United States Air and Energy Environmental EPA/600/9-90/005e
Environmental Protection Research Laboratory January 1990
Agency Research Triangle Park NC 27711
Research and Development _^_^^___________
c/EPA The 1990 International
Symposium on Radon
and Radon Reduction
Technology:
Volume V. Preprints
Session VIII: Radon
Prevention in New
Construction
Session C-VIII: Radon
Preventionin New
ConstructionPOSTERS
Session \X: Radon in
Schools and Large
Buildings
February 19-23.1990
Stouffer Waverly Hotel
Atlanta, Georgia
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Session VIII:
Radon Prevention in New Construction
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VIII -1
EVALUATION OF RADON RESISTANT NEW CONSTRUCTION TECHNIQUES
by : Terry Brennan
Mike Clarkin
Camroden Associates, Inc.
Oriskany, NY 13424
Michael C. Osborne
USEPA/AEERL
Research Triangle Park, NC 27711
Bill Brodhead
WPB Enterprises
Riegelsville, PA 18077
ABSTRACT
In 1989 a project to evaluate three approaches to radon
resistant new construction was undertaken by the Radon Mitigation
Branch of the EPA Air and Energy Engineering Research Laboratory.
Test houses were selected. Indoor radon was measured to evaluate
the effectiveness of foundation sealing and passive and active soil
depressurization at preventing radon entry into the houses. Tracer
gas methods were developed to estimate the fraction of air that was
being drawn through the cracks and holes in the foundation by the
soil depressurization system. Below grade leakage area was
estimated using tracer gas data. It was found for the small number
of houses in the study that a very small amount of below grade
leakage can still result in elevated indoor rtdon levels. Passive
soil depressurization systems were found to perform better than
mechanical barriers alone, but did not keep radon levels as low as
active systems. Active soil depressurization systems were found to
perform very well.
KEY WORDS
Radon, Active Sub-slab Depressurization, Passive Sub-slab
Depressurization, Barrier.
This paper has been reviewed in accordance with the u. s,
Environmental Protection Agency peer and administrative
review policies and approved for presentation and
publication.
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INTRODUCTION
Growing concern about the health risks associated with indoor
radon, a radioactive gas found in varying amounts in nearly all
houses, has underscored the need for dependable radon-resistant
residential construction techniques. In response to this public
health exposure the United States Environmental Protection Agency
(EPA) has developed and demonstrated a variety of methods that have
been used to reduce indoor radon levels in existing houses. Many
of these methods are being included in the design and construction
of new houses. In an effort to determine whether a house built with
radon resistant techniques would have had elevated radon levels if
the radon resistant techniques had not been used and to evaluate
the effectiveness of those techniques, EPA sponsored the Evaluation
of Radon Resistant Construction Techniques project. This project
addressed active versus passive sub-slab depressurization systems,
investigated the effectiveness of using the foundation as a
barrier, and assessed the energy penalties associated with the use
of a sub-slab depressurization system. Because of the limited scope
of this paper, the energy penalty issues will not be covered.
Two houses in Northern Virginia and two houses in Allentown,
Pennsylvania, were selected for this project. All houses had
sub-slab depressurization systems installed or provided for during
construction. Careful attention was paid to foundation detail.
Measurements made in these houses included continuous radon
measurements with the sub-slab depressurization system operating
under various conditions and, to some extent, monitoring of
pressure differentials and airflows.
INVESTIGATION OF HOUSES ~ RADON RESISTANT TECHNIQUES USED
The two Virginia houses, designated VA1 and VA2, are nearly
identical 2-story frame houses built in a subdivision. The two
houses are approximately 300 ft apart. Each house was constructed
with radon resistant techniques including a layer of DOT #2 or ASTM
#57 stone pebbles placed beneath the slab prior to pouring, a
single-point sub-slab depressurization system, and perforated pipe
placed within the stone layer. Additional techniques used were
poured concrete foundation walls, sump holes capped and vented to
the outdoors, and caulked floor/wall joints, form ties, and
expansion joints.
The two Pennsylvania houses, designated PA1 and PA2, each
has a layer of DOT #2 or ASTM 157 stone pebbles beneath the slab,
a single-point sub-slab depressurization system, poured concrete
foundation walls, capped sump holes, and caulked floor/wall joints
and form ties. Both houses have perforated sub-slab interior
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footing drains connected to the sump holes. In House PA1, the
sub-slab depressurization penetration is located approximately 18
in.* away from the footing drain. The House PA2 sub-slab
depressurization system is connected directly to the sump hole.
RADON SOURCES
Sub-slab radon grab samples were taken at all houses. The two
Virginia houses averaged less than 100 pCi/L beneath the slab. The
two Pennsylvania houses averaged concentrations in excess of 1000
pCi/L beneath the slab.
ACTIVE VERSUS PASSIVE SUB-SLAB DEPRESSURIZATION SYSTEMS
Radon measurements were taken with the sub-slab system in the
active and passive modes at Houses VA1, PA1, and PA2. The results
of the radon measurements are illustrated in Figures 1,2, and 3,
respectively. As can be seen, the radon concentrations in House
VA1 are quite low. This was to be expected because the sub-slab
radon grab samples indicated radon concentrations less than 100
pCi/L. For this reason it was decided that this house and House VA2
were not appropriate for this portion of the study. In order to
determine the effectiveness of radon resistant construction
techniques, it was felt that radon levels of at least 700 pCi/L
(Br88) beneath the slab should be present.
(*) Readers more familiar with metric units may use
the factors listed at the end of this paper.
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C Sub-slab passive 1/20/89 1/31/89
B Sub-slab active 1/31/89 - 2/3/89
m Barrier only 2/24/89 -3/25/89
Figure 1. House VA1 basement radon concentrations with sub-slab
system in the passive and active nodes and with the exhaust pipe
capped. (Error bars show 1 standard Deviation)
House PA1 averaged 1.1 ± 0.2 pCi/L in the active node fron
March 31 to April 5, 1989. During this sane period, the sub-slab
depressurization system was maintaining an average pressure
difference between the basement and the sub-slab air of -210 Pa. The
system was placed in the passive node on April 7, 1989, and allowed
to run passively until April 13. During this period, the basement
radon concentration averaged 8.2 ± 2.4 pCi/L. Unfortunately,
equipment malfunctions resulted in the loss of the pressure
differentials during this period; however, for the period between
April 5 and 7, the sub-slab system maintained an average pressure
differential of -1 Pa in the passive mode. While this should not be
considered the pressure differential that the system was developing
during the April 7 to 13 period, it does represent the pressure
differential that the passive system can develop. A pressure
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differential of 1 Pa is very small and can be easily overcome. In
fact the pressure differential switched from negative to positive
during the April 5 to 7 monitoring period. On April 13, 1989, all
radon monitoring equipment was removed from the field for
calibration checks, and not placed back in the field until Nay 5.
The system was again placed in the passive mode on May 5, and
allowed to run passively until May 11. Basement radon concentrations
during this period averaged 9.9 ± 3.6 pCi/L. In order to determine
how the active system would perform under stress, the basement was
depressurized to an average of -10 Pa during the period from June
6 to 27, 1989. During this period basement radon concentrations
averaged 1.5 i 0.6 pCi/L. This is not significantly different from
the non-stressed test.
While it is obvious that active soil depressurization has a
dramatic impact on indoor radon concentrations the case is much less
clear for passive soil depressurization. During the two periods in
April and May that passive soil depressurization was monitored the
radon concentrations were 8 to 10 pCi/L. However in the barrier-only
testing in May immediately following the passive test the radon
concentration was 9.4 ± 2.8 pCi/L (see Figure 4). This implies that
the passive soil depressurization had little effect on the basement
radon concentrations, but is not conclusive. Later the barrier-only
method resulted in indoor radon levels of 20 ± 8 pCi/L.
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20-
IB"
£ 16-
S 14-
i 12.
10-
e-
6-
4-
2-
0-
E2 Sub-slab active 3/31/89 4/5/89
ED Sub-slab passive 4/7/89 -4/13/89
D Sub-slab passive 5/5/89 -5/11/89
E2 Sub-slab active basement depressurized to 10 Pa 6/7/89 - 6/27/89
1 1, I ,! | t
Figure 2. House PA1 basement radon concentrations with sub-slab
system in the active and passive nodes and active node with basement
depressurized to 10 Pa.
House PA2 was also subjected to cycling between active and
passive sub-slab depressurization systens. From February 6 to 8,
1989 (admittedly a very short period), the basement radon
concentration averaged 0.4 + 0.3 pCi/L with the system in the
active node. From February 8 to 11, the basement averaged 3.5 ± 3.4
pCi/L with the system in the passive node. On March 3, the system
was placed in the active node and run until April 1. Basement radon
concentrations over this period averaged 0.6 ± 0.7 pCi/L. The system
was again placed in the passive node on May 5 and run passively
until May 18. Basement radon concentrations averaged 1.5 ± 0.5 pCi/L
over this tine period. After a series of experiments that involved
the testing of the barrier in this house, the system was again run
passively from July 24 to August 18. Basement radon concentrations
over this period averaged 2.23 ± 0.7 pCi/L.
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Note that, in this house, passive soil depressurization worked
better than barrier-only in consecutive tests in May [1.5 ± 0.5
pCi/L passive and 5.2 ± 2 pCi/L barrier-only (see Figure'5)].
Another interesting bit of data for the passive soil
depressurization in this house was that it kept radon levels at 5.2
±5.1 pCi/L when a 16 sq in. hole in the slab was resulting in 36.7
±8.9 pci/L with barrier-only technique. This is rather encouraging
for passive soil depressurization in some cases.
15
n-
13-
12-
11 -
10-
9-
6-
7-
6-
5-
4-
3
2
1
0
n
m Sub-slab active 2/6789 - 2/B/B9
U Sub-slab passive 2/8/89 -2/11/89
E Sub-slab active 3/3/89 -4/1/89
^ Sub-slab passive 5/5/89 -5/18/89
D Sub-slab passive 7/24/89 - 8/18/89
\\x\\
Figure 3. House PA2 basement radon concentrations with sub-slab
system in the active and passive nodes.
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EFFECTIVENESS OF BARRIERS
Although the radon source at House VA1 was considered too low
to include the house in this portion of the study, measurements were
made to see how effective the barrier was. The basement radon
concentration was continuously monitored from February 24 to March
25, 1989. Basement radon concentrations during this period averaged
1.3 ± 0.3 pCi/L.
House PA1 was subjected to a series of experiments designed
to determine both the effectiveness of a barrier and the effect
various size holes in the barrier have on the indoor radon
concentration. As can be seen in Figure 4, even the best laid plans
of the most conscientious researchers often go awry. Radon
concentrations in the basement varied greatly with no regard for
hole size even when radon source strengths were similar. One would
have expected that increasing the size of the hole would have
resulted in higher radon concentrations.
It is hypothesized that the leakage area already present is
large enough so that increasing the area and allowing more air to
be drawn in through the soil is diluting the soil air and lowering
the soil air concentration faster than the production and transport
of radon can replenish it.
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60
65-
60-
' 45-
40-
35-
30-
8 25 H
O 20 H
I ,,-
10 -
5-
0
m Barrier only 5/12/89 -6/18/89
B Barrier with 144 sq in. hole 6/29/89 - 7/10/69
D Barrier with 10 sq In. hole 7/10/89 - 7/16/89
K Barrier with 1 sq in. hole 7/18/89 - 7/31/89
D Barrier only 7/31/89 - 8/17/89
Figure 4. House PA1 basement radon concentrations during barrier-
only tests.
The effectiveness of the barrier in House PA2 was also tested.
This house followed the idea that increasing the below-grade leakage
area should result in an increase in basement air radon
concentrations. As seen on Figure 5, a 16 sq in. hole in the barrier
resulted in increased concentrations, compared to the intact
barrier. Radon concentrations with the 16 sq in. hole increased
rapidly to an average of 36.7 ± 9 pCi/L. From July 13 to 24, the
sub-slab system was operated in the passive node with the same 16
sq in. hole in the barrier as in the previous period. The passive
sub-slab system maintained the basement radon concentration at 5.2
± 5 pCi/L. Because of this behavior it is believed that the amount
of below-grade leakage area is smaller than the critical size at
which soil air dilution puts a cap on the basement air
concentration. This hypothesized phenomenon would be very dependent
on the strength of radon sources and their geometry with respect to
low airflow resistance pathways beneath the house and through the
foundation.
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70
60-
50-
40-
30 -
10-
m Barrier only 6/18/89-5/26/89
E3 Barrier only 6/21/89-7/10/89
D Barrier with 16 sq In. hole 7/10/89 - 7/13/89
& Barrier with 16 sq in. hole.Sub-slab passive 7/13/89 - 7/24/89
Figure 5. House PA2 basement radon concentration during barrier-only
tests.
BELOW GRADE LEAKAGE AREA (BGLA)
The BGLA was estimated in three of the houses (VA1, VA2, and
PA1). The measurement was not made in House PA2 because it was
occupied and access was limited. This is unfortunate because it
seems to have had the best results for the mechanical-barrier-only
technique. The technique used to estimate the BGLA is as follows.
The total airflow out of the active sub-slab stack and the fraction
10
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of that exhaust air coining from the basement was estimated using a
tracer gas technique (described in detail in a poster paper (Cl 90).
The air pressure differential between the sub-slab air and the
basement air was measured using a micromanometer at several test
holes. Because of the tightness of the foundation and the
surrounding low-permeability soil it was found that the layer of
stone pebbles beneath the slab acted like an air plenum. That is,
there was very little difference in pressure differences (DPs)
measured at different locations (all DPs were within 3% of each
other from one end of the basement to the other in all three
houses). Given this special case it is possible to calculate the
leakage area of a sharp-edged orifice (SaB9) that would give the
same airflows at the same DPs as was measured in each house. Figure
6 summarizes the measurements and the calculated BGLAs.
House
ID
VA1
VA2
PA1
Average DP
(in. WC)
0.44
0.22
0.78
Total stack
Airflow (cfra)
78
24
16
Basement
Airflow(cfm)
34
11
3
BGLA
(sq in
3
1.4
0.2
Notice that the BGLAs are a few square inches or less. In fact,
for one of the houses it is only 0.2 sq in. As a check on the BGLA
soil gas concentrations, basement infiltration rates and the airflow
characteristics of the BGLAs were used to estimate basement radon
concentrations if the basements were depressurized by 1 to 2 Pa. The
results for Houses VA2 and PA1 compared well with actual radon
measurements made in them (an estimated range of 20 to 30 pCi/L
compared to 9 to 20 pCi/L measured for PA1 and an estimated 1 to 2
pCi/L compared to <1 pCi/L measured for VA2). However, the estimated
concentration for VA1 was 20 to 30 pCi/L and the measured indoor
radon concentration in VA1 was 1.3 ± 0.3 pCi/L. It is hypothesized
that the BGLA in VA1 actually is close to the 3 sg in. estimate: the
explanation for the much lower measured indoor radon concentrations
than would be predicted is the result of outdoor air leaking under
the slab at the corner of the basement with a walkout door. Air
leaking in at this site would not pass through much soil and could
be diluting the air beneath the slab. The exterior door was tightly
sealed.
The remarkable thing about these BGLA measurements is that
under some circumstances it takes only a tiny leakage area to result
in elevated indoor radon. The implications are not encouraging for
depending on a mechanical barrier technique to control indoor radon.
11
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CONCLUSIONS
The conclusions of this study must be considered as
representing only a few houses, located in specific soils and
climates, and (except for PA2) unoccupied. Because all of these
houses had tight foundations and relatively tight soils, they also
represent only one of four possibilities (tight soil - tight
foundation, loose soil - loose foundation, tight soil - loose
foundation, and loose soil - tight foundation).
The limited sample studied shows that making mechanical
barriers that can prevent soil air entry nay be impractical with the
ordinary amount of quality control found in the construction of most
houses. This study includes an example of a house with a very tight
foundation (10 to 100 times tighter than the tightest of building
shells) that still has elevated indoor radon levels. Additionally
it was found that enlarging the leakage area in this foundation had
no dramatic impact on the indoor radon concentrations, implying that
tightening efforts had little impact on the radon levels observed
in the barrier-only mode in this particular house.
Passive soil depressurization seemed to work fairly well in
House PA2, but did not seem to work at all in PA1. This result is
not unexpected considering the wide variety of environmental and
site specific variables that impact on indoor radon concentrations.
The question that remains to be answered is how often or under what
circumstances is passive soil depressurization a viable option? Both
houses meet a goal of radon levels as low as possible using active
soil depressurization.
Active soil depressurization proved to be extremely effective
in all houses tested. In PA1 indoor radon levels averaged 0.57 pCi/L
and never got above 3 pCi/L in the active node, and in PA2 indoor
radon averaged 1.4 pCi/L and was never above 2 pCi/L in the active
mode. Both houses spent a good deal of time below 1 pCi/L of radon.
At these low levels, uncertainty due to measurement accuracy begins
to become an important source of error in hourly measurements.
METRIC CONVERSION FACTORS
Readers more familiar with metric units may use the following
to convert to that system:
Nonmetrlc Multiply by Yield Metric
ft'/min 0.00047 m'/sec
ft 0.305 m
ft1 0.028 m'
in. 2.54 cm
in.' 6.45 cm'
in. WC 0.249 kPa
12
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REFERENCES
Br(88) Brerman, T. (Camroden Associates), Informal poll of EPA field
investigators at EPA contractors meeting, Research Triangle Park,
NC, 1988.
Cl(90) Clarklin, M. "Energy Penalties Associated with the Use of a
Sub-slab Depressurization system,11 Presented at 1990 International
Symposium on Radon and Radon Reduction Technology, Atlanta, GA,
February 19-23, 1990.
Sa(89) Saum, D. (Infiltec, Inc.), Personal communication, August 30,
1989.
13
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VI! 1-2
Radon Mitigation Performance of Passive Stacks In
Residential Hew Construction
By: David W. Saum
Infiltec
Falls Church, VA 22041
and Michael C. Osborne
U.S. EPA, AEERL
Research Triangle Park, NC 27711
ABSTRACT
Passive stacks have been proposed and installed as a radon
resistant measure in new houses, but little quantitative data
on their performance has been collected. This study involved
continuously monitoring several houses that were recently
built with radon resistant features including crack sealing,
porous subslab aggregate, and a stubbed off pipe penetrating
the slab for use in installing a radon mitigation system. For
this project, the pipe systems were completed so that they
exited from the roof, and half of the houses had radon
mitigation fans installed on the pipes. Houses were
continuously monitored with the pipes sealed, then with the
pipes open but no fans operating, and finally with the fans
(if installed) operating. The results show significant radon
mitigation performance by the passive stack systems in most
cases, and excellent mitigation by the active systems.
Failures by the passive stack systems appear to be due to
basement depressurization by heating, ventilation, and air-
conditioning (HVAC) duct leakage, poor installation of subslab
piping, and poor communication between multilevel slabs.
This paper has been reviewed in accordance with the U.S.
Environmental Protection Agency's peer and administrative
review policies and approved for presentation and publication.
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INTRODUCTION
A passive stack (PS) radon mitigation system is a type of
subslab depressurization (SSD) system where the source of
exhaust power in the stack is buoyant air rather than an
electric fan. The buoyant force is generated whenever the
air in the pipe is at a higher temperature than the outdoor
air. Since the major cause of radon entry into houses is
thought to be pressure driven flow of radon into the house
that is primarily caused by temperature differentials, the PS
has been suggested as an inexpensive, low energy solution to
radon problems that automatically compensates for changes in
temperature.
Several problems with PS radon mitigation have been
suggested: reverse pressures from wind, pressure losses under
the slab, reverse pressures during the summer, and reverse
pressures due to mechanical and heating appliances. Although
some mitigators report installing PS systems, there is little
quantitative data on their performance. This paper reports
on a study of PS in 16 new houses constructed by Ryan Homes
in Maryland and Virginia. These houses had basement radon
levels between 4 and 20 pCi/L before the stacks were
installed. During construction, a pipe stub was imbedded in
the slabs, 4 in. (10 cm) of clean coarse aggregate was
installed beneath the slabs, and the floor-wall cracks were
sealed with polyurethane caulk. In half of these houses the
passive stack performance was compared to conventional fan
powered SSD performance. This paper contains a discussion of
the passive stack theory, a summary of results, and
conclusions.
PASSIVE STACK THEORY
The term stack effect is commonly used to describe the
pressures and flows that are generated when buoyant warm air
is enclosed in a building. The ASHRAE Handbook of
Fundamentals1 contains an extensive discussion of building
stack effect. Figure 1 is a schematic diagram of the stack
pressures that would be expected in a house when there is no
wind and the inside temperature is higher than the outdoors.
In order to understand the stack effect, two terms column
pressure and neutral pressure level must be defined.
Column Pressure
Column pressure is the maximum differential pressure that
can be induced across any point on the building shell by an
inside-outdoor temperature difference. The column pressure
is proportional to the building height and the temperature
difference between inside and outdoors. For example, a 45°F
(25°C) temperature difference and an 8 ft (2.4 m) building
height will induce a column pressure of 0.01 in. (0.025 cm)
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we pressure across the building envelope. In Figure 1 the
column pressure is the sum of the top and bottom pressures.
Note that the column pressure is not affected by the
airtightness of the building.
Neutral Pressure Level
The neutral pressure level (NPL) is the imaginary line
around the enclosure where the differential pressure inside-
outdoors is zero. In Figure 1 the top pressure is shown to
be equal in magnitude to the bottom pressure. This results
in a NPL that is half way up the side of the enclosure. The
NPL location and stack pressure distribution across the
building envelope are determined by the building airflow
resistance, including the resistance of both the building
shell and any internal partitions. In houses, there are
generally large openings (doors) or leaks between floors, and
the internal airflow resistance is assumed to be small
relative to the shell airflow resistance. Therefore, the
shell openings determine the location of the NPL and the
pressures across the top and bottom of the shell. Note that
the NPL and the pressures on the enclosure are determined by
the distribution of leaks on the enclosure surface, and not
by the overall airtightness or leakiness of the enclosure.
Leakier enclosures will require more heat to maintain the
inside-outdoor temperature difference, but the column pressure
will be independent of the airtightness. If the majority of
leaks are near -the top of the enclosure, then the NPL will be
near the top, but the maximum pressures will be at the bottom.
When top and bottom openings are equal in size, the NPL is
midway up the side of the enclosure.
Effects of Sealing
Sealing leaks in the enclosure will not change the column
pressure, but the NPL will be shifted if leaks near the top
or bottom of the enclosure are sealed. Since radon entry may
be proportional to the depressurization of the slab, sealing
the upper part of the shell should be beneficial since it will
reduce this depressurization, but sealing leaks in the lower
part of the shell should be detrimental since it will increase
the depressurization of the lower part of the enclosure. If
a house could be sealed as completely as a hot air balloon,
with all remaining leaks concentrated at the bottom, then
there would be no stack induced depressurization on the slab
that would pull radon into the house. Appendix A contains
a calculation which relates shell leakage distribution to
pressure on the lower surface of the enclosure.
Figure 2 shows the changes in pressure on the upper and
lower surfaces of an enclosure under a variety of leakage
configurations. Figures 2. A and 2.B have already been
discussed, Figure 2.C shows the effect of sealing half the
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leaks in the bottom, while Figure 2.D shows the effect of
sealing half the leaks in the top. As a general rule for
radon control, air sealing should be limited to the upper
surfaces of the house in order to minimize depressurization
of the slab. Since a PS system does not have much suction
power, the reduction of stack effect in the building may be
necessary to maximize its performance.
Passive Stack System
A PS radon mitigation system is shown schematically in
Figure 3, and its performance is determined by the interaction
of two stacks. The house acts as a stack which creates
depressurization above the slab, and the PS pipe generates a
counteracting depressurization below the slab. For the PS to
operate successfully, the PS must induce slightly more
depressurization beneath the slab than the house induces
above. For best performance of the PS five conditions must
be met.
Raise the column pressure of the PS
The PS depressurization beneath the slab should be
maximized by keeping the temperature of the stack as high as
possible relative to the outdoor air temperature. Most
important, the PS should not be run though unheated spaces,
such as garages.
Raise the NPL of the stack
The flow though the stack should be minimized by sealing
the slab to keep the NPL of the PS as high as possible which
will increase the depressurization below the slab. A PS that
is open at both ends will have a NPL at its midpoint, and a
PS that is connected to an airtight subslab cavity will have
a NPL at its top.
Lower the NPL of the house
The house stack depressurization above the slab should be
minimized by air-sealing of the house envelope to lower the
NPL of the house as much as possible. Air-sealing of the
upper surfaces of the house will lower the house NPL, but
sealing the lower part of the house will raise the NPL and
increase the stack depressurization above the slab. Lowering
the temperature of the house would decrease house stack
depressurization, but it is not generally practical, and
would also result in a lower stack temperature. Note that
if the house NPL is below the stack NPL, then the PS will not
provide radon mitigation.
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Maximize air-flow communication under the slab
If there is any airflow into the stack, there will be a
pressure drop in the aggregate that will reduce the
depressurization of some areas of the subslab. Good airflow
communication by using clean coarse aggregate and laying
perforated pipe under the slab may minimize this problem.
Minimize anv mechanical source of house deoressurization
Any negative pressure in the house will add to house
depressurization above the slab. Examples of this problem
include imbalances in forced air distribution systems,
fireplaces, exhaust fans such as dryers, and combustion air
exhausted from the house by fossil fuel heating systems.
SUMMARY OF RESULTS
An Example of Passive System Performance
Figures 4 and 5 show the radon mitigation performance of
a typical house (#MIL) in which a PS was installed. This
house was built in 1987 and has 1600 sq ft (149 m2) of
finished space with 800 sq ft (74 m2) of unfinished basement
area. The basement has poured concrete walls, is about 4 ft
(1.2 m) below ground, and has a sump connected to an external
footing drain. The passive stack goes up about 12 ft (3.7 m)
through a chase inside the house and exits about 2 ft (0.6 m)
below the roof line. During construction, a perforated pipe
was laid in the 4 in. (10 cm) deep gravel bed beneath the slab
and was run diagonally across the basement to provide
communication. One end of the perforated pipe is connected
to the sealed sump, and a T fitting was used to bring a 4 in.
(10 cm) diameter pipe stub up through the slab for possible
connection to a future radon control system. All visible slab
cracks were sealed with polyurethane caulk. When the passive
stack was installed in late 1988, a long twisted run of 4 in.
(10 cm) pipe was necessary to connect the pipe stub at one
side of the basement to the chase located in the center. The
heating system is a heat pump with a fan system located in the
basement, and the distribution ductwork is contained within
the shell of the building. Blower door measurements showed
about 5 air changes per hour (ACH) at 20 in. we (50 Pa) which
is relatively airtight for the Maryland climate.
Winter performance
Figure 4 shows the winter performance of the passive
stack. Although the radon mitigation performance is
significant (85%), the radon spikes suggested that some
unknown depressurization source in the house was occasionally
overcoming the PS system. When the basement was reexamined,
it was found that the homeowner had sealed off all the supply
ducts in the unfinished basement to save energy, but he had
-------
neglected to seal a large return vent. Therefore any tine the
basement door was closed, the basement was depressurized by
about 0.030 in. (0.076 cm) vc. This counterpressure overcame
the passive stack system and brought in radon but only when
the basement door was closed.
Summer performance
Figure 5 shows the summer performance in house #MIL after
the air return vent in the basement was sealed in order to
prevent basement depressurization by the heat pump fan.
Although the summer radon levels were much lower than the
winter levels in this house, the PS radon reduction was still
substantial (70%). There is no sign of the spikes that were
seen in the winter, and the pressures measured under the
basement door were less than 0.004 in. (0.01 cm) we. During
the period shown in Figure 5, the house was air conditioned,
and there were several periods when the outdoor air
temperature was higher than indoors. These data do not
indicate that passive system performance decreases when the
temperature differentials are reversed.
PS performance conclusions
In several of the PS houses, the stack provided radon
mitigation well below 1 pCi/L during all seasons of the year.
Performance did not seem to be affected by pipe straightness,
position of the vent on the roof, or wind conditions. Houses
with poorer mitigation performance seemed to have four main
problems: 1) depressurization of the basement because of large
leaks in the return ducts in the basement, 2) multilevel slabs
that were not connected to the PS pipe system, 3) stack pipes
run through unheated spaces, and 4) improperly connected stack
pipes that were blocked by debris during construction. Even
in houses where there was a combination of problems, the PS
generally gave mitigation performance of at least 50%.
Passive Versus Active System Performance
In half the houses, SSD systems with fans were installed:
these houses were studied to compare the performance of the
PSs with the active systems. The stack was sealed for several
days to approximate premitigation conditions, the stack was
opened without fan operation to approximate a PS system, and
finally the fan was turned on to demonstrate fan assisted SSD
performance. The resistance of the fan in the pipe was
assumed to be small enough to ignore because of the small
airflows in the pipes under passive conditions. House #TIN
had some of the highest radon levels in this study, but it was
otherwise quite typical of the active houses. This house had
2000 sq ft (186 m ) of finished floor area on two floors, and
an unfinished 800 sq ft (74 m2) walk-out basement below. The
basement has poured concrete walls with the same crack sealing
-------
and stubbed off pipe described in the passive house. There
was no sump and the pipe stub was connected only to a
perforated pipe in the aggregate beneath the slab. The blower
door measurement showed that this house was about 4 ACH at 20
in. we (50 Pa) which is quite tight.
Winter performance
When the fan was on, the radon levels were well below l
pCi/L, but they quickly rose to about 30 pCi/L when the fan
was turned off and the pipe was sealed. When the passive
stack was simulated by opening the stack without turning on
the fan, the radon levels were significantly depressed, but
there were occasional large spikes that could not be
explained. Even so, the radon reduction due to the PS was
about 75% (Figure 6).
Summer performance
The house was retested during warm weather in September:
the radon levels during the PS test were lower than for the
comparable winter levels. Since the measurements did not
include a test period when the stack was sealed, it is not
possible to determine the absolute mitigation performance.
There were some spikes in the radon levels but not as many as
the winter data showed. After this monitoring was concluded,
a reexamination of the heat pump fan system showed that a
construction defect had left a large hole in the return duct
in the basement. The hole generated a depressurization of
0.050 in. (0.13 cm) we in the basement every time the fan came
on and the basement door was closed. The September PS data
may be low for this house because the mild weather did not
require much heat pump operation (Figure 7).
Active versus passive
The conventional active SSD system is a very reliable
solution to radon problems in new construction houses because
it will overcome most of the inadequacies of PSs highlighted
in this study. Even the severe depressurization that was
found in this house was negligible compared to the pressures
of about 0.75 in. (1.9 cm) we that are commonly generated
under the slab by most SSD fans. The only problem in the
test houses that this excess fan power could not overcome is
the lack of communication between multilevel slabs that was
seen in several houses.
CONCLUSIONS
This study suggests that PS systems in new house
construction can provide radon mitigation that is comparable
to the performance of active systems if there are no
interfering sources of house depressurization. However, the
study also suggests that forced air heating systems are major
-------
sources of house depressurization due to duct leakage. Since
PS systems are very sensitive to pressure imbalances in the
house, they provide a sensitive tool for studying the
interaction of the other systems in the house.
Duct Leakage
The pressure imbalances in houses due to duct leakage and
flow imbalance were recently studied in Florida houses by
Cummings'. That study indicated that Florida houses typically
have heat pumps in the attic outside the house envelope, and
that duct leakage can cause depressurization or pressurization
of the entire house. Since the houses in this study had no
ductwork outside the conditioned space, the leakage could only
cause room to room variations in pressure rather than changes
in whole house pressure. However, when the HVAC fans are in
the basement, as they were for all of the houses in this
study, the probability of significant pressures in the
basement is quite high. All of the houses in this study had
pressurization of the upstairs bedrooms when the doors were
shut because of the lack of returns in the rooms. This
problem does not seem to produce significant basement
depressurization. It seems to be more of an energy
conservation problem than a contributor to the radon problem.
Cummings2 reports a similar problem in Florida.
Adequate Ventilation
The houses in this study were found to be almost airtight.
If they did not have forced air heating and cooling systems,
and the pressure or leakage problems previously discussed,
then they might be under-ventilated when compared to ASHRAE
recommendations1. If the duct leakage and imbalances were
corrected for reasons of energy conservation or radon
mitigation, then the ventilation impact should be considered.
Limitations and Suggestions for Further Work
This study was very limited in the housing stock studied
since it only dealt with heat pump houses within a limited
area. Future studies might look at Florida or Minnesota
houses with their different climates and HVAC systems. All
of the stacks in this study were 4 in. (10 cm) schedule 40 PVC
pipe. It would be useful to study 3 in. (7.6 cm) pipe since
it would be simpler and cheaper to run smaller pipe through
the house.
Recommendations to Builders
Passive stacks appear to be the most effective passive
radon mitigation technique for new construction. This study
suggests that the stack should be run through the warm part
-------
of the house, excellent subslab communication can be provided
with 4 in. (10 cm) of clean coarse aggregate, and the stack
pipe should be run up to the roof line. Additional guidance
should include avoidance of duct leakage that depressurizes
the basement and connecting stack pipes to each level of
multilevel slabs. Things that can be ignored include wind
caps for the stack, multiple bends in the pipe, and failures
due to cooling situations.
REFERENCES
1. ASHRAE Handbook of Fundamentals, Chapter 23 Infiltration
and Ventilation, Section 23.2 Driving Mechanisms, American
Society of Heating, Refrigeration, and Air-Conditioning
Engineers, Inc., Atlanta, Georgia, 1989.
2. Personal communication with J. B. Cummings, Florida Solar
Energy Center, 300 State Road 401, Cape Canaveral,
Florida, Sept. 13, 1989.
3. ASHRAE Std. 62-1989, Ventilation for Acceptable Indoor Air
Quality, American Society of Heating, Refrigeration, and
Air-Conditioning Engineers, Inc., Atlanta, Georgia, 1989.
-------
APPENDIX A
CALCULATIONS
Column pressure Peol can be computed from barometric
pressure Pb, enclosure height H, inside temperature Tin, and
outdoor temperature T^:
Peol = 0.52PbH(l/Tout - l/Tln) (1)
where H = height of building in ft
Pb = ambient (barometric) pressure in psia (14.7 at
sea level)
T = Rankine temperature (459 + Fahrenheit
temperature)
The stack pressures can be computed in the case of an
enclosure with sharp edged holes in the top and bottom with
areas Ahi and A10. The equation for air flow Q under standard
conditions through a sharp edged hole is given by:
Q = 16.9AP0'5 (2)
where Q = flow in cfm
A = Area in sq in.
P = Pressure in in. we
If air flows through an enclosure because of stack effect,
then flow rate in Q10 must equal flow rate out QM:
Qio = Qhi (3)
or 16.9A10P10°-5 = 16.9AhiPhl°-5 (4)
Rearranging, Plo = Phl (Ahl/A10) 2 (5)
But column pressure Pcol is the sum of the high Phi and low P10
pressures:
Peol - Phi + Plo (6)
Combining 5 with 6:
PIO = P.oi/[(Alo/Ahi)2 + 1] (7)
Note that lower pressure P10 is determined by the ratio of
upper Abi and lower A10 leaks and not by total leakage A.
10
-------
Neutral Pressure Level
t
Assume no wind and warmer indoors than outdoors
Arrow length represents pressure magnitude
FIGURE 1 Schematic Diagram of Stack Effect Pressures in a House
A ^^ B
1
NuM frm*
i
n M (IH)
^ X
t
t
4
m.
A
1
^ x-
t
1
m.
4
Arrow length represents pressure magnitude
Assume houses are warmer indoors than outdoors
FIGURE 2 Stack Pressures for Several Leakage Configurations
11
-------
Outdoor
colder air
Stack neutral pressure level
House neutral pressure level
Indoor
warmer air
Lower house depresssurization
I Stack
Underground
Stack induced depressur'aaVion
FIGURE 3 Schematic Diagram of Passive Stack Radon Mitigation System
Stack inside house
Sump, deep basement
Passive stack = 2.9 pCi/L
stack sealed « 19-9 P?i/L
- Stack open
Stack sealed
350 360
Thursday 12/15/88
Basement Radon Levels
370 380
1988 Julian Day
Figure 4 Winter Performance of Passive Stack System
12
-------
^^x
O
CL
O
O
(0
20
15
10
5
Stack inside house
Sump, deep basement
Passive stack = 0.7 pCi/L
Stack sealed = 2.4 pCi/L
- Stack open
Stack sealed I Stack open
240 250
Monday 8/28/89
Basement Radon Levels
260 270
1989 Julian Day
280
290
FIGURE 5 Summer Performance of Passive Stack System
b
o.
o
o
(0
ex.
70
60
50
40
30
20
10
Stack inside house
Walkout basement, no sui
Passive stack = 7.5 pCi/L
StaclJ sealed = 29.0 pCiA
Fan on = 0.2 pCi/L
Fan off, stack open
80 90
Tuesday 3/21/89
Basement Radon Levels
100 110
1989 Julian Day
120
FIGURE 6 Winter Performance of Active and Passive Stack Systems
13
-------
30
.i 20
O
Q.
I
10
Stack inside house
Walkout basement, nb sump
Fan off, passive = 3.7 pCi/L
SSO fan on = 0.3 pCi/L
SSO fan turned on
250 260
Thursday 9/7/89
Basement Radon Levels
270 280
1989 Julian Day
290 300
FIGURE 7 Summer Performance of Active and Passive Stack Systems
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VIII-3
SUB-SLAB PRESSURE FIELD EXTENSION STUDIES
ON FOUR TEST SLABS TYPICAL OF FLORIDA CONSTRUCTION
by: Richard A. Furman
School of Building Construction
University of Florida
Gainesville, FL 32611
David E. Hintenlang, Ph.D.
Department of Nuclear Engineering Sciences
University of Florida
Gainesville, FL 32611
ABSTRACT
The State of Florida is currently in the process of developing, under
legislative mandate, a radon resistant building code for new construction. One
of the research projects funded by the State is to examine the influences that
various construction practices have on the effectiveness of sub-slab
depressurization systems. Four test slabs have been constructed and pressure
field extension studies have commenced. The influences of several construction
practices and techniques including stemwall curtains, types of sub-slab fill,
fill depth and sub-slab plumbing influences will be investigated. Climatic and
other environmental conditions will be monitored to determine their influence
on the sub-slab depressurization systems.
This paper will discuss which typical Florida construction practices have
the most significant impact on the effectiveness of different sub-slab
depressurization systems.
INTRODUCTION
Indoor radon has been identified as a problem in Florida for more than a
decade. Early research in the phosphate mining areas of central Florida reported
that substantially elevated levels of radium and radon were present in reclaimed
mining lands. Not until the mid to late 1980's did indoor radon become
acknowledged as a legitimate health hazard, thereby prompting nationwide
political action. In 1988 the Florida Legislature passed legislation mandating
the development of a radon resistant building code for new construction. As a
result of that legislation the State University System was tasked with developing
-------
a draft building code for delivery to the Florida Department of Community Affairs
by February 1, 1990. The Florida Board of Regents established the State
University System Radon Advisory Board (SUSRAB) to coordinate the research and
development activities relating to the production of the draft code.
Early on, the SUSRAB recognized the proven effectiveness of sub-slab
depressurization systems and funded several studies to investigate the
operational characteristics of these systems. Regional construction techniques
and procedures play a critical role in the success or failure of these systems.
Differences between the construction features of northern homes with basements
and the Sunbelt-type construction have resulted in varying levels of
effectiveness of the sub-slab depressurization technique. In order to study the
effects of various construction techniques on the sub-slab depressurization
system, four test slabs were constructed and tested.
The study, from which this paper was developed, was funded by the Florida
Board of Regents to determine what construction processes have the greatest
impact on the sub-slab pressure field. From this work guidance was provided to
the SUSRAB in the development of the draft radon resistant building code.
FLORIDA TYPICAL CONSTRUCTION
An informal survey of homebuilders conducted by the authors during the 1988
Summer Board Meeting of the Florida Home Builders Association found that over
95X of all residential construction built in Florida is constructed with concrete
slabs-on-grade. In the colder climates of the more northern states where there
is less rainfall, sub-grade construction of basements is common. In Florida,
however, sub-grade construction is a rarity. This result was not unexpected but
confirmed that the emphasis of radon control efforts should be focused on slab-
on- grade construction. Further analysis of the survey data indicated that a
geographical distribution of the type of slab-on-grade system used was evident.
Monolithic concrete slabs were found to be the slab system of choice in those
areas south of Orlando; slabs constructed on masonry stemwalls or foundation
walls were more prevalent in those geographical areas north of Orlando. The
preference for slab systems with stemwalls north of Orlando is due to increased
topographic relief.
Florida's sub-tropical climate and high precipitation levels significantly
influence the construction techniques used. The most significant regional
construction difference is the type of media used under the slab. Gravels, used
primarily in northern U.S. sub-grade construction to facilitate water removal,
have substantially higher air permeabilities than the sand fills used in the
Sunbelt region. The permeability of these base materials coupled with the
effective leakage of the confining construction are of major importance in the
effectiveness of the sub-slab depressurization system. However, in slab-on-
grade construction sub-grade water control is not normally required resulting
in the extremely infrequent use of gravels as a slab base material. Gravel or
stone aggregate is a non-standard building component in typical Florida
construction.
-------
To facilitate the construction of concrete slabs on grade, Florida's
abundant supplies of clean construction-grade sands are used as compactable fill
material. Fill-sands are frequently relocated from one area of the project site
to another or may be hauled in from distant borrow pits. Some of these sands
may possess moderate to high radium content thereby raising a concern of
transporting radon contamination from one locale to another.
SLAB CONSTRUCTION CATEGORIES
Concrete floor slabs constructed on grade in Florida typically represent
one of the following three general slab construction categories: monolithic
slabs, floating slabs and slab-in-stemwall slabs (Figure 1).
A. Monolithic
C. Slab-in-stemwall
B. Floating
Figure 1. Typical Florida slab construction techniques and soil gas entry routes.
Monolithic Slabs
Slabs constructed on near-level ground in areas not subject to flooding
are constructed most cost effectively as monolithic slabs (Figure 1-A). When
site modifications to create a level building platform are more cost effective
-------
in areas of irregular terrain. Monolithic slabs are characterized as having the
footing and the slab cast as one integral unit. Foundation depth is minimized
and radon entry routes through the slab are usually confined to cracks (planned
or unplanned) and mechanical system penetrations for plumbing, electrical, etc.
In general, fewer foundation entry conditions are present in monolithic
construction than in the two other categories.
Floating Slabs
Where terrain features, water considerations and/or other conditions demand
the use of foundation walls, which elevate the slab some distance above natural
grade, floating slabs are one of two construction techniques commonly employed.
Floating slabs are cast against, not into, the foundation wall (Figure 1-B).
Expansion joint materials are normally used to separate the slab from the inside
face of the foundation wall forming a continuous radon entry route along the
perimeter of the slab. In addition to the typical entry conditions associated
with slab cracking and penetrations, foundation wall conduction of radon from
below the floor slab into the superstructure walls is also common. Most
superstructure walls erected on floating slabs are constructed of masonry block.
The masonry block wall's thickness is sufficient for the baseboard to conceal
the perimeter crack; the crack is virtually inaccessible after construction.
The continuous perimeter crack and the foundation/superstructure wall conduction
are the most significant radon entry routes associated with this slab system.
Slab-in-Stemwall Slabs
Many contractors prefer frame superstructure walls to masonry and have
eliminated the perimeter crack associated with floating slabs by adopting a
system of casting the slab into the masonry foundation wall (Figure 1-C). Two
types of masonry block may be used to form the edge of the slab. The lintel
block can be used so only the outer face shell remains as the slab form. The
header block, however, when used retains part of the web partitions as well as
the outer face shell. This condition is important because, depending upon the
method utilized to prevent concrete from being lost down the block cores, entry
routes from the foundation wall into the superstructure may result. If the
contractor is careful, the foundation wall superstructure conduction problem can
be eliminated. However, contractors have been observed draping the vapor barrier
over the header block. After the slab was cast, large holes were found to exist
where the concrete had been held away from the outer face shell of the block by
the vapor barrier. These holes result in foundation/superstructure conduction.
TEST SLAB PROGRAM
The U.S. Environmental Protection Agency and others have conducted numerous
studies in the eastern U.S. over the past several years and have found that sub-
slab depressurization systems appear to be more consistently successful than
other experimental radon mitigation systems. Most of the early tests of sub-
slab depressurization systems were conducted on basement structures using stone
aggregate as the slab-bed material. Permeabilities in these stone materials were
sufficient to provide adequate pressure field development from usually one
-------
suction point. Permeability of the sub-slab media was recognized as the
principle characteristic affecting system performance and effectiveness. It is
expected that this mitigation technique will maintain a high level of
effectiveness in the event that post-construction penetrations occur (2). It
was believed that if major entry conditions could be prevented near the suction
point, then the negative sub-slab pressure field could successfully protect
against radon transport through new pathways caused by aging of the building.
The following testing program was developed to investigate the performance
characteristics of sub-slab depressurization systems under conditions typical
of Florida. The primary factors that may significantly impact the effectiveness
of sub-slab depressurization systems installed in typical Florida homes and that
the researchers felt necessary to investigate were: 1) the effects of the type
and permeability of fill material; 2) the vertical depth or volume of the fill
material; 3) the size and configuration of the "suction pit"; 4) the effects
of air infiltration through the stemwall; and 5) the influence of sub-slab
plumbing systems (3).
The objective of this testing program was to determine the area of
effective depressurization under various conditions created by these factors.
Four test slabs were constructed using the slab-in-stemwall technique ensuring
that the concrete completely sealed the slab/stemwall junction against any
leakage (Figure 2).
Each slab was built with the outside dimensions of 24' x 48' by a local
contractor using standard construction practices. Following construction of the
footings and masonry stemwalls each slab was provided with a polyethylene
"stemwall curtain" placed along the inside face of the stemwall for half of the
slab's perimeter (Figures 2-A & 2-B). The curtain extended from the footing to
the top of the fill material where it folded over the vapor barrier for a
distance of 24 inches. The purpose of this curtain was to effectively seal the
masonry stemwall against air infiltration for that portion of the slab.
Two simulated waste plumbing systems were installed to determine the
significance of the pipe or its trench of disturbed soil on the pressure field.
Where the plumbing penetrated the slab and stemwall, great care was taken to seal
against air infiltration.
The clean sand fill used in each test slab was provided from the same
borrow pit by one supplier. Uniformity of the fill material was maintained as
much as could be reasonably achieved.
All four slabs were constructed such that the foundations were at the same
elevation, and they penetrated into the native soil to the same distance. This
procedure provided uniform conditions so the movement of atmospheric air under
the foundation could be examined.
Specific construction details for each test slab follow.
-------
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. .' : * ».:>
VAPO* |A«*IC«
STCUWALL CURTAIN
(sec FLAN)
A. Typical Section
c.o.
TWCAL
PLUUVIMO J
LAYOUT
(2 CACM SLA*)
CVCKSC
^LuweiNC
LAYOUT
4..
B. Typical Plan
" STONC
C. Test Slab #1
«" COMOCTC WITH
(>P)
E. Test Slab //3 /
Figure 2. Test slab construction details
D. Test Slab //2
-------
Test Slab #\
Test Slab #1 was constructed to simulate the sub-slab conditions found in
basement structures previously studied and to provide a means of evaluating the
permeability of various sub-slab materials (Figure 2-C). A six-inch layer of
3/4" to 1 1/2" crushed drain- field stone similar to that used in basement
construction was placed as the slab bed over several inches of clean sand fill.
It was assumed that during placement and grading one to two inches of stone would
be compressed into the underlying sand fill resulting in a nominal four inch
permeable stone layer.
Test Slab #2 & #3
These slabs were constructed in order to study the effects of fill depth
and stemwall leakage. Both Test Slab #2 and #3 were constructed with sand fill
to different depths (Figures 2-D & 2-E). Test Slab #2 had a 24" deep layer of
clean sand fill while Test Slab #3 had only an 8" deep layer of fill over the
native soil. Test Slab #2, after final grading, had 288 square feet of stemwall
with half of it protected by the stemwall curtain. Test Slab #3 had 96 square
feet of exposed stemwall with half of it protected by the stemwall curtain.
Test Slab #4
While the other three test slabs were designed to study various media and
leakage conditions, Test Slab #4 was constructed to evaluate an extended suction
pressure distribution system. This slab was constructed with four separate
strips of plastic drainage matting installed over 8 inches of fill with each
strip having a separate suction point (Figure 2-F). This test platform provided
the opportunity to study the effectiveness of a continuous, linear suction pit
versus the point source suction pit used on the other three test slabs. The
stemwall curtain on this slab was not only installed around half the perimeter
of the slab but extended across the midsection of the slab to effectively divide
the fill into two separate regions. This was done to minimize the communication
of pressure fields developed in different suction strips.
Test Procedure
Following construction of the test slabs, multiple suction points and
monitoring points were installed. The suction points were installed at the time
the testing was to commence at that location. A3" hole was cored through the
slab and the pit excavated by hand to the desired configuration. Following the
pit excavation a 4" PVC clean-out adapter with plug was installed and sealed.
The suction device was then attached to this adapter when testing commenced.
The monitor points were installed by drilling a hole through the slab and sealing
a 3/4" PVC pipe 6" long into place. The pipes were then plugged with rubber
stoppers. Figure 3 illustrates the arrangement of the suction and monitor
points.
-------
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Test Slabs #1, 2, 3
Test Slab //4
Figure 3. Test slab suction & monitor point locations.
Pressure testing was conducted using an industrial vacuum cleaner as the
suction source regulated through a bleed-valve assembly. Pressure measurements
were made at the suction point and the monitoring points using a Neotronics
Model MP20SR micromanometer. Air flow measurements were taken with a Kurz model
440 air velocity meter at the suction point and periodically at a remote
monitoring point.
Testing routinely started with a measure of air flow at the suction point
at suction pressures ranging from 500 Pa to as high as 6000 Pa. After this
procedure was finished the suction pressure was reduced to approximately 500 Pa
and a pressure measurement at each monitor point was taken. A commercial
software package (Surfer, Golden Software) was used to interpolate between data
points, using a Kriging algorithm, and to develop contour lines of constant
pressure.
-------
RESULTS AND DISCUSSION
Figure 4 illustrates the difference In air flow rates for a high
permeability condition (Test Slab f 1) and a low permeability condition (Test Slab
#2). A comparison of the four curves from the sand fill (low permeability) with
the stone fill (high permeability) demonstrates the dramatic increase In air flow
that is generated at any given pressure for high permeability fills. The line
representing Test Slab #1 (stone media) indicates that high permeability
materials require fans capable of handling high flow rates in order to achieve
the desired pressure conditions under the entire slab. The large amount of air
Infiltration into the system on Test Slab #1 must be entering both through the
unsealed stemwall and/or under the foundation from the atmosphere. The pressure
field for this test slab is nearly uniform in all directions. The half of the
slab protected by the stemwall curtain has slightly high pressure produced by
limiting infiltration through the stem wall.
3000
FIST MAK II (stone fill)
2 3
Suction Pressure (KPa)
Figure 4. Comparison of airflow rates of high and low permeability fills.
Figure 5 and Figure 6 illustrate the effects of different suction pit
configurations. Four different suction pit configurations were constructed at
the same suction location on Test Slab #2. Each configuration was tested for'
air flow and pressure field development. Figure 5 illustrates the relationship
of pit contact area to air flow. The greater area of sub-slab media exposed to
the highest suction pressure allows a larger pressure field to develop and the
induces a larger air flow.
Figure 6 shows the pressure field contours for each suction pit
configuration. Note must be made of the contour values to properly compare the
effectiveness of the suction systems. All plots on Figure 6 indicate a better
field development toward that half of the slab with the stemwall curtain.
-------
600
.£ *oo
200
2 «
Suction Pressure
-------
1200
000
000
000 400 600 1200 1600 2000 2400 2800 3200 36 OO 4000 4400 4800 000 400 800 12 00 16 00 20 00 24 DO 2800 1200 3600 4000 4*00 4800
1" diameter 12" deep cylinder
4" diameter 12" deep cylinder (no stone)
000 400 BOO 1200 1600 2000 2400 2600 MOO 3600 4000 4400 48 00 000 400 8 OO 12 OO 16 OO 20 OO 2< OO 2800 35 OO 36 CO 4000 44 CO 4800
2*00
000
000 <00 SOO 1200 1600 2000 2400 2800 3200 3600 «0 00 44 CO 4800 000 400 800 1200 16 OO 2000 2400 2800 3200 3600 «0 00 4400 4600
A" diameter 12" deep cylinder with stone 12" hemisphere
Figure 6. Pressure contours produced on Test Slab //2 by various suction pit configurations.
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A. Test Slab #2 - Suction point //2
B. Test Slab #2 - Suction point it3
0.00 4.00 800 12.00 1600 20.00 24 00 2800 32.00 3600 4000 44.CO 4S.30 0 -,O » CC 100 12.00 '.i.OO 2000 24.00 38 CO 32.00 36 OD 4000 4400 4800
Ti 1I !II1:1iII| 2< ~ ,i ::: ;Ii! !iiI 11 i :i ; :> : ! 1i 24.00
i . .
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-i -2." -
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000 4.00 8.00 '7.30 1600 JO 00 ?« 00 2800 JJ.OO 36 CO
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Che stemwall induces significant infiltration through both the stemwall and soil
under the footing. Since Suction Point #2 is located immediately adjacent to
a curtained stemwall, the air flow at this suction point must come primarily from
under the footing. The curve for Suction Point #3 results from both stemwall
infiltration and atmospheric transport under the footing since the stemwall
curtain is absent. The difference between the plots for Suction Point //I and
//4 is very small and results from the fact that the pressure differential at the
stemwall and ground surface is greatly reduced by having located the suction
strip several feet in from the edge of the slab. The pressure field plots
contained in Figure 9 illustrate the degree of pressure field development for
each suction strip. Figures 9-A & 9-D show that, where the strip is several
feet inside the stemwall, the field development is virtually identical for both
suction strips. Marginal stemwall leakage is expected. However, Figure 9-B
and 9-C show marked differences in pressure field development. These results
demonstrate how eliminating stemwall leakage allows higher suction pressures to
be developed and that stemwall infiltration limits pressure field extension.
These tests demonstrate a very promising approach to cost effective pressure
field development. Locating the suction strip 8 ft. to 15 ft. inside the
stemwall would likely have resulted, on this slab, in only one strip being
necessary to develop adequate pressure field coverage.
3000
Suction Point 12
2000
1000
Figure 8. Airflow rate comparison for different suction points on Test Slab
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0.00 4.00 8.00 12.00 16.00 20.00 24.OO 28.00 32.00 36.00 40.00 44.00 48.00 0.00 4.00 8.00 12.00 16.00 20.00 2».00 38.00 32.00 36.00 40.00 44.00 48.00
24-00 r-7-1 1 III| 1 1 1 1 1 1 --+-- i 1 1 1 1 1 1 1 1 1 24.00
- 20.00 -
- U.OO -
- 4.00
0.00 4.00 8.00 12.00 16.00 20.00 24.00 28.00 32.00 36.00 40.00 44.00 *8.00 0.00 4.00 8.00 12.00 16.00 20.00 24.00 28.00 32.00 36.00 40.00 44.00 43.00
Suction point #1 (stemwall curtain) Suction point #2 (stemwall curtain)
24.00
20.00
te.oo
12.00
8.00
4.00
0.00 4.00 B.OO 12.00 16.00 20.00 24.00 28.00 32.00 36.00 40.00 «4.00 48.00 0:00 4.00 8.00 12.00 1600 20.00 24.00 28.00 32.00 3600 4000 4400 «S 00
24.00
0.00
20.00 -
8.00
4.00
0.00
0.00 4.00 8.00 12.00 16.00 20.00 24.00 28.00 32.00 36.00 40.00 44.00 48.00 0.00 4.00 8.00 12.00 16.00 20.00 24.00 28.00 32.00 36.00 4C.OO 44.00 "8.00
Suction point #3 (no stemwall curtain) Suction point #4 (no stemwall curtain)
Figure 9. Pressure contours produced at each suction point on Test Slab M.
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CONCLUSIONS
The studies conducted thus far in this research effort seem to provide the
following guidelines.
The amount of suction contact area is vital to pressure field development.
Larger pits shaped to maximize surface area function much better than pits of
smaller surface area. The drainage matting material used as suction strips
appear to be very promising in its effectiveness if placed 8-15 ft. inside of
a perimeter stemwall. This suction system took several minutes to install versus
several hours for the excavated pits.
Stemwall curtains in slabs with deep layers of fill and corresponding large
stemwall areas will perform better with the protection of the stemwall curtain.
Slabs with short stemwalls probably will not realize a positive cost benefit of
the stemwall curtain.
Finally, highly permeable fill, such as the stone used in Test Slab #1,
provides for excellent pressure field development if it is placed over low
permeability soil and could be used effectively as an active sub-slab vent?. Ration
system. On the other hand, in Florida, where stone is not a locally produced
material it appears to be the most expensive option.
The work described in this paper was not funded by the U.S. Environmental
Protection Agency and therefore the contents do not necessarily reflect the views
of the Agency and no official endorsement should be inferred.
REFERENCES
1. Roessler, C.E., Kautz, R., Bolch, W.E., Jr. and Wethington, J.A., Jr.
The effects of mining and land reclamation on the radiological
characteristics of the terrestrial environment of Florida's phosphate
region. The Natural Radiation Environment III (Proceedings of symposium
April 1978) U.S Department of Energy Publication CONF-780422. pp. 1476-
1493, 1980.
2. Hintenlang, D.E. and Furman, R.A. Sub-slab suction system design for low
permeability soils. In: Proceedings of the 1990 International Symposium
on Radon and Radon Reduction Technology, Atlanta, Georgia, to be published.
3. Fowler, C.E., Williamson, A.D., Pyle, B.E., Belzer, F.E., Coker, R.N.,
Sanchez, D.C., and Brennan, T. Engineering design criteria for sub-slab
depressurization systems in low-permeability soils. 1m Proceedings of
the 1990 International Symposium on Radon and Radon Reduction Technology.
Atlanta, Georgia, to be published.
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VIII-4
EVALUATING RADON RESISTANCE OF FILMS AND SEALANTS
USING PERFLUOROCARBON TRACER GASES
Mark Nowak and Ban-Huat Song
NAHB National Research Center
Upper Marlboro, Maryland
Abstract
Movement of radon into a home is controlled by two mechanisms: diffusion and convective
flow. Although many different materials have been suggested as mechanical barriers to reduce
radon flow, there is very little data to substantiate a material's effectiveness. This paper
discusses a relatively low-cost laboratory method to evaluate materials using perfluorocarbon
tracer (PFT) gases to simulate diffusion of radon.
The test method uses a modified version of the Air Infiltration Measurement Service (AIMS),
originally developed for measuring infiltration rates into homes. The procedure is conducted
in an enclosed glass desiccator that is divided into two zones by the test material. The PFT
source is placed in the lower chamber and samplers are located in the upper chamber. Two
results are reported: the reduction in diffusion achieved by the material as compared to
diffusion in an open chamber, and the rate of diffusion through the barrier.
INTRODUCTION
Movement of radon from soils into a home is controlled by two mechanisms: Diffusion,
which is a random scattering of a gas across a concentration gradient; and convection, which
results from driving forces that transport radon with other gases.
The driving force behind convective flow can occur in homes as a result of a reduced pressure
that develops in the lower level of a home relative to surrounding soil. The thermal stack
effect, wind, and operation of HVAC equipment are principal factors contributing to this
pressure differential. Diffusion is generally thought to be less significant than convective
flow, and consequently most attention has been focused on developing barriers to reduce
convective flow of radon into homes. However, in some areas diffusion could result in
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elevated indoor radon levels. Barriers that effectively retard both mechanisms of transport
will increase the radon-resistance of a building.
Barriers are recommended as the first line of defense in new construction by most radon
mitigation experts. Barriers are frequently used under floor slabs and on below-grade walls
to reduce radon entry through cracks, pores, and other openings. Another important use of
barriers - as interior sealants applied over building materials - will become increasingly
important if the national goal to reduce radon levels to outdoor levels is to be taken seriously.
Testing the effectiveness of barriers is difficult One method is to locate a home with high
radon levels and measure indoor levels or radon flux through the wall before and after
application of the barrier. Another is to test the barrier's resistance to radon movement in
a laboratory setting using a controlled radon source. Each of these methods have practical
limitations that, in effect, prohibit most manufacturers from testing their products. Costs
associated with construction and uncertainties in comparing before and after test results in
the first method, and the specialized equipment and use of a radioactive source in the
laboratory method are the primary factors that discourage testing.
THE AIMS METHOD
An alternative method discussed here employs a tracer gas to simulate movement of radon.
The method incorporates the perfluorocarbon tracer (PFT) gas technology used in the Air
Infiltration Measurement Service (AIMS) operated by the NAHB National Research Center.
AIMS was developed in the mid-1980s at Brookhaven National Laboratory as an alternative
to higher cost tracer gas systems in use at that time. The system can be used effectively to
simultaneously measure infiltration rates in up to four different zones. PFT sources used in
the AIMS program emit the gas at a constant rate. Sampler tubes, which passively adsorb
the tracer gas, are placed in the measurement area. At the end of the test period, samplers
are returned to the AIMS Laboratory and analyzed using a gas chromatograph equipped with
an electron capture detector to determine the concentration of the tracer gas in the sampled
airspace.
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Dietz et aL,(1985) discussed the analytical procedure and assumptions for determining
infiltration rates using PFT tracers, termed the steady-state tracer gas method. As the term
implies, the critical assumption is that steady-state infiltration conditions occur within a well
mixed chamber. Calculations (by Dietz et. al.) shown below are based on conservation of
mass (mass-balance) within a single zone. The mass-balance equation for a single-zone room
or chamber yields:
dC/dt = (S/V) - nC (equation 1)
where,
C = tracer concentration in chamber (pL/L),
S = tracer source strength (nL/hour),
V = volume of area to be sampled (m3),
n = air changes per hour (ACH).
Under steady-state conditions, dC/dt = 0, and the equation becomes:
n = S/VC (equation 2)
MEASURING RADON RESISTANCE
Perfluorocarbons are gases whose physical behavior is similar to radon. PFTs are also very
similar to radon in size: radon has a molecular weight of 222, the PFTs used in the procedure
have a molecular weight of 3SO. This similarity permits application of AIMS technology to
evaluate the radon resistance of a barrier using a low-cost laboratory procedure.
TESTING PROCEDURE AND EQUIPMENT
The modified AIMS test of a radon barrier employs a small scale dual-zone chamber. The
two chambers of the glass testing device are separated by an aluminum disk with a six-inch
diameter opening. The test sample is sealed to the opening to form a barrier between the
upper and lower chambers. A PFT source with an emission rate of 24.1 nL/min at 2S°C was
placed in the lower chamber and multiple sampler tubes were deployed in the upper chamber.
The samplers were removed and analyzed with a gas chromatograph after a 30 minute
sampling period.
Two tests of the procedure were conducted on four different samples. Sample No. 1 consisted
of 4-mil polyethylene film typically used as a vapor barrier in construction and generally
believed to be a good radon-resistant material. No. 2 consisted of a single coat of a common
water-based acrylic paint applied over a porous paper backing. The third sample consisted of
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a second coat of paint applied over sample No. 2. Sample No. 4 consisted of the paper used
as a backing for the paint samples.
RESULTS AND CONCLUSIONS
Results of the testing are shown in Table 1. Reduction percentages shown in Column 3 are
based on a comparison with a value calculated for diffusion in an unobstructed chamber.
The diffusion rates in Column 4 are of primary importance in evaluating the relative
effectiveness of barriers. This value was calculated from the measured concentration per unit
time and the internal sampling area.
Under the conditions of this test, the one-coat paint sample was partially effective at slowing
the diffusion rate of the PFT. The polyethylene and the two-coat paint sample were much
more effective at slowing diffusion. Diffusion through the polyethylene occurred at a rate
approximately 2.8 times that of the two-coat paint sample. Due to different properties of the
backing material, it is expected that the painted sample would not perform as well if applied
to a more porous surface like concrete.
In summary, this procedure offers a relatively inexpensive method to measure and compare
the effectiveness of materials in resisting movement of gases. It is expected that future
modifications will be made to more closely reflect conditions of use. For example, the test
can be run with a pressure differential between the chambers induced with a small vacuum
pump. The pressure differential could range from three to five pascals, which is similar to
pressure differentials in some homes during winter. Modification to the procedure could also
be made to more closely simulate the block or concrete substrates to which paints and other
sealants are applied in construction.
The work described in this paper was not funded by the U.S. Environmental Protection Agency
and therefore the contents do not necessarily reflect the views of the Agency and no official
endorsement should be inferred.
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REFERENCES
Dietz, D.N., Goodrich, R.W. and Cote, E.A. 1984. "Detailed Description and Performance of
a Passive Perfluorocarbon Tracer System for Building Ventilation and Air Exchange
Measurements." Symposium on Measured Air Leakage Performance of Buildings, American
Society for Testing and Materials, Philadelphia, PA.
Mortimer, C., Chemistry. A Conceptual Approach. 1975, Van Nostrand Co., New York, NY
Table 1 - Test Results
Average
Concentration* Diffusion Rate
Test Sample (pL/L) % Reduction** (mole/L-hr.-sq.in.)
Polyethylene 19.524 99.977 7.063 x lfru
Paint-1 coat 619.048 99.268 2.281 x lO"
Paint-2 coats 7.024 99.992 2.542 x I0ra
Paper 51.310.242 39.322 1.856 x 104
* 1 picoliter (pL) of PFT gas is equivalent to 1.79 x 10* grams.
** Based on a comparison of the average concentration to a value of 84,561.40 pL/L in
the open chamber (calculated from an emission rate of 24.10 nL/min and a volume of
8.55 L).
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VIII-5
The Use of Coatings and Block Specification to Reduce
Radon Inflow Through Block Basement Walls
John S. Ruppersberger
U. S. EPA, Air and Energy Engineering Research Laboratory
Research Triangle Park, NC 27711
ABSTRACT - Samples of six different coatings were evaluated in specially designed
chambers built around 1.5 m2 concrete block wall sections. Data were collected over a
pressure range of 1 to 12 Pa with flows ranging from less than 0.01 standard liters per
minute (SLPM) to 50 SLPM. A major preliminary finding is that all these coatings
proved to be highly effective (98+%) when enough material was carefully applied.
Baseline (uncoated) flows varied by a factor of 2 (12.1 to 23.5 SLPM/m2 at 3 Pa)
between the two batches of lightweight block used for coatings testing that came from
a North Carolina manufacturer; these differed by an order of magnitude from normal
weight blocks received later from a Minnesota manufacturer (1.8 SLPM/m2 at 3 Pa). This
large difference found in a small sampling of blocks is significant not only in the potential
impact on coating performance, but more significantly that specification of blocks with
low air permeability for new construction of substructures could greatly reduce soil gas
entry, even if left uncoated.
INTRODUCTION - Pressure driven transport of soil gas carrying radon is believed to be
the major entry mechanism for indoor radon. For houses with basements that have been
mitigated as part of the EPA's research program, the perimeter crack where the floor slab
meets the basement walls has often been considered the primary entry route. Generally,
sound poured concrete has not been found to offer a significant entry route, even with
typical hairline cracks. Therefore, coating poured concrete as part of a radon mitigation
effort is not considered worthwhile when working toward a guideline of 4 pCi/L.
Basement walls built of hollow concrete masonry units (CMUs) have always been suspect,
and mitigation has included some work with this type of wall. The surfaces of these
walls have been known to be an entry route, but given less treatment since other
mitigation techniques such as active (fan driven) suction on the soil side of the
substructure/soil interface have been shown to often be effective in achieving a 4 pCi/L
This paper has been reviewed in accordance with the U. S.
Environmental Protection Agency's peer and administrative
review policies and approved for presentation and publication.
-------
guideline. Active systems are often powerful enough to extend their suction into the
core of the CMU wall, effectively reversing the premitigation condition of the basement
air, typically being the suction side of a slight pressure on the order of -3 to -5 Pa.
Efforts to quantify the CMU wall source term is not commonly included in radon
mitigation work to date. When quantified, it was found to contribute up to
approximately 20% (1). Reports of the effectiveness of painting the surface of CMU walls
have been mixed with success credited to the treatment by some mitigators and no
benefit even after thorough treatment with expensive paints by others. The recent
development of the long term goal of ambient radon concentration supports more effort
toward the more common houses, those with a premitigation level of less than 4 pCi/L.
The relative significance of radon entry routes may be different for this large group of
houses. Another major concern of active soil ventilation systems is the large volume of
conditioned indoor air they draw through a typical uncoated CMU basement wall,
producing inefficiency in the system and resulting in an energy penalty of conditioning
the outside replacement air that is brought to the temperature of the house. Trace gas
experiments indicated that 50% of the air exhausted from one active sub-slab mitigation
system was from the basement. (1) Extension of the suction to all essential areas of the
soil/substructure interface is made more difficult if CMU walls allow large flows of indoor
air into the system.
In a Canadian study, external coatings were evaluated for their ability to form an
airtight membrane that would remain intact even if cracks occurred in the substrate
subsequent to their application. Coatings were applied to two adjacent concrete blocks,
which were then moved apart to simulate opening of a crack. (2)
Recent work performed at Princeton University found that block wall air
permeability was reduced by 99.5+% with two coats of a special rubberized paint, a
polysulfide copolymer. One coat was 91% effective. Two coats of either ordinary latex
or oil base paints reduced wall permeabilities by 95%. Air permeabilities were
determined from flow versus pressure data. (3)
A "standard test method for rate of air leakage through exterior windows, curtain
walls, and doors" has been established by ASTM. (4) This test method covers the
determination of resistance of curtain walls to pressure driven air infiltration. The EPA
test method complies with the ASTM test method in every major aspect, and differs only
in data collections at lower pressure differentials, in the range of 1 to 12 Pa. Its
instrumentation exceeds accuracy requirements to permit precise measurements at these
very low pressures and flows.
MATERIALS AND PROCEDURES - Concrete masonry units of the type used in this test
are covered by an ASTM "standard specification for hollow load-bearing masonry units".
(5) This specification covers hollow load-bearing concrete masonry units made from
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Portland cement, water; and mineral aggregates with or without the inclusion of other
materials. The three weight classifications are normal, medium, and lightweight.
Coatings selected for evaluation include a two part catalyzed water based epoxy
paint, an elastomeric paint, a cementaceous block filler, a fiber reinforced surface bonding
cement, a polysulfide vinyl acrylic paint, and a latex paint. Selection criteria included
an attempt to sample various types of coatings that might be used on CMU basement
walls under various conditions. Some coatings are not well suited, or even recommended
by the producers for negative side (inside) basement walls, but were evaluated because
they may already exist on some walls of basements needing mitigation, or might be better
suited for application to walls under certain conditions than other coatings. Coatings
were applied separately to bare wall specimens even though the desired result of a
continuous gas flow resistant film might better be achieved by a combination, such as a
block filler and a coat of paint. This was done to collect data on each coating separately
- - performance of various combinations may be estimated from the data, but to be more
precise, and perhaps more realistic in some instances, reasonable recommended
combinations should be subjected to further evaluations. The effectiveness of a single
coat of the two part water based epoxy argues against a strong need for further tests.
Freshness of samples and adherence to application directions were emphasized. No two
coatings were produced by the same manufacturer.
The test stand was designed for a 16 ft2 (1.5 m2) CMU wall. The wall assembly
is made by pouring a concrete footing (48 x 16 x 6 in., or 122 x 41 x 15 cm) on which
a block wall of 15 standard blocks and 6 half blocks is carefully built. Mortar
construction techniques vary; these walls were built with two fairly generous strips of
mortar on which the base course of blocks are laid. Mortar is applied to all horizontal
surfaces of the previous course and to the end of the next block that will butt up against
the last block on a course in progress. After the wall has set up for over a week it is
caulked generously and, while wet, the side and top panels are assembled then fitted with
covers to encapsulate the wall with a plenum on either side. Closed cell rubber gasket
material is sandwiched between all mating metal surfaces, and between the metal and
acrylic plastic covers.
The completed assembly is leak tested by pressurizing to between 2 and 3 in.
H20 (500 to 750 Pa) using helium gas, and tested for leaks using a halogen gas leak
detector. Leak testing is also conducted on the pressure side of the air delivery
equipment. The control panel is composed primarily of computer controlled mass flow
controllers, a pressure transducer a pump, and a bypass valve that provide precise control
of flows from less than 0.01 to 50 SLPM over a pressure range of 1 to 12 Pa. The
acrylic plastic cover over the side of the wall to be painted is then removed. After
baseline data are collected, the coating is carefully applied. Care is taken to quantify
material used. Additional coats were applied a day after the previous coat except when
data collection needs dictated longer periods or when it might be reasonable to stop
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application of that paint with that coat. It is important to note that the coatings were
applied by brush, carefully working material into the block surface and leaving as much
material on the wall as possible without runs. Primary consideration was sealing the
porous block surface, not the amount of material used. Exceptions are the elastomeric
paint which was applied at the maximum recommended rate and the surface bonding
cement which was applied using a steel trowel.
The initial wall was constructed as part of prototype development and was used
for the polysulfide vinyl acrylic paint evaluation. Its baseline flow was as shown in
Figure 1, Line a, 35 SLPM at 3 Pa, or about 2 SLPM per full block. The remaining five
coatings were evaluated from walls built later; from a different batch^of blocks. Although
from the same local North Carolina manufacture]; meeting the same ASTM specifications
for CMUs, and with no noticeable difference in appearance, the baseline flows were
approximately half of that of the prototype wall, as shown in Figure 1, Line b, 18 SLPM
at 3 Pa, or about 1 SLPM per full block. Then an opportunity developed to evaluate
blocks received from a Minnesota manufacturer. The baseline flow for these blocks is on
average approximately an order of magnitude lower than the local blocks, as shown in
Figure 1, Line c, 2.7 SLPM at 3 Pa or about 0.15 SLPM per full block. Blocks from both
manufacturers are typical of those used in their geographical regions for residential
construction. The more air permeable North Carolina block is lighter, 12.1 kg, and has
become common in the southeast. It contains expanded lightweight aggregate, filled
with numerous discrete voids that do not appear to be interconnecting. The less air
permeable Minnesota block weighed 16.9 kg, uses natural aggregate, and has a smoother,
less porous surface appearance.
WATER BASED EPOXY PAINT - This is a water based catalyzed (two part) epoxy resin
paint. Its analysis by weight, as supplied by the manufacture]; is 16.5% titanium dioxide
pigment and 83.5% vehicle (7.7% epoxy resin, 6.6% ethylene glycol and alcohol, 20.7%
acrylic resin, 46.5% water, and 2.0% additives). The data for this paint are summarized
with other coatings in Table 1. Even with a slightly higher baseline flow of 19.8 SLPM,
a single coat of this epoxy paint resulted in the lowest airflow for one coat of any paint
evaluated, 0.75 SLPM (96.2% reduction) at 1 day drying time, and was also lowest for
any two coats of paint evaluated, at 0.01 SLPM (99.9% reduction). The paint film is
very smooth, and dried specimens exhibited unexpected elongation and strength upon
being pulled apart, although these observations were not quantified by any standard
testing techniques. Application was considered easier than average to provide a
continuous film for both the first and second coats.
ELASTOMERIC PAINT - The analysis of this elastomeric acrylic emulsion paint was not
given. Application rate for concrete block was specified as 50 to 125 ftVgal. (1.23 to
3.07 mVL). The first coat was applied at 50 ftVgal. Based on the performance of the
first coat, a second coat was also evaluated. About a third of the quantity of paint used
for the first coat was used for the second coat. The data for this paint are summarized
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with other coatings in Table 1. The measured effectiveness of the elastomeric paint was
second only to the epoxy: 1.36 SLPM (92.1% reduction) for one coat, and 0.025 SLPM
(99.9% reduction) for two coats. Application by brush was considered the easiest of any
paint evaluated.
CEMENTACEOUS BLOCK FILLER - This is a portland cement plaster that can be troweled,
sprayed, or brushed. There was no information concerning composition on the container
(a bag holding 50 lb, or 23 kg) or sales literature, other than references to portland
cement. In keeping with the general trend of brush application, this product was applied
with a "masonry brush" purchased from the dealer It required a different technique than
typical paints, but application progressed satisfactorily after a brief time. Application was
considered more difficult than average to provide a continuous coating with reasonable
surface appearance. Experience would probably improve both application rate and
appearance. The other cementaceous product evaluated was troweled on, but that
product specified a 1/8-in. thick coating; this cementaceous block filler (also called a
"finish coat" by the manufacturer) was applied at a thinner consistency and thinner than
1/8-in. by brush. The data for this coating are summarized with other coatings in Table
1. The single thick coating resulted in an air flow of only 0.06 SLPM (99.7% reduction);
only about half of the flow through the fiber reinforced surface bonding cement, and over
an order of magnitude less than one coat of the most effective paint.
SURFACE BONDING CEMENT - This is a mixture of portland cement, fiberglass
reinforcement fibers, and unspecified (proprietary) ingredients. Application is specified
as a minimum of 1/8-in. thick with coverage per 50 lb bag of approximately 50 ft2.
Trowel or spray application options are in the product literature supplied by the producer.
Application was with a steel trowel by an experienced mason to a thickness of slightly
over 1/8-in (0.32-cm). The data for this coating are summarized with other coatings in
Table 1. The single application resulted in an air flow of only 0.10 SLPM.
This is more than the other portland cement coating evaluated in this study, but
still is highly effective at 99.5% flow reduction in one application. This single application
allowed less than 14% of the flow of one coat of the most effective paint.
POLYSULFIDE VINYL ACRYLIC PAINT - The supplier described it as polysulfide/vinyl
acrylic dispersion without giving any further specifics on composition. It was offered at
the time the program was started and was used for the original prototype test stand and
equipment testing. Since it was accepted for those first developmental tests, it was
decided to evaluate it as the first coating using the equipment after it was fully calibrated
to QA/QC specifications. It is currently available commercially to radon mitigators.
Application was considered average to provide a continuous film for both the first and
second coats, although pinholes were observed soon after application and their apparent
number and size increased with drying time. The data for this paint are summarized
with other coatings in Table 1. Specifically, the baseline flow was much higher than for
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the walls built later from another batch of blocks. The measured effectiveness of one
coat of this paint was 78.6%; many pinholes were apparent in one coat. The second coat
reduced air flow at 3 Pa substantially, with an effectiveness of 99.4%: 0.20 SLPM of the
baseline flow of 35 SLPM. The observed time dependence on measured effectiveness
resulted in reconsideration of a standard condition of 2 weeks drying time since data
collected at different drying times exhibited different slopes and a consistent trend of
increasing flows with increasing drying time. Performance deteriorated further between
2 weeks and 2 months with visual pinholes becoming more numerous and larger.
LATEX PAINT - This is a latex semi-gloss paint. It is commonly sale priced at retail and
might be considered the type of latex paint homeowners would often buy; there are both
less and more expensive latex paints available. Its analysis did not list ingredients by
weight, merely as pigment (titanium dioxide, and hydrous aluminum silicate) and vehicle
(polystyrene resin, acrylic latex, vinyl acrylic resin, 1, 2 propanediol, additives, and
water). Application information on the label stated 400 ftYgal.(9.82 mz/L) or less, and
that textured surfaces may require more paint. Actual application rate on the test wall
was approximately 100 frYgal (2.46 m2/L). That first coat took as much paint as the
next two coats combined, resulting in a coverage after the three coats of approximately
50 ftVgal (1.23 mz/L). Application of the paint by brush was considered slightly more
difficult and time consuming than the average of the paints evaluated. The data for this
paint are summarized with other coatings in Table 1. The measured effectiveness of this
latex paint was less than any of the other three paints evaluated for either one or two
coats. One coat was not very effective, about an order of magnitude less effective than
the epoxy or elastomeric paints, allowing 11 of the baseline 19 SLPM (42.1% reduction)
to pass at 3 Pa after 1 day drying time. It was the only paint applied with three coats,
but that third coat greatly increased the effectiveness, from 84.2% with two coats up to
98.1% (0.37 SLPM) at three coats.
DISCUSSION - Reduction of air entry is the primary concern that motivated this work
and all aspects of the test program. Several observations are especially noteworthy. The
first is that, of these coatings, everything works well in reducing air flow across these test
walls (initially at least, under these ideal conditions) if sufficient material and care are
used in their application. A major finding, and a surprising one after discussions with
several paint chemists working to formulate especially, effective radon flow resistant
paints, and seeing fairly expensive specialty paints being advertised specifically as radon
resistant, is that all these coatings, when carefully applied with sufficient quantity,
demonstrated that they can be highly effective in reducing gas flow across the face of
concrete masonry units. Another is the interesting observation that the data for any
particular set of flow vs pressure plots are a straight line on arithmetic paper.
Apparently, flow through these small openings at low pressure differentials is laminar.
-------
A comparison of percent effectiveness in reducing the baseline flow and estimated
cost associated with do-it-yourself (approximated by the material cost) and professional
application total cost is summarized in Table 1. Among the paints, the polysulfide vinyl
acrylic offered as specifically formulated for radon control performed much less effectively
(78.6%) than either the epoxy (96.2%) or elastomeric (92.1%) with only one coat.
Cost of the polysulfide vinyl acrylic paint sold by the manufacturer to radon mitigators
is nearly equal to that of the water based expoxy. Of commercially available paints, the
latex is the least expensive material for three coats. However, a do-it-yourselfer would
have to be strongly motivated to save a few pennies per square foot and get about 2%
more effectiveness, to go to the trouble of applying three coats of a slightly more difficult
to apply paint, than one coat of the epoxy that provided almost equivalent effectiveness.
The better appearance and other desirable properties of this epoxy over the latex paint
might also influence a final decision. Considering just the paints, one coat of an
equivalent water based epoxy might be a reasonable choice since the trouble and expense
of a second coat produce only a little over 3% increase in effectiveness.
From these data, the clear performance value leader is the cementaceous block
filler. This product contains portland cement, but no fiberglass. The product evaluated
was white; if a natural grey color similar to the original block wall is acceptable, it would
be approximately^ penny less per square foot material cost. This type of coating, highly
effective at the lowest cost, and with the effect of significantly changing the block wall
appearance to a much smoother plastered look, is an apparent first choice unless
conditions in the basement do not favor its application. Such adverse conditions would
also produce problems with paints in general. The surface bonding cement is only
slightly more expensive. It has added advantages of its fibers providing added tensile
strength that may be helpful for walls experiencing problems with minor cracking, and
also has a higher portland cement content that imparts improved waterproofing
performance ~ although this and most others are recommended for exterior application.
In summary, considering both cost and effectiveness, for coating an existing wall,
a cementaceous product such as the cementaceous block filler is apparently the first
choice. If a paint is desired, the choice is more complicated based on these results, but
one coat of a similar performing water based epoxy would be good if about 96%
effectiveness is acceptable. If top effectiveness is the only criterion, two coats of the
water based epoxy is found to be the most effective of the coatings evaluated. Of course,
building the wall with low air permeable blocks in the first place could decrease the need
for any coating at all. Dry stacking with fiber reinforced surface bonding cement would
also provide soil gas entry resistance.
-------
PRELIMINARY CONCLUSIONS AND RECOMMENDATIONS:
1) All of the six coatings selected for evaluation can provide highly effective
reductions in air flow under the conditions of the tests when sufficient quantity is
carefully applied.
2) Considering both cost and effectiveness, a cementaceous product such as the
cementaceous block filler offers highly effective flow reductions in a single application at
low cost. Among paints, two coats of the water based catalyzed epoxy was found to be
most effective in these tests, although one coat may be adequate for some situations.
3) The variation in air flow characteristics between similar looking blocks is
large; in this limited sampling of only two batches of lightweight blocks from a North
Carolina manufacture]; it was found to vary by about a factor of 2 (12.1 to 23.5
SLPM/m2 at 3 Pa). The difference between the North Carolina blocks (lightweight, 17.8
SLPM/m2 average flow at 3 Pa) and Minnesota blocks (normal weight, 1.8 SLPM/m2 at
3 Pa) is an order of magnitude. This large difference found in a small sampling of blocks
is significant not only in the potential impact on coating performance, but more
significantly that specification of blocks with low air permeability for new construction
of substructures could greatly reduce soil gas entry, even if left uncoated.
4) Flow vs pressure data collected for these carefully constructed test walls and
at this very low pressure range were found to be linear.
REFERENCES:
1. Hubbard, L.M., et al. Research on Radon Movement in Buildings in Pursuit of
Optimal Mitigation. Proceedings of American Council for an Energy Efficient
Economy 1988 Summer Study. Vol. 2. Asilomar. California. August 1988.
2. DSMA ATCON LTD. Atomic Energy Control Board Development Program for
Radon Reduction, Report 9, "Laboratory Tests External Coatings," August
1979.
3. Maryonowski, J.M. "Measurement and Reduction Methods of Cinder Block Wall
Permeabilities," Center for Energy and Environmental Studies, Princeton
University, Working Paper No. 99, 1988.
4. ASTM E 283-84, "Standard Test Method for Rate of Air Leakage Through Exterior
Windows, Curtain Walls, and Doors," September 1984.
5. ASTM C 90-85, "Standard Specification for Hollow Load-Bearing Concrete Masonry
Units," July 1985.
8
-------
First botch of local blocks
Second botch of local blocks
Blocks from Minnesota
§ 20 -
10 -
456789
PRESSURE (Pa)
FIGURE 1. Air flow through block walls.
10 11 12 13
TABLE 1. EFFECTIVENESS OF COATINGS IN REDUCING AIR FLOW THROUGH
CONCRETE BLOCKS AT 3 PASCALS
Effectiveness f%)
Estimated Cost (dollars) 1989
Per Sauare Foot
Greater Than 99% Effective
Epoxy, 2 coats water based
Elastomeric, 2 coats
Cementaceous Block Filler
(brushed thick)
Surface Bonding Cement
(1/8 in. troweled)
Polysulfide Vinyl Acrylic,
2 coats
Greater Than 98% Effective
Latex, 3 coats
Greater Than 90% Effective
Epoxy, 1 coat, water based
Elastomeric, 1 coat
Greater Than 75% Effective
Latex, 2 coats
Polysulfide Vinyl Acrylic,
1 coat
Less Than 75% Effective
Latex, 1 coat
99.9
99.9
99.7
99.5
99.4
98.1
96.2
92.1
84.2
78.6
42.1
Material
0.37
0.50
0.14
0.20
0.36
0.22
0.25
0.37
0.17
0.23
0.11
Labor
0.34
0.30
0.20
0.22
0.30
0.42
0.20
0.18
0.30
0.18
0.18
Total
0.71
0.80
0.34
0.42
0.66
0.64
0.45
0.55
0.47
0.41
0.29
Typical Basement'
D.I.Y Professional
440 850
600 960
170
240
430
260
300
440
200
280
130
410
500
790
770
540
660
560
490
350
1 Typical" is assumed to be approximately 1200 ft* of wall surface, in good
condition, ready to be painted. Costs for brushes, dropcloths, preparing the base-
ment area and walls, etc. are not included. D.I.Y. Means Do It Yourself.
9
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Session C-VIII:
Radon Prevention in New ConstructionPOSTERS
-------
C-VIII-1
N WOOD FOUNDATION SYSTEM
by: Roscoe J. Clark
Permanent Wood Foundation, Inc.
Flint, Michigan 48501
ABSTRACT
Radon, ...an issue of growing concern to the building industry.
Silently, invisibly, it invades existing structure ...as it will future
foundation structures.
This paper will address the nature and causes of radon, and cost-
effective prevention and retrofit techniques used for wood foundation systems.
Radon also can enter homes with foundations that use the under-floor as
an air distribution system. These building practices will be shown; even
materials used in construction may release radon, for example, this may be a
problem in a house that has a solar heating system in which its heat is stored
in large beds of stone. Stone is most often used in wood foundation
construction.
The common radon entry points will be looked at, and the latest
prevention techniques will be illustrated, such as natural and forced
ventilation, sealing major radon sources and entry routes, and sub-slab and
sump crock ventilations.
P.W.F. STUDY
The U.S., Canada and overseas are studying the effectiveness of various
ways to reduce high concentrations of radon in houses.
Each year the study gives us a better understanding about radon and its
effects. This paper describes methods that have been designed for successful
reduction in permanent wood foundations. The information presented here is
concerned primarily with radon which enters a house from the underlying soil.
FACTS
The first fact about radon reduction is "no two houses are alike."
Houses that are built exactly the same have small differences in them that
affect radon entry. These differences can effect the design and effectiveness
-------
of radon reduction techniques. P.W.F. homes can have major differences in
radon sealing techniques compared to conventional foundations.
This paper is intended primarily for permanent wood foundations and
those who have decided that they need to incorporate radon-reduction methods.
The two basic goals are to minimize radon entry and the removal of radon gas.
In fact, it is potentially more cost-effective to build a P.W.F. Home that
resists radon entry than to remedy a radon problem after construction. This
paper should only be used as an attempt to remedy a radon problem, and to give
an understanding so not to cause other performance problems to be discussed
below.
THE RISKS
The known health effect associated with exposure to elevated levels of
radon is an increased risk of developing lung cancer. There is no doubt that
sufficient doses of radon and its progeny can produce lung cancer in humans.
Radon is believed to be the greatest risk of getting lung cancer for non-
smokers .
As with other pollutants, when studying the exposure to radon, there is
some uncertainty about the amount of health risk. The risk estimates are
based on scientific studies of miners exposed to varying levels of radon in
underground work. A more certain estimate of risk (than on studies) rely
solely with animals. Despite that same uncertainty in the risk estimates for
radon, the greater your exposure to radon, the greater your risk of developing
lung cancer.
RADON ENTRY
Radon is a gas which can move through small spaces in the soil and
gravel on which a house is built. Radon can seep into a home through the sump
crock, joints, floor drains, cracks in concrete floors, etc. Radon has been
found in well water and can release radon into the home when the water is
used.
Some building materials have released radon; for example, stone
fireplaces or solar systems which used stone beds for heat storage. However,
building materials are not a major source of indoor radon.
The physical relationship between the major sources of radon and the
indoor structure of a house is illustrated in figure 1. Common entry routes
for radon gas into the house are shown. The major entry points for radon into
the house include:
A. Cracks in concrete floors
B. Joints in building materials
C. Sumps - exposed soil and tile
D. Stone materials (i.e., granite)
E. Water (i.e., shower)
-------
The soil is believed to be the greatest contributor of indoor radon in
typical homes.
NEW CONSTRUCTION
1. Homes should be designed and built to maintain a
neutral pressure differential between indoors and
outdoors.
2. Homes should be designed and constructed to
minimize pathways for soil gas to enter.
3. Features can be incorporated during construction that
will facilitate radon removal after completion of the
home if prevention techniques prove to be inadequate.
4. The first step in building new radon-resistant
permanent wood foundations is to determine the
potential for radon problems at the building site.
Check with neighbors or state and local health
agencies for soil test results.
CONSTRUCTION TECHNIQUES
Some of the radon prevention techniques are common building practices in
permanent wood foundations. Others are less costly if accomplished during
construction. The cost to retrofit an existing home with the same features
would be significantly higher. These construction techniques do not require
any fundamental changes in building design. Supervision over quality control
is needed for certain construction details. Radon entry techniques can be
grouped into two basic categories:
1. Methods to reduce pathways for radon entry.
2. Methods to reduce the vacuum effect of a home
on surrounding and underlying soil.
These techniques are used in conjunction with each other (see figure 2).
UNDERSTANDING THE PERMANENT MOOD FOUNDATION BASIC REQUIREMENTS
The Permanent Wood Foundation is a load-bearing wood frame wall system
designed for below-grade use as a foundation for light-frame construction.
The stress-graded lumber framing and plywood sheeting in the system are
carefully engineered to support lateral soil pressure as well as live, dead
and climatic loadings. Vertical loads are distributed to the supporting soil
by a composite footing consisting of a wood footing plate and a structural
gravel layer.
-------
All lumber and plywood in contact with or close to the gravel is
protected against decay and insects by pressure treating with time proven wood
preservatives.
Moisture control measures based on the latest development in foundation
engineering, construction practice and building materials technology are
employed to achieve dry and comfortable living space below grade.
The most important of these measures is a porous gravel envelope
surrounding the lower part of the basement. This porous layer directs ground
water to a positive drain or sump, thus preventing hydrostatic pressure on the
basement walls or floor. Similarly, moisture reaching the upper part of the
basement foundation wall is deflected downward to the gravel drainage system
by polyethylene sheeting or by the treated plywood itself. The result is a
dry basement space that is readily insulated for maximum comfort and
conservation of energy.
WORD OF CAUTION
What works for conventional foundations may have significant negative
effects when applied to Permanent Wood Foundations. It is important to
understand the basic requirements of the Permanent Wood Foundation system
before applying mitigation measures which could cause problems to the system's
performance. This Radon Check List may be helpful when applying mitigation
measures.
RADON CHECK LIST
SEALING WALL POLY FOR RADON CONTROL
Six-mill thick polyethylene sheet should be applied over the below grade
portion of exterior basement wall prior to backfilling. Joints in the
polyethylene sheet shall be lapped 6 inches and bonded.
The top edges of the polyethylene sheeting should be bonded to the
plywood sheeting. A treated lumber strip should be attached to the wall to
cover the top edges of the polyethylene sheeting. The wood strip shall extend
8 inches above and 4 inches below finish grade level as required to protect
the polyethylene from exposure to light and from mechanical damage at or near
grade. The joint between the strip and the wall shall be caulked full length
prior to fastening strip to the wall. The polyethylene sheet shall extend
down to the bottom of the wood footing plate but shall not overlap or extend
into the grave footing. Do not seal the bottom of the polyethylene sheet to
the plywood wall for radon resistance. Moisture is deflected downward to the
gravel drainage system by this polyethylene sheeting and by the treated
plywood wall itself. Sealing this joint would result in preventing positive
drainage to the gravel. Simply put, the basement may leak.
SEALING FLOOR POLY FOR RADON CONTROL
-------
A six mill thick polyethylene moisture barrier shall be applied over the
porous layer of gravel. Overlap the seams in the barrier 12 inches and seal.
Penetrations of the barrier by plumbing should be sealed and care should be
taken to avoid puncturing the barrier when pouring the floor. The floor
polyethylene should not lap under the footer plate or seal to the wall poly
for radon control. This will prevent positive drainage of the wall poly or
moisture from inside the basement wall plates draining through the footer
plate to the gravel footer. Moisture would be drained on top of the floor
poly causing hydrostatic pressure and dampness. The poly can be brought up on
the inside wall surface and sealed to the screed board.
INSTALLING POLY FOR WOOD FLOOR SYSTEM
Where wood basement floors are used, the polyethylene sheeting six mill
shall be placed over the wood sleeper supporting the floor joist and,
provisions are made for drainage to the porous layer below at the end of each
bay. The sheeting should not extend beneath the wood footer plate. The poly
is overlapped 12 inches and is not sealed for radon control.
Water that accumulates on top of the moisture barrier during
construction can be dried out by venting the wood floor. Radon gas can also
be vented out through these vents by convection. The studies show that three
vents work better than two and should be placed 4 feet or farther away from
any corners for best performance, (see figure 3)
USING LARGE GRAVEL TO VENT RADON
Gravel should be washed and well graded. The maximum size stone should
not exceed 3/4 inch. Gravel shall be free from organic, clay or salty soils.
Sand shall be coarse, not smaller than 1/16 inch grains and shall be
free from organic, clay or salty soils.
Crushed stone shall have a maximum size of 1/2 inch. Crushed stone must
also be compacted before installing footer plate.
The Permanent Wood Foundation system incorporates a composite footing
consisting of a wood footing plate and a layer of gravel, coarse sand or
crushed stone. The wood footing plate distributes the axial design loads from
the framed wall to the gravel layer which in turn distributes it to the
supporting soil:
*the use of larger than 3/4 inch stone for radon
mitigation can cause inadequate bearing transfer.
This means less wood to stone surfaces that can cause
the stone to crush into the wood footer plate causing
settling of the foundation.
*the use of larger than 1/2 inch crushed rock will have
jagged edges that will break off under load causing
settling.
-------
*larger stone makes it harder to level foundation walls.
CAULKING THE P.W.F.
The sealant used for caulking joint in plywood wall sheeting should be
capable of producing an effective moisture seal under the conditions of
temperature and moisture content at which it will be applied and used. Buytl
caulking is commonly used for this purpose. To correctly apply caulking into
joint, apply caulking on edges of plywood joint, push next sheet into place.
Be careful not to slide off caulking. This has several purposes; one is to be
an expansion joint for the plywood, and another is to give resistance to
moisture flowing down the wall and can have sealing effects in radon control.
Caulk end and center seam of wall plywood. Do not caulk the bottom edge of
plywood where it buts up next to bottom plate. This will stop the pathway for
any water that accumulates from condensation on the inside plywood surface
during winter construction. This damming of water can be picked up by the
wall insulation and lead to mildew and drywall staining.
TOOLING BASEMENT FLOOR/WALL FLOOR JOINT
The more common radon entry pathway are inside perimeter floor/wall
joints. To reduce radon entry through these joints, install a wide plywood
screed board along the perimeter of the foundation. This wider screed board
can be sealed to the drywall finish installed later on the foundation wall
above. Mud and tape this joint when finishing the drywall above.
The concrete floor is poured against the screed board and the concrete
edge is tooled round for a caulk sealer to be applied later.
Oversize tooling of this joint may cause lateral wall deflection at the
floor/wall assembly. Proper floor height against studs will allow adequate
bearing area. This bearing area is figured from the bottom of the tool joint.
Remove all grade stakes and fill the holes as the slab is being
finished. This will prevent future radon pathways through the slab which
might otherwise be created, as embedded untreated wood eventually
deteriorates.
Carefully seal around all pipes and wires penetrating the slab. Pay
careful attention to the bathtub, shower, and toilet openings around traps.
Floor drains, if installed, should drain to a sealed sump crock, and
used traps in all floor drains.
Sump should be sealed at the top with a plywood and gasket lid. Use
only submersive-type sump pumps in the crock to prevent high humidity
corrosion. For sump crock sub-slab ventilation, drill holes near the top of
the sump wall to let soil gases enter crock, (see figure 4)
METHODS TO REDUCE PATHWAY FOR RADON ENTRY
-------
The most effective way to seal a P.W.F. basement wall is by drywalling
the wall. First, the bottom seal must be applied. This is done by applying a
gasket to the bottom edge of a added plywood screed board. This is pushed
down into place and the wood strip is nailed into place (use 1/2 inch plywood
for 1/2 inch drywall). Next, install a gasket at the top top-plate. Now
install new drywall, compressing the gasket between the plate and the drywall.
(see figure 5)
SUB-SLAB VENTILATION USING WOOD FLOOR SYSTEM
To seal a wood basement floor system, first install a wider plywood
screed board. A gasket is installed to the plywood screed where it will be
sandwiched between the wood floor ban joist. A gasket is installed on the top
edge of the ban joist so that gasket will be sandwiched between the plywood
and ban. The gasket makes a more permanent seal over caulk or glue.
Caulk plywood edges as the floor is installed with buytl caulking. If
mechanical ventilation is needed, put suction pipe under poly film for better
performance. Keep above the water line. A tee fitting will add to the
performance, (see figure 6)
SUB-SLAB VENTILATION USING SUMP SUCTION APPROACH
Where better performance is needed, the P.W.F. sump can be vented by
sealing the top with a plywood lid and gasket. The water enters the sump from
the bottomless crock. This system will cause a water trap effect. Therefore,
drilling holes at the top of the crock will help let in the soil gases so it
can be vented, (see figure 7)
SUB-SLAB VENTILATION OF WOOD FLOOR SYSTEM
To vent a wood basement floor, cut out a section of the ban joist.
Install 2x2 and sheeting to make a pathway to the outside up the foundation
wall. Install a screen vent cover on the outside, (see figure 3)
SUB-SOIL VENTILATION USING HORIZONTAL RUN UNDER VAPOR RETARDER
When using the crawlspace as a heat plenum, always have the crawlspace
in a positive air flow. Running the blower constantly will minimize the
negative pressure differences. A polyethylene film is installed over a 4 inch
layer of gravel and the polyethylene is covered with 2 inches of sand.
Overlap the polyethylene 12 inches at all seams and seal. Seal polyethylene
to film on the wall. For better performance, a tee or cross network of 4 inch
p.v.c. can be connected to a fan-driven system.
(see figures 8 and 9)
The work described in this paper was not funded by the U.S.
Environmental Protection Agency and therefore the contents do not necessarily
reflect the views of the agency and no official endorsement should be
inferred.
-------
MAJOR RADON ENTRY ROUTES
CRACKS
JOINTS
SUMP
MATERALS
WATER
FIGURE 1
-------
METHODS TO REDUCE THE VACUUM EFFECT
SEAL AROUND
FLUES AND
CHIMNEYS
AVOID RECESSED
CEILING LIGHTS
IN UPPER CEILING
v-SEAL AROUND
\ALL OPENINGS
SEAL AROUND
PLUMBING
PENETRATIONS
SEAL
ACCESS
MAKEUP
AIR
CPAWL SPACE
KNGHT
SEALING
WINDOWS
FIGURE z
VAPOR RETARDER-
-------
SUB-SLAB VENTILATION OF WOOD FLOOR SYSTEM
VENTo-?0
GRADE
SEAL DRYWALL
TO PLATE
SHEATHING
&
DRYWALL TO
SCREED BOARD
SEAL JOINTS
ff *~ W
J _ o_ _ .. _P xrxav
0f°&~SG* ° <2,°1&° ^O*0 Q° O " °/5*O
o/^« e °_To .i <>*?__l»^ a ^o o^i er v%» r~l ^o^f1
QPop «CSc7 ^ o o^P.0 "oC? o o 0-0-o° . °^
BSBiilfisH '
SOIL GAS
VAPOR RETARDER
FIGURE
-------
Sub-slab ventilation using individual suction point approach.
Exhaust
Seal drywall to plate
Grade level
Tape drywall to screed board
Seal joints
4
Connect
to other
suction points
House air through
sealed cracks
and joints
Soil gas
FIGURE 4
-------
METHODS TO REDUCE PATHWAYS FOR RADON ENTRY
rAm
GRADE LEVEL
SEAL DRYWALL
TO PLATE
SEAL ALL PLUMBING
PENETRATIONS
TAPE DRYWALL TO
ADDED SCREED BOARD
SEAL JOINTS-7
CAULK CRACKS
SOIL GAS
*-VAPOR RETARDER
FIGURE 5
TRAPPED DRAIN
TO SUMP, SEWER
OR DAYLIGHT
-------
Sub-slab ventilation using wood floor system
Exhaust
Grade level
ISeal drywall to
plate
Soil gas
Soil gas'
FIGURE 6
-------
Sub- slab ventilation using sump suction approach.
Exhaust'
Seal drywall
to plate
House air through
unsealed cracks
and joints
Utility pipe
FIGURE 7
-------
Perimeter drain tile ventilation where tile drains to sewer or daylight.
Protective cover
Exhaust
Riser connecting drain tile
to fan
Condensate
|(35)--Fan
Seal drywall
to plate
House air through
unsealed cracks
and drains
Capped riser toadd
water to trap
j^-»-/*Va
*S»o0oo<'<'Ws<» «5U
Water trap to prevent air from being
drawn up from sewer or daylight
FIGURE 8
-------
Sub- soil ventilation using horizontal run under vapor retarder.
Exhaust
'V
Ife
I I y-Floor register
U1
Grade level
HVAC
Unit
3///////I
1
Positive air crawl
space plenum
FIGURE 9
-------
Session IX:
Radon in Schools and Large Buildings
-------
IX-1
Radon Measurements in 130 Schools Across the US
R. Thomas Peake
Anita Schmidt
US Environmental Protection Agency
ABSTRACT
During the winter of 1989, screening Rn measurements were
made in 130 schools geographically dispersed across the U.S. The
purpose of the study (Phase I) was to identify a subset of
schools suitable for year long follow-up study (Phase II), the
results of which will be used to udpdate EPA's guidance for Rn
testing in schools. The 130 schools were selected nonrandomly
using school characteristics and accessibility in areas where
there were known or suspected radon problems in homes. Because
of this selection, it is postulated that levels found in this
study may represent an upper boundary for screening radon
measurements in US schools.
The findings from this study confirm previous findings (1)
that Rn concentrations can vary significantly from room to room
within a school. The average Rn level for the 130 schools is 3.7
pCi/L (geometric mean of 1.4 pCi/L) ; over half of the schools
tested had at least one screening Rn measurement above 4 pCi/L.
The study also indicates that schools in the same area can have
similar or significantly different radon concentrations.
This paper has been reviewed in accordance with the U. S. Environmental
Protection Agency's peer and administrative review policies and approved for
presentation and publication.
ind tedon Reduction Techniques
-------
IX-2
RADON DIAGNOSTICS AND MITIGATION IN TWO PUBLIC SCHOOLS
IN NASHVILLE, TENNESSEE
by: Alfred B. Craig, Kelly V. Leovic,
and D. Bruce Harris
U.S. Environmental Protection Agency
Air and Energy Engineering Research Laboratory
Research Triangle Park, North Carolina 27711
Bobby E. Pyle
Southern Research Institute
Birmingham, Alabama 35255-5305
ABSTRACT
Diagnostic measurements and mitigation studies were carried out in two
schools in Nashville, Tennessee, as part of the Environmental Protection Agency's
(EPA's) School Radon Mitigation Development/Demonstration Program. Diagnostic
studies included architectural plans and building examination, sub-slab radon
concentrations, sub-slab communications measurements, and detailed classroom
radon measurements using 2-day charcoal canisters, electret ion chambers, and
continuous monitors. Although sub-slab communications varied significantly
between the two schools, both were amenable to mitigation using sub-slab suction.
Average premitigation levels of 39.5 and 29.7 picocuries per liter (pCi/L) were
reduced to 0.78 and 1.7 pCi/L in the two schools.
This paper has been reviewed in accordance with the U.S. Environmental
Protection Agency's peer and administrative review policies and approved for
presentation and publication.
See conversion factors listed at end of paper.
-------
INTRODUCTION
In February 1989, the Environmental Protection Agency (EPA), in coopera-
tion with state and local officials, measured radon levels in over 3,000
classrooms in 130 schools located in 16 states spread across the United States
using 2-day charcoal canisters. The purpose of these tests was to select 20
schools for detailed testing over a 1-year period to improve interim radon
measurement protocols for schools. Two of the schools in Nashville, Tennessee,
with very high levels of radon in most of the classrooms were selected for
inclusion in EPA's School Radon Mitigation Development/Demonstration Program.
These were the Two Rivers Middle School and Glenview Elementary School, both
located in a high radon-risk area of Nashville where numerous outcroppings of
Mississippian-Devonian black shale, commonly referred to as Chattanooga shale,
occur. This shale deposit runs through the middle of the state of Tennessee and
is the source of high radon levels in houses in the central Tennessee area,
including parts of Nashville. EPA has also been studying the mitigation of radon
in existing houses in Nashville over the past 3 years.
Results of diagnostic and mitigation techniques used in the two schools
are discussed separately and compared.
TWO RIVERS MIDDLE SCHOOL
Figure 1 is a floor plan of the first floor of Two Rivers Middle School
with dates of construction of each area and classroom numbers. This school was
TWO RIVERS MIDDLE SCHOOL
\9M
uDoniw
Figure 1. Floor plan and eonccrueclon ditci
-------
built as a high school between 1960 and 1963 in four phases. The school contains
19 slab-on-grade classrooms and 2 classrooms located over a crawlspace on the
first floor, and 2 basement classrooms. In addition to these classrooms, there
are two gymnasiums with boys' and girls' locker rooms, cafeteria, kitchen, and
three rooms for music and shop. Part of the locker rooms and gymnasium are over
cravlspace and the rest is slab-on-grade. The two classroom wings contain a
second story with 23 classrooms and a library. Mitigation studies at this school
were limited to the two, two-story classroom wings and the two basement rooms
under the end of one classroom wing.
Thirty classrooms were initially tested over the weekend of February 4,
1989. The average of these tests was 39.5 picocuries per liter (pCi/L) and
ranged from 1.5 to 136.2 pCi/L. Only three rooms were below 4 pCi/L. These
measurements are shown on the floor plan in Figure 2. The three highest rooms
were tested 2 weeks later to verify these high readings. One room, initially
measured at 136.2 pCi/L, increased to 148.8 pCi/L, and radon levels in the other
two rooms decreased to about 50 pCi/L. The average decrease of the three rooms
was 18.5 percent. Retest data are given in parentheses in Figure 2. Testing
was carried out in accordance with Report EPA-520/1-89-010, "Radon Measurement
in Schools, An Interim Report."(1)
TWO RIVERS MIDDLE SCHOOL
DOTE- IKMIM. TCS1S MIX IN {»Rl»
1989 MOUSES IK
PARENTHESES U( IEPEMS WK
III UUC FEBRUABT
Baden mr«B«nct. February 1969. pCl/L
Because of the very high readings, school maintenance personnel sealed
floor cracks and openings in the 10 classrooms with the highest readings, all
but one of which were above 50 pCi/L. These 10 rooms were reduced from an
average of 81.7 pCi/L in the initial test to 29.0 pCi/L, a 64.5 percent
reduction. However, the readings in all 10 rooms were still above 20 pCi/L
after sealing, the highest level being 41.7 pCi/L.
Prior to initiating diagnostic studies in early June, the building was re-
tested over a weekend under the same test conditions as the first set. The 26
rooms had an average level of 10.1 pCi/L and ranged from 1.9 to 32.4 pCi/L, with
6 of the 26 rooms being below 4 pCi/L. This decrease could be partially
attributed to the sealing carried out by the school maintenance personnel, but
it was also probably the result of the difference in summer and winter readings.
However, the levels were sufficiently high to cause a health concern;
consequently, diagnostic measurements were made and mitigation carried out.
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DETAILED DIAGNOSTIC STUDIES
Inspection of Architectural Drawings and Building
Examination of the foundation and wall section plans disclosed that the two
hall walls in the slab-on-grade areas are load bearing, resting on a thickened
slab footing, with aggregate shown extending under the footing. The walls
between classrooms are not load-bearing and do not extend through the slab. The
addition of the four classrooms at the north end of the building resulted in what
appeared to be a solid wall under the slab between the last four rooms and the
initial part of the building.
Eight classrooms in the south wing are slab-on-grade and the southernmost
part is a four classroom addition built partly over crawlspace and partly over
basement. This is shown in Figure 1. The drawings show that aggregate had been
used under the slab throughout the building, including the basement.
The building has hot water radiant heat along the outside walls in all
areas except the basement. (These two basement rooms had two separate HVAC
systems.) The portion of the building heated with hot water has no active
ventilation except infiltration. The original windows have been replaced with
a combination of solid panels and weather stripped windows, reducing the
potential for ventilation through infiltration. A blower test run on a segment
of four rooms indicated a very tight building. The entire building is air-
conditioned by window units installed in one of the solid panels in each of the
classrooms. All of the fresh air supplies for the air-conditioning units were
closed for energy conservation.
Measurement of Sub-slab Radon Levels
Sub-slab radon levels were measured by "sniffing" through a 1/4 in. hole
in the center of each room using a Pylon AB-5 continuous monitor. Levels under
the original building ranged from 2600 to 5700 pCi/L. The four-room addition
on the north end of the building ranged from 1300 to 1700 pCi/L. The portion
of the south wing of the building which was slab-on-grade ranged from 200 to 2200
pCi/L. The levels under the cafeteria were 4100 pCi/L. Levels under the two
basement rooms at the south end of the building were 500 and 800 pCi/L. Sub-
slab radon levels for individual rooms are shown in Figure 3.
»««*»!
TWO RIVERS MIDDLE SCHOOL
Figure 3. Sub-*Ub radon
net. pCIA
-------
Sub-slab Communication Testing
Sub-slab communication was measured using an industrial vacuum cleaner.
The hose of the vacuum was inserted through a 1-1/2 in. hole drilled through the
slab in the closet in Classroom 104 (north wing). The speed of the industrial
vacuum cleaner was varied to draw vacuum in the hose of 2, 4, and 6 in. V.C.
Pressure difference between the sub-slab and the room was then measured at the
center of each room (as a minimum) using a micromanometer sensitive to less than
0.001 in. V.C. The measurement was made in the hole (in the middle of the room)
which had been drilled for radon sub-slab profile measurements. The suction hose
of the vacuum cleaner and the hose from the micromanometer were carefully sealed
at the floor surface using rope caulking. Negative sub-slab pressures shown in
Figure 4 were measured at 4 in. V.C. on the vacuum cleaner line.
Excellent sub-slab depressurization was measured from Classrooms 101 to 106.
Depressurization under the rooms on the east side of the hall appeared to be as
good as those on the west side of the hall, showing that pulling under the
thickened slab sections under the two hall walls did not cause any significant
loss of pressure confirming that there was aggregate under the thickened slab
as indicated on the plans. The negative pressure found in the slab under Rooms
107 through 110 was surprising: it was not anticipated that these rooms would
communicate with the rest of the rooms in the wing because they were added at
a later date, leaving the north wall of the building in place. (These brick
walls were left exposed in Rooms 107 and 108.) However, when the wall at the
end of the initial hall was broken out to extend the hall, the foundation was
apparently broken below the aggregate level; the aggregate continues down the
hall. Consequently, it was possible for the suction to reach these other four
rooms. The center of Room 109 was approximately 120 ft from the suction point.
Sub-slab communication was measured in the south wing by placing a suction
point in the office in the south west corner of Classroom 121. Negative
pressures under the slab in these rooms are also shown on Figure 4. Note that
the suction field extension is not nearly as great in this wing as in the north
TWO RIVERS MIDDLE SCHOOL
Figure 4. N«g*clv« cub-slab pr«nur««, In. V.C.
-------
wing; apparently sub-slab communication is not as good. Although Room 126
(farthest from the suction hole) did not show a negative pressure under the slab
with the vacuum cleaner test, it was anticipated that the installation of a
suction point where the suction hole was would reach Room 126. The larger
suction hole and fan of the permanent system normally give a greater suction
field extension than is typically seen with the vacuum cleaner test.
Sub-slab communication was measured in the basement rooms (containing the
art and TV rooms) at the south end of the building. A suction point was made
in one corner of the art room, and it was possible to measure negative pressures
in the middle of the room. However, there was no indication of any negative
pressure under the slab of the TV room.
MITIGATION DESIGN AND INSTALLATION
The degree of sub-slab communication in the north wing was much greater
than had been found in any other school tested in EPA's School Radon Mitigation
Development/Demonstration Program. Sub-slab depressurization in the original
building was measured at 0.05 in. V.C. as far as 60 ft from the suction point.
Even in the four rooms of the addition at the north end of the wing,
depressurization was readily achieved from the one suction point in the original
building. The center of the farthest classroom (109) in the north addition was
110 ft from the suction point and still showed a negative pressure of 0.003 in.
V.C. at a vacuum suction of 6 in. V.C., in spite of the intervening sub-slab
wall. Consequently, it was anticipated that one suction point in the storage
room of Classroom 104 would be satisfactory for the entire north wing (about
15,000 sq ft).
Although the communication in the south wing was not as good as in the
north wing, it was adequate to expect mitigation in all the rooms (except the
basement rooms and possibly the rooms over the crawlspace) with a single suction
point located in the office of Classroom 121.
Two temporary mitigation systems were installed using 6-in. diameter
flexible PVC drain pipes exiting through the classroom windows and attached to
individual fans. The turbo fan had a rating of 410 cfm at 1 in. V.C. Vith the
temporary system operating in the north wing, all rooms measured below 4 pCi/L
during weekend charcoal canister measurements except for the classroom closest
to the exhaust line through the exterior of the building. This classroom
measured 5.3 pCi/L; it was suspected that the higher level was the result of
reentrainment. All the rooms in the south wing were below 4 pCi/L except those
over the crawlspace and basement and the basement rooms. (These tests were made
before the basement sub-slab system was installed in the TV and art rooms.)
Sub-slab communication was again measured in all the rooms with the temporary
systems in place and later with the permanent systems in operation. As expected,
the negative sub-slab pressure, achieved with the temporary and permanent
systems, was greater than had been achieved with the vacuum cleaner as shown by
comparing the negative sub-slab pressures in Figures 5 (permanent systems in
operation) and 4 (vacuum cleaner tests). The center of the classroom at the far
end of the north wing was 112 ft from the suction point and had a negative sub-
slab pressure of 0.007 in. V.C. with the permanent system in operation.
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TWO RIVERS MIDDLE SCHOOL
SUCTION rams
Kf
il^M ^SUCTION nilT -1.91
M-.l? ,
:TIM POINT 1.75
Figure 5. Post-Bltlgetlon fugitive tub-slab preuures. In U C.
In view of these findings, a decision was made to convert the temporary
systems into permanent systems. In both cases the pipes were run overhead to
the rear of the building and up the outside of the building with the fan located
under the overhang and the exhaust extended over the top of the roof. There are
no air intakes within 50 ft of these exhaust points. (Note that Tennessee State
codes require any exhaust to be a minimum of 10 ft from any fresh-air intake.)
The two basement rooms had much poorer communication than the first floor
slab-on-grade wings. It appeared that there was a subslab barrier between the
TV room and the art room; consequently, a 4-in. suction point was installed in
each of the two rooms manifolded to a common exhaust line run out the back of
the building and to the roof using the same configuration as in the other
systems. With this third system in operation, pressure field extension
measurements under the slab of the two basement rooms showed that adequate sub-
slab depressurization had been achieved as shown in Figure 5.
MITIGATION RESULTS
Installation of the sub-slab system in the two basement rooms was completed
during the last week of July. All rooms in the two classroom wings, including
the basement, were tested over the first weekend of August with charcoal
canisters under closed building conditions. Results of these tests are shown
in Figure 6. The average level of all measurements in August, with the three
mitigation systems operating, was 0.78 pCi/L, ranging from 0.5 to 1.3 pCi/L.
TWO RIVERS MIDDLE SCHOOL
Figure 6. Posc-Blclgeclon redan levels. Auguet 1989, pCl/L
-------
Pressure-actuated switches served the three permanent systems: a green
light indicated when negative sub-slab pressures were being maintained, and a
red light shoved when the system was inoperable. These warning lights are
checked daily by the custodial staff.
All the rooms were retested during cold weather in December. Results of
mid-winter tests will be reported at the Symposium.
GLENVIEV ELEMENTARY SCHOOL
Glenview is a 21-classroom elementary school. The original part of the
building was constructed in 1954 and included 13 classrooms, an
auditorium/cafeteria, a kitchen, and administrative offices. The first addition
was built in 1957 and consisted of four classrooms at the south end of the
original building. Both the original structure and the 1957 addition are slab-
on- grade; the addition is about 4 ft lower than the original building because
of the topography of the site. The second addition, built in 1964, consisted
of a four-classroom separate structure on the northwest side of the building.
This addition is a raised slab over a crawlspace. Hitigation studies during the
summer of 1989 were limited to the slab-on-grade portion of the building. The
crawlspace wing will be mitigated during the 1989-90 school session. Figure 7
is a floor plan showing dates of construction and classroom numbers.
GLENVIEW ELEMENTARY SCHOOL
Figure 7 Floor plan and ceiutrucclon dat»
All classrooms and the two administrative offices were initially tested
over the weekend of February 4, 1989. The average level of the 22 locations
tested was 29.7 pCi/L, ranging from 8.9 to 52.5 pCi/L. Individual classroom
levels are shown in Figure 8. The four rooms with highest radon levels (average
of 44.5 pCi/L, ranging from 40.1 to 52.5 pCi/L) were retested the weekend of
February 18. Retests of these four rooms gave an average level of 37.5 pCi/L,
ranging from 30.0 to 42.6 pCi/L. This was less of a decrease than found in the
Two Rivers School during the sane period, indicating that seasonal variation is
school-specific. All the rooms were retested in late June and again in July.
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NOfE: INITIAL TESTS MADE IN EARlf
FEBRUARY 1M9 FIGURES IN
PARENTHESES ARE REPEATS MADE
IN LATE FEBRUART.
GLENVIEW ELEMENTARY SCHOOL
28.4 12.21
Flgur* 8. Radon ocaiureaent. February 1989. pCl/L
Levels in both tests were approximately 25 percent lower than they were in
February. The room that measured highest in February decreased from 52.5 to 13.4
pCi/L in June and to A.A pCi/L in July. The next highest room, which was 44.8
pCi/L in February, increased to 93.4 pCi/L in June and to 108.9 pCi/L in July.
DETAILED DIAGNOSTIC TESTING
Inspection of Architectural Drawings and Building
Examination of the foundation and wall section plans disclosed that block
walls on all four sides of all rooms and closets extended to footings under the
slab with no indication of breaks in these sub-slab walls, reducing the potential
for sub-slab communication between rooms. The wall section drawings showed the
presence of 4 in. of aggregate of unspecified size under the slab.
Each room is heated by a fan coil unit mounted above the dropped ceiling.
The heated air from the fan coil is ducted to the ceiling registers near the
outside wall. Cold air return is through an unducted opening very close to the
air intake of the fan coil. Consequently, it is unlikely that the fan coil
causes much of a negative pressure in the plenum above the ceiling. The rooms
are cooled in the wanner months by individual window-mounted air-conditioners
in each room. The fresh air intakes for these have all been closed off. Five
wind-driven turbine roof ventilators exhaust air from the building. These are
located in the hallways in the plenum above the suspended ceiling. Host of the
classrooms in the original structure also have small ventilator fans mounted in
the hall wall and exhausting into the hall. It is not certain how these fans
are operated, if at all. There are two large kitchen exhaust fans, an exhaust
hood over the cooking unit, and an exhaust fan for the dishwasher.
The foundation drawings of the 1957 addition, containing four slab-on-grade
rooms, indicated that not all the walls go through to footings; there was a
possibility of good sub-slab communication between these four rooms. This was
confirmed by communication testing reported later in this paper.
-------
Measurement of Sub-slab Radon Levels
Sub-slab radon levels were measured through a 1/4-in. hole in the center
of each room using a Pylon AB-5 continuous monitor. Sub-slab radon levels were
between 300 and 1900 pCi/L as shown in Figure 9, much lower than those found at
the Two Rivers School. There appears to be no correlation between the levels
in the room and the sub-slab levels.
OLENVIEW ELEMENTARY SCHOOL
To!
800
j8ft f IT IO'J
| fl.LJLJ 400 |
'"
400 l?00
Figure 9. Sub-sUb radon Icvcli. pCl/L
Sub-slab Communication Testing
Sub-slab communication test measurements were carried out using the test
method described previously for the Two Rivers School. The initial suction hole
was placed Just inside Room 110, near the door. It was possible to pull a
negative pressure in Classrooms 109 and 111, and in the hall just outside of
Classroom 110. However, no communication could be detected with Classroom 120,
the room across the hall. Similar results were obtained at the other end of the
building. From these tests, it was concluded that sub-slab communication could
be extended about 30 ft in the original building and could pull through one sub-
slab wall, but not two. Even within the same room, pressure-field extension was
much poorer than found at Two Rivers. Consequently, it was felt that the
aggregate was not as open as it was at Two Rivers. This was confirmed when
aggregate from the two slabs was removed during the installation of mitigation
systems. At Two Rivers, the stone was very large, from 3/4 to 1 in. in
diameter. At Glenview, it was much finer, averaging about 1/4 in. in diameter
and contained some fines and dirt. Both were screened river gravel.
A suction point in Classroom 114 of the four-room addition indicated good
sub-slab depressurization in Classrooms 112 to 115 as expected from the
examination of the foundation drawing.
MITIGATION DESIGN AND INSTALLATION
In view of the relatively poor sub-slab communication, it was decided that
a minimum of one suction point in every other room would be necessary on both
sides of the hall. Three systems were laid out as shown in Figure 10. Two
multi-point systems had 6 in. trunk lines in the hall plenums with 4 in.
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GLENVIEW ELEMENTARY SCHOOL
fVCTIO* ft
Figur. 10. Mitigation lyttem layout
drops to suction points in the rooms. Trunk lines were run over the dropped
ceiling of the hall and 4-in. drops were placed as indicated in Figure 10. In
the trunk lines, T's were installed and capped off to facilitate the addition
of suction points to all of the remaining rooms if necessary. One mitigation
system had five suction points and the other had six, as shown in Figure 10.
Each used a turbo fan rated at 410 cfn at 1 in. W.C.
Communication testing in the 1957 four-room slab-on-grade addition at the
south end of the building indicated that one suction point would likely mitigate
all four rooms. A 4-in. suction point was put in the corner of ROOD 114 behind
the door and the pipe was run overhead through the outside wall at the rear of
the building. Suction was achieved using a turbo fan rated at 210 cfm at 1 in.
W.C.
Pressure activated visual alarms, as described for Two Rivers, were
installed for each mitigation system. These were put on the mitigation trunk
lines and are checked daily by the custodial force.
MITIGATION RESULTS
Mitigation installation was completed the first week of August, and all
systems were put in continuous operation. The following weekend all rooms were
tested with charcoal canisters under closed conditions with all air handlers off.
Average radon levels in all rooms were 1.7 pCi/L, ranging from 1.2 to 2.9 pCi/L.
Post-mitigation radon levels in each room are shown in Figure 11.
Glenview Elementary School was also retested in December, and the average
levels during cold weather will be reported at the Symposium.
As stated above, the 1964 four-classroom addition is built over a crawl-
space and will be mitigated in early 1990. Suction under polyethylene sheeting
in the crawlspace will be compared to pressurization and depressurization of
the crawlspace. This will be EPA's first detailed study of mitigating a school
building over a crawlspace. This addition is ideal for these studies since it
is small with adequate headroom and contains no asbestos.
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1.
121
1.1
GLENVIEW ELEMENTARY SCHOOL
121
MDITUUIM'
CAftHBIA
1.«
uri 112'
1.6 I 2.1
nT"~" n«i i«!»-i;Tf?T" toil iu| l
,.."|,.. 1 .., j*j.uj;?f TryTi
" ^^^^^^^^
Figur* 11. Po«t.nltig«tlon radon level*. August 1989. pCl/L
CONCLUSIONS
The following conclusions are drawn from these studies.
1. The two schools studied had widely different sub-slab communication
resulting from different sub-slab construction details and from
differences in aggregate. The poorer sub-slab communication in
Glenview was overcome by increasing the number of suction points.
The number used was based on the communication determined using vacuum
cleaner communication testing.
2. Two Rivers Middle School was built using a thickened slab under
interior load-bearing walls but contained no interior sub-slab block
walls on separate footings. This resulted in a continuous aggregate
layer under each classroom wing. As a result, one suction point was
capable of depressurizing the sub-slab area of an entire classroom
wing (IS rooms) of over 15,000 sq ft. Negative sub-slab pressure of
0.004 in. V.C. was measured as far as 120 ft from the suction point.
Average radon levels in the mitigated portion of the building were
reduced from 39.5 to 0.78 pCi/L.
3. All interior walls in Glenview Elementary School extended through the
slab to footings. This resulted in a compartmentalized sub-slab area
equivalent to the room configuration of the school. In addition, the
aggregate had a smaller average particle size and contained more fines
and dirt. As a result of these two factors, sub-slab communication
was found to be much poorer than at Two Rivers. Pressure field
extension was limited to a maximum of 30 ft. Mitigation was
accomplished with three suction systems containing 12 sub-slab suction
points or an average of about 1 suction point for every 2 rooms.
Average radon levels were reduced from 29.7 to 1.7 pCi/L.
REFERENCES
United States Environmental Protection Agency, Office of Radon Programs,
Radon Measurements in Schools - An Interim Report.* Washington. D.C.
20460, EPA-520/1-89-010, NTIS PB89-189-419AS, March 1989.
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CONVERSION FACTORS
1 pieoeurie/liter (pCi/L) - 37 becquerels/cubic meter
1 inch (in.) - 2.4 centimeters
1 inch (in.) water column (U.C.) - 249 pascals
1 foot (ft) - 300 centimeters
1 square foot (sq ft) - 929 square centimeters
1 cubic foot/minute (cfm) - 472 cubic centimeters/second
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IX-3
THE EFFECTS OF HVAC SYSTEM DESIGN AND OPERATION
ON RADON ENTRY INTO SCHOOL BUILDINGS
by: William A. Turner
Harriman Associates
Auburn, ME 04210
Kelly W. Leovic and Alfred B. Craig
U.S. EPA, AEERL
Research Triangle Park, NC 27711
ABSTRACT
Heating, ventilating, and air conditioning (HVAC) systems in schools vary
considerably and tend to have a greater impact on pressure differentials - - and
consequently radon levels -- than do heating and aiu-conditioning systems in
houses. If the HVAC system induces a negative pressure relative to the subslab
area, radon can be pulled into the building. If the HVAC system pressurizes the
building, it can prevent radon entry as long as the fan is running. However,
school HVAC systems are normally set back or turned off on evenings and weekends
and, even if the HVAC system pressurizes the school during operation, indoor
radon levels may build up during setback periods.
Many of the historical methods utilized to deliver ventilation air (outdoor
air) over the past 40 years are summarized. In addition, for each type of system
presented, the possible impact the ventilation system might be expected to have
(positive or negative) on the pressure of the building envelope (and subsequent
radon levels in the building) is discussed.
This paper has been reviewed in accordance with the U.S. Environmental
Protection Agency's peer and administrative review policies and approved for
presentation and publication.
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INTRODUCTION
THE EFFECTS OF VENTILATION ON BUILDING PRESSURE DIFFERENTIALS
The primary mode of radon entry into a school is normally from soil gas
that is drawn in by pressure differentials between the soil surrounding the
substructure and the building interior. If the building interior is at a lower
pressure than the soil surrounding the substructure, radon can be pulled in
through cracks and openings that are in contact with the soil. The amount of
radon in a given classroom will depend on the level of radon in the underlying
material, the ease with which the radon moves as a component of the soil gas
through the soil, the magnitude and direction of the pressure differentials, the
number and size of the radon entry routes, and dilution and mixing of the room
air.
Pressure differentials that contribute to radon entry can result from
operation of a heating, ventilating, and air conditioning (HVAC) system under
conditions that cause negative pressures (in the building relative to the subslab
area), indoor/outdoor temperature differences (including the "stack effect"),
use of appliances or other mechanical devices that depressurize the building,
and wind.
HVAC systems in schools and other large buildings vary considerably and
tend to have a greater impact on radon levels than do heating and
air-conditioning systems in houses^ ? The design, installation, and operation
of the ventilation equipment will cause the building envelope to be at a
positive, negative, or neutral pressure with respect to the outdoors, depending
on the system design, how it was initially installed and balanced, and how it
has been historically maintained and operated. Sometimes schools and similar
buildings were not designed with adequate ventilation, and in other instances,
ventilation systems are not operated properly due to factors such as increased
energy costs or uncomfortable conditions caused by a design or maintenance
problem. Such circumstances may enhance radon entry into the building.
If the HVAC system induces a negative pressure in the building relative to
the subslab area, radon can be pulled into the building through floor and wall
cracks or other openings in contact with the soil. (Even if the HVAC system
does not contribute to pressure differentials in the building, the natural stack
effect in a leaky building can cause the building to be under a negative pressure
so that radon-containing soil gas is pulled into the school.)
If the HVAC system pressurizes the building -- which is a common design in
many systems -- it can prevent radon entry as long as the fan is running.
However, school HVAC systems are normally set back or turned off during evenings
and weekends, and even if the HVAC system pressurizes the school during
operation, indoor radon levels may build up during setback periods. Once the
HVAC system is turned back on, it may take several hours for radon levels to be
reduced. Consequently, how the ventilation air (outdoor air) is supplied Co the
building (i.e. , whether the ventilation system is pressurizing or depressurizing
the building) can be expected to drastically affect the radon levels in a
building when the ventilation system is operating. Even when a building is
operated overall slightly positive with respect to the outdoors, localized
-------
negative pressures may exist. If openings to the earth are present where these
localized negative pressures exist, soil gases will be drawn in.
BUILDING VENTILATION HISTORY
Buildings designed for human occupancy (in particular, public buildings
such as schools) have historically been required to be designed to provide
ventilation air (outdoor air) to the occupants. This outdoor air has been
provided historically by non-powered design features such as operable windows
and gravity ventilators (which allow air movement created by wind and temperature
differences), more recently by powered ventilating equipment, or some combination
of both. In many areas of the country where air conditioning has not been
utilized, it has been popular to provide a base level of ventilation by
mechanical systems and to allow supplemental ventilation to occur through the
use of large operable windows as weather conditions allow.
Historically, the introduction of fresh outdoor air into buildings has been
relied upon to dilute the contaminants which are generated by the occupants
within the building and to provide free (economizer) cooling when weather
conditions permit. The American Society of Heating, Refrigerating and Air
Conditioning Engineers (ASHRAE) standards documents have provided, and continue
to provide, engineering professionals with guidelines to the suggested minimum
quantities of outdoor air which should be provided to the occupants . Building
Codes (laws) also govern the amounts of outdoor air to be provided; often these
codes refer to the ASHRAE guidelines. The most up-to-date ASHRAE ventilation
standard, ASHRAE 62-1989, prescribes that 15 cfm (1 cfm - 0.47 L/s) of outdoor
air be supplied to a classroom for acceptable indoor air quality ^ I
MULTIPLE ZONING OF VENTILATION AIR
In large buildings with multiple exhaust fans, supply air systems, and
system balancing dampers, some section of the building will frequently be
designed to be operated negative and other sections positive with respect to
adjoining areas in order to minimize the spread of an internally generated
irritant or odor. Thus, with regard to radon entry from the soil, the expected
and measured overall pressure balance of the total building envelope and the
expected and measured pressure relationship in individual areas of the building
must be considered.
Typical areas which might be expected to be designed and operated negative
with respect to adjoining areas include any area where identifiable sources of
pollutants may be generated; e.g., toilets, locker rooms, shops, print rooms,
art areas, laboratories, kitchens, gymnasiums, hallways, lounges, and janitor's
closets. Areas which might be expected to be designed and operated positive with
respect to adjoining areas include classrooms, computer rooms, and libraries
Thus, it is important to know the expected and measured pressure relationship
of individual zones within the envelope as well as the overall building envelope.
In addition to affecting the pressure relationships, the ventilation air
(outdoor air) will also be available to dilute radon gas once it has entered
the building. The dilution effect of outdoor air (ventilation air) is primarily
a control strategy for other pollutants (bioeffluents) generated primarily by
-------
the occupants; however, dilution alone is seldom adequate to reduce elevated
levels of radon without the proper pressure relationship.
The following section presents an overview of the various types of
ventilation systems which might be found in school buildings and the potential
(positive or negative) impact each type of system would be expected to have with
regard to radon entry (i.e., the expected overall impact on the pressure
relationship between the building envelope and the soil).
TYPES OF HVAC SYSTEMS
Many of the HVAC systems discussed below have the option of being designed
to supply a fixed or variable amount of outdoor air. In addition, the total
supply air moved by an air handling system (i.e., the combination of outdoor
and recirculated air) may be fixed (constant volume) or modulated (variable
volume). A variable air volume (VAV) system is typically designed to deliver
more total supply air as additional cooling is called for. With a VAV system,
the amount of outdoor air delivered may also be designed to be fixed or
modulated.
EXHAUST-ONLY SYSTEMS
One of the basic systems is an exhaust-only system; i.e., the system
consists of exhaust fans (often installed in hallways, bathrooms, and locker
areas). Building leakage or the opening of windows is typically the source of
outdoor makeup air. Even more basic systems include gravity ventilators (non-
powered exhaust shafts dependent upon the building stack effect, and operable
windows). Such systems that do not supply tempered makeup air typically lead
to stuffy conditions in the winter time, when occupants are hesitant to open
windows due to cold drafts.
Exhaust-only systems would be expected to cause the overall pressure within
the building to be negative with respect to the outdoors, thus increasing the
flow of soil gas into the building envelope. Depending on the degree of building
depressurization, and the location and size of the envelope leakage, the radon
levels in a building should increase during operation of an exhaust-only system.
RADIANT HEAT SYSTEMS
Radiant heat systems in schools tend to be of three types: hot water or
steam radiators, baseboard heaters, or warm water radiant heat within the slab.
Schools heated with radiant systems should have a ventilation system to achieve
the fresh air requirements recommended by ASHRAE; however, many of these schools
provide no ventilation other than natural infiltration. In other schools, there
are exhaust ventilators on the roof. These can be passive, allowing some
ventilation through the stack effect, or they can be powered. Powered roof
ventilators (PRVs) can cause significant building depressurization, particularly
if a fresh air supply is not provided. This can cause considerable radon entry
into the building while such exhaust systems are operating.
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UNIT VENTILATORS
The use of unit ventilators in schools has been and continues to be very
popular. They are available in a number of different arrangements: horizontal,
vertical, draw-through, and blow-through; and are made by a wide variety of
manufacturers.
In a typical unit ventilator system, by design, there is a connection to
the outdoors, providing makeup air for ventilation and free cooling. In a
typical unit ventilator configuration, the outdoor air mixes with return air
from the classroom in the plenum portion of the unit ventilator and is supplied
to the space typically through the top.
The advantages of this type of system are often economics and architectural
flexibility: generally no ductwork is required. Some of the disadvantages of
this system are the noise levels generated by the unit ventilators and the
numerous wall penetrations that at some points downgrade the architects'
elevation aesthetics. Also, a serious concern is the draftiness of these types
of units especially in northern climates. Drafts are of concern because, with
20 to 25 students in a typical modern classroom, coupled with well insulated
walls and ceilings and 1.5-2 W/ft2 (335-446 kW/m2) of lighting, the internal
heat gains often outweigh any envelope losses of the classroom. This can require
fresh air to be introduced for cooling during major portions of the school year.
Unit ventilator systems would be expected to cause the overall pressure
within the building to be positive with respect to the outdoors, thus reducing
the flow of soil gas into the building envelope when the unit is operating and
outdoor air is being drawn into the unit, whether or not the space served by
the unit ventilator is actually pressurized with respect to the soil will depend
on the degree of overall building pressurization or depressurization. If other
areas of the building have exhaust-only systems which exhaust more air than is
made up by the unit ventilators, then soil gases will still be drawn into the
building in areas where the net pressure is negative. The radon levels in a
building should decrease when a unit ventilator system is operating properly,
if adequate overall makeup air is provided.
TERMINAL AIR BLENDERS
Terminal air blenders have also been used. Initially, this type of system
was a good alternative to unit ventilators. There are a number of ways terminal
air blenders have been used. They were installed to help combat the energy
crunch, while still delivering outdoor air for cooling and ventilation. With
these systems in the classroom, even in northern climates, over 90 percent of
the time approximately 5 cfm (0.00236 ft3/s) of outdoor air per student would
typically be introduced. Because of the high internal heat gains in the
classroom, the intent was to thermostatically control the outdoor air quantity,
bringing in the appropriate amount of outdoor air required to satisfy the
internally generated heat load. These systems are generally connected to an air
duct system to distribute the ventilation air evenly, reducing drafts, and are
less noisy than unit ventilators. A consistent outdoor air supply is not
provided; however, typically, 90 percent of the time more than 5 cfm per student
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outdoor air is provided with a thermostatically controlled terminal air blender
ventilation system that is functioning properly.
Terminal air blender systems would be expected to cause the overall pressure
within the building to be positive with respect to the outdoors, thus reducing
the flow of soil gas into the building envelope when the unit is operating and
outdoor air is being drawn into the unit and distributed to the occupants.
whether or not the space served by the terminal air blender is actually
pressurized with respect to the soil will depend on the degree of overall
building pressurization or depressurization. That is, if other areas of the
building have exhaust-only systems which exhaust more air than is made up by the
terminal air blender, then soil gases will still be drawn into the building in
areas where the resultant pressure Ls negative. The radon levels in a building
should decrease when a terminal air blender system is operating properly, if
adequate overall makeup air is provided.
UNITARY HEAT PUMPS OR FAN-COIL UNITS
Heat pump units have been utilized to a limited degree in schools. They
appear similar to a fan-coil unit and may or may not have outdoor air ducted to
the unit. Fan-coil units consist of a fan and heating and/or cooling coils and
may or may not have outdoor air ducted to the unit. (They may just recirculate
air.)
Unitary heat pumps or fan-coil units would be expected to cause no overall
pressure change within the building even when outdoor air has been ducted to
the unit unless additional dampers and controls have been added to convert it
to function as a unit ventilator. If outdoor air has been provided and the unit
converted to a unit ventilator, then the unit would be expected to cause a
positive pressure inside the building with respect to the outdoors, thus reducing
the flow of soil gas into the building envelope when the unit is operating and
outdoor air is being drawn into the unit and distributed to the occupants.
Whether or not the space served by the unit is actually pressurized with respect
to the soil will depend on the degree of overall building pressurization or
depressurization. That is, if other areas of the building have exhaust-only
systems which exhaust more air than is made up by the heat pump or fan-coil
units, then soil gases will still be drawn into the building in areas where the
net pressure is negative. The radon levels in a building should decrease only
when a fan-coil or heat pump unit has been equipped with outdoor air, and
converted to a unit ventilator (if adequate overall makeup air is provided).
If the units are not supplied with outdoor air then the only impact should be
from the normal natural stack effect of a leaky building.
HEAT RECOVERY VENTILATORS (HRV)
In general, HRVs are either ducted systems with supply and return ducts
servicing different parts of the building or room, or wall-mounted units, similar
to wall-mounted air-conditioning units. In both types of units, fresh air is
brought in through a heat recovery device, then distributed, or passed through
a preheat coil and then out to the system's zones. The exhausts from these zones
pass through a separate section of the heat recovery device, and then discharge
far enough from the fresh air intake to minimize re-entrainment. One
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disadvantage of these types of systems is that condensation on the surface of
the heat exchanger may frost up and block the heat exchanger when outdoor
temperature drops below 20°F [°C=5/9(°F-'32) ] . To avoid that problem, bypass
sections and defrost controls are often available with units as standard
features. By temporarily bypassing the outdoor air and, thus, raising the
exchange surface temperature to above the dewpoint, frost on the exchanger
surface is avoided.
If balanced correctly, HRV systems would be expected to cause the overall
pressure within the building to be neutral or very slightly positive with respect
to the outdoors, thus reducing the flow of soil gas into the building envelope
when the unit is operating and outdoor air is being drawn into the unit and
distributed to the occupants. Whether or not the space served by the device is
actually pressurized with respect to the soil will depend on the degree of
overall building pressurization or depressurization. That is, if other areas
of the building have exhaust-only systems which exhaust more air than is made
up by the HRVs, then soil gases will be drawn into the building in areas where
the resultant pressure is negative. The radon levels in a building should
decrease when a HRV system is operating properly, if adequate overall makeup air
is provided. One exception is exhaust-only heat recovery devices which would
be expected to raise radon levels similar to exhaust-only ventilation systems
discussed earlier.
CENTRAL STATION AIR HANDLERS
There are many types of central station systems, many with features similar to
those discussed above. The common features of all central units include an air
handling unit supply fan and/or return fan and associated tempering coils,
dampers and controls, distribution ductwork, exhaust (or relief), mixing box,
and outdoor air intake. In the past, constant volume systems, which consisted
of central station air handling systems that generally had fixed minimum outdoor
air dampers, were used in schools. Typically the outdoor air would be controlled
by a two-position damper closed and opened to whatever percentages were
predetermined, to be mixed with return air, passed through the supply fan, and
introduced to the occupied space.
If designed correctly, central station air handler systems would be expected
to cause the overall pressure within the building to be slightly positive with
respect to the outdoors, thus reducing the flow of soil gas into the building
envelope when the unit is operating and outdoor air is being drawn into the unit
and distributed to the occupants. However, in a building with multiple zones,
some spaces served by the central system may be adjusted to be positive with
respect to the soil, and other areas may be negative. Many areas of the building
tray have exhaust fans which exhaust more air than is made up by the central
system by design. Thus, even if the overall pressure relationship for the
building is positive, soil gases will still be drawn into the building in areas
where the local resultant pressure is negative. The radon levels in a building
should decrease when a central station system is balanced to be slightly positive
and operated properly, if adequate overall makeup air is provided. The following
sections present a few of these central station air handler systems in detail.
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Conventional Constant Volume (CV)
Central stations, predominantly with constant volume air systems with fixed
minimum outdoor air entry and reheat coils, have been utilized for many years
in a limited number of schools. They are somewhat energy efficient and are
easily balanced.
Variable Air Volume (VAV)
With the energy crunch, several manufacturers of air handlers introduced
VAV control. The most immediate savings are fan energy and elimination of reheat
coils (if individual room VAV diffusers are used); however, outdoor air control
is difficult. In many VAV systems, there is no way to control outdoor air to
bring the room above bare minimum fresh-air quantities. Central station VAV
systems, with static pressure devices in the outdoor air stream and addition of
reheat coils, were an answer to outdoor air control. With static pressure
control of the outdoor air stream, it is possible to maintain an overall positive
pressure within the building under various operating conditions.
VAV with Economizer
As just noted, the VAV helps cut down on fan energy when not dealing with
peak cooling loads. If only minimum air movement is needed, the reduced air
flow will save energy dollars. Whenever outdoor air is critical (e.g., if all
areas must be kept under positive pressure to keep radon out), shutting off the
VAV distribution boxes in individual spaces is a concern. One disadvantage of
most VAV systems is that they have no sensing in the outdoor air stream that
would guarantee the correct amount of outdoor air during part-load operation.
One way to avoid this situation is to use an outdoor air flow sensor. With this
type of metering system, a drop in velocity in the outdoor air stream will
control the air dampers, bringing In more air from the outdoors. (This would
be typically called an outdoor air reset.)
VAV with Outdoor Air Control and Heat Recovery
This type of package combines efficient operation with temperature control.
Most importantly, the ability to deliver outdoor air capacity is greatly
increased, and the facility is not penalized in terms of energy costs, nearly
as much as without the heat recovery feature.
Central station heat exchangers are currently being considered in many
schools being designed for northern climates. In this type of design, a central
air handling system incorporates a heat exchanger. Some reheat may be required
in such system.
HVAC SYSTEMS AND RADON MITIGATION
A potential mitigation approach for schools is adjustment of the air-
handling system to maintain a positive pressure in the school relative to the
subslab area, discouraging the inflow of radon. This technique, referred to as
pressurization, has been shown to be an effective temporary means of reducing
radon levels in some schools, depending on the design of the HVAC system. If
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pressurization through the HVAC system is under consideration as a long-term
radon mitigation solution in a given school, proper operation and maintenance
of the system are critical. Responses to changes in environmental conditions
and any additional maintenance costs and energy penalties associated with the
changes in operation of the HVAC system must also be carefully considered1 i
Important factors that need to be considered when utilizing the HVAC system
for radon control include: (1) How much outdoor air was the system originally
designed to supply under what design conditions? (2) How leaky is the shell of
the building and can pressurization be utilized? and (3) Is the system currently
operating as designed, or has it been modified purposely or through neglect?
Once the limitations of the HVAC system and building shell are determined,
decisions can be made on the best or most reasonable course of action which can
be taken. Some approaches to radon control through the HVAC system that have
been used temporarily and permanently are generalized below.
EXHAUST-ONLY VENTILATION AND RADIATION HEAT SYSTEMS
For schools with either exhaust-only ventilation systems or radiant heat,
positive pressurization will probably require major modifications if the HVAC
system is considered as part of the mitigation strategy.
UNIT VENTILATORS AND EXHAUST-ONLY SYSTEMS
Radon mitigation strategies in schools with unit ventilators might include
(1) opening the fresh-air vents (if they have been closed) to improve ventilation
and running the unit ventilator fans continuously (or prior to occupancy) to
pressurize the room; (2) replacing an exhaust-only ventilation system with a
system that operates under a slight positive pressure; or (3) installation of
a subslab depressurization (SSD) system that could overpower all negative
pressures in the building. If the current HVAC system is providing adequate
ventilation to the building or if options (1) and (2) are not feasible, option
(3), installation of a SSD system, would be the most practical near-term strategy
if there is good subslab communication.
CENTRAL AIR HANDLING SYSTEMS
Although most central HVAC systems are commonly designed to operate at
positive or neutral pressures, pressure measurements in schools have indicated
that such systems can cause significant negative pressures in the building.
HVAC system modifications (such as reducing the amount of fresh-air intake),
lack of maintenance (such as dirty filters), unrepaired damage, or other factors
can result in substantial negative pressures in some rooms, thus increasing soil
gas entry. In addition, operation of localized exhaust fans can cause
significant negative pressures in areas of operation.
If positive pressures are not being achieved in a central single-fan system,
the system should be checked to ensure that the fresh-air intake meets design
specifications and that the intake has not been closed or restricted. Increasing
the fresh-air intake if it has been restricted, and operating the fan for a
sufficient time prior to occupancy and continuously while the school is occupied
will help to reduce radon levels that have built up during setback periods and
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will maintain low radon levels during occupied hours by preventing radon entry
by maintaining a positive pressure and by providing fresh (dilution) air.
In a central dual-fan system, the return-air fan can be set back or
restricted so that all of the rooms are under a positive pressure. The fresh-
air intake to the supply fan can also be increased up to the design limit of
the system, if it has been reduced. If radon control through HVAC system
operation is under consideration as a permanent mitigation strategy, proper
system operation and maintenance are critical.
Many schools with highly elevated radon levels have installed SSD systems
in order to control radon levels even when the HVAC system is not operating.
REFERENCES
1. Leovic, K. W. , Craig, A. B. , and Saum, D. W. The influences of HVAC design
and operation on radon mitigation of existing school buildings. In:
Proceedings of ASHRAE IAQ '89, San Diego, November 1989, NTIS PB89-218-762.
2. ASHRAE Std. 62-1989. "Ventilation for acceptable indoor air quality,"
American Society of Heating, Refrigerating, and Air-Conditioning Engineers,
Inc., Atlanta, Georgia, 1989.
3. Radon reduction techniques in schools - interim technical guidance. EPA-
520/1-89-020, U.S. Environmental Protection Agency, Office of Research and
Development and Office of Radiation Programs, Washington, D.C., October
1989.
ACKNOWLEDGEMENTS
The authors would like to thank the support staffs of AEERL and Harriman
Associates for their assistance in preparing this paper.
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IX-4
RADON MITIGATION EXPERIENCE IN DIFFICULT-TO-MITIGATE SCHOOLS
by:
Kelly W. Leovlc and A. B. Craig
Air and Energy Engineering Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
and
David W. Saura
Infiltec
Falls Church, VA 22041
ABSTRACT
Initial radon mitigation experience in schools has shown subslab
depressurization (SSD) to be generally effective in reducing elevated levels of
radon in schools that have a continuous layer of clean, coarse aggregate
underneath the slab. However, mitigation experience is limited in schools
without subslab aggregate and in schools with characteristics such as return-air
ductwork underneath the slab or unducted return-air plenums in the drop ceiling
that are open to the subslab area (via open tops of block walls). Mitigation
of schools with utility tunnels and of schools constructed over crawl spaces is
also limited.
Three Maryland schools exhibiting some of the above characteristics are
being researched to help understand the mechanisms that control radon entry and
mitigation in schools where standard SSD systems are not effective. This paper
discusses specific characteristics of potentially difficult-to-mitigate schools
and, where applicable, details examples from the three Maryland schools.
This paper has been reviewed in accordance with the U.S. Environmental
Protection Agency's peer and administrative review policies and approved for
presentation and publication.
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INTRODUCTION
Subslab depressurizaCion (SSD) has typically been a very effective radon
mitigation approach in schools and in houses that are underlain with a continuous
layer of clean, coarse aggregate. Recent experience has shown that in schools
with 4 in. (1 in. = 2.54 cm) of subslab aggregate -- approximately 0.75 to 1.5
in. in diameter with no fine material - - one SSD point can sometimes mitigate
an entire school wing of 10 classrooms or about 15,000 sq (1 ft = 0.09 sq m).
Costs of mitigation under these conditions of excellent subslab communication
may be as little as $3,500 for materials, in addition to approximately 120
person hours for diagnostics and 160 person hours for installation, depending
on the number of suction points needed (1,2).
However, mitigation experience has also identified certain types of schools
that are difficult -- and consequently expensive -- to mitigate with current
technology. Characteristics of potentially difficult-to-mitigate schools
include (but are not limited to): 1) schools with poor subslab communication,
2) schools with return-air ductwork underneath the slab, 3) schools with unducted
return-air plenums in the drop ceiling (that are open to the subslab area via
open tops of block walls), 4) schools with utility tunnels, and 5) schools
constructed over crawl spaces. Mitigation of such schools could be very
expensive, especially if the mitigation involves a complete retrofit of the
heating, ventilating, and air-conditioning (HVAC) system.
These characteristics that may cause a school to be difficult-to-mitigate
are discussed below, and examples from three difficult-to-mitigate schools,
currently being researched by the U.S. EPA in Maryland, are discussed. School
A is located in Prince Georges County, and Schools B and C are located in
Washington County. Note that since School A exhibits more than one of the
difficult-to-mitigate characteristics, it is discussed in two sections.
SCHOOLS WITH POOR SUBSLAB COMMUNICATION
Although poor subslab communication is a relative term, for the purposes
of this paper it is roughly defined as the inability to measure a negative
pressure (in the subslab relative to the building interior) of at least 0.001
in. WC (1 in. WC - 250 Pa) in a 0.25 in. test hole located approximately 10 ft
from a 1.5 in. suction point when maximum suction is applied to the suction point
with a variable speed Industrial vacuum cleaner. As a comparison, in the school
with excellent communication mentioned in the Introduction, subslab depressuri-
zation was measurable in a test hole 100 ft from the suction point.
Schools with poor subslab communication typically have slabs that are poured
directly onto tightly packed soil such as sand or clay, with little or no subslab
aggregate. The tightly packed fine material greatly restricts the subslab
airflow and limits the practicality of installing a SSD system. Even if a
school does show relatively good subslab communication within a given classroom,
communication between classrooms may be limited by below-grade walls and
footings. As a result, it may be necessary to install a suction point in every
or every other classroom in order to control radon entry. An example of such
a school is discussed in Reference 1.
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If poor communication reduces the subslab area depressurized by a suction
point, it may be possible to achieve effective mitigation by installing more
suction points. Typically these suction points are installed around the edge
of each room in order to depressurize the major cracks between the floor and the
walls. A related technique involves the installation of an enclosed channel
between the floor and the wall (channel drain) which can be depressurized. Both
of these approaches have the disadvantage that they represent a significant
investment in time and labor, and they be unsightly or take up excessive space.
The area depressurized by each SSD suction point may also be increased by
measures that increase the suction, reduce air leakage, and increase
communication. Sealing of floor cracks, excavation of subslab cavities under
suction points, and increased fan suction are often used to increase pressure
field extension. Previous school research has shown that pressure field
extension is often doubled by these measures (2). Research on houses in Florida
has shown the effectiveness of very high pressure fans (greater than 4 in. WC)
in cases of very poor communication due to sandy soils.
SCHOOL A
As shown in Figure 1, initial charcoal canister measurements made in this
school in March 1988 averaged 4.2 pCi/L (1 pCi/L = 37 Bq/m3), with the highest
room measuring 12.3 pCi/L. A second set of charcoal measurements made in
November 1989 averaged 5.0 pCi/L, with two rooms measuring 10.0 pCi/L.
The school is slab-on-grade construction. Inspection showed that the
material under the slab is a mixture of sand and clay. A utility tunnel runs
parallel to the corridor in part of the building, as indicated on the floor plan
in Figure 1. The original HVAC system consists of a perimeter hot water system,
with air movement by convection. There are also overhead exhaust fans in the
classrooms; however, school personnel stated that these exhausts are rarely used.
As a result of other indoor air quality problems, overhead air-conditioning
units in the classrooms -- that were designed with the capability to provide
outdoor air -- have been modified to provide heating so that they can be used
year round. Measurements are in progress to determine the ability of these units
to pressurize the building to prevent radon entry; however, operation of each
unit is controlled in the classroom by the teacher and, consequently, continuous
operation cannot currently be ensured.
Room 13, the classroom with the highest initial radon level (12.3 pCi/L in
Figure 1) was selected to evaluate the applicability of subslab depressurization
in this school with poor subslab communication. (Previous efforts by school
personnel to seal the floor/wall cracks did not reduce radon levels
sufficiently.) As seen in Figure 2, three 3 in. diameter subslab
depressurization points were installed in the corners of Room 13 and manifolded
to a 4 in. overhead line, exiting through the window at point A. To improve
communication, pits approximately 2 ft in diameter and 1 ft in depth were
excavated under the slab at the three suction points. A fan rated at 270 cfm
(1 cfm = 0.47 L/s) at 0 in. WC was installed.
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In schools vith good subslab communication, 4 to 6 in. diameter vertical
drops are typically installed because of the high air flow; however, because
of the low flow rates anticipated in the mixture of subslab sand and clay, 3 in.
diameter vertical drops were used in this school.
Communication measurements made in Room 13 with suction being applied to
all three points are summarized in Table 1. With all three suction points
operating, a slight depressurizatLon was measurable in the far corner of the
room.
TABLE 1. Subslab Communication Measurements, December 1989
(School A - Room 13)
Suction Suction Distance from Pressure in
Point in Pipe, in. WC Suction Point, in. Test Hole, in.
A - 1.48 1 - 0.860
A - 1.48 60 - 0.171
B - 1.47 1 - 0.045
B - 1.47 60 - 0.011
B - 1.47 120 (toward center) - 0.086
C - 1.45 1 - 1.300
C - 1.45 60 - 0.331
C - 1.45 180 (near door) - 0.001
Radon levels measured in this school with the SSD system in operation are
shown in Figure 2. It should be noted that a utility tunnel depressurization
system -- that will be discussed later -- was also in operation in another part
of the building during these measurements. The radon levels in Room 13 and the
adjacent room were reduced from premitigation radon levels of 7.1 and 7.4 pCi/L
to 1.3 and 1.6 pCi/L, respectively. It is obvious from Figure 2 that radon
levels are lower throughout the building -- not only in the areas where
mitigation was being applied. However, radon reductions in parts of the building
where no mitigation was being applied were about 45 percent (attributed to
natural variations resulting from weather, for example), and reductions in these
two classrooms were about 80 percent, indicating the positive effects of the SSD
system.
FUTURE RESEARCH PLANS
Further work in School A will assess the possibility of installing SSD
systems in the other rooms with elevated radon levels (other than the rooms being
treated by the tunnel depressurization system). In spite of the poor subslab
communication, it is reassuring to learn that the radon levels could be reduced
in this classroom by installing enough suction points. However, questions that
still remain include: 1) Would this approach work in a similar school with much
higher radon levels? 2) What are the mechanisms controlling radon reduction
in the adjacent classroom? and 3) If every room in a school with poor subslab
communication has elevated levels of radon, would one suction point (or more)
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in each classroom be a practical mitigation approach or should alternatives be
sought?
SCHOOLS WITH RETURN-AIR DUCTWORK UNDERNEATH THE SLAB
Schools with return-air ductwork under the slab are a concern if elevated
levels of radon are present in the surrounding soil. Since the ducts are under
a negative pressure when the return-air fan is in operation, radon can be pulled
into the ducts through unsealed openings in the ductwork. Any radon that enters
the ducts from the soil under the slab can then be distributed throughout the
school by the HVAC system. In fact, the American Society of Heating,
Refrigerating and Air-Conditioning Engineers (ASHRAE) has recommended that,
where soils contain high concentrations of radon, ventilation practices that
place crawl spaces, basements, or underground ductwork below atmospheric pressure
be avoided since such practices tend to increase indoor radon concentration (3).
Unsealed supply-air ductwork located underneath the slab may also be of concern
since radon can enter the ductwork if it is subjected to negative pressures when
the HVAC system is off and the ductwork is below the neutral pressure plane.
SCHOOL B
In April 1988, initial charcoal canister measurements in this school showed
that radon levels in 28 of 39 rooms exceeded 4 pCi/L. Follow-up canister
measurements made In 24 of these rooms in December 1988 showed all 24 rooms above
4 pCi/L. All of these measurements were made with the HVAC system off and the
building unoccupied.
The original school was constructed in 1954, and four four-room additions
were added in 1964. The entire school is slab-on-grade construction, and the
foundation plans and specifications call for 4 in. of aggregate under the slab.
For the purposes of this paper, only the four additions (which are referred to
as pods) are discussed. Each pod has four classrooms and a central media area.
There is a two-fan HVAC system with the return-air ducts located under the
slab in each pod. Room air enters the return-air ductwork from registers located
on the exterior wall of each classroom and is pulled through the subslab ductwork
to a central cold-air return located in the media area. Supply air (including
recirculated air from the subslab ducts) is distributed to each classroom through
overhead ducts mounted near the interior wall. Radon grab samples collected in
the supply air when the system was operating were about 20 pCi/L, indicating that
the return-air ducts under the slab were drawing in soil gas and recirculating
it throughout the school. Subslab differential pressure measurements (relative
to the building interior) made in one of the pods showed a pressure field that
ranged from - 0.001 to - 0.1 in. WC with the HVAC system in operation. The
greatest negative pressures were near the central cold-air return in the center
of the pod. These measurements suggested that it may be possible to install a
SSD system to exert a greater negative pressure under the slab than the return
air fan.
To evaluate the ability of a SSD system to overcome the negative pressures
generated by the return-air system in one of the pods, an exhaust fan rated at
500 cfm (at 0 in. WC) was mounted on the roof, with a 6 in. manifold pipe
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connected to two 4 in. diameter vertical drops. These two suction points were
placed near the return-air exhaust stack in order to maximize the suction in the
area where the negative pressures of the return-air ducts were the strongest.
The pod with the highest initial screening measurements was selected for
installation of the SSD system; however, it should be noted that the most recent
measurements in this school show radon levels in this pod to be slightly lower
than in the other pods -- even when the mitigation system is not in operation.
Post-mitigation diagnostics indicated that this SSD system could not
overcome the negative pressures generated by the return-air ducts and, as a
result, radon-containing soil gas was still being pulled into the ductwork with
both the HVAC and SSD systems in operation. Pressure measurements made through
a test hole drilled in one of the return-air ducts showed a negative pressure
of 0.80 in. WC in the duct; whereas, the initial differential pressure
measurements made in the subslab aggregate measured only the negative pressure
caused by the duct leakage, rather than the actual negative pressure in the duct.
Based on the above results, the school recently installed a new overhead
return-air system in all four pods. The new return-air registers are located
overhead near the interior walls of the classrooms, and the supply-air ductwork
has been extended to supply air closer to the exterior walls. However, the
abandoned return-air registers have not yet been sealed off and, consequently,
there are still openings from the classrooms to the subslab.
Continuous radon monitors (CRMs) were placed in Classrooms 111 and 115 for
a 10-day period as shown in Figure 3. Rooms 111 and 115 are in different pods
but are at the same orientation within the pods. The two SSD points are located
in Room Ill's pod, with one point adjacent to Room 111. As seen in Figure 3,
radon levels in Room 115 are consistently higher than those in Room 111, even
with the SSD system off. These results are consistent with those from electret
ion chamber (E1C) measurements in the other three classrooms in each pod. As
shown in Figure 3, the SSD system was on in Room Ill's pod from 0 to 120 hours
and off from 120 to 240 hours. The averages indicate that the SSD system clearly
has an effect on the radon levels, although the effect is much less dramatic than
one might expect since the return-air registers have not yet been sealed.
The next plan for this school is to seal the return-air registers in all
16 classrooms. Radon measurements will be made with the registers sealed and
the new HVAC system in operation. If necessary, SSD systems will then be
installed in the other three pods.
An effort will also be made to tap into the sealed-off return-air system
with the SSD system in Room Ill's pod to compare its effectiveness in reducing
radon levels with that of the current system.
FUTURE RESEARCH PLANS
School B showed that it was not reasonably possible to overcome the negative
pressures of leaky return-air ductwork with a typical SSD system, even if the
slab is constructed on aggregate. These results will be confirmed with research
in additional schools; however, under such circumstances, the current
recommendation is to abandon (and seal off) the subslab ductwork and replace the
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system with an overhead return-air system. Although this may be an expensive
retrofit (about $40,000 for the 16 classrooms in School B), the guidance is
directly applicable in the design of new buildings or in the remodeling of
existing ones.
SCHOOLS WITH UNDUCTED RETURN-AIR PLENUMS IN THE DROP CEILING
(THAT ARE OPEN TO THE SUBSLAB AREA VIA OPEN TOPS OF BLOCK WALLS)
Schools with unducted return-air plenums in the drop ceiling may be of
concern if elevated levels of radon are present in the surrounding soil and there
are openings between the soil and the plenums through the unsealed tops of block
walls. The potential problem for radon entry exists if the load-bearing hollow
block walls penetrate the slab as shown in Figure 4. The radon-containing soil
gas can enter the block walls and be pulled into the unducted plenum which is
under negative pressure when the fan is in operation. The soil gas that enters
from the block walls could then be mixed with the recirculated room air and
redistributed to the building, presenting a potentially difficult mitigation
problem.
This specific issue is not currently being addressed in the field but will
be included in future studies.
SCHOOLS WITH UTILITY TUNNELS
In some slab-on-grade schools, utility lines are located in a subslab
utility tunnel that typically runs parallel to the corridor with sections
sometimes branching off to individual rooms. Sizes of utility tunnels may vary
from about 5 ft wide and 5 ft deep (to allow maintenance workers to enter them)
to 1 ft wide and 0.5 ft deep. Utility tunnels may or may not have poured
concrete floors. Even tunnels with poured concrete floors may have many openings
to the soil beneath the slab-on-grade, facilitating radon entry. Risers to unit
ventilators or fan-coil units frequently pass through unsealed penetrations in
the floor so that soil gas in the tunnel has an easy entry route to the
classrooms.
Although utility tunnels can be a major radon entry route if the surrounding
soil contains elevated levels of radon, depressurization of the utility tunnel
has been considered as a potential mitigation approach. If utility tunnel
depressurization is attempted, any asbestos in the tunnel should be removed or
encapsulated according to the Asbestos Hazard Emergency Response Act (AHERA)
before attempting any radon reduction activities (4).
SCHOOL A
A large utility tunnel (about 5 ft wide and 5 ft deep) runs under or near
eight of the classrooms in this school as shown in Figures 1 and 2. Radon levels
in these eight classrooms averaged 4.4 and 4.3 pCi/L without depressurization
being applied to the tunnel. (It should be noted that --as with the other
classroom in school A discussed earlier -- sealing of the floor/wall cracks was
attempted in two of these classrooms with negligible results.) Radon levels in
the utility tunnel typically range from about 10 to 30 pCi/L.
-------
An exhaust fan rated at 270 cfm (at 0 in. WC) was Installed in the tunnel
at the end of the corridor. A 4 in. diameter pipe penetrates the tunnel from
the outdoors, and the fan is mounted on a vertical riser at roof level.
Differential pressure measurements were made with the depressurization fan in
operation at the two tunnel access doors; one is located about 3 ft from the
suction pipe penetration, and the other is located near the tunnel T by the two
farthest classrooms. These measurements showed depressurization of the tunnel
of about 0.03 in. WC at both points in the tunnel. A subslab pressure
measurement was also made in a classroom test hole about 10 ft from the tunnel,
and depressurization from the tunnel was negligible. (Remember from above that
this school is constructed on a mixture of sand and clay and, consequently, has
poor subslab communication.)
Charcoal canister measurements shown in Figure 2 indicate a reduction in
radon levels in the eight classroom area with the tunnel depressurization fan
in operation. The classroom levels averaged 1.8 pCi/L with the fan in operation
compared to 4.4 and 4.3 pCi/L (Figure 1), a reduction of about 60 percent. (It
should again be noted that the unmitigated areas averaged about 45 percent
reduction in these measurements.)
Figure 5 shows continuous radon levels for 22 days in one of the classrooms
with the tunnel depressurization fan cycled on and off. To include measurements
during both occupied and unoccupied periods, the fan was on from Wednesday noon
to Saturday noon and off from Saturday noon to Wednesday noon. Radon levels in
the classroom averaged 1.2 pCi/L for the 8 days that the fan on and 5.1 pCi/L
for the 14 days that the fan was off. The overall average for the 22 days was
3.6 pCi/L.
Recent continuous measurements collected in the tunnel showed that radon
levels are similar when the fan is on and when the fan is off. This implies
that the radon levels in the classrooms are being reduced because of the reversed
pressure differentials between the tunnel and the rooms, rather than by dilution
of the radon in the utility tunnel. This will be investigated further by
collecting simultaneous radon measurements in the classrooms and tunnel.
FUTURE RESEARCH PLANS
Research on this school will continue at least through the winter months.
In addition, utility depressurization will also be studied in other schools to
determine its overall applicability.
In slab-on-grade schools with utility tunnels it may also be possible to
reduce radon levels with a SSD system if subslab communication is good. However,
two potential problems could be 1) too much SSD system air may be lost to the
tunnel, and 2) the depressurization may not be able to reach the radon entry
routes in the tunnel. This will be addressed in future research.
SCHOOLS CONSTRUCTED OVER CRAWL SPACES
Mitigation techniques applied in crawl space houses include: submembrane
depressurization (SMD) in the crawl space, depressurization or pressurization
of the crawl space, and natural ventilation of the crawl space. To date,
-------
research of crawl space houses has shown SHD to be the most successful technique
of the four in reducing radon levels in the living area. However, since schools
constructed over crawl spaces are typically much larger than houses constructed
over crawl spaces, the practicality of installing a SMD system in a school crawl
space may be very limited. In addition to the larger size of the crawl space,
school crawl spaces often have structural support walls and piers throughout,
which could quickly increase the cost of installing a SMD system. If the crawl
space contains asbestos, any techniques that may increase air movement or require
entering the crawl space should be avoided.
SCHOOL C
Crawl space depressurization is currently being tested in a school in
Washington County, Maryland. Half of this single-story school is constructed
over a crawl space with two slab-on-grade additions. The crawl space part of
the building was built in 1936 and is wooden floor joist construction with a dirt
floor. The HVAC system is a single-fan system with overhead ductwork. The crawl
space is approximately 14,000 sq ft and has numerous support piers that would
make installation of a SMD system very difficult.
A 500 cfm (at 0 in. WC) fan was installed to depressurize the crawl space.
Figure 6 shows continuous radon levels in the school office and in the crawl
space for a 16-day period cycling the crawl space depressurization fan on and
off for 4-day periods. Operation of the depressurization fan tends to smooth
out the peaks in the indoor radon levels, although spikes above 4 pCi/L do occur.
Spikes exceeding 10 pCi/L occur during periods when the fan is not operating.
School vacation began on day 357 and continued until day 369. Radon levels
in the office drop considerably on day 369 when school was back in session even
though the crawl space depressurization fan was off and radon levels in the crawl
space were still quite high. The lower radon levels on days 369 to 371 seem
to indicate that normal HVAC operation creates a positive pressure, but that
during setback periods (nights, weekends, and holidays), the building is under
negative pressure.
FUTURE RESEARCH PLANS
Research of mitigation approaches in a relatively small crawl space (4,800
sq ft) will be initiated in early 1990. The school is located in Nashville,
Tennessee, and is a four-classroom addition to one of the slab-on-grade schools
discussed in Reference 1. SMD, crawl space depressurization, crawl space
pressurization, and natural ventilation of the crawl space will be tested and
compared for effectiveness. Available data will be presented at the Symposium.
CONCLUSIONS
Based on the authors' experience in these schools, the following conclusions can
be made:
1. In schools with poor subslab communication, it may be possible to
adequately depressurize the subslab area by adding enough suction
points (three in one classroom in this case), excavating a pit under
-------
the suction point, and using a high suction fan. However, the
applicability and practicality of this approach in schools with highly
elevated radon levels throughout the entire building, must still be
addressed.
2. Since subslab return-air ductwork is under a negative pressure when
the HVAC system is in operation, radon can be pulled into the ductwork
through unsealed openings, and then distributed in the building with
the recirculated supply air. In some cases, it may be necessary to
relocate the subslab ductwork overhead since a SSD system may not be
able to overcome the negative pressures generated in the subslab
ductwork. If this is done, the return-air registers should be sealed
since they are a radon entry route. Future research will determine
the possibility of depressurizing the sealed subslab duct system for
radon reduction.
3. Schools with unducted return-air plenums in the drop ceiling that are
open to the subslab via uncapped block walls should be researched to
determine their impact on radon entry.
4. In slab-on-grade schools with utility tunnels, it is sometimes possible
to reduce radon levels in the classrooms by depressurizing the utility
tunnels. This approach needs to be studied in additional schools.
5. Thus far, crawl space depressurization has shown some potential for
reducing radon levels in schools constructed over crawl spaces. Future
research will look at the applicability of SMD, crawl space
depressurization, crawl space pressurization, and natural ventilation
of the crawl space in more detail to determine their performances in
large crawl spaces typical of schools.
REFERENCES
1. Craig, A.B., Leovic, K.W., Harris, D.B. and R.E. Pyle, "Radon Diagnostics
and Mitigation in Two Public Schools in Nashville, Tennessee," presented
at the 1990 Radon Symposium on Radon and Radon Reduction Technology in
Atlanta, GA, February 19-23, 1990.
2. Saum, D.W., Craig, A.B., and Leovic, K. W. "Radon Reduction Systems in
Schools," in Proceedings: The 1988 Symposium on Radon and Radon Reduction
Technology. Volume 1. Symposium Oral Papers. EPA-600/9-89-006a, NTIS
PB89-167480, March 1989.
3. ASHRAE Draft Standard 62-1981R. Ventilation for Acceptable Indoor Air
Quality. ASHRAE, Atlanta, GA, 1986.
4. Asbestos Hazard Emergency Response Act (AHERA), Public Law 99-519, October
1986.
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Prealtlgatlon ridnn lenels (ptl/L)
Set 1 March 11-13. 1988 (upper)
Set 2- Nmeafter 17-20. 1989 (Iner)
Figure 1. Premitigation radon levels in School A.
Radon leveli IpCI/L) «'th 3-polnt SSD
syitn and tunnel depressuriiation lysten
in operation
Oecenber 1-4. 1989
vpn^ui up, _,-,.,
.-tJ"... I ,., l.rn
-TTTT"! I J
Figure 2. Radon levels in School A with SSD and tunnel depressurization
systems in operation.
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^-»
o
AVERAGE RADON
ROOM 115 ROOM 111
40
200
240
HOUR
Figure 3. Continuous radon measurements in Rooms 111 and 115;SSD fan
in Room 111 on and off (12/1-11/89).
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POSSIBLE
FRESH-AIR INTAKE
ROOF
I
AIR
HANDLER
AIR SUPPLY DUCT
RETURN AIR
RETURN
AIR
HALL
UNDUCTED PLENUM
T -
DROP
CEILING
CLASS ROOM
SUPPLY
AIR
Figure 4. Example of school with unducted return-air plenum in drop ceiling.
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30
20
C_5
O.
o
O
10
0
Total period = 22 days, radon * 3.6 pCi/L
Fan on 8 days, radon - 1.2 pCi/L
Fan off 14 days, radon * 5.1 pCi/L
HOURS
Depressurization fan.on (Wednesday noon to Saturday noon)
Depressorization fan off (Saturday noon to Wednesday noon)
Figure 5. Continuous radon measurements in School A with utility tunnel
depressurization fan on and off (9/27 - 10/22/89).
-------
Ion on ",<. Fort off
--- X fon ofj > - On
0
120
HOURS
Figure 6. Crawl space depressurization in School C with fan on and off
(12/22/88 - 1/7/89).
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Paper IX - 5
AIR PRESSURE DISTRIBUTION AND RADON ENTRY PROCESSES
IN EAST TENNESSEE SCHOOLS
L. D. Sinclair', C. S. Dudney", D. L. Wilson, and R. J. Saultz
Health and Safety Research Division
Oak Ridge National Laboratory
Oak Ridge, TN 37831-6113
ABSTRACT
Many building characteristics have been found to influence radon entry, including building size and
configuration, substructure, location of utility supply lines, and design and operation of the heating,
ventilation, and air conditioning (HVAC) system. One of the most significant factors is room
depressurization resulting from the HVAC system exhausting more than it supplies. This paper represents
a preliminary assessment of HVAC characteristics and how they may relate to radon entry. During the
summer of 1989, a limited survey was made of air pressure and radon levels in four schools in eastern
Tennessee. Short-term samples of radon and pressure were made in all rooms in contact with the soil using
alpha scintillation cells and an electronic micromanometer, respectively. The pressure differences and radon
concentration changes induced by operation of the building ventilation system varied among sites within
individual schools.
" Permanent address: Lexington High School, Lexington, SC 29072.
" Author to whom correspondence should be addressed.
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INTRODUCTION
Radon-222 is a radioactive, colorless, odorless, chemically inert gas with a half-life of 3.8 days. It
is the parent of several short-lived, alpha-emitting radionuclides that occur naturally in the environment and
have caused lung cancer in some exposed human populations (1). Recent attention has focused on radon
in schools because of legislation passed by the U.S. Congress (2).
Radon studies have been conducted in schools in 13 states. Elevated radon levels have been found
in many of these schools. Although there are no studies to determine whether children are more sensitive
to radon than adults, some studies of other radiation exposures indicate that children may be more
sensitive (3). Consequently, children exposed to radon could at greater risk than adults from exposure to
radon. Indoor radon in large structures such as schools is a topic of concern to the U.S. Environmental
Protection Agency (EPA), the U.S. Department of Energy, and various public health officials in all levels
of government. It now appears that the benefits of making schools more energy efficient by sealing up
cracks and cutting back on HVAC operation must be evaluated against the substantial risks associated with
decreased indoor air quality. In addition, Saum et al. (3) have shown that air pressure varies significantly
between rooms in a single elementary school in Maryland. We suspect that at the time of initial installation,
the HVAC system is balanced for each room (i.e., the system is adjusted so that supply exceeds exhaust by
a small amount), and there is positive pressure in every room. As the system ages, some rooms come under
negative pressure. In rooms with negative pressure, some of the air that is drawn into the room comes from
cracks in or near the floor. The source of most radon is uranium in the soil(4). So if a schoolroom is both
under negative pressure and connected to a portion of the soil with elevated radon concentrations, the room
may have elevated radon levels. Therefore, the purpose of this study was to monitor HVAC operation,
pressure, and radon concentrations at selected sites in four school buildings to gain greater insight into the
variations and relations among these variables in large structures such as school buildings.
EXPERIMENTAL MATERIALS AND METHODS
The primary criteria used to select the four schools were:
1. Some rooms with radon levels above 4 pCi/L, were expected based on earlier surveys (6,7),
2. Schools were under normal or near normal operation due to summertime use of the
building,
3. Schools were similar in size, construction, and design, and
4. The full range of public school grade levels were represented.
School A is a high school, constructed in 1969. It is a block and brick veneer structure built on
a concrete slab with underlying aggregate. It consists of a two-story classroom wing containing 40
compartmentalized rooms, a one-story gymnasium wing with perimeter classrooms, and a one-story
auditorium wing which also houses the band and chorus facilities. The three wings are connected to a
center commons area which contains the cafeteria, library, and administrative offices. The HVAC system
consists of individual unit exchangers in the classroom wing. These exchangers allow air to pass through
heating and cooling coils. The heat is furnished by hot water from a central boiler and cooling is furnished
by chilled water from a central chilled water unit. Air returns are located in the exchanger. In the
auditorium wing, air is split into two streams after the air supply fan: one stream is heated by hot water
coils, and the other is chilled by cold water coils. The two streams are carried in parallel ducts to each
room. A mixing box in each room controls the percentage of heated and cooled air entering the room
depending on the room thermostat. Returns were located in the wall or in the slab. There are three
-------
ventilation systems. One (roof mounted) for the first and second story classroom wing, one for the office
and cafeteria area, and a third for the auditorium areas. There exists a sub-slab ventilation system (return)
unique to the band practice room area located between the band and chorus rooms. Other returns in this
area (assembly) were located in the wall.
School C is an elementary school, constructed in 1968. It is a two-story block and brick veneer
structure of modified open space design. The lower level includes three clusters (pods), each consisting of
five classrooms and a teacher planning center. A maintenance corridor is located along the back side. Since
this school was built into the side of a hill, the lower level classrooms are walk-out basements and are in
contact with the soil on three sides. The upper level consists of three pods identical to and directly above
the lower level. There is also a one-story gym, cafeteria, media center, and office area which fronts the
school. The HVAC system is of the dual air supply design with returns located in special light fixtures that
have a chamber around them for exhausting air to the ceiling plenum. It is turned on locally at 6:30 a.m.
and off at 2:30 p.m. The system is shut down at 2:30 on Friday for the weekend.
School D is a junior high school, constructed in 1954. Also of block and brick veneer construction,
it consists of a separate two-story classroom building with 35 self-contained classrooms, library, and offices.
Another separate building contains the gym and still another two-story building contains the cafeteria,
auditorium, and basement level shop classrooms and storage. The classroom building is built into the side
of a hill and has one wall in total contact with the soil. The basement level has no air conditioning. A
dual air supply system provides both heated and cooled air (added in 1988) in both the two-story building
and in the auditorium-cafeteria level of the other building. The gym area has forced air heat exchangers
but no air conditioning. The HVAC system is turned on at 6:30 a.m. and off at 3:30 p.m. and is shut down
for the weekend.
Constructed in 1976, School E is a high school and is constructed of a slab on grade with block
walls and a veneer of bricks. The main building consists of two stories of classrooms with a hexagonal
commons area, cafeteria, and administrative offices at the center. This building was built into the side of
a hill and portions of it have all areas in contact with the soil. The lower west wing was situated
considerably below grade. In fact, the hallway leading to it is inclined. A separate building contains the
gymnasium-auditorium complex. It has a basement (girls and boys locker and shower rooms) and a first
and second floor (balcony level). The HVAC system consists of roof mounted ventilators and individual
room air exchangers that differ from those at school A in that they are on the outside wall and vented to
the outside. They bring in fresh air as well as circulate room air. The operation of the HVAC is under
computer control from the district office and operates from 6:30 a.m. until 3:30 p.m. on weekdays during
the summer with some provision for manual override at the school. The vocational complex was not studied
because of time limitations. However, it has construction and location characteristics that would make it
of interest.
From June 22 until August 14, 1989, four schools were surveyed for radon using several
measurement methods. Results reported here were all obtained with a Pylon AB-5 monitor operating with
room air flowing through a 163 cm3 Lucas cell at about 1 L min'1. After steady state conditions were
achieved within the Lucas cell, at least ten consecutive 1-minute readings were recorded and averaged. The
efficiency (CPM per pCi/L) of each Lucas cell was determined in a chamber at ORNL using instruments
that had been compared with instruments at EPA's Eastern Environmental Radiation Facility or instruments
at DOE's Environmental Measurements Laboratory. During any day in which data were collected, the
operation of the instrument was checked with a ^Ra source and the background count rate was determined
by sampling outdoor air for at least ten minutes. Background count rates were subtracted from observed
count rates before calculating radon concentrations. The sampling was performed according to established
EPA guidelines, in that, sampling was done in the center of the room, away from windows, doors, corners,
and HVAC ducts.
-------
Pressure readings (referenced to the air mass in a central hallway) were recorded for each location
with a digital micromanometer. The micromanometer was turned on and, after a warm-up period, the zero
point was established by connecting the two pressure connections together with tubing. For differential
pressure measurements, the micromanometer was connected to a length of tubing inside the room to be
tested, and to an identical length of tubing that was placed under the closed door and opened into the
adjacent hallway. The instrument was electronically zeroed immediately before each measurement. Data
were recorded after allowing a few seconds for the instrument readings to stabilize. The position of the
HVAC return and supply in the room was noted and whether or not the HVAC system was on or off in
that particular location.
RESULTS AND DISCUSSION
Figure 1 and Table 1 summarize the results from the survey. The highest ^Rn concentrations
were seen in School A in the auditorium wing during periods of HVAC operation. Moderately elevated
concentrations were also seen in Schools A, C, and E when the HVAC was not operating. Lower
concentrations were observed in School D. In Schools A and D, the cases of elevated ^Rn were generally
limited to those instances when the pressure was low (see Figure 1), similar to what has been reported in
a school in Maryland (4). A similar trend may be present in the data from School E, but because the ^Rn
concentrations are lower, the signal to noise ratio is lower and no conclusive statements are possible. There
is no apparent correlation between radon and pressure data from School C, where the ^Rn concentrations
are lowest on average among the four schools.
In School A, we observed considerable variation among zones of the building. For further
evaluation of this phenomenon, we divided the building into zones. Zone U consisted of all rooms not in
contact with the soil. Zone A consisted of the auditorium and music rooms. Adjoining Zone A was Zone
B, consisting of the cafeteria and nearby rooms. Adjoining Zone B was Zone C, consisting of the central
office and nearby rooms. Zone D adjoined both Zones C and E and consisted of the ground floor of the
classroom wing. Zone E was the gymnasium and shop areas. Figure 2 summarizes the means of all mRn
and pressure measurements made in these zones during periods of HVAC operation and non-operation.
There is much variation among zones with regard to the mean levels of ^Rn and pressure. There is also
considerable variation among zones as to both (he magnitude and algebraic sign of the change induced by
operation of the HVAC system.
Results in this paper confirm and extend the observations of Craig and his coworkers (4). These
results strongly suggest that the impact of HVAC operation on radon entry processes in schools and other
large buildings is very important and can vary considerably within a building.
These results have important implications for the design of surveys of mRn in large buildings.
This study shows that care must be taken in the analysis of results from surveys of large buildings to reflect
the status of the HVAC system during the survey in comparison to its status during normal occupancy. To
reduce costs, some survey designs may include only sparse sampling of rooms within a large building using
passive monitors. Such survey designs have limited ability to reduce the occurrence of falsely negative
findings (i.e., cases where buildings are falsely declared "radon-free"). An alternative approach may be to
screen a building with a manometer and to place radon monitors in known low-pressure rooms.
ACKNOWLEDGEMENTS
The authors are very grateful to the staff of the schools in which these data were collected. Without
their patience, this study would not have been possible. One of us (L. D. S.) was a Teacher Research
Associate at Oak Ridge National Laboratory under the auspices of a program sponsored by the Office of
-------
Energy Research of the U.S. Department of Energy. This research was sponsored by the Office of Health
and Environmental Research of the U.S. Department of Energy under Martin Marietta Energy Systems, Inc.,
contract DE-AC05-84OR21400 with the U.S. Department of Energy.
The work described in this paper was not funded by the U.S. Environmental Protection Agency
and therefore the contents do not necessarily reflect the views of the Agency and no official endorsement
should be inferred.
"The suborned manuscript has bMn
authored by a contractor of the U S
Government under connect No 0-
ACOS-B40R21400 Accorehnoiy. the US
Government retorts e normdusrva.
royalty-free license to pubhsh or reproduce
tn6 pubbstwd form of this coflintxrtioo, or
aDow others to do so. for U S Government
purposes'
-------
REFERENCES
1. National Research Council. Health risks of radon and other internally deposited alpha-emitters.
Washington, DC: National Academy Press; 1988.
2. Indoor Radon Abatement Act. U.S. Congress. 1988.
3. Cook-Mozaffari, P.; Darby, S.; Doll, R.; Forman, D.; Hermon, C; Pike, M.; Vincent, T.
Geographical variation in mortality from leukaemia and other cancers in England and Wales in
relation to proximity to nuclear installations 1969-78. British Journal of Cancer. 1989.
4. Saum, D.; Craig, A. B.; Leovic, K. W.; Radon reduction systems in schools. Paper X-4 in Proc.
of 1988 EPA Symposium on Radon and Radon Reduction Technology (Available from U.S.
Environmental Protection Agency, Washington, DC 20460). 1988.
5. Nero, A. V.; Nazaroff, W. W. Characterising the source of radon indoors. Radiation Protection
Dosimetry 7(l/4):23-39; 1984.
6. Hawthorne, A. R., Gammage, R. B., and Dudney, C. S. An indoor air quality study in forty east
Tennessee homes. Environment International 12:221-239. 1986.
7. Dudney, C S.; Hawthorne, A. R.; Wallace, R. G.; Reed, R. P. Radon-222, mRn progeny, and
progeny levels in 70 houses. (In press) 1989.
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IX-6
RADON IN SCHOOLS OF MASSACHUSETTS
by: Lee Grodzins
NITON Corporation, Bedford, MA 01730
Massachusetts Institute of Technology
ABSTRACT
NITON Corporation has completed the testing of more than 7,000
classrooms in about 500 buildings of more than 80 public and private school
systems in Massachusetts. This paper presents our protocols and summarizes
our results based on about 5,000 of the tests. Only 6% of the rooms had
radon levels, measured in weekend screen tests, above 4 pCi/L, a factor of 3
smaller than found in a recent EPA survey. Our protocols are similar to those
recommended by the EPA, with three exceptions: 1. Long-term tests that
include nights, weekends and school vacations are never carried out; they are
manifestly unrealistic measures of radon levels during occupancy. 2. Follow-
up tests of elevated measurements are made during hours of occupancy; i.e.,
during the daytime when schools are in use. 3. Successful screen tests, with
the buildings closed and unoccupied and with ventilation systems dampened or
off, are carried out in warm weather.
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INTRODUCTION
We treat our children differently from ourselves. We set for them a
higher standard. Their environment must be ultra-clean, whether ours is or
not. So we demand that their schools be free from asbestos, free from lead
paint, free from radon.
A few states have passed laws requiring that schools be tested and
mitigated, if necessary. Most states will probably follow. But schools cannot
and are not waiting. Massachusetts, for example, has no radon testing law,
nor is one imminent. Nevertheless, thousands of classrooms of Massachusetts
have already been tested, for school administrators are all too aware that the
wide knowledge of the risks of radon have, de facto, made the schools
accountable.
We report here on the testing of more than 5,000 classrooms in some 70
school systems. NITON's basic protocol is a three-stage procedure similar to
that advocated by the EPA1. We begin with a broad-coverage screening test
using charcoal, liquid scintillatoc, passive detectors. The tests are carried
out under "worst case conditions," over a week-end or during a vacation. The
initial test is followed, where necessary, with tests carried out when the
school is in session, again using liquid scintillation, passive charcoal
detectors. Finally, in those cases where there are elevated radon levels
during occupancy, we make diagnostic tests with electronic radon monitors to
recommend mitigation procedures.
Schools are different from houses, but two generalizations are much the
same: There is yet no way of telling, a priori, which school buildings, or
which rooms in a given building, will have a high radon level; every
frequently occupied room on or below grade must be tested. And the mitigation
of elevated levels is idiosyncratic; there are few commonalties and no magic
bullets that will solve the radon problem in all schools.
This report begins by reviewing those differences in construction and
usage that bear on the protocols one should use. Section III describes the
NITON detectors and our early results for a few school systems that led us to
adopt the protocols described in Section IV. Section v presents the full
results of our school tests. Case studies give examples of different classes
of school buildings, demonstrate the differences between radon levels found
over weekends and during week days, and between daytime and nighttime
concentrations, and give examples of successful mitigation. The final section
presents our conclusions relevant to this conference.
II. SCHOOLS ARE DIFFERENT FROM HOUSES
The upper section of Table 1 summarizes the main differences in
construction, ventilation and usage that bear on the radon problem. In
particular, the almost universal use of on- or below-grade rooms in sprawling,
decentralized schools make a strong case for testing every such occupied room.
The lower section of Table 1 summarizes the obvious differences in the
profiles of occupancy between a home and a school, differences that argue
compellingly that long-term, uninterrupted radon testing is inappropriate for
schools.
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Table I.
Houses Schools
Small Footprint. Very Large Footprint.
Basements often not used. Ground Floors almost always used.
Basements usually isolated from Ground floor often open to upper
the first floor. floors through wide stairwells.
The rooms of a given floor are Classrooms, especially in the
generally open to each other. lowest grades, are often isolated,
with rooms closed for extended
periods.
The stack effect of the furnace is The boiler room has little
a paramount concern in the winter, relevance to the radon problem.
N.E. homes are rarely on slab. Schools are often on slab.
N. E homes usually have 2 floors Schools are often single or two
plus a basement and attic. story; on or below grade.
No ventilation code. Mass, code requires 10 cfm of
fresh outdoor air per person.
One type of heating system. Usually a complex HVAC system.
Occupied day and night, especially Occupied during the day. Rarely at
at night. night.
Occupied on weekends. Used sparingly on weekends and
then only during daytime.
Occupied during the summer. Used sparingly during the summer.
School construction is remarkably varied. Some buildings are built on
slab, some over crawl space. Old buildings may still have fieldstone
foundations. A school may have one to several additions, each constructed
years apart under different codes and designed by different architects.
Schools are supposed to have ventilation systems operating whenever the
building is occupied. Massachusetts, for example, requires that schools
supply at least 10 cfm of fresh outdoor air for each occupant; for most
classrooms that is about 2 air exchanges per hour. To meet this code, some
schools have central HVAC but many have complex, hybrid systems. Modern
schools in our area often have central ventilation plus independent univent
heating systems in every classroom to heat fresh make-up air. Nevertheless,
the ventilation system is often the offender when a radon problem is found in
a school. One reason is that older school buildings generally have antiquated
ventilation systems, or none at all. Another can be traced to the 1970's when
the sharp increase in the cost of energy prompted many custodians to minimize
the amount of fresh air brought in during the colder months.
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Finally, we note that the stack effect can be important in every
building, but the causes and consequences are different in a school and a
home. In particular, unrelated parts of a large, one-story school may exhibit
widely different stack effects and, hence, widely different radon
concentrations.
III. Early Results and Protocols
All screening measurements have been carried out with our patented NITON
Liquid Scintillation detectors. These small vials, weighing about half an
ounce, contain a perforated plastic container filled with activated charcoal
and desiccant. The adsorption time constant makes them appropriate for
sensitive testing from 8 to 72 hours. Removing the cap exposes the charcoal
to the ambient air; screwing the cap back on seals the, gasket and completes
the test. The detectors are highly resistant to problems of high humidity and
air movements.
We carried out radon tests of several school systems in the fall of 1988.
Fig. 1 shows the extreme variations that one can encounter in different school
buildings of the same town. School A had no radon level above 1 pCi/L; School
B had a few isolated high radon values, difficult to find without a thorough
test; the majority of the rooms in School C had radon levels above 2 pCi/L,
though no room had a serious problem; the majority of tests in school D were
greater than 10 pCi/L.
V
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Radon Concentration, pCI/L
Figure 1. Radon Screen Teat Results in 4 School Buildings
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In one town, we worked closely with a superintendent who had an excellent
custodial staff and was himself conversant with the construction and use of
every building. He had also done his radon homework. When we walked through
the system, he knew where he wanted the detectors to be placed. One modern
school in particular was especially suspect, being built into a granite ledge
so as to be surrounded on two sides by stone up to the top floor. Another, a
modern, one-story, well-ventilated school, situated on top of a knoll would,
he felt, be no problem. However, former school building had a radon
distribution similar to School A of Figure 1, no radon levels above 2 pCi/L.
The latter school building had the radon distribution of School D.
When these results were confirmed with a second weekend test, in which
the radon concentrations reached 100 pCi/L in one classroom, the
superintendent considered shutting the school down until the radon levels were
mitigated. William Bell of the Mass. Department of Public Health and I
persuaded him to allow us to first carry out some long-term, time-dependent
radon tests. These results, which are commented on more thoroughly below, are
shown in Fig. 2. The radon levels in that school were varying from day to
night by more than a factor of 25; on one day the variation was close to a
factor of 50.
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Figure 2. 12 Days of Radon Tests in One Classroom in School D.
A careful examination of our results convinced us that we could neither
predict which buildings nor which rooms in a given building might show high
concentrations of radon. School B, with 5% of its rooms above 4 pCi/L, showed
that every occupied room on grade should be tested, or one can miss the odd
room or the special wing that might be seriously polluted.
The results of School D also made evident that follow-up tests must
measure the radon concentrations during occupancy; we care minimally about the
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concentrations when no one is in the building to be at risk.
Our early conclusions have been confirmed and strengthened by a year of
testing school systems. The protocols outlined in the next section are
designed to uncover problems and obtain insight into a mitigation strategy.
XV. NITON PROTOCOLS
1. THE INITIAL SCREEN TEST: A screen test is a short-term test carried out in
such a manner as to create "worst case" conditions. The radon concentration
found in the screen test should be higher than the radon concentration in that
location averaged over an entire year of occupancy.
The key word is occupancy. Schools are typically occupied by a given
staff member for no more than 25% of the hours of the year; a child is in
school for no more than 15% of the year. It is the radon levels during these
fractions of a year that we seek to screen.
The data in section V show that a "closed school" test almost always
yields a higher elevated concentration than that found during a school day.
2. WHEN TO TEST: Start the test on a Friday afternoon, harvest them Monday
morning. By Saturday morning, the school building will have had closed
conditions for about 12 hours; by Monday morning, a charcoal diffusion
detector, which gives greater weight to the radon levels in the later times of
the tests, will give a good measure of the radon concentrations.
A Friday to Monday test is not written in stone. Two-day tests during
vacation periods or tests pulled early because of impending school functions
or stormy weather are also successful. But a weekend test is generally the
most economical, requiring the minimum overtime pay for the custodians.
Winter or Summer? The EPA states that "radon screening measurements in
schools should be made in the colder months (October through March) when
windows and doors as well as interior room doors are more likely to be closed
and the heating system is operating." We know of no evidence to support this
recommendation. Indeed, one can generally get better "closed conditions" in
the summer since schools are often completely closed during parts of the
summer. The remaining justification for cold weather screen testing presumes
that the heating system exacerbates the radon problem. Our view is that the
emphasis on the heating system is misplaced. The proper emphasis should be on
the fresh air input systems, required by Massachusetts and most states. If
such systems are shut off, and the school is closed and unused, then a screen
test is likely to be as "worst case" in the summer as in the winter. NITON
tested several large school systems this past summer. We expect to retest a
number of the buildings this winter with the hope that the data will provide
convincing evidence for or against year round screen testing of schools.
3. WHERE TO TEST: Every frequently occupied room on or below grade should be
tested. Closed rooms that are occupied for only short periods file rooms,
storage rooms, boiler rooms and the like should be tested only with full
knowledge that acceptable levels can exceed 4 pCi/L without undue risk.
Cafeterias, gymnasiums,libraries and other large open rooms seem to have
higher radon levels than do classrooms. Perhaps it is because they are seldom
well sealed against soil gas. Auditorium stages, for example, are sometimes
built directly over the ground. We recommend one detector for every 2,000
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square feet of floor space; that is, a 60 by 60 room would have 2 detectors.
Washrooms and showers. These tend to have elevated concentrations due to
gaps around pipes that go through the floor. But a given individual spends
little time in these rooms, so that testing should be done with insight.
Upper floors: The open structure of schools expose the upper floors to a
radon problem if it exists in the ground floor. A thorough screening of the
on-grade rooms should uncover the problem. We recommend that a few upper
floor rooms be tested in every wing.
4. CONDITIONS FOR TESTING: We all agree that the school should be closed as
much as is practical during the weekend test. And no one disagrees that high
winds and stormy weather should be avoided, if at all possible. There is,
however, disagreement on the matter of the operation of the HVAC system and on
summer time versus winter time testing. I will take up the latter point again
in the last section. On the question of the operation of the HVAC system,
NITON prefers to make the tests with the ventilation system throttled so as to
bring in the least amount of fresh outside make-up air and provide a better
"worst case" screening test. The EPA, however, recommends that the heating
system be kept on during the entire weekend, a procedure that produces a
"worst case" only when the ventilating system is not bringing in outside air.
5. WHO SHOULD DO THE TESTING? A school can save a great deal of money by
putting out and harvesting the tests themselves. The testing procedure itself
is simple. So too are the directions for placement. If one can handle taking a
pill from a child-proof bottle, one can conduct a passive radon test. But our
experience shows that there are no free lunches here. The school
superintendent must decide whether there are competent custodians who will
responsibly put out and harvest the tests and, most important, keep proper
records of what they have done. If not, we believe that the school will
benefit from having a professional radon expert who will assume all
responsibilities; in any case, the expert will be needed if problems are
uncovered. On the other hand, the budgets of many schools preclude hiring an
outside professional for the first screen test. In that case, NITON provides
a number of aids:
a. Clear written instructions as to how to make the test.
b. Record-keeping sheets so that each custodian will provide us with the basic
information of location and testing periods.
c. Where practical, we hold a meeting of the custodial staff to explain radon,
hand out material, demonstrate the test, stress the need for record keeping,
accuracy, promptness and diligence, and answer questions.
d. A successful strategy is to give a free test to custodians so that they
could test their own home to become familiar with the entire procedure.
FOLLOW-UP TESTS:
1. Criteria; what should be the criteria for retesting? At what screening
level do we pronounce a room cleared? There are no one-line answers.
Prudence dictates that we recognize that radon levels can fluctuate markedly
from day to day, from week to week, from season to season, and that a
screening test is not invariably a "worst case."
NITON asks for follow-up tests whenever:
a. A room has a radon concentration above 3 pCi/L.
b. A cluster of rooms has radon concentrations above 2 pCi/L.
c. An entire school has a mean radon level above 1 pCi/L.
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The isolated high-radon-level room may be a fault of the test, but we
have found that the problem is almost always real and often caused by a faulty
ventilation unit or a unique radon entry point. Isolated rooms with elevated
radon levels should be tested with two detectors placed side-by-side.
Areas of radon concentrations exceeding 3 pCi/L should be retested
thoroughly, with additional tests in rooms above or adjacent to the area.
Duplicate tests are satisfying but not necessary since the tests validate each
other.
Clusters of rooms that have weekend values between 2 and 4 pCi/L point to
a problem that could be serious in another season or year. We highlight this
region and ask for early follow-up tests on most of these rooms.
Some school buildings show no radon concentration greater than 3 pCi/L,
but yet are far from being radon free. These buildings must be watched. We
begin with follow-up tests of about 20% of the rooms.
Having determined which rooms to retest, we now must decide how to make
the tests in the most direct, economical manner possible. Follow-up tests can
simply repeat the initial screening test to confirm their findings. NITON has
long since discarded this approach since we found that we rarely failed to
confirm the earlier findings. Our preferred follow-up tests address the radon
problems directly.
The NITON follow-up tests are carried out during school days when the
rooms are occupied. The tests are done with our LS vials so as to
differentiate between radon levels in the daytime and those in the nighttime.
2. The Day versus Night Follow-up Test: We seek to know the radon
concentration that students and staff are exposed to. We thus need to measure
the radon concentrations during a weekday, from roughly 7 A.M. to 7 P.M; the
duration depends on the school use. Continuous monitors, in place for at
least one day, would give the most complete information, but such monitors are
expensive and the first follow-up tests, like the initial screening, often
involve a number of rooms.
We prefer to make the tests using our inexpensive NITON LS detectors. We
have carefully calibrated the sensitivity and accuracy of these detectors for
periods ranging from 8 to 72 hours. The sensitivity at 8 hours is more than
adequate; a 10 minute liquid scintillation count is sensitive to 0.4 pCi/L
with an uncertainty of 25%. The accuracy of an 8 hour measurement, as
determined from tests at a National Radon Facility, is well within 15%; the
typical precision of multiple tests is about 10%. Both the accuracy and the
precision are considerably worse than we generally obtain with a 2 day test,
but they are quite acceptable for screening tests of elevated radon values.
Consistency checks of this procedure are constantly made by exposing, in
classrooms, three sets of detectors: one during the day; a second set during
the night; a third set for the full 24 hours.
The custodial staff (now expert in handling our detectors) or a
professional exposes one set of detectors from, typically, 8 A.M. to 6 P.M.
and another set from 6 P.M. to 8 A.M. An equivalent combination is a daytime
exposure together with an overlapping 24 hour exposure.
DIAGNOSTIC TESTS:
Daytime concentrations are generally 30% to 50% smaller than the "worst
case" screen tests. Thus, many of the rooms found to have screen-tested radon
levels in the 2 to 6 pCi/L range, are found, with daytime testing to have
acceptable values during occupancy. These rooms must be checked periodically
but need not be mitigated.
The rooms that have elevated radon concentrations during occupancy must
be dealt with expeditiously. Section V gives a few examples.
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V.
Results
SCREENING TESTS:
Fig. 3 presents the results of 5,200 screening tests carried out in 350
school buildings in 68 school systems of Massachusetts, mainly public, during
the past 12 months. Most of the tests were conducted during the period from
November, 1988 to May, 1989 but every season of the year is represented.
Most of the screening tests were carried out by the school custodians. An
additional 2,000 screening tests (not shown) were carried out by professionals
in private schools in this area. The results are shown on a semilog plot to
show the overall trend to high radon values. The abscissa values above 10
pCi/L are grouped in 5 pCi/L bins, shown as 5 identical vertical bars. Some
overall results:
61% of the rooms had radon levels below 1 pCi/L.
6% of the rooms had radon levels above 4 pCi/L.
1.1% of the rooms had radon concentrations above 10 pCi/L.
0.7% of the rooms (37) had radon concentrations exceeding 20 pCi/L.
The elevated radon concentrations are far less frequent than found in the
recent EPA study of 3,000 classrooms.2 In that study, 20% of the school rooms
had radon levels exceeding 4 pCi/L, and 3% had radon levels above 20 pCi/L.
We have no explanation for the factor of 3 to 4 between the EPA results
obtained in 130 schools and the Massachusetts school results.
Radon Distribution in 5,200 School Rooms In Massachusetts.
100 -t
.001
Radon Concentration, pCl/L
Figure 3. Radon Distribution of 5200 School Rooms in Massachusetts
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The gross averages tell little about the individual schools, which have
widely different distributions, as Figure 1 illustrates. The point is
emphasized by noting that 25% of the buildings accounted for all of the radon
levels exceeding the EPA "action level" of 4 pCi/L. Said the other way, 260
buildings, that is, 75% of the total, had no "elevated" radon concentration.
And 25 school buildings, 7% of the total, accounted for all of the radon
concentrations above 10 pCi/L. Some of these "high radon" buildings were old,
most were not. Some were built on slab, some were not. Some were in towns
that have higher than average radon levels, others were not. No pattern has
emerged so far.
The elevated levels found in the weekend tests are only indicators of
possible problems. Before one rushes to mitigate, one must confirm that the
results apply to people when they occupy the building.
DAY-NIGHT FOLLOW-UP TESTS:
Radon concentrations observed during a regular school day are almost
always lower than the values found either on the weekend or at night. An
example of our observations is given in Table 2, which shows the results
obtained for two school buildings in one system. The second column gives the
values found over a weekend in October. The third column gives the values
found a few weeks later during the daytime (12 hours) of a school day; the
fourth column gives the concentration found during the following night (12
hours.)
Table 2. Weekend, Daytime and Nighttime Testa
in One School System
Room pCi/L, Weekend pCi/L, Daytime pCi/L Nighttime
5: 13 6.8 3.0 2.8
E: Gym 5.5 2.3 2.9
E: 10 6.2 1.9 3.0
E: Library 6.4 2.9 3.8
E: 16 5.2 2.5 2.9
F: Teachers Room 7.0 1.8 7.9
F: Cafeteria 5.1 2.5 6.4
F: Spec. Ed 3.6 1.5 7.1
F: 11 3.6 1.2 3.6
F: 10 5.4 2.1 6.0
F: Janitor 10.0 2.4 6.1
F: Girls Room 5.4 2.1 6.0
In building E, the daytime and nighttime values are similar, and both are
about a factor of 2 less than the weekend results. In this building, the
ventilation system was never turned off on weekdays.
In building F, the nighttime concentrations are similar to those found on
the weekend, and both are about a factor of 2 higher than the daytime
concentrations. In this building, the ventilation system is damped at night.
The results of 40 such tests are summarized in Figure 4; four sets in
which a ratio exceeded 1.5 have been excluded to emphasize the main body of
data. On the Y axis, we have plotted the ratio of the daytime to the weekend
concentration; on the X axis is the ratio of the nighttime to the weekend
concentration. (The division of the two values gives the ratio of the daytime
to nighttime concentrations.)
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Figure 4. Day to Night to Weekend Concentrations of Radon.
The scatter of both ratios is wide. But on average, using all data from
tests of some 60 rooms, the daytime concentrations were 42% of the
nighttime concentrations, with a standard deviation of 32%; on average, the
nighttime concentrations were 97% of the weekend results;
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systems being turned off. When the air exchange system was left running all
the time, the maximum values dropped to just below 4 pCi/L. The univent
system lowered the radon levels to below 2 pCi/L.
The one-week average for the radon concentration in School B was
approximately 11 pCi/L, far above the EPA guideline, and a demand for
mitigation. But the one-week average of the radon concentration from 8 A.M.
to 6 P.M was only 1.9 pCi/L, well within the EPA guideline.
LONG-TERN TESTS
In every school building we have investigated, a long-term test that
includes the nighttime and weekend concentrations would give a totally
erroneous representation of the radon exposure to the occupants.
EXAMPLES OF MITIGATION
1. The Odd High Radon Level. We frequently find that a building has only one
room or a limited area with an elevated concentration. Such problems are often
easy to diagnose and correct. An example was the multi-winged, one-story
school built on slab. An examination uncovered two problems.
The ventilation system was defective. For one thing, the air returns
inside the classroom closets were so covered with books and paraphernalia as
to be ineffective. For another, the make-up air brought in by the univents
and central ventilation system had been deliberately restricted years ago to
reduce the cost of heating. When the returns were cleared, the radon problem
in the rooms of one wing disappeared.
But the radon problem in two end rooms of another wing not only persisted
but remained well above 10 pCi/L during the daytime. Further tests with the
LS detectors, carried out by the custodians, showed that the back of one of
the classrooms was about 20 pCi/L - almost twice the concentration found in
the front of the room.
When William Bell and I investigated, we found that the radon was gushing
in from the clearance space around the sink drain pipe. Foaming this space
solved most of the remaining radon problem.
2. School D. School D, the modern grade school building of Figs. 1 and 2 is
a one-story building built over a crawlspace whose height ranges from about 3
to more than 6 feet. Service ducts and pipes form a tangle above the dirt
floor. The radon concentration in the crawl space was very high and clearly
the cause of the radon problem in the school.
Sealing the dirt floor, with the possibility of pumping under the seal,
was and remains an expensive option. Instead, the decision was made to
mitigate by controlling the cycles of heating and ventilation. The air
exchange system is kept on during the week to supress excessively high
concentration. The univent systems are turned on by 6 A.M. and turned off
around 6 P.M., later if there is an evening activity. We periodically monitor
the building and have advised installing a permanent radon monitor.
VI. Conclusions:
NITON has tested some 7,000 classrooms in about 500 buildings in more
than 80 school systems. The first measurements were screen tests carried out
over a weekend under "worst case" conditions. The follow-up tests were
carried out during school session; daytime and nighttime concentrations were
obtained separately. Finally, where necessary, diagnostic tests were
conducted with electronic sniffers and monitors to determine'the origin of the
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radon infiltration. He draw the following conclusions from these data:
1. A week-end test, beginning Friday afternoon and ending Monday morning, when
carried out under closed building conditions, provides a reliable screening
measurement. The radon concentrations are, with few exceptions, higher than
concentrations found during occupancy.
2. The ventilation system in the school should be restricted during the
screening test if one is to simulate "worst case" conditions.
3. Follow-up tests of elevated readings should distinguish daytime and
nighttime radon concentrations. Such tests can be carried out economically
using passive LS charcoal detectors.
4. Long-term testing of radon that includes nighttime, week-end and vacation
concentrations produces manifestly improper measurements of the radon exposure
to humans. EPA'a insistance in suggesting alpha track and long-term EPERM
measurements as a preferred alternative for screening measurements weakens
their entire program for schools.
The results of a long-term test can be dangerously wrong if radon levels
at night and weekends are much lower than those during the daytime. In that
case, a serious radon problem may be missed. The more likely scenario is that
the higher radon concentrations generally found on weekends and nighttimes
will result in a falsely high radon concentration. Schools will then be
compelled to spend considerable funds to "fix what ain't broke."
5. We are now testing whether warm-weather testing gives erroneously low
radon results, as is implied by the EPA recommendation to test only in cooler
months. We hope to present the data at the conference.
6. Our data reinforces the EPA's conclusion that one cannot predict which
buildings, or which rooms in a given building, will have a radon problem.
Every occupied room on or below grade should be tested.
7. Finally, we emphasize that school buildings differ from one another in
construction and usage. Testing them for radon is now a straightforward
protocol. Mitigation of serious radon problems is, however, not well
understood. We do not yet know how to systematically approach a radon problem
in buildings with complex, hybrid heating and ventilating systems.
Acknowledgements
The data described here was obtained by the technical staff of NITON
Corporation, whose watchful and meticulous work is deeply appreciated. I
would also like to thank William Bell, with whom I did most of the early
diagnostic measurements; his teaching and advice are of continuing benefit.
The work described in this paper was not funded by the U.S. Environmental
Protection Agency and therefore the contents do not necessarily reflect the
views of the Agency and no official endorsement should be inferred.
REFERENCES:
1. Radon Measurements in Schools. An Interim Report. United States Environ-
mental Protection Agency, March, 1969. EPA 520/1-89-0010.
2. Phase I School Protocol Development Study. EPA, Private Communication.
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IX-7
RADON GAS TESTING IN KENTUCKY SCHOOLS:
SUMMER TESTING PRAGMATIC CONCERNS AND PRESSURE / HVAC CONSIDERATIONS
by: Patrick Holmes
Alpha Spectra of KY., Inc.
Louisville, KY 40243
ABSTRACT
This study examines the radon gas levels and related mechanisms in
elementary, middle, high and special schools. The Jefferson Co. Project
consists of 4,000 to 5,000 screening data points on 158 sites in Louisville,
Kentucky. The primary instruments consist of short-term electret perms and
open-face design AC canisters with CRM's as cross-checking devices.
Due to political, operational and financial considerations, this project
was mandated to be initiated and completed in summer 1989. Modifications and
specific concerns were addressed, in order to adhere as closely as possible to
EPA's Interim Guidelines for school testing (see summary).
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IX-8
RADON SURVEYS IN LARGE BUILDINGS;
THE UCF RADON PROJECT
Ralph A. Llewellyn
Department of Physics
University of Central Florida
Orlando, FL.32816
ABSTRACT
Documented protocols for surveying the distribution of radon in large
buildings do not currently exist. Those developed for one/two family
residential structures and draft versions of those being developed for
schools provide inadequate guidance for investigators and diagnosticians
charged with determining radon levels throughout large office buildings or
interconnected multi-building complexes. To support the development of
protocols for large buildings, the UCF Radon Project has completed the
initial phase of a detailed data collection and analysis program.
Measurements of radon levels were made under known, controlled conditions
in twelve large buildings ranging in size from 25,000 sq.ft. to
225,000 sq.ft. and up to five floors above ground. An average of more
than 100 radon measurements were made per building. Results from the
study indicate that (i) radon levels often do not decrease as expected in
the upper floors of multistory buildings and (ii) sampling rates currently
being proposed for the above ground-level floors of large buildings may be
too low.
INTRODUCTION
As is the case in several states, Florida is currently in the throes
of developing a building construction code intended to make all structures,
from single family residences through schools to high-rise office towers,
resistant to the intrusion of radon gas. A legislatively mandated team
drawn from the Florida State University System has been working with
pertinent state agencies since September 1988 on the drafting of the
comprehensive code. At the outset of their task the group recognized
that existing experimental data that could provide the basis for a
radon-resistant construction code which could apply to large buildings
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was exceedingly meager. Even the most fundamental knowledge, such as
characteristic concentrations, radon movement pathways, and the extent of
exposures to occupants, was (and is) not yet available in the literature.
Indeed, standard protocols to govern the conduct of radon surveys and
follow-up measurements for large and/or high structures do not exist. As
a consequence of the dearth of information, the drafting of codes and
regulations pertaining to the prevention of radon hazards in large
structures must await additional measurements and research.
UCF RADON PROJECT
In mid-1989 the small environmental physics group at the University of
Central Florida initiated ~a research program, the UCF Radon Project,
directed toward filling a small part of the information gap. The project
is organized in three phases:
Phase 1: Baseline determination. Collection and analysis of detailed radon
concentration data in a number of large buildings. Development
of a computer program and database to aid the analysis and to
facilitate diagnostic measurements and interpretation.
Phase 2: Study the effects on radon concentrations and transport of
changing the environmental control settings in selected
structures. Extend computer programs to include the results of
phase 2 work.
Phase 3: Utilize the results to develop a draft protocol for radon
analysis of large buildings.
The University's complex of large buildings of varying numbers of
floors, up to 5, and areas, up to 225,000 sq.ft. (20,900 mZ), provided a
convenient and in many ways ideal "laboratory" for the project. All of
the buildings are of masonary construction and relatively new, the oldest
just over 20 years and the newest less than a year. Types of building
utilizations include exclusively offices, mixtures of offices and
laboratories, a library, and exclusively residential suites. The HVAC of
all but the latter are controlled by a central computer system on a floor-
by-floor basis. Table 1 identifies 12 of the buildings used in Phase 1
of the study as to their size and type of utilization.
DATA COLLECTION
The data collection for the project was to serve a dual purpose.
First, it was to provide research data pertaining to large buildings that
would assist in the development of future measurement protocols and
construction codes. Secondly, it was to provide the University with timely
information regarding the levels of exposure to radon gas received by its
employees and student body. To this end, all rooms were assigned to one
of four categories based on occupancy time, ranked in order of
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TABLE 1. BUILDING DESCRIPTIONS
Building
No . Name
1
2
5
12
14
18
20
21
29
32
40
45
Administration
Library
Chemistry
Physics
Phillips Hall
HFA
Biology
Education
ecu
Seminole Hall
CEBA I
CEBA II
Utilization
type (a)
A
B,A
D,A
D,C,A
A,C
A
D,A
A,C
A,D
E
D,C,A
A,C
Number of
floors
4
5
3
4
4
5
4
3
2
4
4
4
Gross area
(sq.ft.)
87,700
226,500
49,100
106,500
64,600
84,000
62,800
110,300
23,400
42,100
130,900
119,700
a Key to utilization type: A = offices; B = library; C = classrooms;
D = laboratories; E = residence suites
measurement priority. They were: 1 - offices, 2 - residential suites,
3 - laboratories and classrooms, and 4 - mechanical and service areas.
Elevator shafts were initially of high priority interest and were
included in category 1.
Data collection and measurements were carried out on the basis of an
a priori draft "UCF Radon Measurement Protocol" (1) for large
structures, the detector deployment and measurement procedures of which were
based closely on pertinent USEPA documents (2) (3) (4). The resources
available to the project have thus far enabled screening measurements to be
made in all first priority rooms (offices) and some second priority rooms
(residential suites). A total of approximately 1500 measurements have
been completed to date.
Radon samples were collected using charcoal canisters exposed from 48
to 72 hours. The radioactivity of each exposed canister was measured using
one of two 3 in x 3 in (7.6 cm x 7.6 cm) NaI(T£) scintillation detectors,
ORTEC electronics, and an IBM PC/XT configured as a 2048-channel analyzer
operating in four 512-channel segments. The individual analyzer segments
were programmed to record gamma rays from radon daughters in the energy
range from 0.25 MeV to 0.61 MeV. Typical operational characteristics of
the two detector systems are recorded in Table 2.
F&J Specialty Products, Inc. model RA40V
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TABLE 2. DETECTOR CHARACTERISTICS
Channel Resolution
%
A 6.0
B 6.0
Efficiency
0.263
0.272
Error
% b
7.7
7.3
Minimum Detectable
Activity(pCi/liter) a
0.27
0.25
a At the level of 3 standard deviations.
b At the level of 2 standard deviations for a 4.0 pCi/liter result.
DATABASE
The net gamma ray counts measured for each canister were entered into
a specialized database (UCFRADON), together with information that enabled
the program to calculate the radon concentration in pCi/liter according to
the procedures outlined in reference 4. Its design is especially 'user
friendly! Information is also entered that permits relating the radon
results to the HVAC status of the building maintained by the University's
indoor environmental control computer. File structures in UCFRADON have
been arranged to facilitate analysis on a building-by-building, floor-by-
floor, and room-by-room basis.
There are currently approximately 1500 records in the UCFRADON data
files. The data retrieval routines currently provide a variety of options,
including, e.g., printouts of rooms with radon concentrations exceeding
user selected levels. Additional options under study include floor-by-
floor contour plots and 3-dimensional building-wide concentration
histograms to aid in radon transport analysis. The existing data and any
added subsequent to this writing as available to interested individuals
on request.
RESULTS
ELEVATION DEPENDENCE
Initial analysis of the data collected in the first phase of the
UCF Radon Project has yielded some interesting results. That fickle
predictor, conventional wisdom, tells us that the concentration of radon
should decrease as we move upward in a multistory structure. Assuming
that any radon in the building emanates from the ground rather than from
the materials used in the construction, it is easy to understand physically
why the concentration should decrease with elevation.
Treating radon diffusion in air as a random walk problem, let's
consider some concentration of radon, n(z,t) atoms/in-*, which is introduced
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at the ground level slab where z = 0 at time t = 0. Straightforward
application of statistical mechanics leads to the conclusion that
z2 = (l/3)v2 t t
(1)
where v = mean square velocity of the atoms and f
collisions (5) .
mean free time between
Equation 1 implies that the standard deviation of the z component of
)^
the displacement vectors of the radon atoms Az =
is proportional
to t5, where t is the time after the radon was introduced. Figure 1 shows
curves for the concentration n(z,t) vs z for three different times
0
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that the air in buildings circulates, to a certain extent due to natural
forces, but mainly because of very effective HVAC systems. Still, the
expectation has always been that the radon concentration will decrease
as we move upward through the building. The few sampling protocols that
have been drafted for large structures seem based on that assumption (7).
However, results of experimental measurements on the large buildings
studied in the UCF Radon Project suggest strongly that the expectation is
not well founded. Results for the five largest buildings studied, graphed
in Figure 2, show that in 80% of the cases the average concentration on
the 2nd and 3rd floors substantially exceeds that on the 1st floor, as do
more than half of the cases at the 4th floor level. For the two buildings
with 5 floors, the average radon concentration on the top floor was still
40% of that on the ground floor.
These results, if substantiated by further work, have serious
implications for the development of protocols intended to guide the
accurate assessment of the health risks to occupants of large buildings
arising from long-term exposure to radon gas. They also have something to
say about the design of big buildings. Namely, the way to reduce radon
intrusion into floors above the ground level would be to isolate the ground
floor HVAC system from that of the rest of the building. Our interest
here, however, is in the first of the implications, which will be discussed
briefly in the next section.
SAMPLING FREQUENCY
Draft protocols currently being discussed for measuring radon
concentrations in large buildings specify sampling rates on floors above
the ground level that are much lower than that for the ground floor. For
example, reference 7 specifies a 20% sampling rate for second floors and
10% for the third floors. However, the results shown in Figure 1 suggest
that such low sampling rates will not yield a reliable profile of the
radon concentration distributions on the upper floors. The large number of
measurements made during this study enabled a test of that suggestion.
Using a number of floors in the larger buildings for which 100% of
the first priority rooms had been measured, a pt? 'goodness of fit1 test was
done for random samples at several sampling rates from 20% to 80%. This
test answers the question, "What is the probability that the sample
distribution agrees with the parent, or actual distribution?" (8).
Table 4 records the results of the test for three floors in two of the
large buildings studied. Figure 3 shows the curves of probability of
goodness of fit used in evaluating the reliability of the random samples.
Clearly, a 20% sampling rate on the 2nd floor of CEBA I provided a poor
representation of the actual distribution of radon. Indeed, sampling rates
in excess of 60% were necessary in order to achieve probabilities of 'good
fit* in the 0.7-0.8 range. While these numbers are in part a function of
the statistical uncertainties of the relatively low radon concentrations in
the University's buildings, they suggest that sampling rates defined by
protocols be considered with great care.
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TABLE 4. RELIABILITY OF SAMPLE
Building
and
Floor
CEBA I, 2nd
CEBA I, 3rd
HFA, 4th
Sampling Rate %
20 33 50
0.02 0.05 0.18
0.01 0.01 0.11
0.01
67
0.75
0.75
0.25
80
-
-
0.85
Tabulated values are probabilities of agreement between sample and
parent distributions.
CONCLUSION
Based on the results discussed above, it would be prudent for those
developing protocols for guiding radon measurements in large structures
to assess very carefully the sampling rates proposed for floors above the
ground level in large buildings. Assumptions typically made regarding
radon concentrations and adequate sampling rates that are implicit in
current draft protocols may be seriously in error and could well lead to
substantial underestimation of the radon exposures received by occupants
of large buildings.
The work described in this paper was not funded by the U.S.
Environmental Protection Agency and, therefore, the contents do not
necessarily reflect the views of the Agency and no official endorsement
should be inferred.
ACKNOWLEDGEMENTS
The author wishes to express his appreciation to Hugh Ivie, Director
of the UCF Office of Environmental Health and Safety for his steadfast
encouragement and support of the UCF Radon Project, to Mark Llewellyn for
his design of a truly first rate database for the project, and certainly
not least to Bruce Dean for the countless hours he worked on data
collection and measurement.
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REFERENCES
1. Llewellyn, R.A. UCF Radon Measurement Protocol, unpublished draft,
University of Central Florida, Orlando, Florida, 1989.
2. Ronca-Battista, M., Magno, P., Windham, S., and Sensintaffar, E.
Interim indoor radon and decay product measurement protocols.
EPA 520/2-86-04, U.S. Environmental Protection Agency, Washington,
D.C., 1986. 50 pp.
3. Ronca-Battista, M., Magno, P., and Nyberg, P. Interim protocols for
screening and followup radon and radon decay product measurements.
EPA 520/1-86-014, U.S. Environmental Protection Agency, Washington,
D.C., 1987. 22 pp.
4. Gray, D. and Windham, S. EERF standard operating procedures for
radon-222 measurement using charcoal canisters. EPA 520/5-87-005,
U.S. Environmental Protection Agency, Montgomery, Alabama, 1987. 30 pp.
5. Reif, F. Elementary Theory of Transport Processes. In; Statistical
Physics, McGraw-Hill, New York, NY, 1967.
6. Feynman, R., Leighton, R., and Sands, M. Molecular Diffusion.
In; The Feynman Lectures on Physics, Addison-Wesley, Reading, MA, 1963.
7. 'Summary of Proposed Radon Standard' developed by Occupational Health
Conservation, Inc. for the Florida Department of Health and
Rehabilitative Services for use by schools and 24 hour care
facilities, 1989.
8. Young, H. Probability Distributions. In: Statistical Treatment
of Physical Data, McGraw-Hill, Reading, MA, 1962.
9. Morse, P. and Kimball, G. Probability. In: Methods of Operations
Research, The Technology Press/Wiley, New York, NY, 1958.
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H|(z.f)
0 z
Figure 1. Concentration n(z,t) vs z for various tjnn.-s aftei t = 0.
1.0
* +
21 0
2.0 Normalized
Radon Concentration
Fipuri- 2. R.idon concentration vs elevation in 5 l.irgc buildings.
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TOTAL OF n
mi OF THEM
WHERE THERE
RESULTS {; «1
EXPECTED VALUE OF m, IS npif
WHERE I « /
60 100
Figure 3. Contours of probability for goodness of fit. (9)
* U.S. GOVERWCNT FRINT1NG OFFICE- 1990 748-010/25005
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