Presented by N.W. PieterseGAUTENG BRANCH WORKSHOP24 NOVEMBER 2015

ELECTROMAGNETIC FIELD RADIATION IN THE WORKPLACE

SCOPE OF PRESENTATION• Introduction to EMF and UV Radiation.• Definition of EMF Radiation.• Key concepts related to EMF Radiation.• Sources of EMF Radiation.• Health effects related to EMF Radiation.• Measurement methodology, Instrumentation and

Special Considerations.• Standards and OEL’s related to EMF Radiation.• Case Sudy.

INTRODUCTION

DEFINITION EMF RADIATION• An electromagnetic field (also EMF or EM field) is a

physical field produced by moving electrically charged objects. It affects the behavior of charged objects in the vicinity of the field.

• The electromagnetic field extends indefinitely throughout space and describes the electromagnetic interaction.

• EMF has both electric and magnetic field components, which stand in a fixed ratio of intensity to each other, and which oscillate in phase perpendicular to each other and perpendicular to the direction of energy and wave propagation.

• In a vacuum, electromagnetic radiation propagates at a characteristic speed, the speed of light.

ELECTRIC AND MAGNETIC FIELDS

OHM’S LAW• Ohm's law states that the current through a conductor (Atmosphere)

between two points is directly proportional to the potential difference across the two points. Introducing the constant of proportionality, the resistance, one arrives at the usual mathematical equation that describes this relationship:

• where I is the current through the conductor in units of amperes, V is the potential difference measured across the conductor in units of volts, and R is the resistance of the conductor in units of ohms. More specifically, Ohm's law states that the R in this relation is constant, independent of the current.

• Atmospheric Resistance = 377 ohm

EMF CONCEPTS

• ELECTRIC FIELD STRENGTH (E): The magnitude of the electric field vector expressed in V/m.

• MAGNETIC FIELD STRENGTH (H): The magnitude of the magnetic field vector expressed in A/m.

• POWER DENSITY (S): Power per unit area normal to the direction of propagation, expressed in mW/cm2.

EMF CONCEPTS (CONT)• EMISSION: Radiation produced by a single radiofrequency

source.

• INMISION: Radiation resulting from the contribution of all radiofrequency sources whose fields are present in the place.

• OCCUPATIONAL EXPOSURE: A situation in which people are subjected to electrical, magnetic or electromagnetic fields, or to contact or induced currents associated with electromagnetic fields of radiofrequencies.

• POPULATION OR NON-CONTROLLED EXPOSURE: Situations in which the general public may be exposed or in which people exposed in the course of their work may not have been warned of the potential exposure and may not be able to control it.

OMNIDIRECTIONAL SOURCES OF EMF RADIATION EXPOSURE

Cell Phone Towers Radio Towers High Voltage Power Lines

Transformer Station Mobile Military Radio Mast

DIRECTIONAL SOURCES OF EMF RADIATION

Microwave AntennaFixed Radar Antenna Mobile Radar Antenna

HEALTH EFFECTS - EMF• Coupling to low-frequency electric fields. The interaction of

time-varying electric fields with the human body results in the flow of electric charges (electric current), the polarization of bound charge (formation of electric dipoles), and the reorientation of electric dipoles already present in tissue.

• Coupling to low-frequency magnetic fields. The physical interaction of time-varying magnetic fields with the human body results in induced electric fields and circulating electric currents.

• Biological effects and epidemiological studies (100 kHz–300 GHz). Available experimental evidence indicates that the exposure of resting humans for approximately 30 min to EMF producing a whole-body SAR of between 1 and 4 W kg21 results in a body temperature increase of less than 1 °C. Animal data indicate a threshold for behavioural responses in the same SAR range.

• Exposure to more intense fields, producing SAR values in excess of 4 W kg21, can overwhelm the thermoregulatory capacity of the body and produce harmful levels of tissue heating.

HEALTH EFFECTS• Electric Dipoles: In physics, the electric dipole moment is

a measure/moment of the separation of positive and negative electrical charges in a system of electric charges, that is, a measure of the charge system's overall polarity. An atom in which the centre of the negative cloud of electrons has been shifted slightly away from the nucleus by an external electric field constitutes an induced electric dipole.

HEALTH EFFECTS – EMF (CONT)• Data on human responses to high-frequency EMF that

produce detectable heating have been obtained from controlled exposure of volunteers and from epidemiological studies on workers exposed to sources such as radar, medical diathermy equipment, and heat sealers. They are fully supportive of the conclusions drawn from laboratory work, that adverse biological effects can be caused by temperature rises in tissue that exceed 1°C.

• Indirect effects of electromagnetic fields. In the frequency range of about 100 kHz–110 MHz, shocks and burns can result either from an individual touching an ungrounded metal object that has acquired a charge in a field or from contact between a charged individual and a grounded metal object.

HEALTH EFFECTS – EMF (CONT)• Health effects closely related to the frequency and

type of EMF radiation.• Recent studies indicated that exposure to EMF might

be related to leukaemia and other types of cancer.• EMF radiation might interfere with pacemakers and

medical implants.• Exposure to EMF radiation in the microwave range

might cause damage to the retina.• Induced current may cause tissue damage in areas

surrounding metal implants (Case in the DoD).• Research on-going regarding Electromagnetic field

Radiation’s Health Effects.

SPECIAL CONSIDERATIONS -THE MEASUREMENT OF EMF• Identify the Frequency (Hz) and Wavelength (λ)of

the EMF source or sources that will be assed.• Calculate the near and far fields (3 λ).

• Determine whether measurements will be done within the near of far field (few cm’s to km’s depending on frequency and wavelength).

SPECIAL CONSIDERATIONS FOR MEASUREMENT - EMF RADIATON• Consider interference from other sources (Same

Frequency):

Equipment Considerations – EMF RADITION• Commercial instruments and probes for

measuring radiofrequencyNon-tuneable

TuneableInterchangeable

antennae for measuring E or H field (Isotropic)

EMF MEASUREMENT PROTOCOL Near Field measure E, H or both (must comply with MPE limits imposed). Far Field measure E or H and obtain S [S = E2/Z0 = H2*Z0] (must comply with

MPE limits imposed).

If uncertain measure both. Imission: use of broadband instruments (non-tunable electromagnetic radiation

detectors), with isotropic E and H measurement probes Emission: use of narrowband instruments (field intensity meters, tunable

spectrum analyzers, etc.), with antennae suitable for measurement frequency ranges

All instruments, antennae and probes must have a calibration certificate (manufacturer or laboratory accredited in country of origin).

Record the value of the measurement, plus the uncertainties specified (manufacturer), plus the error of the method used.

NIOSH: Manual for Measuring Occupational Electric and Magnetic Field Exposures

6 min Moving Average.

377 ohm

E=V/mH=A/

m

EMF Measurement PROTOCOL (CONT)

• Points of measurement:

• General in house areas with only a single source - Take measurement at workstation if EMF Exposure at a workstation need to be measured.

• General in house areas with multiple sources - Divide area into square meter squares. Take measurements in the middle of each square to determine areas of high radiation (Map).

• Omni-directional systems (Antennas – Environmental/Community):

a minimum of 16 points

• Directional systems (Antennas – Environment/Community): a minimum of 4 points in direction of max. propagation12 remaining points according to character of radiation

lobe.

OCCUPATIONAL EXPOSURE LIMITS FOR EMF

PUBLIC EXPOSURE LIMITS

OCCUPATIONAL EXPOSURE LIMIT - BRV

CONTROL MEASURES FOR EMF RADIATION• Inverse square law also applies to EM Fields. By

increasing the distance from the source will decrease exposure proportionally.

CONTROL MEASURES FOR EMF RADIATION (CONT)• Metal enclosures or EMF shielding can be used to shield

workers from EMF Radiation (depending on type of EM Fields).

• Ensure that all metal objects and structures in the vicinity of an EMF source are properly earthed (Electrical Charge).

• Prevent workers with implanted medical devices or metal implants to perform work near any EMF sources.

• Reduce exposure time exposed to EMF radiation.• Conduct regular assessments in all high risk areas to

determine the efficacy of control measures.• Conduct regular medical surveillance.•

Personal Alarm

Fence to Limit Access

RF Protective Suits

CASE STUDYMEASUREME

NT REFERENCE No.

WORK AREA/PERSON FREQUENCY RANGE FIELD VECTOR

EMF (ELF) X VECTOR - MAX RMS

VALUE

EMF (ELF) Y VECTOR - MAX RMS

VALUE

EMF (ELF) Z VECTOR - MAX RMS

VALUE

EMF (ELF) MEAN

ISOTROPIC.RMS VALUE

REFERENCE VALUE

(UNPERTURBED RMS

VALUESMeasurement Position - 3 

 

Welgedag Substation (6.6 kV Substation Yard area). Measurements  were  conducted  in central part of the yard at about 7m underneath  the  11  kV  overhead feed power line.  

50 Hz E-Field Strength (V m-

1)

310.7 777.5 789.3 1150 10,000 V m-1

50 Hz B-Field (Magnetic fluxDensity) (µT)

0.5867 0.3048 0.3246 0.74 500 µT

TASKS AND COMMENTS

The calculated mean isotropic RMS value (derived from the max field strengths on the X, Y and Z vectors) for the E-Field at 11.50% of the Reference Value did not exceed the Reference Value of 10,000

V m-1 (@50 Hz) as prescribed by the ICNIRP Guidelines. It is unlikely that health effects related to E-Fields at the current frequency (50 Hz). The calculated E-Field Isotropic RMS value exceeds the 1 kV

m-1 action level for cardiac pacemakers, suggested by the ACGIH.

The calculated mean isotropic RMS value (derived from the max field strengths on the X, Y and Z vectors) of the B-Field at 0.148 % of the Reference Value did not exceed the Reference Value of 500 µT 

(@ 50 Hz) as prescribed by  the  ICNIRP Guidelines  for  the  frequency established.  It  is unlikely  that health effects  related  to B-Fields  for  the 50 Hz  frequency might develop. The calculated B-Field 

Isotropic RMS value did not exceed the 100 µT action level for cardiac pacemakers, suggested by the ACGIH.

Employees perform general maintenance, instrument checking and inspections near the 6.6 kV transformers.

The employees work a 9.5-hour shift in the area performing such activities.

No PPE was provided or worn by the employees while conducting the surveys in the mentioned area.

The source of exposure is the 11,000 V AC (50 Hz) feed cables/conductors and the transformer, situated in the close vicinity where maintenance is conducted.

No effective EMF shielding is provided for, serving as a barrier between the workers and the source in reducing exposure to EMF (ELF) Radiation.

No persons with cardiac pacemakers or any other implanted electronic medical devices are employed in the area.

QUESTIONS

•?