magnetic fields from electrical appliances and devices · broadband spot measurements. broadband...

Introduction and BackgroundA major emphasis of research addressing potential health effects associated with power-frequency magnetic fields has been on assessing exposure to magnetic fields attributable to loads and their associated ground currents flowing on electrical transmission and distribution systems. Though these exposures can vary widely both over time and among residences, they are nonetheless pres-ent virtually all of the time. These exposures have remained a focus of attention for the scientific community largely because of the association reported in the epidemiologic literature between average residential fields above 3 to 4 milligauss (mG) and childhood leukemia. In the United States roughly 5% of residences have average magnetic fields of 3 mG or greater (Figure 1). There also remain uncertainties concerning associations of magnetic fields with other health endpoints, such as Alzheimer’s disease and miscarriage.

In addition to the ever-present magnetic fields in residences from the electrical power system, we also use a variety of electrical appliances and devices that in their immediate proximity can produce magnetic fields up to a thousand times (or more) greater than the 3 to 4 mG cutpoint used in the epidemiologic literature. However, electrical appliances and devices are wired in such a manner that the magnetic fields diminish very rapidly with increasing distance from the appli-ance. Thus, while background low-level exposures from outdoor lines and residential grounding occur steadily (Figures 2 and 3), exposure due to operation of appliances is usually sporadic at comparatively higher levels of exposure.

Resource Paper - Electric and Magnetic Fields (EMF) Health Assessment and Radio-Frequency Safety Program

Copyright © 2010 Electric Power Research Institute September 2010

Table of Contents Introduction 1andBackgroundMethods 5andProcedures

Broadband 5 SpotMeasurements

Waveform 6 Measurements Results 7 Broadband 7 SpotMeasurements

Waveform 9 Measurements

Conclusions 11

References 12

Magnetic Fields from Electrical Appliances and Devices

2 MagneticFieldsfromElectricalAppliancesandDevices

Through the 1990s and into the early part of the 2000s, a substantial amount of research has been published on field levels from appliances, their contributions to overall magnetic field expo-sure, and their possible relationship with childhood leukemia. Two efforts, worthy of note is the oft-cited study published in 1985 by Gauger in the IEEE literature in which magnetic field mea-surements were recorded for 25 electrical appliances and devices [1]. The other source of data,

We use a variety of electrical appliances and devices that in their immediate proximity can produce magnetic fields up to a thousand times (or more) greater than the background fields in our homes.

Figure1.AccordingtoEPRI’s1,000-HomeStudy,magneticfieldstrengthinU.S.residencesisdistributedroughlyaccordingtoaclassicbell-shapedcurve.About5%ofresidenceshaveanaveragemagneticfieldabove3mG(greenshadedarea)(Source:EPRIJournal,Spring2006).

Figure2.ResidentialMagneticFieldSources.Residentialmagneticfieldsresultfromprimary,secondaryandneutralcurrentsonthedistributionsystem,aswellasfromcurrentsinothergroundpathways,includingthewaterpipesandtheearth.

MagneticFieldsfromElectricalAppliancesandDevices 3

Figure3.MagneticFieldProfilefromaTransmissionLine.Inthisexample,themagneticfieldhasdroppedtobackgroundlevelsattheresidence,butthefieldswithintheresidencecanexceedbackgroundwithgreaterloadsatfurtherdistances.

EPRI’s “1,000-Home Study”, published in 1993, which characterized 22 sources. Figure 4 shows the profile summary for microwave ovens in 485 residences [2,3]. The National Cancer Institute conducted a study of childhood leukemia across nine states, reporting a 70% increased risk of

Figure4.MagneticFieldProfilesfromaSampleof485MicrowaveOvensinthe1,000-HomeStudy[2,3].L5referstolevelsexceededin5%ofcases;L95referstolevelsexceededin95%ofcases.Thetoptrace,labeledMAX,showsthemaximumreadings,andtheminimumreadings,labeledMIN,areshownatthebottomofthechart.


childhood leukemia for average residential fields greater than 3 mG. Follow-up analyses focused on exposures from appliances reported that appliances were a minor contributor to overall aver-age magnetic field exposure, and with regard to potential risk concluded, “the results of our appli-ance measurements do not provide much support for the hypothesis that the ELF magnetic fields produced by home appliances are causally related to increased leukemia risk in children.” [4]

The extent of the contribution to exposure from one’s mobility throughout the residence with the corresponding variability of background fields combined with the proximity to appliances and devices is seen in Figure 5, adapted from EPRI’s the “Long-Term Wire Code Study.” [5] This study explored residential exposure in depth in over 200 residences in eight diverse geographic regions of the United States. The area measurement (green curve) is the distribution of fields on meters located in a fixed position within each residence, while the personal exposure (blue curve) is the distribution of fields recorded on personal monitors worn by the study participants while at home. The chart reflects the fact that personal exposures are marginally, but not dramatically, greater than area measurements, with the difference likely accounted for by local sources of magnetic fields.

Since the previous measurement studies of the 1980s and 1990s a great variety of new electri-cal appliances and devices have been introduced into the consumer marketplace, and the EMF Health Assessment Program conducted a study to characterize the magnetic fields from a repre-sentative sample of these. A detailed presentation of the study can be found in EPRI Appliance Measurement Study. EPRI, Palo Alto, CA: 2010, 1020862 [6]. In addition, the report is bundled with the complete measurement data base in two files: (1) EPRI Appliance Measurement Study - Summary of Appliance Measurements 03-22-10.xlsx and (2) EPRI Appliance Measurement Study - Summary of Wavecorder Measurements 03-22-10.xlsx.

Appliances appear to be a minor contributor to overall average magnetic field exposure within a residence.

Figure5.EPRILong-TermWireCodeStudyResult.Percentofsamplewithpersonalandareameasurementatorbelowthefieldontheverticalaxis[5].


Methods and ProceduresMost of the measurements of personal appliances were performed in private residences and not in a controlled environment. This introduced several challenges to the measurement of these devices. Whenever possible, measurements of portable appliances were made in an area of the residence where the ambient magnetic field levels were low (under 1.0 mG) and stable. In ad-dition, the measurement area was sought that allowed unobstructed measurements up to 7 feet away from the device. However, some residences exhibited ambient fields that showed significant spatial and temporal variation. Many of the devices produced very low magnetic fields and their fields were dominated by the ambient magnetic field environment. In these cases, the technician made a best estimate of the contribution of the ambient field at each measurement location.

Related to the problem of fluctuating ambient fields was the difficulty introduced by the presence of other magnetic field sources in the vicinity of the appliance. This was particularly trouble-some for appliances which were too large to conveniently locate to a low-ambient location. For example, printers were often located near a computer that produced its own magnetic field. Large LCD television sets were typically located next to other entertainment system components such as DVD players or audio amplifiers. In these cases, the measurement technician estimated the magnitude of the confounding fields and their contribution to the ambient level.

Broadband Spot Measurements

An EMDEX II magnetic field meter (Figure 6) was used to perform these magnetic field mea-surements. The EMDEX II Magnetic Field Digital Exposure Meter is a computer-controlled, three-axis, AC exposure meter designed to measure the frequency range of 40-800 Hz. Each of the three-axis sensors measures the magnetic field and the on-board computer calculates a resultant field value (the resultant is comparable to a maximum field value and is calculated as

Figure6.TheEMDEXIIMeterUsedforBroadbandMeasurements(40-800Hz).


the square root of the sum of the squares for all three orthogonal axes (Br=SQRT[Bx 2 + By 2 + Bz 2]). Although the data are stored in the meter’s memory and can be downloaded to a personal computer for analysis, the EMDEX II was used as a survey meter and the measurements were manually recorded on a data form. The EMDEX II meter has a range of 0.1 milliGauss (mG) up to 3,000 mG (3 Gauss). The accuracy of the EMDEX II meter is ± 2%.

A series of spot measurements from the appliance was taken at the same distances used in the Gauger survey: 1.2”, 3”, 6”, 9”, 1’, 2’, 3’, 5’, and 7’ from the surface of the appliance having the highest magnetic field. A measurement jig was used whenever possible to insure that the distance measurements were as accurate and consistent as possible. The jig (Figure 7) was constructed of PVC pipe with slots for the meter at the preset distances of 1.2”, 3”, 6”, 9”, 1’, 2’, and 3’. A tape measure was used for distances beyond 3 feet.

In addition to the Gauger study distances, the user of the appliance was asked to identify a “user distance”, a typical distance between the user and the appliance when in normal use. A mea-surement was then taken at a distance equal to the distance of the appliance from the head or torso of the user, whichever distance was shortest. If a user was not available, the field technician estimated a user distance. At each of the Gauger locations and the user distance, the technician read the EMDEX II for several seconds and estimated the average reading from the three or four readings displayed during that time.

Waveform Measurements

The EMDEX WaveCorder (Figure 8) is a magnetic field spectrum analyzer that records several waveforms in the range of 30-3000 Hz. The data are stored in the meter’s internal memory and

Figure7.JigforMeasuringFieldsatPre-setDistances.


Broadband magnetic field measurements were taken of 164 devices in 39 appliance types…Appliances with electric motors such as massagers, power tools, and leaf blowers generated the strongest fields.

downloaded to a computer for analysis and display. A Fast Fourier Transform (FFT) was then performed on the WaveCorder data to produce a table of magnetic field flux densities by fre-quency.

A WaveCorder reading was taken at the “user distance”, the shortest distance from the appliance to the user’s head or torso. If an appliance produced a negligible field when measured with the EMDEX II, the technician sometimes took an additional measurement within 1” of the appli-ance to obtain fields large enough to characterize the output waveform of the appliance.

ResultsBroadband Spot Measurements

Broadband magnetic field measurements were taken of 164 devices in 39 appliance types. In the full EPRI report (1020862), Figures 3-7 through 3-49 show the magnetic field data for each of these appliance types as the magnetic field flux density plotted as a function of distance from the surface of the appliance.

Table 1 provides a summary of the broadband spot measurements taken with the EMDEX II; the shaded rows indicate those devices with magnetic fields at the user distance above background levels. Figures 9 and 10 provide examples of magnetic field profiles for two devices that recorded user-level fields above background.

As exemplified in Figures 9 and 10, the magnetic field of all devices in the survey showed the rapid field attenuation with distance characteristic of appliance-generated fields. Appliances with electric motors such as massagers, power tools, and leaf blowers generated the strongest fields. Newer semiconductor-based devices had very low fields unless they were equipped with an AC transformer power supply, cooling fan, or were motor driven (such as DVD players and blood

Figure8.TheWavecorderUsedforHarmonicAnalysis(30-3,000Hz).


1Compactfluorescentbulbballasttestedwith13-,18-,and26-wattbulbs2Waterheatermeasuredwithgasburneroffandon

Table 1. Summary of Broadband Magnetic Field Appliance Measurements

Appliance TypeNumber

of Devices

Magnetic Field (mG)

AC Adapters 3 1.4 – 863 0 - 7.5 0 - 0.8

Blood Pressure Monitors 4 4.2 - 39.6 0 - 0.3 0 – 0.2

Bluetooth Headsets 3 0 0 0

Coffee Grinders 3 60.9 – 779 0.3 – 6.5 0.8 - 40.9

Compact Fluorescent Bulbs 15 0 – 32.8 0 - 0.1 0 - 0.6

Compact Fluorescent Bulb Ballast 1 8.5 – 23.51 0 – 0.11 0 - 0.11

Computers, Desktop 3 3.8 – 68.9 0 -1.1 0.1 – 0.5

Computers, Laptop 4 0 – 5.1 0 0 – 0.1

Digital Cameras 3 0 0 0

Digital Photo Frames 5 0 0 0

Digital Video Recorders 4 0 – 29.6 0 – 0.2 0

Dimmer Switches 4 11.5 – 32.1 0 – 0.8 0 – 0.8

DVD Players 5 0 – 28.9 0 – 0.5 0

Electric Lawn Mower 1 1939 156 14.1

Electric Leaf Blowers 4 272 – 4642 17.1 – 155 28.3 – 61.5

Electric Toothbrushes 5 3.6 - 742 0 – 4.8 3.6 – 742

Electric Toothbrush Chargers 5 0 – 4.2 0 0

External Hard Drives 4 0.6 – 1.7 0 0

Gaming Consoles 10 0 – 215 0 – 0.5 0 – 0.6

GPS, Handheld 5 0 – 0.1 0 0

Hobby Tools 2 126 – 438 1.4 – 2.4 1.4 - 438

Hot Glue Guns 3 0 – 0.9 0 0

LCD Computer Monitors 4 0 – 4.5 0 0

LCD Televisions 4 1.1 – 3.9 0 – 2.5 0 – 0.6

Massagers/Massage Chairs 3 81.9 – 500 0.6 – 2.3 214 - 500

MP3 Players 5 0 0 0

Noise Cancellation Headphones 1 0 0 0

Paper Shredders 4 11.0 – 4841 0.5 – 102 0.5 – 33.4

Plasma Televisions 2 45.1 – 73.6 1.4 – 2.2 0 – 0.1

Power Tools – Corded 3 784 – 982 8.8 – 31.3 46.8 - 123

Power Tools – Cordless 6 9.0 – 227 0 – 2.2 0 – 13.7

Printers 5 0.1 – 6.2 0 – 0.3 0 – 0.3

Scanners 3 0.6 – 6.7 0 – 0.3 0

Security System Panels 3 0 – 0.3 0 0

Tankless Hot Water Heater 1 10.1 – 21.92 1.2 0.2

Track Lighting 5 0.2 – 4.0 0 – 0.3 0

Vacuum Cleaners, Personal/Car 3 75.5 – 2226 0.6 – 23.3 0.1 – 23.1

Wireless Game Controllers 11 0 0 0

Wireless Routers 4 0 – 0.5 0 0-0.3

1.2” (0.1 feet) 12” (1.0 feet) User Distance


pressure monitors). Several appliance types produced no measurable magnetic field:

Waveform Measurements

In addition to broadband flux density measurements, waveform measurements from 30-3000 Hz were taken of devices in the survey. Waveform capture was excluded for the following devices because their levels were too low to capture a significant waveform above the ambient magnetic field:

Nearly all appliances measured in the survey showed significant harmonic distortion. Appliances with motors such as massagers, hobby tools, vacuum cleaners, and power tools, generally showed the highest distortion. Wireless devices, such as wireless routers and wireless game controllers, generally did not produce magnetic fields high enough to accurately measure. These appliances operate in the UHF band beyond the 30-3000 Hz bandwidth of the EMDEX Wavecorder used to capture the waveform data.

Figure9.BroadbandProfileforCoffeeGrinder.

• Compact Fluorescent Bulb Brands 1, 4, and 5

• Digital Cameras• Digital Picture Frames• Digital Video Recorders• Electric Toothbrush Chargers• Handheld GPS• MP3 Players

Nearly all appliances measured in the survey showed significant harmonic distortion.

• Digital cameras• Digital photo frames• MP3 players• Noise calcellation headphones

• Noise Cancellation Headphone• Printers• Security System Panels

• Track Lighting• Wireless Routers• Wireless Game Controllers• Bluetooth Headsets

• Wireless game controllers• Bluetooth earpieces• Handheld GPS• Security system panels


Figure11.HarmonicContentofHandheldVacuumCleaner.

Figure10.BroadbandProfileforHobbyTool.

Figures 11 and 12 illustrate the spectra for two devices that recorded user-level fields above back-ground. Note that magnetic field flux densities are normalized to the maximum flux density recorded in the frequency range.


ConclusionsThe appliance types measured in this survey were selected based on public interest, availability, and coverage in the existing literature. Particular attention was paid toward devices and appli-ances available since the 1985 Gauger and 1993 1,000-Home studies study and their popularity since 2000.

Although as many devices as possible were measured in a controlled, low magnetic field ambi-ent location, a significant number of measurements were performed in private residences where the magnetic field environment could vary both temporally and spatially. In those cases the field technician performed a best estimate of the ambient field at the time and location of the measure-ment. Access to the appliance also varied so areas with the maximum field could not be uniformly characterized.

Like the Gauger study [1], this survey is not comprehensive in the scope of the types of appliances measured or in the makes and models in a given appliance type. This survey allows an order-of magnitude estimate of those devices not covered in the previous studies [2,3].

The field levels observed in this study do not appear to be unlike those observed in other studies. It is also likely that electric appliances and devices will continue to be a minor contributor to average residential magnetic field exposures, as discussed earlier.

One point to note is that harmonics induce electric fields and currents in the body in a manner proportional to frequency. Thus, a device rich in harmonics could produce significantly greater dose to the body, compared to a device with the same broadband field confined to the funda-mental.

Figure12.HarmonicContentofCordlessDrills.

The field levels observed in this study do not appear to be unlike those observed in other studies.

1021221 September2010

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References1. J. R. Gauger, “Household Appliance Magnetic Field Sur-vey”, IEEE Transactions on Power Apparatus and Systems, Vol. PAS-104, No. 9, September 1985.

2. EPRI. Survey of Residential Magnetic Field Sources, Volume 1: Goals, Results, and Conclusions, EPRI Technical Report 102759-V1, Electric Power Research Institute, Palo Alto, CA, June 1993.

3. EPRI. Survey of Residential Magnetic Field Sources, Volume 2: Protocol, Data Analysis and Management, EPRI Technical Report 102759-V2, Electric Power Research Institute, Palo Alto, CA, June 1993.

4. W. T. Kaune, M. C. Miller, M. S. Linet, E. E. Hatch, R. A. Kleinerman, S. Wacholder, A. H. Mohr, R. E. Tarone and C. Haines, Magnetic fields Produced by Hand Held Hair Dryers, Stereo Headsets, Home Sewing Machines, and Elec-tric Clocks. Bioelectromagnetics Vol. 23, 14-25, 2002.

5. R. F. Rankin, T. D. Bracken, R. S. Senior, R. Kavet and J. H. Montgomery, “Results of a Multisite Study of U.S. Resi-dential Magnetic Fields”. J Expo Anal Environ Epidemiol Vol. 12, No. 1, 9-20, 2002.

6. EPRI Appliance Measurement Study. EPRI, Palo Alto, CA: 2010. 1020862.

Robert Kavet

Electric Power Research Institute

H. Christopher Hooper

Enertech Consultants

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