United States
Environmental Protection
Agency
Office of
Radiation Programs
Washington, D.C. 20460
EPA 520/1-86-014-1
February 1987
Radiation
£EPA
Interim Protocols For
Screening And Followup
Radon And Radon Decay
Product Measurements
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520/1-86-014
INTERIM PROTOCOLS FOR SCREENING AND FOLLOW-UP RADON
AND RADON DECAY PRODUCT MEASUREMENTS
U.S. Environmental Protection Agency
Office of Radiation Programs
January 1987
M. Ronca-Battista
P. Magno
P. Nyberg
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CONTENTS
Page
Acknowledgements ii
Summary iii
1. INTRODUCTION 1
2. SCREENING MEASUREMENTS 2
2.1 Screening Measurement Location 3
2.2 Interpretation of Screening Measurement Results . 5
3. FOLLOW-UP MEASUREMENTS 7
3.1 Follow-up Measurement Location 7
3.2 Interpretation of Follow-up Measurement Results . 10
4. EXAMPLES OF APPROPRIATE MEASUREMENT LOCATIONS 12
5. RECOMMENDED USES OF GRAB SAMPLING 13
6. CLOSED-HOUSE CONDITIONS 14
7. INSTRUMENT SELECTION 16
7.1 Continuous Radon Monitors (CRM) or Continuous
Working Level Monitors (CWLM) 16
7.2 Alpha-Track Detectors 17
7.3 Charcoal Canisters 18
7.4 Radon Progeny Integrating Sampling Units 18
7.5 Grab Sampling 19
References 21
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ACKNOWLEDGEMENTS
There are many generous individuals who have contributed
substantially to this document during months of discussion
and review. The authors wish to extend special thanks to
Thomas Gerusky, Larry Lloyd, Eileen Hotte, Larainne Koehler,
Bill Belanger, Dan Egan, and the Environmental Protection
Agency's (EPA) Radon Action Program staff. Their efforts
enabled the authors to better address the needs of homeowners.
States, and other organizations performing radon measurements.
11
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SUMMARY
This document presents guidance for making reproducible
measurements of radon concentrations in residences, including
recommendations for using the results to make well-informed
decisions about the need for additional measurements or
remedial action. The Environmental Protection Agency (EPA)
recognizes that radon concentrations in homes may vary greatly
over time (Ge83; He85; St79; F184; Wi86; Ny83). Furthermore,
concentrations at different locations in the same house often
vary by a factor of two or more (Geo84; Ke84; He85). Because
of these temporal and spatial variations, the EPA does not know
of a way to provide an accurate estimate of health risks or
make a well-informed decision on the need for remedial action
with a single measurement. What is necessary, therefore, is a
logical system for making the fewest measurements possible,
while ensuring that there are not serious underestimations of
the concentrations.
The EPA recommends a two-step measurement strategy for
assessing radon levels in homes. The first step is a screening
measurement, made to quickly and inexpensively determine
whether a house has the potential for causing high exposures
to its occupants. There are two possible outcomes from a
screening measurement: (1) if the result is above the
screening level, additional follow-up measurements are
recommended as the second step to both estimate the health risk
to the occupants and assess the urgency for remedial action;
and (2) if the result is below the screening level, follow-up
measurements are probably not needed.
Screening measurements should be made under conditions
that maximize the probability of finding elevated radon
concentrations. Screening measurements should be made in the
lowest livable area of the house (closest to the underlying
soil) that the residents now use o_r could adapt for use as a
living area. In many houses this will be a basement that could
be converted to a den, playroom, or bedroom without major
structural changes. Furthermore, screening measurements
should be made under closed-house conditions when the doors
and windows of the house are kept closed as much as practical
and the use of ventilation systems mixing indoor and outdoor
air is minimized. Both these conditions will help to ensure
that short-term measurements are made during the time of
highest and most stable radon concentration and will also
increase the reproducibility of the measurements.
If the screening measurement result is above 4 pCi/1
(0.02 WL), follow-up measurements are recommended. The EPA
does not recommend taking any significant remedial action on
the basis of a single screening measurement. Therefore, the
appropriate response to an elevated screening result is
additional measurements.
111
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Follow-up measurements should be made in at least two
locations in the house, preferably on each of the different
living levels, if there are more than one. The results from
each location should be averaged to obtain an overall average
result for the living areas of the home.
The duration of the follow-up measurements depends on the
magnitude of the screening measurement result. If the
screening result is significantly elevated, then a short-term
follow-up measurement should be made, which will minimize the
additional exposure of the occupants. If the result is only
moderately elevated, then a full-year schedule of follow-up
measurements is recommended, with the expectation that the
additional exposure of the occupants during that period will
not significantly increase health risk. The recommended
follow-up procedure is based on the screening result as follows:
1. If the screening measurement result is less than about
4 pCi/1 (or about 0.02 WL), follow-up measurements are
probably not needed, as it is highly unlikely that
radon levels in the living areas of the home would
exceed 4 pCi/1 or 0.02 WL as an annual average.
2. If the result of the screening measurement is greater
than about 4 pCi/1 (0.02 WL) but less than about
20 pCi/1 (0.1 WL), EPA recommends that the follow-up
measurements consist of 12-month integrated measure-
ments made in several areas of the house. The average
annual concentration in the living space can be used
to estimate health risks and to compare to guidance
levels on the need for remedial action. This guidance
is available in "A Citizen's Guide to Radon," published
by EPA, the U.S. Department of Health and Human
Services, and the Centers for Disease Control. This
pamphlet can be obtained from the Government Printing
Office by calling (202) 275-2091 and asking for
document number 055-000-00258-4.
3. If the screening measurement result is greater than
about 20 pCi/1 (0.1 WL), then EPA recommends that a
short-term follow-up measurement over at least 24
hours be made in several living areas of the house
under closed-house conditions. A short-term follow-up
measurement will minimize additional significant
exposure to the occupants while providing reproducible
results that conservatively estimate the annual
average concentration.
IV
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1. INTRODUCTION
This document supplements "Interim Radon and Radon Decay
Product Measurement Protocols" (EPA 520/1-86-04) prepared by
the Office of Radiation Programs of the Environmental Protection
Agency (EPA) and published in February, 1986 (EPA86). That
report provides guidance for measuring radon concentrations
with continuous radon monitors (CRM), charcoal canisters,
alpha-track detectors (ATD), and grab radon techniques; it also
provides guidance for measuring radon decay product concen-
trations with continuous working level monitors (CWLM), radon
progeny integrating sampling units (RPISU), and grab radon
decay product methods. The 1986 report includes a discussion
of recommended quality control practices for each method.
Copies of that protocols report, numbered EPA 520/1-86-04, can
be obtained by contacting the Program Management Office
(ANR-458), Office of Radiation Programs, Environmental
Protection Agency, 401 M Street, S.W., Washington, D.C., 20460;
your EPA regional office; or your State radiation control
office.
This report provides guidelines that are primarily
intended to aid State radiation control programs, other
organizations conducting measurements, and homeowners who want
detailed information on measurements. They can be adopted as
part of a State program as particular circumstances and
resources allow or can be provided by States to homeowners and
measurement firms as recommendations.
The philosophy presented here serves as the basis
for consistent radon measurements that produce accurate and
reproducible results within a reasonable time and for a
reasonable cost. Consistency is important, because decisions
about the need for remedial action should be based on a common
rationale and comparable measurements. In addition,
consistency among measurement programs will help assure valid
comparison of measurement results from different State or
regional programs. These guidelines will be periodically
evaluated and may be refined to reflect increasing knowledge
and experience with indoor radon.
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2. SCREENING MEASUREMENTS
Screening measurements may be conducted by homeowners
wanting to make single measurements to quickly determine
whether their homes contain high radon concentrations, 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. However,
the screening measurement alone usually will not provide enough
information to decide on the need and timing of remedial action.
Screening measurements should be made in the lowest
livable area in the house that the residents now use or could
adapt for use as a living area, which will be the basement in
many houses. (The guidance presented here assumes the source
of radon to be the underlying soil, rather than building
materials or water. If other radon sources are suspected,
additional types of measurements should be made.) Any
screening measurement should be made during closed-house
conditions (described on page 14) to ensure that information is
obtained on the maximum concentrations to which the house
occupants may potentially be exposed. Under these conditions,
EPA believes that there is a low probability that a home with a
low screening result could have a high long-term average
concentration in the living area.
There is a growing body of data indicating that basement
concentrations tend to be a factor of two to three times higher
(Ge83; Geo84; F184, Mo82) and are more reproducible, i.e.,
less variable over time (DOE86; DOE87), than concentrations
in nonbasement rooms. Therefore, if the result of a screening
measurement is very low, there is a high probability that the
long-term average concentrations in the rooms currently used as
living areas are even lower, and the homeowner can eliminate
the need for further measurements with confidence.
Screening measurements will minimize the number of false
negatives, or homes that contain concentrations at which EPA
recommends that remedial action be considered but which would
not be identified as such because of a low measurement result.
The outcome of a false positive screening measurement should be
a follow-up measurement, which would reveal that the concentra-
tions in the house are low. However, the outcome of a false
negative is no further measurements, so that potentially high
concentrations may never be identified. In the interests of
reducing radon exposures, therefore, EPA believes that a
significant fraction of false positives is preferable to a high
rate of false negatives.
Guidelines for the duration of screening measurements are
summarized in Table 2-1.
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2.1 Screening Measurement Location
The screening measurement should be made in the room or
area in which the highest and most stable radon or radon decay
product concentration is expected. The following criteria
should be used to select this room:
1. The measurement should be made in a livable room on a
level closest to the underlying soil, such as the
basement. The room need not be currently lived in or
frequently occupied but should be in a condition that
would allow it to be easily converted to a bedroom,
playroom, den, etc. Measurements may be made in
unfinished basements, but usually not in a room that
would require major structural changes (such as the
installation of a floor) before it could be used as a
living area.
2. The instrument should be placed in the room expected
to have the lowest ventilation rate, such as an
interior room with tight doors and few or no windows.
3. The measurements should not be made in a kitchen,
because of the likelihood that an exhaust fan system
and changes in small, airborne particles (caused by
cooking) may affect the stability of working level
measurements. In addition, measurements should not be
made in a bathroom, because relatively little time is
spent in a bathroom and high humidities may affect the
sensitivity of some detectors. (If radon in water is
expected to be a major contributor to the concentra-
tion of airborne radon, diagnostic measurements may be
made in the bathroom to determine the contribution
from this source; however, such diagnostic measure-
ments should not be used to estimate the resident's
exposures.)
These criteria are flexible, and sound judgment is
required as to what space actually constitutes a room.
Measurements should not be made in closets, cupboards,
sumps, crawl spaces, or nooks within the foundation.
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Table 2-1
Screening Measurements
Made in Lowest Livable Area
Under Closed-House Conditions
Instrument
Charcoal Canister
Alpha Track Detector
Radon Progeny
Integrated Sampling
Unit
Continuous Working
Level Monitor
Continuous Radon
Monitor
Grab WL*
Sampling Times
2 to 7 days
3 months (or less if laboratory uses
adequate lower limit of detection)
100 hours minimum, 7 days preferred
6 hours minimum, 24 hours or
longer preferred
6 hours minimum, 24 hours or
longer preferred
5 minutes
Grab Rn
5 minutes
*Grab measurements, because of the short 5-minute sampling
duration, have a relatively large uncertainty and are
recommended only for the purposes described on page 13.
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2.2 Interpretation of Screening Measurement Results
If the screening measurement result is less than about
4 pCi/1 or 0.02 WL, follow-up measurements are probably not
needed. If the screening measurement was made in the lowest
livable area under the closed-house conditions described on
page 14, there is relatively little chance that the concen-
trations in the general living areas on nonbasement floors of
the house are greater than about 4 pCi/1 or 0.02 WL as an
annual average.
If the result of the screening measurement is between
about 4 and 20 pCi/1 or between about 0.02 and 0.1 WL, the
occupant should be aware that, while there is a concern about
the long-term exposure to these radon concentrations, there
will probably be no large increase in risk with an additional
12 months of exposure. Therefore, since guidance for action
to reduce radon levels is usually expressed in terms of annual
average concentrations, we recommend a 12-month measurement
whenever possible.
If the result of the screening measurement is between
about 20 and 200 pCi/1, or between about 0.1 and 1 WL, a
short-term follow-up measurement should be made within the
next several months under closed-house conditions. Since the
occupants may be exposed to elevated concentrations in their
living areas, an annual average measurement alone is usually
not recommended because the additional 12 months of exposure
during the measurement could cause a significant increase in
health risk.
If the results are greater than about 200 pCi/1 or 1 WL,
the State radiation control program or regional EPA office
should be contacted for advice on a follow-up measurement
and immediate reductions in concentrations. The recommended
follow-up measurements are summarized in Table 2-1.
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Table 2-1
Recommended Actions Based on Results of Screening
Measurements
Screening Measurement Result
Greater than 1 WL or 200 pCi/1
Recommended Action
Perform short-term
follow-up measurements
and consider short-term
actions to reduce the
radon levels as soon as
possible
Between 0.1 and 1 WL
or
Between 20 pCi/1 and 200 pCi/1
Between 0.02 and 0.1 WL
or
Between 4 pCi/1 and 20 pCi/1
Perform short-term
follow-up
measurements within
several months
Perform follow-up
measurements over
the next 12 months
Less than 0.02 WL or 4 pCi/1
Relatively low
probability of
significant health risk
from concentrations in
general living areas of
home; follow-up measure-
ments are probably not
needed, but may be made
at the discretion of the
resident
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3. FOLLOW-UP MEASUREMENTS
The results of follow-up measurements will enable a
homeowner to make a well-informed decision about possible
health risks and the need for remedial action. As this
decision often entails spending a significant amount of money,
follow-up measurements should be reliable and reproducible
estimators of the actual or maximum potential exposures of the
occupants.
These guidelines represent EPA's current thinking on the
optimal method for obtaining these estimates. An individual
homeowner or a State may be limited by available resources to
making follow-up measurements in only one living area, rather
than in two areas as outlined here. However, in those
situations involving the investment of a large amount of money
or whenever a good estimate of average concentrations in living
areas is critical, all efforts should be made to perform
follow-up measurements in more than one area of the house.
If the result of the screening measurement is between
about 4 and 20 pCi/1 or between about 0.02 to 0.1 WL, measure-
ments to estimate the annual average concentrations should
be made. The occupant should consider using a long-term
measurement device, such as a 12-month alpha-track detector
(ATD), to estimate the annual average concentrations in the
living areas. An alternate, but less accurate, method for
estimating an annual average is to use the average of
four measurements made at 3-month intervals. The year-long
measurement is more reliable for determining long-term
exposure, because both short-term and seasonal variations
will be incorporated into the annual estimate. All measure-
ments made to estimate annual averages, whether 12-month
integrated or a series of quarterly measurements, should be
made under normal living conditions rather than closed house
conditions. The results of the four measurements in each
living area are then averaged to estimate the annual average.
Guidelines for the duration of follow-up measurements are
summarized in Table 3-1.
3.1 Follow-up Measurement Location
The following criteria should be used to select the rooms
in which follow-up measurements are made.
1. The measurements should be made in each level (floor)
of the house that is frequently used as a living ^
area. Living areas include family rooms, living
rooms, dens, playrooms, and bedrooms.
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2. The measurements should be made in the most frequently
occupied room in each of the above levels. A bedroom
may be a good choice, because most people generally
spend more time in their bedrooms than in any other
room in the house (Sz72; Ch74; Mo76).
3. If there are children in the house, it may be
appropriate to measure the concentrations in their
bedrooms or in other areas where they spend a lot of
time, such as a playroom. There is some concern that
children may be more sensitive to the effects of
inhaled radon decay products.
4. The measurements should not be made in a kitchen,
because of the likelihood that an exhaust fan system
and changes in small, airborne particles (caused by
cooking) may affect the stability of working level
measurements. In addition, measurements should not be
made in a bathroom, because relatively little time is
spent in a bathroom, and high humidities may affect
the sensitivity of some detectors. (If radon in water
is expected to be a major contributor to the concentra-
tion of airborne radon, diagnostic measurements may be
made in the bathroom to determine the contribution
from this source; however, such diagnostic measure-
ments should not be used to estimate the resident's
exposures.)
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Table 3-1
Follow-up Measurements
Made in General Living Areas
Instrument
If Screening Result is If Screening Result is
Greater than 20 pCi/1
Less than 20 pCi/1
Alpha Track
Detector
3-month measure-
ments (may be less
than 3 months if
laboratory uses
adequate lower limit
of detection), made
under closed-house
(winter) conditions*
12-month measurements
made under normal living
conditions
Charcoal
Canister
Measurements of
2 to 7 days made
under closed-house
conditions
Four measurements made
under normal living
conditions every 3 months
Radon Progeny 100-hour measure-
Integrating ments, made under
Sampling Unit closed-house
conditions
Four 100-hour
measurements made
under normal living
conditions every 3 months
Continuous 24-hour measure-
Working Level ments, made under
Monitor closed-house
conditions
Four 24-hour
measurements made
under normal living
conditions every 3 months
Continuous 24-hour measure-
Radon Monitor ments, made under
closed-house conditions
Four 24-hour measurements
made under normal living
conditions every 3 months
'It the result of the screening measurement is greater than
about 200 pCi/1, a short-term, follow-up measurement over
days or weeks may be appropriate.
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3.2 Interpretation of Follow-up Measurement Results
The purpose of the follow-up measurement is to estimate
the long-term average radon or radon decay product concentra-
tions in general living areas with sufficient confidence to
allow an informed decision to be made about risk and the need
for remedial action. It should be noted that if the results of
the screening measurement was above 20 pCi/1 or 0.1 WL and
short-term follow-up measurements were conducted under closed-
house conditions, an over-estimation of the annual average
concentration may result. However, the EPA recommends short-
term follow-up measurements in these situations because an
additional 12 months of exposure could cause a significant
increase in health risk.
The average of the follow-up measurements made in the two
different living areas in the home are intended for comparison
to guidance levels given- in terms of annual average concentra-
tion. Such guidance levels are discussed in the "Citizen's
Guide to Radon," published by the EPA Office of Radiation
Programs and available through your EPA regional office or your
State radiation control office. The following four paragraphs
are excerpted from that document and summarize the EPA guidance
for action based on the results of follow-up measurements.
If the follow-up measurement results are about 1.0 WL or
higher, or about 200 pCi/1 or higher, residents should be aware
that exposures in this range are among the highest observed in
homes and should undertake action to reduce levels as far below
1.0 WL (200 pCi/1) as possible. EPA recommends that action be
taken within several weeks. If this is not possible, residents
should determine, in consultation with appropriate State or
local health or radiation protection officials, if temporary
relocation is appropriate until the levels can be reduced.
If the follow-up measurement results are about 0.1 to
about 1.0 WL, or about 20 to about 200 pCi/1, residents should
be aware that exposures in this range are considered greatly
above average for residential structures, and should undertake
action to reduce levels as far below 0.1 WL (20 pCi/1) as
possible. EPA recommends that such action be taken within
several months.
If the follow-up measurement results are about 0.02 to
about 0.1 WL, or about 4 pCi/1 to about 20 pCi/1, EPA advises
that exposures in this range are considered above average for
residential structures. Residents should undertake action to
lower levels to about 0.02 WL (4 pCi/1) or below. EPA
recommends that residents take action within a few years,
sooner if levels are at the upper end of this range.
10
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If the follow-up measurement reults are about 0.02 WL or
lower, or about 4 pCi/1 or lower, residents should be aware
that exposures in this range are considered average or slightly
above average for residential structures. Although exposures
in this range do present some risk of lung cancer, reductions
of levels this low may be difficult, and sometimes impossible,
to achieve.
Diagnostic measurements made to determine the source of
radon influx into the house and to guide the choice of
mitigation techniques are beyond the scope of this document.
However, since a follow-up measurement should be made before
the need for permanent mitigation is decided, a similar
follow-up measurement conducted after the mitigation work is
completed can be used as a benchmark to estimate the efficacy
of the mitigation effort.
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4. EXAMPLES OF APPROPRIATE MEASUREMENT LOCATIONS
The following are examples of locations where screening
and follow-up measurements should be made.
1. A split-level house is built over a garage on the
lowest level and has a den and a bedroom built several
feet higher than the garage, a kitchen on a middle
level over the garage, and bedrooms on a level over
the den several feet higher than the kitchen. The
screening measurement should be made in the lowest
bedroom on the floor next to the garage. The
follow-up measurement should be the average of
measurements made in that same lower bedroom and
measurements made in one of the upper bedrooms.
2. A farm house has an uninhabitable dirt-floor cellar, a
ground floor containing a kitchen and a living room,
and an upper floor containing bedrooms. The screening
measurement should be made in the ground floor living
room, and the follow-up measurement should be the
average of measurements made in the same living room
and measurements made in one of the upper floor
bedrooms.
3. A multi-story apartment building has a livable,
finished basement used as a laundry room. The
screening measurement should be made in the basement,
and if the results warrant follow-up measurements,
they should be made in the bedroom and living room of
each apartment unit. If the source of radon is
believed to be the underlying soil, only the apartment
units on the lowest floors need to be tested.
4. A one-story, no basement, slab-on-grade house is
tested for radon. The screening measurement should be
made in a bedroom, and the follow-up measurement
should consist of measurements made in a bedroom and
the living room.
12
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5. RECOMMENDED USES OF GRAB SAMPLING
Short-term or grab sampling techniques can be used to
measure concentrations of either radon gas or radon decay
products in the air. Samples are usually acquired over a
5 or 10 minute sample period, which may be considered a
virtually instantaneous measurement when compared with most
other measurement techniques commonly used in homes. While an
individual grab sample may be quite accurate in representing
the concentration of radon or radon decay products at the
moment of sampling, it is usually a poor indicator of the
long-term average concentration because of the inherent
variability of the radon concentration in homes. For this
reason, grab sample results should be interpreted with
caution. However, grab sampling methods have two distinct
advantages over other measurement techniques. First, grab
samples can produce results within a matter of minutes to
hours, enabling one sampling team to test and produce results
for several houses each day. Second, the conditions at the
time of measurement are known to the sampler who must be
present during the measurement and who can take note of
unusual weather or other factors that may influence the result.
If grab samples are to be used, it is important to
remember that, unlike the other measurement techniques, the
results are greatly influenced by conditions that existed in
the home for 8 to 12 hours prior to the moment of measurement.
The results of measurements made in a tightly closed home will
differ significantly from the results of measurements made in
the same home after it has been thoroughly ventilated. The
results of integrated measurements of at least 24 hours in
duration, however, are most influenced by conditions during the
measurement period. It is therefore especially important when
taking grab samples to make every effort to conform to the
closed-house conditions for 12 hours before the measurement.
Grab sampling has been particularly useful in situations
in which homes located near sites of known high concentrations
must be screened quickly. Grab samples are also very useful as
diagnostic tools to trace the probable cause of elevated levels
in a home, although that application is beyond the scope of
this document. Grab techniques are not recommended for
follow-up measurements, however, because of their poor
correlation with long-term averages.
Because of the high uncertainties associated with the
short measurement duration, the results of a single grab sample
should not be used as the sole estimate of average
concentrations upon which a decision, such as the need for
remedial action, is based.
13
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6. CLOSED-HOUSE CONDITIONS
Short-term measurements used for comparison to guidance
levels should be made under closed-house conditions. (Short-
term measurements are made over a shorter period of time than
12 months and are not part of a series of four measurements
made over a year's time.) Closed-house conditions are
necessary for short-term measurements to stabilize the radon
and radon decay product concentrations and increase the
reproducibility of a measurement. To the extent reasonable,
windows and external doors should be kept closed (except during
normal entry and exit). Normal entry and exit includes a brief
opening and closing of a door, but an external door should
not be left open for more than a few minutes. In addition,
external-internal air exchange systems (other than a furnace)
such as high-volume, whole-house attic and window fans should
not be operating. For measurement periods of 3 days or less,
these conditions should exist for 12 hours prior to beginning
the measurement. It may be difficult to verify these
conditions or to implement them for an extended period, but
they should be adhered to as closely as possible.
Closed-house conditions will generally exist as normal
living conditions in northern areas of the country when the
average daily temperature is low enough so that windows are
kept closed. Depending on the area, this can be the period
from late fall to early spring. In some houses, the most
stable levels occur during late fall and early spring, when
windows are kept closed but the home heating system (which
causes some ventilation and circulation) is not used.§ If
information about variations of indoor radon levels i'n a
particular area is available, the information can be used to
choose a measurement time when the radon concentrations are
highest and most stable.
We recommend that measurements in northern climates be
made during the winter season for two major reasons. First,
closed-house conditions exist as normal living conditions, so
there is a fairly good assurance that the proper conditions
will exist prior to and during the measurement period. Second,
information on factors other than ventilation rates that
influence indoor radon concentrations indicate that concentra-
tions during the winter are generally higher than during the
summer.
It may be necessary, however, to make measurements in
northern climates during the summer, when closed-house
conditions are not the normal living conditions. It will then
be necessary to establish some means for providing reasonable
assurance that closed-house conditions exist prior to and
during the measurements.
14
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Organizations performing measurements in southern areas
that do not experience extended periods of cold weather should
evaluate seasonal variations in living conditions and identify
if there are times of the year when closed-house conditions
normally exist. If such times can be identified, that is when
measurements should be conducted. Air conditioning systems
that recycle interior air can be operated during the closed-
house conditions if radon measurements are being made. Home
owners should be aware that any air circulation system can
drastically alter the radon decay product concentration without
significantly changing the radon concentration.
Measurements lasting a few days or less should not be
conducted if severe storms with high winds are predicted.
Severe weather will affect the measurement results in the
following ways. First, a high wind will increase the
variability of radon concentration because of wind-induced
differences in air pressure between the house interior and
exterior. Second, rapid changes in barometric pressure
increase the chance of a large difference in the interior and
exterior air pressures, therefore changing the rate of radon
influx. The rate of radon released from the ground is also
affected. Weather predictions available on local news stations
should be sufficient to determine if this criterion is
satisfied.
A measurement made over 12 months, whether it is an
integrated measurement or a series of measurements, provides
information about the average concentrations during an entire
year, so the closed-house conditions do not have to be
satisfied for annual average measurements.
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7. INSTRUMENT SELECTION
There are several different measurement systems that may
be used to determine the radon or radon decay product concentra-
tions in houses. In practice, the choice of a system is often
dictated simply by availability -- if an adequate system is
available, you use it. If alternative systems are available,
then the cost or the duration of the measurement may become the
deciding factor. EPA has developed measurement protocols for
seven different systems (EPA86), and the Agency believes that
any of these systems, when used in accordance with the guidance
in that protocol document, can produce valid results. This
does not mean that all such measurements will produce results
with identical uncertainties, but rather that any of the listed
systems is capable of producing adequate results for screening
or follow-up purposes. Each system has its own advantages and
disadvantages, however, and the user must exercise some
judgment in selecting the system best suited to the individual
situation. The following sections detail the characteristics
of the seven systems, pointing out some of the advantages and
disadvantages of each one. This summary is not exhaustive but
is intended to guide the user in making an informed selection
of a measurement system.
7.1 Continuous Radon Monitors (CRM) or Continuous Working Level
Monitors CCWLM):
These two types of measurement systems are similar in that
they use an electronic detector to accumulate and store
information related to the periodic (usually hourly) average
concentration of radon gas or radon decay products. They are
installed in the house, turned on or programmed for the desired
operating time, and then left to operate for the programmed
time.
Advantages:
o Relatively short measurement duration (minimum of 6
hours for screening, 24 hours for follow-up
measurements).
o Hourly results can track the variation of concentra-
tions in the house.
o Most models have small precision errors.
o Results are available onsite.
Disadvantages:
o Costly (each unit may cost from $2500 to $10,000,
depending on model).
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o Some models are heavy and awkward to move.
o Requires extensive calibration in a radon calibration
chamber.
o Requires a trained operator.
7.2 Alpha-Track Detectors
Alpha-track detectors consist of a small sheet of a
special plastic material. The material is permanently marked
when exposed to alpha particles, such as those emitted by the
decay of radon or some of the short-lived radon decay
products. The detectors are usually in a filtered container
that serves to make the measurement specific for radon gas.
They are installed in the home and left for periods of up to 1
year. At the end of that period, they must be returned to a
laboratory for processing and analysis.
Advantages:
o Relatively low cost per detector.
o Convenient to handle and install.
o Unobtrusive when installed.
o No special skills required for deployment.
o Can be distributed by mail.
o Completely passive, needs no external power.
o Can measure the integrated average concentration over
a 12-month period, which is the optimal measure of
long-term concentration.
Disadvantages:
o Relatively long measurement period necessary (3 months
recommended minimum for currently available detectors)
o Large inherent variability (precision errors)
particularly at low concentrations if the area of the
detector that is counted is small.
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7.3 Charcoal Canisters
Charcoal canisters are small, flat containers filled with
a measured amount of activated charcoal. The top is often
perforated or screened to keep the charcoal from falling out,
and the container is covered with an airtight seal when the
canister is not being used for measurement. Some systems now
use a filter bag to contain the charcoal. The canisters are
usually obtained from a supplier and are typically left in
place for 2 to 7 days, resealed, and returned to the supplier
or analytical laboratory for evaluation. Analysis usually
consists of counting the gamma radiation emission rate from the
radon decay products resulting from the radon adsorbed on the
charcoal.
Advantages:
o Low cost per canister.
o Convenient to handle and install.
o Unobtrusive when installed.
o No special skills needed for deployment.
o Can be distributed by mail.
o Completely passive, needs no external power.
o With proper analysis, can yield precise results.
Disadvantages:
o Some canister types are sensitive to temperature and
humidity.
o The charcoal adsorption technique is inherently
limited to a few days of sampling, which makes a
longer term measurement impossible with a single
detector.
7.4 Radon Progeny Integrating Sampling Units (RPISU)
The RPISU is a radon decay product measurement system
consisting of a low flow-rate air pump that pulls air
continuously through a detector assembly containing a
thermoluminescent dosimeter (TLD). The unit is operated for
periods of 100 hours or longer. At the end of that time the
unit is removed, and the detector assembly is returned to the
analytical laboratory. The analysis consists of measuring the
light given off by the TLD during heating.
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Advantages:
o Measures radon decay product concentration directly.
o Relatively short measurement period.
o The detector assembly (not the entire unit) can be
sent by mail.
o There is extensive experience in the use of RPISUs,
and measurement errors are well established.
Disadvantages:
o The entire unit may be both heavy and awkward to move-
o May be limited to location with a.c. power.
o Significant capital cost per unit ($500-$3,000)
and for the readout system ($5,000-$10,000).
o Units must be installed and picked up by trained
personnel.
o Proper operation may be affected by high
concentrations of airborne particulates, such
as those caused by smoking.
7.5 Grab Sampling
Grab sampling consists of taking a small sample of air from
the home and analyzing the radon or radon decay product concen-
tration it contained. The radon grab sample is collected in a
special flask containing 100 to 2000 cubic centimeters of air.
The radon decay product grab sample consists of particulates
collected on a small filter. Both samples can be acquired
simultaneously with some systems. The samples should be taken
in accordance with guidelines in the protocols and evaluated
according to standard procedures using an electronic
scintillation counting system.
Advantages:
o Results are quickly obtained.
p Equipment can be portable.
o Can measure both radon and its decay products
simultaneously.
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o Can acquire and evaluate several samples per day.
o Conditions during the measurement are known to the
sampler.
Disadvantages:
o Very short measurement period may not be
representative of long-term average.
o Requires a skilled operator.
o Requires careful control of house conditions
for 12 hours before the measurement.
o System cost is $2,500 to $10,000.
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EPA86
DOES 6
DOE87
F184
Geo84
Go83
He85
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