United States
                 Environmental Protection
                Office of
                Radiation Programs
                Washington DC 20460
September 1987
EPA 520/1-87-20

                                      EPA  520/1-87-20
           September 1987
U.S. Environmental  Protection Agency
    Office  of Radiation Programs
       Washington,  DC  20460



1.    INTRODUCTION                                                  1-1

     Purpose                                                          1-1
     Organization                                                      1-1

2.    WHAT  IS RADON?                                                2-1

     Chemical Properties                                               2-1
     Natural Sources of  Radon                                         2-2
     Uranium-238 Decay  Series                                         2-5
     Radon  Decay Products                                            2-5
     Units of Measurement                                             2-6

3.    WHERE  DOES RADON COME FROM?                                3-1

     Geologic Factors                                                  3-1
          Identifying Areas with Potential  for
           High Indoor Radon  Levels                                   3-2
          Radon in Rocks                                              3-2
          Radon in Soil                                                3-5
          Radon in Water                                              3-7
          Radon in Earth-Based Building Materials                      3-8

     HOW CERTAIN  ARE SCIENTISTS OF THE RISKS?                  4-1

     Derivation of Risk Estimates                                       4-2
          Relationship Between  Radon and Radon
           Decay Product Concentration                                4-2
          Estimation of Cumulative  Exposure to
           Radon and  Radon Decay  Products                            4-3
          Conversion of Cumulative  Exposure to
           Lifetime Risk                                               4-4
          Projection of Lifetime Risks  to
           Entire Population                                           4-10
     Relationship Between  Smoking and Radon Risks                   4-11
     Relationship of Radon Risks to Lung  Cancer
      Mortality Rates                                                 4-16
     Uncertainty  in  Risk Estimates                                     4-16

                         CONTENTS (Continued)


5.    HOW  DOES  RADON CAUSE LUNG CANCER?                        5-1

     Mechanism of Lung Cancer Induction                              5-1
     Risk  From Attached and Unattached
      Radon Decay  Products                                           5-2
     Association  of  Radon and Lung  Cancer                             5-3
     Other Possible Health Risks  from Radon                           5-4

6.    WHEN DID RADON BECOME  A  PROBLEM?                          6-1

     Uranium Miners and  High Incidence of  Lung Cancer                6-1
     Elevated Radon Levels from  Contaminated
      Building Materials                                               6-2
     Elevated Radon Levels from  Natural Sources                       6-3

7.    DOES EVERY HOME HAVE A PROBLEM?                           7-1

     Distribution  of Radon in U.S.  Homes                              7-1
     Where Radon Has Been Found                                     7-2
     Radon in Multilevel  Buildings                                     7-3
     EPA-Sponsored Assessment  Programs                              7-4

8.    HOW  DOES  RADON GET INTO  A HOME?                           8-1

     Mechanisms Inducing Radon  Flow                                  8-1
     Radon Transport  from Soil                                        8-2
     Radon Transport  Through Water Supplies                          8-3
     Radon from  Earth-Based Building Materials                        8-4

9.    HOW  IS  RADON DECTECTED?                                     9-1

     Relationship Between Radon  and Decay
      Product Concentrations                                          9-1
     Selection of  Sampling Methods                                     9-2
     Measurement Condition and  Quality Objectives                      9-3
          Standardized Measurement Conditions                         9-3
          House  Conditions                                            9-4
          Quality Assurance Objectives                                 9-4
     Measurement Instruments                                         9-6
          Alpha-Track Detector                                        9-6
          Charcoal Canister                                           9-7
          Radon Progeny  Integration
           Sampling  Unit (RPISU)                                     9-8
          Continuous  Radon Monitor (CRM)                             9-9
          Continuous  Working Level  Monitor  (CWLM)                   9-10
          Grab Sampling                                             9-10
     Radon Measurements in Water                                    9-12
     Selecting a  Sampling Method                                     9-12

                         CONTENTS (Continued)

10.   HOW CAN  I GET A RADON DETECTOR?                          10-1

     Steps to Obtain a Detector                                      10-1
     EPA's Radon Measurement  Proficiency
      Program (RMP)                                                 10-2

11.   HOW SHOULD RADON DETECTORS BE  USED?                     11-1

     Screening  Measurements                                         11-1
     Follow-up Measurements                                         11-3

12.   WHAT DO  MY TEST RESULTS MEAN?                             12-1

     Lung  Cancer  Risk  Illustrations                                   12-1
     Radon Risk Evaluation  Chart                                     12-3

13.   HOW QUICKLY SHOULD I  TAKE ACTION?                         13-1

     How  EPA Arrived at  its Guidelines                               13-1
     Factors  EPA Considered                                         13-2
     Interpretation of the Guidelines                                  13-4


     Smoking                                                        14-1
     Risks to Children                                               14-2
     Time Spent at Home                                             14-5
     Sleeping in the Basement                                        14-6
     Lifetime  Exposure Period                                        14-7

15.   HOW CAN  I REDUCE MY RISK FROM RADON?                     15-1

     Stop Smoking                                                   15-2
     Avoid Living Areas with Suspected High Levels                   15-2
     Ventilate Home and Crawl-Spaces                                 15-2

16.   SOURCES OF INFORMATION                                     16-1

     References  Cited in Previous  Chapters                            16-1
     References  for General Reading                                 16-15


Radiological Unit Definitions

Meaning of Common Unit Prefixes

Conversion Table


Number                                                              .Pa9.e

2-1        Uranium-238 Decay Series                                     2~3

2-2        Thorium-232 Decay Series                                     2~U

3-1        Radon Emanation Process                                      ^-6

4-1        Comparison of Absolute Risk and  Relative
            Risk  Projection Models                                      4~6

4-2        Possible Overlap of  Radon and Smoking  Related
            Lung Cancer  Deaths                                       **~15

4-3        Total and  Possible Radon Induced Lung  Cancer
            Mortality By Year                                         4-17

14-1       Lung Cancer  Appearance  Rate Following
            a  Single Exposure to Radon Daughters                     14-4

4-1        Risk  Studies                                                 4-9

4-2        Simplified Derivation  of  Estimates  for Under 600 CWLM
           Exposure to  Radon Decay Products                          4-12

4-3        Relative and Absolute Risk  Estimates for Under 600 CWLM     4-19
           Exposure to  Radon Decay Products

11-1       Follow-up Measurements  Made in General Living Areas        11-4

14-1       Lifetime  Risk  of Excess  Lung Cancer Mortality  Induced
           by  Radon Decay  Product Exposure (N/1,000)                14-8

                                Chapter 1

The  "Radon  Reference  Manual"  (Reference Manual)  has been  prepared  by
EPA  to  assist public officials  in  responding  to  questions about  the EPA
pamphlet entitled  "A Citizen's Guide to Radon:  What It Is and What To  Do
About   It"   ("A  Citizen's  Guide").   The  need   for  and  usefulness  of  a
reference manual  as a source of technical  clarification  became  apparent  as
EPA  reviewed  the numerous comments  it  received  from State  and Federal
officials  on   the   March  1986  draft   of  "A  Citizen's  Guide."   Several
commentators  requested  more detailed technical information  than the general
discussion  contained in  "A  Citizen's Guide."  This  document  provides  the
background information  developed for and used to prepare the  pamphlet.

The  Reference Manual  organization follows  the  question  and answer format
presented  in  "A  Citizen's  Guide."   Each section  of the Reference  Manual
provides a more detailed  discussion of the issues underlying  each section of
the pamphlet and  cites the sources of information used by EPA  to  formulate
each  answer.  In  addition,  the  derivations  of  certain  estimates  (such  as
total  lung  cancer  deaths  and radon risk levels) are  explained to allow State
officials  to compare EPA's  methodology with other approaches  presented in
the scientific literature.

Chapters 2 and  3  discuss the  nature and  origin  of  radon.   Chapter  4
presents  the  risk estimates  of  radon  exposure  and  the  uncertainties
involved in these  risk estimates.  Chapter 5 discusses  how radon causes
lung  cancer.  Chapter  6  describes  the  history of the indoor  radon problem.

In Chapter 7,  what we  know about the geographic distribution of the radon
problem  is discussed.  Chapter 8  discusses the ways  in  which radon enters
a  home.   Chapter  9  describes   the  various  detection  devices  currently
available  and  Chapter   10  discusses  how  to  obtain   a  radon  detector.
Chapter   11  lays  out  the  procedures  for  radon  screening and  followup
measurements and  explains  how to  interpret the results.   In Chapter 12,
the implications of the  test results  for  homeowners are  analyzed.   Chapter
13 advises  on  the timing  for  remedial  action.   Chapter 14  explains other
factors   influencing  radon  exposure.    Chapter  15  discusses  mitigation
techniques  for immediate,  short-term  reduction  of  radon levels.   The  last
chapter  (Chapter  16)   lists  the  technical  references  cited  earlier  in  the
Manual  and  provides  a  selected  bibliography,  as  sources of  reference
material  for State officials and  as  recommended  reading  for  homeowners
requesting additional information.   Finally,  the  Reference Manual  includes a
glossary, a list of measurement unit definitions and prefix meanings,  and a
conversion table  between commonly used radiological  measurement  units  and
Standard  International (SI) units.

                                 Chapter 2
                             WHAT  IS  RADON?
"A  Citizen's Guide" describes radon as a naturally-occurring  radioactive gas
that  is  not  detectable  by  the  human  senses.   This  chapter  provides
information on  the chemical  properties of  radon.   The primordial natural
elemental sources  of  radon in our environment — uranium and  thorium —
are  also discussed,  with  information on  the uranium-238  and  thorium-232
decay  series.  Another section addresses radon's radioactive  decay  products
and  their  potential to induce cancer  in lung tissue.   Finally,  a discussion
on  the units  of measurement used to describe concentrations of radon  and
radon  decay  products is provided as an introduction to  the  nomenclature
used in  later  chapters.

Radon is a naturally-occurring,  chemically inert,  radioactive gas.  Because
radon  is chemically unreactive  with  most materials, it  is free to travel  as a
gas.   It can  move easily  through very small  spaces  such as those between
particles of soil and  rock.  Radon  is odorless, invisible, and without taste;
thus,  it cannot   be detected  with  the  human  senses.   Radon  is  also
moderately  soluble  in water  and,  therefore,  can  be  absorbed  by  water
flowing through  rock or  sand  containing  radon.  Its solubility depends  on
the  water temperature;   the  colder the  water,  the  greater  the  radon's
solubility.    A  measure  of  gas  solubility   is   given  by  the  solubility
coefficient.   The  radon solubility coefficient  is  defined as the ratio  of the
radon  concentration  in water to that in air  (Co86).   The  warmer  the  water
temperature,  the  more radon  is released and,  therefore,  the   lower  the
solubility coefficient.  The  maximum solubility  coefficient  of radon is  about
0.5  at  water temperatures  near  0° C,  decreasing  exponentially as  water
temperatures  increase.  For example, at 20°  C, the  solubility  coefficient  is
about 0.25; at 90° C, the coefficient is about 0.1.


Thorium and  uranium  are  common,  naturally-occurring  elements  that  are
found  in low  concentrations in rock  and soil.   Through  radioactive  decay,
both  are  constant  sources  of  radon.    Radon  is  produced   from  the
radioactive decay  of the element  radium, which  is itself a decay  product of
either   uranium  or  thorium.  -   Average  soil  activity   concentrations  of
uranium-238  and  thorium-232  are each about  0.68  picocuries   per gram
(Ne83).  Uranium-238  decays  in  several steps to  radium-226,  which  decays
into radon-222.   Radon-222  has a half-life  of  3.8  days and,  therefore,  has
enough time  to  diffuse  through  dry, porous  soils or to be  transported in
water  for a considerable distance before it decays.   Similarly,  thorium-232
decays  into radon-220 (a different radon isotope,  also called thoron),  which
has a half-life of only 55 seconds.  Because of its short half-life and  limited
ability  to  migrate  into  residences,   radon-220 is  usually a  less  important
source  of  radon exposure  to  humans.   The average  exposure from  indoor
radon-220 decay products  has been estimated to  be about 25 percent  of that
from radon-222  (UNSCEAR82).  Only radon-222  is addressed specifically in
"A  Citizen's  Guide" and is  the radon isotope of most concern to the  public.
Although radon-220,  or thoron,  has  not been measured  separately  in  most
homes,  radon  control actions will  also reduce exposure to thoron.  Radon-222
is  in   the  uranium-238  decay  series,  illustrated  in   figure  2-1.   The
thorium-232 decay  series,  which  includes radon-220,  is illustrated in figure
-    Radioactive  decay  is  a  process  in  which  an  unstable  atomic  nucleus
     undergoes  spontaneous  transformation,  by  emission  of  particles  or
     electromagnetic  radiation,   to  form  a  new  nucleus  (decay  product),
     which  may or  may  not  be  radioactive.  The  level  of radioactivity  is
     measured  in curies, where 1 curie  equals 37 billion  disintegrations  per
     second.  The time required for a given  specific activity of an isotope
     to be  reduced  by  a  factor  of  two  is  called its  half-life.   A picocurie
     (pCi)  is   equal  to   one-trillionth  of  a  curie"Specific  activities
     concentrations  are typically measured in  picocuries  per gram  (in  a
     solid) or picocuries  per  liter (in a gas, such as  air).

                      Rgure 2-1.  Uranium-238 Decoy Series
      Atomic Weight


  Of  = alpha decay
     *> beta decay

  J  = gamma decay
          =  Minor
SOURCE:  Putnam. Hayes ft Bartlett. Inc.. September 1987.


                       Figure 2-2.  Thorium-232 Decay Series
      Atomic Weight


  Of = alpha decay

  f?  = beta decay

  J  = gamma decay
SOURCE:  Putnam, Hayes & Bartlett, Inc., September 1987.


Radon-222  is  preceded  in  the  uranium-238  decay series by radium-226,
which  has a half-life  of  1,600 years.   Radon-222 decays in several  steps  to
form  radioactive  isotopes   with  short  half-lives:  polonium-218,  lead-214,
bismuth-214,  and  polonium-214  (see figure 2-1).  These  isotope  particles
are  commonly   referred  to   as  radon  decay  products.  —    Radon  decay
products  are chemically  reactive  and can attach  themselves to  walls, floors,
or  airborne particles  that  are  inhaled  into  the lungs.   Unattached  radon
decay   products  also can   be   inhaled  and,   subsequently,   can  become
deposited on lung tissue.

The four radon-222 decay products just mentioned all have half-lives of less
than  30 minutes.   This  short half-life is significant since, once  deposited on
lung  tissue,  the  radon decay products  can  undergo  considerable  decay
before  the  action of  mucus   in  the  bronchial  tubes  can  clear   these
radioactive  particles  (see  Chapter  5).   Two  of  the  short-lived  decay
products, polonium-218  and  polonium-214,  emit  alpha particles -  during the
decay process.  Chapter  5  provides an explanation of  how alpha particles
can damage lung tissue  and  lead to lung cancer.
-    Radon decay products are also often referred to as radon daughters  or
     radon  progeny.
-    An alpha particle is  a subatomic  particle  that has  two protons and two
     neutrons and has a double positive electrical charge.   It  is identical  to
     a helium nucleus.


The  specific activity  of radon or  individual radon  decay  product isotopes
can  be measured  in  picocuries  per  liter  (pCi/l).   However, the  specific
activity of short-lived  radon  decay products collectively is  also measured in
units called  working  levels  (WL).   One  working  level  is  defined as  the
quantity of short-lived decay products  that have  the potential  to release 130
billion  electron  volts  of  alpha  particle  energy per   liter  of  air.   The
correspondence   between   working  levels   and   picocuries   per   liter  is
discussed in Chapter  10,  but it  generally depends on  the  degree of radio-
active equilibrium  between radon  and  radon  decay products.   Under  resi-
dential  conditions, radon  gas  and radon  decay  products  tend  to reach  a
state such that one working level is approximately equivalent to 200 pCi/l of
radon-222 (assuming 50  percent equilibrium).

                                 Chapter 3
                    WHERE DOES RADON  COME FROM?
Radon-222  is  found virtually everywhere in at least  small amounts because
its  predecessor,  radium-226 (or, more  distantly,  uranium-238),  is found  in
all  rock and  soil.   In  outdoor  air,  radon concentrations are  usually  less
than one  picocurie  per  liter (pCi/l),  with typical  concentrations  less than
0.5  pCi/l.   Higher  concentrations  of  radon  outdoors  may  be  observed
during  brief periods,  such as during a temperature inversion, when  a warm
air  mass traps a colder one  beneath it.   Isolated outdoor levels  have been
found above 4  picocuries per liter.   Indoor air concentrations can vary from
around  0.5  pCi/l to over  2,000  pCi/l,  with  limited data suggesting that an
average  value  for  homes  is  likely  to  be  in  the  range of 1 to 2 pCi/l  of
radon (Ne86).

Most indoor  radon  comes  from  the  rocks and  soil around  a  home, although
other,  usually  less  significant, sources of indoor  radon  are  water  and some
construction materials.    It  is  the  combination  of a  number  of factors,
however,  that  determines  the  indoor levels of  radon.   These  include
geologic factors  and  building  characteristics.    The  effects  of  building
design on indoor radon  concentration is discussed  in Chapter 8.

The  geologic factors controlling  radon occurrence can be grouped into three
broad  categories  (Nh86):  the radium (or uranium)  content  of  nearby  rock
and  surficial material;  the  physical  characteristics of the  surficial material;
and  fracturing or  faulting  of the rock or surficial material.  These factors
determine the  amount of radon  that will  be produced  in  the soil  gas and
how  easily  this  radon-contaminated  gas  will move  through the  soil.  The
amount of radon  in the soil gas  and the permeability of the surficial material
are  probably  the  most significant  natural  factors  affecting  indoor   radon

concentrations,  but it  is the interaction between the radon in soil gas,  soil
permeability,  and  a home's  structural  characteristics  that determines  the
actual  indoor  radon levels.

Identifying  Areas with  Potential  for High Indoor Radon  Levels

Data describing the natural  occurrence of  radon and radium in the U.S.  are
limited to a few  small-scale  studies, so more  indirect methods  must be used
to identify  areas with  potentially elevated radon  levels.   The  presence of
uranium  is  often  used as  an   indicator to  predict  areas with  potentially
elevated  radon   levels  because  uranium is  the precursor of  radium  and
radon.   Studies  support  the contention  that there is a relationship between
the uranium content of the ground and  radon  levels in  houses.  The  higher
the uranium content,  the greater  the risk of higher  indoor  radon  levels,
regardless of house or foundation type  (Ak84).  A  large volume of uranium
occurrence  information  has been compiled over the  past 40 years, gathered
largely to  assist  in locating uranium ore.   Much  of  the information  was
obtained  during  the  Department of  Energy's  National  Uranium  Resource
Evaluation  (NURE)  program  of  the 1970s and early 1980s.  Although there
are limitations to using  uranium information to search  for  radon, it is quite
useful  for  screening   large  areas  and  determining  an area's  approximate
radon  potential.   At a  specific location,  however, other information, such as
radon  concentrations in soil  gas and  soil permeability (or  radon availability
information),  must be  known to  provide  an  accurate  appraisal  of the  location
in question.   EPA  is currently developing  land evaluation criteria.

Radon  in Rocks

An  estimated  average  uranium  concentration  for the Earth's  crust is 2   to
4   parts   per  million  (ppm) -  or  0.7   to  1.3 pCi/g  (Fi73  and  Er73).
     One part per  million  (by weight) uranium-238 is approximately equal to
     an  activity  concentration   of   0.33  pCi/g  material,   or  0.33   pCi/g
     radium-226  in  equilibrium  with  uranium.   One pCi/g  is equal  to  37
     Becquerels  per  kilogram.    Becquerels  (Bq)  are  the  SI   units  for

However, there can  be a wide  variability in uranium  concentrations, even
within the  same  rock formation or  same  rock  type.   Under  the  proper
geologic  setting,  almost  any  rock  type can  have  an  elevated  uranium
concentration  (e.g.,  vein  deposits with uranium concentrations  greater than
1,000  ppm  can  be   found in many  types  of rock),  but  the  rocks most
commonly enriched in  uranium  are  certain types  of  granitic rocks,  black
(carbonaceous)  shales, and phosphatic rocks.  It is also true that,  in some
cases,  rocks   normally  low  in  uranium  content  which  are located near
uranium-rich  zones may contain  uranium  and  can be responsible for  indoor
radon  problems.

It is  common  for  uranium concentrations  in granites to range between 2  to
10  ppm,  with  averages  around 3  to  4  ppm uranium.   Although  precise
relationships  between uranium content in granitic  rocks and  radon levels
have  not been  established,  granites  with  uranium concentrations  above  4
ppm may be considered a moderate  to high  source of radon.  Any granite
with more than  10 ppm uranium  should be suspected of having a high radon
potential.   In  particular,  granitic rocks  have the potential  to  cause acute
radon  problems in some areas of the  U.S.  because of fracturing,  faulting,
and elevated uranium  concentrations.

In general, black  (carbonaceous)  shales  are more likely to have  uranium
than  other  shales  because of the carbon content and  oxidizing conditions
under which the black shale  forms.   Uraniferous black shales often average
up  to  20 ppm uranium,  but can contain  more than 250 ppm  (Sw61).   Black
shales, especially phosphatic  shales,  may produce  the greatest number  of
indoor radon problems due to their wide distribution and uranium content  if
the shales  are  located  close  to the  surface.  Black  shales with  uranium
contents greater than 4 ppm  should  be considered  at least a  moderate radon
source.   Uraniferous black  shales   occur  mainly  in  parts of  Wyoming,
Montana,  South  Dakota,  Nebraska,  Kansas,  Oklahoma,  Texas,  Tennessee,
Kentucky,  Indiana, and New  York.

Because of  uranium's  chemical  affinity for  phosphates,  phosphatic rocks
often  contain  greatly  elevated   levels of   uranium.    It  is  common   for
phosphate  rocks  to average TOO ppm  uranium or higher, with more uranium
being  associated  with  greater phosphate  content.   In addition,  localized
phosphate  concentrations,  such  as phosphate nodules  in black shales,  can
contain much higher uranium  concentrations.   High grade  phosphates occur
in parts of  Florida,  southern Georgia, and  in  the Phosphoria  Formation  in
several Western  States.   Low-grade  phosphate  lands  occur  in  North  and
South  Carolina,  coastal  Georgia,  and  T«$>nessee.   Some  unpublished data
suggest that lower-grade  phosphates  may  not pose as  significant  a problem
as do other rocks, but it  is too soon  to know for certain.

Carbonate  rocks  (limestones and dolomites) usually average only around  2  to
3 ppm uranium.    In some instances,  however, they can be host  rocks  for
uranium.   This is  especially true  when fracture  or fault zones  are  present.
It is possible  that  phosphatic carbonates  may be a problem  in some areas
due  to their  weathering characteristics  and their potential for  above-average
uranium contents,  but  this has not been confirmed.

In general, sandstones are not uraniferous,  although continental  sandstones
derived  from  uranium-rich  source  rocks,   such  as  those  found  in  the
western uranium mining  districts,  are often  uraniferous.   The rocks least
likely  to  contain  uranium  are  basaltic   lavas,  or  their  metamorphic
equivalents,  and  rocks that have  similar chemical  compositions.

The  fracturing and faulting  of   a  rock  can alter its  radon  potential  in
several  ways.    Fracturing and   faulting  can  create  extensive  migration
pathways  for radon, thus increasing  the  radon  flow  and enhancing radon
movement  into  a  house.  Fractures and faults are sometimes associated with
elevated uranium concentrations  because uranium-bearing fluids deposit the
uranium within the fracture  or  fault  zones.   Fracture or fault zones with
very high  concentrations  of uranium  and radium  seem  to be associated with
homes having the  most  severe  indoor  radon problems.

Soils  as  well as rock can  be affected by  fracturing or cracking.  Some soils
can   shrink  and  produce   cracks   with  a  relatively  high   permeability.
Sometimes   surficial   materials   can   have   fractures   that   can  increase
permeabilities  up to  three or more  orders of magnitude (We86).   In  these
cases of extreme soil permeability,  soils with relatively low radium content
may pose potential radon  hazards.

Radon in Soil

Soils  play  two  important roles in radon occurrence.   Many  soils are derived
from  the immediately underlying rock,  so they tend  to  have similar mineral
compositions as the parent  rock.  If the underlying  rock  is suspected as a
source of  radon, the associated soils can also  be a  potential  source of the
radon.   Soils contain an average of about 1  to  3  ppm uranium  and  a similar
amount  of  radioactivity,  but these  levels can  vary,  depending  upon  the
rock  from  which  the   soil   was formed  and  the  environmental conditions
during the time of the  soil's formation.

Soil   radium  levels  in   the  U.S.  average  around  1   pCi/g (De86; My83);
however, even this amount  of radium can cause  problems in some instances.
Calculations  to this effect have  shown that what may  be considered  a normal
level  of  1  pCi/g radium in  the  soil  can easily produce between 200 to over
1,000 pCi/l radon  in the  soil over a range of typical soil  conditions  (Ta86;

Figure 3-1  illustrates how a  radon  atom produced by  radium  decay in  the
soil or rock  can  migrate into soil gas and possibly enter a  home.  Not all of
the  radon  produced  in  soil  and  rock  will  be  available  to  fill  soil  pore
spaces.   Some  of the radon  produced will remain  trapped within the grains
of the soil or  rock itself  or  will become  lodged  in adjoining grains and  will
not be  able to escape  into pore spaces.   This will be a  function  of  the
grain size  and  porosity  of the parent material.   Perhaps the most important
factor in radon  production  and migration  is the  presence  of  water in  the
soil.  Water in the soil pore enchances  the apparent production  of  radon


                    Figure 3-1.  Radon Emanation Process

                           (Not Drawn to Scale)

    •   Radium-226

    A   Radon-222

    Of   Alpha  Particle
R   Recoil Range - The  distance that a
    radon-222 atoms travels when  the
    radium-226  atom disintegrates
Adapted from WIL83, p. 21,

because  it reduces  radon's  recoil range and may  prevent radon atoms  from
lodging  in adjacent soil  grains.   The radon atom can then  diffuse into the
pore's air space where  it  is  available to  readily  migrate  through the  soil.
If the pore  spaces  are  totally saturated,  as  is  the  case below  the  water
table or temporarily after  a heavy  rain,  the radon atom  will probably not
become part of the  soil  gas.  This  is  true because water  hinders  radon's
migration by  lowering  the  diffusion coefficient and  by absorbing  the  radon
atoms  (Ta80).   In summary,  radon  transport through soil  increases as soil
moisture  increases, until the soil moisture content is  so great that  further
increases in  soil moisture begin to reduce  radon transport.

Soil  permeability  also  plays a  prominent  role in determining  whether the
radon  produced  will  be  able to enter  homes.  Because soils are  one medium
through  which radon  travels, high soil  permeabilities  promote higher  indoor
radon  levels, while low permeabilities  retard  radon movement  and  reduce the
probability of  radon  entering a home.   Large amounts of radium  in the soil
tend  to  increase  indoor  radon  levels, although  the soil's  permeability can
change that  tendency.   If combined with high permeability,  it is possible to
have  high  indoor  radon  levels  with  low   radium  levels.    As   mentioned
earlier,  fracturing  can  also  increase  a   soils   permeability.   It  is   still
unknown,  however,  whether it  is the average permeability  or the zones of
above-average   permeability  that  contribute  the  most  to  indoor   radon
concentrations.  It is theoretically possible that one fracture may be enough
to produce indoor radon  problems in areas of normally low permeability.

To  summarize,  the amount  of uranium  or  radium in  an  area  can only be
used  as  a rough approximation of an area's radon potential  because   many
other  factors,  both  natural and manmade,  determine  if  a land's   radon
potential  will  be realized in indoor  radon  levels.  To determine  the actual
radon  potential  at  a  site,  it  is  necessary  to  take into  account  several
variables,   including   the   soil  radium   content,   soil   permeability,   and

Radon in  Water

Another  source  of indoor radon is groundwater.   As with radon in the soil,
the primary risk from radon in water is  the  risk of lung cancer induced by
inhaling  radon that  has been  released from  water  into the air.   Overall,  it
is estimated  that drinking  water  contributes  only one  percent  to  seven
percent of the radon found in  indoor  air (Co85).

Any process that exposes water to air releases radon.  Radon is  released  in
the home  during activities such as showering, washing  clothes, and flushing
toilets.  Most homes are served by  public water supplies  that  are  aerated  at
treatment facilities  before  the  water reaches the home  and, therefore,  have
relatively low radon levels.  Homes with water from other  sources,  such  as
private wells, may contain extremely elevated radon levels.

The national average population-weighted concentration of radon in drinking
water  from  public water supplies  serving more than  1,000 people is  about
210 pCi/l (Co86).   The  average for all public drinking water supplies from
groundwater sources is  about  420 pCi/l (Co86).  The  highest  level of  radon
In drinking  water, 2,000,000 pGi/l was found in a  private well (Co85).

Models have been developed  to  estimate  the relationship between radon  in
water  and the resulting level  of  radon  in air.   Roughly stated,  the  model
estimates  that 10,000 pCi/l of  radon in water will lead to  1  pCi/l of radon  in
indoor air,  assuming  normal  water  usage  and   household   characteristics

The  Environmental  Protection  Agency  has published an  advanced  notice  of
proposed  rule making for Maximum Contaminant  Level  Coals (MCLCs)  and
National  Primary Drinking  Water  Regulations  (NPDWR)  including Maximum
Contaminant Levels  (MCLs) for radionuclides in water. Including  radon.   A
final rule has  not yet been developed.

Radon in  Earth-Based Building Materials

Radon is  also  released  from many building materials,  but  normally  at very
low  levels.   Wood  materials  tend  to  emit the  least  radon,  while   brick,
cement,   and cinder  block  emit  more.   Radon is  released  from all of these
sources  at  such  a  low  rate  that these  materials  are  rarely  important
contributors to  elevated  radon  levels.   However,  there have  been  a  few
cases  in  which  materials  containing significant radium  concentrations were
used  to  form  building  materials.  Examples  of these situations are  houses
built  using materials  contaminated with uranium or  radium mill  tailings  and
uraniterous  phosphogypsum  waste.   There may also  be problems in  homes
that use radium-containing heat storage rock (e.g., large pieces of granite)
which circulate volumes of air into the  living areas.

For most  homes, the greatest contributor of radon  will be  the underlying
soil,   especially  if  it  contains   significant  amounts  of  radium.    The
contribution  of  radon   from  water  will  not  be  as   significant  as  the
contribution from soil in most cases.   Building  materials will contribute' the
least  amount of  radon to  a  home,  except  in  those unusual cases  where the
materials   are   derived  from naturally-  radioactive  source  or have  been
contaminated with radium-containing waste.

                                 Chapter 4
                      HOW DOES RADON AFFECT ME?
As  stated  in  "A  Citizen's  Guide,"  an increased  risk  of  developing  lung
cancer  is the only known health effect associated with exposure  to  elevated
concentrations of radon.  This chapter discusses two related  sections of "A
Citizen's  Guide," which both address radon health  risks.   The first of the
pamphlet  sections, "How  Does  Radon Affect  Me?,"  presents  EPA's  estimate
that 5,000 to 20,000  lung  cancer deaths per year are  potentially attributable
to radon  and then compares  this estimate  to  the  85 percent of 130,000 lung
cancer  deaths from  all  sources that are  attributed  to  smoking.   The first
two  parts of this  chapter discuss  the derivation of EPA's  population  risk
estimates  and  compare  the  radon and smoking  lung cancer  figures.   The
second  section on  risk  in "A Citizen's Guide," "How Certain  Are Scientists
Of  The  Risks?," puts  the  uncertainty underlying  radon  risk estimates  in
perspective  and  acknowledges  the  influence of the Science Advisory  Board
(SAB)  on  EPA's estimates.   The  last  part  of  this chapter expands the
discussion  of  uncertainty  and  compares  other  risk  estimates to  the SAB

It is important to recognize  that  the  derivation of quantitative risk estimates
is a  difficult  scientific undertaking  that must  be  based on  health  risk
studies  which  are subject to  various  interpretations.   As new  information
becomes available  (especially regarding  the distribution of exposure  levels
and  the dose/response  relationship  between radon decay products  and lung
caricer),  EPA  will   revise  its  estimates  appropriately.    However,  the
fundamental  purpose  of the  estimates  presented in  "A  Citizen's Guide"  is
not  to  provide definitive estimates  of lung  cancer  deaths,  but rather  to
emphasize for homeowners the overall significance of radon risks.


The derivation  of  EPA's risk estimates  involves  a  variety  of technical and
medical assumptions.   For purposes  of  explanation,  this derivation can  be
divided  into   four  steps:   (1)   determination   of   radon   decay  product
concentration  from  radon concentration;  (2)  estimation of cumulative  radon
decay  product  exposure; (3) conversion of  individual cumulative exposure
to lifetime risk; and (4) projection of individual  lifetime  risks to the entire
population.  Each of the steps  is explained  in the following  discussions.

Relationship Between Radon and Radon  Decay Product Concentration

As  will be  explained further in Chapter 5, it  is the  radon  decay  products
rather than the radon  itself that are believed to be  responsible  for most  of
the  health risk  due  to indoor  radon.   Depending on  the  measurement
device,  either   radon  or  radon  decay   product   concentrations  can   be
measured directly (in picocuries per liter and  working levels, respectively).
The relationship  between  the  two units depends  on the  extent to   which
radioactive equilibrium  is reached  between  radon and the  decay products.
As  decay  products are  formed  from radon,  they in turn disintegrate into
other  isotopes.   If the  rate of  formation  and disintegration  of the   decay
products  is exactly equal, 100 picocuries  per liter of radon  would exist  in
equilibrium with 1  working  level  of decay  products  (this state is termed
secular equilibrium).   However,  other  processes  (such  as  attachment  of
decay  products to the walls or floor) tend  to  remove some  decay  products
from the  air  before  they disintegrate,  so that secular equilibrium  is  never
achieved.   Based on simultaneous  measurements  of  radon and  radon   decay
products,  it has been found  that the equilibrium  fraction  ranges  from  0.3  to
0.7, with an average of around 0.5.  Using  the  average equilibrium fraction
of 0.5, a  ratio of 200  picocuries per liter  of radon  to  1 working level  of
decay  products is  fairly typical  for  residential  environments  (Ce85).   The
relationship between radon  and  its  decay  products  is  explained  in  more
detail in Chapter 9.  EPA used this ratio to convert radon concentrations  to
working levels.

Estimation  of Cumulative  Exposure to Radon and  Radon Decay  Products

The biological  factor  of  most interest  in  determining  the  cancer risk  from
radon  decay products  is the actual radiation dose delivered to the cells of
the  lung.   To  determine  this,   it  is   first  necessary  to  estimate  the
cumulative exposure  to radon decay products.  By  convention, cumulative
exposure  to radon decay  products  is  measured  in  working  level  months
(WLM), which  is defined  as  the  exposure a miner receives  during 170 hours
(the approximate number of working hours in 1 month)  in  a 1-working  level
environment.    However,   since   exposures  to  miners   and  to   average
homeowners  differ, and  since  medical  estimates  of  the  lung  cancer  risk
induced  by  a  given  radon  exposure  are  based  on  miner  populations,
cumulative residential  exposures must be adjusted.

The first adjustment factor  is inhalation rate, which  determines the volume
of  air drawn  into  the lungs  and,  hence, the potential  for  radon  decay
products  to  be  inhaled  and deposited  on the  walls  of the  airways.   On
average, the inhalation rate of a miner is  somewhat higher than the rate for
the  general  population as  a result of increased  physical  activity.  The
breathing rate  of a miner is about 30 liters per minute if half of his activity
is heavy  work  and half is  "light  activity" (ICRP79),  while  the breathing
rate of an average adult is about  15.3  liters  per  minute (ICRP75).  Thus,
one  adjustment  routinely   made   when   estimating   cumulative residential
exposures  is to correct the  exposure estimate  for this difference in average
breathing rate.

A second factor  affecting cumulative exposure  to  the general population is
the  duration of  exposure over  a  year.   While miners  are  assumed  to  be
exposed  only  for  170  hours  each  month,  residential  exposures  occur
throughout the portion of the year spent in the residence.  EPA's estimates
assume that  the  resident is  exposed to a given  radon  level  75 percent of
the  time  (i.e.,  the  resident  is  in the house  75  percent of the   day,  on

average).   This assumption is based  on two studies  (Mo76;  Oa72),  and  is
consistent  with  a  more  recent British survey  (Bn83)   (see  Chapter  14).
Thus, correcting for  both the differences  in  breathing  rate  and  in  the
proportion of time exposed,  continuous exposure of an  average adult  to a
concentration  of 1 working level  for  a year  is  approximately equal to  an
annual cumulative exposure of about 20 WLM for a miner:

    365 days x 2k hrs x 0.75 x 15.3 lpm/30 1pm x 1 WLM   - 19.71 WLM (effective)
      yr     day                        170 hrs      yr

A  number of other factors  also  influence the effective cumulative exposure,
including the  size of the lung, the location and type of lung cells irradiated
(which  depends on  where the decay  products  are deposited),  and  the
differences  in the sensitivity of lung  cells  depending on  age and sex.  Due
to  incomplete  information,  EPA's  estimates  do  not account  for  potential
variations  in  lung  cell  sensitivity,   and  both  sexes  and  all  ages  are
considered  to  be  equally  sensitive  to lung  cancer  induction.   The  EPA
estimates also  do not  address  the  question of  deposition versus  number,
type, and  sensitivity of cells  at risk  in the airways.  However, the  smaller
lung  size  of  children,  and,   therefore,  the  differences  in  age-specific
breathing rates, is accounted  for in the EPA estimates.

Conversion of Cumulative Exposure to Lifetime  Risk

The objective  of this  step  is  to  estimate the  lifetime  risk  faced  by  an
individual who receives a  known cumulative exposure.   In practice,  this  is
the  most complicated  step  and  the  one  that  encompasses  most  of  the
biological uncertainty.     The  complexity  results  both  from  uncertainties
regarding  the  mechanism  of  cancer  formation  and  the   limitations  of  the
epidemiological   data  used  to  estimate  cancer  risk.   A large number   of
factors are involved, as explained  subsequently .

Estimates of the risk of lung cancer associated with exposure to radon  and
radon  decay products are obtained primarily  from  epidemiological studies of
underground  miners.   For  example,  in a  hypothetical  study of  1  million
miners,  each  exposed to 1  WLM over a  lifetime, if 200 miners died of lung
cancer,  a lifetime  risk  estimate of 200  fatal cancers per  million persons  per
WLM could be  derived.   However,  in the epidemiological studies to date,  the
entire population  of  miners in the study  group  has  not  yet died.   As  a
result, the risks  observed over  part of a  lifetime  must be extrapolated in
order  to  estimate the lifetime risk for  a  given exposure.

To estimate the risk of exposure  beyond the  years of observation, various
risk projection  models may  be  used.  A  relative risk  projection model  or an
absolute  risk  projection model  are  frequently used.   Figure  4-1 illustrates
the  difference  between  the two  types  of  risk  projection  models.    The
relative   risk  model  extrapolates  an expected percentage  increase  in  lung
cancer risk  per unit dose  into future years, while an absolute  risk  model
extrapolates the average observed  number of excess  cancers  per unit dose
into future years of risk.  Relative  radon  risk  is stated  in terms  of  the
percentage increases  in  annual  lung cancer  risk per WLM of exposure, while
absolute  risk is expressed  as  the number  of fatal lung  cancers  per million
persons  per WLM of exposure,  per year at risk (or per lifetime).

Because  the  underlying  cumulative  risk  of  lung  cancer  increases rapidly
with age, the  relative risk model  predicts a  larger cumulative probability of
excess lung  cancer towards  the end of  a person's  lifetime. -   In contrast,
the absolute risk  model  predicts a constant incidence  of excess  lung cancer
across time.  Given the incomplete data (i.e., less than  lifetime follow-up)
we have  now,  a relative risk model projects  somewhat greater risk  than an
absolute  risk  model.
—    Although cumulative  risk  increases, annual  risk  (as shown in  figure
     4-1)  peaks during  middle age,  and then  declines due  to the greater
     competing  risk of other causes of death.


   Rgure 4—1.  Comparison of Absolute Risk and Relative Risk Projection Models

                   ABSOLUTE RISK  MODEL




       Excess Cancer
       Risk (Constant Value
       over the
       Baseline Risk)
                                          Risk of Cancer with
                                          Radon Exposure
                          Baseline Risk of Cancer
                          Without Radon Exposure
      Excess Cancer
      Risk (Constant
      Proportion of the
      Baseline Risk)
                    REU\TIVE  RISK  MODEL
                                          Risk of Cancer with
                                          Radon Exposure
                          Baseline Risk of Cancer
                          Without Radon Exposure

NOTE: The relative and absolute risk levels shown are for
      illustration purposes only.
SOURCE:  Putnam. Hayes it Bartlett, Inc., September 1987.

Scientists  have  not  agreed  on which  projection  mode!  is the  appropriate
choice for most  radiogenic cancers,  although  evidence  is  accumulating  that
supports  the  relative risk model for most solid  cancers.   Reports from the
National  Academy of  Sciences' Committee on the Biological  Effects of Ionizing
Radiation (BEIR80),  among others,  have favored the use  of a  relative  risk
model  for  those  cancers,  other than leukemia or  bone  cancer,  observed  to
result from radiation exposure.

Prior  to  1983,  the  EPA  Office of  Radiation  Programs   (ORP) used  both
absolute and relative risk models to estimate the  risk from radon and radon
decay products.   Since 1983. ORP has  used  only relative risk  models,  and
used  a range  of  1.2 percent to 2.8 percent increase per WLM  as of 1984.
In  1985.  the  Radiation Advisory Committee  of the  EPA  Science  Advisory
Board supported the  use of the  relative risk  model,  and  the Committee
recommended  that a  range of one to four percent would  better reflect the
uncertainty and  range.   EPA adopted that recommendation and  now  uses a
relative  risk  of  one percent  to four percent increase  in risk  per WLM  of

In addition to the risk projection model assumed,  three  other  factors  must
be  considered in  order  to  project  lifetime  risks.   The  most  important  of
these  factors  is  the  underlying  dose/response  relationship, that is,  how the
risk  depends  on the  level  of exposure received.   This  assumption  is
important  when  extrapolating  exposures  and  risks  measured  at one  level
(e.g., in a mine)  to risks from exposures at different  (often lower)  levels.
In general, threshold  levels of exposure below which  no risk  occurs  have
not  been  identified  for  physical  carcinogens.   Theoretically,  the  smallest
quantity  of  energy  deposition  can  transform  a  cell and lead to cancer.
There  is  evidence  at   the  level  of   microdosimetry   and   cell   biology
which supports this  argument, but there  is no definitive  proof  of it  as  yet.
EPA's calculations are  based  on a linear dose/response relationship (with  no
threshold), which appears to be consistent with  studies to date.  Based  on
this  assumption,  a higher cumulative exposure results  in a proportionally
higher risk.


While  a  short time ago, one spoke of extrapolating  from  the  high  exposures
characteristic of  mines to  the  lower  environmental  exposure levels,  this is
no longer true.   Until recently,  the  exposures reported in most  studies of
miners were high:  821  to  1180 cumulative working  level months (CWLM) in
U.S.  uranium miners (NIOSH85;  Th82); 289 to 313  CWLM in Czech  uranium
miners  (NIOSH85;  Th82);  204  to  248  CWLM in  Newfoundland  fluorspar
miners (Th82);  270  CWLM in Zinkgruven metal  miners  (Th82);  etc.   (See
table  4-1.)   In   contrast,  before 1985,  estimated  exposures in  residences
usually  ranged  from 11 CWLM at  1  pCi/l  of radon to 22  CWLM  at  4  pCi/l of
radon  (18 CWLM to  36   CWLM  if  a  100 percent occupancy factor  was
assumed).   Thus,  extrapolation  downward  from  the  miner   data   was

However, the  recent  discoveries  in   Pennsylvania  and  New  Jersey  have
revealed  that radon decay product concentrations  in some homes  can  be so
high  (e.g., 5  WL  to  10  WL) that 2  or  3 years of exposure  in  the  home
would be equivalent to the exposures  reported in  some  of  the more highly
exposed  study  groups of  miners.   In  addition,  more  recent  studies of
miners  include  cumulative  exposures   well within  the  range  of  the  older
assumptions about  residential exposure' levels: 31  to  131  CWLM  in  Ontario
uranium  miners  (Mu83);  81.4 CWLM in Malmberget  metal miners (NIOSH85);
43 CWLM in Norwegian niobium miners  (So85);  15  to 25 CWLM in Cornish tin
miners (NIOSH85);  20.2 CWLM  in Saskatchewan uranium miners  (Ho86);  etc.
(See  table 4-1.)   Furthermore, in the recent large study of  Saskatchewan
uranium  miners  (Ho86), the  risk of excess lung  cancer  death  was  elevated
for all   exposures  above  5  CWLM.    Therefore,   questions of  theoretical
thresholds and  extrapolating downward  are  now  less  important  since the
available epidemiological studies now encompass many of  the  exposure levels
found  in  the   indoor  environment.    Hence,   the   linear  dose/response
assumption, which is required for extrapolation,  is  less important.

In addition  to the dose/response relationship, a second factor to  be con-
sidered  is  that  the  incremental  risk  attributable to  radon  decay products
depends  on the  other competing  risks to  which  a person  is  exposed.  In
projecting  lifetime  risks,   competing  risks  are accounted for  by  using  an


                                Table 4-1
                               Risk Studies
              Follow-up in
       Mean      Person-
          (per 10 PY/WLM)(per WLM)
 Risk %    SMR  Exposure     Years     Reference
                (CWLM)      (PY)

(12.243 M)
 2.82    862.00    270

         1.451     716
          436     140

U.S. Metal
25,033     NIOSH85
25,033     Th82
Tin Miners
(1,333 M)
                       211    15-25
                           27,631     NIOSH85
(124 M)
         40543   2,970
SOURCE:  U.S. Environmental  Protection  Agency. July 1987.

 actuarial  calculation  (a  life-table analysis)  that  depends on  the age-specific
 underlying mortality  rate.   EPA's  current  risk  projections  in  the  Radon
 Risk Evaluation  Chart  (page  10)  in  "A  Citizen's  Guide" use  1980  mortality
 rates  and  the  1980  life table.  An  important  implication  of considering
 competing risks  is that  the cumulative lifetime  risk is  not  a linear  function
 of  exposure,  even  when the dose/response relationship is assumed  to  be
 linear.    This  non-linearity,  which  is  most  apparent  at   high  cumulative
 exposures, accounts  for the fact that the probability of death  cannot exceed

 The third factor  affecting lifetime risk projections is the assumed  induction
 period, i.e., the lag or latency between when the exposure occurs and the
 onset  of  disease.  Most cancers  (including  lung  cancer) have an  average
 latency period of between 20 and 30  years,  although this period may depend
 on  age.  -   The risk  estimates in   "A  Citizen's  Guide" assume  a  minimum
 induction  period  of  10  years  in conjunction with a  relative risk  of 1 to 4
 percent per WLM, as  well as a linear dose/response  relationship.

 Projection of  Lifetime Risks  to Entire Population

 To   derive  the estimates in  "A Citizen's  Guide" of 5,000  to 20,000  lung
 cancer  deaths per year from radon  requires that the   relationship  between
 individual lifetime risk  and  exposure be  used to project risks  to the  entire
 population.  This calculation depends on  the size of the population  exposed,
 the  exposure duration and  level, and the  risk/exposure relationship.  The
 factors  necessary to  convert  indoor  radon  levels to individual lifetime risk
 have been explained  in  earlier steps.  The third  factor, the distribution of
 indoor  radon  levels, is  currently   uncertain.   However,   as  explained  in
 Chapter 3, "A Citizen's Guide" assumes an average indoor radon  level of
 0.004 WL  based on a study of New York  and New  Jersey homes (Ge78).
-    For  example,  the  induction period  can  be modeled by  a  minimum  age
     (or latency)  before which no  cancers  appear, together with a minimum
     induction period between  the time of exposure  and the appearance of

The  estimate  of  5,000  to  20,000  lung  cancer  deaths  was  derived  by
calculating  the  age-average risk  per WLM  of exposure  across  the 1980
population.   Using  a  relative risk of 1  percent to 4  percent  per WLM,  an
average  radon  decay  product  concentration of 0.004  WL,  and  1980 vita!
statistics  results  in  a calculated range  of 4,852  to  19,196  lung  cancer
deaths.  To reflect the uncertainty underlying  these estimates,  "A Citizen's
Guide" reports a range of 5,000 to 20,000  lung  cancer  deaths  attributable to
radon exposure.   These  estimates may be  updated  in light  of new vital
statistics and exposure data.

The entire  estimation  procedure  is summarized  in table 4-2.   As noted in
this  table,   several  of the steps have  been   simplified  for  the  sake  of
illustration   (especially,  consideration  of  age-specific  risk  and  induction
period),   resulting  in slightly  different  values  than  were  stated  in  "A
Citizen's Guide."

Current evidence  suggests  that  smokers  are at  higher  risk from  radon
exposures  than  nonsmokers.   Analyses  of the U.S.  uranium  miner cohort
(Wh83;   Th85;  Ho86),  the  only  group  of  miners   for  which  extensive
individual  smoking  data  are available,   indicate  that  the  joint  effects of
smoking and  radon  are  more than  additive  in  causing  lung cancer.   A
smaller  study of residential  exposures  in Sweden  provides further  support
for this conclusion (Ed83).   A laboratory study of combined cigarette  smoke
and  radon exposure  in  rats indicates a  synergism  between the two factors
in inducing lung cancer,  consistent with the  hypothesis that  radiation  acts
as an  "initiator" and  tobacco smoke as a  "promoter" of the  carcinogenic
process  (Ch81).

In contrast to these results, however, an  epidemiological  study of  Swedish
miners  (Ra84)  and a  study  of dogs  exposed  to radon  and cigarette  smoke
(Cr78)  suggest  a  less  than  additive interaction  between  the  two  factors.
One  speculative  explanation of these results is  that  an  increased  mucus


                            Table 4-2
            Simplified Approximation Of Estimates For
        Total U.S. Lung Cancer Deaths Due To Indoor Radon
A.   Equation
     RADON (1980) = CR * T * FWLM * RRRM * TCR * POP


     CR       =    average (mean) lifetime indoor radon decay
                   product concentration
                   0.004 WL-life

     T        =    average interval of lifetime exposure in
                   hours, following a 10 year minimum induction
                   period during which no lung cancer will be
                   observed, assuming 75% occupancy and 73.88
                   year life span (1980 vital statistics)
                   .75 * (73.88-10) * 365 *24= 419,691.6

     FWLM     =    factor converting average cumulative indoor
                   exposure in WL hours to working level months
                   (WLM) for a miner (since risk estimates are
                   based on miner data), accounting for 170 hours
                   per month exposure period per WLM (by
                   definition), and the difference in breathing
                   rate between the average adult (15.3 liters
                   per minute) and a miner (30 liters per minute)
                   1/170 * 15.3/30 = 0.003 WLM per hour.

     RRRM     =    relative lung cancer risk for lifetime
                   exposure to radon, per WLM, using relative
                   risk model
                   1% to 4% per WLM

     TCR      =    underlying annual average of U.S. lifetime
                   lung cancer risk (1980 vital statistics).
                   4.584 * 10~4 per person.

     POP      =    1980 U.S. population

                      Table 4-2  (Continued)

            Simplified Approximation Of Estimates For
        Total U.S. Lung Cancer Deaths Due To Indoor Radon

B.   Calculation:

     TOTAL LUNG CANCER DEATHS =  0.004 * 419,691.6 * 0.003
                                 * 0.01 (lower risk estimate)
                                 * 4.584 * 10~4 * 226,545,805

     TOTAL LUNG CANCER DEATHS =  0.004 * 419,691.6 * 0.003
                                 * 0.04 (upper risk estimate)
                                 * 4.584 * 10~4 * 226,545,805
                              =  20,921

C.   Notes:

The above calculations differ from the estimates in "A Citizen's
Guide" of 5,000 to 20,000 lung cancer deaths principally due to
two simplifications used in the  equation above:

1.   The factor FWLM doesn't include correction for the smaller
     lung size and higher breathing rate of children.  Both are,
     in fact, recognized in the  detailed analysis.

2.   The product of TCR and POP  is replaced in the detailed
     analysis by calculations using 1980 mortality rates and 1980
     life table statistics.  The detailed actuarial analysis more
     properly accounts for latency effects, competing risks, and
     lower underlying risk of lung cancer at younger ages and,
     hence, results in a lower estimate.

Use of the 10 year latent period leaves an average lifespan of
63.88 years [73.88 years-10 years] during which the potential
excess lung cancer risk can be expressed.

SOURCE:       Putnam, Hayes & Bartlett, Inc., September 1987.
              The numerical assumptions listed in Part A of this
              table are based on EPA analysis.  Specific sources
              are noted in the text.

thickness associated  with  smoking bronchitis shields  the  target cells  in  the
lung  from the alpha  radiation  emitted  by  deposited  radon  decay products
(Cr78;  Sg83).

While subject to  revision in light of future scientific  findings, EPA believes
the  weight  of current  evidence  supports the  concept that the  risks from
exposure to radon  and cigarette  smoke  are greater  than  the sum  of  the
risks  from  either  alone.    In  fact,  they may  interact  so  strongly  as  to
produce multiplicative  risks.  When estimating  excess  lung  cancers  due  to
radon  exposure, EPA employs  a  relative  risk  model in which  the excess is
proportional  to  radon exposure and  to  the baseline lung  cancer  rate  in  the
population.    Implicitly,  this  model  assumes  a  multiplicative   interaction
between  radon   and  all  other  risk  factors   for  lung  cancer,   including

By far, smoking is  the most  important  risk  factor  for  lung  cancer.   "A
Citizen's  Guide" notes  that  the American Cancer Society estimates 130,000
people will die of lung cancer from  all causes in 1986,  and that according to
the  U.S. Surgeon  General, approximately 85 percent  of  these (i.e., about
110,000  deaths)  could  be  attributed  to  smoking.   As  noted also  in  "A
Citizen's  Guide,"   5,000   to  20,000   lung   cancers  each  year may  be
attributable  to   radon.   This   range  for  estimated  radon   induced lung
cancers, moreover,  does not fully  reflect recent increases  in  baseline lung
cancer  rates or  higher estimates of radon levels  in  homes, and  it may be
revised upward  in  the future.   At first,  it may  seem that  the numbers  are
inconsistent,  since   the  sum  of lung  cancers  attributable  to   radon  and
smoking  approaches  or  exceeds   the  total   number actually  observed.
However, there  is no inconsistency.   It is implicit in  the  relative  risk model
that smoking and  radon  exposure  are both causal  factors  for  some lung
cancers  ~  for about 85 percent of all lung cancers attributable to  radon,
indeed,  smoking is  a  joint causal  factor.  The envisioned overlap  in  the
estimates of risk from smoking and  radon is  illustrated  in  figure U-2.

           Illustrative  Breakdown of  U.S.  Lung  Cancer  Deaths*

I    60
                                                     Attributable Cause
Radon &
                                                     nor Radon
           * Presumes a 20%  attributable fraction for radon  in each category.
            Attributable fraction for smoking in current smokers  is 92%, in former
            smokers is 83%, and in all categories combined is 85%.  Effects of
            passive smoking  are not  considered.


Some have pointed out  that  EPA's estimate  of  the  increase  in  lung cancer
rate attributable to radon exceeds  the  actual reported mortality  rate of the
disease only  a few decades  ago.   As with the relationship between  smoking
and  radon,  there  is  no  inconsistency.   A  large  part  of the  increase  is
thought  to be due to  increased  exposure to various carcinogens, especially
tobacco smoke,  and some  of the observed increase  in  lung cancer mortality
reflects  more accurate  reporting of the disease.  According to the relative
risk model,  the rate  of  radon induced  lung  cancers  (assuming  constant
radon  exposure rates)   increases in proportion  to the baseline rate of the
disease,  hence  it  is the  proportion  of lung cancers  attributable to  radon
which  should remain fairly constant over time —  not  the absolute  rate.
The  time  trend   in  observed  lung  cancer  deaths  and  in  the  radon
attributable fraction is  illustrated  in figure 1-3.

Estimates of the  risk  of lung  cancer associated with  exposure  to  radon
decay  products are  obtained  primarily  from  epidemiological  studies   of
underground miners.   About  13  groups of  miners  have  been studied (see
table  4-1),  and risk coefficients  derived  for those  studies  range from 2  to
50 fatal  lung cancers  per million  persons  per WLM  per year  at  risk  (an
absolute  risk estimate),  or  0.3  percent to  U  percent  increase  per WLM  (a
relative  risk estimate).   Because  none of the exposed  groups of miners has
been observed  long enough  to assess  the  full effects  of their exposures, a
risk   projection  model  must  be   used  to   estimate  the risk  for  lifetime

The  risk coefficients, since they  are  obtained from studies of miners, are
for healthy  adult  males, about  average  in  smoking habits  for  employed

        Rgure 4-3.  Total and Possible Radon Induced Lung Cancer Mortality by Year


                             Possible Lung Cancer
                             Mortality due to Radon
                            1% Increose/WLM
                                 0.0075 WL for lifetime
Assumptions:  Risk Factor
             Average Exposure •
             Occupancy - 75%
Observation:  8.83% ± 0.55% of total lung cancer
SOURCE:  Putnam, Haves it Bartlett, Inc., September 1987.  Based on EPA assumptions
         and calculations.


males.   These  risk coefficients must be  projected for different  populations:
populations  of different  age and  sex  (women  and  children),  of  different
socioeconomic   classes,   with   exposure  to  different   occupational   and
environmental  pollutants,  with  different  radon  decay   products,   aerosol
exposures,  etc.   In  spite  of the  uncertainty in these extrapolations,  until
epidemiologica!  studies  for  residential  exposure are  completed,  these miner
studies are  our best  source of risk coefficients.

Risk coefficients and risk  estimates sometimes are developed  as part of an
epidemiological   study;  in  other  cases  they may be  developed  by other
groups using the papers published by the study investigators.  Table 4-3
gives  both  the  relative  and absolute risk  estimates derived  from   various
investigations that primarily considered  miners  with  less  than  600  CWLM of
exposure.   EPA  chose  to exclude  studies that reflected  lifetime exposures
greater than  600 CWLM  from  the  risk  estimate calculations because,  until
recently,  it  was assumed that virtually  no members  of the public  could be
expected to receive over  700 CWLM exposure during their  lifetimes.

Studies of miners which  EPA  did  not  use to estimate  the risks from radon
decay  product exposure  include  the  Canadian  study  of  fluorspar  miners,
where  25  percent of the  person-years of exposure  were  in  excess  of 600
WLM,  and  the  full  U.S.  uranium  miner cohort,  where  30 percent  of the
miners had  over 840  CWLM. The reduced  level  of cancer  induction per WLM
of  exposure  observed  above  about  700  CWLM  causes  the  risk   factor
estimated  for the entire U.S. miner cohort to be one-half  to one-third lower
than the risk factor estimated  for exposures  of  less  than 600 CWLM.

More recent  findings regarding indoor radon levels, however, suggest  that
many members  of the public may  be  exposed to more  than 700 CWLM over
their lifetimes.   This means that  the  risks  of cumulative exposures above
700 CWLM  need to be  addressed  and  the  interaction of competing risks at
the higher exposures must be evaluated.  EPA has begun this  process and
will continue to  re-evaluate the  range over  which relative  risk coefficients
are expected to remain  constant.


                                Table  4-3
            Relative and Absolute  Risk  Estimates  For Under 600
                 CWLM Exposure To Radon  Decay Products

    Primary Source Studies

    U.S. Uranium  Miners  (Hg86)
    Ontario Uranium Miners  (Mu83)
    Saskatchewan  Uranium Miners  (Ho86)
    Smoking Malmberget Iron Miners (Ra84)
    Non-smoking Malmberget Iron Miners (Ra84)
    Non-smoking Navajo Uranium Miners (Sa84)

    Secondary Source Estimates

    Jacobi  et al.,  1985 (Jc85)
    Steinhausler and Hofmann,  1985  (St85)
    NIH Ad Hoc Working Croup, 1985 (NIH85)
    Thomas et al., 1985 (Th85)
    Archer et al., 1979 (Ar79)
    Increase in
   Fatal Lung
   Cancer  Per
    0.9 to 1.4
    0.9 to 2.3
     over 14.0
    2.2 to 3.1

    Secondary Source Estimates

    Evans et al., 1981  (Ev81)
    NCRP, 1984  (NCRP84/78)
    ICRP, 1981 (ICRP81)
    Cliff et al.,  1979 (CI79)
    UNSCEAR, 1977 (UNSCEAR77)
    NRC, 1979 (NRC79)
    Archer et al., 1979 (Ar79)
   Fatal Lung
  Cancers  Per
Million Persons
   Per WLM
    100 to 200
    150 to 450
    200 to 450
   780 to 1170
SOURCE:   U.S.  Environmental  Protection Agency,  July  1987.

Variations  in  primary study  estimates  reflect differences  in  epidemiological
techniques and  duration of the follow-up  period; differences in  latent period
or  lag  period  used  in calculating  risk  coefficients;  and,   if dosimetry  was
used  to estimate the risk  coefficient, differences in  dosimetric models.   The
differences  in the  estimates  for those  using published reports as  a  data
source  (i.e.,  the  "secondary  source")  also  reflect  the authors'  selections
and interpretations of results  from the various primary studies.   That is,
the authors selected those data sets which  they considered best and, either
implicitly  or explicitly, weighted the results based on their interpretation.

As  mentioned earlier, EPA used a  lifetime absolute risk of 360  fatal cancers
per million  persons per WLM and  a relative  risk of  3 percent  increase  per
WLM  until  1983,  a  relative  risk   of  1.2 percent  increase to   2.8  percent
increase per  WLM  in  1984; and, in 1985,  at  the  Science  Advisory Board's
suggestion,  EPA  increased the range of  relative risk  to  1  to 4  percent
increase per WLM.   With the  exception  of the U.S. uranium miners, relative
risk coefficients of radon  decay product exposure have ranged from about
one  to  five  percent,  with   an  inverse  relationship  to  cumulative  WLM
(EPA78).    With the  update  of the  U.S.   uranium  miners through  1982
(Hg86),  all miners have  relative  risk  coefficients of one  percent increase
per WLM or more in the range  of  exposures  most relevant to environmental
exposures.  Hence, use of a  relative risk coefficient  of one percent increase
per WLM as a lower bound seems reasonable.

Identifying  an upper  bound is more difficult.   Relative  risk  estimates  have
not been calculated for  all  studies.   However,  a   crude estimate can  be
made,  if the  Standard Mortality  Rates (SMR) and the  mean  exposure  have
been  included in  the published report,  through the following  relationship:
Percent  Relative   Risk  =  (SMR-100)/mean  CWLM.   Using data  from  the
current  NIOSH   (NIOSH85)   and  AECB  (Th82)  reviews,  the   following
approximate estimates result:

                                                             Increase  Per
Czech  Uranium Miners                                         1.3  to  1.92
Kiruna Iron Miners                                                1.74
Chinese Tin Miners                                             1.89 to 2.4
Zinkgruven Zinc  Miners                                        2.3  to 2.8
Norwegian  Niobium Miners (based on So85)                      4.4  to 7.4
Many of the  study groups  listed above and  in tables 4-1  and 4-3 are small
and  not  very stable  in a statistical sense.  However,  since one of the large
studies has a relative risk  coefficient above three percent increase  per WLM
(Ho86)  and  several  smaller  studies have relative risk coefficients  greater
than three percent,  the recommendation  of the EPA Science Advisory  Board
that the upper bound of risk estimates be placed  at a  four percent increase
per WLM appears reasonable.

Although  the risk  coefficients derived from the  miner  studies are directly
applicable  only  to  healthy  adult  males,  they are  the only ones  available
now.   Support  for  the  theory that they reflect  the risk in environmental
exposures  is provided by animal studies  and by some  epidemiological studies
of environmental exposure.   The comparability of  animal and  human risks at
high  cumulative  exposures  is pointed  out  by  the  NCRP  Report  No.  78
(NCRP84/78).   Since animals  have shown increased risk  at low  cumulative
exposures, it is expected that humans  will also.

In  Sweden,  epidemiological  studies  (case control or case  reference)  have
demonstrated   that   increased  exposure  to  radon   in   the   residential
environment  is associated with elevated lung cancer mortality (Ax79,  Ed84).
The  risk  per unit  exposure  in these  studies appeared  to  be similar  to the
risk per  unit  exposure  in  various  miner studies.   One  recent  study  has
found  significantly  higher  age-adjusted lung   cancer  rates  in  counties

associated with the  Reading  Prong (Ar87).   This suggests  risks  estimated
using  relative risk coefficients for miners  will approximate  what  would be
expected from residential exposures.   However,  until  larger  epidemiologica!
studies  of  residential  exposure  are completed,  the  numerical  similarity of
risk   coefficients   in   mining  and   residential   environments   cannot  be
demonstrated conclusively.

In summary,  the risk estimates contain the following uncertainties:

•    Follow-up  is  incomplete  — more  than half of the study group is  still
     alive in  most  studies,  so the  true magnitude of the  lifetime  risk is still
     not  known.

•    Exposure history is uncertain — there are no personal  dosimeters  for
     radon  or radon decay  products,  and area measurements in mines are a
     fairly  recent  development.   Hence, exposures  are  estimated  rather than
     directly  measured.

•    Smoking  history  —   the  interaction  of smoking  with  radon  decay
     product  exposure is not  yet understood.

•    Miners  studied  are  mostly adult  males — there are  no  data on women
     and  children;  therefore,  there are no direct risk estimates  for those

•    All projection models are best guesses — until the  last member of one
     of the study groups dies, the true dose-response  factor for that group
     will  not  be available.

•    The residential exposure levels of the miners were generally unknown.

Even  with the  uncertainties just   listed, most scientists  feel that the  risk
estimates  used  today  represent the  true  risks  within  a  factor  of about

                                 Chapter 5
This  section of  "A Citizen's  Guide" notes briefly  that  inhalation of radon
decay  products  followed  by their radioactive  decay within the  lungs can
lead  to  lung  cancer.   The  risk of  lung  cancer was  described  in the
previous  chapter.  This chapter  summarizes  the   general  mechanisms  by
which  radon can  lead to cancer  and  explains  the particular uncertainties
associated  with the distinction between  attached  and unattached radon decay
products.   Next,  the chapter  summarizes the  epidemiological  studies  that
associate  radon and  lung cancer  (specific references  are cited  in  Chapter
4).  Finally, while lung  cancer  is the only health effect generally associated
with radon, the  last section of  this chapter discusses  other potential health
effects that might  result from  radon exposure.

The primary concern when discussing the risks from exposure  to radon-222
is  not  exposure  to  the  radon  gas  itself,   but  exposure to  its  decay
products.   When  radon-222   decays,  a  number  of short  half-life  decay
products  are formed, principally  polonium-218, lead-214,  bismuth-211,  and
polonium-214.  Polonium-218,  the first decay product,  has a half-life of just
over  three  minutes.   This  is  long  enough   for most  of  the electrically
charged  polonium  atoms  to attach themselves  to microscopic airborne dust
particles.   When   inhaled, these  small  particles  have  a  good  chance  of
sticking  to the moist epithelial lining  of the bronchi.

Most  dust  particles that  deposit in  the  bronchi  are  eventually  cleared
(removed)  by  mucus,  but   not  quickly  enough  to  keep  the  bronchial
epithelium  from   being   exposed  to  alpha particles   from  the  decay  of
polonium-218  and  polonium-214.   Although  they  cannot  travel far, alpha

particles  produced  in  the  lungs can  damage  sensitive cells.   This  highly
ionizing  radiation passes  through  and delivers  radiation  doses to  several
types of  lung  cells.  An  alpha  particle that penetrates the epithelial cells
can  deposit  enough energy  in  a  cell  to  kill  or  to  transform  it.   The
transformed  cell,  alone  or  through  interaction  with  some  other  agent, has
the potential to develop eventually into a  lung cancer.

A  scientific question  that remains unresolved regards  the  relative number  of
health  effects  associated  with  attached  versus  unattached  radon  decay
products.  When radon decays, most  of the decay  products  become attached
to dust particles  or aerosols of  submicron  size.   However,  some  decay
products may be inhaled  before they  become attached.

Some models  of  the  ways  that radon decay  products expose  the lungs  to
alpha particles suggest that the  radiation dose to the lungs  from unattached
decay products  can be from 9 to 35 times the calculated dose from attached
decay  products  (Ja81).   This  is  because  these  models  assume  that the
unattached  decay  products  preferentially  deposit  in  those  portions  of the
lung  (the  main  and  lower  bronchi)  known to  be the  most vulnerable  to
induction  of lung cancer.   In contrast,  these models assume that a  smaller
proportion of attached decay  products deposit  in these  sensitive areas  of
the lungs, therefore producing less lung  cancer risk.   At the  present time,
however,  there  is little  experimental  evidence to determine  whether  these
theoretical models of lung exposure are correct.

If  the risk from  unattached  radon decay  products is in  fact  much greater
than  that  from  attached,  there  are  important  implications.   Air cleaning
systems   which   reduce   particulate  concentrations  and,   hence,  the
concentrations of attached decay  products, may  not  reduce  the overall lung
cancer  risk unless the total of  attached  and  unattached  decay  products  is

reduced  by a factor  of  10  or  more.  Therefore, air  cleaning alone may  not
correct   a  situation  of   high  risk  and  may,  under  some  circumstances,
actually  increase the  risk.   Monitoring corrective measures  which depend on
air   cleaning  will  require  radon  daughter  monitors  and  may  require
concentration   measurements  of  both   attached  and  unattached  decay
products.  Special  instrumentation would be needed for these measurements.

The  effect of exposure to "emanations" from radium  (actually  radon and its
decay products)  was first mentioned relative to the lung  cancer mortality in
Bohemian  uranium miners in  the  early  1900s  (Hu42).   The same association
of radon-radon decay  product exposure with  lung  cancer is observed  in
current epidemiological  studies of  underground miners,  not  only uranium
miners but  also  fluorspar, iron,  zinc, and  tin miners exposed to elevated
levels  of  radon  and radon  decay  products.   There have  also  been some
recent epidemiological  studies  in  Sweden  showing  increased  lung  cancer
associated  with elevated  radon  decay  product exposure in  homes  (Ed83;
     ; Ax79).
Although other occupational  carcinogens  have been suspected of causing the
increase  in  lung  cancer,  available  reports conclude  that  silica,  cobalt,
nickel,  bismuth,  chromium,  arsenic,  colds,  and genetics  were not causally
involved  in  the  production  of lung  cancers  in  Bohemian  miners  (Hu12;
Hu66).   In more  contemporary  studies, exposure to diesel  exhaust  fumes
was  excluded as a causal  factor  (Ho86; Ra84).   The  only  common  thread
linking  all  the miner  studies is the exposure to  elevated  radon and  radon
decay product levels.

EPA's risk estimates are based  solely on human studies such as those just
discussed.    Laboratory  studies have  also  demonstrated,  however,  that

exposure  to elevated levels  of  radon decay products  is sufficient to induce
increased lung  cancer  in animals.   In  neither  the  French  studies  of  rats
(Ch81)  nor the American studies  of hamsters  and dogs  (Cr78) did  silica,
uranium,  dust,  or diesel exhaust  fumes contribute appreciably to  induction
of lung  cancers;  only  radon  decay products appear  to  produce  the  lung
cancers observed.

The  risk  from  inhaled  radon-222  is  small compared  to  the  risk  from  inhaled
radon-222  decay products;  however, the  primary risk is  still  induction  of
lung  cancer.    In addition, if radon-222  is  ingested  rather than  inhaled,
little  of the radon or its decay products will  be  desposited  in body tissues,
so the expected health  effects are  negligible.

Doses  from decay products of radon-220, which has one  long  half-life decay
product,  will  occur  not only in  the  lung but  also in  other body  tissue.
Significant  quantities  of  radon-220  decay  products  could  be  absorbed
and deposited,  primarily in bone.    Therefore, there might be some  risk  of
other cancers in addition to lung  cancer.  However,  the  lung cancer  risk
from  radon-220  or radon-222  should still  be  the most significant,  whether
the source of  radon is  from  water (ingestion  and  inhalation)  or  soil  gas

                                 Chapter 6
Although  radon  has always  been present  in our  environment,  it was  not
until  scientists  began to analyze the higher incidence of lung cancer among
uranium and zinc miners that radon decay  products,  and,  therefore,  radon
gas,  were considered a problem.  This chapter will discuss the evolution of
radon as a  major  health  concern by  highlighting  some of the  discoveries
concerning   elevated  radon  levels:   high  lung  cancer  incidence  among
uranium miners  in  the  U.S.  and other  countries, the  existence of  radon
decay products  in  homes built  with materials that were contaminated  with
uranium  mining  waste,  and   the  discovery  of  elevated   indoor   radon
concentrations  from naturally-occurring radon sources.

As  early as  1940,  scientists were  recommending occupational  exposure limits
to safeguard against the possible  health risks associated with radon and  its
decay  products.   Radon was first  demonstrated  to  be  a   problem  when
epidemiological studies in the  1950s showed  a significantly higher incidence
of  lung  cancer  among  underground  uranium  and  zinc  miners.    This
increased  risk  of  lung  cancer  was  attributed  to   exposure  to  high
concentrations  of  radon   present  in   the  mines.  -    In   1971,   the
Environmental  Protection  Agency   established an  exposure  standard  of  4
WLM/year  (EPA71).  As  noted in  Chapter 4, a working level month  (WLM)
is a unit of  cumulative exposure.    It  is  defined as a  miner's  exposure to
-    See Chapter  4  for a discussion of the uncertainties involved with inter-
     preting these  data,  and references to specific epidemiological  studies
     that have associated  radon  and lung cancer.

a  radon  decay  product concentration  of  one working  level  for  170  hours.
This time period approximates the number  of hours  worked in one month by
a  miner.   By  comparison,  exposure  to  one working level  in  a residential
environment, 75  percent  of the  time during  one year,  is equal to  about 20
WLM.  This  conversion  includes  a  correction  which considers  the  higher
breathing rate  of underground miners  engaged  in a  more strenuous level of
physical  activity than the general  population.

Beginning  in  the late  1960s,  several  significant  discoveries  were  made
linking   elevated   indoor   radon  concentrations  to  radioactive   building
materials.   In  Sweden,  residential structures made with  alum shale  brick
were  discovered to  have seriously elevated  indoor  radon levels  (Be84).   A
few years  later, in  the  United States, homes were discovered  in Monticello,
Utah,  and  Grand  Junction,  Colorado,  that had  been  constructed  with
building  materials contaminated with  vanadium  and  uranium  mill  tailings,
respectively  (Ni84;  Gr86).   In  Idaho  and  Montana,  surveys  by  State
agencies   identified   more  than   100  homes  with  elevated   radon  levels
attributable to  the  high uranium  content  of concrete  made from  phosphate
slag,  a  byproduct of the thermal  process  for phosphorus reduction (Ka79).
Wallboard constructed with phosphogypsum  can  also contribute  to  elevated
radon levels.   Elevated  indoor  radon  caused by  industrial  activity,  such as
uranium  mill  tailings used for  building  materials,  is  differentiated  from
naturally-occurring  indoor radon  for  a  variety  of  reasons.   Regulatory
controls  have been imposed on radon exposure in  both occupational settings
and residential  situations,  when  the  exposure is caused by man's  activity.
Radon from  natural  sources  is  not  regulated.    In  most   cases,  radon
exposure  from  naturally-occurring sources  will  be a  more serious  problem
than that from  manmade  sources.


Initially,  scientific  investigations  and  cleanup  efforts focused  on  homes
constructed  with  building  materials contaminated  with  manmade radioactive
waste and  on homes  built on top of uranium  tailings  (e.g.,  in  Colorado) or
on  reclaimed  phosphate  rock mining  sites (in  Florida).   However,  recent
discoveries  have shown that naturally-occurring  radon  in  soil  can result in
extremely high  indoor  radon levels.  In December 1984, the  Watras home in
northeastern  Pennsylvania  drew  national attention when it was accidentally
discovered  to  have   a   radon  level   of  over  2,000 pCi/l.    Scientists
investigating  the site  attributed the high radon  concentration in the home to
the  uranium-rich  soil and  rock  on  which  it  was  built.   This  area of
Pennsylvania  was located on a geologic  formation called the  Reading Prong.
The Reading  Prong  is a uranium-bearing formation  that  extends through
eastern Pennsylvania,  northern New Jersey, and southern  New York.   To
date, the  highest levels  of indoor radon ever discovered  were  found in
homes  built on  this formation.  These  discoveries have prompted  expedited
State and Federal research and assistance to  address  the problem.   Tests in
homes  throughout this area confirm that natural deposits of uranium  in the
soil and  rock beneath a home are a significant  source of the elevated  indoor
radon  levels  (Ne85).   In early 1986, the  greatest concentration of severely
contaminated  homes ever  found was discovered  on a dolomite  formation in
Clinton,  New  Jersey, which is  near,  but  not actually  on,   the Reading
Prong.   In this particular  area,  40 of the  105 homes studied had  indoor
radon  levels  exceeding 200  pCi/l, and  all  105  homes had  levels  above 4

As  a result  of these discoveries, radon  can  no longer  be  considered a
problem  isolated  to  a few   areas  where  industrial   activities   have caused
increased indoor radon levels.  Recent  studies predict that elevated radon
levels are  likely to be found in homes in States across the  U.S. (Ne85).
However,  significant  numbers  of  indoor measurements have been made  in
only a few areas.   EPA has efforts underway  that will help to characterize
the  distribution of  indoor   radon   levels  nationwide,  including  a national
survey and a program to provide  technical assistance to States that wish  to
conduct statewide surveys  (see Chapter 7).

                                 Chapter 7
                  DOES EVERY HOME HAVE A  PROBLEM?
This   chapter  discusses  the   uncertainty   involved   in  assessing  the
distribution of  radon in homes  across the country.   While  most houses  in
this  country are unlikely to  have a radon problem,  several  studies indicate
that the  occurrence  of  elevated  radon  levels could  be  very  widespread.
Reliable  predictive models  that  identify  houses likely to have a  problem do
not yet  exist.  There is,  however, current  research that helps to  answer
some of the questions concerning the potential for  radon occurrence.

The  first two sections of this chapter summarize existing information on the
distribution of radon  in U.S.  homes and specific areas of the country where
elevated  radon levels  have already  been  detected.

The  third  section  addresses the  issue  of  radon in  multilevel  buildings.
This topic  was originally  included  in  EPA's draft version  of  "A Citizen's
Guide."   However, since current scientific investigation has  concentrated on
elevated   radon  levels  in  single-family  detached  dwellings, not much  is
known concerning radon  distribution within multilevel  buildings.   Therefore,
EPA omitted this topic in "A  Citizen's  Guide," but  provides some information
in this chapter.

The  final section describes some of the  EPA-sponsored current and  future
programs for  radon assessment.   These  programs  will help EPA  characterize
the distribution  of radon  levels nationwide  and  develop  predictive models
that can  be used to identify  areas with high  radon potential.

Although  every home has  some radon,  the  large  majority of homes in this
country  are  not  likely   to  have  radon   levels   exceeding  EPA's  lowest
recommended  action  level  of M pCi/l  (0.02  WL).   A  study  by Andreas C.

George,  et al.  (Ce78)  estimated  the  average indoor radon  concentration  to
be  about 0.8 pCi/l (or 0.00*1 WL);  this  study  serves as the  basis  for the
Radon Risk  Evaluation  Chart (see Chapter  12).   Another  study,  by  A.V.
Nero,  aggregated  the  results  of  19  separate studies  covering  1500 homes
and estimated  that the  average  radon concentration  in a  single-family  home
is approximately 1.5 pCi/l  (or 0.0075 WL)  (Ne86).  These studies indicate
that  1  to 3 percent of the single-family homes  in  the  nation  have radon
concentrations  of 8 pCi/I or more.   The studies also  confirmed that radon
levels  tend to  follow a  lognormal  distribution  (with  a geometric mean of 0.9
pCi/l and a geometric  standard deviation of  2.8).   However,  in developing
these  estimates, Nero  sought  to  exclude measurements  for which a  prior
expectation of  elevated  levels existed (since  these measurements would bias
upward  the estimate  of an  average  level).   For  individual  data  sets,
geometric means  ranged from 0.3  pCi/l to 5.7 pCi/I.

The variation  in radon  concentration throughout  the country  is determined
by   many  different  factors,   including  radon   source   strength,   house
construction, ventilation rates, and  air  pressure  differences  between the
indoor air  and the  soil gas.   Radon source strength is one of  the  most
important  contributions  to  a  potential   indoor  radon  problem.   Although
current  data suggest that  areas  with significant  radon source strength are
limited in geographical  scope, there  is still much  uncertainty concerning the
actual  distribution  of radon  throughout the United States.

Elevated  levels of  naturally-occurring  indoor  radon  have  been  found  in
nearly  every state across  the  country.   Several  areas  of  the  country,
however,   have exhibited  extremely  elevated  indoor  radon  levels.   The
highest indoor  levels  have  been measured in the  Reading  Prong  areas  of
eastern Pennsylvania,  New  Jersey,  and  New  York.  Another area  in  New
Jersey, near Clinton,  has also exhibited  extremely elevated levels.   Some
homes   in  these areas  exceeded  10  WL.   Surveys  in  other  States  have


indicated  that,  although  we have not  identified  additional  areas with  the
extremely high  levels found in  the Reading  Prong, nearly every  State  will
find some levels above 20 pCi/l.

Another  source  of elevated indoor  radon  levels  is  contaminated  building
sites  or  materials.   Several  areas  in  the  country  have  identified  these
problems.   In Polk  and  Hillsboro counties  in  Florida,  15  percent of  the
homes   built  on   reclaimed  phosphate   mining  lands  had  indoor   radon
concentrations between 0.03 to 0.10 WL  (FRN79).   Some homes  in  Colorado,
Utah, and North Dakota  that were built  on or near  uranium mill tailings,  or
with contaminated building materials,  also  have elevated indoor radon levels.
Another  site  in Montclair/Clen  Ridge,  New Jersey  was found  where homes
were  built  on land  contaminated  with  radium.   Areas like  these are  not
expected  be  widespread,  and  do  not  affect  as  many  homes   as  does
naturally-occurring radon.

Another  potential  contributor to elevated indoor radon levels is  radon  found
in water  (see Chapter 3  for a more  detailed discussion of radon in  water).
Elevated  levels  of  radon  in domestic  water  supplies  have  been  found  in
areas of New  England, including  Maine and New Hampshire.

Investigations are  currently underway in many States to locate areas with
elevated  indoor   radon   problems.   As  results  from  these  studies  are
analyzed, we  will  be  able to refine our  predictions of where in the United
States  indoor  radon may  be a  problem.

Since most of the current data on  radon are from single-family homes,  it is
difficult   to   estimate  concentrations   in   apartment  buildings  and  other
multilevel buildings.   The  few studies available indicate that concentrations
in  multilevel  structures  are  typically  a  few  tenths  of  a  picocurie,
substantially  lower than  concentrations in  single-family homes (Ne85).   This


is  possibly because  average living or working  space is  usually  well isolated
from  the  ground.   For most apartment  dwellings  and  multilevel  buildings,
the major contributions  to  indoor  radon  concentrations  may  be  expected to
be   outdoor   air  and   building   materials.    Larger   European  studies
concentrating  on apartment  building  exposures  confirm  this  expectation

In  areas  where  the  chief  indoor radon  source  is  soil  gas,  upper-floor
dwellers   are   likely  to have   a  much   lower  exposure  to  radon  than
ground-floor and basement  dwellers.   However,  in areas where  the  chief
indoor radon source is  the well water,  indoor concentrations could  be high
in the upper floors,  as  groundwater may be first aerated at that  level.  In
general,  however,  most multilevel  buildings and apartments  are  located in
city areas and  are  linked  to  public water  supplies  rather  than to  wells.
Public water supplies  usually are fed through  reservoirs in which the water
is  aerated and  any dissolved  radon is released  into  the outside air.

As  part  of  its overall  Radon  Action Program, EPA is  conducting a number
of activities,  including a national survey.   The national survey will provide
information  on the  national distribution of  radon concentrations  in  homes
and  should  be completed in a few years.  Activities also  include assistance
to States with the  design  and  conduct of  surveys  to identify  areas with
elevated  radon  levels.   As  part of  this  program,  EPA can  help  States
conduct  radon surveys  by assisting  with  survey  design  and  by providing
laboratory  support and  measurement  devices.   Many States  have requested
EPA assistance and EPA worked  with  10 States on  radon surveys during the
1986-1987 heating  season.    EPA  will  assist  as   many  States  as  possible
during the  next  several  years.   EPA is also  conducting  research aimed at
developing a  predictive model that will  help to identify  areas  with  a high
indoor radon  potential.   Results from this  study  will not  be available for
one to two years.


In addition  to  these  activities, EPA is  conducting a number of other efforts
as  part of  its  overall  Radon  Action  Program.   These activities  include
mitigation training,  demonstration and  research  projects, cooperative efforts
with other Federal agencies to develop State and private sector capabilities,
and various forms of public information and assistance.   Further information
about  EPA's   radon  activities  can  be  obtained   by contacting  the  U.S.
Environmental  Protection Agency,  Office of  Radiation Programs (ANR-464),
401 M  Street,  S.W.,  Washington, DC  20460 or your EPA Regional  Office.

                                 Chapter 8
                  HOW DOES  RADON GET INTO A HOME?
The  primary  source  of indoor  radon  in  dwellings  is  the  soil  and  rock
adjacent to the building;  secondary sources include domestic  water  supplies
from  wells  and  earth-based  building  materials.   Chapter  3  discussed
characteristics  of  rock,   soil,  water,  and  building   materials   that  are
associated  with  high  radon  concentrations.   This  chapter  explains  how
radon  is transported  into  the  home  from these  sources.  Specific  areas of
discussion  include:  (1)  flow-inducing  mechanisms,  (2)  factors  influencing
radon  transport from  soil  into homes,  (3)  radon  transport  through water
supplies, and (4) earth-based  building materials  as a source of radon.

The predominant source  of  indoor  radon is  the  decay of radium in the soil
adjacent to  the  building.   Generally,   the  soil  is indigenous  to  the  site;
however,  in  some cases,  industrial  products such as mill tailings and wastes
from phosphate mining are the dominant source of radon in the soil.   Radon
in  the  soil  can  enter  the  home   through  two  gas  transport  mechanisms:
molecular  diffusion  (movement from  an area  of high concentration  to low
concentration at constant  pressure)  and  pressure-driven flow  (movement
from  a  high  to a   low  pressure area).   Scientific   investigations  have
indicated  that  diffusion cannot account  for  the  high  levels of indoor radon
discovered in some homes,  but, rather,  pressure differences between indoor
and outdoor  air seem  to be the major determinant

Pressure-driven  flow,  where radon is actually drawn into the structure,  is
influenced   by   several  factors.    During   the  heating  season,  indoor
temperatures  are  often  higher   than  outdoor   temperatures,  causing  a
tendency  for warm indoor air  to be  displaced by  cooler  outdoor  air.  This
tendency  is  called  a  stack  effect  since  the warm  air tends to rise as in a

chimney.   Inward pressure  on  the  lower  walls and  floor resulting  from this
effect causes  radon to be drawn into the home  from the  surrounding  soil.
Wind  is  another  important  factor  that causes  a  pressure difference and
drives the flow  of radon  into a building.   Wind causes an  exchange between
the air  in the structure and the soil.   Indoor air  flows  to the soil on the
leeward side of  the  building (where outdoor pressures are  lower) and  flows
from the soil  into the  house on the windward side (where outdoor pressures
are  higher).    Barometric  pressure  and  precipitation  are two additional
factors  that can affect  the  flow  of radon  into a  structure,  although  some
scientific   uncertainty  remains  on   how  these   factors   affect  indoor
concentrations (Ne2/84).

Pressure  differences  caused by  mechanical  devices or  appliances  in the
home  are  equally  important.  Exhaust fans in the  kitchen  or  bathroom and
clothes  dryers  draw air out of the  house.   Open fireplaces  also create  a
significant  draw on indoor  air.  On the  other  hand,  some room  fans can
draw  outdoor air into the house.   The  net  effect  of  these  processes will
determine  whether  the  resulting  pressure  difference  between  indoor and
outdoor air will  draw radon  into the home.

In addition to flow-inducing pressure  differences,  the  transport of radon
into  a structure  from the soil is  affected by  other factors such  as the  rate
of radon production  in the soil,  the  soil  permeability and  moisture content,
and  the  building substructure  type (see  Chapter  3  for a description of the
formation of radon  in soil  gas).   Research suggests that the strength of the
radon  source  can   better  explain  the differences  among  radon  levels  in
various homes  than the rate of indoor  ventilation  (Ne2/84).   This  indicates
that   energy-efficient homes will  not  necessarily  have elevated  levels  of
radon, although  a  reduction in air exchange  rates  may exacerbate already
elevated  levels.   Soil  permeability can  strongly  affect  radon entry,  since
the greater the  permeability, the easier  it  is  for  radon to be  transported
through  the soil.

Building  substructure also affects  the  radon entry  rate.   Of  the three
genera] substructure  types -- basements,  crawl-spaces,  and slab-on-grade
— basements tend  to  be more  susceptible to high radon entry rates because
of the  large  area exposed to the  soil  and the  greater  efficiency of the
pressure-driven  flow  mechanism  (Ne2/84).   Even  if there  is  a  ventilated
crawl-space separating  the soil  from  the house,  radon entry  into  a  home
from  the  underlying  soil  may  still  be significant.   Once again,  pressure
differences  between indoor and outdoor air  may cause a  stack  effect.   The
stack effect can  promote an even greater flux of radon into  the crawl-space
if the  crawl-space  is unvented  (Ne2/84).   Slab-on-grade  foundations  are
considered  less  susceptible to high  rates  of radon  entry.   As  with  all
substructures,  however,   radon  can  enter  structures  with slab-on-grade
foundations through   floor  and  wall cracks,  joints, utility  openings,  floor
drains, and  (in  the  case  of basements)  sumps.   Measurements of  elevated
levels  in  slab-on-grade  homes  built  on reclaimed  phosphate  mining  lands  in
Florida  affirm   the   overall   importance  of  soil  source   strength  as  a
determinant of indoor  radon levels.

Radon can also enter the home  by being released from water  used in daily
activities.   As  mentioned in Chapter 2, radon  can be  easily absorbed by
water  flowing  through soil  or  rock  containing  radon  gas, especially  since
the solubility of radon is greater in the colder water temperatures  typical  of
groundwater.   Studies indicate  that while very few  public water supplies
contain enough radon  to be a  significant source of indoor radon, elevated
levels  of  radon  have  been  observed in  water  from  private  wells in some
areas of the country, particularly in the northeast.  It is  estimated that,  in
most  cases,  radon  from drinking   water  contributes only  one  to  seven
percent of the radon concentration  in indoor air.

Waterborne  radon  is released into  the  home  when  the water  is  exposed  to
air  and/or  when  its heated.  Thus, radon  is  released from  water through


the  use  of items  such as  showers,  washing machines,  dishwashers,  and
toilets.   Domestic  activities that involve heating  water  result  in  a higher
transfer   of  the  radon   to  air.    These  activities  contribute  to  the
concentration  of  radon  in indoor  air  and,  hence,  inhalation  exposure.
Radon that  remains  in  the  water  can  be  ingested,  although   research
indicates  that ingestion  is generally  not  the  most significant  source  of
exposure  and, therefore,  is not  the  primary concern.  It is  the  release  of
radon  from  water  to air  and  the  subsequent  inhalation  that   normally
dominate exposure  (NCRP84/77).

Radon can  also  emanate  from  earth-based  building  materials  containing
elevated  concentrations  of radium,  although,  in  the U.S.,  this source of
radon  is  substantially  less  significant than  radon  coming  from the  soil
(Ne83).  An example  of  a  case in which building materials were considered
a major source  of elevated  indoor  radon  levels  occured  in  Sweden,  where
houses were built  using  alum shale,  a material high  in radium  (Sw80).  In
the U.S.,  some homes were built using phosphate  slag as an  ingredient in
concrete   (Ka79).    Other  examples  of  building  materials  known to  have
slightly elevated  radium concentrations include  fly ash  used  in concrete,
phosphogypsum  (a  waste product from  processing  phosphate ore)  used in
wall  board,  and red mud (a  byproduct  of bauxite ore processing sometimes
used  for bricks) (Ne83).   In each situation above,  the  source of radon was
building  materials  contaminated by wastes  from industrial activities.  With
the exception  of  these  examples and similar incidences, the  predominant
source of  radon entry is naturally-occurring radon  in the soil.

As mentioned  in  "A Citizen's Guide,"  natural materials  used  in  construction
(e.g., shale or  granite)  may  sometimes contain  naturally elevated  radium
levels and could emanate radon.  Such  materials might be used,  for example,
in  the construction of fireplaces or  in solar  heating  systems in which heat
is stored in large  beds of stone.


                                Chapter 9
                        HOW  IS  RADON DETECTED?
Since radon cannot  be  detected  by the human  senses,  special equipment is
needed  to measure the  concentration  of  radon  and  its decay  products.
Since both radon and  radon decay products may be measured, this chapter
first explains the  concepts  required  to  convert from one unit to another.
Homeowners should  be  made aware  of the types  of devices  available for
radon detection  and the different purposes for each sampling method.  While
"A  Citizen's Guide" briefly describes  the charcoal canister  and alpha track
detector,   this  chapter  explains  the  three  general  methods  for  radon
sampling and describes in detail  seven measuring systems that  are currently
in use.   For  further  information  concerning each  of the detection devices
mentioned, consult  EPA's "Interim Indoor  Radon and  Radon Decay  Product
Measurement   Protocols"   (EPA86a).    An  explanation  of   screening   and
follow-up  measurement protocols  is provided in Chapter 11.

As  mentioned in Chapter  5,  most of the health risk  from indoor radon  is
associated   with  radon   decay   products.    Therefore,  measuring   the
concentrations of the alpha-emitting  radon decay products (also  referred  to
as  the   Potential  Alpha   Energy  Concentration  or  PAEC)  would  be  an
appropriate  choice.   For  various  reasons,   however,  measurements  are
frequently  made  of  radon  concentrations  rather  than  of  radon  decay
products.   Radon concentrations, which are measured  in  units of picocuries
per liter  (pCi/l), can be  converted into  working levels  (WL),  the  unit  of
measurement for radon decay products,  by assuming an average  relationship
between  radon and its decay  products.

In a closed space, a given activity concentration of  radon (which represents
a  rate  of  radioactive decay  per  unit  volume)  tends  to reach  a state of
equilibrium with its decay  products,  where the rates of formation (via decay
of the predecessor element) and decay of each decay product are equal.  In
perfect equilibrium,  100  pCi/l  of  radon  are in balance with  exactly 1  WL of
radon  decay  products.   However,  a number of factors  tend  to  cause the
radon  decay  product  concentration to  be  lower  than  it  would  be  in
equilibrium   (e.g.,   plate-out  on   walls  and   floors).    The  degree  of
disequilibrium is measured by the  equilibrium  fraction.   The  equilibrium
fraction  is  the  ratio  of  decay   product  concentration   to  the   radon
concentration multiplied by 100:

               Equilibrium Fraction =  [WL] x 100

Data  collected from  typical houses  in which  radon  and  its decay  products
were  measured concurrently indicated that this  equilibrium fraction  ranges
from  0.3  to 0.7,  with  an  average  of  around  0.5   (Ce85).   With  an
equilibrium fraction of 0.5, 200 pCi/l of radon is equivalent  to  1 WL.   Using
this relationship,  measurements of  either  radon or its  decay  products can
be  compared  (i.e.,  divide  picocuries per  liter by  200  to  estimate working

EPA has  issued  two  reports  recommending  measurement  techniques  and
strategies.   The  first  report,   titled  "Interim  Radon  and  Radon  Decay
Product  Measurement  Protocols"  (EPA86a),  provides  guidance for  making
measurements in  residences using  the  seven  techniques  evaluated  by  EPA
and  found  to  be  satisfactory;  procedures  for other  instruments  may be
added  as  they are evaluated by EPA.   The  second report, titled  "Interim
Protocols  for Screening  and  Follow-up  Radon  and  Radon  Decay  Product

Measurements"   (EPA87a), outlines  the  recommended  strategy  for  making
reliable,  cost-effective  measurements in homes.  Below is a brief description
and explanation of the  recommendations in the two reports.

EPA protocols  provide procedures for measuring  radon concentrations with
continuous  radon  monitors,  charcoal  canisters, alpha-track detectors,  and
grab  radon  techniques.   The  protocols  also  recommend  procedures   for
measuring  radon  decay product concentrations with continuous working level
monitors,  radon progeny integrating  sampling units,  and  grab radon decay
product  methods.   The  discussion  of each  method   includes  recommended
quality  control  procedures,  such  as  frequency  of  calibration,  desirable
operational checks,  and background and replicate  measurements.

There  are,  however,  some  general  guidelines   concerning   standardized
measurement conditions  and quality assurance objectives which apply to all
measurement devices.

Standardized Measurement Conditions

EPA's  protocols  specify  that  measurements  be made when the  radon  and
radon decay product  concentrations  are likely to  be  the most stable, e.g.,
in a closed  building  with  a  minimum level of ventilation  (EPA86a).   Such
measurements will  generally  be  higher than  the  average concentrations  to
which the occupants are exposed.

Making  measurements  under  standardized conditions is  important for   two
reasons.     First,   measurements   should   be   reproducible,   i.e.,   the
measurement results can be  related  to either  potential  or actual exposures
in the house and  have the smallest  possible variability with the  technique.
The most   reproducible  measurements are  those taken  when  the  house
conditions  are standardized, with the house closed, and after  sufficient  time


has  elapsed  for  the concentrations to stabilize.  Reproducible  results  are
especially important when deciding whether remedial  action  is necessary  or
when evaluating the effectiveness  of remedial action.

Second,  it is important to quantitatively estimate the variability associated
with the  results  of a measurement.  This  variability can  only  be estimated
from  data  taken   under  similar  conditions  and,  since  average   living
conditions are  difficult  to   define  and   reproduce,  specifying   standard
conditions allows  for valid application of the estimates of error.

House Conditions

Measurements  should  be  made  under  "closed-house"  conditions.    To  a
reasonable extent,  windows and  external  doors  should  be closed,  allowing
for  normal  entry  and  exit.   In  addition,  external-internal  air  exchange
systems  (other than a furnace) such  as high-volume attic and  window fans
should not be operated.   For measurement periods  of three days  or less,
these  conditions   should  exist   for  12   hours  prior   to   beginning  the
measurement  (EPA86a).

Severe weather will  also affect the measurement results.   Again, measure-
ments of less  than three  days should  not be  conducted if severe  storms
with high winds  are  predicted.   Wind-induced  differences  in air  pressure
between   the  house  interior  and  exterior  will  increase  the variability  of
radon concentrations.   Rapid  changes in  barometric pressure  increase  the
chance of a  large shift  in  the  interior and exterior  air pressures,  affecting
the rate  of radon  influx.

Quality Assurance Objectives

Another  important part  of  measurement is  quality assurance.  The  objective
of quality assurance is  to  ensure  that data  are scientifically sound  and of
known precision and accuracy.  The  following are several aspects of  quality

assurance that should be included in any measurement program:  controlled
calibrations,  replicate measurements,  background measurements,  and routine
sensitivity checks.

Controlled calibrations  are  samples  collected  or measurements  made in a
known  radon  environment   such  as  a  calibration  chamber.    Detectors
requiring  laboratory  readout,   such  as  charcoal   canisters,  alpha-track
detectors, and  RPISU   samplers,  would  be  exposed   in  the   calibration
chamber and then analyzed.   Instruments providing immediate results, such
as continuous working level  monitors  and continuous  radon monitors,  should
be operated in a chamber to establish calibration.

There are two types  of calibration  measurements that should be made  for
alpha-track  detectors  and  charcoal  canisters.    The  first  measurements
determine  and  verify   the   conversion   factors   used  to  derive   the
concentration   results.    These  measurements,   commonly  called   spiked
samples,  are  done   at  the  beginning  of  the  measurement  program  and
periodically thereafter.   The  second  calibration measurements monitor  the
accuracy  of  the  system.  These are  called  blind  calibration measurements
and  consist  of detectors that  have  been  exposed  in  a  radon  calibration
chamber.   They  are not  labelled  as  such  when  sent  to  a   processing

Background measurements,  or blanks, should also be conducted  frequently.
Such  measurements  should be made  using  unexposed passive detectors  or
should  be instrument measurements conducted  in very low  (outdoor) radon
concentration   environments  and separated  from  the  operating  program.
Generally, these should  be  equivalent  in  frequency  to the  spiked  samples
and should  also  not  be  identified as  blanks  when  submitted  for  analysis to
external laboratories.  In addition  to these  background measurements,  the
organization  performing  the  measurements should calculate  the lower limit of
detection  (LLD)  for  the measurement system.   This  LLD is based on  the
system's  background and  can  restrict  the  ability  of   some measurement
systems to measure low concentrations.


Duplicate   measurements  provide  an  estimate  of  the   precision  of  the
measurement results.  Duplicate measurements should be included in at least
10 percent  of the samples.  If enough measurements are made,  the number
of duplicates  may be  reduced, as long as enough are used  to  analyze the
precision of the method.

A  quality  assurance program  should  include a written plan  for  satisfying
the preceding objectives.   A system for monitoring the results  of the four
types  of   quality   assurance  measurements  should  also   be   maintained
continuously and made available for inspection.

The  EPA  has established  a Radon/Radon  Progeny Measurement  Proficiency
Evaluation  and  Quality  Assurance  (RMP)  Program.  This  program enables
participants to demonstrate their  proficiency in measuring  radon and  radon
decay  product concentrations and  to have  their quality assurance  programs
evaluated.   Contact the  Radon  Quality   Assurance  Coordinator  at  (919)
511-7131  for further information about this  program.

Alpha-Track  Detector

The  alpha-track detector (ATD)  consists of a small piece of plastic enclosed
in  a container with a  filter-covered  opening.   Alpha particles emitted  by
radon  decay  products   in  the   air  strike  the   plastic   and   produce
submicroscopic damage  tracks.   At the end of the measurement period, the
detectors  are returned  to a laboratory,  where  the  plastic  is  placed  in  a
caustic solution  that accentuates the damage tracks so they can be  counted
using a microscope or an  automated counting system.  Data  generated at a
calibration facility  is used to correlate the number of tracks per unit area
to  the  radon  concentration in air.

Many factors contribute  to  the variability of the  ATD results,  including
differences  in the  detector  response within and between  batches  of  plastic,
non-uniform  plateout   of  decay  products   inside  the  detector   holder,
differences  in  the number  of  tracks used as  background,  variations  in
etching  conditions,  and  differences  in  readout.   The  variability  in ATD
results   decreases  as  the  number  of  net  tracks  counted  increases,   so
counting  more  tracks  over  a  larger  area of the  detector will  reduce  the
uncertainty of  the result.   Deploying duplicate  ATDs  will also  reduce  the
error.   However,  if cost considerations  make it  necessary to  deploy single
ATDs,   the  data  obtained  should  be  evaluated  and  used  taking  into
consideration  the  relative  errors  associated  with  counting  the area  and
number of net tracks specified to the  processing  laboratory.

The  advantages of the alpha-track detector include its  relatively  low  cost
(about  $20  to $50  per  detector  including  the analysis)  if installed  by  the
homeowner.   Because  of  its small  size,  the  alpha-track detector  is  not
intrusive.   The  primary disadvantage of this detector is the  relatively  long
measurement  period   it  requires.   For  currently available  models,  three
months  is  the minimum  recommended exposure period.   Also, this detection
device is not  always  precise  for measurements of  low radon  concentrations.

Charcoal Canister

Like  the  alpha-track  detector,  charcoal  canisters  are  passive   devices
requiring no  power  to  function.  The activated  charcoal  allows  continuous
adsorption  and   desorption  of  radon, and the  adsorbed  radon  undergoes
radioactive  decay during the measurement period.   Therefore,  the technique
does  not  uniformly   integrate  radon  concentrations  during   the exposure

The   charcoal canister  measurement  technique   is  described  in detail   by
Cohen and  George (Co83 and  Ce8^).  The charcoal canister  now  used  by
several  groups  is  a  circular container,  6 to 10  centimeters in diameter  and

approximately 2.5 centimeters  deep, filled  with  25  to  100  grams of activated
charcoal.   One  side  of the container is  fitted with a screen that keeps  the
charcoal in  but  allows air to diffuse into the charcoal.   When the canister is
prepared  by the  supplier, it  is sealed with a cover until it is ready  to be

To  initiate  the  measurement,  the  cover is removed to allow  air  to  diffuse
into the charcoal  bed.   Radon  in the air will be adsorbed onto the  charcoal
and will subsequently decay, depositing  decay products in the  charcoal.  At
the  end of  a measurement period,  the  canister is resealed and is returned
to a laboratory  for analysis.

At  the  laboratory, the canisters are analyzed for  radon  decay products by
placing  the  charcoal,  still  in  its  canister,  directly  on  a  gamma  detector.
Gamma  rays of energies  between  0.25  and  0.61  MeV  are counted.   It  is
usually  necessary to correct  for the  reduced sensitivity of the charcoal due
to absorbed  water.   This may be done by  weighing each  canister  when  it is
prepared  and then  reweighing  it when it  is  returned  to  the  laboratory  for
analysis.   Any  weight   increase  is  attributed  to  water   absorbed  by  the
charcoal.   The  weight of water gained  is correlated to a  correction factor
that  should  be  empirically   derived  (Ge84),  and  used  to   correct  the
analytical results.

Radon Progeny  Integrating Sampling Unit (RPISU)

This  continuous sampling unit  consists of an air  sampling  pump that draws
a continuous flow  of air  through a  detector assembly containing a filter and
at least two thermoluminescent dosimeters  (TLDs).  One  TLD  measures  the
radiation emitted from radon decay  products collected on  the filter, and  the
other TLD   is  used  for background  gamma correction.  The  pump and
assembly are usually operated for  three  to seven  days.   At the end  of that
time, the unit  is  removed  and the detector assembly is  returned  to  the
analytical laboratory.  The  analysis  consists of measuring the  light  given
off  by the TLD  during heating.


This  device provides  a  short-term measurement  of  radon  decay  product
concentration,  rather than radon  gas  levels.  There is extensive experience
in the use  of  RPISUs,  and  measurement  errors  are  well  established.  The
drawbacks of using  a RPISU  are  its cost and the  difficulty of handling the
device.   These  devices  may  be  both  heavy  and difficult  to  move,  and
trained personnel  are  required for  installation and  removal.   In addition,
most RPISUs cost about $500 to $3,000  for the device,  and  $5,000 to $10,000
for the analysis equipment.   While  the analysis  is relatively accurate,  the
RPISU  is  sensitive  to  airborne  particles  and,  therefore,  may  not work
properly if  there are high  concentrations of particulates in  the air.

Continuous  Radon Monitor  (CRM)

A  CRM samples the ambient air by  pumping air into a  scintillation cell after
passing  it   through  a   particulate   filter   that  removes   dust  and radon
decay  products.  As the  radon in  the  air decays, the ionized  radon decay
products  plate  out  on  the interior  surface of the scintillation cell.  The
radon  decay  products decay  by  alpha emissions, and the  alpha  particles
strike  the coating  on the inside of  the  cell, causing scintillations to occur.
The  scintillations are detected by the  photomultiplier  tube in  the detector,
which  generates electrical  signals.    The  signals  are  processed  and  the
results are either  stored  in  the  memory of the CRM  or printed on paper
tape  by  the printer.    The  CRM  must  be calibrated in a  known radon
environment to  obtain  the conversion factor used  to  convert count rate to
radon  concentration.

The  CRM may  be  a flowthrough-cell  type  or  a  periodic-fill  type.   In the
flowthrough-cell type,   air  flows   continuously  into  and   through   the
scintillation  cell.  The  periodic-fill type  fills  the cell once  during  each
preselected  time interval,  counts the  scintillations,  then  begins the cycle

Continuous Working Level  Monitor  (CWLM)

A CWLM samples the ambient air by filtering airborne particles as the air is
drawn  through  a  filter cartridge at a low flow rate of about 0.1 to 1  liter
per  minute.    An  alpha   detector   such   as   a   diffused-junction   or
surface-barrier  detector counts  the alpha particles produced by the radon
decay products  as  they decay on the filter.  The  detector  is normally set to
detect   alpha  particles  with  energies  between  2   and  8  MeV.   The alpha
particles  emitted   from   the  radon   decay  products   polonium-218   and
polonium-214  are  the  significant   contributors  to  the   events  that   are
measured  by the detector.  The event count is directly proportional to  the
number of  alpha  particles  emitted  by  the  radon  decay  products  on  the
filter.   The unit typically contains a microprocessor that  stores  the  number
of counts and elapsed time.   The unit can be set to record the total counts
registered over specified  time periods.   The  unit  must be calibrated  in a
calibration facility  to  convert count  rate  to  working level  (WL)  values.
This  may be   done initially  by   the  manufacturer  and   should  be  done
periodically  therafter by the operator.

The  cost  of a CWLM device  ranges from $2,500 to $10,000, and a three-day
measurement can cost from  a few  hundred  dollars to nearly one  thousand

Crab Sampling

The  term "grab sampling" refers   to  very  short-term  (about  five minutes)
sampling.  This method consists of evaluating a small  volume of air from  the
home for  either  radon or  radon decay  product  concentration.

In the  radon grab sampling  method,  a sample  of air  is drawn  into and
sealed  in a flask  or cell  that has a zinc  sulfide  phosphor  coating on  its
interior surfaces.   One surface of the cell is fitted  with a  clear window that
is  put  in  contact  with   a  photomultiplier  tube  to  count  light  pulses

(scintillations) caused  by alpha disintegrations from  the  sample interacting
with the zinc sulfide  coating.  The number of pulses  is proportional  to the
radon concentration in the cell.

The cell is counted  about four hours  after  filling to allow  the short-lived
radon  decay  products  to reach  equilibrium  with the  radon.  Correction
factors  are applied  to the results  to compensate  for  decay during the time
between  collection and counting and to  account for decay during counting.

Crab  sampling measurements of radon  decay  product concentrations  in air
are performed by  collecting  the  decay products  from a  known  volume of
collection.   Several methods  for  performing  such measurements have been
developed  and have been  described by  George (CeSOb).  Comparable  results
may be obtained using  all of these methods.  This summary,  however, will
describe two procedures that have been most widely used  with  good results:
the Kusnetz  procedure and the modified Tsivoglou  procedure.

The Kusnetz  procedure  (Ku56;  ANSI73) may  be  used  to  obtain  results in
working  levels (WL)  when the concentration of individual decay products  is
not important.  Decay products  in up to 100 liters of air are collected on a
filter  in a 5-minute sampling period.   The total alpha activity  on  the filter
is  counted any time between  40  and 90 minutes after  sampling  is completed.
Counting can  be done  using  a   scintillation-type counter  to   obtain gross
alpha counts  for the selected period.   Counts from the filter are converted
to   disintegrations   using   the   appropriate   counter  efficiency.    The
disintegrations from  the  decay  products  may be converted  into  working
levels using  the appropriate "Kusnetz factor" for  the  counting  time utilized.

The Tsivoglou procedure, as modified  by  Thomas  (Ts53; Th72), may be
used  to  determine  WL and the concentration of the individual radon decay
products.  Sampling  is the same as in the  Kusnetz procedure;  however, the
filter  Is counted  three  separate  times following  collection.   The  filter  is
counted  between  2  and  5  minutes,  6 and 20 minutes,  and 21  and 30  minutes

after   sampling  is  completed.   Count  results  are  used  in  a  series  of
equations to calculate concentrations of the three radon decay products  and

The  cost of a  measurement  can be  several  hundred to  several  thousand
dollars  since  a  trained  technician  must be  sent on  site to take  the grab
sample.   The  advantages  of  grab  sampling  are  that the  test  period  is
relatively short,  results are ready  immediately, and  conditions  during  the
measurement are known  to  the sampler.  One  disadvantage,  however, is  the
relatively  high  cost.   In  addition,  grab  sampling   does  not  provide  a
long-term average and  house conditions must  be  controlled for  12 hours
prior  to measurement.

Radon in drinking water  can  be detected either by  the  liquid scintillation
method  or by  using  alpha-track  detectors  (BI85).   The  liquid scintillation
method  uses a liquid  which emits light when struck  by  a nuclear particle.
The  water sample containing  radon  is mixed  with  this liquid and the  light
flashes are then counted on a  liquid scintillation  counting  system  (Co86).

Alpha-track detectors, similar to those used  to  measure  radon in air,  can
be placed in the bottom of a weighted cup which is inverted and placed at
the bottom of a toilet tank.  As  the water  rises in the tank  the  cup traps
air  and the radon  gas can emerge  from  the water and cause a track to  be
formed on the detector (Co86).

The  choice  of an  appropriate  measurement  method depends on whether the
measurement  is  intended  as   a  quick  screening  measurement,  or  as  a

follow-up  to determine  average  exposure.   In  practice,  the choice  of  a
measurement system is often  dictated by availability.  If alternative  systems
are available,  the cost  or  duration of  the  measurement  may  become  the
deciding factor.   Each  system has  its own  advantages and  disadvantages,
and  the user  must  exercise  some  judgment  in selecting  the system  best
suited to the individual  situation.   More information on this subject is  found
in Chapter  11  and in EPA's  "Interim  Protocols for Screening and  Followup
Radon and Radon Decay Product Measurements" (EPA87a).

                                Chapter  10
                  HOW CAN I  GET A RADON DETECTOR?
"A  Citizen's  Guide" advises  homeowners  to  contact  their  State  radiation
protection  offices or EPA regional  offices  to obtain  information on  vendors
or testing  services provided by  State or local governments or private firms.
In the event that information about obtaining detectors is not available, this
chapter provides information on  methods for obtaining  measurement devices.
In  addition,  the  EPA-sponsored  Radon   Measurement  Proficiency  (RMP)
program  is also  discussed.

The  choice  of an   appropriate  measuring  device  depends  upon  several
considerations.   The  purpose  of  the  measurement  (quick  screening  or
follow-up),  how much difficulty is involved, and how  much a homeowner  is
willing  to spend  are  all  factors  a  homeowner  should  consider  prior to
investigating  types  of detectors  and  companies  selling  testing  devices.
Once  these decisions are  made,  the  homeowner  is advised to contact the
State  radiation protection office  or regional EPA office  by letter or  phone
for information on   types  of  devices;   these  offices  are  listed  in  local
telephone books  and in "A  Citizen's Guide."   State representatives  can
provide  a list of  vendors that  provide  measurement services within the
State.    EPA  suggests  that  a  homeowner  contact several  of the  listed
companies and  request  information concerning qualifications, warranties, and
costs.   With this  information,  a homeowner can  make an  informed  decision
concerning testing devices.


EPA  is  sponsoring  a  voluntary  program,   known  as  the  Radon/Radon
Progeny  Measurement  Proficiency  and Quality Assurance  (RMP)  program,
which is designed to evaluate  the  qualifications and expertise of firms and
laboratories with  respect  to radon  measurement  and analysis.   The RMP
program  is not  designed  for  laboratory accreditation  and  EPA  does not
certify, recommend,  or endorse participating laboratories.

In the RMP program,  testing periods  are  referred to as  test  rounds.   Each
round  consists  of two  tests:   a  performance test and a  follow-up  test.
Successful  completion  of either test  is  considered  successful  completion of
the test round.   Both  tests follow  the same procedures as described below.

All   testing  is  conducted  at  the  radon   chamber   at   EPA's  Eastern
Environmental  Radiation  Facility   (EERF)  in  Montgomery,  Alabama.   Each
participating company  may enroll with any or  all of the seven measurement
methods  described  in  EPA's   "Interim  Indoor  Radon  and   Radon  Decay
Products Measurement  Protocols"   (EPA86a).   Once a  company is  enrolled,
EPA specifies the  number of each type of detector to be submitted, and the
detectors   are  exposed  to  known  radon  and/or   radon   decay  product
concentrations.  The radon  or  radon decay product  concentrations are not
revealed  to the companies.   After  exposure, the detectors  are returned to
the  companies,  which  then  have  two   working  weeks to  analyze  their
detectors and report the results  to EPA for evaluation.

EPA evaluates the results by comparing the companies' results to the  known
levels  of  exposure.    If a  company's  results  are  within   the  established
screening-measurement  criteria,  and  the  company  meets all  other  program
requirements, they pass  the performance test.   If  a  company fails any of
the  program  requirements,  the  method  is  automatically  retested  in the
follow-up  test.   Companies  that  fail again in  the  follow-up test  are not
listed in the proficiency report for that  test round,  but may participate  in
the next test round.


EPA conducts  the  test  rounds  semi-annually,  and  issues reports  of  the
results.   State-specific  proficiency  reports  list  the  companies  that  serve
each State.  The report is issued to  States  for public distribution.  A more
detailed  report,  the  Cumulative  Proficiency Report,  lists  the  performance
record  for  each  participating company as  well as  other information.   This
report is issued to  participants as well as to State officials.

                                Chapter 11
It  is widely recognized that radon concentrations in homes can vary  greatly
over   time   (FI84;   Ge83;   He85;   Ny83;   St79;   Wi86).    Furthermore,
concentrations  at different  locations in the same house can often  differ by a
factor  of  two  or more (Ce84;  He85;  Ke84).   Because of these temporal  and
spatial variations,  EPA  cannot use  the  result  of  a  single  measurement to
provide an  accurate estimate  of health  risks  or  to  make  a  well-informed
decision  on the need  for  remedial  action.   What  EPA  has recommended,
therefore, is a system for making the least number of measurements possible
to obtain accurate and reliable results.

EPA  recommends  a  two-step   strategy,   beginning   with  a   screening
measurement made  under  closed-house  conditions  in  an  area where radon
concentration   is   greatest   (usually  the   basement  or  ground  level).
Depending on  the results  of the  screening measurement,  a second series of
follow-up  measurements  may be  recommended to assess more  completely the
average concentrations in the living  areas of the  house.   EPA  recommends
that any  decision concerning  permanent corrective action to reduce  indoor
radon  concentrations  be  made  only  after  the  completion  of  follow-up

EPA  advises  that  the  first  measurement  in  a   house   be  a  screening
measurement.    A   preliminary   screening   can   determine   quickly   and
inexpensively  whether  or  not  occupants may  be   exposed to high  radon
concentrations and if additional  measurements  are  needed.   Another use of
screening measurements is in  multiple-house surveys designed to identify.

as  efficiently  as   possible,   houses  that  contain  high  concentrations.
Screening  measurements  should  be  inexpensive   and  simple,   so  that
unnecessary time or money  is not spent in houses that do not pose a health
threat.    EPA's   guidance  emphasizes,   however,   that  the   screening
measurement  alone  does not provide  a  homeowner sufficient information  to
decide on the  need for  remedial action.

A  screening  measurement  should  provide  information  about  the  maximum
concentrations  to which the occupants may  be  exposed, and should also  be
reproducible  during occupied conditions.   Therefore, EPA recommends  that
screening measurements be made in (1)  the lowest  area  of the house  that
the residents currently use or could adapt for  use as a  living area,  and (2)
under closed-house conditions.   In  many houses, the lowest  livable area will
be  a  basement  that  could  be converted  to a  den,  playroom,  or bedroom
without major  structural changes.   The  highest concentrations of  radon  or
radon decay products will  usually be  found in  areas  of  the  house  closest  to
the underlying soil.   Radon  concentrations  should  be  highest  and  most
stable  when  doors  and windows  are not  opened  for  more  than  a  brief

There  is a growing  body of  data  (EPA85;   Ce83;   Ge81)  indicating  that
basement concentrations tend  to  be a factor  of two to three  times  higher
than concentrations  in  rooms  above the basement.   Therefore,  if  the result
of a screening  measurement is  very low,  there  is a high probability that the
long-term average  concentrations  in the  rooms  currently  used  as living
areas  are even lower, and  the homeowner can eliminate  the need for further
measurements.   There  has  been  some  criticism  that  EPA's  protocols will
result  in a significant number of  erroneous  identifications  of high  levels.
This may be  true;  however, EPA believes  that  a  false positive measurement
result  is  less  serious because  it will  result in  further measurements, which
would  reveal that the  concentrations in  the house  are  low.  Adherence  to
the EPA protocols  for  screening  measurements  will  decrease the  number  of
false  negatives  and   as   well   as   the   number  of houses  that  contain
concentrations  high  enough to  warrant  remedial  action (EPA86a)  but  that


are not identified as such  because of a low screening measurement result.
The  outcome of a false negative is that  no further  measurements are made,
and potentially high concentrations may never be identified.   In the interest
of reducing radon exposures, therefore,  EPA believes  that a significant rate
of false positives is preferable to a high  rate of false negatives.

Another  EPA  recommendation  is  that  all  short-term  measurements  (i.e.,
measurements  of  less  than  three months in  duration)  be  made  during
periods of  the year  when  windows  are  normally  kept  closed.   For most
climates in this country,  this will  be  during the winter months.   The intent
of this recommendation is to  ensure  that short-term measurements are made
during the  time  of  highest and most stable concentrations.   The occupants
should  be  instructed to  keep  windows  and  doors  closed  during the
measurement period.  Doors should be opened only  for a  few minutes  to get
in and out of the  house.  External-internal air exchange  systems such as
high-volume  attic  and window  fans  should not  be  operated,  except for
furnaces,  which may be essential to the  occupant's comfort.

The   EPA  guidance  for  follow-up  measurements  is   intended  to  provide
homeowners with an estimate  of  annual  concentrations  in  living areas,  while
minimizing  excessive exposures.   This  guidance  closely parallels the tiered
set of  recommendations  to  homeowners described  in  "A  Citizen's Guide"
regarding  the  need for  and urgency of remedial action.   The need  to make
follow-up  measurements  depends   upon  the  results  of   the  screening
measurement.   A  summary of recommended follow-up  measurements  appears
in table  11-1.

                               Table 11-1

                          Follow-up Measurements

                       Made in General  Living Areas

Radon Progeny
Sampling Unit
Working Level
Screening Result
Greater than 20 pCi/l

3-month measure-
ments  (may  be less
than 3 months  if
laboratory uses
adequate lower limit
of detection),  made
under  closed-house
(winter) conditions*

Measurements  of
2 to 7  days  made
under  closed-house

100-hour measure-
ments, made under

24-hour measure-
ments, made under
 Screening Result
Less than 20 pCi/l

12-month measurements
made under normal  living
4 measurements made
under normal living
conditions every 3 months
4 100-hour
measurements made
under normal living
conditions every 3 months

4 21-hour
measurements made
under normal living
conditions every 3 months
Radon Monitor
21-hour measure-
ments, made under
closed-house conditions
4 24-hour measurements
made under  normal  living
conditions every 3 months
     If  the  result of the screening measurement  is greater than about  200
     pCi/l,  a short-term follow-up measurement  in  a  few  days or  weeks
     would be more appropriate.

If the screening measurement result  is  less than about  4  pCi/l -   or  0.02
WL,  follow-up  measurements  are probably  not  required.   If  the  screening
measurement was made in a lowest  livable area  of the  house,  under closed-
house   conditions,   then  there   is  relatively  little  chance  that   the
concentrations  in the  general  living  areas  on  non-basement  floors  of  the
house are greater than about 4 pCi/l  or  0.02 WL as  an annual  average.

If the result of the screening measurement is  less than about  20  pCi/l  or
0.1 WL,  but greater than about 4  pCi/l   or 0.02  WL,  EPA recommends  that
the follow-up measurement  consist of  an  integrated measurement  or  series of
measurements over  a 12-month  period made in several living areas  of  the
house.   Although   there  is  the  possibility  that  the  average  long-term
concentrations  in  the living areas  of the house will  be in  the range where
remedial  action  should  be  considered,  the  levels  are not  high enough  to
warrant  immediate   action.   Follow-up measurements  spanning  a  year  are
recommended  for  estimating  exposures  because  the  result  will  incorporate
the variations  in concentration  due  to  seasonal  and  lifestyle  differences.
This  measurement   provides  the household  with  the  best  measure  of  the
long-term concentrations  to which they are  actually exposed.

     If  the screening  measurement result was greater than about  20 pCi/l
or 0.1 WL, EPA recommends that  a  short-term follow-up measurement  over
at least  21  hours  be made  in  several  living areas  of the house under
closed-house   conditions.    EPA  recommends   a    short-term   follow-up
measurement because an  additional  year  of  exposure to these  concentrations
could cause  a  significant increase  in health  risk.   A short-term  follow-up
measurement quickly provides the occupants with a reproducible result that
is a  conservative estimate of the annual  average concentration.  The higher
the result  of the screening measurement, the shorter should be  the duration
of the follow-up measurement.
Q /
-    EPA has published guidance  levels in the traditional radon and  radon
     decay  product units that are  still widely used  in the United States.
     See  the Conversion  Table  at  the end of  this  Reference Manual to
     convert to SI units.


Follow-up measurements should  be  made  in  areas of the  house currently
used  as  living  areas.   Whenever possible,  EPA  recommends that separate
follow-up  measurements  be  made on  at least  two different floors  of the
house.   EPA  also  advises  that one  of the  measurements  be  made  in  a
bedroom,  because most  people  spend  more time  in their bedrooms  than in
any other room  in  the  house (Ch74; Mo76; Sz72).  Follow-up measurements
should not be made in kitchens or  in  bathrooms, because  exhaust fans or
high concentrations  of  airborne  particles caused by cooking can affect the
results of short-term  radon and radon  decay product  measurements.   The
results  of  the   measurements  in   the  different  living  areas  should  be
averaged; the average result can be compared to guidance levels (published
in terms  of  annual average  concentrations  in  EPA86b)  in order  to estimate
health  risks  and to decide on the  need  for remedial  action.   It should be
noted that the  EPA recommendations  discussed  here  were  not  designed to
apply  to  measurements  made   for   real  estate  transactions,   where  the
measurement  time period is a serious constraint.

The EPA guidance for making radon and radon decay product measurements
in homes is  interim, and EPA plans to update the documents based on  new
information  as   it becomes  available'.    As screening  and  annual  averagd
measurements are gathered and  analyzed, EPA may refine the protocols.  In
the meantime, however, the intent  of  the  recommendations  in the protocol
documents is to  help  both  individual homeowners as well as States and other
organizations  perform  measurements  that  produce  consistent   and  useful

                                Chapter  12
                   WHAT DO MY TEST RESULTS MEAN?
The  results  of  the  follow-up  measurements  described  in  the  previous
chapter provide an  indication  of  the average  radon concentration to which a
homeowner  is  exposed.   As  explained  in  "A  Citizen's  Guide,"  the  risk
caused by this exposure depends on the duration  of  exposure;  "A Citizen's
Guide"  presents estimates  of total population  risk  that  are  based on  a
75 percent  occupancy  rate and  a  lifetime of approximately  70 years  (see
Chapter 4 for a detailed explanation of  the total population risk estimates).
In this section  of  "A  Citizen's Guide," the  individual  risks  resulting from
exposure  to  various   radon  concentrations  are  presented   in  two  ways.
First,  individual risks are  illustrated in charts which  depict the  expected
number of additional lung cancer deaths resulting  from  radon exposure  at H
pCi/l,  20  pCi/l,  and  200 pCi/l assuming 70  years  of exposure; and  at 200
pCi/l  assuming 10  years  of  exposure  from birth  to 10  years   of age.
Second, the risk from  exposure  to  radon  is  compared to  other  health risks
(risks  from chest x-rays and  from smoking)  in the  Radon Risk Evaluation
Chart.  The follow-up measurement results and the  Radon Risk Evaluation
Chart  together  allow  the homeowner to estimate the individual risk  he or
she may face.

This chapter explains the derivation of  the risk estimates presented  in the
lung cancer risk  illustrations  on page  9 of  "A Citizen's Guide,"  and the
Radon  Risk Evaluation  Chart  on  page 10.  The  first section  of the chapter
considers  the  risk  illustrations  and the second  discusses  the Radon  Risk
Evaluation Chart.

The  risk  illustrations  on page  9 of "A Citizen's Guide"  provide  a  visual
representation  of  individual  risks attributable  to  various levels  of radon

exposure.   For the most  part,  the derivation  of the risk estimates  follows
the first three  steps  of  risk estimation described in detail  in Chapter 4 of
this  Manual.   Important  assumptions underlying  the risk  estimates include:
(1) a linear  dose/response model;  (2)  a  relative-risk projection  model, witti
a  risk ranging  from  1 to 4  percent per WLM  of  exposure; (3) a  life-table
analysis  to  account for  competing  risks, based  on 1980 vital statistics;  (*»)
an  age-dependent correction of  exposure  to  account  for anatomical  and
physiological  differences  between  the  underground  miners  (the population
from whom the  risk estimates are derived) and the general population;  and
(5) a 10-year minimum induction  period to account for the  latency period of
cancer.  The range in the relative  risk estimates accounts for  the  range of
fatal cancers cited in  the  text under each risk illustration; however,  due to
competing risks,  the  high and low  fatal cancer estimates  do not vary by a
factor  of four.  Finally,  a 75 percent occupancy rate is assumed to estimate
annual  exposure   (this   assumption  implies  about  20   WLM  per  year  for
exposure to  a  1 WL environment.   This figure includes  a  correction for  the
breathing rate difference  between miners and average adults.

As  noted,   "A Citizen's  Guide"  illustrates   the  risks  for   three   radon
concentration levels after 70 years of  exposure,  and at 200 pCi/l  after 10
years of exposure.  In  calculating the  latter  estimate,   it  was assumed that
the exposure is  received in the  period between  birth  and age 10.   As  a
result  of anatomical differences between children and adults (principally  the
smaller  lung  size  of  children) and the  influence  of competing risks,  this
assumption  results in a  somewhat higher  estimate  of fatal  cancers  than
would have  been calculated for 10 years of exposure  received later  in  life.

Finally, in presenting the risk illustrations,  "A  Citizen's  Guide" notes that
on average,  about 4  people  out  of 100  die of  lung  cancer from all  causes
combined.   This  figure  is derived  from a cohort analysis using 1980 vital
statistics and 1980 standard mortality rates (NCHS83; NCHS85).


The  Radon  Risk Evaluation Chart  was developed  to  try to place  the risk
associated   with  radon   and  radon  decay   product   exposure  into   some
perspective.   Fatal  lung cancer  risks  associated  with chest  x-rays and
smoking cigarettes  were selected as relatively commensurable risks, but also
risks that most people could understand.   The risks associated with various
radon  concentrations  employ  the same  assumptions  used  for   the  risk
illustrations  on  page 9  of "A  Citizen's  Guide"  over  an   average 70-year
lifetime.   The  sources of x-ray and smoking risk  estimates  are described in
the following discussions.

The  risk of lung cancer  from  a chest x-ray  was taken as 92 x 10~  per low
                                                             g /
LET  rad  (derived  from  relative  risk estimates  in  BEIR80).  -   The  lung
dose in a chest  x-ray was taken  as  9 to 20 millirad  per exposure (Sc73),
using  mean active  bone  marrow  dose as  a  surrogate for  lung dose.  The
risk  of a chest x-ray is then  0.9 x 10   to 1.8  x  10   per  exposure.

The  smoking risk was estimated by calculating  the  cumulative risk of dying
of lung cancer for a life  table cohort.   The calculations  made  using 1980
vital statistics showed 4.74 percent of the cohort would die of lung cancer.
This risk was  then reapportioned  for the  general  population on  the basis of
data from several sources  (NIH85;  OSH80; OSH82).   In this apportionment,
the  risk in nonsmokers  was  taken as 20  to  25  percent of the risk of the
general population, the  risk for 1-pack-a-day smokers as 8 to 10 times that
for nonsmokers, and the risk of 2-pack-a-day smokers as 18 to 20  times
that  for nonsmokers.
-    A  rad  is  a  unit of absorbed  radiation dose that represents the energy
     imparted by  ionizing  radiation to a unit mass of absorbed  tissue.   One
     rad is  equal to 0.01  joules per kilogram.  A millirad is one thousandth
     of  a   rad.    LET  represents   Linear   Energy  Transfer  and is  an
     expression  of "the  amount  of energy lost per  unit distance.  Greater
     energy loss  per unit distance  increases  the dose  and  results in  more
     cell damage.  Thus,  low LET rads have a  lesser biological effect than
     high LET rads.


The  estimates  of  risk  relative to  nonsmokers may be  overestimates  since
they  are  weighted  heavily  by  the data  on males.   The  risk in  female
smokers  relative to  nonsmokers  is  lower  than  in  males and  is  not  well
documented.   There is  some indication  that it  is  increasing  as  female
smoking habits  become  more  like  those  of  males  and so, in this document,
female and male risks are made about the same in magnitude.  If the  female
risks  for smokers versus  nonsmokers remains the same as they are now, the
risks  for smoking in this  document are biased slightly  high.

Finally,  the   Radon   Risk   Evaluation  Chart  compares   various  radon
concentrations with average indoor and outdoor levels.   The average  indoor
level  (0.8  pCi/l)  is  derived  from  a  study  of  New Jersey  and  New  York
homes  (Ce78).   The average  continental outdoor radon  level ranges from
0.08  pCi/l to 0.25  pCi/l, with a figure of about 0.2 pCi/l used in the  Radon
Risk  Evaluation  Chart (UNSCEAR82; Ce83;  Ne2/8U).

                                Chapter  13
To  provide homeowners  with  specific guidance  in  the  event that elevated
indoor  radon  levels  were  present  in  their  homes,  "A  Citizen's  Guide"
presents  recommended  timeframes  for   action  based  on  various  annual
average  radon concentrations.   These  recommendations are  organized  in  a
four-tier scheme, with higher  radon levels  warranting  faster action.   This
chapter  describes  how  EPA arrived  at these  guidelines,  summarizes  the
factors  that  were  considered,  and  provides additional  discussion  of  the
intent of the guidelines themselves.

EPA was  faced  with  a  difficult and sensitive task  in developing the  action
guidelines  found in  "A Citizen's Guide."   The  Agency  had to balance the
need  to  compel people  to  take  action  with the  need to avoid  frightening
them.   To  do  this, the  Agency  considered  various alternatives  along  a
decisionmaking spectrum.

On  one  end of the spectrum,  EPA considered  simply presenting the  risks
from  radon  and   stating  that,   in general,   one's  risk   increases  with
exposure.   This alternative  was thought to be the least  intrusive  on  an
individual's decisionmaking,  while   relying  the  most on  that  individual's
ability to understand and  evaluate  those  risks.   On the other  end of the
spectrum,  EPA  considered  providing very little  risk  information  and  simply
stating that at a certain radon concentration, homeowners should take action
to reduce  their exposure within a  given timeframe.  This  alternative was
thought  to provide  the homeowner with  the  most  specific  guidance but
offered  the least flexibility in evaluating personal risk.

Based  on  the  results  of  several  discussion  groups  consisting  of EPA
personnel and homeowners who were somewhat  knowledgeable about radon,
it  became very apparent  that  homeowners  desire definite  guidance on how
quickly to take action  if they discover a radon problem.  While  no level of
radon  can be  considered  risk  free, an  absence of specific  guidance could
alarm homeowners unnecessarily and could  cause  them to attempt to reduce
radon  levels  below  the  point at which reduction  is currently feasible.

Consequently,  the Agency  chose to provide homeowners  with  some  fairly
specific recommendations as  to how  quickly  action  should  be taken to reduce
exposure  at various radon concentrations.   In addition, however, EPA chose
to include detailed risk information  to allow homeowners some  flexibility  in
applying the EPA guidelines to their personal situations.   In other  words, a
homeowner could choose to  delay, or even  forgo,  remedial  action  based  on
his or her acceptance  of  the associated  risk.   By providing information  on
the risks at  various  concentrations  of radon, a  homeowner can  more  easily
make this kind of decision.

In developing the  action guidelines,  the  Agency  considered  it important to
not only indicate a level at which action should be taken  almost immediately,
but also to indicate  a  level that could be  used  as  a  target  for  corrective
action.   To meet this  objective,  EPA  arrived  at the four-tier  scheme of
action  guidelines  contained  in  "A  Citizen's  Guide."   These guidelines  are
meant  to provide  homeowners  with  some  indication of whether and  how
quickly they may need  to take remedial action based on their  indoor  radon

To  choose  the values and timeframes of  the four tiers,  EPA  considered a
number of  factors.  One of the factors  EPA considered — perhaps the most
important factor  — was the  potential risk  from  exposure to  indoor  radon.
Radon  exists  at  low  levels at  all times in  the environment.   As  noted in


earlier  chapters,  the  health  risks  from  radon  are  significant  even  at
relatively low levels,  often  in excess of the risks  associated with regulated
environmental  contaminants.    Therefore,   EPA  considered  the  effect  of
recommending that  homeowners reduce  the radon  levels in their homes  as
low as possible.   Our experience, however, indicated that it is difficult,  if
not  impossible,  to  reduce  indoor  radon  to  levels  that  approach  average
outdoor  radon concentrations  (0.08 pCi/l   to 0.25  pCi/l).   The next  step
involved taking a practical  look at  what reductions were possible given the
state of  current knowledge about radon reduction.  The  choice  of 0.02 WL
(4 pCi/l) as a lower bound  reflects  this consideration.

Before  making  the  final decision  to  recommend  4  pCi/l  as  a  target for
corrective  action, EPA examined alternative action  guidelines, such as the 8
pCi/l recommendation made  by  NCRP.   Data available at  the time  indicated
that even at an 8 pCi/l  action level, as many as one million homes  might  be
affected   (Ne9/8i»).    Based   on  that  information,  EPA  chose  the  lowest
technologically feasible target level,  i.e., 4 pCi/l,  in  order to  encourage  as
much reduction  of risk to the population as possible.

Another  concern  was the  availability  of  contractors  to  fix  homes.   In
selecting  its  recommended   timeframes  for  action,  the  Agency   felt   it
important  to  choose  realistic  timeframes  that  would   not  result  in  an
excessive demand on the then  developing   mitigation  industry.   Again, the
use  of  a  tiered system emphasizes the need  for  faster  action  at  higher
radon  concentrations.   EPA  believes that   the  timeframes  for  action in  "A
Citizen's  Guide" are  realistic  and  attach  an  appropriate  sense  of  urgency
for various radon concentrations  based on  the  associated  risks,  but do not
create unwarranted  mitigation activity.

Finally,   EPA's  choice  of  action   levels   recognizes  the  desirability  of
consistency  with  previous  EPA actions  and with  existing  State  programs.
In earlier  guidance to the State of Florida, EPA recommended  0.02  WL as a
target for  radon mitigation  for houses built on  phosphate  lands  (EPA78).

EPA   has  also  established  0.02  WL  as  a   remedial  action  standard  for
Superfund cleanups  and for  remediation  under the  Uranium  Mill  Tailings
Radiation  Control Act  of houses  built  on or  near  uranium mill tailings.
Based  in  part  on  these  EPA  actions,  a number  of States have  already
established indoor radon  programs using 0.02  WL as a mitigation  target.  In
combination  with the  other factors EPA  considered,  the issue of  consistency
reaffirmed our choice of 0.02 WL   (4 pCi/l) as a goal  for radon reduction.

There  are several important things  to  remember  when  interpreting  EPA's
guidelines.  First, the guidelines are based  on annual average radon  levels
in lived-in areas  of the house.   EPA strongly recommends that homeowners
make  follow-up  measurements  (to determine  average  levels)  before making
final decisions about  mitigation.

The  intent of these  guidelines  is to  communicate the point that there is a
greater risk,  and thus  a  greater urgency  for remedial  action, as  radon
concentrations  increase.   The  guidelines  do  not  represent  standards  for
indoor radon.   EPA does not intend  (nor  does it currently have authority)
to regulate  indoor radon levels.   Rather,  the  decision to  pursue mitigation
depends  on  the homeowners'   level of risk acceptance and individual  living
habits.   The purpose of "A Citizen's Guide" is to  provide homeowners with
the risk  information they need to make informed decisions.

Finally,  the use  of  0.02  WL  as  a  target  for  corrective  action  simply
represents a lower  technological  bound  of radon reduction achievable with
current methods.   Similarly, there  is nothing definitive about  the  use of
1  WL  as  a trigger for immediate action.   Homeowners  should compare  their
follow-up  measurements  to  the entire range  of action guidelines  and should
evaluate  their  personal  risk using  the  information provided  in  "A Citizen's
Guide."   Having  made this  evaluation, they  may choose  to act more or less
quickly   than   "A   Citizen's   Guide"  recommends,  depending  on   their
perceptions  of their individual risk.

                                Chapter l/i
The earlier  questions in "A  Citizen's Guide" discuss the risks  from  radon in
general.   The  question  "Are  There  Other  Factors  I  Should  Consider?"
applies  to several  conditions that could significantly influence risks  for an
individual homeowner or  household.   In evaluating their risks,  homeowners
should take these  factors into  account.  However, as  noted in  the general
discussion   of   radon   risk  presented   in  Chapter  4,  the  precise  risk
implications  of  many  factors  are  still  uncertain.   The  objective  of this
chapter is to  discuss the  uncertainties  underlying the five  factors cited in
"A Citizen's Guide":   (1)  smoking; (2)  risks  to  children; (3)  time  spent at
home;  (4) sleeping in the  basement;  and (5) lifetime exposure  period.

In general, stopping smoking will  reduce one's  overall risk of  lung  cancer.
However,  the  interaction   between  radon  decay  product  exposure  and
smoking  is  not well  understood.   There are data  from human and animal
studies that could support  widely varying  models,  including  models that:
(1) suggest that the combined risks from radon  decay products and  smoking
are  less  than the  risks attributed  to  each carcinogen  separately  (Cr78;
Lu79;  Ax78;  Da79);  (2) suggest  that  there is  no interaction between  the
two  types of  exposure (Ch81;  Ra84);  or  (3)   suggest that the combined
risks from the two carcinogens  are  greater  than the  sum  of the  risks that
would  be  calculated  separately (called a synergistic model)  (Wh83;  Lu79).

For  example.  Sterling   (Sg83)  has  proposed that increased  mucus  in  the
lung,  such as that associated with smoking,  leads to reduced lung cancer in
smoking  miners  compared to non-smoking  miners exposed to  radon  decay
products,  workers exposed to arsenic,  and workers exposed to chloromethyl
ethers.   This is  in  line with findings  by Cross,  et  al.  (Cr78)  that fewer

lung  cancers  occurred in smoking  dogs than  in  non-smoking  dogs exposed
to  radon decay products.   Other  scientists,  such  as Dr.   E.A. Martell,
argue that  smoking  promotes  the  cancer-causing  effects  of radon  decay
products  (C6EN5/86).  Such a  result  could  be attributed  to the naturally
elevated levels  of polonium-210 (an alpha emitter)  present  in  tobacco,  or  to
the tendency  for tobacco tars  present in the lungs  of  smokers to promote
the deposition of radon  decay products in the lung.   In any  case, it seems
clear  that the interaction  between smoking and radon  decay products is not
simple and  more study  is needed.   However,  since  smoking  increases the
overall  risk  of  lung cancer  and  since  it  may  also greatly increase the
risk  attributable to  radon  exposure,  EPA   advises  homeowners  to  stop

Since  EPA  uses a   relative  risk  model  (a   synergistic model with simple
multiplicative  interaction)  to project radon  risks,  the potential  interaction
between  radon  exposure  and smoking  is important  (see  Chapter  4  for  a
discussion  of  relative risk).   In  the current relative-risk  projection model,
the age-specific baseline  lung cancer mortality rates  are multiplied  by the
appropriate  risk conversion  factor to calculate the number of cancers due  to
radon daughter  exposure up to  a  specific age.   Therefore,  anything that
increases the  baseline lung  cancer mortality  rates  (such  as  smoking) will
increase the   calculated  risk  due  to  radon  exposure  as  long  as  an
age-constant,  time-constant  relative  risk coefficient is  used in  the model.

The risks of exposure to radon  decay  products for infants and  children
compared to adults are  uncertain.   In  general,  differences  may  exist  for
two  reasons:  (1)  the  exposure  risk  resulting  from a  given  radon decay
product  concentration  in the  home  may  differ  at  different  ages  due  to
physiological  and  anatomical  differences  (e.g.,   lung  size  and breathing
rate),  and (2)  the sensitivity to  induction  of  lung  cancer  per  unit  of
exposure may also  differ by age.


NCRP  Report No.  78 shows a higher dose  calculated per  unit exposure in
infants  and children than  in adults (NCRP84/78).  A similar conclusion  was
reached   by  Hofmann  and  Steinhausler   (St77).    They  estimated  that
exposures received  during  childhood  are  about  50  percent greater  than
adult exposures.   It appears that the  smaller bronchial area of children as
compared  with  that of  adults  more than  offsets  their  lower  per-minute
breathing  volume;  therefore, for a given concentration of radon-222 decay
products,  the dose to their bronchi is greater (see Chapter  4).

However, there is  still a  great deal  of  uncertainty concerning  the  effect of
radon exposure on  children.   Indeed, tables 10.1  and  10.3  of NCRP  Report
No.  78  indicate  that children  may be  at a  lower risk than persons older
than 20  years  of age.   This result is arrived at,  however,  through the use
of certain assumptions  that are significantly  different than  those  used  by
the EPA.

The NCRP risk estimates,  like the EPA individual risk estimates, are based
on  a life-table  analysis  of a  lifetime risk projection  model.  However,  the
NCRP  uses  an absolute-risk  projection  model  with  a relatively  low   risk
coefficient: 10 cases per  million  person WLM per  year  at risk,  which is the
smallest  of those  listed by the National  Academy  of  Sciences' Committee on
the  Biological   Effects  of  Ionizing  Radiation  (BEIR80).    Another  critical
assumption in the  NCRP estimates is that the risk of  lung  cancer  following
irradiation decreases exponentially with a 20-year half-life, and, therefore,
exposures occurring early  in life present very little  risk.   This  exponential
decline is illustrated for  an absolute  risk  projection  model in figure   14-1
(assuming a 5-year minimum induction period and  no tumors before age  40),
and is explained further in Ha81.

In  contrast,  EPA,  as  noted in  Chapter  4,  uses a  relative-risk projection
model.    EPA's  risk  projection  model  uses  a  time-constant  relative   risk
coefficient  (one  to  four  percent  increase  in  base-line  risk  per   unit
exposure)  to   calculate   the  risk  of  excess  lung  cancer deaths.   EPA
questions the assumed decrease in risk  used by NCRP.  If  lung  cancer risk


             Figure 14-1. Lung Cancer Appearance Rate Following a Single

                         Exposure to Radon Daughters

                      ABSOLUTE RISK  MODEL A -  NO DECAY



                 ABSOLUTE RISK  MODEL B -  20 YEAR HALF-LIFE

     (A-1J Model A-exposure at age <40. (A- 2) Model A-exposure at age >40.
     (B-1) Model B-exposure at age <40. (B-2) Model B-exposure at age >40.

  Adopted from Ho81, p. 309.

decreased  over  time  with  a  20-year  half-life,  the  excess  lung  cancer
observed  in  Japanese A-bomb  survivors  would have decreased during  the
period of  observation  (1950-1980);  to the  contrary,  their absolute  lung
cancer risk has increased  markedly (Ka82).

The  question  of the sensitivity of children  to induction  of  lung  cancer is
virtually unanswered for  radon  exposure, and  not  well answered  for  x-ray
or  gamma-ray  exposure.   However,   the evidence  developing  in   Japan
indicates that  the  relative risk  is higher  the  younger the age  of  exposure
and  for  the  same  age  at  death; similarly, the absolute  risk is higher  the
younger  the  age of exposure for all cancers except leukemia (Ka82).   Since
this  information is available and appears  to  have stronger support in each
succeeding report  on  the Japanese A-bomb  survivors, it seems prudent to
mention  the  possibility  that children  are more susceptible  than  adults to
radiation  induced  cancers.   The  major uncertainty in  the data right  now
appears  to  be whether  those exposed  as  children  will continue to develop
two  or  three  times more  cancer  than  those exposed  as  adults  for  the
remainder of their life spans, or if the increased  susceptibility will diminish
at some age.

The risk  estimates given in "A  Citizen's  Guide" assumed  that 75 percent of
a person's time is  spent at  home.  At  lower  levels of exposure (below 0.01
WL), spending more  or  less  time  at home  would,  respectively,  linearly
increase or decrease  lung cancer  risk,  provided  that indoor  exposure at
home is the dominant source of radon exposure (as is normally true).

In  a variety  of EPA  rulemakings, the Agency has  also  assumed that,  on
average,  residents spend  75  percent  of  their  time  in their  homes.   This
assumption  is  taken  from  two  studies  (Mo76  and  Oa72)  which  estimate
radiation  exposure and  population  dose  in  the  United  States.   Similar
findings  have been reported  for  England; that  is,  people spend about 75
percent of  their time  in their  dwellings (Bn83).


The  risk  estimates also  assume that the remaining 25 percent of a  person's
time  is spent in a virtually radon-free environment.  However,  if this is not
the case,  homeowners should  adjust their individual risk  to reflect this.

In most  cases,  indoor  radon  originates in  the  soil  and  rock  below  and
around the house  and,  thus, enters a home  through the basement floor or
walls  (if  a basement is present) or through the lowest floor slab.   Although
radon  is  then carried to other parts of the house,  radioactive decay  and
ventilation of the  upper floors tend to cause  the  highest radon  levels to
occur in  the basement.  As a result, individuals spending a large portion of
their  time  in the  basement   (such  as  when  they  sleep  in  a  basement
bedroom)   will  face a  slightly  higher  risk  from  radon.   In some cases,
homeowners can  verify  whether higher  levels indeed  are  present  in  the
basement  by  taking radon  measurements in multiple  locations  in  the  house
(as recommended for follow-up  measurements;  see  Chapter 11).

In some  cases,  lower floor  and  basement  levels may  not be higher  than
elsewhere  in the house.  For example,  if a major source of radon  is water,
showers  or  dishwashers could be  the  principal  entry  routes  of  radon.
Similarly,  if building  materials or fireplace stones are  the major source of
radon, the principal radon  entry point  could  be on  the first floor.  Interior
hollow block  foundation  supports,  if present, could provide a  route for
radon to  enter on  the first floor.   Finally, a central air circulation system
would tend to distribute  radon  throughout the home  if basement  intakes are
used.  However, in all  of  these cases,  the impact  on radon distribution in
the home  is still  relatively  uncertain, and it is  generally thought  that water
or building materials are usually not the primary  sources of indoor radon in
most homes.   Until more is  learned,  it appears to  be prudent to assume  that
radon  levels  are  highest  in  the  basement  when  evaluating  risk  to the


There  are a number of factors  that  can affect estimates  of lifetime  risk  to
the individual homeowner.  The  risk  estimates in  "A Citizen's Guide"  assume
that the homeowner is exposed  to a  constant concentration  of  radon decay
products  for  about 74 years  (the average  life  expectancy).  However,  an
individual's risk is affected by  both cumulative  exposure and by  exposure
rate.   Variations  in  the  radon  decay  product  concentration,  duration  of
exposure,  and age at which exposures  started can  all  affect the estimate  of
lifetime risk  for  an  individual.   Table  14-1  displays  risk estimates for
several  different  choices  of  these  parameters,  including   the   set   of
assumptions  (i.e., lifetime exposure  beginning  at birth)  used  to create the
chart on page  10 of "A Citizen's  Guide."

In  addition,  an  individual  may  occupy a  number  of different residences
throughout a  lifetime, each with  a  potentially different radon decay product
concentration.    It  is,  therefore,  important to  remember that  the  risk
estimates  presented in "A Citizen's Guide" should be used only as indicators
of what might be  true under  specified  conditions.   It  should also  be noted
that even  short exposures to high radon decay  product  concentrations can
be  associated  with significantly  increased  risks (e.g.,  as shown  in the
chart on  page 9  in "A  Citizen's Guide,"  the lifetime  risk from 10 years  of
exposure  to 1  WL is  14 to 24 chances out of 100 of dying  of lung  cancer;
or, as shown in table 14-1, it can be seen that 1 year of exposure at 1  WL
at almost any  age under 60 years  appears to have a greater risk  than a
lifetime of exposure at 0.01  WL).

                   Table 14-1

  Lifetime Risk Of Excess Lung Cancer Mortality
Induced By Radon Decay Product Exposure (N/1000)
Age At First Exposure
Exposure Year
Birth 1
00 5 Years 1
15 Years 1
Radon Decay Product Exposure




Level (WL)



                                                                                   Table continued

                                                             Table  14-1  (Continued)

                                                  Lifetime Risk Of  Excess Lung Cancer Mortality
                                                Induced By Radon Decay Product Exposure  (N/1000)
Age At First Exposure
Exposure Year
25 Years 1
40 Years 1
(— i
r io
60 Years 1

0 .1-0.4

Radon Decay
Product Exposure Level (WL)
Assumptions:   1 percent  - 4 percent per WLM Relative Risk Coefficient, 1980 Life Table, 1980 Vital Statistics, 75 percent Occupancy Factor;
               General Population.

SOURCE: U.S. Environmental Protection  Agency, July  1987.

                                Chapter 15
Scientists commonly  agree  that the risk of  lung cancer  is dependent on  both
the  level  of  indoor  radon  in  the  home  and  the  length  of time one  is
exposed.   For  homes  with  high  radon entry  rates,  "A  Citizen's Guide"
recommends several  short-term steps  that, if taken immediately, can reduce
the risk  from radon.   EPA stresses  that  although these techniques can  be
implemented  quickly,  they  are  unlikely  to  provide  a long-term  solution.
For  further  information on  permanent mitigation measures  as  well  as  these
short-term mitigation  techniques, consult EPA's "Radon Reduction Methods:
A  Homeowners  Guide."  In addition, EPA has a guidance document  available
that provides  technical  information  on  both short-term  and  longer-term
mitigation techniques,  "Radon Reduction Approaches  For  Detached Houses:
Technical Guidance" (EPA/625/5-86-019).

Ideally,  the  short-term  mitigation  methods  discussed   here  should   be
implemented  during  periods of decisionmaking  or  when  waiting  for  test
results.   In  addition, these short-term actions should be  taken as soon  as
possible  if homeowners find levels  of radon  above 1  WL or 200 pCi/l after
the  screening  measurement.   Homeowners finding levels  below 1  WL  (200
pCi/l)  and  above  0.02 (4  pCi/l)  WL may  wish  to use  these  short-term
techniques  whenever  practical.    Clearly,   the   urgency   to   implement
mitigation  techniques  will  depend  on  the  level  of radon detected,  with
higher levels requiring immediate  attention.  This  chapter  discusses  the
four short-term  techniques  recommended  in  "A  Citizen's  Guide":  (1)  stop
smoking,  (2) avoid living  areas with high  exposure,  (3) ventilate the home,
and  (4) ventilate crawl- spaces.


Although  the  interrelationship  between smoking and  radon exposure  remains
unclear,  stopping smoking  immediately  reduces one's overall  risk  of lung
cancer.  As  discussed  in Chapter 14, medical  studies are currently unable
to determine  whether smoking increases  or  decreases  lung cancer  risks from
radon.  However, the relationship between smoking  and lung cancer is well
established,  and  some researchers  believe  there  is  a  strong  synergistic
effect  between radon  and tobacco smoke.   On this  basis,   EPA believes it
appropriate to  recommend that  homeowners  stop smoking.

Research performed on  houses with elevated radon concentrations found  that
the distribution of radon  throughout  a house  is not uniform.  In  general,
those living  areas closest to the source of radon  entry had  higher radon
levels  than those farther away.   In  most  houses, the  primary  source  of
radon entry is from the  soil  and rock  underneath the house.  Other  sources
include potable drinking water and building  materials.   Since drinking water
and  building  materials  have  been  determined  to be  usually  an  almost
negligible  source,  the  underlying soil is the main  contributor   (Ne83).
Therefore, EPA recommends  that homeowners spend as little time as possible
in the basement  or  in  parts of the home  directly above the  soil or other
areas of  the home that have  been found to  have elevated  levels  of radon.

Indoor radon concentrations are determined by  the  balance between the rate
of entry  from radon  sources and  the rate  of removal,  by ventilation or
radioactive decay.  Proper ventilation techniques within  the  home have been

found to reduce radon concentrations  by about 30 to 90  percent,  depending
on  the  time  of year  (ASHRAE81).   This  reduction  is due  to  both  the
removal of radon-laden  air and the dilution of the total  indoor volume with
cleaner  incoming air.

Natural  ventilation occurs  in  a home  because of temperature  and pressure
differences   between   indoor   and   outdoor   air.    Changing   seasonal
temperatures  and winds are  major natural forces causing this occurrence.
Because  natural  ventilation takes  place  through all  passageways connecting
indoor and outdoor  air,  indoor air can  be exchanged with outdoor air even
when doors and  windows are  closed.

Forced  or  mechanical ventilation  relies  on  the use  of  fans  that force  an
increase in air  exchange  rates  by drawing  in outdoor  air  or  exhausting
indoor air  while  replacing it with cleaner air from the outside.

In return, natural air exchange rates rely  heavily  on pressure  differences
arising  from  temperature  differentials  and  wind  effects.   These  factors
cause small pressures across walls  separating  indoor and  outdoor  air.  As  a
result,  the  stack  effect  discussed  in  Chapter  8  is  created,  in  which
pressure  at  the bottom  of  the  wall  causes  air  flow  toward  the  heated
interior and  pressure at  the  top of the wall  causes air  flow  toward cooler
temperatures.   The  stack effect  causes  the  exchange  of indoor  air with
outdoor air,  which   is  drawn  from the understructure  during  the  heating
season (Ne85).

For  natural  and forced ventilation  to  be effective mitigation  techniques,
homeowners must open all windows  in  the  home to  ensure uniform ventilation
throughout the  house.   For  example, opening  windows  only  on  the north
side of a  house may  have the effect  of causing  pressure  differences  to
occur between indoor and outdoor air.   Winds blowing by these windows will
depressurize the house,  causing pressure driven air  to flow into the  house.
The appropriate action  is to open windows on all sides of the  house  to allow
pressure  differences to equalize.   The  same  technique should be  applied  to


crawl-spaces.   Vents  should  be opened  on all  sides of  the  crawl-space to
allow  uniform air flow.

As mentioned in  "A  Citizen's  Guide,"  the ventilation  methods just  discussed
should be  implemented only when  weather  permits.  This means  that this
type  of ventilation is  relatively  inexpensive for  only about four months of
the year.   Proper ventilation during  summer  and  winter months  requires
different  methods,   usually   at  a   greater   cost.   Again,   for   further
information  on   permanent   ventilation   methods  and   the   recommended
short-term mitigation techniques,  consult EPA's "Radon  Reduction  Methods:
A  Homeowners  Guide"  or the  more  detailed  document,   "Radon Reduction
Approaches  For  Detached Houses: Technical Guidance" (EPA/625/5-86-019).

                               Chapter  16
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Ke84           Keller, C.,  K.H.  Folkerts, and  H. Muth.   "Special Aspects
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Ku56           Kusnetz, H.L., 1956, "Radon  Daughters in  Mine Atmospheres
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Ku86           Kuntz, Charles and  B.  Kothari.  "Indoor Radon Measurement
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Lu79           Lundin, F.E., Jr.,  V.E.  Archer,  and J.K. Wagoner.   "An
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Mo76           Moeller, D.W.  and  D.W.  Underhill.   Final  Report on  the
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Mu83           Muller, J., W.C.  Wheeler, J.F. Gentleman.  C.  Suranyi,  and
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Nero  A.V.,  M.B.   Schwehr,  W.W.  Nazaroff,  and   K.L.
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Nero,  A.V. and  W.S.  Nazaroff.  "Transport  of  Radon from
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Indoor   Air   Quality   and  Climate,  Stockholm,   Sweden,
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Nero,  A.V.,   M.B.  Schwehr,  W.W.  Nazaroff,   and  K.L.
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Absolute Risk
Projection Model
A model which estimates the risk of exposure
beyond  the  years of observation of a studied
population    by   projecting    the    average
observed number  of excess  cancers per unit
dose into the  future  years at risk.
Absorbed Dose
The  amount  of  energy per  unit  mass trans-
ferred  to  human  or  animal  tissue  from
radiation.    Measured   in   rads  or   grays
standard  international  (SI  unit).   One  gray
equals  one  joule  per  kilogram.    One  rad
equals 0.01  gray.
The  rate of atomic disintegration, measured
in curies.
Activity  Concentration
(specific activity)
Activity    per   unit   volume.    Commonly
measured in picocuries  per liter  (in air) or
picocuries  per gram  (in  a solid).
Exposing  to  the  action of air.   For example,
a  liquid can  be aerated by agitation  or  by
means  of a fine spray.
Atomized  particles  of a substance  suspended
in air.

Air Changes  per  Hour
Air Exchange  Rate
A  measure of  the  movement  of a  volume of
air  in  a given  period  of  time  (i.e.,  of the
Air  Exchange  Rate).   One  air  change  per
hour is equivalent  to replacing all  of the air
in   a  house  in  a one-hour  period.    Air
changes also may  be expressed in  cubic  feet
per minute.

The  rate  at  which  air  inside  a  house is
exchanged  or replaced  with air from outside
the house  as a  result  of  ventilation,  seepage
through cracks, open windows or doors, etc.
Measured in air changes per hour (ach).
Alpha Activity
The    rate   of   atomic   disintegration   or
radioactive  decay  that  is  accompanied   by
release of an  alpha  particle.   Measured  in
Alpha Particle
Alpha Energy
A   positively  charged  subatomic   particle
emitted  from a nucleus during  some types of
radioactive  decay,  indistinguishable  from  a
helium  atom nucleus  and  consisting of  two
protons and  two  neutrons.

The energy  released  when an  alpha  particle
emitted  during radioactive decay  is halted by
collision  with  a   substance  (e.g.,   lung
tissue).   The  amount of energy  depends on
the velocity of the alpha  particle,  which in
turn  depends  on  the source  of radioactive
decay (e.g.,  decay of U-238  versus Ra-226).

Alum  Shale  Brick

Attached  Radon
Decay  Product
   Brick building material  made with a  type of
   shale rock  that  has been  found  to  contain
   naturally elevated levels of uranium.

-  Tiny air sacs  in the lung.
   A  radon  decay product that is attached to  a
   particle of dust or  other material  in the air.
Basaltic  Lavas
   A  dense,   dark  igneous  rock  formed  by
   cooling  volcanic  material  that  can  contain
   uranium  minerals  at  low  levels.   Uranium
   minerals  are finely disseminated through  the
   rock and  concentrations  are  typically  of  low
Basement Foundation
   Underlying   structure   of  a   building   or
   dwelling.    Usually   constructed  of  cinder
   block or  cement.   May  have  a dirt  floor.
   One   of   three  types   of   substructures
   commonly  used   in  U.S.  home construction
   (see    Crawl-Space    and    Slab-On-Crade
Bequerel  (Bq)
   The  SI  unit  of  radioactivity  equal  to  one
   disintegration  per  second.   One  picocurie
   equals 0.037 Bequerel.
Beta Particle
   A   negatively   charged   subatomic  particle
   (electron)  emitted  from  a  nucleus  during
   some types of radioactive  decay.

Beta Energy
   The  energy released when  a beta particle is
   halted  by  collision  with  a  substance.   The
   amount  of  energy depends on  the  source of
   radioactive decay (see Alpha Energy).
Black Shales
   A laminar type of sedimentary rock  found in
   parts   of   the   central    United    States
   characteristically  rich   in   organic   matter,
   such as marine black shale and carbonaceous
   shale.   Although  the   uranium  content  is
   normally  less  than 0.005  percent U30g,  the
   uranium  level  tends  to  be  higher  than  in
   other sedimentary rock.
Breathing Rate
-  The rate of oxygen/air intake  by the lungs.
Bronchial  Epithelium
-  The cellular lining of the bronchi.
   The  two  main  branches  leading  from  the
   trachea  to- the lungs.

   Relating  to,  containing, or  composed  of  the
   element  carbon.
Carbonate Rock
   Rock  composed  principally  of  carbonates,
   especially if  at  least 50  percent by  weight.
   Carbonate  is  an  ester  or  salt  of  carbonic
   acid.     Calcium    carbonate   and   calcium
   magnesium     carbonate     are     principal
   constituents of limestone and dolomite rock.
   Cancer-causing  agent.   Any agent  that in-
   cites  development  of  a  carcinoma   or   any
   other form of malignancy.

A  large homogeneous group  of people  tested
in  epidemiological or  socioeconomic  studies.
EPA's  lung cancer  estimates  are based  on
calculations for a cohort of 100,000 people.
Concentration Gradient
                              The change  in  concentration (mass  per unit
                              volume) per  unit distance.
An  area  beneath some types of houses which
are constructed  so  that  the floor  is  raised
slightly  above  the ground, leaving a space
between  the floor and ground to allow  access
to  utilities   and   other   services.     (See
Slab-On-Crade    Foundation   and   Basement
Cumulative Working
Level Month  (CWLM)
A  unit  of cumulative  radon  exposure.   The
sum  of lifetime exposure to  radon working
levels   expressed  in  total   working  level
Curie (Ci)
A   unit  of  radioactivity,  defined  as  that
quantity  of  any  radioactive  nuclide  which
spontaneously   undergoes   3.7    x    10
disintegrations  per   second.   One  gram  of
radium-226 has an activity of one curie.
Decay  Series
The  consecutive  members  of  a  family  of
radioactive   isotopes  formed  by  sequential
radioactive   decay.    A   complete    series
commences with a  long-lived parent  such as
U-238  and ends with a  stable  element  such
as  Pb-206.   See figures 2-1  and  2-2.

A   condition   that   occurs  when  the   air
pressure inside a house is lower  than  the air
pressure  outside.    Normally,   houses  are
under     slightly     positive     pressure.
Depressurization  can  occur  when  household
appliances  that  consume  or  exhaust  house
air,  such as fireplaces  or furnaces,  are not
supplied with  enough makeup air.   Radon-
containing  soil gas  may   be drawn  into  a
house  more  rapidly under the depressurized
Diffusive Flux  (J)
Diffusion  is  the  condition  of  spontaneous
movement  and   scattering  of  particles  of
liquids, gases, and solids.  Diffusive  Flux is
the weight of a  material diffusing  across unit
area  per  unit   of time  in   response  to  a
pressure     or     concentration    gradient.
Measured  in  grams per square centimeter per
second.   Used  to characterize the  rate  of
radon movement into a  home.
Diffusivity (D)
The constant  by which  Diffusive Flux  and
Concentration   Gradient   are   related   at
constant pressure under Pick's First  Law of
             J = -  D * A£
A  brittle calcium magnesium  carbonate rock
occurring abundantly in  white  to pale pink
rhombohedral  crystals.

Earth-Based Building
Materials  such  as  cinder  block  and  brick
which  are formed  using  naturally-occurring
minerals and rocks.
Effective  Dose Equivalent
Electron Volt (eV)
Epithelial Lining
Dose  equivalent  weighted by  a factor  which
measures   the  relative  sensitivity  of  the
tissue to a radiation-induced cancer.

A  unit  of  energy commonly used  to  measure
energy  releases during radioactive  decay.

The   division  of  medical science  concerned
with  defining  and   explaining   the  inter-
relationships   of  the   host,   agent,   and
environment in causing disease.

Cellular  tissue  covering surfaces,  forming
glands, and lining most cavities of the  body.
Equilibrium Factor
Equivalent Dose
An   adjustment  used   in   converting  from
picocuries  per liter  (pCi/l) to working level
concentration (WL)  which takes  into account
the    possible    absence    of   radioactive
equilibrium   between  radon  and  its  decay

The absorbed  dose  weighted  to account  for
its  relative  biological effectiveness by  use of
quality and  modifying  factors.   Measured in
rem or sievert (SI  unit).

The   amount  of  radiation   present  in   an
environment,  not  necessarily  indicative  of
absorbed   energy,   but  representative   of
potential  health   damage  to  the  individual
present.  Measured  in roentgen.
Follow-up Measurement
A   measurement   taken   after   an   initial
screening  measurement  to determine  annual
average exposure  to home occupants.
Forced or Mechanical
Ventilation  induced by means  of  a  fan  or
other mechanical  device.
Gamma Ray or
Photon Radiation
Emission of a high-energy  photon,  especially
as  emitted   by  a   nucleus  in  a  transition
between two  energy levels.
Grain Size
The  size of a microscopic particle of regular
crystalline  structure.   Grain  size affects  a
number  of  important   macroscopic  physical
properties, such as yield point and porosity.

The   time  it  takes  for  one-half  of  any
quantity of  identical   radioactive  atoms  to
undergo decay.

Indoor Radon
Concentration  of  radon   or   radon  decay
products  in  a   house.    Concentration  is
dependent  on  the geologic formation  under
the house  and  the structural  conditions  of
the house, as well  as other factors.
Inversion Condition
Ionizing  Radiation
A    meteorologic    condition    in    which
temperature    increases    with     altitude,
generally   caused  by  a   warm  air  mass
overlying  a colder one.

Subatomic  particles  or  photons  that  have
sufficient    energy  to   produce   ionization
directly   in   their   passage   through    a
One  of two or  more types  of atoms  having
the  same atomic number but  different mass
number (e.g., radon-220 and radon-222).
LET (Linear  Energy
The   energy  lost   by  a  charged   particle
passing through  a  substance per unit length
of path.
A  form  of cancer  In  the  blood.   Any  of
several  diseases of  the  hemopoietic  system
characterized    by    uncontrolled   leukocyte

Lifetime Risk
                              Exposure-induced   risks   reported   as    a
                              function  of  the  distribution  of  age  in   a
Long-Term Mitigation
                              Mitigation  by  a  homeowner  to  permanently
                              reduce elevated radon  levels in a house.
Maximum Contaminant
Level Goals (MCLCs)
                              Maximum   Contaminant   Level   Coal   -   a
                              non-enforceable  health  goal  under  the  Safe
                              Drinking  Water   Act,   set  at  levels  which
                              would   result  in   no known  or  anticipated
                              adverse health effects  and allow an adequate
                              margin  of safety.
Maximum Contaminant
Levels (MCLs)
                              Maximum  Contaminant Level - an  enforceable
                              standard  under the Safe Drinking Water Act,
                              set as close to the MCLC  as feasible  taking
                              into   consideration   cost,    availability   of
                              treatment  technologies,  and  other  practical
                              A unit  of length equal to one millionth  of  a
                              meter or  one  thousandth of a  millimeter.
Modifying Factor
Molecular  Diffusion
                              A numerical  factor used  to  modify calculation
                              of  the   Equivalent   Dose  to  account  for
                              variation  of the  LET and  radiation  effects
                              with tissue type and exposure.

                              The transfer of mass  between adjacent layers
                              of fluid in laminar flow.

Occurring  naturally in the soil.   Not caused
by  industrial or other human activity.

The capacity of  a porous  rock,  solid,  or
sediment to  transmit  a  fluid without damage
to the structure of the medium.
Picocuries  Per Liter
A    unit    of   measurement   of   activity
concentration.   A curie is  the  amount of any
radionuclide  that  undergoes  exactly  3.7  x
10    radioactive disintegrations per  second.
One  picocurie  per  liter  is  equal  to  10
curies per liter.
Property  of  a  solid  which  contains  many
minute  channels  or  open  spaces  that  are
capable of absorbing liquids.
Pressure Driven Air Flow
Air  flow  in   a   home  that  is   caused  by
differences  in pressure  between  the indoor
and outdoor air.
Quality Factor
The  factor  by which absorbed dose is to be
multiplied   to   obtain    a   quantity    that
expresses,  on   a  common   scale,  for  all
ionizing  radiations, the  irradiation incurred
by exposed persons.
Radiation Dose
The   total   amount   of  ionizing   radiation
absorbed  by material or tissues,  in the sense
of  absorbed  dose   (expressed  in  rads),
exposure  (expressed  in  roentgens),  or dose
equivalent (expressed in rems).

Radioactive Decay
Radioactive Equilibrium
Radioactive  Particles

Radionuclide,  Nuclide

Radium  (Ra)

Radon  (Rn)
Radon  Bearing
-  The  spontaneous transformation of a  nuclide
   into    one   or   more   different    nuclides
   accompanied by either the emission of energy
   and/or  particles from  the  nucleus,   nuclear
   capture  or  ejection  of  orbital  elements,  or

-  A  state  in  which  the  rate  of formation  of
   atoms  by decay  of a  parent  radioactive
   isotope is equal  to  its rate of disintegration
   by radioactive  decay, so that the activity of
   the parent and the decay  product assume a
   constant proportion (equal to one  to  one,  if
   the parent has only one mode of radioactive
   decay).   Because radon decay products tend
   to attach  readily  to surfaces  (plate out),
   equilibrium  between  radon  and   its .decay
   products  is  seldom reached.

-  Products  of radioactive decay.

-  Any    naturally-occurring    or    artificially
   produced radioactive element or isotope.

-  A   naturally-occurring   radioactive   element
   found  in  rock  and  soil.   Atomic number  88.

-  A  colorless, naturally-occurring, radioactive,
   inert gaseous  element  formed  by radioactive
   decay  of radium atoms.   Chemical symbol  is
   Rn,  atomic number 86.

-  Containing or  emitting radon.

Radon  Progeny,  Daughters,
Decay  Products
Radon Source Strength
Terms used  interchangeably  to refer  to the
intermediate  products  in  the  radon  decay
chain.  Each decay product is the ultra-fine
radioactive  particle  that  decays  into  other
radioactive  decay  products  until,  finally,  a
stable nonradioactive lead atom is  formed and
no  further  radioactivity   is produced.    The
Rn-222  decay chain  has  12 decay products,
including  the stable lead  isotype,  Pb-206.

The  intensity,  power,  or  concentration of
radon action from its point of  origin.  Refers
to  the  general  intensity  of  radon  evolution
from  a  specific  soil  or  rock  type  beneath a
The  disattachment of  radon decay  products
from  solid  surfaces  as  a   result  of alpha
decay, causing the atom to  re-enter the air.
Relative  Biological
Effect  (RBE)
An  evaluation of the  impact  of  a  given type
of radiation  on tissue based  on the  LET  of
the radiation  type.   RBE equals the product
of  the  Quality  Factor  and  the  Modifying
Relative  Risk
The  ratio  of  the  rate  of disease in exposed
to unexposed  populations.

Relative Risk Projection
A model which estimates  the  risk of exposure
beyond  the years of observation  of a studied
population   by   projecting   the  currently
observed percentage  increase in cancer  risk
per unit dose  into future years.
REM (Roentgen Equivalent
A  unit  of  equivalent  dose  equal   to  the
amount  that  produces  the  same  damage to
humans  as  one  roentgen  of  high   voltage
x-rays.  Equal  to  0.01  sievert.  Related to
Absorbed Dose  by  the  RBE:   Equivalent
Dose (Rem) =  RBE  * Absorbed Dose (Rad).
Screening Measurement
A  measurement  taken  under  closed-house
conditions  in  the  lowest  livable area  of a
house.     This    initial    measurement    is
recommended   to   determine   whether   a
follow-up measurement is necessary.
Short-Term Mitigation
Temporary  measures   to   reduce   elevated
radon levels  in  a  house.   Usually performed
during  the   time  between   screening   and
follow-up  measurement results.
Slab-on-Crade Foundation
A  substructure type  in which  the  foundation
is    at    approximately   the    same   level
("on-grade")  as  the  surrounding   ground
surface.   Generally, a poured  concrete slab.

Soil Gas
Those  gaseous elements and  compounds that
occur  in  the  small  spaces between  particles
of the earth or  soil.   Rock  can  contain  gas
also.   Such gases can move through or leave
the  soil  or  rock depending on  changes  in
pressure.   Radon  is  a  gas  which  forms  in
the soil wherever radioactive  decay of radium
Solubility Coefficient
A  measure of  gas  solubility  in  a  liquid.
Radon solubility coefficient is defined  as the
ratio  of radon  concentration  in water  to that
in  air  (Co86).
Stack Effect
In houses and other buildings,  the  tendency
toward displacement (due to the difference in
temperature)  of   internal  heated   air   by
unheated outside air which is caused  by the
difference  in  density of  outside  and  inside
air.   Sfmilar  to the  air and  gas  in  a duct,
flue,  or  chimney  rising when  heated  due to
its  lower  density  compared   with   that  of
surrounding air or gas.
Subatomic Particles
The   electrons,   protons,
comprising atoms.
and   neutrons
Below  one micron  in  size or  diameter.  Less
than one-millionth of a meter.
The  underlying  structure of a  building  or
house.   May  be  a  basement,  slab-on-grade
foundation,  crawl-space,  etc.

Surficial  Material

Synergistic Model
Unattached Radon Decay
-  Surface or near surface soil deposits.

-  A  form of cancer  causality whereby  two  or
   more carcinogens act synergistically to cause
   cancer  with  a  greater  probability  than   if
   each were acting alone.

-  A  radioactive  isotope of the element Thorium
   in  the  actinium  series,  symbol  Th,  atomic
   number 90, atomic weight 232.

-  Conventional  name  for  the  isotope of  radon
   with an  atomic weight  of 220  (radon-220).
   Sometimes symbolized Tn.

-  The  windpipe.    The  duct   by  which  air
   passes from the larynx (in  the throat) to the
   bronchi and the lungs.
   A  radon decay  product  that  is  not  electro-
   statically attached to dust or particles in the
   air.   Capable of attaching to  lung  tissue  if

-  Of or containing uranium.

-  A highly toxic,  radioactive metallic isotope of
   the element  uranium  in  the actinide  series,
   symbol  U, atomic  number  92,  atomic weight
   238.     Undergoes    radioactive    decay,
   eventually  to radium-226.

Uranium Ore
A  mineral  deposit  that  can  be  mined  to
recover uranium.
The  act of admitting  fresh air  into  a  space
in order to replace stale or contaminated air,
achieved  by  blowing  air into  the  space.
Ventilation an be achieved  both naturally and
Working  Level  (WL)
A  unit of measure of  the  concentration  of
radon   decay   products   defined  as   the
quantity of short-lived  decay  products that
will  result  in   1.3  x  10  MeV  of  potential
alpha energy per  liter of air.
Working  Level  Month
A  unit  of radon  exposure  equivalent  to  an
exposure   to  one  working  level  of  radon
decay products for one  working month (170

Measured  Quantity    Unit
1  Joule
        Unit Definition

   6.24 X 1012 MeV (million  electron
Source Activity
Source Activity
Source Activity
 Bequerel (Bq) =
Curie (Ci)
Picocurie  (pCi) =
Roentgen  (R)
   1  disintegration per second
   2.22 dis/min  =  0.037  Bq

   3.7 x 10   disintegrations
   per second

   10    curies
   2.22 disintegrations per minute
   0.037 Bq

   2.58 x 10   coulombs per
   kilogram (in  air)
Absorbed  Dose
=  0.01  joules per kilogram =
   62. H  x 106 MeV/g
Absorbed Dose
=  1  joule per kilogram = 100 rads
Equivalent Dose
=  RBE x (dose in rads)
Equivalent Dose
=  RBE x (dose in grays)
Relative Biological
  Effectiveness       RBE
                =   quality factor x  modifying  factor
    Indicates Standard  International  (SI) unit.

Unit Multiple
Gig a
                          CONVERSION TABLE
Multiply Common Unit              By                  To Get SI Unit

       Curies                  3.7 x 10                    Bequerels

     Picocuries                   0.037                    Bequerels

 Picocuries  per  liter                37              Bequerels  per  cubic meter

        Rad                      0.01                      Grays

        Rem                      0.01                     Sieverts

        MeV                 1.60290 x 10~13                Joules

     Roentgen                2.58 x 10             Coulombs per kilogram
                                                         (in air)