United States Eastern Environmental EPA-520/5-77-011
Environmental Protection Radiation Facility October 1978
Agency P.O. Box 3009
Office of Radiation Programs Montgomery AL 36109
Radiation
The Effects of
Home Ventilation Systems
on Indoor Radon-Radon
Daughter Levels
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EPA-520/ 5-77-011
THE EFFECTS OF HOME VENTILA TION SYSTEMS
ON
INDOOR RADON-RADON DAUGHTER LEVELS
S. T. Windham
E. D. Savage
C. R. Phillips
Eastern Environmental Radiation Facility
P. O. Box 3009
Montgomery, Alabama 36109
October 1978
&EPA
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Radiation Programs
Waterside Mall East
401 M Street, S.W.
Washington, DC 20460
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EPA Review Notice
This report has been reviewed by the Environmental Protection Agency (EPA) and approved for
publication. Approval does not signify that the contents necessarily reflect the views and policies of the
EPA, nor does mention of trade names or commercial products constitute endorsement or recommendation
for use.
11
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FOREWORD
The Office of Radiation Programs carries out a national program designed to evaluate the
exposure of man to ionizing and nonionizing radiation, and to promote the development of controls
necessary to protect the public health and safety and assure environmental quality.
Technical reports allow comprehensive and rapid publishing of the results of Office of
Radiation Programs' intramural and contract projects. The reports are distributed to State and local
radiological health offices, Office of Radiation Programs' technical and advisory committees,
universities, laboratories, schools, the press, and other interested groups and individuals. These
reports are also included in the collections of the Library of Congress and the National Technical
Information Service.
I encourage readers of these reports to inform the Office of Radiation Programs of any
omissions or errors. Your additional comments or requests for further information are also solicited.
W. D. Rowe, Ph.D.
Deputy Assistant Administrator
for Radiation Programs
in
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PREFACE
The Eastern Environmental Radiation Facility (EERF) participates in the identification of
solutions to problem areas as defined by the Office of Radiation Programs. The Facility provides
analytical capability for evaluation and assessment of radiation sources through environmental
studies and surveillance and analysis. The EERF provides technical assistance to the State and local
health departments in their radiological health programs and provides special analytical support for
Environmental Protection Agency Regional Offices and other federal government agencies as
requested.
This study is one of several current projects which the EERF is conducting to assess
environmental radiation contributions from naturally occurring radioactivity.
Charles R. Porter
Director
Eastern Environmental Radiation Facility
IV
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ABSTRACT
A study was conducted in a house in Polk County, Florida, to determine the effects of
normal home ventilation methods on radon, radon progeny, and working levels. Three
ventilation conditions were studied which approximate those found during normal
occupancy. The effects of the central air conditioner, the central blower without air
conditioning and outside air ventilation were studied, with radon, radon progeny, and
working level measurements made sequentially until significant changes ceased to be
observed.
In all three experiments, radon, radon progeny, and working levels decreased, with
the decreases corresponding to estimated increases in house ventilation rate.
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CONTENTS
Page
FOREWORD ffl
PREFACE iv
ABSTRACT v
List of Tables vii
List of Figures vii
I. Introduction 1
II. The Study Site 4
III. Methodology 4
IV. Results 6
Baseline Conditions 6
Air Conditioning Operations 7
Central Fan Operation 10
Outside Air Ventilation 12
Ingrowth from Background 14
V. Discussion 14
VI. Summary and Conclusions 18
REFERENCES 19
VI
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TABLES
Page
1. Air Conditioning Experiment Data 9
2. Central Fan Experiment Data 10
3. Outside Air Ventilation Data 14
FIGURES
Page
1. Uranium and Thorium Decay Series 3
2. Floor Plan of Study House 5
3. Air Conditioner Depletion 8
4. Central Fan Depletion 11
5. Window Fan Depletion 13
6. Ingrowth 15
vu
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Vlll
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I. Introduction
The U.S. Environmental Protection Agency's Office of Radiation Programs is
conducting a multifaceted study of the radiological implications of the phosphate
mining and milling industry in the United States. The study began in June 1974 and has
concentrated mainly on facilities located in Florida, North Carolina, and Idaho. The
purpose of this study is to evaluate the radiological impact of this industry on the
environment and develop appropriate radiation protection guidelines in areas where
existing controls are determined to be inadequate.
Phosphate deposits throughout the world are known to contain elevated
concentrations of natural radioactivity. This radioactivity originates from the decay of
naturally occurring uranium and thorium present in the phosphate ores. Through
mining and processing, the radioactive materials are redistributed in the products,
by-products, and wastes of the industry. Levels of radioactivity in these media are
described by Guimond and Windham (1).
Mining of phosphate ores in the United States began in 1867. Mining at that time
entailed the removal of overburden using horse-drawn pans and screening to remove
only the pebble phosphate material. Mining was conducted principally on phosphate
deposits covered only with shallow overburden and little reclamation was performed on
the land. This mining technique, removing only the larger pebble phosphate, resulted in
redistributing much of the previously buried radioactive materials on or near the
surface. In later years some of the mined areas were reclaimed and returned to uses as
any other unmined land. As an indication of the large amount of phosphatic material
(and associated radioactivity) not removed by these coarse mining techniques, some of
this previously mined but not reclaimed land has been remined in recent years using
modern flotation techniques to remove this remaining phosphate matrix.
Modern mining and benefication techniques are much more efficient in the
removal of phosphate matrix from the ground. Large electric powered draglines often
remove 15.2 - 21.3 meters of overburden which is set aside to fill the mined-out pits. The
phosphate matrix is removed by the dragline and dropped into a sluice pit where it is
slurried with water and pumped to the washer plant. In the washer plant the slurry is
separated into three parts: the phosphate rock, sand tailings, and slime. The
radioactivity in these three products is associated principally with the phosphate rock
(42%) and the slimes (48%), with a lesser amount (10%) in the sand (1). The sand tailings
and slimes (a very fine clay in water suspension) are waste products. The slimes are
very slow to dewater and must be maintained in storage ponds for extended periods of
time. Modern reclamation techniques make use of the mined-out areas as disposal sites
for the sand tailings, slimes, and the overburden which may be used in various
combinations for reclamation.
Reclamation techniques vary widely depending on how recently the land was
mined, the availability of adequate materials for use in the project, the use for which the
land is being reclaimed, etc. Radioactivity in the reclaimed land varies considerably
based on the radioactivity in the materials used in reclamation and the proximity of the
radioactivity to the surface. For example, if the top 3-6 meters of material applied on the
reclaimed surface is clean overburden which was removed prior to mining, the
reclaimed land will be similar in surface radioactivity levels to the original unmined
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land. We found this overburden in Florida typically contains radium-226 concentrations
of 1-2 pCi per gram. The phosphate matrix material which is mined typically contains
40-50 pCi per gram of radium-226. Therefore, depending on the completeness of
removal of the phosphate matrix, the materials used in reclaiming, and the degree of
mixing of the materials during reclamation, the reclaimed land could have radium-226
levels ranging from 1 pCi per gram to 50 pCi per gram. It was found in sampling some of
the reclaimed land that radium concentration varied widely both horizontally and
vertically within small areas such as single building lots.
Vast reclamation projects have been initiated in recent years. An estimated 1.3 x 108
m2 to 1.4 x 108 m2 of phosphate mined land has been reclaimed in Florida. The
Polk County Health Department estimates that about 1.0 x 108 m2 have been
reclaimed in Polk County and is used as follows:
Use Percentage
Residential 29
Commercial or Industrial 8
Farming 16
Grazing 41
Miscellaneous 6
Presently in Florida about 5.3 x 108 m2 of land have been mined, and the
industry is currently mining about 2.2 x 107 m2 per year, about half of which is not
committed to slime ponds and is thus reclaimable. Consequently, vast amounts of
reclaimed land are expected to be made available in Florida for general use.
The radioactivity associated with reclaimed land usage results primarily from
radium-226 and its daughter products. Radium-226 is a member of the chain produced
by the decay of uranium-238 (figure 1). As the radium decays in the soil it produces
radon-222, a noble gas, part of which is free to migrate through the soil to the surface.
Radon-222 is radioactive and decays through several daughters to stable lead. Radon
reaching the ground surface is normally diluted in the atmosphere and dispersed.
However, if a structure is built on the land, the radon diffuses through the slab or floor
into the structure and may accumulate. Whether or not the radon and daughters
become hazardous depends on the quantity of radon entering the structure and the
degree to which it accumulates or remains in the structure. This accumulation rate for
radon and its decay products depends mainly on the influx rate and the ventilation or
leakage rate from the structure. Under theoretical conditions where no leakage from a
structure existed, the radon and its decay products would reach transient equilibrium
after some finite period of time. However, the natural infiltration or leakage from
structures precludes equilibrium from being attained. In fact, radioactive decay as a
removal process is generally small when compared to losses via ventilation effects. The
radon/radon daughter composition in structures varies temporally to a degree which
makes characterization through repetitive measurements extremely difficult. "Working
level" is the unit used to describe radon daughter product concentrations in air. It is
defined as any combination of short-lived radon daughters in 1 liter of air that will result
in the ultimate emission of 1.3 x 10s MeV of potential alpha energy (2).
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URANIUM - 238 DECAY SERIES
THORIUM - 232 DECAY SERIES
238
92u
45x1C?yr
f,
•
23-4
90Th
24 da
234
9, Pa
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9^
25«105yr.
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as"3
1620 yr
|..
222
86""
3.8 da
"
218
84PO
3nmn
'
214
82Pb
27 mn
214
83Bl
19.7 mm
Jl
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214
84 Po
16, 10* sec
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^
210
82Pb
194 yr
210
83Bl
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/.
...
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84 Po
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/n
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82°*
Stable
232
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61 hr
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90*
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//M
4
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I
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86Rn
54 sec
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212
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016 sec
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10.6 hr
212
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31 min
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...
Figure 1. Uranium and Thorium Decay Series
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To determine the radiological significance of radon and radon daughters in
structures built on phosphate reclaimed land in central Florida, a limited study was
begun in 1975. Monitoring devices to determine working level were placed in 125
structures, two-thirds of the structures being on reclaimed land and one-third on
land believed to be normal soil. In retrospect, some of the "control sites" were found to be on
land in which unmined phosphate formations were present or where phosphate slag or other
phosphate material was nearby. The data collected over several weeks indicated that some
structures built on reclaimed land had indoor radon daughter levels significantly greater than
structures not built on reclaimed land (3). Because of these findings, additional work was begun
to evaluate the many parameters which affect the working levels found in structures built on
phosphate reclaimed land. The purpose of the work described in this report is to quantify effects
of typical home ventilating systems on radon and radon daughter concentrations in homes built
on reclaimed land.
II. The Study Site
In July 1976 an unoccupied single family house located in Polk County, Florida, was
studied extensively over a period of 17 days and nights to characterize ventilation effects on
radon and radon daughter levels.The house studied was located in a subdivision constructed
almost totally on reclaimed land.
The house was typical of most houses in the development and of most houses built in that
area. It was built on a concrete slab-on-grade and was of concrete block construction. The area
of the house was approximately 186.5 m2 (heated and cooled) with an attached carport. Figure 2
shows the floor plan and salient features of the house. At the time of the study the house had
drapes and carpets, but no furniture.
The house was equipped with central heating and cooling, with the furnace and cooling coil
located in the attic and ducts delivering the conditioned air to the various parts of the house via
ceiling vents. There were two ducts to return air to the central'System. One intake grill was
located on an interior living room wall near the floor and the other in the ceiling of the hall. The
central system was designed to totally recirculate the air with no provision for introduction of
outside makeup air. This is typical of most home heating and cooling systems designed for use in
this area. A single thermostat located in the central hall controlled the operation of the unit. The
house had aluminum cased and framed windows which could be opened for natural ventilation
as weather permitted.
III. Methodology
In the course of the study, many parameters were measured in and around the
study house. These included radon and radon daughter concentrations, working level,
condensation nuclei, temperature, relative humidity,' and outside meteorological
conditions.
Measurements of radon concentration in the house were made using scintillation
counting cells. The cells have a nominal 125 cc volume and are coated on the inner
surface with activated zinc sulfide. The ends of the cells are fitted with a quartz window
which is optically coupled to a photomultiplier tube for counting. Decaying radon and
daughters in a cell produce scintillation in the zinc sulfide coating which are counted by
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l/l
Storage
i i iii
i
1
1 -1
Pamnrt
1
1
1
1
1
L
1
i
Dining
•
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•
•
•
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Kitchen
J
living Room
» •
*
k
Den
1 i— f—h
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Bed roo
• i
i r •
1 1
B
a
»
h
m
Bath
Closet '
Bedroom
L ' '
IBedroon
r
i
\
Window fan Installed for experiment (see text).
Figure 2. Floor Plan of Study House
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the photomultiplier detector. An air sample to be counted for radon is drawn into an evacuated
cell through a drying column to remove water vapor and radon daughters. The sample is
counted after an appropriate time for radon daughter ingrowth is allowed.
Measurements of radon daughter concentration and working level were performed
in several ways. In one method, depending on the daughter levels expected, 50 to 300
liters of air were drawn through an 0.8 micrometer pore size filter which was then
counted on an alpha spectroscopy system utilizing a surface barrier detector. Data was
accumulated in a 1024 channel analyzer and computer-reduced using the methods
described by Martz, et al. (4) for determining the working level and radon daughter
values. Methods of data reduction described by Harley and Pasternack (5) were also
used in some cases to obtain immediate results at the study site.
Measurements of working level and radon daughters were also made using a prototype
instant working level meter (IWLM) developed by Groer, et al. (6) at Argonne National
Laboratory. This instrument draws approximately 20 liters of air through a 1.2 micrometer pore
size filter, then counts the filter for 3 minutes using both alpha and beta detectors. Data is
reduced in the instrument and the working level and daughter concentrations are displayed
digitally. From sampling to readout of data requires only 6 minutes.
This ability to sample and obtain data rapidly was very useful in the ventilation experiments
performed in the house. Working level determinations shown in the remainder of this report
were made using the IWLM. Comparisons of data were made between those produced by the
alpha spectroscopy methods described previously and by the IWLM (7). Comparison of these
two measurement techniques showed that the data produced agreed satisfactorily. The radon
daughter concentrations used to estimate ventilation rates and equilibrium ratios were
determined by alpha spectroscopy.
Because of the importance in making projected dose calculations from the indoor
radioactivity measurements, concentrations of airborne submicron particles were determined.
An Environment One Condensation Nuclei Monitor Model Rich 100 was used to monitor the
real-time concentration of nuclei in air. The instrument detects particles with diameters of
0.0025 micrometer and larger in concentrations from 50 particles per cubic centimeter up to 106
particles per cubic centimeter of air. A recording hygrothermograph was used inside the house to
measure relative humidity and temperature. Outdoor meteorological data were obtained from a
National Weather Service facility located approximately 9.7 kilometers from the house.
Air velocities through windows or through the ducts and grills of the central
heating/cooling system were measured using an Alnor Instrument Company Thermo-
Anemometer Type 8500.
IV. Results
Baseline Conditions
At the beginning of the study, the house had been unoccupied and closed for about 10 days.
The central heating and air conditioning system had been off for this period and all the windows
had been closed. The only air exchange with outside air was due to leakage around or through
window and door cracks, flaws in the weather stripping, etc. It was felt that the working level in
the house at this time would be at a maximum for the particular set of environmental parameters
which affect radon influx into the structure. Several measurements of the working level for the
closed structure ranged from .17 to .20 working levels. Outside ambient radon levels (0.5 -1.5
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pCi/1, .003 - .005 WL) determined prior to experiments were sufficiently lower than unventilated
levels found in the house (.17 .20 WL) to preclude interference from diurnal variation.
Measurements showed the relative radon daughter equilibrium (WLXlOO/Rn) to range from
.41 to .44 for this set of conditions. Only once during the study at this house did the working level
rise significantly above these values. Following a very heavy rain late one afternoon the working
level rose to a value of .25. At the same time the radon emanation rate from the soil outside the
house dropped sharply. It is speculated that the heavy rainfall saturated the soil surrounding the
house and in effect "capped" the radon in the ground. The relatively dry soil underneath the slab
of the house remains uncapped and allows the radon emanation rate into the house to increase,
thus the increase in working level. This hypothesis, along with data on other outside the house
measurements, will be examined in a later report.
The degree of radioactive equilibrium between radon and its daughters in a dwelling is
dependent on the ventilation rate. These relations have been described by Haque and Collinson
(8). If the daughter ratios are known, the ventilation rate may be calculated from the above-
mentioned relationship. Due to the short half-life of Ra A, in relation to the time between
removal of the filter and counting and the relative low concentrations of daughters involved, the
equilibrium between 2l4Pb (Ra B) and 214Bi (Ra C) is used to estimate ventilation rates. Since the
ventilating air contains negligible daughter concentrations in comparison with room air, the
relationship between Ra C and Ra B can be solved for the fractional ventilation rate V (min"1).
V = XC [(CB/Cc)-l]
where CB and Cc are the concentrations of Ra B and Ra C, respectively, and Ac is the decay
constant for Ra C (.035 min"1).
Based on the concentrations of Ra B and Ra C measured in the house during the closed con-
ition, it was estimated that the house had an inherent ventilation or leakage rate of
approximately 0.4 - 0.6 air changes per hour. This is consistent with commonly accepted
values of .5 to 1.5 air changes per hour for occupied homes (9,10). An unoccupied home such as
this one was would be expected to have a slightly lower ventilation rate.
Air Conditioning Operation
Previous unpublished work by this facility and others indicated that operation of a central
heating or air conditioning system would reduce the radon and working level inside a home.This
was reportedly true even in houses equipped with a system which did not introduce "fresh or
makeup" air into the central system. The reduction in working level might be explained by the
increased "plate-out"of radon daughters caused by the circulation of house air in the duct
system. However, plate-out would not explain the concurrent reduction in radon levels which
had been observed. This more likely had resulted from dilution with outside air caused by
increased ventilation.
A study was conducted in the house to quantitatively determine the reduction in radon and
working level caused by operation of the central air conditioning system. The house had been
closed and the air conditioning system off for at least 12 hours prior to the beginning of the
study. Measurements of radon and radon daughters were made prior to and at selected intervals
for approximately 700 minutes after the air conditioning system was turned on (figure 3, table 1).
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- WORKING LEVEL
- RADON CONC. (PCI/L)
oo
360
TIME IN MINUTES
Figure 3. Air Conditioner Depletion
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Table 1
Air Conditioning Experiment Data
Condensation Ventilation
Equilibrium Nuclei Rate (Air
Rn (WLxlOO/ (Nuclei changes
(pCi/1) WL Rn) per cm3' per hr)
Baseline 34 .11 .35 6xl03 .50
Steady State 7 .01 .10 3xl03 2.5
Data presented in figure 3 are an average of two separate but duplicate experiments. After
approximately 180 minutes of continuous running, the working level had been reduced by a
factor of approximately 10 (from. 11 to .01 working level). Radon levels were reduced by a factor
of approximately 5.
This reduction in radon concentration would indicate an increase in the effective ventilation
rate from .5 air changes per hour up to approximately 2.5 per hour caused by the central air
moving system. Since no makeup air is intentionally introduced into the system, it is assumed the
increased ventilation rate results from leaks in the duct system and alteration of the relative
indoor/outdoor pressures. The radon daughter equilibrium at the onset of the test was .35 and
fell to a value of .10 at 300 minutes of operation, where it remained.
At the time the air conditioner was turned on the indoor temperature was 30° C.. The
system thermostat was set at 24° C and the system ran continuously for approximately 180
minutes to lower the temperature sufficiently for the unit to cycle. After reaching this point, the
unit continued to cycle with approximately 10 minutes off-time and 20 minutes on-time.
Outdoor temperatures varied between 28° C and 32° C during the experiment. This setting of
the thermostat and resultant operating cycle are as might be expected in a typical occupied
home.
Measurements of condensation nuclei concentrations inside the house were made prior to
starting and throughout the air conditioning experiment. The initial concentration of nuclei was
6xl03/cm3. During the first 60 minutes of operation of the air conditioning system the
concentration rose steadily to a high of 15xl03/cm3 at which time the level began to decline. At
approximately 300 minutes after startup the concentration had fallen to 3xl03/cm3 where it
remained for the duration of the experiment. The initial rise in the concentration of nuclei was
due to resuspension of small particles by the increased air movement. Continued operation of
the air conditioning system tended to "clean" the air in the house by circulating it through the
filter system.
Air-flow through the air conditioning duct system was measured using a
thermoanemometer at the return air ducts. The measured value was approximately 0.47 m3/s
entering the return plenum. Literature for this particular air conditioning system lists desirable
air flows between 0.56 - 0.66 m3/s.
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Central Fan Operation
It is believed that the reductions in working level and radon as measured during the air
conditioning experiment resulted from the movement of air and not as a result of cooling the air.
If this were the case, then the central heating system or simply the operation of the central fan or
blower would have the same effect.
Measurements of radon concentration and working level were made prior to and at selected
intervals for 600 minutes after the central blower was started (figure 4, table 2).
Table 2
Central Fan Experiment Data
Condensation Ventilation
Equilibrium Nuclei Rate (Air
Rn (WLxlOO/ (Nuclei changes
(pCi/1) WL Rn) per cm3) per hr)
Baseline 25 .09 .33 5xl03 .57
Steady State 5 .01 .15 3xl03 2.1
Data presented in figure 4 are an average of two separate but duplicate experiments. After
approximately 180 minutes of operation the working level had been reduced from .09 to .01, a
reduction of 9. Radon levels had been reduced by a factor of 5. These reductions are consistent in
magnitude and time with those achieved in the air conditioning experiment. The radon daughter
equilibrium was .33 at the onset and fell to a value of .1-.2 after 300 minutes of operation.
Estimated ventilation rates increased from .57 air changes per hour at the beginning of the
experiment to 2.1 air changes per hour after 300 minutes.
The central fan system ran continuously during the experiment with no cycling. Air flow in
the duct system was the same as in the air conditioning experiment. Inside temperatures ranged
from 28. - 35° C during the experiment. Outdoor temperatures ranged from 28° C to
approximately 34° C. Indoor temperatures were higher than outdoor because of the air being
circulated through the hot duct system in the attic.
Condensation nuclei concentrations varied much the same as in the air
conditioning experiment. At the start of the experiment the concentration was
5xl03/cm3, rose to 12xl03/cm3, then declined to approximately 3x10*/cm3 where it
remained.
10
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s?-
i
§
60
• - WORKING LEVEL
A - RADON CONC. (PCI/t)
120
180 240
TIME IN MINUTES
300
Figure 4. Central Fan Depletion
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All reductions in working level and radon, changes in equilibrium, increases in
ventilation rate, and condensation nuclei concentrations were consistent with those
measured in the air conditioning experiment. This indicates that the reduction in radon
and daughters was the result of increased ventilation rate due to air movement in the
central duct system, not the cooling of air.
Outside Air Ventilation
Another ventilation condition commonly encountered in most homes is when
windows are opened and outside air is purposefully allowed to circulate through the
house. The outside air at the time of this study had radon concentrations between 0.5
and 1.5 pCi/1 and working levels between .003 and .005. While both the radon and
working level values are slightly high for normal outside air, it is believed that the large
amount of radon entering the atmosphere from nearby large phosphate land tracts may
cause somewhat elevated levels in this area. It was expected that these levels would
quickly dilute the indoor levels when ventilation was initiated.
To obtain an accurate measurement of the quantity of outside air entering through
the open windows, a window fan was used to exhaust a measured amount of inside air.
Measurements showed that the influx rate of outside air equaled the exhaust rate of the
fan. The fan was installed in a den window (see figure 2) and used to exhaust indoor air
from this location. Windows in the other rooms of the house were opened different
amounts to assure approximately equal air-flow through each room. The fan exhausted
0.68 m3/s with approximately equal movement of air throughout the various areas of the
house. The interior of the house had a volume of approximately 453 m3, thus the flow of
0.68 m3/s represents an air turnover rate of 5.4 changes per hour. Though many houses
don't use window fans, it was felt that the relatively low flow rate through the house
caused by the fan would be typical of what may be encountered with all windows
opened fully and a slight breeze outdoors. As an example, assuming two open windows
(.61 x .45 m openings) on the upwind side of the house, adequate outlet windows open
on the downwind side, and a 4.8 - 8.0 kilometer per hour outside breeze, the ventilation
rate was calculated to be between 0.41 and .69 m'/s (11). Thus the condition established
by operation of the window fan is typical of what might be seen if house windows
remained open on a typical day with light winds.
All measurements of radon and working level in the house were made in the central
hall to avoid sampling in a direct flow of incoming outside air. Measurements of radon
and daughters were made prior to and at selected intervals for 160 minutes after the
windows were opened and the window fan started (figure 5, table 3).
Data presented in figure 5 are an average of two separate but duplicate
experiments. Working level values dropped from .11 to background (approx. .01) in 20
minutes. Radon concentrations also fell in 20 minutes from 25 pCi/1 to 1.5 pCi/1 which
also is background. Based on the volume of air being moved by the fan, this reduction
occurred after 1.8 air changes in the house.The radon daughter equilibrium also fell
rapidly from .30 down to .08 at 26 minutes.
Condensation nuclei concentrations prior to starting the fan were 1.7xl03/cm3. At
18 minutes after the windows were opened and fan started the nuclei concentration had
risen to 36xl03/cm3 and began to decline slightly. This was caused by the influx of dusty
outside air (and/or the pickup of indoor dust).
12
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• - WORKING LEVEL
A - RADON CONC. (PCI/L)
o
s-
TIME IN MINUTES
rigure 3. window Fan Depletion
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Table 3
Outside Air Ventilation Data
Condensation Ventilation
Equilibrium Nuclei Rate (Air
Rn (WLxlOO/ (Nuclei changes
(pCi/1) WL Rn) per cm3) per hr)
Baseline 25 .11 .30 1.7xl03 .50
Steady State 1.5 .01 .08 20-36xl03 5.4
Ingrowth from Background
The rate of ingrowth or buildup of radon and daughters depends primarily on the input rate
of the radon and the leakage rate from the house. As mentioned previously, the input rate is
dependent also on soil moisture and atmospheric conditions such as barometric pressure. For
this given house and its leakage rates and a given set of influx conditions, the ingrowth rate was
determined. The house had been opened and completely ventilated prior to start of the
experiment. Working level and radon concentration in the house were at background or
outdoor levels. The ingrowth was measured through approximately 750 minutes after the house
was closed (figure 6). Data presented in figure 6 are an average of three separate but identical
experiments. It is interesting to note that after 80 minutes of ingrowth the working level only
reached approximately 5 percent of the final baseline or equilibrium value of 0.2 working level
which was found in the house after being closed for 2 weeks. During normal operating cycles of
the air conditioning and heating units in which the house would normally be closed, an "off
cycle of 80 minutes or longer would be unusual. Therefore, under these conditions for this house
the working level would not be expected to approach the "closed house" equilibrium value. After
approximately 10 - 12 hours the ingrowth rate declines but continues to increase toward the
equilibrium level.
Prior to closing the house when the indoor levels were at outside or background levels, the
radon daughter equilibrium was .03. After approximately 500 minutes the equilibrium had risen
steadily to .32. Baseline equilibria were reported earlier and were measured at .41 to .44 for this
particular house.
V. Discussion
The study house located in the central Florida phosphate area was built using
construction materials and methods typical to many if not most other houses built in that area in
the past several years. Other than the normal weatherstripping which is built into aluminum
windows and pre-hung door units, no steps had been taken to reduce the natural infiltration of
outside air into the house. The estimated turnover rate of .5 air changes per hour is what might be
expected from an unoccupied house of this design. The best available data suggests that the
average turnover rate for an occupied single family house may be as high as 1.5 changes per hour
14
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• - WORKING LEVEL
A - RADON CONC. (PCI/L)
160 240 320 400 480 560 640 720 800
TIME IN MINUTES
Figure 6. Ingrowth
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(9,10). Therefore, it is felt that data obtained in the study house would be generally applicable to
other structures of similar design if the different radon influx rates are factored in. This has been
confirmed to a degree by a similar set of experiments, though less extensive, conducted in 3 other
houses in the area. The reductions in working level and radon were very similar in time and
magnitude to those measured in this study house.
Some structures which differ appreciably in natural infiltration or ventilation rate would
produce depletion and ingrowth rates different from those described above. In an old or poorly
built new structure in which the natural leakage rate was high, the working level buildup would
not be as great for the same radon influx. Likewise, the operation of a central air movement
system would produce a more rapid reduction in radon and working level. In a newly built house
which incorporated extensive measures toward being an "energy efficient" structure the natural
infiltration or leakage would be low and thus depletions would occur less rapidly and buildups
more rapidly for a given radon influx. It has been reported (10) that the greatest percent WL
reduction occurs where the initial ventilation rate is lowest, with the percent WL reduction
gradually decreasing until little further reduction is seen. For these reasons, in conducting
surveys of homes in which working level is to be measured, it may be necessary in some cases to
have an indication of the natural leakage rate. This can be obtained by actual measurement or
through estimation. Measurement of this parameter is more accurate but requires greater time
and equipment. Several techniques have been reported which employ the measurement of the
depletion rate of gases such as sulfur hexafluoride or helium which had been introduced into the
structure. The method used in our study and described earlier in this report employs the ratios of
the daughters of radon to estimate the ventilation rate. The American Society of Heating,
Refrigeration, and Air-Conditioning Engineers Handbook (11) describes methods for
estimating leakage based on numbers and sizes of windows and doors plus other factors. For
houses which are suspected of falling outside of the normal leakage rate of .5 to 1.5 air changes
per hour, one of these methods should be used to find the actual ventilation rate.
In addition to the effects of the leakage rates, the living habits of the occupants have a great
influence on the working level which may be measured. For example, a home which has several
children who frequently exit and enter the house will have a greater turnover rate than a home
which has no children and the adult occupants work during the day. The preference of the
occupants for running the air conditioning system versus that for fresh air and opening windows
must also be taken into account. Seasonal changes in the natural climatic conditions will also
have an influence on the extent to which the occupant depends on outside air or the air
conditioning/ heating system.
As a result of the factors discussed, it follows that a "grab sample" or short duration
measurement of working level will generally not represent the average or typical condition for a
structure. It was shown that for a given radon input rate for a particular house, the working level
as measured at any one period in time would be dependent on where the heating or cooling
system was in its operating cycle or the number of windows and/or doors open. If the central
heating/cooling system was operating on a relatively short cycle (3-6 cycles per hour) then the
working level as measured could vary by a factor of 10. For this reason we believe that a single
measurement of working level with no regard for these other factors could be very misleading in
estimating an average value. To circumvent these problems, it would be necessary either to
account for these variables at the time of measurement or take an integrated measurement over a
sufficient time period to find the average working level. For purposes of expediency it may be
necessary in some houses to take a grab sample and factor in these variables. In such a case it
would be desirable to know the maximum working level which could be expected at equilibrium
and the average working level. Because of the many parameters which affect the working level
16
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and all of the factors which would have to be accounted for a separate report is being prepared
which deals with this problem. Mathematical models are being prepared which can be used in
conjunction with limited measurement data in a structure to estimate a maximum and average
working level for the structure taking into account these variables.
One method of working level determination which minimizes many of these measurement
problems employs techniques that integrate the measurement over an extended period. One
method used extensively in the reclaimed phosphate land evaluation is the track etch film
dosimeter (3). This is a passive measurement device left in a structure for a 6 to 18-month period
to measure the average working level. Alpha energy released by the airborne radioactive
daughters causes ionization tracks on the film surface. Upon development or etching the tracks
can be counted and the density of the tracks related through calibration factors to the working
level in the house. For the house employed in this study a track etch film was in place for 9863
hours during which time the house was occupied and recorded an average of .077 working levels
for the period. As noted in the previous discussion, an instantaneous measurement could have
fallen anywhere between 0.2 and .005 working levels.
Another integrating measurement technique which has been used in this house is the
thermoluminescent dosimeter (TLD) air pump (3). With this device air inside the house is
pumped through a filter system which collects the radon daughters. Alpha energy from the
daughters exposes a TLD chip which is evaluated in a reader to indicate the total alpha energy
absorbed by the chip. A TLD chip is normally exposed for a 1-week period. To determine aver-
age working level and to average seasonal effects, at least four separate pumpings should be
conducted over a 1-year period. Because of logistics problems, only three pumping periods were
obtained in the study house during normal occupancy. These produced an average working level
value of .067 for the three periods. The total sampling time for the three periods was 74 hours,
somewhat short of the desirable time of 600-700 hours for four pumpings in 1 year.
The Office of Radiation Programs publication, "A Preliminary Evaluation of the Control
of Indoor Radon Daughter Levels in New Structures," describes technology for control of
radiation levels in new structures(lO). Of the technologies described for the control of indoor
radon daughters, several are not easily applicable to structures which have already been built.
For instance, the removal of reclaimed material, or pouring an extra thick concrete slab, or the
use of a sealant could not easily be applied to existing structures. One method described in the
report, improved effective ventilation, is more easily applied to existing structures. Methods of
increasing effective ventilation require either introducing controlled amounts of relatively radon
free air for dilution or physical removal of daughter products on a filter or electronic air cleaner.
Data presented earlier in this report substantiate the usefulness of outside air as makeup air
for dilution and reduction of working level. From our evaluation of the natural infiltration rate
for the study house (approximately .5 air changes per hour, unoccupied), it appears that this
volume of dilution plus the increased dilution gained by operation of the central blower is
adequate to reduce the indoor working level a considerable amount. In the case of the study
house, should it be deemed necessary based on any applicable guidance to lower the indoor
working level, it may be sufficient to assure periodic operation of the central blower system. This
could be accomplished with a tinier used in conjunction with the central blower control to cause
periodic operation of the blower, regardless of the normal demand placed on the blower by the
heating/cooling thermostat. This system should be cheaper to install, operate, and maintain
than a combination of intentionally introduced makeup air and daughter product removal. In
addition to the reduction in working level obtained, there would be the added benefit of air being
circulated in the house which helps maintain more comfortable living conditions throughout.
17
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In some cases it may be desirable to assess the effectiveness of a blower system prior to the
purchase and installation of control timing devices. This assessment is easily accomplished by
closing the structure without operating any ventilation system for a time sufficient for ingrowth
(12 - 14 hours), and measuring the working level. The blower is then operated for several hours
and the working level measured again. If the percent reduction is adequate, then an appropriate
timer can be selected and installed to operate the blower as required to maintain the working
level within acceptable guidelines. If the central blower system alone did not acceptably reduce
the level, then other methods of control may be considered.
VI. Summary and Conclusions
Data are presented in this report as to the effect of natural ventilation and operation of
central heating/cooling systems on radon concentration and working level in a house built on
reclaimed phosphate land. The effects of these systems on condensation nuclei concentrations,
radon daughter equilibrium states, and air turnover rates are also discussed. From the data
presented in the report the following conclusions are reached:
1. The influx of outside air through open windows is very effective in reducing indoor
working level.
With airflows through the house which are typical of that expected during a day with a 4.8-
8.0 kilometer per hour outside breeze and windows open, the working level is reduced by a
factor of 10 or more in 20 minutes.
2. Operation of the central blower system, through forcing increased ventilation, is
effective in reducing indoor working level.
The increased ventilation rate resulting from operation of the central blower system causes a
reduction by a factor of 10 in the indoor working level after approximately 180 minutes of
operation. More limited measurements in three other houses produced similar results.
3. Ingrowth or radon daughters and resultant working level occurs at a rate dependent on
several factors.
The influx rate of radon into the structure and the effective ventilation rate of the structure
primarily determine the working level ingrowth rate. Factors such as recent heavy rainfall
were seen to greatly influence the radon influx rate and thus working level in the structure.
4. A single grab sample or short term measurement of working level could vary
significantly from the average working level.
Trying to estimate an average working level for a structure based on a short term sampling
method will in all probability produce results which are in error, possibly by as much as a
factor of 10. The central heating/ cooling system in its normal operating cycle can produce
widely varying results. For an accurate determination of average working level either the
many influencing parameters must be accounted for or an integrated type measurement
must be made.
18
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REFERENCES
1. GUIMOND, R. J. and SAM T. WINDHAM. Radioactivity Distribution in Phosphate
Products, By-Products, Effluents, and Wastes, ORP Technical Note, ORP/CSD 75-3
(August 1975).
2. U.S.PUBLIC HEALTH SERVICE. Publication No. 494, Control of Radon and
Daughters in Uranium Mines and Calculations on Biologic Effects (1957).
3. U.S. ENVIRONMENTAL PROTECTION AGENCY. Preliminary Findings - Radon
Daughter Levels in Structures Constructed on Reclaimed Florida Phosphate Land,
ORP/CSD-75-4 (September 1975).
4. MARTZ, D. E., et al. Health Physics H, 131 (1969).
5. HARLEY, N. H. and B. PASTERNACK, Health Physics!!, 109 (1969).
6. GROER, P. G., et al. Argonne National Laboratory Report P7334C (1974).
7. PHILLIPS, C. R. Radon and J^adon Daughter Measurements and Methods Utilized by
EPA's Eastern Environmental /Radiation Facility. A paper presented at HASL
Workshop on Radon Measurements (February 1977).
8. HAQUE, A.K.M.M. and CpLLINSON, A.J.L. Radiation Dose to the Respiratory System
due to Radon and its Daughter Products, Journal of Health Physics Society,
Volume 13, pp. 431-443 (1967).
9. HANDLEY, T. H. and C. J. BARTON. Home Ventilation Rates: A Literature Survey,
ORNL-TM^318 (September 1973).
10. FITZGERALD, J. E., et al. A Preliminary Evaluation of the Control of Indoor Radon
Daughter Levels in New Structures, EPA-520/4-76-018 (November 1976).
11. AMERICAN SOCIETY OF HEATING, REFRIGERATING, AND AIR-CONDITIONING
ENGINEERS, INC. Handbook of Fundamentals, pp. 343-346 (1974).
19
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-520/5-77-011
2.
3. RECIPIENT'S ACCESSION NO.
4. TITLE AND SUBTITLE
The Effects of Home Ventilation Systems on
Indoor Radon-Radon Daughter Levels
5. REPORT DATE
October 1978
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
S. T. Windham, E. D. Savage, and
C. R. Phillips
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
10. PROGRAM ELEMENT NO.
Eastern Environmental Radiation Facility
P. 0. Box 3009
Montgomery, AL 36109
11. CONTRACT/GRANT NO.
12. SPONSORING AGENCY NAME AND ADDRESS
U. S. Environmental Protection Agency
Office of Radiation Programs
401 M Street, SW
Washington, DC 20460
13. TYPE OF REPORT AND PERIOD COVERED
Final
14. SPONSORING AGENCY CODE
EPA/200/03
15. SUPPLEMENTARY NOTES
16. ABSTRACT
A study was conducted in a house in Polk County, Florida, to
determine the effects of normal home ventilation methods on radon,
radon progeny, and working levels. Three ventilation conditions
were studied which approximate those found during normal occupancy.
The effects of the central air conditioner, the central blower with-
out air conditioning and outside air ventilation were studied, with
radon, radon progeny, and working level measurements made sequentially
until significant changes ceased to be observed.
In all three experiments, radon, radon progeny, and working
levels decreased, with the decreases corresponding to estimated
increases in house ventilation rate.
7.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
Radon Isotopes
Environmental Radioactivity
Natural Radioactivity
b.lDENTIFIERS/OPEN ENDED TERMS C. COSATI Field/Group
Radon Progeny
Radiation Surveys
Working Level
1802
1806
1808
18 Oi'^rP'B'jTIOM STATt WENT
Release to public
19. SECURITY CLASS (This Report)
Unclassified
21. NO. OF PAGES
24
2O SECURITY CLASSJTVi/jmyfe;
Unclassified
22. PRICE
EPA Foe- 2270-1 rR... 4-77i
20
•U.S.GOVERNMENT PRINTING OFFICEi 1978-640-708/6178. Region 4.
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