Final Technical Report D49 FactSheet

8/14/2019 Final Technical Report D49 FactSheet

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______________________________________________________________________

Project no.

SSPE-CT-2004-502173Project title

EMF-NET: EFFECTS OF THE EXPOSURE TO ELECTROMAGNETICFIELDS: FROM SCIENCE TO PUBLIC HEALTH AND SAFER WORKPLACE

Instrument:

Co-ordination actionThematic Priority:

Priori ty 8, POLICY ORIENTED RESEARCH AREA 2.3, Call Identi fier FP6-2002-SSP-1

Deliverable D49 - Fact SheetEMF-NET Main Task MT2 WORKEN

Due date of deliverable: March 2008, Actual submission date:April 2008

Start date of project: March 2004 Duration: 54 months

Organisation name of lead contractors for these deliverables:

CIOP-PIB (MT2 coordinator), FIOH, ISPESL, NIWL, VITO


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CONTENT

Practical guidance on occupational EMF exposure assessment

Occupational exposure fact sheet: Microwave dryers

Occupational exposure fact sheet: Mobile phone base station

Occupational exposure fact sheet: RF wood glue drying

Occupational exposure fact sheet: RF plastic welding machines

Occupational exposure fact sheet: Assessment of occupational exposure tointermediate frequency electromagnetic fields in practice

Occupational exposure fact sheet: ELECTROSURGERY. Occupational exposure toelectromagnetic fields - assessment in practice

Occupational exposure fact sheet: Hand held Magnetic Reactivator

Occupational EMF Exposure Database

Practical Guidance for Occupational Low Frequency Exposure Assessment

Occupational exposure fact sheet Hand held Magnetic Reactivator

Practical guidance for occupational EMF exposure assessment Numericaldosimetry


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Practical guidance on occupational

EMF exposure assessmentradiofrequency range (100 kHz300 GHz)

What are Electromagnetic fields, EMFs?Electromagnetic fields (EMF) are present everywherein our environment but are invisible to the human eye.EMF is described in terms of electric and magneticfields. Electric fields are created by differences in

voltage: the higher the voltage, the stronger will be theresultant f ield. Magnetic fields are created when electriccurrent flows: the greater the current, the stronger themagnetic field. An electric field will exist even whenthere is no current flowing. If current does flow, thestrength of the magnetic field will vary with powerconsumption but the electric field strength will beconstant. The strength of the electric field is measuredin volts per meter (V/m). The strength of the magneticfield is measured in amperes per meter (A/m); morecommonly in EMF research, scientists specify a relatedquantity, the flux density (in microtesla, T) instead.

Electric fields are produced by the local build-upof electric charges in the atmosphere associated withthunderstorms. The earths magnetic field causes acompass needle to orient in a North-South direction

and is used by birds and fish for navigation. Besidesnatural sources the electromagnetic spectrum alsoincludes fields generated by human-made sources:

The electricit y that comes out of every power sockethas associated low frequency electromagnetic fields.

And various kinds of higher frequency waves are usedto transmit information whether via TV antennas,radio stations or mobile phone base stations. Mobiletelephones, television and radio transmitters and radarproduce radio frequency (RF) fields. Microwaves areRF fields at high frequencies in the GHz range.

At radio f requencies, the elect ric and magnetic fieldsare closely interrelated and we typically measure their

levels as power densities in watts per square meter(W/m2).

What makes the various forms ofelectromagnetic fields so different?One of the main characteristics which definean electromagnetic field is its frequency or itscorresponding wavelength. Fields of differentfrequencies interact with the body in different

ways. One can imagine electromagnetic wavesas series of very regular waves that travel at anenormous speed, the speed of l ight. The frequencysimply describes the number of oscillations orcycles per second, while the term wavelengthdescribes the distance between one wave andthe next. Hence wavelength and frequency are

inseparably intertwined: the higher the frequencythe shorter the wavelength.


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Practical guidance

The electromagnetic spectrum. This broschure deals with the radiofrequency range, 100 kHz to 300 GHz.

Frequency in Hertz (Hz) kHz MHz GHz THz PHz0 102 104 106 108 1010 1012 1014 1016 1018 1020 1022

Radiofrequency waves (Hz)

MHz GHz105 106 107 108 109 1010 1011

Visible

light

Visiblelight

Non-ionization radiation Ionizing radiation

UV

X-rayInfrared

radiationStatic fields 01 Hz

Low frequency waves Gamma-ray

optical radiationRadiofrequency waves

Microwaves

What is the difference betweennon-ionising electromagnetic fieldsand ionising radiation?

Wavelength and frequency determine anotherimportant characteristic of electromagnetic fields:

Electromagnetic waves are carried by particlescalled quanta. Quanta of higher frequency(shorter wavelength) waves carry more energythan lower frequency (longer wavelength) fields.Some electromagnetic carry so much energyper quantum that they have the ability to breakbonds between molecules. In the electromagneticspectrum, gamma rays given off by radioactivematerials, cosmic rays and X-rays carry thisproperty and are called ionising radiation. Fields

whose quanta are insuf ficient to break molecularbonds are called non-ionising radiation.

What are the effects of RF fields?

Radiofrequency waves are used either for energyabsorption depending on electrical propertiesof the material or are used for different kinds of

wireless communication or signal transfer.Occupational exposure to RF fields has

increased during the last decades due to moretechnical application of new techniques andmainly the use of RF for communication.

Within the RF frequency range differentestablished adverse effect can be expected ifthe RF field intensity is high enough. Inducedcurrent in head and trunk have effects on the

central nervous system in the range up to 10 MHz.Furthermore from 100 kHz and up to 10 GHzenergy absorption and thereby tissue heating canoccur. From 10 GHz and up to 300 GHz there is arisk for tissue heating at or near the body surface.

Regulations (ICNIRP, EU-directive)In 2004 the European Parliament agreed ona directive concerning minimum health andsafety requirements regarding workers risksarising from exposure to electromagnetic fields(Directive 2004/40/EC). This directive, which isthe 18th individual directive within the meaningof Article 16(1) of directive 89/391/EEC, laysdown minimum requirements for the protectionof workers from risks to their health and safetyarising or likely to arise from exposure toelectromagnetic fields during their work.

The directive includes fields with frequenciesfrom 0 Hz to 300 GHz and is based on thedocument on risk evaluation produced by theInternational Commission on Non-IonizingRadiation Protection, ICNIRP (ICNIRP, 1998).

The EU directive should be implemented in allcountries in EU latest April 2012.

The occupational exposure limit values in theEU directive, are based on established biologicaleffects and biological considerations. In the RFrange the direct ive is set to protect workers againstacute established effects as harmful tissue heatingand induced current. Specific energy Absorption


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Contact current (IC) between a person and an

object is expressed in amperes (A). A conductive

object in an electric f ield can be charged by the

field.

Electric field strengthis a vector quantity (E) that

corresponds to the force exerted on a charged

particle regardless of i ts motion in space. It is

expressed in vol ts per metre (V/m).

Magnetic field strengthis a vector quantity (H),

which, together with the magnetic flux density,

specifies a magnetic field at any point in space. It

is expressed in amperes per metre (A/m).

Magnetic flux densityis a vector quantity (B),

resulting in a force that acts on moving charges,

expressed in teslas (T). In free space and in

biological materials, magnetic flux density and

magnetic field strength can be interchanged using

the equi valence 1 A/m = 4107T.

Power density (S)is the appropriate quantity

used for very high frequencies, where the depth

of penetration in the body is low. It is the radiant

power incident perpendicular to a surface, divided

by the area of the surface and is expressed in

watts per square metre (W/m2).

Rate (SAR) in the whole body or part of thebody is a widely accepted measure for thermaleffects in the RF range. It is expressed in theunit watts per kilogram (W/kg). Another

measure in the RF range is the current density(j) defined as the current flowing through thebody or part of it and expressed in amperesper square meter (A/ m2). In the frequencyrange above 10 GHz where the depth of thepenetration of the field into the body is verylow, power density is the appropriate quantityand expressed in watts per square meter(W/ m2).

In most situations it is not possible tomeasure the limit values but the directivealso contains action values which give themagnitude of direct physical measurable

parameters.Depending in what part of the RF frequency

range the exposure occurs, from three to sixdifferent parameters need to be measured toensure compliance with the directive.

If the limits given by the values for allparameters in the actual frequency rangeare below the stated action value, the basicrestrictions are fulfilled. If any of the action

values are exceeded, the basic restrictions canstill be accomplished. In this case numericalcalculations are needed to show compliance

with the exposure l imits of the directive.

Frequencyrange

Electric Fieldstrength, E

(V/m)

Magnetic Fieldstrength, H

(A/m)

Magneticflux density,

B (T)

Equivalentplane wave powerdensity, S

eq(W/m2)

Contactcurrent,Ic(mA)

Limb inducedcurrent, I

L

(mA)

0.11 MHz 610 1.6/f 2/f 40

110 MHz 610/f 1.6/f 2/f 40

10110 MHz 61 0.16 0.2 10 40 100

110400 MHz 61 0.16 0.2 10

4002000 MHz 3f1/2 0.008f1/2 0.01f1/2 f/40

2300 GHz 137 0.36 0.45 50

Frequency range Current density forhead and trunk j(mA/m2) (rms)

Whole bodyaverage SAR

(W/kg)

Localised SAR(head and trunk)

(W/kg)

Localised SAR(limbs)(W/kg)

Powerdensity S(W/m2)

100 kHz10 MHz f/100 0.4 10 20

10 MHz10 GHz 0.4 10 20

10300 GHz 50

Table 1. The exposure limit values in the RF range (100 kHz 300 GHz).

Table 2. Actions values (unperturbed rms values)

The following physical quantities can be

measured directly and are used to describe the

exposure to electromagnetic fields in the RF

range (Directive 2004/40/EC):


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Practical guidance

Occupations exposed to RFThe use of RF fields in our workplaces hasincreased rapidly during the last decade, mainlydue to the increased use of wireless communicat ion

technique, security devices and in medicalapplications. However, workers exposure in thesecases is in general low and not in conflict with theEU directive, but there are exceptions.

In office as well as in industry and transportationenvironment wireless communications arefrequently used. The indoor base stations as wellas different blue tooth equipment and WLANused for man to machine or machine to machinecommunication have a low output power andtherefore the possible exposure of workers is notin conflict w ith the regulations.

Low exposure can also be expected when the

sources are enclosed. Examples in the industryare plasma metallization and polymerization,plasma deposition and etching and microwaveheating, for instance vulcanization of rubber.

These processes are normally performed in closedchambers, but there might be leakages especiallyafter reconstructions or changes in process andtherefore a simple recurrent check might be a partof the assessment.

The number of devices used for securitypurpose, as anti-theft and personal access controlhave increased rapidly in shops, libraries, airportsand restricted areas. These devises works at

different frequencies depending on what techniqueis used. Several works below 100 kHz, but theRFID equipment (Radiofrequency IdentificationDevice) works at 120-154 kHz and there are also

devices working at 4.9 GHz. Electronic ArticleSurveillance (EAS) systems works usually in the

MHz range both in continuous swept frequencyand at fixed pulsed frequency at the detector.Normally, the staff is only passing trough andtherefore are only exposed during a short periodand not in conflict with the regulations. However,there might be devises situated near a permanent

working place, for instance a cashier and in thatcase actions must be taken to insure that theregulations are fulfilled.

RF exposure that need special attention

In some workplaces it will be necessary to takemeasurement for showing compliance with theEU directive. Examples of such workplaces aregiven below:

Dielectric heatersRF sealers and glue dryers are two examples ofdielectric heaters frequently used in the industryto seal plastic objects and to glue wood details.

In workplaces where these devices are used itis necessary to perform detailed measurements ofboth electric and magnetic fields as well as contactand induced currents. These measurements often

need to be done on a regular basis, perhaps yearly,since the radiation pattern from the machinery ischanging with use. See further the separate factsheets on dielectric heating.

Induction heatingInduction heaters are usually operating atfrequency ranges from a few Hz up to 10 MHz. Insome processes the operator get near the devisefor visual control of the object and might thereforebe highly exposed. See separate fact sheet.

Industrial microwave ovens andmicrowave dryingOften these ovens are closed and no access is givento areas where high intensity microwave can beencountered. However, there may be leakage insome cabinets and connections, and a regularmaintenance program is recommended.

Microwaves are also used for drying of waterdamage in buildings. These applications areusually high powered devices and with anapplicator that has some potential leakage. Dueto the high intensity microwave energy used it isalso possible to get exposure on the other side ofthe wall or floor where the applicator is located.

Operating a machine like this the exposure to the headand hands are strong due to the closeness to unshieldedelectrode.


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Great care in use of these devices is needed, andin some countries there is a demand for licensingfor the use of these machines.

RadarIn general it would be exceptionally to find casesof staff being exposed to direct emissions of radarsignals from the antennas. Often measurement isnot needed and the exposure assessment can bedone by numerical calculations. However, duringmanufacturing, service and repair it may happenthat staff accidentally can be exposed.

Medical applicationsMainly there are three applications in medicineof interest in this context: Physiotherapeutic useof diathermy, Surgical diathermy and Magnetic

resonance imaging (MRI).In medical clinics RF are used in physiotherapy

in shortwave or microwave diathermy treatment.In these cases the applicators are open, andpossible overexposure of the staff can occur.Strict adherence to safety instructions isneeded, but seldom is there a need to take newmeasurements.

In the operation theatre surgical diathermyis used. RF energy is used to cut and coagulate,and since unshielded electrodes are used thefields are rather intense and special attention isneeded to ensure compliance with the directive

on occupational exposure.In the MRI, RF is one the electromagnetic

components that are used. With normal MRIapplications only inside the magnet bore isthe RF field of intensity high enough to causeconcern. This exposure is easily avoided be safety

instructions to the staff. See separate fact sheeton MRI. However, with use of interventional

MRI the RF exposure might be of concern, andan exposure assessment is needed.

Broadcasting and other communicationsRadio and TV broadcasting installations areusually safe work places. However, there is apotential for involuntary, accidental intenseexposure of staff. In most the cases, technical staff

working at radio/TV broadcasting equipments,are technically well informed and trained.However, when working near antennas with repairor adjustment during broadcasting occupationalexposure is likely to be in conflict with the EUdirect ive. These situations should be avoided.

Rooftop workers near base stations antennas

might be exposed to RF fields about 9002000 MHz. Examples of such workers are sheet-metal workers, chimney-sweeper and painter.In these cases the emission properties are welldefined and simple instructions are more relevantthan measurements. See separate fact sheet onbase station exposure.

In case measurement of a mobile phone basestation antenna site is needed there is a CENELECdocument to be follow.

How to do the assessment of RF fieldexposure in the workplace

The responsibil ity for the assessment is on theemployer, defined according to directive 89/391/EEC as any natural or legal person who has anemployment relationship with the worker andhas responsibility for the undertaking and/orestablishment. In most cases the employer willdelegate the practical part of the assessmentto a safety engineer, occupational hygienist ortechnician familiar with the process and if neededto contact an EMF consultant for measurementsor help with the interpretation of numericalcalculations or what proper actions have to betaken.

A flow sheet for the assessment procedure isshow below. The first step is to identify if thereare any RF emitting sources at the workplace.

In surgical diathermy unshielded cables are used forthe active electrode, and the patient is placed on theground electrode. This gives rise to high intensityelectric f ield around the cables and often the actionlevels in the EU directive are exceeded.


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If there are no such equipment the assessmentis finished. If on the other hand there are someRF emitting equipments and there are availabledocument showing that the entire emission from

these devises are not in conflict with the actionvalues the EU directive is fulfilled. If however,there are no documents available, measurementsmust be performed according to the procedurestated in available standard documents or if nosuch document exist, according to best practice.It should be noted that sometimes the standardis only for emission measurement and not forexposure assessment. For instance, measurementaccording to standard are to be taken at a distancefrom the device but the user of the device makes

contact with it, then the exposure has to be assessfrom this perspective.

If the action values are exceeded, actions must betaken to reduce the exposure. If the values still are

above the action values and no more actions couldbe taken numerical calculations might be neededto ensure that the limit values are not exceeded.

This is a very costly process and mainly reservedfor trade organizations, for instance corporations of

welding industry, MRI manufactures, mobile phoneindustry and so on. For more information about thenumerical calculation see separate brochure.

Available exposure/emission standards.Most standards for measurements are to be

regarded as emission standards, i.e.they are useful in comparing different

devices/appliances, but when it comes toexposure assessment other aspects needto be taken into account. As an example

we can take the standard for how tomeasure handheld electrical machinesor welding equipment. The standardsare given measuring distances of 20to 30 cm from the machine or cable,but the worker is having the cable andthe machine in contact with the body.

Another aspect is that the standardseldom applies to the worst casescenario although it might be seldom

used but for the exposure assessmentthis case is what we are looking for. Itis therefore necessary to adopt anotherprocedure in order to make a correctexposure assessment.

As a base for the assessmentCENELEC has newly issued a draftto a European Standard EN 50499,Determination of workers exposure ofelectromagnetic fields. This documentgives an overview of the assessmentprocedure in the frequency range from0 Hz to 300 GHz and is based on andtaken into account other documentand available standards of interest forthe assessment. Available documentof interest for the RF exposureassessment are l isted below.

Instrumentation neededTo make EMF measurement in thefrequency range 100 kHz to 300 GHzone needs to have different sets ofinstruments for each of the frequencyspans. Usually the instrumentationonly covers a certain range of

Flow sheet for the assessment of RF exposurein the work places

Yes

Yes

Yes

Yes

YesNo

No

No

No

No


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frequencies, for instance from 100 kHz to 30 MHz,another set goes from 10 MHz to 300 MHz andother from 100 MHz to 10 GHz, and then for thehigher GHz another set is needed.

For frequencies below 300 MHz typically oneneeds to measure both the electric and magneticfields. Usually commercial instruments areequipped with exchangeable probes for E andH fields. Below 100 MHz there is also a need tomeasure both the contact and the induced current,and this demands another set of instruments.

For most measurements in the lower part ofthis frequency range it is useful to have some

way to measure the main frequency of the deviceunder test, since the limit values are frequencydependent. However, some of the moderncommercial instruments do have a weighted

frequency response and give a percentage readingin relation to the limit values.

Preparation before measurementThe following quest ions are of importance toanswer before the visit to the work place:

averaging have to be done on the E2or H2values,since the exposure limit is based on SAR which isdirectly proportional to the these values.

If the averaged value then is below the action

level then the directive is fulfilled. If not the nextstep is time averaging. The SAR limit is timeaveraged over any 6 minute period, and the nextstep will be to see the timing of the exposure andhow long duty cycle the process has. This shouldthen be applied to the spatial average value to seehow it then compares with the action levels.

If nothing of the above is sufficient to showcompliance then we have numerical calculation,i.e. to see how the measured values give riseto current and SAR in the body. This shouldreally be treated as a last resort, and long beforethis is applied, reduction measures should be

undertaken.To reduce the exposure to RF often a

maintainence program is of help; make sure allcovers are in place and with all screws thightlydrawn; replace damage brass foils used forconducting the current and grounding; make surethe operator is not in contact with ground; keepthe safety distance to the machine; is the settingsof the machine optimal for field reduction.

Demands on the ReportThe measurement report should state:

Why are the measurements ordered

Has RF been measured at the workplace

earlier

What type of sources are emitting RF

Is there any information about theemitting equipment, model

What are the operating frequencies

What is the duty cycle, (worst case

situation)

What is the output power

Are there any earlier protocols available

How to measure RF fieldsWhen you have done the preparation as out linedabove and are ready to start the measurements,always approach the source with caution until youknow what to expect. In the simplest case you findthat all values, E or H field, are below the actionlevels, then there is no need to go any further.

However, if some of the values are above theaction values, the measurements have to be donemore carefully and with a spatial averaging overthe body. Select about 46 spots head, chest,groin, thighs and make the recordings. Notethe measurements have to be done without theoperator present since the fields are stronglydistorted by the presence a person. The spatial

Who ordered the measurement

Who did the measurement and when

Who were present from the company

What instrument was used and when

where these calibrated

What measurement method was used,

Identification of the machine and site,

serial number or equivalent

What was the production during the

measurement, i e worst case

Values given as mean with the

estimated uncertainty in the

measurements

Was there a need to measure induced

and contact current, if not state why

The report should also have a clear statement asto whether the action levels are met or not, and whatmeasures to reduce exposure can be taken. It shouldalso give a statement if there is a need for numericalcalculation to show compliance with the directive.


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References

ICNIRPGeneral approach to protection againstnon-ionizing radiation. Health Physics; 82; No. 540-548; 2002.

ICNIRP Statement on Medical Magnetic Resonance(MR) Procedures: Protection of Patients. HealthPhysics 87(2): 197-216; 2004.

IEEE Std C95.1.Standard for Safety Levels withRespect to Human Exposure to Radio FrequencyElectromagnetic Fields, 3 kHz to 300 GHz. 2005Edition Published by the Institute of Electrical andElectronics Engineers, New York, USA, 2006.

IEEE recommended practice for Radio FrequencySafety Programs, 3 kHz to 300 GHz. Published 22March 2006. IEEE Std C95.7-2005.

NCRP.A practical guide to the determination ofhuman exposure to radiofrequency fields. NCRPReport no 119. 1993.

NIOSHManual for measuring occupational electricand magnetic field exposure. U.S. Departmentof Health and Human Services. Public HealthService. Centres for Disease Control and Prevention.National Institute for Occupational Safety andHealth. DHHS (NIOSH) Publication No. 98-154.

NIOSH/WHO Occupational EMF document.Evaluation and managing occupational exposureto EMF. A Joint Publication of the World HealthOrganization International EMF Project and theU.S. Centres for Disease Control and Prevention,National Institute for Occupational Safety andHealth. In preparation.

WHO Fact Sheet.Medical response to radiofrequency overexposure.

Arpansa, 2003.Radiation protect ion standard.Maximum exposure levels to radiofrequency fields

3 kHz to 300 GHz. Radiation protection Series no3. Australian radiation protection and nuclear safetyagency.

CENELEC 2004. Generic standard to demonstratethe compliance of electronic and electrical apparatuswith the basis restrictions related to human exposureto electromagnetic f ields (0 Hz 300 GHz)EN 50392.

CENELEC 2006. Basic standard on measurement

and calculation procedures for human exposure toelectric and magnetic and electromagnetic fields( 0 Hz 300 GHz). Draft pr EN 50413.

CENELEC 2006. Basic standard on measurementand calculation procedures for human exposure toelectric and magnetic and electromagnetic fields(0 Hz 300 GHz). Draft pr EN 50477.

CENELEC 2006. Determination of workersexposure to electromagnetic f ields. EN 50499.

Directive 2004/40/EC of the European Parliament

and of the Council of 29 April 2004 on the minimumhealth and safety requirements regarding theexposure of workers to the risks arising from physicalagents (electromagnetic f ields) (18th individualDirective within the meaning of Article 16(1) ofDirective 89/391/EEC), O.J. nr L-184 of 24 May2004.

ICNIRP Guidelines for Limiting Exposure to Time-Varying Electric , Magnetic, and ElectromagneticFields (up to 300 GHz), Health Physics, vol. 74, No.4 (April), 494-522, 1998.

An in formation publication from the EMF NET project

Authors:Kjell Hansson Mild, Dept. of Radiation Physics and Monica Sandstrm,

Occupational and Environmental Medicine, Ume University, Ume, Sweden

Phone+46 (0)90 785 00 00 http://web.jrc.ec.europa.eu/emf-net/

Graphic design and illustrations:Guldbrand & Guldbrand


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Occupational exposure fact sheet

Microwave dryers

Microwaves at frequencies of 915 and 2 450 MHz arecommonly used for drying of building components,such as ceilings and exterior wall surfaces, requiredin construction and repair work. In addition, it is verycommon to use microwave technology for drying ofwater damages in wet walls or water flooded floorsafter fires and other accidents.

An information publication from the EMF NET projectSSPE-CT-2004-502173 EMF-NET MT2 working groupEffects of the Exposure to Electromagnetic Fields:From Science to Public Health and Safer Workplace.Coordination Action 8. Policy Support and AnticipatingScientific and Technological Needs

Microwave energy from the magnetron is guidedto structures in order to vaporise water from wetmaterial. Thus, the principle is the same as appliedfor heating foodstuffs inside household microwaveovens. However, the power of the portable dryingunit is higher, typically ranges from 1 to 5 kW.


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A mobile microwave dryer contains a generator withhorn antenna mounted inside of metallic housing.In typical operation an antenna is put against wetwall and set is turned on by push on control device.Microwave energy from the generator is emittedto the wall and heat the water uncovered inside ofthe wall capillary. In order to avoid stray radiation,the microwave applicators are directed downrighttowards the material to be heated.

Power densities of microwave radiation emitted

by drying appliances are very high, being more than100 kW/m2 in front of the applicator, and about10 kW/m2at a distance of 20 cm. In some cases,power density on the backside of the wall to be driedmay sti ll exceed 1 kW/m2, diminishing to 100 W/m2at a distance of about 2 m behind the wall.

In addition, stray fields from surroundingsurfaces may exceed the occupational exposure

limit value (50 W/m2) at a distance of 50 cm.Therefore, microwave drying units should beused only by authorized users who are aware ofthe potential health risks. The present drying technology should applyremote control to ensure that cut-off occurs assoon as someone enters the danger area. Safety canbe increased still further by room screening usingaluminized films or composites of aluminiumfilms and paper. The safety systems may consist

of photocells, movement sensors, infraredradiation sensors etc. More conventional methodswith uncomplicated electric contact switches areuseable too. A locking system, that makes surethat only qualified operators having keys are ableto restart the microwave dryers after cut-off, canensure that unintended starting cannot endangerworkers or other persons close-by.

An informat ion publication from the EMF NET projec t

Author:Maila Hietanen, Finnish Institute of Occupational Health, Helsinki, Finland.

Phone+358 (0)30 4741 http://web.jrc.ec.europa.eu/emf-net/Photo:Martt i Kainulainen, Lehtikuva.

Graphic design:Guldbrand & Guldbrand


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Mobile phone base station

Mobile telephony base stationsMobile phones communicate by radiofrequency (RF)signals passing between the phone and base stationantennas. Base station antennas are placed on masts,roof tops, building facades and inside buildings, andon other suitable places having good coverage area.Base station antennas usually send and receive radiotransmissions, but some antennas operate as receiveonly antennas, thus having no transmissions.

Exposure to base station antennas

RF emissions vary depending on the design and powerof base station. The transmission powers are relativelylow, usually less than 40 W. Generally, most powerfulantennas are sited on highest places, such as onbroadcasting towers. On the other hand, base stationantennas situated inside the buildings have lowesttransmission powers, usually less than 1 W. Theselow power antennas can be considered to be safe fromthe point of occupational exposure at any distance.Occupational exposure is possible during maintenanceof base station, as well as during construction andsimilar tasks on the roof in close proximity to the

antenna. Antennas should be mounted so that generalpublic can not get access to area where correspondingexposure limits may be exceeded.

Certain occupational groups may have to work closeto the base station antennas. For example, occupationalexposure is possible during maintenance of basestation, as well as during construction and similartasks on the roof in close proximity to the antenna.These occupations include maintenance and operatorpersonnel, janitors, painters, chimney sweepers,window cleaners, etc., and generally workers that haveto work on roof tops and building facades.

Working close by the antennaModern base station antennas are sector antennas thattransmit only to the forward direction.



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RF wood glue dryingThis fact sheet gives practicaladvice on how to work safely withwood glue drying machines. It alsoprovides information on what radiofrequency (RF) electromagneticfields are and how they can affectyour health and what parameters

should be measured to make aproper risk assessment.

How does an RF wood gluedrying machine work?Wood glue drying machine aremainly used to quick-dry glue

when manufacturing items suchas tabletops. A typical wood gluedrying machine has an input area

where the wood material is fed in andan output area where the material

comes out again. Inside the metalcasing there are long electrodes to

which a RF current is led from a RFgenerator. Radio frequency currentis transferred via the electrodes tothe material, which heats up anddries the glue. It usually takes nomore than a few minutes of exposurefor the glue to dry.

The strength of the RF fielddepends on which type of machineis being used. Generally, machines

with visible, open electrodes(unshielded) are surrounded withstronger fields than machines withenclosed electrodes.

More on RF fieldsWhen describing RF electromagnetic fields, the fields frequency isoften mentioned. The permitted operating frequencies for glue dryersare 13.56, 27.12, or 40.68 megahertz (MHz).

There is a risk of interfering with other equipment, such as radioand TV receivers, if other frequencies are used. The manufacturersets the frequency, but after several years of use it can vary, so its

important to measure the frequency regularly.The RF fields from a wood glue drying machine spread out around

the machine, but most often it is only right next to the machine thatthe field is so strong that precautions need to be taken. The fieldsstrength decreases sharply with distance from the source.

The strength of the field is given in two different measurements:the electric field strength (E) is measured in volts per metre (V/m),and the magnetic field strength (H) is measured in amperes per metre(A/m). Both of these must be measured to get an idea of how strongthe RF field is. The current that goes through you if you touch the



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changes have been made to the machine. Thesemeasurements are difficult to make, and thenecessary measuring devices are expensive and youmay need to contact experts on electromagnetic

field measurements.

How can strong fields be avoided?Generally, the workplace should be designed insuch a way that it isnt necessary for the operatorto have direct contact with the machine duringthe drying process and that there is as muchdistance as possible between the operatorsmanoeuvring bench and the inputs and outputs.It is also important that the machine is wellmaintained and in good condition. It is especiallyimportant to ensure that all the screws holding

the metal parts together in the machine chassisare in place and properly tightened. The RFfields could otherwise leak out from gaps inthe panels, screw holes and so on. The machinemust also be properly grounded. It is not enoughto use the thin copper wires used for groundingordinary electrical equipment a proper strip ofmetal is required. Grounding can be difficult,and you may need to turn to an expert such asthe machines manufacturer for help. However,it is of importance for the exposure that theoperator is NOT in contact with ground, because

if so the absorbtion of RF energy will increasesubstantially. It is therefore recommened that ifthe floor in the factory is reinforced concrete,which it usually is, then the operator should bestanding on a non conducting material that gives

a distance of 510 cm from the f loor, for instancea rubber mat or some wood platform. Note thatthis has to be made so that the ergonomy of theworkplace is not impered.

For completely enclosed processes where themachine is in a separate, shielded room and whereemployees are not allowed during the dryingprocess, exposure outside the room is often so lowthat the risk of injury is negligible.

New employees must go through introductorytraining on how to work safely with glue dryingmachines.

What about pregnant women?Currently, there is no collective practice forhow this type of work should be regulated for

pregnant women. Many glue drying companiestemporarily transfer pregnant women so they arenot working directly with the machine while theyare pregnant.

Would you like to read more?Directive 2004/40/EG of the European Parliamentand of the Council on the minimum health and safetyrequirements regarding the exposure of workers to therisks arising from physical agents (electromagneticfields).

Safety in the use of radio frequency dielectric heatersand sealers. Occupational safety and health series 71,International Labour Office (ILO), Geneva. ISBN92-2-110333-1

All screws holding the metal chassis

together must be in place and properly

tightened. It is especial ly important to

remember this after the chassis has been

opened.

The work process must be designed so

that the operator stands at the appropriate

distance from the glue dryers opening.

A wood or plastic platform on the floor

reduces the amount of current that is

induced in the body.


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Occupational and Environmental Medicine, Ume University, Ume, SwedenPhone+46 (0)90 785 00 00 http://web.jrc.ec.europa.eu/emf-net/



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spots head, chest, groin, thighs and make therecordings. Note that the measurements haveto be done without the operator present, sincethe fields are strongly distorted by the presenceof a person. The spatial averaging have to be

done on the square of the E and H values, sincethe exposure limit is based on SAR (SpecificAbsorbtion Rates, read more in the general texton RF exposure) which is directly proportional tothe these values.

If the averaged value is below the action levelthe directive is fulfilled. If not the next step istime averaging. The SAR limit is time averagedover any 6 minute period, and the next step willbe to see the timing of the exposure and how longduty cycle the process has. This should then beapplied to the spatial average value to see how it

compares with the action levels.

When to make measurements?Control measurements of RF plastic sealer shouldoccur regularly every few years or after major changeshave been made to the machine.These measurementsare difficult to make, and the necessary measuringdevices are expensive and you may need to contactexperts on electromagnetic f ield measurements.

How can strong fields be avoided?Generally, the workplace should be designed in

such a way that it isnt necessary for the operatorto have direct contact with the machine whilewelding and that the welding electrode is placedas far away from the operator as possible.

It is also important that the machine is wellmaintained and in good condition. It is especiallyimportant to ensure that all the screws holding themetal parts together in the machine chassis are inplace and properly tightened. The radio frequencyfields could otherwise leak out from gaps in thepanels, screw holes and so on. It is very importantto use a grounding bar. If it is dismounted, the

return current will not go back to the groundpoint and exposure will increase considerablyaround the machine. The grounding bar will notfunction as it should if too much plastic materialcomes between the bar and the bench.

The machine must also be properly grounded.It is not enough to use the thin copper wires usedfor grounding ordinary electrical equipment a proper strip of metal is required. Groundingcan be difficult, and you may need to turn toan expert such as the machines manufacturerfor help. However, it is of importance for the

exposure that the operator is NOT in contactwith ground, because if so the absorpt ion of RFenergy will increase substantially. It is therefore

recommended that if the floor in the factory isreinforced concrete, which it usually is, then theoperator should be standing on a non conductingmaterial that gives a distance of 510 cm from thefloor, for instance a rubber mat or some wood

platform. Note that this has to be made so thatthe ergonomy of the workplace is not impered.

New employees must go through introductorytraining on how to work safely with a plasticwelding machine.

One way of avoiding direct contact with themachine when welding while standing is touse a starter rope.

All screws holding the metal chassis togethermust be in place and properly tightened. It isespecially important to remember this af ter

the chassis has been opened.

Two-hand grip when starting to weld whilesitting. For instance, the start button canbe mounted on the chair to avoid directcontact with the machine while welding.

What about pregnant women?Currently, there is no collective practice for howthis type of work should be regulated for pregnant

women. Many plastic welding companies temporarilytransfer pregnant women so they are not working

directly with the machine while they are pregnant.

Would you like to read more?Radio frequency electromagnetic fields from plasticwelders. Measurements and reduction measures.

Investigative report 1983:24, National Institute forWorking Life, Stockholm, ISSN 0347-2248

Guidelines for the measurement of RF welders.Investigative report 1991:8, National Institute forWorking Life, Stockholm, ISSN 0284-7620

Directive 2004/40/EG of the European Parliament

and of the Council on the minimum health and safetyrequirements regarding the exposure of workers to therisks arising from physical agents (electromagneticfields).

IEEE Std C95.3.Recommended practice formeasurements and computations of radio frequencyelectromagnetic fields with respect to human exposureto such fields, 100 kHz-300 GHz. Published by theInstitute of Electrical and Electronics Engineers,New York, USA, 2002.

Safety in the use of radio frequency dielectric heaters

and sealers. Occupational safety and health series 71,International Labour office (ILO), Geneva. ISBN92-2-110333-1


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Occupational and Environmental Medicine, Ume University, Ume, SwedenPhone+46 (0)90 785 00 00 http://web.jrc.ec.europa.eu/emf-net/



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Assessment of occupational exposure to intermediate

frequency electromagnetic fields in practiceJolanta Karpowicz, Krzysztof Gryz

ver. 1 - April 2008

INTRODUCTION

Electric currents and voltages produce

electromagnetic fields (EMF).

The majority of population are subject tosimultaneous exposure to EMF from broadcasting

and power distribution installations, as well as

various electrical appliances. The characteristics ofEMF in the workplace is often very specific incomparison with the fields in the general publicenvironment:

in the workplace the locations of the EMFsource against the worker's body can changesignificantly

distance between the source and the humanbody can be very short

the workers body can even touch EMF source geometry of the source, frequency and level of

EMF produced by it can also be unstable

exposure level of an operator can varysignificantly also as a result of his physicalactivity in the vicinity of the source

the workers exposure level can be high, evenexceeding international safety guidelines.

EMF exposure assessment adequate to the physicalcharacteristics of exposure and real exposure levelis the crucial step towards appropriate:

risk assessment for occupational safety andhealth (OSH) engineering

testing the compliance of exposure conditionswith safety guidelines or requirements from

legislation design or re-design of devices emitting EMF

and work environment containing such sources

epidemiological studies of EMF-exposedgroups

environmental monitoring.The strongest demands for the use of detailed EMFexposure assessment protocol come from theregulations concerning mandatory control of

occupational or environmental EMF exposure, e.g.European Directive on workers EMF exposurelimitation or national legislation on occupational

safety and health.

ENVIRONMENTAL EMF OF

INTERMEDIATE FREQUENCY RANGE (IF)

EMFs of frequency from the range of 300 MHz 300 GHz are called microwaves (MW).Wavelength of MW is sufficiently short for thepractical use of waveguides to transmit or receiveit. EMF of any frequency, which is useful fortelecommunication, is called radiofrequency (RF)

EMF. It is possible to find various definitions ofRF, e.g. 300 Hz 300 GHz (according to IEEE).

EMFs of the frequency below 300 Hz are calledextremely low frequency (ELF) fields. Powerfrequency means the frequency of currents used for

electrical power transmitting and of EMFs itproduces (50 Hz in Europe, 60 Hz in NorthAmerica).

The Intermediate Frequency(IF) range of EMFspectrum is specified as the band between theextremely low frequency (ELF) and radiofrequency (RF) ranges. The limits of IF range is notdefined univocally (e.g. according to WHO factsheet it is the range from 300 Hz to 10 MHz) (seeFigure 1). The basic parameters of IF EMF are

presented in Table 3.

50Hz

10Hz 100Hz 1kHz 10kHz 100kHz 1MHz 10MHz 100MHz

Figure 1. Example of definition for IF EMF

The basic properties of EMF are related to thewavelength and field polarisation, characterised bythe so-called near- or far-field condition of

exposure (see Table 1).

IF EMF which exists in the work environment is

usually near field.

Electric field strength, E, and magnetic field

strength, H, should be considered for the

assessment of IF EMF.

WHO 300 Hz - 10 MHz


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Table. 1. Basic parameters of IF EMF

Frequency,

f

Wavelength,

,m

Nearfield

approximation

distancefrom

fieldsource

-upto

,m

Farfield

approximation

distancefrom

fieldsource

-exceeding3

,m

50 Hz 6000000 6000000 18000000

300 Hz 1000000 1000000 3000000

1 kHz 300000 300000 900000

10 kHz 30000 30000 90000

100 kHz 3000 3000 3000

1 MHz 300 300 900

10 MHz 30 30 90

27 MHz 11 11 33

100 MHz 3 3 9

HAZARDS CAUSED BY IF EMF

Within IF EMF, three basic mechanisms related todirect adverse effects in the living matter were

established:

effects of exposure to time-varying electricfields - a flow of electric current, polarisationand reorientation of electric dipoles alreadypresent in the tissue (dominating up to 100kHz, but under consideration up to 5-20 MHz)

effects of exposure to time-varying magneticfields - induced electric fields and circulatingelectric currents, the so-called eddy currents inthe body (dominating - up to 100 kHz, but

those under consideration - up to 5-20 MHz) effects of absorption of energy from EMF -

temperature increase inside the exposed body

(under consideration - above 100 kHz, but thedominant - above 10 MHz).

Except direct effects of EMF exposure and

interaction of EMF with the human body, indirecteffects can be a significant source of hazards such

as:

contact currents coupling of EMF to medical devices transient discharges (sparks).EXPOSURE ASSESSMENT CRITERIA

APPLICABLE FOR IF EMF

Exposure assessment regarding IF EMF isextremely complex almost all estimators of EMFcan be used in this case:

Internal measures:

SAR induced currents in situelectric fieldExternal measures

electric field strength (E)

magnetic field strength (H) magnetic flux density (B)

contact and induced currents flowing throughthe limbs (I).

Various estimators can be necessary for theassessment of EMF of different patterns:

RMS value peak value time derivative dB/dt exposure factor time-averaged exposure level spatially-averaged field strength spatially-averaged squared field strength, etc.All estimators (except SAR) have been establishedas frequency-dependent exposure limitations and

they refer to various frequency ranges.

MEASUREMENTS OF IF EMF

The assessment of IF EMF can be based on theresults of the series of spot measurements of RMS

value of unperturbed electric and magnetic fieldstrength.

The first step of the assessment procedure can bebased on searching for maximum over the workers

body position. If the results are above the limit ofexposure then the next step could be timeaveraging, if relevant time-averaged exposurelimitation is available, e.g. 6-minutes averaging ofE and H-fields of the frequency above 100 kHz.

For the case when the worker's body is in contactwith electric field sources, the above mentionedlevel of exposure should be establishedsignificantly below environmental limit forunperturbed field (like action values from EMFdirective) because spatial distribution of exposure is

heterogeneous and there is a risk of exceeding thelocal thermal effect. The details should be discussedwith the use of the results of numerical calculationsand contact/induced currents measurements. Theuse of commercial broadband RMS electric andmagnetic field strength meters should be verycarefully considered in the case of highly

modulated fields. Laboratory tests indicate thatcorrection factors for modulated fields can be

established for typical waveforms, but uncertaintyof such procedure will significantly rise incomparison with measurements of sinusoidalwaves.

In the case of hand operating sources of strong

electric field or contact of the worker's body withtheir elements, the assessment of induced currentresulting from coupling between workers body andelement with high electric potential (e.g. activeelectrode or cable of electrosurgery unit) isproblematic. The EMF directive criteria for induced

current in limbs are not given for frequency below10 MHz, however local thermal effect in the limbs


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(local SAR) was limited for frequencies exceeding100 kHz. The assessment of these quantities may becarried out following the permissible values asspecified in the directive for contact current orpermissible values for induced current in the feetspecified in IEEE standard. Very few instruments

measuring current flowing through limbs (clamp-onmeter or stand-on meter) are currently available.

The following basic problems with EMFmeasurements and assessment of workers exposurewere specified:

heterogeneous distribution of EMF causemeasurement error as a result of field averagingover the EMF sensor

measurements in direct proximity of thepowered cables or other elements of EMFsources at high electric potential are connectedwith strong coupling between the meter probe

and EMF source what can influence on themeter sensitivity and lead to additionalmeasurement error not covered by calibrationof the device

according to general rules, the assessment ofthe workers exposure should be based onunperturbed field. In many cases, e.g. ofelectrosurgical devices, measurement of thisfield is not possible for technical reasons.Exposure assessment performed duringsimulated work of EMF sources does not take

into account the results of capacitive couplingand induced or contact current flowing through

the workers body

EMF measurements over the position of trunknot cover the hands' exposure, usually the most

exposed part of body.

use of meters calibrated in harmonic referencefield for measurements of pulse modulatedfield may be a source of additional significant

measurement error.

NUMERICAL CALCULATIONS

According to the provisions of European Directive

2004/40/EC, in the case of environmental exposureconditions exceeding limits given for exposure

action values, workers' exposure assessment shouldbe performed on numerical calculations of physicalquantities inside numerical phantom of exposedbody, i.e. exposure limit values, such as currentdensity (J) and specific energy absorption rate(SAR). The conclusive assessment of workers

exposure to EMF needs the use of the workersbody models (numerical phantoms) and an adequate

representation of the workplace.

The basic problems for calculations are:

representation of the realistic posture of theworker's body

adequate representation of the electricalgrounding conditions at the workplace

adequate representation of realistic impedanceof near-field produced by devices being use

adequate representation of dynamic changes ofEMF level in the course of working activity.

Fig. 2.Numerical model of exposure conditions, realisticfor surgeon's exposure from electrosurgery device

Adequate calculations for assessment of particularexposure situations need high professional skills,specialised software and can be very time-consuming and expensive.

OCCUPATIONAL EXPOSURE TO IF EMF

Significant occupational exposure to EMF from theIF range is caused by various:

- industrial appliances:

o induction heaters, operating usually from1 kHz to low MHz

o welding devices, common sources of ELFEMF but can be also a source of EMF oftens/hundreds kHz frequency

- medical devices (electrosurgery units, usuallysources of 300 kHz - 1.5 MHz)

- anti-theft devices and many others.

Usually, impedance of EMF in the workplace is

high or low in comparison with Z0=377 and inconsequence, exposure assessment can be executedon the basis of testing only one dominating

component, e.g. magnetic in the case of inductionheaters or electric in the case of electrosurgery.


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Figure 3.Internal and external measure applicable for the assessment of IF EMF

Comments:

According to the European Directive, the workers exposure assessment should be performed on the results of measurements of

RMS value of unperturbed (existing in the workplace during the absence of workers) electric and magnetic field strength averagedover the workers body position and averaged for particular time, which depends on the frequency of assessed fields (e.g. for the

EMF of the frequency 100 kHz - 10 GHz, EandHshould be averaged within any 6 minutes of worker's exposure and E2andH2

should be averaged over the worker's body position.Workers exposure assessment can be performed on the results of a spatial averaging RMS value in the straight line in the center of

the projected area equal to workers position (according to IEEE standard) or on results of the spot measurements of RMS value

(the maximum result of measurements over the workers body position in the workplace).According to Directive 2004/40/EC in the cases of non-sinusoidal EMF exposure peak action values for the field strengths are

calculated by multiplying the relevant RMS values by coefficient (i.e. multiplied by approx. 1.5 for 100 kHz, 4.4 for 500 kHz, 6.9

for 1 MHz).

References

1. Directive 2004/40/EC of the European Parliament and of the Council of on the minimum health and safety requirementsregarding the exposure of workers to the risks arising from physical agents (electromagnetic fields) (18th individual Directive

within the meaning of Article 16(1) of Directive 89/391/EEC), O.J. Nr L-184, 2004.

2. ICNIRP Guidelines for Limiting Exposure to Time-Varying Electric, Magnetic, and Electromagnetic Fields (up to 300 GHz),Health Physics, 1998, 74, 4 (April), 494-522.

3. IEEE Std C95.1, Standard for Safety Levels with Respect to Human Exposure to Radio Frequency Electromagnetic Fields, 3kHz to 300 GHz. 2005 Edition Published by the Institute of Electrical and Electronics Engineers, New York, USA, 2006.

4. Internet service: http:/www.ciop.pl/EMF

Jolanta Karpowicz ([email protected]), Krzysztof Gryz ([email protected])

Central Institute for Labour Protection - National Research Institute (CIOP-PIB), Laboratory of Electromagnetic Hazards

Czerniakowska 16, Warszawa, POLAND, http://www.ciop.pl & http://www.ciop.pl/EMF

This issue was compiled in relation to activities of EMF-NET project and is related to the following deliverables: D50 (WP10), D53

(WP11), D56 (WP11.1), D59 (WP11.2), D62 (WP11.3), D67 (WP12), D72 (WP12.1) and D77 (WP12.2).

Contract no.

Project acronym:

Project title

Instrument

Thematic Priority

SSPE-CT-2004-502173

EMF-NETEffects of the Exposure to Electromagnetic Fields:

From Science to Public Health and Safer Workplace

Coordination Action8. Policy Support and Anticipating Scientific and Technological Needs

The results of National Programme Adaptation of Working Conditions in Poland to European Union Standards supported by the

State Committee for Scientific Research of Poland, international project Centre for Testing and Measurement for Improvement of

Safety of Products and Working Life (European Union 5thFramework Programme) were also used for compilation, as well as

results of investigations executed in the cooperation with enterprises.

0.1

1

10

100

1000

10000

100000

1000000

1.E+00 1.E+01 1.E+02 1.E+03 1.E+04 1.E+05 1.E+06 1.E+07 1.E+08 1.E+09 1.E+10 1.E+11 1.E+12

frequency, Hz

electricfieldstrength,V/m.

magneticfieldstrength,A/m

E - ICNIRP, EU Directive E - IEEEH - ICNIRP, EU Directive H - IEEE

SAR

current density

induced currentIL ICNIRP, EU Directive

IEEE

contact currentIC


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ELECTROSURGERY

Occupational exposure to electromagnetic fields - assessment in practiceKrzysztof Gryz, Jolanta Karpowicz

ver. 1 - April 2008

ELECTROSURGERY DEVICES

Electrosurgery means the use of electric currents to

cut or to coagulate a patients tissues for variousmedical treatments. The sources of occupationalexposure to electromagnetic fields (EMF) include:

an active electrode at a high electric potential

cables connecting the generator (output powerof up to 500 W, usually during surgicaltreatment of 50-150 W) with the active

electrode, held in the hand by a surgeon, andwith the passive electrode (grounded plate),mounted to the patients body (Fig. 1)

a generator in case of not leak-proof housing(generator with insufficient electromagneticshield)

metallic objects located in the vicinity of cables

(e.g. surgical or instrumentation tables), whichcan become secondary sources of EMF.

Fig. 1.Electrosurgery device

OCCUPATIONAL EMF EXPOSURE

Electrodes and supplying cables are sources of

electric field (E-field) of high level because of theapplication of supplying intermediate frequency(IF) high voltage, of frequency exceeding 300 kHz

(up to 1 MHz).

The waveforms of EMF produced in the vicinity ofcables depend on a type of a device and its mode ofoperation (Fig. 2).

Fig 2.EMF of electrosurgery device - E-field v. time

The exposure to EMF of a surgeon and health carestaff (attending physicians and nurses) depends on:

mode of device operation

type of active electrode in use

location of cables connecting electrodes withgenerator.

The surgeon, who holds an active electrode in the

hand, is usually the most exposed person from theteam.

a) cut pure, 0.97 s/div

b) coagulation soft", 0.66 s/div

passive

electrodeactive

electrodes

cables supplying

electrodes

generator


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The hand exposure always exists, but other areas ofthe body can be also exposed as a result of a contactwith cables, e.g. head or torso EMF exposure.

The surgeon is usually exposed to non-homogenousE-field. Metallic objects, which are in the operating

theatre influence the spatial distribution of E-field.

The level of exposure of health care staff canchange 2 or 3 fold, as a consequence of changes inthe location of these objects.

In the worst case (use of a monopolar electrode andnon-shielded cables, approx. 100-150 W outputpower), the surgeons hand can be exposed toE-field exceeding 1000 V/m, but head and torso- up to a few tens of V/m only. When cables touchthe surgeons body then torso exposure is stronger,up to the level of the exposure of the hand holding

the electrode. Magnetic field (H-field) is usuallybelow 1 A/m in the distance of 5-10 cm from

electrodes and cables. If cables create loops, anincreased magnetic field exists also in their vicinity.

Level and waveform of EMF depend on the modeof electrosurgery devices operation (Fig. 3, Tab. 1).

Fig. 3. Examples of variability of E-field produced invarious modes of electrosurgery devices - comparison ofrelative E-field (mean RMS for "pure" cut = 1),

registered by wide-band E-field meter

Table 1.Example of relation of peak value (Ep) to mean RMS

values (ERMS) of E-field strength, registered byoscilloscopic method in the vicinity of cables ofelectrosurgery devices

Operation Mode -output power

Ratio,Ep/ERMS

Waveform of EMF

cut pure - 150 W 1,4 sinusoidal 400 kHz

coagulation spray- 100 W 4,1

sinusoidal 400 kHz + pulsemodulation 25-40 kHz

cut blend withargon - 100 W 1,8

sinusoidal 400 kHz +amplitude modulation 27 kHz

coagulation spray

with argon - 100 W3,8

sinusoidal 400 kHz + pulse

modulation 40 kHz

The execution of electrosurgical treatment with anelectric arc burned under an active electrode leads

to a significant increase of E-field affecting onmedical staff. The level of exposure during electricarc-surgery can be 4-fold higher in comparison tothe operation without visible arc.

As a result of exposure to E-field and capacitive

coupling between elements of electrosurgery device

and the workers body, induced electric current isflowing through the workers body, similarly tocurrents penetrating the patients tissues (Fig. 4).

Fig. 4. Induced current measured at surgeons hand,keeping an active electrode, and E-field measured over a

surface of this hand (for various modes of operation andcable location, 5-minutes registration)

OCCUPATIONAL EMF EXPOSURE

ASSESSMENT

Measurements

The level of EMF exposure of health care staff canbe assessed with the use of three parameter, whichcan be measured in the workplace:

electric field strength,E, in V/m

magnetic field strength,H, in A/m

induced current,I, in mA.

The measurements of EMF have to be executed bybroadband meters. The frequency response of

equipment used for measurements has to beadequate to the frequency of EMF produced by

electrosurgery devices.

EMF exposure of health care staff should bemeasured following the procedures established by

requirements of national regulations and standards,or in the case of the lack of such documents,following the internationally published standards(e.g. CENELEC or IEEE standard). The use of theresults of laboratory measurements of EMFemission from electrosurgery devices is verylimited because spatial distribution of E-field canbe highly modified by the metallic structures and

humans present in the vicinity of the field source.

The results of measurements of exposureparameters have to be analysed following thenational regulations and standards, or in case of the

0123456789

101112131415161718

cut "pure" coagulation "spray" cut "blended" wi thargon

coagulation "spray"with argon

peak RMS value

mean RMS value

0,1

1

10

100

1000E field

induced current

E-field, V/minduced current, mA


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lack of such document, following theinternationally published limitations and standards(e.g. European Directive 2004/40/EC, ICNIRP'sguidelines or IEEE standard see table 2). It shouldbe considered that the permissible level ofexposure, applicable for assessment of exposure

from various modes of operation of electrosurgerydevices, can be different as a result of the use of

frequency-dependent exposure limitations.

Methods of measurements should be harmonisedwith assessment criteria (see Table 2 and 3).

Analysis of results of RMS measurements ofE,H,Ishould take into account the waveforms of theinvestigated EMF - the most universal method forits identification is oscilloscopic registration. Incase of modulated fields, the broadband meters

calibrated for RMS value of sinusoidal fields canproduce a significant error (exceeding 50 %) and

correction factors harmonized with the waveformsof the assessed field should be considered beforeperforming the worker's exposure assessment. As aconsequence, for measurements of modulated EMFit is necessary to identify the waveform of EMF

time-variability, as well as information on detailedtechnical parameters of the meter being used

concerning the sensitivity of readings of this meterto various parameters of modulated fields.Exposure assessment criteria can also be modifiedin case of modulated fields (see Table 2 and 3).

Measurements can be performed during a simulatedoperation only, with phantom equivalent to thepatients body (e.g. absorbent cotton with saline,fresh fruit, vegetable, meat, etc.).

Assessment of surgeons exposure can be performedon the basis the measurements of RMS value ofcurrent flowing through the surgeons hand holdingan active electrode and through his feet, performedwith the use of clamp-on meter (Fig. 5).

Criteria for induced current in limbs, given in theDirective 2004/40/EC, do not cover frequencybelow 10 MHz. Limitation of induced current of thefrequency from the range typical for EMF produced

by electrosurgery devices were published by IEEEstandard (Table 3).

Fig. 5. The clamp-on meter for measurements of thecurrent in the surgeon's hand

Numerical calculations

According to the provisions of European Directive2004/40/EC in case of environmental exposure

conditions exceeding limits given for exposureaction values, the workers' exposure assessment

should be performed using numerical calculations

of physical quantities inside the numerical phantomof exposed body, i.e. exposure limit values, such ascurrent density (J) and specific energy absorptionrate (SAR). The conclusive assessment of thesurgeons exposure to EMF needs the use of the

workers body models (numerical phantoms) and anadequate representation of the workplace (Fig. 6).

Fig. 6. Numerical simulations of the surgeon's exposure

to EMF (numerical model and SAR distribution)

The basic problems for calculations are as follows:

representation of the realistic posture of theworker's body

adequate representation of the electricalgrounding conditions at the workplace

adequate representation of realistic impedanceof near-field produced by electrosurgery

devices

adequate representation of dynamic changes ofEMF level in the course of surgery treatment.

For the surgeon's EMF exposure, adequatecalculations for assessment of particular exposure

situations need high professional skills, specialisedsoftware and can be very time-consuming andexpensive.


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Occupational EMF Exposure

Database

http://www.occupemf.info/

The Occupemf-database is a uniquerepository for scientific articles relatedto occupational exposure toelectromagnetic fields (EMF). It isdesigned to be a tool in searching forinformation on health risk evaluations

of EMF exposure associated withvarious occupations. The databasegives references to relevant scientificpapers and reports, and in particular,the Occupemf-database contains theproducts of EMF-NET MT2 project(including the Fact Sheets) indownloadable format, aimed to befreely used by all parties interested inoccupational EMF aspects.

The articles can be searched accordingto article titles, authors, publicationyear and free text search. The searchescan be made conveniently with onesearch questionary field. In addition to

conventional targets, the articles canalso be searched using occupation orEMF sources as a search parameter.The database search function enablesalso finding of articles focusing ondifferent frequencies (single frequenciesor frequency ranges). Furthermore, thearticles are sorted according to theexposure assessment method(measurements, calculations, epidemio-logical study).
http://www.occupemf.info/http://www.occupemf.info/


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The Occupemf-database contains theproducts of EMF-NET MT2 project(including the Fact Sheets) indownloadable format, aimed to befreely used by all parties interested inoccupational EMF aspects.

Detailed instruction for the use can befound at the EMF-NET database webpages http://www.occupemf.info/

http://www.occupemf.info/

An information publication from the EMF NET projectAuthors: Tommi Alanko and Maila Hietanen, Finnish Institute of Occupational Health, Helsinki, Finland.Phone +358 (0)30 4741 http://web.jrc.ec.europa.eu/emf-net/
http://www.occupemf.info/http://www.occupemf.info/http://web.jrc.ec.europa.eu/emf-net/http://web.jrc.ec.europa.eu/emf-net/http://www.occupemf.info/http://www.occupemf.info/


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Practical Guidance for

Occupational Low Frequency

Exposure Assessment

An information publication from the EMF NET project SSPE-CT-2004-502173 EMF-NET

Effects of the Exposure to Electromagnetic Fields: From Science to Public Health and SaferWorkplace. Coordination Action 8. Policy Support and Anticipating Scientific and Technological Needs


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Industry or the workplace in general is a very vastdomain of low frequency fields (LFs)

electromagnetic fields (EMFs) from which theextreme low frequency (ELF: 30 300 Hz) field

sources are important representatives. Since there is

still no clear definition about the borderlines of thefrequency ranges within the non-ionising frequency

spectrum the LFs where this guidance is dealing

with range from 0 Hz up to 20 kHz. Since every

electrical device, apparatus or machine is in fact an

ELF EMF source, there are so many sources that itis impossible to consider them all. Hence, the

guidance is only based on our experience with the

exposure assessment of the most importantindustrial high exposure LF sources:

electrical installation for electrolysis (0 Hz)

electrical arc furnace (50 Hz)

induction ovens (300 Hz 10 kHz)

arc welding (DC, AC, DC-ripple)

resistance or spot welding (50 Hz 20 kHz)

What is an Electromagnetic field?

The electromagnetic field(EMF) is a combinationof an electric and magnetic field propagating in a

wavelike manner..

.

It is characterised by wave length, frequency and

quantum energy The lower the frequency, the lowerthe quantum energy, the longer the wave length and

the longer the penetration depth.

LF classification in the electromagnetic

frequency spectrum?

EMFs are classified in a electromagnetic frequencyspectrum divided in the spectrum for non-ionising

radiation (0 Hz 3 PHz, E < 12.4 eV) and ionising

radiation (f> 3 PHz and E > 12.4 eV). Notice that

the energy of non-ionising radiation and certainlythe LFs is much to weak to ionise matter.

(source RF-guidance 2008)

After the electromagnetic frequency spectrum theLF EMFs are defined as being fields up to about

100 kHz. At this frequency the wavelength [= c/f(c = velocity of light = 3.10

8m/s in vacuum)] is

3 km. When we calculate the wave length for our

exposure assessment applications we find at 0Hz, 6000 km at 50 Hz, 1000 km at 300 Hz, 30 km

at 10 kHz and 15 km at 20 kHz. In this frequency

range workers are always exposed in near-field


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conditions where, in contradiction to the far-fieldexposure, the ratio of the electric (E) and the

magnetic (H) is different from the 377 ohms ()

which is characteristic impedance in free space.Hence the amplitudes of E and H may not be at

their maximum at the same time so that in the LF-

range E and H have to be measured and evaluated

separately..

Since E-field strength depends on the voltage andthe distance it is measured in volts per meter (V/m).

The strength of the magnetic field which is current

dependent is measured in amperes per meter (A/m).When taking into account the magnetic properties

(magnetic permeability ) of the propagation

medium the magnetic field (H) is defined as the

magnetic induction field (B = H) and measured intesla (SI units) or a subunit such as the microtesla

(T) or millitesla (mT).

Exposure guidelines

Though many safety and product standards for

protecting workers and the general public against

EMF have been published over the past decades thepresent guidance summarises only the ICNIRP

guidelines and statement for the static and time

varying EMFs on the one hand and the European

directive 2004/40/EC for workers on the other

hand.

ICNIRP (1994) guideline.

Deals with the protection against static magneticfields. It is the fundament of the Directive

2004/40/EC for the occupational action value of the

magnetic induction field (B-field) for frequenciesbelow 1 Hz. Note that the action values of the

directive are the same as the reference levels used

by ICNIRP. The reference levels used for testingthe compliance of the measured static B-field are:

200 mT working day averaged whole body

exposure. The current density by moving in this

field is estimated between 10 100 mA/m

2 T instantaneous whole body limit

5 T instantaneous limit for limbs

Notice that the natural static magnetic fieldgenerated by the dynamo effect of earth varies

between 30 and 70 T.

ICNIRP (1998) guideline

Deals with the protection of the general public and

workers against time varying EMFs up to 300GHz. A distinction is made between basic

restrictions and reference levels.

Basic restrictions for LF EMFs

Are based on the current density (J) induced in the

body.. J is a calculation metric which is based onan established heath effect.

In the ELF range 100 mA m-2 is considered as thethreshold current density limit for acute changes in

the central nervous system excitability and otheracute effects such as reversal of the visually evoked

potential. . Based on the precautionary principle a

safety factor of 10 is used so that occupational

fields up to 1 kHz should be limited to fields that

induce a Jless than 10 mA m-2 .

Basic restrictions for frequencies between < 1

Hz and 100 kHz

Frequency range Current density for headand trunk J (mA m-2 )

(rms)

Up to 1 Hz 40

1 4 Hz 40/f

4 1000 Hz 10

1 kHz 100 kHz f/100 (f in Hz)

Reference levels

Are measurements metrics which are provided for

comparison with measured values for compliance

testing. If reference levels are exceeded the bodyinduced current density has to be calculated and

compared with the basic restriction limits. If thereference values are exceeded it doesnt necessarilymean that the basic restriction is exceeded.

Reference levels for frequencies between

0 Hz and 65 kHz

Frequency range E-field

(V/m)

H-field

(A/m)

B-field

(T)

0 1 Hz 1.63 105 2 105

1 8 Hz 20 000 1.63 105/f2 2 105/f2

8 25 Hz 20 000 2 104/f 2.5 104/f2

0,025 0,82 kHz 500/f 20/f 25/f

0,82 2,5 kHz 610 24.4 30.7

2,5 65 kHz 610 24.4 30.7

ICNIRP statement (2003)

In the frequency range up to 100 kHz there are a

number of EMF-sources (EAS, metal detectors,

demagnetizers, welding equipment) with complexnon-sinusoidal magnetic field wave forms which


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5

Measurement equipment

As shown in the next figure, there are differentinstruments needed for performing EMF

measurements in the low frequency range.

Measurement equipment often used in

occupational exposure assessment

The commercial instruments shown in the figurecover the frequency range from 0 Hz 400 kHz.

They also make it possible to measure the wave

form as well as the harmonic content of the fieldunder test. Since the electric and magnetic fields

have to be measured and evaluated separately somemeters are equipped with exchangeable probes for

E and H fields while in others both sensors are

integrated in the same probe. Moreover, lowfrequency spectrometer blocks contain selectable E-

and H-spans covering a frequency range from 5 Hz

up to 100 kHz. Other instruments contain a

weighted frequency response so that the magneticinduction field can be displayed as a wide band

value or as a percentage of the reference level of a

selected exposure limit guideline. Morespecifications about these instruments can be found

on the website of the instrument dealers.

Industrial High LF Exposure sources

The EMF sources this chapter is dealing with range

from 0 Hz up to 20 kHz. Strictly speaking, they

consist of a mixture of static, ELF and IF field

sources and are therefore better defined as low

frequency than as ELF sources. The followingsources are discussed:

Electrical electrolysis (0 Hz)

Arc oven ( 50 Hz)

Induction ovens (300 Hz 10 kHz)

Arc welding (DC, AC, DC-rippel)

Spot welding (50 Hz 20 kHz

Sample of occupational LF sources

,


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6

Electrical installation for electrolysis

When an electrical DC current is passing a liquidsolution electrolysis by which chemically bonded

elements or compounds are separated occurs.

In manufactures this process is used in biginstallations which may cover a relatively big area.

ROW B ROW AC83A C63A C41A

C83B C63B C41B

C83C C63C C41C

C39A C19A C1A

C39B C19B C1B

C39C C19C C1C

C84A C64A C42A

C84B C64B C42B

C84C C64C C42C

C40A C20A C2A

C40B C20B C2B

C40C C20C C2C

ROW C ROW D

ELECTRICAL SWITCH ROOM

Ground plan of an electrolysis area with one measurement point per electrolysis cell

Since industrial electrolysis requires high DCcurrents (up to about 130 kA), workers might be

exposed to a relatively strong static magnetic

induction field which can vary from oneelectrolysis cell to the other with a facto 5.

C83AC83B

C83CMid

C84AC84B

C84C

C83-84

C63-64

C41-42

Mid

C39-40

C19-20

C1-2

4

6

8

10

12

14

16

18

20

B-field(mT)

West

South

18-20

16-18

14-16

12-14

10-12

8-10

6-8

4-6

Static B-field (mT) distribution over the electrolysis area

E

L

E

C

T

R

O

L

Y

S

I

S


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7

Operators of the electrolysis unit may be exposedto a DC B-field gradient varying from 4 to 20 mT.

If the induced current density by moving in a DC

B-field of 200 mT is estimated to be 10 100

mA/m, a simple calculation tells us then that the

induced current in the operators moving in 20 mT

(worst case exposure) electrolysis unit varies from1 to 10 mA/m. It is compliant with the 40 mA/m

basis restriction limit for head and trunk of ICNIRP

(1998) and the exposure limit values of thedirective 2004/40/EC. On the basis of the

interpretation of these exposure limits no direct

health effect is to be expected for workers ofelectrolysis installations. However, this statement

has to be interpreted with precaution because there

still is a lack on representative measurement data

which can be used as input data for performing

reliable dosimetrical calculations about induced

current density by workers of industrial electrolysisinstallation..

As for the possible indirect effect which may occurat a 5 mT threshold level, it is recommended that

carriers of pacemakers and other electronic devices

know that levels of 0.425 mT and average levels of

0.352 mT may be encountered.

Notice that this paragraph only deals with the static

field exposure of industrial electrical electrolysis

installations and not with medical (e.g. MRI),

pharmaceutical/biochemical (NMR-spectroscopy)

or other occupational static field applications.

Electric arc furnaces

Most modern electrical arc furnaces (EAF) convert

solid raw materials to liquid crude steel and refine itfurther in subsequent secondary steelmaking

processes.

The EMF exposure assessment of the EAF we are

dealing with is an ultra high power (AC) 96 MWfurnace operating at 50 Hz for the production of

liquid steel. The two following pictures illustrateshow the heart and the outside (switch room side)

of an EAF from which the EMFs were also

measured.

Heart of arc furnace

Switch room side of a arc furnace

The exposure assessment of the B-field from big

installations requires a good planning, prospection

and measurement design by which instantaneous

point measurements and field registration over a

certain time can be performed respectively.

The next figure illustrates the ground plan and themeasurement design of a switch room besides the

arc furnace.


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8

Ground plan of a switch room and measurement design

The next figure illistrates the current load of the installatioon per phase .

0

10

20

30

40

50

60

70

80

90

0,00 0,10 0,20 0,30 0,40 0,50 0,60 0,70

Time [h]

C

urrent(kA)

kA phase 1 kA phase 2 kA phase 3

Current load versus time

Switch boxes

Switch box

rdoor

: Measurementpoint

123

4

5

6

Switch boxes

Emdex Lite Monitor

Switchboxes

Operators desk

door


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9

Then the wave form and the harmonic content haveto be checked

Wave form

Harmonic content

Since the wave form is sinusoidal and no harmonics

above 1000 Hz are present a first view of the 3 Dexposure of the installation can be obtained by

means of the EMDEX II meter fixed on a linear

data acquisition (LINDA) wheel (Enertech Ltd).

electrisch onderstation oven 1 in werking

500 .. 545454 .. 500409 .. 454364 .. 409319 .. 364273 .. 319228 .. 273183 .. 228138 .. 18393 .. 13847 .. 932 .. 47

3 D map of B-field (T) of arc oven installation

In order to get insight in the real B-field strength in

space and time on the one hand and in t

Documents

Final Technical Report D49 FactSheet