United States
Environmental Protection
Agency
Region 10
Radiation Program M/S 533
1200 Sixth Avenue
Seattle WA 98101
Air & Hazardous Materials February 1979
&EFK
Population Exposure to
VHP
Broadcast Radiation
In the Seattle and Portland
Metropolitan Areas
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POPULATION EXPOSURE TO VHP BROADCAST RADIATION
IN THE
SEATTLE AND PORTLAND METROPOLITAN AREAS
Edward Cowan*
and
Richard A. Tell**
July 1979
U.S. Environmental Protection Agency - Region 10
Air & Hazardous Materials Division
Waste Management Branch
1200 Sixth Avenue
Seattle, Washington 98101
*Radiation Representative, EPA - Region 10
**Physicist, Electromagnetic Radiation Analysis Branch
Office of Radiation Program, P.O. Box 18416,
Las Vegas, Nevada 89114
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Population Exposure to VHP Broadcast Radiation
in the
Seattle and Portland Metropolitan Areas
Introduction
The U.S. Environmental Protection Agency (EPA) conducts a nationwide
program of monitoring and assessment of radiofrequency (RF) and
microwave (MW) levels as they relate to the potential for hazards in
the environment. EPA began measuring RF and MW radiation in urban
areas in 1975 as part of a program to determine the need for standards
to control environmental radiofrequency exposure. Current population
exposure levels will be a major factor in determining if guidance is
needed to limit population exposure. Seattle, Washington and Portland,
Oregon were among 15 metropolitan areas surveyed for environmental
levels (Table 1). This report provides the results of environmental
measurements for the Seattle and Portland metropolitan areas and
presents estimates of population exposure based upon the
measurements. Measurements were made in urban areas because sources
are concentrated in and around regions of high population density.
Broadcast bands are the principal bands of interest with other bands
contributing insignificantly to general environmental levels of
radiofrequency radiation.
The measurement system is installed in a 27 foot van. The system
consists of seven antennas, and a scanning spectrum analyzer
interfaced to a minicomputer data acquisition system. Antennas are
mounted on a telescoping mast which is elevated about six meters above
ground level. Signals from the antennas are detected by the spectrum
analyzer then digitized and processed by the minicomputer with data
correction and analysis routines. A computer algorithm uses these
measurements to estimate the broadcast exposure for census enumeration
districts within the metropolitan boundaries.
Nonionizing Radiation Sources
Virtually everyone is exposed to radiofrequency waves. Nonionizing
sources of interest include the following:
- radio and television broadcast stations
- radars
- satellite communications system earth terminals
- point to point microwave communications
- mobile communications systems
- microwave ovens
- industrial heating equipment
-1-
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This paper is concerned only with nonionizing radiation from radio and
television broadcast radiation. Ionizing radiation is a different
kind of radiation which is produced by medical, dental, and industrial
x-ray equipment and by radioactive materials which emit particles such
as protons, betas, neutrons and alphas.
Previous studies have determined that FM radio and VHP and UHF
television transmissions are responsible for almost all of the RF and
MW exposure in the general environment. Table 2 summarizes the
broadcast bands for which data is presented in this report. Though
field intensity measurements were also performed in the AM standard
broadcast band (0.54-1.6 MHz), these data are not considered here
because of significantly decreased absorption of these lower
radiofrequencies by the human body. No UHF television stations
operate in Seattle or Portland. The frequency range of the surveyed
sources was from 54 to 216 megahertz.
Effects of Nonionizing Radiation
Radiofrequency radiation can be absorbed by tissue and can interact
with biological systems. Absorption depends on the radiation
wavelength and its relationship to the physical shape, size and
orientation of the body to the incident electromagnetic field,
electrical characteristics of the body tissues at specific frequencies
and the intensity of the radiation. Localized heating or nonuniform
absorption can occur in humans because the complex tissue structure
absorbs energy differently in different parts of the body.
Two kinds of effects on humans due to exposure to radiofrequency
radiation are usually discussed: thermal effects from high-level
exposures, and possible low-level or "nonthermal" effects.
Thermal effects, normally thought to result from irradiation with
power densities above 10,000 microwatts/square centimeter (uW/cm2)
involve tissue heating with the possibility of thermal damage. They
may include increased body temperature and resulting heat stress,
cataract formation, and testicular effects. (Table 3)
Low-level effects are a subject of controversy. Effects of exposure
to 1,000 (uW/cm2) or less have not been well documented. In fact, all
U.S. scientists do not agree that they exist. Some Russian scientists
believe that they occur, but as a result of nonthermal effects or
effects which occur without an increase in tissue temperature. Their
views are based on animal research and statistical studies of workers'
exposure histories and medical records. Considered to be mainly
central nervous system effects, symptoms attributed to low-level
nonthermal exposure include headache, weariness, dizziness,
irritability, emotional instability, partial loss of memory, loss of
appetite, cardiovascular effects, blood chemistry changes, changes in
respiration, and possible genetic effects.
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While U.S. scientists are skeptical of the conclusions of the Eastern
European experts, there has been little research conducted in the U.S.
involving long term exposures to low-level microwave and
radiofrequency radiation. Some U.S. scientists believe that the
effects observed, could result from non-uniform energy distributions
and very small localized temperature changes in the body.
Exposure Standards
At present, there are no Federal standards or guides for controlling
environmental levels of radiofrequency waves in the U.S. There is an
advisory standard for occupational exposure issued by the Occupational
Safety and Health Administration. This advisory standard specifies an
upper limit of 10,000 uW/cm2 for exposure durations greater than 6
minutes and allows higher values for shorter durations. (Table 4)
The U.S.S.R has the most conservative standards with an occupational
limit of 10 uW/cm2 and a general environmental exposure limit of one
uW/cm2. Canada, Great Britian and West Germany have occupational
exposure standards similar to those of the U.S. Canada is considering
a general population standard of 1,000 uW/cm2. The U.S.S.R.'s more
restrictive occupational and general population standards are
presumably based upon the occurrence of nonthermal effects while the
U.S. and most Western European standards are based upon thermal
effects without consideration of possible nonthermal effects.
Population Exposure in Seattle and Portland
Population exposure to nonionizing radiation means the number of
people exposed to various levels of power density. To obtain
population exposure, two kinds of information are required; the
distribution of the population and the distribution of power densities
in the area of interest. The population is obtained through the use
of the Census Bureau's Census Enumeration Districts (CED) and power
densities are measured using EPA's electromagnetic radiation analysis
van. Measurements were taken at 35 sites in metropolitan Seattle and
at 38 sites in Portland. The measurement data was subsequently used
in a computer modeling program to estimate the exposure which would
exist at each CED in Seattle and Portland. Resulting exposure at each
CED is assumed to apply to all the population within each CED. Final
results are presented in terms of the accumulative fraction of the
population which are exposed to certain power density levels. Summary
field study information is presented in Table 5.
Table 6 lists each measurement location in Portland with the determined
power density. Table 7 does the same for the Seattle area. The
geographic location of all measurement locations are shown for
Portland and Seattle on Maps 1 and 2. The location numbers in Tables
6 and 7 correspond to location numbers used on Maps 1 and 2.
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Table 8 shows the fraction of Portland population exposed as a
function of power density for FM radio, high VHP, low VHP television
transmissions and the total exposure from all of these. Table 9 does
the same for the population of Seattle. It can be seen that FM radio
broadcast transmissions create the highest ground levels of field
intensity and is clearly most responsible for overall exposure.
Conversely, the high VHP and low VHP television transmissions make
relatively small contributions to the total power density.
The results of the Seattle and Portland survey are presented in Table
10. Three different indices can be used to discuss the results. The
first is the median exposure, that level to which 50 percent of the
population are exposed less than and 50 percent are exposed to more
than. The other indices are the percent of the population exposed to
less than 1 uW/cm2 and the percent of the population exposed to more
than 10 uW/cm2. In Seattle the median exposure level is 0.007 uW/cm2
which is exactly the median level for 10 other cities previously
surveyed. The median exposure level for Portland is higher but is
still only 0.020 uW/cm2. In both Seattle and Portland over 99 percent
of the population is exposed to less than 1 uW/cm2. Only a small
fraction of the population is exposed to more than 10 uW/cm2, 0.001
percent in Seattle and 0.016 percent in Portland.
The highest power density level in Portland was measured at site
number 13. This level, 153 uW/cm2, was determined directly under a
transmitter so the exposure levels in nearby houses would be somewhat
lower. Site number 36 taken on Cougar Mountain had the highest power
density level in the Seattle survey. The power density level of 87
uW/cm2 was not included in the Seattle results because the site was
outside the area used for calculating population exposure. Cougar
Mountain was a specific source type of measurement because of its
location and the few people affected.
Summary
Environmental power densities have been measured and the population
exposure estimated for the Seattle and Portland metropolitan areas.
FM radio transmitters are the most significant environmental sources
of nonionizing radiation.
In Seattle, 99.81 percent of the population is exposed to less than 1
uW/cm2 and only 0.001 percent of the population is exposed to over 10
uW/cm2.
In Portland, 99.70 percent of the population is exposed to less than 1
uW/cm2 and only 0.016 percent of the population is exposed to over 10
uW/cm2.
There are no Federal standards or guides for controlling envirnomental
levels of radiofrequency waves in the U.S. However, the environmental
exposure levels for over 99 percent of the population in Seattle and
Portland would meet the very restrictive U.S.S.R. standard of one
uW/cm2.
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Table 1. Environmental Surveys
Survey Period Sites Surveyed
Portland 7/25-8/5 1977 38
Seattle 7/10-7/21 1978 35
Table 2. Frequency Range of Measured
Broadcast Bands
Frequency* Use
54-88 Low VHF Television Broadcast
88-108 FM Broadcast
174-216 High VHF Television Broadcast
* Megahertz (millions of cycles per second)
-5-
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Table 3
EFFECTS OF NONIONIZING RADIATION
Pain Threshold in Humans
830
150
100
60
oc
UJ
tL
5
P
z
UJ
O
LU
GC
<
D
O
CO
oc
i
25
13.0
10.0
Cataractogenic Threshold in Rabbits
» Warmth Sensation Threshold in Humans
Aversive Reaction in Rats
— Warmth Sensation Threshold in Humans
Thermal Effects
Dominate
5.0
Area of Uncertainty
For Transient
Behavioral Changes
1.0
OC 0.3
D
0)
O
Q. 0.2
X
111
0.1
0.02
0.01
0.001
Possible
Nonthermal Effects
Avoidance Behavior in Rats
.Evoked Auditory Response Threshold in Humans
• Evoked Auditory Response Threshold in Cats
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Table 4
NONIONIZING RADIATION STANDARDS
10.0'
.U.S. Standard for
Occupational Exposure
OC
UJ
UJ
O
UJ
OC
<
D
O
(/>
OC
UJ
Q.
5.0
1.0
FDA Standard for
• Microwave Oven
Leakage
0.1
UJ
OC
D
(/)
O
Q.
X
UJ
0.01
USSR Standard for
Occupational Exposure
0.001
USSR Standard for
' General Population Exposure
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Table 5. Summary of Field Study Information
No. Field
No. of Stations
CED's Population Strength Values FM
Seattle 1315 872,442 820 16 2
Portland 1194
818,040
816
12
VH Total
20
18
No. of
Sites
35
38
Radio-frequency detection van on display at University of Washington.
-8-
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Table 6 Power Density Measurements for Portland Area
(microwatts per square centimeter)
Site Location Number Total Power Density
1 .0109
2 .0101
3 .0258
4 .0651
5 .0334
6 .1090
7 .0549
8 .0149
9 .0775
10 .0991
11 .0726
12 .1090
13 153.7900
14 .5000
15 1.0600
16 .1660
17 .1140
18 .5330
19 16.4600
20 .5620
21 .1190
22 .2850
23 .1200
24 .1300
25 .1070
26 .0270
27 .0272
28 .0440
29 .0757
30 .0158
31 .0426
32 .0236
33 14.2600
34 .0172
35 .0826
.0295
.0686
.0239
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Table 7 Power Density Measurements for Seattle Area
Site Location Number Total Power Density
1 .0872
2 .1450
3 .3200
4 .1650
5 .1730
6 .1650
7 .1910
8 .4330
9 1.4000
10 6.5300
11 22.7400
12 1.1900
13 .4340
14 .0175
15 .0315
16 .0685
17 .1170
18 .0576
19 .0555
20 .0264
21 .0224
22 .5010
23 26.6000
24 .8660
25 6.0400
26 .0195
27 .0280
28 .0949
29 .0093
30 .1180
31 .1930
32 .0207
33 .0270
34 .1130
35 .0337
36 87.9000
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MAP 1: MEASUREMENT LOCATIONS IN THE PORTLAND AREA
Scale in Miles
12345
O
Less than one microwatt
per square centimeter
Greater than one microwatt
per square centimeter
Greater than five microwatts
per square centimeter
•O
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MAP 2: MEASUREMENT LOCATIONS IN THE SEATTLE AREA
Greater than one microwatt
Greater than five microwatts
per square centimeter
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FRACTION OF POPULATION EXPOSED
AS A FUNCTION OF POWER DENSITY
Q>
cr
00
.99
.95
.90
.80
.70
3 .60
&••>
°- .40
U.
O .30
z
O .20
.10
.05
.01
PORTLAND
0
o
1
n
A
D
n
A
B
S
A Total Exposure
D FM Radio
O High VHF TV
• Low VHF TV
.00001
.0001 .001 .01 .1
POWER DENSITY
(Microwatts per square centimeter)
10
100
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FRACTION OF POPULATION EXPOSED
AS A FUNCTION OF POWER DENSITY
0)
z
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Table 10. Population Exposure Results for
Seattle, Portland, and Ten other Cities
Location
Median Exposure
Percent of Pop
Exposed to Less
Than 1 microwatt
Percent of Pop.
Exposed to More
than 10 microwatt
Seattle
Portland
Ten Cities
.007
.020
.007
99.81
99.70
99.33
.001
.016
__ _
Radiofrequency detection equipment and minicomputer inside equipment van
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REFERENCE
1. Tell, R.A. and E.D. Mantiply, "Population Exposure to VHP and UHF Broadcast
Radiation in the United States," Technical Note, ORP/EAD 78-5, U.S.
Environmental Protection Agency, Las Vegas, NV
June 1978
2. Athey, T.W., R.A. Tell, N.N. Hankin, D.L. Lambdin, E.D. Manitiply, and
D.E. Janes, "Radiofrequency Radiation Levels and Population Exposure
in Urban Areas of the Eastern United States," Technical Report,
EPA-520/2-77-008, U.S. Environmental Protection Agency, Silver Spring,
MD, May 1978
3. Tell, R.A., "A Measurement of RF Field Intensities in the Immediate
Vicinity of an FM Broadcast Station Antenna," Technical Note, ORP/
EAD-76-2, U.S. Environmental Protection Agency, Silver Spring, MD,
January 1976.
4. Tell R.A. and P.J. O'Brien, "An Investigation of Broadcast Radiation
Intensities at Mt. Wilson, CA." (ORP/EAD-77-2), U.S. Environmental
Protection Agency, Las Vegas, NV, April 1977.
5. Tell, R.A., "An Analysis of Radiofrequency and Microwave Absorption
Data With Consideration of Thermal Safety Standards," Technical Note,
ORP/EAP-78-2, U.S. Environmental Protection Agency, Las Vegas, NV.
April 1978.
6. Radiological Quality of the Environment in the United States, 1977.
U.S. Environmental Protection Agency, Office of Radiation Programs,
Washington, D.C. 20460.
7. Radiation Protection Activities 1977. U.S. Environmental Protection
Agency, Office of Radiation Programs, Washington D,C. 20460
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