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<pubnumber>520173004</pubnumber>
<title>Assessment of Potential Radiological Health Effects From Radon in Natural Gas</title>
<pages>69</pages>
<pubyear>1973</pubyear>
<provider>NEPIS</provider>
<access>online</access>
<origin>hardcopy</origin>
<author></author>
<publisher></publisher>
<subject></subject>
<abstract></abstract>
<operator>LM</operator>
<scandate>20120216</scandate>
<type>single page tiff</type>
<keyword></keyword>


                               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

 image: 






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

 image: 











^"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

 image: 






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.

 image: 






 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).

 image: 






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
<T04
1.07
0
0
0
Hat
marketed
production
19.532.622
Percentage of United
0
0

0
0
0
0.35
0
0.01
0.34
0.47
0
0
0.11
0.36
0
4.11
0
3.94
0
0
0.02
0.15
0 ,
1.05
0
0
0

0
0
0
0.01
1.04
0.85
0
0.32
0.53
0
82.2
0.77
35.93
7.49
38.01
7.70
0
0.48
0
0.15
0
5.19
0.19
1.69
3.26
0.54
2.72
0
0
0
Approximate
gaa
rnnsimaitloa
20.268.101
States
1.11
0.27

0.05
0.68
0.11
g.jg
1.46
1.22
1.60
18.14
5.74
2.48
1.65
4.77
1.50
8.96
1.52
2.84
1.51
1.87
0.92
0.16
0.14
6.79
0.12
1.45
1.52

0.81
0.70
0.68
0.64
0.85
ill
1.20
1.15
1.67
1.17
34.81
1.52
9.31
1.01
20.99
5.71
0.91
1.27
0.22
0.41
0.29
1.44
0.5*
0.59
lO.e?
0.31
9.51
0
0.4*
0.69
           ( 'total gaa walls, product Ion and consumption la millions of cubic feat.
       Consumption was derived from net Interstate receipts and deliveries of natural
       gas Including foreign Imports and exports.

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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-

 image: 






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

 image: 






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 Products—San Juan Plant,"
Memorandum to C.L. Weaver. August 31, 1973.

 image: 






 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

 image: 






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

 image: 






N5
             LNG facilities
              Gas  production areas
                     Figure  3.   LNG facilites  and gas  production areas  in the United  States

 image: 






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

 image: 






  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 — <b>


      (a\
        Bernhardt,  D.E.,  Radon-222 concentrations in natural gas,
Memorandum to D.T.  Oakley,  April 2, 1973.
               ,  T.F.  op.  cit.
14

 image: 






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

 image: 






 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

 image: 






            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

 image: 






       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

 image: 






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

 image: 






       (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

 image: 






     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

 image: 






                                =  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

 image: 






     Table  5.   Summary of dose conversion factors for radon and radon daughters
Radon-daughter
equilibria
10, 10, 10, 10 <b>
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<d>
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.<c>
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

 image: 






 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

 image: 






 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<corresponding health effects can be corrected
 or extrapolated for the general population and for possible variations in
 exposure conditions.

Postulated exposure conditions

      The initial analysis will be based on parameters specified by
 Barton et al.-'(19)' for dose calculations of radon in natural gas.   The
primary source of radon from use of natural gas in homes comes from an
unvented kitchen range.  The Gas Engineers Handbook (15) indicates the
average kitchen range uses 0.765m3 (27 ft3) of gas per day.  When the
range is turned on, the radon in the gas combustion products is assumed
 to be dispersed in a home with a volume of 226.6m3 (8,000 ft3) and having
an air change rate of once per hour.  (This gives a dilution volume of
 226.6 x 24 = 15,438 m3.)

     Barton et al.  (19) concluded from mathematical analyses that the
average 24-hour concentration of radionuclides is not affected by the
kitchen range-use schedule.  That is, it makes no difference whether the
 gas is used in three 1-hour periods during the day or in 1-hour followed
by a 23-hour decay period.

     A computer program has been written at ORNL (19) to handle the cal-
culation of radon daughter concentrations in the dynamic situation where
radon builds up in the home in proportion to the use of natural gas, and
 the daughters are removed by radioactive decay and ventilation.  This
program computes the cumulative average number of atoms of radon and
daughters f.or 1 minute intervals over a 24-hour period for a given radon
 input and ventilation rate.  The average 24-hour values are converted to
 concentrations for uniform dispersion in the house.  These concentrations
     8Gesell, op. cit.

                                                                       25

 image: 






  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

 image: 






        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<d>
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<d>
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

 image: 






            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

 image: 






 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

 image: 






         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

 image: 






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

 image: 






      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

 image: 






                  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

 image: 






 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

 image: 






          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 <a)

        linear

        linear



        1.9

        1.3

        1.0

        0.84

        0.39



        0.75

        1.0

        1.3

        2

        linear

        linear

        linear
     'a'A linear correction means the correction is proportional
to the variation in the parameter
     (b)Estimated from Jacobi  (33, 34), Altshuler et al.  (25).
                                                                  35

 image: 






 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

 image: 






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

 image: 






 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

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            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 <b>
30
30
100 <b>
100 <b>
30<b>
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

 image: 






      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

 image: 






              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

 image: 






 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

 image: 






 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

 image: 






 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

 image: 






          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

 image: 






      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

 image: 






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

 image: 






      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

 image: 






         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

 image: 






      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

 image: 






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

 image: 






      (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

 image: 






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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)

 image: 






   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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