NUREG-1400
text
Air Sampling in the Workplace
Final Report
U.S. Nuclear Regulatory Commission
Office of Nuclear Regulatory Research
E. E. Hickey, G. A. Stoetzel, D. J. Strom, G. R. Cicotte, C. M. Wiblin, S. A. McGuire
Air Sampling in the Workplace
'
Final Report
Manuscript Completed: February 1993
Date Published: September 1993
E. E. Hickey*, G. A. Stoetzel*, D. J. Strom*, G. R. Cicotte*, C. M. Wiblin**, S. A. McGuire
Division of Regulatory Applications
Office of Nuclear Regulatory Research
U.S. Nuclear Regulatory Commission
Washington, DC 20555-0001
- Pacific Northwest Laboratory
Richland, WA 99352
- Advanced Systems Technology, Inc.
3490 Piedmont Road, NE - Suite 1410
Atlanta, GA 30305
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Use of NUREG-1400 by Licensees
This report, NUREG-1400, was written to provide technical information to licensees using Regulatory Guide 8.25, Revision 1, .A..ir Sampling in the Workplace." The report was reviewed by the U.S. Nuclear Regulatory
Commission (NRC) staff for its technical content.
NUREG-1400 is not and should not be used as a regulatory compliance document, because it neither establishes
regulatory positions nor defines what is acceptable to the NRC. For the case in which a licensee has made a
commitment to conduct air sampling in accordance with the recommendations in Regulatory Guide 8.25, NUREG-1400
should not be used in compliance reviews to determine whether the recommendations have been followed. Instead,
NUREG-1400 is a technical resource for the licensee to use to obtain technical information when information is wanted.
Regulatory Guide 8.25 specifically states that the guide does not apply to activities conducted under 10 CFR Part 50 at reactor facilities, however, NUREG-1400 provides examples of reactor facilities to demonstrate all types of air
sampling programs.
iii NUREG-1400
Abstract
This report provides technical information on air sampling that will be useful for facilities following the
recommendations in the NRC's Regulatory Guide 8.25, Revision 1, 'i\ir Sampling in the Workplace." That guide
addresses air sampling to meet the requirements in NRC's regulations on radiation protection, 10 CPR Part 20. This
report describes how to determine the need for air sampling based on the amount of material in process modified by the
type of material, release potential, and confinement of the material. The purposes of air sampling and how the purposes
affect the types of air sampling provided are discussed. The report discusses how to locate air samplers to accurately
determine the concentrations of airborne radioactive materials that workers will be exposed to. The need for and the
methods of performing airflow pattern studies to improve the accuracy of air sampling results are included. The report
presents and gives examples of several techniques that can be used to evaluate whether the airborne concentrations of
material are representative of the air inhaled by workers. Methods to adjust derived air concentrations for particle size
are described. Methods to calibrate for volume of air sampled and estimate the uncertainty in the volume of air
sampled are described. Statistical tests for determining minimum detectable concentrations are presented. How to
perform an annual evaluation of the adequacy of the air sampling is also discussed.
Contents
Use of NUREG-1400 by Licensees . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . w
Abstract ............................................................................... : . v
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Xll1
1 Evaluation of the Need for Air Sampling ................................................ . 1.1
1.1 When to Evaluate the Need for Air Sampling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.1
1.2 Air Sampling Based on Potential Intakes and Concentrations . . . . . . . . . . . . . . . . . . . . . . . . . . 1.2
1.2.1 Release Fraction R . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.2
1.2.2 Confinement Factor C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.2
1.2.3 Dispersibility D . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . 1.2
1.2.4 Examples of How to Determine Air-Sampling Needs . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.3
1.2.4.1 Nuclear Medicine Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.3
1.2.4.2 Uranium Fuel Fabrication Pellet Grinding Area Example . . . . . . . . . . . . . . . . . . 1.3
1.3 Air-Sampling Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.4
1.3.1 Sample Collectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.4
1.3.1.1 Sample Collectors for Particulates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.4
1.3.1.2 Sample Collectors for Gas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.5
1.3.1.3 Sample Collector Holders . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.6
1.3.2 Air Movers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . · 1.6
1.3.3 Types of Samplers . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1. 7
1.3.3.1 Lapel Samplers ........... ; . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.7
1.3.3.2 Pottable Air Samplers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.8
1.3.3.3 Fixed-Location Samplers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.8
1.3.3.4 Air Monitors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.8
1.4 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.9
2 Location of Air Samplers ............................................................ . 2.1
2.1 Purpose of Airflow Studies ..................................................... . 2.1
2.1.1 Stratification and Stagnation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2
2.1.2 Water-Filled,Pools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4
2.1.3 Doors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4
2.1.4 Bi-Level Airflow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4
vii NUREG-1400
Contents
2.1.5 Recirculating Airflow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.6
2.1.6 Wall and Floor Penetrations ............................ : . . . . . . . . . . . . . . . . . . . 2.6
2.2 Determination of Airflow Patterns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.7
2.2.1 Preparation for Airflow Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.8
2.2.2 Methods of Airflow Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.9
2.2.2.1 Qualitative Airflow Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.9
2.2.2.2 Quantitative Airflow Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.10
2.2.3 Performing Qualitative Airflow Pattern Studies ........... ,. . . . . . . . . . . . . . . . . . . . . . 2.13
2.2.3.1 Examples of a Qualitative Airflow Study
in a Laboratory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.14
2.2.3.2 Airflow Study at a Nuclear Power Plant . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.16
2.2.4 Quantitative Airflow Pattern Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.16
2.2.4.1 Example of a Quantitative Airflow Pattern Study . . . . . . . . . . . . . . . . . . . . . . . . 217
2.3 Selecting Sampler Location .................................................... . 2.21
2.3.i Factors in Locating Samplers .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.21
2.3.2 Examples of Determining Sample Locations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.21
2.3.2.1 Effective Confinement of Radioactive Material . . . . . . . . . . . . . . . . . . . . . . . . . 2.22
2.3.2.2 E~timation of Worker Intakes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.23
2.3.2.3 Early Warning of Elevated Air Concentrations . . . . . . . . . . . . . . . . . . . . . . . . . 2.24
2.4 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.25
3 Demonstration that Air Sampling Is Representative
of Inhaled Air ................................................................... . 3.1
3.1 Need to Demonstrate that Air Sampling Is Representative
of Breathing Zone Air . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
3.2 Comparison of Fixed-Location Air Sample Results with Lapel Sample Results . . . . . . . . . . . . 3.1
3.3 Comparison of Fixed-Location Air Samples with Bioassay Results . . . . . . . . . . . . . . . . . . . . . . 3.2
3.4 Comparison with Air Sampler Results Using Multiple Samplers . . . . . . . . . . . . . . . . . . . . . . . 3.8
3.5 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.8
4 Adjustments to Derived Air Concentrations ............................................. . 4.1
41 Adjusting Derived Air Concentrations for Particle Size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1
4.2 Methods for Adjusting DACS . .. . . .. . . . . . . . . . .. . .. .. . . . . . . . . . . . . . . . . .. .. . . . . . . . . . 4.6
4.2.1 Use of a Cascade Impactor to Determine Particle Size . . . . . . . . . . . . . . . . . . . . . . . . . 4.6
4.2.2 Using Cyclones to Compensate for Particle Size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.6
4.3 Adjusting Derived Air Concentrations for Solubility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.6
NUREG-1400 viii
5
6
Contents
4.4 References ................................................................... . 4.7
Measuring of the Volume of Air Sampled ................................................ . 5.1
5.1
5.2
Means to Determine Volume of Air Sampled ...................................... .
5.1.1
5.1.2
5.1.3
5.1.4
5.1.5
Flow Control for Portable Air Samplers .................................... .
Flow Control for Air Samplers Connected to Central Vacuum Systems ........... .
The Importance of Having a Gauge to Indicate the Filter Load ................. .
The Importance of Constant Flow .............. : .......................... .
Total Volume Measurement Devices ....................................... .
Calibration Frequency and Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ............ .
5.2.l
5.2.2
5.2.3
5.2.4
5.2.5
Calibration Frequency ................................................... .
Calibration to Primary Standards .......................................... .
Calibration to Secondary Standards ........................................ .
Calibration of Rotameters ....... ; ....................................... .
Calibration of Flow Totalizers ............................................ .
5.1
5.1
5.3
5.3
5.3
5.3
5.4
5.4
5.5
5.5
5.5
5.7
5.3 Uncertainty . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.7
5.4 Method for Determining Air In-Leakage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.8
5.5 Pressure and Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.8
5.6 References .......... '... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.11
Evaluation of Sampling Results ....................................................... . 6.1
6.1
6.2
6.3
6.4
Detecting Changes in Air Concentrations Over Time ............................... .
Efficiency of Collection Media .................................................. .
Detection Sensitivity ..................... ' ..................................... .
6.1
6.1
6.2
6.3.1 Determining the Activity Concentration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.3
6.3.2 Deciding Whether an Air Sample Is Above Background:
the Decision Level . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.5
6.3.3 Measuring Detection Capability for a Counting System:
Minimum Detectable Activity .................... ; . . . . . . . . . . . . . . . . . . . . . . . . . 6.5
6.3.4 Measuring Detection Capability for an Air-Sampling Program:
Minimum Detectable Concentration ................................... : . . . . 6.6
6.3.5 MDC for a Mixture of Radionuclides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.7
6.3.6 Checking Counter Background for Non-Random Fluctuations . . . . . . . . . . . . . . . . . . . 6.7
References .................................................................. . 6.8
Appendix A - Additional Decision Level Equations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A.1
lX NUREG-1400
Figures
2.1
2.2
2.3
2.4
2.5
2.6
2.7
2.8
2.9
2.10
2.11
2.12
2.13
3.1
3.2
3.3
3.4
3.5
4.1
4.2
5.1
5.2
5.3
5.4
5.5
5.6
Figures
Example of Stratification of Air Layers ................................................ .
Airflow Modification Due to Water ................................................... .
Example of Variable Flow Through Openings .. ; ....................................... .
Example of Bi-Level Flow Reversals .................................................. .
Example of Unexpected Flows ...................................................... .
Quantitative Dispersion Factors ...................................................... .
Diagram of Example Work Area ..................................................... .
Preliminary Airflow Pattern Survey in Cube at 262-ft Level ............................... .
Airflow Patterns as Determined by Smoke Candles at Selected Locations .................... .
Example Work Area, Test 1 ......................................................... .
Example Work Area, Test 2 .......•.............••...................................
Example Work Area, Multiple Release Points in a New Facility ............................ .
Analytical Laboratory Work Area .................................................... .
Example Work Area Coµfiguration for One Worker and
Two Fixed-Location Samplers ....................................................... .
Example Multi-Workstation Configuration for Six Workers and
Seven Fixed-Location Air Samplers ................................................... .
Sample Work Sheet (1) Showing the Results of a Comparison Study
of Air Sampling with Bioassay ....................................................... .
Sample Work Sheet (2) Showing the Results of a Comparison Study
of Air Sampling with Bioassay ....................................................... .
Sample Work Sheet (3) Showing the Results of a Comparison
with Multiple Samplers ............................................................. .
Values for Ratios of Deposition Fractions .............................................. .
DAC Ratios for 235U ............................................................... .
Rotameter ............................. : ......................................... .
Orifice Meter ........................................ , ............................ .
Calibration Setup of a Rotameter Using a Wet Test Meter ................................ .
Calibration Setup of a Rotameter Using a Spirometer .................................... .
Typical Rotameter Floats and Reading Indicator Positions ................................ .
In Place Calibration of Sample Collector ........ , ....................................... ·
2.3
2.5
2.6
2.7
2.8
2.12
2.15
2.17
2.18
2.19
2.20
2.23
2.24
3.3
3.3
3.6
3.7
3.9
4.2
4.5
5.2
5.2 I
5.6
5.6
5.9
5.10
ll
2J
2.2
2.3
3J
3.2
4J
4.2
4.3
4.4
5J
6J
6.2
·6.3
Tables
Release Fractions ....... .
Purposes and General Placement of Air Samplers and Monitors ........................... .
Comparison of Techniques Used to Determine Airflow Patterns
Within the Workplace .............................................................. .
Common Tracer Gases and Measurement Techniques ................................... .
Comparison of Lapel Samplers and Fixed-Location Air Samplers,
One Worker with Two Fixed-Location Air Samplers ..................................... .
Comparison of Lapel Samplers and Fixed-Location Air Samplers,
Six Workers with Seven Fixed-Location Air Samplers .................................... .
Ratios for Deposition Fractions ...................................................... .
Percentages of Committee Dose Equivalent,
Factors and H50,T (Sv /Bq) for Cobalt 60, Class W ....................................... .
Values of Deposition Fraction Ratios, Committed Dose Equivalents and Weighted
Committed Dose Equivalents for Cobalt 60, Class W, and AMAD = 7 µm ................... .
Ratios of DAC to DAC for 235U ...................................................... .
Types of Flow Rate Measurement Instruments .......................................... .
Filter Efficiencies for the Oxide Conversion Building ........•.............................
Summary of Symbols, Quantities, and Units ............................................ .
Chi2 Calculation for the Example .................................................... .
1.3
2.2
2.10
2.13
3.4
3.4
4.2
4.3
4.4
4.5
5.4
6.3 I
6.4
6.9
xi NUREG-1400
Acknowledgments
The authors would like to thank the many people who contributed to the development, production, and
publication of this report. We greatly appreciate their guidance, technical assistance, and patience as this document
has evolved from the original drafts of Stephen McGuire, NRC project manager. Wayne Knox and Claude Wiblin of
Advanced Systems Tuchnology are acknowledged for their technical contributions, especially on the hazard evaluatipn
method and flow pattern studies, and Allen Brodsky for the 10-6 factor and its use. A special thanks is given to Alfred
C. Schmidt, Schmidt Instrument Co., for assistance in revising information on air sampling devices. Other technical
contributors include Judson Kenoyer, Timothy Lynch, Jofu Mishima, and Paul Stansbury. Andrew McFarland and N ..
K Anand of Tuxas A&M provided review and technical input on deposition in sampling lines. Many helpful comments were also received from the following NRC reviewers: Jack Bell, Donald Cool, George Kuzo, Cynthia Jones,
Ron Nimitz, Scott Pennington, Alan Roecklein, Sarni Sherbini, Dennis Sollenberger, Joseph Wang, and James
Wigginton. The reviewers at the Pacific Northwest Laboratory included Don Bihl, Jerry Martin, Jack Selby, Paul
Stansbury, Ken Swinth, and Bruce Vesper. Information was contributed for examples by Michael Orcutt of Nuclear
Fuel Services, Richard Dubiel of Philadelphia Electric, Jay Maisler of NUMARC, and Bob Robinson of GE Nuclear
Energy. The assistance from Nora Nicholson, North Anna Power Station, in obtaining data for examples is greatly
appreciated. The review by Tuny Weadock, U.S. Department of Energy, is also appreciated. Finally, a special thanks
is given to the Jim Jamison, Paul Stansbury, and George Vargo for their advice as the final peer reviewers of the
document, to Diana Mcinturff, Marianna Cross, and Mary Heid for text processing, and to the technical editors, Jim
Weber and Susan Ennor, for all the effort necessary to edit and coordinate production of this report.
xiii NUREG-1400
1 Evaluation of the Need for Air Sampling
This document provides examples, methods, and
techniques for air sampling that may be useful for
implementing the recommendations in Regulatory
Guide 8.25, "Air Sampling in the Workplace," and the
requirements of 10 CFR Part 20.
As discussed in Regulatory Guide 8.25 (NRC 1992), the
purposes of air sampling are to determine if the
confinement of radioactive material is effective, to
measure airborne radioactive material concentrations in
the workplace, to estimate worker intakes, to determine
posting requirements, to determine what protective
equipment and me~sures are appropriate, and to warn of
significantly elevated levels of airborne radioactive
materials. Workplace air sampling for both airborne
particulates and radioactive gases is addressed; however,
air sampling of radiological effluents is not addressed.
1.1 When to Evaluate the Need for Air
Sampling
The need to perform surveys and monitoring is based on
• the need to limit dose to workers. According to 10 CFR 20.1502(b)(l), worker intakes of radioactive materials
must be monitored if the intakes are likely to exceed
10% of the applicable annual limit on intake (ALI) in
1 year. If a worker's intake is likely to exceed 10% of the
ALI, monitoring of intake is required (10 CFR 20.1502)
and the licensee must record the intake, the committed
effective dose equivalent, and the committed dose to the
organ receiving the highest total dose (10 CFR 20.2106).
For most licensee employees, intakes approaching 10%
of the ALI are unlikely and monitoring of intakes under
10 CFR 20.1502 is unnecessary. However, for a small
fraction of licensee employees, intakes exceed 10% of the
ALI and monitoring is required. Some employees
cannot be easily put in either category. These are the
employees for whom 10 CFR 20.1502 requires that the
licensee predict the annual intake.
Thus, in effect, the new 10 CFR Part 20 requires a
method for predicting likely int~kes for some workers
who might (or might not) have a significant intake. The
following method provides a system for determining
whether projected airborne concentrations may be high
1.1
enough that workers are likely to exceed 10% of an ALI,
thereby requiring monitoring and indicating the need for
a licensee to perform air sampling. This two-step
method is acceptable to the U.S. Nuclear Regulatory
Commission (NRC) through endorsement in Regulatory
Guide 8.25.
The first step is to estimate the quantity Q of unencapsulated radioactive material that is available to be inhaled
by a worker during 1 year in a room or work location.
For facilities that have routine operations throughout the
year in each work area, such as fuel fabrication or
pharmaceutical production operations, estimating the
total amount of material processed is relatively straightforward. For facilities where the process or activity
varies throughout the year, estimates can be based on the
best available knowledge of what will be processed in the
area during the year. All potential radionuclides and
amounts that may be used are to be considered in the
estimate. If more than one radionuclide is present, the
value of the ALI is calculated according to methods
described in the notes in Appendix B of 10 CFR 20.1001-
20.2401. Likewise, if the radioactive material is of several
classes (D, W, or Y) of the same radionuclide, it. may be
evaluated as a mixture of different radionuclides. This
step of the process addresses only the total estimated
amount of material handled in the room or area, without
considering how many workers may be exposed.
The second step in the method is to estimate the potential for the intake of material by a worker. Based on
observations and experience \vith a wide range of facilities, equipment, and processes, Brodsky has concluded
that the fractional amount of radioactive material inhaled
by a worker is generally less than one millionth (10-6) of
the amount of radioactive material processed (Brodsky
1980). This means that the potential intake is one
millionth of the unencapsulated radioactive material in
the work location during 1 year.
Regulatory Guide 8.25 recommends that the need for air
sampling be considered when the quantity Q of
radioactive material being processed in a year in
unsealed or loose form exceeds 104 times the ALI, a
quantity not likely to cause intakes more than 1 % of the
ALI or average concentrations more than 1 % of the
I
Need for Air Sampling
DAC. Thus, Regulatory Guide 8.25 recommends that
the need for air sampling be considered if:
Q > 104 ALI (1.1)
where Q is the total quantity of unencapsulated material
processed in a year for a given work location. The values ·
for ALis are taken from Appendix B of 10 CFR 20.1001-
20.2401.
Therefore, to meet the intent of the regulations, if the
quantity of unencapsulated material handled or
processed annually is approximately 10,000 times the ALI
for inhalation, Regulatory Guide 8.25 recommends that
the need for air sampling be considered.
Table 1 of Regulatory Guide 8.25, "Recommended Air
Sampling Based on Estimated Intakes and Airborne
Concentrations," recommends air sampling based on
estimated fractions of the ALI or the derived air
concentration (DAC).
1.2 Air Sampling Based on Potential
Intakes and Concentrations
After it is decided that air sampling is needed in a certain
area, several additional factors are involved in
• determining the amount of material that may actually be
inhaled by a worker, the potential intake 1i,. These
factors include the release fraction R for the radioactive
material based on its physical form and use, the type of
confinement C for the material, and dispersibility D of
the material. Using the rule of thumb that, when normal
precautions are tal<en, a worker is not likely to have an
intake 1i, exceeding 10-6 of the material being handled, the
modified potential intake IP will be:
IP = Q x 10-6 x:R x C x D (1.2)
where the modifying factors are described below.
1.2.1 Release Fraction R
The release fraction R is the fraction of the radioactive
material likely to be released into the workplace, as
determined by its physical and chemical form.
NUREG-1400 1.2
The NRC has published suitable release fractions in
10 CFR 30.72. Although the values published in the
NRC regulations were developed specifically for
emergency planning, they are generally suitable for
releases to air in the workplace. The technical basis for
the release fractions, and the experiments from which
they are derived, are described by McGuire (1988). A
simplified list of release fractions adapted from 10 CFR 30.72 is presented in Table 1.1. Adjustments were made
to provide an "order of magnitude" value so that some of
the values used in Table 1.1 differ from those contained
in 10 CFR 30.72. Other references give values for solids
between 10-6 and 10-s (Watson and Fisher 1987). The
value of the release fraction for liquids was estimated
from a maximum spill release in static air (Sutter et al.
1984). For example, the potential intake for a
nonvolatile powder (R = 10·2) would be:
I = Q x 10-6 x 10-2
p
1.2.2 Confinement Factor C
(1.3)
The confinement factor C takes into consideration
whether the material is separated and confined while a
worker is present or whether it is actually handled in the
open. Suggested values for the confinement factor would
be one hundredth of the material handled in a glovebox
(Q x 0.01), one tenth of the material handled in a wellventilated hood (Q x 0.1), and one for material handled
in an open work area (Q x 1).
1.2.3 Dispersibility D
Another factor that may be appropriate to consider is the
dispersibility that comes from adding energy to the
system through grinding, milling, boiling, or exothermic
chemical reactions. A dispersibility factor D of 10 can be
applied to the calculation if cutting, grinding, heating, or
chemical reactions of materials are performed. Therefore, the potential intake for a nonvolatile powder
(R = 10-2) that is being ground (D = 10) in a glovebox
(C = 10-2) would be:
I = Q x 10-6 x 10-2 x 10-2 x 10 p (1.4)
Need for Air Sampling
Table 1.1. Release Fractions
Physical Form
Gases or volatile material
Nonvolatile powders
Release Fraction
Solids, e.g., uranium fuel pellets,
1.0
0.01
0.001
Liquids
Encapsulated material
1.2.4 Examples of How to Determine
Air-Sampling Needs
The following two examples describe the methods for
determining if air sampling is appropriate and the
suggested modifying factors used to help establish the
extent and type of air sampling needed in a facility.
1.2.4.1 Nuclear Medicine Example
A lab technician makes up 125I injections in a fume hood.
The maximum activity that is prepared at one time, and
• on average, once per week is 10 mCi. Therefore, the
yearly throughput of 125I is approximately 0.5 Ci (1.9 x
1010 Bq). The ALI is 6 x 10-5 Ci (2.2 x 106 Bq) from
Appendix B to 10 CFR 20.1001~20.2401. The predicted
maximum likely intake as a fraction of the ALI (Ir) can
be estimated from the 10-6 fractional potential intake of
material processed:
I = 0.5 Ci x rn-6
= 0.0083 (1.5) 1 6 x 10-5 Ci
Similarly, the average annual airborne concentration of
radioactive material as a fraction of the DAC is
estimated to be 0.0083.
When the estimated concentration is less than 1 % of the
DAC, Table 1 of Regulatory Guide 8.25 has the
following recommendation: "Air sampling is generally
not necessary. However, monthly or quarterly grab
samples or some other measurement may be appropriate
to confirm that airborne levels are indeed low."
0.01
0
1.2.4.2 Uranium Fuel Fabrication Pellet Grinding
Area Example
I? one step in the manufacturing of uranium fuel,
sintered pellets of U30 8 are ground to a uniform
diameter. This grinding is mostly an automated dry
process. The apparatus is contained in a well-ventilated
shroud, but the containment is not as tight as a glovebox.
The annual throughput for a grinding station is 100,000
kg of uranium. At 3% enrichment, this amount is 170 Ci
(6.3 x 1012 Bq). The material is class Y with an ALI of
0.04 x 10-6 Ci (1480 Bq).
Using the 10-6 fractional potential intake, the potential
annual intake is 1.7 x 10-4 Ci, which is far greater than an
ALI. To further modify this number to the actual
situation, the factors to modify the intake would be a
release factor of 10-3 since the material is fuel pellets, an
estimated confinement factor of 10·1 (because the shroud
is not as tight as a glovebox, the value for a hood is used),
and an additional modifying factor of 10 (because
' grinding of the material is done). Therefore, the
modified potential intake Ir as a fraction of the ALI is:
1.3
I = 170 Ci x 10-6 x 10-3 x 10-1 x 10
f (1.6)
0.04 x 10-6 Ci
I
1 = 4.25 (1.7)
Since the potential intake is 4.25 times the ALI,
monitoring of worker intake is required by 10 CFR 20.1502, either by air sampling or bioassay. Table 1 of
Regulatory Guide 8.25 recommends that the
Need for Air Sampling
representativeness of the air sampling be demonstrated
and that an early warning capability should exist to warn
of higher than normal airborne concentrations.
1.3 Air-Sampling Systems
Once the need for and extent of air sampling is determined, an appropriate air-sampling system can be
chosen. Air-sampling systems consist of an air sample
collector with an appropriate collection medium, an air
mover to move the air through the collector, and a means
for controlling the rate of flow. The type of system
chosen depends on the purpose of the air-sampling,
system, type of airborne radiological hazard (particulate
or gas) and concentrations that must be measured.
1.3.1 Sample Collectors
The sample collector typically consists of the collection
medium and a holder, which directs the flow through the
collection medium and permits, it to be removed for
analysis.
The proper collection medium for air-sampling systems
depends on the physical and chemical properties of the
materials ~o.b: collected and analyzed .. In using a sample
collector, 1t IS important to take into account its
• c?llection efficiency, size (filter area), and resistance to
airflow. Other factors may also be important, depending
upon the application, e.g., background activity of the
filter, cost, self-absorption, fragility, chemical solubility
and the environment in which the filter will be placed.
However, sample collectors nor~ally vary according to
whether they are meant to sample particulates or gases.
1.3.1.1 Sample Collectors for Particulates
Airborne radioactive particulates may be sampled with a
number of different kinds of filters depending on how the
analysis is going to be performed and on the nature of
the radioactivity. Of these, the most commonly used
kinds are glass microfiber filters and cellulose ester
membrane filters. Glass microfiber filters are made with
different efficiency ratings and frequently come with a
thin spun-bonded polyester outer layer to keep the fibers
in place. Cellulose ester membrane filters are available
in a wide range of compositions and pore sizes, with
different collection efficiencies and flow resistances.
NUREG-1400 1.4
Generally, glass fiber filters are a better choice than
cellulose filters.
Four characteristics are important to consider when
choosing a filter: collection efficiency, airflow resistance
blocking rate, and burial depth of particulate aerosols. A
high collection efficiency is needed both for collecting the
smallest airborne· radioactive particles that may be
present, and for keeping particles from contaminating
the _rest of the s~stem. Low resistance to airflow helps
avoid the necessity for excessive vacuum pump power to
collect the sample. Low blocking rate reduces filter
loading. Finally, a low depth of burial of the particulates
in the filter, improves counting efficiency.
The collection efficiency of a filter varies, based on the
flo~ velocity, properties of the filter, and the particle size
bemg collected. Users of filters typically accept the
manufacturer's stated collection efficiency for conditions
under which sampling is conducted. If there is reason to
question the validity of the manufacturer's collection
efficiencies (e.g., using the filter under conditions not
tested by the manufacturer), then the user can conduct a
collection efficiency test using the method described in
Section 6.2.
The collection efficiency and the flow resistance of filters
~sually are specified in terms of the "face velocity," which
1s the flow per unit of usable flow area. Thus, if the
sampling flow rate is 28.3 L/min (1 cfm) and the
effective flow area of the filter holder is 9.6 cm2 the face
velocity will be 49.2 cm/s (96.8 ft/min). Inasm~ch as the
collection efficiency of most filters increases with face
velocity, it is important to use a high enough face velocity
so th~t the filter will be operating efficiently. A high face
velocity also helps the analytical sensitivity by
concentrating the collected particles on a small filter
area, and it saves on filter costs by permitting the use of
small filters.
Small pressure drops are wanted for the sample flow rate
being used. Resistance to airflow through a sample filter
(equivalent to pressure drop across a sample filter)
increases with increasing flow velocity. Section O,
"Sampling Aerosols by Filtration," in Air Sampling
Instruments for Evaluation of Atmospheric Contaminants
(ACGIH 1989) provides pressure drop data for different
types of filters at typical sample face velocities (53, 106,
and 211 cm/s (106, 212, and 422 ft/min]) used in air
sampling~ The flow resistance and the blocking tendency
of the filter must also be kept in mind because the higher
the face velocity and the higher the initial pressure drop,
the sooner the filter will become loaded to the point that
it will have to be changed. Blocking will be slower with
glass microfiber filters than with membrane filters, and
slower with large-pore membrane filters than with smallpore membrane filters. A disadvantage of membrane
filters with pore sizes larger that 3 µm is that they can act
like depth filters which reduce the radiation counting
efficiency.
Automatic flow control makes it possible to operate
filters at higher face velocities and for longer periods of
time between filter changes than does manual flow control. Some automatic flow con~rol systems can compensate for flow resistance changes of 254-cm (10-in.) Hg
with less than a 3% change in the incoming flow rate. In
contrast, a positive displacement pump with manual flow
control will have a 5% drop for every 254-mm (1-in.) Hg
increase in the flow resistance of the filter.
1.3.1.2 Sample Collectors for Gas
Iodine is normally collected by adsorption on chemically
impregnated activated charcoal. Collection efficiencies
depend on flow rate, temperature, humidity, particle size,
iodine concentration, and impregoant used. To
maximize the collection efficiency, the optimal grain size
is 12 to 30 mesh. This mesh size provides adequate
packing density to minimize channeling and provides
• adequate surface area for adsorption (APHA 1977).
Adsorption of contaminants in the charcoal cartridge can
be minimized by keeping the cartridge in an air-tight
sealed package before use.
For other halogens, noble gases, and water vapor,
activated charcoal is also an efficient absorber. Because
the adsorption process is not radionuclide-specific, the
analysis of other radioactive halogens and noble gases
with charcoal will require analytical discrimination to
measure the iodine concentrations. Purging the charcoal
after sampling is a procedure that can be used to drive
off the noble gases. Another alternative is to use silver
zeolite cartridges, which collect negligible amounts of the
noble gases compared to activated charcoal cartridges
(Kathren 1984).
Readers can consult Section S, "Gas and Vapor Sample
Collectors," in Air Sampling Instrnments for Evaluation of
Atmospheric Contaminants (ACGIH 1989) for a detailed
discussion of activated charcoal adsorbents. A method of
Need for Air Sampling
analyzing a charcoal cartridge for 1311 is found in Methods
of Air Sampling and Analysis (APHA 1977).
Sampling for airborne tritium (usually as tritiated water
vapor or hy.drogen gas) is most commonly done by
collecting the tritiated water vapor (HTO or T20) using
desiccants and bubblers. Condensation or freezing
techniques can also be used but are not as common.
The use of bubblers is perhaps the simplest method for
collecting airborne tritium. However, gaseous tritium is
not directly collected with bubblers. The gaseous tritium
is first passed over a catalyst such as palladium to convert
it to tritiated water vapor. The tritiated water vapor is
then passed through a water-filled bottle and the tritium
is collected in the water. The collection efficiencies are
high (greater than 90%) if the HTO /H20 ratio in the
water is low (NCRP 1976). The efficiency of specific
' bubblers can be determined by placing several bubblers
in series.
1.5
To collect tritiated water vapor, a desiccant such as silica
gel, molecular sieves (alumino-silicates), anhydrous
calcium sulfate, and activated alumina can also be used.
The relative humidity of the sampled air affects the
quantity of moisture the desiccant can hold at equilibrium; the greater the relative humidit)r, the smaller the
quantity of moisture that can be held. Loss of the sample
occurs if the collection capacity is reached during
sampling. Information about the adsorptive capacities is
usually provided by the desiccant manufacturer.
Choosing a desiccant with a capacity approximately
double the maximum anticipated loading minimizes the
chances of saturation. Collection materials are available
that change color when nearing saturation to assist the
user in determining the appropriate time to replace the
collector. Distillation at normal or reduced pressure is
common for the extraction of tritiated water vapor
collected on the desiccant.
A real-time monitoring instrument for directly measuring
tritium in air is the flow-through ionization chamber. A
particulate filter is placed on the inlet to remove dust and
particulates. Ionization chambers also respond to other
radioactive gases and external radiation fields; therefore,
shielding of the chamber or discrimination techniques
may be necessary. Sensitivity is a function of the
chamber volume, with larger chambers having greater
sensitivity.
Need for Air Sampling
More detailed discussion on the collection of tritium
from air with bubblers or desiccants is found in NCRP
(1976).
1.3.1.3 Sample Collector Holdfrs
Sample collector holders provide structural support for a
sample filter, prevent flow from passing around the filter,
and ease filter removal. A porous metal backing of wire
mesh or beaded screen is often used. A filter backing
with a smooth surface will minimize tearing during
changing of the filter. Cross-contamination of samples
can be avoided by using filter holders designed for easy
cleaning and decontamination.
Rubber gaskets are frequently used to seal the filter to
the backing plate. A gasket in contact with the filter
along its entire circumference ensures a good seal and is
best located on the downstream side of the filter (i.e., the
clean side) to minimize contamination. Care must be
taken to select a rubber gasket that will not adhere to the
filter medium and damage it. Periodic inspection of the
gasket helps detect degradation and buildup of dust and
filter material that can cause leakage around the filter.
Leakage may occur in filter holders that are not designed
properly or maintained properly. It most often occurs
between the edge of the filter and the sealing face of the
holder, and can result in deceptively low concentration
measurements because it allows part of the air sample to
·bypass the filter. A simple leak test consists of installing
a thin plastic flow barrier (such as polyethylene) in place
of the filter, and connecting the filter holder through a
bubble jar to a controlled source of vacuum. If there is a
leak, there will be a continuous stream of bubbles in the
bubble jar; if not, the bubbles will stop quickly. Testing
at the time of purchase assures that filter holders are
designed properly and periodic testing thereafter assures
that filter holders are properly maintained.
A frequently asked question is, "How much leakage is
permissible?" The answer is that an air-sampling filter is
a quantitative device with a carefully controlled pore size.
Unless the filter holder is as good as the filter itself,
specified filter performance will not be realized.
Furthermore, it is not difficult to make filter holders that
are leak-tight; it mainly requires the manufacturer to
have adequate quality control, and the user to accept no
filter holder without testing it.
Charcoal cartridge holders also are subject to leakage,
especially those that use the ends of the charcoal canister
NUREG-1400 1.6
as a flow seal. Sources of leakage include dents and
other imperfections in the ends of the canisters, variations in the height of the canisters, variations in the
thickness and smoothness of the rubber gaskets, and
imperfections in the pipe threads. Because charcoal
cartridge holders invariably are located downstream from
filter holders, any leakage in them may reduce the flow
through the filter holder, also. Leak-testing of charcoal
cartridge holders can be performed using a bubble jar.
1.3.2 Air Movers
The air mover may be small and serve one air sampler,
or it may be on a central vacuum system that serves a
number of air-sampling stations. The function of the air
mover and associated flow control system is to draw air
through the sample collector at a predetermined flow
rate. The means for controlling the flow rate may be
either manual or automatic and may include an indicating flow meter, as discussed in Section 5. How well the
air flow is controlled can be determined by connecting a
portable flowmeter to the inlet with a valve to simulate
the filter load, and a vacuum gauge or manometer to
measure the filter load. The flow rate, measured at
atmospheric pressure, is then plotted against the filter
load to show how well the system performs.
Adequate air sampling uses a unique combination of flow
and vacuum that is best met by air movers that are
designed to operate at between 127-mm (5-in.) and
379-mm (15-in.) Hg vacuum. At less than 127-mm
(5-in.) Hg, there is not enough vacuum to produce
satisfactory face velocities through the filter medium and
to compensate for filter blocking; at more than 379 mm
(15-in.) Hg, there is too little flow for the size of the
pump and motor. Other desirable features of the air
mover are its quiet operation at the selected operating
vacuum, its nearly pulsation-free flow, and its need for
little maintenance.
Some of the different kinds of air movers that have
proven satisfactory for air sampling include:
• oil-less rotary vane pumps (with carbon vanes) for
flow rates between 14 and 570 L/min (1/2 and 20
cfm) (508 mm [20-in.] Hg maximum operating
vacuum)
• lubricated rotary vane pumps (with phenolic vanes)
for flow rates between 28 and 1416 L/min (1 and
50 cfm) (686-mm [27-in.] Hg maxi~um operating
vacuum)
• rotary positive blowers (Roots type) for flow rates
between 142 and 2832 L/min (5 and 100+ cfm)
(203-to 356-mm [8-in. to 14-in.] Hg maximum
operating vacuum, depending on the size of the
blower and its construction) :
• vacuum cleaner blowers for flow rates between 283
and 1416 L/min (10 and 50 cfm) (127-mm [5-in.] Hg
maximum operating vacuum)
• turbo blowers (1 and 2 stage) for flow rates above
1416 L/min (50 cfm) 152- to 254-mm ([6-in. to 10-in.]
Hg maximum operating vacuum, depending on the
size of the blower and the number of stages)
Piston and diaphragm pumps are not included in the
above list because their pulsating flow affects the
behavior of the airborne particles being sampled and is
difficult to damp to an acceptable level.
Because the noise from air movers varies between
different makes and models, as well as with the operating
vacuum and the kind of muffler provided, evaluation of
noise prior to purchase through actual tests of the air
movers and air samplers is recommended.
Soundproofing enclosures may increase the temperatures
• of the pump and motor, and consequently shorten their
operating life.
Because all air movers have close operating clearances, it
is important to keep out pipe debris and flakes of paint
during their assembly. A protective (or backup) filter
may be used to keep out particulate matter that might
get past the sample collector.
As a general rule, the smaller-size air movers and carbon
vane pumps are built more inexpensively and will operate
continuously for only about a year (8000 hours0.0926 days <br />2.222 hours <br />0.0132 weeks <br />0.00304 months <br />) without
major repairs or replacement. Consequently, for
continuous air sampling, it is often desirable to use one
of the larger heavy-duty air movers.on a central vacuum
system that serves a number of air-sampling stations.
This also enables the air mover to be located in a
machinery room where its noise will not disturb the
people at the sampling stations, saves valuable space at
the sampling stations, and requires only one proof of
operation for the entire system.
1.7
Need for Air Sampling
1.3.3 Types of Samplers
There are four basic types of air-sampling systems. The
first consists of a lapel sampler, which is worn by the
worker and can be used to determine intake. The second
and third types are the portable air samplers and fixedlocation air samplers, which are usually used to
determine airborne radioactive concentrations in the
workplace and to ensure that confinement control is
maintained. The fourth sampling system is air monitoring, which samples and measures airborne concentrations for use as an early warning of higher-than-expected
airborne radioactive concentrations.
1.3.3.1 Lapel Samplers
Lapel samplers (also called personal air samplers) are
worn by the worker, with the filter holder worn on or
near the shirt collar and the battery-powered vacuum
pump worn on the belt. Lapel samplers may be the best
method of estimating breathing zone concentrations
because they are located close to the worker's nose and
mouth. ·
Although lapel samplers appear to be the sampler of
choice for breathing zone samplers, they have several
disadvantages. A primary problem is that they have a
low flow rate (2 L/min), which may make them unsuitable for airborne radioactivity areas, just at the point
where breathing zone sampling may be appropriate
according to Regulatory Guide 8.25, Table 1. However,
the problem of a low flow rate can be overcome by
collecting the sample for a longer time, counting the
samples long enough to detect radioactivity, or having a
more sensitive counting system. Another disadvantage is
that lapel samplers may become contaminated by
improper handling, which may cause the instrument to
give a higher reading. Contamination on a lapel sampler
may also result in erroneous worker intake. Lapel
samplers are expensive, many workers think they are
uncomfortable to wear, and the worker must be sure to
turn them on and off. Advancements made by various
manufacturers have improved lapel samplers and, even
with some drawbacks, lapel air samplers may be the
sampling system of choice for determining intake.
When a lapel sampler fails, it is most likely due to battery
failure or inadequate charging, debris in the sample
pump, leakage caused by vibration, fatigue in its valves or
diaphragms, or the mechanical failure of rotary vane
pumps or motor. Approximately 5% to 10% of lapel
NURiEG-1400
I
Need for Air Sampling
samplers can be expected to be out of service for
maintenance and calibration at any given time.
Consult Ritter et al. (1984), The Role of Personal Air
Sampling in Radiation Safety Programs and Results of a
Laboratory Evaluation of Personal Air-Sampling Equipment, NUREG/CR-4033, for more information about
the types and use of lapel samplers and an evaluation of
personal air samplers.
1.3.3.2 Portable Air Samplers
Portable samplers are usually used in facilities where the
location of airborne radioactivity changes frequently,
such as nuclear power plants, where routine and special
maintenance often create actual or potential radioactive
airborne areas. Because the samplers are portable, they
can be located close to the worker.
The most common portable air samplers are lightweight,
rugged AC samplers designed for taking grab samples.
They are made for heavy-duty industrial applications for
sampling airborne particulates and iodines. The air is
drawn in through an inlet, pulled through the filter, and
exhausted. Usually, a rotameter is used to indicate the
airflow rate. Sample heads on portable air samplers
commonly hold 5-cm-(2-in.-) or 47-mm-(l.9-in.-)
diameter filters. In addition to the commonly used AC
portable air sampler, battery-powered air samplers with
• air volume totalizers are available, as are constant airflow
air samplers with the sampler on a telescoping goose
neck, both of which facilitate collection of the sample in
the breathing zone.
Portable samplers are categorized by their airflow rates
as low-volume and high-volume samplers. For breathing
zone sampling, low-volume portable samplers are used,
with sample airflow rates from 28 to 56 L/min (1 to
2 cfm). High-volume samplers are not typically used for
breathing zone sampling because they are very noisy. I
If a portable sampler meets the criterion in Regulatory
Guide 8.25 for representativeness (i.e., located within
30 cm [1 ft] of the worker's head) and the sampler is
sensitive enough to obtain a lower limit of detection less
than 4 DAC-h for samples collected over a 40-hour
period, the sample result may be considered a breathing
zone sample. If the sampler is not located in the breath-
•
ing zone, representativeness would have to be demonstrated, which probably would not be feasible.
NUREG-1400 1.8
1.3.3.3 Fixed-Location Samplers
A major difference between the locations of general air
samplers and breathing zone samplers is that, according
to Regulatory Guide 8.25, breathing zone samplers
should intercept radioactive material before it reaches or
soon after it passes the individual worker. Therefore, if
fixed-location air samplers are placed strategically in a
work area, they too can be used to collect representative
samples of the air that workers inhale. A facility with a
history of operations may have air concentration data
that can be used in conjunction with airflow pattern
studies to determine the best location for fixed-location
air samplers.
1.3.3.4 Air Monitors
Some air-sampling systems are designed to help prevent
or minimize worker exposure to higher-than-expected
levels of airborne radioactive materials by indicating the
presence of elevated concentrations. This early warning
sampling is conducted in either of two ways: by prompt
sample analysis, which involves collecting an air sample
and analyzing it in a counting laboratory; or by continuous monitoring, a real-time monitoring method to
alert staff when concentrations rise far above and remain
above the DAC. A continuous air monitor may have an
automatic alarm that sounds at a predetermined activity
or rate of collection of activity on the collection medium.
In general, commercially available monitors may be
divided into two types: those that measure the presence
of radioactive particulates (either alpha-emitters or beta/
gamma-emitters) and those that measure radioactive
gases or vapors. Among particulate monitors, the alpha
monitors use either solid-state devices (such as surface
barrier or diffused junction detectors) or scintillators
(such as zinc sulfide) as detectors. Beta detectors, on the
other hand, are Geiger-Mueller (GM) tubes, betascintillator material, or ion chambers. The beta monitors
that use GM tubes are generally much larger and heavier
than alpha monitors due to the amount of lead or other
shielding material necessary to reduce the background
radiation to acceptable levels.
Monitors of gases and vapors use ion chambers for their
detection devices. Tritium monitors, for instance, usually
use fairly large ion chambers as their detectors; the
larger the ion chamber, the more sensitive the
measurement. Some instruments have the capability of
simultaneously measuring the presence of particulates
(beta particles), radioiodine, and noble gases. These are
large semi-mobile systems with arrays of monitoring configurations and detectors, shielding to reduce background
radiation effects, and electronic units to control data
acquisition, analysis, and documentation.
1.4 References
10 CPR 20. 1991. U.S. Nuclear Regulatory Commission,
"Standards for Protection Against Radiation." U.S. Code
of Federal Regulations.
10 CPR 30. 1988. U.S. Nuclear Regulatory Commission,
"Rules of General Applicability to Domestic Licensing of
Byproduct Material."
American Conference of Governmental Industrial
Hygienists (ACGIH). 1989. Air Sampling Instruments
for Evaluation of Atmospheric Contaminants, 7th ed.
Cincinnati, Ohio.
American Public Health Association (APHA). 1977.
Methods of Air Sampling and Analysis, 2 ed., ed. M. Katz.
Washington, D.C.
Brodsky, A. 1980. "Resuspension Factors and
Probabilities oflntake of Material in Process (Or 'Is 10·6
a Magic Number in Health Physics?')." Health Physics
39:992-1000.
Kathren, R. L. 1984. Radioactivity in the Environment -
Sources, Distribution, and Surveillance. Harwood
Academic Publishers, New York.
McGuire, S. A. 1988. A Regulatory Analysis of
Emergency Preparedness for Fuel Cycle and Other
Radioactive Material Licensees. NUREG-1140, U.S.
Nuclear Regulatory Commission, Washington, D.C.
National Council on Radiation Protection and
Measurements (NCRP). 1976. Tritium Measurement
Techniques. NCRP Report No. 47, NCRP Publications,
Bethesda, Maryland.
Ritter, P. D., B. L. Huntsman, V. J. Novick, J. L. Alvarez,
and B. L. Rich. 1984. The Role of Personal Air Sampling
in Radiation Safety Programs and Results of a Laboratory
Evaluation of Personal Air-Sampling Equipment.
NUREG/CR-4033, U.S. Nuclear Regulatory
Commission, Washington, D.C.
1.9
Need for Air Sampling
Sutter, S. L., J. Mishima, M. Y. Ballinger, and C. G.
Lindsey. 1984. Emergency Preparedness Source Term
Development for the Office of Nuclear Material Safety and
Safeguards-Licensed Facilities. NUREG/CR-3796, PNL5081, U.S. Nuclear Regulatory Commission, Washington,
D.C.
U.S. Nuclear Regulatory Commission. 1992. "Air
Sampling in the Workplace." Regulatory Guide 8.25,
Washington, D.C.
Watson, E. C., and D.R. Fisher. 1987. Feasibility Study
on a Data-Based System for Decisions Regarding
Occupational Radiation Protection Measures. NUREG /
CR-4856, PNL-6137, U.S. Nuclear Regulatory
Commission, Washington, D.C.
2 Location of Air Samplers
Regulatory Guide 8.25 (NRC 1992) notes that concentrations of airborne materials can vary widely within a room
so that improperly placed samplers and monitors can
give misleading results. Even air samplers placed close
to workers, for example, at the end of a hood or
glovebox, may not accurately reflect the air concentrations of radionuclides in the workers' breathing zones.
There have been many instances in which significant
releases of airborne radioactivity Were undetected by
existing air-sampling systems in a work area. The major
cause of such system failures was the improper placement of the air samplers. To locate fixed air samplers,
~ontinuous air monitors, and portable samplers in areas
fo ensure adequate air sampling, health physicists need a
clear understanding of the flow of air in a work area.
Proper placement of samplers cannot be determined by
simply observing the position of room air supply and
exhaust vents. Published experiences with airflow studies
attest to their value.
2.1 Purpose of Airflow Studies
Health physicists can use systematic airflow studies, such
as the release of smoke aerosols, to determine the airflow in a work area. The significance of airflow pattern
studies and the use of the information for locating
samplers depend, of course, on the purpose of the
sample being collected-whether for estimating worker
intakes, warning of high concentrations, testing for
confinement or leakage of radioactive materials from
apparatuses or enclosures, or defining airborne radioactivity areas. Table 2.1 lists the purposes and general
placement of air samplers and monitors to best achieve
the desired measurements.
Studies have shown the extreme differences that are
possible between the concentrations in a worker's
breathing zone and those measured at fixed locations or,
as commonly done, in the area exhausts. In one study, an
aerosol was released from multiple release points and
sampling was conducted in the worker's breathing zone,
at eight area samplers, and at four continuous air
monitors, two located near exhausts and two inside the
2.1
exhausts (Scripsick et al. 1978). Dilution measurements
were made between the breathing zone sampler and the
other 12 sampler locations. Quantitative dispersion
factors, equal to the ratio of the concentration at a
remote location to the concentration at the release point,
were then determined for each exhaust vent. Results
showed that the average dispersion factor was 3 x 10-3 for
the closest exhaust vent and 4 x 10·2 for the further
exhaust vent, i.e., exhaust vent measurements
underestimated breathing zone concentrations by a
factor of between 25 and 330.
Other studies have shown that there can be a significant
difference in sample measurements between lapel samplers worn by workers and fixed-location air samplers.
One study compared results for lapel samplers with those
for nearby fixed-location samplers in a work area
containing concentrations of uranium (Brunskill and
Holt 1967). The lapel samplers showed uranium concentrations up to 80 times greater than those of the fixedlocation samplers; .the average was 10 times greater for
lapel samplers than for fixed-location samplers. This
study also noted differences up to a factor of two for
personal samplers located on the right side and on the
left side ofa worker's body. A second study found
similar results when workers' activities caused increased
airborne concentrations of radioactive materials. The
ratio of the concentrations from lapel samplers to fixedlocation samplers varied from 1.5 to 50; 85% of the ratios
were less than 10 (Schulte 1967). Because the lapel
samplers were typically closer to the airborne source
than were the fixed-location samplers, they were
measuring materials with particle sizes larger than those
collected by the fixed-location sampler a short distance
away.
Based on airflow pattern studies conducted by Advanced
Systems Technology, Inc., a significant number of air
samplers in facilities were not positioned adequately to
sample airborne radioactive material released from
potential sources. Air sampler placement based on
'One Securities Centre; 3490 Piedmont Road, NE; Suite 1410; Atlanta,
Georgia 30305-1550.
Location of Air Samplers
Table 2.1. Purposes and General Placement of Air Samplers and Monitors
Purpose of Sampling/Monitoring
Estimate worker's intake for calculating
internal dose
Identify area needing confinement control
Provide early warning of elevated airborne
release
Test for leakage of radioactive materials
from sealed confinement system
Determine total concentration from many
potential release points
Determine if an airborne radioactivity area
exists
Special purposes, e.g., determining particle
size
location of ventilation supply and exhaust vents alone
was found to be inadequate because of the considerations discussed below. Although the following examples
do not describe all possible work environments, they
demonstrate how airflow is affected by various features
of the work area.
2.1.1 Stratification and Stagnation
Stratification, the accumulation of contaminants in
distinct layers, can occur in radiological facilities under
several circumstances. Thermal stratification is often
observed in large rooms with high ceilings. Equipment
that introduces a large heat load into a room can produce thermal currents that alter airflow patterns significantly. Heat loads can reverse the normal airflow
patterns from corridors into labmatories or process
areas, with warm air flowing out from the top of a
doorway and cooler air flowing into the room at floor
level, despite the presence of supply and exhaust vents
within the room. The presence of large structures,
equipment, or partitions within rooms can produce
areas with stagnant airflow conditions. This problem
General Placement of Samplers/Monitors
Sampler located in worker's breathing zone,
near nose and mouth
Sampler in airflow pathway near actual or
potential release point
Continuous air monitors placed between
workers and release point(s)
Samplers located downstream of confinementcontrol area
Downstream at exhaust point
Samplers at workers' locations
Case by case, depending on airflow patterns
2.2
can be particularly significant if a facility has undergone
modification since its ventilation system was originally
designed. Added equipment can disrupt laminar airflow
patterns within a room and produce low-velocity vortices and eddies with elevated local concentrations of
airborne radioactive material. In the study represented
in Figure 2.1, air was supplied through several vents
located throughout the room. Air was exhausted
through the roof at several evenly spaced vents high on
the walls and also through the floor to the room below.
The air was being pulled up and down, resulting in the
creation of a stratification layer in one section of the
room. The stratification layer was detected by releasing
a smoke candle at an elevated sampling station. The
smoke drifted downward and pooled in a layer approximately 0.6 m (2 ft) thick and about 1.5 m (5 ft) from the
floor. The layer moved slowly southward down one side
of the room. Next, the pooled layer crossed to the other
side of the room, turned northward, and slowly dissipated. Known releases and associated intakes had
occurred in this facility. The releases were generally not
detected by fixed-location air samplers due to the
unusual and .unexpected airflow patterns.
•
Barricade
,.....,
I
Door
=West wall supply duct locations
.... = Floor exhaust duct locations
~_,__,_,D I II
J
llorth •
D
Office
Note: This exhaust
is located beneath
the dissipating
stratified layer
Location of Air Samplers
I
Station
Sampling
Station
'---~;mililim---------------~iliiiJ~il--------------------...
=Wall supply duct locations
Ill = Floor exhaust duct locations
Figure 2.1. Example of Stratification of Air Layers
2.3 NUREG-1400
Location of Air Samplers
2.1.2 Water-Filled Pools
Water-filled pools, such as spent fuel pools, can modify
airflow patterns as a result of thermal currents. This is
particularly true during periods of high thermal loading,
such as those encountered during full-core, off-load
conditions. Thermal uplift over the surface of the water
can draw air from the walls of the refuel floor or fuel
handling building to the pool. Warm moist air that
reaches the ceiling is cooled and flows downward along
the exterior walls. This problem can be particularly
severe during winter outages. tn some cases, these
thermal air currents can act as flow boundaries that
prevent or restrict flow across the pool.
Thermal uplift can also modify flow patterns observed
under conditions where the pool temperature is '
approximately equal to the building ambient temperature. Performing airflow studies using smoke tubes or
smoke candles during outages or periods of major
activity around water-filled pools provides a realistic
picture of airflow under those operating conditions.
In the facility shown in Figure 2.'2, air was supplied on
the west side of the spent fuel pool through a series of
vents located about 4.5 m (15 ft) from the floor. Air was
vented through a similar arrangement of vents located
on the east side. Air samplers were placed on the east
side of the pool. The health physicist assumed, because
• the air flowed from west to east, that releases from the
pool would move accordingly.
However, based on the study using smoke candles and
smoke tubes to simulate releases at the water surface,
the flow pattern in Figure 2.2 was determined. The
smoke moved westward instead of eastward and then
travelled along the west walkway where no samplers
were located. Releases on the east side of the pool also
moved westward and then upward toward the exhaust
vents. The samplers located on the east walkway would
not intercept a release from the pool.
The airflow at levels above 3.6 m (12 ft) generally flowed
from west to east.
2.1.3 Doors
Under some conditions, cool air may enter a room
through the bottom of a doorway while, at the same
time, warm air flows out through the top. Airflow
NUREG-1400 2.4
studies and air sampler placement verification 'Pade
under the same conditions as experienced during operation helps ensure that samplers will be positioned in the
best locations to collect airborne radioactivity. If the
facility is to be operated with the doors normally open,
making necessary changes to the room air balance
ensures adequate control of potential airborne radioactive sources. Reverse airflow from laboratories or other
engineered facilities can also be induced when the airflow through a corridor is significantly higher than
normal. This can happen when delivery or service
entrances are opened to the outdoors. The increased
airflow through the corridor may be sufficient to draw
air from the laboratories into the corridor.
In one airflow study test of a laboratory, the hood was
used as the principal room exhaust. Air was also vented
through vents located on the mezzanine level above.
Air was supplied through the open doorways and
through small ceiling vents. Smoke tests demonstrated
that air flowed into the bottom of an adjacent office
after bypassing the hood and passing through a surface
contamination area. The airflow entered through the
bottom part of the door even though only air supplies
with no exhausts were located in the office (see
Figure 2.3).
2.1.4 Bi-Level Airflow
Air can flow'in opposite directions within the same
room. This typically occurs in poorly designed ventilation systems, such as the case in which the supply vent
is located near the door to a long, narrow room or
gallery with no exhaust vent provided. In this case,
supply air would flow from the vent toward the rear wall
of the room or gallery where it is deflected back toward
the supply vent and door. In cases of bi-level airflow,
the proper air sampler placement depends heavily on
the elevation of the release point and the worker's
breathing zone. In such cases, it may not be possible or
practical to use a single fixed air sampler. Multiple fixed
air samplers or lapel samplers worn by workers may be
needed to adequately intercept releases of radioactive
material.
In the example shown in Figure 2.4, air was supplied at
the northern end of a long corridor with cells.on both
sides. The air traveled southward and was vented into
some cells and an exhaust pit located on the floor near
the middle of the corridor. The air velocity was high at
I
Supply Ducts C4.6 m [15 ft] Above Catwalk· Level)
Air Sa""lers Located at Head Height Along This \./all
Legend
.... =\.lest wall supply duct ~nd east wall exhaust duct locations,
!iliiilii = Catwalk around pool
VIE\./ FROM ABOVE
Exhaust "<i:;....----- Duct
Galleries
0
Catwalk ~Catwalk
'----.Pool Surf ace------'
VIE\./ FACING SOUTH FROM NORTH \./ALL
Supply
Duct
Galleries
Location of Air Samplers
=Location of ducts (supply on west [right side] and exhaust on east Cleft side])
D = Location of air sa""lers above catwalk
Figure 2.2. Airflow Modification Due to Water
2.5 NUREG-1400
Location of Air Samplers
Doorway
Office '\_~
i ro=._oorwa_y -----
Doorway
Legend:
= Supply duct locations
Figure 2.3. Example of Variable Flow Through Openings (Doors)
1.8 m/s (350 lfpm) near the northern end. This high
velocity caused air to flow rapidly to the rear of the
corridor, which does not contain an exhaust vent. The
air was then forced upward and returned northward
where it was exhausted into the pit.
Bi-level flows represent a particular problem when
valves and lines transporting radioactive materials are
• located at the top of the cell. Positioning the sampler at
the lower level downstream of the release point (valve)
would not capture the release. The release would
actually flow in the opposite direction.
In this example, personnel had received significant
contamination during the operation of leaking valves,
which were located at the top of the cell. The releases
were not detected. The air circulated across the airborne radioactivity area boundary rope located in the
southwest corner. The health physicist had assumed
incorrectly that air in-leakage through the door would
create a flow toward the center of the room and exhaust
in the cells and pit.
2.1.5 Recirculating Airflow
A recirculation pattern may be established by a poorly
designed ventilation system, or a room configuration
that is different from that for which the original system
was designed. Recirculation patterns can develop if the
NUREG-1400 2.6
supply and exhaust ducts are configured so that the
supply air impinges on a wall, is transported vertically,
and moves back in the direction of the supply without
being intercepted by the exhaust ducts. In such cases,
lobes of higher concentration will be formed.
Samplers could be placed in each recirculating lobe to
capture a representative sample. A redesign of the
ventilation system or reconfiguration of the room layout
could also correct this problem.
2.1.6 Wall and Floor Penetrations
Unsealed wall and floor penetrations represent a potential pathway for movement of airborne radioactive material to or from adjacent rooms or spaces. Aerosols may
be transported by either differential air pressure or
thermal currents. Airflows may be reversed under some
conditions (e.g., open versus closed door, transient heat
loads, etc.).
Performing airflow studies for all possible conditions
helps to determine airflow patterns between rooms for
both proper air sampler placement and protective
requirements. Although sealing of penetrations is
recommended, many considerations, such as thermal
expansion or environmental qualification requirements,
may preclude this.
Location of Air Samplers
North •
-( .....
,.
1\(1~ Cell Cell Cell Cell Cell
- I I -
I A Tent Area I I
I /( - 100 lfpm along floor - • 350 l fpm along floor I '
A
J~ \ .....
~ Cell Cell , Cell· ·~
VIEi.i FROM ABOVE
/
Top-of-Cel l-Ual l----------.....::11-.,--------
Labyrinth Labyrinth
Door Door • 1 O lfpm along floor
Labyrinth
Door
'
Tent Area
• 350 lfpm along floor
VIEi.i FACING I.JEST AT SECTION A-A
Figure 2.4. Example of Bi-Level Flow Reversals
The control room areas, where personnel may stay
during release events, are generally provided with a
separate ventilation system that can be isolated. In
Figure 2.5, the control room was surrounded by sources
of potential airborne release. During the study, smoke
released from the source points entered the reportedly
sealed control room through the air conditioner intake
located outside the control room.
2.7
2.2 Determination of Airflow Patterns
Regulatory Guide 8.25, suggests that an airflow study be
conducted after any work-area changes, including
changes in the setup of work areas, ventilation system
changes, or seasonal variations that might change
airflow patterns (such as opening doors and windows in
Location of Air Samplers
potentially contaminated area I
Recirculation
I Air ,.-----------, Supply Duct
Conditioner
~m
Potential Ly
Contaminated
Area
Control Room
Potentially Contaminated Area
Figure 2.5. Example of Unexpected Flows
the spring or summer). Changes in the configuration of
work areas often involve the addition of contamination
containment structures or partitions, or of hoods or
waste compactors; any of these added features in a work
area can change the airflow. A new hood, for example,
will act as another exhaust point in the room, and the
• waste compactor's exhaust vent, if directed into the
room, could modify the airflow. Equipment that
generates waste heat, such as chillers, power supplies,
large motors, or other process or experimental equipment, can produce the airflow pattern changes described
in Section 2.1. Ventilation system changes to be aware of
include rebalancing the ventilation system, adding or
removing supply air or exhaust vents, or changing the
location of an existing supply air or exhaust vent.
Regulatory Guide 8.25 also recommends a routine
evaluation of fixed-location samplers-10% evaluated
once a year-to determine if their locations are still
appropriate. Such spot tests would most profitably
concentrate on samplers near the points in a work area
with greatest potential for release.
Finally, informal observations of changes in airflow
patterns, such as a change in the direction of flow or a
noticeable increase or decrease in flow velocity, would
require further investigation and a proper airflow study.
NUREG-1400 2.8
2.2.1 Preparation for Airflow Studies
Certain preparations provide a good starting point for
making an airflow pattern study. First, review the
significant features of the work area, the area's airsampling history, and any facility changes that may have
affected airflow patterns since the last study to determine
which areas to test. Additional useful information can be
gained by determining potential radiological source
terms for each work area, noting those that have the
greatest potential for release, and mapping the normal
configuration of the work areas, both for the current
study and for future reference. The maps could include
the locations of current air samplers and monitors,
supply air vents, exhaust vents, doors, and major pieces
of equipment, such as process equipment, gloveboxes,
and hoods.
Recording normal working conditions that may affect
airflow is also suggested, including whether each door is
open or closed during normal operations, or whether the
heating, ventilation, and air conditioning (HV AC) unit is
normally on or off. Heat-generating sources, such as
ovens or furnaces, and equipment exhaust fans may also
affect airflow. Note that the engineering drawings of the
ventilation system ~ay not accurately reflect how the
system currently works unless they have been carefully
maintained to reflect as-built conditions. The HVAC
maintenance staff may be the best source of information;
they may be able to supply differential pressure readings
and hood and stack flows. A health physicist may want
to determine if modifications to the ventilation system
have altered the airflows, or if future alterations can be
expected to change airflows. If major ventilation system
modifications are planned within the next several
months, delaying the study until after modifications are
finished may eliminate the need for retesting.
In areas of high external dose rate or high concentrations
of airborne radioactive materials, it is desirable to keep
airflow testing to a minimum. Regulatory Guide 8.25
recommends that worker dose be maintained as low as
reasonably achievable (ALARA) during airflow studies.
For example, instead of using smoke candles with two
people observing the dispersal of the aerosol, a single
observer using smoke tubes would reduce the disruption
during operating hours and perhaps be more representative of normal airflow. Another possibility would be to
videotape the airflow tests, removing workers from the
area while the test is being conducted.
2.2.2 Methods of Airflow Studies
The two types of airflow pattern studies are qualitative
studies, which use an aerosol that can be visually
observed and recorded, and quantitative methods, which
.actually provide measurements of dilution effects in the
work area. Qualitative studies are generally adequate for
placing air samplers. The quantitative methods, which
are more expensive and time-consuming, determine how
well ftxed-location samplers actually measure the
concentration in air that workers breathe. The
advantages and disadvantages of the methods are
summarized in Table 2.2.
2.2.2.1 Qualitative Airflow Stu.dies
Qualitative methods are the primary means of determining airflow patterns to assist in the placement of air
samplers. Qualitative methods include the use of smoke
candles and smoke tubes, helium-filled balloons, and
isostatic bubbles. A combination of smoke candles and
smoke tubes is in common use today at nuclear facilities
because they are readily available and relatively
inexpensive.
2.9
Location of Air Samplers
The airflow direction and transit times can be readily
determined by visual observation of the smoke aerosol.
The airflow patterns can be recorded on worksheet
drawings with narrative descriptions or by using
photographs or videotapes.
Smoke candles, sometimes referred to as smoke bombs,
are available in a variety of sizes ( e.g.,120 m3 [4000 ft3]
and 240 m3 (8000 ft3]) and produce a grayish white
smoke. The smoke is actually a mist, seeded by zinc
chloride, and contains a large percentage of atmospheric
moisture. The diameter of smoke particles is 0.01 to
1 µm. The smoke is somewhat buoyant because of the
heat generated by the smoke candle.
Smoke candles are best used to determine the general
airflow patterns in large areas. The observation of
smoke as a means to determine airflow is limited to
situations of relatively low air velocity. At high velocity
(greater than 30 m/min (100 ft/min]), the smoke diffuses
too rapidly to allow tracking with the naked eye. Most
work areas have airflow velocities of less than 30 m/min
(100 ft/min), except for those locations near supply air
vents, narrow corridors, or entrances into rooms.
The appropriate amount of smoke released during a test
depends on the size of the work area. To protect the
floor surface, smoke candles are typically placed in a
metal can before being lighted. Enough smoke is
released to create a visible haze but not enough to totally
obscure vision. The amount of smoke can be varied by
the size of the candle used or by smothering the candle
to stop the smoke (i.e., placing a lid on the metal can).
During testing, personnel wear full-face respirators with
special cartridges for particulates, smoke, mists, and
vapors (e.g., MSA-GMC-H chemical cartridges) because
the smoke is a respiratory irritant.
Smoke tubes produce less aerosol than smoke candles,
approximately the amount produced by a burning
cigarette. The smoke generated is a cold smoke produced by a corrosive acid, which is not as dense as that of
smoke candles and has no initial buoyancy. Smoke is
generated from the plastic or glass tube containing the
corrosive acid material by squeezing air through the tube
with an aspirator bulb.
I
Location of Air Samplers
Table 2.2. Comparison of Techniques Used to Determine Airflow Patterns Within the Workplace
(Mishima et al. 1988)
Technique
Qualitative Methods
Smoke candles
Advantages
Equipment readily available;
provides visible evidence of
airflow
Disadvantages
Semi-quantitative; limits visibility; may
affect operations; leaves residue; makes
thermal plume
Smoke tubes Readily available; visible evidence
of airflow, leaves no residue
Can only evaluate small areas at a time;
not quantitative
Isostatic bubbles Visible; more persistent than
smoke
Semi-quantitative; may affect operations;
leaves residue
Quantitative Methods
Tracer aerosols Quantitative for range of particle
sizes
Choice of tracer particles limited; costly;
requires large array of detectors
Tracer gases Quantitative for gases, vapors, and
particles
Can require many detectors;< 2-µm
activity median aerodynamic diameter
(AMAD); choice of tracer gases limited
Smoke tubes are used primarily in small work areas less
than 27 m2 (300 ft2), where smoke candles would produce too much smoke to allow observation of the airflow. In laboratories or work areas with sensitive
analytical equipment, smoke tubes are used because
they leave less residue than do smoke candles. Sensitive
equipment can be covered for protection from the
smoke candle residue. Smoke tubes can be used to
quickly show if airflow direction is different at various
heights above the floor. They also give initial information on workplace airflow before using smoke candles.
Air velocity measurement instruments, such as hot-wire
anemometers, can provide useful information on air
velocities in work areas. Such air velocity measurements, used in conjunction with smoke test results,
provide information on airflow patterns. For example,
air velocity measurements would tell ttie time it will take
a release to reach a key location in the work area (e.g.,
the exhaust vent); these measurements could then be
compared with the velocities estimated from the smoke
drift over a known distance. In another kind of
NUREG-1400 2.10
application, air velocity measurements can be used to
help determine the size of an area of stagnant air noted
during the smoke testing. For instance, if smoke tests
revealed little air movement in a certain location, a
hot-wire anemometer reading of less than 3 m/min
(10 ft/min) in the same location would reinforce the
smoke test results.
2.2.2.2 Quantitative Airflow Studies
Quantitative methods, such as tracer studies, provide
measurements of dilution effects in the work area, but
are more expensive and time-consuming than qualitative
methods. To characterize the aerosol dispersion, nonradioactive tracer aerosols are released at the potential
release points for radioactive materials and then the
concentrations of the aerosol are measured at selected
points in the work area. The dispersion of the aerosol at
a remote location from the release point is expressed as
the ratio of the concentration measured at the remote
location to tlie concentration measured at the release
point.
I
An application of this concept is illustrated in
Figure 2.6. The largest concentration is measured near
the release point (Location A) and the dispersion
factors (D) at remote locations are determined by the
ratio of the concentration at the remote location to the
concentration at Location A From the dispersion
factor data in Figure 2.6, one can conclude that most of
the flow is toward the east into the exhaust vent sampled
by Sampler C.
Quantitative methods of analyzing airflow patterns can
be used to determine the representativeness for breathing zone samples, as discussed in Section C.3.2 of
Regulatory Guide 8.25. These methods can be especially effective when the workplace air concentrations
are normally near the lower limit of detection, making it
difficult to use any one of the other three methods for
determining that breathing zone samples are representative (i.e., comparison with lapel sampler results,
comparison with bioassay results, and comparison with
multiple measurements near tl'le breathing zone).
Quantitative methods can also be used for placing fixedlocation air samplers. For example, they can be used to
quantify the amount of dilution between a release point
and an exhaust vent, allowing a health physicist to
determine if the counting equipment is sensitive enough
to measure a release for the given sampling conditions.
Several kinds of tracers can be used: tracer gases (e.g.,
helium and sulfur hexafluoride), fluorescent particle
tracers, ice nucleus particle tracers, and nonspecific
aerosol particle tracers. Tracers are not used routinely
in the nuclear industry as an aid in placement of workplace air samplers. Therefore, facilities that elect to use
one of these methods either to show sample representativeness or to aid in determining sampler placement are
likely to have to perform some development work.
The desirable properties of tracer gases are detectability
at a relatively low concentration in ambient air, nonreactivity, and nontoxicity. If a large area is to be tested,
tracer gas can become costly. Although sulfur hexafluoride, halocarbon refrigerants, and perfluorocarbons
have been found to be the most cost-effective for large
areas, they are environmentally unsound and are being
phased out. Common tracer gases and their typical
measurement techniques are noted in Table 2.3 and discussed below. Refer to the report by Mishima et al.
(1988) for more detailed information on using tracer
gases for determining airflow patterns.
2.11
Location of Air Samplers
Fluorescent Particle Tracer
Fluorescent particle tracers have the advantage of more
closely simulating the inertial properties of particulate
aerosols (e.g., uranium aerosols) than do gaseous
tracers. A disadvantage of this method is that only timeintegrated concentrations can be determined from the
sample analysis.
One successfully concluded quantitative airflow study
using a fluorescent particle tracer was done in an area
containing.several plutonium gloveboxes (Scripsick
et al. 1978). Simulated airborne releases at gloveboxes
were made from 20 potential release locations in the
work area under study. The fluorescent particle test
aerosol was generated from a 0.1 % solution of fluorescein in 0.01 N NH40H. Fluorescein is an organic compound used to generate test aerosols in the laboratory.
Its fluorescent properties permitted detection of
airborne concentrations down to 0.1 µ,g/m3. The aerosol
generator used was designed and built at Los Alamos
National Laboratory and consisted of 24 nebulizers
suspended in a 30-cm- (12-in.-) diameter canister filled
with the 0.1 % fluorescein solution. Releases were made
at about 1.3 m ( 4.3 ft) above the floor. During the
release, air samples were collected with the room airsampling system. Additional air samples were collected
with samplers located at both room ventilation exhausts.
Air sample filters from the tests were placed in bottles
containing 0.01 N NH40H solution. These solutions
were analyzed using a fluorometer. Blanks for this test
were made by placing clean filters into 0.01 N NH40H
solution. The breathing zone concentration to an
individual at the release location was measured by air
sampling at -0.4 m (1.3 ft) above the generator exhaust,
i.e., about 1.7 m (5.6 ft) above the floor. The results
were used to calculate dilution factors between the
worker's breathing zone and the sampler locations.
Ice Nucleus Particle Tracer
Ice nuclei are particles that nucleate ice crystals in
super-cooled clouds. Only a few chemicals (e.g., silver
iodide and phloroglucinol) can nucleate ice crystals
efficiently. The advantages of using this type of tracer
are that it can be detected in very low concentrations
and pro"?de a real-time indication of air concentrations.
The major disadvantage of this method is that detectors
are bulky and heavy, making multipoint sampling difficult. Laser particle counting is better suited for
Location of Air Samplers
•
®E
D =0.6
Release
Point
'
t
N
D = 0.1
@F D= 0.2
D = 0.45
®o
Legend
® Sampler Location
0 Exhaust
0 = Concentration at Sampler
Concentration at Point A
D = 0.05
Figure 2.6. Quantitative Dispersfon Factors
multipoint sampling. A single-particle, real-time
detector has been used to track ice nuclei particles in a
plutonium area (Langer 1987). The detector consisted
of a 10-L cloud chamber and associated refrigeration.
NUREG-1400 2.12
For more information, refer to the report by Mishima
et al. (1988), where experience in using ice nuclei
particle tracers is reviewed.
I
..
Location of Air Samplers
Table 2.3. Common Tracer Gases and Measurement Techniques
Tracer Gases
Hydrogen (H2), helium (He), and carbon
dioxide (COz)
Sulfur hexafluoride (SF 6), refrigerants, and
perfluorocarbons
Ethane (CzH6)
carbon monoxide (CO), C02, SF6, N20, CzH6,
and methane ( CH4) 1
Ethyl iodide (CH3CH2I)
Nonspecific Aerosol Particle Tracer
A nonspecific aerosol tracer is useful because instrumentation for counting aerosol particles by optical
means is readily available and relatively inexpensive.
One type of nonspecific aerosol tracer system is the laser
particle counter, which has the advantage of showing the
effects of particulate depositions, that a gaseous aerosol
cannot show. Moreover, a laser particle counter system
provides data in real time, the detectors can be multiplexed, and the data output can be routinely compu-
•terized. Commercial software and a multiplexer system
are available that can handle data from up to 64 laser
particle counter detectors simultaneously. A laser
particle counter system has been used to study airflow
patterns at a plutonium facility (Langer 1987). A simple
pneumatic atomizer produced solid tracer particles with
two particle-size ranges (greater than 0.5 µm and less
than 5.0 µm) from the evaporation of sugar solution
droplets.
2.2.3 Performing Qualitative Airflow Pattern
Studies
Ideally, qualitative airflow studies would be performed
with staff positioned in the work area, performing their
normal jobs to best represent airflow patterns. In
reality, however, studies are typically done with no
workers in the work area (i.e., no movement in the area)
because it is neither practical nor desirable to have
workers wearing respirators during smoke testing.
2.13
Measurement Technique
Thermal conductivity detector
Electron capture gas chromatograph
Flame ionization gas chromatograph
Infrared absorption
Neutron activation analysis (see Contreras
and Schlapper 1985)
Often to avoid exposing workers to the smoke, testing is
performed during off-shifts or at other times when
workers are not present. However, during work activities, airflow patterns could vary, particularly in the
localized area around a worker who is .moving. Thus,
the health physicist anticipated the actual airflow
patterns, based on observations of work habits in the
area and on the qualitative airflow study, in order to find
suitable locations for the samplers.
Preparation for a qualitative airflow pattern study using
smoke candles includes covering sensitive equipment
such as computers to keep out potentially damaging
smoke residues. Because smoke plumes are tracked in
the work area during testing, the room is well lit. If the
light in the area is dim, portable lighting may be used for
better visibility of the smoke; it is important to
remember, however, that portable lighting could produce unwanted thermal effects on the airflow.
To begin a qualitative airflow pattern test, the smoke
candle is placed near the points at which radioactive
materials are potentially or actually released. After the
smoke is released, it is recommended that at least two
persons observe the dissipation of the smoke in the
work area: one person standing downwind of the
release point and one person standing upwind. Both
observers record 1) the pattern of smoke flow and 2) the
time it takes for the smoke to be dissipated (i.e., until it
is not visible to the naked eye). In addition, the downwind observer notes the time required for smoke to
Location of Air Samplers
reach key locations, to enable estimates of air velocities
in the work area. Each observer independently records
observations. The results are then documented on
drawings of the work area. After the smoke has cleared,
the observers consolidate their observations into a
single airflow pattern description for the work area.
2.2.3.1 Examples of a Qualitative Airflow Study in a
Laboratory
The following example, which is based on real data,
outlines the steps a health physicist would take in
conducting an airflow pattern study for the work area
shown in Figure 2.7.
First, the health physicist identifies potential release
points for radioactive materials in this work area: the
hot cell loadout port, the hot cell manipulator area,
Hood 1, and Hood 2. The areas with the largest source
term potential are the hot cell loadout port and the hot
cell manipulator area. The health physicist also takes ·
into account the physical and chemical form of the
material. The next step is to document the configuration of the ventilation system in the work area. Supply
air to the work area is from two ceiling supply air vents
and through the south door, which is left open during
work activities. The room air is vented through the wall
exhaust vent in the northeast comer of the room and
through Hoods 1 and 2. There are no temporary activities, such as opening large service-bay doors, nor are
• there other equipment or a heat-generating source that
might affect airflow in the room.
The health physicist now documents routine work activities. During routine operations, two workers operate
the manipulators located on the east side of the hot cell.
Work in the hot cell is typically done during two shifts
per week. Hoods 1 and 2 are used for sample preparation activities on a daily basis. Review of past air sample
results for the four air samplers located in the room
indicates no elevated results for the past 2 years.
Next, the health physicist documents the status of the
work area's ventilation system before beginning the
airflow study. No ventilation system upgrades were
performed during the past year and none are currently
planned by the maintenance staff. Monthly differential
pressure readings taken at various locations throughout
NUREG-1400 2.14
the work area have been consistent for the past several
months. Monthly air velocity measurements for
Hoods 1 and 2 have been consistent. The latest ventilation system data (before the current airflow study) were
recorded.
The health physicist then performs the smoke test and
observes airflow patterns. Smoke candles are lit in front
of the hot cell loadout port and between the hot cell
manipulators because these areas have the greatest
potential source term. Smoke tubes are used to define
airflow near the hoods. The smoke aerosol from the
candle in front of the loadout port travels north and
west, with most of the aerosol flowing towards Hood 2.
A smaller portion of the aerosol flows into the northeast
corner exhaust vent. The smoke aerosol that does not
flow directly into either exhaust vent continues to the
north wall and recirculates in a southward direction,
filling the north third of the room. Eventually, the
aerosol is exhausted through Hood 2 and the northeast
comer eXhaust vent. The smoke aerosol from the candle
near the manipulators rises and mixes with the supply
air and quickly disperses through the width of the room.
The aerosol then drifts to the north and is vented
through the northeast exhaust vent and Hood 2. More
of the aerosol is observed flowing into the northeast
exhaust vent.
Based on the smoke test, the health physicist draws the
following conclusions and makes the associated recommendations regarding the locations of the four samplers:
• Sampler 1 - This sampler is upwind of the loadout
port and would be better located to the east side of
the loadout port.
• Sampler 2 - This sampler appears to be in a good
location to sample any releases that may occur near
the manipulators.
• Sampler 3 - This sampler is located in the supply
airflow coming in the south door. The sampler
would be better located on the front surface of
Hood 1.
• Sampler 4 - This sampler appears to be in a good
location to sample any releases from Hood 2.
Hot
Cell
Legend
t
N
Loadou~ ~
~
Manipulators
2~_J •L-..-J
Manipulators
Door
Open
@ = Ceiling Supply Air Vent
~ = Wall Exhaust
3
•
• = Fixed Air Sampler Location
3
0
Hood 1
0 = Recommended Air Sampler Location
(!) = Smoke Candle Location
Figure 2.7. Diagram of Example Work Area
2.15
Location of Air Samplers
Location of Air Samplers
2.2.3.2 Airflow Study at a Nuclear Power Plant
The following example outlines the steps a health
physicist could take in conducting an airflow pattern
study at a nuclear power plant.
A health physicist at a pressurized water reactor power
plant needs to determine the air-sampling needs for a
nonroutine radiation work permit. The job requires
removing insulation and preparing welds and
components for nondestructive examinations for inservice inspection programs. For this particular task, the
insulation is removed and the loop stop valves are
inspected. The health physicist expects that the work
may cause higher-than-normal airborne radioactive
material levels. The health physicist reviews the general
area survey data, the air-sampling data from similar past
operations, and data from the adjacent operating unit.
Before the work begins, there are some surface
contamination levels above 1000 dpm/100 cm2 and the
general area survey reads about 20 mrem/h. Because of
the surface contamination levels, there is the potential
for increased airborne contamination requiring
continuous air sampling during the job.
While not done in this case, the health physicist could
decide to perform qualitative smoke tests to determine if
the portable air samplers are well-located to measure
airborne radioactive material levels. In making that
• decision, the health physicist would have to decide if the
improvement in the air sampling data would be worth the
dose that would be received while ~he smoke tests were
being performed. If the dose received due to conducting
airflow tests is likely to be a substantial fraction of the
dose received when performing the in-service inspection
work, smoke tests probably would not be justified. On
the other hand, if the dose likely to be received during
the in-service inspection work was likely to be
substantial, it would be acceptable to receive some dose
while doing airflow tests in order to improve the quality
of the measurements of dose received during in-service
inspection. In this example, it is assumed that the health
physicist has concluded that more accuracy in the air
sampling measurements is important and that the air
flow tests are thus necessary.
There are little data on the ventilation systems that
would be useful in determining the flow patterns of the
cubicle in question. However, in the cubicle being
evaluated, the cooling coil banks are suspended from the
ceiling above the 81-m (271-ft) level. Below the cooling
coil banks is the loop stop valve that will be worked on.
NUREG-1400 2.16
In general, containment air flows from the top of the
dome ~d upper elevations to lower elevations. Four 3.1
x la5 L/min (11,000-cfm) fans, two for supply and two for
exhaust, are located in the auxiliary building; they are
operated in various combinations to yield flow rates
through containment that range from 3.4 x 104 - 6.2 x ia5
L/min (1200 cfm to 22,000 cfm).
Because the cubicle is an odd shape with large open bays
to the steam generator and reactor coolant pumps that
might affect the airflow, the health physicist makes a
thorough survey of the area with smoke tubes to determine the expected flow and determine where to locate
the smoke candles. Figure 2.8 illustrates the flow
patterns obtained from the smoke tubes.
After the general survey using smoke tubes, smoke
candles are lit one at a time in the areas numbered 1
through 4 in Figure 2.9. However, because the areas are
rather confined, with the large bays open to levels below,
the health physicist has several assistants who are
assigned to observe the smoke at various elevations (i.e.,
floor level, about eye level, and overhead). However,
because of the high exposure rates in the area, the number of personnel to observe the test is minimized. The
smoke patterns observed are also shown in Figure 2.9.
Based on the smoke tests, the health physicist concludes
that most of the air near the loop stop valves located
under the cooling coil banks (at the top left corner of the
cubicle) is swept east and down the opening to the loop
stop valves on the lower level. The health physicist
recommends the following sampler locations:
• Sampler 1 -A portable air sampler is recommended
to be located east of and as close as possible to the
loop stop valves, about 1.5 m (5 ft) from the floor, if
possible.
• Sample 2 -A second sampler is recommended to be
located west of the loop stop valves at the elevation
below 80 m (262 ft), about 1.5 m (5 ft) above the
floor. This air sampler would probably sample airborne contamination from the adjacent loop stop
valve and, if work was going on at the same time, at
the loop stop valve on the 83-m (271-ft) level.
2.2.4 Quantitative Airflow Pattern Studies
Before choosing a quantitative method for an airflow
study, the type of potential release is characterized in as
Location of Air Samplers
North
Figure 2.8. Preliminary Airflow Pattern Survey in Cube at 262-ft Level
much detail as possible. For example, for a potential
noble gas release, a gaseous tracer would be applicable;
for a potential uranium release, the laser particle counter
method or fluorescent particle tracer method would be
better. Particle sizes of the released material are
matched with the particle sizes of the tracer material so
that the effect of particle deposition will be similar.
2.2.4.1 Example of a Quantitative Airflow Pattern Study
The following example, which is based on real data that
have been adjusted for the example, outlines the steps a
health physicist would take in conducting a quantitative
airflow pattern study. The health physicist has already
conducted a qualitative (smoke testing) study and knows
the general airflow patterns in the work area. Those
results are included in the example above of a qualitative
airflow pattern study of a laboratory (see Figure 2.7).
2.17
The health physicist uses a fluorescent particle tracer
method to perform the quantitative airflow study (see
Scripsick et al. 1978). An aerosol generator is located at
the loadout port for Test 1 and at the manipulator area
for Test 2. The following conditions exist at each test
location:
• Releases are made at the height of the loadout port
for Test 1 and at the height of the manipulators for
Test 2 to simulate potential release heights.
• Six portable air samplers capable of collecting
samples at a rate of 75 L/min (2 cfm) are located as
indicated in Figures 2.10 and 2.11. The locations
were chosen based on the smoke test results, which
showed the major portion of the smoke aerosol passing these locations. The sample collectors are
Location of Air Samplers
Leoend:
® = Smoke Candle
• North
Figure 2.9. Airflow Patterns as Determined by Smoke Qlndles at Selected Locations
located at the worker's head level or about 1.7 m
(5.5 ft) above the floor to simulate the worker's
breathing zone.
• The aerosol is generated during the first 15 minutes
of each run. The portable air samplers are started
with the aerosol generator and continue to operate
for an additional 15 minutes after the aerosol I
generator is stopped. Six runs are completed fi;>r
each test, based on the study completed by Scripsick
et al. (1978). Sufficient time is allowed between runs
for the aerosol to dissipate to several orders of
magnitude below test concentrations.
• Sample filters are placed in bottles containing a
0.01 N NH40H solution and analyzed using a
fluorometer.
NUREG-1400 2.18
The health physicist averages the concentrations for the
six runs for each sampler and then calculates the quantitative dispersion factor (D) by dividing the average air
concentration for each sampler by the average concentration for the sampler located above the aerosol
generator. The D values are shown in Figures 2.10 and
2.11 for the example work area.
Based on the results of the tracer test, the health
physicist concludes that the quantitative dispersion
factors in the loadout port area (Figure 2.10) are greater
than 0.7, which Regulatory Guide 8.25(NRC1992)
defines as a representative sample. The health physicist
recommends the following locations for samplers:
I
t
N
H
0 2
0 •6
d
•2
•
1
Hot
Cell
p
2 = 0.72
3 = 0.75
4 = 0.30
5 = 0.05
6 = 0.20
Legend
•4
•3
Loadout Port
®
Manipulators·.
Manipulators
Door
Open
@) Ceiling Supply Air Vent
l:8J Wall Exhaust
• Fixed Air Sampler Location
•
5
Hood 1
0 Aerosol Generator and Air Sampler
R9010060.2
Figure 2.10. Example Work Area, Test 1 (Loadout Port)
2.19
I
Location of Air Samplers
Location of Air Samplers
H
0 2
0
d
t
N
Loadout Port
Hot • Manipulators
Cell 1
p
2 = 0.35
3 = 0.30
4 = 0.2
5 = 0.05
6 = 0.001
Legend
•2
Manipulators
Door
Open
@ Ceiling Supply Air Vent
~ Wall Exhaust
• Fixed Air Sampler Location
•
5
Hood 1
0 Aerosol Generator and Air Sampler
R9010060.3
Figure 2.ll. Example Work Area, Test 2 (Manipulator Area)
2.20
I
• Sampler 1 - A fixed air sampler should be positioned
within 0.6 m (2 ft) north or east of the loadout port
to be representative of the worker's breathing zone.
• Sampler 2- Hood 2 would be a better place to locate
a fixed-location air sampler than the northeast
exhaust vent because the D value for Sampler 6 in
front of Hood 2 is four times greater than the D
value for the northeast corner exhaust.
Based on the test results in the manipulator area, the
health physicist concludes that the influence of the
supply air resulted in a greater dilution within several
feet of the release points (as shown in Figure 2.11 ),
producing dispersion factors o~ approximately 0.3. The
effect of the supply air mixing was to decrease the
concentration gradient in the local area around the
release point. The D values at the exhaust were low,
indicating that a fixed-location air sampler at the
exhaust vent may not be appropriate. Thus the health
physicist recommends that the samplers would be better
positioned closer to a potential release point (i.e., a
loadout port or manipulators).
2.3 Selecting Sampler ~ocation
The steps taken to determine air sampler locations
include identifying the purpose of the sample, identifying release points, and determining airflow patterns
around these release points, as discussed in Sections 2.1
and 2.2. This section provides information on using the
sample purpose, the release points, and airflow patterns
along with other modifying factors (e.g., worker movements and influence of supply air ventilation) to determine air sampler locations.
2.3.1 Factors in Locating Samplers
When workers' locations within the workplace during
various processing operations are defined in enough
detail, a health physicist can ensure that air sampler
placement does not interfere with the normal conduct of
work. For example, if a potential release point is a hood
or glovebox, the air sampler can be placed where it cannot be bumped by a worker. Fixed-location air samplers
on hoods are typically placed at a height of 1.8 m (6 ft)
or less from the floor on the front face of the hood. The
ideal sampler height is 1.5 to 1.8 m (5 to 6 ft) from the
floor to the sampler; however, in corridors and busy
2.21
Location of Air Samplers
work areas, samplers may be placed overhead, preferably
not higher than 2.4 m (8 ft), or at the sides of the areas.
Air samplers are generally placed so as to avoid the
influence of supply airflow. An air sampler placed in the
supply airflow wilt' be sampling air that is representative
of the supply instead of the ambient workplace air. This
could result in the underestimation of ambient workplace air concentrations. If an air sampler is in the
supply airflow just downwind of a potential or actual
release point, then information on the airflow patterns
in the area is used to reposition the sampler out of the
supply air and in position to sample material from the
potential release point. If ~he ventilation system is
operated in the recirculation mode, sampling the supply
air may be warranted because the supply air now
becomes a potential airborne release point in the work
area. Some other rules-of-thumb for locating samplers
include the following:
• Samplers are placed so that they are easily accessible
for changing filters and servicing.
• High-volume samplers are positioned so that their
exhaust is directed downstream from the sample
collector to avoid sampling their own clean exhaust
air.
• If a sampler is operated on a horizontal surface, as a
convenient means of support, the air discharged
from the sampler is not directed at the surface, where
it could cause localized excessive air concentration
from resuspended surface contamination.
• When sampling at an exhaust duct with an area of
more than 0.09 m2 (1 ft2), the health physicist
evaluates the need for a multi-nozzle sample inlet. If
there is good mixing of the air before the exhaust,
the use of one sample inlet may be justified. If the
air is not well mixed, it is recommended in American
National Standards Institute Standard N13.1 that the
multi~nozzle sample inlet be used (ANSI 1969).
2.3.2 Examples of Determining Sample
Locations
Several examples of how to determine air sampler locations are presented below, based on the purpose of the
measurement identified in Section 2.1. Examples are
Location of Air Samplers
provided for locating air samplers to 1) verify confinement of radioactive materials, 2) estimate worker
intakes, and 3) provide early warning of elevated concentrations. The examples are based on real data that were
adjusted for the purpose of the examples.
2.3.2.1 Effective Confinement bf Radioactive Material
The two examples presented in this section involve work
areas with multiple release points in a new facility tpat is
not yet operational and in an existing operational facility.
Determining sample locations is not an exact science,
and qualified health physicists' interpretations of the
following examples may vary.
' Example 1-Sampler Locations for a New Facility
Figure 2.12 depicts a work area in a new facility that is
not yet operational. The hot cell loadout port and the
hood are the two potential release points. Supply air
enters the room through perforated ceiling panels from
diffusers, located above the panels, that distribute the
supply air evenly over the surface area of the ceiling. A
qualitative airflow study shows that the general airflow is
to the west, with air exiting through either the hood or
the exhaust vent in the southwest corner.
Air concentrations in the work area are estimated to be
about 10% of the DAC during work operations that
• would result in about 4-DAC-h/wk exposure to the
workers. Therefore, continuous air sampling is recommended, based on Table 1 of Regulatory Guide 8.25
(NRC 1992).
An appropriate place for a continuous air sampler is on
the front face of the hood (see Figure 2.12), preferably at
a height less than 1.8 m (6 ft) from the floor. The
sampler is best placed so as not to hinder the movement
of the worker using the hood. The sampler at the loadout port should be located just downwind of the release
point, as shown on Figure 2.12. Again, the sampler is
located less than 1.8 m {6 ft) from the floor, but not
hindering worker activities at the loadout port.
If the airflow pattern study had shown that most of the
air flowing from the loadout port was exhausted through
the hood, one sampler placed at the hood might cover
the entire work area. However, to be sure that releases
would not be so diluted as to escape detection, a
quantitative airflow study of potential releases from the
NUREG-1400 2.22
loadout port would have to be done to justify placement
of a single sampler.
Example 2-Sampler Locations for an Existing
Operational Facility
An existing operational facility contains a sample
preparation room in an existing analytical laboratory (see
Figure 2.13). The five hoods in the work area are the
potential release points. High-activity process samples
are prepared in Hoods 4 and 5, while lower-activity
process samples are handled in Hoods 1, 2, and 3.
Supply air enters the room through the doors to Corridor
A and the perforated ceiling panels from diffusers
located above the panels. This results in an even
distribution of supply air over the surface area of the
ceiling. Smoke testing shows that the general airflow is
to the east, with air exhausting through the hoods or into
Corridor B.
Routine sample results for the continuous air sampler
located between Hoods 4 and 5 average about 5% of the
DAC. Based on these results and the guidance in
Regulatory Guide 8.25, the health physicist recommends
that the continuous air sampling near the two hoods be
continued. However, the location of the sampler needs
to be reevaluated based on the airflow patterns in the
room. A release from Hood 4 would travel to the east
and might escape detection by the sampler in its current
location. Because each hood has the same potential for a
release, the health physicist considers relocating the
sampler to the east side of Hood 4 (see Figure 2.13) to
allow sampling of a potential release from either hood. I
Air sampler results for the sampler located between
Hoods 1 and 2 average less than 1 % of the DAC.
According to guidance in Regulatory Guide 8.25, no air
sampling is needed. However, based on the location of
the air sampler and the airflow patterns, the health
physicist cannot be certain that a release from Hood 1
would not exceed 1 % of the DAC near the hood and be
diluted to less than 1 % of the DAC by the time it
reached the current sampler. Also, the sampler is
located upstream of any releases from Hoods 2 or 3. To
properly evaluate this situation, the health physicist could
either 1) conduct temporary air sampling at Hoods 1, 2,
and 3 for several weeks to verify actual concentrations
near the hoods (i.e., worker location), or 2) calculate
potential releases for each hood to determine if air
sampling is needed.
I
..
Legend
8 Recommended Air Sampler Location
t
N
Hot
Cell
Log Unit Port
Location of Air Samplers
Doors
Closed
Figure 2.12. Example Work Area, Multiple Release Points in a New Facility
2.3.2.2 Estimation of Worker Intakes
Air samplers that collect samples for estimating worker
intake intercept radioactive material before it reaches or
soon after it passes the individual worker. Fixedlocation air samplers can be used to collect representative samples of the air that workers inhale if they are
strategically placed in the work area (see Section 3).
Two examples are presented below illustrating how to
locate fixed-location air samplers to obtain sample
results that can be used to estimate worker intake. One
example discusses sampling in a new (not-yetoperational) facility and the other covers sampling in an
existing operational facility.
Example 1-Locating Fixed-Location Samplers in a New
Facility
Fixed-location air samplers are to be placed in a new
facility, depicted in Figure 2.12 (above). Workers will
be located at 1) the hot cell loadout port and 2) in front
of the hood. Smoke testing showed that the general airflow is to the west, with air venting'through either the
2.23
hood or the exhaust vent in the southwest corner. A
worker exposure greater than 12 DAC-h was estimated
for work near the hot cell loadout port. Therefore,
according to Table 1 of Regulatory Guide 8.25, the
sample collected should be representative of the air
inhaled by the worker. Placing the fixed-location air
sampler just downwind of the loadout port will serve to
monitor the integrity of the confinement. However,
because it is not possible to position the sample within
30 cm (1 ft) of the worker's mouth and nose, an evaluation needs to be performed to determine if the sample is
representative. Results from this single sampler could
serve both as the basis for estimating worker intake and
for monitoring the integrity of confinement control.
Example 2-Locating Fixed-Location Samplers in an
Existing Operational Facility
Fixed head air samplers are to be installed in the existing facility shown in Figure 2.13. The work area is a
sample preparation room in an analytical laboratory.
The five hoods in the work area are the potential release
points. Smoke testing revealed that the general airflow
Location of Air Samplers
Doors
Open
Hood 1
_)
t
N
Hood 2
_)
/ r-----~I Work Bench . Doors
Open
<(
....
~ ....
....
0
(.)
Hood 5 Hood4 Hood3
Legend
• Existing Air Sampler Location
0 Recommended Air Sampler Location
Figure 2.13. Analytical Laboratory Work Area
is to the east, with air venting either through the hoods
or into Corridor B.
Air sampler results for the past year show that sample
results for the continuous air sampler located between
Hoods 4 and 5 were greater than 30% of the DAC.
Therefore, air sampling is required for Hoods 4 and 5
and the location of the air sampler needs to be evaluated
to determine if it is representative of what the worker
inhales, as found in Table 1 of Regulatory Guide 8.25 ..
Because the air sample results will be used to determine
worker intake, air samplers are located on the front
faces of Hoods 4 and 5, positioned to avoid being
bumped by workers.
NUREG-1400 2.24
2.3.2.3 Early Warning of Elevated Air Concentrations
Regulatory Guide 8.25 states that early warning
samplers should be located close to release points,
preferably between workers and release points, and
should be capable of detecting a release. For work areas
with a single release point and where workers may
exceed 40 DAC-h in 1 week, placing the air sampler
immediately downwind from the release point provides
the best indication of elevated airborne concentrations.
Placement at an exhaust is also appropriate if dilution
effects would still allow detection of a release in a
reasonable amount of time; such a determination can be
made with quantitative methods of analyzing airflow
!!!!
(see Section 2.2.2.2). For an area with multiple release
points and where workers may exceed 40 DAC-h in 1
week, two alternatives are possible. First, samplers can
be placed downwind of each release point. Second, a
sampler can be placed at each room exhaust vent, when a
quantitative evaluation shows that dilution effects
between the sampler and the exhaust vent will still allow
prompt detection of the release. If there are multiple
exhaust vents, air samplers located at all the vents that
would receive airflow from any release points would
provide coverage for all possible releases. Thus, the
health physicist can analyze airflow data to determine
which exhaust vents receive most of the releases.
As in locating samplers for evaluating confinement
control and worker intake estimates, early warning
sampler locations are determined differently for new and
for existing facilities. For new (or proposed) facilities, an
estimate of workplace air concentrations is used as a
basis for determining the need for early warning
samplers because there are no measurement data from
which to draw information. At existing facilities,
however, use data from past air sample results to
determine the need for early warning sampling.
An example of the situation a health physicist faces when
locating early warning samplers in a new facility that has
multiple release points is described here. Figure 2.13
shows the work area. The hot cell loadout port, the
glovebox, and the hood are the three potential release
• points. Observation and diagrams of the facility reveal
that the supply air enters the room through perforated
ceiling panels from diffusers located above the panels. It
appears that there is an even distribution of supply air
over the surface area of the ceiling. The room air is
vented through the hood and the wall exhaust vent
located in the southwest corner of the room. Smoke
tests show that the general airflow is to the west, with air
venting through either the hood or the southwest-corner
exhaust vent.
The health physicist obtains data on source terms and
then estimates weekly worker exposures in DAC-h for
the hood, the glovebox, and the hot cell loadout port,
with the results of 5, 15, and 50 DAC-h, respectively.
Based on this information and Table 1 of Regulatory
Guide 8.25, the following conclusions can be drawn:
2.25
Location of Air Samplers
• Continuous fixed-location air sampling should be
performed at the hood and the glovebox. In addition,
the air sampling at the glovebox needs to be
evaluated to determine if it is representative of air
inhaled by the worker.
• Early warning sampling should be performed at the
loadout port. Samples should be evaluated at the end
of each shift or a continuous air monitor should be
used.
Because airflow in the room (specifically from the hot
cell) is towards the hood, a fixed-location air sampler is
placed on the front face of the hood, at a height slightly
less than 1.8 m (6 ft) from the floor, making sure that the
sampler does not interfere with the movements of the
worker using the hood.
A fixed-location air sampler is also placed 1.8 m (6 ft)
from the floor, on the center of the glovebox's north face,
where the worker will be located. Once the facility is
operating, one of the methods in Section C.3 of
Regulatory Guide 8.25 will be used to demonstrate that
the samples are representative.
Finally, the hot cell loadout port warrants placing a
continuous air monitor downwind of the loadout port. A
fixed-location air sampler is also placed near the loadout
port to determine the representativeness of the sample,
using one of the methods in Section C.3 of Regulatory
Guide 8.25 once the facility is operating.
2.4 References
American National Standards Institute (ANSI). 1969.
Guide to Sampling Airborne Radioactive Materials in
Nuclear Facilities. ANSI N13.1, New York.
Brunskill, R. T., and F. B. Holt. 1967. "Aerosol Studies
on Plutonium and Uranium Plants at the Windscale and
Springfield$ Works of the United Kingdom Enetgy
Authority." SM-95/30, In Proceedings of a Symposium
on Instruments and Techniques for the Assessment of
Airborne Radioactivity in Nuclear Operations, July 3-7,
1967, International Atomic Energy Agency, Vienna.
I
Location of Air Samplers
Contreras, Y. R., and G. A Schlapper. 1985. "Aerosol
Dilution and Dispersion in a Nuclear Research Facility.•
Radiation Protection Management 2( 4 ):41-50.
Langer, L. 1987. Ventilation Air Change Rate Versus
Particulate Contaminant Speed. RFP-4154, Rockwell
International, Golden, Colorado.
Mishima, J., J. Hunt, W. D. Kittinger, G. Langer, D.
Ratchford, P. D. Ritter, D. Rowan, and R. G. Stafford.
1988. Health Physics Manual of Good Practices for the
Prompt Detection of Airborne Plutonium in the
Workplace. PNL-6612, Pacific Northwest Laboratory,
Richland, Washington.
Schulte, H. F. 1967. "Personal Air Sampling and
Multiple Stage Sampling: Interpretation of Results
from Personal and Static Air Sampler."
CONF-670621-3, in Proceeding of ENEA Symposium
on Radiation Dose Measurements, June 12-16, 1967.
NUREG-1400 2.26
Scripsick, R. C., R. G. Stafford, R. J. Beckman, M. I.
Tillery, and P. 0. Romero. 1978. Evaluation of a
Radioactive Aerosol Surveillance System. IAEA-SM229/62, In Proceedings of an International Symposium
on Advances In Radiation Protection Monitoring, June
26-30, 1978, International Atomic Energy Agency,
Vienna.
U.S. Nuclear Regulatory Commission. 1992. "Air
Sampling in the Workplace." Regulatory Guide 8.25,
Washington, D.C.
I
3 Demonstration that Air Sampling Is Representative of Inhaled Air
When air sampling results are being used to determine
intake, correct interpretation of the air sampling data is
important, and includes the knowledge of the physical
and chemical properties and particle size of the
contaminant, the extent to which samples represent the
air inhaled by the workers, the time the workers are in
the work area are other details.
3.1 Need to Demonstrate that Air
Sampling Is Representative of
Breathing Zone Air
Many factors can contribute to samples taken using area
air samplers not being representative of the breathing
zone of workers. For instance, even if air samplers are
located in what appears to be the airflow pattern from
the release point to the worker, airflow may be disturbed
by worker movement and equipment operation. Air
sampling rate and particle size are also factors that affect
the representativeness of the sample. For these and
other reasons, air ~amples may not be truly
representative of the air breathed by the worker.
Regulatory Guide 8.25 (NRC 1992) states that if the
decision is made to monitor a worker because the worker
will exceed 10% of an ALI and 1
the dose of record will be
based on air sampling, then the air sample should be
representative of the air breathed by the worker.
Further, if the sample is taken with a lapel sampler, then
it is considered to be representative of the air breathed
by the worker. If the air sampler is either fixed, portable
or a continuous monitor, the sampler must be shown to
be in the breathing zone of the worker (approximately
30 cm [1 ft] from the head) or the air sample location
must be shown to be representative of the breathing
zone. If air samples are not taken within about 30 cm
(1 ft) of the worker's head, Regulatory Guide 8.25
suggests the use of one of four methods to demonstrate
that samples are representative. The Guide also
provides a mechanism for correcting sampling results
that are not within its suggested acceptance criteria.
Four methods are used, as follows: comparison of area
3.1
air sample results with 1) lapel sampler results,
2) bioassay results, 3) multiple measurements taken near
the breathing zone, and 4) quantitative airflow tests
(discussed in Section 2.2.4).
3.2 Comparison of Fixed-Location
Air Sample Results with Lapel
Sample Results
Comparing fixed-location air sampler results with those
of lapel samplers ·is useful when airborne radioactivity
levels are routinely above the detection limit. This
method of comparison, as described in Regulatory Guide 8.25, is appropriate for workers whose intake is likely to
exceed 10% of an ALI and whose dose of record will be
based primarily on air sampling. If airborne levels are at
or near the' lower limit of detection for the lapel sampler,
this comparison will be difficult because the lapel
samplers may not detect radioactive air concentrations
that the fixed-location samplers can detect for the same
sampling time.
Fuel fabrication facilities have used this method of
comparison to determine whether their fixed-location
samplers are representative of the air breathed by the
workers. The studies are usually conducted on all shifts
for comparison purposes and there is often a significant
difference between the comparison ratio on day shift,
when most of the work is performed and the swing and
midnight shifts. Results from the studies are used to
determine whether lapel sampling is desirable (if the
criteria for sample representativeness are not met) or
whether other corrective actions are appropriate. These
corrective actions could include better contamination
control, repair of equipment for better confinement
control, and modification of ventilation systems.
Lapel sampler and fixed-location air sampler comparisons were taken from information from actual fuel fabrication facilities and are presented in the following
paragraphs. Although the data in the example provided
are taken from real situations, they have been adjusted
Inhaled Air
to adequately describe specific circumstances and
information considered crucial to understanding air
sampling practices.
The example scenario is as follows, Staff at a fuel
fabrication facility want to perform a comparison study,
as described in Regulatory Guide 8.25, to determine if
the air sampled by fixed-location air samplers used for
breathing zone sampling is representative of the air
breathed by the workers. By company policy, they perform such studies annually. The facility staff evaluated
each fixed-location air sampler location used to collect
breathing zone samples. Each worker who may have an
intake of 10% of an ALI or more is equipped with a
lapel sampler, which is worn for at least one week or
three operations. Sample results from the fixed-location
air sampler and lapel samplers are each measured for
equivalent time periods; that is, the filter on the fixedlocation sampler is changed and counted at the same
frequency as the lapel sampler, or adjustments are made.
The study compares lapel air sampler results with fixed
air sample results for two areas in the facility that show
greater than 10% of a DAC for the fixed air samplers.
The first area is occupied by a single individual who
spends most of his/her time at or near a hood (see
Figure 3.1); two fixed-location air samplers are placed in
this work area. The second area is larger, with seven
fDced-location air samplers and six workers during a shift
• (see Figure 3.2). To perform the comparison stud~es,
workers wear lapel samplers for 5 days during the time
they are working in the specified area. The lengths of
the sampling times are recorded. The fixed-location air
samplers are run as usual for an 8-hour shift; they are
then replaced and the samples are counted.
Table 3.1 shows the data collected for the small work
area with one worker and two fixed-location air
samplers. The health physicist averages the readings
from the two fixed-location samplers and calculates the
DAC-h based on the sample time of the lapel samplers.
As described in Regulatory Guide 8.25; the ratio of the
intakes is calculated by dividing the intakes calculated
from the fixed-location air samplers by the intakes from
the lapel samplers. To determine the DAC-h, the measured concentration, in µCi/mL is multiplied by the
sample time and divided by the DAC for 234U, class Y
(2 x 10-11 µCi/mL). The ratios range from 0.2 to 0.5.
According to Regulatory Guide 8.25, the ratio for an
NUREG-1400 3.2
individual worker should exceed 0.5 or corrective
actions should be taken.
The health physicist determined the correction factor by
taking the total DAC-h for the fixed-location air samplers and the lapel samplers, and determining the ratio.
The correction factor that makes the fixed-location air
sample data comparable to the lapel sampler data is
3.58. The correction factor is applied to all the intakes
calculated previously for that area for the year. For
further corrective actions, airflow pattern studies of the
room were made and the locations of the fixed-location
samplers were adjusted based on the studies.
The second area studied for comparison involved the six
workers in, the larger room with many work stations and
seven fixed-location air samplers, which have been
placed according to the results of an airflow pattern
study. Table 3.2 shows the data collected for this work
area.1 The ratios for the daily intake calculations varied
from 0.09 to 0.46. The correction factor calculated to
adjust the ALis of the workers is 4.75. This correction
factor is applied to all intakes calculated for that area
for the previous quarter. The health physicist decided
that because three of the five daily ratios are so low
(below 20% of the lapel sampler intake calculations)
even though the samplers were located based on airflow
studies, it would be preferable to put the workers in
lapel samplers rather than trying to change the locations
of the fixed-location air samplers.2
3.3 Comparison of Fixed-Location Air
Samples with Bioassay Results
To meet the intent of Regulatory Guide 8.25 in demonstrating the representativeness of fixed-location air
1
Although the workers stay primarily at one assigned work location
each day, the study was performed by averaging all the results from
fixed-location air samplers and averaging the results from the lapel
samplers.
2nie health physicist also considered the possibility of performing
quantitative airflow studies, but decided to wait until the next cycle of
lapel/fixed-location sampler studies before making such a
recommendation.
Sink e
6
I Exha~sl Ventilation
Filters
,___+---- e
5
I Hood el•
I e
I
I
L Area of Interest ------- - - -
0 = Air sampler head location lfE = Face of exhaust duct opening
Figure 3.1. Example Work Area Configuration for One Worker
and Two Fixed-Location Samplers
Hood
3
Hood 0
mm omm iiliil
Hood
Hood 0 0
Inhaled Air
0
Hood
2
=-======-=-----
) = Supply ventilation duct 0 = Exhaust ventilation extraction duct
Louvered Door
0 = Air sampler head location
Figure 3.2. Example Multi-Workstation Configuration for Six Workers and Seven Fixed-Location
Air Samplers
3.3 NUREG-1400
I
Inhaled Air
Table 3.1. Comparison of Lapel Samplers and Fixed-Location Air Samplers, One Worker with Two
Fixed-Location Air Samplers
LaJ!el SamJ!ler Fixed-Locatioi:i Air SamJ!lers
Time Calculated Calculated
Concentration Sampled Intake Concentration<a)
Day (µCi x 10·12 mL) I (h) (DAC-h) (µCi x 10-12 mL)
1 14.5 4 2.9 2.3
2 8.2 4 1.4 I 2.8
3 11.3 4 2.3 5.7
4 11.6 4 2.3 2.8
5 15.3 5 3.8 3.1
Total 12.7
(a) Average of the two air samplers located near work station.
(b) Ratio of intakes (air sampler DAC-h/lapel sampler DAC-h).
Sample Time/ Intake
Exposure Time (DAC·h)
8/4 0.5
8/4 0.6
8/4 1.1
8/4 0.6
8/5 0.8
Total 3.6
Table 3.2. Comparison of Lapel Samplers and Fixed-Location Air Samplers, Six Workers with
Seven Fixed-Location Air Samplers
LaJ!el SamJ!ler Fixed-Location Air SamQlers
Time Calculated Calculated
Concentration Sampled Intake Concentration<a) Sample Time/ Intake
Day (µCi x 10-12 mL) (h) (DAC-h) (µCi x 10·12 mL) Exposure Time (DAC-h)
1 8.3 5 2.1 0.87 8/5 0.22
2 6.1 5 1.5 0.55 8/5 0.14
3 9.9 5 2.5 1.73 8/5 0.41
4 10.2 5 2.6 3.44 8/5 0.86
5 3.9 4 0.8 1.83 8/4 0.37
Total 9.5 Total 2.0
(a) Average concentrations for four workers.
(b) Average of seven air samplers located in work area.
(c) Ratio of intakes (air sampler DAC-h/lapel sampler DAC-h).
NUREG-1400 3.4
Ratio(b>
0.2
0.4
0.5
0.3
0.2
Ratio(b>
0.1
0.09
0.16
0.33
0.46
sampling, a comparison can be made of area air sampled
by fixed-location air samplers with bioassay results of
workers located in the area of the air sampler. This
comparison method is probably the hardest to do and
has the most limitations. For instance, if air sampling is
used as the method of choice to determine intake
because detection limits for bioassay are not sensitive
- enough to measure intakes close to 10% of an ALI, then
comparison with bioassay results to determine
representativeness is not appropriate. Other drawbacks
include the need to keep the worker only in the location
being studied or in areas with no potential intakes so
that the bioassay result is only related to that of the air
sampler being compared against. Finally, it is best for
the study duration to be long enough to have a positive
bioassay of the worker(s) of interest. Using routine air
sampling data and bioassay data probably will not show
a true correlation of the intake by the workers working
at the air samplers of interest.
Although a less rigorous study may be adequate, if
comparison of air samples with bioassay results is
chosen the following method will provide the most
accurate comparison. The method includes setting up
and conducting the study, as well as applying
appropriate correction factors, as needed.
Parameters for setting up the study are as follows:
- The air sampler filters are to be indicative of the
time the worker(s) is at the work location. Installing
a new filter when the worker starts work and
changing the filter when the work is stopped will
assure that the air sample data are for a time period
comparable to the bioassay results. To provide
continuous sampling of the work location, sampling
can continue during normal operations, but the data
from the samples taken when the worker is not
present are not used in the study.
• All air samplers that represent a given work location
are to be used in the study.
• One or more workers can participate in the study. If
more than one worker is involved, the workers are to
be in the area of study at the same time. Any time
the workers are not in the area of study, they are to
be located in an area with no for potential for an
intake.
3.5
Inhaled Air
• Baseline bioassays are to be performed prior to the
start of the study, and preferably the workers have no
body burden.
• The study is to be conducted long enough so that the
potential intake necessary to exceed the minimum
detectable activity for the bioassay counting system is
obtained.
The comparison study is conducted by completing the
following steps in sequence:
1. Determine which fixed-location samplers are located
in areas that have the potential for airborne
radioactivity concentrations 10% of a DAC or
higher. ·
2. Identify the workers who will be monitored under 10
CPR 20.1502 and whose dose of record will be based
primarily on air sampling, but who are on a bioassay
program with results routinely above the minimum
detectable activity.
a. In addition, ensure that the workers are working
in, the area of the fIXed-location air sampler of
interest.
b. For best results, perform this study with several
workers in the same work location.
c. Work is not performed wearing respirators.
3. Carefully track the air sampling data to ensure that
the air samples are collected for the same time the
workers are in the work location. (Sample work
sheets are shown in Figures 3.3 and 3.4.)
4. Record the time that the worker is at the work
location being studied, and when the worker is not in
this area, limit him/her to areas where there is a no
likelihood of intake.
5. Change the air sampler filter when the worker comes
to the work location of interest and record the time
of the filter change on the work sheet.
a. Replace the filter when the worker leaves the
area and again record that time on the work
sheet.
b. Record the reading of the filter on the data sheet.
I
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COMPARISON STUDY OF AIR SAMPLING
WITH BIOASSAY
NAME: Andy Anderson AREA: Baseline Bioassay: 0 DAC-h
BLDG: 333 AREA: Lab AIR SAMPLER NO(s).: 222
Date Times Worked Air Sample Filter Changed Filter Reading (DAC-h)
03/01/92 7:30-noon Yes 0.7
1-4 pm Yes 1.1
03/02/92 7:30-noon Yes 0.3
03/03/92 7:30-noon Yes 0.9
2:30-4 Yes 0.4 -
03/04/92 7:30-noon Yes 1.0
1-4 Yes 0.2
03/05/92 1-4 Yes 1.0
Total: 5.6
BIOASSAY: 13.3 DAC-h
DATE: 03/06/92
RATIO 5.6 DAC-h = O 42 13.3 DAC-h .
Figure 3.3. Sample Work Sheet (1) Showing the Results of a Comparison Study of Air Sampling with Bioassay
....
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COMPARISON STUDY OF AIR SAMPLING
WITH BIOASSA Y '
NAME: James Jameson AREA: Baseline Bioassay: 0 DAC-h
BLDG: 333 AREA: Lab AIR SAMPLER NO(s).: 222
Date Times Worked Air Sample Filter Changed Filter Reading (DAC-h)
03/01/92 7:30-noon Yes 0.7
1-4 pm Yes 1.1
03/02/92 7:30-noon Yes 0.3
03/03/92 7:30-noon Yes 0.9
2:30-4 Yes 0.4
03/04/92 7:30-noon Yes 1.0
1-4 Yes 0.2
03/05/92 1-4 Yes r.o
Total: 5.6
BIOASSA Y: 9.4 DAC-h
DATE: 03/06/92
RATIO 5.6 DAC-h = o. 6
9.4 DAC-h
Figure 3.4. Sample Work Sheet (2) Showing the Results of a Comparison Study of Air Sampling with Bioassay
- '
- r
~
8:
- -
..,
Inhaled Air
c. Convert the data so that the units are the same
for both the air sample data and the bioassay data
(see Figure 3.1).
6. Upon completion of the study, total the results of
the air samples taken, obtain the bioassay results,
and determine the ratio of the total air sampled to
the bioassay results.
The following example describes the data from a comparison study made using bioassay data and a fixedlocation air sampler. Figures 3.3 and 3.4 present data
obtained from actual workers at a fuel fabrication
facility, however modifications have been made to better
illustrate the method for performing this comparison
study. Both individuals for whom the study was
performed had intakes higher than calculated for the
fixed-location sampler being studied.
The study made on the air sampler did not meet the
acceptance criteria of exceeding 0.7 when averaged for
all the workers in the comparison. One worker met the
0.5 acceptance criteria, but the other did not. Based on
Regulatory Guide 8.25, a correction factor should be
applied to the workers. The average between the two
ratios was about 0.5, so a correction factor of 2 should
be applied to both workers intake estimates made within
the last year. It may be appropriate to only apply the
correction factor to the dose estimates made while the
• workers were at that location if the records are adequate
to allow such a determination. The Regulatory Guide
also suggests that the problem be corrected. Either the .
air sampler can be moved and the evaluation can be performed again, or the workers can be put in lapel
samplers while working in that area, or the bioassay data
can be used to estimate the intake of the workers.
3.4 Comparison of Air Sampler Results
Using Multiple Samplers
This method for determining whether air samplers are
sampling air that is representative of the breathing zone
NUREG-1400 3.8
air is probably the easiest and most reliable. The studies
can be performed during normal operations, although
there may be some inconvenience to the workers during
the time. A multiple sample comparison can use portable air samplers located in the breathing zone or a
simple apparatus can be devised connecting several fixed
samplers that can be situated around a workers head and
connected to a pump or house vacuum.
The results of a multiple sampler comparison are shown
in Figure 3.5. In this example, four fixed-location
samplers were used in one work area of a decontamination facility. The samplers were run 24 h/day and the
filters were changed after each shift. A four-head test
air sampler was placed as conveniently as possible
around a worker in the decontamination facility during
the day shift. The test samplers were run and the filters
were changed after the swing shift and midnight shift
even though the facility was not in use. The data show
that the ratio of the fixed-location samplers to the
averaged value of the multiple test air samplers was
between 0.7 and 1.0. Therefore, the conclusion is that
the four samplers, as placed in the decontamination
facility, adequately demonstrate that the air sampled was
representative of the air the worker breathes.
3.5 References
10 CFR 20. 1991. U.S. Nuclear Regulatory
Commission, "Standards for Protection Against
Radiation." U.S. Code of Federal Regulations.
U.S. Nuclear Regulatory Commission. 1992. "Air
Sampling in the Workplace." Regulatory Guide 8.25,
Washington, D.C.
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COMPARISON WITH MULTIPLE SAMPLERS
LOCATION: Decon Facility
DATE: 10/05/92
Air Sampler Test Air Sampler Concentration in µCi/ml x 10-11
Concentration
in µCi/ml x 10-11 MIDNIGHT - DAYS SWING
Sampler MidNo. night Days Swing 1 2 3 4 Avg. 1 2 3 4 Avg. 1 2 3
111 0.3 15.3 0.2 0.3 0.2 0.4 0.3 0.3 18.0 17.2 21.2 16.0 18.2 0.4 0.2 0.3
112 0.2 2.4 0.3 0.2 0.2 0.4 0.3 0.3 3.1 2.8 3.2 4.0 3.3 0.3 0.4 0.2
113 0.2 22.9 0.3 0.3 0.4 0.2 0.2 0.3 29.0 31.0 24.0 27.0 27.8 0.2 0.2 0.3
114 0.3 16.5 0.3 0.3 0.2 0.4 0.2 0.3 20.0 19.0 18.7 17.9 18.9 0.2 0.4 0.2
RATIO
Saml!ler 111 = 0.3 = 1.0 Saml!ler 111 = 15.3 = 0.84 Saml!ler 111 = 0.2 = 1.0
Midnight Avg. 0.3 - . Days Avg. 18.3 Swing Avg. 0.3 Average: 0.95
Sam[!ler 112 = 0.2 = 0.7 Sam[!ler 112 = 2.4 = 0.7 Saml!ler 112 = 0.3 = 1.0
Midnight Avg. 0.3 Days Avg; 3.3 Swing Avg. 0.3 Average: 0.8 -
Saml!ler 113 = 0.2 = 0.7 Saml!ler 113 = 22.9 = 0.8 Saml!ler 113 = 0.3 = 1.0
Midnight Avg. 0.3 Days Avg. 27.8 Swing Avg. 0.3 Average: 0.8
Sam[!ler I 14 = 0.3 = 1.0 Sam[!kr I 14 = ~ = 0.9 Saml!ler I 14 = 0.3 = 1.0
Midnight Avg. 0.3 Days Avg. 18.9 Swing Avg. 0.3 Average: 0.95
Figure 3.5. Sample Work Sheet (3) Showing the Results of a Comparison Using Multiple Samplers
4 Avg.
0.1 0.3
0.2 0.3
0.4 0.3
0.3 0.3
II
........
- s
- s'
!:»
(b'
0.
r:-:
....
4 Adjustments to Derived Air Concentrations
With the prior approval of NRC (based on 10 CFR 20.1204 [c]), the committed effective dose equivalent can
be calculated by adjusting the DAC or ALI to better
represent the physical and biochemical characteristics of
the radionuclides taken into the body or their behavior in
an individual. This section reviews.considerations for
adjusting DACs by particle sizing (e.g., aerosol size
distribution or density), by measuring the respirable
fraction of airborne particles (using size selective inlets
like cyclone separators), and by identifying compound
solubility.
4.1 Adjusting Derived Air Concentrations for Particle Size
The calculations of committed effective dose equivalent
presented in Publication 30 of the International Commission on Radiological Protection (ICRP 1979) are
based on a standard aerosol with 1-µm activity median
aerodynamic diameter (AMAD). For an aerosol with an
AMAD between 0.2 µm and 10 µm and a geometric
standard deviation less than 4.5, an adjustment can be
• made to the 50-year committed dose equivalent, Hso.
Each radionuclide will have its own dose adjustment, due
to the differing contribution to committed dose
equivalent of radionuclides dep0sited in the three lung
compartments: nasal passage (N-P), trachea and
bronchial tree (T-B), and pulmonary parenchyma (P).
The following equation expresses the adjustment tQ the
committed dose equivalent in terms of ~he changed
deposition in the different lung compartments:
Hso(AMAD) DN_P(AMAD)
Hso(l µm) = fN-P DN-P(l µm)
(4.1)
+ f DT_B(AMAD) + !. Dp(AMAD)
T-B D (1 ) p D (1 ) T-B µm p µm
where f N-P• fT-B• and fp are fractions of the committed dose
equivalents in the reference tissues resulting from
4.1
deposition in the N-P, T-B, and P regions, and DN-P• DT-B•
and Op are the fractions of inhaled material initially
deposited in the three compartments ofthe lung.
The values for fN-P• fT-B• and fp are found in the
Supplement to Part 1 of ICRP 30. These values are
presented in the Supplement and are given as
percentages of the committed dose equivalent. The
numbers are in parentheses beneath the value of the
committed dose equivalent and must be converted to
decimal fractions before use.
Values for the ratios of deposition fractions (AMAD to 1
µm) are derived from the data in Part 1 ofICRP 30
(pages 24 and 25) and are presented in NUREG/CR4884 (page B-801) as shown here in the Table 4.il.. Figure 4.1 plots the data in Table 4.1 and allows the user to
interpolate.values other than those specifically given in
the table. · ·
Substitution of the fractions of committed dose
equivalent and the ratios of deposition fraction into
Equation (4.1), for a given AMAD, will provide a
correction value for the Hso (the 50-year committed dose
equivalent). Because the fractions of committed dose
equivalent routinely differ for the various tissues, this
correction value is likewise different for each tissue. This
is important in the formulas for deriving stochastic ALI
but not for deriving a nonstochastic ALis. Regulatory
Guide 8.34, Monitoring Criteria and Methods to Calculate
Occupational Radiation Doses, discusses how to
determine the appropriate ALI to use when adjusting
DA Cs.
0.05 Sv ALI (1 µm) otocbutic = (4.2) LT WT Hso,T Sv/Bq
ALI (1 µm) nomtccbutic
0.5 Sv (4.3)
Hso,T Sv/Bq
Air Concentrations
-E
- i.
-
Q
c(
- e
c(
0
.,
0
...
c( •
Table 4.1. Ratios for Deposition Fractions (AMAD to 1 µm)
Aerosol IlN.p(AMAD) IlT.u(AMAD) .Qp(AMAD}
AMAD (µm) DN_p(l µm) DT_8 (1 µm) Dp(l µm)
0.2
0.5
0.7
1.0
2.0
5.0
7.0
10.0
8
6
4
2
0
0.17 1.00
0.53 1.00
0.77 1.00
1.00 1.00
1.67 1.00
2.47 1.00
2.70 1.00
2.90 1.00
Dlb(AMAD)
¥
2
Deposition Fraction Ratios (D [AMAD])
2.00
1.40
1.20
1.00
0.68
0.36
0.28
0.20
Figure 4.1. Values for Ratios of Deposition Fractions
4.2
3
where WT is the weighting factor for tissue (T) and has
the values from 10 CFR 20.1003. The H50,T per unit
intake (in Sv/Bq) is the committed dose equivalent in
tissue (T) from the uptake of unit activity of the
radionuclide.
This task can become tedious, as seen in the following
example using the percentages of H50,T, weighting factors,
and the H50,T (Sv/Bq) for class W cobalt-60 that are
presented in Table 4.2.
The E WT H50(1 µm) value is inserted into Equation
(4.2). The maximum value of H50(1 µm) occurs for the
lung in this example and is used in Equation ( 4.3).
ALI (1 m) = 0.05 Sv (4.4)
µ stochastic 7.97 X 10-9 Sv/Bq
ALI (1 µm) llochastic i' 6.27 x 106 Bq (4.S)
0.5 Sv ALI (1 µm) nonotocbutic = (4.6) 3.6 x 10-s Sv /Bq ,
Air Concentrations
ALI (1 µm) nomlocbutic = 1.39 X 107 Bq (4.7)
The stochastic At.I used in this example is found on page
41, of ICRP 30, Supplement to Part 1 (ICRP 1979).
Changing the deposition percentages into fractions and
inserting deposition fraction ratios from Table 4.1 into
Equation (4.1) produces the value of H50(7 µm)/H50(1
µm) for the various organs. To continue the ex~mple,
Equation (4.1) is used, as shown in Equation 4.8, for an
AMAD particle size of 7 µm and the results shown in
Table 4.3.
H50 (
7 µm) = f (2.70)
H50 (1 µm) N-P
+ f T-B (1.00) + fp (0.28)
The E WT H50(7 µm) value is inserted into Equation
(4.2). The maximum value of H50(7 µm) into
(4.8)
Equation ( 4.3) to perform an evaluation of the maximum
ALI allowed, as follows:
Table 4.2. Percentages of Committed Dose Equivalent , Factors,
and H50,T (Sv /Bq) for Cobalt 60, Class W
Percentage
Tissue (fN-P,f.r.u1fp) WT Hso,T x 10·' WTHso,T x 10·9
Gonads (35,21,44) 0.25 4.0 1.00
Breast (19,17,64) 0.15 4.2 0.62
Red marrow (20,17,63) 0.12 4.2 0.51
Lungs (02,02,96) 0.12 36.0 4.32
LLI wall (45,15,40) 0.06 8.2 0.49
Liver (21,19,60) 0.06 9,2 0.55
Remainder (10,09,81) 0.06 8.0 0.48
EWTH50,T = 7.97
4.3 NUREG-1400
I
Air Concentrations
Table 4.3. Values of Deposition Fraction Ratios, Committed Dose Equivalents and Weighted
Committed Dose Equivalents for Cobalt 60, Class W, and AMAD = 7 µm
Tissue Ratio H50,T(l µm) x 10_,
Gonads 1.28 4.0
Breast 0.86 4.2
Red Marrow 0.89 4.2
Lungs 0.34 36.0
LLI wall 1.48 8.2
Liver 1
o.93 9.2
Remainder 0.59 8.0
0.05 Sv
ALI (7 µm) 11ochas1ic = -------
5.26 x 10-9 Sv /Bq
(4.9)
ALI (7 µm) stochastic = 9.51 X 106 Bq (4.10)
ALI (7 µm) nonstochastic 0.5 Sv (4.ll)
1.22 x 10-s Sv /Bq
ALI (7 µm) nonsl<'Cha.stic = 4.10 X 107 Bq (4.12)
To complete the example, a relationship between the
DAC = [ALI/2.4 x 103 ] Bq/m 3 (4.13)
Therefore, with rounding, the DAC for the ALI (1 µm)
of 6.0x106 Bq for class W 00Co, class W, is 3.0 x 103
Bq/m3
, while the DAC for the ALI (7 µm) of 1.0 x 107
Bq is 4.0 x 103 Bq/m3
•
Not all calculations will be as straightforward as in the
case of class W 00Co. Computer programs are developed
that compute adjusted DACs and ALis for particle-sizing
corrections. The computer program used to develop the
Environmental Protection Agency's, Federal Guidance
Report No. 11, Limiting Values of Radionuclide Intake
and Air Concentration and Dose Conversion Factors for
Inhalation, Submersion and Ingestion (EPA 1988), does
NUREG-1400 4.4
H50,T(7 µm) x 10..,, WTHso,T(7 µm) x 10_,
5.12 1.28
3.61 0.54
3.74 0.45
12.24 1.47
12.14 0.73
8.56 0.51
4.72 0.28
EWTH.so,T = 5.26
not employ rounding methods as suggested in ICRP 30
and effective dose equivalent factors may be slightly
higher (by 10 to 20% ). The described program gives
slightly higher doses for the same intake described in 10 CFR Part 20.
There are examples of the ratio of the 50-year committed
dose equivalents (Equation [4.1)) becoming simple
ratios, such as for 235U, classes Wand Y (Thind 1986).
This is primarily true because of the reported deposition
percentages of H.so,T are (0,0,100). Thus for class Y 235U,
Equation 4.8 simplifies to
H50 (AMAD)
H50 (1 µm)
DAC (1 µm)
DAC (AMAD)
(4.14)
Table 4.4 and Figure 4.2 present the calculated data for
class D, W, and Y 235U. The data presented clearly show
that various multiples of a DAC are appropriate,
depending upon the particle size and solubility class. The
data indicate that for class Y 235U for an AMAD of 7 µm,
the DAC may be increased by a multiple of 3.6.
According to ICRP 35 (1982), "If the AMAD of the
aerosol is known to be markedly different from 1 µm, the
retained fraction will differ from the standard aerosol
and the need for correction factors should be
considered." Particle-sizing devices, such as cascade
impactors, are useful for measuring the AMAD of the
Air Concentrations
Table 4.4. Ratios of DAC (AMAD) to DAC (1 µm) for 235U
Ratio of DAC (AMAD) to DAC (1 M:m)
Particle
Class D ClassW ClassY Size (µm)
0.2 0.81 0.5 0.5
0.5 0.94 0.71 0.71
0.7 0.98 0.83 0.83
1.0 1.00 1.00 1.00
2.0 0.96 1.5 1.5
5.0 0.86 2.8 2.8
7.0 0.84 3.6 3.6
10.0 0.82 5.0 5.0
5
-E 4
- I.
--
0
c
Q
0 3
-
Q
-
c
- &
c
- 2 0
c
Q
-0
.2
a: -
•
O-t-~--StriderTol (talk)--~~..-~..-~...-~--~....-~---~--t
0 2 4 6 8 1 0
Particle Size (µm) '
Figure 4.2. DAC Ratios for 235u
4.5 NUREG-1400
Air Concentrations
sampled radioactive aerosol. Section 4 of Regulatory
Guide 8.25 notes that particle size measurements and
adjustments of DACs and ALis are not required, but are
permitted (with NRC approval as stated in 10 CFR 20.1204) for determining adjusted DACs and ALis and
subsequent change in effective dose equivalent. Particle
size measurements may sometimes reduce the calculated
dose equivalent due to internal 1
radionuclide exposure,
because particle size distributions found in the nuclear
industry are often significantly greater than the default
value of 1-µm AMAD, which is used in ICRP 30 (ICRP
1979).
4.2 Methods for Adjusting DACS
The DAC or ALI can be adjusted by determining particle sizes using measurements made with a cascade
impactor or a cyclone separator or by determining the
solubility classes of the materials and adjusting the DAC
based on the fraction of material that is class D, W, or Y.
Additional information on particle size sampling can be
found in Particle Size-Selective Sampling in the Workplace
(ACGIH 1985).
4.2.1 Use of a Cascade Impactor to
Determine Particle Size
Particle size distributions can be determined using a
• cascade impactor or similar method. The cascade
impactor separates particulate aerosols into many
different size fractions for analysis of particle size
distributions. Practical guidance on the operation of
cascade impactors can be found in the monograph,
Cascade Impactor Sampling and Data Analysis (Lodge
and Chan 1986). (See Section 6.4 of this publication for
plotting lognormal distributions of particle size
measurements.) To determine whether the entire workplace can be represented by a single particle size,
measurements of aerosols in each work area or process
can be made. If the results of the particle-size
determination indicate a geometric standard deviation of
less than 4.5 for all measurements, one particle size can
be assumed, and used in adjusting the DAC.
A geometric standard deviation of 4.5 or greater is likely
to indicate a bimodal distribution of aerosols. Resolution of a composite distribution into two components that
can be accounted for in ICRP 30 (ICRP 1979) methodology may require complicated procedures (Cheng 1986).
Coarse particles are created by mechanical processes
NUREG-1400 4.6
such as cutting, abrasion, and mixing, while operations
involving high-temperature processes such as heating,
welding, and distillation produce particles smaller than 1
µm. It is possible that with several and different ongoing
operations in a workplace, multiple size modes will be
found.
4.2.2 Using Cyclones to Compensate for
Particle Size
Cyclone separators can discriminate against large particles and thus are useful in directly measuring
particulates that are respirable. Inspection of cyclone
efficiency curves shows that a cyclone separator can be
operated at a flow rate to collect a sample of an aerosol
that mimics the deposition of particles in the pulmonary
parenchyma (P region of the lung as modeled in the
ICRP 30 lung model) (Bartley and Breuer 1982).
According to Regulatory Guide 8.25, the use of a cyclone
is acceptable for insoluble radionuclides as long as
collection efficiency of the cyclone is at least 50% for a
particle of 4 µm aerodynamic diameter.
Cyclone separators can only be used to estimate the
intake of insoluble radionuclides (class Wand class Y).
For insoluble radionuclides material deposited in the P
region of the lungs is the principal contributor to the
dose because most material deposited in the N-P and TB regions is cleared without much uptake. For soluble
radionuclides (class D), there is significant uptake of
material deposited in the N-P and T-B regions, and thus
a significant contribution to dose from soluble materials
deposited in those regions. Since larger particles are
preferentially deposited in those regions, there is a
significant contribution to dose from large particles that
would not be collected by a cyclone sampler. Thus,
cyclone samplers are not suitable for sampling soluble
(class D) radionuclides.
4.3 Adjusting Derived Air Concentrations for Solubility
The DAC may be adjusted based on chemical characteristics of the radionuclide. The DACs for inhalation
are given for three classes (D, W, and Y) of radioactive
material, which refer to their retention (approximately
days, weeks, or years) in the pulmonary region of the
lung. This classification applies to a range of clearance
half-times for class D material of less than 10 days, for
class W from 10 to 100 days, and for class Y greater than
100 days. Generally, if the physical and biochemical
properties of the radionuclides or the behavior of the
material in the body are known and different from the
ICRP assumptions, the DAC can be adjusted using that
information. A variation in intake retention factors or
discovery of a classification not listed for a radionuclide
are examples of two situations that could lead to a DAC
adjustment. Lessard et al. (1987) provide information to
, relate biological data to estimates of intakes. From this
estimate of intakes and associated doses, a correction
factor to the DAC may be made. · The process for
making DAC adjustments based on solubility involves
sampling a workplace for the respirable fraction of the
radionuclide in question. Samples are then subjected to
dissolution in simulated lung fluid, which chemically
represents the pulmonary environment. A detailed
discussion of a method for performing a solubility study
is provided by Briant and James (1990).
.
4.4 References
10 CFR 20. U.S. Nuclear Regulatory Commission."
Standards for Protection Against Radiation." U.S. Code
of Federal Regulations.
American Conference of Governmental Industrial
Hygienists (ACGIH). 1985. Particle Size-Selective
Sampling in the Workplace. ACGIH, Cincinnati, Ohio.
Bartley, D. L., and G. M. Bruer. 1982. "Analysis and
Optimization of the Performance of the 10 mm Cyebne."
American Industrial Hygiene Association Journal
43:520-528.
Briant, J. K., and A. C. James. 1990. Dissolution and
Particle Size Characterization of Radioactive
Contaminants in Hanford Facilities: Criteria for Methods
of Measurement. PNL-7438, Pacific Northwest
Laboratory, Richland, Washington.
International Commission on Radiological Protection
(ICRP). 1978. Limits for Intakes of R:idionuclides by
Workers. ICRP Publication 30, Part 1, and ICRP
Publication 30, Supplement to Part 1, Pergamon Press,
Oxford.
International Commission on Radiological Protection
(ICRP). 1982. General Principles of Monitoring for
Radiation Protection of Worker. ICRP Publication 35,
Pergamon Press, Oxford.
4.7
Air Concentrations
Lessard, E.T. et al. 1987. Interpretation of Bioassay
Measurements, NUREG/CR-4884, U.S. Nuclear
Regulatory Commission, Washington, D.C.
Lodge, J.P., and T. L. Chan, eds. 1986. Cascade Impactor
Sampling and Data Analysis. American Industrial
Hygiene Association (AIHA), Akron, Ohio.
Thind, K. S. 1986. "Determination of Particle Size for
Airborne U02 Dust at a Fuel Fabrication Work Station
and Its Implication on the Derivation and Use ofICRP
Publication 30 Derived Air Concentration Values."
Health Physics 51(1):97-105.
U.S. Environmental Protection Agency (EPA). 1988.
Limiting Values of Radionuclide Intake and Air
Concentration and Dose Conversion Factors for
Inhalation, Submersion and Ingestion. Federal Guidance
Report No. II, Cincinnati, Ohio.
U.S. Nuclear Regulatory Commission (NRC). 1992. Air
Sampling In the Workplace. Regulatory Guide 8.25,
Rev. 1, Washington, D.C.
U.S. Nuclear Regulatory Commission (NRC). 1992.
Monitoring Criteria and Methods to Calculate
Occupatibnal Radiation Doses. Regulatory Guide 8.34,
Washington, D.C.
International Commission of Radiological Protection
(ICRP). 1979. Limits for Intakes of Radionuclides by
Workers. ICRP Publication 30, Pergamon Press, New
York, NY.
5 Measurement of the Volume of Air Sampled
Determining the concentration of radioactive materials
in the air involves accurate measurements of both the
sample activity collected and the volume of air collected
during the sampling interval. Regulatory Guide 8.25
(NRC 1992) recommends that an air-sampling program
provide for an annual calibration of all flow-rate
measurement instruments (airflow or volume meters).
Regulatory Guide 8.25 also recommends that additional
calibrations be performed after repairs or alterations are
made or ifthe flow-rate measurement instrument is
damaged.
5.1 Means to Determine Volume of Air
Sampled
For most workplace air-sampling applications, the
sample volume is measured with a flow-rate measurement instrument such as a rotameter or orifice meter.
These instruments are relatively inexpensive,
lightweight, compact, and useful over a wide range of
flow rates. With proper handling and maintenance, they
provide acceptable measurement accuracy.
The rotameter typically consists of a tapered transparent
tube with a solid float inside (see Figure 5.1). The crosssectional area of the tube increases from the bottom to
the top. A scale in flow-rate units is marked on the
outside surface. The airflow raises the float until the
buoyant and kinetic forces of the air balance the gravitational force on the float. The height of the float varies
in proportion to the volumetric flow rate. There are
rotameter designs to measure flow rates from less than
1 cm2
/min. to hundreds of cubic feet per minute. Float
design will vary depending on the manufacturer and the
flow rate. Readings are conventionally taken at the
widest point of the float, but the user's manual for a
particular instrument will specify the reading point.
The orifice meter consists of a carefully machined
constriction in a tube between the upstream and
downstream pressure taps (see Figure 5.2). The flow
rate is calculated from the orifice diameter, the pressure
upstream of the orifice, the ratio of the orifice
5,1
diameter to the tube diameter, and the upstream
temperature. (Refer to Section F of the ACGIH'sAirSampling Instruments for Evaluation of Atmospheric
Contaminants [1989]) for a discussion of the equation
used to calculate flow rate.)
In addition to rotameters and orifice meters, mass flow
meters are commonly used as flow-rate measurement
devices in continuous air monitors. A mass flow meter
contains a heating element in a duct section between
two points where the temperature of the air is measured.
The temperature difference between the two points is
dependent on the mass flow rate and the heat input.
Pressure loss through the mass flow meter is usually
negligible.
For more information on the design and operating characteristics of the rotameter, orifice meter, mass flow
meter, and other types of flow-rate measurement
instruments Section F (Calibration of Air-Sampling
Instruments) in ACGIH (1989) can be consulted.
5.1.1 Flow Control for Portable Air Samplers
Constant flow for portable air samplers to avoid
correction problems can be maintained as follows:
• flow control with a vacuum gauge at the pump
calibrated to indicate the entering flow rate,
regardless of the filter load
• manual adjustment of the flow with a rotameter
located between the control valve and the pump; the
rotameter can be calibrated to indicate the entering
volumetric flow rate regardless of the filter load
• automatic flow control with a vacuum regulator in
series with each sample collector to compensate for
the filter load
• automatic flow control with a differential regulator
in series with each sample collector to compensate
for the filter load
Measuring Air Sampled
Flow
Tapered
Tube
Reading
Typical _ _....._
Float
Figure 5.1. Rotameter
Diameter
- - - - - Orifice Diameter - ::. - - -
- --
Figure 5.2. Orifice Meter
5.2
I
• automatic flow control with a thermal anemometer
used to control the speed of the pump.
Contrary to popular belief, orifice flow control (in which
the velocity in the orifice is at the speed of sound) cannot
compensate for changing filter loads, and consequently is
not recommended for use in air samplers that employ a
filter as the sample collector.
5.1.2 Flow Control for Air Samplers
Connected to Central Vacuum Systems
Flow control for air samplers connected to central
vacuum systems is simplified greatly if the system is used
only for air-sampling, and if the pump and piping are
operated at a constant vacuum. This makes each sampling station independent of the others (like electrical
appliances on a 115-V electrical circuit), provides a
constant reference vacuum for flow control purposes,
and permits the air mover to be optimized for one
operating condition. The vacuum most frequently
selected is 254-mm Hg (10-in. Hg), which is adequate for
most air-sampling purposes and is within the operating
range of most of the heavy-duty air movers.
The sampling flow rate to air samplers connected to a
constant vacuum system can be controlled, while at the
same time avoiding flow meter correction problems, by
one of the following methods:
• manual flow control with the flowmeter located
downstream from the control valve and calibrated for
the constant vacuum in the piping system
• automatic flow control with a differential regulator
and an adjustable metering orifice in series with the
sample collector, to compensate for the filter load
• automatic flow control with a thermal anemometer
used to operate a control valve in series with the
sample collector.
5.1.3 The Importance of Having a Gauge to
Indicate the Filter Load
A vacuum gauge for indicating the filter load is recommended for a number of reasons: 1) it shows whether
the load from a newly installed sampling filter is normal;
5.3
Measuring Air Sampled
2) it shows whether the load from the protective (or
backup) filter is normal; 3) it shows the effect of using
different sample collectors; 4) it shows how fast the filter
load is increasing, which is an indication of the amount of
a particulate in the air; 5) it simplifies the testing of the
flow control system; and 6) it shows how close the filter
load is to the limit of the flow control system.
5.1.4 The Importance of Constant Flow
Accurate interpretation of air-sampling data depends
upon knowing how much air the sample came from and
obtaining a true time average of the changing concentrations of contaminants in the air during the test. With
constant flow, the amount of air sampled is simply a
product of the flow rate and the elapsed time. Without
constant flow, the sample may contain a disproportionately large amount of particulate from the start of the
test when the filter was clean and a disproportionately
small amount from later periods. Thus, under varying
flow conditions, a short radioactive burst might be
collected at either a high or a low flow rate, depending
on the condition of the filter, making the sample
unrepresentative and jeopardizing its usefulness in
radiation protection.
5.1.5 Total Volume Measurement Devices
For some air-sampling applications, the total volume of
the sample is measured, rather than calculating the flow
rate and integrating over time. The method of operation
of flow totalizers may vary, but most use some adaptation
of rate measurement. Some devices use electronic
calculation of integrated flow based on critical orifice
parameters or the position of a rotameter or similar
device; however, the most commonly used totalizers use
timing devices that assume a continuous flow rate and
read out in units of total volume sampled. Compositor
samplers are usually of the latter type, with a timedoperation positive displacement air mover. Under
normal conditions, the reliability and accuracy are
comparable to rate measurement devices. Totalizers can
be made more accurate than rate measurement devices
by designing them to correct for fluctuations in flow rate.
A summary of the types of flow-rate measurement
instruments is in Table 5.1.
Measuring Air Sampled
Table 5.1. Types of Flow-Rate Measurement InstrumentsCa)
Type of Meter Quantity Measured Typical Range
Spirometer Integrated volume 6 to 600L
Soap film meter Integrated volume 0.002 to lOL
Wet test meter Integrated volume Unlimited volumes, maximum rates
Dry gas meter Integrated volume Unlimited volumes, maximum flow
rates from 10 to 150 L/min
Venturi meter Volumetric flow rate Depends on tube and orifice diameters
Orifice meter Volumetric flow rate Depends on tube and orifice diameters
Rota meter Volumetric flow rate From 0.001 L/min
(a) Adapted from Table F-4 of the ACGIH document (1989).
5.2 Calibration Frequency and
Methods
calibration of flow-rate measurement instruments used
in the field (typically, rotameters or critical orifice
meters) is performed by comparing the flow rate measured by the field instrument with the flow rate measured
by a primary standard instrument, such as a spirometer
or soap film flowmeter, or a secondary standard instrument, such as a dry gas meter or wet test meter.
5.2.1 Calibration Frequency
Regulatory Guide 8.25 states that licensees should
calibrate airflow rate meters annually and after
modifications, repairs, or any indication that the meter
is not performing properly. The annual frequency was
established as follows:
1. Five vendors were queried on, the recommended
frequency of calibration based on historical
performance of the instruments. Three of the
vendors recommended annual calibration, one
vendor suggested semiannual calibration as use and
operating experience dictates, and one vendor did
not recommend recalibration of their meters.
NUREG-1400 5.4
2. In addition to the annual frequency, ANSI N42.17B,
Performance Specification for Health Physics
Instrumentation-Occupational Airborne Radioactivity
Monitoring Instruments (ANSI 1989), Section 4.9,
•Alteration and Modification," states, "Instruments
that have been altered, changed or modified by the
manufacturer in any manner which could affect the
capability of the instrument to meet the specifications provided in this standard shall be re-evaluated
to ensure conformance ... ."
Other criteria in ANSI N42.17B are also given to help
determine when calibration is needed between the
annual scheduled calibrations. When these criteria
(listed below) are not met, repair and or recalibration is
suggested.
• Section 9.1, "Flow-Rate Meter Accuracy," states,
•Airflow rate meters shall be accurate to within
±20% of the conventionally true flow-rate values."
• Section 9.2, "Air In-Leakage," states, "The leakage of
air into the monitoring unit upstream of the flowrate meter shall be less than 5% of the nominal flow
rate."
• Section 9.3, •flow-Rate Stability; states, "The
manufacturer shall state the nominal flow rate for
the type of filter that is used. After the warm-up
time specified by the manufacturer for the
monitoring unit, the measured flow rate shall not
vary more than 10% from the nominal flow rate.•
5.2.2 Calibration to Primary Standards
The spirometer and soap film flowmeter are examples of
primary standards that measure volume directly. The
spirometer is a cylindrical bell with its open end under a
liquid seal. Tite soap film flowmeter is a graduated tube .
in which a suap bubble is created. These are primary
standards because they are a direct measurement of
volume based on the physical dim~nsions of an enclosed
space. Recalibration of primary standards is not
necessary, except when there is physical damage that can
change the volume of the enclosed air space used for the
flow-rate measurement.
Refer to the American Society of Testing and Materials
Standard 01071, Standard Methods for Volumetric
Measurement of Gaseous Fuel Samples (ASTM 1983a),
for a calibration procedure for spirometers using standard cubic-foot bottles. A calibration procedure for a
soap film flowmeter using a liquid positive-displacement
technique is contained in Volume II of the EPA's
Quality Assurance Handbook for Air Pollution
Measurement Systems (EPA 1985).
5.2.3 Calibration to Secondary Standards
The wet test and dry gas meters are examples of
secondary standards, tracing their calibrations to
primary standards. Although secondary standards
require recalibration, they can maintain their accuracy
for extended periods with proper handling and maintenance. A calibration procedure for a wet test meter
can be found in Section 19 of ASTM Standard 01071
(ASTM 1983a). A wet test meter measures volume by
displacement of the liquid in the meter by the air being
measured; a dry gas meter measures volume by displacement of the air in the meter by the air being measured.
A more complete description of the operation of these
meters is provided by ACGIH (1989; Section F).
Air-Sampling Instruments for Evaluation of Atmospheric
Contaminants (ACGIH 1989) refers to rotameters and
critical orifice meters as "additional secondary
5.5
Measuring Air Sample~
standards; meaning that they usually have an accuracy
less than either a wet test meter or a dry gas meter.
These additional calibration standards have accuracy
characteristics similar to those of field rotameters and
orifice meters. Therefore, if they are used to calibrate
field instruments, it is appropriate to calibrate them
against a primary or secondary standard at the same
frequency specified for field instruments. The
calibration hierarchy is as follows:
• primary standard (e.g., spirometer)
• secondary standard (e.g., wet test meter)
• additional secondary standard (e.g., rotameter).
Thus, a rotameter can be calibrated with a wet test
meter, which in turn can be calibrated with a spirometer,
or the rotameter can be calibrated directly with a
primary standard.
5.2.4 Calibration of Rotameters
Because rotameters are the flow-rate meters most often
used in the field, their calibration and maintenance are
of common concern to users. The ASTM Procedure
03195, Standard Practice for Rotameter Calibra'tion
(ASTM 1983b), provides a method for calibrating a
rotameter with either a wet test meter or a spirometer
(gasometer). Beginning with a wet test meter or
spirometer, the rotameter output (usually at the top of
the rotameter) is connected to the wet test meter or
spirometer, as shown in Figures 5.3 and 5.4. Keeping
connections as short as possible, with a maximum
inside-line diameter helps avoid appreciable pressure
drops. It is important to the calibration process that air
leakage be avoided and that tight connections be made
between the rotameter and the standard. Leakage can
be checked in several ways. Plugging the line upstream
of the connection will cause the flow to drop to zero if
the connection is tight. A smoke test or small amounts
of soap solution applied near potential leak points can
also be used to detect leaks.
The ASTM Procedure 01071, Standard Methods for
Volumetric Measurement of Gaseous Fuel Samples
(ASTM 1983a), suggests that a minimum of five readings be taken over the entire range of flow rates for the
particular instrument. The average of a pair of timed
readings on the wet test me~er or spirometer should be
I
Measuring Air Sampled
Air
Rotameter
Under
Test
Source --.j ......... ,,.
Needle
Valve
Manometer
Thermometer
Wet
Test
Vacuum
Pump
Figure 5.3. Calibration Setup of a Rotameter Using a Wet Test Meter
Rotameter
Under
Test
Needle
Valve
Source
Gasometer
Figure 5.4. Calibration Setup of a Rotameter Using a Spirometer
5.6
I
Exhaust
determined for each measurement point. When taking
readings, the meter is first read from lowest to highest
measurement point and then from highest to lowest. The
manometer reading and the meter water temperature are
recorded for each measurement. In addition, the room
temperature, the barometric pressure, and the relative
humidity are recorded before and after the calibration
run; the average values are used in the calculations.
An alternative calibration procedure for a rotameter is in
Volume Il ofEPA's Quality Assurance Handbook for Air
Pollution Measurement Systems (EPA 1985). The
procedure uses a soap-film meter for the calibration. A
calibration procedure for the s_pecial situation of
calibrating a lapel-sampler rotameter is contained in
Appendix A.1 of ASTM Procedure 04185, Methods for
Calibration of Small Volume Air Pumps (ASTM 1983c).
Again, the procedure described uses a soap-film meter
for the calibration.
5.2.5 Calibration of Flow Totalizers
Two methods of calibration are typically used. One is to
calibrate the flow-rate measurement portion and independently test the time integration. The other is to pass
a specific volume through the device, and compare this
with the measured result, most often by slowly releasing
a compressed gas of known mass, with corre-:tions for
pressure 2.nd temperature.
5.3 Uncertainty
As specified in Regulatory Guide 8.25, air-sampling
instruments, including personal air samplers having flowrate meters or total-volume meters, should have the
meters calibrated so that the overall measurement
uncertainty in determining the sample volume is less than
20%. The overall uncertainty or measurement error is
calculated by adding 1) the estimated uncertainty that
arises when a user reads the meter scale, 2) the
estimated uncertainty in the measurement instrument's
calibration factor, and 3) the estimated uncertainty in the
measurement of sampling time. Each of these
uncertainties is e>:-iressed as a percent uncertainty, i.e.,
the absolute value of an arbitrary allowance for
uncertainty (absolute uncertainty) divi:led by a relevant
true value and then multiplied by 100. For example, in
determining the percent uncertainty in reading the meter
scale, the arbitrary uncertainty is customarily assumed to
be one-half of the smallest scale division on the
instrument. Thus, if an instrument scale reads a total of
5.7
Measuring Air Sampled
50 L/min, with each L/min divided into segments of 0.1
L/min, the absolute uncertainty is 0.1/2, or 0.05 L/min.
(That is, the uncertainty is arbitrarily assumed to be
±0.25 L/min around a middle value; then, the absolute
uncertainty is the absolute value of the number, or 0.05
L/min.) To find the percent of uncertainty in reading
the meter scale, this absolute uncertainty is dived by the
flow rate (in this example, 2 L/min) of the instrument
and then multiplied by 100:
(0.05 L/min / 2 L/min) x 100 = 2.5% (5.1)
Similar approaches yield the percent of uncertaipty in the
calibration and in the measurement of sampling time.
The calibration percent of uncertainty is found relative to
a standard. The percent uncertainty in sampling time,
which is used only for samplers with flow-rate meters,
has been assumed to be 1 % for most sampling times.
Once the uncertainties for meter reading, calibration,
and sampling are obtained, the overall measurement
uncertainty (Uv) in computing the total volullle of air
sampled can be calculated using Equation (5.2):
where U, = the percent uncertainty in reading the
meter scale. The absolute uncertainty in
the meter reading is converted to a percent uncertainty before being inserted in
Equation (5.2). This is done by dividing
the absolute uncertainty by the flow rate
( cfm) and multiplying by 100. An estimate of the absolute uncertainty in reading a meter scale for both flow-rate
instruments and total flow volume instruments is one-half of the smallest scale
division.
·u. = the uncertainty in determining the calibration factor. An estimate is the
percent uncertainty associated with the
standard instrument used in the
calibration.
ul = the percent uncertainty in the
measurement of sampling time. When
using a timing device to measure sample
volume, an appropriate value of the
percent uncertainty for usual sampling
Measuring Air Sampled
volume, an appropriate value of the
percent uncertainty for usual sampling
intervals is 1 %. For an instrument with
a total volume meter, this term is
dropped from the equation.
Assuming some typical values,ithe overall uncertainty
(U ) associated with a calibration factor (Uc)
un~rtainty of 1 %, a scale reading (U8) uncertainty of
2%, and a sampling time (U1
) uncertainty of 1 % is
determined as follows:
UV = [(2.5)2 + 12 + 12 ]1/2 = 2.9% (S.3)
Minimizing the uncertainty in reading the scale requires
a consistent method for reading the rotameter. Most
manufacturers recommend reading the float at the
widest point. Establishing procedures for reading the
scale will help reduce the variation among readings from
individuals using different methods. Figure 5.5 shows
several float designs and the recommended points for
reading the flow rate.
5.4 Method for Determining Air
In-Leakage
Regulatory Guide 8.25 recommends that continuous air
• monitors be checked for in-leakage when they are
calibrated for volume of air sampled. In-leakage
upstream of the flow-measuring device is limited to a
maximum of 5% by ANSI N42.18 (1985). A potential
problem affecting the accuracy of volume measurements
is system leakage downstream of the sample collector
and upstream of the flow measurement instrument.
Under these conditions, the indicated flow is more than
the airflow through the sample collector and will lead to
overestimates of the air volume that is sampled. A field
test for system in-leakage can be performed simply by
blocking the sample inlet and seeing if the flow drops to
zero. If it does not, there is in-leakage to the system.
Caution is necessary for systems with components that
are either fragile or sensitive to rapid pressure changes,
such as continuous air monitors with thin-window
detectors located in the sample stream. The preferred
method,
using rotameter intercomparisons upstream and
downstream of the sample collector, is contained in
ANSI N42.7B (1985), Section 9.2.2.
5.5 Pressure and Temperature
There are many variables that may affect the accuracy of
an air-sample measurement. Two of these are pressure
and temperature variations. Appropriate corrections,
using the ideal gas laws, when either the absolute
pressure or absolu'te temperature exceeds 5%, can
assure that the pressure and temperature variations do
not cause inaccurate measurement results. Two commonly performed tasks that may involve pressure differences are cited: calibration of an instrument at a
different altitude (and thus a different air pressure) than
that at which the instrument will be used, and measurement of flow rate on the downstream side of the
collector (resulting in measurement under a vacuum).
The difference in altitude can be evaluated by
comparing the barometric pressure readings at the
calibration location with those at the sampling location.
Measurements under a vacuum can be accounted for by
connecting a manometer to the sampling assembly
downstream of the collector and taking pressure
readings with the collector present and the collector
removed.
One method used to account for the pressure drop is to
calibrate the field instrument in place with the sample
collector, as shown in Figure 5.6. The primary or
secondary standard flow-rate measurement instrument
is connectted to the air-sampling assembly upstream of
the sample collector and one leg of the standard
instrument is open to the atmosphere. The field
instrument flow (e.g., a rotameter) can be directly
related to the flow at atmospheric pressure, as measured
. by the standard instrument.
5.8
The ideal gas laws can be used to normalize volume
(flow-rate) measurements taken in the field to those
taken under calibration conditions, using
Equation (5.4):
(S.4)
Measuring Air Sampled
IOI Read--1~1 I I I I I ~Here I I
I I I I
I ! ! I 1 Spherical Plumb Bob
~Read l~I I I Here-.; I
I I I I I I I . . I Spool Cyhndncal
(Marked)
Figure 5.5. Typical Rotameter Floats and Reading Indicator Positions
where Ve= volume under calibration conditions
(m3)
Vs = volume under field conditions (m3)
Pc = absolute pressure during calibration
(mm Hg)
Ps = absolute pressure during sampling
(mm Hg)
Tc = absolute temperature during calibration
(oK)
Ts = absolute temperature during sampling
(oK).
Conversion equations to obtain absolute temperatures
and pressures are as follows:
°K = °C + 273 (5.5)
°K = ((°F - 32)/1.8] + 273 <
5·
6)
mm Hg = in. of water x 1.87 (5.7)
5.9
mm Hg =, kPa x 7.5 (5.8)
Although clean dry air behaves similarly to an ideal gas,
some variation may occur. Comparing the calculations
in Equations (5.4) through (5.8) to the manufacturer's
performance curve for the flowrate measurement instrument will verify performance.
The following examples illustrate the use of the ideal gas
laws to correct the volume of air sampled to calibration
conditions.
Temperature Co"ection Example - A health physicist
calculates that a sample volume of 90 m3 (VJ is
collected by a rotameter in the field, based on the
flow rate. The health physicist learns that the
rotameter was calibrated at a temperature of 72 °F
and that the temperature in the field during sampling
was 7°C (45°F). To determine if an adjustment
should be made to the volume of the sample, the
health physicist converts the temperatures to the
absolute (Kelvin) scale, using Equation (5.6). Thus,
the sampling temperature (T J is 295°K. The difference is 5.4%. Because the difference exceeds 5%, a
corrected volume should be calculated, as recommended in Regulatory Guide 8.25. The health
'
Measuring Air Sampled
Atmospheric
Pressure
Primary or Secondary
Flow Measurement
Instrument
Sample
Collector Rota meter
Pressure
Regulating
Valve
Figure 5.6. In Place Calibration of Sample Collector
physicist finds that the sampling and calibration
absolute pressures are equivalent (at 760-mm Hg
[29-in. Hg]), so only the temperature differences
need to be used in changing the sampling volume.
The health physicist uses Equation (5.4) to adjust
sample volume to calibration conditions, as follows:
(5.9)
= 90 (760) (295) = 95 m3
760 280
If the calibration was done at normal room temperature 22 °C (72 °F), the correction would be less than
5 % if the temperature in the field was within 15 °C
(26 °F) of normal room temperature. Thus, a correction would be needed only for operating temperatures below about 46°F or above about 98°F.
Pressure Correction Example - Later, the health
physicist discovers that the absolute pressure during
sampling with the rotameter described in the previous example was 700-mm (28-in.) Hg and that the
absolute pressure during calibration was 760-mm
(29-in).) Hg. Because the difference in absolute
pressure between the sampling and the calibration is
NUREG-1400 5.10
8%, a corrected volume is calculated. Using Equation (5.4), the health physicist calculates the sample
volume corrected to calibration conditions:
v, - v, [::] (~:] (5.10)
= 90 (700) (295) = 87 m3
760 280
If the calibration was done at sea level (760-mm
[29-in.] Hg), the difference will be less than 5% if
the field pressure is within 38-mm (1.5-in.) Hg of
760-mm (29-in.) Hg.
Pressure Drop Example - A health physicist calculates a sample volume of 100 m3 based on the flow
rate as determined by a rotameter (located downstream of the sample collector) and the same time.
A manometer placed in series after the sample
collector indicates an absolute pressure 720-mm
(28-in.) Hg. To correct the sample volume for this
pressure drop, Equation (5.4) becomes:
v, = v, [::] (5.11)
where Va = volume collected under atmospheric
pressure
V 8 = volume collected under sampling
conditions
Pa = atmospheric pressure
P 8 = pressure at which sample volume was
measured.
Using Equation (5.11), the adjusted sample volume
becomes
V = V [ps] = 100 (
720) = 95 m3 (5.12) a s p 760 a
5.6 References
American Conference of Governmental Industrial
Hygienists (ACGIH). 1989. Air-Sampling
Instruments for Evaluation of Atmospheric
Contaminants. 1th edition, Cincinnati, Ohio.
American National Standards Institute (ANSI).
·1985. Specification and Performance of On-Site
Instrumentation for Continuously Monitoring
Radioactivity in Effluents. ANSI N42.18, New
York, New York.
5.11
Measuring Air Sampled
American National Standards Institute (ANSI).
1989. Performance Specifications for Health
Physics Instrumentation-Occupational Airborne
Radioactivity Monitoring Instrumentation. ANSI
American Society for Testing and Materials
(ASTM). 1983a. Standard Methods for Volumetric
Measurement of Gaseous Fuel Samples. ASTM
01071, Philadelphia, Pennsylvania.
American Society for Testing and Materials
(ASTM). 1983b. Standard Practice for Rotameter
Calibration. ASTM 03195, Philadelphia,
U.S. Environmental Protection Agency (EPA).
1985. Quality Assurance Handbook for Air
Pollution Measurement Systems, Volume II, Ambient
Air Specific Methods. EPA-600/4-77-027a,
Washington, 0.C.
U.S. Nuclear Regulatory Commission (NRC).
1992. Air-Sampling in the Workplace. Regulatory
Guide 8.25, Rev. 1, Washington, 0.C.
I
6 Evaluation of Sampling Results
Regulatory Guide 8.25 recommends that several
evaluations be made on the results of an air sample.
First, if the air sample is used to determine if
confinement is being maintained, the guide recommends
that air-sampling results be evaluated for changes in
concentrations over time. Second, the guide
recommends that consideration be given to sample
adjustments for the filter efficiency. Finally, the guide
recommends that detection sensitivity of the
measurement equipment be established.
6.1 Detecting Changes in Air
Concentrations Over Time
Regulatory Guide 8.25 recommends that the results of
fixed-location sampling, whose purpose is to confirm
radioactive material confinement during routine or
repeated operations, be either 1) analyzed for trends or
2) compared with administrative action levels. Trend
analysis (for example, by use of control charts) can be
performed to determine whether airborne concentrations
• are within the normal range, to verify that administrative
and engineering controls are operating properly to
maintain occupational doses ALARA. Administrative
action levels can be used to serve as a basis for
determining when confinement is satisfactory.
6.2 Efficiency of Collection Media
Regulatory Guide 8.25 (NRC 1992) recommends that for
collection efficiencies of less th\m 95%, the sample result
be adjusted to account for airborne radioactive material
not collected from the sampled atmosphere. The
collection efficiency varies based on several factors,
including the sample velocity across the medium,
properties of the medium itself, and the range of particle
sizes being collected.
Manufacturers of sample collection equipment routinely
determine the efficiency for collection of the sample of
interest (respirable particles, for example). For particles
in the respirable range, manufacturer's data on collection
6.1
efficiency are generally adequate. However, if such data
are not available or are not specific to the particle sizes
of interest, determination of the efficiency by the user
may be appropriate. The collection efficiency of a
medium can be determined by evaluating losses to a
filter such as glass fiber or membrane with a known
collection efficiency near 99.9%. The filter to be
evaluated is placed, first backed up by a filter known to
be highly efficient for particles much smaller than the .
minimum particle size in the range of interest. The
filters are then subjected to an atmosphere containing
long-lived radioactive material under field conditions and
evaluated. The collection efficiency (E) may then be
calculated as given by Equation (6.1):
(6.1)
where A1 is the activity collected on the filter to be
evaluated and A1c1 is the activity collected on the backup
filter with known efficiency.
The potential for burial of radionuclides within the filter
medium cah also be evaluated, which can be especially
important for alpha counting. To perform the
evaluation, a second filter with a known efficiency is
placed in parallel with those described above. After
normalizing the data to account fot any differences in
airflow, the activity lost, Au to absorption in the medium
is simply the difference and can be determined as given
by Equation (6.2):
(6.2)
where Ak2 is the activity on the known filtyr that was used
in parallel. The activity lost is then included to adjust for
particle burial and Equation (6.1) is modified:
E (6.3)
Evaluation of Sampling Results
EXAMPLE 1. The following is an example using
Equation (6.1) when alpha counting is not a
consideration.
A paper filter with an unknown efficiency is backed up by
a membrane filter with an efficiency of 99.9%. Activity
measured on the filter in question, Ah is 100 dpm and
activity on the backup (well-known) filter is 10 dpm.
E = 100 = 0.91
110
Because the efficiency of the filter is calculated to be
(6.4)
91 % and Regulatory Guide 8.25 recommends that a
correction factor be used if the efficiency of the
collection media is less than 95%, the calculated activity
on the filter should be increased by 9%.
EXAMPLE 2. Use of the above equations when burial
may be a problem.
A filter with a known high efficiency is placed in parallel
with the two filters in series as in Example 1. This time
the atmosphere contains uranium and the samples are to
be analyzed by direct alpha counting. Activity measured
on the questionable filter, Ai. is 210 dpm and activity on
the backup (well known) filter is 8 dpm. The activity on
the filter placed in parallel was 300 dpm.
First, the activity buried in filter Ah which cannot be
analyzed by direct alpha counting, is calculated.
I
" = ~ - 1 - A 1 = 82 dpm (6.5)
Adjusting for this loss through Equation (6.3) yields the
following efficiency: '
E A1 + " = 292 = 0.97 (6.6)
~ 300
The filter met the 95% level of efficiency, but each
analysis should now be increased' by the absorption
factor, which in this case is Ai/ A1 + AL) or about 71 %.
To illustrate the value of determining the collection
media efficiency, a short experiment was conducted at a
fuel fabrication facility. Membrane filters, which are
considered to be the closest to 100% efficient, were used
NUREG-1400 6.2
as backup filters for Whatman 41 and glass fiber filters.
Sample times were varied to see if dust loading affected
efficiency. The site of the study was originally chosen to
be the pellet area, but the airborne concentrations were
not great enough to allow collection of sufficient
radioactivity on the backup filter. Although it would
have been best to sample in a location that showed little
variation in particle size, the oxide building was chosen
next because the airborne levels proved to be consistently
greater. The instrument used to analyze the samples was
a Canberra high-throughput proportional counter.
Table 6.1 shows the results of this experiment. The level
of radioactivity was still low, but in most of the
Whatman 41 cases the instruments used could detect the
presence of radioactivity on the backup filters. The
average efficiency calculated for the glass fiber filters was
99.7%, while the average efficiency for the Whatman 41
was 89.7%. To meet the intent of Regulatory
Guide 8.25, a correction of 10.3% should be applied to
all air samples taken in this area. Because particle size
distributions may vary in different areas of a facility, the
licensee may want to test the filter efficiency in other
areas where the particle size distribution is not well
characterized. Because it may not be feasible to
determine collection efficiency for different areas of a
facility, the cellulose filters may be replaced with filters
that have a higher efficiency for the range of particle
sizes encountered.
6.3 Detection Sensitivity
There are no specific requirements in 10 CFR Part 20 for
the sensitivity of a workplace air monitoring program.
However, a licensee may want to evaluate the detection
capability of an air-sampling program to see if it will
adequately support the licensee's dose measurement and
Al.ARA goals. ·
For operational purposes, the statistical concept of
"decision level" is useful for deciding if a sample contains
radioactivity. Results of individual or pooled
measurements are compared with the decision level.
The decision level is a value chosen so that results above
it are unlikely to be false alarms. Thus, the operational
health physicist chooses the decision level to be far
enough above zero so that there is an acceptably low rate
of false alarms due to random statistical fluctuations in
the counting process (known to statisticians as "false
positives"). ,
Evaluation of Sampling Results
Table 6.1. Filter Efficiencies for the Oxide Conversion Building
Filter Sample Face Velocity
Tested Duration (h) cm/s
W41 8 37
W41 14 37
W41 16 37
Another concept a licensee may want to use is that of
"minimum detectable activity" or "minimum detectable
concentration." Unlike the decision level, the minimum
detectable quantities are performance gauges of a
program that can be compared with a performance goal.
For example, suppose a licensee wanted to ensure
detection of airborne conditions that would lead to
intakes resulting in more than a 10-mrem committed
effective dose equivalent. Because 2000 DAC-h result in
5000 mrem, 4 DAC-h result in 10 mrem. Thus, the
licensee may decide to implement an air monitoring
program capable of detecting 4 DAC-h in, say, any 40-
hour work period. To do this, the licensee would require
a program with a minimum detectable concentration of
• 0.1 DAC when operated for 40 hours4.62963e-4 days <br />0.0111 hours <br />6.613757e-5 weeks <br />1.522e-5 months <br />.
Many air-sampling systems use a pump to draw air
through a filter that is later removed and counted.
Measurements derived from counting the filter can be
used to deduce an average air concentration during the
sampling time. The various hardware and procedural
~nd statistical factors that determine the detection
sensitivity of a measurement system are discussed in this
section. This section also gives formulas and examples
(including solutions) for calculating the activity
concentration (µCi/cm3
), decision level, minimum
detectable activity, minimum detectable concentration,
and, when results of many measurements are pooled, the
minimum detectable average concentration. A summary
of the symbols, quantities, and units used is presented in
Table 6.2.
6.3.1 Determining the Activity Concentration
An integral part of an air-sampling program is the
measurement of radioactivity and the subsequent
interpretation of the data. Counts in a radioactivity
Activity on Activity on Filter
Filter (cpm) Back-up (cpm) Efficiency
6.3
5.3 0.5 0.91
4.7 1.4 0.77
30.8 3.6 0.90
measurement system come from both the background
and samples. The result of a measurement of radioactive
materials in or on an air-sampling medium is the number
of gross counts, N,, during the gross counting time, T,;
the result of a measurement of an appropriate blank is
the number of background (or blank) counts Nb during
the background (or blank) counting time, Tb. Background may be counted once per shift for a period of
time equal to or longer than the time the samples are
counted. If background can be counted longer than
samples, the licensee may choose to make one long
background count or several replicate counts each for the
same length of time as for the samples. The latter
alternative affords the opportunity to test for nonrandom changes in background count rate, thereby
building confidence in a program. For example, if
samples are counted for 1 minute and background for
ten minutes, the background could be coupled for 10
one-minute intervals and the data analyzed for stability.
Little statistical precision is gained by counting
background more than 10 times as long as the sample.
Because there are purely statistical fluctuations in
background count rates, and because background
contributes both to the blank and the sample counts, a
statistical test may be applied to the net count rate to
decide if activity is present. For counting times
expressed in minutes (or seconds), the net count rate R,.
in counts per.minute (cpm) (or counts per second [cps])
is
(6.7)
where R, and Rb are the gross and background count
rates, respectively.
Evaluation of Sampling R1.:sults
Table 6.2. Summary of Symbols, Quantities, and Units
Symbol
R,.
F
E
K
- >..
c
Sc
DL(R,.)
n
Quantity
background counting time
gross counting time
duration of sample collection
decay time between sampling and counting
number of background counts observed
number of gross counts observed
number of net counts observed
number of counts in the ith observation
background count rate
gross count rate
net count rate
air flow rate through the air sampler
fractional filter efficiency = (%eft)/100
counting efficiency
radioactive half-life
decay constant = 0.693/T112
activity concentration
standard deviation of activity concentration
decision level for net count rate
minimum detectable concentration
number of air samples
a bar over a symbol denotes "average," e.g., R,.,
C,N,MDC
chi-squared statistic
Traditional Unit SI Unit
mm. s
min. s
mm. s
mm. s
counts min·1 s-1
counts min-1 s-1
counts min·1 s-1
cm3 min·1 m3 s·l
counts min·1 µCi-1 s-1 Bq-1
mm s
min·1 s-1
µCi/cm3 Bqm·3
µCi/cm3 Bqm·3
counts min·1 s-1
µCi/cm3 Bqm·3
If several background measurements are made during a
24-hour period to check for consistency, the counts and
the times may be combined to improve the precision of
the measurement as follows:
Under the assumption of constant concentration of
radioactivity in the air during the time the sample is
collected, and if sampling, decay, and counting times are
short with respect to the half-life, the activity
concentration is given by
D D
Nb = L Nb,i and Tb = L Tb,i i • l i •I
(6.8)
c
R D (6.9)
NUREG-1400 6.4
where
c
R,.
E
F
K
concentration of radioactive material in
the air in µCi/cm3 (or Bq m-3
)
net count rate in cpm (or cps)
fractional filter efficiency ( %
efficiency /100)
airflow rate through the sampler in
cm3 /min (or m3 s-1
)
counting efficiency in cpm/ µCi (or cps
Bq-1)
duration of sample collection in min (ors).
EXAMPLE. An air sampler operating at 10 L/min is
run for 10 minutes to sample for gross beta-emitting
particulates. The filter efficiency is 90%. The filter is
promptly counted for 1 minute, giving 60 counts. The
background is counted for 10 minutes, giving 110 counts.
The counter efficiency is 33%. What is the activity
concentration?
SOLUTION. First make sure all quantities are in the
units appropriate for the equations:
lmin
lOmin
60 counts/1 min = 60 cpm
110 counts/10 min = 11 cpm
60 - 11 = 49 cpm
90% /100% = 0.90
10 L/min x 1E3 cm3 /L = 1E4 cm3 /min
0.33 count/disintegration x 2.22E6
dis/ µCi = 732,600 cpm/ µCi)
lOmin
Then calculate the concentration as follows:
c 49cpm
(.9) (104 cm 3 /min)(732,000 cpm/ µCi) {10 min)
= 7.4E-10 µCi/ cm 3 (6.10)
6.3.2 Deciding Whether an Air Sample Is
Above Background: The Decision Level
Any net count rate greater than the decision level '
represents the presence of activity in the sample. The
decision level for the net count rate is as follows (Strom
and Stansbury 1992; Lochamy 1976):
6.5
Evaluation of Sampling Results
(6.11)
where the 1.645 value corresponds to a 5% false alarm
rate (i.e., 1 sample in 20 that has no activity present will
exceed this count rate simply due to random statistical
fluctuations). Licensees may assume that no activity is
present in air if the net count rate is less than the
decision level; however, it is a good practice to record all
air-sampling results, whether above the decision level or
not.
EXAMPLE. Using the data from the previous example,
calculate the decision level.
SOLUTION. For Rb= 11 cpm, Tb= 10 min., and T, =
1 min., the decision level is
DL{Rn) = 1.645 11 cpm ( l . +-1
-. ] (6.12) 10 mm 1 mm
= 1.645 Ju x 1.1 = 5.7 cpm
Using this counting scenario, any net count rate above
5.7 cpm would be judged to be significant, with only a 5%
chance of being a false alarm.
Equations are given in Appendix A for cases where
radioactive decay during sampling and counting may
affect results. Equations are also provided in the
appendix that may improve precision and detection
capability.
6.3.3 Measuring Detection Capability for a
Counting System: Minimum Detectable
Activity
A counting system may be characterized by a minimum
detectable activity for a specified choice of parameters
such as counting times. Once a decision level has been
specified by the choice of count times and the false alarm
rate (this document uses a 5% false alarm rate), it is
possible to determine a value of activity that would yield
a count rate less than the decision level a certain fraction
of the time. This value of activity is called the minimum
detectable activity. The fraction of the time that an
activity equal to the minimum detectable activity would
actually result in a count rate less than the decision level
I
Evaluation of Sampling Results
is called the false negative rate. This document uses a 5%
false negative rate, i.e., 1 time in 20 a sample with an
activity equal to the minimum detectable activity would
actually result in a count rate less than the decision level.
Under these assumptions, the iµinimum detectable
activity for the activity on the filter becomes
MDA 2.71 + 3.29 V~T,(1 + T/TJ
KT,
(6J3)
where the terms are defined above (Currie 1968, 1984;
Brodsky 1984; NCRP 1985). Note that the filter
efficiency does not appear in Equation (6.10).
The filter efficiency, E, appears in the equation on page 8
of Regulatory Guide 8.25 because that equation
describes the minimum amount of activity in the air that
was sampled (some of which passed through the filter),
while Equation (6.13) refers to the activity actually
trapped by the filter.
The minimum detectable activity is a performance
indicator for a counting system. Normally the minimum
detectable activity is compared with a performance goal
rather than with the result of a measurement. The
minimum detectable activity is an amount of activity that
yields a result above the decision level most of the time
(95% of the time for this document). To contrast the
• decision level and the minimum detectable activity,
consider the following: the decision level represents a
count rate large enough that it is unlikely to be a "false
alarm," but the minimum detectable activity represents
an activity large enough that it is unlikely .nQ1 to "set off
the alarm," that is, an activity at or above the minimum
detectable activity~ likely to result in a count above the
decision level (likely to "set off the alarm"). Note that it
is quite possible that an activity less than the minimum
detectable activity will "set off the alarm" or result in a
count rate above the decision level.
For example, suppose that a licensee has determined that
4 DAC-h are expected to result in an activity of 4 x 10-s
µCi (1.5 Bq) on the filter of an air sampler run for
8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br />. Would the counting system described in the
example above have adequate detection capability to
detect a 4 DAC-h exposure? The minimum detectable
activity becomes
NUREG-1400 6.6
2.71 + 3.29 Jll x 1 (1 + 1/10) = l.9E-5 µd6.14)
732,600 x 1
This is below the desired performance of 4E-5 µCi (1.5
Bq), so the licensee can conclude that the counting
system is adequate. If the minimum detectable activity
had been greater than 4E-5 µCi (LS Bq), then the
licensee could have .chosen to count the sample longer,
used a more efficient counter, or chosen a counter with a
lower background to reduce the minimum detectable
activity until it was less than the desired goal. For other
options when the minimum detectable activity is too
high, refer to the section on "minimum average
concentration."
Normally, measurement results (in terms of count rates)
are compared with the decision level or other action
levels. The minimum detectable activity, on the other
hand, is normally compared with performance goals.
Because it is convenient to think of air-sampling
programs in terms of concentrations, not activities, and
because there are several other variables to be
considered in determining concentrations, a more useful
performance indicator for an air-sampling program (as
contrasted with a counting system that is only a part of
the program) is the minimum detectable concentration,
described below. '
6.3.4 Measuring Detection Capability for an
Air-Sampling Program: Minimum
Detectable Concentration
Suppose a licensee wants to set a performance goal for
an air-sampling program of being able to detect 0.1 x
DAC. Such a choice would ensure that, for workers
continuously present in the area, no intakes would occur
that would result in a committed effective dose
equivalent in excess of 500 mrem/y.
To determine if a program would meet this goal, the
licensee may calculate the minimum detectable
concentration (MDC) of the equipment and procedures
in the program. The MDC for any single measurement
IS
MDC 2.71 + 3.29 JRb T,(1 + T,/Tb) (6JS)
EFKTS T,
where the symbols are as defined above.
To have an air-sampling program that meets this
detection capability goal, the licensee may select
procedures and equipment with values of flow rate,
duration of sample collection, filter efficiency, counting
efficiency, and gross and background counting times so
that the MDC in Equation ( 6.15) is less than or equal to
0.1 x DAC (unless a weighted average of sample results
for intervals less than 40 hours4.62963e-4 days <br />0.0111 hours <br />6.613757e-5 weeks <br />1.522e-5 months <br /> is used; see below).
'
EXAMPLE. Using the data given above, calculate the
MDC for this scenario.
SOLUTION.
The MDC
Evaluation of Sampling Results
where AJA is the proportion of the total sample activity
from radionuclide i.
6.3.6 Checking Counter Background for
Non-Random Fluctuations
A license.e may want to use a statistical test called a "chisquared" (x2) test to determine whether the fluctuations
in a series of background measurements are consistent
with purely statistical fluctuations, or whether the
variability in the measurements is greater or less than
would be expected due to random fluctuations. For a
Poisson process such as background measurements, the
'I statistic is '
(6J.8) = 2.71 + 3.29 _...:...._~ Jucpm _____ x lmin x {1 .;.._ + _________ lmin/lOmin) '.'""""'."'"
.9 {let cm 3 /min) (732,600cpm/ µCi) {lOmin)
E (N; -N)2
1°1 N
= 2.lE-10 µCi/ cm 3 (6J.6)
This choice of count times, flow rate, filter efficiency,
duration of sample collection, counting efficiency, and
counting equipment results in an MDC of 2.2 E-10
µCi/cm3
• This means that a true concentration of 2.2 E10 µCi/cm.3 would result in a count rate less than 5.7 cpm
only 5% of the time.
If the licensee wanted to be able to detect (that is, only
miss 5% of the time) 1 E-10 µCi/cm3 (3.7 Bq/mL), then
he/she would have to use some combination of longer
sample collection time, higher filter efficiency, higher
flow rate, longer count time, lower background counting
equipment to achieve a lower MDC. In this case, little
improvement in filter efficiency can be obtained; liquid
scintillation counting might give a higher counting yield,
but it might be prohibitively costly; so modifying other
parameters is sensible.
6.3.5 l\IDC for a Mixture of Radionuclides
If the proportion of the total activity of a sample that is
due to a specific radionuclide in a mixture is known, the
MDC for that radionuclide may be reduced
proportionately:
I A (6J.7)
6.7
where each of the n background counting results, N;,
came from counting a blank for the same time interval
and N is the average of N1 (Bevington 1969, Beyer 1984).
The result is compared with tabulated values of ilie 'I
statistic (or (n - 1) degrees of freedom at a specified
significance level Za for a two-tailed test (that is, either
too much or too little variability).
If 'I is greater than the upper tabulated value, there is
more variation in the N1 than would be expected from
random statistical fluctuations alone; if 'I is less than the
lower tabulated value, then there is less variation in the
N1 than would be expected from random statistical
fluctuations alone.
If 'I is too large, there are several possible causes:
1. This was the one time in 1/2a (e.g., 1in20 for 2a =
0.05) that random fluctuations were larger than
expected. The licensee may want to repeat the 'I test
for new measurements.
2. The equipment or the power supply is unstable or
unreliable. The licensee may need to repair or
replace the equipment.
3. Background changed during or between the
measurements due to cosmic radiation, radioactive
sources being moved in the area, use of radiationproducing machines, changes in radon and radon
progeny levels, contamination of the detector, etc.
Evaluation of Sampling Results
If x2 is too small, there are several possible causes:
1. This was the one time in 1/2a (e.g., 1 in 20 for 2a =
0.05) that random fluctuations were smaller than
expected. The licensee may want to acquire more
data and repeat the x2 test.
2. There is a nonrandom component of the counts, such
as periodic electrical noise in the circuitry or double
pulses from single events.
3. Background counts were not random, e.g., the
detector is seeing a parent with short-lived progeny so
that events come in pairs. (This may only be a
problem with high-efficiency detectors.)
The licensee may want to plot the background count rate
for a given counter as a function of time to observe
whether there are short- or long-term changes. Single
points that are several standard deviations above or
below the line may be a sign of short-term instability. A
non-zero slope over time (e.g., background rate is
increasing or decreasing) may indicate gradual increase
or decrease in gain, high voltage, etc. An abrupt rise in
background may indicate that the counter has become
contaminated.
EXAMPLE. During 10 repeated 20-minute counts of
background, a licensee observes 48, 29, 40, 44, 35, 39, 46,
45, 43, and 30 counts. Is the variability in the background
.more or less than expected due to random statistical
fluctuations alone?
SOLUTION. Compute a x2 statistic and compare It with
values tabulated in Table 6.3 for a two-tailed test at 2a =
0.05. (The data in Table 6.3 have been sorted in
ascending order.)
Because the observed x2 is between 2.7 and 19, the data
have neither too little nor too much variability to be
consistent with random fluctuations. The licensee may
conclude with confidence that the system is functioning
as expected insofar as background is concerned.
6.4 References
Bevington, P.R. 1969. Data Reduction and E"or
Analysis for the Physical Sciences. McGraw-Hill, New
York, New York.
NUREG-1400 6.8
Beyer, W. H. 1984. CRC Standard Mathematical Tables.
27th ed., CRC Press, Boca Raton, Florida.
Brodsky, A. 1986. Accuracy and Detection Limits for
Bioassay Measurements in Radiation Protection:
Statistical Considerations. NUREG-1156, U.S. Nuclear
Regulatory Commission, Washington, D.C.
Currie, L. A. 1968. "Limits for Qualitative Detection
and Quantitative Determination." Analytical Chemistry
40(3):586-593.
Currie, L. A. 1984. Lower Limit of Detection: Definition
and Elaboration of a Proposed Position for Radiological
Effluent and Environmental Measurements.
NUREG/CR-4007, National Technical Information
Service, National Technical Information Service,
Springfield, Virginia.
Lochamy, J. 1976 .. "The Minimum Detectable Activity
Concept." In: National Bureau of Standards Report,
NBS-SP456, pp. 169-172, Washington, D.C.
National Council on Radiation Protection and
Measurements. 1985. A Handbook of Radioactivity
Measurements Procedures. NCRP Report No. 58, 2nd.
ed, Bethesda, Maryland.
Strom, D. J., and P. S. Stansbury. 1992. "Minimum
Detectable Activity when Background Is Counted Longer
than the Sample." Health Phys. 63(3):360-361.
Table 6.3. Chi2 Calculation for the Example'•>
Observation i N,
1 29
2 30
3 35
4 39
5 40
6 43
7 44
8 45
9 46
10 48
mean (N) 39.9
standard deviation ( s) 6.64
n 10
degrees of freedom 9
x.2 statistic
2a = 0.05, lower limit
2a = 0.05, upper limit
-10.9
-9.9
-4.9
-0.9
0.1
3.1
4.1
5.1
6.1
8.1
(N,. N)2
118.8
98.0
24.0
0.8
0.0
9.6
16.8
26.0
37.2
65.6
Evaluation of Sampling Results
(N1 -N}2
/N
2.98
2.46
0.60
0.02
0.00
0.24
0.42
0.65
0.93
1.64
9.95
2.70
19.02
(a) The N; (column 2) are the observed numbers of counts for observation~ N is the mean
of the data, ands is the sample standard deviation. The differences between the mean
and each observation (N; - N) are given in column 3, the squared differences in column
4, and the individual contribution to the X:- statistic in column 5. Because the X:- value of
9.95 falls between the lower limit (looked up in a X:- table) of2.7 and the upper limit of
19, the data have "passed" the test, that is, they have neither more nor less variation
than would be expected from random fluctuations in the counting process.
6.9 NUREG-1400
I
I
Appendix A
Additional Decision Level Equations
APPENDIX A
A.1 General Form of Equations to Account for Radioactive Decay During
Sampling and Counting, or Between Sampling and Counting
The equations in Section 6.3 are valid for the usual case in which the halflife of the radionuclide is much longer than the
sample collection time and the counting time. If the halflife is not much longer, then the equations in Section 6.3 must
be modified to account for radioactive decay during sample collection and counting.
If T, = T.,, the number of net counts to be used in the formulas below is simply the difference between N, and Nb:
N = N - N (if T = T ) D ' b & b
(A.1)
However, ifT, '¢Tb, then the number of net counts should be computed using the background count rate:
N =N -»T D ' ' ~"b &
(A.2)
Under the assumption of constant concentration during sample collection, the concentration of radioactive material in
air is given for any combination of times by a general equation of the form
A.2N 1
C in µ.Ci/cm 3 (or Bq/m-3
) = __ 0
EFK (1 - e -).T,) e -).T•(l - e -).T,) (A.3)
where>.. denotes the radioactive decay constant in inverse minutes (or s'1
) (>.. = 0.693/T112), and T0 denotes the decay
time between sampling and counting in min (ors), and the other symbols are as previously defined. All time units must
be the same in the decay constant, flow rate, and various time quantities (that is, use minutes and per minute
throughout, or use seconds and.per second throughout).
'
The formula for the decision level (Equation 6.11) does not change when radioactive decay is taken into account. The
formula for the MDC (Equation 6.15) becomes
MDC (µ.Ci/ cm 3
)
where the symbols are as defined in Table 6.2.
>..2
(2.71 + 3.29J~T,(1 + T,/TJ)
EFK~-e~~eStriderTol (talk)-e~~
(A.4)
EXAMPLE. A grab sampler is run for 20 minutes in a low radon area to collect a sample of particulate 88Rb (T112 =
17.7 min). It takes 15 minutes to get the sample to the lab, where it is counted for 10 minutes. The gross counts are 300,
while a 60-minute background measurement results in 600 counts. The flow rate was 2 cfm and the filter is taken to be
90% efficient. A simulated 88Rb standard showed a counting efficiency of 5E5 cpm/µ.Ci. What was the concentration of
A.1 NUREG-1400
Appendix A
88Rb? What is the decision level for such a counting scenario? What concentration would result in a count rate above
the decision level 9S% of the time (i.e., the MDC)?
SOLUTION. Clearly, this is a case for the exact formula, because sample collection occurs over more than one half-life,
decay between sampling and counting is nearly one half-life, and the count itself lasts for a significant fraction of a halflife. Here,
X 0.693/17.1 min= 0.039 min·1
N0 N, - RbT, = 300 - (10 cpm x 10 min) = 200 counts
E 90%/100% = 0.90
F = 2 cfm x (30.48 cm/foot)3 = S.7E4 cm3 /min
K 5E5 cpm/µCi
Ts = 20 min
T0 15 min
T, 10 min
From Equation (A.3) the concentration of 88Rb was
c (0.039min-1)
2 200counts
(0.90) (S.7E4cm 3 /min) (SEScpm/ µCi)
x 1
(l _ e-<>.039mm·•x20min) e-<>.oo9mm·•xumin (l -e-<>.oo9mm·1 x1omm)
0.0392 X200
0.9 x S.7E4 x SES x 0.54 x O.S6 x 0.32
- !. 1.2E-10 µCi/ cm 3
(A.S)
Note that the long half-life Equation (6.9) gives an answer of 3.9E-ll µCi/cm3
, less than one third of the correct answer.
The decision level from Equation (6.11) for this example is
DL(RJ = 1.64S J10cpm x lOmin(l + 10min/60min) (A.6)
= 1.8cpm
NUREG-1400 A.2
Appendix A
Thus, for observed count rates above 1.8 cpm, the licensee decides that there is airborne activity above background. The
MDC for this counting situation (Equation A.4) is
MDC = (0.039min-1 ) 2 (2.71 + 3.29J10cpm x lOmin (1+10min/60min)
(0.90) (5.7E4cm 3 /min) (5E5cpm/ µCi)
x 1
( 1 - e -0.039min"' X20min) e -0.?39min"1 x Umin ( 1 - e -0.039min"1 x IOmin)
0.0392 x 38.2
0.9 x 5.7E4 x 5E5 x 0.54 x 0.56 x 0.32
2.4E-llµCi/cm 3
(A.7)
This means that the licensee can legitimately claim to be able to detect an activity concentration of 2.4.E-11 µCi/cm3
•
This activity concentration would fail to produce a count rate above the decision level only 5% of the time (i.e., a 5%
false negative rate).
A.2 Averaging Multiple Concentration Measurements to Improve Precision and
Detection Capability
A licensee can achieve better precision and detection capability by performing appropriate time-weighted averaging of
air-sampling results. The better precision and detection capability only apply to an average over many samples, but this
may be quite helpful.
• If a 40-hour week is divided into n egual sampling intervals (e.g., five 8-hour air samples are collected to measure the
activity in air for a 40-hour week), the MDC for each air sample would have to be 0.1 x DAC unless concentrations
were averaged. If results are not· averaged, the 0.1 x DAC requirement means that the sampling/ counting system as a
whole would have to be n times more sensitive than it would have to be for a single 40-hour air sample.
The concentration during an air-sampling interval (if there is no decay during sampling and counting or between
sampling and counting) is given by Equation (6.9). Ignoring systematic errors, its standard deviation is
s in µCi/cm3 (or Bqm-3
) = H c EFK~
(A.8)
A.3 NUREG-1400
Appendix A
For n (not necessarily equal) sampling intervals during a week, the time-weighted average concentration is
n
- LTs,;C.
c l•l (A.9) n
LTs,1
i• 1
and its standard deviation is
Ri..1 R.
n +~
Tb.1 Ts.I :E
i• l E2F.2K2 (A.10)
s- 1 1 1
c [tT,.]' 1• l
where the subscripts i denote the i
111 time, concentration, filter efficiency, count rate, flow rate, or counting efficiency.
If all counting times, background count rates, air-sampling times, filter efficiencies, counting efficiencies, and flow rates
are the same, then Equations (A.9) and (A.10) simplify to
- 1 n (A.11) c -LC1
n ;.1
and
sSc (A.ll) c rn
The time-weighted average count rate is
(A.13)
NUREG-1400 A.4
and the decision level for a time-weighted average count rate is
1.65
R.
+ __.!:.:
T.
'"
Appendix A
(A.14)
If all counting times, background count rates, air sample collection times, filter efficiencies, counting efficiencies, and
flow rates are the same, then Equation (A.14) simplifies to
DL(RJ DL(RJ.
Ill
where DL(R,,) for a single air sample is given by Equation (6.11).
The MDC for a time-weighted average of air samples is
MDC=
[
- ·~ . ] + 3.29
E , .. i• 1
D
E (E;F;Ki Ti,J
i•l
1 1 Rb,. - +_ D l Tb. T . ~ ,1 S.,l
L,,--'--~
i • 1 E.2p,2v 2 l l ~"I
(A.15)
(A.16)
If all counting times, background count rates, air sample collection times, filter efficiencies, counting efficiencies, and
flow rates are the same, then Equation (A.16) simplifies to
- MDC 2.71
+
(A.17)
A.5 NUREG-1400
Appendix A
For numbers of counts large with respect to 2.71, Equation (A.17) can be approximated by Equation (A.18), as follows:
-
MDC • (A.18)
where MDC1 is the MDC for a single air sample given by Equation (6.15).
EXAMPLE. In a fuel fabrication facility, breathing zone air-sampling for class Y uranium is performed for workers ..
Each sampler is worn for 6 h/ day, 5 days/week. The samplers operate at 1.8 L/min. After waiting for the decay of ·
radon progeny, the filters are counted for 5 minutes each, and a 20-minute background measurement is made once
pershift. The background count rate is stable at 2.0 cpm. The counter efficiency is 40%. The filters have been shown to
be 95% efficient for the particle sizes encountered. What is the MDC? What is the minimum detectable average
concentration for a week, for a year (50 weeks)?
SOLUTION. The MDC for one sample is
2.71 +3.29 J2cpm X 5min(l +5min/20min) MDC = 15:15, 23 September 2020 (EDT)-,-15:15, 23 September 2020 (EDT)15:15, 23 September 2020 (EDT)15:15, 23 September 2020 (EDT)
(0.95) (1800cm 3 /min) (890,000cpm/ µCi) (360min) (5min) (A.19)
= 5.2E-12µCi/cm 3
This value is below the DAC of 2E-11 µCi/cm3
. For a 6-hour sample, the minimum detectable exposure is
Exposure in DAC-h = 5.2E-12µCi/cm3 X6h
= 1.6 DAC-h
For 5 days, the sum of the minimum detectable exposures would be 8 DAC-h, above the performance goal of 4 DAC-h
in a 40-hour period. The licensee can meet the performance goal by averaging concentrations as described below.
In five 5-minute counts at 2 cpm, 50 counts are expected due to background. Because 50 is large with respect to 3, the
simple formula Equation (A.18) will be adequate for the week-long average. The MDC for 1 week is
- MDC
MDC • --
1 = 2.3E-12µCi/cm 3
{5
(A.21)
NUREG-1400 A.6
Appendix A
and the exposure is 5 days x 6 h/day X 2.3E-12/2E-11 = 3.5 DAC-h, within the desired performance goal. The MDC
for 50 5-day weeks (250 days) is
- MDC
MDC "" --
1 = 3.3 E-13µCi/cm 3
J250
(A.22)
corresponding to an exposure of 250 days x 6 h/day x 3.3E-13/2E-11 = 24.8 DAC-h over a year. An average of
25 DAC-h in a 50-week calendar year is only 0.5 DAC-h/week, well within the licensee's performance goal of 4 DAC-h
in a week.
The results of this example are shown in Table A.1. Treating each sample individually does not permit the licensee to
optimize use of the available information. Averages of 5 or 250 samples provide lower minimum detectable exposures
(in DAC-h) and lower minimum detectable dose equivalent values (in mrem) over a year. This improved precision is
obtained because the random statistical fluctuations tend to cancel out over a year.
Table A.1. Comparison of MDC, Exposure, and Minimum Detectable Dose for One-, Five-, and 250-Sample
Averages
Minimum
Detectable Average Minimum Minimum Minimum
Average Over Concentration (MDC) Detectable Exposure Detectable Dose Detectable Dose
Group of (10·12 µCi/cm3
) (DAC-h) per group (mrem) per year (mrem)
1 sample 5.2 1.6 3.9 984
5 samples 2.3 3.5 8.8 440
250 samples 0.33 25 62 62
A.7 NUREG-1400
NRC FORM 335 IHl91
NRCM 1102.
3201, 3202
U.S. NUCLEAR REGULATORY COMMISSION
BIBLIOGRAPHIC DATA SHEET
1. REPORT NUMBER
CAcclgned by NRC. Add Vol., S..pp., R~ .•
end Addendum fllumbert, If •nv.1
(See instrvcrions on rhe reverse/
1---------------------------------------------------------...,NUREG-1400
2. TITLE ANO SUBTITLE
Air Sampling in the Workplace
Final Report
5. AUTHOR(S)
E.E.
G.R.
Hickey*,
Cicotte*,
G.A. Stoetzel*,
C.M. Wiblin**,
D.J. Strom*,
S.A. McGuire
3. DATE REPORT PUBLISHED
MONTH I YEAR
September
4. FIN 0 R G R-A-,-Nc-::T:-,Nc:-U-M:-:-::-B::-E R------1
1993
6. TYPE OF REPORT
7. PERIOD COVEREO//nctu1i..,.D•res/
8. PERFORMING ORGANIZATION - NAME ANO ADDRESS /If NRC. provi<k Divilion, Off ff:< or Region. U.S. Nucte.r R•gul•rory Commiuion. and ~ihng address; if conrractor, provide
--mailing Midreu.I
Division of Regulatory Applications
Office of Nuclear Regulatory Research
U.S. Nuclear Regulatory Commission
Washington, D.C. 20555
- Pacific Northwest Laboratory
Richland, WA 99352
- Advanced Systems Technology, Inc.
3490 Piedmont Road,NE, Atlanta, GA30305
9. Sl'ONSORING ORGANIZATION - NAME ANO ADDRESS (If NRC. 'YM '-S.me., abow"; if contncror. provide NRC Division. Office or Regk>n. U.S. N~~., Regul•IOIY Commiaion.
- malling addrnr..J
Division of Regulatory Applications
Office of Nuclear Regulatory Applications
U.S. Nuclear Regulatory commission
Washington, D.C. 20555,
10. SUPPLEMENTAllY NOTES
11. ABSTRACT (200 word• or ~ul
This report provides technical information on air sampling that will be useful
for facilities following the recommendations in the NRC's Regulatory Guide 8.25,
Revision 1, "Air Sampling in the Workplace." That guide addresses air sampling to
meet the requirements in NRC's regulations on radiation protection, 10 CFR Part 20.
This report describes how to determine the need for air sampling based on the amount
of material in process modified by the type of material, release potential, and
confinement of the material. The purposes of air sampling and how the purposes
affect the types of air sampling provided are discussed. The report discusses how
to locate air samplers to accurately determine the concentrations of airborne'
radioactive materials that workers will be exposed to. The need for and the methods
of performing airflow pattern studies to improve the accuracy of air sampling
results are included. The report presents and gives examples of several techniques
that can be used to evaluate whether the airborne concentrations of material are
representative of the air inhaled by workers. Methods to adjust derived air
concentrations for particle size are described. Methods to calibrate for volume of
air sampled and estimate the uncertainty in the volume of air sampled are described.
Statistical tests for determining minimum detectable concentrations are presented.
How to perform an annual evaluation of the adequacy of the air sampling is also
discussed.
12. KEY WORDS/OESCR\PTORS (List words or phnue• mat wilt ,.,.ist trsearchen in locating rh<I report.I
Air Sampling
Airborne Radioactive Materials
NRC FORM 335 12-1!91
13. AVAILABILITY STATEMENT
Unlimited
14. SECURITY CLASSIFICATION
Unclassified
(Thn Report/
Uncla_ssified
15. NUMBER OF PAGES
16. PRICE