United States
Environmental Protection
Agency
Office of
Radiation Programs
Washington, D.C. 20460
EPA 520/1-86-04
April 1986
Radiation
&EPA
Interim Indoor
Radon Decay Prod
Measurement Protocol!?
i
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c
EPA 520/1-86-04
INTERIM INDOOR RADON AND RADON DECAY PRODUCT
MEASUREMENT PROTOCOLS
U.S. Environmental Protection Agency
Office of Radiation Programs
February 1986
M. Ronca-Battista
P. Magno
S. Windhara
E. Sensintaffar
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CONTENTS
PAGE
EXECUTIVE SUMMARY i i i
Section 1: GENERAL CONSIDERATIONS 1
1.1 Introduction and Background 1
1.2 Standardized Measurement Conditions 1
1.2.1 House Conditions 2
1.2.2 Location Selection 3
1.3 Quality Assurance Objectives 4
Section 2: RADON MEASUREMENT PROTOCOLS 7
2.1 Protocol for Using a Continuous Radon Monitor
to Measure Indoor Radon Decay Product
Concentration 7
2.2 Protocol for Using Alpha-Track Detectors to
Measure Indoor Radon Concentration 11
2.3 Protocol for Using Charcoal Canisters to
Measure Indoor Radon Concentrations 19
2.4 Protocol for the Determination of Indoor Radon
Concentration by Grab Sampling 26
Section 3: RADON DECAY PRODUCT MEASUREMENT PROCEDURES .. 33
3.1 Protocol for Using a Continuous Working Level
Monitor to Measure Indoor Radon Decay Product
Concentration 33
3.2 Protocol for Using Radon Progency Integrated
Sampling Units (RPISU) to Measure Indoor
Radon Decay Product Concentration 37
3.3 Protocol for the Determination of Indoor
Radon Decay Product Concentration by
Grab Sampling 43
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CONTENTS--Continued
PAGE
REFERENCES 49
Appendix A: Supplementary Information for Grab
Radon Sampling A-l
Appendix B: Supplementary Information for Grab
Radon Decay Product Sampling B-l
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EXECUTIVE SUMMARY
There are many organizations now performing indoor radon and
radon decay product measurements or planning measurement programs.
It is important that different groups follow consistent procedures,
to enable valid intercomparison of measurement results from
different programs.
This document outlines procedures for making measurements and
describes standardized house conditions that should exist at the
time of the measurement. The procedures outlined here are those
that have been evaluated by the Environmental Protection Agency
(EPA) and found to be satisfactory; procedures for other instruments
may be added as they are evaluated by EPA.
The procedures specify that measurements be made where and when
the radon and radon decay product concentrations are likely to be
the most stable: in a closed house with a minimum level of
ventilation. Such measurements will generally be higher than the
average levels to which the occupants are exposed. Specifying
standard conditions is necessary for two reasons. First, the
primary objective of the protocols is to produce measurement results
that can be related to potential exposures in the house and that
have the smallest possible variability with the technique, i.e.,
that are reproducible. Second, it is important to quantitatively
estimate the variability; and that can only be estimated from data
taken under similar conditions. Since average living conditions are
difficult to define and reproduce, we have defined the standardized
conditions as closed-house conditions.
This document provides procedures for measuring radon
concentrations with continuous radon monitors, charcoal canisters,
alpha-track detectors, and grab radon techniques. It also provides
procedures for measuring radon decay product concentrations with a
continuous working level monitor, a radon progeny integrating
sampling unit (RPISU), and grab radon decay product methods.
Specifications for the location of the measurement, the house
conditions during the measurement, and minimum requirements for
quality control are included in each procedure.
111
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Section 1: GENERAL CONSIDERATIONS
1.1 Introduction and Background
Increases in the risk of lung cancer due to exposure to
radon and its decay products are of growing concern to State and
Federal health officials. There is increased awareness that indoor
radon concentrations may be greater than had once been estimated and
that there are areas in the country where the indoor levels are such
that even short-term exposures can cause a significant increase in
risk. It is extremely important to locate houses with the potential
for causing high exposures. However, the urgency to measure
concentrations in houses can result in unreliable or misleading data.
There are many Federal, State, university, and private
organizations now performing measurements or planning measurement
programs. Consistent procedures must be followed to permit valid
intercomparison of measurement results from different programs.
Problems encountered when measuring indoor radon and radon
decay product (RDP) concentrations include variability due to (l)
nonstandardized procedures, (2) different house conditions prior to
and during the measurement, (3) seasonal and other weather
conditions, and finally, different interpretations of the results.
The protocols in this document reduce the uncertainty caused by
these sources of variability by providing standardized measurement
procedures and criteria for house and weather conditions that can
exist prior to and during the measurement. The primary objective of
the protocols is to provide procedures for making reproducible
measurements, with a known and limited variability.
This document first presents some general considerations
relevant to all the instruments discussed, then outlines seven
technique-specific procedures. The procedures provide information
needed by an experienced user to calibrate, deploy, and operate the
instruments as well as to develop an adequate quality assurance
program for instrument use. Each technique-specific protocol
includes sufficient information to allow it to be used independently
of the entire document.
1.2 Standardized Measurement Conditions
These protocols specify that measurements be made when the
radon and radon decay product concentrations are likely to be the
most stable, e.g., in a closed building with a minimum level of
ventilation. Such measurements will generally be higher than the
average concentrations to which the occupants are exposed.
Specifying that measurements be made under standardized conditions
is necessary for the following two reasons.
First, the primary objective of the protocols is to produce
measurement results that can be related to either potential or
actual exposures in the house and that have the smallest possible
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variability with the technique, i.e., that are reproducible. The
most reproducible measurements are those taken when the house
conditions are standardized, with the house closed, and after
sufficient time has been allowed for the concentrations to
stabilize. To achieve such a measurement, the ventilation rates
should be as low as possible. Reproducible results are of utmost
importance when measuring indoor radon or RDP concentrations in a
home before and after it undergoes remedial action, so that the
effectiveness of the remedial action can be measured. Having a high
degree of confidence that the results of a measurement represent the
radon or RDP concentration in a building under standardized
conditions is important when deciding whether remedial action is
necessary or when comparing the measurement results to guidance
levels.
Second, it is important to quantitatively estimate the
variability associated with the result of a measurement. This
variability can be estimated only from data taken under similar
conditions, and since average living conditions are difficult to
define and to reproduce, specifying standard conditions allows for
valid application of the estimates of error.
The following paragraphs discuss how these standard
conditions are to be achieved.
1.2.1 House Conditions
The measurement should be made under "closed-house"
conditions. To a reasonable extent, windows and external doors
should be closed (except for normal entrance and exit). Normal
entrance and exit includes a brief opening and closing of a door,
but an external door should not be left open for more than a few
minutes. In addition, external-internal air exchange systems (other
than a furnace) such as high-volume attic and window fans should not
be operating. For measurement periods of 3 days or less, these
conditions should exist for 12 hours prior to beginning the
measurement. It may be difficult to verify these conditions or to
implement them for an extended period, but they should be adhered to
as closely as is reasonable.
Closed-house conditions will generally exist as normal
living conditions in northern areas of the country when the average
daily temperature is less than 40°. Depending on the area, this
can encompass the winter period from late fall to early spring.
There are two. reasons why measurements in northern climates
should be made during the winter season. First, during the winter,
closed-house conditions exist as normal living conditions. Thus,
there is a greater assurance that the proper conditions will exist
prior to and during the measurement period. Second, information on
factors that influence indoor radon concentrations indicate that
concentrations during the winter are generally higher than during
the summer.
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If, however, it is necessary to make measurements during
the summer when closed-house conditions are not the normal living
conditions, then it will be necessary to establish some means for
providing reasonable assurance that closed-house conditions will
exist prior to and during the measurements.
Organizations performing measurements in southern areas
that do not experience extended periods of cold weather should
evaluate seasonal variations in living conditions and identify if
there are time periods when closed-house conditions normally exist.
If such periods exist, that is when measurements should be
conducted. Air conditioning systems that recycle interior air can
be operated during the closed-house conditions.
To better address measurements made during summer months in
cold climates and at any time in warm climates, additional data are
needed.
Measurements of 3 days or less should not be conducted if
severe storms with high winds are predicted. Severe weather will
affect the measurement results in the following ways. First, a high
wind will increase the variability of radon concentration because of
wind-induced differences in air pressure between the house interior
and exterior. Second, rapid changes in barometric pressure increase
the chaace of a large difference in the interior and exterior air
pressures, therefore changing the rate of radon influx. Weather
predictions available on local news stations will provide sufficient
information to determine if this criterion is satisfied.
1.2.2 Location Selection
The location of the measurement within a room should be
decided with the objective of measuring the most stable
concentrations. The following criteria should be applied, in order
of importance, when selecting the measurement location within a room.
1. The measurement should be taken in an area away from
drafts caused by heating, ventilation, air conditioning
(HVAC) vents, doors, windows, and fireplaces. This will
reduce the influence of changes in ventilation and
condensation nuclei concentration on radon and RDP
concentrations.
2. The measurements should be taken away from exterior
house walls to reduce the effect of ventilation through
cracks in the walls.
3. The passive device or the air intake of an instrument
should be placed at least 50 centimeters (20 inches)
above the floor to reduce possible effects of plate-out
or drafts near the floor.
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1. 3 Quality Assurance Objectives
The object of quality assurance is to ensure that data are
scientifically sound and of known precision and accuracy. There are
several aspects of quality assurance that should be included in any
measurement program. These are: controlled calibrations, replicate
measurements, background measurements, and routine sensitivity
checks.
Controlled calibrations are samples collected or
measurements made in a known radon environment such as a calibration
chamber. Detectors requiring laboratory readout, such as charcoal
canisters, alpha-track detectors, and RPISU samplers, would be
exposed in the calibration chamber and then analyzed. Instruments
providing immediate results, such as continuous working-level
monitors and continuous radon monitors, should be operated in a
chamber to establish calibration.
There are two types of calibration measurements that should
be made for alpha-track detectors and charcoal canisters. The first
are the measurements that must be conducted to determine and verify
the conversion factors used to derive the concentration results.
These measurements, commonly called spiked samples, are done at the
beginning of the measurement program and periodically thereafter.
The second calibration measurements are performed to monitor the
accuracy of the system. These are called blind calibration
measurements and consist of detectors that have been exposed in a
radon calibration chamber. They are not labelled as such when sent
to a processing laboratory.
Background measurements, or blanks, should also be
frequently conducted. Such measurements should be made using
unexposed passive detectors or should be instrument measurements
conducted in very low (outdoor) radon concentration environments and
separated from the operating program. These should be generally
equivalent in frequency to the spiked samples and should also not be
identified as blanks when submitted for analysis to external
laboratories. In addition to these background measurements, the
organization performing the measurements should calculate the lower
limit of detection (LLD) for the measurement system. This LLD is
based on the system's background and can restrict the ability of
some measurement systems to measure low concentrations.
Duplicate measurements provide an estimate of the precision
of the measurement results. Duplicate measurements should be
included in at least 10 percent of the samples. If enough
measurements are made, the number of duplicates may be reduced, as
long as enough are used to analyze the precision of the method.
A quality assurance program should include written
procedures for obtaining the preceding objectives. Also a system
for monitoring the results of the four types of quality assurance
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measurements should be continuously maintained and available for
inspection.
The EPA has established a Radon/Radon Progeny Measurement
Proficiency Evaluation and Quality Assurance Program. This program
will enable laboratories to demonstrate their proficiency at
measuring radon and radon decay product concentrations and to have
their quality assurance programs evaluated. Contact the U.S. EPA
Quality Assurance Officer by calling (Federal Telecommunications
System (FTS) or 703) 557-7380, or call 800-334-8571, extension 7131,
for further information about this program.
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Section 2: RADON MEASUREMENT PROTOCOLS
2.1 PROTOCOL FOR USING A CONTINUOUS RADON MONITOR TO MEASURE
INDOOR RADON CONCENTRATION
2.1.1 Pu rp o s e
This protocol provides guidance for using a continuous
radon monitor (CRM) to measure indoor radon concentrations
accurately and to obtain reproducible results. Following the
protocol will help assure uniformity among measurement programs
and allow valid intercomparison of results. Measurements made in
accordance with this protocol will produce measurements of radon
concentrations representative of standardized closed-house
conditions. Such measurements of closed-house concentrations have a
smaller variability and are more reproducible than measurements made
when the house conditions are not controlled.
2.1. 2
This protocol covers, in general terms, the sample
collection and analysis method, the equipment needed, and the
quality control objectives of measurements made with a CRM. It is
not meant to replace an instrument manual, but rather provides
guidelines that should be incorporated i-nto standard operating
procedures. More information about the procedures may be obtained
from the U.S. EPA Office of Radiation Programs (ANR-460), 401 M
Street, S.W., Washington, D.C., 20460.
2.1.3 Method
A CRM samples the ambient air by pumping air into a
scintillation cell after passing it through a particulate filter
that removes dust and radon decay products. As the radon in the air
decays, the ionized radon decay products plate out on the interior
surface of the scintillation cell. The radon decay products decay
by alpha emissions, and the alpha particles strike the ZnS(Ag)
coating on the inside of the scintillation cell, causing
scintillations to occur. The scintillations are detected by the
photomultiplier tube in the detector, which generates electrical
signals. The signals are processed by the electronics, and the
results are either stored in the memory of the CRM or printed on
paper tape by the printer. The CRM must be calibrated in a known
radon environment to obtain the conversion factor used by the
electronics to convert count rate to radon concentration.
The CRM may be a flowthrough-cell type or the periodic-fill
type. In the flowthrough-cell type air continuously flows into and
through the scintillation cell. The periodic-fill type fills the
cell once each preselected time interval, counts the scintillations,
then begins the cycle again.
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2.1.4 Equipment
In addition to the CRM, equipment needed includes a readout
device and printer (if not part of the CRM), an air-flow rate meter,
and aged air or nitrogen to pump through the CRM to measure the
background count rate.
2.1.5 Pre-development Testing
The CRM should be carefully tested before and after each
measurement to:
o Verify that the correct input parameters and the unit's
clock are set properly.
o Verify the operation of the pump.
After every 1000 hours of operation the unit should be
examined to check the background count rate by purging with clean,
aged air or nitrogen in accordance with the procedures identified in
the operating manual for the instrument. In addition, the
background count rate should be more frequently monitored by
operating the instrument in an outdoor or other low radon
environment.
In addition, participation in a laboratory intercomparison
program should be conducted at least semiannually to verify that the
conversion factor used by the CRM is accurate. This is done by
comparing the unit's response to a known radon concentration. At
this time, the correct operation of the pump should be verified and
the flow rate measured.
2.1.6 Measurement Criteria
The following house conditions should exist prior to and
during a measurement, to standarize the measurement conditions as
much as possible.
o The measurement should be made under closed-house
conditions. To the extent reasonable, windows and
external doors should be closed (except for normal
entrance and exit) for 12 hours prior to and during the
measurement period. Normal entrance and exit includes
opening and closing of a door, but an external door
should not be left open for more than a few minutes.
These conditions are expected to exist as normal living
conditions during the winter in northern climates. For
this reason and other reasons discussed in section
1.2.1, measurements should be made during winter periods
whenever possible.
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o Internal-external air exchange systems (other than a
furnace) such as high-volume attic and window fans
should not be operating during the measurement and for
at least 12 hours before the measurement is initiated.
o In southern climates or when the measurements must be
made during a warm season, the standardized closed-house
conditions are satisfied by meeting the criteria just
listed. These criteria can be most conveniently
satisfied if the measurement is begun in the morning,
after the occupant has been instructed to keep the
windows closed during the night and not to open them
until the measurement has been completed. Air
conditioning systems that recycle interior air may be
operated. The closed-house conditions must be more
rigorously verified and maintained, however, when they
are not the normal living conditions.
o The measurement should not be conducted if severe storms
with high winds are predicted during the measurement
period. Weather predictions available on local news
stations will provide sufficient information to
determine if this condition is satisfied.
2.1.7 Deployment and Operation
2.1.7.1 Location Selection
The following criteria should be applied to select the
location of the CRM within a room.
o The measurement should not be made near drafts caused by
heating, ventilating and air conditioning (HVAC) vents,
doors, windows, and fireplaces.
o The measurement location should not be close to the
outside walls of the house.
o The unit should be placed on a table or stool so that
the air intake is at least 50 centimeters (20 inches)
from the floor.
2.1.7.2 Operation
The CRM should be programmed to run continuously, recording
the hourly integrated radon concentration measured and, if
applicable, the total integrated average radon concentration. The
sampling period should generally not be less 24 hours. An increase
in operating time decreases the uncertainty associated with the
measurement result.
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Care should be taken to eliminate data that is produced
before equilibrium conditions have been established in a
flow-through cell. Generally, conditions stabilize after the first
several hours during which the measurements are very low and should
be discarded. After this period, the periodic results should be
averaged to obtain an integrated measurement result.
2.1.7.3 Documentation
It is important that the operator of the CRM records enough
information about the measurement in a permanent log so that data
interpretations and comparisons can be made. This information
includes:
o Start and stop times and date of the measurement.
o Information about how the standardized conditions, as
previously specified, were satisfied.
o Exact location of the instrument, on a diagram of the
room and house, if possible.
o Other easily obtained information that may be useful,
such as the type of house, type of heating system,
existence of crawl space, occupants smoking habits, and
operation of humidifiers, air filters, electrostatic
precipitators, or clothes dryers.
2.1.8 Quality Assurance
The elements of a quality assurance program for the CRM are
o Calibration in a radon-exposure calibration chamber at
least every 6 months, or after instrument repair or
modification.
o Background count-rate checks before and after
approximately 1000 hours of operation.
The EPA has established a Radon/Radon Progeny Measurement
Proficiency Evaluation and Quality Assurance Program. This program
will enable laboratories to demonstrate their proficiency at
measuring radon and radon decay product concentrations and to have
their quality assurance programs evaluated. Contact the U.S. EPA
Office of Radiation Programs Quality Assurance Officer by calling
(FTS or 703) 557-7380 or call 800-334-8571, extension 7131, for
further information about this program.
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2.2 PROTOCOL FOR USING ALPHA-TRACK DETECTORS TO MEASURE INDOOR
RADON CONCENTRATION
2.2.1 Purpose
This protocol provides guidance for using an alpha-track
detect'or (ATD) to obtain accurate and reproducible measurements of
indoor radon concentrations. Following the protocol will help
ensure uniformity among measurement programs and allow valid
intercomparison of results. Measurements made in accordance with
this protocol will produce measurements of radon concentration
representative of standardized, closed-house conditions. Such
measurements of closed-house concentrations have a smaller
variability and are more reproducible than measurements made when
the house conditions are not controlled.
2.2.2 Scope
This procedure covers, in general terms, the equipment,
procedures, and quality control objectives to be used when
performing the measurements. This document provides guidelines to
be adopted into standard operating procedures. More information
about the procedures may be obtained from the U.S. EPA Office of
Radiation Programs (ANR-460), 401 M Street, S.W., Washington, B.C.,
20460.
2.2.3 Method
An alpha-track detector (ATD) consists of a small piece of
plastic enclosed in a container with a filter-covered opening.
Alpha particles emitted by the radon decay products in air strike
the plastic and produce submicroscopic damage tracks. At the end of
the measurement period, the detectors are returned to a laboratory,
where the plastic is placed in a caustic solution that accentuates
the damage tracks so they can be counted using a microscope or an
automated counting system. The number of tracks per unit area is
correlated to the radon concentration in air, using a conversion
factor derived from data generated at a calibration facility.
Many factors contribute to the variability of the ATD
results, including differences in the detector response within and
between batches of plastic, non-uniform plateout of decay products
inside the detector holder, differences in the number of tracks used
as background, variations in etching conditions and differences in
readout. The variability in ATD results decreases with the number
of net tracks counted, so counting more tracks over a larger area of
the detector will reduce the uncertainty of the result. In
addition, deploying duplicate ATDs will reduce the error. However,
if cost considerations make it necessary to deploy single ATDs, the
data obtained should be evaluated and used taking into consideration
the relative errors associated with counting the area and number of
net tracks specified to the processing laboratory.
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2.2.4 Equipment
Alpha-track detectors are available from commercial
suppliers. These suppliers offer contract services in which they
provide the detector and subsequent data readout and reporting for a
fixed price. Establishing an in-house capability to provide
packaged detectors, a calibration program, and a readout program
would probably not be practical or economically advantageous.
Therefore, details for establishing the analytical aspects of an ATD
program will be omitted from this protocol. If additional details
are desired, they have been reviewed by Fleischer and Lovett (F165;
Lo69).
Assuming ATDs are obtained from a commercial supplier, the
following equipment is needed to initiate monitoring in a house:
o The alpha track detector in an individual, sealed
container, such as an aluminized plastic bag to prevent
extraneous exposure before deployment,
o A means to attach the ATD to its measurement location,
if it is to be hung from the wall or ceiling,
o Instruction sheet for the occupant, and a shipping
container and, if it is to be mailed, a prepaid mailing
label for returning the detector to the laboratory,
o At the time of retrieval, some means (such as tape) will
be needed to reseal the detector prior to returning it
to the supplier for analysis.
2.2.5 Predeployment Considerations
The plans of the occupant during the proposed measurement
period should be considered before deployment. The ATD measurement
should not be made if the occupant knows he will be moving during
the period. Deployment should be delayed until the new occupant is
settled in the house. Likewise, the measurement should be delayed
if the occupant is planning remodeling, changes in the heating,
ventilating and air conditioning (HVAC) system, or other
modifications that may influence the radon concentration during the
period.
2.2.6 Measurement Criteria
The following house conditions should exist during the
measurement period, to standardize the measurement conditions as
much as possible.
o To a reasonable extent, the house should be closed, with
all windows and external doors closed (except for normal
extrance and exit) during the measurement period. These
conditions are expected to exist as normal living
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conditions during the winter in northern climates. For
this reason and other reasons discussed in section
1.2.1, AID measurements (other than 12-month
measurements) should be conducted during the winter
whenever possible.
o Internal-external air exchange systems (other than a
furnace) such as high-volume attic and window fans
should not be operated.
o In warm conditions, the standardized conditions are
satisfied by the criteria just listed. Air conditioning
systems that recycle interior air can be operated. The
closed-house criteria must be more rigorously verified
and maintained, however, when they do not exist as
normal living conditions. For a 3-month sampling
period, however, a few days with the windows open will
not invalidate the measurement.
A 12-month AID measurement will provide information about
the concentrations in the house during an entire year, so the
closed-house conditions do not have to be satisfied for a valid
12-month deployment.
2.2.7 Deployment
2.2.7.1 Timely Deployment
A group of ATDs should be deployed into houses as soon as
possible after delivery from the supplier. Groups should not order
more ATDs than they can reasonably expect to install within the
following few months to minimize chances of high background
exposures. If the storage time exceeds more than a few months, the
background exposures from a sample of the stored detectors should be
assessed. Consult the manufacturer's instructions regarding storage
and background determination.
2.2.7.2 Location Selection
The following criteria should be applied to select the
location of the detector within a room.
o A position must be selected where the ATD will not
disturbed during the measurement period.
o The detector should not be placed near drafts caused by
HVAC vents, windows, doors, etc. Avoid locations near
excessive heat, such as fireplaces.
o The detector should not be placed close to the outside
walls of the house.
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It is usually convenient to suspend the detector from the
ceiling. The detector should be positioned at least 20 centimeters
(8 inches) below the ceiling. If the detector is installed during a
site visit, the final site selected should be shown to the home
occupant to be certain it is acceptable for the duration of the
measurement period.
The sampling period is begun when the protective cover or
bag is removed. Cut the edge of the bag or remove the cover so that
it can be reused to reseal the detector at the end of the exposure
period. Inspect the detector to make sure it is intact and has not
been physically damaged in shipment or handling.
Fill in the information called for with the detector.
Also, record the detector serial number in a log book along with a
description of the location in the house in which the detector was
placed. If during the exposure period it is necessary to relocate
the detector, make certain it is noted in the log book, along with
the date it was relocated.
2.2.8 Retrieval of Detectors
At the end of the measurement period, the detector should
be inspected for damage or deviation from the conditions entered in
the log book at the time of deployment. Any changes should be noted
in the log book. The date of removal is entered on the data form
for the detector and in the log book. The detector is then resealed
using the protective cover or bag with the correct serial number for
that detector or the cover originally provided. If a bag is used,
the open edge of the bag is folded several times and resealed with
tape. If the bag or cover has been destroyed or misplaced, the
detector should be wrapped in several layers of aluminum foil and
taped shut. After retrieval, the detectors should be returned as
soon as possible to the analytical laboratory for processing.
2.2.9 Documentation
It is important that enough information about the
measurement is recorded in a permanent log so that data
interpretations and comparisons can be made. Information that
should be recorded includes:
o The start and stop dates of the measurement.
o Whether standardized conditions, as previously
specified, are satisfied.
o Exact location of the ATD(s), on a diagram of the room
and house if possible.
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o Other easily gathered information that may be useful,
such as the type of house, type of heating system,
existence of crawl space, occupants smoking habits,
operation of humidifiers, air filters, electrostatic
precipitators, and clothes dryer.
2.2.10 Analysis Requirements
2.2.10.1 Sensitivity
The sensitivity of an AID system is dependent upon the area
of the detector that is counted for alpha tracks. Table 2-1
illustrates this dependence of precision on the number of net tracks
counted. The organization performing the measurements should verify
that the area or number of net tracks counted by the ATD processor
provides an adequate sensitivity at the radon concentration at which
a decision is made. In the past, the EPA and the Centers for
Disease Control have used 4 pCi/1 as a decision point, and it is
recommended that enough net tracks be counted to allow for a
reasonable sensitivity at this concentration. As can be seen from
Table 2-1, if few net tracks are counted, a very poor precision is
obtained. Thus, it is critical that the organization performing the
measurements with an ATD arranges for an adequate sensitivity.
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Table 2-1
DEPENDENCE OF PRECISION ON NUMBER OF NET TRACKS COUNTED
Number of Net
Tracks Counted 2 Sigma Error (%)la)
4 100
6 82
10 63
15 52
20 45
50 28
75 23
100 20
(a) This is the minimum error for the number of net tracks
indicated; the absolute error is dependent on the actual
number of background tracks counted.
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2.2.10.2 Precision
The coefficient of variation should be monitored using the
results of the duplicate detectors described in section 2.2.11.2 of
this protocol, rather than a precision quoted by the manufacturer.
2.2.11 Quality Assurance
The quality assurance program for measurements with ATDs
involves three separate parts: (1) calibration or accuracy testing,
(2) duplicate detectors as a test of the precision, and (3) control
detectors to check for exposure during shipment or storage.
The EPA has established a Radon/Radon Progeny Measurement
Proficiency Evaluation and Quality Assurance Program. This program
will enable laboratories to demonstrate their proficiency at
measuring radon and radon decay product concentrations and to have
their quality assurance programs evaluated. Contact the U.S. EPA
Office of Radiation Programs Quality Assurance Officer by calling
(FTS or 703) 557-7380, or call 800-334-8571, extension 7131, for
further information about this program.
2.2.11.1 Calibration
Conversion Factor Determination
Determination of a calibration factor requires exposure of
ATDs to a known radon concentration in a radon exposure chamber.
These calibration exposures are to be used to obtain or verify the
conversion factor between net tracks per unit area and radon
concentration. The following guidance is provided to the supplier
of alpha-track services as minimum requirements in determining the
calibration factor.
o ATDs should be exposed in a radon chamber at several
different radon concentrations or exposure levels
similar to those found in the tested houses (a minimum
of three).
o A minimum of 10 detectors should be exposed at each
level.
o The period of exposure should be sufficient to allow the
ATD to achieve equilibrium with the chamber atmosphere.
o A calibration factor should be determined for each batch
of detector material received from the material supplier.
Blind Calibration Detectors
Both suppliers of alpha-track services and large users of
these services should submit ATDs with known radon exposures for
analysis on a regular schedule. Blind calibration detectors should
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be labelled in the same manner as field detectors to assure
identical processing. The number of blind calibration detectors
submitted for analysis should be a few percent of the total number
of detectors analyzed.
The concentrations that the detectors are exposed to during
calibration should be in the same range that the field detectors are
exposed to. For users who accumulate detectors over a period of
time and submit relatively large groups of detectors for analysis,
the preferred approach is to include blind calibration detectors
with each group of detectors analyzed. The results of the
calibration detector analysis should be monitored for any-
significant deviation from the known concentration to which they
were exposed.
2.2.11.2 Duplicates
The organization performing the measurements should place
duplicate detectors in enough houses to test the precision of the
measurement. The number of duplicate detectors deployed should be
either 10 percent of the number of detectors deployed each month or
50, whichever is smaller. The pair of detectors should be treated
identically in every respect. They should be shipped, stored,
opened, installed, removed, and processed together and not
identified as duplicates to the processing laboratory. Data from
duplicate detectors should be evaluated using the procedures
recommended for internal quality control programs for replicate
analysis (Ro65; EPA80). The method should achieve a coefficient of
variation of 20 percent (1 sigma) or less. Consistent failure in
duplicate agreement indicates an error in the measurement process
that should be investigated.
2.2.11.3 Control Detectors
Control detectors should include a minimum of five percent
of the detectors that are deployed every month, or 25, whichever is
smaller. They should be selected and stored by the organization
performing the measurements. The control detectors should be stored
in sealed containers with radon concentrations of less than about
0.5 pCi/1. These detectors should be handled and shipped using the
same procedures that are used for the other detectors in the
exposure group with the exception of the storage during the field
measurements. The results of the control detector analyses should
be monitored. If the results approach a significant fraction of the
results from the field detectors, the control detector results can
be subtracted from the results of the other detectors in the
exposure group. The cause for the high exposures can then be
investigated. A significant result from the control detector
analyses may indicate a problem in the shipping, storage, or
processing of the detectors.
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2.3 PROTOCOL FOR USING CHARCOAL CANISTERS TO MEASURE
INDOOR RADON CONCENTRATIONS
2.3.1 Pu rp o s e
This protocol provides guidance for using a charcoal
cani.ster to obtain accurate and reproducible measurements of indoor
radon concentrations. Following the protocol will help ensure
uniformity among measurement programs and allow valid intercomparison
of results. Measurements made in accordance with this protocol will
produce measurements of radon concentration representative of
standardized, closed-house conditions. Such measurements of
closed-house concentrations have a smaller variability and are more
reproducible than measurements made when the house conditions are
not controlled.
2.3.2 Scope
This protocol covers, in general terms, the equipment,
procedures, and quality control objectives to be used in performing
the measurements. This document provides guidelines to be adopted
into standard operating procedures. More information about of the
procedures may be obtained from the U.S. EPA Office of Radiation
Programs (ANR-460), 401 M Street, S.W., Washington, D.C., 20460.
2.3.3 Method
Charcoal canisters are passive devices requiring no power
to function. They are integrating detectors and can be used to
determine the average radon concentration in the device's location
during the measurement period.
The charcoal canister measurement technique is described in
detail by Cohen and George (Co83 and Ge84). The charcoal canister
now used by several groups consists of a circular, 6-to-10
centimeters diameter container approximately 2.5 centimeters deep
filled with 25 to 100 grams of activated charcoal. One side of the
container is fitted with a screen that keeps the charcoal in but
allows air to diffuse into the charcoal. When the canister is
prepared by the supplier it is sealed with a cover until it is ready
to be deployed.
To initiate the measurement, the cover is removed to allow
air to diffuse into the charcoal bed. Radon in the air will be
adsorbed onto the charcoal and will subsequently decay, depositing
decay products in the charcoal. At the end of a measurement period,
the canister is resealed using the cover and is returned to a
laboratory for analysis.
At the laboratory, the canisters are analyzed for radon
decay products by placing the charcoal, still in its canister,
directly on a gamma detector. Gamma rays of energies between 0.25
and 0.61 Mev are counted. It is necessary to make a correction to
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account for the reduced sensitivity of the charcoal due to adsorbed
water. This may be done by weighing each canister when it is
prepared and then reweighing it when it is returned to the
laboratory for analysis. Any weight increase is attributed to water
adsorbed on the charcoal. The weight of water gained is correlated
to a correction factor that should be empirically derived using a
method discussed by George (Ge84). This correction factor is used
to correct the analytical results.
This correction is not needed if the charcoal canister
configuration is modified to significantly reduce the adsorption of
water and the user has experimentally demonstrated that, over a wide
range of humidities, there is a negligible change in the collection
efficiency of the charcoal.
The charcoal canister system can be calibrated by analyzing
canisters exposed to known concentrations of radon in a calibration
facility.
2.3.4 Equipment
Charcoal canisters made specifically for ambient radon
monitoring can be obtained from commercial suppliers or can be
manufactured using readily available components. Some canisters
designed for use in respirators or in active air sampling may be
adapted for use in ambient radon monitoring, as described by Cohen
and George (Co83; Ge84).
The following equipment will be required to initiate
charcoal canister monitoring in each house:
o Charcoal canister(s) sealed with protective cover.
o Instruction sheet for occupant, and a shipping container
and, if sent by mail, a prepaid mailing label for
returning canister(s) to the analytical laboratory.
Laboratory analysis of the exposed canisters is performed
using a sodium iodide gamma scintillation detector to count the
gamma rays emitted by the radon decay products on the charcoal. The
detector may be used in conjunction with a multichannel gamma
spectrometer or with a single-channel analyzer with the window set
to cover the appropriate gamma energy window.
2.3.5 Predeployment Considerations
The measurement should not be made if the occupant is
planning remodeling, changes in the heating, ventilating and air
conditioning (HVAC) system, or other modifications that may
influence the radon concentration during the measurement period.
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The canister should not be deployed if the occupant's
schedule prohibits terminating the measurement at the time selected
for closing the canister and returning it to the laboratory.
2.3.6 Measurement Criteria
The following conditions should exist during a measurement
period to ensure that the conditions are as standardized as possible.
o To a reasonable extent, the house should be closed, with
all windows and external doors shut (except for normal
extrance and exit) for at least 12 hours prior to and
during the sampling period. Normal entrance and exit
includes a brief opening and closing of a door, but an
external door should not be left open for a period of
more than a few minutes. These conditions are expected
to exist as normal living conditions during the winter
in northern climates. For this reason and other reasons
discussed in section 1.2.1, measurements should be made
during the winter periods whenever possible.
o Internal-external air exchange systems (other than a
furnace) such as high-volume attic and window fans
should not be operated for at least 12 hours prior to
and during the measurement period. This condition can
be most conveniently satisfied if the measurement is
begun in the morning, after the occupant has been
instructed to keep the windows closed during the night
and not to open them until the measurement is
completed. Air conditioning systems that recycle
interior air may be operated. The closed-house
conditions must be more rigorously verified and
maintained, however, when they are not the normal living
conditions.
o The measurement should not be conducted if severe storms
with high winds are predicted during the measurement
period. Weather predictions available on local news
stations will provide sufficient information to
determine if this condition is satisfied.
2.3.7 Deployment
2.3.7.1 Timely Deployment
Charcoal canisters should be deployed into houses as soon
as possible after they are prepared. Until they are deployed, they
should remain tightly sealed to maintain maximum sensitivity and low
background.
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2.3.7.2 Location Selection
The following criteria should be applied to select the
location of a canister within a room.
o A position must be selected where the canister will not
be disturbed during the measurement period.
o The canister should not be placed near drafts caused by
HVAC vents, windows, and doors. Avoid locations near
excessive heat, such as fireplaces or in direct, strong
sunlight.
o The canister should be placed flat on a shelf or table
at least 50 centimeters (20 inches) above floor level
and with the detector's top face at least 10 centimeters
(4 inches) from other objects.
o The canister should not be placed close to the outside
walls of the house.
The protective cover should be removed from the canister to
begin the sampling period. The cover must be saved to reseal the
canister at the end of the measurement. Inspect the canister to see
that it has not been damaged during handling and shipping. It
should be intact, with no charcoal leaking. Place the canister with
the open side up toward the air. Nothing should impede air flow
around the canister.
Accurately fill in the information called for on the data
form on the canister. Record the canister serial number in a log
book along with a description of the location in the house where the
canister was placed. If the canister is relocated during the
measurement period the new location should be noted in the log book.
2.3.8 Retrieval of Detectors
The canisters should be deployed for a 3 to 7 day
measurement period. If the occupant is terminating the sampling,
the instructions given to the occupant should tell the occupant when
to terminate the sampling period and should indicate that a
deviation from the schedule by up to 6 hours is acceptable so long
as the time of termination is documented on the canister. In
addition, the occupant should also be instructed to send the
canister to the laboratory as soon as possible, preferably the day
of or the day following termination.
At the end of the monitoring period, the canister should be
inspected for any deviation from the conditions described in the log
book at the time of deployment. Any changes should be noted. The
canister should be resealed using the original protective cover.
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After the canister is retrieved, it must be returned to the
laboratory as soon as possible for analysis. The canister should
not be analyzed before 3 hours after the end of sampling to allow
for ingrowth of decay products.
2.3.9 Analysis Requirements
Canisters should be analyzed in the laboratory as soon as
possible following removal from the houses. The maximum allowable
delay time between the end of sampling and analysis will vary with
the background experienced in each laboratory and should be
evaluated, especially if sensitivity is of prime consideration.
Corrections for the Rn-222 decay during sampling, during the
interval between sampling and counting, and during counting should
be made. The canister should be weighed, and, if necessary, a
correction should be applied for the increase in weight due to
moisture adsorbed. A description of the procedure used to derive
the moisture correction factor is provided by George (Ge84).
2.3.9.1 Sensitivity
For a 3 to 7 day exposure period, the lower level of
detection (LLD) (delay-time corrected) should be 1 pCi/1 or less.
This can be normally achieved with a counting time of up to 30
minutes. This LLD should be calculated using the results of the
charcoal background determination that is described in section
2.3.11.3 of this protocol.
2.3.9.2 Precision
The coefficient of variation should not exceed 10 percent
at radon concentrations of 4 pCi/1 or greater. This precision
should be monitored using the results of the duplicate canister
analyses described in section 2.3.11.2 of this protocol.
2.3.10 Documentation
It is important that enough information about the
measurement be recorded in a permanent log so that data
interpretations and comparisons can be made. The information
includes:
o The date and start and stop time of the measurement.
o Whether standardized conditions, as previously
specified, are satisfied.
o Exact location of the instrument, on a diagram of the
room and house, if possible.
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o Other easily gathered information that may be useful,
such as the type of house, type of heating system,
existence of crawl space, occupants smoking habits, and
operation of humidifiers, air filters, electrostatic
precipitators, or clothes dryers.
2.3.11 Quality Assurance
The quality assurance program for charcoal canisters
includes three parts: (1) calibration canisters, (2) duplicate
canisters, and (3) controls. The purpose of this program is to
identify the accuracy and precision of the measurements and to
assure that the measurements are not influenced by exposure from
sources outside the intended structure.
The EPA has established a Radon/Radon Progeny Measurement
Proficiency Evaluation and Quality Assurance Program. This program
will enable laboratories to demonstrate their proficiency at
measuring radon and radon decay product concentrations and to have
their quality assurance programs evaluated. Contact the U.S. EPA
Office of Radiation Programs Quality Assurance Officer by calling
(FTS or 703) 557-7380, or call 800-334-8571, extension 7131, for
further information about this program.
2.3.11.1 Calibration
Determination of Calibration Factors
Determination of calibration factors for charcoal canisters
requires exposure of canisters to known concentrations of radon-222
in a radon exposure chamber. The calibration factors are dependent
upon both the exposure time and the amount of water adsorbed by the
canister during exposure. These calibration factors should be
determined using the procedures described by George (Ge84).
Calibration factors should be determined for each charcoal canister
system (container type and amount of charcoal).
Blind Calibration Canisters
Both suppliers of charcoal canister services and large
users of these services should submit charcoal canisters with known
radon exposures for analysis on a regular schedule. Blind
calibration canisters should be labelled in the same manner as the
field canisters to assure identical processing. The number of blind
calibration canisters submitted for analysis should be a few percent
of the total number of canisters analyzed. The results of the
calibration canister analysis should be monitored for any
significant deviation from the known concentration to which they
were exposed.
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2.3.11.2 Duplicates
Duplicate canisters should be placed in enough houses to
monitor the precision of the instrument. This will usually be
approximately 10 percent of the houses to be tested each month, or
50, whichever is smaller. The duplicate canisters should be
shipped, stored, exposed and analyzed under the same conditions.
Data from duplicate canisters should be evaluated using the
procedures recommended for internal quality control programs for
replicate analysis (Ro65, EPA80). The method should achieve a
coefficient of variation of 10 percent (1 sigma) or less.
Consistent failure in duplicate agreement indicates an error in the
measurement process that should be investigated.
2.3.11.3 Control Canisters
Charcoal Background
A background gamma count can be obtained for an entire
batch of charcoal by counting several canisters from each batch of
charcoal. This is the background that should be subtracted from the
field canister results.
Background Exposure Monitoring
In addition, a minimum of 5 percent of the detectors that
are deployed every month, or 25, whichever is smaller, should be set
aside from each shipment. They should be kept in a low radon (less
than 0.5 pCi/1) environment and sent back with one shipment each
month for analysis. These canisters measure the background exposure
due to radon that may accumulate during shipment. The results from
these field canisters should be monitored; and if the results
approach a significant fraction of the results from the field
detectors, the control detector results can be subtracted from
results of the other detectors in the exposure group. The cause for
the elevated readings should then be investigated.
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2.4 PROTOCOL FOR THE DETERMINATION OF INDOOR RADON
CONCENTRATION BY GRAB SAMPLING
2.4.1 Purpose
This protocol provides guidance for using the grab sampling
technique to provide accurate and reproducible measurements of
indoor radon concentrations. Following the protocol will help
ensure uniformity among measurement programs and allow valid
intercomparison of results. Measurements made in accordance with
this protocol will produce measurements of radon concentration
representative of standardized, closed-house conditions. Such
measurements of closed-house concentrations have a smaller
variability and are more reproducible than measurements made when
the house conditions are not controlled.
2.4.2 Scope
This protocol covers, in general terms, the equipment,
procedures, and quality control objectives to be used when
performing measurements. This document provides guidelines to be
incorporated into standard operating procedures used by a State or
other laboratory. More information about the procedures may be
obtained from the U.S. EPA Office of Radiation Programs (ANR-460),
401 M Street, S.W., Washington, D.C., 20460.
2.4.3 Method
In this grab sampling method, a sample of air is drawn into
and sealed in a flask or cell that has a zinc sulfide phosphor
coating on its interior surfaces. One surface of the cell is fitted
with a clear window that is put in contact with a photomultiplier
tube to count light pulses (scintillations) resulting from alpha
disintegrations from the sample interacting with the zinc sulfide
coating. The number of pulses is proportional to the radon
concentration in the cell.
The cell is counted about 4 hours after filling to allow
the short-lived RDPs to reach equilibrium with the radon.
Correction factors (see Appendix A) are applied to the counting
results to compensate for decay during the time between collection
and counting and to account for decay during counting.
2.4.4 Equipment
The equipment needed to obtain the sampling includes:
o A scintillation cell or cells to be filled at the site.
o A pump to flow air through the cell or to evacuate the
cell (depending on the valve arrangement on the cell in
use).
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o A clock to measure time from collection to counting.
o A filter and filter holder to attach to the air inlet
valve of cell.
The equipment required for cell counting includes:
o A photomultiplier tube and high-voltage assembly in a
light-tight chamber.
o A sealer-timer for registering pulses from
photomultiplier the tube assembly and timing the
counting interval.
o A National Bureau of Standards (NBS)-traceable alpha
check source and scintillation disc.
o A calibration cell.
o A vacuum pump and cell flushing apparatus.
o Aged air or nitrogen for flushing counting cells.
2.4.5 Premeasurement Considerations
Prior to collection of the sample, proper operation of the
counting equipment must be verified, and counter efficiency and
background must be determined. In addition, a background for each
cell should be determined prior to sampling. This may be done using
the procedures described in Appendix A.
For highly accurate measurements, it is necessary to
standardize cell pressure prior to counting, because the path
lengths of alpha particles are a function of air density. For
example, a cell calibrated at sea level and used to count a sample
collected at Grand Junction, Colorado (1370 meters ASL) would
overestimate the radon activity of the sample by about 9 percent
(Ge83). This error probably approaches the maximum that would be
encountered; therefore, it may not be necessary to make this
correction if this error can be tolerated. Correction procedures
are given elsewhere (Ge83).
2.4.6 Measurement Criteria
The following conditions should exist prior to and during
the sampling to ensure that the conditions are as standardized as
possible.
o The sampling should be made under closed-house
conditions. To a reasonable extent, external doors and
windows should be closed for 12 hours prior to the
measurement (except for normal entrance and exit).
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Normal entrance and exit includes a brieE opening and
closing of a door, but an external door should not be
left open for more than a few minutes. No windows or
doors should be open during the sampling period. These
conditions are expected to exist as normal living
conditions during the winter in northern climates. For
this reason and other reasons discussed in section
1.2.1, measurements should be conducted during winter
whenever possible.
o Internal-external air exchange systems (other than a
furnace) such as high-volume attic and window fans
should not be operated for at least 12 hours prior to
and during the sampling.
o In southern climates or when measurements must be made
during a warm season, the closed-house conditions will
be satisfied by meeting the preceding criteria. In
other seasons and climates, this condition can be most
conveniently satisfied if the sampling is done after the
occupant has been instructed to keep the windows closed
and all internal-external ventilation systems off during
the night until after the measurement is made. Air
conditioning systems that recycle interior air may be
operated prior to the measurement, if necessary, but not
during the measurement. The closed-house conditions
must be more rigorously verified and maintained,
however, when they are not the normal living conditions.
o The sampling should not be conducted if severe storms
with high winds have occurred in the previous 12 hours
or are present at the sampling time.
2.4.7 Documentation
It is important that enough information about the
measurement is recorded in a permanent log so that data
interpretations and comparisons can be made. This will include:
o The time and date of the start and end of the
measurement,
o Whether standardized conditions, as previously
specified, are satisfied,
o Exact location of the measurement, on a diagram, of the
room and house, if possible,
o Other easily gathered information that may be useful,
such as the type of house, type of heating system,
existence of crawl space, occupants smoking habits, and
operation of humidifiers, air filters, electrostatic
precipitators, or clothes dryers.
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2.4.8 Sampling Operations
2.4.8.1 Location in Room
The sample should be collected in an area away from
drafts. The sample should not be collected near heating,
ventilation, or air conditioning (HVAC) vents, windows and doors,
clothes dryer or stove vents, and fireplaces. The sample should not
be taken near the outside walls of the house. If possible, entrance
into a basement room for sampling should be made through an interior
stairway rather than an exterior door, to reduce the ventilation
caused by the opening of the door.
2.4.8.2 Sampling
All air samples drawn into cells must be filtered to remove
airborne radioactive participates including RDPs. This prevents
contamination of the cells and helps maintain low cell backgrounds.
Filters may be reused many times as long as they remain undamaged.
To collect a sample using a single-valve cell (Lucas type),
the cell is evacuated to at least 25 inches of mercury, the filter
is attached to the cell, and the valve is opened allowing the cell
to fill with air. Allow at least 10 seconds for the cell to
completely fill. To assure good vacuum at the time of sampling, the
cell may be evacuated using a small hand operated pump in the room
being sampled. It is good practice to evacuate the cell at least
five times, allowing it to fill completely with room air each time.
Make sure the air to be sampled flows through the filter each time.
If it can be demonstrated that the cells and valves do not leak, it
is acceptable to evacuate the cells in the laboratory and simply
attach the filter and open the valve in the house to collect a
sample.
To sample using the double-valve, flowthrough type cell,
attach the filter to the inlet valve and a suitable vacuum pump to
the other valve. The pump may be motor driven or hand operated.
Open both valves and operate the pump to flow at least 10 complete
air exchanges through the cell. Stop the pump and close both valves.
Record all pertinent sampling information after taking the
sample. Include the date and time, location, cell number, name of
person collecting the sample, and any other significant conditions
within the house or notes on the weather conditions. Store the
cells for return to the counting location carefully so that the
samples will not be lost due to cell breakage or valves being opened.
2.4.9 Counting and Calculations
Cells should not be counted for at least four hours
following the time of collection. Background and check sources
should be counted as described in Appendix A. The cell to be
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counted is placed on the photomultiplier tube, the cover placed over
the cell, and the system allowed to dark adapt. The cell may then
be counted for a sufficient period to collect an adequate number of
counts for good counting statistics in relation to the system
background counts.
The results in picocuries per liter of radon in air are
calculated using the formulas and tables in Appendix A, which
includes a sample calculation.
2.4.10 Cell Flushing and Storage
After the cells have been counted and data are
satisfactorily recorded, the cells must be flushed with aged air or
nitrogen to remove the sample. Flowthrough cells are flushed with
at least ten volume exchanges at a flow of about 2 liters per
minute. Cells with single valves are evacuated and refilled with
aged air or nitrogen at least five times. The cells are left filled
with the aged air or nitrogen and allowed to sit overnight before
being counted for background. If an acceptable background is
obtained, the cell is ready for reuse.
2.4.11 Results
2.4.11.1 Sensitivity
The sensitivity of the method is dependent on the volume of
the cell being used. However, sensitivities of 0.1 picocuries per
liter are achievable (GeSOb, Ge83).
2.4.11.2 Precision
The coefficient of variation for duplicate samples should
not exceed 30 percent at radon concentrations of 1 picocurie per
liter or more. This precision should be monitored using the results
of duplicate measurements described in Section 2.4,12.2 of this
protocol. Sources of error in the procedure may result from
improper cell calibration, leaking cells, and improperly calibrated
counting equipment.
2.4.12 Quality Assurance
The quality assurance program for radon concentration
measurements using grab sampling includes calibration and duplicate
measurements.
The EPA has established a Radon/Radon Progeny Measurement
Proficiency Evaluation and Quality Assurance Program. This program
will enable laboratories to demonstrate their proficiency at
measuring radon and radon decay product concentrations and to have
their quality assurance programs evaluated. Contact the U.S. EPA
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Office of Radiation Programs Quality Assurance Officer by calling
(FTS or 703) 557-7380, or call 800-334-8571, extension 7131, for
further information about this program.
2.4.12.1 Calibration
The counting system consisting of the sealer, detector, and
high-voltage supply must be calibrated. The correct high voltage is
determined via a plateau (incrementing the high voltage and plotting
the resultant counts). This procedure is described elsewhere
(Ge83). Each counting system should be calibrated before being put
into service, after any repair, or at least once per year. Also, a
check source or calibration cell should be counted in each counter
system each day to demonstrate proper operation prior to counting
any samples.
An accurate calibration factor must be obtained for each
counting cell. This is done by filling each cell with radon of a
known concentration and counting the cell to determine the
conversion factor of counts per minute per picocurie. The known
concentration of radon may be obtained from a radon calibration
chamber or estimated from a bubbler tube containing a known
concentration of radium. These calibration procedures are discussed
elsewhere in more detail (Ge76; Ge83; Lu57; Be75).
At least once a year, grab measurements should be made in a
known radon environment in a radon calibration chamber to verify
the conversion factor.
2.4.12.2 Duplicates
Duplicate samples should be collected with sufficient
frequency to test the precision of the procedure. This number
should be at least 10 percent of the total radon grab samples
collected. Care should be taken to ensure that the samples are
duplicates to the greatest extent possible. Duplicate cells should
be filled close to each other and away from drafts. Data from
duplicate samples should be evaluated using the procedures
recommended for internal quality control programs for replicate
samples (Ro65, EPA80). The method should achieve a coefficient of
variation of 30 percent (1 sigma) or less. Consistent failure in
duplicate agreement indicates an error in the measurement process
that should be investigated.
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Section 3: RADON DECAY PRODUCT MEASUREMENT PROTOCOLS
3.1 PROTOCOL FOR USING A CONTINUOUS WORKING LEVEL MONITOR TO
MEASURE INDOOR RADON DECAY PRODUCT CONCENTRATION
3.1.1 Purpose
This protocol provides guidance for using a continuous
working level monitor (CWLM) to obtain accurate and reproducible
measurements of indoor radon decay product concentrations.
Following the protocol will help assure uniformity among measurement
programs and allow valid intercomparison of results. Measurements
made in accordance with this protocol will produce measurements of
radon decay product (RDP) concentrations representative of
standardized closed-house conditions. Such measurements of
closed-house concentrations have a smaller variability and are more
reproducible than measurements made when the house conditions are
not controlled.
3.1.2 Scope
This protocol covers, in general terms, the sample
collection and analysis method, the equipment needed, and the
quality control objectives of measurements made with a CWLM. It is
not meant to replace an instrument manual, but provides guidelines
that should be incorporated into standard operating procedures.
More information about the procedures may be obtained from the U.S.
EPA Office of Radiation Programs (ANR-460), 401 M Street, S.W. ,
Washington, D.C., 20460.
3.1.3 Method
A GVLM samples the ambient air by filtering airborne
particles as the air is drawn through a filter cartridge at a low
flow rate of about 0.1 to 1 liter per minute. An alpha detector
such as a diffused-junction or surface-barrier detector counts the
alpha particles produced by the RDP as they decay on the filter.
The detector is normally set to detect alpha particles with energies
between 2 and 8 MeV. The alpha particles emitted from the radon
decay products Po-218 and Po-214 are the significant contributors to
the events that are measured by the detector. The event count is
directly proportional to the number of alpha particles emitted by
the RDP on the filter. The unit typically contains a microprocessor
that stores the number of counts and elapsed time. The unit can be
set to record the total counts registered over specified time
periods. The unit must be calibrated in a calibration facility to
convert count rate to working level (WL) values. This may be done
initially by the manufacturer and should be done periodically
thereafter by the operator.
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3.1.4. Equipment
In addition to the CWLM, equipment needed includes
replacement filters, a readout or programming device (if not part of
the CWLM), an alpha-emitting check source, and an air-flow rate
meter.
3.1.5 Predeployment Testing
The CWLM should be carefully tested before and after each
measurement to:
o Verify that a new filter has been installed and the
input parameters and clock are set properly,
o Measure the detector's efficiency with a check source
such as Am-241 or Th-230 and ascertain that it compares
well with the technical specifications for the unit,
o Verify the operation of the pump.
After every 100 hours of operation, the unit should be
checked to measure the background count rate using the procedures
that may be identified in the operating manual for the instrument.
In addition, participation in a laboratory intercomparison
program at least semiannually will verify that the conversion factor
used in the microprocessor is accurate. This is done by comparing
the unit's response to a known RDP concentration. At this time, the
correct operation of the pump should also be verified by measuring
the flow rate.
3.1.6 Measurement Criteria
The following house conditions should exist prior to and
during a measurement to standarize the measurement conditions as
much as possible.
o The measurement should be made under closed-house
conditions. To the extent reasonable, windows and
external doors should be closed (except for normal
entrance and exit) for 12 hours prior to and during the
measurement period. Normal entrance and exit includes
an opening and closing of a door, but an external door
should not be left open for more than a few minutes.
These conditions are expected to exist as normal living
conditions during the winter in northern climates. For
this reason and other reasons discussed in section
1.2.1, measurements should be made during winter
whenever possible.
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o Internal-external air exchange systems (other than a
furnace) such as high-volume attic and window fans
should not be operating during the measurement and for
at least 12 hours before the measurement is initiated.
o In southern climates or when the measurements must be
made during a warm season, the standardized closed-
house conditions are satisfied by meeting the preceding
criteria. These criteria can be most conveniently-
satisfied if the measurement is begun in the morning,
after the occupant has been instructed to keep the
windows closed during the night and not to open them
until the measurement has been completed. Air
conditioning systems that recycle interior air may be
operated. The closed-house conditions must be more
rigorously verified and maintained, however, when they
are not the normal living conditions.
o The measurement should not be conducted if severe storms
with high winds are predicted during the measurement
period. Weather predictions available on local news
stations will provide sufficient information to
determine whether this criterion is satisfied.
3.1.7 Deployment and Operation
3.1.7.1 Location Selection
The following criteria should be applied to select the
location of the CWLM within a room.
o The measurement should not be taken near drafts caused
by heating, ventilating and air conditioning (HVAC)
vents, doors, windows, and fireplaces.
o The measurement location should not be close to the
outside walls of the house.
o The unit should be placed on a table or stool so that
the air intake is at least 50 centimeters (20 inches)
from the floor.
3.1.7.2 Operation
The CWLM should be programmed to run continuously,
recording the hourly integrated WL measured and, when possible, the
total integrated average WL. The sampling period should not be less
24 hours for most purposes. The longer the operating time, the
smaller the uncertainty associated with the measurement result. The
integrated average WL over the measurement period should be used as
the measurement result.
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3.1.7.3 Documentation
It is important that the operator of the CWLM records
enough information about the measurement in a permanent log so that
data interpretations and comparisons can be made. This will include
o The time and date of the start and end of the
measurement,
o Whether standardized conditions, as specified, are
satisfied,
o Exact location of the instrument, on a diagram if
possible.
o Other easily gathered information that may be useful,
such as the type of house, type of heating system,
existence of crawl space, occupants smoking habits, and
operation of humidifiers, air filters or electrostatic
precipitators, and clothes dryers.
3. 1. 8
are:
Quality Assurance
The elements of a quality assurance program for the CWLM
o Calibration in a radon decay product exposure
calibration chamber at least every 6 months, or after
instrument repair or modification, and
o Checks using an Am-241 or Th-230 similar-energy alpha
check source (before and after each measurement),
o Background count-rate checks (after each 100 hours of
operation).
The EPA has established a Radon/Radon Progeny Measurement
Proficiency Evaluation and Quality Assurance Program. This program
will enable laboratories to demonstrate their proficiency at
measuring radon and radon decay product concentrations and to have
their quality assurance programs evaluated. Contact the U.S. EPA
Office of Radiation Programs Quality Assurance Officer by calling
(FTS or 703) 557-7380, or call 800-334-8571, extension 7131, for
further information about this program.
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3.2 PROTOCOL FOR USING RADON PROGENY INTEGRATING SAMPLING UNITS
CRPISUj TO MEASURE INDOOR RADON DECAY PRODUCT CONCENTRATIONS
3.2.1 Purpose
This protocol provides guidance for using a RPISU to
produce accurate and reproducible measurements of indoor radon decay
product concentrations. Following the procedure will help ensure
uniformity in measurement programs and allow valid intercomparison
of results. Measurements made in accordance with this protocol will
produce measurements of radon decay product concentrations (RDP)
representative of standardized closed-house conditions. Such
measurements of closed-house concentrations have a smaller
variability and are more reproducible than measurements made when
the house conditions are not controlled.
3. 2.2
This protocol covers, in general terms, the equipment,
procedures, analysis, and quality control objectives for measure-
ments made with RPISUs. It is not meant to replace an instrument
manual, but provides guidelines to be adopted into standard
operating procedures. More information about the procedures may be
obtained from the U.S. EPA Office of Radiation Programs (ANR-460),
401 M Street, S.W., Washington, B.C., 20460.
3. 2.3 Method
The RPISU contains an air sampling pump that draws a
continuous flow of air through a detector assembly. The detector
assembly includes a filter and at least two thermoluminescent
dosimeters (TLDs). One TLD measures the radiation emitted from
radon decay products collected on the filter, and the other TLD is
used for background gamma correction. The pump and detector
assembly are operated inside the structure for 3 to 7 days.
Analysis of the detector TLDs is performed in a laboratory
utilizing a thermoluminescent dosimeter reader. Interpretation of
the results of this measurement requires a calibration for the
detector and an analysis system based on exposures to known
concentrations of radon decay products.
3.2.4 Equipment
The RPISU sampling system includes the sampling pump and
the detector assembly. Analysis requires a thermoluminescent
dosimeter reader.
3.2.4.1 Sampling Pump
The air sampling pump must be capable of moving air at a
flow rate ranging from 0.1 to 4 1pm through the detector assembly.
37
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The pump must be suitably quiet to allow operation in an occupied
residence without creating a major annoyance. The pump should also
include a running-time meter. High-flow-rate pumps require an
automatic shut-down system if the flow rate is reduced to less than
an adequate rate or if the pump overheats. A calibrated flow meter
to measure the flow rate through the detector must also be available.
3.2.4.2 Detector Assembly
The detector assembly includes a holder suitable to contain
the filter and TLDs that will allow entry of air to the filter. One
TLD is placed directly adjacent to the face of the filter to detect
alpha radiation coming from the particles collected on the filter.
The other TLD is placed behind a stainless steel shield to measure
the gamma and beta radiation received during exposure, storage, and
shipment. The filter for the detector should present a uniform
surface with pore sizes no larger than 0.8 microns.
3.2.4.3 Thermoluminescent Dosimeter Reader
The TLD reader is an instrument that heats the TLDs at a
uniform and reproducible rate and simultaneously measures the light
emitted by the thermoluminescent material. The readout process is
carefully controlled, with the detector purged with nitrogen to
prevent spurious emissions. The TLD reader should be periodically
tested using dosimeters exposed to a known level of alpha or gamma
radiation prior to analyzing the RPISU dosimeters. TLDs are
prepared for reuse by cleaning and annealing at prescribed
temperatures in an oven.
3.2.5 Predeployment Considerations
Prior to installation in the house, the pump should be
checked to assure that it is operable and capable o£ maintaining an
adequate flow through the detector assembly. Extra detector
assemblies should be available during deployment in case a problem
is encountered.
Arrangements should be made with the occupant of the house
to assure that entry to the house can be made at the time of
delivery and to determine availability of a suitable electrical
outlet near the sampling area in the selected room.
3.2.6 Measurement Criteria
The following house conditions should exist during a
measurement period to ensure that the conditions are as standardized
as possible.
o To a reasonable extent, the house should be closed, with
all windows and external doors shut (except for normal
entrance and exit) for 12 hours prior to and during the
measurement period. Normal entrance and exit includes a
38
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brief opening and closing of a door, but an external
door should not be left open for more than a few
minutes. These conditions are expected to exist as
normal living conditions during the winter in northern
climates. For this reason and other reasons discussed
in section 1.2.1, measurements should be made during the
winter whenever possible.
o Internal-external air exchange systems (other than a
furnace), such as high-volume attic and window fans,
should not be operated for at least 12 hours prior to
and during the measurement.
o In southern climates or when measurements must be made
during a warm season, the closed-house conditions are
satisfied by meeting the preceding criteria. This
condition can be most conveniently satisfied by
beginning a sampling period in the morning after the
occupants have been instructed to keep the windows
closed and not to open them until the measurement is
completed. Air conditioning systems that recycle
interior air may be operated. The closed-house
conditions must be more rigorously verified and
maintained, however, when they are not the normal living
condi tions.
o The measurement should not be conducted if severe storms
with high winds are predicted for the measurement
period. Weather predictions available on local news
stations will provide sufficient information to
determine if this criterion is satisfied.
3.2.7 Deployment and Operation
Install the RPISU and check the air flow rate with a
calibrated flow meter. Record the location, date, starting time,
running time meter reading, and flow rate on the detector assembly
envelope and in a log. Observe the RPISU for a few minutes after
starting, to assure continued operation; also inform the occupants
about the RPISU and request that they report any problems or pump
shut down. The occupant should be aware of the length of time the
RPISU will be operated, and an appointment should be arranged to
retrieve the unit. The criteria for the standardized measurement
conditions should be repeated to the occupants.
The sampling period should be at least 72 hours. A longer
operating time decreases the uncertainty associated with the
measurement result.
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3.2.7.1 Location Selection
The following criteria should be used to select the
location of the RPISU within a room:
o The RPISU should not be placed close to the outside
walls of the house.
o The air intake (sampling head) should be placed at least
20 centimeters (8 inches) from surfaces that may
obstruct flow.
o The RPISU should not be placed near drafts caused by
HVAC vents, windows, fireplaces, or doors.
3.2.8 Retrieval
Prior to pump shut-down the flow rate should be measured
with a calibrated flow meter and the unit should be observed briefly
to assure that it is operating properly. If the sampling pump is
not operating, attempt to restart it even briefly to perform flow
measurements. Return the detector assembly to its envelope and
record the date, time, running time meter reading, and flow rate
both on the detector assembly envelope and in a log book. Also,
record any other observed conditions that might affect the
measurement. Remove the RPISU sampling pump and any ancillary
equipment.
3.2.9 Analysis
Analysis of the RPISU detector assembly should be performed
in a laboratory under controlled conditions. The analysis should be
delayed for at least 3 hours after the sampling is completed to
allow for decay of radon decay products collected on the filter.
Prior to analysis, the TLDs should be removed from the
detector assembly, and the filter should be checked for observable
holes or leakage. The TLD identification numbers should be checked
against the recorded numbers, and, if specified by the TLD supplier,
the TLDs should be cleaned using the manufacturers recommended
procedures.
The TLDs are then analyzed in the TLD reader using
established procedures. Note that the side of the TLD that received
the exposure from the filter should be placed adjacent to the
photomultiplier tube.
Dosimeter numbers (if available) and readings for both the
alpha TLD and background (gamma/beta) TLD should be recorded as well
as all other pertinent information on the detector assembly envelope
or data sheet.
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3.2.10 Documentation
It is important that enough information about the
measurement is recorded in a permanent log so that data
interpretations and comparisons can be made. This will include:
o The time and date of the start and end of the
measurement,
o Whether standardized conditions, as previously
specified, are satisfied,
o Exact location of the instrument, on a diagram, of the
room and house, if possible,
o Other easily gathered information that may be useful,
such as the type of house, type of heating system,
existence of crawl space, occupants smoking habits, and
operation of humidifiers, air filters, electrostatic
precipitators, or clothes dryers.
3.2.11 Quality Assurance
The quality assurance program for measurements of radon
decay product concentrations in terms of working levels comprises
three elements: (1) calibration or accuracy testing, (2) duplicate
measurements and (3) control dosimeters to measure exposure during
shipment and storage.
The U.S. EPA has established a Radon/Radon Progeny
Measurement Proficiency Evaluation and Quality Assurance Program.
This program will enable laboratories to demonstrate their
proficiency at measuring radon and radon decay product
concentrations and to have their quality assurance programs
evaluated. Contact the U.S. EPA Office of Radiation Programs
Quality Assurance Officer by calling (FTS or 703) 557-7380, or call
800-334-8571, extension 7131, for further information about this
program.
3.2.11.1 Calibration
Calibration of RPISU dosimeters requires exposure in a
controlled radon-exposure chamber where the radon decay product
concentration is known during the exposure period. The detector
assembly must be exposed in the chamber using a flow rate similar to
the normal operating flow rate for the RPISU sampling pumps. The
environmental conditions in the chamber during all exposures should
be similar to those that are found in the tested houses. Calibration
should include exposure of a minimum of four detectors exposed at
different RDP concentrations representative of the range found -in
field measurements. The relationship of thermoluminescent dosimeter
reader units to working level for a given sample volume and the
41
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standard error associated with this measurement should be
determined. Calibration of the RPISUs also includes testing of
air-flow meters to ensure accuracy of the flow rate measurement.
After the initial calibration, periodic processing of
exposed detectors should be done to assure that the detection system
has not changed.
3.2.11.2 Duplicates
The organization performing the measurements should make
duplicate measurements with RPISUs in enough houses to test the
precision of the measurement. This number should be at least 10
percent of the houses tested. The two RPISUs should be located in
the same area in the house, and all handling and analysis of the
detectors should be identical. Data from duplicate detectors should
be evaluated using the procedures recommended for internal quality
control programs for replicate analysis (Ro65, EPA80). The method
should achieve a coefficient of variation of 10 percent (1 sigma) or
less. Consistent failure in duplicate agreement indicates an error
in the measurement process that should be investigated.
11.3 Control Dosimeters
Control dosimeters for RPISUs are included in each detector
assembly. The purpose of these control dosimeters is to identify
any exposure from sources of radiation other than the radon decay
products accumulated on the filter and from nonradiation-induced
thermoluminescence. Typically the value for the control dosimeters
is less than 5 percent of the value for the primary dosimeter unless
the RDP concentration is very low. If the value for the control
dosimeter exceeds approximately 5 percent of the value for the
primary dosimeter for concentrations greater than 0.01 WL and on a
regular basis, the cause should be investigated.
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3.3 PROTOCOL FOR THE DETERMINATION OF INDOOR RADON DECAY
PRODUCT CONCENTRATION BY GRAB SAMPLING
3.3.1 Purpose
This protocol provides guidance for using the grab sampling
technique to provide accurate and reproducible measurements of
indoor radon decay product (RDP) concentrations. Following the
protocol will help ensure uniformity among measurement programs and
allow valid intercomparison of results. Measurements made in
accordance with this procedure will produce measurements of RDP
concentration representative of standardized, closed-house
conditions. Such measurements of closed-house concentrations have a
smaller variability and are more reproducible than measurements made
when the house conditions are- not controlled.
3.3. 2
This procedure covers, in general terms, the equipment,
procedures, and quality control objectives to be used when
performing measurements. This document provides guidelines to be
incorporated into standard operating procedures. More information
about the procedures may be obtained from the U.S. EPA Office of
Radiation Programs (ANR-460), 401 M Street, S.W., Washington, D.C.,
20460.
3.3.3 Method
Grab sampling measurements of RDP concentrations in air are
performed by collecting the decay products from a known volume of
air on a filter and by counting the activity on the filter following
collection. Several methods for performing such measurements have
been developed and have been described by George (Ge80b).
Comparable results may be obtained using all these methods. This
procedure, however, will describe two methods that have been most
widely used with good results. These are the Kusnetz procedure and
the modified Tsivoglou procedure.
The Kusnetz procedure (Ku56; ANSI73) may be used to obtain
results in working levels (WL) when the concentration of individual
decay products is unimportant. Decay products from up to 100 liters
of air are collected on a filter in a 5-minute sampling period. The
total alpha activity on the filter is counted at any time between
40 and 90 minutes after the end of sampling. Counting can be done
using a scintillation-type counter to obtain gross alpha counts for
the selected period. Counts from the filter are converted to
disintegrations using the appropriate counter efficiency. The
disintegrations from the decay products collected from the known
volume of air may be converted into working levels using the
appropriate "Kusnetz factor" (see Appendix B, Table B-l) for the
counting time utilized.
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The Tsivoglou procedure, as modified by Thomas (Ts53;
Th72), may be used to determine WL and the concentration of the
individual RDPs. Sampling is the same as that used for the Kusnetz
procedure; however, the filter is counted three separate times
following collection. The filter is counted between 2 and 5
minutes, 6 and 20 minutes, and 21 and 30 minutes following
completion of sampling. Count results are used in a series of
equations to calculate concentrations of the three RDPs and working
level. These equations and an example calculation appear in
Appendix B.
3.3.4 Equipment
Equipment required for RDP concentration determination by
grab sampling consists of:
o An air pump capable of collecting samples at the desired
flow rate.
o A filter holder to accept a 25 to 47-mm diameter,
0.8-micron membrane or glass fiber filter.
o A calibrated flow meter to determine air flow through
the filter during sampling.
o A clock for accurate timing of sampling and counting.
o A scintillation counter (such as the Randam^aJ
Electronics Model SC-5, or the EDA^a^ Instruments
Model RD-200) and a zinc sulfide scintillation disc.
o A National Bureau of Standards (NBS)-traceable alpha
calibration source to determine counter efficiency
3.3.5 Premeasurement Considerations
Prior to collection of the sample, proper operation of the
equipment must be verified, and the counter efficiency and
background must be determined. This is especially critical for the
Tsivoglou procedure, in which the sample counting must begin
2 minutes following the end of sampling.
The air pump, filter assembly, and flow meter must be
tested to assure there are no leaks in the system. The
scintillation counter must be operated with the scintillation tray
(where applicable) and scintillation disc in place to determine
background for the counting system. Also, the counter must be
operated with an NBS-traceable alpha calibration source in place of
Use of trade names does not constitute EPA endorsement
44
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a filter in the counting location, to determine system counting
efficiency. Both the system background and system efficiency are
used in the calculation of results from the actual sample.
3.3.6 Measurement Criteria
The following conditions should exist prior to and during
the sampling to ensure that the conditions are as standardized as
possible.
o The sampling should be made under closed-house
conditions. To a reasonable extent, external doors and
windows should be closed during the 12 hours prior to
the measurement (except for normal entrance and exit).
Normal entrance and exit includes a brief opening and
closing of a door, but an external door should not be
left open for more than a few minutes. No windows or
doors should be open during the sampling period. These
conditions are expected to exist as normal living
conditions during the winter in northern climates. For
this reason and other reasons discussed in section
1.2.1, measurements should be conducted during the
winter whenever possible.
o Internal-external air exchange systems (other than a
furnace) such as high-volume attic and window fans
should not be operated for at least 12 hours prior to
and during the sampling.
o In southern climates or when measurements must be made
during a warm season, the closed-house conditions are
satisfied by meeting the preceding criteria. This
condition can be most conveniently satisfied if the
sampling is done after the occupant has been instructed
to keep the windows closed and all internal-external
ventilation systems off during the night and until after
the measurement is made. Air conditioning systems that
recycle interior air should not be operated prior to the
measurement, if reasonable. No ventilation systems
should be operated during the measurement. The
closed-house conditions must be more rigorously verified
and maintained, however, when they are not the normal
living conditions.
o The sampling should not be conducted if severe storms
with high winds have occurred in the previous 12 hours
or are present at the sampling time.
3.3.7 Documentation
It is important that enough information about the
measurement is recorded in a permanent log so that data inter-
pretations and comparisons can be made. This information includes:
45
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o The time and date of the start and end of the
measurement,
o Whether standardized conditions, as previously
specified, are satisfied,
o Exact location of the measurement, on a diagram, of the
room and house, if possible,
o Other easily gathered information that may be useful,
such as the type of house, type of heating system,
existence of crawl space, occupants smoking habits, and
operation of humidifiers, air filters, electrostatic
precipitators, and clothes dryers.
3.3.8 Sampling Operations
3.3.8.1 Location in Room
The sample should be collected in an area away from
drafts. The sample should not be collected near heating,
ventilation, or air conditioning (HVAC) vents, leaking windows and
doors, clothes dryer or stove vents, fireplaces, etc. The sample
should not be taken near the outside walls of the house. If
possible, entrance into a basement room for sampling should be made
through an interior stairway rather than an exterior door to reduce
the ventilation caused by the opening of the door.
3.3.8.2 Sampling
A new filter should be placed in the filter holder prior to
entering the house. Care should be taken to avoid puncturing the
filter and to avoid leaks. The sampling is begun by starting the
pump and the clock simultaneously. Note the air flow rate and
record it in a log book. Also record the time the sampling was
begun. The sampling period should be 5 minutes, and the time from
the beginning of sampling to the time of counting must be precisely
recorded.
3.3.9 Analysis
Analysis may be done using the Kusnetz, modified Tsivoglou,
or other procedure described elsewhere (GeSOb). If the Tsivoglou
procedure is used, the counting must be started 2 minutes following
the end of sampling. Analysis using the Kusnetz procedure must be
performed between 40 and 90 minutes following the end of sampling.
A counting time of 10 minutes during this period is usually used.
Remove the filter from the holder using forceps and
carefully place it facing the scintillation phosphor. The side of
the filter on which the decay products were collected must face the
phosphor disc. The chamber containing the filter and disc should be
46
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closed and allowed to dark-adapt prior to starting counting. For
the Tsivoglou method this procedure of placing the filter in the
counting position must be done quickly, since the first of the three
counts must begin two minutes following the end of sampling. If the
counter used has been shown to be slow to dark-adapt, the counting
should be done in a darkened environment. Additional details on the
procedure and calculations may be found in the references (Ku56;
Ts53; Th72).
3.3.10 Grab Sampling Results
3.3.10.1 Sensitivity
For a 5-minute sampling period (10 to 20 liters of air) on
a 25-mm filter, the sensitivity using the Kusnetz or modified
Tsivoglou counting procedure should be approximately 0.0005 working
level (GeSOb).
3.3.10.2 Precision
The coefficient of variation should not exceed 30 percent
at RDP concentrations of 0.005 WL or greater. This precision should
be monitored using the results of duplicate measurements described
in section 3.3.11.2 of this protocol. Sources of error in the
procedure may result from inaccuracies in measuring the volume of
air sampled, characteristics of the filter used, and measurement of
amount of radioactivity on the filter.
3.3.11 Quality Assurance
The quality assurance program for RDP concentration
measurements by grab sampling includes calibration and duplicate
measurements.
The U.S. EPA has established a Radon/Radon Progeny
Measurement Proficiency Evaluation and Quality Assurance Program.
This program will enable laboratories to demonstrate their
proficiency at measuring radon and radon decay product
concentrations and to have their quality assurance programs
evaluated. Contact the U.S. EPA Office of Radiation Programs
Quality Assurance Officer by calling (FTS or 703) 557-7380, or call
800-334-8571, extension 7131, for further information about this
program.
3.3.11.1 Calibration
Pumps and flow meters used to sample air must be routinely
calibrated to assure accuracy of volume measurements. This may be
performed using a dry-gas meter or other flow measurement device of
traceable accuracy. This should be done every 6 months or after any
instrument repair or modification.
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The radiological counters should have calibration checks
run daily to determine counter efficiency. This is particularly
important for portable counters taken into the field that may be
subject to rugged use and temperature extremes. These checks are
made using an NBS-traceable alpha calibration source such as
Thorium-230.
At least once per year, grab measurements should be made in
a calibration chamber with known RDP concentrations to verify the
calibration factor. These measurements should also be used to test
the collection efficiency and self-absorption of the filter material
being used for sampling. A change in the filter material being used
during the year requires checking the new material for collection
efficiency in a calibration chamber.
3.3.11.2 Duplicates
Duplicate grab samples should be collected with sufficient
frequency to test the precision of the measurement. The number of
duplicates should be at least 10 percent of the total samples
collected. Care should be taken to ensure that the samples are
duplicates to the greatest extent possible. The filter heads should
be relatively close to each other and away from drafts. Care should
also be taken to ensure that one filter is not in the discharge air
stream of the other sampler.
Data from duplicate samples should be evaluated using the
procedures recommended for internal quality control programs for
replicate analysis (Ro65, EPA80). The method should achieve a
coefficient of variation of 30 percent (1 sigma) or less.
Consistent failure in duplicate agreement indicates an error in the
measurement process that should be investigated.
48
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REFERENCES
ANSI73
Be75
Co83
EPA80
F165
Ge76
GeSOa
GeSOb
Ge83
Ge84
American National Standards Institute, 1983, "American
National Standard for Radiation Protection in Uranium
Mines", ANSI N13.8-1973.
Beckman, R.T., "Calibration Procedures for Radon and
Radon Daughter Measurement Equipment", U.S. Department
of Interior, Mining Enforcement and Safety
Administration Information Report 1005.
Cohen, B.L. and Cohen, E.S., 1983, "Theory and Practice
of Radon Monitoring with Charcoal Adsorption", Health
Physics, Vol. 45, No. 2.
U.S. Environmental Protection Agency, 1980,
Guidelines and Specifications for Preparing
Assurance Project Plans", Washington, D.C.,
"Interim
Quality
QAMS-005/80,
Fleischer, R.L., Price, P.B., and Walker, R.M., 1965,
"Solid State Track Detectors: Applications to Nuclear
Science and Geophysics", Annual Review of Science, pg.l.
George, A.C., 1976, "Scintillation Flasks for
Determination of Low Level Concentrations of Radon", in
Proceedings of Ninth Midyear Health Physics Symposium,
Denver, Colorado.
George, A.C. and Breslin, A.J., 1980, "The Distribution
of Ambient Radon and Radon Daughters in Residential
Buildings in the New Jersey-New York Area", Natural
Radiation Environment III, Vol. 2, p.1272, CONF-780442.
George, A.C., 1980, "Radon and Radon Daughter Field
Measurements", Paper presented at the National Bureau
of Standards Seminar on Traceability for Ionizing
Radiation Measurements", May 8-9, Gaithersburg,
Maryland.
George, J.L., 1983, "Procedures Manual for the
Estimation of Average Indoor Radon Daughter
Concentrations by the Radon Grab Sampling Method",
Bendix Field Engineering Corp., Grand Junction,
Colorado, GJ/TMC-lK 83) UC-70A.
George, A.C., 1984, "Passive, Integrated
of Indoor Radon Using Activated Carbon",
Physics, Vol. 46, No. 4.
Measurements
Health
49
-------
Ku56 Kusnetz, H.L., 1956, "Radon Daughters in Mine
Atmospheres - A Field Method for Determining
Concentrations", American Industrial Hygiene
Association Quarterly, Volume 17.
Lo69 Lovett, D.B., 1969, "Track Etch Detectors for Alpha
Exposure Estimation", Health Physics, Vol. 16, pp.
623-628.
Lu57 Lucas, H.F., 1957, "Improved Low-Level Alpha
Scintillation Counter for Radon, Review of Scientific
Instruments", Vol. 28, p.680.
PHS57 Public Health Service, 1957, "Control of Radon and
Daughters in Uranium Mines and Calculations on
Biological Effects", PHS Report 494, U.S. Department of
Health, Education and Welfare, Washington, B.C.,
pp.41-42.
Ro65 Rosenstein, M. and Goldin, A.S., 1965, "Statistical
Techniques for Quality Control of Environmental
Radioassay", Science, volume 2, pp 93-102.
Th72 Thomas, J.W., 1972, "Measurement of Radon Daughters in
Air", Health Physics, volume 23, pg.783.
TsS3 Tsivoglou, E.G., Ayer, H.E., and Holaday, D.A., 1953,
"Occurance of Nonequilibrium Atmospheric Mixtures of
Radon and Its Daughters", Nucleonics, Volume 1, pg.40.
50
-------
APPENDIX A
SUPPLEMENTARY INFORMATION FOR
GRAB RADON SAMPLING"
EQUIPMENT
Equipment to measure radon concentration using grab sampling
into scintillation cells is available from several commercial
suppliers. Equipment required includes:
o Scintillation cells
o Pump to evacuate single valve cells or to flow air through
double valve cells
o Filter holder and filter to remove particulates
4
o Detector-scaler-high voltage assembly for counting
o Timer
o Calibration cell or check source
o Aged air or nitrogen
GENERAL METHOD DESCRIPTION
o Air to be sampled for radon is either flushed through a
cell using a low volume air pump or is drawn into an
evacuated cell through a filter.
o The sample in the cell is allowed to equilibrate to
optimize counting efficiency.
o The cell is placed on a photomultiplier tube and
scintillations counted.
o Radon concentration is calculated based on the sample
counts and corrected using appropriate ingrowth and decay
factors.
PROCEDURE
The procedure described below is that used by the U.S.
Environmental Protection Agency Office of Radiation Programs in its
field measurement programs. It is designed for measurements made
using the Randani^3' Electronics Model SC-5 cell counters and
associated cells or the EDA^a) Instruments Model RD-200 System.
(a) Use of trade names does not constitute EPA endorsement.
A-l
-------
However, equipment is available from several suppliers, and it may
be necessary to modify the procedure slightly to accomodate these
differences. For example, the correct cell volume must be used in
the calculations. A. general procedure using the Randam or EDA
equipment includes:
1. The cells to be used are flushed with aged air or nitrogen
to remove traces of previous sample. It may be necessary
to store cells for 24 hours prior to reuse if the cell had
contained a high activity sample. Place each cell in
counter, wait 2 minutes for the system to become dark
adapted, and count background of the cell for 10 minutes.
Record background data for each cell.
2. At the site to be surveyed, collect the sample by flowing
air into the longer tube in the top of the EDA cell
k (double valve) for a period sufficient to allow 10 air
exchanges. For the Randam (single valve) cells it is only
necessary to open the valve on the evacuated cells and
allow 10 to 15 seconds for complete filling. Cells must
be filled with air forced through a filter to prevent
entry of airborne particulates.
3. The filled cells must be allowed to equilibrate for 4
hours prior to counting. The cells should not be exposed
to bright light prior to counting.
4. The cells are placed in the counters, the systems are
allowed to dark adapt for 2 minutes, and the cells are
counted. Counting time will vary based on the activity in
the cell, however, at least 1,000 counts is desirable to
provide good statistics.
5. The activity in the sample is calculated and corrected for
ingrowth and decay as described below.
CALCULATION OF RESULTS
The radon concentration in picocuries per liter is determined
using the following formula:
DCi/i - cpm(s) - cpm(bkg) C 1_
P E A V
where
cpm(s) = Counts per minute for the sample
cpm(bkg) = Counts per minute for background
A-2
-------
E = Efficiency of system determine for each cell as
described in Section 11.1 of the protocol. For
the EDA and Randam cells the factor is
typically 4-5 cpm/pCi.
C = Correction for decay during counting from table
A-l.
A = Correction for decay of radon from time of
collection to start of counting from table A-l.
V = Volume of counting cell in liters,
V = 0. 170 1 for EDA cells
V = 0.125 1 for Randam cells
SAMPLE CALCULATION
The following sample calculation demonstrates the
procedure for calculating results.
o Background Count for system = 10 counts in 10 minutes
or 1 cpm
o Sample Count for 120 minutes = 1200 counts or 10 cpm
o System Efficiency (E) from cell calibration = 4.62
cpm/pCi
o Count time correction (C) for 120 minutes = 1.00757
o Delay time correction (A) for 4 hours = 0.97026
o Volume correction (V) for EDA cell = 0.170 1
pCi/1 = 10 CP"1 - 1 CP"1 x 1-00757 x I = n 9
4.62 cpm/pCi 0.97026 0.170 1
A-3
-------
Table A-l
Radon Correction Factors
A. - Correction for radon decay from time of collection to
start of counting
C. - Correction for radon decay during counting
A.
Tl«* Minutes
0.999D7
0.99975
0*99962
0.999b(>
0.99937
0.99925
0.9991?
0.99899
0.998*7
0.99874
99862
99849
99637
99824
99811
9774
rJBii
•tfzu
0.99686
.99673
.99661
-.99648
0*99<>36
0.99623
I.MUI
0.99511
01,99498
0.99486
0.99473
0,99461
0*9944*
0*99435
0.99423
t:lim
8:1!!!!
0.99360
0^99348
0.99335
8.99323
199310
0.99298
- -9286
Hours
1.00000 1.00000
0.99248
0.98502
0*,97761
0?97076
0.96296
0.95572
0.94854
0.94140
0*93432
0*92730
0.92031
o°:9voil4n
MHJ"
0.8
Slim?
0.84063
km
8:S?Hi
i:KH?
0179737
0.73384
0^72832
0 .69084
0^68564
.48049
^67537
*67029
0.66525
0.66025
0.45528
0,65036
0.83431
0.69607
0.5P074
0.4(451
0.40423
0.33726
l:l\W
0.116)3
0*1)374
0.09490
l:Wdl
Wltil
0.03836
8:8^8
8:8?iii
0*01551
0*0)294
0,01079
0.00901
0*00751
0*0062?
0.00523
0.00436
0.00364
0.00304
0.00253
S.00211
.00176
0.00147
S.00123
'00102
0.00085
0.00071
0.00059
0.00050
0.00041
0,00015
0,00029
0,00024
0,00020
0*00017
".00014
0.
0*
-Mill
.64061
*,43S79
0001
0.00010
O.OOC06
O.OOOC7
0.00006
0.00005
0,00004
0.00003
0,00001
0,00002
0.00002
1.00000
i. 00178
1.00757
1*01116
1.01517
1.01199
1.02281
1*02665
1.03050
1.03435
1.03821
1.04209
1.04597
.04
..09331
1.09732
.11790
1.14201
*14613
: *15026
.15440
1*15854
1.16270
1.166f-
A-4
-------
APPENDIX B
SUPPLEMENTARY INFORMATION FOR
GRAB RADON DECAY PRODUCT SAMPLING
EQUIPMENT
a. Air sampling pump - A pump capable of maintaining a
flowrate of 2 to 25 liters per minute through the selected
filter is required. The flowrate should not vary
significantly during the sampling period. A calibrated air
flow measurement device is also required.
b. Filters and filter holder assembly - Membrane type filters
are recommended with a pore size not exceeding 0.8 microns
and a filter holder assembly suitable for the type of
filters being used. Adapters for attachment of the filter
holder to the pump are also required.
c. Alpha counting system - A detector and sealer timer system
is required that can accurately measuring the alpha
particles emitted by radon decay products on a filter. The
counting system must be calibrated and the efficiency
should not vary significantly with alpha energy over the
range of 4 to 7 MeV. Downward-looking detectors with a
mylar seal are very energy dependent, and if such detectors
are used the efficiency is best determined using Po-214.
d. Timer - A stopwatch or timer to measure the sampling time
and time after sampling is required.
GENERAL DESCRIPTION OF METHODS
Two methods commonly used are described below. There are
several other methods reported in the literature. Sampling in these
methods requires collection of radon decay products on a filter and
measuring the alpha activity of the sample with a calibrated
detector at time intervals that are specific for each method. The
results of the alpha measurement and the sample volume are treated
with calculations that are also specific for each method to
determine the working level.
PROCEDURE
a. Sample Collection;
i. Install the filter in the filter holder assembly and
attach to the pump.
ii. Operate the pump for exactly 5 minutes pulling air
through the filter. Record starting time and air flow
rate.
B-l
-------
iii. Stop the pump at the end of
time and start or reset the
the 5 minute
stopwatch.
sampling
Note: Sample counting an
techniques are described.
and
analysis for two different
b. Sample Counting - Modified Tsivoglou Technique
i. Carefully transfer the filter from the filter
holder assembly to the detector. Orient the
collection side of the filter toward the face
the detector.
of
ii. Operate the counter for the following time
intervals, after sampling stopped: 2 to 5
minutes, 6 to 20 minutes, and 21 to 30 minutes.
Record the total counts for each time period.
Sample Counting - Kusnetz Technique
i. Carefully transfer the filter from the filter
holder assembly to the detector. Orient the
collection side of the filter toward the face
the detector.
of
ii. Operate the counter over any 10 minute time
interval between 40 minutes and 90 minutes after
sampling starts. Record the total counts for the
sample and the time (in minutes after sampling)
at the center of the 10 minute time interval.
Data Analysis - Modified Tsivoglou Technique
The concentration in pCi/1 of each of the radon decay
products, Po-218, Pb-214, and Po-214 can be determined
by using the following calculations:
|rg
(0.16746 G
- 0.0813 G ,+ 0.0769 G ,- 0.0566R)
L 3
C.. =
(0.00184 G
- 0.0209 G7 +
L
0.0494 G.. - 0.1575R)
C. =
(-0.0235 G, +
0.0337 G7 - 0.0382
- 0.0576R)
Note : The constants in these equations are based on a
3.11 minute half-life of Po-218, and are therefore
slightly different than those used by Thomas (Th72).
B-2
-------
The working level associated with these concentrations
can then be calculated using the following relationship
WL = (1.028xlO-3xC2-t-5.07xlO-3xC3 + 3. 728xlO-3xC4)
where:
G£ = concentration o£ Po-218 (RaA) in pCi/1
€3 = concentration of Pb-214 (RaB) in pCi/1
04 = concentration of Po-214 (RaC1) in pCi/1
F = sampling flow rate in 1pm
E = counter efficiency in cpm/dpm
GI = gross alpha counts for the time interval 2
to 5 minutes
G£ = gross alpha counts for the time interval 6
to 20 minutes
63 = gross alpha counts for the time interval
21 to 30 minutes
R = background counting rate in cpm
Reference: (Th72).
e. Data Analysis - Kusnetz Technique
Calculate WL as follows:
WL C
K(t)V E
where
C = Sample cpm - Background cpm
K,1 = Factor determined from Table B-l for time from end of
collection to midpoint of counting
V = Total sample air volume in liters from:
flow rate (1/m) x sample time (m)
E = Counter efficiency in cpm/dpm.
B-3
-------
TABLE B-l
Kusnetz Factors (PHS57)
Time K, x
40 150
42 146
44 142
46 138
48 134
50 130
52 126
54 122
56 118
58 114
60 110
62 106
64 102
66 98
68 94
70 90
72 87
74 84
76 82
78 78
80 75
82 73
84 69
86 66
88 63
90 60
B-4
-------
MODIFIED TSIVOGLOU TECHNIQUE
SAMPLE PROBLEM
F = Sampling Flow Rate =3.5 1pm
E = Counting Efficiency = 0.47 cpm/dpm
GX = 880
G2 = 2660
G3 = 1460
R =0.5
C2 = 1 (0.16746x880-0.0815x2600+0.0769x1460-0.0566x0.5)
3. 5 x 0.47
C2 = 26.3 pCi/1
C3 = 1 (0.00184x880-0.0209x2660+0.0494x1460-0.1575x0.5)
3. 5 x 0.47
C3 = 11.0 pCi/1
C4 = 1 (-0.0255x880+0.0557x2660-0.0582x1460-0.0576x0.5)
3.5 x 0.47
C3 = 8.0 pCi/1
WL = (I.028xl0~3x26.3+5.07xl0~3xll.0+3.728xl0~3x8.0)
WL = 0.113
B-5
-------
KUSNETZ TECHNIQUE
SAMPLE PROBLEM
Background Count = 3 counts in 5 minutes or 0.6 cpm
Standard Count = 5,985 counts in 5 minutes or 1,197 cpm
Efficiency = 1>197 cPm"°-6 °Pm = 0.49 (known source of 2430 dpm)
2,430 dpm
Sample Volume =4.4 liter/minute x 5 minutes = 22 liters
Sample Count at 45 minutes (time from end of sampling
period to midpoint of counting period) = 560 counts in 10
minutes or 56 cpm
K, •> at 50 minutes from Table B-l = 130
WL = 56 cpm-0.6 cpm - o 04
130 x 22 1 x 0.49
* U.S. Government Printing office: 1986—491-191/52931 n r:
D - 0
------- |