What are Ambient ELF and RF Levels?
Average Residential Exposures to ELF (Power Frequency Fields)
A nation-wide survey in the United States by Zaffanella et al (1993) collected
engineering data on sources and levels of 60 Hz electric power magnetic fields that exist
inside residences in the United States.
Approximately 1000 residences were randomly selected for the survey. The goals were
to 1) identify all significant sources of magnetic field, 2) estimate for each source the
percentage of residences where magnetic fields exceeded specified levels, 3) to determine
the relation between magnetic field and sources and 4) to characterize the field varations
The median field was identified as 0.5 mG and the average field was 0.9 mG. Thus, this
confirms that average residential magnetic fields based on the 1000-home study is less
than 1 mG.
Appliances produce magnetic fields but these diminish rapidly with distance (at 1/R3),
Power lines generally produce the largest average residential magnetic field when the
entire living space of a residence and a 24-hour period are considered. Power line
magnetic field exceeds 1 mG in 17%, exceed 2.5 mG in 9.5% and exceed 5 mG in 0.3%
of all the residences surveyed.
Zaffanella (1998) conducted measurements to characterize typical EMF exposure levels
in persons living in the United States - a study called the 1000-Person Study. Table A-
S.2 shows that about half of all people in the US have EMF exposures at home under
0.75 mG; in bed are 0.48 mg; at school 0.60 mG; at work 0.99 mG; and 0.87 mG is the
median EMF exposure for an average 24-hour day.
Table S.2 Descriptive Statistics for Different Activity Periods
Number of Valid
In Sweden, Mild et al (1996) report that overall mean residential ELF exposures are 0.4
mG, and in Norway are 0.13 mG.
Average Occupational Exposures to ELF
Average occupational exposures in commercial office buildings are 1-2 mG or less and
have been reported fairly consistently across numerous studies of exposure assessment
(Table 1). Powerline and electrical workers have higher average occupational exposures
from 10 mG to 16.6 mG.
Table A-2: Average Occupational Exposures to ELF
EMF RAPID Program – Questions and Answers, NIEHS,
EMF RAPID Program Engineering Project #3 Executive
Summary, May 1996
Electric and Magnetic Field Fundamentals (EPRI Resource Paper, March 1994)
Typical magnetic fields in offices
1 – 2 mG
Power line workers
Occupational EMF Exposure Assessment (EPRI Resource Paper, February 1994)
Office Worker Comparison Group
All Occupationally Exposed Utility Workers
Table 7 – Other Studies Cited
Bracken Study (1990)
Deadman Study (1988)
Bowman Study (1992)
0.9 – 1.8 mG
Limits on Operation of Sensitive Electronic Equipment
Companies that manufacture or use equipment in nanotechnology and biotechnology and
found 1.0 mG is generally the limit for proper operation of electron beam devices (mass
spectrometers, scanning electron microscopes, lithography, etc) used in these
technologies. Ten (10) milligauss (mG) is the EMF limit for normal computers – above
10 mG can introduce “computer jitter” and other problems.
What are Ambient Radiofrequency Radiation/Microwave Levels?
Prior to the rapid development of wireless communications for personal and business
usage, RF power density levels were primarily related to AM, FM and television
broadcasting signal in both urban and rural areas of the United States. Microwave
frequencies used for wireless communications were negligible.
Original extra-planetary sources of microwave radiation were infinitesimally small, on
the order of a billionth of a microwatt per centimeter squared (10 –12 uW/cm2). Human
evolution took place without any appreciable exposure to microwave radiation from
background sources. The human body has no evolutionary protection against microwave
radiation, as it does for ultraviolet radiation from the sun (Johannson, 2000). Wireless
voice and communications have introduced unprecedented levels of public exposure in
the last decade.
Mantiply (1997) measured and reported common sources and levels of RF in the
environment. He identified areas near cellular base stations on the ground near towers to
be from 0.003 to 0.3 µW/cm2. Background level ambient RF exposures in cities and
suburbs in the 1990’s were generally reported to be below 0.003 µW/cm2.
Hamnerius (2000) reported that ambient RF power density measurements in twelve (12)
large cities in Sweden were roughly ten times higher than in the United States for
equivalent measurement locations by Mantiply in 1978 (when no cellular phone service
existed in the US). He reported a total mean value of 26 measured sites in the study was
0.05 µW/cm2 and the median value was 40 µW/cm2. An office location with a base
station nearby at about 300 feet distance tested 150 µW/cm2. A train station with
antennas mounted indoors tested at about 3 µW/cm2. Both indoor and outdoor ambient
RF power density measurements showed high variability depending on proximity to
Sage Associates reported on microwave frequency RF power density levels at outdoor
locations both near and far from wireless antenna sites in the United States (Sage, 2000).
Within the first 100-300 feet, power density levels have been measured at 0.01 to 3.0
µW/cm2. Elevated RF power density levels from a major wireless antenna site can often
be detected at 1000 feet or more. Power density levels away from wireless antenna sites
measure between 0.001 µW/cm2 to 0.000001 µW/cm2.
Vegetation often reduces signal (and therefore the reach of elevated RF exposures) but
dry building materials used to visually screen wireless sites do not appreciably diminish
signal transmission. Therefore, many sites that are “out-of-sight” because of stealth
design can still produce elevated RF levels in nearby areas where people live, work and
go to school. For purposes of this evaluation, a 10 dB attenuation has been incorporated
to take building material shielding effects into account.
Electric Power Research Institute (EPRI) 1994. Electric and Magnetic Field Fundamentals -
EPRI Resource Paper, March 1994.
Electric Power Research Institute (EPRI) 1994. Occupational EMF Exposure Assessment - EPRI
Resource Paper, February 1994.
Hamnerius I. 2000. Microwave exposure from mobile phones and base stations in Sweden.
International Conference on Cell Tower Siting, June 7-8, 2000. Sponsored by the University of
Vienna and LandSalzburg, Salzburg, Austria.
Hansson Mild et al. 1996. Measured 50 Hz Electric and Magnetic Fields in Swedish and
Norwegian Residential Buildings. IEEE Transactions on Instrumentation and Measurement.
Mantiply E. et al., 1997. Summary of measured radiofrequency electric and magnetic fields (10
kHz to 30 GHz) in the general and work environment. Bioelectromagnetics 18:563-577.
NIEHS, 1996. EMF RAPID Program Engineering Project #3 Executive Summary, May 1996.
NIEHS, 2002. EMF RAPID Program – Questions and Answers.
NIEHS, 2002. EMF RAPID Program – Questions and Answers on EMF, June 2002.
Sage C. 2000. International Conference on Cell Tower Siting, Salzburg, Austria June 7-8, 2000
Zaffanella LE. 1993. Survey of residential magnetic field sources. Vol 1. Goals, results,
and conclusions. (Report no. TR-102759-VI). Palo Alto, CA: Electric Power Research
Zaffanella LE, Kalton GW. 1998. Survey of Personal Magnetic Field Exposure Phase II: 1000-
Person Survey.EMFRapid Program Engineering Project No.6 Lee MA: Enertech Consultants.