United States .
Environmental Protection
Agency
Office of
Radiation Programs
Washington.DC 20460
EPA 520-1/89-009
March 1989
Radiation
&EPA
Indoor Radon and
Radon Decay Product
Measurement Protocols
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INDOOR RADON
AND
RADON DECAY PRODUCT
MEASUREMENT PROTOCOLS
U.S. Environmental Protection Agency
Office of Radiation Programs
Problem Assessment Branch
Radon Division
Eastern Environmental
Radiation Facility
Las Vegas Facility
March 1989
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CONTENTS
PAGE
Section 1: GENERAL CONSIDERATIONS
1.1 Introduction and Background 1-1
1.2 Recommended Two-Step Strategy 1-2
1. 3 Screening Measurements ; . . . „ 1-3
1.4 Quality Assurance 1-7
Section 2: RADON MEASUREMENT PROTOCOLS
2.1 Protocol for Using Continuous Radon Monitors
to Measure Indoor Radon Concentrations 2-1
2.2 Protocol for Using Alpha-Track Detectors to
Measure Indoor Radon Concentrations 2-6
2.3 Interim Protocol for Using Electret Ion Chambers
(EIC) to Measure Indoor Radon Concentrations .... 2-15
2.4 Protocol for Using Charcoal Canisters to Measure
Indoor Radon Concentrations 2-22
2.5 Interim Protocol for Using Charcoal Liquid
Scintillation Devices to Measure Indoor Radon
Concentrations 2-30
2.6 Interim Protocol for Using Evacuated
Scintillation Cells to Make 3-Day, Integrated
Measurements of Indoor Radon Concentrations 2-37
2.7 Interim Protocol for Using Pump/Collapsible Bag
Devices to Measure Indoor Radon Concentrations ... 2-44
2.8 Protocol for the Determination of Indoor Radon
Concentrations by Grab Sampling 2-49
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CONTENTS—Continued
Section 3: RADON DECAY PRODUCT MEASUREMENT PROTOCOLS
PAGE
3.1 Protocol for Using Continuous Working Level
Monitors To Measure Indoor Radon Decay Product
Concentrations 3-1
3.2 Protocol for Using Radon Progeny Integrating
Sampling Units (RPISU) to Measure Indoor Radon
Decay Product Concentrations 3-6
3.3 Protocol for the Determination of Indoor Radon
Decay Product Concentrations by Grab Sampling .... 3-13
References « - R-l
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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DISCLAIMER
Mention of trade names or commercial products in this document
does not constitute EPA endorsement or recommendation for their
use.
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ACKNOWLEDGEMENTS
This document represents the combined efforts of many
individuals, including Paul Magno, Sam Windham, Dick Hopper, Ed
Sensintaffar, Mike Boyd, Kirk Maconaiighey, Lew Battist, John
MacWaters, and Melinda Ronca-Battista, as well as many other
radon measurement experts who provided assistance.
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Section 1: GENERAL CONSIDERATIONS
1.1 INTRODUCTION AND BACKGROUND
The risk of lung cancer due to exposure to radon and its decay
products is 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 some 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 exposure. However, in spite
of the urgency to locate houses with high concentrations, the
collection of unreliable or misleading data must be avoided.
There are many Federal, State, university, and private
organizations now performing measurements or planning measurement
programs. It is important for these different groups to follow,
consistent procedures to assure accurate and reproducible
measurements, and to enable valid intercomparison of measurement
results from different studies. ,
This document updates the interim EPA Radon Measurement Protocols
by providing guidance for using a total of 11 measurement
techniques. EPA has extensive laboratory and field experience
with seven of the methods: continuous working level and radon
monitors, alpha-track detectors, charcoal canisters, RPISUs, and
grab techniques. The remaining four methods are interim; EPA has
evaluated these techniques in the laboratory and found them to be
satisfactory. However, the Agency has not conducted large-scale
field tests using the interim techniques, and the interim
protocols have been prepared with the assistance of respected
researchers who have field experience with the methods. As EPA
and others acquire more experience with these interim techniques,
these guidelines may be revised.
These protocols provide instrument-specific technological
guidance that can be used as the basis for standard operating
procedures. The Agency also has issued a report titled "Interim
Protocols for Screening and Follow-up Radon and Radon Decay
Product Measurements" (EPA 1987), that outlines the recommended
strategy for assessing indoor radon levels and provides guidance
for interpreting measurement results. This strategy is
summarized in the following section.
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1.2 RECOMMENDED TWO-STEP STRATEGY
The EPA recognizes that radon concentrations in homes may vary
greatly over time (Gesell 1983; Hess et al. 1985; Stranden et al.
1979; Fleischer and Turner 1984; Wilkening and Wicke 1986; Nyberg
and Bernhardt 1983). Furthermore, concentrations at different
locations in the same house often vary by a factor of two or more
(George et. al. 1984; Hess et. al. 1985; Keller, et. al. 1984).
Because of these temporal and spatial variations, the EPA does
not know of a way to use the result of a single measurement to
provide an accurate estimate of health risks or make a well-
informed decision on the need for remedial action. What the EPA
recommends, therefore, is a two-step strategy for making the
fewest measurements possible, while ensuring that radon
concentrations are not seriously underestimated.
The first step is a screening measurement, which is used to
quickly and inexpensively estimate the highest concentrations to
vrtiich occupants may be exposed, and to decide whether and what
type of additional measurements are needed. Another use of
screening measurements is in multiple-home surveys designed to
efficiently identify homes that contain high concentrations.
Screening measurements should be inexpensive and simple, so that
time or money is not wasted in houses that do not pose a health
threat. The screening measurement alone, however, does not
provide sufficient information to decide on the need for remedial
action.
The second st.ep of making follow-up measurements is recommended
when the screening measurement exceeds 4 pCi/L-(.02 WL). Follow-
up measurements make a conservative estimate of the annual
average concentration in living areas. This document describes
the house conditions under which screening measurements should be
made. The procedures for making follow-up measurements, if
required, are presented in "Interim Protocols for Screening and
Follow-up Radon and Radon Decay Product Measurements" (EPA 1987).
The_EPA recommends that any decision on permanent corrective
action to reduce indoor radon concentrations be made only after
the completion of follow-up measurements.
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1.3 SCREENING MEASUREMENTS
The EPA recommends that screening measurements be made under the
following conditions:
a. Screening measurements should be made in the lowest
area in the house that residents now use or could adapt
for use as a living area. In many houses, the lowest
livable area will be a basement that could be converted
to a den, playroom, or bedroom without major structural
changes. The highest concentrations of radon are
usually found in areas of the house closest to the
underlying soil,.* as shown by a growing body of data
(Gesell 1983, George et. al. 1984) which indicate that
basement concentrations tend to be a factor of two to
three times higher than concentrations in rooms above
the basement.
b. Screening measurements should be made under "closed-
house" conditions (Section 1.3.1); that is, in a closed
building with a minimum level of ventilation. Radon
concentrations under these conditions are likely to be
as reproducible as feasible during occupied conditions
(Ronca-Battista and Magno 1988), and are also higher
than the average concentrations in almost all cases.
Screening measurements estimate the highest potential concentra-
tion to which an occupant may be exposed. Therefore, if the
result of a screening measurement is very low, there is a high
probability that the long-term average concentration in the rooms
used as living areas are even lower, and the need for further
measurements can be eliminated with confidence. Adherence to
these procedures for screening measurements will decrease the
number of false negatives, or homes that contain concentrations
high enough to warrant remedial action (EPA and CDC 1986), but
that are not identified as such because of a low measurement
result. The outcome of such a false negative is no further
measurements, so potentially high concentrations may never be
identified. A false positive measurement result is less serious
because it would result in further measurements, which would
reveal that the concentrations in the house are low. In the
interest of reducing radon exposures, the EPA believes that false
positives are preferable to false negatives.
* The guidance presented here assumes the source of radon to be
the underlying soil, rather than building materials or water. If
sources other than soil are suspected, radon in water or radon
flux measurements should be made.
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1.3.1 Closed-House Conditions
All short-term (that is, less than three months in duration)
screening measurements should be made during periods of the year
when windows are normally kept closed. For most climates in this
country, this will be from late fall to early spring. The
occupants should be instructed to keep windows and doors closed
during the measurement period. Doors should be opened only for a
few minutes to get in and out of the house. 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 four days or less, closed-
house conditions should exist for 12 hours prior to the beginning
of the measurement. It may be difficult to verify these condi-
tions or to implement them for an extended period, but they
should be adhered to as closely as is reasonable.
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 in the winter
that proper conditions 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, thus maximiz-
ing the probability of finding those houses with elevated radon
concentrations.
If, however, it is necessary to make measurements during the
summer, when closed-house conditions are not the normal living
conditions, it will be necessary to establish a means of
providing reasonable assurance that closed-house conditions exist
prior to and during the measurements.
Organizations performing measurements in southern areas that do
not experience extended periods of cold weather should evaluate
seasonable variations in living conditions and identify if there
are time periods when closed-house conditions normally exist. If
such periods exist, it is during those periods that measurements
should be conducted. Air-conditioning systems that recycle
interior air can be operated during screening measurements.
Additional data are needed to better address measurements made
during summer months in cold climates and at any time in warm
climates. The interim data taken under these conditions need to
be interpreted in the light of present knowledge of seasonal
variability.
Measurements of four days or less should not be conducted if
severe storms with high winds are expected. Severe weather can
affect the measurement results in the following ways. First, a
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high wind can increase the variability of radon concentrations
because of wind-induced differences in air pressure between the
house interior and exterior. Also, rapid changes in barometric
pressure increase the chemce of a large difference between the
interior and exterior air pressure, thus, changing the rate of
radon influx. Weather predictions available on local news
stations may provide sufficient information to determine if this
criterion is satisfied.
1.3.2 Duration of Screening Measurements
The duration of screening measurements can range from one day to
three months depending upon the method used. Because of the
variability of radon concentrations with time (Section 1.1),
screening measurements with longer sampling periods should be
less variable than short--period samples (Ronca-Battista and Magno
1988) . If a sampling period of one to several days is used, the
sampling period should be a multiple of 24 hours in order to
avoid a possible bias introduced by sampling only a portion of
the diurnal cycle of radon concentration. Grab samples (five
minutes) are not recommended for screening measurements, except
for quick screening of homes located near sites of known high
concentrations; however, the average of several grab measurements
made in a 24-hour period can be substituted for a one-day
integrated screening measurement. When screening measurements of
four days or less are made, particular care should be taken to
ensure that closed-house conditions are implemented at least 12
hours before the beginning of the measurement, and that the
caution about weather conditions is observed.
1.3.3 Location Selection
The location of the measurement within a room should be decided
with the objective of mecisuring the most stable concentrations.
The following criteria should be applied, in order of importance,
when selecting a measurement location within a room.
a. The measurement should not be made near drafts caused
by heating, ventilation, air conditioning vents, doors,
windows, and fireplaces. Especially for measurements
using charcoal absorption, locations near heat, in
strong sunlight, and in areas of high humidity should
be avoided. In general, measurements should not be
made in kitchens and bathrooms.
b. The measurements should be made away from exterior
house walls to reduce the effect of ventilation through
cracks in the walls. Sampling locations should be at
least ten centimeters (four inches) from other objects.
c. The passive device or the air intake of an instrument
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should be placed at least 75 centimeters (30 inches)
above the floor to reduce possible effects of drafts
near the floor.
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1.4 QUALITY ASSURANCE
The objective of quality eissurance is to ensure that data are
scientifically sound and of known precision and accuracy.
Manufacturers, suppliers, radon analysis laboratories, and
commercial users of radon and radon decay product measurement
devices should establish and maintain quality assurance programs.
These programs should include written procedures for attaining
quality assurance objectives and a system for recording and
monitoring the results of the quality assurance measurements
described below. The quality assurance program should include
the maintenance of control charts and related statistical data,
as described by Goldin (Goldin 1984).
1.4.1 Calibration Measurements
Calibration measurements 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, EICs, and RPISU samplers are
exposed in a 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 individual instrument calibration factors.
Calibration measurements must be conducted to determine and
verify the conversion factors used to derive the concentration
results. These factors are normally determined for a range of
concentrations and exposure times, and for a range of other
exposure and/or analysis conditions pertinent to the particular
device. Determination of these calibration factors is a neces-
sary part of the laboratory analysis, and is the responsibility
of the supplier or analysis laboratory. These calibration
measurement procedures, including the frequency of tests and the
number of devices to be tested, should be specified in the
quality assurance program maintained by manufacturers, suppliers,
and analysis laboratories.
Known exposure measurements or spiked samples consist of
detectors with known exposures in radon calibration chambers that
are labeled and submitted to the laboratory in the same manner as
ordinary samples to preclude special processing. The results of
these measurements are used to monitor the accuracy of the entire
measurement system. Suppliers and analysis laboratories should
provide for the blind introduction of spiked samples into their
measurement processes and the monitoring of the results in their
quality assurance programs. Commercial users of more than a
small number of detectors should arrange for the introduction of
blind spiked samples in their routine shipments and monitor the
results in their quality assurance programs.
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1.4.2 Background Measurements
Background measurements are required both for continuous monitors
and for detectors requiring laboratory analysis. Sufficient
instrument background measurements should be made to establish a
reliable instrument background and to act as a check on
instrument operation.
Detectors or devices requiring laboratory analysis require two
types of background measurements made in both the laboratory and
the field. Suppliers and analysis laboratories routinely should
measure the background of a statistically-significant number of
unexposed detectors from each batch or lot to establish the
laboratory background for the batch and the entire measurement
system. This laboratory blank value is routinely subtracted by
the laboratory from the results reported to the user for field
samples, and should be made available to commercial users of
detectors for quality assurance purposes. In addition to these
background measurements, the organization performing the measure-
ments should calculate the lower limit of detection (LLD) for its
measurement system (Altshuler & Pasternack 1963). This LLD is
based on the system's background and can restrict the ability of
some measurement systems to measure low concentrations.
Commercial users of more than a few detectors should provide
field controls (called blanks) equal to approximately five
percent of the detectors that are deployed, or 25 each month,
whichever is smaller. These controls should be set aside from
each detector shipment, kept sealed and in a low radon
environment, labeled in the same manner as the field samples to
preclude special processing, and returned to the analysis
laboratory along with each shipment. These field blanks measure
the background exposure that may accumulate during shipment and
storage, and the results should be monitored and recorded. The
recommended action to be taken if the concentrations measured by
one or more of the field blanks is significantly greater than the
LLD is dependent upon the type of detector and is discussed in
the section for each method.
1.4.3 Duplicate (Colocated) Measurements
Duplicate measurements provide a check on the quality of the
measurement result, and allow the user to make an estimate of the
relative precision or coefficient of variation. Provision of
sufficient replicate measurements to establish the relative
measurement error of the measurement system is the responsibility
of the manufacturer or the analysis laboratory.
Commercial users of more than a few detectors should provide
duplicates for side-by-side measurements for at least ten percent
of their samples, or 50 each month, whichever is smaller. The
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samples selected for duplication should be systematically
distributed throughout the entire population of samples. Groups
selling measurements to homeowners can do this by providing two
measurements instead of one to a random selection of purchasers,
with the measurements made side-by-side. If passive devices are
used, consideration should be given to providing some means to
ensure that the duplicate devices are not separated during the
measurement period. As with spiked samples introduced into the
system as blind measurements, the precision of duplicate
measurements should be monitored and recorded in the quality
assurance records. The analysis of data from duplicates should
follow the methodology described by Goldin in section 5.3 of his
report (Goldin 1984). If the precision estimated by the
commercial user is not within the precision expected of the
measurement method, the problem should be reported to the
analysis laboratory and the cause investigated.
The EPA has established the National Radon Measurement
Proficiency (RMP) Program. This quality assurance program
enables participants to demonstrate their proficiency at
measuring radon and radon decay product concentrations. For
further information please write to the U.S. Environmental
Protection Agency; Radon Division; Mitigation, Prevention, and
Quality Assurance Branch; National RMP Program; 401 M Street, SW;
Washington, D.C., 20460.
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Section 2: RADON MEASUREMENT PROTOCOLS
2.1 PROTOCOL FOR USING CONTINUOUS RADON MONITORS TO
MEASURE INDOOR RADON CONCENTRATIONS
2.1.1 Purpose
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 ensure uniformity among measurement programs and allow valid
comparison of results. Measurements made in accordance with this
protocol will produce screening measurements of radon
concentrations representative of closed-house conditions. Such
screening measurements of closed-house concentrations have a
smaller variability and are more reproducible than measurements
made when the house conditions are not controlled.
If measurements with CRMs are for a purpose other than a
screening measurement, the investigator should follow guidance
provided by EPA in "Interim Protocols for Screening and Follow-up
Radon and Radon Decay Product Measurements" (EPA 520/1-86-014-1,
1987) .
2.1.2 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 CRM. It is not meant to
replace an instrument manual, but rather provides guidelines to
be incorporated into standard operating procedures. Questions
about these guidelines should be directed to the U.S.
Environmental Protection Agency (EPA), Office of Radiation
Programs, Radon Division (ANR-464), Problem Assessment Branch,
401 M Street S.W., Washington, D.C. 20460.
2.1.3 Method
There are two general types of continuous radon monitors covered
by this protocol. In the first type of CRM, ambient air is
sampled for radon in a scintillation cell after passing through a
filter that removes radon decay products and dust. As the radon
in the cell decays, the radon decay products plate out on the
interior surface of the scintillation cell. Alpha particles
produced by subsequent decays, or by the initial radon decay,
strike the zinc sulphide coating on the inside of the
scintillation cell producing scintillations. The scintillations
are detected by a photo-multiplier tube in the detector which
generates electrical pulses. These pulses are processed by the
detector electronics and the data usually are stored in the
memory of the CRM where results are available for recall or
transmission to a data logger or printer.
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This type of CRM uses either a flow-through cell or a periodic- >
fill cell. In the flow-through cell, air is continuously drawn !
through the cell by a small suction pump. In the periodic-fill .
cell, air is drawn into the cell once each preselected time
interval; then the scintillations are counted and the cycle
repeated. A third type of cell operates by radon diffusion ;
through a filter area with the radon concentration in the cell
varying with the radon concentration in the ambient air, after a
small diffusion time lag. The concentrations measured by all
three types of cells lag the ambient radon concentrations by a .
small amount because of the inherent delay in the radon decay
product disintegration process.
A second type of continuous radon monitor operates as an
ionization chamber. Radon in the ambient air diffuses into the /
chamber through a filtered area so that the radon concentration.
in the chamber follows the radon concentration in the ambient air
with some small time lag. Within the chamber, alpha particles
emitted during the decay of radon atoms produce bursts of ions
which are recorded as individual electrical pulses for each
disintegration. These pulses are processed by the monitor
electronics; the number of pulses counted is usually displayed on
the monitor, and the data are usually available for processing by
an optional data logger/printer.
A third type of continuous radon monitor functions by allowing
ambient air to diffuse through a filter into a detection chamber.
As the radon decays, the alpha particles are counted using a
solid-state silicon detector.
2.1.4 Equipment
Equipment required depends on the type and model of CRM used.
Aged air, or nitrogen, should be available for introduction into
the CRM to measure the background count rate. (Outdoor air can be
used if necessary.) Sealed scintillation cells with measured low
background should be available as spare cells.
2.1.5 Pre-Samplincf Testing
The CRM should be carefully tested according to manufacturer's
directions before and after each measurement to:
* Verify that the correct input parameters and the unit's
clock .or timer are set properly, and
* Verify the operation of the pump. Flow rates
within the range of the manufacturer's -
specifications are satisfactory.
After every 1000 hours of operation the unit should be examined
to check the background count rate by purging with clean, aged
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air or nitrogen in accordance with the procedures identified in
the operating manual for the instrument. In addition, the
background count rate should be monitored more frequently by
operating the instrument in an outdoor or other low radon
env i ronment.
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.
2.1.6 Measurement Criteria
The following conditions should exist prior to and during a
measurement to standardize the measurement conditions as much as
possible.
• 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 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 discusssed in section 1.3.1, measurements
should be made during winter periods whenever
possible.
* Internal-external air exchange systems (other than
a furnace) such as high-volume attic and window
fans should not be operated during the measurement
and for at least 12 hours before the measurement is
initiated. Air conditioning systems that recycle :;
interior air may be operated.
* In southern climates or when the measurements must
be made during a warm season, the closed-house
conditions are satisfied by meeting the criteria
just listed. The closed house conditions must be
more rigorously verified and maintained, however,
when they are not the normal living conditions.
* Short-term measurements should not be conducted if
severe storms with high winds or rapidly changing
barometric pressure are predicted during the
measurement period. Weather predictions available
on local news stations may provide sufficient
information to determine if this condition is
satisfied.
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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.
* The measurement should not be made near drafts caused by
heating, ventilating and air conditioning (HVAC) vents,
doors, and windows.
* The measurement location should not be close to the
outside walls of the house.
* The unit should be placed on a table or stool so that
the air intake is at least 75 centimeters (30 inches)
from the floor and at least 10 centimeters (4 inches)
from other objects.
* In general, measurements should not be made in kitchens
or bathrooms.
2.1.7.2 Operation. The CRM should be programmed to run
continuously, periodically (usually hourly) recording the radon
concentration. The sampling period should generally not be less
than 24 hours. An increase in operating time decreases the
uncertainty associated with the measurement result.
Care should be taken to eliminate data that are produced before
equilibrium conditions have been established in a flow-through
cell. Generally, conditions stabilize after the first four
hours. Measurements taken prior to this are low and should be
discarded. After this four hour period, the periodic readings
can be averaged to obtain an integrated measurement result (e.g.
a 24-hour average concentration).
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 the following:
* Start and stop times and date of the measurement;
* Information about how the standardized conditions, as
previously specified, were satisfied;
* Exact location of the instrument, on a diagram of
the room and house, if possible;
* Other easily obtained information that may be useful,
such as the type of house, type of heating system, or
the existence of a crawl space;
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* Serial numbers of the CRM, scintillation cells, and
other equipment.
2.1.8 Results
2.1.8.1 Lower Limit of Detection. Most CRMs are capable of an
LLD of 0.5 pCi/L or less (Altshuler and Pastenack 1963).
Special cells are available for some CRMs which have LLDs of 0.1
pCi/L.
2.1.8.2 Precision. Most CRMs can achieve a coefficient of
variation of less than 10% (1 sigma) at 4 pCi/L or greater.
2.1.9 Quality Assurance
The elements of a quality assurance program for CRM measurements
are (1) calibration, (2) background checks, and (3) duplicate
samples. The quality assurance program should include the
maintenance of control charts, as described by Goldin (Goldin
1984) .
The EPA has established the National Radon Measurement
Proficiency (RMP) Program. This quality assurance program
enables participants to demonstrate their proficiency at
measuring radon and radon decay product concentrations. For
further information please write to the U.S. Environmental
Protection Agency; Radon Division; Mitigation, Prevention, and
Quality Assurance Branch; National RMP Program; 401 M Street, SW;
Washington, D.C., 20460.
2.1.9.1 Calibration. CRMs should be calibrated in a radon
calibration chamber before being put in service, after any
repairs, and at least every six months. Spare cells should have
individual calibration factors determined. Where design of the
CRM permits, a calibration check source or cell should be counted
to demonstrate proper operation prior to beginning sampling.
2.1.9.2 Background. After every 1000 hours of operation the CRM
background should be checked by purging with clean aged air or
nitrogen in accordance with the procedures given in the
instrument operating manual. In addition, the background count
rate should be monitored frequently by operating the instrument
in an outdoor or other low radon environment. Cells which
develop a high background after prolonged use should be
reconditioned by the manufacturer.
2.1.9.3 Duplicate Samples. When two or more CRMs are available,
the coefficient of variation of the measurements can be estimated
by operating the CRMs side by side. The analysis of duplicate
results should follow the methodology described by Goldin in
section 5.3 of his report (Goldin 1984).
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2.2 PROTOCOL FOR USING ALPHA-TRACK DETECTORS TO MEASURE INDOOR
RADON CONCENTRATIONS
2.2.1 Purpose
This protocol provides guidance for using alpha-track detectors
(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 screening measurements of radon
concentration representative of closed-house conditions. Such
screening measurements with closed-house concentrations have a
smaller variability and are more reproducible than measurements
made when the house conditions are not controlled.
If measurements with ATDs are for a purpose other than screening
measurement, the investigator should follow guidance provided by
EPA in "Interim Protocols for Screening and Follow-up Radon and
Radon Decay Product Measurements" (EPA 520/1-86-014-1, 1987).
2.2.2 Scope
This protocol covers, in general terms, the equipment,
procedures, and quality control objectives to be used in
performing the measurements. It provides guidelines to be
adopted into standard operating procedures. Questions about
these guidelines should be addressed to the U.S. Environmental
Protection Agency, Office of Radiation Programs, Radon Division
(ANR-464), Problem Assessment Branch, 401 M Street, S.W.,
Washington, D.C., 20460.
2.2.3 Method
An alpha-track detector (ATD) consists of a small piece of
plastic or film enclosed in a container with a filter-covered
opening. Radon diffuses through the filter into the container
and alpha particles emitted by the radon and its decay products
strike the detector and produce submicroscopic damage tracks. At
the end of the measurement period, the detectors are returned to
a laboratory. Plastic detectors are 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. The number of tracks produced per unit of
time is proportional to the radon concentration', so" 'a'n ATD
functions as a true integrating detector and measures the average
concentration over the measurement period.
Many factors contribute to the variability of the ATD results
including differences in the detector response within and between
2-6
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batches of plastic, non-uniform plateout of decay products inside
the detector holder, differences in the number of background
tracks and variations in etching conditions. Since the
variability in ATD results decreases with the number of net
tracks counted, particularly at low exposures, counting more
tracks over a larger area of the detector will reduce the
uncertainty of the result.
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 for most
users. Therefore, details for establishing the analytical
aspects of an ATD program are omitted from this protocol. If
additional details are desired, they have been reviewed by
Fleischer and Lovett (Fleischer 1965; Lovett 1969).
Assuming ATDs are obtained from a commercial supplier, the
following equipment is needed to initiate monitoring in a house:
* The alpha track detector in an individual, sealed
container, such as an aluminized plastic bag to
prevent extraneous exposure before deployment;
* A means to attach the ATD to its measurement
location, if it is to be hung from the wall or
ceiling;
* Instruction sheet for the occupant, a sample log
sheet, a shipping container and, if it is to be
mailed, a prepaid mailing label for returning the
detector to the laboratory;
« At the time of retrieval, some means (such as tape)
for resealing the detector prior to returning it to
the supplier for analysis;
« Data collection log.
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
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heating, ventilating and air conditioning (HVAC) systems, or
other modifications that may influence the radon concentration
during the period.
2.2.6 Measurement Criteria
The following conditions should exist during the measurement
period to standardize the measurement conditions as much as
possible.
* 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) 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 extended periods. 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 1.3.1, measurements should be made during
winter periods whenever possible.
* Internal-external air exchange systems (other than
a furnace) such as high-volume attic and window
fans should not be operated during the measurement.
Air conditioning systems that recycle interior air
may be operated.
* In southern climates or when the measurements must
be made during a warm season, the closed-house
conditions are satisfied by meeting the criteria
just listed. The closed house conditions must be
verified and maintained more rigorously however,
when they are not the normal living conditions.
A 12-month ATD measurement provides information about radon
concentrations in a house during an entire year, so the closed-
house conditions do not have to be satisfied to measure the
annual average concentration over 12 months.
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 reasonably can 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.
2-8
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2.2.7.2 Location Selection. The following criteria should be
applied to select the location of the detector within a room.
* A position should be selected where the ATD will not be
disturbed during the measurement period.
* The detector should not be placed near drafts
caused by HVAC vents, windows, doors, etc.
* The detectors should be located at least 75 centimeters
(30 inches) from the floor and at least 10 centimeters
(4 inches) from other objects.
* The detector should not be placed close to the
outside walls of the house.
* In general, detectors should not be placed in
kitchens or bathrooms.
It is often 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 and the radon proof container to
make sure they are intact and have 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
2-9
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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 is
shown below.
* The start and stop dates of the measurement.
* Whether standardized conditions, as previously
specified, are satisfied.
* Exact location of the detector, on a diagram of the
room and house if possible.
* Serial number and manufacturer of the detector
along with code number or description which
uniquely identifies customer, building, room, and
sampling position.
* Other easily gathered information that may be
useful, such as the type of house, type of heating
system, or the existence of a basement or crawl
space.
2.2.10 Analysis Requirements
2.2.10.1 Sensitivity. The lower limit of detection (LLD)
(Altshuler and Pasternack 1963) and the precision of an ATD
system is dependent upon the total number of tracks counted, and
therefore the area of the detector that is analyzed. With
present ATDs, routine counting achieves an LLD of 1 pCi/L-month,
and an LLD of 0.2 pCi/L-month is achieved by counting additional
area. Table 2-1 illustrates the dependence of precision on the
number of net tracks counted. As can be seen from Table 2-1, if
few net tracks are counted, poor precision is obtained. Thus, it
is important that the organization performing the measurements
with an ATD arranges for counting an adequate area or number of
net tracks.
2.2.10.2 Precision. The coefficient of variation should be
monitored using the results of the duplicate' detectors described
in Section 2.2.11.3 of this protocol, rather than a precision
quoted by the manufacturer. The coefficient of variation should
not exceed 20 percent (1 sigma) at radon concentrations of 4
pCi/L or greater.
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Table 2-1
Dependence of Precision on Number of Net Tracks Counted
Number of Net
Tracks Counted
4
6
10
15
20
50
75
100
2 Sigma Error (%) (a)
100
82
63
52
45
28
23
20
(a) This is the minimum error for the
number of net tracks indicated
based only on counting statistics.
Additional error may be introduced
during processing.
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2.2.11 Quality Assurance
The quality assurance program for measurements with ATDs involves
four separate parts: (1) calibration detectors, (2) known
exposure (spiked) detectors, (3) duplicate detectors as a test of
the precision, and (4) control (blank) detectors to check for
exposure during shipment or storage. The quality assurance
program should include the maintenance of control charts as
described by Goldin (Goldin 1984).
The EPA has established the National Radon Measurement
Proficiency (RMP) Program. This quality assurance program
enables participants to demonstrate their proficiency at
measuring radon and radon decay product concentrations. For
further information please write to the U.S. Environmental
Protection Agency; Radon Division; Mitigation, Prevention, and
Quality Assurance Branch; National RMP Program; 401 M Street, SW;
Washington, D.C., 20460.
2.2.11.1 Calibration Factors. 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 manufacturers and suppliers of alpha-
track services as minimum requirements in determining the
calibration factor.
* 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 different concentrations).
* A minimum of ten detectors should be exposed at
each level.
* The period of exposure should be sufficient to
allow the ATD to achieve equilibrium with the
chamber atmosphere.
* A calibration factor should be determined for each
batch or sheet of detector material received from
the material supplier.
2.2.11.2 Known Exposure Measurements. Both suppliers of alpha-
track services and large users of these services should submit
ATDs with known radon exposures (spiked samples) for analysis on
a regular schedule. Known exposure (spiked) detectors should be
labeled in the same manner as field detectors to ensure identical
processing. The number of spiked detectors submitted for
analysis should be a few percent of the total number of detectors
analyzed. The results of the spiked detector analyses should be
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monitored and recorded. Any significant deviation from the known
concentration to which they were exposed should be investigated.
2.2.11.3 Duplicate (Colocated) Detectors. 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 approximately 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. The
samples selected for duplication should be systematically
distributed throughout the entire population of measurements.
Groups selling measurements to homeowners can do this by
providing two detectors instead of one to a random selection of
purchasers, with instructions to place the detectors side-by-
side. Consideration should be given to providing some means to
ensure that the duplicate devices are not separated during the
measurement period. Data from duplicate detectors should be
evaluated using the procedures described by Goldin in section 5.3
of his report (Goldin 1984). The method should achieve a coeffi-
cient of variation of 20 percent (1 sigma) or less at radon
concentrations of 4 pCi/L or greater. Consistent failure in
duplicate agreement may indicate a problem in the measurement
process that should be investigated.
2.2.11.4 Control Detectors.
2.2.11.4.1 Laboratory Control Detectors. The laboratory
background level for each batch of ATDs should be established by
each supplier. Suppliers should measure the background of a
statistically significant number of unexposed ATDs that have been
processed according to their standard operating procedures. This
laboratory blank value normally is subtracted by the analysis
laboratory or supplier from the results obtained from the field
detectors to arrive at the net readings used to calculate the
reported sample radon concentrations.
2.2.11.4.2 Field Control Detectors. Field control ATDs (field
blanks) should consist of a minimum of 5 percent of the devices
that are deployed every month or 25, whichever is smaller.
Commercial users should set these aside from each shipment, keep
them sealed and in a low radon (less than 0.5 pCi/L) environment,
label them in the same manner as the field ATDs to assure
identical processing, and send them back to the supplier with the
field ATDs for analysis. These control devices are necessary to
measure the background exposure that accumulates during shipment
and storage. The results should be monitored and recorded. If
the average value from the field control devices (field blanks)
is significantly greater than the LLD established by the
supplier, this average value should be subtracted from the
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individual values reported for the other devices in the exposure
group.
If one or a few field blanks have concentrations significantly
greater than the LLD established by the supplier, it may indicate
defective packaging or handling. If the average reading of the
blanks is significantly greater than the LLD, it should be
subtracted from the individual concentrations reported for the
field samples.
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2.3 INTERIM PROTOCOL FOR USING ELECTRET ION CHAMBER RADON
DETECTORS (EICs) TO MEASURE INDOOR RADON CONCENTRATIONS
2.3.1 Purpose
This protocol provides guidance for using electret ion chamber
radon detectors (EICs) to obtain accurate and reproducible
measurements of indoor radon concentrations. Following the
protocol will help ensure uniformity among measurement programs
and allow valid intercomparision of results. Measurements made
in accordance with this protocol will produce screening measure-
ments of radon concentration representative of closed-house
conditions. Such screening measurements of closed-house con-
centrations have a smaller variability and are more reproducible
than measurements made when the house conditions are not con-
trolled.
If measurements with EICs are for a purpose other than a
screening measurement, the investigator should follow guidance
provided by EPA in "Interim Protocols for Screening and Follow-up
Radon and Radon Decay Product Measurements" (EPA 520/1-86-014-1,
1987) .
2.3.2 Scope
This protocol covers, in general terms, the equipment,
procedures, and quality control objectives to be used in perform-
ing the measurements. It is not meant to replace an instrument
manual, but rather provides guidelines to be adopted into
standard operating procedures. Questions about these guidelines
should be addressed to the U.S. Environmental Protection Agency,
Office of Radiation Programs, Radon Division, Problem Assessment
Branch (ANR-464), 401 M Street, S.W., Washington, D.C., 20460.
2.3.3 Method
Electret ion chamber radon detectors (EICs) have been described
by Kotrappa et. al. (Kotrappa 1988). They require no power and
function as true integrating detectors, measuring the average
concentration during the measurement period.
EICs contain a permanently charged electret0} which collects ions
formed in the chamber by radiation emitted from radon decay
products. When the device is exposed, radon diffuses into the
chamber through filtered openings. Ions which are generated
continuously by the decay of radon and radon decay products are
drawn to the surface of the electret and reduce its surface
voltage. The amount of voltage reduction is directly related to
d)
An electrostatically charged disk of Teflon .
2-15
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the average radon concentration present during the exposure
period. There are both short-term (2 to 7 day) and long-term (1
to 12 month) EICs that are currently marketed. The thickness of
the electret affects the usable measurement period.
The electret must be removed from the canister and the electret
voltage must be measured with a special surface voltmeter both
before and after exposure. The difference between the initial
and final voltage is divided first by a calibration factor and
then by the number of exposure days to determine the average
radon concentration during the exposure period. Electret voltage
measurements can be made in a laboratory or in the field.
2.3.4 Equipment
The following equipment is required to measure radon using an
EIC:
* A short-term or long-term EIC;
* An instruction sheet for the user and a shipping
container with a label for returning the EIC(s) to
the laboratory;
* A specially built surface voltmeter for measuring
electret voltages before and after exposure;
* A data collection log.
2.3.5 Predeplovment Considerations
The measurement should not be made if the occupant is planning
remodeling, changes in the heating, ventilating and air
conditioning system, or other modifications that may influence
the radon concentration during the measurement period.
The EIC should not be deployed if the occupant's schedule
prohibits terminating the measurement at the appropriate time.
2.3.6 Measurement Criteria
The following conditions should exist prior to and during a
measurement to ensure that the conditions are as standardized as
possible.
* 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
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a few minutes. These conditions are expected to
exist as normal living conditions during the winter
in northern climates. For this reason and others
discussed in Section 1.3.1, measurements should be
made during winter periods whenever possible.
* Internal-external air exchange systems (other than
a furnace) such as high-volume attic and window
fans should not be operated during the measurement
and for at least 12 hours before the measurement is
initiated. Air conditioning systems that recycle
interior air maiy be operated.
* 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. The closed house conditions must be verified
and maintained more rigorously, however, when they are
not the normal living conditions.
* Short-term measurements should not be conducted if
severe storms with high winds or rapidly changing
barometric presisures are predicted during the
measurement period. Weather predictions available
on local news stations may provide sufficient
information to determine if this condition is
satisfied.
A 12-month EIC measurement provides information about radon
concentrations in a house during an entire year, so the closed-
house conditions do not have to be satisfied to measure the
annual average concent rait ion over 12 months.
2.3.7 Deployment
The EIC should be inspected prior to deployment to see
that it has not been damaged during handling and shipping.
2.3.7.1 Timely Deployment. Both long and short-term EICs should
be deployed as soon as possible after their initial voltage is
measured. Until an EIC is deployed, an electret cover should
remain in place over th€t electret to minimize background loss of
voltage.
2.3.7.2 Location Selection. The following criteria should be
applied to select the location of an EIC within a room.
* A position should be selected where the detector
will not be disiturbed during the measurement
period.
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i* The detector should not be placed near drafts caused by
HVAC vents, windows, and doors.
* The detector should be placed at least 75
centimeters (30 inches) above the floor level and
at least 10 centimeters (4 inches) from other
obj ects.
* The detector should not be placed close to the
exterior walls of the house.
* In general, detectors should not be placed in
kitchens or bathrooms.
2.3.8 Retrieval of Detectors
Short-term EICs may be deployed for a two to seven day
measurement period, and long-term EICs for one to twelve months.
If the occupant is terminating the sampling, the instructions
given to the occupant should tell the occupant when and how to
terminate the sampling period. A deviation from the schedule by
up to few days is acceptable for short-term EICs and up to three
weeks for long-term EICs, if the time of termination is
documented on the EIC information form. In addition, the
occupant also should be instructed to send the EIC to the
laboratory as soon as possible, preferably within a few days
following exposure termination.
At the end of the monitoring period, the EIC 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 EIC
electret should be covered again using the mechanism provided. ;
2.3.9 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 the following:
* The dates and start and stop times of the measurement;
* Whether standardized conditions, as previously
specified, are satisfied;
* Exact location of the detector, on a diagram of the
room and house, if possible; ,.
* Other easily gathered information that may be
useful, such as the type of house, type of heating
system, and the existence of a crawl space;
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* Serial number and supplier of detector along with a
code number or description which uniquely iden-
tifies customer, building, room, and sampling
position.
2.3.10 Analysis Requirements
In general, all EICs should be analyzed in the field or in the
laboratory as soon as possible following removal from houses. A
background correction must be made to the radon concentration
value obtained because EICs have a small response to background
gamma radiation.
2.3.10.1 Sensitivity. For a 7-day exposure period using a
short-term EIC the lower level of detection (LLD) (Altshuler and
Pasternak 1963) is about 0.3 pCi/L. For a long-term EIC, the LLD
is also about 0.3 pCi/L.
2.3.10.2 Precision. The coefficient of variation should not
exceed 10 percent (1 sigma) at radon concentrations of 4 pCi/L or
greater. This precision should be monitored by using the results
of duplicate detector analyses described in Section 2.3.11.3 of
this protocol.
2.3.11 Quality Assurance
The quality assurance (QA) program for measurements with EIC
detectors includes four parts: (1) calibration detectors, (2)
known exposure (spiked) detectors, (3) duplicate detectors as a
test of the precision and (4) control (blank) detectors to check
for exposure during shipment or storage. The purpose of a QA
program is to identify the accuracy and precision of the
measurements and to assure that the measurements are not in-
fluenced by exposure from sources outside the environment to be
measured.
The EPA has established the National Radon Measurement
Proficiency (RMP) Program. This quality assurance program
enables participants to demonstrate their proficiency at
measuring radon and radon decay product concentrations. For
further information please write to the U.S. Environmental
Protection Agency; Radon Division; Mitigation, Prevention, and
Quality Assurance Branch; National RMP Program; 401 M Street, SW;
Washington, D.C., 20460.
2.3.11.1 Calibration Factors. Determination of calibration
factors for EIC detectors requires exposure of detectors to known
concentrations of radon-222 in a radon exposure chamber. Since
EICs are also sensitive to exposure to gamma radiation (see
Section 2.3.11.4), a gamma background measurement is also
required.
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The following guidance is provided to manufacturers and suppliers
of EIC services as minimum requirements in determining the
calibration factor.
* Detectors 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 different concentrations).
* A minimum of ten detectors should be exposed at
each level.
* The period of exposure should be sufficient to
allow the detector to achieve equilibrium with the
chamber atmosphere.
2.3.11.2 Known Exposure Detectors. Both suppliers of EIC
detector services and large users of these services should submit
detectors with known radon exposures (spiked samples) for
analysis on a regular schedule. Blind calibration detectors
should be labeled in the same manner as the field detectors to
ensure identical processing. The number of devices submitted for
analysis should be a few percent of the total number of detectors
analyzed. The results of the spiked detector analysis should be
monitored and recorded and any significant deviation from the
known concentration to which they were exposed should be
investigated.
2.3.11.3 Duplicate (Colocated) Detectors. Duplicate EICs should
be placed in enough houses to monitor the precision of the
measurement. This will usually be approximately 10 percent of
the houses to be tested each month or 50, whichever is smaller.
The duplicate devices should be shipped, stored, exposed, and
analyzed under the same conditions, and not identified as
duplicates to the processing laboratory. The samples selected
for duplication should be systematically distributed throughout
the entire population of samples. Groups selling measurements to
homeowners can do this by providing two detectors instead of one
to a random selection of purchasers, with instructions to place
the detectors side-by-side. Consideration should be given to
providing some means to ensure that the duplicate devices are not
separated during the measurement period. The analysis of
duplicate data should follow the methodology described by Goldin
in section 5.3 of his report (Goldin 1984). The method should
achieve a coefficient of variation of 10 percent (1 sigma) or
less at radon concentrations of 4 pCi/L or greater. Consistent
failure in duplicate agreement indicates an error in the
measurement process that should be investigated.
2.3.11.4 Control EICs for Background Gamma Exposure and Electret
Stability Monitoring. Electrets should exhibit very little drift
in surface voltage due to internal electrical instabilities.
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Neither the short-term or the long-term electrets should show
voltage reductions of more than that which they exhibit when
exposed to 0.3 pCi/L. A minimum of 5 percent of the electrets,
or 10, whichever is smaller, should be set aside from each
shipment and evaluated for voltage drift. They should be kept
covered with protective caps in a low radon environment and
analyzed for voltage drift over a time period similar to the time
period used for those deployed in homes. Any voltage drift found
in the control electrets of more than 2 volts per week for short-
term electrets or 1 volt per month for long-term electrets should
be investigated.
EICs also are sensitive to background gamma radiation. The
electret voltage drop due to the background gamma radiation needs
to be assessed so that an appropriate correction can be made to
the measured concentration value. This background voltage drop
should be subtracted from the total voltage drop exhibited by the
electret, to produce a net voltage difference due only to the
exposure to the ions produced by the decay of radon in the EIC
chamber. A background correction of 0.8 pCi/L is routinely
subtracted from both long and short-term EIC readings to correct
for an average background value of 10 uR/hr. This background
correction is made by the analysis laboratory or by the user if
the detector is read in the field. In cases where higher than
normal background radiation is suspected or known to exist, a
gamma background measurement should be made (preferably with an
energy-compensated scintillometer), and an additional correction
of 0.08 pCi/L for each eidditional uR/hr should be made.
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2.4 PROTOCOL FOR USING CHARCOAL CANISTERS TO MEASURE
INDOOR RADON CONCENTRATIONS
2.4.1 Purpose
This protocol provides guidance for using a charcoal canister 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 screening measurements of radon
concentrations representative of closed-house conditions. Such
screening measurements have a smaller variability and are more
reproducible than measurements made when the house conditions are
not controlled.
If measurements with charcoal canisters are for a purpose other
than a screening measurement, the investigator should follow
guidance provided by EPA in "Interim Protocols for Screening and
Follow-up Radon and Radon Decay Product Measurements"
(EPA 520/1-86-014-1, 1987).
2.4.2 Scope
This protocol covers, in general terms, the sample collection and
analysis method, the equipment needed, and the quality control
objectives of measurements. It is not meant to replace an
instrument manual, but rather provides guidelines to be adopted
into standard operating procedures. Questions about these
guidelines should be directed to the U.S. Environmental
Protection Agency (EPA), Office of Radiation Programs, Radon
Division (ANR-464), Problem Assessment Branch, 401 M Street,
S.W., Washington, D.C., 20460.
2.4.3 Method
Charcoal canisters are passive devices requiring no power to
function. The passive nature of the activated charcoal allows
continual adsorption and desorption of radon. During the
measurement period the adsorbed radon undergoes radioactive
decay. Therefore, the technique does not uniformly integrate
radon concentrations during the exposure period. As with all
devices that store radon, the average concentration calculated
using the mid-exposure time is subject to error if the ambient
radon concentration adsorbed during the first half of the
sampling period is substantially higher or lower than the average
over the period.
The charcoal canister measurement technique is described in
detail by Cohen and by George (Cohen 1983 and George 1984). The
charcoal canister now used by several groups consists of a
circular, 6-to-10 centimeter diameter container approximately 2.5
2-22
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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.
In some cases the canister contains a diffusion barrier over the
canister opening which improves the uniformity of response to
variations of radon concentration with time for longer exposures.
Desiccant also is incorporated in some canisters to reduce
interference from moisture adsorption during longer exposures.
All charcoal canisters are sealed with a radon proof cover or
closure after preparation.
The measurement is initiated by removing the cover to allow
radon-ladened air to diffuse into the charcoal bed where the
radon is adsorbed onto the charcoal. At the end of a measurement
period, the canister is securely resealed and returned to a
laboratory for analysis.
At the laboratory, the canisters are analyzed for radon decay
products by placing the charcoal, still in its container,
directly on a gamma detector. If it is necessary to make a
correction to 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 (George 1984). 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 within the specified
exposure period.
Charcoal canister systems are calibrated by analyzing canisters
exposed to known concentrations of radon in a calibration
facility.
2.4.4 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
(Cohen 1983; George 1984).
2-23
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The following equipment will be required to measure radon with
charcoal canisters.
* Charcoal canister(s) sealed with protective cover;
• Instruction sheet and sampling data sheet for the
occupant, a shipping container and, if sent by
mail, a prepaid mailing label for returning
canister(s) to the analytical laboratory;
* Data collection log.
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. The detector
system and detector geometry must be identical with the system
used to derive the canister calibration factors.
2.4.5 Predeplovment 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.
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.
'> i.( .;;
2.4.6 Measurement Criteria
The following conditions should exist prior to and during a
measurement to ensure that the conditions are as standardized as
possible.
* 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 others
discussed in Section 1.3.1, measurements should be
made during winter periods whenever possible.
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* Internal-external air exchange systems (other than
a furnace) such as high-volume attic and window
fans should not be operated during the measurement
and for at least 12 hours before the measurement is
initiated. Air conditioning systems that recycle
interior air may be operated.
* 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. The closed house
conditions must be verified and maintained more
rigorously however, when they are not the normal
living conditions.
* Short-term measurements should not be conducted if
severe storms with high winds or rapidly changing
., . barometric pressure are predicted during the
measurement period. Weather predictions available
on local news stations may provide sufficient
information to determine if this condition is
satisfied.
2.4.7 Deployment
2.4.7.1 Timely Deployment. Charcoal canisters should be
deployed within the shelf life specified by the supplier. Until
they are deployed, they should remain tightly sealed to maintain
maximum sensitivity and low background.
2.4.7.2 Location Selection. The following criteria should be
applied to select the location of a canister within a room.
* A position should be selected where the canister
will not be disturbed during the measurement
period.
* 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, and areas of high
humidity.
* The canister should be placed at least 75
centimeters (30 inches) above the floor and at
least 10 centimeters (4 inches) from other objects.
* The canister should not be placed close to the
outside walls of the house.
« Canisters should not be placed in kitchens or
bathrooms.
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The protective cover and sealing tape should be removed from the
canister to begin the sampling period. The cover and tape 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.
2.4.8 Retrieval of Detectors
The canisters should be deployed for a two- to seven-day
measurement period as specified in the suppliers instructions.
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 six hours is acceptable if 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.
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 three hours after the end of sampling to
allow for ingrowth of decay products.
2.4.9 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 the following:
* The date and start and stop time of the
measurement;
* Whether standardized conditions, as previously
specified, are satisfied;
* Exact location of the canister, on a diagram of the
room and house, if possible;
* Serial number of the canister and a code number or
description which uniquely identifies customer,
building, room, and sampling position;
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* Other easily gathered information that may be
useful, such as the type of house, type of heating
system, and the existence of a basement or crawl
space.
2.4.10 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 radon-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 (George 1984).
2.4.10.1 Sensitivity. For a two- to seven-day exposure period,
the lower level of detection (LLD) (Altshuler and Pasternack
1963) should be 0.5 pCi/L or less. This can normally be 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 2.4.11.3 of this
protocol.
2.4.10.2 Precision. The coefficient of variation should not
exceed 10 percent (1 sigraia) at radon concentrations of 4 pCi/L or
greater. This precision should be monitored using the results of
the duplicate canister analyses described in this protocol.
Charcoal canisters can achieve an average coefficient of
variation of less than 5 percent at concentrations of 4 pCi/L or
greater.
2.4.11 Quality Assurance
The quality assurance program for charcoal canisters includes
four parts: (1) calibration canisters, (2) known exposure
(spiked) canisters, (3) duplicate canisters, and (4) 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 extraneous exposures. The quality
assurance program should include the maintenance of control
charts, as described by Goldin (Goldin 1984).
The EPA has established the National Radon Measurement
Proficiency (RMP) Program. This quality assurance program
enables participants to demonstrate their proficiency at
measuring radon and radon decay product concentrations. For
2-27
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further information please write to the U.S. Environmental
Protection Agency; Radon Division; Mitigation, Prevention, and
Quality Assurance Branch; National RMP Program; 401 M Street, SW;
Washington, D.C., 20460.
2.4.11.1 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 depend on the exposure time and also may
depend on the amount of water adsorbed by the canister during
exposure. These calibration factors should be determined using
the procedures described by George (George 1984). Calibration
factors should be determined for each charcoal canister system
(container type, amount of charcoal, etc.).
2.4.11.2 Known Exposure Canisters. Both suppliers of charcoal
canister services and large users of these services should submit
charcoal canisters with known radon exposures (spiked samples)
for analysis on a regular schedule. Known exposure (spiked)
canisters should be labeled in the same manner as the field
canisters to assure identical processing. The number of
canisters submitted for analysis should be a few percent of the
total number of canisters analyzed. The results of the spiked
canister analysis should be monitored and recorded and any sig-
nificant deviation from the known concentration to which they
were exposed should be investigated.
2.4.11.3 Duplicate (Colocated) Canisters. Duplicate canisters
should be placed in enough houses to monitor the precision of the
measurements. 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, and not identified as
duplicates to the processing laboratory. The samples selected
for duplication should be systematically distributed throughout
the entire population of samples. Groups selling measurements to
homeowners can do this by providing two detectors instead of one
to a random selection of purchasers, with instructions to place
them side-by-side. Consideration should be given to providing
some means to ensure that the duplicate devices are not separated
during the measurement period. Data from duplicate canisters
should be evaluated using the procedures described by Goldin in
section 5.3 of his report (Goldin 1984). The method should
achieve a coefficient of variation of 10 percent (1 sigma) or
less at radon concentrations of 4 pCi/L or greater. Consistent
failure in duplicate agreement may indicate a problem in the
measurement process that should be investigated.
2.4.11.4 Control Devices.
2.4.11.4.1 Laboratory Control Canisters. The laboratory
background level for. each batch of charcoal canisters should be
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established by each supplier. Suppliers should measure the
background of a statistically significant number of unexposed
canisters that have been processed according to their standard
operating procedures (laboratory blanks). This value normally is
subtracted by the analysis laboratory or supplier from the
results obtained from the field devices to arrive at the net
readings used to calculate the sample radon concentrations.
2.4.11.4.2 Field Control Canisters. Field control canisters
(field blanks) should consist of a minimum of 5 percent of the
devices that are deployed every month or 25, whichever is
smaller. Commercial users should set these aside from each
shipment, keep them sealed and in a low radon (less than 0.2
pCi/L) environment, label them in the same manner as the field
canisters to ensure identical processing, and send them back to
the supplier with one shipment each month for analysis. These
control devices measure the background exposure that may
accumulate during shipment or storage, and results should be
monitored and recorded. If one or only a few of the field
control canisters have concentrations significantly greater than
the LLD established by the supplier it may indicate defective
canisters or poor procedures. If most of the controls have
concentrations significantly greater than the LLD, the average
value of the field controls should be subtracted from the
reported field canister concentrations and the supplier notified
of a possible problem.
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2.5 INTERIM PROTOCOL FOR USING CHARCOAL LIQUID
SCINTILLATION DEVICES TO MEASURE INDOOR RADON
CONCENTRATIONS
2.5.1 Purpose
This protocol provides guidance for using charcoal liquid
scintillation (CLS) devices 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 screening measurements
of radon concentration representative of closed-house conditions.
Such screening measurements have a smaller variability and are
more reproducible than measurements made when the house
conditions are not controlled.
If measurements with CLS devices are for a purpose other than a
screening measurement, the investigator should follow guidance
provided by EPA in "Interim Protocols for Screening and Follow-up
Radon and Radon Decay Product Measurements" (EPA 520/1-86-014-1,
1987).
2.5.2 Scope
This protocol covers, in general terms, the equipment,
procedures, and quality control objectives to be used in perform-
ing the measurements. It is not meant to replace an instrument
manual, but rather provides guidelines to be adopted into
standard operating procedures. Questions about these guidelines
should be directed to the U.S. Environmental Protection Agency
(EPA), Office of Radiation Programs, Radon Division (ANR-464),
Problem Assessment Branch, 401 M Street, S.W.,. Washington, D.C.,
20460.
2.5.3 Method
CLS devices are passive detectors requiring no power to function.
The passive nature of the activated charcoal allows continual
adsorption and desorption of radon, and the adsorbed radon
undergoes radioactive decay during the measurement period.
Therefore, the technique does not uniformly integrate radon
concentrations during the exposure period. As with all devices
that store radon, the calculated average concentration is subject
to error if the ambient radon concentration adsorbed during the
first half of the sampling period is substantially higher or
lower than the average over the period.
The charcoal liquid scintillation detector technique is described
by Prichard (Prichard and Marien 1985). A type of CLS device now
provided by several companies is a capped, 20 ml liquid
scintillation vial that is approximately 25 mm. in diameter by 60
2-30
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mm. and contains 1 to 3 grams of charcoal. In some cases the
vial contains a diffusion barrier over the charcoal which
improves the uniformity of response of the device to variations
of radon concentration with time, particularly for longer
exposures. Some CLS devices include a few grams of desiccant
which reduces interference from moisture adsorption by the
charcoal (Perlman 1989) ., All CLS devices are sealed with a
radon-proof closure after preparation.
A measurement with the CLS device is initiated by removing_the
radon-proof closure to allow radon-ladened air to diffuse into
the charcoal where the radon is adsorbed. At the end of the
measurement the device is securely resealed and returned to the
laboratory for analysis,,
s
At the laboratory the devices are prepared for analysis by radon
desorption techniques which reproducibly transfer a major
fraction of the radon adsorbed on the charcoal into a vial of
liquid scintillation fluid. The vials of liquid scintillation
fluid containing the dissolved radon are placed in a liquid
scintillation counter and counted for a specified number of
minutes (for example, ten minutes) or until the standard
deviation of the count is acceptable (for example, less than 10
percent).
2.5.4 Equipment
CLS devices made specifically for ambient radon monitoring are
supplied and analyzed by several commercial laboratories.
The following equipment will be required to measure radon with a
CLS device:
* CLS devices properly sealed by the supplier;
* Instruction sheet for occupant, a shipping
container, if sent by mail, a prepaid mailing label
for returning devices to the analytical laboratory;
* Data collection log.
2.5.5 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.
The CLS device should not be deployed if the occupant's schedule
prohibits terminating the measurement at the time selected for
closing the device and returning it to the laboratory.
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2.5.6 Measurement Criteria
The following conditions should exist prior to and during a
measurement period to ensure that the conditions are as
standardized as possible.
* 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 1.3.1, measurements
should be made during winter periods whenever
possible.
* 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. Air conditioning systems that recycle
interior air may be operated.
* 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. The closed house
conditions must be verified and maintained more
rigorously, however, when they are not the normal
living conditions.
* Measurements should not be conducted if severe
storms with high winds or rapidly-changing
barometric pressure are predicted during the
measurement period. Weather predictions available
on local news stations may provide sufficient
information to determine if this condition is
satisfied.
2.5.7 Deployment
2.5.7.1 Timely Deployment. CLS devices should be deployed into
houses within the shelf life specified by the supplier. Until
they are deployed, they should remain tightly sealed to maintain
low background.
2.5.7.2 Location Selection. The following criteria should be
applied to select the location of a CLS device within a room.
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* A position should be selected where the device will
not be disturbed during the measurement period.
* The device 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, and areas of high humidity.
* The device should be placed on a shelf or table at least
75 centimeters (30 inches) above floor level and at
least 10 centimeters (4 inches) from
other objects.
* The device should not be placed close to the outside
walls of the house.
* The device should not be placed in kitchens or
bathrooms.
The protective cap should be removed from the device to begin the
sampling period. The cap must be saved to reseal the device at
the end of the measurement. Inspect the device to see that it
has not been damaged during handling and shipping. It should be
intact, with no charcoal leaking. Place the device with the open
vial mouth up. Nothing should impede air flow around the device.
Accurately fill in the information called for on the data form on
the device. Record the device serial number in a log book along
with a description of the location in the house where the device
was placed. If the device is relocated during the measurement
period the new location and data should be noted in the log book.
2.5.8 Retrieval of Devices
The device should be deployed for the measurement period
(usually less than one week) specified in the instructions
supplied by the analytical laboratory. 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 the actual time of termination must be
documented on the device. In addition, the occupant also should
be instructed to send the device to the laboratory as soon as
possible, preferably the day of sample termination.
At the end of the monitoring period, the device 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 device should be resealed using the original protective cap.
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2.5.9 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 the following:
* The date and start and stop time of the measurement;
* Whether standardized conditions, as previously
specified, are satisfied;
* Exact location of the instrument, on a diagram of
the room and house, if possible;
* Serial number of the device and a code number or
description which uniquely identifies customer,
building, room and sampling position;
* Other easily gathered information that may be
useful, such as the type of house, type of heating
system, and existence of basement or crawl space.
2.5.10 Analysis Requirements
CLS devices should be returned to the supplier's analysis
laboratory as soon as possible following removal from the houses.
The maximum allowable delay time between the end of sampling and
analysis should not exceed the time specified by the supplier's
instructions, especially if sensitivity is an important
consideration. Corrections for radon-222 decay during sampling,
during the interval between sampling and counting, and during
counting will be made by the analysis laboratory. The procedures
followed by an individual supplier's analysis laboratory may in-
clude a correction for moisture as measured by weight gain if
this is significant for their device configuration. The other
correction or calibration factors applied by the analysis
laboratory must include factors accounting for the transfer of
radon from the charcoal to the scintillation fluid under
rigorously controlled conditions, and for the counting efficiency
achieved with the specified scintillation mixture and liquid
scintillation counting system.
2.5.10.1 Sensitivity. The lower limit of detection (LLD)
(Altshuler and Pasternak 1963) should be specified by individual
suppliers for CLS devices exposed and shipped according to their
directions. It'is estimated that LLDs of a few tenths of a
picocurie per liter are achievable for some CLS devices.
(Prichard 1988, Cohen 1988, Grodzins 1988, Perlman 1988). The
LLD should be calculated using the results of the laboratory
control devices discussed in this protocol.
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2.6.10.2 Precision. The coefficient of variation should not
exceed 10 percent (1 sigma) at radon concentrations of 4 pCi/L or
greater. This precision should be monitored and periodically
recorded using the results of the duplicate device analyses
described in Section 2.5.11.3 of this protocol.
2.5.11 Quality Assurance
The quality assurance (QA) program for CLS devices includes four
parts: (1) calibration devices, (2) known exposure (spiked)
devices, (3) duplicate devices, and (4) control devices. The
purpose of a QA program is to identify the accuracy and precision
of the measurements and to ensure that the measurements are not
influenced by exposure from sources outside the environment to be
measured. The quality assurance program should include the
maintenance of control charts, as described by Goldin (Goldin
1984) .
The EPA has established the National Radon Measurement
Proficiency (RMP) Program. This quality assurance program
enables participants to demonstrate their proficiency at
measuring radon and radon decay product concentrations. For
further information please write to the U.S. Environmental
Protection Agency; Radon Division; Mitigation, Prevention, and
Quality Assurance Branch; National RMP Program; 401 M Street, SW;
Washington, D.C., 20460,
2.5.11.1 Calibration Factors. Determination of calibration
factors for charcoal liquid scintillation devices requires
exposure of calibration devices to known concentrations of
radon-222 in a radon exposure chamber at carefully measured radon
concentrations. The calibration factors depend on the exposure
time and may also depend on the amount of water adsorbed by the
device during exposure. Calibration factors should be determined
for a range of different exposure times and, if appropriate,
humidities.
2.5.11.2 Known Exposure Devices. Both suppliers of CLS device
services and large users of these services should submit devices
with known radon exposures (spiked samples) for analysis on a
regular schedule. Known exposure (spiked) devices should be
labeled in the same manner as the field devices to ensure
identical processing. The number of blind calibration devices
submitted for analysis should be a few percent of the total
number of devices analyzed. The results of the spiked device
analysis should be monitored and recorded, and any significant
deviation from the known concentration to which they were exposed
should be investigated.
2.5.11.3 Duplicate (Colocated) Devices. Duplicate devices
should be placed in enough houses to monitor the precision of the
measurements. This usually will be approximately ten percent of
2-35
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the houses to be tested each month or 50, whichever is smaller.
The duplicate devices should be shipped, stored, exposed, and
analyzed under the same conditions. The samples for duplication
should be systematically distributed throughout the entire
population of samples. Groups selling measurements to homeowners
can do this by providing two detectors instead of one to a random
selection of purchasers with instructions to place them side-by-
side. Consideration should be given to providing some means to
ensure that the duplicate devices are not separated during the
measurement period. Data from duplicate devices should be
evaluated using the procedures described by Goldin in section 5.3
of his report (Goldin 1984). The method should achieve a
coefficient of variation of 10% (1 sigma) or less at radon
concentrations of 4 pCi/L or greater. Consistent failure in
duplicate agreement may indicate a problem in the measurement
process that should be investigated.
2.5.11.4 Control Devices.
2.5.11.4.1 Laboratory Control Devices. The laboratory
background level for each batch of CLS devices should be
established by each supplier. Suppliers should measure the
background of a statistically significant number of unexposed CLS
devices that have been processed according to their standard
operating procedures (laboratory blanks). This value normally is
subtracted by the analysis laboratory or supplier from the
results obtained from the field devices to arrive at the net
readings used to calculate the sample radon concentrations.
2.5.11.4.2 Field Control Devices. Field control devices (field
blanks) should consist of a minimum of five percent of the
devices that are deployed every month, or 25, whichever is
smaller. Commercial users should set these aside from each
shipment, keep them sealed and in a low radon (less than 0.2
pCi/L) environment, label them in the same manner as the field
devices, and send them back to the supplier with one shipment
each month for analysis. These control devices measure the
background exposure that may accumulate during shipment or
storage, and the results should be monitored and recorded. If
one or only a few of the field control canisters have
concentrations significantly greater than the LLD established by
the supplier it may indicate defective devices or procedures. If
most of the controls have concentrations significantly greater
than the LLD, the average value at the field controls should be
subtracted from the reported field device concentration and the
supplier notified of a possible problem.
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2.6 INTERIM PROTOCOL FOR USING EVACUATED SCINTILLATION CELLS TO
MAKE THREE-DAY INTEGRATED MEASUREMENTS OF INDOOR RADON
CONCENTRATIONS.
2.6.1 Purpose
This protocol provides guidance for using an evacuated
scintillation cell to obtain accurate and reproducible
measurements of indoor radon air concentrations integrated over a
3-day period. Following the protocol will help ensure uniformity
among measurement progreims and allow valid comparisons of
results. Measurements made in accordance with this protocol will
produce screening measurements of radon concentrations
representative of closed-house conditions. Such screening
measurements have a smaller variability and are more reproducible
than measurements made when the house conditions are not
controlled.
If measurements with this device are for other than a screening
measurement, the investigator should follow guidance provided by
EPA in "Interim Protocols for Screening and Follow-up Radon and
Radon Decay Product Measurements" (EPA 520/1-86-014-1, 1987).
2.6.2 Scope
This protocol covers, in general terms, the equipment,
procedures, and quality control objectives to be 'used in perform-
ing the measurements. It is not meant to replace an instrument
manual, but rather provides guidelines to be adopted into
standard operating procedures. Questions about these guidelines
should be directed to the U.S. Environmental Protection Agency
(EPA), Office of Radiation Programs, Radon Division (ANR-464),
Problem Assessment Branch, 401 M Street, S.W., Washington, D.C.
20460.
2.6.3 Method
The three-day evacuated cell radon collectors are Lucas-type
scintillation cells that have been outfitted with a restricter
valve attached to the main valve. Samples are collected by
opening the valve on an evacuated cell. The restricter valve is
set so that the cell fills from a 30-inch Hg vacuum to about 80
percent of its capacity over a three-day period. At the end of
the measurement period, the valve is closed and returned to the
analysis laboratory. Since the volume of the cell is known, the
exact volume of filtered air collected over the three-day
measurement period can tae calculated from the vacuum gauge
reading at the end of the sampling period.
The sample is analyzed on an alpha scintillation counter. Prior
to counting, the pressure in the cell is brought to one
atmosphere by adding radon-free (aged) air so that the sample is
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analyzed under the same conditions that prevailed during calibra-
tion of the cell. The sample is counted no sooner than six hours
after the end of the measurement period to allow radon and its
daughter products to grow into equilibrium and to allow any radon
daughter products that may have been collected to decay.
During the three-day sampling period, some of the radon that has
been collected decays. The midpoint of the sampling period
cannot be used for the decay correction factor, however, because
the airflow into the cell is greater during the initial time of
sampling. The fraction of radon that decays must therefore be
calculated from the shape of a plot of percent fill versus time.
This must be measured for each cell. This factor is applied as a
correction during data reduction.
Since this method accumulates radon over a period of time for
subsequent analysis, it is not a true integrating method. Radon
peaks occurring early in the sampling period will leave less
radon for analysis than the same size peak occurring toward the
end of the sampling period.
2.6.4 Equipment
The following equipment will be required to measure radon with an
evacuated cell:
* An evacuated cell with restricter valve and vacuum
gauge prepared by the supplier;
* Instruction sheet, a shipping container and, if it
is to be mailed, a prepaid mailing label for
returning the detector to the laboratory;
2.6.5
Data collection log.
Predeplovment Considerations
The measurement should not be made if the occupant is planning
remodeling, changes in the heating, ventilating, and air
conditioning system, or other modifications that may influence
the radon concentration during the measurement period.
The evacuated cell device should not be deployed if the
occupant's schedule prohibits terminating the measurement at the
time selected for closing the valve and returning the cell to the
laboratory.
2.6.6 Measurement Criteria
The following house conditions should exist prior to and during a
measurement to standardize the measurement conditions as much as
possible.
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* 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 others discussed in Section 1.3.1,
measurements should be made during winter periods
whenever possible.
* Internal-external air exchange systems (other than
a furnace) such as high-volume attic and window
fans should not be operated during the measurement
and for at least 12 hours before the measurement is
initiated. Air conditioning systems that recycle
interior air may be operated.
* 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. The closed house
conditions must be more rigorously verified and
maintained, however, when they are not the normal
living conditions.
* Measurements should not be conducted if severe
storms with high winds or rapidly changing
barometric pressure are predicted during the
measurement period. Weather predictions available
on local news stations may provide sufficient
information to determine if this condition is
satisfied.
2.6.7 Deployment
2.6.7.1 Timely Deployment. Evacuated cell devices should be
deployed within the period specified by the supplier. Until they
are deployed, they should remain tightly sealed to maintain
maximum sensitivity and accuracy.
2.6.7.2 Location Selection. The following criteria should be
applied to select the location of an evacuated cell device within
a room.
* A position should be selected where the device will not
be disturbed during the measurement period.
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* The device should not be placed near drafts caused by
HVAC vents, windows, and doors.
* The device should be placed on a shelf or table at least
75 centimeters (30 inches) above floor level and at
least 10 centimeters (4 inches) from other objects.
* The device should not be placed close to the outside
walls of the house.
To deploy the evacuated cell device, the reading of the attached
vacuum gauge must be recorded on the log sheet along with the
start date and time for the sample. The sample collection is
started by opening the main valve according to the supplier's
instructions.
2.6.8 Retrieval of Devices
The device should be deployed for the measurement period
specified in the instructions supplied by the analytical
laboratory. If the occupant is terminating the sampling, the
instructions given to the occupant should tell the occupant when
and how to terminate the sampling period and should indicate that
the actual time of termination must be documented on the data
form. In addition, the vacuum gauge reading must be recorded on
the data form after the sampling valve is closed. The occupant
also should be instructed to send the device to the laboratory as
soon as possible, preferably the day of sample termination.
At the end of the monitoring period, the device should be
inspected for any deviation from the conditions described in the
log book at the time of deployment. Any changes should be noted.
2.6.9 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 the following:
* The date and start and stop time of the measurement;
* Whether standardized conditions, as previously
specified, are satisfied;
* Exact location of the device, on a diagram of the
room and house, if possible;
* Other easily gathered information that may be useful,
such as the type of house, type of heating system, and
existence of basement or crawl space;
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* Serial number and supplier of the evacuated cell device
along with a code number or description which uniquely
identifies customer, building, room, and sampling
position.
2.6.10 Analysis Requirements
Evacuated cell devices should be returned to the supplier's
analysis laboratory as soon as possible following removal from
the houses. The maximum allowable delay time between the end of
sampling and analysis should not exceed the time specified by the
supplier's instructions especially if sensitivity is an important
consideration. Corrections for the radon-222 decay during
sampling, during the interval between sampling and counting, and
during counting will be made by the analysis laboratory.
2.6.10.1 Sensitivity. The lower limit of detection (LLD)
(Altshuler and Pasternack 1963) should be specified by individual
suppliers for evacuated cell devices exposed and shipped
according to their directions. It is estimated that LLDs of a
few tenths of a picocurie per liter are achievable with these
devices. The LLD should be calculated using the results of the
laboratory control devices. A commercial supplier of evacuated
cell devices has reported that for samples analyzed within four
days of collection, concentrations as low as 0.2 pCi/L can be
measured to within 25% and concentrations of 1 pCi/L can be
measured to within 10%.
2.6.10.2 Precision. The coefficient of variation should not
exceed ten percent (1 sigma) or less at radon concentrations of 4
pCi/L or greater. This precision should be monitored and
periodically recorded using the results of the duplicate device
analyses described in Section 2.6.11.3 of this protocol.
2.6.11 Quality Assurance
The quality assurance program for evacuated cell devices includes
four parts: (1) calibration devices, (2) known exposure (spiked)
devices, (3) duplicate devices, and (4) control devices. The
purpose of this program is to identify the accuracy and precision
of the measurements and to ensure that the measurements are not
influenced by exposure from sources outside the intended
structure. The quality assurance program should include the
maintenance of control charts as described by Goldin (Goldin
1984).
The EPA has established the National Radon Measurement
Proficiency (RMP) Program. This quality assurance program
enables participants to demonstrate their proficiency at
measuring radon and radon decay product concentrations. For
further information please write to the U.S. Environmental
Protection Agency; Radon Division; Mitigation, Prevention, and
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Quality Assurance Branch; National RMP Program; 401 M Street, SW;
Washington, D.C., 20460.
2.6.11.1 Calibration Factors. Determination of calibration
factors for evacuated cell devices requires exposure of
calibration devices to known concentrations of radon-222 in a
radon exposure chamber at carefully measured radon
concentrations. Since the cells are subject to shipping and
handling they should be periodically recalibrated at radon levels
similar to those found in tested houses. Scintillation counting
systems used to count exposed cells should either be the system
used to calibrate the cell or one calibrated against that system.
2.6.11.2 Known Exposure Measurements. Both suppliers of
evacuated cell device services and large users of these services
should submit devices with known radon exposures (spiked samples)
for analysis on a regular schedule. Known exposure (spiked)
devices should be labeled in the same manner as the field devices
to assure identical processing and avoid bias. The number of
blind calibration devices submitted for analysis should be a few
percent of the total number of devices analyzed. The results of
the calibration device analysis should be monitored and recorded,
and any significant deviation from the known concentration to
which they were exposed should be investigated.
2.6.11.3 Duplicate (Colocated) Devices. Duplicate devices
should be placed in enough houses to monitor the precision of the
measurements. This usually will be approximately ten percent of
the houses to be tested each month or 50, whichever is smaller.
The duplicate devices should be shipped, stored, exposed, and
analyzed under the same conditions, and not identified as
duplicates to the processing laboratory. The samples selected
for duplication should be systematically distributed throughout
the entire population of samples. Groups selling measurements to
homeowners can do this by making two measurements side-by-side in
a random selection of homes. Data from duplicate devices should
be evaluated using the procedures described by Goldin in section
5.3 of his report (Goldin 1984). The method should achieve a
coefficient of variation of 10 percent (1 sigma) or less for
radon concentrations of 4 pCi/L or greater. Consistent failure
in duplicate agreement may indicate a problem in the measurement
process that should be investigated.
2.6.11.4 Control Devices.
2.6.11.4.1 Laboratory Control Devices. The background level for
each evacuated cell device should be established by each
supplier. Suppliers should measure the background of each cell
before each use or periodically, with a frequency based on
experience. The background for each cell should be subtracted
from the field readings taken with that cell in order to
calculate the radon concentrations of the sample.
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2.6.11.4.2 Field Control Devices. Field control devices (field
blanks) should consist of a minimum of five percent of the
devices that are deployed every month or 25, whichever is
smaller. Commercial users should set these aside from each
shipment, keep them sealed and in a low radon (less than 0.2
pCi/L) environment, label them in the same manner as the field
devices, and send them back to the supplier with one shipment
each month for analyses. It will be clear to the analysis
laboratory that these cells are blanks because they will still
indicate full vacuum but it is not feasible to fill these cells
with radon-free air in the field. Careful initial and final
readings of the vacuum gauges on these control cells and the cell
background counts on analysis will be of some use in detecting an
occasional leaking cell, but any background detected is not
relevant to the measured field sample concentrations.
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2.7 INTERIM PROTOCOL FOR USING PUMP/COLLAPSIBLE BAG DEVICES
TO MEASURE RADON CONCENTRATIONS
2.7.1 Purpose
This protocol provides guidance for using a pump with a
collapsible bag as a device 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 screening measurements
of radon concentration representative of closed-house conditions.
Such screening measurements have a smaller variability and are
more reproducible than measurements made when the house
conditions are not controlled.
If measurements with these devices are for a purpose other than a
screening measurement, the investigator should follow guidance
provided by EPA in "Interim Protocols for Screening and Follow-up
Radon and Radon Decay Product Measurements" (EPA 520/1-86-014-1,
1987) .
2.7.2 Scope
This protocol covers, in general terms, the equipment,
procedures, and quality control objectives to be used in perform-
ing the measurements. It is not meant to replace an instrument
manual, but rather provides guidelines to be adopted into
standard operating procedures. Questions about these guidelines
should be directed to the U.S. Environmental Protection Agency
(EPA), Office of Radiation Programs, Radon Division (ANR-464),
Problem Assessment Branch, 401 M Street, S.W., Washington, D.C.,
20460.
2.7.3 Method
One of the older and simpler methods of making an integrated
measurement of the concentration of radon over a period of time
is to collect a sample of ambient air in a radon proof container
over the desired sampling time period and measure the resulting
radon concentration in the container.
A practical method is to use a small pump with a very low and
uniform flow rate to pump ambient air into a collapsible radon
proof bag (Sill 1977). After the desired sampling period the
concentration of radon in the bag can be analyzed by any of the
standard methods such as the scintillation cell grab sample
2-44
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protocol (Section 2.8) using the appropriate radon decay
correction factors (Appendix A). The main purpose of the
collapsible bag is to avoid variation in pump flow rate due to
build up of back pressure in a container. Suitable bags with a
measured very low loss of radon by diffusion through the bag have
been made of laminated Mylar, aluminized laminated Mylar, and
Tedlar". The pump flow rate is not critical as long as it is
suitable for the size of the bag and the sample duration, but
variation of the flow rate over the collection time period of the
sample will affect the accuracy of the measurement. A number of
suitable battery and/or charger operated pumps with controlled
flow rates are commercially available.
Since this method accumulates radon over a period of time for
subsequent analysis it is not an integrating method. Radon peaks
occurring early in the sampling period will leave less radon for
analysis than the same size peak occurring toward the end of the
sampling period.
2.7.4 Equipment
The following equipment will be required to conduct measurements
using the pump/collapsible bag method.
* Pump with a suitable uniform flow rate. The materials
of the pump should not absorb or off-gas any substantial
amount of radon.
* Collapsible bag of tested low radon loss material.
• Data collection log.
2.7.5 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.
2.7.6 Measurement Criteria
The following conditions should exist during a measurement period
to ensure that the conditions are as standardized as possible.
* 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
2-45
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conditions during the winter in northern climates. For
this reason and others discussed in Section 1.3.1,
measurements should be made during winter periods
whenever possible. ,
* Internal-external air exchange systems (other than a'
furnace) such as high-volume attic and window fans
should not be operated during the measurement and for at
least 12 hours before the measurement is initiated. Air
conditioning systems that recycle interior air may be
operated.
* 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. The closed house
conditions must be verified and maintained more
rigorously, however, when they are not the normal
living conditions.
* Measurements should not be conducted if severe
storms with high winds or rapidly changing
barometric pressures are predicted during the
measurement period. Weather predictions available
on local news stations may provide sufficient
information to determine if this condition is
satisfied.
2.7.7 Location Selection
The following criteria should be applied to select the location,
of a pump/collapsible bag device within a room.
* A position should be selected where the device will ,
not be disturbed during the measurement period and
where there is adequate room for the device.
* The device 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.
* The air sampled should be from at least 75
centimeters (30 inches) above floor level and at
least 10 centimeters (4 inches) from other objects.
* The air sample should not be from close to the
outside wall of the house.
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2.7.8 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 the following:
• The date and start and stop time of the measurement;
* Serial numbers of bags, pumps, and equipment used
for analysis of the radon concentration;
* Whether standardized conditions, as previously
specified, are satisfied;
* Exact location of the instrument, on a diagram of
the room and house, if possible;
• Other easily gathered information that may be useful,
such as the type of house, type of heating system, and
existence of basement or crawl space.
2.7.9 Analysis Requirements
If the radon concentration in the collapsible bag is to be
analyzed on site, the appropriate radon grab sample protocol
(Section 2.8) should be followed.
If the radon concentration is to be measured by an analysis
laboratory, the bag should be delivered to the laboratory as soon
as possible following completion of sampling, especially if low
concentrations are being measured.
2.7.9.1 Sensitivity. The lower limit of detection (LLD) for a
pump/collapsible bag device will depend on the method used to
analyze the contents of the bag. If a scintillation cell method '
is used, an LLD of a few tenths of a picocurie per liter should
be possible.
2.7.9.2 Precision. The coefficient of variation for split
measurements (from the same bag) using the scintillation cell
analysis method should not exceed 10 percent (1 sigma) at radon
concentrations of 4 pCi/L or greater.
2.7.10 Quality Assurance
The quality assurance program for radon measurements using the
pump/collapsible bag method includes calibration and duplicate
measurements. The quality assurance program should include the
maintenance of control charts, as described by Gdldin (Goldin
1984) .
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The EPA has established the National Radon Measurement
Proficiency (RMP) Program. This quality assurance program
enables participants to demonstrate their proficiency at
measuring radon and radon decay product concentrations. For
further information please write to the U.S. Environmental
Protection Agency; Radon Division; Mitigation, Prevention, and
Quality Assurance Branch; National RMP Program; 401 M Street, SW;
Washington, B.C., 20460.
2.7.10.1 Calibration. If a scintillation flask method of
measuring the radon concentrations is used, the appropriate
procedure on calibration given in Section 2.8 should be followed.
2.7.10.2 Duplicate Samples. Duplicate samples should be
collected with sufficient frequency to test the precision of the
procedure. This number should be at least ten percent of the
total samples collected. Care should be taken to ensure that the
samples are duplicates to the greatest extent possible.
Duplicate samples should be taken in close proximity and away
from drafts. The samples selected for duplication should be
systematically distributed throughout the entire population of
samples. Data from duplicate samples should be evaluated using
the procedures described by Goldin in section 5.3 of his report
(Goldin 1984). Consistent failure in duplicate agreement may
indicate a problem in the measurement process that should be
investigated.
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2.8
PROTOCOL FOR THE DETERMINATION OF INDOOR RADON
CONCENTRATION BY GRAB SAMPLING
2.8.1 Purpose
This protocol provides guidance for using grab sampling
techniques 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 closed-house conditions. (See Section 1.3.2.)
Such screening measurements have a smaller variability and are
more reproducible than measurements made when the house
conditions are not controlled.
The results of grab sampling are greatly influenced by conditions
that exist in the house during and for up to 12 hours prior to
the measurement. It is therefore especially important when
making grab measurements to conform to the closed-house
conditions for 12 hours before the measurement. Grab techniques
are not recommended for follow-up measurements made to estimate
health risks or to determine the need for remedial action.
2.8.2 Scope
This protocol covers, in general terms, the equipment,
procedures, and quality control objectives to be used in
performing the measurements. It is not meant to replace an
instrument manual, but rather provides guidelines to be adopted
into standard operating procedures. Questions about these
guidelines should be directed to the U.S. Environmental
Protection Agency (EPA), Office of Radiation Programs, Radon
Division (ANR-464), Problem Assessment Branch, 401 M Street,
S.W., Washington, D.C. 20460.
2.8.3 Method
There are two grab sampling methods covered by this protocol. In
the first 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 flask 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 air sample interacting with the zinc
sulfide coating. The number of pulses is proportional to the
radon concentration in the flask. The flask is counted about
four hours after filling to allow the short-lived radon decay
products 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.
2-49
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A second method covered by this protocol uses air pumped through
activated carbon to collect the sample. A charcoal filled
cartridge is placed into a sampler and air is pumped through the
carbon cartridge. The pump-carbon cartridge is not flow
dependent but must remain operational at the sampling location
until the charcoal collects enough radon to be in equilibrium
with the radon at the sampling location. A sampling duration of
one hour has been found to be optimal for most systems. The
cartridge must be weighed prior to and after sampling so a
correction can be applied for the reduced sensitivity of the
charcoal due to absorbed water. The cartridges are analyzed by
placing them on a sodium iodide gamma scintillation system or a
germanium gamma detector. The pump-carbon cartridge system must
be calibrated by analyzing cartridges pumped with known
concentrations of radon in a qualified facility.
2.8.4 Equipment
2.8.4.1 Flask Grab Sampling. The equipment needed for flask
sampling includes the following:
* A scintillation flask or flasks to be filled at the
site;
* A"pump to flow air through the cell or to evacuate the
cell (depending on the valve arrangement on the cell in
use) ;
* A clock to measure time from collection to counting;
* A filter and filter holder to attach to the air inlet
valve of the cell;
* A data collection log.
The equipment required for analyzing the air sample includes
the following:
* A photomultiplier tube and high-voltage assembly in a
light-tight chamber;
* A sealer-timer for registering pulses from the
photomultiplier tube assembly and timing the counting
interval;
* A National Bureau of Standards (NBS)-traceable alpha
check source and scintillation disc;
* A calibration flask or cell;
* A vacuum pump and flask flushing apparatus;
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* Aged air or nitrogen for flushing counting flasks.
2.8.4.2 Pump-Carbon Sampling. The equipment needed for pump-
carbon samplers includes the following:
* Charcoal cartridge with both apertures sealed with
protective metallic or other impermeable covers;
*
*
*
A pump to pull air through the cartridge;
A data collection log; , ,..,,
Sodium iodide gamma scintillation detector and analyzer;
* Analytic scale capable of weighing the small difference
in weight (up to several grams) due to water adsorbed by
the charcoal.
Laboratory analysis of the saturated pump-carbon cartridge is
performed using a sodium iodide gamma scintillation detector to
count the gamma rays emitted by the radon decay products adsorbed
on the carbon. The detectors may be used in conjunction with a
multichannel gamma spectrometer or with a single-channel analyzer
calibrated to include the appropriate gamma energies.
2.8.5 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 cartridge or flask should be determined prior to sampling.
This may be done using the procedures described in Appendix A for
flask counting.
For highly accurate flask measurements, it is necessary to
standardize flask pressure prior to counting, because the path
lengths of alpha particles are a function of air density. For
example, a flask calibrated at sea level and used to count a
sample collected at Grand Junction, Colorado (1370 meters above
sea level) would overestimate the radon activity of the sample by
about nine percent (George 1983). 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 (George 1983).
2.8.6 Measurement Criteria
The following conditions should exist prior to and during the
sampling to ensure that the conditions are as standardized as
possible.
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* 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 others discussed in Section 1.3.1,
measurements should be made during winter periods
whenever possible.
* Internal-external air exchange systems (other than
a furnace) such as high-volume attic and window
fans should not be operated during the measurement
and for at least 12 hours before the measurement is
initiated. Air conditioning systems that recycle
interior air may be operated.
* 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. The closed house
conditions must be verified and maintained more
rigorously, however, when they are not the normal
living conditions.
* Short-term measurement should not be conducted if
severe storms with high winds or rapidly changing
barometric pressure are predicted during the
measurement period. Weather predictions available
on local news stations may provide sufficient
information to determine if this condition is
satisfied.
2.8.7 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 the following:
* The time and date of the start and end of the
measurement;
* Whether standardized conditions, as previously
specified, are satisfied;
* Exact location of the measurement, on a diagram, of the
room and house, if possible;
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* Other easily gathered information that may be
useful, such as the type of house, type of heating
system, existence of crawl space or basement, and
operation of humidifiers, air filters, or
electrostatic precipitators?
* Serial numbers of flasks, cartridges, and counting
equipment.
2.8.8 Sampling Operations
2.8.8.1 Location Selection. The following criteria should be
applied to select the location of the measurement within a room.
* The sample should not be collected near drafts caused by
HVAC vents, windows, doors, etc. Avoid locations near
excessive heat, such as fireplaces or in direct, strong
sunlight.
* Measurements should be made at least 75 centimeters (30
inches) from the floor and at least 10 centimeters (4
inches) from other objects.
* The measurement should not be made close to the outside
walls of the house.
* In general, measurements should not be made in kitchens
or bathrooms.
2.8.8.2 Sampling. All air samples drawn into scintillation
flasks must be filtered to remove radon decay products and other
airborne radioactive particulates. Filters may be reused many
times as long as they remain undamaged.
For collection of a sample using a single-valve flask (Lucas
type), the flask is evacuated to at least 25 inches of mercury,
the filter is attached to the flask, and the valve is opened
allowing the flask to fill with air. Allow at least ten seconds
for the flask to completely fill. To ensure good vacuum at the
time of sampling, the flask may be evacuated using a small hand
operated pump in the room being sampled. It is good practice to
evacuate the flask 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 demons-
trated that the flasks and valves do not leak, it is acceptable
to evacuate the flasks 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, flow-through type flask, 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 ten
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complete air exchanges through the flask.
close both valves.
Stop the pump and
Sampling using the pump-carbon cartridge method is accomplished
by opening a prepared sealed cartridge and attaching it to the
sampling pump. The pump should draw air through the cartridge at
approximately the rate used in calibrating the system. Sampling
should continue until the charcoal collects enough radon to be in
equilibrium with the radon at the sampling site. A one-hour
sampling period is typical for most pump-carbon cartridge
systems.
All pertinent sampling information should be recorded after
completing the sample, including the date and time, location,
flask/cartridge number, name of person collecting the sample, and
any other significant conditions within the house or notes on the
weather conditions. The detectors should be carefully packaged
for return to the counting location so that the samples will not
be lost due to breakage, valves being opened, or loss of cartri-
dge integrity.
2.8.9 Counting and Calculations
2.8.9.1 F-lask Sampling. Flasks 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 flask to be counted is placed on the photomultiplier tube,
the cover placed over the flask, and the system allowed to dark
adapt. The flask then may be counted for a sufficient period to
collect an adequate number of counts for good counting statistics
in relation to the system background counts. L
2.8.9.2 Pump-Carbon Sampling. Cartridges should not be analyzed
for at least four hours after the end of sampling to allow for
ingrowth of the radon decay products. Cartridges then should be
analyzed in a laboratory following removal from the sampling
location. The cartridge should be weighed, and if necessary, a
correction should be applied for the increase in weight due to
moisture absorption. 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. The
cartridge should be analyzed on a calibrated sodium iodide gamma
scintillation system or a germanium gamma detector.
2.8.10 Flask Flushing and Storage
After the flasks have been counted and data are satisfactorily
recorded, the flasks must be flushed with aged air or nitrogen to
remove the sample. Flow-through flasks are flushed with at least
ten volume exchanges at a flow of about two liters a minute.
Flasks with single valves are evacuated and refilled with aged
2-54
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air or nitrogen at least five times. The flasks are left filled
with aged air or nitrogen and allowed to sit overnight before
being counted for background. If an acceptable background is
obtained, the flask is ready for reuse.
2.8.11
Results
2.8.11.1 Sensitivity. The sensitivity of the flask method is
dependent on the volume of the cell being used. However,
sensitivities of 0.1 pCi/L are achievable (George 1980, George
1983). For the pump-carbon method, the lower limit of detection
should be 1.0 pCi/L or less. This can normally be achieved with
a counting time of up to 30 minutes.
2.8.11.2 Precision. The coefficient of variation for duplicate
flask samples should not exceed 10 percent (1 sigma) at radon
concentrations of 4.0 pCi/L or more. This precision should be
monitored using the resxilts of duplicate measurements described
in this protocol. Sources of error in the procedure may result
from improper cell calibration, leaking flasks, and improperly
calibrated counting equipment. The coefficient of variation for
the pump-carbon method should not exceed 10 percent (1 sigma) at
radon concentrations of 4.0 pCi/L or more.
2.8.12 Quality Assurance
The quality assurance program for radon measurements using grab
sampling includes calibration, duplicate, and background
measurements.
The EPA has established the National Radon Measurement
Proficiency (RMP) Progrctm. This quality assurance program
enables participants to demonstrate their proficiency at
measuring radon and radon decay product concentrations. For
further information plecise write to the U.S. Environmental
Protection Agency; Radon Division; Mitigation, Prevention, and
Quality Assurance Branch; National RMP Program; 401 M Street, SW;
Washington, B.C., 20460.
2.8.12.1 Calibration.
2.8.12.1.1 Flask Calibration. The flask 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 (George 1983).
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 flask should be counted in each
counter system each day to demonstrate proper operation prior to
counting any samples.
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A separate calibration factor must be obtained for each flask in
the counting system. This is done by filling each flask with
radon of a known concentration and counting the flask to deter-
mine the conversion factor or 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 (George 1976; Lucas 1957;
Beckman 1975). Recalibration of each cell should be done every
six months.
2.8.12.1.2 Pump-Carbon Cartridge Calibration. The pump-carbon
cartridge method must be calibrated in a radon calibration
chamber to establish a calibration factor for a specific
cartridge model. Samples should be taken at different humidities
and temperatures to establish correction factors. Calibration
should be carried out at several flow rates and exposure times to
verify the acceptable limits. Calibration factors must be
established with the identical gamma counting system and counting
geometry used in sampling.
2.8.12.2 Duplicates. Duplicate samples should be collected with
sufficient frequency to test the precision of the procedure.
This number should be at least ten percent of the total radon
grab samples collected or 50 per month, whichever is smaller.
Care should be taken to ensure that the samples are duplicates to
the greatest extent possible. Duplicate samples should be taken
in close proximity and away from drafts. The samples selected
for duplication should be systematically distributed throughout
the entire population of samples. Data from duplicate samples
should be evaluated using the procedures described by Goldih in
section 5.3 of his report (Goldin 1984). The method should
achieve a coefficient of variation of 10 percent or less for the
flask and 10 percent or less for the cartridge. Consistent
failure in duplicate agreement may indicate a problem in the
measurement process that should be investigated.
2.8.12.3 Backgrounds. A background count for each cell is
determined prior to measurement, as described in Appendix A.
When the pump-carbon cartridge method is used, the background of
the carbon should also be routinely assessed.
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Section 3: RADON DECAY PRODUCT MEASUREMENT PROTOCOLS
3.1 PROTOCOL FOR USING CONTINUOUS WORKING LEVEL MONITORS
TO MEASURE INDOOR RADON DECAY PRODUCT CONCENTRATIONS
3.1.1 Purpose
This protocol provides guidance for using continuous working
level monitors (CWLM) to obtain accurate and reproducible
measurements of indoor radon decay product 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
screening measurements of radon decay product (RDP) concentra-
tions representative of closed-house conditions. Such screening
measurements have a smaller variability and are more reproducible
than measurements made when the house conditions are not
controlled.
If measurements with CWLMs are for a purpose other than a
screening measurement, the investigator should follow guidance
provided by EPA in "Interim Protocols for Screening and Follow-up
Radon and Radon Decay Product Measurements" (EPA 520/1-86-014-1,
1987).
3.1.2 Scope
This protocol covers, in general terms, the sample collection and
analysis method, the eguipment needed, and the quality control
objectives of measurements made with a CWLM. It is not meant to
replace an instrument manual, but rather provides guidelines that
should be incorporated into standard operating procedures.
Questions about these guidelines should be directed to the U.S.
Environmental Protection Agency (EPA), Office of Radiation
Programs, Radon Division (ANR-464), Problem Assessment Branch 401
M Street, S.W., Washington, D.C., 20460.
3.1.3 Method
A CWLM 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 radon decay products 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. Some CWLMs are capable of measuring individual radon
and thoron decay products, and others can measure the percentage
of thoron decay products. The event count is directly
proportional to the number of alpha particles emitted by the
3-1
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radon decay products on the filter. The unit typically contains
a microprocessor that stores the number of counts and elapsed
time. The CWLM 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.
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
* Verify that a new filter has been installed and the
input parameters and clock are set properly,
* 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, and
* Verify the operation of the pump.
When feasible, the unit should be checked after every 168 hours
of operation 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 radon decay product
concentration. At this time, the correct operation of the pump
also should 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 standardize the measurement conditions as much as
possible.
* 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
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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 others discussed in Section 1.3.1,
measurements should be made during winter periods
whenever possible.
* Internal-external air exchange systems (other than a
furnace) such as high-volume attic and window fans
should not be operated during the measurement and'fof,at
least 12 hours before the measurement is initiated. Air
conditioning systems that recycle interior air may be
operated.
* 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. The closed house conditions must be verified
and maintained more rigorously, however, when they are
not the normal living conditions.
* Grab measurements should not be conducted if severe
storms with high winds or rapidly changing barometric
pressure are predicted. Weather predictions available
on local news stations may provide sufficient
information to determine if this condition 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.
* The measurement should not be made near drafts caused by
heating, ventilating and air conditioning vents, doors,"
windows, and fireplaces.
* The measurement location should not be close to the
outside wails of the house.
* The unit should be placed on a table or stool so that
the air intake is at least 75 centimeters (30 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 than 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 record enough information about the measurement in a
permanent log so that data interpretations and comparisons can be
made. This will include the following:
* The time and date of the start and end of the
measurement;
* Serial number of the CWLM and calibration factor used;
* Whether standardized conditions, as specified, are
satisfied;
* Exact location of the instrument, on a diagram if
possible;
* 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.
3.1.8 Results
3.1.8.1. Lower Limit of Detection.
LLD of 0.005 WL or less.
Most CWLMs are capable of an
3.1.8.2. Precision. Most CWLMs can acheive a coefficient of
variation of less than 10% (1 sigma) at radon concentrations of 4
pCi/L or greater.
3.1.9 Quality Assurance
The elements of a quality assurance program for the CWLM are as
follows.
* Calibration in a radon decay product exposure
calibration chamber before being put in service and at
least every 6 months, and after instrument repair or
modification.
* Checks using an Am-241 or Th-230 similar-energy alpha
check source (before and after each measurement).
* Background count-rate checks (after at least every 168
hours of operation).
* When two or more CWLMs are available, the coefficient of
variation of the measurements can be estimated by
operating the CWLMs side by side. The analysis of
duplicate results should follow the methodology
described by Goldin in section 5.3 of his report (Goldin
1984) .
3-4
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The quality assurance program should include the maintenance of
control charts, as described by Goldin (Goldin 1984).
The EPA has established the National Radon Measurement
Proficiency (RMP) Program. This quality assurance program
enables participants to demonstrate their proficiency at
measuring radon and radon decay product concentrations. For
further information please write to the U.S. Environmental
Protection Agency; Radon Division; Mitigation, Prevention, and
Quality Assurance Branch; National RMP Program; 401 M Street, SW;
Washington, D.C., 20460.
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3.2 PROTOCOL FOR USING RADON PROGENY INTEGRATING SAMPLING
—UNITS (RPISU) 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 inter-
comparison of results. Measurements made in accordance with this
protocol will produce screening measurements of radon decay
product (RDP) concentrations representative of closed-house
conditions. Such screening measurements have a smaller
variability and are more reproducible than measurements made when
the house conditions are not controlled.
If measurements with RPISUs are for a purpose other than a
screening measurement, the investigator should follow guidance
provided by EPA in "Interim Protocols for Screening and Follow-up
Radon and Radon Decay Product Measurements" (EPA 520/1-86-014-1,
1987).
3.2.2 Scope
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 rather provides guidelines to be adopted into
standard operating procedures. Questions about these guidelines
should be directed to the U.S. Environmental Protection Agency ;
(EPA), Office of Radiation Programs, Radon Division (ANR-464),
Problem Assessment Branch, 401 M Street, S.W., Washington, D.C.,
20460.
3.2.3 Method
3.2.3.1 TLD RPISU. There are two types of RPISUs. The TLD type
contains an air sampling pump that draws a continuous uniform
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. This RPISU is intended for a
sampling period .of three days to a few weeks.
Analysis of the detector TLDs is performed in a laboratory using
a thermoluminescent dosimeter reader. Interpretation of the
results of this measurement requires a calibration for the
detector and the analysis system based on exposures to known
concentrations of radon decay products.
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3.2.3.1 ATP RPISU. The second type of RPISU consists of an air
sampling pump and a detector assembly. The air sampling pump
draws a continuous uniform flow of air through a filter in the
detector assembly where the radon decay products are deposited.
Opposed to the side of the filter where the RDPs are deposited is
a cylinder with three collimating cylindrical holes. Alpha
particles emitted from the radon decay products on the filter
pass through the collimating holes and through different
thicknesses of energy absorbing film before impinging on a disc
of alpha track detecting plastic film (LR-115). Analysis of the
number of alpha particle tracks in each of the three sectors of
the film allows the determination of the number of alpha
particles derived from Reidium A (Po-218) and Radium C1 (Po-214) .
This feature allows the determination of the equilibrium factor
for the radon decay products. This type of RPISU is intended for
a sampling period of three days to a few weeks.
Etching and counting of the alpha track assembly is carried out
by mailing the detector film to the analysis laboratory.
Interpretation of the results of this measurement requires a
calibration for the detector and the analysis system based on
exposure to known concentrations of radon decay products.
Both types of RPISUs are true integrating instruments if the pump
flow rate is uniform throughout the sampling period.
3.2.4 Equipment
Both types of RPISU sampling systems include the sampling pump
and the detector assembly. Sampling with the TLD-type RPISU
requires either a fresh detector assembly or fresh TLD chips to
be inserted in the detector assembly. Sampling with the alpha
track detecting RPISU requires a fresh film disc. An air flow
rate meter should be available for checking flow rates with
either RPISU, and spare filters should be available as replace-
ments as needed.
3.2.5 Predeployment Considerations
Prior to installation in the house, the pump should be checked to
ensure that it is operable and capable of maintaining a uniform
flow through the detector assembly. Extra pump assemblies should
be available during deployment in case a problem is encountered.
Arrangements should be made with the occupant of the house to
ensure that entry to the house can be made at the time of
installation, 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 prior to and during a
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measurement to standardize the measurement conditions as much as
possible.
• 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 1.3.1, measurements should be made during winter
periods whenever possible.
* Internal-external air exchange systems (other than a
furnace) such as high-volume attic and window fans
should not be operated during the measurement and for at
least 12 hours before the measurement is initiated. Air
conditioning systems that recycle interior air may be
operated.
* 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. The closed house conditions must be verified
and maintained more rigorously, however, when they are
not the normal living conditions.
* Short-term measurement should not be conducted if severe
storms with high winds or rapidly changing barometric
pressure are predicted during the measurement period.
Weather predictions available on local news stations may
provide sufficient information to determine if this
condition is satisfied.
3.2.7 Deployment and Operation
Install the RPISU and, if possible, 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 ensure continued operation; also inform
the occupants about the RPISU and request that they report any
problems or pump shut down. The occupants 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
3-8
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operating time decreases the uncertainty associated with the
measurement result.
3.2.7.1 Location Selection. The following criteria should be
used to select the location of the RPISU within a room:
• A position should be selected where the device will not
be disturbed during the sampling period;
* The RPISU should not be placed near drafts caused by
HVAC vents, windows, or doors;
* The air intake (sampling head) should be placed at least
75 centimeters (30 inches) above the floor and at least
20 centimeters (8 inches) from surfaces that may
obstruct flow;
* The RPISU should not be placed close to the outside wall
of the house;
3.2.8
The RPISU should not be placed in kitchens or bathrooms.
Retrieval
Prior to pump shut-down the flow rate should be measured with a
calibrated flow meter if possible and the unit should be observed
briefly to ensure that it is operating properly. Return the
detector assembly or detector film to its envelope and record the
date, time, running time meter reading, and flow rate both on the
envelope and in a log book. Check the filter for holes or dust
loading and record any other observed conditions that might
affect the measurement. If TLDs or film discs are to be removed
from the detector assembly, removal should be delayed for at
least three hours after sampling is completed to allow for decay
and registration of radon decay products on the filter.
3.2.9 Documentat i on
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 the following:
* The time and date of the start and end of the
measurement;
* Serial numbers of RPISUs, film discs or TLDs;
* Whether standardized conditions, as previously
specified, are satisfied;
* Exact location of the instrument, on a diagram of the
room and house, if possible;
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* 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.
3.2.10 Analysis
Analysis of the film from the alpha track detector RPISUs
requires an analysis laboratory equipped to etch and count alpha
track film.
Analysis of TLD type RPISUs requires a 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 the prescribed temperature in an oven.
3.2.10.1 Sensitivity. The lower limit of detection (LLD)
(Altshuler and Pasternack 1963) should be specified by individual
suppliers for RPISU detectors exposed according to their
directions. The LLD will depend upon the length of the exposure
and the background of the detector for materials used. The LLD
should be calculated using the results of the laboratory control
devices.
3.2.10.2 Precision. The coefficient of variation should not
exceed ten percent (1 sigma) at radon decay product
concentrations of 0.02 WL or greater. This precision should be
monitored and recorded using the results of the duplicate
detector analyses described in section 3.2.11.3.
3.2.11 Quality Assurance
The quality assurance program for measurements of radon decay
product concentrations in terms of working levels comprises four
elements: (1) calibration, (2) known exposure (spiked) detectors
(3) duplicate measurements and (4) control dosimeters to measure
exposure during shipment and storage. The quality assurance
program should include the maintenance of control charts, as
described by Goldin (Goldin 1984).
The EPA has established the National Radon Measurement
Proficiency (RMP) Program. This quality assurance program
enables participants to demonstrate their proficiency at
measuring radon and radon decay product concentrations. For
3-10
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further information please write to the U.S. Environmental
Protection Agency; Radon Division; Mitigation, Prevention, and
Quality Assurance Branch; National RMP Program; 401 M St., SW;
Washington, D.C., 20460.
3.2.11.1 Calibration. Calibration of RPISUs requires exposure
in a controlled radon-exposure chamber where the radon decay
product concentration is known during the exposure period. The
detector must be exposed in the chamber using 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 routine measurements. The relationship of
thermoluminescent dosimeter reader units or etched track reader
units to working level for a given sample volume and the standard
error associated with this measurement should be determined.
Calibration of the RPISUs also includes testing 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 Known Exposure Devices. Both suppliers and large users
of RPISU services of both types should submit detectors with
known radon exposures (spiked samples) for analysis on a regular
schedule. Known exposure detectors should be labeled in the same
manner as the field detectors to assure blind processing. The
number of known exposure detectors submitted for analysis should
be a few percent of the total number of devices analyzed. The
results of the known exposure detector analysis should be
monitored and recorded, and any significant deviation from the
known concentration to which they were exposed should be
investigated.
3.2.11.3 Duplicate (Colocated) Detectors. Large users should
make duplicate measurements in enough houses to monitor the
precision of the measurements. This usually will be
approximately ten percent of the houses to be tested or 50,
whichever is smaller. The duplicate detectors should be shipped,
stored, exposed, and analyzed under the same conditions. The
samples selected for duplication should be systematically
distributed throughout the entire population of samples. Groups
selling measurements to homeowners can do this by making two
side-by-side measurements instead of one in a random selection of
homes. Data from dupliceite detectors should be evaluated using
the procedures described by Goldin in Section 5.3 of his report
(Goldin 1984). The method should achieve a coefficient of
variation of 10 percent (1 sigma) or less at radon decay product
concentrations of 0.02 WL or greater. Consistent failure in
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duplicate agreement may indicate a problem in the measurement
process that should be investigated.
3.2.11.4 Controls. Thermoluminescent dosimeter RPISUs use a TLD
that is shielded from the gamma radiation emitted by the material
on the filter. This TLD is incorporated in the detector assembly
to measure the environmental gamma exposure of the individual
detector assemblies. The two TLDs are processed identically and
the environmental gamma exposure is subtracted from the sample
reading.
3.2.11.4.1 Laboratory Control Detectors. The laboratory
background level for each batch of assembled thermoluminescent
detectors should be established by each supplier. Suppliers
should measure the background of a statistically significant
number of unexposed thermoluminescent assemblies that have been
processed according to their standard operating procedures. This
laboratory blank value is subtracted by the analysis laboratory
from the results obtained from the field detectors to arrive at
the net readings used to calculate the reported sample radon
concentrations.
Similarly, the laboratory background level for each batch of
alpha track RPISUs should be established by each supplier of
these detectors. Suppliers should measure the background of a
statistically significant number of unexposed detector films that
have been processed according to their standard operating
procedures. This laboratory blank value is subtracted by the
analysis laboratory from the results obtained from the field
detectors to arrive at the net readings used to calculate the
reported sample concentrations.
3.2.11.4.2 Field Control Detectors (Blanks). For
thermoluminescent detector RPISUs and alpha track RPISUs, field
control detectors (field blanks) should consist of a minimum of
five percent of the detectors deployed each month or 25,
whichever is smaller. Commercial users should set these aside
from each shipment, keep them sealed, label them in the same
manner as the field detectors, and send them back to the supplier
as blind controls with one shipment each month. These field
blank detectors measure the background exposure that may
accumulate during shipment or storage, and the results should be
monitored and recorded. If one or a few of the field blanks have
concentrations significantly greater than the LLD established by
the supplier, it may indicate defective material or procedures.
If the average value from the background control detectors (field
blanks) is significantly greater than the LLD established by the
supplier, this average value should be subtracted from the
individual values reported for the other detectors in the ex-
posure group. The cause for the elevated field blank readings
should then 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 closed-house conditions. Such
screening measurements have a smaller variability and are more
reproducible than measurements made when the house conditions are
not controlled.
The results of grab sampling are greatly influenced by conditions
that exist in the house during and for up to 12 hours prior to
the measurement. It is therefore especially important when
making grab measurements to conform to the closed-house
conditions for 12 hours before the measurement. Grab techniques
are not recommended for follow-up measurements made to estimate
health risks or to determine the need for remedial action.
3.3.2 Scope
This procedure covers, in general terms, the equipment
procedures, and quality control objectives to be used in perform-
ing the measurements. it is not meant to replace an instrument
manual, but rather provides guidelines to be adopted into
standard operating procedures. Questions about these guidelines
should be directed to the U.S. Environmental Protection Agency
(EPA), Office of Radiation Programs, Radon Division (ANR-464)
Problem Assessment Branch, 401 M Street, S.W., Washington, D.C.,
£ \J ~r O \J •
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 (George 1980). 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 (Kusnetz 1956, ANSI 1973) 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
3-13
-------
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 used.
The Tsivoglou procedure, as modified by Thomas (Tsivoglou et al.
1953; Thomas 1972), 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 the following items:
* An air pump capable of collecting samples at the desired
flow rate;
* A filter holder to accept a 25- or 47-mm diameter, 0.8-
micron membrane or glass fiber filter;
* A calibrated flow meter to determine air flow through
the filter during sampling;
* A clock for accurate timing of sampling and counting;
* A scintillation counter (such as the Randam Electronics
Model SC-5, or the EDA Instruments Model RD-200) and a
zinc sulfide scintillation disc;
* A National Bureau of Standards (NBS)-traceable alpha
calibration source to determine counter efficiency;
* A data collection log.
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
3-14
-------
the Tsivoglou procedure, in which the sample counting must begin
two minutes following the end of sampling.
The air pump, filter assembly, and flow meter must be tested to
ensure 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 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.
s
3.3.6 Measurement Criteria
The following house conditions should exist prior to and during a
measurement to standardize the measurement conditions as much as
possible.
* 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 others discussed in Section 1.3.1,
measurements should be made during winter periods
whenever possible.
* 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.
Air conditioning systems that recycle interior air may
be operated.
* 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. However, the closed-house conditions must be
verified and maintained more rigorously, when they are
not the normal living conditions.
* Short-term measurement should not be conducted if severe
storms with high winds or rapidly changing barometric
pressure are predicted during the measurement period.
Weather predictions available on local news stations may
provide sufficient information to determine if this
condition is satisfied.
3-15
-------
3.3.7 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 information includes the
following:
* The time and date of the start and end of the
measurement;
* Serial numbers of equipment and a description which
uniquely identifies customer, building, room, and
sampling position;
* Whether standardized conditions, as previously
specified, are satisfied;
* Exact location of the measurement, on a diagram of the
room and house, if possible;
* Other easily gathered information that may be useful,
such as the type of house, type of heating system, the
existence of crawl space or basement, occupants smoking
habits, and operation of humidifiers, air filters, or
electrostatic precipitators.
3.3.8 Sampling Operations
3.3.8.1 Location in Room. The following criteria should be
applied to select the location of the measurement within a room.
* The measurement should not be made near drafts caused by
heating, ventilating and air conditioning vents, doors,
and windows.
* The measurement location should not be close to the
outside walls of the house.
* The unit should be placed on a table or stool so that
the air intake is at least 75 centimeters (30 inches)
from the floor and at least 10 centimeters (4 inches)
from other objects.
* In general, measurements should not be made in kitchens
or bathrooms.
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 five
3-16
-------
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 (George 1980) If the
Tsivoglou procedure is used, the count irufmust be started two
minutes following the end of sampling. Analysis using the
Kusnetz procedure must be performed between 40 and 90 minutes
dSrina^is S ^V^ 8M*1*n*- A counting time of ten m?nu?es
during this period is usually used.
n™-i from the holder using forceps and carefully
place it facing the scintillation phosphor. The side of the
tiiter on which the decay products were collected must face the
bfcloled ,1£T if6 Shamber containing the filter anf diSc should
be closed and allowed to dark-adapt prior to starting countincr
For the Tsivoglou method this procedure of placing ?L f^te^in
the counting position must be done quickly, since the first of
the three counts must begin two minutes following th2 end of
»SSSin& " ^ °OUnter USed has been shown togbe slSw to dark-
Additiona? ST^ 8hSJld bS d°ne ln a dar*ened environment
Additional details on the procedure and calculations may be found
in the references (Kusnetz 1956, Tsivoglou 1953, Thomas 1972)?
3 • 3 • 10 Grab Sampling
s!!ns:!-tivitY. For a five-minute sampling period (10 to
° ^ °n a 25~mm filter' the sensitivity using the
Kusnetz or modified Tsivoglou counting procedure should bl
approximately 0.0005 working level (George 1980).
3.3.10.2 Precision. The coefficient of variation should not
?erCent (1 Slgma) at radon deca^ Prodic? concentrations
he results of I™?^ ThiS precision should ^ monitored usJng
tne results of duplicate measurements. Sources of error in 1-h^
aT?0^ H^ TSU1J f^0m. ^accuracies in measuring Se vo?uS of
air sampled, characteristics of the filter used, and measurement
of amount of radioactivity on the filter. measurement
3.3.11 Quality Assurance
a?surance Program for RDP concentration measurements
grab sampling includes calibration and duplicate mealurlmJnts
cSntro? chL?:SUranr Pr
-------
further information please write to the U.S. Environmental
Protection Agency; Radon Division; Mitigation, Prevention, and
Quality Assurance Branch; National RMP Program; 401 M Street, SW;
Washington, D.C., 20460.
3.3.11.1 Calibration. Pumps and flow meters used to sample air
must be routinely calibrated to ensure 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 six months or after any instrument repair or
modification.
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 a 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 that the new
material be checked 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 ten
percent of the total samples collected or 50 per month, whichever
is smaller. 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 also should be taken to ensure that one filter is not in the
discharge air stream of the other sampler. The measurements
selected for duplication should be systematically distributed
throughout the entire population of measurements.
Data from duplicate samples should be evaluated using the
procedures described by Goldin in Section 5.3 of his report
(Goldin 1984). The method should achieve a coefficient of
variation of 10 percent (1 sigma) or less for radon decay product
concentrations of 0.02 WL or greater. Consistent failure in
duplicate agreement may indicate a problem in the measurement
process that should be investigated.
3-18
-------
REFERENCES
Altshuler, B. and Pasternack, B., 1963, "Statistical Measures of
the Lower Limit of Detection of a Radioactivity Counter " Health
Physics. Vol. 9, pp. 293-298. ~
American National Standards Institute, 1973, "American National
Standard for Radiation Protection in Uranium Mines," ANSI
N13.8-1973.
Beckman, R.T., 1975, "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. 1988, Personal Communication, August 1988.
Cohen, B.L. and Cohen, E.S., 1983, "Theory and Practice of Radon
Monitoring with Charcoal Adsorption," Health Physicsr Vol. 45,
JN O •
-------
George, A. C., Duncan, M., Franklin, H., 1984, "Measurements of
Radon in Residential Buildings in Maryland and Pennsylvania,
U.S.A.," Radiation Protection Dosimetrv. Vol. 7, pp. 291-294.
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-11(83) UC-70A.
Gesell, T.F., 1983, "Background Atmospheric Radon-222
Concentrations Outdoors and Indoors: A Review," Health Physics,
Vol. 45, pp. 289-302.
Hess, C.T., Fleischer, R.L., Turner, L.G., 1985, "Field and
Laboratory Tests of Etched Track Detectors for Radon-222:
Summer-vs-Winter Variation and Tightness Effects in Maine
Houses," Health Physics. Vol. 49, pp. 65-79.
Goldin, A.S., 1984, "Evaluation of Internal Quality Control
Measurements and Radioassay," Health Phvsics. Vol. 47, No. 3, pp.
361-364.
f
Grodzins, L. , 1988, Personal Communication, September 1988.
Keller, G., Folkerts, K.H., Muth, H., 1984, "Special Aspects of
the Radon-222 and Daughter Product Concentrations in Dwellings
and the Open Air," Radiation Protection Dosimetrv. Vol. 7, pp.
151-154.
Kusnetz, H.L., 1956, "Radon Daughters in Mine Atmospheres - A
Field Method for Determining Concentrations," American
Industrial Hvaiene Association Quarterly. Vol. 17.
Kotrappa, P., Dempsey, J.C., Hickey, J.R., and Stieff, L.K.,
1988, "An Electret Passive Environmental Rn-222 Monitor Based on
lonization Measurements," Health Physics. Vol. 54, No. 1, pp. 47-
56.
Lovett, D.B., 1969, "Track Etch Detectors for Alpha Exposure
Estimation," Health Phvsics. Vol. 16, pp. 623-628.
Lucas, H.F., 1957, "Improved Low-Level Alpha Scintillation
Counter for Radon," Review of Scientific Instruments." Vol. 28,
p. 680.
Nyberg, P.C., Bernhardt, D.E., 1983, "Measurement of Time-
Integrated Radon Concentrations in Residences," Health Physics,
Vol. 45, pp. 539-543.
Perlman, D. 1988, Personal Communication, September 1988.
R-2
-------
Perlman, D. 1989, "Method of, and Passive Apparatus for,
Detecting Radon," Brandeis University, Patent No. 4812648.
Prichard, H.M. and Marien,, K. , 1985, "A Passive Diffusion Rn-222
Sampler Based on Activated Carbon Adsorption," Health Physics.
Vol. 48, No. 6., pp. 797-803.
Prichard, H.M., Personal Communication, September 1988.
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, D.C., pp. 41-42.
Ronca-Battista, M. and Magno, P., 1988, "A Comparison of the
Variability of Different Techniques and Sampling Periods for
Measuring Rn-222 and its Decay Products," Health Physics, Vol.
55, No. 5, pp. 801-807.
Sill, C.W., 1977, "Integrating Air Sampler for Determination of
Rn-222," in the Program Report on the Workshop on Methods for
Measuring Radiation In and Around Uranium Mills, Vol. 8, No. 9,
pp. 97-104, Atomic Industrial Forum, Inc., Washington, D.C.
Stranden, E., Berteig, L.„ Ugletveit, F., 1979, "A Study on Radon
In Dwellings," Health Physics. Vol. 36, pp. 413-421.
Thomas, J.W.; 1972, "Measurement of Radon Daughters in Air,"
Health Physics. Vol. 23, p. 783.
Tsivoglou, E.G., Ayer, H.E., and Holaday, D.A., 1953, "Occurrence
of Nonequilibrium Atmospheric Mixtures of Radon and Its
Daughters," Nucleonics,, Vol. 1, p. 40.
Wilkening, M., Wicke, A., 1986," Seasonal Variation of Indoor
Radon at a Location in the Southwestern United States," Health
Physics. Vol. 51, pp. 427-436.
R-3
-------
-------
APPENDIX A
SUPPLEMENTARY INFORMATION FOR
G1HAB RADON SAMPLING
(SCINTILLATION CELL METHOD)
A.I EQUIPMENT
Equipment to measure radon concentration using grab sampling into
scintillation cells is available from several commercial
suppliers. Equipment required is listed below.
* Scintillation cells
* Pump to evacuate single valve cells or to flow air
through double valve cells
* Filter holder and filter to remove particulates
* Detector-scaler-high voltage assembly for counting
* Timer
* Calibration cell or check source
* Aged air or nitrogen
A.2 GENERAL METHOD DESCRIPTION
* 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.
* The sample in the cell is allowed to equilibrate to
optimize counting efficiency.
* The cell is placed on a photomultiplier tube and
scintillations counted.
* Radon concentration is calculated based on the sample
counts and corrected using appropriate ingrowth and
decay factors.
A.3 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 Randam Electronics Model SC-5 cell counters and
associated cells or the EDA Instruments Model RD-200 System.
A-l
-------
However, equipment is available from several suppliers, and it
may be necessary to modify the procedure slightly to accommodate
these differences. For example, the correct cell volume must be
used in the calculations. The following is a general procedure
using the Randam or EDA equipment.
1. The cells to be used are flushed with aged air or
nitrogen to remove traces of the 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 the counter, wait two minutes for the
system to become dark adapted, and count background of
the cell for ten 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 (double valve) for a period sufficient to allow ten
air exchanges. For the Randam (single valve) cells it
is only necessary to open the valve on the evacuated
cells and allow ten to fifteen 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 four
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 two 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.
A.4 CALCULATION OF RESULTS
The radon concentration in picocuries per liter is determined
using the following formula.
pCi/L =
where
cpm(s) - cpm(bkg)
E
C
A
1
X -
V
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,
For tlie 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 L for EDA cells
V = 0.125 L for Randam cells
A.5 SAMPLE CALCULATION
The following sample calculation demonstrates the procedure for
calculating results.
* Background Count for system = 10 counts in 10 minutes,
or 1 cpm
* Sample Count for 120 minutes = 1200 counts, or 10 cpm
* System Efficiency (E) from cell calibration =4.62
cpm/pCi
* Count time correction (C) for 120 minutes = 1.00757
* Delay time correction (A) for 4 hours = 0.97026
* Volume correction (V) for EDA cell = 0.170 L
pCi/L =
10 cpm - 1 cpm
4.62 cpm/pCi
x
1.00757
0.97026
= 11.9
0.170 L
A-3
-------
Table &-1: Radon Correction Factors
A. - Correction for radon decay from time of collection to
start of counting
C. - Correction for radon decay during counting
Time
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
Minutes
1.00000
0.99987
0.99975
0.99962
0.99950
0.99937
0.99925
0.99912
0.99899
6.99887
0.99874
0.99862
0.99849
0.99837
0.99824
0.99811
0.99799
0.99786
0.99774
0.99781
0.99749
0.99736
0.99724
0.99711
0.99699
0.99686
0.99673
0.99661
0.99648
0.99636
0.99623
Hours
1.00000
0.99248
0.98502
0.97761
0.97026
0.96296
0.95572
0.94854
0.94140
0.93432
0.92730
0.92033
0.91340
0.90654
0.89972
0.89295
0.88624
0.87958
0.87298
0.86640
0.85988
0.85342
0.84700
0.84063
0.83431
0.82803
0.82181
0.81563
0.80950
0.80341
0.79737
Days
1.00000
0.83431
0.69607
0.58074
0.48451
0.40423
0.33726
0.28138
0.23475
0.19588
0.16341
0.13633
0.11374
0.09490
0.07917
0.06605
0.05511
0.04598
0.03836
0.03200
0.02670
0.02228
0.01859
0.01551
0.01294
0.01079
0.00901
0.00751
0.00627
0.00523
0.00436
A-4
Hours
1.00000
1.00378
1.00757
1.01136
1.01517
1.01899
1.02281
1.02665
1.03050
1.03435
1.03821
1.04209
1.04597
1.04986
1.05377
1.05768
1.06160
1.06553
1.06947
1.07342
1.07738
1.08135
1.08532
1.08931
1.09331
1.09732
1.10133
1.10536
1.10939
1.11344
1.11749
-------
Table A-l: Radon Correction Factors (Continued)
A.
C.
B - ' -*1
Correction for radon decay from time of collection "to
start of counting .
I j.
Correction for radon decay during counting
A C
Ti»o
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Minutes
0.99811
0.99598
0.99586
0.99573
0.99561
0.99548
0.99536
0.99523
0.99511
0.99498
0.99486
0.99473
0.99461
0.99448
0.99435
0.99423
0.99410
0.99398
0.99385
0.99373
0.99380
0.99348
0.99335
0.99323
0.99310
0.99298
0.99286
0.99273
0.99261
0.99248
Hours
0.79137
0.78542
0.77951
0.77365
0.76784
0.76208
0.76633
0.75064
0.74500
0.73940
0.73384
0.72832
0.72284
0.71741
0.71201
0.70668
0.70134
0.69607
0.69084
0.68564
0.68049
0.67537
0.67029
0.86525
0.66025
0.65528
0.65036
0.84547
0.64061
0.63579
Days
0.00384
0.00304
0.00253
0.00211
0.00178
0.00147
0.00123
0.00102
0.00085
0.00071
0.00059
0.00050
0.00041
0.00035
0,00029
0.00024
0.00020
0.00017
0.00014
0.00012
0.00010
0.00008
0.00007
0.00006
0.00005
0.00004
0.00003
0.00003
0.00002
0.00002
Hours
1.12155
1.12562
1.12971
1.13380
1.13790
1.14201
1.14813
1.15026
1.15440
1.15854
1.18270
Iil6687
1.17105
1.17523
1.17943
1.18363
1.18784
1.19207
1.19630
1.20054
1.20479
1.20905
1.21332
1.21780
1.22189
1.22619
1.23050
1.23481
1.23914
1.24347
A-5
-------
-------
APPENDIX B
SUPPLEMENTARY INFORMATION FOR
GRAB RADON DECAY PRODUCT SAMPLING
B.I EQUIPMENT
d.
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.
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.
Alpha counting system A detector and sealer-timer
system is required that can accurately measure 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.
Timer A stopwatch or timer to measure the sampling time
and counting times is required.
B.2 GENERAL DESCRIPTION OF METHODS
Two commonly used methods are described below. There are several
other methods reported in the literature. Sampling using 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.
B.3 PROCEDURE
a.
Sample Collection
d)
(2)
Note
Install the filter in the filter holder assembly
and attach to the pump.
Operate the pump for exactly 5 minutes, pulling air
through the filter. Record starting time and air
flow rate.
Sample counting and analysis for two different
techniques are described.
B-l
-------
(3) Stop the pump at the end of the 5-minute sampling
time and start or reset the stopwatch.
b. Sample Counting
(1) Modified Tsivoglou Technique
(a) Carefully transfer the filter from the filter
holder assembly to the detector. Orient the
collection side of the filter toward the face
of the detector.
(b) Operate the counter for the following time
intervals, after sampling has stopped: 2 to 5
minutes, 6 to 20 minutes, and 21 to 30 minutes.
Record the total counts for each time period.
(2) Kusnetz Technique
(a) Carefully transfer the filter from the filter
holder assembly to the detector. Orient the
collection side of the filter toward the face
of the detector.
(b) 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 midpoint of the 10-minute time
interval.
c. Data Analysis
(1) Modified Tsivoglou Technique
The concentration in pCi/L of each of the radon decay
products, Po-218, Pb-214 and Po-2i4 can be determined by
using the following calculations:
(0.16746 G1 - 0.0813 G2 + 0.0769 G3 - 0.0566R)
FE
c !.== •—i. (0.00184 G, - 0.0209 G2 + 0.0494 G3 - 0.1575R)
FE
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
(Thomas 1972). The working level associated with
these concentrations can then be calculated using
the following relationship:
B-2
-------
C4 = (-0.0235 G1 + 0.0337 G2 - 0.0382 G3 - 0.0576R)
FE
WL = (1.028X10"3 X C2 + 5.07X10"3 X C3 + 3.728 X 10~3 X CJ
where:
C2 = concentration of Po-218 (RaA) in pCi/L
C3 = concentration of Pb-214 (RaB) in pCi/L
C4 = concentration of Po-214 (RaC1) in pCi/L
F = sampling flow rate in 1pm
E = counter efficiency in cpm/dpm
G1 = gross alpha counts for the time interval 2 to 5
minutes
G2 = gross alpha counts for the time interval 6 to 20
minutes
G3 = gross alpha counts for the time interval 21 to 30
minutes
R =' background counting rate in cpm
Reference: (Thomas 1972).
(2) Kusnetz Technigue
Calculate WL as follows:
WL C
K(t) V E
where:
C = Sample cpm - Background cpm
Kt = 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 (Public Health Service 1957).
Time
40
42
44
46
48
50
52
54
56
58
60
62
64
66
68
70
72
74
76
78
80
82
84
86
88
90
150
146
142
138
134
130
126
122
118
114
110
106
102
98
94
90
87
84
82
78
75
73
69
66
63
60
B-4
-------
MODIFIED TSIVOGLOU TECHNIQUE
SAMPLE PROBLEM
F = Sampling Flow Rate =3.5 1pm
E = Counting Efficiency = 0.47 cpm/dpm
G1 = 880
G2 = 2660
'G, = 1460
= 0.5
= 1 (0.16746 X 880-0.0813 x 2660+0.0769 x 1460-0.0566 X 0.5)
3.5 X 0.47
26.3 pCi/L
1 (0.00184 X 880-0.0209 X 2660+0.0494 X 1460-0.1575 x 0.5)
3.5 x 0.47
11.0 pCi/L
1 (-0.0235 X 880+0.0337 X 2660-0.0382 X 1460-0.0576 x 0.5)
3.5 X 0.47
C, =8.0 pCi/L
R
C
o
o
—
•y
C =
^—°z
C =
/.
WL = (1.028 X 10"3 X 26.3+5.07 X 10"3 X 11.0+3.728 X 10"3 X 8.0)
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
1,197 cpm-0.6 cpm
= 0.49 (known source of
2430 dpm
Sample Volume = 4.4 liter/minute x 5 minutes = 22 liters
- Efficiency =
Sample Count at 45 minutes (time from end of sampling period to start
of counting period) = 560 counts in 10 minutes, or 56 cpm
Kt at 50 minutes from Table B-l =130
WL =
WL
56 cpm-0.6 cpm
130 x 22 L x 0.49
0.04
B-6
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