EPA-520/1-73-004
ASSESSMENT OF POTENIAL RADIOLOGICAL
HEALTH EFFECTS FROM RADON
IN NATURAL GAS
U.S. EN VI RON MENTAL PROTECTION AGENCY
Office of Radiation Programs
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ASSESSMENT OF POTENTIAL RADIOLOGICAL
HEALTH EFFECTS FROM RADON
IN NATURAL GAS
Raymond H. Johnson, Jr.
David E.Bernhardt
Neal S. Nelson, D.V.M.
Harry W. Galley, Jr.
November 1973
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Radiation Programs
Washington, D.C. 20460
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FOREWORD
The Office of Radiation Programs carries out a national program
designed to evaluate the exposure of man to ionizing and nonionizing
radiation, and to promote development of controls necessary to protect
the public health and safety and assure environmental quality.
Within the Office of Radiation Programs, the Field Operations
Division conducts programs relating to sources and levels of environ-
mental radioactivity and the resulting population radiation dose.
Reports of the findings are published in the monthly publication, Radi-
ation Data and Reports, appropriate scientific journals, and Division
technical reports.
The technical reports of the Field Operations Division allow
comprehensive and rapid publishing of the results of intramural and
contract projects. The reports are distributed to State and local
radiological health programs, Office of Radiation Programs technical
and advisory committees, universities, libraries and information serv-
ices, industry, hospitals, laboratories, schools, the press, and other
interested groups and individuals. These reports are also included in
the collections of the Library of Congress and the National Technical
Information Service.
Readers of these reports are encouraged to inform the Office of
Radiation Programs of any omissions or errors. Comments or requests
for further information are also invited.
W. D. Rowe, Ph.D.
Deputy Assistant Administrator
for Radiation Programs
iii
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ABSTRACT
Natural gas contains varying amounts of radon-222 which becomes
dispersed in homes when natural gas is used in unvented appliances.
Radon decays to alpha-emitting daughter products which can contribute
to lung cancer when inhaled and deposited in the respiratory system.
For the average use of unvented kitchen ranges and space heaters, the
tracheobronchial dose equivalent to individuals was estimated as 15
and 54 mrem/yr, respectively, or 2.73 million person-rems/yr to the
United States population. A review of exposure conditions, lung model
parameters, dose conversion factors, and health effect factors indi-
cated this population dose equivalent could potentially lead to 15
deaths a year from lung cancer. This represents only 0.03 to 0.08
percent of normal lung cancer mortality. Since control of radon levels
in gas would cost over $100 million for each reduction of one health
effect, it was concluded that a requirement for such controls would not
be cost effective on a national basis.
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CONTENTS
FOREWORD iii
ABSTRACT.. ... .. v
INTRODUCTION..... .'....' ... .............. 1
Radon in natural gas 1
Radon: Health effects 1
Approach 1
Scope and objectives 3
RADON CONCENTRATION IN NATURAL GAS
At production wells 3
In distribution systems 7
Gas processing. 7
Transmission lines 10
Storage. 10
Radon data 11
Radon concentrations in the home 15
POPULATION EXPOSURE 16
Exposure conditions 16
Daughter products. 16
Working level .. 17
Degree of equilibrium 18
Attached daughter products 18
Critical mode of exposure 18
Lung models 19
Free ions 21
Dose conversion factors. 22
Quality factor 24
Conditions for this analysis 25
Postulated exposure conditions 25
Dose to an individual 26
Radon dose ... 28
Beta-gamma dose. 28
Average dose equivalent to the United States population 29
POTENTIAL HEALTH EFFECTS 31
Dose equivalent to health effect conversion factors..... 31
Health effects estimate 34
vii
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CONTENTS
Page
DISCUSSION 36
Review of uncertainties. .' 36
Interpretation of estimated health effects 38
Current guides and recommendations 38
Natural background radon 40
Normal excess mortality from respiratory cancer. 42
Conservatism in health effects estimate 44
ALTERNATIVE METHODS FOR REDUCING HEALTH EFFECTS. 46
Analysis of cost for control of radon in natural gas..... 46
Comparison of radon control costs to reduction in potential
health effects 50
CONCLUSIONS 51
REFERENCES 53
FIGURES
Figure 1. Model for estimating potential health effects from radon
in natural gas 2
Figure 2. Normal operations on natural gas from production to
consumption 8
Figure 3. LNG facilities and gas production areas in the United
States 12
TABLES
Table 1. Radon-222 concentrations in natural gas at production
wells 5
Table 2. Gas wells, marketed production, and use of natural gas by
regions and states 6
Table 3. Liquified Petroleum Gas 9
Table 4. Radon-222 concentrations in natural gas distribution
lines *.. 14
viii
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TABLES
Table 5. Summary of dose conversion factors for radon and
radon daughters .. 23
Table 6. Exposure conditions and possible variation in parameters
for analyzing dose from radon in natural gas 27
Table 7. Dose equivalent to U.S. population from radon in natural
gas 30
Table 8. Organ dose ratios and absolute risk ; 33
Table 9. Corrections to adjust estimated health effects for
different exposure conditions 35
Table 10. Guides for radon-222 concentrations in air above natural
background. 39
Table 11. Comparison of indoor radon concentrations from natural
gas with the ICRP No. 2 guide of 0.33 pCi/1 41
Table 12. Atmospheric radon-222 concentrations from all uses of
natural gas in metropolitan areas 43
Table 13. Conclusions on estimates of excess mortality from radon-
222 in natural gas used in unvented kitchen ranges and
space heaters 45
Table 14. Cost summary for natural gas storage (1972 basis) 49
Table 15. Annualized cost estimate for storage of natural gas....... 49
ix
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ASSESSMENT OF POTENTIAL RADIOLOGICAL HEALTH
EFFECTS FROM RADON IN NATURAL GAS
INTRODUCTION
Radon in natural gas
Radon-222 is a radioactive gaseous daughter product of radium-226
found in naturally occurring uranium minerals throughout the earth's
crust. This heavy inert gas permeates porous geological formations and
is collected along with methane in production wells for natural gas.
When this natural gas is useji in unvented appliances, such as kitchen
ranges and space heaters, the combustion products and radon are released
within the home. This radonll constitutes an additional source of radia-
tion in the home which has not been adequately evaluated for potential
health effects.
Radon; Health effects
The hazard to persons working in radon-contaminated atmospheres was
first associated with radiation exposure to uranium miners in the 1920*s.
Since then the correlation of radon daughter concentrations and the inci-
dence of lung cancer among miners has prompted stricter controls on radon
and radon daughters and many studies on radon dosimetry. These studies
concluded that the primary concern for exposure to radon was from inhala-
tion and deposition of radon daughters which release their alpha decay
energy to tissues of the respiratory system.
The potential for health effects resulting from the use of natural
gas containing radon was not recognized until about 1966. Even now,
this source of radon exposure has had only limited evaluations. However,
studies still in progress at the National Environmental Research Center-
Las Vegas, Oak Ridge National Laboratory, and the University of Texas
Health Science Center at Houston have provided information which can be
used to place the question of health effects from radon in natural gas in
perspective. Data from these studies will be reviewed here along with
an analysis of radon dosimetry as a summary of present knowledge on po-
tential radon exposure and consequences resulting from use of natural
gas.
Approach
Estimates of potential health effects from radon in natural gas will
be derived following a sequential analysis outlined in figure 1. This
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^"Rn concentration
Well location,
depth and pressure
seasonal
variations
production
rate,
Na,lr' Storage
1 i
Gas use, heating, cooking,
etc.
Use rate, venting, dilution
volume,
222Rn concentration
1
Daughter product equilibria,
free ion fraction, ventilation
rate, aerosol properties,
dispersion and removal processes
Home use
wells Transport natural gas
i
1
Radon doslmetry
Critical mode of
exposure
Critical organ
Population statistics
Geographical gas use
Dose
person-rem
Morbidity
Mortality
Health
> risk
Gas processing Radon concentration Dose equivalent to
and distribution, to dose conversion health effects
mixing from factors conversion factors
different well
fields '
I
|
' 1
' 1
SOURCE i EXPOSURE i POPULATION
TERM | CONDITIONS | EXPOSURE
0 : © ; 0
1 i
HEALTH
EFFECTS
0
Figure 1. Model for estimating potential health effects from radon In natural gas
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figure shows a generalized model for assessing health effects and some
of the factors to be considered. Reference to this model will assist
in relating these factors for a logical approach to calculating and
interpreting the significance of potential health effects from radon.
Scope and objectives
This review will primarily cover the estimation of health effects
from release of radon in dwellings through use of natural gas in unvented
cooking ranges or space heaters. The significance of these estimates
will be interpreted in terms of reasonable variations which could be
expected in the assumptions used in the model for calculating health
effects. Particular attention is given as to how conservative the vari-
ous parameters may be which enter into the analysis.
items:
This report is intended to provide information on the following
(a) radon-222 concentrations in natural gas,
(b) natural gas usage and exposure conditions,
(c) critical mode of exposure and radon dosimetry,
(d) population dose,
(e) potential health effects and interpretation of
significance, and
(f) alternative radon controls and comparison of costs
for reduction in potential health effects.
RADON CONCENTRATION IN NATURAL GAS
At production wells
Bunce and Sattler (1) conducted an extensive study in 1965 to
determine the radon-222 concentrations in natural gas production wells
in the San Juan Basin area of Colorado and New Mexico. They sampled
over 300 wells and found an average radon level of 25 pCi/1. Individual
wells were sampled with levels as high as 160 pCi/1 and as low as 0.2
pCi/1. .A review by Barton (2) showed that 1,250 wells in Texas, Kansas,
and Oklahoma had average radon concentrations of 100 pCi/1 or less. Con-
centrations in these wells varied from 5 to 1,450 pCi/1.
Paul and coworkers (3), with the United States Geological Survey,
determined the radon content of about 500 producing gas wells in the
Texas panhandle area. They observed levels from about 10 to 520 pCi/1
at standard temperature and pressure. They also noted that the radon
content is nearly constant for a given well under normal production con-
ditions. A significant change in radon concentration was measured in
several wells on restarting after being shut down during the summer.
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The radon values rose sharply with initial production and leveled off
after removal of about twenty to fifty thousand cubic feet of gas (less
than one hour's production for wells normally producing two to three
million cubic feet daily). They interpreted this behavior, along with
an analysis of transient gas flow and steady state conditions, as an
indication that radon originates in the immediate vicinity of the bore
in most wells.
Seasonal variations in radon content of natural gas were also ob-
served by Bunce and Sattler (1). They measured radon in 11 wells in
three geologic strata over 3-month intervals from May to October 1964.
The earlier samples, corresponding to reduced summer production, had
average levels of 22.5 pCi/1. The later samples, in September and
October, had levels of about 17.8 pCi/1. They attributed these differ-
ences mainly to changes in the rate of gas production (or usage).
Many measurements have also been made of radon in gas in conjunc-
tion with tests for nuclear stimulation of natural gas. Data from
Boysen (4), Gotchy (5), and NERC-LV (6) on studies of the Rulison and
Rio Blanco gas stimulation projects indicate the average radon level for
wells in the Rulison area during 1969-1970 was 25.4 pCi/1 (range 11 to 45
pCi/1). McBride and Hill (7) reported that levels of radon-222 in pre-
shot samples-for project Gasbuggy had an average value of 19.4 pCi/1.
Postshot samples indicated that nuclear stimulation did not raise radon-
222 concentrations in neighboring wells above the naturally occurring
levels.
The NERC-LV Technical Support Section (8) also sampled natural gas
from two trunk lines serving all 28 producing gas wells within 5 miles
of Project Gasbuggy from November 1969 to November 1970. The average
radon level was 29.4 pCi/1 with a range of 12 to 59 pCi/1. These results
were essentially the same as before Project Gasbuggy and confirmed that
nuclear stimulation does not increase radon levels. Some seasonal vari-
ation was apparent with the higher levels occurring between March 31 and
September 15, 1970.
A summary of data on radon-222 concentrations in natural gas at
production areas is given in table 1. The Gulf Coast region of Louisiana
and Texas has the lowest average radon concentration at about 5 pCi/1.
Upper Texas, Kansas, Oklahoma, and California have average levels up to
about 100 pCi/1. When all the data are averaged a level of 37 pCi/1 is
obtained. However, many individual wells could have radon levels 10 to
20 times this value. In addition, the average level calculated here
does not account for the relative gas production volumes from different
regions of the country (see table 2).
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Table 1. Radon-222 concentrations in natural gas at production wells
Area
Radon-222 level, pCi/1
Average Range
Reference
Colorado
New Mexico
Texas, Kansas,
Oklahoma
Taxas Panhandle
Colorado
Project Gasbuggy Area
Project Gasbuggy Area
California
Gulf Coast (Louisiana,
Texas)
Kansas
Wyoming
Overall
average
25 0.2-160
<100 5-1450
10-520
25.4 11-45
15.8-19.4
29.4 12-59
1-100
5 _
100
i n ________
xu ^^
37
1
2
3
5-7
7
8
10
11
11
11
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Table 2. Gas wells, marketed production, and use of natural
gas by regions and states (2) ...
Division and State
United States <>
I~ F*.l-~t
Connecticut
Maine, Sew Bansphlre.
Vermont
Massachusetts
Rhode laland
Middle Atlantic
New Jersey
Hew Tork
Pennsylvania
Eaat north Central
Illinois
Indiana
Michigan
Ohio
Hlaconsln
Heat north Central
Ions
Kansas
Minnesota
Missouri
Bebraska
Horth Dakota
South Dakota
South Atlantic
Delaware
Florida
Georgls
Maryland, District of
Columbia
Horth Csrollna
South Carolina
Virginia
Heat Virginia
East South Central
Alabama
Kentucky
Mississippi
Tennessee
West South Central
Arkansas
Louisiana
Oklahoma
Texaa
Mountain
Arizona
Colorado
Idaho
Montana
Bevada
Bew Mexico
Utah
Wyoming
Psclflc
Alasks
California
Hawaii
Oregon
Washington
Producing
mils
117.300
0.
0
0
0
0
14.58
0
0.52
14.06
7.47
0.01
0.04
0.25
7.17
0
7.37
0
7.32
0
0
0.02
0.03
0
17.82
0
0
0
0.01
0
0
0.12
17.69
6.21
0
5.89
0.31
0.01
35.84
0.74
8.16
6.94
20.00
9.60
0.01
0.76
0
0.45
0
7.67
0.07
0.64
1.11
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The relative numbers of gas producing wells by regions and states
are also shown in table 2. It is worthwhile to note that about 36 percent
of the gas wells are located in the West South Central region (Arkansas,
Louisiana, Oklahoma, Texas) which produces over 82 percent of this coun-
try's natural gas. Furthermore, most of this gas is consumed outside of
this region. Therefore, the low radon concentrations reported for the
Gulf Coast may be especially significant when one considers the large con-
tribution (40-60 percent) which this region produces for the national
supply of natural gas. Likewise, the production regions of higher radon
concentration in Texas, Kansas, Oklahoma, and California may produce only
15 to 20 percent of this country's natural gas. At the present time,
however, insufficient radon measurements have been made in these states
to correlate radon levels and production volumes. Therefore, it is not
possible to determine an average radon level for the country that is
weighted for" production volumes from different regions of the country.
In distribution systems
The concentration of radon in distribution systems near points of
consumer use is determined by a number of factors which include (12):
(a) concentration at the wellhead,
(b) production rate,
(c) pipeline dilution,
(d) gas processing,
(e) pipeline transmission time, and
(f) storage time
The relationship of these factors is shown in figure 2. The normal
operations on natural gas which may affect radon concentrations will be
reveiwed briefly in the following sections.
Gas processing
Natural gas processing facilities receive gas from the well fields
which contains from 55 to 98 percent methane and various percentages of
other heavier hydrocarbons (ethane, propane, butane), as well as carbon
dioxide, nitrogen, helium, and water vapor. This gas is processed to
give a marketable fuel with the following average properties (volume
percent)T
Methane Ethane Propane Butane COp N£
84 6 2 1 1 8
Primarily, the processing plant removes water vapor, propane and longer
chain hydrocarbons as fractionated liquid products. The heavy hydro-
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00
Production
well fields
Cities
Gas processing
plant
Distribution
Center
Cross country transmission line .
Liquified petroleum
gas (LPG)
Storage
Underground reservoirs
pressurized tanks
liquified natural gas (LNG)
Figure 2. Normal operations on natural gas from production to consumption
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carbons are then bottled under pressure for sale as liquified petroleum
gas (LPG) with properties shown in table 3.
Table 3. Liquified Petroleum Gas (13)
Component
Methane
Ethane
Radon
Propane
Butane
Percent
of LPG
0.2-2.0
2.4-9.5
88-96
0.5-1.5
Boiling
Point (°C)
-161.5
- 88.3
- 61.8
- 42.2
- 0.5
This processing is of particular interest because radon tends to
separate with LPG due to its boiling point which is between that of pro-
pane and ethane (table 3). Removal of LPG (primarily propane) can remove
30 to 75 percent of the radon from natural gas (10). Since virtually all
natural gas receives this processing before distribution to customers,
significant reductions in radon concentrations may be effected by this
aspect of routine gas industry operations.
On the other hand, the transfer of radon from natural gas into LPG
may result in a shift of potential health effects (from radon) to users
of LPG as the critical population at risk. The significance of radon in
LPG is presently under study by Gesell (14). As part of this study,
weekly measurements of radon in LPG have been made in the Houston, Texas
area which indicate annual average concentrations from 25 to 180 pCi/1
for six LPG retailers. Similar measurements in other parts of Texas and
California gave maximum radon concentrations in LPG from 287 to 1,288
pCi/1. The maximum levels for other southern states ranged from 1.9 to
119 pCi/1. Other data at a gas processing plant in New Mexico indicate
that the inlet natural gas radon level of 56 pCi/1 was increased to 1,100
pCi/1 in the separated propane.1 These high levels of radon indicate a
need to evaluate the use of LPG in the same manner as presented here for
natural gas.
1Bernhardt, D.E., "Radon in Natural Gas ProductsSan Juan Plant,"
Memorandum to C.L. Weaver. August 31, 1973.
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Transmission lines
As the natural gas moves from the production wells through processing
plants and through trunk line systems, it becomes mixed with gas from many
wells. For example, Jacobs, et al. (12) estimated that gas leaving
San Juan Basin of New Mexico came from over 6,000 wells. Consequently,
the production from wells with higher radon levels becomes diluted. The
mixing and dilution process becomes more significant as the gas is piped
over longer distances and is combined with gas from widely separated pro-
duction areas.
In addition to mixing and dilution, as the gas is moved cross-country
through transmission lines, the transmission time allows radon to decay
away. Pipeline transit rates apparently vary from 10 to 12 miles per hour
(15). Thus, a transit distance of about 1,500 miles would allow time for
radon decay by 1 to 2 half-lives (half-life 3.83 days). This distance is
typical of many transmission lines from Texas and Louisiana production
well fields to eastern distribution centers in New York, Pennsylvania,
Ohio, West Virginia, and west to California.
According to the American Gas Association these main transmission
lines are normally intended to be operated at full capacity. This
requires -that well field production rates and gas processing be maintained
nearly constant. Pipeline pumping varies only about 3.5 percent during
the year. The constant production rate is balanced with seasonal demands
for gas by storage operations.
Storage
Storage reservoirs are located close to market areas to meet peak
demands of the winter season which could require more gas than normal
transmission line capacity. These storage reservoirs are usually former
depleted oil or gas wells. At present there are 330 storage reservoirs
with a total capacity of 5.6 trillion cubic feet or about 29 percent of
the 1971 net marketed production of 19.5 trillion cubic feet (9, 16).
The possible extent of storage is significant because the additional
time could allow more radon to decay away. Within the storage reservoirs
additional mixing would also tend to reduce fluctuations in the radon
levels. On the other hand, the reduction in radon with storage time may
be partly offset by further accumulations of radon from storage in
depleted well reservoirs. However, there is no information available to
evaluate this possibility.
Furthermore, it should be noted that most of the depleted well
storage capacity is presently being utilized, and the costs for developing
10
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additional underground reservoirs are leading to more economical storage
by liquefaction of natural gas.
The construction of liquified natural gas (LNG) facilities is rapid-
ly increasing. There are presently 46 LNG facilities operating or under
construction in the United States with capabilities for liquefaction,
LNG storage, and regasification as noted in figure 3 (17). These facil-
ities in conjunction with 46 satellite facilities, which only have storage
and regasification capability, are operated for "peak shaving," i.e.,
supplementing the normal supply of pipeline gas during periods of peak
winter demands. The liquefaction of natural gas results in a volume
reduction of nearly 600 fold thus allowing economical storage. The stored
LNG must be regasified prior to introduction into regular natural gas
lines for distribution. Liquefaction does not alter the chemical proper-
ties of the gasj however, LNG storage could allow a significant reduction
in radon by radioactive decay. As of June 1973, LNG storage capacity
existing or under constructions in the United States is about 6.6 x 1010
ft3 or 0.34 percent of the annual net marketed production (9, 17).
While the bulk of the gas may be transported over long distances
and undergo a significant delay in transmission and storage times, there
are many users close to production areas where these times could be short.
Some closed systems do not use storage but vary production and processing
rates to meet seasonal demands. Then high winter demands result in short
times. This situation is partially compensated by shorter times for
radon accumulation in the production wells at higher production rates.
Short pipeline times may also be significant for another group of
gas users near production fields. Apparently gas companies allow farms
through which gas lines pass to tap into the pipeline. These "farm taps"
allow use of natural gas directly from the wells with no processing and
a minimum delay time (12).
Radon data
Barton (2) and Klement et al. (18) noted that very little data are
available-for radon levels at consumer use points. However, radon has
been measured in gas distribution lines and that data will be reported
here as estimates of concentrations at .points of gas usage.
Barton et al. (19) concluded that a nationwide natural gas sampling
program would be Impractical, presumably on the basis of analytical costs
and the priority need for the information. Instead they sampled the gas
supplied to several large metropolitan areas including Chicago, New York
City, and Denver. Two sources supplying each of the market areas were
sampled and the average pipeline concentration was 20 pCi/1. This
average included measurements on radon in a high pressure line from
11
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N5
LNG facilities
Gas production areas
Figure 3. LNG facilites and gas production areas in the United States
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Kansas to Denver which had a level of 95 pCi/1. Excluding this value,
the average level was 10 pCi/1.
The Rocky Mountain Natural Gas Company (RMNG) has measured radon
in its city main pipelines in the Colorado towns of Aspen, Glenwood
Springs, and Delta. Average levels were about 25 pCi/1. The RMNG
distribution system is closed, i.e., it neither supplies nor obtains
gas from other systems.
McBride and Hill (7) reported radon levels of about 8 pCi/1 at two
metering stations on the way to Las Vegas and Los Angeles. Levels were
also measured in natural gas at the Farmington Laboratory in New Mexico,
and the average radon content was about 45 pCi/1.
Gesell2 measured radon in a distribution main in Houston weekly
from November 1972 to January 1973. The average radon level was 8
pCi/1.
A summary of available data on radon in natural gas distribution
lines in gas consumption areas is shown in table 4. These data indicate
that average radon levels at points of use are about 50 pCi/1 or less.
It should be noted, however, that the highest levels occur in the
Colorado and New Mexico areas which are closest to sources of natural
gas. The coastal regions farthest away from natural gas sources have
the lowest radon levels. This can be attributed to pipeline trans-
mission time and storage which allows significant radon decay. Also,
gas may be mixed and diluted with that from several supply systems while
in transit to areas such as New York City or Chicago.
It should be noted that variations in radon levels at consumer use
points could also be attributed to production rates as a function of
seasonal gas use. For example, the highest levels occurred in the winter
during peak use periods, presumably due to shorter transport times.
For dose calculations, Barton et al. (19) selected a value of 20
pCi/1 for radon concentrations at consumer use points. However, this
figure does not adequately reflect the higher levels found near the
natural gas fields in Kansas, Colorado, New Mexico, and the Texas pan-
handle regions. For these areas a level of 50 pCi/1 should be used.
The value of 20 pCi/1 could be used as a reasonably conservative estimate
for radon levels in natural gas for the remainder of the United States.
More definitive information will be available in the future from
three studies now in progress. One study is being sponsored by the
Resell, T.F., Unpublished data, University of Texas, School of
Public Health, Houston, Texas, 1973.
13
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Table 4. Radon-222 concentrations in natural gas distribution lines
Area
Chicago
New York City
Denver
West Coast
Colorado
Nevada
New Mexico
Houston
Overall
average
Radon-222
Average
14.4
1.5
50.5
15
25
8
45
8
23
level, pCi/1
Range Reference
2.3-31.3 19
0.5-3.8 1
1.2-119 19
1-100 10, 19
6.5-43 (a>
5.8-10.4 7
10-53 1
1.4-14.3
(a\
Bernhardt, D.E., Radon-222 concentrations in natural gas,
Memorandum to D.T. Oakley, April 2, 1973.
, T.F. op. cit.
14
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Colorado Interstate Gas Company (GIG) to investigate radon concentra-
tions in its own system and that of the Rocky Mountain Natural Gas
Company.3
ORNL is also conducting a related study in cooperation with several
gas transmission companies to analyze monthly samples for several metro-
politan areas (19). A similar study is being performed by Dr. Thomas
Gesell1* of the School of Public Health, University of Texas, for a con-
sortium of gas companies.
Radon concentrations in the home
Determining the radon-222 concentrations in natural gas at the
point of use is only part of the analysis. The next step is to deter-
mine radon concentrations within the home resulting from use of natural
gas in various appliances. Measurements on this source of radon have not
actually been made in homes, however, estimates may be made by determining
the quantity of gas consumed, the fraction of combustion products vented
inside the home, and the home dilution factor (based on house volume and
ventilation or rate of exchange with outside air).
When natural gas is burned in the home, the radon and daughter
products are released within the dwelling. Mixing is not instantaneous
but, as inhabitants move about, it is assumed they are exposed to the
average concentration level. This level is affected by the quantity of
gas consumed and the fraction of combustion products vented inside the
home. These factors, in turn, depend on what the gas is used for, i.e.,
heating, or ranges, water heaters, refrigerators, clothes dryers, and
other non-heating appliances. Gas furnaces are normally vented outside
the home, although Jacobs et al. (12) have assumed non-ventilated heating
to represent a "worst" case for assessing nuclide concentrations in gas
from nuclearly stimulated wells. On the other hand, gas ranges are
normally vented into kitchen areas and initial studies by Barton (19)
take this source as the main contributor of radon-222 from natural gas
usage in homes. Data compiled by Gesell5 indicate that in addition,
there is also widespread use of unvented space heaters. These heaters
are commonly used in the warmer states where permanent heating systems
are not-necessary.
Dilution by air within the home is another factor affecting radon
concentrations. This factor is a function of house volume and the rate
at which the air is changed by ventilation with outside air. A conserva-
ative assumption is that the air inside the dwelling unit will be
changed once per hour. Barton et al. (19) have calculated the accumula-
tion of radon and daughters for air change rates of 0.25 to 2.0 per hour.
3Bernhardt, op. cit. (April 2, 1973).
^Gesell, op. cit.
5Gesell, op. cit.
15
-------
Kaye (20) determined after consultation with home ventilation experts
that present information does not justify choice of a single value for
annual average air change rates for United States homes. He did indi-
cate that the rate probably was between 0.5 and 1.5 changes per hour.
The same range of air changes per hour was derived by Handley and
Barton (22) from a literature survey of studies on home ventilation
rates. United Nations data (21) suggests that air change rates are
typically from 2 to 5 changes per hour. Yeates, et al. (23) measured
ventilation rates in several single family dwellings as part of a study
on radon-daughter concentrations in the urban environment. They observed
air change rates from 1 to 3 per hour for basements and from 2 to 6 per
hour for upper levels in homes. Multiple family dwellings had air change
rates from 5 to 9 per hour.
Since no measurements have been made on radon concentrations
resulting from use of natural gas in homes, there are no data to report
here. However, the preceding parameters will be used to calculate radon
concentrations later in the section on postulated exposure conditions.
POPULATION EXPOSURE
Exposure conditions
Several factors have to be considered when assessing the exposure
conditions resulting from release of radon within a home, such as (24):
(a) the amount of daughter products dispersed in the air,
which is a function of radon concentration and the
extent of decay product equilibrium, and
(b) the proportion of daughter products present as free
ions or attached to various size aerosol particles.
Evaluation of these parameters provides a model for estimating the
radon daughter product mixture of the atmosphere in terms of radioactive
decay, dispersion, and removal processes (25).
Each of these factors will be reviewed in further detail preparatory
to a discussion of the critical mode of exposure to radon.
Daughter1 products
Radon-222 decays to daughter products according to the following
scheme:
16
-------
0.7 MeV B
26.8 min
21l*Bi (RaC) 3-3 MeV g 2ltpo (RaC.y
19.7 min
7.687 MeV «. 210pb (RaD) 0.02 MeV B^ 2ioB1 (RaE)
164 ysec 21 yr
The radon daughters of primary concern in determining radiation
exposure are RaA, RaB, RaC land RaC*. However, the total dose is due
mainly to alpha emissions firrom RaA and RaC*. For dose estimates, the
alpha energy contribution o£ RaC1 follows almost instantaneously from
RaC. Also RaB, as a beta emitter, does not contribute significantly
to the total dose, but it is included in decay calculations to determine
the activity of RaC (RaCf).
Working level
The concentration of radon-222 and daughters is customarily given
in terms of a working level (WL). One WL is the total potential alpha
energy from any combination of the short-lived radon daughters (through
RaC* that will impart 1.3 x 105 MeV per liter of air (26). This level
was intended to be one, "which appears to be safe, yet not unnecessarily
restrictive to industrial operations (27)." This was the philosophy of
the United States Public Health Service when establishing the working
level as a standard for the uranium mining industry in 1957. Since that
time a better understanding of radon dosimetry and health effects has led
to development of stricter recommendations by the Federal Radiation Coun-
cil and the Environmental Protection Agency (28-31).
A standard of 4 working level months per year (WLM) is now recom-
mended by EPA (30). One WLM is the exposure resulting from inhalation
of air containing a radon daughter concentration of 1 WL for 170 working
hours. The same exposure for 2,040 hours gives one working level year
(WLY). Continuous exposure for a full year of 8,760 hours gives 8,760/
2,040 =4.3 times the exposure for 1 WLY.
The working level is often related to radon activity by calculating
the number of radon daughter disintegrations required to impart 1.3 x
105 MeV of alpha energy. The relationship is defined by Evans (32) as:
1 WL = 100 pCi/1 of radon-222 in secular equilibrium with
daughter products RaA, RaB, RaC (RaC*).
17
-------
The working level definition is often misunderstood as a unit of
radon concentration. However, it is a concentration of only the short-
lived daughters RaA, RaB, RaC (RaC1). It can be applied to any mixture
of these decay products. The conversion of 1 WL per 100 pCi/1 of radon-
222 applies only for secular equilibrium of radon and daughters.
Degree of equilibrium
When radon is dispersed into a clean air atmosphere, it will reach
radioactive secular equilibrium with the above daughters after 3 hours
(27). However, the extent of decay product equilibrium in the usual
home is markedly affected by the rate of ventilation. Exchange with out-
side air results in removal of daughter products from the atmosphere
within the home. Removal will also occur by deposition of daughter pro-
ducts on surfaces. Jacobi (33, 34) noted that these removal processes
prevent the establishment of radioactive equilibrium between radon and
its daughters. He therefore includes a factor for degree of nonequili-
brium in calculating the potential alpha energy concentration from daugh-
ter products in air according to the WL definition.
Attached daughter products
A fraction of the daughter products will also become attached to
dust particles and condensation nuclei in the air. For example, radon
decay to RaA results in a single polonium ion which moves like an elec-
trostatically charged gas molecule until it collides with an aerosol
particle, where it remains attached (35, 36). The attached RaA no longer
follows the diffusional behavior of a gas but moves with other aerosol
particles. The proportion of ions attached to aerosols and those which
remain free or uncombined will reach an equilibrium for each decay product
(24).
Studies by Raabe (36) showed that the attachment rate of radon
daughters to aerosols is proportional to the surface area of the particles.
Increased humidity also affects the proportion of daughter ions which
become removed by attachment to water molecules. Measurements by Wachsman,
et al. (37) show a dramatic decrease in radon daughters in home atmospheres
following rainy weather.
Critical mode of exposure
The primary concern for exposure to radon is from inhalation and
retention of radon daughters which release their alpha decay energy to
tissues of the respiratory system. The specific respiratory areas most
susceptible to damage have been determined by evaluating the areas showing
injury (lung cancer) in uranium miners (38, 39). Such cancers predomi-
nantly appear in the area of the large bronchi. These are believed to
18
-------
occur as a result of ionization from alpha particles in the basal layer
cells of the upper bronchial epithelium.
Some controversy still remains unresolved as to the most important
mode of exposure within the lung. The issue in question is whether
local, or "hot spot," doses are more effective introducing cancer in
the respiratory system than is uniform radiation exposure to the entire
epithelium (26). Lung cancers usually arise at bifurcations of the
bronchial tree, which are areas of the pulmonary structure where radio-
active materials could become lodged. Altshuler et al. (25) concluded
that this contribution to lung dose could not be treated quantitatively
because of insufficient knowledge of localized tissue exposures. However,
recent animal studies by Grossman et al. (40) indicate that a higher loca-
lized dose from alpha particles was not more carcinogenic than the same
amount of energy delivered uniformly to surfaces of the airways in the
respiratory system. Consequently, today most investigators assume the
most important mode of exposure is from uniform alpha irradiation of the
epithelium. This lung exposure is modeled by a series of tubes of known
dimensions containing a uniform concentration of radon daughters.
Lung models
Since tissue dose cannot be measured directly, the rad dose to the
critical cells of the tracheobronchial tree is derived from the lung
models. Such models allow calculation of dose as a function of environ-
mental conditions, anatomy, respiratory physiology, and radon dosimetry
as follows:6
(a) Characteristics of the ambient atmosphere affecting
deposition of radon daughters in the respiratory
system (25, 35, 36);
1. Degree of equilibrium between radon and daughter
products.
2. Relative concentrations of radon daughters.
3. Adsorption of radon daughters to aerosols.
4. Fraction of unattached daughter products or
free ions.
5. Abundance of dust particles or aerosol carriers
for .attached daughter products, and their size
distribution.
6. Ventilation rate or air change rate.
Of these characteristics, numbers 3 and 5 are probably the most
important.
The reader is referred to the literature for detailed discussion
of these variables which is beyond the intended scope of this paper.
19
-------
(b) Biological factors influencing site and deposition of
radon daughters in the lung include (25. 35, 38, 39. 41);
1. Method of breathing, i.e., mouth breathing vs.
nose breathing.
2. Rate and depth of respiration, tidal volume.
3. Diameter and surface area in different regions of
the lung.
4. Changes in diameter of the tracheobronchial tree
during respiration.
5. Angles and irregularities in the tracheobronchial
tree.
6. Fraction of daughter products deposited in different
regions of the respiratory system.
7. Clearance rates of deposited dust and other materials.
8. Retention, translocation by ciliary transport, mucus
flow, and elimination.
9. Pile-up or collection of mucus impregnated with radon
daughters at bifurcations in the tracheobronchial tree.
10. Effect of fumes, smoke, and other aerosols on lung
clearance rates.
11. Medical status of the individual, e.g., some
pneumonias and perhaps smoking can cause radical changes
-=iri clearance rates and lung retention of dust.
Factor numbers 2 and 11 are especially important.
(c) Dosimetric factors influencing the dose due to deposited
daughters (24, 25, 39, 42);
1. Location of radiation-sensitive epithelial basal
cells or precancerous cells at risk.
2. Variable thickness of mucus blanket covering bronchial
epithelium.
3. Thickness of bronchial epithelium.
4. Variation in distance of daughters from epithelial surface.
5. Energy loss characteristics of alpha particles of
different energies, depth of penetration.
6. Dose rate effect, if any, for alpha particles.
7. Appropriate quality factor to use.
The location of the precancerous cells at risk is the most important
factor. A review of radon daughter exposure and respiratory cancer
effects indicates that the epithelial basal cells in the walls of the
bronchi are the biological target (39). The integrity of the basal cells
determines the continued integrity of the epithelial tissue (42). Of
these cells, 70 percent are considered near enough to the epithelial
surface to be within the range of alpha particles of radon daughters (39).
20
-------
The range of alpha particles in soft tissue for RaA is about 47
microns and about 71 microns for RaC* (25). The distance from the upper
mucus layer (the area of initial deposition of radon daughters) to basal
target cells is from 36 to 63 microns for minimum to median epithelium
thickness (25. 42). The average distance from source to biological tar-
get is believed to be about 60 microns (21). This means that few of the
basal cells receive any alpha radiation from RaA. Studies reported by
Morken (43}, however, indicate that much of the deposited radon daughters
becomes dissolved in the mucus layer and absorbed in the epithelial tissue.
This means more basal cells are within the range of alpha particles f romf
RaA but the dispersion within the epithelial tissues of both RaA and RaC
results in a lower dose to the basal cells than when these daughters are
retained in the narrow zone of the mucus layer.
The International Commission on Radiological Protection (ICRP) Task
Group on Lung Dynamics noted that the estimated average whole lung dose
for radon and daughters is also a measure of dose to specific areas, such
as the trachea (38). This was taken as justification for the concept of
calculating dose to the lung based on a lung model.
It was concluded by ICRP (38) that the properties of the carrier
aerosol are the major determinants for deposition of radon daughters in
the lung. However, these properties do not appear to be important in
determining the clearance of radon daughters, mainly, because radon
daughters appear to be weakly attached to dust particles which become
solvated in the lung thereby enhancing removal processes. Even short
half-lived daughters are rapidly removed from the lung with removal
half-times of 10 to 30 minutes.
Fvee ions
The fraction of daughter ions which remain free, or unattached to
surfaces or aerosols, is defined for RaA ions in particular as (44);
_ RaA atoms uncombined
RaA atoms in equilibrium with radon
This fraction is related to the aerosol content of home atmospheres such
that f_ increases as the ventilation rate increases or as.the aerosol
content decreases.
ICRP (38) took particular note of the work of Chamberlain and Dyson
(45) which regarded the radiological importance of free ions of RaA.
The uncombined fraction of RaA, f_, was found to preferentially deposit
in the upper passages of the respiratory system where uranium miners*
lung cancers develop. This factor was taken into account in the ICRP
formula for occupational radon MPCa,
21
-------
= 3 x 10"6
1 + lOOOf cm3
The listed 40 hour per week MPCa for radon-222 was given as 30 pCi/1 on
the basis of an uncombined RaA fraction of 0.1 as determined by Chamberlain
and Dyson (45). George et al. (44) measured _f values for New Mexico
uranium mines and found an average of about 0.03. They concluded that
higher values of 0.05 to 0.10 were found only in relatively clean air
(particle concentrations of 1 x 101* cm"3 or less). Hague et al. (24)
estimated that the f_ value is 0.35 for an aerosol spectrum of 0.006 to
0.1 microns and a concentration of 3 x 101* cm"3, typical of a country
atmosphere. This value was then used to calculate radon daughter doses
in living accommodations and industrial premises. Jacobi (35) plots f_
versus aerosol concentration and this curve gives an f_ value of about
0.25 for air with lO1* particles per cubic centimeter, which he concludes
is a reasonable mean value for ordinary room and city air.
Barley and Pasternack (46) also noted that unattached RaA ions deposit
with 100 percent efficiency in the tracheobronchial region. Subsequent
decay to RaC gives rise to a substantial fraction of the total alpha
dose. Jacobi (34) concluded that about half of the free ions of RaA
which are inhaled become deposited in the nasopharynx region and the other
half in the tracheobronchial region. Further studies by Jacobi (47) indi-
cate that the uncombined fraction of the total potential alpha energy,
f_p_, (for RaA -F RaC ) is a better parameter to observe. This is because
the inhaled potential alpha energy deposited in the tracheobronchial.
region is directly related to fp and is independent of ventilation rates
in the working or living area.
Dose conversion factors
The calculation of dose from exposure to a given concentration of
radon-222 in pCi/1 or WL requires that values be assumed for many vari-
ables as described in the preceding sections. A variety of values have
been reported over the years as each investigator attempted to charac-
terize particular exposure conditions. In addition, improvements in lung
models and better understanding of the behavior of radon daughters have
led to refinements in the .calculations. Consequently, the literature
contains a wide range of factors for converting radon concentrations to
dose. A summary of these factors is presented in table 5 based on reviews
by Bernhardt7 and Barton et al. (19). This summary is presented here to
show the range of values from which one may select according to assumptions
on exposure conditions for a particular situation.
The dose conversion factors tabulated in table 5 are not directly
comparable to each other for several reasons, the most important of which
7Bernhardt, D.E., "Radon-222 Dose Caluclations," Memorandum to the
Files, ABR-LV, March 15, 1973.
22
-------
Table 5. Summary of dose conversion factors for radon and radon daughters
Radon-daughter
equilibria
10, 10, 10, 10
4Z free RaA
10,6.3,2
42 free RaA
10,9.6,4
8.5Z free RaA
Nonequilibriua ,
little free RaA
Honequllibriun
Honequilibriua,
1-2Z free RaA
ii
10,10,6,4
10,10,10,10
25Z free RaA
10,9,6.4 W>
8.51 free
RaA
H
10,9,5.3.5
10,9.6,4
Exposure
conditions
0.3ii particles
Rn-100 pCi/1 annual
occupational exposure
it
ii
WLM - 170 hra.
500 hours per
month in hones :
Clean air MPAI of
4 WLM(c)
High aerosol cone.
0.05-0. 2pm particles
Normal room air
change- 1 hr"1,
10,000 particles
cm-3, 0.09um
10 pCi/l-Rn
Natural radiation
exposure, 0.09um
0.1 pCi/l-Rn
0.3um particles
Rn-100 pCi/1,
occupational
exposure
ii
Adequately
ventilated room,
6,000 hr/yr
>0.1pm particles
Rn-100 pCi/1
Lung model. Dose ( actor {)
critical tissue rads/year
Welbel model (A)
15 1/min, segmental
bronchi
' ii
Landahl model
Epithelial base
cells of large
bronchi
Bronchial
epithelium
Revised ICRP model
(38), bronchial
region
w
Flndeisen-Landahl
model, bronchial
epithelium, 14 1/nin
ii
Landahl model,
segmental bronchi,
15 1/min., mouth
breathing
n
Nose breathing
Segmental
bronchi, 15 1/min.,
mouth breathing
Segmental bronchi
15 1/min.
12
18.5
86
25.8-51.5
34
19.3-51.5
15.5-25.8
88
140
103
56
89-620
111
Range 12-620
Reference
Barley and
Pasternack
(46)
(46)
(46)
BEIR (26)
Toth (48)
Jacob! (34)
(34)
Jacob! (35)
(35)
Altshuler
et al. (25)
Lundin (39)
(25J
Hague and
Collinson
(24)
Burgess and
Shapiro (49)
factor " rads/year for continuous exposure (8,760 hours) to one
working level. One WL - any combination of short-lived radon daughters (through
2ll*Po, RaC1) leading to a total emission of 1.3 x 105-HeV of alpha energy per
liter of air (28). One WL is also defined as 100 pCi/1 of radon in equilibrium
with its dauthters.
(b)Relative concentrations of 222Rn, RaA, RaB, and RaC (RaC').
(C)ULM, 1 working level month - 170 hours exposure at 1 WL. Jacob! (34)
defines 1 WLM as 2.6 x 1010 MeV potential alpha-energy inhaled at 20 1/min. for
166.7 hours/month. MPAI - maximum permissible annual intake.
W)These conditions represent typical dwellings.
23
-------
is that each exposure situation has involved different radon-daughter
equilibrium conditions, free ion fractions, and carrier particle sizes
for attached daughters. Tsivoglou et al. (50) present data showing that
these differences could be 20 percent or more depending on the estimation
of equilibrium ratios alone. In addition, the choice of parameters to
characterize the interaction of radon daughters in various lung models
has led to differences in dose conversion factors.
The dose conversion factors tabulated from the literature (table 5)
had a range from 12 to 620 rads per year after being normalized for con-
tinuous exposure (8,760 hours/year) at one working leveL
Barton et al. (19) obtained an average value of 85 rads per year
after discarding high and low values of 620 and 12 rads per year,
respectively. A literature review by Walsh (51) indicated that con-
tinuous exposure to radon daughters at 1 WL for a. year should not
result in more than 50 to 100 rads to the bronchial epithelium, and
possibly less than 50 rads to the basal cells. Lundin (39) concluded
that (for uranium miners) an occupational exposure of one WL year
(2,040 hours) gave 24 rads averaged over the tracheobronchial epithelium.
This becomes 24 x 8,760/2,040 = 103 rads per year for continuous exposure.
After review of the literature, Barton (19) selected a conversion factor
of 100 rads per year to the bronchial epithelium for continuous exposure
at 1 WL. According to Holleman (52), this corresponds to a dose to the
total lung mass (1,000 grams) of approximately one-tenth of the dose
estimate for the bronchial epithelium.
The dose conversion factors derived for conditions in normal rooms
[footnote (d) table 5] are representative of typical dwellings. They may
be high by 25 percent on the basis of RaA and free RaA assumptions. In
addition, the assumption of continuous exposure may be high by 25 to 40
percent. With these considerations in mind, the dose conversion factor
selected for this analysis is 100 rads per year for a radon concentration
of 100 pCi/1. Reasonable variations could range from 50 to 125 rads per
year at 100 pCi/1. This factor assumes continuous exposure by mouth
breathing in a normal home atmosphere with an aerosol concentration of less
than 10,000 particles cm"3 and a mean aerosol diameter of about 0.1 micro-
meter. The ratio of radon daughters is assumed to be about 1.0, 0.8, 0.6,
0.4 (for Rn, RaA, RaB, RaC (RaC*), respectively).
Quality faetor
There is some controversy about the appropriate quality factor (Q)
that should be applied to alpha radiation dose from radon daughters to
convert from rads to rems (25, 53). The Q is intended to account for
differences in linear energy transfer (LET) and depends on type of damage
24
-------
under consideration, dose rate, and specific ionization of the ionizing
particles (54). The ICRP (55) recommends a Q of 10 for internal exposure
to alpha particles. This Q was therefore selected by Barton et al. (19)
for radon dose calculations. On the other hand, Bernhardt (11) concluded
that, while Q values ranged from 1 to 20 in the literature, the most
predominant value was 3. Gesell8 also agreed that a Q of 3 more accu-
rately reflected present knowledge of biological- effects of alpha radia-
tion. The FRC has also reported that a Q of 3 may be more appropriate
than 10 (32-page 1239). Initial dose estimates in this study will use a
Q of 10 to be conservative.
Conditions for this analysis
Radon dosimetry is a complex subject with many parameters which
cannot be definitely specified at the present state of knowledge.
Therefore, this analysis will take the approach of first making a pre-
liminary estimate of dose tojan individual for hypothetical exposure con-
ditions. Then this dose and
-------
are then converted to working levels by use of known decay constants and
alpha energies for each daughter. The conversion factor for dose was
taken as 100 rads per year for continuous exposure at one WL (100 pCi/1
of radon in secular equilibrium with daughters).
The dose to an individual for these conditions is given in the next
section. Barton et al. (19) also give tables of doses for various air
change rates and contributions from radon in outside ventilation air.
In the present study, the additional contribution to radon dose from
gas used in unvented space heaters was determined on the basis of data
compiled by Dr. Thomas Gesell9 of the University of Texas. He noted that
the widespread use of such heaters could add significantly to dose from
radon daughters.
The exposure conditions pertinent for both sources of radon in
natural gas. i.e., unvented kitchen ranges and space heaters, are tabu-
lated in table 6.
Dose to an individual
For an unvented kitchen range and the exposure conditions specified
in the previous section, Barton's (19) computer program calculated an
average annual dose equivalent to an individual of 15 millirems to the
bronchial epithelium. This assumed there were no radon daughters in the
natural gas. Gesell8 concludes this is the most likely situation, because
radon daughters would tend to plate out on pipeline surfaces in distribu-
tion systems. Also, Barton et al. (19) noted that radon daughters have
not been detected in gas lines at points of use.
For comparison with Barton's (19) computer-estimated dose equivalent
to an individual, a sampler calculation may be made by assuming that radon
daughters dispersed in the home are at equilibrium with the incoming radon
from natural gas. First, the radon concentration in the home is calculated
on the basis of dilution into a volume equal to 24 air changes per day.
This gives a dilution factor of
226.6 m3 house x 24 air changes _ -,-,-\-\
0.765 m3 gas used per day (in ranges)
Dividing the assumed natural gas radon concentration of 20 pCi/1 by the
dilution factor gives an average radon concentration in the home of
0.0028 pCi/1 from use of unvented kitchen ranges. At secular equilibrium,
this is also the concentration of radon daughters. Dose is then calcu-
lated by multiplying this concentration by the dose conversion factor of
(100 rads/year)/(100 pCi/1). This gives an absorbed dose of
9Gesell, op. cit.
26
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Table 6. Exposure conditions and possible variation in parameters
for analyzing dose from radon in natural gas
Parameter
Condition for
analysis
Possible Variation0*)
Radon concentration in
gas at point of use
Gas appliances
Gas use:
Ranges
Heaters
Degree-days
Appliance venting
House size
Air change rate
Radon concentration in home
from ranges
from heaters(c>
Radon daughters:
in gas
in home
Percent free RaA
Critical mode of exposure
Critical organ
Dose conversion factor(e)
Quality factor
20 pCi/1
Cooking ranges
Space heaters
0.765m3/day
0.354m3/degree-day
Average for each state
Unvented
226.6m3
one per hour
0.0028 pCi/1
0.01 pCi/1
No daughters
1, 0.8, 0.6, 0.4
8.5 percent
Inhalation of radon
daughters
Bronchial epithelium
100 rads/year for
continuous exposure
at 1 WL (100 pCi/1)
10
10 - 100 pCi/1
Could include
refrigerators, clothes
dryers, etc.
Up to 1.19m3/day
0.28-0.42m3/degree-day
± 252 within states
Ranges could be
partly vented
142 - 425m3
0.25 - 5 per hour
0.001-0.05 pCi/1
0.005-0.3 pCi/1
, , , u
1, 1, 1, 1 to
1.0, 0.5, 0.25, 0.1
5-25 percent
Radon alone gives
< 1% of dose
Some exposure also to
nasopharynx, lung,
and whole body
50 - 125 rads/year
3 - 10
'a)xhese are intended to be typical average conditions, although some of
the less well understood parameters were chosen to give a higher or more con-
servative dose estimate.
0>)These are reasonable variations which could be encountered for a large
fraction of the exposure conditions or population at risk.
(c)See table 7 for average annual degree-days and table 11 for variation
with degree-days/day.
WJRatio of Rn, RaA, RaB, RaC (RaC*).
feJthis-factor includes assumptions for daughter equilibria, critical mode
of exposure, lung model, and other doslmetry factors.
27
-------
0.0028 pci/l x SYear ' °-0028 ^ads/year
The absorbed dose in rads for alpha radiation to the bronchial epithelium
is converted to dose equivalent in reins by use of a quality factor of 10.
0.0028 x 10 = 0.028 rems/year.
year J
This estimate of dose to an individual is higher than Barton's (19) esti-
mate of 0.015 rem/year, because he calculated lower radon daughter concen-
trations due to nonequilibrium conditions as a function of air change rate.
The latter approach is more realistic, although it does not account for
other mechanisms by which radon daughters may be removed from a home
atmosphere, such as plating out on walls and surfaces and deposition with
dust particles.
The above dose equivalent estimate of- 0.028 rem/year corresponds to
Barton's computer calculations for radon at equilibrium with its daughters
in the incoming natural gas. As noted previously, however, there is prob-
ably very little radon daughter activity in the natural gas at points of
use.
Dose was__jiot calculated specifically for an individual from use of
space heaters, mainly because a typical individual could not be defined,
since the use of space heaters depends largely on weather conditions and
geographical location. Therefore, annual doses were estimated for average
space heater use by each State as shown in the section on population dose.
All the assumptions and calculations for estimating dose equivalent from
radon released by space heaters were the same as for kitchen ranges except
space heaters use different volumes of natural gas.
Radon dose
The radon itself does not contribute significantly to radiation
exposure. Since radon is a gas, most of a given amount inhaled is
expelled in breathing before it can decay (50) . Holleman (52) reported
that the absorbed radon produces only about 0.5 percent additional dose
to the tracheobronchial tree. Tsivoglou et al. (50) noted that alpha
emissions from radon alone contribute about 0.3 percent of the total dose
from inhalation of radon together with daughters. Holaday et al. (27)
reported that radon dose in the lung is about 1/20 and in the bronchi
about 1/260 of the dose from radon daughters.
Beta-gamma dose
Altshuler et al. (25) determined that beta and gamma radiation from
radon daughters deliver a negligible dose (less than 5 percent of alpha
28
-------
dose). This is because their greater penetrations distribute their
ionizing energy over much more tissue than the alpha radiation.
Average dose equivalent to the United States population
Tracheobronchial (T-B) doses to the United States population are
given in table 7. This table was prepared from data compiled by T. F.
Gesell10 from 1970 Census Bureau statistics. The States are ranked
according to total T-B dose in person-rem per year from the combined
effects of unvented kitchen ranges and space heaters.
The population T-B dose, equivalent in person-rems was calculated by
extrapolation of Barton* s ^19) estimate of 15 mrem/year for tracheo-
bronchial dose to an individual as described in the previous section.
By this approach, for kitchen ranges the extrapolation factor was:
n. 11- 4 occupants n n,c
Dwellings x dwel£ing x 0.015 rems =
«. 11 n nf person-rems
Dwellings x 0.06 = *
° year
The factor 0.06 includes the necessary dimensions for converting from
dwellings to person-rems/year. This factor was applied to the number of
dwellings with gas ranges in each State. The total population T-B dose
from use of gas kitchen ranges was estimated as 1.87 million person-rems
per year for the United States.
For space heaters the degree-day11 parameter was included as
follows:
_ ,,. degree-days 0.354m^ 4 occupants
Dwellings x 6 * x 3 3 x :rr-J
° year degree-day dwelling
x 0.015 rem x
0.765m3/day 365 days/year
Dwellings x degree-days x 0.0000761 = person-rems
10Gesell, op. cit.
11A degree-day is a term used by the heating industry to specify
heating or fuel requirements as a function of outdoor temperature. The
number of degree-days on any given day is determined by the difference
between a constant indoor temperature of 65° F and the daily mean temper-
ature outdoors. If the outdoor temperature varied from 20° F to 30° F
for one day the degree-days would be 65 - (20 + 30)/2 = 40 degree-days.
The cumulative degree-days per day for a year give the annual degree-days
shown in table 7.
29
-------
Table 7. Dose equivalent to U.S. population from radon in natural gas
(All numbers in thousands')
Ho.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25 _=-
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
Total
State
Calif.
H.Y..
Tex.
111.
Pa.
Ohio
B.J.
Mich.
La.
Okla.
Ga.
Mass.
Ala.
Miss.
Ark.
Ho.
Ind.
Md.
Vis.
Minn.
W. Va.
Ky.
Va.
Fla.
^-H.C.
Tenn.
Iowa
Kans.
Ariz.
Conn.
Colo.
S.C.
Waah.
N. Hex.
D.C.
Nebr.
Oreg.
R.I.
Utah
Mont.
Me.
S. Dak.
Del.
Hev.
Idaho
H. Dak.
H. H.
Wyo
Vt.
Hawaii
Alaska
(a)
Dwellings
with
invented
heaters
214
58.7
942
48.6
47.9
33.2
24.9
40.4
373
204
280
21.5
246
271
166
27.2
23.1
21.6
22.1
19.2
61.6
39.1
40.3
289
93
68.6
8.9
10.8
29.3
10.0
8.4
75.9
30.0
19.1
4.6
6.0
16.5
5.4
4.6
5.5
5.4
4.9
2.5
4.8
8.5
3.5
2.7
2.1
3.0
0.2
2.1
3.950.7
(b)
Average
Annual
Degree-
Dava
2.76
6.27
1.94
5.90
5.53
5.84
4.80
7.37
1.63
3.79
2.44
6.52
2.37
2.19
3.02
4.92
5.69
4.62
7.68
8.89
4.84
4.87
3.78
0.74
3.28
3.49
6.87
5.28
3.30
5.92
6.31
2.34
5.37
4.65
4.62
6.68
6.05
5.88
6.11
8.09
8.64
7.80
4.93
6.19
6.13
9.31
7.38
7.59
8.27
8.09
Population
T-B dose
person-rem
yr
44.7
27.9
139
21.8
19.8
14.7
9.1
22.6
46.2
58.7
51.8
10.7
44.3
45.2
38.0
10.2
10.0
6.6
13.1
12.9
22.6
14.5
11.6
16.3
23.2
18.2
4.7
4.3
7.3
4.5
4.0
13.5
12.2
6.7
1.6
3.1
7.6
2.4
2.1
3.4
3.5
2.9
0.9
2.3
4.0
2.5
1.5
2.5
1.9
__
1.3
854
(a)
Dwellings
with gas
ranges
4,350
4,190
2.150
2.510
1,950
1,670
1,610
1.260
763
515
446
. 914
296
233
320
780
778
706
511
442
280
389
424
323
136
211
393
358
299
327
284
99.7
69.2
146
226
186
54.3
138
83.3
54.4
33.7
43.1
65.6
41.5
12.6
27.8
38.8
41.2
14.3
36.5
9.6
31,234.6
Population
T-B dose
person-rem
yr
261
251
129
150
117
100
96.8
75.5
45.8
30.9
26.8
54.3
17.8
14.0
19.2
46.8
46.7
42.3
30.6
26.5
16.8
23.3
25.5
19.4
8.2
12.7
23.6
21.5
17.9
19.6
17.0
6.0
4.1
8.8
13.6
11.1
3.3
8.3
5.0
3.3
2.0
2.6
3.9
2.5
0.7 ,
1.7
2.3
1.2
0.9
2.2
0.6
1.874
Total
Population
T-B dose
Derson-rem
yr
306
279
268
172
137
115
106
98.1
92.0
89.6
78.6
65.0
62.0
59.2
57.2
57.0
56.7
49.9
43.7
39.4
39.4
37.8
37.1
35.7
31.4
30.9
28.3
25.8
25.2
24.0
21.0
19.5
16.3
15.5
15.2
14.2
10.9
10.7
7.1
6.7
5.5
5.5
4.8
4.8
4.7
4.2
3.8
3.7
2.8
2.2
1.9
2,728
Census Bureau data for 1970 compiled by T.F. Cesell, University of Tezaa.
Each dwelling Is assumed to have four occupants.
(b)Data compiled by T.P. Cesell from an Isodegree-day map of the united States
and tabulations of ASBBAE (56). In terms of degree-days per year.
30
-------
Again, for consistency the necessary dimensions are included with the
factor 0.0000761. Thus, the population dose equivalent from use of
unvented space heaters was determined by relating the average quantity
of gas used in heaters to the quantity of gas used in ranges and the
corresponding d^se equivalent for ranges. The average quantity of gas
used by space heaters was 2.75 m3 per day (7.77 degree-days at 0.354 m3
per degree-day). The total population T-B dose equivalent from space
heaters was calculated to be 0.854 million person-rems per year.
By assuming four occupants per dwelling, the population at risk for
exposure to radon from kitchen ranges is about 125 million or roughly
60 percent of the United States population. For space heaters, the
potential population affected is about 15.8 million or 7.5 percent of
the population. However, the average individual receives a higher dose
from use of space heaters due to; the greater quantity of natural gas
required for heating. This may be estimated indirectly by dividing the
total T-B dose from space heaters by the exposed population, i.e.,
854,000/15,800,000 = 0.054 rem/year
for an average individual. This can be compared with 0.015 rem/year for
an individual's exposure from use of kitchen ranges.
The combined population T-B dose equivalent for exposure to radon
daughters from use of natural gas in unvented kitchen ranges and space
heaters was estimated as 2.73 million person-rems per year for the United
States.
POTENTIAL HEALTH EFFECTS
Dose equivalent to health effect conversion factors
The health effects analysis in this study will be based on the
absolute somatic and genetic risks from radon daughters as outlined in
the report by the National Academy of Science on the biological effects
of ionizing radiation (BEIR report) (26). To place the significance of
the estimated health effects from radon daughter exposure to the bronchial
epithelium in perspective, the corresponding health effects to other parts
of the body will also be considered.
The proportional dose to other organs can be estimated by first con-
sidering the ratio of bronchial epithelium dose to alveolar dose. This
ratio was determined by Albert (57) as 34.3 to 1, respectively; i.e., the
alveolar dose is 0.0291 times the bronchial dose. The relationship of
alveolar dose to other organs, as caluclated by Pohl and Pohl-Ruling (58),
is then applied to complete the extrapolation from bronchial epithelium
dose.
31
-------
Table 8 shows the relative dose to each organ in comparison with
dose to the critical tissue, which is the basal cells of the bronchial
epithelium. Dose to this tissue is often referred to as the tracheo-
bronchial or T-B dose according to ICRP respiratory tract model (38).
The proportional doses to other organis are given as fractions of the
T-B dose, for the condition where the.body is in equilibrium with the
radon containing atmosphere.
The T-B dose effect or risk of concern from radon daughter expo-
sure is lung carcinoma. Since lung cancer has such a high mortality
rate, it is assumed that morbidity for this dose effect is equivalent
to mortality. Morbidity does not equal mortality for the corresponding
dose to other organs. However, the relative doses to other organs are
so small that their contribution to either morbidity or mortality is
insignificant when added to the risk from T-B dose.
The dose equivalent to health effects conversion factors for each
organ are also shown in table 8. These factors are in terms of absolute
risk, which means excess risk or mortality from the source of radiation
in this study (radon daughters).
The absolute risk from T-B dose was calculated from the BEIR report,
table 3-2 (26), by multiplying the sum of the fractional risks by age
times the expected plateau region. In this case, the plateau region, or
time beyond the lajtent period during which the risk remains elevated,
was taken as 30"years. The calculation for risk in terms of lung cancer
deaths was based on the following analysis, where the adult risk for
cancer of the lung from T-B dose is 1.3 deaths/106 persons at risk/year/
rem.
Age Percent of Proportion of Fractional risk
group population adult risk deaths/106 persons/year/rem
10+ 80 1 1.3x1x0.8 =1.04
0-9 20 0.2 1.3x0.2x0.2=0.05
In 1.3 5 1.3 x 5 x 0.013 = 0.08
Utero12 1.17
Annual risk = 1.17 deaths/106 persons/year/rem
This annual risk is then multiplied by 30 to estimate excess deaths for a
plateau region of 30 years to give the absolute risk as
1.17 x 30 - 35 excess deaths/106 persons/year/rem
12Exposed through placental transfer of radioactivity in maternal
blood.
32
-------
Table 8. Organ dose ratios and absolute risk
Organ to T-B Absolute
Organ dose ratiqw deaths /106 persons /year /r em (26)
Somatic effects
Bronchial epithelium 1.000 35
Alveoli 0.0291 (c)
Liver 0.0013
Gonads 0.0009
I '
Bone 0.0005 3
Bone marrow 0.0011 26
Kidneys 0.0066
Blood 0.0026
Muscle (soft tissue) 0.0007 67
Total - 35.077 deaths/106 persons/year /rem for T-B dose
Genetic effects
Gonads 0.0007 200 effects/106 persons /year/rem
Total - 0.14 effects/106 persons /year /rem for T-B dose
'a'Ratio of organ dose to T-B dose for conditions where the body is in
equilibrium with the radon containing atmosphere.
(b)For organ at risk.
CC)NO risk factor data available.
33
-------
This number represents a combined population at risk estimate, weighted
for age group distribution and proportional risk for continuous exposure
to radon daughters.
The absolute risks for the other organs were derived in the same
manner as described above for risk from T-B dose. Risk factor data were
not available for some organs. However, the relative contribution of
the organs to excess deaths for a given T-B dose is very small (0.077
deaths/106 persons/year/rem for organs where data was available in table
8). Thus, it is concluded that the combined effects from all the organs
would not significantly increase the absolute risk for T-B dose. This
study will therefore use the absolute risk estimate of
35 excess deaths/106 persons/year/rem
as a dose to health effects conversion factor for continuous exposure to
radon daughters.
It should be noted, however, that very little data are available on
carcinogenic alpha dose to the lung (25). Furthermore, the above health
risk estimate was derived by extrapolation from effects observed at high
doses and dose rates to those for low doses. Information is still vitally
needed to establish whether lung cancer production has a threshold dose
(42). If the relevent damage to man is indeed a nonthreshold effect, as
assumed in this^study, then the question of permissible limits on concen-
trations of radon and daughters requires a complex answer which relates
economics, benefits, and risks.
Health effects estimate
The total dose equivalent for continuous exposure to radon daughters
from use of natural gas in unvented kitchen ranges and space heaters in
the United States is estimated to be 2.728 x 106 person-rems per year.
This dose may be converted to potential health effects by the factor 35
deaths per 106 persons/year/rem. This conversion gives an estimate of
95 excess deaths per year.
However, the significance of this estimate of potential mortalities
should only be interpreted by comparison with other reference guides and
by consideration for the uncertainties in this analysis. Such compari-
sons are made in the Discussion Section to provide the basis or proper
perspective for interpreting estimates of mortality.
The estimate of potential health effects will vary for different
exposure conditions. The nature of corrections to be applied to the
estimate of 95 excess deaths per year for other exposure conditions are
illustrated in table 9. Each of these corrections will not be applied
34
-------
Table 9. Corrections to adjust estimated health
effects for different exposure conditions
Parameter
Air changes per hour (19)
0.25
1.0
2.0
Radon activity
Quantity of gas used
House size
Daughter equilibria (50)
Ratio 1, 1, 1, 1
1, 0.9, 0.8, 0.7
1, 0.8, 0.6, 0.4
1, 0.75, 0.5, 0.3
1, 0.5, 0.25, 0.1
Percent unattached RaA^)
3
8.5
10
25
Dose conversion factor
Quality factor
Health effects conversion factor
Correction multiplier
6.01
1.0
0.339
Linear
-------
here specifically; however, the influence of variations in exposure
conditions will be included in the discussion of uncertainties.
DISCUSSION
Review of uncertainties
The fundamental problem in an analysis of potential health effects
as derived in this study is the necessity of extrapolating from a few
measurements or reported values to average conditions for large popula-
tions. Because of inadequate information, values often have to be esti-
mated or assumptions made to represent typical exposure conditions or
population at risk. Assumed values are normally selected so the calcu-
lated dose or health effects will be overestimated, i.e., conservative.
However, without more supporting data some of the estimates used in this
analysis may not represent average conditions, and other values may be
overly conservative. Both aspects of this analysis will be considered
as far as possible for two purposes: (1) to place the estimate of health
effects in reasonable perspective, and (2) to indicate where better
values might be obtained from field measurements or studies of exposure
conditions which would significantly enhance the estimate of potential
health effects from radon in natural gas.
The possible variations which could be encountered for reasonable
exposure conditions were summarized previously in table 6. The correc-
tions to adjust estimated health effects for these possible differences
in exposure conditions were also given in table 9. It should be empha-
sized that this analysis considers only those variations which could be
typical for exposure of a large part of the population. Extreme con-
ditions for small parts of the population, such as users of 'farm taps',
cannot be evaluated from present information.
Considering the model for analysis of health effects depicted in
figure 1, the first parameter of concern is radon-222 concentration in
the natural gas at the point of use. A level of 20 pCi/1 was chosen as
an average for the United States, however, Barton et al. (19) noted that
a level of 10 pCi/1 may be more representative. On the other hand, large
segments of the population may use natural gas with an average of 50 pCi/1
of radon-222. Ideally, therefore, the estimate for the United States
should be based on regional concentrations in natural gas, as well as
regional gas use and populations.
Another parameter of special concern to Barton et al. (19) was the
influence of home ventilation or air change rates. An average air change
rate of one per hour was assumed in this study. This is considered typical
for air infiltration in normal home with windows closed and doors opened
36
-------
only for entry or exit at an outside wind velocity of 7.5 mph. A typi-
cal home is also assumed to have no makeup air for heating or air con-
ditioning. In contrast, apartments may have 25 percent makeup air from
central heating and air conditioning systems. Barton*s calculations
indicate that an air change rate of 0.25 per hour could increase the
dose a factor of 6 over that at one change per hour. However, a United
Nations study (21) indicates that better ventilated dwellings more
commonly have air changes of five or more per hour which could reduce
the dose hy a factor of four or more. Again, one air change per hour
is considered conservative by architects, but information is not avail-
able for better estimates for average dwellings. Resolution of this
factor would require an evaluation of air infiltration by house type,
and a regional distribution according to use of heating or air condi-
tioning for closed houses or the proportion of houses with open windows
for summer cooling. Such a study could also provide information on the
distribution of house sizes for calculating dilution volumes.
The third parameter for consideration is reflected by the dose con-
version factor and has to do with radon daughter product equilibria.
The ratio of daughters to radon is of concern for dose calculation from
all sources of radon. Most studies have determined this ratio for uranium
mine conditions where secular equilibrium is prevented by air circulation
which removes daughters as they are formed. Normal air change in a house
also prevents daughter product secular equilibrium with radon. Barton's
(19) calculations show that the dose at one air change per hour for non
equilibrium conditions (15 mrem/year) is only 53 percent of the dose for
secular equilibrium (28.1 mrem/year). The nonequilibrium condition was
based only on air change rate; therefore the dose would be even less if
loss of daughter products by plating out or deposition on surfaces was
considered. When Barton's data are compared with Tsivoglou et al. (50),
it was determined that 53 percent of the equilibrium dose corresponds to
a radon-daughter ratio of about 1, 0.8, 0.6, 0.4. This ratio agrees well
with studies by Altshuler et al. (25). Table 9 indicates that the dose
could vary by ± 16 to 30 percent for small variations from the above
ratio which would be expected to include normal variations in equilibrium
conditions for typical dwellings in the United States.
Another parameter which affects the dose conversion factor is the
percentage offree ions of RaA. The dose conversion factor from this
study (100 rads/WL for continuous exposure) was based on 8.5 percent of
free RaA ions (25, 39). This percentage of free ions is determined
largely by the presence of dust particles or condensation nuclei for
attachment of daughter products. Therefore, dusty air (more than 10,000
particles cm-^) has a lower free ion fraction of about 3 percent. Rela-
tively clean air of normal dwellings could have from 8.5 to 25 percent
free ions. The latter condition would result in about twice the dose at
37
-------
8.5 percent. This is because free ions are essentially 100 percent
deposited in the respiratory system (38, 59). In contrast, only about
10 percent of the daughters attached to dust particles are retained in
the tracheobronchial region.
The two parameters, daughter equilibria and free ion fraction,
largely determine the dose conversion factor. Also, these two parameters
may be more easily quantified than other variables included in the dose
conversion factor. The overall analysis of health effects could be
improved by better definition of these parameters. Since neither of
them depends on the source of radon, a review of studies on radon from
uranium mill tailings or construction materials may provide better infor-
mation. Otherwise a special study could be directed at determining
daughter product ratios and percent free ions from natural radon for a
few typical dwellings.
The uncertainty in the dose to health effects conversion factor in
terms of absolute risk is rather hard to determine. This risk estimate
is based on extrapolation from observed incidences of lung carcinomas
in uranium miners receiving relatively high exposures from radon daughters.
However, no health effects have been reported for exposures to less than
4 working level months (WLM) or 1/3 of a WL for a year (39). Therefore,
the potential health effects estimated in this study for exposures to
radon levels of 0.01 pCi/1 (0.0001 WL) or less are statistical projec-
tions for evaluation of large populations, based on the assumption of a
linear nonthreshold dose response to alpha radiation from radon daughters.
Interpretation of estimated health effects
The previous review of uncertainties has indicated a few of the
possible variations in parameters which determine the significance of
the overall estimate of health effects. To further place the potential
for health effects from radon in natural gas in perspective, parameters
in this analysis will be related to current guides and recommendations,
natural background radon in the ambient environment, and normal respira-
tory cancer mortality.
Current guides and recommendations
The guides for control of radon have been primarily oriented towards
health protection of uranium miners. These guides have undergone several
changes over the years as the potential for lung carcinomas from radon
daughters became better understood. This development of guides is shown
in table 10. Of particular interest here are those guides for continuous
exposure (168 hour week) for the general public. These vary from 0.33 to
4 pCi/1. The lowest recommendation of 0.33 pCi/1 is derived from ICRP
No. 2, I960, (60). This was derived as 1/30 of the radon-222 guide for
continuous occupational exposure.
38
-------
Table 10. Guides for radon-222 concentrations
in air above natural background(a)
Rn-222 concentrations
for occupational exposure (pCi/1)
40 hour week 168 hour week
Source, date
and reference
10
30
300
300
100
30
30
100
100
30
100
30W
none
10
100
100
none
10
0.33(c)
none
none
none
4(c)
none
U.S. X-ray and radium
Protection Committee,
1941, (61)
NCRP, 1953, (62)
ICRP, 1955, (63)
NCRP, 1955, (64)
PHS, 1957, (27)
NCRP, 1959, (65)
ICRP, 1960, (60)
ASA, 1960, (66)
Governors Conference,
1961, (67)
Secretary of Labor,
1967, (32)
10 CFR 20, 1970, (68)
FRC, 1971, (31)
by David E. Janes, EPA, Office of Radiation Programs.
ues originally expressed in working levels.
'c'General public or unrestricted areas.
39
-------
For comparison, the concentration of radon-222 released in an
average home (226.6m3 and one air change an hour) from the use of
0.765m3 a day of natural gas containing 20 pCi/1 of radon) in an
unvented kitchen range is 0.0028 pCi/1. This represents about 0.85
percent of the ICRP No. 2 guide.
If the same home had an unvented space heater, the radon concentra-
tions shown in table 11 could be expected for various heating require-
ments. These concentrations were estimated for the exposure conditions
postulated previously in table 6. For these conditions, even with an
extreme heating requirement of 100 degree-days/day (corresponds to out-
door temperature of 35° F below zero), the indoor radon concentration is
less than 40 percent of the ICRP guide. It is not likely this guide would
be exceeded, therefore, for normal conditions, unless the radon concentra-
tion in thegas was much higher than 20 pCi/1. For example, at a heating
requirement of 50 degree-days/day, the guide would not be exceeded unless
the gas contained over 100 pCi/1 of radon.
For the average annual heating requirement of 7.77 degree-days/day
plus use of a gas range, the indoor radon concentration would be 0.0129
pCi/1 or 3.87 percent of the guide. At these average conditions, the
natural gas could contain up to 516 pCi/1 before the ICRP guide would be
exceeded for continuous exposure to the general public.
Natural background radon
Natural radon in the ambient environment goes through a daily cycle
of concentrations from 0.03 to 3.50 pCi/1 of air (21, 69). The average
atmospheric content of radon from one to four meters above the ground is
about 0.3 pCi/1 (69). It is interesting to note here that the ICRP guide
of 0.33 pCi/1 is about the level of natural background radon. Of course,
the ICRP guide applies to controllable radon concentrations above back-
ground levels.
Indoors the radon levels are typically from 3 to 4 times the outdoor
levels due to emanation of radon from building materials. The indoor
radon concentration is also influenced by infiltration from outside air.
Thus, radon levels inside homes might be 0.6 to 1.2 pCi/1 for ventilation
rates below four air changes an hour, and from 0.1 to 0.3 pCi/1 for over
six air changes an hour (21).
In this analysis the air change rate was conservatively assumed to
be one per hour. Therefore, the average radon concentration from use of
natural gas in kitchen ranges (0.0028 pCi/1) represents from 0.23 to 0.47
percent of ambient indoor radon levels for less than four air changes an
hour. The average combination of radon from kitchen ranges and space
heaters (0.0129 pCi/1) would still be only about 1.1 to 2.2 percent of
expected indoor radon concentrations from natural background. The higher
40
-------
Table 11. Comparison of Indoor radon concentrations
from natural gas with the ICRP No. 2 guide of 0.33 pCi/1
Degree-days (a)
day
0
10
20
30
40
50
60
70
80
90
100
Radon-222 concentration (fe)
Space heaters Heaters + ranges ^
0.0
0.013
0.026
0.039
0.052
0.065
0.078
0.091
0.104
0.117
0.130
0.003
0.016
0.029
0.042
0.055
0.068
0.081
0.094
0.107
0.120
0.133
Percent of
ICRP guide
0.85
4.8
8.7
12.6
L6.5
20.4
24.3
28.2
32.1
36.0
39.9
(a) t
\v Heaters use about 0.354 tn3 of natural gas per degree-day.
* 'For radon in natural gas at 20 pCi/1.
(c)Gas use in ranges produces an indoor radon concentration of
about 0.003 pCi/1.
41
-------
percentages of expected indoor radon concentrations which would result
from increased use of space heaters may be derived from the data in
table 11. For example, at 100 degree-days/day the resulting radon con-
centration would represent about 11 to 22 percent of normal indoor radon
levels for ventilation rates below four air changes an hour.
It is pertinent at this point to also consider how the total usage
of natural gas may affect ambient levels of radon. Barton et al. (70)
evaluated total gas usage in the metropolitan areas of Los Angeles and
San Francisco to determine atmospheric concentrations of tritium which
might occur from use of gas from nuclearly stimulated wells. Computer
modeling was used to determine dilution parameters resulting from domes-
tic and industrial gas use as ground level sources of pollutant, as well
as from gas use in electric generating plants having tall stacks for
release of combustion products. Applying these same dilution parameters
to the total use of natural gas (containing 20 pCi/1 of radon-222) gave
the atmospheric concentrations shown in table 12. It is apparent that
even the highest expected concentration of 0.002 pCi/1 is still only
about 0.6 percent of the natural atmospheric content of radon. These
data also indicate that the radon concentrations indoors from household
use of natural gas significantly exceed concentrations in the atmosphere
from all uses of natural gas.
Normal excess mortality from respiratory cancer
Using data provided^in Patterns of Cancer Mortality in the United
States: 1950-1967 (71) and population statistics for the United States:
1972 (72), a reasonable estimate of respiratory cancer mortality would
be 40,000 to 45,000 deaths per year in the United States. This estimate
is'probably high since it classifies tumors of the bronchus, lung, and
pleura with pulmonary tumors as one group. Of these deaths, about
20,000 are due to primary tumors, i.e., those originating in the respi-
ratory system. The other 20,000 to 25,000 are not specified as to point
of origin.
In this study, a conservative estimate is made that radon from
natural gas could lead to a potential of 95 excess deaths from lung
cancer per year. This would represent about 0.2 to 0.5 percent of the
normal lung cancer mortality of 20,000 to 45,000 per year. Even if the
normal mortality estimate was reduced to 10,000 lung cancer deaths per
year to account for the population at risk from radon in natural gas, and
the fact that 50-75 percent of the normal lung cancers may not originate
in the tracheobronchial region, the comparative risk from radon in
natural gas is still less than one percent.
42
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Table 12. Atmospheric radon-222 concentrations from all uses
of natural gas in metropolitan areas
Radon concentration-pCi/1
Maximum 'a'
Population Weighted
Average 0* )
Los Angeles Basin
San Francisco Bay Area
0.002
0.00026
0.00026
0.000074
'a'At point of peak concentration.
concentration for entire area.
43
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Conservatism in health effects estimate
Further insight may be had as to the significance of this study's
initial estimate of 95 excess deaths a year from radon in natural gas
by applying the same dose and health effects conversion factors to
natural background radon. Barton et al.(19), using the same exposure
conditions and dose model as for the earlier dose estimates, calculated
that a background concentration of 0.13 pCi/1 of radon-222 in secular
equilibrium with its daughters would result in 1,300 mrem/year for T-B
dose to an individual. This would lead to 273 x 106 person-rems for a
United States population of 210 x 106. The corresponding estimate of
potential effects, at 35 excess deaths/106 persons/year/rem, gives 9,555
excess lung cancer mortalities or about 20 to 50 percent of normal respi-
tatory cancer mortality. If the average background, radon is actually
0.3 pCi/1 or more, then the corresponding estimate of excess lung cancer
deaths would exceed 22,000 deaths per year or 50 to 110 percent of :the
normal annual mortalities.
The above calculation for potential health effects from natural
background radon indicates that most or all of the normal lung cancer
mortality could be attributed to radon-222. This is not a likely con-
clusion, because this ignores all the other known carcinogenic factors
influencing lung cancer, such as smoking, smog, and other naturally
occurring isotopes in the atmosphere. What can be concluded from this
calculation is that ^ihe dose and health effects conversion factors used
in this study are very conservative in terms of overestimating potential
health effects.
The philosophy in the health physics profession is to estimate high
for calculating health effects in order to develop conservative criteria
for protection of public health and safety. However, in this study the
initial choice of parameters from available data in the literature for
estimating health effects from radon appear to be more conservative than
necessary as noted above. The conservatism in many of the parameters
used in this overall health assessment has been discussed in the previous
section on review of uncertainties. However, the most important factors
will be listed here again with an indication of the extent of overcon-
servatism.
(1) Daughter product ratios: no account was taken for loss
of daughter products by plating out or deposition on
surfaces. Possible adjustment multiplier - 0.75 (50).
(2) Ventilation rate: the ventilation rate could readily
be 2 to 3 times the one air change per hour assumed in
this study (21). Adjustment multiplier - 0.34 (19).
(3) Mouth breathing was assumed in this study but nose
breathing would reduce the inhalation of daughters due
44
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to deposition in the nasopharynx areas. Adjustment
multiplier - 0.5 (25).
(4) Exposure time: a continuous residence time in dwellings
is not very likely for the average population. An
average time spent in the home of about 70 percent
would be more representative. 'Adjustment multiplier r
0.7.
In addition, it should be noted that about 30 percent of the total
population dose was estimated from use of unvented space heaters.
However, use of such heaters is illegal in most states, and many states
are becoming more strict in limiting these heaters. Furthermore, many
houses with gas kitchen ranges also have outside vents or recirculating
charcoal filters to remove cooking odors. The use of these vents or
filters would reduce the amount ojf radon and daughters dispersed within
the home. Other adjustment factors could also be enumerated, but appli-
cation of those above leads to a considerable reduction in the initial
estimate of potential health effects, as indicated in table 13. This
table also shows the conclusions which this study determined as to the
probability of various estimates of excess deaths. This analysis indi-
cates that radon in natural gas could possibly lead to 15 excess deaths
per year due to tracheobronchial cancer. This estimate is only 0.03 to
0.08 percent of the normal respiratory cancer mortality. As such, the
increase in mortality can be projected on a theoretical basis, as done
in this assessment, but the actual increase in mortality could not be
detected due to normal variations in respiratory cancer mortality.
Table 13. Conclusions oh estimates of excess mortality from radon-222
in natural gas used in unvented kitchen ranges and space heaters
Estimated Percent of
excess mortality normal respiratory
Conclusion deaths/year mortality
Impossible
Improbable
Possible
Likely
95
30
15
5
0.2 to 0.5
0.07 to 0.15
0.03 to 0.08
0.01 to 0.02
45
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The overall conclusion of this assessment of potential health
effects from radon in natural gas is that in the United States from
5 to 15 excess deaths from T-B dose may be postulated on the basis of
available data. However, a review of uncertainties in this analysis
indicates that many of the dosimetry parameters and conversion factors
may be overly conservative. Also, it should be noted-that this analysis
is based on the assumption of a linear-nonthreshold dose response for
low concentrations of radon. But, very little data is available relating
lung carcinogensis to dose from radon daughters (25) and no lung carcino-
mas have been confirmed for radon levels expected in homes resulting from
use of natural gas (39).
ALTERNATIVE METHODS FOR REDUCING HEALTH EFFECTS
Potential health effects arising from use of natural gas containing
radon-222 may be reduced in several ways. These include controls on
radon concentrations or on the use of natural gas, as follows:
Production - Control production of wells with highest radon
contents or levels above a given concentration.
Processing - Route gas with higher radon levels to special
processing for LPG separation and inherent
radon removal. This should be followed by LPG
storage to reduce the radon concentration in
LPG. The natural gas could also be routed
through special processing just for radon removal,
i.e., by methods in use at nuclear reactors for
removing other noble gases (krypton, xenon) from
off-gas streams.
Distribution - Route gas with higher radon content, (a) to more
distant points of use to allow maximum decay
during transport, (b) to industrial or commercial
users, and (c) to storage for one or more half-
lives to allow radon to decay.
Gas Use - Regulate use of gas by 'farm taps', e.g., perhaps
by requiring some storage delay before use. Regu-
late venting requirements for cooking ranges and
space heaters. Require installation permits and
inspections.
Analysis of cost for control of radon in natural gas
The simplest approach for control of radon in natural gas would be
to limit production from gas wells with high radon levels. However, with
46
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increasing demands for natural gas, production from every available well
may be required, and therefore the costs for radon removal should be con-
sidered.
At the present time the most feasible method for removing radon
from natural gas would be to store the gas and take advantage of the
relatively short half-life of radon-222 (3.83 days). For example, a
storage period of two weeks between production at the well head and
the use of natural gas would reduce radon levels by radioactive decay
to less than 10 percent of the original content. Storage is also a
first consideration for radon control, because this is already an
integral part of the gas industry. As noted previously, storage is
used to provide the necessary balance between a constant production
rate and seasonal demands for natural gas. Most storage operations
are now carried out by using underground reservoirs, mainly depleted
gas and oil wells. Such reservoirs presently have sufficient capacity
to store about 30 percent of the annual net marketed production of
natural gas. Since the average!storage time is probably between 2 and
6 months, then much more than 30 percent of the annual production could
be routed through storage.
Ideally, storage reservoirs should be located near distribution
centers for meeting peak demands. At present, most of the readily
accessible underground reservoirs in the desired locations have already
been developed. Therefore, additional storage for meeting seasonal
demands or for radon control would require development of other storage
methods such as cryogenic storage of liquified natural gas (LNG) or
pressurized tank storage. The gas industry is rapidly increasing the
number of LNG facilities, in particular, in order to provide cost effec-
tive storage where it is most needed.
It should also be noted that the use of underground gas storage may
not result in a reduction in radon concentrations. Gas stored in depleted
wells may accumulate additional radon in the same manner that radon builds
up in regular production wells. This potential for radon buildup would
not be a problem for LNG storage. In addition, LNG storage for radon
control has the advantage that LNG facilities could be located where-
ever necessary in conjunction with the wellfield needing radon control.
The same factors apply to use of pressurized tank storage.
The following cost analysis for LNG and pressurized tank storage is
intended to provide order-of-magnitude estimates for comparison with the
reduction in potential health effects which might be expected with a
reduction of radon levels in natural gas. The actual costs for these
storage methods can vary widely as functions of facility size, processing
rates, compression and pumping costs, and distribution logistics.
47
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For this analysis, costs will be estimated for a two week storage
of ten percent of the presently net marketed gas volume, which is 19.5
x 1012 ft3 per year. This should allow sufficient reduction for most
anticipated radon levels at well heads. The storage requirement for
two weeks would then be
19.5 x 1012 ~^ x i|j x 0.1 = 7.5 x 1010 ft3
The costs for storing 7.5 x 1010 cubic feet of natural gas will be
estimated by the present worth method for annualized costs. This method
estimates the yearly capital cost by multiplying the total capital cost
by an annual fixed charge rate, i.e.,
capital cost x fixed charge rate = annual capital cost
The fixed charge rate includes interest, taxes, insurance, and depreci-
ation for a 30 year plant life (73). The fixed charge rate used in this
analysis was 16.6 percent per year (74). The sum of the annual capital
costs and annual operating cost gives the annualized costs which can be
compared with the potential reduction in yearly health effects due to
reduction in radon levels in natural gas.
Using the cost data from table 14, the annualized costs for storage
of natural gas were estimated according to the present worth method as
tabulated in table 15.
The total annualized costs for storage of natural gas to allow
radon to decay would be from about 0.89 to 8 billion dollars depending
on the storage method as shown in table 15. These cost estimates also
indicate that liquified natural gas would be less expensive than storage
in pressurized tanks. This is partly because a liquified natural gas
facility would be designed for a daily liquifaction rate with subsequent
storage of the liquified gas which has been reduced in volume by a factor
of 650. In contrast, a pressurized tank facility would be designed to
accommodate two weeks of production without the great volume reduction
inherent to LNG. A LNG facility would also be designed for regasifica-
tion to return the liquified gas to the normal gaseous state for distri-
bution to customers. After regasification, the gas would typically be
stored further to coincide with market demands.
It should be noted also that pressurized gas storage would be less
favorable than LNG for reasons other than cost. Namely, pressurized
storage of gas has a greater hazard potential for explosion and the huge
tanks required would be aesthetically unfavorable.
48
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Table 14. Cost summary for natural gas storage (1972 basis)
Capital
Costs
Operating
cost
Pressurized tank storage (15)
Low pressure (1 atmosphere)
High pressure (50-100 psi)
Liquified natural gas (LNG)
Liquif ication
Plant total
Storage
Regasif ication
Depot total
Storage
(75)
$500/MCF(a>
$500/MCF
$350-450/MCF/Day
$340-450/MCF/Day
$30-40/MDF/Day
$150-250/MCF/Day
$20-30/MCF/Day
$25/MCF
$25/MCF
$75-125/MCF/Day
$10-17/MCF/Day
(a)
MCF = Gas industry notation for 1,000 cubic feet.
Table 15. Annualized cost estimate for storage of natural gas
(a)
Storage method
Total annualized cost
Annualized unit costs
dollars per thousand
cubic feet
Low pressure tanks
High pressure tanks
Liquified natural gas
$8 x 109
$6.5 x 109
$0.89 x 109 to
$1.35 x 109
$4.10
$3.85
$0.46 to
$0.69
^Storage of 10 percent of the annual marketed production, i.e.,
1.95 x 1012 cubic feet.
49
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The annual unit costs for storage are also shown In table 15.
These costs may be compared with the value of natural gas which varies
from $0.20 to $0.30 per thousand cubic feet at the well head to $1.50
to $2.00 per thousand cubic feet at the point of consumer use. The
annual unit cost for LNG ($0.46 to $0.69) represents about twice the
cost which gas transmission companies would normally pay for natural
gas at the well head. Therefore, the customer price would have to be
raised accordingly.
The American Gas Association noted that a LNG facility would not
be practicable for storage control of radon at an individual well. How-
ever, a LNG facility might be constructed for a small group of wells
where radon control would be desirable. Such facilities are commonly
designed in multiples of a daily processing rate of 250 million cubic
feet. A typical well produces about 2 million cubic feet a day. There-
fore, the normal facility would handle production from 125 wells. A
smaller facility might be designed, but the cost could not be scaled pro-
portionately. Therefore, the unit cost for a smaller facility would make
the market value of the gas even less favorable. For example, the unit
cost for a small LNG facility could be $2.00 per thousand cubic feet or
higher. A facility to handle 25 wells with a combined daily production
of 50 million cubic feet would then have an annualized cost of $36.5
million. The value of this gas to transmission companies would be only
about $5.5 million a year.
There are no cost data available for evaluating alternative methods
other than storage for reducing radon exposures from use of natural gas.
Some of the methods used in nuclear reactors for removing noble gases
might be applicable to individual or small groups of wells. However,
none of these methods have been tested for removing radon from natural
gas.
Comparison of radon control costs to reduction in potential health
effects
The cost estimates for control of radon in natural gas by storage
in pressurized tanks or as liquified gas would be a billion dollars or
more a year for 10 percent of normal annual production. For this storage
to be effective in reducing radon levels, it would have to be oriented
towards the well fields with the highest radon levels. Even then, the
overall average radon level for the country may not be reduced by even
a factor of 2. Such a reduction would correspondingly reduce the esti-
mated possible health effects (15 excess deaths a year) by less than a
factor of 2 by such storage endeavors.
Thus, for a reduction of 8 to 10 hypothetical excess deaths from
radon in natural gas, an expenditure of about $1 billion would be
required. This corresponds to an investment of $100 million or more
for each reduction of one potential excess death. Therefore, this
50
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approach for radon control at the national level is clearly not cost
effective in terms of the possible reduction in health effects.
It should be noted, however, that local or regional conditions
could exist where individuals might receive doses from radon daughters
which are much higher than the national average. For example, natural
gas users with 'farm taps' close to wells or well fields with high radon
content could possibly receive higher radon exposure. Similar circum-
stances could also occur for small closed gas systems where there is
little or no storage and short transmission lines from processing plants
to consumers.
For such conditions, it is possible that storage provisions for a
small group of wells could be more cost effective than radon control at
the national level. However, special studies would be required to deter-
mine which wells had the highest radon contents. Then the use of gas
from each well would have to be
evaluated to determine whether a signifi-
cant population T-B dose could potentially result. For example, if most
of the gas from a given well with jhigh radon content is used industrially
and combustion products are vented to the atmosphere, then very little T-B
dose is likely. In contrast, the same well may supply only nearby resi-
dential customers using unvented appliances. In this case, storage con-
trols may be justified, but such cases would have to be identified first.
At the present time, there is no information by which to determine the
extent or significance of these local conditions.
CONCLUSIONS
The conclusions that can be drawn from this evaluation of potential
radiological health effects from radon in natural gas are as follows:
(a) The use of natural gas containing radon-222 for average
exposure conditions does not contribute significantly
to lung cancer deaths in the United States.
(b) Controls for reducing radon concentrations in natural
gas by storage methods would cost over $100 million for
each reduction in one potential excess death. Therefore,
it would not be cost effective to require controls on
radon in natural gas by storage on a national basis.
(c) No information is available to evaluate local conditions
where individuals may receive exposures from radon daugh-
ters much higher than the national average. There is also
no information on control methods or costs applicable to
such local conditions even if they could be identified.
Materials Belong To-
OPPT Library ' 51
401 M Street, SW (TS-793)
Washington, DC 20460
-------
(d) For average exposure conditions the radon from
natural gas produces indoor radon concentrations
about 3.9 percent of the guide of 0.33 pCi/1
derived from ICRP No. 2, 1.1 to 1.2 percent of
the average indoor radon concentrations from
natural background, and 0.03 to 0.08 percent
of normal lung cancer mortality.
(e) Continuous exposure to the bronchial epithelium
by alpha radiation from radon daughters could
potentially result in 35 excess deaths from lung
cancer for each million person-rems.
(f) The average population tracheobronchial dose
equivalent resulting from use of unvented kitchen
ranges and space heaters in the United States is
2.73 million person-rems per year.
52
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59
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THE ABSTRACT CARDS accompanying this report
are designed to facilitate information retrieval.
They provide suggested key words, bibliographic
information, and an abstract. The key word con-
cept of reference material filing is readily
adaptable to a variety of filing systems ranging
from manual-visual to electronic data processing.
The cards are furnished in triplicate to allow for
flexibility in their use.
60
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ASSESSMENT OF POTENTIAL RADIOLOGICAL HEALTH EFFECTS FROM
RADON IN NATURAL GAS, EPA-520/1-73-004. Raymond H.
Johnson, Jr., David E. Bernhardt, Neal S. Nelson, and
Harry W. Galley, Jr. (November 1973).
ABSTRACT: Natural gas contains varying amounts of
radon-222 which becomes dispersed in homes when natural
gas is used in unvented appliances. Radon decays to
alpha-emitting daughter products which can contribute
to lung cancer when inhaled and deposited in the re-
spiratory system. For the average use of unvented
kitchen ranges and space heaters, the tracheobronchial
dose equivalent to individuals was estimated as 15 and
54 mrem/yr, respectively, or 2.73 million person-
Cover)
ASSESSMENT OF POTENTIAL RADIOLOGICAL HEALTH EFFECTS FROM
RADON IN NATURAL GAS, EPA-520/1-73-004. Raymond H.
Johnson, Jr., David E. Bernhardt, Neal S. Nelson, and
Harry W. Galley, Jr. (November 1973).
ABSTRACT: Natural gas contains varying amounts of
radon-222 which becomes dispersed in homes when natural
gas is used in unvented appliances. Radon decays to
alpha-emitting daughter products which can contribute
to lung cancer when inhaled and deposited in the re-
spiratory system. For the average use of unvented
kitchen ranges and space heaters, the tracheobronchial
dose equivalent to individuals was estimated as 15 and
54 mrem/yr, respectively, or 2.73 million person-
Cover)
ASSESSMENT OF POTENTIAL RADIOLOGICAL HEALTH EFFECTS FROM
RADON IN NATURAL GAS, EPA-520/1-73-004. Raymond H.
Johnson, Jr., David E. Bernhardt, Neal S. Nelson, and
Harry W. Galley, Jr. (November 1973).
ABSTRACT: Natural gas contains varying amounts of
radon-222 which becomes dispersed in homes when natural
gas is used in unvented appliances. Radon decays to
alpha-emitting daughter products which can contribute
to lung cancer when inhaled and deposited in the re-
spiratory system. For the average use of unvented
kitchen ranges and space heaters, the tracheobronchial
dose equivalent to individuals was estimated as 15 and
54 mrem/yr, respectively, or 2.73 million person-
(over)
-------
rems/yr to the United States population. A review of
exposure conditions, lung model parameters, dose con-
version factors, and health effect factors indicate
this population dose equivalent could potentially lead
to 15 deaths a year from lung cancer. This represents
only 0.03 to 0.08 percent of normal lung cancer mor-
tality. Since control of radon levels in gas would
cost over $100 million for each reduction of one health
effect, it was concluded that a requirement for such
controls would not be cost effective on a national
basis.
KEYWORDS: Control costs; dosimetry; health effects;
natural gas; population dose; radon.
rems/yr to the United States population. A review of
exposure conditions, lung model parameters, dose con-
version factors, and health effect factors indicate
this population dose equivalent could potentially lead
to 15 deaths a year from lung cancer. This represents
only 0.03 to 0.08 percent of normal lung cancer mor-
tality. Since control of radon levels in gas would
cost over $100,million for each reduction of one health
effect, it was^ concluded that a requirement for such
controls would not be cost effective on a national
basis. ,
KEY WORDS: Control costs; dosimetry; health effects;
natural gas; population dose; radon.
rems/yr to the United States population. A review of
exposure conditions, lung model parameters, dose con-
version factors, and health effect factors indicate
this population dose equivalent could potentially lead
to 15 deaths a year from lung cancer. This represents
only 0.03 to 0.08 percent of normal lung cancer mor-
tality. Since control of radon levels in gas would
cost over $100 million for each reduction of one health
effect, it was concluded that a requirement for such
controls would not be cost effective on a national
basis.
KEY WORDS: Control costs; dosimetry; health effects;
natural gas; population dose; radon.
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