1. home and garden
2. environmental safety

Radon
What is It ?
Why is it an Issue ?
October 7, 2013
Presentation to
Potomac Chapter
American Industrial Hygiene Association
Ray Johnson, MS, PSE, PE, FHPS, CHP
Director
Radiation Safety Counseling Institute
16440 Emory Lane
Rockville, MD 20853
301-370-8573
[email protected]
Raymond H. Johnson, MS, PSE, PE, FHPS, CHP
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Director,
Radiation Safety Counseling Institute 301-370-8573
BS - Civil Engineering, University of Vermont (1961)
MS - Sanitary Engineering, Massachusetts Institute of Technology (MIT) (1963)
PSE - Professional Sanitary Engineer Degree, MIT and Harvard University (1963)
PE – Licensed Professional Engineer, Vermont (1965 – present)
PhD Studies, Radio and Nuclear Chemistry, Rensselaer Polytechnic Institute (1966–1972)
Greater Washington Institute for Transactional Analysis - Counseling (1977–1980)
CHP – Certified Health Physicist, American Board of Health Physics (1983–present)
Johns Hopkins Fellow, Organizational Systems (1984–1985)
FHPS - Fellow of the Health Physics Society and Past President (2000)
President, American Academy of Health Physics (2013)
Commissioned Stephen Minister – Counselor, United Methodist Church (2003–present)
Experience
2010 – pres. Director , Radiation Safety Counseling Institute. Workshops, training, and counseling for individuals,
companies, universities, or government agencies with concerns or questions about radiation and x-ray safety.
Specialist in helping people understand radiation, what is safe, risk communication, worker counseling,
psychology of radiation safety, and dealing with fears of radiation and nuclear terrorism for homeland security.
2007 – pres. VP, Training Programs and consultant to Dade Moeller Radiation Safety Academy, training and consulting in
x-ray and radiation safety, safety program audits, radiation instruments, and regulatory requirements.
1984 - 2007 Director, Radiation Safety Academy. Providing x-ray and radiation safety training, audits, and consulting to
industry (nuclear gauges and x-ray), universities, research facilities, and professional organizations.
1988 - 2006 Manager and Contractor to National Institutes of Health (NIH) for radiation safety audits of 3,500 research
laboratories and 2,500 instrument calibrations a year, along with environmental monitoring, hot lab and
analytic lab operations, and inspections of three accelerators and over 100 x-ray machines.
1990 - 2005 President of Key Technology, Inc. a manufacturer and primary laboratory for radon analysis with over
1,500,000 measurements since 1985. Primary instructor at Rutgers University for radon, radon measurements,
radiation risks, radiation instruments, and radon risk communication courses (1990-1998).
1986 - 1988 Laboratory Director, RSO, Inc. Directed analytical programs and Quality Assurance for samples from NIH,
Aberdeen Proving Ground, radiopharmaceutical companies, and the nuclear industry.
1970 - 1985 Chief, Radiation Surveillance Branch, EPA, Office of Radiation Programs. Directed studies of radiation
exposures from all sources of radiation in the US, coordinated 7 Federal agencies for nuclear fallout events, QA
officer 8 years. Head of US delegations to I.A.E.A and N.E.A. on radioactive waste disposal. ANSI N-13
delegate (1975-1985). Retired as PHS Commissioned Officer (0-6) in 1985 with 29 years of service.
1963 - 1970 U.S.P.H.S. Directed development of radiation monitoring techniques at DOE National Labs, nuclear plants,
and shipyards in the US and Chalk River Nuclear Laboratory in Canada.
Health Physics and Professional Activities
Health Physics Society (HPS) plenary member 1966; President-elect, President, Past President (1998-2001), Fellow (2000),
Treasurer (1995-1998); Secretary (1992-1995); Executive Cmte. (1992-2001), Chair, Finance Cmte. (1996-1998); Head of U.S.
delegation to IRPA X (2000). RSO Section Founder and Secretary/Treasurer (1997-2000); Co-founder and President, Radon Section
(1995-1996). Co-Chair Local Arrangements Cmte. Annual Meeting in DC (1991); Public Info. Cmte. (1985-1988); Summer School
Co-Chair (2004); Chair, President’s Emeritus, Cmte (2006); Chair, Awards Cmte. (2002); Chair, History Cmte. (2005-2012);
Historian (2012-Pres.) Continuing Education Cmte. (2005-2012). Academic Dean for HPS Professional Development School on
Radiation Risk Communication (2010). PEP, CEL and AAHP Instructor; Journal Reviewer; Treasurer, AAHP (2008 – 2011). AAHP
President (2013). Baltimore-Washington Chapter: President (1990-1991) and Honorary Life Member; Newsletter Editor (19832005); Public Info. Chair (1983-1991), Science Teacher Workshop Leader (1995 – Pres.). New England Chapter HPS, Newsletter
Editor, Board of Directors, Education Chair (1968-1972). President, American Association of Radon Scientists and Technologists
(1995-1998) and Honorary Life Member, Charter Member; Board of Directors; Newsletter Editor (1990-1993). Founder and first
President, National Radon Safety Board (NRSB) (1997-1999). Member of American Industrial Hygiene Association (1997-Pres.)
(Secretary, Vice Chair, Chair, Ionizing Radiation Committee, 2009-2012), Conference of Radiation Control Program Directors
(1997-Pres.), Studied H.P. communication styles and presented Myers-Briggs seminars to over 3500 H.P.s since 1984. Over 35
professional society awards. Licensed Professional Engineer since 1965. Certified Health Physicist since 1983.
Publications
Authored over 500 book chapters, articles, professional papers, training manuals, technical reports, and presentations on radiation
safety. Author of monthly column, “Insights in Communication” HPS Newsletter 1984 – 1989, 1994 -2001, and 2012- 2013..
Contact at: 301-990-6006, [email protected]; 301-370-8573, www.radiationcounseling.org
Radon - What is It? Why is it an Issue ?
Radon - What is It?
Why is it an Issue?
Radon – An Overview
What is Radon?
 Where does it come from?
 How is it measured?
 What are the risks?
 What are the guidelines for safety?
 What can you do about it?

Potomac Chapter
American Industrial Hygiene Association
October 7, 2013
Ray Johnson, MS, PSE, PE, FHPS, CHP
Director
Radiation Safety Counseling Institute
301--370
301
370--8573
[email protected]
 What
are the ways to reduce
radon risks?
2
Radiation Safety Counseling Institute
Its Not Regulated as a Source of
Radiation – So Why the Concern?


Sources of Radiation
(620 mrem / year - NCRP Rpt 94, 2006)
For most of us, inhaling radon decay
products delivers 75% of our radiation
dose from natural sources
How
H is
i that
th t useful
f l to
t Industrial
I d t i l Hygienists?
H i it?
Natural – 310
50 % of dose

When talking to a concerned coco-worker
who just learned that his / her dosimeter
registered 20 mrem
 It provides a basis of comparison –
helps demystify occupational radiation dose
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Radiation Safety Counseling Institute
cosmic
terrestrial
radon
internal
We Live in a Sea of
Natural Radiation
Man-made – 310
Man50 % of dose




medical
industrial (< 0.1%)
occupational (< 0.1%)
consumer products
food and water
4
Radiation Safety Counseling Institute
Inhaled Radionuclides
Air - 229
Cosmic
19
Terrestrial
31
Food and
Water
Radon and Thoron
ecay Products
oducts
Decay
(mostly at home)
Internal
31
Natural Radiation Dose
310 mrem / year = 50 % of total
Radiation Safety Counseling Institute
Inhaled Radiation Dose
229 mrem / year = 37 % of Total
5
Radiation Safety Counseling Institute
Presentatioin to AIHA Potomac Chapter - October 7, 2013
6
1
Radon - What is It? Why is it an Issue ?
238
92
4.5 x10 9 yr
U
What is Radon - 222?

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Naturally occurring
Radioactive gas
 3.8 day T1/2
 alpha emitter
From Uranium - 238
and Radium - 226
Noble gas
Invisible, odorless
Collects in buildings
Radiation Safety Counseling Institute
226
88
1 620 yr
Ra
222
86
3 .8 days
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218
84
3 min

214
82
27 min
Pb
7
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15,000 to 22,000 LCDs / yr (BEIR VI)
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9
Occupational Exposure to Radon

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Subway tunnel workers / Construction excavators
Power plant workers,
including geothermal power and coal
Employees of radon health mines
Waterborne 222Rn sources

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Bi

, 
, 

210
82
19 . 4 yr
Pb
8
Radiation Safety Counseling Institute

1 pCi / L = about 230 mrem
mrem/yr
/yr
Radiation Safety Counseling Institute
214
84
1 .6 x 10  4 sec
Po
214
83
19 .7 min
Occupational Exposure to Radon
– Very Common
Damages lung tissue
Leads to lung cancer


Po
Radioactive gas
Collects in buildings
Forms decay products (RDPs)
 Po
Po--218 and PoPo-214,  emitters
RDPs deposit in lungs
Largest radiation dose



Rn
What is the Radon Problem?

Radon
and
Decay Products
Employees of radon health spas
Water plant operators
Fish hatchery attendants
Employees who come in contact with
technologically enhanced sources of
naturally occurring radioactive materials
Incidental exposure in almost any occupation from
local geologic 222Rn sources
Mine workers, including uranium, hard rock,
and vanadium
Workers remediating radioactive contaminated sites,
including uranium mill sites and mill tailings
Workers at underground nuclear waste repositories
Radon mitigation contractors and testers
Employees of natural caves
Phosphate fertilizer plant workers
Oil refinery workers
Utility tunnel workers
Radiation Safety Counseling Institute
Radon Exposure Pathway

Source: Radium - 226
Transport in ground

Drawn into houses
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Diffusion
Negative air pressure
Hot air stack effect
Wind
Equipment exhausts
Water - aeration
Radiation Safety Counseling Institute
Presentatioin to AIHA Potomac Chapter - October 7, 2013
12
2
Radon - What is It? Why is it an Issue ?
Radon in Homes

Infiltrates from soil under house

Penetrates any openings

Major Radon Entry Routes
A. Cracks in concrete slabs
B. Spaces behind brick veneer
walls that rest on uncapped
hollow--block foundation
hollow
C. Pores and cracks in concrete
blocks
D. Floor
Floor--wall jjoints
E. Exposed soil, as in a sump
F. Weeping (drain) tile, if drained
to open sump
G. Mortar joints
H. Loose fitting pipe penetrations
I. Open tops of block walls
J. Building materials such as
some rock
K. Water (from some wells)
in floor,
floor walls,
walls foundation,
foundation
sumps, drains, etc.

Drawn in by negative pressure


houses always under negative pressure
due to wind, heating, appliances
Radiation Safety Counseling Institute
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Radiation Safety Counseling Institute
Stack Effect on Radon
Radiation Safety Counseling Institute
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Wind Effect on Radon
15
Radiation Safety Counseling Institute
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What Determines Radon Level?
Rainfall Effect on Radon
Concentration of Radium in soil
 Pathways
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Driving forces
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Radiation Safety Counseling Institute
17
permeability of soil
entry routes to home
negative air pressure in house
barometric pressure
temperature, season, rainfall
Radiation Safety Counseling Institute
Presentatioin to AIHA Potomac Chapter - October 7, 2013
18
3
Radon - What is It? Why is it an Issue ?
Do You Have Radon?
Homer Simpson



Sometimes I think there's no
reason to get out of bed . . .
then I feel wet, and I
realize there is.
A fool and his money are soon
parted. I would pay
anyone a lot of money to
explain that to me.
When will I learn? The
answer to life's problems
aren't at the bottom of a
bottle, they're on TV!
 Yes, it is found in every home
 If

Amount depends on

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Radiation Safety Counseling Institute
in contact with the ground
radium in soil,
pathways, and
driving forces
Amount can only be determined by
sensitive measurements
Radiation Safety Counseling Institute
20
Radon Measurements

Integrating Devices
(Passive)
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Continuous Devices
(Active)

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21
Radiation Safety Counseling Institute
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No perfect detectors

diurnal cycles

weather factors

occupancy factors
Radiation is random
Radiation Safety Counseling Institute
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Types of Charcoal Devices
Devices should pass

Open face: 3 inch or 4 inch

Diffusion Barrier

Charcoal Bags

Liquid Scintillation
performance tests
Problem radon variability


Radon Monitors
RDP or Working Level
Monitors
Radiation Safety Counseling Institute
What is Best Radon Detector?

Charcoal Canisters
Electret Ion Chambers
Al h T
Alpha
Track
kC
Counters
t

Calibration is important

QA program

Ask about uncertainty
of measurements
23
Radiation Safety Counseling Institute
Presentatioin to AIHA Potomac Chapter - October 7, 2013
24
4
Radon - What is It? Why is it an Issue ?
How Charcoal Works - Diffusion
Activated Charcoal

Charcoal has a very large surface area
 collects radon gas from the air

Collects radon until reachingg equilibrium
q
in
about 12 to 24 hours

Prompt return to lab is important (4 day T1/2)

Lab analyzes for gammas from radon decay
products, PbPb-214 and Bi
Bi--214
Radiation Safety Counseling Institute
25
Radon and
Moisture
Equilibrium
on Charcoal
Surface
Time - Hours
Radiation Safety Counseling Institute

Radon gives 75% of avg. radiation dose
from natural sources of radiation
229 mrem/yr,
mrem/yr, revised average - NCRP Rpt 94
212 from radon decay products, 17 from thoron
 21,000
21 000 lung cancer deaths / yr in U.S.
US
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Evidence from studies of uranium miners
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Health Concern for Radon
If you want results, press
the
red button. The
rest are useless.
I hope I didn't brain my
damage
Operator! Can your give me
the number for 911
Trying is the first step
towards failure.
Radiation Safety Counseling Institute
It’s easy to measure and it’s easy to fix
Radiation Safety Counseling Institute
More of Homer

Homeowners have to decide on risk
Spend their own money to fix
Good news about radon

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What is the Radon Problem?
1. Measure weight gain
to correct for moisture uptake
2. Count gamma rays
 from RDPs
RDPs,, Pb
Pb--214 and Bi
Bi--214
 do not open the canister
 subtract background
3. Results available in 10 minutes

Ch
Charcoal
l
Radon
Concentration
Charcoal Analysis
Radiation Safety Counseling Institute
Air
29


Risk is not from radon directly
Radioactive decay products


Att h tto airborne
Attach
i b
particles
ti l



Po--218, PoPo
Po-214, both are alpha emitters
Inhaled into lungs
Alpha energy deposited in sensitive
bronchial tissues
Alpha damage leads to lung cancer
Radiation Safety Counseling Institute
Presentatioin to AIHA Potomac Chapter - October 7, 2013
30
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Radon - What is It? Why is it an Issue ?
Radon Exposure Pathway
Fate of Radon in Indoor Air

Unattached
Fraction
Radon
Decay
Products
Radon - 222
3.8 days
Attached to
Dust Particles
Attached to
External Object
Radon ---->
----> RDPs

Primary
Health
Risk


Plated Out
31
Radiation Safety Counseling Institute
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Equilibrium ratio

ER = WL x 100
pCi / L


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
Po--218, Po
Po
Po--214 alpha emitters
Exposure in WLM
WL x Hours
170 Hours / Month
33

Estimate radon
LCDs from lung
cancer risk in
bomb survivors
(BEIR V)
Radiation Safety Counseling Institute
WL = 1.3 x 105 MeV alpha

WL = 100 pCi/L at equil.

WL = 200 pCi/L at 50% ER

ER goes down if:

ER goes up if:

dust goes down
dust goes up
32
Two Methods for relating
exposure to risks

Risk Models

Exposure conditions

Dose

Response (risk)
Radiation Safety Counseling Institute
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RDP Inhalation
Dosimetry Approach
Calculate alpha dose
to bronchial
epithelium

 WLM

Radiation Safety Counseling Institute

Meas. RDPs in WL
 Dosimetry
70 m depth
WLM =


Inhaled into lungs
Alpha energy deposits in
bronchial tissues

Meas. Radon in pCi / L
Radon Risk Assessment
RDPs attach to dust


Radiation Safety Counseling Institute
Inhalation Pathway

Free Ion Fraction
Attached to dust
Plated Out: 50%
Scaling Factors

Dose rate correction

Acute vs low dose
rates

Low LET gamma vs
high LET alpha
35
Radiation Safety Counseling Institute
Presentatioin to AIHA Potomac Chapter - October 7, 2013
36
6
Radon - What is It? Why is it an Issue ?
Differences: Mines to Homes
Radon Dosimetry and Risks

Exposure
Conditions
Dose
Risk
Physical factors


•Particle size
•Ventilation pattern
•Bronchial morphometry
•Deposition pattern
•Clearance rate
•Mucus thickness
•Exposure
Exposure rate
•Age at exposure
•Age at risk
•Sex
•Smoking
•Other Circumstances
•Airway Injuries
Radiation Safety Counseling Institute

Activity
y factors - Breathing
g pattern
p

Biological factors

Age, gender, exposure pattern, smoking
 Bronchial morphometry, mucus clearance,
thickness, target cells
37
Radiation Safety Counseling Institute
Diameter and
area of lung

RDP deposition
Clearance rates
Effect of smoke
Medical Status



Location of sensitive cells

Mucus thickness

RDP di
distance
t
tto surface
f

Alpha energy loss

Alpha quality factor - 20
Mouth vs nose

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38
Dose Factors
Method of breathing


Ventilation volume, rate, nose or mouth

Lung Dosimetry Parameters

Aerosols, Attached / unattached fraction
Equilibrium ratio
Angles and bends
Radiation Safety Counseling Institute
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Radiation Safety Counseling Institute
And the Problem Is ?
40
Critical Cells at Risk

Requirements:
in alpha range
proliferating
 transformed into cells leading to neoplasia



Range of alphas:



Radiation Safety Counseling Institute
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Po - 218 = 48 microns
Po - 214 = 71 microns
Epithelium is thicker in upper bronchi
Radiation Safety Counseling Institute
Presentatioin to AIHA Potomac Chapter - October 7, 2013
42
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Radon - What is It? Why is it an Issue ?
Alpha Particle Deposition
Radiation Safety Counseling Institute
Cross--Section of Lung Tissue
Cross
43
Radiation Safety Counseling Institute
Alpha Tracks
44
Lung Cancer Risk
Cell

Determined by comparison with
uranium miners

Risk depends upon:
 Amount
of radon and most importantly
the concentration of radon decay products
 Length
of exposure
 Smoking
Radiation Safety Counseling Institute
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Lung Cancer Risk Estimate

Updated risk estimates based on NAS
BEIR VI report (1999)

Lung cancer mortality projections (lung cancer
deaths) in the general public (1995)



47
16 in 1,000 for current smokers
10 in 1,000 for “ever” smokers (current and former)
1.8 in 1,000 for non
non--smokers

How do these risks compare with other
environmental risks?

Public interpretation
Smokers
Radiation Safety Counseling Institute
Risks for lifetime exposure to 1 pCi/L

18,200 LCDs from radon out of
146,400 LCDs in smokers (12%)
 Non
Non--smokers 2,900 LCDs from radon out of
11,000 LCDs in nonnon-smokers (26%)

46
Radon Risk Probabilities
Pawel and Puskin
Puskin..
The U.S. EPA’s Assessment of Risks From
Indoor Radon. HP Journal 87(1):68
87(1):68--74; 2004

Status
Radiation Safety Counseling Institute


Events will or will not happen
Radiation is dangerous, but radon is not !
Radiation Safety Counseling Institute
Presentatioin to AIHA Potomac Chapter - October 7, 2013
48
8
Radon - What is It? Why is it an Issue ?
How to Catch the Train
What is the EPA Action Level?
 The
EPA advises mitigation for levels
above 4 pCi / L
 This is a Guideline –
 Not
a regulated limit
 Also, not good science
 Guideline
should be for total exposure
 Concentration
Radiation Safety Counseling Institute
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times exposure time
Radiation Safety Counseling Institute
50
How to Reduce Radon Risks

Intercept the Source of Radon
Radon
Removal
M th d
Methods
Sub-slab suction
Sub Block wall suction
 Drain tile suction


Block the source


Sub-slab
SubSuction
Seal cracks, cover sumps, cover earth floors
Ventilation
Radiation Safety Counseling Institute
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Radiation Safety Counseling Institute
52
Summary

Radon
Removal
Methods


It’s not regulated, so why do we care?
 Largest source of radiation dose,
avg. 229 mrem / yr in homes for 1 pCi / L
 Probably
y far exceeds occupational
p
doses
Magnitude of doses, home vs work
Risk estimates

Radiation Safety Counseling Institute
53
radon risk is greater than all other
environmental risks combined
Radiation Safety Counseling Institute
Presentatioin to AIHA Potomac Chapter - October 7, 2013
54
9
Radon - What is It? Why is it an Issue ?
Conclusions

Radon is largest source of public exposures
229 mrem / year for 1 pCi / L

Every home has radon

It is easy to measure – charcoal canisters

It is easy to fix – sub
sub--slab suction

Risk is about 2 / 1000 exposed for a
lifetime at 1 pCi / L (non(non-smokers)
Radiation Safety Counseling Institute
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Presentatioin to AIHA Potomac Chapter - October 7, 2013
10
Radon in Houses*
Ray Johnson, MS, PSE, PE, FHPS, CHP
Director, Radiation Safety Counseling Institute
The following discussion on radon in houses is intended only as an introduction to the
subject for people who have to deal mainly with issues of Naturally Occurring Radioactive
Material (NORM) and Technologically Enhanced NORM (TENORM) in the workplace. Since
radon is one of the predominant naturally occurring radionuclides, an understanding of radon
measurements, exposures, health risks, and radon mitigation in houses might help put workplace
NORM / TENORM issues into perspective.
1. What is Radon?
Radon is an inert, invisible, and odorless radioactive gas that comes from the radioactive
decay of radium-226, a divalent cation similar to calcium, that is a natural component of soil
everywhere. As an inert (noble) gas, radon created on the outside of soil grains near the surface
of the ground can migrate through porous soils and escape into the outdoor air where it is diluted
to low concentrations. A house or building is simply a box sitting on the ground which can
collect or accumulate radon that would normally be diluted in outdoor air. As radon collects
inside a house, it also decays to several short-lived decay products as shown in Figure 1 below.
Figure 1
238
92
4.5x10
Radon and Decay
Products
U
9
yr

226
88
1620 yr
Ra
222
86
3.8 days

Rn
218
84
3 min

214
82
27 min
Pb
214
84
1.6x10  4 sec
Po
Po
214
83
19.7 min
Bi

, 
, 
210
82
19.4

Pb
yr
____________________________________________________________________________
*Johnson, R.H., Radon in Houses (Chapter 9, 24 pages) In: Naturally Occurring Radioactive
Materials (NORM) and Technologically Enhanced NORM (TENORM). P. Andrew Karam and
Brian Vetter, Editors. A textbook for the Health Physic Society Professional Development
School, Minneapolis, MN July 16-18, 2009. Medical Physics Publishing, Madison, WI (549
pages).
1
What is the Problem with Radon? - The health significance of radon is not actually due to the
radon itself. As an inert gas, when you breathe in radon, you basically breathe it back out again
before it has time to decay or release any alpha particles in the lungs. Radon is essentially the
carrier or vector for the creation of radon decay products (RDPs) in houses. The RDPs of health
significance are the atoms of Po-218 and 214 which also emit alpha particles. Because these
RDPs are electrically charged (strongly positive), they easily attach to dust or other aerosols in
the air. When you breathe in these dust particles, most are also breathed back out again.
However, some dust particles with attached polonium atoms may collect on the surface tissues of
the lung and remain there long enough to emit their alpha particles into sensitive cells. The
subsequent damage to these cells could become the basis for lung cancer.
2. Source of Radon in Houses
Since radon comes from radium-226 found in the ground everywhere, if a house has any
contact with the ground, then it is in contact with the source of radon. The mechanism for radon
transport through the ground is concentration gradient diffusion, often called simply “diffusion.”
Diffusion means that radon atoms will move naturally from a location of higher concentration or
higher partial pressure to an area of lower concentration or lower partial pressure. Since radon is
created in the ground, it will always be at a higher concentration in the ground than in the
outdoor or indoor air. Of course radon has to find entry ways into a house, but there are many.
Radon may also enter houses from building materials such as stone, cinder block, concrete, or
brick that may contain radium-226. Houses that use underground water supplies may also get
radon that is dissolved in the water and then released into the air by aeration as the water is
exposed to the air in the house.
The amount of radon in a house will be affected by the concentration of radium in the
adjacent soil, the permeability of the soil, the entry routes into the house, and driving forces that
affect the movement of radon. Radon may not move as well in soils that are impermeable, such
as tight packed clay. However, houses are normally built on a foundation of crushed stone
aggregate, which would be very permeable to radon. Some of the major entry routes for radon in
houses are shown in Figure 2.
Figure 2
Major Radon Entry Routes
A. Cracks in concrete slabs
B. Spaces behind brick veneer walls that
rest on uncapped
hollow-block foundation
C. Pores and cracks in concrete blocks
D. Floor-wall joints
E. Exposed soil, as in a sump
F. Weeping (drain) tile,
if drained to open sump
G. Mortar joints
H. Loose fitting pipe penetrations
I.
Open tops of block walls
J. Building materials such as some rock
K. Water (from some wells)
2
Any opening in contact with the ground, even the tiniest crack in the concrete, will be a
wide open channel for radon entry. Since radon exists only as individual atoms, it does not
require much of an opening to enter a house. In fact, radon can diffuse through what would
appear to be solid materials. The movement of radon into a house is also related to a variety of
driving forces. In particular, houses are almost always under a negative pressure relative to
outdoor air. Two factors account for this negative air pressure in houses. First of all, when the
wind is blowing across a roof it creates a negative air pressure under the roof. This is the
Bernoulli principle and the basis for lift under an airplane wing. The negative air pressure under
the roof extends all the way down to the foundation of the house. Secondly, when a house is
heated, warm air rises. The rising air is replaced by air drawn in at the lower part of the house.
This is called the “stack effect.” Indoor air pressure can also be reduced by use of exhaust fans
above cooking ranges and in bathrooms, or by whole house exhaust fans. Clothes driers and
fireplaces also exhaust indoor air to the outside, which has to be replaced from within the house.
These mechanisms for lowering air pressure at the foundation of a house, mean that radon is not
simply diffusing into the house, but it is being pulled in under a negative air pressure. Houses
are like a huge vacuum cleaner pulling radon from the ground along with everything else in the
soil including water vapor, soil gas, molds, mildew, and fungi.
The movement of radon into houses is also affected by barometric pressure, temperature,
season of the year, and rain or snowfall. Radon can more easily diffuse into the air when the
barometric pressure is lower (typical of storms). The season of the year and temperature also
affect radon movement. For example, if the ground is frozen and covered with snow, radon
cannot easily migrate into the outdoor air, so it diffuses towards the ground that is not frozen,
namely under a house. Likewise if the ground is saturated with water and sealed by rainfall,
radon will migrate towards the drier and more permeable soil under the house. I have observed
radon levels in my own home to vary by a factor of ten over a weekend as a result of freezing
and thawing of the ground in the winter (Johnson 1994).
3. What Happens to Radon in Houses?
The fate of indoor radon is shown in Figure 3.
Fate of Radon in Indoor Air
Unattached
Fraction
Radon - 222
3.8 days
Radon
Decay
Products
Attached to
Dust Particles
Attached to
External Object
Primary
Health
Risk
Plated Out
3
Once RDPs are formed in air they may exist in two forms, attached and unattached
fraction. Unattached RDPs, called “free ion fraction,” exist for a short time until they collide
with a surface to which they will be strongly attracted by positive electrostatic charge. The most
likely surface for attraction is due to aerosols or dust in the air. Even clean air will have 10,000
particles or more per cubic centimeter. Thus, there are lots of particles to which RDPs can
adhere. RDPs move like electrostatically charged gas molecules until attaching to aerosol
particles. Attached RDPs do not follow the diffusional behavior of a gas, but move with other
aerosol particles of size 5 to 500 nm.
Once RDPs are attached to particles in the air, they will go wherever the particles go.
This includes all the surfaces in a house, such as floors, walls, carpets, drapes, and furniture.
RDPs that become attached to objects in the house are called “plated out” and are no longer
available for inhalation and thus do not contribute to lung cancer risk. The primary concern for
lung cancer risk is the inhalation of the unattached fraction of RDPs or those attached to
suspended dust particles. The concentration and size of particles in the air are important because
this determines inhalation and deposition of RDPs in the lung.
Typically 50 to 60% of the RDPs attached to dust particles will plate out. The degree of
plate out is measured by the equilibrium ratio (ER). The ER is determined by the ratio of radon
decay products in the air (measured in units of working level (WL)) to the radon gas
concentration in the air (measured in units of picocuries of radon gas per liter of air (pCi / L) or
(Bq/cubic meter)). The calculation for ER is as follows:
ER
=
WL x 100
pCi / L
WL is a measure of the concentration of RDPs per liter of air that can be collected on a filter
(this does not include the RDPs that are plated out). WL is determined by measuring the alpha
particle energy emitted by RDPs collected on the air filter. One WL is defined as a cumulative
alpha particle energy of 130,000 MeV in a liter of air. This quantity of alpha particle energy
corresponds to the emission of alpha particles from 100 pCi/L of radon when all of the RDPs
stay in the air. This would be considered full equilibrium or an ER of 1.0. Since typically only
40% to 50% of the RDPs remain in the air, the ER would normally be from 0.4 to 0.5. Thus, to
achieve a WL of 1.0 would require a radon concentration of 200 to 250 pCi/L.
The higher the ER, the more RDPs are available for inhalation and the greater the health
risk. The ER and quantity of RDPs in the air will go down as the quantity of dust particles goes
down. This occurs as a result of filtering the air or operation of ceiling fans. As fans circulate
air in a room, more dust particles are brought in contact with surfaces where they plate out.
Moeller has advised that operation of a ceiling fan can be used to lower the exposure to RDPs in
a house (Maher, et.al, 1987). Conversely, ER will go up as dust loading in the air goes up. This
can occur from cooking fumes, steam from boiling water, smoke from cigarettes, lighted candles
or incense, smoke from a fireplace, or creation of aerosols from a shower. I found that the
smoke from a single cigarette can cause the ER to go to 1 and the WL measurement remains
elevated for hours after. Thus, anyone living in the home of a cigarette smoker will not only be
exposed to side stream cigarette smoke, but also to elevated concentrations of RDPs in the air
(Johnson 1995).
4
While it is customary today to measure radon concentrations in air (pCi/L) as an indicator
of risk from radon, historically underground uranium miners were protected according to
measurements of RDPs collected on air filters (WL). Since risk is related to the cumulative
exposure (WL concentration times exposure time), the measurement for protection of miners was
in units of working level months (WLM). This is determined by the following equation:
WLM
=
WL x Hours
170 Hours / Month
In this equation, 170 is the average number of hours in a working month. The Mine Safety and
Health Administration (MSHA) limits the exposure to miners to 4 WLM per year (MSHA 2008).
4.
Radon Risk Assessment
Two methods have been used customarily for estimating risks from exposure to radon, namely
dosimetry as applied traditionally by health physicists for determining radiation risks, or by
means of relating observed radon risks to exposures in WLM.
Dosimetry Approach – By this approach the alpha particle dose is calculated from
deposition of RDPs on the bronchial epithelium. The risk of lung cancer deaths (LCDs) is then
estimated from lung cancer risks observed in atomic bomb survivors (BEIR V, NRC 1990).
Scaling factors have to be applied to atomic bomb data to account for acute bomb exposures vs
low dose rates for RDPs, and to account for low LET gamma exposures vs high LET alpha
particle exposures. Other factors for estimating dose and risk for RDPs are shown in Figure 4
below.
Figure 4
Radon Dosimetry and
Risks
Exposure
Conditions
•Particle size
•Ventilation pattern
•Bronchial morphometry
•Deposition pattern
•Clearance rate
•Mucus thickness
Dose
Risk
•Exposure rate
•Age at exposure
•Age at risk
•Sex
•Smoking
•Other Circumstances
•Airway Injuries
5
Since we are interested in risks from RDP exposures in homes and our LCD risk data are
for underground miners, we also have to take into account the differences in exposure conditions.
In particular, we need to account for differences in physical factors, such as aerosol properties,
attached vs unattached fraction, and the equilibrium ratio. There are also differences in activity
factors including breathing patterns, ventilation volumes, breathing rates, and nose vs mouth
breathing. There is a large difference in the tidal volume (amount of air breathed) for miners vs
people in homes. For example, men may have a lung size of three liters whereas a child’s lung
size may only be one liter. Working men presumably would also breathe more deeply. There is
also a difference in respiration rate related to degree of exertion between working and resting.
Miners under exertion also may breathe more through their mouths, whereas most people breathe
through their noses.
There are also biological differences such as age, gender, pattern of RDP deposition in
lungs, smoking, bronchial morphometry, mucus clearance rates, thickness of mucus layer, and
location of target cells. Deposition of RDPs has to consider three morphometry regions: 1) the
head airway region which includes the nasal, oral, pharynx, and glottis, 2) the conducting
airways region which includes the larynx, trachea, bronchi, and bronchiols, and lastly, 3) the
conducting airways region which consists of the alveolar ducts and alveoli. Studies of uranium
miners exposed to high levels of RDPs indicate that lung cancers are bronchogenic.
Other lung dosimetry factors include: the method of breathing (whether through the nose
or mouth), the diameter and area of the lung airways as well as angles and bends, RDP
deposition and clearance rates, the effects of smoking, and a person’s medical status (do they
have lung ailments already). Additional factors include the location of the sensitive cells relative
to the location of the deposited RDP, the thickness of the mucous layer, the deposition of alpha
particle energy, and the quality factor for alpha particles (20).
For bronchial cells to be at risk they have to be within the range of alpha particles, they
have be proliferating cells, and capable of transforming into cells leading to neoplasia. The
range of alpha particles from Po-218 (6.0 MeV) is 48 microns and for Po-214 (7.69 MeV) the
range is 71 microns. A cross of section of the sensitive cells is shown in Figure 5 below.
Alpha Particle Deposition
6
The cells at most risk are the basal cells near the connective tissue just below the surface
cells of the bronchial epithelium. These are the newly growing cells that will eventually become
the surface cells (ciliated and secretory cells) of the epithelium. How a cell might be damaged
by alpha particles is shown in Figure 6.
Figure 6
Alpha Tracks
Cell
This figure shows a photomicrograph of alpha particle tracks from a small point source of
radium in a thin gelatin. If the dense tracks of ionization pass through a living cell, significant
damage may occur. If the damage is too great the cell dies. The damage may also be repaired or
repaired imperfectly and later become a cancer cell.
5. Lung Dose and Risk from RDP
Taking into account all of the above dosimetry factors, the NCRP has derived a dose
conversion factor for radon as,
1 Bq/m3 = 32  Gy/yr to the lung (NCRP 1988)
Thus, 40 Bq/m3 (1 pCi/L) = 1.28 mGy/yr (128 mrad/yr)
Converting this to units of Sieverts for a quality factor of 20 for alpha particles gives 25.6
mSv/yr (2.56 rem/yr) for 1 pCi/L. It is also customary to assign a weighting factor of 0.08 to
convert from bronchial dose to effective whole body dose, as follows:
Effective Dose Equivalent, He = wtHt
He = 0.08 x 25.6 mSv/yr = 2.05 mSv/yr (205 mrem/yr)
This corresponds to the contribution of 200 mrem/yr to the average population dose as reported
by NCRP Report 94 (NCRP 1988).
7
The risk may now be estimated by comparison with RDP exposures in WLM. Assuming
an ER of 0.4 at an average radon concentration of 1 pCi/L, the average WL exposure becomes;
WL = ER x pCi/L / 100
WL = 0.4 x 1 / 100 = 0.004
The total exposure in WLM can now be calculated for an occupancy or exposure time of 18
hours a day, 365 days a year as follows;
WLM = WL x Hours / 170
WLM = [0.004 WL x 18 h/d x 365 d/yr] / 170 h/m = 0.156 WLM/yr
If we assume a 1985 US population of 260 million, then the population exposure in units of
person-WLM/yr becomes
0.156 WLM/yr x 260 million = 40.5 million P-WLM/yr
BEIR gives a risk factor of 350 lung cancer deaths (LCDs) per million P-WLM (BEIR IV – NRC
1988). Thus the estimated risk for the average radon concentration of 1 pCi/L is
LCD / yr = 40.5 x 350
= 14,100 lung cancer deaths / yr
This is the basis of the estimated LCDs/yr from radon exposures in the US reported by EPA for
most of the 1990s. Subsequently, the National Cancer Institute (Lubin, et al. 1994) has estimated
15,000 LCDs/yr and the National Academy of Sciences (BEIR VI - NRC 1999) has estimated
about 15,000 to 22,000 LCDs/yr.
6. A Quick Review of BEIR IV (NRC 1988)
The BEIR IV model for radon exposure and lung cancer risk was based on an analysis of
four epidemiologic studies of underground miners (NRC 1988): 1) Eldorado, Beaverlodge,
Canada, 2) Ontario, Canada, 3) Malmberget, Swedish iron mines, and 4) the Colorado Plateau.
Some of the uncertainties from these studies include: variability of miner exposure data and
WLM, risk projection over time (radon risks decrease with age and time since exposure), age
dependence of risk, exposure rate effects, extrapolation from men to women, and the effects of
cigarette smoking.
BEIR IV estimated radon lung cancer risk with a relative risk, time since exposure, model
as follows:
r(a) = r0 (a) [ 1 + 0.025  (a) (W1 + 0.5 W2 )]
where r0 (a) is the age-specific normal LCD rate
 (a) is 1.2 for ages less than 55 yr, 1.0 for ages 55 - 64, and 0.4 for age > 65
W1 is cumulative exposure in WLM incurred between 5 and 15 yr before age (a)
W2 is WLM incurred > 15 yr before age (a)
On the basis of this model, BEIR IV estimated radon lung cancer risk in the US as
15,000 LCDs/yr (out of 167,000 total LCDs) with a range of 7,000 to 30,000 LCDs due to radon.
8
7. A Quick Review of BEIR VI (NRC 1999)
The empirical data used in BEIR VI consisted of epidemiological studies of 11 cohorts of
underground miners, which included 65,000 men and 2700 lung cancer deaths. A preliminary
study by the BEIR VI committee justified the new review of radon risks based on new
epidemiological studies of underground miners (11 cohorts), the extension of existing studies,
and new findings on molecular and cellular basis of carcinogenesis of alpha particles. BEIR also
added information on alpha dose to lung from radon progeny from National Research Council’s
Panel on Dosimetric Assumptions. A number of case control studies that estimate indoor radon
risk have also been completed since the BEIR IV report.
BEIR VI provides a review of the cellular and molecular basis of radon carcinogenesis,
the dosimetry of radon in the lung tract, epidemiologic studies of miners and the general
population, and the combined effects of radon and other occupational carcinogens with smoking.
Some of the critical issues addressed by BEIR VI include: 1) extrapolation from high to low
exposures, 2) extrapolation from high to low exposure rates, 3) interactions of radon progeny and
other agents, 4) susceptibility factors, and 5) links between biologic evidence and risk models.
On evaluation of the biological basis for radon related lung cancers, BEIR VI concluded
that there was “good evidence” that a single alpha particle can cause mutation and transformation
of cell. Also, even with repair, there is potential for substantial damage in cells not killed and
lung cancers probably come from damage to a single cell. However, BEIR VI concluded that,
“At low radon exposures, typical of those in homes, a lung epithelial cell would rarely be
traversed by more than one alpha particle per human life span.”
BEIR VI evaluated animal studies to determine the combined effects of radon and
smoking. They found conflicting evidence on synergism and that animal studies may not
represent human exposures very well. Six of the 11 miner studies allowed some evaluation of
the combined effects of smoking and radon. A synergistic effect was found to be submultiplicative, that is the combined risks are more than the sum of risks, but less than if the risks
are multiplied.
BEIR VI Risk Model - BEIR VI used the linear non-threshold model to relate lung
cancer risk and radon exposures. They did concede, however, that other models cannot be
excluded. They also determined that, after accounting for all differences, both plus and minus,
doses per unit of exposure were approximately the same for mines and in homes. They did note
that exposures to miners were about an order of magnitude larger that the exposures in average
homes. They chose NOT to use the dosimetric approach (used by BEIR IV and described earlier
in this chapter), because of major differences in the types of radiation exposure between bomb
survivors and miners. They concluded that radon risks were better estimated from exposures in
WLM rather than doses. They also concluded that radon exposure has a multiplicative effect on
the background rate of lung cancer. Thus they used an Excess Relative Risk (ERR) model based
on risk as a linear function of past exposure to radon and a multiplicative increment to excess
lung cancer beyond the normal background. The mathematical model is shown in Figure 7:
9
Figure 7
BEIR VI Mathematical Model
ERR= (w5-14+ 1515-24w1515-24+ 25+w25+) age z
► Linear
multiplicative model
  represents the slope of the
exposureexposure-risk curve
  is the relative effect = 1 for 5 - 14 years
 wx-n exposure during a time frame
5-14 years, 15 - 24 years, 25+ years
 age concerns age risk factor

The ERR decreases with increasing age, therefore z for two models is, either, 1) for the
duration of exposure, the exposure-age-duration model or, 2) average concentration over the time
of the exposure, the exposure-age-concentration model. BEIR VI found that the Lifetime
Relative Risks (LRR) - are similar for both models. LRR is risk due to indoor radon exposure
beyond that due to outdoor background radon. This is used to characterize risk to individuals as
an increment of increased risk. It assumes residential radon concentration is log-normally
distributed
BEIR IV vs. BEIR VI Mathematical Models – Both models were almost the same.
BEIR VI has: 1) an additional term for exposure rate, 2) more detailed categories for time since
exposure, and 3) a term for attained age. Lifetime Relative Risk (LRR) calculated using BEIR
IV and VI were found to be similar. Women have a slightly steeper increment of LRR per unit
exposure due to different mortality patterns. Attributable Risk (AR) using BEIR VI is slightly
higher than for BEIR IV. AR indicates how many lung cancers could be prevented if radon is
reduced to background levels.
BEIR VI Analysis - BEIR VI concluded that 15,400 to 21,800 LCDs/yr out of 157,400
LCDs in 1993 could be attributed to radon exposures in homes (wth a range of 3,000 to 33,000)
Homes below 0.7 pCi/L (50%) give 13% of the AR. Homes below 1.25 pCi/L (the US average
home radon concentration), give 30% of the AR. Homes above 4 pCi/L (the EPA recommended
action level) give 30% of the AR. Only 10 to 15% of all lung cancers are estimated to be
attributable to radon. Eliminating exposures above 4 pCi/liter would prevent 3 to 4% of all
LCDs, or about 1/3 of the AR.
10
BEIR VI noted that the AR for smokers will be lower than for non-smokers, where the
AR for smokers only includes risk from radon, not from smoking. When the AR for smoking is
included, the overall AR will be significantly greater than for non-smokers
BEIR VI Conclusions for Underground Miner Studies – The ERR of lung cancer is
linear with WLM for miners. The ERR/WLM decreased with age, time since exposure and time
after cessation of exposure. Nonsmokers are at increased risk from radon. In comparison, BEIR
IV found higher risks at low exposure rates, while BEIR VI found risks are not increased at low
exposure rates. BEIR IV also concluded that about 9% of LCDs are due to radon, while BEIR
VI found that 10 to 15% of LCDs are due to radon.
Ecologic Studies - Ecological studies of populations show that radon may be weakly
linked to leukemia and non-lung cancers. However, the pooled analysis of 11 miner studies
showed no evidence of excess risk for cancers other than lung cancer.
Overall BEIR VI Conclusions - Radon has been conclusively shown in epidemiologic
studies of underground miners to cause lung cancer. Radon is second to smoking as the cause of
lung cancer in the US. Radon is universally present in homes and radon in homes is at least one
order of magnitude lower than in mines. BEIR VI estimated excess radon lung cancer risk in
homes based on pooled miner exposures. They found also that risk depends upon the radon
concentration (RDPs), the duration of exposure, attained age, age at time of exposure, time since
exposure, and whether you smoke. BEIR IV found that smoking increases risk by 10 to 15
times, whereas BEIR VI found that smoking increases AR by 0.9.
8. EPA - Radon Risk Probabilities
The US Environmental Protection Agency’s assessment of risks from indoor radon was
reviewed in 2004 (Pawel and Puskin 2004). This review was an update of BEIR VI and assumed
that people were exposed for 70% of the time in houses with an ER of 40%. The risk or dose per
WLM was found to be balanced between mines and homes, with all differences taken into
account. Risk estimates were made using life-table methods and vital statistics for the US in
1989-1991 and looking at ever smokers (ES) and never smokers (NS), both male and female.
The LCD was estimated for NS and multiplied by 14 for ES males and by 12 for ES females.
Risks were projected for 1995 based on a scaled version of the BEIR VI ageconcentration model. The results are shown in Table 1 below
Table 1. Lung Cancer Risks from Radon in Homes
Smoking
Ever Smokers (ES)
Never Smokers (NS)
Combined
LCD all causes
146,400
11,000
157,400
Fraction from Radon
0.12
0.26
0.13
LCD From Radon
18,200
2,900
21,100
The estimated risks for a lifetime exposure at 37 Bq/cubic meter (1 pCi/L) are as follows:
 16 LCDs per 1,000 for current smokers
 10 LCDs per 1,000 for ever smokers
11


1.8 LCDs per 1,000 for never smokers
5.8 LCDs per 1000 for all together
Since we accept that smokers are already at a high risk from lung cancer, with or without radon,
it may be helpful to look at the radon risks for never smokers. Rounding the projection to 2
LCDs per 1,000, is this a high risk or a low risk? How does it compare with the regulation of
risks for other environmental pollutants. It is common to regulate other risks at levels of 1 in
100,000 or 1 in a million. For comparison, the risk from radon LCD is 200 in 100,000 or 2,000
in a million. This comparison would seem to indicate that radon is a considerable contributor to
environmental risks.
There is also another way to look at such risk projections. Namely, based on the
projections above, if 16 LCDs per 1,000 are expected for current smokers, this means that 984
per 1,000 would not die of lung cancer. Also for never smokers, if 2 per 1,000 may die from
lung cancer due to radon exposures, then 998 per 1,000 will not. Since the public tends to
perceive that they are either at risk or they are not, it would appear from lack of public response
to radon risks, the most people believe they are among the group that will not get lung cancer
from radon.
9. Case – Control Radon Studies
One of the first large scale case-control studies was funded by the National Cancer
Institute in Missouri (Alavanja et al. 1994). This study looked at 530 LCDs in non-smoking
women, compared with 1,183 matched controls at an average radon level of 1.82 pCi/L. The
study concluded that there was little evidence for an increase in lung cancer with an increase in
radon levels. Thus, the association between lung cancer and the exposure to domestic levels of
radon was not convincingly demonstrated. This led critics of the EPA’s radon program to claim
that the whole issue of radon was a hoax. No one seems to have raised the question about what
effects would likely be seen at radon levels below 2 pCi/L. The analogy might be similar to
looking for radiation effects at levels of 100 mrem or less.
A more extensive case-control study was published in 2000 based on studies in Iowa
(Field et al. 2000). In the Iowa study, 60% of the basements and 33% of the living areas of the
studied homes had radon levels above the EPA action level of 4 pCi/L. The study included
1,027 women of whom 413 had lung cancer and 614 served as controls. All had spent 20 years
in the same home. The study found an ERR of 0.5 or 50% excess risks for a 15 year exposure at
4 pCi/L.
Some problems have been identified in comparing or evaluating case-control studies.
Namely, estimates of radon lung cancer risks are imprecise because the excess lung cancer risk is
small. There are also errors in estimating exposures and limited potential for studying modifying
factors, such as smoking. Also different methods were used for data collection. Despite these
limitations a meta-analysis was conducted for 8 completed studies (Lubin and Boice 1997). The
conclusions of this analysis were consistent with the conclusions drawn from miner studies as
reported by BEIR VI.
12
10. Ecological (Geographical) Studies
Numerous reports by Cohen (Cohen and Colditz 1990 and 1995) have found an inverse
relation between radon levels and LCDs in 1,600 counties across the US. Cohen thus claims
that this is evidence of failure of the linear non-threshold model for radiation exposures
commonly used to estimate risks. Others would note, however, that there is a fallacy in
ecological studies. Namely, group data do not properly reflect individual level associations.
Also, to adjust for confounding factors such as geographic or smoking effects, requires a linear
relationship of radon and other risks. The analogy could be for example, more people die from
drowning in the summer and more people eat ice cream in the summer. Therefore, as ice cream
consumption goes up, drownings go up, which implies some causal relationship between ice
cream and drowning.
11. Do you have Radon in your House?
The answer will always be YES, if your house is in direct contact with the ground. If
your house is sitting above the ground on posts or pilings with free air circulation under the floor,
then you may not have a good entry way for radon from the ground. The amount of radon in
your house will depend upon the amount of radium in the soil under your house, the permeability
of the soil, entry pathways into your house, and driving forces, such as negative air pressure in
the house. The amount of radon in your house can only be measured by special instruments
designed for radon testing. Normal radiation detectors used in radiation safety or for NORM
measurements (such as ion chambers, Geiger counters, or NaI scintillation detectors) will not
work for radon.
12. Radon Measurements
There are two categories of radon detectors, passive and active. The passive detectors
require no power supply and include charcoal as an equilibrium device, as well as electret ion
chambers and alpha tract detectors which are integrating devices. The active detectors require
power for collecting a sample of radon or RDPs for WL measurements. When evaluating
various devices for measuring radon, one should understand that there are no perfect radon
detectors, all have problems. Even a perfect detector will have to contend with radon variability
which fluctuates due to diurnal cycles, weather factors, and house occupancy factors. Since all
radiation is a series of random events, all radiation measurements are only best estimates. All
radon devices in the market place should have passed performance tests. As with any radiation
measurement, however, calibration and quality control are important.
12.1 Activated Charcoal Devices –
Charcoal is used to sample radon in several devices, including 3 and 4 inch diameter open
faced canisters, diffusion barrier canisters, charcoal bags, and charcoal liquid scintillation
detectors. Charcoal is useful for sampling radon primarily because of its very large surface area.
Radon collects on the surface of the charcoal by concentration gradient diffusion until it comes
to equilibrium with radon in the air over about 12-24 hours. The mechanism for how charcoal
collects radon is shown in Figure 8;
13
Figure 8
How Charcoal Works
Radon Atoms
Water Vapor
Air
Radon and
Moisture
Equilibrium
Charcoal
Radon
Concentration
Radiation Safety Academy
Time - Hours
12
When a closed charcoal container is opened to the air, radon atoms will begin to migrate
to surface of the charcoal by diffusion. At some point, the number of radon atoms on the
charcoal surface will come to equilibrium with the number in the air. At that point, radon atoms
are going to and leaving the surface of the charcoal at the same rate, which is then a state of
equilibrium with the air. Beyond the time it takes to achieve equilibrium, the charcoal will
essentially track the radon level in the air until the container is closed, usually in two to four
days. It is important that the charcoal device be returned promptly to the laboratory for analysis
since radon has a half-life of only about 3.8 days and will quickly decay away.
Since charcoal will also pick up water vapor from the air, during the laboratory analysis a
correction is made to account for moisture uptake where the molecules of water could take up
space on the charcoal and reduce the uptake of radon. This is done by weighing the charcoal
device before and after use to determine the weight gain due to moisture. Charcoal canisters are
analyzed with sodium iodide scintillation crystals and gamma spectroscopy. Basically the
analysis is a non-destructive test on an unopened charcoal container that measures the gamma
rays from the RDPs, Pb-214 and Bi-214. Since the RDPs are assumed to be in secular
equilibrium with the radon trapped in the charcoal, when you measure the activity of either of the
RDPs, they will be at the same activity (rate of radioactive decay) as the radon. The radon
concentration at the time the charcoal canister was closed in a home is then calculated backwards
from the time of analysis to account for radon decay. A typical analysis can be done in about ten
minutes per device.
Open Faced Charcoal – Charcoal canisters are typically small round metal cans holding
from 25 to 100 grams of charcoal. Twenty five grams of charcoal has a surface area equivalent
to about 3 football fields. Sampling is initiated by removing the cover from the charcoal canister
and exposing the charcoal to the air. Radon will begin collecting on the charcoal until it reaches
equilibrium as described above. It is important to follow sampling protocol directions carefully,
record the start and stop times of sampling, and return the canister promptly to the laboratory for
gamma spectrum analysis. These devices are normally used for two to four day sampling times.
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Diffusion Barrier Charcoal – In a diffusion barrier device, typically the metal can is not
opened, but rather a small opening in the top is uncovered to begin radon sampling. Behind this
opening is a diffusion barrier, usually paper. Behind the paper is a small bag of silica gel. These
two features reduce the rate of radon collection (allowing a longer time to achieve equilibrium)
and also remove the interference of water vapor. Thus, these devices are usable for sample times
from four to seven days. The diffusion barrier also reduces the effects of air currents that may
cause the device to read too high.
Charcoal Bags – In this device, charcoal is contained in a paper bag stored in a radon
proof outer bag. To start the radon sample, the outer bag is removed and radon then diffuses
through the paper bag to collect on the charcoal until reaching equilibrium. The sampling is
stopped by placing the paper bag back into the radon proof outer bag. This bag is then returned
to the laboratory for gamma spectrum analysis.
Charcoal Liquid Scintillation – This device uses a small plastic vial of about 20 ml. A
small capsule with about one to three grams of charcoal is located in the upper end of the vial.
Sampling is initiated by removing the cover from the vial. At the end of the sampling period
(usually 2 to 4 days), the cover is replaced and the vial is returned to the laboratory. Analysis is
done by filling the vial with a liquid scintillation solution. In this solution, the energy from alpha
and beta particles is converted to photons of light (scintillation) and counted in a liquid
scintillation counter. This device can be made for use as an open face or diffusion barrier radon
detector.
Charcoal Advantages – Charcoal is not very expensive and the devices for holding the
charcoal are sturdy and not easily damaged. Anyone can collect a radon sample with a charcoal
device following simple instructions. These devices are usually fairly small and thus easy to
mail back to the analytical laboratory. They are ideal for short measuring times, such as two to
four days, and they can be analyzed quickly in the laboratory. Thus, these devices have been
very popular for a quick measurement to answer immediate concerns for radon health risks or to
evaluate radon as a factor in a home sale. These devices have now been in widespread use for
about 25 years and have repeatedly demonstrated good precision and accuracy in quality control
tests. Anyone can buy charcoal devices and conduct measurements without qualifying as a
primary laboratory since the devices will be sent to a qualified laboratory for analysis.
Charcoal Disadvantages - Because charcoal works as an equilibrium device, the
collection of radon may be biased towards the last 12 to 24 hours. However, under varying
radon conditions, the charcoal seems to do quite well for averaging the results over short
sampling times of two to four days. Open face charcoal (by far the most popular because they
allow the shortest sampling times) are susceptible to effects of temperature, humidity, and air
currents. Since charcoal is prepared for use by baking in an oven, if the temperature is raised
during sampling this can remove radon from the charcoal. Humidity can also result in uptake of
moisture which will displace radon atoms and reduce the radon collection efficiency. Also,
when air blows across the open face of the charcoal container, it can result in an increased
amount of radon collection. All charcoal devices must be returned promptly to the laboratory, or
else the collected radon will decay away (4-day half-life) to levels that may not be measurable by
the laboratory.
15
12.2 Alpha Track Detectors
Alpha track detectors use a thin piece of plastic (CR 39, or allyl diglycol carbonate ),
typically a chip of about ½ by 1 inch) placed inside a plastic container. The plastic container is
stored inside a radon proof bag (usually heavy aluminized mylar film). Radon sampling begins
by removing the alpha track chamber from the radon proof bag. As radon diffuses into the plastic
chamber, alpha particles from radon and its short-lived RDPs cause small points of damage on
the surface of the alpha track chip. Alpha tracks are collected continuously as a true integrating
sample for the duration of the sampling time. Sampling is stopped by returning the collection
chamber to the radon proof bag and mailing it back to a laboratory for analysis. In the laboratory
the damage points on the plastic can be enlarged by etching in a caustic solution to allow them to
be counted under a microscope. The number of tracks per square centimeter of the plastic chip
can then be related to a calibration chart in units of pCi/L – days (see Figure 9 below) The
quantity of radon is then determined by dividing by the number of days in the sampling time.
These devices require a large number of alpha tracts for better quality measurements, therefore
they are primarily used for long-term measurements of 90 days up to a year.
Figure 9
Tracks
cm 2
100
pCi
 Days
L
Exposure = Conc. x Time =
pCi
 Days
pCi
L
2
50 Days
L
100
For 50 day sample, Concentration =
81
Alpha Track Advantages – These devices are relatively low cost and simple to
manufacture. As a passive device, no power is required. Similar to charcoal devices, they can be
used by anyone with simple instructions. They allow a variable sampling time for any interval
over about 30 days up to a year. They integrate the radon concentrations over the sampling time
and thus are best suited for determining long-term average radon concentrations. By sampling
for six months to a year, the variations in radon due to occupancy factors and weather conditions
are averaged to give a better representation of actual radon exposures over time. Also, the
person using the device does not have to qualify as a laboratory since the devices are mailed to a
qualified laboratory for analysis.
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Alpha Track Disadvantages – Because these devices require many alpha tracks for best
analysis, they would not generally be used for short-term measurements of less than 30 days.
Usually a minimum of 30 to 100 pCi/L-days are needed for best analysis. A smaller number of
tracks can lead to large errors in precision or reproducibility. The laboratory analysis requires
much more time than the analysis of charcoal devices and typically may require a week or
longer. While an alpha track device is deployed for many months, the sample may represent
unknown sampling conditions (that may not be typical of normal). Also, the alpha track device
may pick up tracks while the device is in storage or in transit. Basically, there is no such thing as
a “radon proof” bag. Radon will eventually diffuse into the storage bag over time and result in
tracks that are not related to the sampling location.
12.3 Electret Ion Chambers
These devices use a positively charged Teflon disk (electret) inside a large chamber as
shown in Figure 10 below. Sampling is started by raising a plastic plunger which uncovers the
electret, thus exposing the electret to alpha particle ionization inside the chamber. Radon
diffuses through and RDP filter in the top of the chamber. As radon collects in the chamber it
releases alpha particles along with the RDPs. The alpha particles cause ionization of the air in
the chamber. The negative electrons released by ionization are collected on the positive electret
resulting in a decrease in electret voltage proportional to the amount of ionization (related to
radon concentration). Radon sampling is stopped by returning the plunger to the closed position,
which covers the electret. The voltage on the electret is measured before and after radon
sampling. The difference in voltage is related to about 2 volts per pCi/L-day. The quantity of
pCi/L-days is then divided by the sampling period in days to determine the radon in pCi/L.
Through the use of different electrets and chamber sizes, electret ion chambers can used for
short-term measurements of 2-4 days or long-term up to a year.
Figure 10
Electret Ion Chamber
Electret Ion Chamber Advantages – These devices, similar to alpha track, are true
integrating devices that should provide a good measure of the average radon level over the
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sampling time. Since only part of the electret voltage may be used for a single sample, the
device can be reused until the voltage on the electret is reduced below a usable level. Since the
user of these devices can purchase the voltage reader and conduct their own measurements in the
field, essentially results can be immediately available. These devices are also not affected by
temperature or humidity. With some modifications, electrets can also be used for measuring
radon-220 (thoron) and radon in water. By placing the electret ion chamber in a radon proof bag,
the device can also be used to measure external gamma radiation.
Electret Ion Chamber Disadvantages – As with any ion chamber, the degree of
ionization is affected by altitude which affects the density of air in the chamber. Also, as an ion
chamber, these devices will measure the background gamma radiation along with ionization
from radon. Thus, if the gamma radiation is high (such as in Colorado), a correction may be
necessary to account for gamma ionization on top of radon related ionization. While the electret
itself may not be affected by temperature or humidity, the electronic voltage reader will be
affected by these factors. Electrets also have to be handled very carefully, because an
inadvertent touch can cause the electret to discharge and become unusable. There may also be
some loss of voltage when electrets are in storage. The biggest disadvantage may be that if the
user also reads out the voltage on the electret, then the user has to qualify as a primary laboratory
and implement a rigorous QA plan.
12.4 Radon Grab Samples
Single samples of radon can be collected from the air by means of a vacuum flask or a pump.
One such sampler uses a cylinder coated on the inside with zinc sulfide which scintillates
(produces a flash of light) when struck by an alpha particle. The flashes of light (scintillations)
are converted to an amplified electronic signal by means of a photomultiplier tube as shown in
Figure 11. Scintillation counting is delayed for about four hours after sample collection, to allow
the short-lived decay products of radon to come to equilibrium with the radon. At this time each
alpha emission from radon will be accompanied by two more from the decay of Po-218 and Po214 occurring at the same time.
Figure 11
Scintillation Cell and
Photo Multiplier Tube
Scintillation Cell
Light Pulse
Window
Photocathode
Focus Ring
Dynodes
Photomultiplier
Tube
Anode
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12.5 Radon Decay Product Grab Samples
Measurements of radon decay products can also be made with an alpha scintillation
detector. The decay products are collected on a membrane filter by pulling air through the filter
with a pump. The filter is then placed in contact with a thin plastic disk coated with zinc sulfide.
The alpha emissions and scintillations are then converted an electronic pulse with a
photomultiplier tube, as shown in Figure 12.
Figure 12
Scintillation Tray and
Photo Multiplier Tube
Radon Decay
Products
Focus Ring
Filter
Alpha Particle
Zinc Sulfide
Phosphor
Photocathode
Photomultiplier
Tube
Dynodes
Anode
Advantages of Grab Samples - The main advantage is that results can be obtained
within about 4 hours for radon or less for RDP. To check for diurnal variations, several samples
can be collected in a day. Both radon and radon decay product measurements can be obtained by
grab samples. During the short sampling times, it is also possible to verify house conditions and
occupancy factors (windows and doors closed, etc.). Grab samples can also be used to check on
radon entry routes by collecting samples at suspected entry ways. Grab samples can be
compared with other longer measurements to possibly detect tampering. For example, if a
charcoal canister gives a reading of 2 pCi/L but grab samples show levels of 8 to 10 pCi/L, this
difference needs to be explained. Some common methods of tampering with radon
measurements include moving the device outdoors, opening nearby doors or windows, or
shutting off the device.
Disadvantages of Grab Samples – One drawback of grab samples is that they give
information only for short sample times. Thus, the results may not be representative of longterm conditions. Grab sampling also requires careful measurement procedures and calculations to
account for equilibrium between radon and its decay products. The normal procedure also
requires closed house conditions at least 12 hours before collecting the samples. The equipment
is complex and expensive and requires careful quality control. Because the results are for very
short-term measurements, they should not be used as a basis for decisions on radon mitigation.
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12.6 Radon Measurement Protocols
The Environmental Protection Agency has recommended the following protocol for
radon testing as a basis for mitigation decisions. Start with a short-term test, defined as 2 to 90
days. This test should be done under closed house conditions (no windows or doors open, except
for normal entry and exit). Then depending on the purpose of the radon test, if it is done by a
homeowner to evaluate their own risk from radon, the test device should be placed in lowest
lived-in level of the house (typically the first floor, unless there is a finished basement). If the
test is related to a home sale, the device should be placed in the lowest level suitable for
occupancy (that could be occupied by a future owner, such as a currently unfinished basement).
If the result of the initial short-term test is greater than the action level of 4 pCi/L, then a
retest should be done for confirmation. If the result is between 4 and 10 pCi/L, then the repeat
test could be either a short-term or a long-term test. If the repeat result is greater than 4 pCi/L,
then mitigation is recommended. If the initial result is greater than 10 pCi/L, then the repeat test
should be another short-term test and a decision is made by averaging the two test results.
Again, if this leads to a level above 4 pCi/L, then mitigation is recommended.
13. Radon Mitigation
The primary method for reducing indoor radon levels is to intercept the source of radon
from the ground. The method is called sub-slab suction or sub-slab depressurization. Suction
can also be applied to block walls, drain tiles, or sumps. Other methods that have been tried but
found to be less effective include blocking the radon source by sealing cracks on the floor or
basement walls, by covering open sumps, or by covering earthen floors. Ventilation could also
be used, but could be expensive due to costs for heating and cooling the air. The sub-slab
suction method is illustrated in Figure 13.
Figure 13
Radon
Removal
Methods
20
In this picture we see that an opening has been cut through the concrete floor and a small
amount of aggregate is removed below the opening. A four-inch diameter plastic pipe is then
sealed into the opening. The pipe is run upwards through the inside or outside of the house with
a small vacuum fan. The fan pulls a suction below the floor which will draw in radon from the
ground for the entire footprint of the house. Usually one suction point is adequate for an entire
house. The vacuum fan has to run continuously for this method to work. However, such
systems have now been in operation for over 25 years. Eventually the fan motor will need
replacement.
14. References
Alavanja MC, Brownson RC, Lubin JH, Chang J, and Boice JD. Residential radon exposure and
lung cancer among nonsmoking women. Journal of the National Cancer Institute, 86
(24):1829-37. 1994.
Cohen BL, Colditz GA. Tests of the linear no-threshold theory of radon induced lung cancer.
Environmental Research. 53:193-220. 1990.
Cohen BL, Colditz GA. Lung cancer mortality and radon exposure; A test of the linear
nothreshold model of radiation carcinogenesis. In: Radiation and Public Perception, Benefits
and Risks. American Chemical Society. Washington, DC. 1995.
Field RW, Steck DJ, Smith BJ, Brus CP, Fisher EL, Neuberger JS, Platz CE, Robinson RA,
Woolson RF, Lynch CF. Residential radon gas exposure and lung cancer: the Iowa Radon
Lung Cancer Study., American Journal of Epidemiology, 151 (11), 1091-102. Jun 2000.
Johnson RH, Geiger E, and Rosario A. Cigarette smoking increases radon working level
exposures to all occupants of the smoker’s home. In: Proceedings of the 1990 Annual
Conference of the American Association of Radon Scientists and Technologists. American
Association of Radon Scientists and Technologists, Fletcher, North Carolina, 1990:1-19.
Johnson RH, Kline RS, Geiger E, and Rosario, A. The effect of passive cigarette smoke on
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U.S. EPA Office of Radiation Programs, and the Conference of Radiation Control Program
Directors. US EPA Research Triangle Park, NC. April 2-5, 1991; 1-19.
Lubin JH, Boice JD, Edling C, Hornung RW, Howe G, Kunz E, Kusiak RA, Morrison HI,
Radford, EP, Samet, JM, Timarche M, Woodward A, Yao SX, Pierce DA. Radon and lung
cancer risk: A joint analysis of 11 underground miner studies. National Institutes of Health,
National Cancer Institute. NIH Publication 94-3644. Washington, DC. US Department of
Health and Human Services. 1994.
Maher E F, Rudnick S N, and Moeller DW. Effective removal of airborne 222 Rn decay
products inside buildings. Health Phys 53(4):351-356, October 1987.
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Mine Safety and Health Administration. Title 30 Code of Federal Regulations Part 57. Safety
and health standards underground metal and nonmetal mines. Annual exposure limits.
57.5038; 2008.
NCRP, Exposure of the Population of the United States and Canada from Natural Background
Radiation. National Council on Radiation Protection and Measurements, Report 94, 1988
NRC (National Research Council). Committee on the Biological Effects of Ionizing Radiation.
Health risks of radon and other internally deposited alpha-emitters. BEIR IV; Washington,
D.C, National Academy Press. 1988.
NRC (National Research Council). Committee on the Biological Effects of Ionizing Radiation.
Health effects of exposure to low levels of ionizing radiation. BEIR V; Washington, D.C,
National Academy Press. 1990.
NRC (National Research Council). Panel on dosimetric assumptions affecting the application of
radon risk estimates. Comparative dosimetry of radon in mines and homes. Washington, D.C,
National Academy Press. 1991.
NRC (National Research Council). Committee on the Health Fffects of Exposure to Radon.
(BEIR VI) and Commission on Life Sciences. Health effects of exposure to radon: Time for
reassessment? Washington, D.C, National Academy Press. 1994.
NRC (National Research Council). Committee on the Health Fffects of Exposure to Radon.
Health effects of exposure to radon, BEIR VI; Washington, D.C, National Academy Press.
1999.
Pawel DJ and Puskin JS, The U.S. EPA’s Assessment of Risks From Indoor Radon. Health
Physics Journal, 87(1):68-74; 2004
22
How to Deal with Worker Concerns
for NORM
Round Table 225
Controlling NORM Hazards
(Naturally Occurring Radioactive Material)
AIHce, Montreal, Canada
Tuesday, May 21, 2013,
2 – 5 PM
Presented by
Ray Johnson, MS, PSE, PE, FHPS, CHP
Director
Radiation Safety Counseling Institute
16440 Emory Lane
Rockville, MD 20853
[email protected]
301-370-8573
Abstract
How to Deal with Worker Concerns for NORM*
Ray Johnson, MS, SE, PE, FHPS, CHP,
Director, Radiation Safety Counseling Institute,
16440 Emory Lane, Rockville, MD 20853
301-370-8573. [email protected].
Industrial hygienists may encounter NORM in workplaces where it is unexpected
and of great concern to workers not trained for radiation safety. Without such
training most of what workers may believe about radiation is mythology (not
technically true). Case studies show that the sound of a clicking Geiger Counter in
response to a NORM signal can set workers into a panic. The unexpected presence
of radiation brings up images of Hiroshima (or Fukushima) and anticipated terrible
consequences from radiation exposure. Helpful responses for concerned workers
begin with active listening to hear their feelings. Workers should be assured that it
is OK to feel afraid. After establishing rapport workers may then be open to
understanding the steps from cause to effect for answering questions on radiation
safety. A one-hour class on NORM safety awareness can also help answer
questions and alleviate concerns when presented by a knowledgeable specialist in
radiation safety.

Raymond H. Johnson, Communication Issues about NORM for Workers, the Public,
and the Media, Chapter 11 in Naturally Occurring Radioactive Material (NORM) and
Technologically Enhanced NORM (TENORM), Edt. by P. Andrew Karam and Brian J.
Vetter. A textbook for the Health Physics Society Professional Development School,
Minneapolis, MN July 16-18, 2009. Medical Physics Publishing, Madison, WI.