United States
Environmental Protection
Agency
National Air and Radiation
Environmental Laboratory
540 South Morris Avenue
Montgomery, AL 36115-2601
EPA402-R-95-012
October 1997
Air and Radiation
EPA National Radon
Proficiency Program
Guidance on Quality
Assurance
Internet Address (URL) http://www.epa.gov
Recycled/Recyclable Printed with Vegetable Oil Based Inks on Recycled Paper (20% Postconsumer)
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NATIONAL RADON PROFICIENCY PROGRAM
GUIDANCE ON QUALITY ASSURANCE
EPA402-R-95-012
U.S. Environmental Protection Agency
Office of Radiation and Indoor Air
National Air and Radiation Environmental Laboratory (NAREL)
540 South Morris Avenue
Montgomery, AL 36115-2601
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Contents
National Radon Health Advisory ................................................ vii
Disclaimer [[[ viii
Notice ........... [[[ viii
Preface [[[ ix
Privacy Act Statement ......................................... ................. x
Acknowledgement [[[ xi
1 . Introduction .................. \ ....................................... 1-1
2. Quality Assurance: Definitions and Philosophy .............................. 2-1
3 . Elements of a Quality Assurance Program for Radon and Decay-Product
Measurements ................ . ........ ............................... 3-1
3.1 Quality Management: Commitment, Quality Assurance Planning, and
Quality Objectives ........................ ....................... 3-1
3.2 Quality Assurance Documentation .................................. 3-1
3.3 Measurement System Calibration ................................... 3-2
3.4 Internal Quality Control and Assessment ............................. 3-2
3.5 Corrective Action ......... ....................................... 3-2
3.6 Training [[[ 3-2
4. Responsibilities of RPP Participants ....................................... 4-1
4.1 Analytical Service Providers ....................................... 4-1
4.1.1 Roles [[[ 4-1
4.1.2 Responsibilities ........................................... 4-3
4.2 Residential Service Providers ...................................... 4-4
4.2.1 Roles [[[ 4-4
4.2.2 Responsibilities ........................................... 4-4
5. Quality Management [[[ 5-1
5.1 Management Commitment and Responsibility ......................... 5-1
5.2 Quality Assurance Officer ......................................... 5-2
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Contents (Continued)
Page
6.3 Quality Assurance Audits 6-5
6.4 Quality Assurance Reporting 6-7
7. Calibration 7-1
7.1 The Calibration Facility 7-2
7.2 Development of a Calibration Plan 7-3
7.3 Calibration Records 7-4
8. Quality Control 8-1
8.1 Measurements to Monitor Precision Errors 8-1
8.1.1 Duplicate Measurements for Analytical Service Providers
Distributing Passive Detectors Directly to Homeowners 8-2
8.1.2 Duplicate Measurements for Analytical Organizations Selling
Passive Detectors to Residential Service Providers 8-3
8.1.3 Duplicate Measurements for Residential Service Providers Using
a Passive Detector System 8-4
8.1.4 Duplicate Measurements and Comparison for Analytical Service
Providers Using an Active System 8-5
8.1.5 Duplicate Measurements for Residential Service
Providers Using an Active System 8-5
8.1.6 The Analysis of Duplicate or Comparison Measurements 8-6
8.2 Background Measurements 8-6
8.2.1 Laboratory Background Measurements for Analytical Service
Providers of Passive Devices 8-6
8.2.2 Instrument Background Measurements for Analytical Service
Providers Using Active Instruments 8-7
8.2.3 Instrument Background Measurements for Residential Service
Providers Using Active Instruments 8-9
8.2.4 Field Blanks for Users of Passive Devices 8-9
8.2.5 The Analysis of Background Measurements 8-10
8.3 Measurements Made to Assess Bias 8-11
8.3.1 Measurements Made to Assess the Bias of Passive Detectors 8-11
8.3.2 Measurements Made to Assess Bias for Analytical and Residential
Service Providers Using Active Instruments 8-12
8.4 Routine Instrument Performance Checks 8-13
8.4.1 Routine Instrument Performance Checks for Analytical Service
Providers of Passive Devices 8-14
11
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Contents (Continued)
Page
8.4.2 Routine Instrument Performance Checks for Analytical Service
Providers Operating Active Monitors 8-14
8.4.3 Routine Instrument Performance Checks for Residential Service
Providers Operating Active Monitors 8-15
9. Quality Assurance Plans 9-1
9.1 Signature Page 9-3
9.2 Table of Contents 9-3
9.3 Description of Operations 9-3
9.4 Organization and Responsibilities 9-4
9.5 Quality Assurance Objectives 9-4
9.5.1 Precision Error 9-5
9.5.2 Relative Bias 9-6
9.6 Measurement Procedures 9-7
9.7 Detector Custody 9-7
9.7.1 Field Operations 9-8
9.7.2 Laboratory Operations 9-8
9.8 Calibration Procedures and Frequency (For Analytical Service Providers
Only) 9-9
9.9 Analytical Procedures (For Analytical Service Providers Only) 9-9
9.10 Data Reduction, Validation, and Reporting 9-10
9.11 Internal Quality Control Checks 9-11
9.12 Quality Assurance Audits 9-12
9.13 Preventive Maintenance 9-12
9.14 Procedures to Estimate Data Precision, Relative Bias, and Lower Limit
of Detection 9-13
9.15 Corrective Action 9-13
9.16 Quality Assurance Reports to Management 9-14
Appendix A: The Analysis and Interpretation of Quality Control Measurements A-l
A.I Routine Instrument Performance Checks A-2
A.2 Background Measurements A-3
A.2.1 Laboratory Background Measurements for Analytical Service
Providers A-3
A.2.2 Field Background Measurements for Analytical and Residential
Service Providers A-3
A.3 Evaluation of Quality Control Data A-4
A.3.1 Means Control Chart for Repeated Measurements of Background
and Routine Instrument Performance Checks A-4
iii
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Contents (Continued)
Page
A.3.2 Means Control Chart to Evaluate Relative Bias from the Results
of Known Exposure Measurements A-9
A.4 Estimating Precision A-10
A.4.1 Control Charts for Monitoring Precision Error A-17
A.4.2 Interpretation of Precision Control Charts A-24
A.5 Minimum Detectable Levels A-25
A.5.1 Lower Limit of Detection (LLD) A-25
A.5.2 Minimum Significant Measured Activity (MSMA) A-29
A.5.3 Use of LLD and MSMA A-30
A.5.4 Reporting Low Values A-31
Appendix B: Information to be Included in a Measurement Report B-l
Appendix C: Acronyms C-l
Glossary and Index G-l
References R-l
IV
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List of Exhibits
Exhibit Page
4-1 Responsibilities of Analytical and Residential Service Providers 4-2
9-1 Required Elements of a Quality Assurance Plan for Analytical and
Residential Service Providers 9-2
A-l Means Control Chart for Background or Check Source Results A-6
A-la Example Means Control .Chart for Background A-7
A-2 Means Control Chart for Spiked Results of Passive Methods A-l 1
A-2a Example Means Control Chart for Relative Bias Based Upon Results of Spikes ... A-12
A-3 Means Control Chart for Crosschecks Using Active Methods A-14
A-4 Range (Difference) Between Two Measurements with a 14% RPD A-18
A-5 Control Chart for Duplicates Using the Range Ratio Statistic A-20
A-5a Example Range Ratio Control Chart for Tracking Precision A-21
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NATIONAL RADON HEALTH ADVISORY
(September 1988)
Indoor radon gas is a national health problem. Radon causes thousands of deaths each
year. Millions of homes have elevated radon levels. Most homes should be tested for radon.
When elevated levels are confirmed, the problem should be corrected.
U.S. Public Health Service
U.S. Environmental Protection Agency
VII
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DISCLAIMER
This Guidance on Quality Assurance was prepared by the U.S. Environmental Protection
Agency (EPA). The purpose of this document is to provide applicants to and participants in the
Radon Proficiency Program (RPP) with the necessary information about the Program's policies,
requirements, and procedures regarding quality assurance. The mention of laboratories,
companies, individuals, trade names, or commercial products herein should not be interpreted as
an endorsement or recommendation.
Neither the EPA nor other persons assisting in the preparation or revision of this
Guidance, nor any person acting on the behalf of EPA, (a) makes any warranty or representation,
expressed or implied, with respect to the information contained in the document; or (b) assumes
any liability with respect to the use of, or for damages resulting from the use of, any information,
method, or process disclosed in this document or any other statutory or common law theory
governing liability.
NOTICE
A listing in the RPP does not confer Federal certification, licensing, or accreditation, and
participants should not represent themselves as having such credentials.
The EPA reserves the right to release all information submitted by participants in the RPP
or generated as a result of participation. This includes information and numerical performance
data created as a result of the device performance tests conducted at EPA laboratories, an
individual's measurement or mitigation exam results, and information relevant to a participant's
history with the Program.
vin
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PREFACE
This Guidance is intended for use by participants in and applicants to the U.S.
Environmental Protection Agency's (EPA) Radon Proficiency Program (RPP). The document
provides guidance in the areas of quality assurance (QA) and quality control (QC) for applicants
to and participants in the RPP.
To obtain an Application or other information about the Program, contact:
Radon Proficiency Program Information Service (RIS) at TEL: (800) 962-4684 or
(334) 272-2797, FAX: (334) 260-9051, or e-mail: maill0554@pop.net
or write: RPP Quality Assurance Coordinator (RQAC)
c/o Sanford Cohen & Associates, Inc. (SC&A)
14181-85 Parkway
Montgomery, AL 36106
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PRIVACY ACT STATEMENT
The Privacy Act dictates: 1) the types of information the Federal government can collect
from individuals, 2) how this information may be used, and 3) to whom this information may be
disclosed. The Act also requires that individuals subject to information requests be informed of
the following:
The information is being collected under the authority of Section 305 of Title III (Indoor
Radon Abatement) of the Toxic Substance Control Act, 15 U.S.C. 2665. Collecting social
security numbers, which are used solely for identification purposes, is also authorized by
Executive Order 9397. The Indoor Radon Abatement provision of Title III directs the
Environmental Protection Agency (EPA or Agency) to develop a program to evaluate the
proficiency of radon mitigation and measurement service providers and provide information to
the public on proficient service providers. Information obtained through the application form,
testing, training, and other aspects of this Program will be used in the development and operation
of this Program.
State and local governments are permitted access to an EPA on-line Proficiency Listing
containing the names of individuals and organizations who have met the requirements of the
Program, their addresses, and telephone numbers. This listing will be made available to the
public upon request. EPA contractors and subcontractors who are engaged to assist the Agency
in the performance of activities under this Program will maintain all information collected under
this Program. Contractors and subcontractors will be required to maintain such information in
confidence. All or part of the information collected under this Program may be disclosed to: 1)
a member of Congress at their request, 2) appropriate law enforcement authorities if the
information indicates a violation of law in connection with litigation involving the government
in which the information is relevant, and 3) the appropriate Federal agency in connection with
records management inspections.
Participation in this Program and furnishing requested information is voluntary, but
failure to provide the information may preclude your participation in the Program and the listing
of your name in the Proficiency Listing.
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ACKNOWLEDGEMENT
This document was prepared for the U.S. Environmental Protection Agency's National
Radon Proficiency Program Manager, by Melinda Ronca-Battista of Sanford Cohen &
Associates, under Contract 68D20185. Many persons provided useful suggestions and
generously provided thorough reviews and comments. In particular, the members of the
American Association of Radon Scientists and Technologists Technical Committee provided
extensive comments in their effort to ensure that this document provides clear, practical, and
state-of-the-art guidance on quality assurance in radon measurements.
XI
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RPP QA Guidance
EPA402-R-95-012
Date: 10/22/97
1. Introduction
This document provides guidance in the areas of quality assurance (QA) and quality control (QC)
for participants in the U.S. Environmental Protection Agency's (EPA) National Radon
Proficiency Program (RPP) (U.S. EPA 1995a). The QA practices described in this repori are
necessary and expected components of high quality radon and radon decay product
measurements. The specific QC measurements, recordkeeping, and analysis methods outlined
here are consistent with routine procedures for radiation measurements and standard practices by
Federal laboratories and contractors.
This report contains recommendations for a variety of organizations involved in the radon
measurement industry, including organizations who do not analyze detectors, but who deploy
devices and provide clients with measurement results (see Section 4.2). The report is designed to
provide a framework of QA practices that can be modified, and added to, according to the
specific needs of the measurement program.
This document first presents a general introduction to quality terminology, including quality
management and quality systems, and introduces current national and international guidance on
these topics. Section 2 reviews the definitions of QA and QC specifically as they relate to radon
measurements, and presents some important considerations regarding quality management.
Basic elements of a quality assurance program are reviewed in Section 3. Section 4 defines the
QA responsibilities of analytical and residential service organizations. Quality management,
including the responsibilities of management regarding quality, the role of a quality assurance
officer, and training are discussed in Section 5. Section 6 describes quality assurance
documentation, reporting, and chain-of-custody, including standard operating procedures and
audits. Section 7 provides guidance for performing calibrations. Guidelines and terminology for
specific quality-control measurements are described in Section 8. The concluding chapter
(Section 9) describes recommended components of a quality assurance plan (QAP). Appendix A
provides methods for analyzing QC measurements, including preparation of control charts and
assessing lower limits of detection. Appendix B reviews information recommended by EPA for
inclusion in a measurement report, and Appendix C provides a list of acronyms. Finally, a
Glossary with an index defines terms used in this report.
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These guidelines are recommendations for the radon measurement industry as a whole. They are
specifically intended to guide RPP participants in meeting their QAP requirements. EPA
recognizes that this guidance will therefore serve as de facto required practices for anyone
operating a radon measurement business in the U.S. Because of this, and because these
guidelines are meant to serve the public and the measurement industry, EPA is interested in
receiving constructive comments about this guidance. If you have comments, please address
them to:
Mr. Sam Poppell
Program Manager
National Radon Proficiency Program
National Air and Radiation Environmental Laboratory
Office of Radiation and Indoor Air
U.S. Environmental Protection Agency
540 S. Morris Avenue
Montgomery, AL 36115-2601
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2. Quality Assurance: Definitions and Philosophy
The International Organization for Standardization (ISO) defines a quality system as the
organized structure, responsibilities, procedures, processes, and resources needed for
implementing quality management (ANSI/ASQC 1994). Quality management includes
defining roles and responsibilities, planning the level of quality provided to the customer, clearly
defining objectives for quality, and defining accountability and reporting. It is implemented at
the management level, and focuses not only on systems, policies, criteria, documentation, and
procedures, but also on program structure, which includes the delegation of authority and
responsibility needed to ensure adequate quality of the product.
Quality Assurance (QA) is defined by the American Society of Testing and Materials (ASTM)
as all activities required to provide the evidence needed to establish confidence that data
provided are of the required precision and accuracy. The U.S. EPA (U.S. EPA 1995b) similarly
defines QA as "an integrated system or program of activities involving planning, quality control,
quality assessment, reporting and quality improvement to ensure that a product or service meets
defined standards of quality."
ASTM defines Quality Control as the process through which an organization measures its
performance, compares its performance with standards, and acts on any differences (ASTM
1988). In other words, the intent of QA/QC is to maintain a good quality-measurement program
and to ascertain and document the quality. Quality control consists of measurements and
associated activities needed to control and assess measurement-program quality, as measured by
estimated precision, relative bias, the lower limit of detection (as well as other factors, such as
the rates of data entry errors) on an ongoing basis and to revise procedures to improve quality if
necessary.
QA/QC must be an integral part of any measurement program. The results of measurements that
are not associated with a program to ensure and document their reliability are useless, because
the validity of each measurement rests upon the QA program. There are many experienced and
knowledgeable measurement experts who perform fine work, but who do not have the time or
support from management to implement and document QA/QC practices. They may produce
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accurate results, or they may have incorporated an erroneous calibration factor and not know it.
In either case, the lack of adequate documentation makes it impossible for their measurement
results to be as incontrovertible as they need to be.
There are benefits of conducting a QA program other than substantiating the adequacy of each
measurement result. First, making some of the types of measurements that are described in this
document will add greatly to an operator's understanding of the methods employed. This will
enable organizations to improve their techniques, or to justify results that they would not
otherwise understand. For example, it is crucial to know how low a concentration can be reliably
measured and the variability that is expected at low concentrations. Second, a QA/QC program
includes procedures for monitoring the performance of equipment, supplies, and operators.
Third, a QA program is often specified as a contractual requirement, and records of a QA/QC
program may be critical in the event of a legal dispute.
A credible measurement program cannot exist without QA activities. Measurement companies
are providing results to clients that may become critical to the sale of property. If the
measurement result is questioned, the tester may be liable if QA records do not provide adequate
documentation of conformance to recommended practices. Although the costs may be
significant and ultimately borne by clients, the substantiated validity of the result is only possible
in a program that implements appropriate QA practices.
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3. Elements of a Quality Assurance Program for Radon and
Decay-Product Measurements
This section briefly describes elements of a program for planning, measuring, and ensuring the
quality of radon and/or decay-product measurements. Each of these elements is discussed in
great detail elsewhere; this section introduces the activities that should be included in a quality
assurance program and that comprise the quality system. The necessary components of a Quality
Assurance Plan are described in Section 9 and are more specific than the five broad categories of
activities described in this section.
3.1 QUALITY MANAGEMENT: COMMITMENT, QUALITY ASSURANCE
PLANNING, AND QUALITY OBJECTIVES
No endeavor will be completely successful without the interest, involvement, and commitment of
management. The role and responsibilities of management regarding QA, including QA
planning and methods of reporting and oversight, should be documented. Small organizations
with limited personnel and resources may have an advantage regarding QA management,
because one person may be responsible for all company policies. In this case, the commitment of
management ensures the commitment of the organization. Quality-assurance management is
discussed in Section 5.
3.2 QUALITY ASSURANCE DOCUMENTATION
There are many forms of documentation that are important in planning and implementing
quality-control procedures. Most of these can be referenced in the QA Plan (QAP), which is a
document that includes specifics on those procedures (chain-of-custody, quality control
measurements, etc.) that are used to ensure that the planned quality is achieved. General QA
documentation is discussed in Section 6, and QA Plans are discussed in Section 9.
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3.3 MEASUREMENT SYSTEM CALIBRATION
Measurement equipment requires initial and periodic calibrations. General guidelines for
calibrations are described in Section 7.
3.4 INTERNAL QUALITY CONTROL AND ASSESSMENT
There are many quality-control measurements that are performed to assess the quality of
procured material and equipment, the continued performance of instruments and procedures,
estimated errors of imprecision and bias, and contributions of field and laboratory background.
Internal quality-control measurements are described in Section 8. Appendix A discusses the
analysis of quality-control measurements.
3.5 CORRECTIVE ACTION
Corrective action may be necessary as a result of unsatisfactory quality control results, client
dissatisfaction, audit reports, or for other reasons. The responsibility for taking action and for
verifying that the action was successful in correcting the problem should be documented for
various personnel and categories of activities. Corrective action for specific occurrences (e.g.,
quality control results outside of specified numeric bounds, more than a specified rate of data
input errors, etc.) should also be documented, along with the timeframe for action and the person
responsible. Corrective action procedures are under the oversight of the QA Officer. Control
charts for quality control are described in Appendix A.
3.6 TRAINING
Training is an important quality issue. The responsibilities, goals, and schedules for training,
both on general procedures and on specific quality-assurance activities, should be clear and
documented. Training issues are generally addressed in Section 5.3.
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4. Responsibilities of RPP Participants
As defined in the EPA Radon Proficiency Program Handbook (U.S. EPA 1995a), an analytical
radon measurement service provider performs the analysis or reading of the radon measurement
devices. A residential service provider is an individual who offers radon measurement services,
but relies on an analytical organization for analysis or reading of the measurement device.
Services provided by a residential service provider may include consulting with the homeowner
or realtor, packaging, placing and retrieving measurement devices, and preparing and issuing
measurement reports (using the values provided by the analytical organization). Over-the-
counter retailers of measurement devices are not considered analytical or residential service
providers, because they merely make the devices available and provide no services to the
consumer.
It is possible for an organization to function as an analytical organization and employ individuals
listed in the RPP to provide residential measurement services. The roles and responsibilities of
analytical and residential service providers in terms of quality assurance are described in this
section and outlined in Exhibit 4-1. The requirements in terms of developing and implementing
a QA Plan are described hi Section 9.
4.1 ANALYTICAL SERVICE PROVIDERS
4.1.1 Roles
Analytical service providers analyze the detectors or read the monitors and produce the final
result that is reported to clients. Any organization or individual that obtains the final results from
continuous radon (CR) or working level monitors (CW), performs grab measurements made with
the pump-collapsible bag (GB) method, the grab activated charcoal (GC) method, the
scintillation cell (GS) method, or the grab working level (GW) method is classified as an
analytical service provider. An organization or individual that uses an electret reader to obtain
results from electret ion chambers (EL or ES) is an analytical service provider. Similarly, the
analysis of detectors such as alpha track detectors (AT), activated charcoal adsorbers (AC),
charcoal liquid scintillation devices (LS), pump-collapsible bag devices (PB), radon progeny
4-1
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Exhibit 4-1
Responsibilities of Analytical and Residential Service Providers
Responsibility
Preparing, updating, and implementing a QA Plan (see Section 9).
Obtaining copies of the analytical organization's QA Plan, including
schedules of calibration, and ensuring their adequacy (see Sections 7
and 9).
Calibrating analysis equipment as recommended by the manufacturer
or at least once every 12 months, as described in EPA's Indoor Radon
and Radon Decay Product Measurement Device Protocols (U.S. EPA
1992a).
Conducting laboratory/field background measurements at a rate in
accordance with the recommendations in Section 8.2; recording the
results in control charts and other documentation; and using the
results to calculate (for analytical service providers) or check against
(for residential service providers) the lower limit of detection.
Employing a QA Officer who is responsible for conducting audits, .
monitoring QC data, the oversight and accountability for corrective
action, and reporting to management (see Section S.2).
Conducting known exposure or cross check measurements at a rate in
accordance with the recommendations in Section 8.3.
Conducting side-by-side duplicate or comparison measurements at a
rate in accordance with the recommendations in Section 8.1.
Making available the results of laboratory background measurements,
the lower limit of detection, and estimates of precision (see Appendix
A) to those service organizations using the analytical service
provider.
Conducting routine instrument performance checks, including
battery, electronics, pump flow rates, and the stability of the system
using a check source or cell, as the instrument configuration allows
(See Section 8.4).
Maintaining a documented system to track measurement devices
(chain-of-custody), locations, dates, clients, methods/laboratories, and
results (see Section 6).
Conforming to EPA guidelines for conducting measurements,
reporting measurement results, and providing information to clients
(Appendix B).
Analytical
Service
Provider
X
X
X
X
X
X
X
X
X
X
Residential
Service
Provider
X
X
X
(Laboratory background
measurements and
calculation of LLD are not
expected)
X
X
X
X
(for residential service
providers using active
instruments, as specified
by the manufacturer and
analytical organization)
X
X
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integrated sampling units (RP), and unfiltered track detectors (UT) classify an organization or
individual as an analytical service provider. The RPP listings are device-specific (U.S. EPA
1995a).
4.1.2 Responsibilities
Analytical service providers are responsible for the following activities:
Preparing, updating, and implementing a QA Plan that adheres to the guidelines
described in Section 9 of this report.
Ensuring that all equipment is calibrated and re-calibrated according to the schedules
described for that method in this report, by the manufacturer, or in EPA's Indoor Radon
and Radon Decay Product Measurement Device Protocols (U.S. EPA 1992a); see
Section 7.
Conducting background measurements (laboratory and field, as appropriate; see Section
8.2), recording the results in control charts and other relevant documentation, and using
the results to calculate the lower limit of detection.
Employing a QA Officer who is organizationally independent of the analysis and
distribution processes. The responsibilities of a QA Officer are described in Section 5.2.
Conducting routine and on-going measurements to assess bias according to the EPA
recommendations (see Section 8.3), and recording and analyzing the results (see
Appendix A).
Conducting routine and on-going measurements to track precision error (see Section 8.1),
recording the results in control charts and other documentation (see Appendix A), and
using the results to estimate precision.
Making available the results of background measurements, the lower limit of detection,
and estimates of precision error (see Appendix A) to residential service providers using
the analytical organization regularly.
Conducting routine instrument performance checks (see Section 8.4).
Maintaining a documented system to track measurement devices (chain-of-custody),
locations, dates, clients, methods/laboratories, and results, as described in Section 6.
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Conforming to EPA guidelines for conducting measurements, reporting measurement
results, and providing information to clients (see Appendix B and U.S. EPA 1993).
4.2 RESIDENTIAL SERVICE PROVIDERS
4.2.1 Roles
Residential service providers distribute measurement devices to clients and report results, but do
not analyze the detectors or generate the result that is reported to the client. These individuals
may, however, have considerable impact on the measurement process and result. Residential
service providers must exercise skill and judgement in assessing measurement conditions,
deploying and retrieving devices, and communicating with clients.
4.2.2 Responsibilities
The QA-related responsibilities of residential service providers are to ensure that their activities
do not contribute to any degradation of the measurement quality (such as by excessive storage
time or storage in unsuitable environments, improper placement, errors in reporting or
recordkeeping, or other factors), and to understand and monitor the performance of their
measurement system, which includes their operation as well as the operation of the analysis
laboratory that they are using. There should be clear and open communication between
residential service providers and the analysis laboratory they use. Specific requirements of
residential service providers include:
Preparing, updating, and implementing a QA Plan according to the guidelines described
in Section 9 of this report.
Reviewing the analytical organization's QA Plan.
Conducting field background measurements (as appropriate; see Section 8.2) and
recording the results in control charts and other relevant documentation.
Employing a QA Officer (see Section 5.2).
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Conducting routine and on-going measurements to assess bias according to the EPA
recommendations (see Section 8.3), and recording and analyzing the results (see
Appendix A).
Conducting routine and on-going measurements to estimate precision error, as feasible,
(see Section 8.1) and recording the results in control charts and other documentation (see
Appendix A).
Conducting routine instrument performance checks according to directions from the
analytical service provider (see Section 8.4).
Maintaining a documented system to track measurement devices (chain-of-custody),
locations, dates, clients, methods/laboratories, and results, as described in Section 5.
Conforming to EPA guidelines for conducting measurements, reporting measurement
results, and providing information to clients (see Appendix B and U.S. EPA 1993).
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5. Quality Management
5.1 MANAGEMENT COMMITMENT AND RESPONSIBILITY
A primary concern of any organization must be the quality of its products and services. In order
to meet its objectives, the organization should function so that the technical, administrative, and
operational factors affecting the quality of its products and services is known and is under
control. An effective quality-management system should be designed to satisfy customer needs
and expectations, while serving to protect the organization's interests (ANSI/ASQC 1994a).
Quality management is just as important in small organizations as in large ones. Small
organizations may, however, find that communicating and implementing changes in policy-
related procedures to be simpler than in large organizations because fewer people are involved.
In addition, small organizations are often comprised of highly motivated people who are
committed to the success of the company. Since small organizations generally consist of people
with multiple responsibilities, they are likely designate their single technical expert as the QA
Officer. In these cases, it may be helpful to obtain the services of an outside expert to serve as an
auditor for several hours each quarter, in order to ensure an outside review of procedures.
The responsibility for and commitment to quality in delivered services belongs to the highest
level of management. If the organization's management does not provide an environment which
supports a QA program and in which concerns and suggestions for improving quality can be
raised, the quality of the measurements will suffer. Management should foster a "no-fault"
attitude to encourage the identification of quality issues and problems (U.S. DOE 1991). The
terms continuous improvement and quality improvement refer to a structure and environment in
which improvement is considered part of the daily work and resources are provided for
eliminating problems at their source (NIST 1995). The quality policy of the organization should
be a statement that is realistic, implemented, and documented in the QA Plan or other written
materials.
QA management is that aspect of the overall management that determines and implements
quality policy. The direct and ultimate responsibility for assuring data quality rests with the
laboratory or field managers. These people have the primary responsibility for developing QA
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policies, procedures, and criteria, and delegating QA authority and responsibility. The term
"management by fact" refers to the use of quality control data, market data, and other
information and their analysis as input to the organization's assessment and improvement.
Accountability is an important part of QA management. Each person in the organization needs
to understand the organizational framework in order to understand, and be accountable for,
his/her own QA responsibilities.
The term "quality system" refers to the organization's structure and function relating to
managing, overseeing, and improving quality. The system includes documentation (quality
assurance plans, procedures, logs and accountability for their maintenance and review) and
procedures for audits and reviews for quality assurance and quality control. The national
standard for quality systems (ANSI/ASQC 1994a) describes elements of quality management.
These include:
Management and organization.
Quality system and description.
Personnel qualification(s) and training.
Procurement of items and services.
Documents and records.
Computer hardware and software.
Planning.
Implementation of work processes.
Assessment and response.
Quality improvement.
These elements are essentially equivalent to the requirements found in other standards, including
the ISO 9000 series (ANSI/ASQC 1994a) and ASME NQA-1 (ASME 1989). These elements of
quality management may be described in the QA Plan or in a separate quality-management plan.
5.2 QUALITY ASSURANCE OFFICER
The establishment of a QA program requires a QA Officer within the organization to supervise
and, as appropriate, carry out the monitoring, recordkeeping, statistical techniques, and other
functions required to maintain high quality data. This person may have these duties as a sole
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responsibility or, in smaller organizations, may have other responsibilities. The QA Officer
should be assimilated into the organization, reporting to the lowest level at which he/she can be
effective and be unbiased in objectively serving the needs of the organization. Even
organizations consisting of one or two people need to designate the responsibilities of a QA
Officer to someone involved in the day-to-day operations. In addition, however, an outside
expert can be used to review statistical methods, procedures, training, or other QA issues.
The QA Officer assists management in interpreting and developing the QA policy for the
organization. The QA Officer also provides technical support and review, and approves QA
products for the top manager. The QA Officer should, at a minimum, be responsible for:
Developing and ensuring the implementation of a QA program, including
procedures for chain-of-custody, statistical analyses, and data verification, among
others, which will help the organization to meet the authorized standards of
quality at minimum cost.
Advising and assisting management in the installation, staffing, and supervision
of a QA program.
Monitoring QA/QC activities of the laboratory to determine conformance with
authorized policies and procedures and with recognized industry practices.
Making appropriate recommendations for correction and improvement of QA/QC
activities, as necessary.
Assisting in the development of specifications and acceptance criteria for
purchased items and materials.
Seeking out and evaluating new ideas and current developments in the field of
QA, and recommending means for their application wherever advisable.
Advising management in reviewing technology, methods, and equipment with
respect to quality aspects.
In addition, the organization's QA Officer needs to have sufficient authority and responsibility to
exercise whatever oversight is necessary to assure that:
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All data-collection activities are covered by appropriate QA planning
documentation (such as in the QA Plan, as discussed in Section 9).
All routinely used procedures that impact data quality are documented in standard
operating procedures (SOPs) that are complete and have been reviewed and
approved by both management and the staff responsible for implementing those
procedures (see Section 6.1.1).
Audits/reviews are done to assure adherence to approved QAPs and to identify
deficiencies in QA/QC systems.
Adequate follow-through actions are implemented in response to audit/review
findings.
All laboratory, field, or office personnel involved in data collection have access to
any training or QA information needed to be knowledgeable in QA requirements,
protocols, and technology.
In implementing these oversight responsibilities, the QA Officer should have a reporting
relationship with the top managers of the organization to assure that the appropriate laboratory or
field managers are aware of their responsibilities for prescribing any needed corrective actions.
For example, the QA Officer should be included in regular staff meetings or conference calls,
and receive all organization memoranda and bulletins regarding staffing, training, equipment,
recordkeeping, and changes in business practice and procedures.
5.3 QUALITY ASSURANCE TRAINING
All personnel involved in any function affecting data quality (detector custody, sample analysis,
data reduction, and QA) should receive training in their appointed jobs to contribute to the
reporting of complete and high quality data. The expectations and qualifications for each
position should be documented (e.g., as in a job description). The QA Officer is responsible for
periodic reviews of the requirements for training.
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6. Quality Assurance Documentation and Reporting
6.1 DOCUMENTATION
6.1.1 Standard Operating Procedures
Organizations should assure that all work affecting quality of results (such as handling, storing,
and analyzing devices) be prescribed in clear and complete written instructions. These work
instructions, known as Standard Operating Procedures (SOPs), provide the criteria for
performing the work, particularly the analytical and testing functions, and prescribe the chain-of-
custody procedures that are necessary to assure that analytical results can be used as evidence.
The preparation and maintenance of, and compliance with, SOPs should be monitored by the
organization's QA Officer. A schedule and responsibility for reviewing and updating SOPs
should be documented as one of the QA Officer's responsibilities.
Anyone performing radon measurements should have a written, device-specific SOP in place for
each radon measurement system used. 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. In addition, both analytical and residential service
providers need to document their procedures for validating data (including client information)
and preparing reports.
6.1.2 Record keeping and Chain-of-Custody
There are sources of error other than errors inherent in the measurement process. Inadequate
recordkeeping can lead to errors such as transposing results from different locations, or
misplacing results or detectors. There are computer spreadsheets and other programs available
that can be adapted for many uses and large quantities of data. When planning procedures for
data entry, the following factors are important. First, ensure that the proper forms and labels are
available and can be easily understood by the homeowner, technician, data entry operator, or
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whoever must use and read them. Second, anyone recording data must receive adequate
instructions that are documented and updated in the SOP for easy reference. Third, the data-
recording process should be monitored for errors. Many organizations use a double-entry
method, wherein each field is entered by two different operators (or entered at two different
times by the same operator) and checked automatically by the computer for differences. If this is
not feasible, organizations should hand check at least a portion of the day's entries for errors. In
general, less involvement of human operators ensures fewer opportunities for error. A very
useful tool in large operations is the bar-code system.
Chain-of-custody procedures to track detectors and placement/analysis dates should be
established and documented in the SOP. These may be as simple as labeling large boxes or
shelves for unexposed detectors ready to be used, detectors ready to be shipped/analyzed, and
detector custody sign in/out sheets. Identical, printed, peel-off sample identification numbers
placed on detectors, information sheets, result letters, and shipping containers can help reduce
mix-ups. For detector types that need to be analyzed immediately following exposure, a daily
check that all detectors received have been shipped/analyzed may be appropriate.
Logbooks are useful tools for maintaining records of QA practices and QC measurements,
including calibration results, background measurements results, and any changes in operators,
materials, or procedures. Logbooks should be bound, and records entered in pen. Every entry
should include the name of the person making the entry and the date. Any relevant printouts or
plots should be photocopied and pasted into the logbook. Such a log can serve as an invaluable
record, with all relevant information in one place.
The following items should be included in a separate QA logbook for each active instrument or
passive method:
Equipment calibration records (for analytical service providers), including:
The date of the calibration and the date the calibration expires, as
appropriate.
The facility where the calibration was performed.
The procedures used (an SOP or calibration report can be referenced).
Results.
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Changes in calibration factors implemented.
Laboratory background measurements (for analytical service providers),
including:
The date of the background measurement.
The location and type of measurement (e.g., aged air or nitrogen).
The procedures used (an SOP can be referenced).
Results.
Changes in LLD or background values.
Field background measurements (for both analytical and residential service
providers), including:
The date and location of the field background measurement.
The procedures used (appropriate documentation can be referenced).
Results.
Changes implemented because of the results.
Results of all QC measurements (for both analytical and residential service
providers), including:
Results of comparison measurements (for users of active instruments).
Results of duplicate measurements.
Results of spiked measurements.
Routine instrument performance checks (for analytical and some residential
service providers using active devices), including the dates and results of
Battery checks/replacement.
Check source/cell measurements.
Pump flow-rate measurements.
Self-diagnostic checks.
Control charts containing the results of any of these QC measurements may be kept in the QA
notebook or posted for easy reference.
Each organization should derive its own system for tracking measurements. Residential service
providers may use a logbook or a system of duplicate copies of data sheets to record the
information gathered and generated for each measurement. Information stored for each
measurement should include:
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A copy of the final report, including the measurement results, and the statement
(or reference to the statement in the SOP) outlining any recommendations
concerning retesting or mitigation provided to the client.
The address of the building and room numbers to identify the location of the
measurement. It may be useful to diagram the test area, noting the exact location
of the detector.
Exact start and stop dates and times of the measurement duration.
A description of the device used, including its manufacturer, model or type, and
identification (serial) number.
A description of the condition of any permanent vents, such as crawl-space vents
or combustion-air supply to combustive appliances.
The name and RPP identification number (U.S. EPA 1995a) of the providers used
to analyze devices.
The name and RPP 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.
A description of any non-interference controls used and copies of signed non-
interference agreements.
A record of any QC measures associated with the test, such as results of
simultaneous measurements.
Regardless of the system used, SOPs for tracking the detectors (part of detector custody) should
be written, adhered to, and revised as appropriate. All personnel should be trained and should
understand the importance of maintaining proper correlation of information with the detector and
measurement result.
Computer files should be copied regularly onto backup disks to ensure against data loss.
Retention time and location for different types of records should be specified in an SOP.
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6.2 DATA VALIDATION
Each step in the process between obtaining the original counts, tracks, or voltage losses and the
final results reported to clients should receive some data validation. In general, at least several
percent of each phase of the data should be checked. Handchecking is sufficient if it is done
conscientiously (e.g., calculations are performed again on a hand-calculator, information is
compared field by field, and these procedures are documented). There must be a record of which
files were checked, by whom, the date, and how any errors found were resolved. Dates and
initials in the records may be sufficient if the procedure used is documented.
6.3 QUALITY ASSURANCE AUDITS
States may audit companies as part of State certification. Clients such as school districts, Federal
agencies, or private companies may conduct audits of the measurement organizations they are
using or are considering using. These audits may be formally specified in a contract, or consist
of less formal on-site visits or written requests for QC data and procedures. In any case, all
logbooks and QA records should be easily available when not actually in use in the field. Both
residential and analytical service providers should maintain records appropriate for their
activities in the event of an audit or a request for information.
The focus of QA audits should be on the following topics:
The existence and adequacy of a written and signed QA Plan (see Section 9) for
all measurement methods and operations.
The performance of measurements to assess precision, their results, and how
frequently they are performed.
The performance of measurements to assess bias, their results, and how frequently
they are performed.
The performance of background measurements, their results, and how frequently
they are performed.
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The proper recording and analysis of QC measurements, including the use of
control charts.
The operating conditions of all equipment.
The existence of SOPs (see Section 6.1.1) for each measurement method and
operation.
The records and the person responsible for preventive maintenance on all
equipment.
The existence of a detector tracking (custody) procedure.
The existence of adequate records for tracking measurement location, condition,
operator, etc.
An adequate system for data validation, including records, procedures, and
corrective action in the case of discovery of errors.
The conditions under which detectors and equipment are stored (e.g., low
humidity, radon concentration).
Documentation of the specific serial numbers of the equipment or counters used in
each analysis.
The backups of all computer files.
Corrective action procedures and how they are implemented.
The complete records of any changes in materials or technicians.
For analytical organizations, audits should be conducted on the topics described above, as well as
on:
Appropriate client reporting, including use of the LLD as calculated from
laboratory background measurements (which may change over time), appropriate
use of significant figures, and furnishing clients with relevant information about
what their measurement results mean (see recommended information in Appendix
B).
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The calibration of the equipment and whether it is done in conformance with the
QA Plan.
The records and results from performance evaluations (Federal, State or industry).
Internal audits may be conducted by the QA Officer or his/her designee. Audits should be
performed by someone not having direct authority or responsibilities in the areas being audited
(U.S. NRC 1991). Checklists prepared by the QA Officer may be helpful during the audit.
6.4 QUALITY ASSURANCE REPORTING
There should be periodic reports to management on the results of QC measurements, reviewing
any problems that were encountered and their solutions, or proposed solutions. These reports
should be included in the QA logbooks and be available during audits. At a minimum, there
should be one report after every six months of operation.
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7. Calibration
The term calibration refers to the process of determining the response of an instrument (or
measurement system) to a series of known values over the range of the instrument (or
measurement system). This process results in conversion factors relating instrument or system
response (in counts, voltage loss, or track density per unit of time) to radon or decay product
concentrations. Before utilizing any given calibration facility, RPP participants and others
should consider the facility's capability to provide the calibration services being sought. The
following provides guidance for designing a calibration program and selecting a facility.
Calibration, as referred to in this report, means that the response of the instrument or system can
be related, or traced, to a radon or decay-product concentration that was derived from a certified
National Institute of Standards and Technology (NIST) radium-226 (Ra-226) standard. NIST
produces Standard Reference Material (SRM) Ra-226 solutions that may be used to produce
working laboratory standards for radon-222. There is no SRM for radon. General procedures for
producing these working standards are described by the NCRP (NCRP 1988), EPA, and NIST
(NIST 1990). These working standards of radon are usually constructed by bubbling nitrogen or
another gas through a vial containing certified radium solution (solutions of Ra-226 in weak
acid). By strict definition, any vial that is opened is no longer a NIST standard. With careful
handling and measurements, however, a vial can be opened and transferred to another vessel
while retaining its quality. If the empty vial and glassware are checked for residual radium, a
laboratory standard that is "NIST-traceable" can be produced.
The U.S. Department of Energy Environmental Measurements Laboratory conducts an
international laboratory intercomparison program (U.S. DOE 1985; U.S. DOE 1994). In this
intercomparison program, radon concentrations are measured in a controlled environment (radon
calibration chamber) using equipment that has been calibrated by exposure to concentrations
produced from a NIST Ra-226 standard using a quantitative gas-transfer system. Several
commercial calibration facilities in the U.S. participate in this program, and with careful
recordkeeping have established traceability to this international de facto standard.
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Calibration is different from routine measurements made to assess relative bias or check the
calibration factor of the system; these are called spiked or known exposure measurements (see
Section 8.3).
The term measurement-assurance program refers to activities designed to relate a
measurement to national standards, and to establish the uncertainty of values reported by the
measurement. Useful information for establishing or evaluating a measurement assurance
program can be found elsewhere (NBS 1985, NCRP 1985, ANSI/ASQC 1994a, ANSI 1994b).
Definitions and nomenclature can be found in American National Standards Institute (ANSI)
documents (ANSI 1978, ANSI/ASQC 1987, ANSI 1994b, ASTM 1988, ISO 1990).
Annual calibrations are required of RPP participants (U.S. EPA 1992a), but the measurement
methods and the magnitude and type of the measurement program, as well as whether equipment
or procedures have changed since the last calibration govern how detailed the calibration needs
to be. For example, a radical change in instrument configuration may necessitate calibrating to at
least three concentrations. If equipment and procedures remain unchanged since the previous
calibration, however, and the instrument's response is well-established, a single-point calibration
plus background measurements may be sufficient.
The range of environmental conditions (temperature, humidity, changing concentrations and
conditions, air flow) under which measurements are routinely or expected to be performed
should be considered when forming a plan for calibration. Environmental conditions that may
effect the measurement result should be measured, and be maintained as stable as possible during
the calibration. The QA Officer and anyone else familiar with the limitations or peculiarities of
the measurement system should provide input to how the calibrations are to be performed.
7.1 THE CALIBRATION FACILITY
The EPA strongly recommends that RPP participants obtain calibration services from facilities
that have successfully participated in recent laboratory intercomparison exercises such as those
hosted by the U.S. DOE EML (U.S. DOE 1994) at their laboratory in New York. The results are
published with coded participant identifications; the calibration facility should provide clients
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with a copy of the EML report identifying their facility's code and any supplementary
information regarding their most recent intercomparisons.
Commercial calibration facilities vary in their design, radon source, and ability to generate and
control radon and decay-product concentrations and other environmental parameters.
Calibrations should be performed at concentrations that are high enough to provide sufficient
signal, but low enough to ensure that concentrations routinely measured (e.g., less than 10 pCi/L
or about 400 Bq/m3) can be considered to be within the range of linearity of the calibration. The
QA Officer should review the capabilities of the facility to ensure that it can meet the objectives
for the calibration.
7.2 DEVELOPMENT OF A CALIBRATION PLAN
The agreement about how the calibration is to be performed should be as specific as possible, so
that all the needed information is obtained during the same operation. The calibration facility
may have established procedures; the QA Officer should carefully review these procedures prior
to initiating the contract.
A calibration plan developed for each calibration should specify:
The number/types/serial or i.d. numbers of the equipment to be calibrated.
The radon concentrations or range of radon concentrations, and the number of
devices to be exposed at each concentration.
Durations of exposure.
Other factors that affect results, including equilibrium ratios, temperature,
humidity, and storage conditions or durations.
Specific protocols for handling/opening/operating the devices, including
unexposed chamber and trip blanks, as appropriate.
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This plan should be reviewed and agreed to by the calibration facility prior to initiating the
measurements.
The QA Officer should be prepared to analyze, report to management, and use the information
obtained during the calibration. The calibration operation should provide useful information
regarding the systematic error (bias) of the measurements of various concentrations under
various conditions. If multiple simultaneous measurements are made, information about the
random component of error (precision error) will also be obtained. The QA Officer is
responsible for ensuring that this information is used appropriately, including changing
calibration factors if warranted. The calibration plan should ensure that sufficient measurements
are made to warrant changing calibration factors if necessary based on the single operation, or
have contingency plans for repeat measurements at the same facility if there is a need to resolve
an uncertainty.
The QA Officer is responsible for ensuring that the calibration results are completely
documented, including the conditions, concentrations, unusual occurrences, and results.
7.3 CALIBRATION RECORDS
Calibration records should be maintained by the QA Officer, and be available for inspection by
management, potential clients, and auditors. Labels should be affixed to active instruments
listing the calibration facility, the calibration date, initials of the measurement organization's QA
Officer (or person designated by the QA Officer), and the projected date for the next calibration.
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8. Quality Control
QA is an umbrella term that includes many activities designed to ensure the validity of
measurements and measure their quality. The measurements that are made for the purpose of
assessing and monitoring data quality are called QC measurements. The QC measurements
described here are those that are recommended specifically by EPA and others for radon
measurements. Guidance for QA in radon or related measurements can also be found in
documents written by the American National Standards Institute (ANSI 1989), the National
Council on Radiation Protection and Measurements (NCRP 1988) and the American Association
of Radon Scientists and Technologists (AARST 1994). Guidance for accreditation of
laboratories used by the American Association for Laboratory Accreditation (ISO 1990) is
available, and the recommendations in this section are consistent with that guidance.
8.1 MEASUREMENTS TO MONITOR PRECISION ERRORS
Duplicates are defined as co-located measurements, in which side-by-side detectors measure over
the same time interval. Replicate measurements, consisting of more than two simultaneous side-
by-side measurements, can be used to estimate the precision error of the system and are
especially useful initially and whenever the measurement system is altered. The purpose of
making duplicate measurements is to track over time the variation(s) that are observed between
two identical measurements of the same concentration. A program of performing duplicate or
replicate measurements allows the organization to monitor the component of measurement error
caused by random differences in devices and/or the measurement process. Some precision error
is unavoidable, and may be due to the detector manufacture or configuration, inconsistent data
transcription or handling by suppliers, laboratories, or technicians performing placements. Since
any one of these factors can change suddenly or gradually over time, continual monitoring of
precision can serve to check on the continuity of the entire measurement system.
The ideal estimate of precision is that which is inherent in the entire measurement system. This
includes random components) of error introduced during shipping, distribution, storage,
placement, and report generation. Different organizations may be involved in only a portion of
this measurement system; for example, some analytical service providers may sell or lease
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detectors to residential service providers and never or rarely perform actual field measurements.
Each measurement organization (e.g. even if they are a residential service provider or an
analytical organization that does not perform field measurements) should perform some
measurements to estimate precision error. In addition, clear and frequent communication
between analytical and residential service providers will help track the quality of the
measurements and quickly identify any changes.
Specific recommendations for different types of organizations are described in the following
sections.
8.1.1 Duplicate Measurements for Analytical Service Providers Distributing Passive Detectors
Directly to Homeowners
Analysis laboratories that sell detectors directly to homeowners can estimate and track the
precision inherent in their entire measurement system, including distribution. Duplicate
measurements for passive detectors should be side-by-side measurements made in at least 10
percent of the total number of measurement locations, or 50 pairs each month, whichever is
smaller. The locations selected for duplication should be distributed systematically throughout
the entire population of samples. Groups selling measurements directly to homeowners can do
this by providing two measurements, instead of one, to a random selection of purchasers, with
instructions for the measurements to be made side-by-side.
The measurement locations selected to receive duplicate detectors should be distributed among
all measurement locations. In other words, it is not adequate to place all duplicate devices in one
basement. Some duplicate measurements must be made in locations that require all the different
handling that are routine in the operation, such as mailing to various locations, traveling by car,
handling by different technicians, counting by different equipment, and recording by different
office personnel. This is the only way to estimate and monitor the average precision error
inherent in all the measurements. One way to implement this program is to target every tenth
detector or client number to receive a duplicate.
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An exception to this rule is when all the systematically selected locations that receive duplicates
have radon concentrations less than 4 pCi/L (about 150 Bq/m3). In this case, a portion of the
duplicates should be placed in environments with higher concentrations. This can be
accomplished by periodically placing side-by-side devices in an environment with radon
concentrations known to be elevated.
8.1.2 Duplicate Measurements for Analytical Organizations Selling Passive Detectors to
Residential Service Providers
An analysis laboratory must estimate the precision error inherent in its portion of the
measurement operation by analyzing devices that have been exposed to the same radon
environment. The QA Officer should manage a program to regularly place at least two detectors
side-by-side in the same radon environment. The QA Officer should determine the frequency of
duplicate measurements, but they should be systematically distributed (e.g., every twentieth
analysis should be a duplicate) so that the entire range of handling, technicians, background, and
other laboratory conditions impact the duplicate analyses just as those conditions impact the
normal analyses of detectors. A range of radon concentrations, spanning the concentrations
usually encountered in the field, should be used. In addition, the QA Officer is responsible for
making these results available to the residential service providers that use the analysis services,
and for obtaining the results of duplicates arranged by the residential service provider.
The organization performing analyses should measure duplicate (or replicate) devices at a
frequency designed to ensure that a reliable estimate of laboratory analysis precision error is
obtained. A rate of at least 25 pairs per month or five percent of the total number of devices
analyzed (whichever is smaller) may be sufficient; this rate is for the analysis portion of the
measurement system only, and assumes that additional duplicate devices as exposed by the
residential service organizations will also be processed by the same analysis laboratory.
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8.1.3 Duplicate Measurements for Residential Service Providers Using a Passive Detector
System
Residential service providers perform activities that may impact the precision of the
measurement. These include handling, storage, shipping, deployment and data transcription. In
fact, it is the residential service provider that bears the responsibility of the critical portion of the
measurementexposureand often the ultimate reporting of the result to the client. Because of
this, it is important that residential service providers expose and arrange the analysis of duplicate
detectors and track their results. The residential service provider's QA Officer should manage a
program ensuring that the following guidelines for duplicate devices are met.
Duplicate measurements for passive detectors exposed by residential service providers should be
side-by-side measurements made in at least five percent of the total number of measurement
locations, or 25 pairs each month, whichever is smaller. The locations selected for duplication
should be distributed systematically throughout the entire population of measurements. The
residential service provider can provide two measurements, instead of one, to a random selection
of purchasers, with the measurements made side-by-side. Special instructions and detector
packaging may be necessary to ensure that the detectors are not separated during exposure.
The measurement locations selected to receive duplicate detectors should be distributed among
all measurement locations. In other words, it is not adequate to place all duplicate devices in one
basement. Some duplicate measurements must be made in locations that require all the different
handling modes that are routine in the operation, such as mailing to various locations, traveling
by car, handling by different technicians, and recording by different office personnel. This is the
only way to estimate and monitor the average precision error inherent in the measurements. One
way to implement this program is to target every twentieth detector or customer number to
receive a duplicate.
An exception to this rule is when all the systematically selected locations that receive duplicates
have radon concentrations less than 4 pCi/L (about 150 Bq/m3). In this case, a portion of the
duplicates should be placed in environments with higher concentrations.
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8.1.4 Duplicate and Comparison Measurements for Analytical Service Providers Using an
Active System
Precision error cannot be easily estimated for users of active systems. The ideal estimate of the
actual precision error inherent in a field measurement would be made by making simultaneous,
side-by-side measurements with two identical units having identical calibration schedules,
procedures and history. Manufacturers can perform such measurements most frequently with
new instruments. Analytical service providers should perform side-by-side measurements in
approximately 10 percent of the total number of measurements, or 50 side-by-side measurements
each month (whichever is smaller), when such monitors are available at the same location.
The precision error caused by the uncertain nature of radioactive decay (counting statistics error)
is only one component of precision, and is usually a deceptively small estimate of the overall
precision error caused by electronic noise, variability in background, and other factors that are
caused by differences between instruments and over time in the same instrument.
8.1.5 Duplicate Measurements for Residential Service Providers Using an Active System
Residential service providers using an active monitor cannot read the results from the instrument.
These organizations must rely completely on the analytical service provider for the estimation of
precision, and should ensure that the analytical service provider is following the procedures
recommended in Section 8.1.4. The residential service organization should request a copy of the
analytical organization's QA Plan as well as the results of duplicate and/or comparison
measurements performed by the analytical service provider. The residential service
organization's QA Officer is responsible for regularly performing some comparison
measurements (as described in Section 8.4.3) to ensure that transport of the monitor or
transmission of data from the monitor to the analytical service provider does not contribute to
any degradation of quality. These comparison measurements cannot be used to assess precision
error, however.
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8.1.6 The Analysis of Duplicate or Comparison Measurements
The analysis of data from duplicates (identical passive or active devices deployed with identical
start and stop times) should follow the methodology described in Section A.4 of Appendix A of
this document. Analytical and residential service providers should regularly communicate and
exchange data on duplicate results; close collaboration may result in streamlined practices for
duplicate placement and analysis.
8.2 BACKGROUND MEASUREMENTS
Background measurements are very important for some types of devices, including alpha track
detectors, scintillation cell instruments, and electret ion chambers in areas of high gamma
exposure (background radiation). All radon or decay product measurement methods require
some type of background measurements.
There are two categories of background measurements: laboratory background measurements
made to assess the background signal of the instrumentation used to analyze the detectors and
any signal generated by the material of the detector itself, and field blanks, made to assess the
background that accumulates or to identify any degradation of measurement quality caused
during shipping and handling in the field (trip blanks).
8.2.1 Laboratory Background Measurements for Analytical Service Providers of Passive
Devices
Laboratory background measurements are used by analytical service providers to assess the
counts or signal that result from instrument "noise" and the signal generated from the detector
material itself, in the case of alpha-track detectors and charcoal-adsorbing devices. In general,
this signal is subtracted from the results of field (the environment being measured) detector
analyses. In the case of electret ion chamber devices, the background of the electret reader is that
signal produced when a metallic but uncharged material replaces the electret in the reader, and
this signal is measured, recorded, and checked for stability and magnitude as per instructions
from the manufacturer.
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Laboratory background measurements are generally interpreted as follows. First, the results of
laboratory blanks are used to derive an average laboratory background level, which is subtracted
from the results of the detectors used to measure radon in the environment being measured. This
may be done for specific time periods (e.g. daily or weekly) or for batches of material and then
re-evaluated. The analytical service provider that processes the detectors assesses laboratory
background. Residential service providers should request copies of and understand their
analytical laboratory's procedures for assessing laboratory background, so that there is no
misunderstanding regarding background, and to ensure that a background value is not subtracted
twice.
The second use of laboratory background measurements is to calculate the lower limit of
detection, or LLD. The method and derivation of the LLD are described in Section A.5 of
Appendix A. Note that this derivation assumes a Poisson distribution of counts, and this is not a
valid assumption for the background distribution of signal from electret ion chamber readers.
The manufacturer of electret ion chambers has derived a minimum detectable activity based upon
a series of assumptions and calculations, and this value quoted by the manufacturer should be
referenced in the QA Plan of the analytical service provider analyzing the electrets.
8.2.2 Instrument Background Measurements for Analytical Service Providers Using Active
Instruments
Analytical service providers using active instruments assess the background of their instruments
using aged air or nitrogen in a glove box or by direct flow into the detector. Manufacturers
provide specific information on recommended techniques for assessing instrument background;
the radon concentration in outdoor air is too variable and high to use successfully for repeatable
background measurements. Background measurements should be made as one of the first steps
of a calibration and, where feasible, crosscheck.
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8.2.2.1 Instrument Background Measurements for Analytical Service Providers Using
Continuous Radon Monitors
The EPA Device Protocols (U.S. EPA 1992a) recommend that users of scintillation-cell type
continuous monitors perform instrument background measurements after at least every 1,000
hours of operation (about every twentieth 48-hour measurement). Background checks this often
may not be necessary for a system that is not used in extremely high radon concentrations and
that exhibits small or stable background count rates. However, a reduced schedule for assessing
background should be supported by data indicating the relative stability of the background count
rate in various environments. If a residential service provider is using the monitor, the analytical
organization needs to document its system for ensuring that the monitor is returned to them for
background measurements according to a schedule that follows the QA Officer's
recommendations. In addition, the analytical organization should make available to the
residential organization their written procedures for measuring background and the results of the
background measurements made during periodic calibrations..
8.2.2.2 Instrument Background Measurements for Analytical Service Providers Using
Continuous WL Monitors
The EPA Device Protocols (U.S. EPA 1992a) recommend that users of continuous working level
monitors conduct instrument background measurements after at least every 168 hours (after
every fourth 48-hour measurement). Background checks this often may not be necessary for a
system that is not used in extremely high decay-product concentrations and that exhibits small or
stable background count rates. However, a reduced schedule for performing background checks
should be supported by data indicating the stability of the background count rate in various
environments. If a residential service provider is using the monitor, the analysis organization
needs to document its system for ensuring that the monitor is returned to them for background
measurements according to a schedule that follows the QA Officer's recommendations. In
addition, the analytical organization should make available to the residential organization their
written procedures for measuring background and the results of the background measurement
made during periodic calibrations.
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8.2.3 Instrument Background Measurements for Residential Service Providers Using Active
Instruments
Residential service providers using active instruments should verify that their analytical
organization performs background measurements according to the minimum schedule described
in Section 8.2.2.1 (for CR users) or Section 8.2.2.2 (for CW users). Residential service providers
should request copies of background reports with the calibration reports.
8.2.4 Field Blanks for Users of Passive Devices
The purpose of field background measurements, or field blanks, is to identify effects due to
exposure other than in the environment being measured, and to identify any unexpected device
response other than due to exposure (e.g., handling causing leakage, effects of high or low
humidities or temperatures, effects due to high background radiation). The detectors used for
blanks must therefore be treated identically to the detectors deployed in homes, except that they
are not opened or brought into the environment to be measured. Blanks can, however, be
transported with other detectors, and this is often critical in cases where detectors to be calibrated
are brought to a calibration facility. If there is any effect due to background exposure of the
detectors used to calculate the calibration factor, it is important that it be accounted for before
calibration factors are calculated.
8.2.4.1 Field Blanks for Analytical Service Providers of Passive Devices
Many analytical organizations sell detectors two ways: in bulk to residential service providers
and individually to homeowners or other end users. Analytical organizations should develop a
system for shipping some field blanks with the bulk detectors to measure any effect due to
shipping or handling. Field blanks (unopened detectors) should be sent with bulk shipment of
detectors at a rate sufficient to measure and track changes in field background.
The rate of field blanks should be determined by the QA Officer. Some types of devices may
exhibit significant and varying background (e.g., alpha track detectors) and therefore require a
thorough program of monitoring background. Other types of devices (e.g., charcoal adsorbing
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devices) may require only occasional field blanks to monitor the measurement-system
background.
The analytical organization should provide instructions to the residential service provider for
handling the blanks. These instructions should specify that the blanks not be deployed, but
remain with the bulk of the detectors to assess background due to shipping, storage, and
handling.
The analysis laboratory should monitor the results of the field blanks and compare the results
with the value of LLD calculated using the laboratory blanks. If the field blank results are
consistently different than the LLD, then an investigation into the cause of the difference should
be conducted. If appropriate, and after the investigation, the average result of the field blanks
can be used to adjust the results of the other detectors in that exposure group.
8.2.4.2 Field Blanks for Residential Service Providers Using Passive Devices
Residential service providers using passive devices are responsible for monitoring the
background of their operations by deploying and tracking the reported results of field blanks.
These blanks are additional detectors purchased for use as blanks, and should not be deployed,
but should remain with the bulk of the detectors to assess background due to storage and
handling. Residential service organizations should consult with the analysis laboratory regarding
the rate of blanks that should be sent for analysis.
8.2.5 The Analysis of Background Measurements
Residential as well as analytical service providers must record and analyze the results of the
background measurements that they conduct. The organization's QA Officer is responsible for
recording and monitoring the results of background measurements, for reporting the results to
management, for corrective action when needed, and for verifying changes in measurement
results. Means control charts can be used for monitoring both laboratory and field background;
this is discussed in Section A.3.1 of Appendix A of this report.
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8.3 MEASUREMENTS MADE TO ASSESS BIAS
The type of QC measurements that are made to determine the relative bias inherent in the
measurements are termed known exposure measurements, or spikes. Analytical and residential
service providers should include known exposure or spiked measurements in their measurement
program and monitor the results. Known exposure measurements are an ongoing and continuous
way to monitor the differences between measurement results and the "correct" value. They are
extremely useful and necessary for ensuring that results are consistently unbiased.
8.3.1 Measurements Made to Assess the Bias of Passive Detectors
Spiked measurements consist of detectors that have been exposed to known concentrations in a
radon calibration chamber. All organizations should arrange for the exposure of devices in a
radon calibration chamber on a regular basis (e.g. monthly, quarterly, biannually). If the
organization uses detectors of different types, at least three per 100 of each type should be
spiked. For those organizations processing few detectors, a minimum of three per year is
recommended. Organizations processing many detectors may be able to obtain useful
information with a maximum number of six spikes per month, although the QA Officer may
deem more to be appropriate.
The EPA recommends that all organizations using passive devices expose, record and
interpret the results of three spikes per 100 measurements (as averaged over the
anticipated number of measurements during a several month period), with a minimum of
three per year and a maximum (although more may be conducted) of six per month.
The QA Officer is responsible for ensuring that the detectors to be spiked include a
representative sample of detectors so that the results will reflect the error inherent in the detectors
being processed for clients. If possible, some of these detectors should be labeled and submitted
to the laboratory in the same manner as ordinary measurements to preclude special processing,
and thereby serving as an internal check on the measurement system. If appropriate, chamber
blanks and trip blanks should be sent with the detectors to be spiked to assess any background
signal due to shipping, handling, gamma exposure in the chamber, or other factors.
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8.3.1.1 The Analysis of Measurements to Assess the Bias of Passive Devices
The QA Officer is responsible for recording and monitoring the results of spiked measurements,
for reporting the results to management, for corrective action when needed, and for verifying
changes in measured results in response to changes in procedures. The results of spikes may be
analyzed following the guidance in Appendix A.
8.3.2 Measurements Made to Assess Bias for Analytical and Residential Service Providers
Using Active Instruments
All active instruments used regularly should be checked for bias on a regular basis. Ideally, such
measurements are made in a radon calibration chamber (see Section 7) in a known radon
environment. Exposure in a calibration chamber is required during calibration of the devices,
and it can be difficult to expose active instruments in a recognized calibration chamber more
often than once every 12 months. It is important, however, to perform some measurements to
assess instrument response more frequently. The EPA recommends that users of active
instruments perform crosschecks with a recently calibrated active instrument during the 12-
month interval between calibrations, and approximately six months after calibration, so that no
more than about six months elapses between either a calibration or a crosscheck.
Crosschecks should be performed according to the following recommendations and any device-
specific directions from the manufacturer. Where feasible, a crosscheck should begin with an
instrument background measurement (see Section 8.2.2) using aged air or nitrogen, and
instrument performance checks. The crosscheck measurement should be made in an
environment that has been chosen for its stability and radon concentration that is well above the
lower limit of detection for both devices (preferably greater than 4 pCi/L or 150 Bq/m3).
A second active instrument that produces results in the same units (i.e., both in pCi/L [Bq/m3] or
both in WL [J/m3]) and that has been calibrated within the last 3 months should be placed with its
air intake adjacent to the instrument to be cross checked. A measurement of at least 48 hours
duration should be conducted, with the first four hours of data not used in the calculation (or as
recommended by the manufacturer).
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Analytical service providers that furnish active devices to residential service organizations and
who analyze the signal from those devices need to provide written instructions and training to the
residential service providers regarding checks of instrument function. Analytical service
providers need to ensure that field checks are being performed.
8.3.2.1 The Analysis of Measurements to Assess the Bias of Active Devices
The comparison of two results from devices that are different (e.g., your organization's device
next to a comparison measurement made with different equipment) should follow procedures
developed specifically for your system by your QA Officer. The QA Officer may designate
values of relative percentage difference (see Glossary) between the active result and the
secondary result as triggers for corrective action. For example, a relative percentage difference
often percent between the active and the comparison measurement may signal the QA Officer to
investigate by performing two similar measurements.
A relative percentage difference of twenty percent may indicate a potential problem and the QA
Officer needs to stop further measurements until either the problem is identified and corrected or
it is determined that there is no problem with the active monitor. (These values often and twenty
percent are given here only as examples and specific values for each system should be
determined, evaluated, and modified as necessary by your organization's QA Officer.) The QA
Officer is responsible for recording and monitoring the results of measurements made to estimate
precision, for reporting the results to management, for corrective action when needed, and for
verifying improvement.
8.4 ROUTINE INSTRUMENT PERFORMANCE CHECKS
This category of QC measurement includes any activity that can be performed to assess how well
the equipment is operating in relation to a previous check or to a standard check source. Regular
monitoring of equipment and operators is vital to ensure consistently unbiased results.
Check sources for alpha counters include thorium or americium sources that are used to test the
counting system and ensure that the electronics are stable and operating the same way they were
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the day before. Analytical service providers find such routine checks extremely useful for
detecting instrument drift or other problems that are minor if corrected quickly. Specific
guidance for such operations is beyond the scope of this document; all organizations should
develop methods for regularly (daily, prior to beginning a measurement) monitoring their
system, and for recording and reviewing results.
8.4.1 Routine Instrument Performance Checks for Analytical Service Providers of Passive
Devices
Analytical service providers of charcoal or alpha track devices use routine instrument
performance checks of their equipment to verify the analysis equipment's continued stable
operation. These may consist of standard detector material with known track densities (for alpha
track detector equipment) or charcoal detectors impregnated with radioactive material.
Analytical service providers analyzing electrets should use a reference electret to check the
response of the reader prior to beginning the analysis of a set of electrets.
The QA Officer is responsible for documenting the procedures for routine instrument
performance checks and for setting criteria for action based upon the results of such checks.
Such criteria could involve the use of means control charts, so that limits are based on the
probability of obtaining certain results. Such schemes are most appropriate for routine
instrument performance checks involving radioactive check sources. Alternatively, criteria can
be based upon upper (and lower) limits, or changes in response of a certain magnitude; this may
be most appropriate for reference electrets.
8.4.2 Routine Instrument Performance Checks for Analytical Service Providers Operating
Active Monitors
Users of active monitors must take special care to ensure that the frequent handling of their
equipment does not impact response. Some types of continuous monitors are designed to allow
the user to perform checks of the instrument's response; this can allow frequent documentation of
stable response. The most useful checks are those that test the majority of the measurement
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system (e.g., a sealed Ra-226 cell for scintillation-cell monitors); other checks of a portion of the
system are also useful (e.g., a check of the electronics). These routine checks should be made
prior to each measurement and the results noted in a log. Critical components, such as pump
flow rate, should be checked prior to and following each measurement and the results noted.
The QA Officer is responsible for documenting the procedures for routine instrument
performance checks and for setting criteria for action based upon the results of such checks.
Such criteria could involve the use of means control charts, so that limits are based on the
probability of obtaining certain results. Such schemes are most appropriate for routine
instrument performance checks involving radioactive check sources (e.g., sealed cells).
Alternatively, criteria can be based upon upper and lower limits; this may be most appropriate for
pump flow rate or other non-Poisson processes.
8.4.3 Routine Instrument Performance Checks for Residential Service Providers Operating
Active Monitors
Residential service providers using active monitors provided by an analytical organization should
have some means to assess the continued satisfactory operation of the active monitor they are
using. The analytical service organization should provide written instructions and training for
performing tests of the equipment and set up a system for obtaining and analyzing results from
the residential service provider. Particularly important are pump flow-rate checks prior to and
after each continuous WL measurement. Also useful are built-in self-diagnostic tests of the
detector and electronics. Routine instrument performance checks can be monitored using means
control charts (see Section A.3.1 of Appendix A).
If a check source is unavailable or incompatible with the type of active monitor being used, and a
system and detector diagnostic check is impossible, the organization should perform a
comparison measurement with approximately ten percent of the measurements. This comparison
measurement will serve as a check of the continued satisfactory operation of the instrument.
Because the two results were not obtained with identical equipment, however, a statistical
analysis for the purpose of assessing precision would not be appropriate.
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The comparison of the two results from devices that are different (e.g., your organization's
device next to a comparison measurement made with different equipment) should follow your
procedures developed specifically for your system by your QA Officer. The QA Officer may
designate values of relative percent difference (see Glossary) between two results triggers for
corrective action. For example, a relative percentage difference often percent between the
measurements may signal to the QA Officer to investigate by performing two similar
measurements.
A relative percentage difference of twenty percent may indicate a potential problem and the QA
Officer may need to stop further measurements until the problem is identified and corrected or it
is determined that there is no problem with the measurement. (These values often and twenty
percent are given here only as examples; specific values for each system should be determined,
evaluated, and modified as necessary by each organization's QA Officer.)
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9. Quality Assurance Plans
A Quality Assurance Plan (QAP) is a written document, which presents, in specific terms, the
policies, organization, objectives, functional activities, and specific QA and QC activities that are
designed to achieve the objectives of the project (U.S. EPA 1980, U.S. EPA 1992b).
The QAP serves three main purposes. First, and most important, it is the culmination of the
discussion and planning that went into designing the operation to produce results that are of the
quality needed. Second, it is a historical record that documents the operation in terms of
measurement methods used, calibration standards and frequencies planned, auditing planned, etc.
Lastly, a QAP provides management with a document that can be used to assess whether the
planned QA activities are being implemented, and to examine the importance of these activities
toward the goal of quality data in terms of relative bias, precision error, and other indicators of
quality.
The Agency's draft interim final requirements for Quality Assurance Project Plans for
Environmental Data Operations (EPA QA/R-5, U.S. EPA 1992a) provides guidance regarding
components of a QA Plan. This and other EPA QA guidance is being written using ANSI/ASQC
guidance (ANSI/ASQC 1994a) as a framework. When EPA QA/R-5 becomes final, it will
supersede previous Agency guidance (QAMS-005/80; U.S. EPA 1980). This guidance is
intended for organizations that gather data on behalf of EPA through contracts, financial
assistance agreements, and interagency agreements. Although most radon measurement
organizations do not fall into this category, this section provides information regarding format
and terminology from both the Agency's 1980 guidance and the draft interim final guidance.
There are 16 elements of a QAP that are described in EPA's guidance for preparing such plans
(U.S. EPA 1980, U.S. EPA 1989). These elements are described here along with terminology
used by other organizations. These elements should be present in a QAP, and presentation in the
order described in this section will facilitate review by EPA and others (for example, by
residential service providers). Exhibit 9-1 describes which elements are necessary for the QAPs
of analytical and residential service providers.
9-1
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Exhibit 9-1
Required Elements of a Quality Assurance Plan for
Analytical and Residential Service Providers
Element
1. Signature page
2. Table of contents, with revision numbers and dates
3. Description of operations
4. Organization and responsibilities
5. QA objectives for measurement data in terms of
precision error and relative bias
6. Measurement procedures (brief discussion of
measurement method, procedures for selecting
measurement location, and procedures for
Record keeping and shipping)
7. Detector custody for field and laboratory operations
8. Calibration procedures and frequency
9. Analytical procedures
10. Data reduction, validation, and reporting
11. Internal QC checks
12. QA audits
13. Preventive maintenance
14. Procedures used to assess precision, relative bias,
and lower limit of detection (LLD)
15. Corrective action
16. QA reports to management
Analytical
Required
Required
Required
Required
Required
Required
Required
Required
Required
Required
Required
Required
Required
Required
Required
Required
. Residential
Required
Required
Required
Required
Required obtain this
information from the analytical
organization
Required
Required describing sample
custody for the residential
organization's operations only
Not required
Not required
Required omitting the data
reduction conducted by the
analytical organization's
operations
Required
Required only pertaining to
activities relevant to the
residential organization's
responsibilities
Required only pertaining to
equipment used by the
residential organization
Required except for the
assessment of LLD
Required only pertaining to
the residential organization's
operations
Required
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There is considerable information available on preparing quality assurance plans and quality
management plans (U.S. DOE 1991, MIST 1995, Taylor 1987). A QAP that is written in
addition to a separate quality management plan and extensively referenced SOPs may be fairly
lean. A QAP that serves as the sole quality document and contains the procedures for many
quality control procedures may be lengthy and detailed.
The responsibility for reviewing and updating the QAP lies with the QA Officer. As this may
require periodic expenditures of time, this task must be supported by management.
9.1 SIGNATURE PAGE
The title page of the QAP must include the signatures of the organization's QA Officer (see
Section 5.2) and his/her supervisor. Other individuals who are also responsible for the quality of
measurements should sign and date the completed QAP, indicating that they have reviewed and
approved of the plan and consider the plan final.
This corresponds with EPA QA/R-5 Element Al: Title and Approval Sheet (U.S. EPA 1992b).
9.2 TABLE OF CONTENTS
The table of contents must include page numbers for each of the elements of the QAP, and the
"revision number," signifying the number of times and most current date that each element was
revised.
This material corresponds with EPA QA/R-5 Element A2: Table of Contents.
9.3 DESCRIPTION OF OPERATIONS
This part of the QAP should provide a complete description of all the relevant organization
operations, including different measurement methods, distribution activities, on-site visits, and
transmittal of results to clients. The description must be sufficiently comprehensive for someone
unfamiliar with the operations to understand the numbers and types of measurements made by
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the organization. Although SOPs may be referenced, the QAP should included a brief
description of operations.
The corresponding elements in EPA QA/R-5 are A5: Problem Definition and A6: Project/Task
Description.
9.4 ORGANIZATION AND RESPONSIBILITIES
This part of the QAP usually includes a detailed organization chart showing management
structure and lines of communication. The names of all key individuals in charge of every major
activity in the project should be included. Telephone numbers should also be provided to
facilitate communication between project officials. Both technical and QA/QC functions should
be listed.
The information presented in this Section corresponds to EPA QA/R-5's Element A4: Project
Task Organization.
An important person to identify is the QA Officer (see Section 5.2), and the line of authority for
his/her activities. This section should include a description of the regular methods of
communication regarding quality assurance issues. Unless a separate Quality Manual or Quality
Management Plan is written, this section should include a statement of commitment to quality
(quality policy) by the organization's management.
Work performed by parties outside the organization should be identified, with a description of
management and technical responsibilities for this work.
9.5 QUALITY ASSURANCE OBJECTIVES
The quantitative QA objectives should be discussed and presented in this section. In general,
objectives for relative bias and precision error should be listed, and other objectives may be listed
as well. These may include, for example, numeric objectives relevant to marketing (e.g.,
measures of customer satisfaction, referrals) or employee performance (e.g., data entry errors).
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Analytical service organizations may need to set objectives for the parameters necessary for the
calculation of final concentrations (for example, flow rates or weight gains). The objectives for
intermediate parameters may be, for example, that flow rate will remain between values x and y;
corrective action will be taken and the QA Officer notified if values deviate beyond these
boundaries.
The corresponding element in EPA QA/R-5 is A7: Quality Objectives and Criteria for
Measurement Data.
9.5.1 Precision Error
Precision is defined as the measure of the variability of a process used to make repeated
measurements under carefully controlled (identical) conditions. Duplicate measurements provide
a check on the quality of the measurement result, and allow the user to monitor precision error.
Large precision errors may be caused by inconsistencies in detector manufacture, or inconsistent
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 error.
Because variability is not usually constant at different concentrations, estimates of precision must
be made at different concentrations in the range of interest. Precision objectives for several
concentrations or ranges should be specified.
The estimate of precision error may be specified in terms of a) relative percentage difference,
defined as the absolute value of the difference between two measurements divided by their
average, b) by coefficient of variation, defined as the sample standard deviation of two or more
measurements divided by their average, c) by the range, defined as the difference between the
two measurements, or d) by some other parameter. The quantitative goals for precision could be
specified, for example, as an average relative percentage difference of less than 25 percent for
duplicates where at least one result is less than 4 pCi/L (150 Bq/m3), and an average relative
Percentage difference of less than 14 percent for duplicates where both results are greater than 4
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pCi/L (150 Bq/m3). Technical guidance for calculating and assessing precision error is found in
Section A.4 of Appendix A.
9.5.2 Relative Bias
Relative bias is defined as the degree of agreement of a measurement result with an accepted
reference or true value. In the case of passive detectors, the reference value is the concentration
in the radon calibration facility where the spiked measurements are performed. In the case of
active instruments for which bias was assessed with a cross check, the reference value is that
given by the recently calibrated instrument. Bias may be expressed in terms of relative percent
error, or as
RPE = [(MV-RV)/RV]*100%
where: RPE = relative percentage error;
MV = measured value of spiked measurement; and
RV = reference value.
Note that the definition of relative percentage error is similar to the definition of Individual
Relative Error (IRE), as defined in the Radon Proficiency Program (RPP) Handbook (U.S. EPA
1995a), except that the numerator of the IRE is the absolute value of the difference while RPE
can have positive or negative values. This formula is identical to the "relative bias" formula used
by the Nuclear Regulatory Commission (U.S. NRC 1986, page 33).
It is advisable to specify ranges over which the relative bias goals are to be met. The quantitative
goal for relative bias could be stated, for example, as a RPE of ±15 percent or less at radon
concentrations greater than 4 pCi/L (150 Bq/m3).
Another expression of bias is performance ratio, which can be defined as the measured value
divided by the reference value. Note that the difference between percentage bias and
performance ratio is 1.0, so that, for example, if percentage difference is 0.25, the performance
ratio will be 1.25.
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More information on the monitoring of relative bias can be found in Appendix A; a discussion of
equipment calibration is given in Section 7.
9.6 MEASUREMENT PROCEDURES
This part of the QAP should describe the following:
The method by which the radon or radon-decay product concentrations are to be
measured. A technical person unfamiliar with the method must be able to
understand the descriptions of the method used. The RPP Handbook (U.S. EPA
1995a) contains a brief description of each of the measurement methods currently
described by EPA's Indoor Radon and Radon Decay Product Measurement
Device Protocols (U.S. EPA 1992a).
The guidelines used to select the locations for detector deployment, including the
procedures for choosing the exact sampling locations.
Measurement conditions, as described in Protocols for Radon and Radon Decay
Product Measurements in Homes (U.S. EPA 1993).
The logbooks or recordkeeping procedures, with a list of the information routinely
gathered with each measurement,
Relevant information about shipping detectors to the laboratory, including the
schedule for shipping detectors.
The corresponding elements in EPA QA/R-5 are Bl: Sampling Process Design and B2:
Sampling Method Requirements.
9.7 DETECTOR CUSTODY
A complete description of all chain-of-custody procedures, forms, documentation, and the
responsibilities of each person is needed to ensure both the technical validity and the legal
defensibility of data obtained from all measurements.
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The information presented in this part of a QA Plan corresponds to EPA QA/R-5's Element B3:
Sample Handling and Custody Requirements.
9.7.1 Field Operations
The information that is relevant under this part is a description of:
Names of field operators/technicians.
How, by whom, and where the records of measurement data, including location,
time, and other pertinent parameters are kept.
Examples of labels, custody seals, and field tracking forms.
Office documentation of procedures for transporting detectors from the field to
the laboratory, including identification of the individuals or organizations
responsible for transport.
9.7.2 Laboratory Operations
This part of the QAP describes how the detectors are handled by each laboratory facility when
they are received after exposure. The following information should be included:
Names of laboratory detector custodians responsible for logging in devices or
data.
Forms for laboratory detector tracking.
Records of laboratory chain-of-custody.
Specification of procedures for detector handling, storage, and final disposition.
Documentation of procedures for disbursement and transfer of detectors within
the laboratory and between the analytical and residential service provider.
A residential service provider's QAP must include the identification of the person responsible for
the detectors, and a description of the laboratory-detector handling procedures.
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9.8 CALIBRATION PROCEDURES AND FREQUENCY (For Analytical Service Providers
Only)
This section of the QAP should include descriptions of the calibration procedures, and frequency
of calibration, for each analytical system, instrument, device, and any components (e.g., scales,
flowmeter) used to obtain measurement results. A summary table should be used, whenever
possible, to present the following information:
References to EPA-recognized, or other standard, methods.
Complete description of non-standard or modified methods.
Appended instrument-specific calibration SOPs, as needed to support SOPs that
do not include detailed calibration procedures.
Definition of specific acceptance criteria for all calibration measurements.
The information that needs to be included in this part of the QAP or the appendix of SOPs should
be specific, for example: shipment of 20 detectors every six months to the calibration facility
(provide the name and address); exposure to humidities and radon levels (specify ranges of
values) at the calibration facility; adjustment of calibration curves accordingly; and other
information as described in Section 7.
Calibration information corresponds to EPA QA/R-5's Element B7: Instrument Calibration and
Frequency.
9.9 ANALYTICAL PROCEDURES (For Analytical Service Providers Only)
This part of the QAP should describe the procedures for analyzing the detectors. The laboratory
SOPs should be reproduced and appended to the QAP, or referenced and kept available.
Element B4: Analytical Methods Requirements is the corresponding section in EPA QA/R-5.
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9.10 DATA REDUCTION, VALIDATION, AND REPORTING
This section of the QAP describes how the organization maintains good data quality throughout
data reduction (i.e., calculation of results), transfer, storage, retrieval, and reporting. The
following topics are recommended for discussion.
For data reduction:
- Names of individuals responsible.
- Summary of data reduction procedures.
- Examples of data sheets.
- Description of how results from field and laboratory blanks are used in the
calculations.
- Presentation of all calculations (equations) and significant underlying
assumptions.
For data validation:
Means by which the data are checked for errors.
- Names of individuals responsible.
- Procedures for determining outliers and flagging data for review by the QA
Officer or others.
For data reporting:
- Names of individuals responsible.
- Flowchart of the data-handling process, covering all data collection, transfer,
storage, recovery, and processing steps, and including QC data for both field and
laboratory operations.
This section must also describe the procedures and persons responsible for non-routine
occurrences, such as when detectors are returned opened, late, or when some other deviation
from the planned circumstances has occurred. Finally, this section of the QAP should describe
the procedures for rechecking results that indicate exposures to radon concentrations greater than
a specified limit (e.g., 100 pCi/L or about 4,000 Bq/m3) or the limit above which all
measurements are recalculated before being reported as final.
The information hi this section corresponds to EPA QA/R-5's Elements Dl: Data Review,
Validation, and Verification Requirements, and D2: Validation and Verification Methods.
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9.11 INTERNAL QUALITY CONTROL CHECKS
Internal QC measurements must be conducted by both analytical and residential service
providers. The following QC activities should be described:
Use of internal laboratory standards (check sources, canisters, etc.), self-
diagnostic tests, and other routine instrument performance checks, their
frequency, treatment of results, (e.g., use of means control charts [see Appendix
A]) and plans for corrective action if results fall outside predetermined criteria.
Duplicate or replicate measurements made to estimate precision, their frequency,
the criteria by which locations for duplicate measurements will be chosen, the
procedures for deploying and documenting duplicates, and the procedures for
assessing the need for corrective action (see Appendix A for control charts for
precision).
Comparison measurements, in which different types of devices are placed side-
by-side and results compared.
Known exposure (spiked) measurements made to assess relative bias, the
calibration facility where spikes are exposed, their frequency, the range of
concentrations to which they will be exposed, the procedures for documenting
their results, and the procedures for assessing the need for corrective action (e.g.,
analysis of results and comparison with predetermined limits).
Proficiency testing of analysts and operators.
In addition, this part should describe the QA checks on incoming detectors, equipment, and
supplies, for both new shipments of detectors and for detectors mailed back after deployment.
For example, some fraction of incoming charcoal canisters should be checked for high
background rates and package Integrity; detectors mailed in after deployment should be checked
to ensure that they were sealed properly and that the paperwork was completed correctly. The
corrective action to be taken if the results of either of these types of internal QA checks indicate
unusual results should be discussed here and referenced in the "Corrective Action" chapter of the
QAP, as described hi Section 9.15.
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9.12 QUALITY ASSURANCE AUDITS
After the procedures for field and laboratory operations have been developed, an audit must be
conducted to ensure that all the procedures work as planned. QA audits are based on the QAP.
Therefore, the QAP should be sufficiently detailed to form the basis of a meaningful audit. QA
audits can be conducted by the QA Officer, or an outside expert, who reviews the written
procedures for completeness. All QA audits should be documented in a written report that
specifies the nature and findings of the audit. Additional audits are conducted periodically
during the operations to check on the accuracy of the reported results.
This section of the QAP should describe the plans for these audits, including who will conduct
them, when they will be conducted, and the focus of the audits. The QA Officer should conduct
an audit after any change in method or procedure, and conduct additional audits at least once
every six months.
The corresponding element in EPA QA/R-5 is Cl: Assessments and Response Actions.
9.13 PREVENTIVE MAINTENANCE
This section should include descriptions of the types of preventive maintenance (for example,
mechanical maintenance of laboratory equipment) needed for adhering to schedules and for
achieving good quality data. The descriptions may include:
A schedule of important preventive maintenance tasks for measurement systems
and the responsible person for their implementation.
A list of critical spare parts.
Reference to current maintenance contracts and standard maintenance procedures
for measurement systems.
This information may not be relevant for a residential service provider, or may apply only to
computer or other non-analysis equipment.
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This information corresponds to EPA QA/R-5's Element B6: Instrument/Equipment Testing,
Inspection, and Maintenance Requirements.
9.14 PROCEDURES TO ESTIMATE DATA PRECISION, RELATIVE BIAS, AND
LOWER LIMIT OF DETECTION
This part of the QAP should describe the processes (including equations and descriptions of
calculations, statistical tests, control charts, etc.) by which the
Duplicate or replicate measurement results will be analyzed to estimate precision,
and the limits of acceptability for precision error.
Known exposure (spikes or crosschecks) measurement results will be used to
assess and monitor relative bias, and the limits for acceptable levels of relative
bias.
Field and laboratory background-measurement results will be used to assess and
track the background level and lower limit of detection, as appropriate for that
method.
The corresponding section in EPA QA/R-5 is Element D3: Reconciliation with User
Requirements of EPA QA/R-5.
9.15 CORRECTIVE ACTION
A corrective action plan is a contingency plan spelled out in IF...THEN... statements ("IF this
happens, THEN we will do the following"). For each critical measurement, the following topics
should be presented (in table form, if adequate):
Trigger points: What pre-specified conditions will automatically require
corrective action?
Personnel: Who initiates, approves, implements, evaluates, and reports corrective
action?
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Response: What specific procedures will be followed if the corrective action is
needed?
There may be different types of corrective actions that will be required as a result of QC
measurement results. This section of the QAP should describe at least three types:
The corrective action to be taken if results are outside the action limits when
plotted on the control charts.
The corrective action taken to correct problems found during audits.
The corrective action to be taken when there are deviations from the routine
circumstances (for example, detectors not returned within 10 days of exposure, or
incoming unused detectors with high backgrounds).
It may be appropriate to describe most types of corrective action in various sections described
previously (e.g., corrective action due to an occurrence related to preventive maintenance may be
discussed in that section); the section on corrective action should mention that other corrective
action procedures are described in other portions of the QAP.
Correction action information corresponds with EPA QA/R-5's Element Cl: Assessments and
Response Actions.
9.16 QUALITY ASSURANCE REPORTS TO MANAGEMENT
The main purpose of this section of the QAP is to: (1) identify the individuals responsible for
reporting; (2) describe the form and contents of anticipated reports; and (3) plan the presentation
of QA/QC data so that management can monitor data quality effectively. This section should
describe:
The names and titles of the people who prepare and receive the reports.
The type of report (written or oral) and their frequency.
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The contents of the various reports, such as
Changes in the QAP.
A summary of the current QA/QC programs, training, and
accomplishments.
- Results of QA audits.
Significant QA/QC problems, recommended solutions, and results of
corrective actions.
Data quality assessment in terms of precision, relative bias, field and
laboratory background, and lower limit of detection.
Limitations on the use of the measurement data.
This information corresponds to EPA QA/R-5's Element C2: Reports to Management,
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Appendix A
The Analysis and Interpretation of Quality Control Measurements
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The Analysis and Interpretation of Quality Control Measurements
This Appendix contains a review of the methods of calculating and monitoring the various
sources of error that can be expected with a radon or radon-decay product measurement system.
The total error is comprised of both random and systematic errors. For the purposes of this
discussion, the following terms are defined:
Error: The difference between the measurement result and the true value (or best estimate) of
the quantity being measured.
Systematic errors: Those errors that occur consistently (errors caused during calibration that
impact all subsequent measurements is a typical example) and cause a consistently high or low
bias in the result (note that there may be multiple systematic errors in a measurement system).
Random errors: Those errors that give rise to a range of results distributed around an average
value (a distribution); random errors cause imprecision.
Precision: The closeness of agreement between measurement results obtained under prescribed
like conditions (e.g., replicate measurements in the same environment).
Accuracy: The closeness of agreement between a measurement result (or the average of more
than one result) and an accepted reference value. There are two schools of thought on defining
the accuracy of a measuring process (Mandel 1984, Murphy 1961). One school argues that
accuracy should connote the agreement between the long-run average of the measurement results
and the reference value, in which case accuracy represents bias or systematic error. (See
Trueness in the Glossary). In this case, errors of precision are reduced because of the use of a
large number of measurements. This definition is in wide use among experimenters.
The other school of thought defines accuracy as the agreement between an individual
measurement result and the reference value. In this case, the errors of precision are not reduced,
and the total error depends on both precision (random errors) and bias (systematic errors).
Because of these different usages, the American Society of Testing and Materials (ASTM)
Standard Practice for Use of the Terms Precision and Bias in ASTMTest Methods (ASTM 1990)
states: "In order to avoid confusion resulting from use of the word 'accuracy,' only the terms
precision and bias should be used as descriptors of ASTM test methods."
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This report will maintain consistency with ASTM nomenclature, and use the terms precision
error and bias (or relative bias) to describe the components of error.
The combination of both systematic errors and random errors comprise the total error. The
estimate of overall uncertainty associated with a measurement result should be comprised of
upper bounds of both bias and precision errors.
This Appendix will also discuss the calculation of the lower limit of detection (LLD) and related
concepts. The LLD is important to understand, report properly, and place in context ofyour
measurement program.
A. 1 ROUTINE INSTRUMENT PERFORMANCE CHECKS
Proper operation of analytical instruments requires that their response to a given radon or decay-
product concentration be as consistent as possible from one measurement to the next. This
consistency can be checked using a reference source, counting background, and verifying that the
results fall within predetermined limits. In addition, proper operation of an energy-sensitive
instrument requires that its energy response be constant. Instrument quality control (QC)
therefore requires regular measurements of the following responses.
Instrument check sources are used for monitoring the constancy of response of an instrument.
The response characteristics of instrument reference sources should be as similar as possible to
those of real measurements, and the response caused in the instrument should be stable (or
predictable) over time.
Energy alignment sources (Coats and Goldin 1966) are used to check the overall gain and
linearity of spectrometers. The sources should emit radiation of two energies at least, and
preferably of a number of energies covering the range for which the spectrometer is set. In some
cases, the same source can be used both for instrument checks and energy alignment. Gamma
alignment sources can be made by the laboratory. They are also available as Standard Reference
Materials from the National Institute of Standards and Technology.
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Internal diagnostics can be performed evaluating specific components of measurement systems,
including voltages, pump flow rates, and other parameters. Some instruments provide pre-
programmed self-diagnostic procedures.
Routine instrument performance checks should be conducted following manufacturer
instructions, whenever the equipment has been significantly handled, whenever the operator
requires assurance that the equipment is providing a stable response, and according to a regular
schedule (e.g., daily, weekly, prior to sets of measurements or each measurement). The results of
the routine instrument performance checks need to be recorded in a log, with the date, time, and
initials of the person who performed the check. If the check yields numeric results, it should be
plotted on a means control chart, as described in Section A3.1. The QA Officer is responsible
for setting up the control chart with limits and guidelines for corrective action, for monitoring the
results, and is accountable for oversight of the investigation and corrective action when needed.
A.2 BACKGROUND MEASUREMENTS
A.2.1 Laboratory Background Measurements for Analytical Service Providers
Laboratory background measurements should be as similar as possible to actual measurements,
but without the influence of radon or decay products. Various types of background
measurements may be needed, including those for incoming materials, equipment, and
unexposed devices. Background measurements for continuous monitors should be made in a
glove box or with direct flow into the detector of aged air or nitrogen. Background
measurements are a component of the calibration process.
A.2.2 Field Background Measurements for Analytical and Residential Service Providers
The results of field background measurements performed by analytical or residential service
providers should be compared with the reported LLD (see Section A.5.1). If the results of the
field blanks are consistently (e.g., more than several blank results in a row) significantly greater
than the LLD, the analytical organization should be consulted and the potential for extraneous
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background be investigated. The analytical organization should be responsible for changing
background labels or adjusting results due to changed background.
The results of field background measurements may also be plotted on a means control chart in
the manner described in Section A.3.1 to ensure that a change in background levels can be
quickly identified.
A.3 EVALUATION OF QUALITY CONTROL DATA
A.3.1 Means Control Chart for Repeated Measurements of Background and Routine Instrument
Performance Checks
Control charts are basic tools for evaluating internal QC data (Goldin 1984, U.S. EPA 1984,
ANSI 1985, ASTM 1992). Taylor (Taylor 1987) provides an excellent discussion of a variety of
control charts, including those described here. See Taylor's "property" or "x-chart" for the
means chart described in this section. A control chart can be used to evaluate the variation of
replicate measurements either about a mean value to assess instrument stability (means chart) or
among themselves to assess precision error (range chart).
A means control chart consists of measurement results plotted on the y-axis and their dates
plotted sequentially with time on the x-axis. Limits (± three-sigma from the mean) are plotted as
horizontal lines, and data falling within these limits indicate that the system is "in control" and
operating as it was when the limits were established based on previous data. A control chart may
be used for a limited period, such as a month or two months, and then replaced by a new chart.
A standard Shewhart (Shewhart 1931, Duncan 1965) means control chart may be used for
making day-to-day checks on whether any repetitive measurement (such as of background or a
check source) is "in control" (see later in this Section). The control chart shows the mean of the
measurements, the warning levels that are two standard deviations above and below the mean,
and the control limits that are three standard deviations above and below the mean. An example
means control chart is shown in Exhibit A-l; example background control chart data are plotted
in Exhibit A-la.
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After data from check sources or background have been gathered for several weeks or months,
and well over 20 measurements have been made and plotted, the data can be analyzed in terms of
the standard deviation. Lines denoting the mean ± one-, two-, and three-sigma can be plotted. If
the system produces results that are consistent, ± one-sigma should contain two-thirds (2/3) of
the points, ± two-sigma should contain 19/20 of the points, and ± three-sigma should contain
nearly all of the points. The probability of obtaining a value outside the control limits is very
low (less than one percent). Note that these limits are two-tailed limits (values near both limits
or tails are of interest), as opposed to the limits for duplicates, which are one-tailed (see Section
A.4.1.4). If a value is obtained that is outside the three-sigma control limits, then the count
should be repeated. If the repeat value is still outside the three-sigma limit, then measurements
should be stopped and the situation evaluated and corrected. If results are outside the warning
levels (± two-sigma), measurements can continue while the QA Officer evaluates the situation.
As the data are plotted, "rule-of-thumb" indicators (Taylor 1985) that the measurement system
may be "out-of-control" include:
Two successive points outside the two-sigma limits.
Four successive points outside the one-sigma limits.
Any systematic trends high or low.
A systematic trend includes a series of points in the same direction or successive points all on the
same side of the mean, even if all are within the control limits. Note that one does expect to see
measurements outside the warning limits, and this does not necessarily mean that the process is
out of control (ANSI/ASQC 1987). Repeated data falling outside the limits are evidence of loss
of control, and requires an investigation. If no cause of increased variability or shift can be
found, then the control limits should be broadened and a sufficient number of data points should
be gathered so that the QA Officer is confident that the new limits are appropriate.
Note that the count rate of radioactive check sources changes with time. If the user is not aware
of the pattern of change, it may appear that the instrument is drifting when, in fact, it is not.
Instead of plotting total counts in a given period of time, it may be appropriate to plot another
parameter, such as counts per disintegration.
A-5
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Exhibit A4
Means Control Chart for Background or Check Source Results
result
3 sigma control limit
2 sigma warning level
average or mean line of results
2 sigma warning level
3 sigma control limit
date
The results plotted on these charts should be in sequential order by date. At least about
20 "in-control" measurements should be made before calculating the sample standard
deviation of the results (see the Glossary for the equation for sample standard
deviation). "In-control" means that the operator has confidence that the instruments
are operating properly and there is no evidence to suspect that there is anything faulty
about the result. The QA Officer is responsible for periodically assessing the spread
of values on the charts, recalculating the sample standard deviation based on new
results and determining whether the limits on the charts should be revised.
A-6
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40
Exhibit A-l a
Example Means Control Chart for Background
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Background Counts
Warning Levels
-Control Limits
Mean Count
A-7
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Exhibit A-la (continued)
Example Means Control Chart for Background
Date
7/10/95
7/11/95
7/12/95
7/13/95
7/14/95
7/15/95
7/16/95
7/17/95
7/18/95
7/19/95
7/20/95
7/21/95
7/22/95
7/23/95
7/24/95
7/25/95
7/26/95
7/27/95
7/28/95
7/29/95
7/30/95
Background Count
(in standard counting interval)
24
22
25
24
25
22
19
20
25
22
23
24
22
21
25
19
22
24
21
25
23
Plotted Results
Mean (average) =
Sample Standard Deviation =
Upper Warning Level =
Lower Warning Level =
Upper Control Limit =
Lower Control Limit =
23 counts
1.95 counts
27 counts
19 counts
29 counts
17 counts
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This report presents one strategy for assessing instrument performance and background based on
control charts; it involves simple "rule-of-thumb" concepts and is taken from Taylor (Taylor
1985, Taylor 1987). Other more sophisticated criteria for evaluating whether a measurement
system is "out-of-control" can also be used (Goldin 1984).
A.3.2 Means Control Chart to Evaluate Relative Bias From the Results of Known Exposure
Measurements
The results of known exposure measurements (spikes for passive methods and crosschecks for
active methods) can also be plotted on a means control chart. Bias may be expressed in terms of
relative percent error, or as
RPE = [(MV-RV)/RV]*100%
where: RPE = relative percent error;
MV = measured value of the spiked measurement or the instrument being
evaluated; and
RV = reference value (chamber or recently-calibrated instrument).
Note that the definition of relative percent error is similar to the definition of Individual Relative
Error (IRE), as defined in the RPP Handbook (U.S. EPA 1995a), except that the numerator of the
IRE is the absolute value of the difference while RPE can have positive or negative values.
The mean line should be set at zero, and the two-sigma and three-sigma limits can be set using
1) the coefficient of variation among the RPE values from at least 20 spikes or
crosschecks,
or, and only until the results of 20 spikes or crosschecks are available,
2) the average standard deviation as determined via duplicate measurements (see
Section A.4.1). Note that this option is a temporary measure that should be used
only at the inception of an operation, until the RPE values from valid spikes or
crosschecks are available.
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It may be appropriate to construct separate control charts for different ranges of radon
concentrations; for example, less than and greater than 4 pCi/L (150 Bq/m3) or 10 pCi/L (370
Bq/m3), for example, if the bias changes nonlinearly with concentration.
An example means control chart for using data from spikes from a passive system is shown in
Exhibit A-2, and a means control chart for plotting the results of crosschecks using an active
system is shown in Exhibit A-3. Data from example spiked measurements are plotted on a
means control chart in Exhibit A-2a.
A.4 ESTIMATING PRECISION
The precision of a measurement expresses the degree of reproducibility (repeatability) of that
measurement. Precision can be expressed in terms of the standard deviation*, s, or equivalently,
by the variance, s2. The variance of a measured quantity x, denoted by s2(x), is the combination
of two contributing variances, sn2(x) and sp2(x):
s2(x) = sn2(x) + sp2(x)
sn2(x) is the component of the variance associated with signal-to-noise problems and is closely
related to the variability of the noise level; sp2(x) is the component of the variance associated with
procedures and with measurements not affected by noise variability, such as weighing and
handling (U.S. EPA 1982a). At low concentrations, sn2 becomes the major part of the total
variance. This assumption is extremely important because it allows the treatment of the counts
measured at low concentrations as exhibiting a Poisson distribution. The value for sigma may be
different at different radon levels, so assess RPE values at different radon concentrations. If
appropriate, keep different control charts for different ranges of radon levels.
The objective of performing more than one measurement is to assess the precision error of the
measurement method, or how well side-by-side measurements agree. This precision error is the
" The standard deviation and the variance are parameters of the population of replicate
measurements. As such, the standard deviation is commonly designated by the Greek letter sigma (o)
and the variance by o2. Since the population parameters are unknown, empirical estimates designated by
s and s2 are used.
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Exhibit A-2
Means Control Chart for Spiked Results of Passive Methods
(Chart Used to Assess Bias)
RPE = [(MV-RV)TRV] * 100
MV = measured spiked result
RV = reference or chamber value
RPE 0
30% 3 sigma control limit
20% 2 sigma warning level
-20% 2 sigma warning level
-30% 3 sigma control level
Run number or date
The value of sample standard deviation (sigma) of the RPE values should be calculated from the
results of at least about 20 spiked results (within the same range of radon concentrations). If this
number of spikes has not yet been conducted, the sigma may temporarily be assumed to be 10%,
and then revised after calculating the sample standard deviation from the actual RPE values of
the spiked results. The control limits on the chart should be drawn at 0 +- 3 * sigma, and the
warning levels at 0 +- 2 * sigma.
The value for sigma may be different at different radon levels, so assess RPE values at different
radon concentrations. If appropriate, keep control charts for ranges of radon levels (e.g., 4-20
pCi/L or about 150 - 750 Bq/m3).
A-ll
-------
Exhibit A-2a
Example Means Control Chart for Relative Bias Based Upon Results of Spikes
Date
7/14/95
7/14/95
7/14/95
7/14/95
7/14/95
7/30/95
7/30/95
7/30/95
7/30/95
7/30/95
8/13/95
8/13/95
8/13/95
8/13/95
8/13/95
8/29/95
8/29/95
8/29/95
8/29/95
8/29/95
Spike Number
1
2
3
4
5
6
7
8
9
10
1 1
12
13
14
15
16
17
18
19
20
Reference (chamber)
Value
25.1
25.1
25.1
25.1
25.1
21.6
21.6
21.6
21.6
21.6
32.5
32.5
32.5
32.5
32.5
45.8
45.8
45.8
45.8
45.8
Measured Value
(pCi/L)
23.5
22.9
28.0
26.1
25.0
19.4
22.0
23.1
21.5
21.6
33.1
34.0
33.0
32.9
31.6
46.5
44.2
48.9
41.8
45.0
Relative Percent Error
(RPE)
-6.4
-8.8
11.6
3.9
-0.4
-10.2
1.9
6.9
0.5
0.0
1.8
4.6
1.5
1.2
-2.7
1.5
-3.5
6.8
-8.7
1.7
Plotted Results
Mean (center) Line =
Coefficient of Variation of the 20
RPE Values =
Warning Limits =
Control Levels =
0
5.60%
+ 11.2%
4- 16.8%
A-12
-------
18
16
Exhibit A-2a (continued)
Control Chart for Spikes
m
0.
o
h.
Ill
*!
o
u
14
12 4-
10
8
6-
4
2
0
-2 I
H 1 I
* * *
I I 1-
a. -4 --
>
-8
-10 -
-12 -
-14 -
-16 -
-18
-20 -
-22
1
9 11 13
Spike Number
15
17
19
* Relative Percent Error (RPE)
Mean (center) Line
Warning Limits
Control Levels
A-13
-------
Exhibit A-3
Means Control Chart for Crosscheck* Using Active Methods
(Chart Used to Assess Bias)
RPE = [(MV-RV)/RV] * 100
MV = measured result from instrument to be checked
RV = reference value from recently calibrated instrument
RPE 0
30%
3 sigma control limit
20%
2 sigma warning level
-20%
2 sigma warning level
-30%
3 sigma control limit
Run number or date
The value of sample standard deviation (sigma) of the RPE values should be
calculated from the results of at least about 20 crosschecks (within the same
range of radon concentrations). The sample standard deviation of the RPE
values is used. If this number of crosschecks has not yet been conducted, the
sigma may temporarily be assumed to be 10%, and then revised after calculating
the sample standard deviation from the actual RPE values of the crosscheck
results. The control limits on the chart should be drawn at 0 +- 3 * sigma, and
the warning levels at 0 +- 2 * sigma.
A-14
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RPP QA Guidance
EPA402-R-95-012
Date: 10/22/97
"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 the errors of the weighing process, and variations of analysis among detectors).
It is critical to understand, document, and monitor precision error. This continual monitoring and
documentation provides a check on every aspect of the measurement system.
For radiation measurements, counting statistics are often given as the measure of the variability
or repeatability of the measurements, primarily because of the ease of calculations. Counting
statistics error (i.e., using the square root of the total number of counts as the one-sigma error) is
a valid description of the variability of a measurement only when:
The quantity of nuclide present is so small that the procedure-calibration
variability is negligible in contrast with the background variability (U.S. EPA
1982b);and
All other sources of variability in the background are negligibly small in
comparison to counting error (a very rare occurrence).
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, 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. It is important to recognize
that a few duplicate results with 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 as
A-15
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RPP QA Guidance
EPA402-R-95-012
Date: 10/22/97
triggers for an investigation into the cause of the large differences. For example, the warning
level, or the level of discrepancy between duplicates which triggers an investigation, may be set
at a five percent probability (or some other level, as desired). This level is a difference between
duplicates that is so large that, when compared with previous precision errors, should only be
observed (for example) five percent of the time. A control limit, where further measurements
should cease until the problem is corrected, may be set at a one percent probability or less. The
normal practice is to set control limits corresponding to a three-sigma level, which means that a
difference this large would only occur by chance about one-tenth of one percent of the time.
If the data from a particular group of measurements are to be used for a study, and it is desired to
attach confidence limits for the precision errors to results, the pooled standard deviation can be
calculated for ranges of different radon concentrations. A method of pooling results of duplicate
detectors is outlined by the NCRP (NCRP 1985).
The range ratio is defined as the difference between two measurements divided by the expected
difference at that concentration (see the following section). Use of this statistic is recommended
because it is normalized to the expected precision at that concentration, and therefore the same
limits can be used for all concentrations. Other 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 control charts 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 150 Bq/m3, and with some upper bound, as
determined by duplicate measurements at various concentrations. At lower concentrations, e.g.,
between 2 pCi/L (or 80 Bq/m3) and 4 pCi/L (or 150 Bq/m3), a control chart may be developed by
plotting these same statistics; however, the proportion of the precision error to the mean will be
greater than the proportion at higher concentrations. In either case, the assumption that the
precision error is a constant fraction of the mean is a simplification and represents a conservative
and convenient way to monitor precision (see Section A.4.2). At concentrations less than about 2
pCi/L, or 80 Bq/m3, the LLD may be approached, and the precision error may be so large as to
render a control chart not useful.
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EPA402-R-95-012
Date: 10/22/97
A.4.1 Control Charts For Monitoring Precision Error
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 simultaneous, side-by-side measurements at each range of radon concentrations for
which a control chart is to be prepared. For example, if you will only estimate precision at
concentrations greater than 4 pCi/L, or 150 Bq/m3, you will need at least 20 measurements at
concentrations greater than 4 pCi/L, or 150 Bq/m3, to assess the "in control" level. The average
precision error should be the "in control" level, and measurements that were suspect should not
be included. If using a range ratio control chart (see below), the average range between
duplicates exposed to similar concentrations can be used as 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; see Exhibit A-4). 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 it is not, a new control chart (using the guidelines below)
should be prepared so that the warning and control limits are set at appropriate probability limits
for your system.
A.4.1.1 Range Ratio Control Chart
A range ratio control chart (Taylor 1987) is an easily understood type of precision control chart
that can be very useful when the variability (precision) cannot be simplified as a constant fraction
of the mean (see Section A.4.2). The range ratio chart allows all results (greater than the LLD) to
be plotted on the same chart, regardless of concentration. This is a sequential chart, on which
duplicate results are plotted as they are analyzed, with the date and/or other identification on the
A-17
-------
Exhibit A-4
Range (Difference) Between Two Measurements
With »14% Relative Percent Difference
(Or a 10% Coefficient of Variation)
where Relative Percent Difference (RPD) = [(A - B) / mean] * 100
and A = the larger result,
B = the smaller result, and
mean = the average of the two results
and where Coefficient of Variation (COV) = s / mean
and s = sample standard deviation (see Glossary)
Note that a 14% RPD corresponds to a 10% COV.
mean range (difference),, based on 14% RPD
4.3pCi/L 0.6pCi/L
4.8 0.7
5.5 0.8
6.1 0.9
7.4 1.0
10.8 1.5
16.2 2.3
21.5 3.0
26.9 3.8
32.3 4.5
43.0 6.0
53.8 7.5
80.6 11.3
108.0 15.0
215.0 30.0
323.0 45.0
430.0 60.0
Conversion from the traditional U.S. units is not provided for each value here;
1 pCi/L corresponds to 37 Bq/m3; see the Glossary for conversions.
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RPP QA Guidance
EPA402-R-95-012
Date: 10/22/97
x-axis. The value that is plotted is the actual difference between duplicates divided by the
expected difference at that concentration.
The range ratio, R, is defined as
where: RO = the observed range between duplicates, and
Re = the expected range between duplicates at that concentration.
The center line for this chart would be set at one, and the upper control limit set at 3.3
(corresponding to about a one-tenth of one percent probability of seeing a range this large) and
warning level of 2.5 (corresponding to about a 2.3 percent probability of seeing a range this
large) or a warning level of 2.2 (corresponding to a 5 percent probability) (ASTM 1992, Taylor
1987, Goldin 1984). An example chart with various limits is shown in Exhibit A-5. Exhibit A-
5a presents example duplicate data plotted on a range ratio control chart.
The expected value of the range can be taken from a plot of range versus concentration, as
determined from previous measurements at or near that concentration. In the absence of a
considerable number of previous measurements, a plot of expected range versus concentration
developed from a ten percent coefficient of variation can be used (see Exhibit A-4). After about
ten "in control" measurements have been made near that concentration, the expected range on the
plot can be changed.
The probability limits for the range ratios (one-tenth of one percent probability at 3.3 and five
percent at 2.2) can be understood using one-tailed statistics, as follows. The difference between
two measurements can be termed the range. A frequency plot of the range on the x-axis versus
the number of observed duplicates with that range on the y-axis would show that most duplicates
have a value near the mean range, and fewer are out in the tails near zero and the maximum
range. The mean range is equal to 1 .128 times the standard deviation of a measurement
(Rosenstein 1965, ASTM 1992). This can be used to calculate the percentiles for the right-hand
tail of the distribution, where large ranges are found. We are not interested in the probabilities in
A-19
-------
Exhibit A-5
Control Chart for Duplicates Using the Range Ratio Statistic
(To Assess Precision)
where the range ratio, R, is defined as
RO = the observed range between duplicates, and
RC = the expected range between duplicates at that concentration.
and the expected range between duplicates is taken from experience with duplicates near that
concentration or, if sufficient data are not yet available, using a plot constructed from the data
in Exhibit A-4.
3.3
2.7
2.2
99.99% control limit; expect to see a range this great
only about 0.13% of the time if all is operating in control
99.0% control limit; expect to see a range this great
only about 1% of the time if all is operating in control
95% warning level; expect to see a range this great
only about 5% of the time if all is operating in control
"in control" level; range ratio results will routinely be
1.0
around this level of precision
date or sequential duplicate i.d. number
A-20
-------
Exhibit A-5a
Example Range Ratio Control Chart for Tracking Precision
data (only when both results > 4 pCi/L)
Date
6/19/95
6/19/95
6/22/95
6/23/95
6/25/95
6/25/95
6/30/95
7/10/95
7/14/95
7/14/95
Oup. No.
1
2
3
4
5
6
7
8
9
10
A(pCi/L)
5.5
6.1 ...
6.0
10.2
4.9
4.7
8.5
6.3
10.4
9.8
B (pCi/L)
4.8
5.8
5.2
11.5
Ro
0.7
l_ 0.3
0.8
1.3
5.3 0.4
5.8 1.1
R.
0.7
0.8
0.8
1.5
0.7
0.7
9.4 0.9 | 1.3
7.0 0.7 | 0.9
9.0 1.4 : 1.4
11.6 1.8 1.5
R = Ro/ R.
1.0
0.4
1.0
0.9
0.6
1.6
0.7
0.8
1.0
1.2
Ro = range observed (larger minus smaller result)
Re = range expected at this concentration (initially based on a 14% Relative
Percent Difference)
«J
£
H
OS
E
3.4
3.2 -
3.0
2.8
2.6
2.4
2.2
2.0
1.8
1.6
1.4
1.2
1.0.
0.8
0.6
0.4
0.2
0.0
xample Range Ratio Control Chart for Tracking
Precision
' A
/\ ^
\/ ^/ v-^
V
»
»
I 2 3 4 56 7 8 9 10
Oup. No.
A-21
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RPP QA Guidance
EPA 402-R-95-012
Date: 10/22/97
the left tail of the distribution, where the ranges are near zero, and will include all those small
values in the percentiles. Therefore approximately 50 percent of the ranges will be between zero
and the mean range, 34 percent will be between the mean range and the mean range plus sigma,
etc. Only about 0.0013 (about one-tenth of one percent) of the ranges should fall outside the
mean range plus three sigma (sigma of the range)..
Experience with control charts in industry has shown that the exact percentages (such as 0.13%)
often do not apply, and these percentiles should not be treated as exact numbers. However, the
limits are useful as trigger points and reference values (Parkany 1993).
The probabilistic interpretations of the control chart (e.g., less than one percent of the
measurements outside the control limit by chance, and five percent outside the warning limit by
chance) will not apply if the expected range is not representative of actual in-control
measurements. However, comparing your results with the range given in Exhibit A-4 can serve
as a starting point.
A.4.1.2 Sequential Control Chart Based on Coefficient of Variation
An alternate method of plotting the results of duplicates is to use a sequential control chart based
on the coefficient of variation.
It can be shown (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 standard
deviation, and Xm is the mean or average of the two measurements). One method for obtaining
percentiles for the distribution of the COV is to apply a chi-squared (x2) test, where x2 can be
approximated as follows (Iglewicz and Myers 1970, McKay 1932):
X2n., - B[(n-l)COVn2/(n+(n-l)COVn2)] (Equation 1)
where: B = n[l + (1/COV2)];
COVn = the observed COV of the n* 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).
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EPA 402-R-95-012
Date: 10/22/97
For duplicates, where n=2, Equation 1 becomes
X2 * [2 + (2/COV2)][COVn2/(2 + COVn2)] (Equation 2)
For a value of 0.10 for COV, it further reduces to
X2 = 202[COVn2/(2
Referring to a x2 chart, one learns that the probability of exceeding a x2 of 3.84 is only
five percent. Inserting this value of 3.84 for x2 and solving for COVn, produces a COVn of 0.20.
This level of probability forms the warning level of 0.20. The control limit corresponds to a x2
of 6.63 and a COVn of 0.26, where the probability of exceeding that value is only about 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.
A.4. 1 .3 Sequential Control Chart Based on Relative Percent Difference
The RPD (or percent difference) is another expression of precision error, and is given by
RPD = [100|xrx2|]/[(x,+x2)/2]
For n=2,
RPD = COV /2
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 28% and 36%, respectively. This sequential
control chart for RPD should be used hi 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.
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RPP QA Guidance
EPA 402-R-95-012
Date: 10/22/97
A control chart using the statistic RPD based on an "in control" level of 25 percent RPD can also
be constructed. 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, or 150 Bq/m3, as determined by multiple simultaneous measurements at these low
concentrations.
A.4. 1 .4 Range Control Chart
A range control chart (Goldin 1984), also termed a Range Performance Chart (Taylor 1987), can
be constructed to evaluate precision, using the statistics of the range (difference between two
measurements) plotted against the mean 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= 1.128 s(x)
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:
Control limit = 3. 69 s(x)
Warning level = 2.53 s(x)
This type of chart is used by plotting the range versus mean concentration as duplicate
measurements are analyzed.
A.4.2 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
A-24
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RPP QA Guidance
EPA402-R-95-012
Date: 10/22/97
analyses also fall outside the control limit, stop making measurements and identify and correct
the problem. If any measurements fall outside the warning level, the QA Officer is responsible
for investigating the system and determining if corrective action is appropriate.
Note that with the exception of the range ratio control chart, the charts described here are
simplifications of actual conditions, because they are premised on the assumption that the
precision error is a constant fraction of the mean 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. However, methods discussed here present a conservative way
to monitor and record measurement error and are useful for comparing observed errors with an
industry standard.
A.5 MINIMUM DETECTABLE LEVELS
Many terms are now used to express the smallest amount of radioactivity that can be reliably
measured. Each term has a specific meaning and is calculated differently. This section reviews
some of these terms, and the purposes for which they can be used.
These limits are based on counting statistics alone and do not include other errors of precision
including errors caused during manufacture, handling, and analysis. Because of this, the
reporting of limits of detection using the following methods must be tempered with the user's
knowledge of his/her system and its capabilities. It is instructional, however, to calculate the
lowest detection limit possible based solely on counting statistics, and to know that a practical
detection limit lies somewhere close to or greater than that level. In addition, it is also useful to
review the various terms and their definitions to allow meaningful comparisons among results
reported by different programs.
A.5.1 Lower Limit of Detection fLLDI
The lower limit of detection (LLD) is defined as "the smallest amount of sample activity that will
yield a net count sufficiently large as to imply its presence" (Pasternack and Harley 1971, U.S.
AEC 1972, U.S. DOE 1990). It is based on work by Altshuler and Pasternack (Altshuler and
Pasternack 1963), and Currie (Currie 1968). It is the quantity that Altshuler and Pasternack
A--25
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RPP QA Guidance
EPA402-R-95-012
Date: 10/22/97
called "minimum detectable true activity" and Currie called LD, the "a priori detection limit."
The LLD is based on a balance of the risk of false detection of activity not actually present (Type
I error, or false positive) against the risk of missing activity which is actually present (Type II
error, or false negative). Values of a and b represent the probabilities of these errors,
respectively.
The derivation of the LLD can be described in the following way. (This discussion is patterned
after Harley and colleagues [U.S. AEC 1972].) A series of measurements of background made at
different times will produce different results. These results will be distributed as a Gaussian
frequency distribution, with a spread indicative of the variability of the background. Some
laboratories base their LLD only on this frequency distribution; for example, by using two times
the standard deviation of the background, and estimating a 95 percent confidence limit from this
value. This method does not take into account the fact that the measurements of true activity
(with background subtracted) will also show a frequency distribution. In cases where the radon
concentration measured is low, the two distributions will overlap.
The LLD can be approximated by:
where
Kg = the value for the upper percentile of the standardized normal variate corresponding
to the preselected risk for concluding falsely that activity is present (e.g., a value
of 1 .96 for an upper-tail risk of a = 0.025);
Kj, = the corresponding value for the predetermined degree of confidence for detecting
the presence of activity (1 - b); and
s0 and sb = the standard deviation for the observed (true activity plus background) and
background activity, respectively.
A-26
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RPP QA Guidance
EPA 402-R-95-012
Date: 10/22/97
If the values of a and b are set at the same level (i.e., if one is willing to take the same risk for
concluding falsely that activity is present as for missing the presence of activity), then K, = K^
The formula then reduces to:
If s0 = Sb (i.e., the variability of the observed activity is the same as the variability of the
background), then
= 23/2K,Sb
The values of K are given as tables of the normal distribution in statistical texts; some common
values are given below.
a JLh K 2!^K
0.01 0.9 2.327 6.59
0.02 0.98 2.054 5.81
0.025 0.975 1.960 5.54
0.05 0.95 1.645 4.65
0.10 0.90 1.282 3.63
0.20 0.80 0.842 2.38
0.50 0.50 0.000 0.00
Therefore, for a 95 percent confidence level for detecting activity when it is present (1-b = 0.95),
the LLD is set equal to 4.65 times the standard deviation of the background counts, or
LLD = 4.65 sb, when the:
1) background is relatively stable;
2) measurement and background counting times are equal;
3) the distribution of the background counts follows a Gaussian distribution.
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RPP QA Guidance
EPA402-R-95-012
Date: 10/22/97
This means that with this LLD, one accepts the chance of detecting activity when it is present 95
percent of the time but missing it five percent of the time. The U.S. NRC (U.S. NRC 1980)
applies the same definition: "the LLD is defined as the smallest concentration of radioactive
material sampled that has a 95 percent probability of being detected, with only a five percent
probability that a blank sample will yield a response interpreted to mean that radioactive material
is present. In other words, there is only a 5% chance of concluding that activity is present when
it is not, and a 95% chance of correctly concluding that activity is present when it actually is."
The value of K for a 50 percent chance shows that the LLD is zero if one is willing to accept a 50
percent chance of detecting activity when it is present.
The nature of the LLD should be kept in mind. It is an a priori estimate of the quantity of
activity that will be detected with a given confidence.
The limitations of the LLD should also be considered. Foremost among these are the
assumptions that s0 = sb and that the variability in the background is entirely Poisson. For
example, with a background count rate of 1 cpm and a 50-minute counting time, the LLD is 4.65
(.02)I/2, or 0.66 cpm. The counting rate for sample-plus-background is 1.66 cpm, so that its
Poisson variance is 1.66/50, or 0.033. Approximating this by the variance of the background
counting rate, 0.02, introduces an underestimate of 15 percent in the LLD. This underestimate is
larger for a small number of background counts (low background counting rate combined with
short counting times) and smaller for a larger number of background counts. This limitation of
the LLD is particularly severe in alpha spectrometry, where the total background count in a peak
area may be only one or two, even with counting times of several hundred minutes. For such low
total counts, the assumption that the Poisson distribution can be approximated by a normal
distribution also breaks down.
An alternate and more statistically sophisticated formula accounts for the case when repeated
measurements of the blank yield significant variation (U.S. NRC 1986). This formula adds a
term(Currie 1968):
LLD = 2.71+4.65sb
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RPP QA Guidance
EPA402-R-95-012
Date: 10/22/97
In the case of stable blank measurements, however, the LLD can be calculated:
LLD = 4.65sb
Note that both formulas apply only for equal blank and sample counting times. For unequal
counting times (Strom and Stansbury 1992):
LLD = [3 + 3.29 (RbtB[l-Hi/td)in]/lg
where Rb = background count rate;
tb = background count time; and
tg = gross count time.
Note that the electret ion chamber manufacturer does not calculate the LLD using these formulas,
which were developed for radiation counting. Users of electret systems should consult the
manufacturer for details of the LLD approximations specific to electret ion chamber systems.
A.5.2 Minimum Significant Measured Activity (MSMA)
Altshuler and Pasteraack defined the minimum significant measured activity (MSMA) as the
smallest measurement interpreted to demonstrate the presence of activity in the sample (Altshuler
and Pasternack 1963). Currie (Currie 1968) called this quantity, Lc, the critical level. These
terms refer to the evaluation of a gross measurement, after it has been made, as being
significantly greater than background, or equivalently, a net measurement as being greater than
zero. The test for this is the conventional statistical test of a difference as being greater than zero
(Student's test).
If expressed in terms of counting rate, the net counting rate, r, is the difference between the gross
observed counting rate, r0, and the background counting rate, rb. The variance of r is:
s2(r) = s2(r0) + s2(rb)
= (rA) + (rA)
A-29
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RPP QA Guidance
EPA402-R-95-012
Date: 10/22/97
when only Poisson variability is included.
If t0 = tb = t (i.e., the counting times for the sample and background are equal),
The net measurement has conventionally been considered to be significantly different from zero
at the .05 level if t > 1.96. Actually, the one-sided test for which t05 = 1.65, is probably more
appropriate.
The t statistic is defined as:
t = (r0-rb)/s(r)
For t = 1.96, the MSMA is the corresponding difference of counting rates:
MSMA = 1.96 (2rA)1/2 = 2.77 (rA)"2
A.5.3 Use of LLD and MSMA
Both the LLD and the MSMA are useful, when each is restricted to its proper sphere. LLD is a
prediction of measurement capability; MSMA is an evaluation of a completed measurement.
The LLD should be used when describing a system's measurement capability (e.g., in proposals).
The LLD has been used improperly to evaluate a completed measurement. When this is done,
there is a gray area between the point where the measurement, as evaluated by MSMA, has not
been shown to be different from background, 2.77 s,,, and the LLD, 4.65 sb. LLD cannot address
measurements in this range.
A-30
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RPP QA Guidance
EPA402-R-95-012
Date: 10/22/97
The MSMA has been used, also improperly, to estimate minimum detectable activity. The
MSMA is equal to an LLD with kb = 0. This corresponds to a probability of 0.5 of detection.
The MSMA, when used in this way, corresponds to only a 50 percent chance of detecting
activity.
A.5.4 Reporting Low Values
The result obtained in a measurement, which is a sample of the infinite population of possible
results, is the best estimate of the mean value of the population. These actual results, whether
greater than or less than the LLD, and whether positive, negative, or zero, should be used in
averaging. Elimination of results less than the LLD, or of results less than zero, introduces a bias
into the overall average value (Wall and Goldin 1966).
Measurement organizations need to maintain records of all results as measured, which will
include negative values in some cases. However, reporting results less than the LLD or less than
zero to most clients will not serve the clients' or the measurement organizations' interests. When
appropriate, results less than the LLD should be reported as "less than the lower limit of
detection of ," including the LLD as recently calculated using results of background
measurements.
A-31
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Appendix B
Information to be Included in a Measurement Report
-------
RPP QA Guidance
EPA402-R-95-012
Date: 10/22/97
Information to be Included in a Measurement Report
Measurement Provider Information:
name, address, phone and fax numbers
RPP ID #
any applicable State ID #
Analysis Laboratory RPP ID #, if different
Measurement Operator (or placement technician) RPP ID # (if applicable)
Date of Report:
Client Information:
name, address, phone numbers
Measurement Location:
address, other information (room, floor)
Measurement #:
The device used to measure radon/decay product concentrations was a serial
#/detector #
Measurement start date/time:
Measurement stop date/time:
Result: Note: The EPA recommends (EPA 1993) that measurement results should be
reported in the units that the device measures, and, when using traditional U.S.
units, that radon concentrations be reported to no more than one numeral to the
right of the decimal (e.g., 4.3 pCi/L) and radon decay-product concentrations be
reported in no more than three numerals to the right of the decimal (e.g., 0.033
WL). If the measured decay-product concentration is converted to a radon
concentration, and the radon concentration was not actually measured, the report
should state that this approximate conversion is based on a typical 50 percent
equilibrium ratio, and that this indoor environment may have a different and
varying ratio.
If result is greater than or equal to 4 pCi/L (150 Bq nv3) or 0.02 WL (4xlO*7 Jnr3): This level is
greater than the EPA action level. You should consult the EPA recommendations for additional
measurements or remedial action. These recommendations are in the enclosed "Citizen's Guide
B-l
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RPP QA Guidance
EPA402-R-95-012
Date: 10/22/97
To Radon" and "Consumer's Guide to Radon Reduction" (and State brochures, if applicable)
along with telephone numbers for State officials who can answer your questions.
If the result is less than 4 pCi/L (150 Bq nv3) or 0.02 WL (4xlO'7 Jnr3): This concentration is
less than the EPA action level. However, the EPA recommends retesting sometime in the future,
especially if occupancy patterns change.
The Environmental Conditions Agreement (agreement to maintain closed-house conditions) was
signed by the client or his/her designee, and the measurement operator found no indications of
deviations from these conditions. In addition, no evidence for tampering with the measurement
equipment was found. However, this organization is not liable for tampering with the equipment
or changes in radon/decay product concentration due to changes in environmental conditions
during the measurement.
If evidence of tampering found: The results of this test cannot be delivered because evidence of
tampering with the measurement equipment was discovered. This includes: description of
evidence. We recommend that another test be conducted.
Disclaimer statement.
B-2
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Appendix C
Acronyms
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RPP QA Guidance
EPA402-R-95-012
Date: 10/22/97
Acronyms
AC Activated charcoal adsorption
AT Alpha-track detection (AID)
Bq Becquerel
CR Continuous radon monitoring
CW Continuous working level monitoring
EL Electret ion chamberlong-term
EML U.S. Department of Energy Environmental Measurements Laboratory
EPA U.S. Environmental Protection Agency
ER Equilibrium ratio
ES Electret ion chambershort-term
eV Electron volt
GB Grab radon/pump-collapsible bag
GC Grab radon/activated charcoal
GS Grab radon/scintillation cell
GW Grab working level
L Liter
LLD Lower limit of detection (see Glossary)
LS Charcoal liquid scintillation
m3 Cubic meter
MeV Mega-electron volt
C-l
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RPP QA Guidance
EPA402-R-95-012
Date: 10/22/97
MV Measured value
NCRP National Council on Radiation Protection and Measurements
ORIA U.S. EPA Office of Radiation and Indoor Air (formerly ORP)
PB Pump-collapsible bag
pCi/L Picocuries per liter
QA Quality assurance (see Glossary)
QAP Quality assurance plan
QC Quality control (see Glossary)
RH Relative humidity
Rn Radon
RP Radon progeny integrating sampling unit (also RPISU)
RPD Relative percent difference (see Glossary)
RPP Radon Proficiency Program
RV Reference value, used as the known or "true" value
SC Evacuated scintillation cell (three-day integrating)
SOP Standard operating procedure (see Glossary)
T Temperature
TLD Thermoluminescent dosimeter
UT Unfiltered track detection
WL Working level
C-2
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GLOSSARY
and
INDEX
-------
Page
Accuracy: See Bias and page A-l of Appendix A.
Analytical service provider: An organization or individual that provides radon 4- 1 , 4-2
measurement services or activities, at a specific business location, that includes the
capability to analyze or read the radon measurement device(s) being used. Such an
analysis or reading capability may involve a laboratory or portable equipment and
operators. This was formerly known as a "primary" in the RMP Program. (See also
Residential service provider, U.S. EPA 199 5 a.)
Audit: A planned and documented investigative evaluation of a program to 6-5,9-12
determine the adequacy and effectiveness of as well as compliance with
established procedures, QA Plans, and other documentation.
Background field measurement (blanks^: Measurements made by analyzing 8-6, 8-9
unexposed (closed) detectors that accompanied exposed detectors to the field.
The purpose of field background measurements is to assess any change in analysis
result caused by exposure other than in the environment to be measured. Results
of background field measurements can be subtracted from the actual field
measurements before calculating the reported concentration. Background levels
may be due to leakage of radon into the detector, detector response to gamma
radiation, or other causes.
Background instrument (analysis system, or laboratory) count rate: The nuclear 8-6, A-2
counting rate obtained on a given instrument with a background counting sample.
Typical instrument background measurements are:
Unexposed carbon: for activated carbon measurement systems.
Scintillation vial containing scintillant and sample known to contain no
radioactivity: for scintillation counters.
Background measurements made with continuous radon monitors exposed
to radon-free air (aged air or nitrogen).
Background radiation: Radiation arising from radioactive materials, the sun, and 8-6, 8-9
parts of the universe, other than that under consideration. Background radiation
due to cosmic rays and natural radioactivity is always present; background radiation
may also be due to the presence of radioactive substances in building materials.
Becquerel rBqV A unit of radioactivity representing one disintegration per
second. The concentration of radon in air can be expressed in units of Becquerels
per cubic meter, or Bq nr3, where 0.027 Bq nr3 = 1 pCi/L.
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Page
Bias: The degree of agreement of a measurement (X, or average of a set of 8-11,9-6
measurements that are assumed to be representative of the long-term average)
with an accepted reference or true value (T); often expressed as the difference
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 performance
ratio (X/T).
Calibrate (calibration): To determine the response or reading of an instrument 7-1
or measurement system relative to one or more known values over the range of
the instrument; results are used to develop correction or calibration factors.
Chain-of-Custody: An unbroken trail of accountability that ensures the physical 6-1
security of devices, data, and records.
Check source: A radioactive source, not necessarily calibrated, which is used 8-13, 9-11
to confirm the continuing consistent and satisfactory operation of an instrument. A-2, A-5
Client: The responsible individual or parties who hire(s) the radon tester. B-l
Coefficient of variation (COV). relative standard deviation (RSD): A measure of
precision, calculated as the standard deviation (s or o) of a set of values divided
by the average (Xavg or u), and usually multiplied by 100 to be expressed as a
percentage.
COV = RSD = (s/Xavg) x 100 for a sample,
or
COV ' = RSD ' = (o/u) x 100 for a population.
See Relative percent difference.
Corrective action: An action taken to rectify conditions adverse to quality and, 3-2,9-11,
where necessary, to preclude their reoccurrence. 9-13
Counting statistics (error!: The inherent variability of a radiation measurement 8-5, A-10
due to the random nature of the radioactive disintegration and detection processes. A-l 5
Curie (CD: A unit of radioactivity equal to 3.7 x 1010 disintegrations per second.
A standard measurement unit for radioactivity, specifically the approximate rate
of decay for a gram of radium = 37 billion decays per second.
Data validation: The process of checking measurement information to ensure 6-5
that it is correctly recorded (transcribed, modemed, faxed, calculated, typed,
printed, etc.). Data validation should be conducted on portions of all recorded
information.
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Page
Duplicate measurements: Two measurements made concurrently and in the same
location, side-by-side. (Charcoal adsorbing devices should be about 4 in. (10 cm)
apart. Other types of devices should be directly adjacent or touching.) The
results are used to monitor the precision error of the measurement method.
Energy alignment source: A source containing alpha- or gamma-emitting
nuclides covering the range of energies for which a spectrometer is used.
Equilibrium ratio, radon: The equilibrium ratio in traditional U.S. units = B-l
[WL(IOO)]/ (pCi/L). At complete equilibrium (i.e., at an equilibrium ratio of
1.0), 1 WL of radon decay products would be present when the radon
concentration is 100 pCi/L. The ratio is never 1.0 in a house. Due to
ventilation and plate-out, the radon decay products never reach equilibrium
in a residential environment. A commonly assumed equilibrium ratio is 0.5
(i.e., the radon 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.
Large buildings, including schools, often exhibit equilibrium ratios less
than 0.5.
Gamma radiation: Short wavelength electromagnetic radiation of nuclear origin,
with a wide range of energies.
Instrument check source: A source used for determining the consistency of
response of an instrument. Instrument check sources are counting samples
with a predictable count rate, such as a plated uranium oxide or lead-210
planchet, or a tritium scintillant gel. The check source need not be a standard
source but counting times should be long enough to give enough counts for
good counting statistics.
Lower limit of detection (LLD): The smallest amount of sample activity 8-7, A-25
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
that activity is present when it actually isn't, the LLD may be approximated
by a value of 4.65 times the standard deviation of the background counts
(assuming large numbers of counts where Gaussian statistics can be used
and for equal background and sample counting times [ANSI 1989, Pasternack
and Harley 1971, U.S. DOE 1990, U.S. NRC 1986]).
Mean: The average. The best estimate of the mean of an entire population,
as calculated from k samples (x,, x2, ...Xi,...x^ is given by:
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Page
m(x) =
Normal approximation to the Poisson distribution: A normal distribution is
described by two parameters, its mean and standard deviation. If a normal
distribution is constructed by assigning the mean value of a Poisson distribution
as both the mean and variance, that normal distribution may be used as an
approximation to the Poisson distribution. The approximation is better for
larger values of the mean value, and is generally considered useable when
the mean exceeds about 20 counts (Jarrett 1 946). .
Picocurie fpCD: One pCi is one trillionth (10"12) of a curie, 0.037 disintegrations
per second, or 2.22 disintegrations per minute.
Picocurie per liter (pCi/L); A traditional unit of radioactivity corresponding B-l
to an average of one decay every 27 seconds in a volume of one liter, or
0.037 decays per second in a liter of air or water. This unit can be
converted to the modern international units of Becquerel per cubic meter;
1 pCi/L = 37 Bq m'3.
Poisson statistics: The number of radioactive disintegrations in a quantity of
radioactive material in a given time is described by the Poisson frequency
distribution. The number of events recorded by a detector system that
counts a constant fraction of the disintegrations is also described by the
Poisson frequency distribution. For example, the number of counts obtained
by repetitive 10-minute counting of a radium source will cluster about a
mean value with a Poisson distribution. The Poisson distribution is described
by a single statistic, the mean, which is also equal to the variance.
Quantities derived from the number of counts, such as the counting rate,
are not necessarily described by Poisson statistics.
Potential alpha energy concentration: The concentration of radon decay
products, in air, in terms of the alpha energy that will be released during
complete decay of Rn-222 through Po-214.
Precision: A measure of mutual agreement among individual measurements 8-1,9-5,
made under similar conditions. Can be expressed in terms of the variance, 9-13, A-10
pooled estimate of variance, range, standard deviation at a particular
concentration, relative percent difference, coefficient of variation or other
statistic.
G-4
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Eage
Quality: The total properties or characteristics of a service and product 2-1,3-1
(e.g., measurement results and delivery) that bear on the ability to meet
the needs and expectations of the client.
Quality assurance: A system of activities whose purpose is to provide the 2-1,3-1
client with the assurance that the product and/or service meets their needs
and expectations in terms of defined standards of quality (precision, bias,
and total error over time, for example). Includes management, planning,
documentation, and quality control and improvement activities.
Quality Assurance Plan (OAP): A formal technical document containing 9-1
the detailed procedures for ensuring and documenting quality. The QAP
will also contain a description of the management policies, organizational
authority, responsibilities, and reporting for ensuring quality services
(unless a separate Quality Management Plan is prepared).
Quality control: The system of activities designed to control the quality 2-1,8-1
of the products, including measurements made to ensure and monitor data
quality. Includes calibrations, duplicate, blank, and spiked measurements,
routine instrument performance checks, interlaboratory comparisons, audits,
and measures of customer satisfaction.
Quality management: That part of the management system that determines 2-1,3-1
and implements quality policies. This may include planning and allocation 5-1
of resources.
Quality system: A documented management system describing the policies, 3-1, 5-2
objectives, principles, organizational authority, responsibilities, accountability,
and implementation plan of an organization for ensuring quality in its work
processes and products. The QA Plan may serve as the documentation of the
quality system.
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 calibration chamber (calibration facility): An airtight enclosure in 7-1,7-2
which operators can measure and, in some cases, induce and control 7-3,8-11
different environmental parameters and concentrations of radon and decay
products. A radon calibration chamber can be used for exposing devices
for initial or periodic calibrations, spikes, or evaluating device response
to various parameters.
G-5
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Page
Relative percent difference (RPD): A statistic used to track precision errors,
calculated by:
= [(|X1-X2|)/Xavg]xlOO
where: X, = concentration observed with the first detector or equipment;
X2= concentration observed with the second detector, equipment;
|X! - X2| = absolute value of the difference between X, and X2; and
Xavg= average concentration = ((X, +X2)/2).
The RPD and coefficient of variation (COV) provide a measure of precision,
but they are not equal. Below are example duplicate radon results (in
traditional units only for this example) and the corresponding values of
RPD and COV:
Rnl Rn2 RPD COV
(%) (%)
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 I ft = COV.
See Coefficient of variation (COV).
Relative standard deviation: See Coefficient of variation.
Residential service provider: An organization that provides consultation 4-1,4-2
(presenting information about radon and its risks, providing advice, making 4-4
recommendations and referrals), packaging radon measurement devices, and
placing or retrieving radon measurement devices in a residential setting.
This was formerly known as a "secondary" in the RMP Program (U.S. EPA 1995a).
Spiked measurements (spikes), pr knowri exposure measurements: Quality 8-11,9-6
control measurements in which the detector or instrument is exposed to a A-9
known concentration in a calibration facility and submitted for analysis.
Used to evaluate relative bias.
Standard deviation (s): A measure of the scatter of several sample values
around their average. For a sample, such as several radon measurements
G-6
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Page
out of the possible population of radon measurements, the sample standard
deviation (s) is the positive square root of the sample variance:
s =
XX -
In general, the sample standard deviation should be used.
For a finite population in which all measurements are known, the
population standard deviation (a) is:
o =
N
Eex,-
where n 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
expressed in the same units as the observed variable X. For example,
the upper 99.5 percent probability limit on differences between two
values is 2.77 times the sample standard deviation.
Standard operating procedure (SOP^: A written document which details 6-1
an operation, analysis, or action whose mechanisms are prescribed
thoroughly and which is officially accepted as the method for performing
routine tasks.
Standard Reference Material (SRM1: A term used by the National Institute 7-1
of Standards and Technology for its calibrated reference materials.
Statistical control chart (Shewhart control chaif): 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).
G-7
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P_age
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 (indicating the need for an
investigation) may be two sample standard deviations above and below
the mean, and the control limit (indicating the need to halt operations until
the problem is identified and corrected) may be three sample standard
deviations above and below the mean.
Trueness: A term used to describe the difference of the mean of a finite
number of measurements from the "true" or assumed value. This term is
related to the term bias, which is used to describe the difference between
the long-term average difference from the "true" value (Parkany 1993).
Uncertainty: The range of values within which the true value is estimated
to lie. It is a best estimate of possible error due to both random errors
(imprecision) and systematic errors (that produce bias).
Variance: The best estimate of the variance, from k samples out of the
entire population (x,, x2,...xi,...xk) is given by:
E (X, - Xavg)2
k - 1
Working level (WD: Any combination of short-lived radon decay products B-l
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 Rn-222. In modern, international units,
1 WL = 2.08xlO-5 Jm-3.
G-8
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