United Slates
Environmental Protection
Air And
Radiation
(6604J)
EPA4Q2-R-i2-Qi3
May, 1993
vvEPA
Protocols For Radon And
Radon Decay Product
Measurements In Homes
Printed on Recycled Paper
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Protocols for Radon and Radon Decay Product Measurements in Homes
Office of Air and Radiation (6609J)
EPA 402-R-93-003, June 1993
Preface
This document, the Protocols for Radon and Radon Decay Product Measurements in Homes (EPA
402-R-92-003, May 1993), is a guidance document. However, one condition of participation in the
Agency's National Radon Proficiency Program (RPP) for radon measurement and radon reduction
(mitigation) proficiency, is conformance with these protocols. Conformance with its companion
document, the Indoor Radon and Radon Decay Product Measurement Device Protocols (EPA 402-R-
92-004, July 1992), is also a condition of participation in the Proficiency Program.
Together these protocol documents provide the technical support for the Agency's radon policy and
guidance to consumers that is contained in, but not limited to, the Home Buyer's and Seller's Guide to
Radon (EPA 402-R-93-003, March 1993), A Citizen's Guide to Radon (EPA 402-K-92-001), and the
Consumer's Guide to Radon Reduction (EPA 402-K-92-003, August 1992).
Table of Contents
Section 1: Introduction
Section 2: Discussion of Guidelines Presented in the Citizen's Guide to Radon
2.1 Introduction and Summary
2.2 Measurement Location
2.3 Initial Measurements
2.3.1 Rationale
2.3.2 Closed-Building Conditions
2.3.3 Interpretation of Initial Measurements Results
2.4 Follow-Up Measurements
2.4.1 Rational
2.4.2 Short-Term and Long-Term Follow-Up Testing
Section 3: Discussion of Guidelines Presented in the Home Buyer's and Seller's Guide to Radon
3.1 Introduction
3.2 Options for Real Estate Testing
3.2.1 Option 1: Sequential Testing
3.2.2 Option 2: Simultaneous Testing
3.2.2.1 Both measurement Results Equal to or Great than 4 pCi/L
3.2.2.2 Both Measurements Result Less Than 4 pCi/L
3.2.2.3 One Measurement Results Greater Than 4pCi/L and One Measurement Results
Less Than 4pCi/L
3.2.2.4 Precision Requirements
3.2.2.5 recommended Language fir Informing the Client that a Retest is Warranted
3.2.3 Option 3: Active Monitor Testing
3.3 Measurement Location
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3.4 Measurement Checklist
3.5 Interference-Resistant Testing
3.5.1 Influencing Test Area Concentration
3.5.2 Equipment Interference
3.5.3 Preventing Interference
3.5.4 Interference-Resistant Detectors
Section 4: General Procedural Recommendations
4.1 Introduction
4.2 Initial Client Interview
4.3 Measurement Recommendations
4.3.1 Selecting a Measurement Approach
4.3.2 Written Measurement Guidance
4.3.3 Conditions for a Valid Measurement
4.3.4 Non-interference Controls
4.3.5 Measurement Documentation
4.4 Quality Assurance in Radon Testing
4.4.1 Calibrate Measurements
4.4.2 Known Exposure Measurements
4.4.3 Background Measurements
4.4.4 Duplicate Measurements
4.4.5 Routine Instrument Measurement
4.4.6 Quality Assurance Plans
4.5 Standard Operating Procedures
4.6 Providing Information to Consumers
4.7 Reporting Test Results
4.8 Temporary Risk Reduction Measures
4.9 Recommendations for Mitigation
4.10 Worker Safety
Appendix A: State and EPA Regional Radon Offices
Appendix B: Interpretation of the Results of Simultaneous Measurements
B.1 Assessment of Precision
B.2 Example Controls Charts for Precision
B.2.1 Sequential Control Chart Based on Coefficient on Verification
B.2.2 Sequential Control Chart Based on Relative Percent Difference
B.2.3 Range Control Chart
B.3 Interpretation of Precision Control Chart
Glossary
References
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Section 1: Introduction
This document presents the U.S. Environmental Protection Agency's (EPA) technical guidance for
measuring radon concentrations in residences. It contains protocols for measuring radon for the
purpose of deciding on the need for remedial action, as presented in the 1992 Citizen's Guide to Radon
(EPA402-K-92-001; U.S. EPA 1992a), and in the Home Buyer's and Seller's Guide to Radon (EPA
402-R-93-003; U.S. EPA 1993).
The guidance for determining the need for mitigation is different in several key aspects from previously
issued recommendations, and this document supersedes a previous report (EPA 520/1-86-014-1)
published in February, 1987 (U.S. EPA 1987). The technical basis for these policy changes is supplied
in the Technical Support Document for the 1992 Citizen's Guide to Radon (EPA 400-R-92-011; U.S.
EPA 1992g), and the revised policies are described in Section 2 of this report.
Section 3 of this report describes the Agency's recommended protocols for measuring radon for a real
estate transaction. This guidance elaborates on Agency recommendations published in the Home
Buyer's and Seller's Guide to Radon (EPA 402-R-93-003; U.S. EPA 1993). The radon testing
guidelines in the Home Buyer's Guide were developed specifically to deal with the time-sensitive nature
of home purchases and sales and the potential for radon device interference. The guidelines are
somewhat different from those in other EPA publications, such as the 1992 Citizen's Guide to Radon
(EPA 402-K-92-001; U.S. EPA 1992a), which provide radon testing and reduction information for non-
real estate situations. Therefore, Sections 2 and 3 of this document will have different guidance for
different situations.
This report is limited to discussions of Agency guidance regarding detector placement, measurement
duration, multiple measurements, and the interpretation of measurement results. EPA has also issued a
technical report describing measurement techniques, titled Indoor Radon and Radon Decay Product
Measurement Device Protocols (EPA 520-402-R-92-004) and published in 1992 (U.S. EPA 1992c).
That report provides technical information for measuring radon concentrations with continuous radon
monitors, alpha track detectors, electret ion chambers, charcoal canisters, unfiltered alpha track
detectors, and grab radon techniques; it also provides guidance for measuring radon decay product
concentrations with continuous working level monitors, radon progeny integrating sampling units, and
grab radon decay product techniques. Copies of the Indoor Radon and Radon Decay Product
Measurements Device Protocols may be obtained by contacting your State or EPA Regional radon
office (Appendix A) A list of EPA documents providing guidance on radon measurements appears in
Exhibit 1-1
* The term "radon" refers to radon-222 and its decay products unless otherwise noted.
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Title of Document
A Citizens Guide to Radon
(U.S. EPA 1992a)
Consumer's Guide to Radon Reduction
(U.S. EPA 1992b)
Indoor Radon and Radon Decay Product
Measurements Device Protocols
(U.S. EPA 1992c)
Interim Radon Mitigation Standards
(U.S. EPA 1992d)
Home Buyer's and Seller's Guide to Radon
(U.S. EPA 1993)
Protocols for Radon and Radon Decay Product
Measurements in Homes
EPA Document Number
EPA 402-K-92-001
EPA 402-K-92-003
EPA 520-402-R-92-004
Regional Training Centers
(see below)
EPA 402-R-93-003
EPA 402-R-92-003
These documents are available from the U.S. Government Printing Office, Superintendent of
Document, Mail Stop: SSOP, Washington, D.C. 20402-9328; from the National Technical Information
Service, U.S. Department of Commerce, Springfield, Virginia 22151; or your State or EPA Regional
Radon office.
EPA Regional Radon Training Centers:
Eastern Regional Radon Training Center, Rutgers University; (908)-932-2582.
Southern Region Radon Training Center, Auburn University; (205)-844-6271.
Western Regional Radon Training Center, Colorado State University; (303)-491-7742
Northern Regional Radon Training Center, University of Minnesota; (612)-624-6786
This report provides guidelines that are primarily intended to aid State radiation control programs, other
organizations conducting indoor radon measurements, and homeowners who want detailed information
on radon measurements. The guidelines herein can be adopted as part of a State program or can be
provided by States to interested individuals as recommendations. Adherence to these guidelines was a
requirement for participation in EPA's former National Radon Proficiency Measurement Proficiency
(RMP) Program (EPA 520/1-91-006; U.S. EPA 1991). The method designations that were used in
EPA's former RMP listed in Exhibit 1-2. A two-letter code for each method has been adopted, although
ATDs (AT), RPISUs (RP), and EICs/ECs (ES or EL) may still be referred to by their traditional
acronyms.
EPA recognizes that radon concentrations in buildings may vary overtime (Arvela et.al. 1988, Dudney
et.al. 1990, Fleischer and Turner 1984, Furrer et.al. 1991, Gesell 1983, Harley 1991, Hess 1985, Martz
et.al. 1991, Nyberg and Bernhardt 1983, Perritt et.al. 1990, Ronca-Battista and Magno 1988, Steck
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1992, Stranden et.al. 1979, Wilkening and Wicke 1986, Wilson et.al. 1991). Furthermore,
concentrations at different locations in the same house often vary by a factor of two or more (Arvela
et.al. 1988, Furrer et.al. 1991, George et.al. 1984, Hess 1985, Keller et.al. 1984, Put and deMeijer
1988, Steck 1992). EPA has carefully evaluated these findings, as well as other factors (EPA 400-R-92-
011; U.S. EPA 1992g), and has developed policies for ensuring that the most representative and useful
information is supplied by the measurement results. These guidelines may be evaluated periodically
and refined to reflect the increasing knowledge of, and experience with, indoor radon.
EPA recommends that initial measurements be short-term tests and performed under closed-building
conditions. An initial short-term test, which lasts for two to 90 days, ensures that residents are informed
quickly should a home contain very high radon levels. Long-term tests, give a better estimate of the
year-round average radon level. The closer the long-term test is to 365 days, the more representative it
will be of annual average radon levels.
Exhibit 1-2
Radon and Radon Decay Product Measurement Method Abbreviations
METHOD CATEGORY
Continuous Radon Monitors
Alpha Track Detectors
Electret Ion Chambers
Short Term
Long Term
Activated Charcoal Adsorption Devices
(formerly called charcoal canisters)
Charcoal Liquid Scintillation
Three-day Integrating Evacuated Scintillation Cells
Pump/Collapsible Bag Devices
(24 hour sample)
Grab Radon Sampling
Scintillation Cells
Activated Charcoal
Pump-Collapsible Bag
Unfiltered Track Detectors
Continuous Working Level Monitors
Radon Progeny Integrating Sampling Units
Grab Sampling - Working Level
Abbreviations
Common
CRM
ATD
EIC/EC
CC
CLS
UTD
CWLM
RPISU
Method
CR
AT
ES
EL
AC
LS
SC
PB
GS
GC
GB
UT
CW
RP
GW
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Section 2: Discussion of Guidelines Presented in EPA's "A Citizen's Guide to Radon"
2.1 Introduction and Summary
2.2 Measurement Location
2.3 Initial Measurements
2.4 Follow-Up Measurements
2.1 Introduction and Summary
The Citizen's Guide to Radon ( EPA 402-K-92-001; U.S. EPA 1992a)presents a measurement strategy
for assessing radon levels in homes for the purpose of determining the need for remedial action. This
measurement strategy is intended to reduce the risk to public health from exposure to radon in air in
homes. The strategy begins with an initial measurement made to determine whether a home may
contain radon concentrations sufficient to cause high exposures to its occupants.
EPA recommends that initial measurements be short-term tests placed in the lowest lived-in level of the
home, and performed under closed-building conditions. An initial short-term test ensures that residents
are informed quickly should a home contain very high levels of radon. Short-term tests are conducted
for two days to 90 days. Closed-building conditions (Section 2.3.2) should be initiated at least 12 hours
prior to testing for measurements lasting less than four days, and are recommended prior to tests
lasting up to a week.
If the short-term measurement result is equal to or greater than 4 picoCuries per liter (pCi/L), or 0.02
working levels (WL), a follow-up measurement is recommended. Follow-up measurements are
conducted to confirm that radon levels are high enough to warrant mitigation. If the result of the initial
measurement is below4 pCi/L, or 0.02 WL, a follow-up test is not necessary. However, since radon
levels change over time, the homeowner may want to test again sometime in the future, especially if
living patterns change and a lower level of the house becomes occupied or used regularly.
There are two types of follow-up measurements that may be conducted, and the choice depends, in
part, on the results of the initial test. An initial measurement result of 10 pCi/L (or 0.05 WL) or greater
should be followed by a second short-term test under closed-building conditions. If the result of the
initial measurement is between 4 pCi/L (or 0.02 WL) and 10 pCi/L (or 0.05 WL), the follow-up test may
be made with either a short-term or a long-term method. Long-term tests are conducted for longer than
90 days, and give a better estimate of the year-round average radon level. The closer the long-term
measurement is to 365 days, the more representative it will be of annual average radon levels. On the
other hand, short-term tests yield results more quickly and can be used to make mitigation decisions. If
the long-term follow-up test result is 4 pCi/L, or 0.02 WL, or higher, EPA recommends remedial action.
If the average of the initial and second short-term results is equal to or greater than 4 pCi/L, or 0.02 WL,
radon mitigation is recommended. These recommendations are summarized in Exhibit 2-1.
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In certain instances, such as may occur when measurements are performed in different seasons or
under different weather conditions, the initial and follow-up tests may vary by a considerable amount.
Radon levels can vary significantly between seasons, so different values are to be expected. The
average of the two short-term test results can be used to determine the need for remedial action.
The testing strategy policies presented here allow homeowners to decide on the need for mitigation
with a high level of confidence that their decision is correct (EPA 400-R-92-011; U.S. EPA 1992g).
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2.2 Measurement Location
Short-term or long-term measurements should be made in the lowest lived-in level of the house. The
following criteria should be used to select the location of the detectors within a room on this level:
• The measurements should be made in the lowest level which contains a room that is used
regularly. Test areas include family rooms, living rooms, dens, playrooms, and bedrooms. A
bedroom on the lower level may be a good choice, because most people generally spend more
time in their bedrooms than in any other room in the house (Chapin 1974, Moellerand Underhill
1976, Szalai 1972). If there are children in the home, it may be appropriate to measure the
radon concentration in their bedrooms or in other areas where they spend a lot of time, such as
a playroom, that are situated in the lowest levels of the home.
• In general, measurements should not be made in kitchens, laundry rooms, or bathrooms. The
measurements should not be made in a kitchen because of the likelihood that an exhaust fan
system and changes in small, airborne particles (caused by cooking) may affect the stability of
WL measurements. Measurements should not be made in a bathroom because relatively little
time is spent in a bathroom, because high humidities may affect the sensitivity of some
detectors, and because of the likelihood that use of a fan may temporarily alter radon or decay
product levels.
Although radon in water may be a contributor to the concentration of airborne radon, radon in air
should be measured before any diagnostic radon-in-water measurements are made. (Diagnostic
measurements may be made in the bathroom; however, such diagnostic measurements should
not be used to determine the need for mitigation.)
• A position should be selected where the detector will not be disturbed during the measurement
period and where there is adequate room for the device.
• The measurement should not be made near drafts caused by heating, ventilating and air
conditioning vents, doors, fans, and windows. Locations near heat, such as on appliances, near
fireplaces or in direct sunlight, and areas of high humidity should be avoided.
• Because some detectors are sensitive to increased air motion, fans should not be operated in
the test area. Forced air heating or cooling systems should not have the fan operating
continuously unless it is a permanent setting.
• The measurement location should not be within 90 centimeters (three feet) of the doors and
windows or other potential openings to the outdoors. If there are no doors or windows to the
outdoors, the measurement should not be within 30 centimeters (one foot) of the exterior wall of
the building.
• The detector should be at least 50 centimeters (20 inches) from the floor, and at least 10
centimeters (four inches) from other objects. For those detectors that may be suspended, an
optimal height is in the general breathing zone, such as two to 2.5 meters (about six to eight
feet) from the floor.
Sound judgment is required as to what space actually constitutes a room. Measurements made
in closets, cupboards, sumps, crawl spaces, or nooks within the foundation should not be used
as a representative measurement.
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2.3 Initial Measurements
2.3.1 Rationale
EPA recommends that a homeowner assessing the need for mitigation should first make a short-term
test. Short-term measurements can be simple, produce results quickly, and allow the public to make
decisions about radon reduction that are cost-effective and protective of human health.
The duration of short-term measurements can range from 48 hours to 90 days, depending upon the
method used.
2.3.2 Closed - Building Conditions
Short-term measurements lasting between two and 90 days should be made under closed-building
conditions. Closed-building conditions are necessary for short-term measurements in order to stabilize
the radon and radon decay product concentrations and increase the reproducibility of the
measurement. Windows on all levels and external doors should be kept closed (except during normal
entry and exit) during the measurement period. Normal entry and exit include a brief opening and
closing of a door, but-to the extent possible-external doors should not be left open for more than a few
minutes. In addition, external-internal air exchange systems (other than a furnace) such as high-
volume, whole-house and window fans should not be operating. However, attic fans intended to control
attic and not whole building temperature or humidity should continue to operate. Combustion or make-
up air supplies must not be closed.
In addition to maintaining closed-building conditions during the measurement, closed-building
conditions for 12 hours prior to the initiation of the measurement are a required condition for
measurements lasting less than four days, and are recommended prior to measurements lasting up to
a week in duration. Normal operation of permanently installed energy recovery ventilators (also known
as heat recovery ventilators or air-to-air heat exchangers) may also continue during closed-building
conditions. In houses where permanent radon mitigation systems have been installed, these systems
should be functioning during the measurement period.
Closed-building conditions will generally exist as normal living conditions in northern areas of the
country when the average daily temperature is low enough so that windows are kept closed. Depending
on the geographical area, this can be the period from late fall to early spring. In some houses, the most
stable radon levels occur during late fall and early spring, when windows are kept closed but the house
heating system (which causes some ventilation and circulation) is not used. Available information about
variations of indoor radon levels in a particular area can be used to choose a measurement time when
the radon concentrations are most stable.
It may be necessary, however, to make measurements during mild weather, when closed-building
conditions are not the normal living conditions. It will then be necessary to establish some more
rigorous means to ensure that closed-building conditions exist prior to and during the measurements.
Those performing measurements in southern areas that do not experience extended periods of cold
weather should evaluate seasonal variations in living conditions and identify if there are times of the
year when closed-building conditions normally exist. Ideally, measurements should be conducted
during those times. The closed-building conditions must be verified and maintained more rigorously
when they are not the normal living conditions. Air conditioning systems that recycle interior air can be
operated during the closed-building conditions when radon measurements are being made. However,
homeowners should be aware that any air circulation system can alter the radon decay product
concentration without significantly changing the radon concentration.
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Short-term tests lasting just two or three days should not be conducted during unusually severe storms
or periods of unusually high winds. Severe weather will affect the measurement results in several ways.
First, a high wind will increase the variability of radon concentration because of wind-induced
differences in air pressure between the building interior and exterior. Second, rapid changes in
barometric pressure increase the chance of a large difference in the interior and exterior air pressures,
consequently changing the rate of radon influx. Weather predictions available on local news stations
can provide sufficient information to determine if these conditions are likely. While unusual variations
between radon measurements may be due to weather or other effects, the measurement system
should be checked for possible problems.
During any short-term test, closed-house conditions should be maintiained as much as possible while
the test is in progress. In test lasting less than four days (96 hours), closed-house conditions should be
maintained for at least 12 hours before conditions should be maintained while the test is in progress;
while recommended, the 12 hour closed-house conditions should be maintained as much as possible
while the test is in progress.
2.3.3 Interpretation of Initial Measurement Results
If the initial measurement result is less than 4 pCi/L, or 0.02 WL, follow-up measurements are probably
not needed. There is a relatively low probability that mitigation is warranted if the result is less than 4
pCi/L or 0.02 WL (EPA 400-R-92-011; U.S. EPA 1992g). Even if the measurement result is less than 4
pCi/L, or 0.02 WL, however, a homeowner may want to test again sometime in the future. If the
occupants' living patterns change or renovations are made to the home and they begin using a
lower level (such as a basement) as a living area, a new test should be conducted on that level.
The average year-round residential indoor radon level is estimated to be about 1.3 pCi/L, and about 0.4
pCi/L of radon is normally found in outside air. The U.S. Congress has set a long-term goal that indoor
radon levels be no more than outdoor levels. There is some risk from radon levels below 4 pCi/L, and
EPA recommends that the homeowner consider reducing the radon level if the average of the first and
second short-term measurements or if a long-term follow-up measurement is between 2 and 4 pCi/L
(0.01 and 0.02 WL). While it is not yet technologically achievable for all homes to have their radon
levels reduced to outdoor levels, the radon levels in some homes today can be reduced to 2 pCi/L or
below.
If the result of the short-term measurement is equal to or greater than 4 pCi/L, or 0.02 WL, the occupant
should conduct a follow-up measurement using a short-term or long-term test, as described in Section
2.4.
2.4 Follow-Up Measurements
2.4.1 Rationale
The purpose of a follow-up measurement is to provide the homeowner with enough information to make
an informed decision on whether to mitigate to reduce radon levels. The follow-up measurement,
whether it is short-term or long-term, provides an additional piece of information to confirm that radon
levels are high enough to warrant mitigation. There are two major reasons why a second measurement
is necessary. First and most important, radon levels fluctuate overtime (see Section 1}, and a second
short-term measurement, when averaged with the first test result, will provide a more representative
value for the average radon level during the period of the test. If a long-term follow-up measurement is
conducted, that result should provide an even more representative value for the long-term average
radon concentration. The second reason for making a follow-up measurement prior to mitigation is that
there is a small chance of laboratory or technician error in all measurements, including radon
measurements, and a second test will serve as a check on the first.
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Homes tested using the protocol in this section should not be mitigated on the basis of a single short-
term test. A follow-up test is necessary for mitigation decision-making regardless of the initial test result.
2.4.2 Short-Term and Long-Term Follow-Up Testing
Follow-up testing should be conducted in the same location as the first measurement (see Section 2.2).
A follow-up test can be conducted with either a short-term or long-term measurement device. Long-
term tests (> 90 days) will produce a reading that is more likely to represent the home's year-round
average radon level than a short-term test. However, if the initial test result is high (for example, greater
than about 10 pCi/L, or 0.05 WL) or if results are needed quickly, EPA recommends a second short-
term test. This will allow the homeowners to obtain information necessary to decide quickly on the need
for mitigation. If the result of the initial measurement is between 4 pCi/L and 10 pCi/L (or between 0.02
WL and 0.05 WL), then either a short-term or long-term test can be taken.
If the long-term follow-up test result is 4 pCi/L, or 0.02 WL, or higher, then EPA recommends remedial
action. Likewise, if the average of the initial and second short-term results is equal to or greater than 4
pCi/L, or 0.02 WL, radon mitigation is recommended. These recommendations are summarized in
Exhibit 2-1.
As with the initial short-term test, the second short-term test should be conducted under closed-building
conditions (Section 2.3.2). These conditions, however, are not necessary for long-term tests (those
lasting longer than 90 days).
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Section 3: Discussion of Guidelines Presented in The Home Buyer's and Seller's Guide to
Radon
3.1 Introduction
3.2 Options for Real Estate Testing
3.3 Measurement Location
3.4 Measurement Checklist
3.5 Interference-Resistant Testing
3.1 Introduction
The unique nature of a real estate transaction, involving multiple parties and financial interests,
presents radon measurement issues not encountered in non-real estate testing. EPA's objectives for
issuing recommended protocols for radon measurements made for real estate transactions are
intended to reduce misunderstanding and protect public health in several ways. First, EPA seeks to
provide home buyers, sellers, real estate agents, and testing organizations with a common basis of
understanding of the recommended procedures for radon measurements. Second, the widespread
implementation of this guidance will produce results that are reliable indicators of the need for
mitigation. A significant proportion of radon measurements are conducted as part of real estate
transactions, and all aspects of these transactions are carefully scrutinized, so specific guidance from
EPA can help to ensure good quality measurements. When the results are interpreted properly and the
appropriate remedial action is taken, these protocols will assist the buyer and seller in reducing the risk
to the occupants from radon exposure. The availability of a nationally-recognized protocol for
measurement and for the interpretation of the measurement results will greatly assist home buyers,
sellers, real estate agents, builders, lenders, and radon measurement experts.
These protocols are designed for use in residences, as described in the EPA document, Home Buyer's
and Seller's Guide to Radon (EPA 402-R-93-003; U.S. EPA 1993). While that document offers general
information on radon and testing, this report presents a more technical description of EPA
recommendations, including discussion of guidelines for the interpretation of measurement results. As
with all of EPA's policies regarding radon measurements, these guidelines have been developed after
review and assistance from the radon measurement community and EPA's Science Advisory Board.
Technical information on a variety of radon measurement methods is available in the EPA report titled
Indoor Radon and Radon Decay Product Measurement Device Protocols (EPA 520-402-R-92-004;
EPA 1992c; these and other EPA publications are available at this web site or from your State or
regional EPA office, see Appendix A).
The radon testing guidelines in the Home Buyer's and Seller's Guide to Radon have been developed
specifically to deal with the time-sensitive nature of home purchases and sales. These guidelines are
somewhat different from the guidelines in other EPA publications, such as the 1992 Citizen's Guide to
Radon (EPA 402-K-92-001; U.S. EPA 1992a), which provide radon testing and reduction information
for non-real estate situations.
There are also guidelines in the Home Buyer's and Seller's Guide to Radon to deal with the potential for
rason test interference. There are approaches that can be used to increase confidence in measurement
results by detecting measurements interference. For example, a device that offers a variety of ways to
detect tampering may serve to deter as well as detect interference with the device's operation or with
proper closed-building measurement conditions. Potential tampering indicators include the ability to a
device to record changes in radon levels, temperature, and humidity, or to detect movement of or
around the device during the measurements. Refer to section 3.5 for information and recommendations
for the interference-resistant testing.
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EPA investigated a variety of options for real estate testing. EPA recommends testing in advance of
putting the house on the market. A long-term test, which is conducted for longer than 90 days, gives the
most representative indication of the annual average radon concentrations in a home. However, for
time-sensitive real estate transactions, the Home Buyer's Guide offers three short-term testing options.
Short-term tests are conducted from two days to 90 days, depending on the measurement device.
Based on extensive quantitative analyses to evaluate the frequency with which long-term and short-
term testing results lead to the same mitigation decision, EPA and its independent Science Advisory
Board concluded that short-term tests can be used to assess whether a home should be remediated.
The reliability of each radon measurement made for a real estate transaction, or for any purpose, is
highly dependent upon the existence and documentation of an adequate quality assurance program
implemented by both the tester and the analysis laboratory. All the parties involved in the real estate
transaction depend upon the testers doing their job. This includes ensuring that the measurements are
valid via the performance of quality control measurements and activities, and detecting measurement
interference. The protocols outlined in this section were developed by EPA for testers and homeowners
adhering to the quality assurance practices summarized in Section 4.4 of this report, and in EPA's
Indoor Radon and Radon Decay Product Measurement Device Protocols (EPA 520-402-R-92-004; U.S.
EPA 1992c).
Three options were determined to be satisfactory and are described here. The availability of three
options will allow flexibility on the part of the party purchasing the test. Each of these options will
produce results that can be used to determine the need for mitigation.
Both Options 1 and 2 require the use of two measurements made for similar durations. Both
measurements should report results in units of pCi/L or both in WL. Similar durations means that the
two measurements must be made for a similar time period, with a two-hour grace period. Specific
information on measurement methods (listed in Exhibit 3-1) can be found in EPA's Indoor Radon and
Radon Decay Product Measurement Device Protocols (EPA 520-402-R-92-004; U.S. EPA 1992c).
Exhibit 3-1
Radon and Radon Decay Product Measurement Method Categories
A
(pCi/L)
AC
AT
LS
CR
PB
SC
EL
ES
UT
Activated Charcoal Adsorption
integrating
Alpha Track Detection
Charcoal Liquid Scintillation
Continuous Radon Monitoring
Pump-collapsible Bag
Evacuated Scintillation Cell
(three-day integrating)
Electret ion Chamber: Long Term
Electret ion Chamber: Short Term
Unfiltered Track Detection
B
(WL)
RP
CW
Radon Progeny Sampling unit
Continuous Working Level
Monitoring
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3.2 Options for Real Estate Testing
3.2.1 Option 1: Sequential Testing
Sequential tests should be conducted under conditions that are as similar as possible, in the same
location, and using similar devices and durations. Both should produce results in the same units (pCi/L
or WL). That is, both methods should be from column A or both from column B of Exhibit 3-1. Any EPA-
recognized method may be used. In addition, the results of the first test should not be reported prior to
making the second measurement: both measurements should be reported at the same time in order to
discourage tampering that may occur if the first test is known to be greater than 4 pCi/L or 0.02 WL.
Note that measuring with different methods (e.g., with AC and ES) may increase the potential for
differences (e.g., measurement bias) between the results. The results of both measurements should be
reported, and the average of the two results should be used to determine the need for mitigation. There
will be some variation between the two results, which may be caused by the radon levels fluctuating in
response to weather or other factors. If the variation is unusually large, it may be due to weather or
other effects, but the measurement system should be checked for possible problems.
3.2.2 Option 2: Simultaneous Testing
This option involves the use of two tests, conducted simultaneously and side-by-side, made for similar
durations, and producing results in the same units (i.e., both methods should be from column A or both
should be from column B of Exhibit 3-1). Any EPA-recognized method may be used. As with Option 1,
using different methods for the two measurements (for example, ES and LS) may increase the potential
for differences between the two results. The two test results should be averaged to determine the need
for remedial action. The collocated devices should be placed four inches (10 centimeters) apart.
Because radon measurements, like any measurements, usually do not produce exactly the same
results, even for simultaneous testing, there will usually be a difference between the two results. EPA
offers the following guidance to testers for judging when two simultaneous, side-by-side measurements
disagree to such an extent that two additional measurements should be performed.
The results of the simultaneous measurements will fall into one of the three categories discussed below
and illustrated in Exhibit 3-2.
3.2.2.1 Both Measurement Results Equal To or Greater Than 4 pCi/L (or 0.02 WL)
In this case, the average of the two results will be equal to or greater than 4 pCi/L, or 0.02 WL, and
mitigation is recommended. The tester should report both measurement results as well as the average
of the two results.
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Exhibit 3-2
Deciding on a Retest When Measurements Vary Significantly
r
Two simultaneous, s(de
-------
Simultaneous measurement results that are equal to 4 pCi/L, or 0.02 WL, or greater should, however,
exhibit some agreement. An example control chart for the precision that may be expected is shown as
Exhibit B-2 in Appendix B, which was constructed using an average relative percent difference of 14
percent. (Relative percent difference is defined as the difference divided by the average.) Using Exhibit
B-2, a relative percent difference greater than 36 percent should be observed less than one percent of
the time. Based upon this, EPA recommends that any side-by-side, simultaneous measurements with
results greater than or equal to 4 pCi/L, or 0.02 WL, and which exhibit a relative percent difference
greater than 36 percent, be cause for informing the client that the two results do not show good
agreement. However, since both results are greater than 4 pCi/L, or 0.02 WL, EPA recommends
mitigation in this case. Testers should investigate the source of the error (see Appendix B).
Results between 2 pCi/L (or 0.01 WL) and 4 pCi/L (or 0.02 WL), should also exhibit some agreement.
The level of agreement expected should be based upon the tester's experience with duplicate
measurements made with that technique in this range of radon concentrations. An example control
chart for the precision that may be expected in this region is shown as Exhibit B-3 in Appendix B, which
was constructed using an average relative percent difference of 25 percent. Using this chart, a relative
percent difference between duplicates greater than 67 percent should be observed less than one
percent of the time. Based upon this, EPA recommends that any side-by-side, simultaneous
measurements with results less than 4 pCi/L, or 0.02 WL, and which exhibit a relative percent
difference greater than 67 percent, be cause for informing the client that the two results do not show
good agreement, but that both are less than 4 pCi/L, or 0.02 WL, and therefore mitigation is not
recommended. Testers should investigate the source of the error (see Appendix B}.
3.2.2.5 Recommended Language for Informing the Client that a Retest is Warranted
If a retest is warranted (see Section 3.2.2.3), EPA recommends that the tester inform the client that
EPA provides guidance for how well two measurements should agree, that the measurements
performed fall outside the range, and that a retest should be conducted. A retest should consist of
measurements performed according to one of the protocols outlined in Sections 3.2.1, 3.2.2, or 3.2.3.
3.2.3 Option 3: Single Test Option
This option requires an active continuous monitor (method CR or CW) that has the capability to
integrate and record a new result at least hourly. Shorter integration periods and more frequent data
logging afford greater ability to detect unusual variations in radon or radon decay product
concentrations. The minimum measurement period is 48 hours. The first four hours of data from a
continuous monitor may be discarded or incorporated into the result using system correction factors
(EPA 520-402-R-92-004; EPA 1992c). There must be at least 44 contiguous hours of usable data to
produce a valid average. (The "backing out" of data [i.e., removal of portions imbedded in the two days]
to account for weather or other phenomena will invalidate the measurement.) The periodic results
should be averaged to produce a result that is reported to the client.
If the monitor cannot integrate over a period of one hour or less then an additional (secondary) passive
or active measurement device must be used. The second measurement, which may be made with a
passive or active device, can be used simultaneously or sequentially, as discussed in Option 1 and 2
(Sections 3.2.1 and 3.2.2). If the two measurements are performed simultaneously, their results should
be evaluated following the guidance in Section 3.2.2 If these two results will be different. As discussed
in Section 3.2.1, the difference between sequential tests may be due to radon levels fluctuating in
response to weather or other factors.
In general, confidence in a radon measurement can be increased by performing another measurement
with a second measurement device. However, there are other approaches or features that can be used
to increase the confidence of a measurement results obtained using active monitor devices. These
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approaches include the use of device self-diagnostic features and data validation or verification
procedures, that could be employed before and/or after the measurement. Example of such
approaches are the use of check sources before and after each measurement, and use of spectrum
readouts. These capabilities are examples, and different technologies may be able to perform other
similar self-diagnostic or quality assurance checks. Other features that increase the confidence of a
single active test include (but are not limited to) the ability to check air flow rates and voltage meters
before and after each measurement. Measurement companies should incorporate such checks into
their routine instrument performance checks as part of their standard operating procedures.
Additional features that can increase confidence in measurement results are those that detect
measurement interference; these features are discussed in Section 3.5. For example, a devise that
offers a variety of ways to detect tampering may serve to deter, as well as detect, interference with the
device's operation or proper closed-building measurement conditions. Potential tampering indicators
include the ability of a device to record changes in temperature, humidity, or movement of or around
device during the measurement.
Instruments with greater efficiency or sensitivity, or a high signal-to-noise ratio (see Glossary for
definitions of these terms), can achieve results with a smaller uncertainty than instruments with low
efficiency, poor sensitivity, or low signal-to-noise ratio. Greater efficiencies, sensitivities, or a hight
signal-to-noise ratio may also facilitate tempering detection by being more sensitive to fluctuations in
radon levels. There have been recommendations for setting minimum efficiency standards for active
decices at 16 counts per hour per hour per pCi/L. EPA plans to conduct research to establish minimum
standards in the future for all categories of devices, passive as well as active detectors. The reliability
of any type of equipment, however, needs to be established and documented via a complete quality
assurance program. This includes routine instrument performance checks prior to and after each
measurement, annual calibrations, semi-annual instrument cross-checks, the performance of duplicate
measurements in 10 percent of the measurement locations, and frequent background and spiked
measurements.
3.3 Measurement Location
EPA recommends that measurements made for a real estate transaction be performed in the lowest
level of the home which is currently suitable for occupancy. This means the lowest level that is
currently lived-in, or a lower level that is not currently used (such as a basement, which a buyer could
use for living space without renovations). Measurements should be made in a room that is used
regularly, such as a living room, playroom, den, or bedroom. This includes a basement that can be
used as a recreation room, bedroom, or playroom. This provides the buyer with the option of using a
lower level of the home as part of the living area, with the knowledge that it has been tested for radon.
3.4 Measurement Checklist
EPA presents the following checklist to help ensure that a radon measurement conducted for a real
estate transaction is done properly. The seller, or an EPA-listed or State-listed tester should be able to
confirm that all the items in this checklist have been followed. If the tester cannot confirm this, another
test should be made.
Before the radon test:
• Notify occupants of the importance of proper testing conditions. Give occupants written
instructions or a copy of the EPA Home Buyer's and Seller's Guide to Radon (EPA 402-R-93-
003; U.S. EPA 1993), or a State-required alternative, and explain the directions carefully.
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• The radon measurement service and device should be listed by EPA's National Radon
Measurement Proficiency (RMP) program (EPA 520/1-91-006; U.S. EPA 1991) or listed by your
State. Follow the manufacture's instructions that come with the device.
• The radon measurement equipment used should be listed by some proficiency organization or
listed by your State. Follow the manufacturer's instructions that come with the device.
• If a testing professional conducts the test, only EPA-listed or State-listed individuals should be
hired. Their photo identification should be provided to the client or homeowner at the time of, or
before, the test, and the contactor's identification number should be clearly visible on the test
report.
• The test should include method(s) to prevent or detect interference with testing conditions or
with the testing device itself.
• Conduct the radon test for minimum of 48 hours. Some devices must be exposed for longer
than the 48-hour minimum.
• In homes with an active radon reduction system, check that the fan is running at least 24 hours
before starting a short-term test lasting less than four days. Air exhaust fans that typically
operate for short periods (e.g., bathroom fan) may be used during the test.
• EPA recommends that short-term radon testing, which lasts for no more than a week in length,
be done under closed-building conditions. Closed-building conditions means keeping all
windows closed, keeping doors closed except for normal entry and exit, and not operating fans
or other machines that bring in air from outside. Note that fans that are part of a radon reduction
system or small exhaust fans operating for only short periods of time may run during the test.
• When doing short-term testing lasting less than four days, it is important to maintain closed-
building conditions for at least 12 hours before the beginning of the test and for the entire test
period. Do not operate fans or other machines that bring in air from the outside.
During the radon test:
• Maintain closed-building conditions during the entire time of a short-term test, especially for
tests shorter than one week in length.
• Operate the home's heating and cooling systems normally during the test. For tests lasting less
than one week, only operate air conditioning units that recirculate interior air.
• Do not disturb the test device at any time during the test.
• If a radon reduction system is in place, make sure the system is working properly and will be in
operation during the entire radon test.
After a radon test:
• If a high radon level is confirmed, fix the home. Pages 21 to 23 of EPA's Home Buyer's and
Seller's Guide to Radon (EPA 402-R-93-003; U.S. EPA 1993) recommends the next steps that
should be taken, such as contacting a qualified radon reduction contractor to lower the home's
radon level.
• The radon tester or homeowner should be able to verify or provide documentation asserting that
testing conditions were not violated during the testing period.
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3.5 Interference-Resistant Testing
EPA strongly encourages the use of radon testing devices with interference-resistant features inherent
in, or associated with, the device.
Interference with a radon measurement is defined as the altering of test conditions prior to or during the
measurement to either change the radon or decay product concentrations or alter the performance of
the measurement equipment. The following discussion reviews some of the types of test interferences
and methods of detecting and preventing such interferences.
Test interference typically causes measurement results to be different than if all proper test conditions
were maintained. False low results have been primarily associated with testing during a real estate
transaction, although they also happen when the occupants of the dwelling are not properly informed
about the necessary test conditions. Test interference can also inadvertently increase measurement
results, although the intent is to lower the results.
The current occupant may have an interest in the test results being as low as possible to avoid
hindering the sale of the dwelling or incurring the added expense of having to install a mitigation
system. The potential for test interference puts the professional radon tester into the position of
verifying that the equipment and the required test conditions have been maintained. A measurement
result that is below the action guideline may be suspect if the tester cannot verify that the necessary
test conditions were maintained.
If the tester arrives at a property and finds windows or doors open, or suspects that closed-building
conditions were not maintained for 12 hours prior to arrival, then the tester should extend the test to
account for this condition.
3.5.1 Influencing Test Area Concentration
The primary method of temporarily reducing radon levels is to ventilate the test area with outdoor air.
Ventilation will slow down radon entry by both reducing negative pressure in the test area and by
diluting the reduced radon concentration. Even small openings of a single window in the test area can
have a large effect. Ventilating the floors above the test area has significantly less effect, unless the test
area is connected with the ventilated room(s) by an operating central air handling system.
Radon decay product levels are sensitive to air movement. As air movement increases, decay products
will plate out on walls and other surfaces, including fans, thereby reducing airborne decay product
concentrations. Decay products will be further reduced if the fan also includes a filter. Radon levels are,
however, not affected by filtering or air movement.
It is also possible to alter concentrations in a tight room if the heating system is operating in an
abnormal fashion. Since this may not be the typical operation of the system, it is, in effect, interfering
with normal house conditions.
It is important to recognize that test interference can increase radon or decay product levels, despite
intent to lower the results.
3.5.2 Equipment Interference
The primary method of interfering with testing equipment is to move the detector to an area of low
radon concentration. Other types of interference vary in their ability to influence different types of
detectors. For example, interfering with the air sampling mechanisms can maintain the radon
concentration at the time of interference, or cause a large decrease in the reported concentration.
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Similarly, covering a decay product or charcoal detector could cause a large drop in the reported
values, while other types of radon detectors would only show a reduced response time to changes in
the test area level. In addition, charcoal detectors are sensitive to heat. Some active radon monitors
and open face charcoal canisters are also sensitive to high humidity. Any detector that yields a single
result could be turned off or sealed in its container or lid during most of its exposure period.
3.5.3 Preventing Interference
EPA recommends that a radon measurement conducted for a real estate transaction be performed
using tamper-resistant testing techniques. It is more advantageous for the tester to take steps to
prevent interference rather than to simply detect it. Preventing interference can best be accomplished
by:
• Educating the parties to a real estates transaction about the necessary test conditions.
• Including in standard documentation for each measurement an agreement signed by the parties
involved in the real estate transaction listing the necessary test conditions and their agreement
not to interfere with the conditions.
The agreement should also state that the tester in their discretion may nullify the test results
were rendered unreliable.
• Informing the client that interference with the test conditions may increase the radon levels.
• Informing the client that the tester is using interference-detecting techniques, and that these
allow the detection and documentation of test interference.
3.5.4 Interference-Resistant Detectors
The following is a partial list of common equipment and measures that can serve to prevent and/or
detect test interference. There may be other methods available. Equipment that offers a combination of
tamper-detecting features also offers a greater chance of detecting interference.
• The ability to integrate and record frequent radon measurements over short intervals (an
hour or less) is an important tamper detection feature. Continuous (active) monitors that
provide frequent measurements can indicate unusual concentration changes that can be
indicators of test interference.
• Measuring other parameters may provide additional indicators of test interference, such as a
detector tilt indicator or a continuous recording of pump flow rate.
• A motion indicator can also indicate when the detector was approached or moved.
• A simultaneous, several-day continuous measurement of both radon and decay product
concentrations will produce a series of equilibrium ratio values. These values can be
inspected for unusual swings or abnormal levels, possibly indicating interference.
• Measurement of CO2 levels can indicate changes in the test area infiltration rate of outdoor
air.
• The performance of a grab radon measurement, a grab decay product measurement, or
both, before and after a longer-term measurement can offer useful information. For
example, the initial and final concentrations and equilibrium ratios can be compared for
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consistency. Note: The results of measurements lasting less than 48 hours (e.g., grab
samples) should not be used as the basis for deciding to fix a home.
• Frequent temperature readings may help to indicate changes in the test area infiltration rate
of outdoor air.
• Humidity (as well as temperature) recordings can be especially helpful in identifying
potential unusual changes in test conditions that occur during the test period that might not
be detected simply through data logging.
• Instruments that do not allow occupants to view preliminary results (via a visible printer or
screen) may reduce occupants' interference.
• Placement indicators can also indicate if a detector has been tampered with or moved. The
position of the detector should be noted so that, upon retrieval, any handling of the detector
can be indicated by a change in its position. A detector may be hung or placed slightly over
the edge of its support to discourage covering it. Passive detectors may be hung or
suspended in a radon-permeable bag that uses a unique strap and seal to prevent removing
or covering it. Cages can be equipped with a movement indicator to deter handling of the
cage or the detector within it.
• Seals can aid in detecting and discouraging test interference, and they are especially
important in the absence of other tamper detection. Non-sealable caulks and/or tapes can
be used to verify that detectors have not been opened. Seals alone will not prevent
excessive ventilation through primary doors.
Seals should be placed on the lowest operable windows and non-primary exterior doors, as
well as between the detector and its support and any other components of the detector that
could be tampered with. It may be advisable to attach to the caulk seal something fragile
that protrudes out, to indicate any handling or covering of the detector.
A number of different products or combination of products can be used for tamper seals. For a seal to
be effective, it needs at least the following unique qualities:
• The seal must adhere readily to a multitude of surfaces, and yet be easily removed
without marring the surface.
• It needs to be non-resealable or show evidence of disturbance.
• It must be unique enough to prevent easy duplication.
• It should be visible enough to discourage tampering.
The tamper resistance of the seal can be increased by using a caulk over the seal edges or by slicing a
large portion of the center of the seal to ensure the seal is broken in case of tampering. Most paper or
plastic tapes and caulks have only some of these qualities. There are, however, a number of seals
manufactured specifically for radon testing. It would be advisable to use one of these products and
follow the manufacturer's installation recommendations. The best caulking to use as a seal is a
removable weatherstripping caulk. This type of caulking adheres readily to most surfaces, yet comes off
easily without leaving a mark or being resealable. Upon retrieval of the detector, the tester should
carefully inspect the following:
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• That all closed-building conditions are still being maintained;
• Any changes in the detector placement;
• The condition of all seals; and
• Any abnormal variations in any of the measurements made.
This information should be recorded, as described in Section 4.3.5.
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Section 4: General Procedural Recommendations
4.1 Introduction
4.2 Initial Client Interview
4.3 Measurement Recommendations
4.4 Quality Assurance in Radon Testing
4.5 Standard Operating Procedures
4.6 Providing Information to Consumers
4.7 Reporting Test Results
4.8 Temporary Risk Reduction Measures
4.9 Recommendations for Mitigation
4.10 Worker Safety
4.1 Introduction
This section outlines basic procedural recommendations for anyone involved in the measurement of
radon in homes for both real estate and non-real estate related measurements.
4.2 Initial Client Interview
Reasonable efforts should be made to determine whether the home is new and/or occupied, and who
will be in charge of the home during the measurement period. Testing organizations should inform the
client and other parties to the real estate transaction of:
• The appropriate EPA testing recommendations as outlined in this report, the 1992 Citizen's
Guide to Radon (EPA 402-k-92-001; U.S. EPA 1992a) , or the Home Buyer's and Seller's Guide
to Radon:(EPA 402-R-93-003: U.S. EPA 1993); and,
• The types of devices they will be using for that test, and EPA documentation indicating that the
testing organization or individual is RM P-listed for that device
4.3 Measurement Recommendations
4.3.1 Selecting a Measurement Approach
The purpose of the measurements, as well as budget and time constraints, dictate the protocol used.
Measurements made for the purpose of assessing the need for mitigation of one's own property should
be made according to the guidance discussed in Section 2 of this document; Section 3 outlines options
for protocols for measurements made for real estate transactions. Organizations that provide consultant
services, or place or retrieve devices, should review the protocol options and the clients' needs, and
inform clients of the buildings and test period conditions necessary for conducting valid measurements.
In some areas, companies may offer different types of radon service agreements. Some agreements
allow for a one-time fee that covers both testing, and if needed, radon reduction.
The organization or individuals performing the measurement service should use only those specific
devices or methods for which that organization or individuals is listed according to the National RMP
Program (EPA 520/1-91-006; U.S. EPA 1991). Adherence to the EPA device protocols, Indoor Radon
and Radon Decay Product Measurement Device Protocols (EPA 520-402-R-92-004; U.S. EPA 1992c)
is a requirement for participation in the RMP program.
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4.3.2 Written Measurement Guidance
Measurement organizations should provide clients with written measurement instructions that clearly
explain the responsibilities of the client and the other parties to the real estate transactions during the
test period. Written and verbal guidance should be in accordance with EPA's Indoor Radon and Radon
Decay Product Measurement Device Protocols (EPA 520-402-R-92-004; U.S. EPA 1992c).and
guidance published in the RMP Program Handbook (EPA 520/1-91-006; U.S. EPA 1991).
• A statement of whether the device measures radon or radon decay products and a
discussion of the units in which all results will be reported.
The results of radon decay product measurements should be reported in working levels
(WL). If the WL value is converted to a radon concentration and is reported to the
homeowner, it should be stated that this approximate conversion is based on a 50 percent
equilibrium ratio (unless the actual equilibrium ratio is determined). In addition, the report
should indicate that this ratio is an assumed average found in the home environment; any
indoor environment may have a different and varying relationships between radon and its
decay products.
• A description of closed-building conditions and a stated requirement that these conditions be
maintained 12 hours prior to and during all short-term measurements lasting less than four
days and preferably for those lasting up to one week.
• Directions that the building's heating, ventilating, and air conditioning (HVAC) system and
any existing mitigation system should be normally operated 24 hours prior to and during all
measurements.
• A permanent radon reduction system should be fully operational for at least 24 hours prior to
testing to determine the mitigation system's effectiveness. The mitigation system is to be
operated normally and continuously during the entire measurement
• Specific information on the minimum and maximum duration of exposure for the device.
• If the client will be performing the test, procedures for placing, retrieving, and handling the
device.
• A written non-interference agreement (see Sections 3.5.3 and 4.3.4) to be signed and
returned by the real estate transaction which confirms that they followed all instructions and
did not interfere with the conditions or the measurement device.
4.3.3 Conditions for a Valid Measurement
Measurements should not be conducted if temporary radon reduction measures have been
implemented. These included the introduction of unconditioned air into the home or closure or normally
accessible areas of the home. In this case, the measurements organization or individual should inform
the slient and other parties to the real estate transactions that these conditions have been corrected.
A permanent radon reduction system should be fully operational for at least 24 hours prior to
testing to determine the mitigation system's effectiveness. The mitigation system is to be operated
normally and continuously during the entire measurements periods.
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4.3.4 Non-interference Controls
The measurement organization should provide parties to a real estate transaction clients with a written
statement that discusses the importance of proper measurement conditions and of not interfering with
the measurement device or building conditions. The reader should refer to Section 3.5.3 for more
information on non-interference agreements.
Organizations that place and retrieve devices should, in addition to providing written guidance, take
steps to identify attempts to interfere with the measurement device or building conditions. There is
increasing use of non-interference agreements signed by parties involved in real estate transactions to
help prevent interference with the radon test and test conditions. The reader should refer to Section 3.5
for more information on tamper-resistant testing.
The signed non-interference agreement, a description of all non-interference controls employed, and a
statement addressing any observed breaches of the non-interference agreement/controls should be
made part of the permanent measurement documentation for each measurement.
4.3.5 Measurement Documentation
Measurement organizations should record sufficient information on each measurement in a permanent
log to allow for future data comparisons, interpretations, and reporting to clients. EPA recommends that
a measurement log be kept with the following information and be maintained for five years. Additional
method-specific documentation is outlined in EPA's Indoor Radon and Radon Decay Product
Measurement Device Protocols (EPA 520-402-R-92-004; U.S. EPA 1992c).
• A copy of the final report, including the measurement results, and the statement outlining
any recommendations concerning retesting or mitigation provided to the building occupant
or agent.
• The address of the building measured, including zip code.
• The exact locations of all measurement devices deployed. It is advisable to diagram the test
area, noting the exact location of the detector.
• Exact start and stop dates of the measurement period as required for analysis.
• A description of the device used, including its RMP device identification number and serial
number if any.
• A description of the condition of any permanent vents, such as crawl space vents or
combustion air supply to combustive appliances.
• The name and PMP identification number (EPA 52071-91-014-3N; U.S. EPA 1992e) of the
service or analysis organizations used to analyze devices
• The name and RMP identification number (or State license number) of the individual who
conducted the test.
• A description of any variations from or uncertainties about standard measurement
procedures, closed-building conditions, or other factors that may affect the measurement
result.
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• A description of any non-interference controls used and copies of signed non-interference
agreements.
• A record of any quality control measures associated with the test, such as results of
simultaneous or secondary measurements.
4.4 Quality Assurance in Radon Testing
Anyone providing measurement services using radon or radon decay product measurement devices
should establish and maintain a quality assurance program. These programs should include written
procedures for attaining quality assurance objectives and a system for recording and monitoring the
results of the quality assurance measurements described below. EPA offers general guidance on
preparing quality assurance plans (QAMS-005/80; U.S. EPA 1980); a draft standard prepared by a
radon industry group is also available (AARST 1991). The quality assurance program should include
the maintenance of control charts and related statistical data, as described by Goldin (Goldin 1984), by
EPA (EPA 600/9-76-005; U.S. EPA 1984), and \nAppendixB of this document.
4.4.1 Calibration Measurements
Calibration measurements are measurements made in a known radon environment, such as a
calibration chamber. Detectors requiring analysis, such as charcoal canisters, alpha track detectors,
electret ion chambers, and radon progeny integrating samplers are exposed in a calibration chamber
and then analyzed. Instruments providing immediate results, such as continuous working level and
radon monitors, should be operated in a chamber to establish individual instrument calibration factors.
Calibration measurements must be conducted to determine and verify the conversion factors used to
derive the concentration results. These factors are determined normally for a range of concentrations
and exposure times, and for a range of other exposure and/or analysis conditions pertinent to the
particular device. Determination of these calibration factors is a necessary part of the laboratory
analysis, and is the responsibility of the analysis laboratory. These calibration measurement
procedures, including the frequency of tests and the number of devices to be tested, should be
specified in the quality assurance program maintained by manufacturers and analysis laboratories.
4.4.2 Known Exposure Measurements
Known exposure measurements or spiked samples consist of detectors that have been exposed to
known concentrations in a radon calibration chamber. These detectors are labeled and submitted to the
laboratory in the same manner as ordinary samples to preclude special processing. The results of
these measurements are used to monitor the accuracy of the entire measurement system. Suppliers
and analysis laboratories should provide for the blind introduction of spiked samples into their
measurement processes and the monitoring of the results in their quality assurance programs. All
organizations providing measurement services with passive devices should conduct spiked
measurements at a rate of three per 100 measurements, with a minimum of three per year and a
maximum required of six per month. Providers of measurements with active devices are required to
recalibrate instruments at least once every 12 months and perform cross-checks with RPP-listed
devices at least once every six months. Participation in EPA's National RMP Program will not satisfy
the need for annual calibration, as this program is a performance test, not a calibration procedure
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4.4.3 Background Measurements
Background measurements are required both for continuous monitors and for passive detectors
requiring laboratory analysis. Users of continuous monitors must perform sufficient instrument
background measurements to establish a reliable instrument background and to check on instrument
operation. For more specific information on how often background measurements should be made,
refer to EPA's Indoor Radon and Radon Decay Product Measurement Device Protocols (EPA 520-402-
R-004; U.S. EPA 1992c).
Passive detectors requiring laboratory analysis require one type of background measurement made in
the laboratory and another in the field. Suppliers and analysis laboratories should measure routinely the
background of a statistically significant number of unexposed detectors from each batch or lot to
establish the laboratory background for the batch and the entire measurement system. This laboratory
blank value is subtracted routinely (by the laboratory) from the field sample results reported to the user,
and should be made available to the users for quality assurance purposes. In addition to these
background measurements, the organization performing the measurements should calculate the lower
limit of detection (LLD) for its measurement system (Altshuler and Pasternack 1963, ANSI 1989, U.S.
DOE 1990). This LLD is based on the detector and analysis system's background and can restrict the
ability of some measurement systems to measure low concentrations.
Providers of passive detectors should employ field controls (called blanks) equal to approximately five
percent of the detectors that are deployed, or 25 each month, whichever is smaller. These controls
should be set aside from each detector shipment, kept sealed and in a low radon environment, labeled
in the same manner as the field samples to preclude special processing, and returned to the analysis
laboratory along with each shipment. These field blanks measure the background exposure that may
accumulate during shipment and storage, and the results should be monitored and recorded. The
recommended action to be taken if the concentrations measured by one or more of the field blanks is
significantly greater than the LLD is dependent upon the type of detector. More information is available
in EPA's Indoor Radon and Radon Decay Product Measurement Device Protocols (EPA 520-402-R-92-
004; U.S. EPA 1992c).
4.4.4 Duplicate Measurements
Duplicate measurements provide a check on the quality of the measurement result, and allow the user
to make an estimate of the relative precision. Large precision errors may be caused by detector
manufacture, and/or improper data transcription or handling by suppliers, laboratories, or technicians
performing placements. Precision error can be an important component of the overall error, so it is
important that all users monitor precision.
Duplicate measurements for both active and passive detectors should be side-by-side measurements
made in at least 10 percent of the total number of measurement locations, or 50 each month, whichever
is smaller. The locations selected for duplication should be distributed systematically throughout the
entire population of samples. Groups providing measurement services to homeowners can do this by
providing two measurements, instead of one, to a random selection of purchasers, with the
measurements made side-by-side. As with spiked samples introduced into the system as blind
measurements, the precision of duplicate measurements should be monitored and recorded in the
quality assurance records. The analysis of data from duplicates should follow the methodology
described in Appendix B of this document. If the precision estimated by the user is not within the
precision expected of the measurement method, the problem should be reported to the analysis
laboratory and the cause investigated.
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4.4.5 Routine Instrument Performance Checks
Proper functioning of analysis equipment and operator usage require that the equipment and
measurement system be subject to routine checks. Regular monitoring of equipment and operators is
vital to ensure consistently accurate results. Performance checks of analysis equipment includes the
frequent use of an instrument check source. In addition, important components of the device (such as a
pump and pump flow rate, battery, or electronics) should be checked prior to each measurement and
the results noted in a log. Each user should develop methods for regularly (daily, or at least prior to
each measurement) monitoring their measurement system, and for recording and reviewing results.
4.4.6 Quality Assurance Plans
All organizations should develop, implement, revise periodically, and maintain a detailed quality
assurance plan (QAP) appropriate to each device or method used. This was a requirement for
participation in EPA's National Radon Measurement Proficiency (RMP) program. Specific guidance on
the necessary quality control measures for each measurement method is provided in EPA's Indoor
Radon and Radon Decay Product Measurement Device Protocols (EPA 520-402-R-92-004; U.S. EPA
1992c).
Organizations that do not use continuous monitors or do not analyze detectors also need to write and
follow a QAP, and conduct quality control measurements. These include duplicate, blank, and spiked
measurements as described in Section 4.4. For more information on EPA's RMP Program, please
contact:
RMP Program Information Services
Research Triangle Institute
3040 Cornwallis Road-Building 7
P.O. Box12194
Research Triangle Park, NC 27709-2194
(919-541-7131/FAX-7386)
4.5 Standard Operating Procedures
Organizations performing radon measurements should have a written, device-specific standard
operating procedure (SOP) in place for each radon measurement system they use. An SOP must
include specific information describing how to operate and/or analyze a particular measurement device.
Organizations that analyze devices should develop their own SOP or adapt manufacturer-developed
SOPs for their devices. Organizations that receive results from a laboratory should have a device-
specific SOP for each brand/model/type of device that they use. All SOPs should be consistent with the
appropriate protocol outlined in EPA's Indoor Radon and Radon Decay Product Measurement Device
Protocols (EPA 520-402-R-92-004; U.S. EPA 1992c).
4.6 Providing Information to Consumers
Organizations should provide the customer with the following information:
• Devices that will be placed by the customer must be accompanied by instructions on how to use
the device. These instructions should be consistent with EPA's Indoor Radon and Radon Decay
Product Measurement Device Protocols (EPA 520-402-R-92-004; U.S. EPA 1992c) and include
specific information on the minimum and maximum length of time that the device must be
exposed.
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• The service organization should inform clients about sources of information on mitigation, such
as EPA's Consumer's Guide to Radon Reduction (EPA 402-K-92-003; U.S. EPA 1992b), and
other information available through their State Radon office. The organizations should also
provide any State-required brochures which provide information on mitigation.
• If service organization distribute the Consumer's Guide brochure, it should be reproduced in its
entirety.
4.7 Reporting Test Results
Organizations should return radon measurement results to clients within a few weeks of retrieving
exposed devices or receiving an exposed device which has been delivered for analysis. At a minimum,
the client report should contain the following information:
• Measurement results reported in the units that the device measures. Any measurement results
based on radon gas (pCi/L of air) should be reported to no more than one decimal place, e.g.,
4.3 pCi/L. Any measurement result based on radon decay products (WL) should be reported
to no more than three decimal places, e.g., 0.033 WL. Any conversions from WL to pCi/L or
from pCi/L to WL should be presented and explained clearly.
If the WL value is converted to a radon concentration, it should be stated in the report to the
homeowner that this approximate conversion is based on a 50 percent equilibrium ratio (unless
the actual equilibrium ratio is determined). In addition, the report should indicate that this ratio is
typical of the home environment, but that any indoor environment may have a different and
varying relationship between radon and its decay products.
• The dates of the measurement period and address of the building tested.
• A description of the device used, its manufacturer, model or type, and the device identification
(serial) numbers.
• The name and any relevant identification numbers of the organization and individual placing and
retrieving the device and the organization analyzing the device, if they are different.
• A statement concerning any observed tampering or deviations from the required test conditions.
• Organizations that offer measurement services with grab sampling devices should provide
clients with written notification stating that grab sample results can be useful diagnostic tools,
but should not be used for deciding whether or not to mitigate.
• Diagnostic measurements should be reported as "for diagnostic purposes only."
4.8 Temporary Risk Reduction Measures
Contractors should refer home's occupants and real estate agents to EPA's Radon Mitigation
Standards (U.S. EPA 1992d) or the Consumer's Guide to Radon Reduction (EPA 402-K-92-003; U.S.
EPA 1992b) for information on temporary and permanent risk reduction measures.
If any radon reduction efforts are identified during measurement procedures, testers should inform
clients and other parties to the real estate transaction that altered conditions during the measurement
will invalidate the results and decline to conduct a measurement until the conditions have been
corrected.
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4.9 Recommendations for Mitigation
The measurement organization should inform consumers that EPA recommends fixing houses with
radon levels equal to or greater than 4 pCi/L, and that EPA recommends in its "Consumer's Guide to
Radon Reduction" the use of EPA Radon Contractor Proficiency (RCP)-listed and/or State-listed
mitigation contractors to perform the work.
Organizations should refer customers to their State radon office for copies of EPA's "Consumer's Guide
to Radon Reduction" (EPA 402-K-92-003; U.S. EPA 1992b) and a list of EPA RCP-proficient and State-
listed mitigators.
Homes should also be tested again after they are fixed to be sure that radon levels have been reduced.
If the occupants' living patterns changes and they begin occupying a lower level of their home (such as
a basement), the home should be retested on that level. In addition, it is a good idea for homes to be
retested sometime in the future to be sure radon levels remain low.
4.10 Worker Safety
Individuals and organizations should comply with all applicable Occupational Safety and Health
Administration (OSHA) standards and guidelines relating to occupational worker exposure, health, and
safety. Information on worker health and safety contained in EPA or State publications is not
considered a substitute for any provisions of the Occupational Safety and Health Act of 1970 or for any
standards issued by OSHA.
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Appendix A - State and EPA Regional Radon Offices
A.1/A.2 State and EPA Region Radon Offices - www.epa.gov/iaq/whereyoulive.html
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Appendix B - Interpretation of the Results of Side-by-Side Measurements
B.1. Assessment of Precision
B.2. Example Control Charts for Precision
B.3. Interpretation of Precision Control Charts
B.1 Assessment of Precision
Radon and working level measurements, like all measurements, usually do not produce exactly
the same results, even for collocated measurements. It is therefore critical to understand, document,
and monitor the variability, or precision, of the measurements. This knowledge and proper will allow
you to characterize precision error to clients. Further more the continual minitoring of precision provides
a check on every aspect of the measurement system.
The objective of performing simultaneous or duplicate measurements is to assess the precision
error of the measurement method, or how well two side-by-side measurements agree. This precision
error is the "random" component of error (as opposed to the calibration error, which is systematic). The
precision error, or the degree of disagreement between duplicates, can be composed of many factors.
These include the error caused by the random nature of counting radioactive decay, slight differences
between detector construction (for example, small differences in the amount of carbon in activated
carbon detectors), and differences in handling of detectors (for example, differences in accuracy of the
weighing process, and variations of analysis among detectors).
There is a variety of ways to quantitatively assess the precision error based on duplicate
measurements. It is first necessary to understand that precision is characterized by a distribution: that
is, your side-by-side measurements will exhibit a range of differences. There is some chance that any
level of disagreement will be encountered, due merely to the statistical fluctuations of counting
radioactive decays. The probability of encountering a very large difference between duplicates is
smaller than the chance of observing a small difference similar to those that are routinely observed. It is
important to recognize that a few high precision errors do not necessarily mean that the measurement
system is flawed.
Ideally, the results of duplicates should be assessed in a way that allows for the determination of what
level of chance is associated with a particular difference between duplicates. This will allow for the pre-
determination of limits for the allowable differences between duplicates before an investigation into the
cause of the large differences is made. For example, the warning level, or the level of discrepancy
between duplicates which triggers an investigation, may be set at a five percent probability. This level is
a difference between duplicates that is so large that, when compared with previous precision errors,
should only be observed five percent of the time. A control limit, where further measurements should
cease until the problem is corrected, may be set at one percent probability.
A control chart for duplicates is not as simple as a control chart used to monitor instrument
performance, as for a check source. This is because the instrument's response to a check source
should be fairly constant with time. Duplicates are performed at various radon concentrations, however,
and the total difference between two measurements is expected to increase as radon levels increase.
Use of statistics such as the relative percent difference (RPD; difference divided by the mean) or the
coefficient of variation (COV; standard deviation divided by the mean) can be used in a control chart for
duplicate measurements at radon concentrations where the expected precision error is fairly constant in
proportion to the mean, e.g., at levels greater than around 4 pCi/L or 0.02 WL. At lower concentrations,
for example, between 2 pCi/L (or 0.01 WL) and 4 pCi/L (or 0.02 WL), a control chart may be developed
by plotting these same statistics; however, the proportion of the precision error to the mean will be
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greater than that proportion at levels above 4 pCi/L or 0.02 WL. At concentrations less than about 2
pCi/L, or 0.01 WL, the lower limit of detection may be approached, and the precision error may be so
large as to render a control chart not useful.
Example control charts, using three different statistics, are described in the following sections.
B.2 Example Control Charts for Precision
Before a control chart can be developed, it is necessary to know, from a history of making good quality
measurements with the exact measurement system (detectors, analysis equipment, and procedures),
the level of precision that is routinely encountered when the system is operating well or "in control." It is
that "in control" precision error that forms the basis of the control chart, and upon which all the
subsequent duplicate measurements will be judged. There are two ways of initially determining this "in
control" level. The first, and preferable, way is to perform at least 20 duplicate pairs of measurements at
each range of radon concentrations for which a control chart is to be prepared. For example, if you will
only assess precision at concentrations greater than 4 pCi/L, or 0.02 WL, you will need at least 20 pairs
of measurements at concentrations greater than 4 pCi/L, or 0.02 WL, to assess the "in control" level.
The average precision error (RPD or COV) should be the "in control" level.
The second way to initially set the "in control" precision error level is to use a level that has been used
by others, and that is recognized by industry and EPA as a goal for precision, for example, a 10 percent
COV (corresponding to a 14 percent RPD). After at least 20 pairs of measurements are plotted, it will
become apparent whether the 10 percent COV (or 14 percent RPD) is appropriate for your system. If
itis not, a new control chart (using the guidelines below) should be prepared so that the warning and
control limits are set at the correct probability limits for your system.
B.2.1 Sequential Control Chart Based on Coefficient of Variation
It can be shown (Iglewicz and Myers 1970, EPA 600/9-76-005; U.S. EPA 1984) that when the expected
precision is a constant function of the mean, control limits can be expressed in terms of the COV
(COV=S/Xm; where S is the variance or the square of the standard deviation, and Xm is the mean or
average of the two measurements). One method for obtaining percent!les for the distribution of the
COV is to apply a chi-squared (X2) test:
X2n-i « B[(n-1)COVn2/(n+(n-1)COVn2)] (Equation 1)
where: B = n[1 + (1/COV2)];
COVn = the observed COV of the nth pair (the pair that is to be evaluated); and
COV = the "in control" COV (e.g., 10 percent at levels greater than 4 pCi/L).
For duplicates, where n=2, Equation 1 becomes
X2 = [2 + (2/COV2)][COVn2/(2 + COVn2)] (Equation 2)
Fora value of 0.10 for COV, it further reduces to
X2 = 202[COVn2/(2 + COVn2)] (Equation 3)
Referring to a X2 chart, you learn that the probability of exceeding a X2 of 3.84 is only five percent.
Inserting this value of 3.84 forX2 and solving for COVn, produces a COVn of 0.20. This level of
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probability forms the warning level shown in Exhibit B-1. The control limit corresponds to a X2 of 6.63
and a COVn of 0.26, where the probability of exceeding those values is only one percent.
This sequential control chart should be used by plotting results from each pair on the y-axis, and noting
the date and measurement numbers on the x-axis.
B.2.2 Sequential Control Chart Based on Relative Percent Difference
The RPD (or percent difference) is another expression of precision error, and is given by
RPD = [100lx1-x2l]/[(x1+x2)/2] (Equation 4)
Forn=2,
RPD = COV SORT 2 (Equation 5)
The control limits for RPD can be obtained simply by multiplying the control limits for COV by the
square root of two, or 1.41. These limits are shown in Exhibit B-2. This sequential control chart for RPD
should be used in the same way as the control chart for COV, that is, with the vertical scale in units of
RPD and the horizontal scale in units of date and measurement numbers.
A control chart using the statistic RPD based on an "in control" level of 25 percent RPD is shown in
Exhibit B-3. The warning level and control limit are set at 50 percent and 67 percent, respectively. Use
of these limits may be appropriate for measured radon concentrations less than 4 pCi/L.
Exhibit B-1
Control Chart* for Coefficient of Variation (COV)
Based on an "In Control" Level of 10%
(For duplicates where average >4 pCi/L or 0.02 WL)
> 20**
*
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o
Control
IB soc cfup.tcaws pfsj^jcw C-OV
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H«aau»tf»nl Numtiet
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COV=standard deviation of two measurements divided by their average
Example: Detector A=5 pCi/L, B=6 pCi/L, COV=13%
If COV exceeds the control limit-cease measurements until the problem is identified and corrected.
If COV exceeds the warning level-follow guidance in Section B.3 and see Exhibit B-5.
*As calculated from guidance provided in "Quality Assurance Handbook for Air Pollution Measurement
Systems: Volume I" (EPA 600/9-76-005; U.S. EPA 1984)
Exhibit B-2
Control Chart* for Relative Percent Difference (RPD)
Based on an "In Control" Level of 14% (=COV of 10%)
(For duplicates where average >4 pCi/L or 0.02 WL)
36*;,
8
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antf Namter
RPD=difference between two measurements divided by their average
Example: Detector A=5 pCi/L, B=6 pCi/L, RPD=18%
If RPD exceeds the control limit-cease measurements until the problem is identified and corrected.
If RPD exceeds the warning level-follow guidance in Section B.3 and see Exhibit B-5.
*As calculated from guidance provided in "Quality Assurance Handbook for Air Pollution Measurement
Systems: Volume I" (EPA 600/9-76-005; U.S. EPA 1984)
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Exhibit B-3
Control Chart* for Relative Percent Difference (RPD)
Based on an "In Control" Level of 25% (=COV of 18%)
(For duplicates where average <4 pCi/L or 0.02 WL)
8
%.
m L, **n
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• impact SB »« eut»cg«s p»acuca RPD cj'^attj"
ihsn 6?"'* only <»'» o! t^e tnva it'tOw cftaoct>;
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TOO 50%, o/i:y *>"*;, at n<» imw • 1 7-1 cmm-UJ.'
*"(« Control"
and Measuraroent w«mb*r
RPD=difference between two measurements divided by their average
Example: Detector A=2 pCi/L, B=3 pCi/L, RPD=40%
If RPD exceeds the control limit-cease measurements until the problem is identified and corrected.
If RPD exceeds the warning level-follow guidance in Section B.3 and see Exhibit B-5.
*As calculated from guidance provided in "Quality Assurance Handbook for Air Pollution Measurement
Systems: Volume I" (EPA 600/9-76-005; U.S. EPA 1984)
B.2.3. Range Control Chart
A range control chart (Goldin 1984) can be constructed to evaluate precision, using the statistics of the
range (difference between two measurements) plotted against the average of the two measurements.
The control limits are again based on the variability of the measurements, as decided upon from
previous results or using an industry standard (e.g., 10 percent).
In this type of control chart, the limits are expressed in terms of the mean range (Rm), where, for n=2,
Rm= 1.128s(x) (Equation 6)
where s(x) is the standard deviation of a single measurement, which reflects counting and other
precision errors. Goldin shows that the limits can be expressed as follows:
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Control limit = 3.69 s(x) (Equation 7)
Warning level = 2.53 s(x) (Equation 8)
An example range control chart, using an assumed s(x) equal to 10 percent of the mean concentration,
is shown in Exhibit B-4. The chart is used by plotting the range versus average concentration as
duplicate measurements are analyzed.
Exhibit B-4
Range Control Chart to Evaluate Precision
(Limits Based on s(x)=0.1xm)
Control Limit
Warning Level
0 5 10 18 20 25
Value of Two Measurements, pCi/L
If results exceed the control limit-cease measurements until the problem is identified and corrected.
If results exceed the warning level-follow guidance in Section B.3 and see Exhibit B-5.
B.3 Interpretation of Precision Control Charts
The control chart should be examined carefully every time a new duplicate result is plotted. If a
duplicate result falls outside the control limit, repeat the analyses if possible. If the repeated analyses
also fall outside the control limit, stop making measurements and identify and correct the problem.
If any measurements fall outside the warning level, use the table in Exhibit B-5. Refer to the row
showing the number of duplicate results outside the warning level. If the total number of duplicate
results accumulated in the control chart is contained in column A, investigate the cause of the high level
of precision error but continue making measurements. If the total number of duplicate results on the
chart is contained in column B, stop making measurements until the cause for the high precision error
is found, and it is determined that subsequent measurements will not suffer the same high level of
precision error.
Note that the example control charts shown here are simplifications of actual conditions, because they
are premised on the assumption that the precision error is a constant fraction of the mean
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concentration. In fact, the total precision error may best be represented by a different function of the
mean concentration, for example, the square root of the concentration. The most accurate control chart
can be rendered by a range control chart using the measurement uncertainty expressed as the
standard deviation, s(x), expected at the concentrations where measurements are made. If the
precision error is not a constant fraction of the mean, the control limits will not appear as straight lines,
but may exhibit changing slope. However, methods discussed here present a conservative way to
monitor, record, and evaluate precision error and are very useful for comparing observed precision
errors with an industry standard.
Exhibit B-5
Criteria for Taking Action for Measurements Outside the Warning Level*
Total Number of Duplicates
Number of |^^^^ ^ _^ Operations
Duplicate Results (continue Operations (Until Problem is Corrected
Outside the ' '
warning Level
2
3
4
5
6
7
A
8-19
17-34
29-51
41-67
54-84
67-100
B
2-7
8-16
17-28
29-40
41-53
54-66
*Modified from Goldin (Goldin 1984) and based upon cumulative
[probability tables of the binomial distribution.
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Glossary
Accuracy: The degree of agreement of a measurement (X) with an accepted reference or true value
(T); usually expressed as the difference (or bias) between the two values (X - T), or the difference as a
percentage of the reference or true value (100[X - T]/T), and sometimes expressed as a ratio (X/T).
Active radon/radon decay product measurement device: A radon or radon decay product
measurement system which uses a sampling device, detector, and analysis system integrated as a
complete unit or as separate, but portable, components. Active devices include continuous radon
monitors, continuous working level monitors, and grab radon gas and grab working level measurement
systems, but does not include devices such as electret ion chamber devices, activated carbon or other
adsorbent systems, or alpha track devices.
Alpha particle: Two neutrons and two protons bound as a single particle that is emitted from the
nucleus of certain radioactive isotopes in the process of decay.
Background instrument (analysis system, or laboratory) count rate: The nuclear counting rate
obtained on a given instrument with a background counting sample. Typical instrument background
measurements are:
• Unexposed carbon: for activated carbon measurement systems.
• Scintillaton vial containing scintillant and sample known to contain no radioactivity: for
scintillation counters.
• Background measurements made with continuous radon monitors exposed only to radon-free
air (aged air or nitrogen).
Background fields measurements (blanks): Measurements made by analyzing unexposed (closed)
detectors that accompanied exposed detectors to the field. The purpose of field background
measurements is to assess any exposure to the detector caused by radon exposure other than from
the concentration in the environment to be measured. Results of background field measurements are
subtracted from the actual field measurements before calculating the reported concentration.
Background levels may be due to electronic noise of the analysis system, leakage of radon into the
detector, detector response to gamma radiation, or other causes.
Background radiation: Radiation arising form radioactivity material, the sun, and parts of the universe,
other than that under consideration. Background radiation may also be due to the presence of
radioactive substances in building materials.
Becquerel (Bq): The International System of Units (SI) definition of Activity. 1 Bq = 1 disintegration per
second.
Calibrate: To determine the response or reading of an instrument relative to a series of known values
over the range of the instrument; results are used to develop correction or calibration factors.
Check source: A radioactive source, not necessarily calibrated, which is used to confirm the continuing
consistent and satisfactory operation of an instrument.
Client: The individual or parties who hire(s) the radon tester.
Closed House Conditions: During any short-term test, closed-house-conditions should be maintained
as much as possible while the test is in progress. In tests of less than 4 days duration, closed-house-
conditions should be maintained for at least 12-hours before starting the test and for the duration of the
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test. While closed-house-conditions are not required before the start of tests that are between 4 and 90-
days, closed-house-conditions should be maintained as much as possible.
Coefficient of variation (COV), relative standard deviation (RSD): A measure of precision,
calculated as the standard deviation (s or s) of a set of values divided by the average (Xave or u), and
usually multiplied by 100 to be expressed as a percentage.
COV = RSD = (s/ Xave) x 100 for a sample,
COV ' = RSD ' = (o/u) x 100 for a population
See Relative percent difference.
Curie (Ci): A commonly used measurements unit for radioactivity, specifically the rate of decay for a
gram of radi
per second.
gram of radium - 37 billion decays per second. A unit of radioactivity equal to 3.7 x 1010 disintegrations
Duplicate measurements: Two measurements made concurrently and in the same location, or side-
by-side. Use to evaluate the precision of the measurement method.
Efficiency, Intrinsic detector: The relationship between the number of events recorded (counts,
voltage lost, tracks) and the number of radioactive particles incident upon the sensitive element of the
detector per unit time. Efficiencies for radon detectors are commonly expressed in terms of the
calibration factor, which is the number of events (counts) per time (hour or minute) per radon
concentration (pCi/L). Methods with high efficiencies will exhibit more counts (signal) per time in
response to a given radon level than will a method with a low efficiency.
Equilibrium ration, radon: Equilibrium ratio = [WL(100)]/(pCi/L). At complete equilibrium (i.e., at an
equilibrium ratio of 1.0), 1 WL of RDPs would be present when the radon concentration was 100 pCi/L.
The ratio is never 1.0 in a house. Due to ventilation and plate-out, the RPDs never reach equilibrium in
a residential environment. A commonly assumed equilibrium ratio is 0.5 (i.e., the decay products are
halfway toward equilibrium), in which case 1 WL would correspond to 200 pCi/L. However, equilibrium
ratios vary with time and location, and ratios of 0.3 to 0.7 are commonly observed.
Equilibrium equivalent concentration (EEC): The radon concentration in equilibrium with its short-
lived progeny, that has the same potential alpha energy per volume as exists in the environment being
measured (see working level).
Exposure time: The length of time a specific mail-in device must be in contact with radon or radon
decay products to get an accurate radon measurement. Also called exposure period, exposure
parameters, or duration of exposure.
Gamma radiation: Short-wavelength electromagnetic radiation of nuclear origin, with a wide range of
energies.
Integrating device: A device that measures a single average concentration value over a period of
time. Also called a time integrating device.
Lower limit of detection (LLD): The smallest amount of sample activity which will yield a net count for
which there is confidence at a predetermined level that activity is present. For a five percent probability
of concluding falsely that activity is present, the LLD is approximately equal to 4.65 times the standard
deviation of the background counts (assuming large numbers of counts where Gaussian statistics can
be used [ANSI 1989, Pasternack and Harley 1971, U.S. DOE 1990]).
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Lowest Level suitable for occupancy: The lowest level currently lived in or a lower level not currently
used, such as a basement, which a prospective buyer could use for living space without renovations.
This includes a basement that could be used regularly, as for example a recreation room, bedroom,
den, or playroom.
Lowest lived-in level: The lowest level or floor of a home that is used regularly, including areas such
as family rooms, living rooms, dens, playrooms, and bedrooms.
Passive radon measurement device: A radon measurement system in which the sampling device,
detector, and measurement system do not function as a complete, integrated unit. Passive devices
include electret ion chamber devices, activated carbon or other adsorbent systems, or alpha track
devices, but do not include continuous radon/radon decay product monitors, or grab radon/ radon
decay product measurement system
PicoCurie(pCi): One pCi is onetrillionth(10A-12) of a Curie, 0.037 disintegrations per second, or 2.22
disintegrations per minute.
PicoCurie per liter (pCi/L): A unit of radioactivity corresponding to an average of one decay every 27
seconds in a volume of one liter, or 0.037 decays per second a liter of air or water. 1 pCi/L = 37
Becquerels per cubic meter (Bq/m3).
Precision: A measure of mutual agreement among individual measurement made under similar
conditions. Can be expressed in terms of the variance, pooled estimate of variance, range standard
deviation at a particular concentration, relative percent difference, coefficient of variation or other
statistic.
Quality assurance: A complete program designed to produce results which are valid, scientifically
defensible, and of known precision, bias, and accuracy. Includes planning, documentation, and quality
control activities.
Quality control: The system of activities to ensure a quality product, including measurements made to
ensure and monitor data quality. Includes calibrations, duplicate, blank, and spiked measurements,
inter-laboratory comparisons, and audits.
Radon (Rn): A colorless, odorless, naturally occurring, radioactive, inert, gaseous element formed by
radioactive decay of radium (Ra) atoms. The atomic number is 86. Although other isotopes of radon
occur in nature, radon in indoor air is primarily Rn-222.
Radon chamber: An airtight enclosure in which operators can induce and control different levels of
radon gas and radon decay products. Volume is such that samples can be taken without affecting the
levels of either radon or its decay products within the chamber.
Relative percent difference (RPD): A measure of precision, calculated by:
RPD = [(|X1 -X2|)/Xave]x100
where:
XT = concentration observed with the first detector or equipment;
X2 = concentration observed with the second detector, equipment, or absolute value;
|X1 - X2| = absolute value of the difference between X1 and X2; and
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Xave = average concentration = ((X1 + X2) / 2)
The relative percent difference (RPD) and coefficient of variation (COV) provide a measure of precision,
but they are not equal. Below are example duplicate radon results and the corresponding values of
relative percent difference and coefficient of variation:
(pCi/L) (pCi/L) i (%) (%)
8 9 12 8
13 15 14 10
17 20 16 11
26 30 14 10
7.5 10 29 20
Note that the RPD divided by the square root of 2 = COV
See Coefficient of variation (COV).
Relative standard deviation: See Coefficient of variation.
Sensitivity: The ability of a radon or WL measurement method to produce reliable measurements at
low concentrations. This ability is dependent upon the variability of the background signal (counts not
due to radon or WL exposure) which the method records, as well as its efficiency. Methods with stable
background rates and high efficiencies will be able to produce reliable measurements at lower
concentrations than methods with variable background rates and low efficiencies. Sensitivity can be
expressed in terms of the lower limit of detection or minimum detectable activity.
Signal-to-noise ratio: For radon and WL detectors, this term expresses the proportion of the number
of counts due to exposure to radon or WP (signal) to the number of counts due to background (noise).
Measurement methods with high signal- to- noise ratios will produce more counts due to radon or WL
exposure (signal) in proportion to the background counts (noise) than will methods with low signal-to-
noise ratios. A method with a high signal-to-noise ratio is more likely to exhibit good sensitivity, i.e., be
able to produce reliable measurements at low concentrations.
Spiked measurements, or known exposure measurements: Quality control measurements in which
the detector or instrument is exposed to a know concentration in a calibration facility and submitted for
analysis. Used to evaluate accuracy.
Standard deviation (s): A measure of the scatter of several sample values around their average. For a
sample, the standard deviation (s) is the positive square root of the sample variance:
For a finite population, the standard deviation (o) is:
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N
, £(*. -
1 k.1
where |j is the true arithmetic mean of the population and N is the number of values in the population.
The property of the standard deviation that makes it most practically meaningful is that it is in the same
units as the observed variable X. For example, the upper 95% probability limit on differences between
two values is 2.77 times the sample standard deviation.
Standard operating procedure: A written document which details an operation, analysis, or action
whose mechanisms are prescribed thoroughly and which is commonly accepted as the method for
performing certain routine or repetitive tasks.
Statistical control chart, (Shewhart control chart): A graphical chart with statistical control limits and
plotted values (for some applications in chronological order) of some measured parameter for a series
of samples. Use of the charts provides a visual display of the pattern of the data, enabling the early
detection of time trends and shifts in level. For maximum usefulness in control, such charts should be
plotted in a timely manner (i.e., as soon as the data are available).
Statistical control chart limits: The limits on control charts that have been derived by statistical
analysis and are used as criteria for action, or for judging whether a set of data does or does not
indicate lack of control. On a means control chart, the warning level may be two standard deviations
above and below the mean, and the control limit may be three standard deviations above and below the
mean.
Systeme Internationale (SI): The International System of Units as defined by the Conference of
Weights and Measures in 1960.
Test Interference: The altering of test conditions prior to or during the measurement in order to change
the radon or radon decay product concentrations or the altering of the performance of the measurement
equipment.
Time Integrated measurement: A measurement conducted over a specific time period (e.g., from two
days to a year or more) producing results representative of the average value for that period.
Uncertainty: The estimated bounds of the deviation from the mean value, expressed generally as a
percentage of the mean value. Taken ordinarily as the sum of (1) the random errors (errors of
precision) at the 95% confidence level, and (2) the estimated upper bound of the systematic error
(errors of accuracy).
Working level (WL): Any combination of short-lived radon decay products in one liter of air that will
result in the ultimate emission of 1.3 x 105 MeV of potential alpha energy. This number was chosen
because it is approximately the alpha energy released from the decay products in equilibrium with 100
pCi of Ra-222. Exposures are measured in working level months (WLM).
Working level months (WLM): (working level x hours or exposure)/(170 hours/working month). In SI
units, 1 WLM = 6 x 105 Bq-h/M3 (EEC).
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