framework for protection based on basic
  restrictions and reference levels

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2) Basis of Exposure Guidelines

• What are the effects of exposure?
• How can the effects be controlled?
• How do the effects depend on frequency?

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Static Magnetic Fields

• Adverse health effects
• Nausea
• Vertigo
• Cardiac arrhythmia
• Impaired mental function
• Other sensory effects when head moved in a field
  gradient
• Set basic restrictions on magnetic flux density
• Also, when B gt 3 mT
• Precautions should be taken to prevent hazards
  from the movement of ferromagnetic objects an
  indirect effect

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Basic Restrictions on StaticMagnetic Flux Density

• Whole-body exposure averaged over the working
  day
• Can be relaxed under certain conditions (see
  guidelines)

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Time-varying Fields (f lt 10 MHz)

• Adverse effects on functions of the central
  nervous system (CNS)
• Control of movement
• Control of posture
• Memory
• Reasoning
• Visual processes
• Magnetophosphenes
• Direct stimulation of nerves and muscles
  (requires higher exposures)
• Set basic restrictions on root mean square
  induced current density in CNS tissues

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Basic Restrictions on Induced Current Density

• Basic restrictions follow frequency dependence of
  biological responses
• Effects are instantaneous therefore time
  averaging is not permitted

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Time-varying Fields (f gt 100 kHz)

• Adverse effects of energy absorption
• Heat stress (38ºC)
• Headaches, dizziness, thirst
• Decreased sperm count (temporary)
• Developmental defects
• Reduced cognitive performance
• Heat stroke (41ºC)
• Convulsions, unconsciousness, organ damage, death
• Set basic restrictions on
• SAR (frequencies below 10 GHz)
• Power density (frequencies above 10 GHz)

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Rationale for Basic Restrictions on SAR

• Restrict whole-body SAR to avoid heat stress and
  heat stroke due to generalised heating
• 1C rise in core temperature results from a
  whole-body averaged SAR of 4 W kg1
• Restrict localised SAR to avoid tissue damage
• Eye damage, fetal abnormalities, etc
• Restrict power density rather than SAR at
  frequencies above 10 GHz
• Heating confined to skin and other surface
  tissues
• Average exposures over a period of time
• Increase in temperature due to energy absorption
  is not instantaneous

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Basic Restrictions on Whole-body SAR

• ICNIRP occupational
• 0.4 W kg1 Reduction factor of 10
• ICNIRP general public
• 0.08 W kg1 Reduction factor of 50
• The distribution of SAR in the body is to be
  averaged,
• 1) over the entire mass of the body, and
• 2) as the maximum occurring over any 6-minute
  period
• before comparison with these values

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Basic Restrictions on Localised SAR

• Averaging masses in grams given in brackets
• These apply to contiguous tissue
• All SARs to be averaged over any 6-minute period
• Note a basic restriction of 10 W kg1 averaged
  over any 10 g mass of tissue is equivalent to
  restricting the total power absorbed in any 10 g
  mass to 0.1 W

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Basic Restriction Quantities (Internal Below 10
GHz)
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3) Implementation of Guidelines

• UK Safety Legislation
• European Directives
• Voluntary Measures

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Status of Guidelines

• There is presently no specific UK legislation
  setting exposure limits on EMFs
• General UK safety legislation provides an
  enabling route for the guidelines
• Section 3 of the Health and Safety at Work etc
  Act (risk assessment)
• Management of Health and Safety at Work
  Regulations 1999
• HSE refers to HPA (NRPB) advice on EMF exposure
• ICNIRP guidelines have been widely adopted on a
  voluntary basis to aid risk assessments
• http//www.hse.gov.uk/radiation/nonionising/hse.ht
  m

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EU Council Recommendation (1999/519/EEC)

• Published on 12 June 1999 and supported by the UK
  government
• Bears on governments in EU Member States
• Framework for restricting EMF Exposure of the
  general public within Europe
• Incorporates the ICNIRP numbers, but with
  provisos,e.g. aim to achieve respect for
• Applies, in particular, to relevant areas where
  members of the public spend significant time
• http//europa.eu.int/comm/health/ph_determinants/e
  nvironment/EMF/emf_en.htm

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EU Mandate M305 Product Standards

• Directives with radiation (taken to include EMF)
  safety clauses
• Radio and Telecommunications Terminal Equipment
  Directive
• Low Voltage Directive
• Machinery Directive
• EU Mandate M305 - 12 October 2000
• Standards bodies to develop harmonised standards
  to allow a presumption of conformity
• The basic restrictions and reference levels in
  the Council Recommendation are to be taken into
  account
• The standards are product emission standards
• http//europa.eu.int/comm/enterprise/standards_pol
  icy/mandates/database/index.cfm?fuseactionsearch
  .detailid89

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Product (Emission) Standards
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Physical Agents Directive(2004/40/EC)

• Was agreed and published in 2004 now postponed
• Would have applied to all workers within the EU
• Exposure limits are similar to ICNIRP
  occupational values
• The EU mandated CENELEC, CEN and ETSI to develop
  exposure assessment standards (M351)
• HSE is the lead Department in the UK
• http//europa.eu/scadplus/leg/en/cha/c11150.htm
• http//www.europa.eu/rapid/pressReleasesAction.do?
  referenceIP/07/1610formatHTMLaged0language
  ENguiLanguageen

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EU Mandate M351 Exposure of Workers

• Standards are required to
• Take into account the limit values and action
  values in Directive 2004/40/EC
• Assess all relevant sources of exposure
• Cover all exposure situations that can
  realistically be expected
• Be proportionate in their practical application
• Take full account of standardisation work under
  M305 and mandates under the medical devices
  Directive
• Avoid introducing measurement where exposure can
  be calculated on the basis of compliance with
  product directives
• Be developed in co-operation with other bodies
  (International standards bodies, WHO, ICNIRP, EU
  Commission)

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Government Response to 2004 Advice from NRPB

• Welcomed the advice and commented
• The NRPB guidelines incorporate a significant
  cautionary element but specifically do not take
  into account social or economic factors or the
  risks or disbenefits that may occur from action
  to limit exposure.
• In 1999, Government agreed an EU Recommendation
  on public exposure (EC/519/1999) which advocated
  the use of ICNIRP levels but accepts the need for
  consideration of risks and benefits when
  implementing the guidelines.
• Following publication of the Stewart Report on
  Mobile Phones and Health (2000), the mobile phone
  industry voluntarily adopted ICNIRP guidelines
  for public exposure to radio frequency fields.
  All cellular radio base stations comply with
  ICNIRP public exposure guidelines.
• For all other sources, the Government expects the
  NRPB guidelines to be implemented in line with
  the terms of the EU Recommendation, that is,
  taking account of the risks and benefits of
  action. Preliminary discussions have already
  taken place to identify what reasonable actions
  might be taken.
• http//www.dh.gov.uk/PolicyAndGuidance/HealthAndS
  ocialCareTopics/HealthAndSocialCareArticle/fs/en?
  CONTENT_ID4089500chknMzeXW

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4) Electromagnetic Modelling of the Human Body

• Calculating SAR and Induced Current Density
• Developing Reference Levels for Guidelines
• Permits Compliance Testing Through Measurements

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Phantom Development NORMAN

• NORmalised MAN
• Height 1.76 m
• Weight 73 kg
• Developed from MRI scans
• 8.3 million voxels (2 mm)3
• 37 different tissue types
• Frequency dependent conductivity and permittivity
• Also scaled to represent children at ages 1, 5
  and 10 years

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RF Exposure at 120 MHz
Anatomy
SAR
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Power Absorption from Radiofrequency Fields

• Relative contributions of the body parts to
  whole-body SAR
• Individual SAR values expressed as a rainbow
  spectrum violet lowest, red highest
• As frequency increases absorption gradually
  moves away from knees and ankles to the upper
  torso

200 MHz
30 MHz
100 MHz
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Power Absorption from RF with Arms Up

• Variation of absorption with frequency
• Field absorbed below chest in a familiar way,
  i.e. in knees and ankles
• Increase in whole-body SAR as a result of
  absorption in arms when held above the head

200 MHz
100 MHz
30 MHz
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Power Absorption from RFwith Arms Out

• Variation of absorption with frequency
• Field horizontally polarised and so absorption
  almost entirely in aligned limbs, i.e. arms
• Remainder of body absorbs very little of
  horizontally polarised field

30 MHz
100 MHz
200 MHz
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Power Absorption from RFwhile Sitting

• Variation of absorption with frequency
• Similar to standing, lower frequencies absorbed
  in knees and ankles
• At higher frequencies absorption occurs on the
  surface of the body

R P Findlay and P J Dimbylow Phys. Med. Biol.
51(2006) 1-14
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Effect of Grounding
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Effect of Body Size
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5) Practical Exposure Assessment

• UK Safety Legislation
• European Directives
• Voluntary Measures

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Basic Restriction Quantities (Internal Below 10
GHz)

• First three quantities are included as Exposure
  Limit Values
• Static B-field is omitted from Directive

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Reference Level Quantities (Measurable)

• Directive uses same quantities and values as
  ICNIRP
• Electric field strength (1 Hz 300 GHz)
• Magnetic field strength (0 Hz 300 GHz)
• Power density (10 MHz 300 GHz)
• Limb current (10 MHz 110 MHz)
• Contact current (0 Hz 110 MHz)
• Termed Action Values in the Directive
• Static magnetic field strength included
• No underpinning Exposure Limit Value

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Electric Field Reference Levelin Relation to
Dosimetry
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Magnetic Field Reference Levelin Relation to
Dosimetry
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Power Density Reference Level in Relation to
Dosimetry
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Limb Current Reference Level in Relation to
Dosimetry
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Compliance Rationale

• HPA-RPD envisages a three stage compliance test
• Consistent with approach in Directive
• See
• http//www.hpa.org.uk/radiation/understand/inform
  ation_sheets/icnirp_exp_guidelines.htm

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Draft CENELEC Umbrella Standard (prEN50499)

• Umbrella standard provides tool for initial
  assessment
• Table 1 Sources/situations that can be assumed
  to comply with no further assessments
• Table 2 Sources/situations that may need
  measurement or calculations to be performed
• Source or workplace specific standards will be
  called up, where necessary, from the umbrella
  standard
• CE marked products where compliance with public
  exposure limits has been shown do not need
  assessment

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Assessment Process(prEN50499 Oct 2006)
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Voluntary Zoning Procedure(prEN50499 Oct 2006)
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Conclusions

• Exposure to electromagnetic fields can give rise
  to health effects of a deterministic (threshold)
  nature
• There are few situations where exposures can
  reach the levels where effects can occur
• International exposure guidelines provide a
  framework for restricting exposures
• Technical standards contain practical exposure
  assessment procedures
• Feel free to contact HPA for advice
• www.hpa.org.uk/radiation