EPA/60Q/A-92/272'
DESIGN OF NEW SCHOOLS AND OTHER LARGE BUILDINGS WHICH ARE
RADON RESISTANT AND EASY TO MITIGATE
Alfred B. Craig, Kelly W. Leovic, and
D. Bruce Harris, U. S. Environmental Protection Agency, Air and
Energy Engineering Research Laboratory, Research Triangle Park, NC
27711
ABSTRACT
The Air and Energy Engineering Research Laboratory (AE1RL) of
the U.S. Environmental Protection Agency (U.S. EPA) started a radon
mitigation research,, development, and demonstration program in
1985. Initial studies were on existing and new houses, and the
program was expanded in 1988 to include mitigation studies in
existing schools.
As a prelude to the preparation of a new construction
technical guidance document for schools, architectural drawings of
all schools researched by AEERL, to date, were carefully studied
to determine which building characteristics affect radon entry and
ease of mitigation. Results of the study were presented at The
International Symposium on Radon and Radon Reduction Technology
held in Philadelphia, PA, April 2-5, 1991.
These radon mitigation design recommendations were recently
incorporated in the construction of a hospital in Johnson City, TN.
These studies resulted in the mitigation of a 5,500 square meter
(ra2) building with only one suction point at an incremental cost of
$1.03 per m2. Extrapolation of the pressure field extension (PPE)
measurements indicated that a much larger building could have been
mitigated with the system used.
The mitigation system was extremely effective lowering the
radon level to below 20 bacquerels per cubic meter (Bq/m3)
throughout the entire building« Levels as high as 1950 Bq/m3 were
measured with the building closed up and with the heating,
ventilation, and air conditioning (HVAC) and mitigation systems
turned off.
A search is underway for larger buildings to be built in radon
prone areas of the 0.S. in order to determine the effectiveness of
this mitigation system in reducing radon in even larger buildings.
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INTRODUCTION
The U.S. EPA's AEERL is carrying out an extensive research,
development, and demonstration program on the mitigation of radon
in structures in the U.S. Initial work was done on houses, both
existing and new. During the past 4 years, this program has been
expanded to include schools and other large buildings. Extensive
diagnostics have been carried out in many existing schools, and
mitigation systems have been installed and evaluated in typical
ones.
Recently, the architectural plans and specifications of the
mitigated schools were carefully studied to identify those features
which affect radon entry and ease of mitigation. The results of
these studies are being used to develop technical guidance for the
design of new schools which are radon resistant and which can be
easily and inexpensively mitigated if a radon problem is found
after the building is completed.
The effect of these variables are currently being quantified
through their use in new schools and other large buildings which
are under construction and which incorporate these features.
Incorporation of these features in a recently completed hospital
has resulted in the mitigation of a 5,500 m2 slab with a single
suction point. Results of this work are reported in this paper,
PREVIOUS STUDIES
In 1989, AE1RL mitigated two schools in Nashville, TN<1>. One
of these schools was easy to mitigate, and the radon concentration
of a 1,100 m2 wing (14 classrooms and offices plus cafeteria and
kitchen) was reduced from an average of greater than 1,800 Bq/jn3 to
less than 30 Bg/m3 with only one suction point. In the second
school of about the same floor space, 16 suction points and 3 fan
systems were required to lower radon from about 1,300 Bq/m* to 60
Bq/m3.
In 1990, architectural features of these two schools and all
others that had been researched by AEERL in the U. S. were
carefully studied to determine those features having the greatest
effect on radon entry and ease of mitigation. This work was
described in a paper presented at The 1991 International Symposium
on Radon and Radon Reduction Technology(2). It is summarized as
follows.
DESIGN FEATURES AFFECTING OF MITIGATION
WITH ACTIVE SUBSLAB DEPRESSURIZATION (ASD)
Review of all school PFE'studies, examination of architectural
plans where available, and discussions with fellow scientists
working on radon mitigation have led to the identification of the
following features which affect PFE and hence the effectiveness of
ASD;
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Subslab barriers (size and location)
Aggregate
Bulk density (or void volume)
Particle size (both average size and particle size
distribution)
Particle shape (naturally occurring stone from
moraine deposits with rounded corners or crushed
bedrock)
Subslab suction pit size
Amount of suction applied
Of these features, the first is by far the most important.
Schools have been found to fall into one of the following four
categories listed in order of decreasing ease of mitigation;
Type 1—No interior walls extend through slab with the roof
load being carried by posts (steel or reinforced
concrete) extending through the slab to footings.
Type 2—Walls between classrooms extend through slab to
subslab footings. Hall walls do not.
Type 3—Hall walls extend through slab to subslab footings.
Walls between classrooms do not.
Type 4—All walls extend through slab to subslab footings.
Unfortunately, a majority of schools built in the U.S. in
recent years are Type 4, the most difficult to mitigate. However,
Type 1 construction is growing in popularity particularly since air
conditioning in schools negates the need for outside windows in all
rooms. In commercial and industrial construction where dimensions
of buildings are large in both directions (length and width), Type
1 (known architecturally as post and beam construction) is almost
always used. It is also believed to be the most economical of the
four types.
Aggregate characteristics are also very important to the
mitigation of large slabs and are being studied for 1PA at
Princeton University135. The following preliminary conclusions are
postulated on the effect of aggregate properties on PFE;
1. PF1 is proportional to average aggregate particle size
—the smaller the particle size, the less the PFE
(assuming the same particle size distribution).
2. The narrower the aggregate particle size distribution
range, the greater the void volume and the PFE.
3. The smoother the shape of the stone, the lower the void
volume; hence moraine stone (with its rounded corners)
has lower void volume and will give less PFI for the same
average particle size and particle size distribution than
crushed aggregate.
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The suction pit size and configuration also increase in
importance as the size of the building increases. A large void
space should be left under the slab, and the interface between this
void and the aggregate should be a minimum area of 0,5 to 0.7 m1.
APPLICATION OF OPTIMUM MITIGATION DESIGN FEATURES TO
JOHNSON CITY REHABILITATION HOSPITAL CONSTRUCTION
Late last year an opportunity presented itself to demonstrate
ASD in a large building under optimum conditions in a hospital
building under construction in Johnson City, TN. The hospital
building is one story with a floor area of about 5,500 m* and is
slab-on-grade construction with no foundation walls penetrating the
slab. Mechanical piping, electrical conduit, and structural
columns penetrate the slab, and the columns sit on footings below
the slab. These columns support steel beams overhead, which in turn
carry the bar joists for the roof. This type of construction is
referred to architecturally as post and beam construction. It is
used in most commercial and industrial buildings currently being
built in the U.S. All internal walls are gypsum board on metal
studs, and the exterior walls are metal stud supporting gypsum
board on the inside surface and an exterior insulation finish
system (1IFS) on the outside. The 10 centimeter (cm) slab was
poured over a 0.022 millimeter (mm) vapor barrier underlain with
a 10 cm layer of crushed aggregate which was continuous under the
entire slab. The slab, exterior walls, and footings were poured
monolithically. The slab was divided into about 5 meter (m)
squares by a combination of pour joints (300 lineal m) and control
saw joints (1,500 lineal m). No expansion joints were used.
1PA was requested to review the plans and specifications and
to recommend a radon mitigation system since the region was known
to have high radon potential. After this review, the following
recommendations were made to the architect designing the building:
1. Good compaction of the clay soil under the aggregate to
decrease permeability of the material under the aggregate.
2. Minimum of 10 cm of crushed aggregate meeting the
specifications for #5 stone as defined in ASTM-33-86 "Standard
Specifications for Concrete Aggregate'**11 carefully placed so
as to not include any soil.
3, Sealing of all pour and control saw joints and any slab
penetrations with a polyurethane caulking,
4. Installation of one subslab suction pit (SP) of the design
shown in Figure 1 in the approximate center of the slab with
a 15 cm stack leading to the roof capped with a Kanalflakt 3B
turbo fan capable of moving 240 liters/second (L/sec) at no
head.
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5. Continuous operation of the HVAC fans in order to pressurize
the building in all areas except those where negative pressure
is necessary to control odors, noxious chemicals, or
infectious diseases (toilets, kitchen, pharmacy, soiled linens
area, isolation wards, etc.)*
All of the recommendations were accepted and incorporated into
the building design. Upon completion of the shell of the building
and sealing of the slab, diagnostic measurements were made to
determine the potential of having a radon problem and the
effectiveness of the ASD system in depressurizing the entire slab.
Test holes were drilled through the slab at varying distances from
the suction pit including a series around the entire perimeter
about 2 m from the slab edge. Radon levels below the slab were
measured by "sniffing" using a Pylon AB-5 continuous monitor.
Levels from 7,000 to 60,000 Bq/m3 were found under the slab. This
is a significant level of radon which could result in indoor
measurements in the 100 to 2,000 Bq/m3 range under some conditions
of building operation.
The depressurization fan was then turned on and subslab
pressure measurements were made using a Neotronics micromanometer.
The fan removed about 100 L/sec of soil gas at a vacuum of about
375 pascals (Pa)» Negative pressure was 115 Pa in the suction pit,
55 Pa 15 m from the SP, and 45 Pa at the farthest point on the
perimeter (a distance of 55 m). This is considered extremely good
PFE, The PFE data are plotted in Figure 2 and give essentially a
straight line on semi-log paper. Extrapolation of these data
indicates that the mitigation system could mitigate a much larger
slab,
Upon completion of the building, radon levels were measured
in half of the building using open faced charcoal canisters and
with the HVAC and the ASD systems off. Radon levels ranged from
less than 18 Bq/m* (lowest detectable level with the open faced
canisters used) to 1950 Bg/ma, Highest levels were in the
bathrooms, particularly those associated with the patient rooms.
The patient room with the highest bathroom radon level had a radon
reading of 360 Bq/nt% the highest radon level found in any non-
bathroom area in the building.
The entire building was then measured with the H¥AC system on
and the ASD system off. Again some of the bathrooms had elevated
radon levels as did some of toe patient rooms. The bathroom with
the highest radon reading on a closed building basis was again the
highest in the building with the HVAC operating, testing 585 Bq/m3.
The final series of tests were made with both the HVAC and
ASD systems operating. The 20 bathrooms with the highest radon
levels in the second series of tests were remeasured. No
measurable radon levels were found in any of the rooms tested.
This is not surprising in view of the relatively large negative
pressure under the slab with the installed ASD system in operation
and with HVAC pressuriiation.
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In the Indoor Radon Abatement Act of 1988, the U.S. Congress
set a long term goal of reducing the radon level in all buildings
in the U.S. to a level as low as that surrounding the buildings
(i.e., ambient). Ambient levels are being measured around this
building and will be compared to long term indoor measurements.
This building, built in &, radon prone area, appears to meet the
long term ambient goal.
MITIGATION COSTS
Incremental costs of the mitigation system were easily
ascertained since the contract for the building had been let before
the mitigation system was added to the design. Hence the cost of
the addition of the radon mitigation system was covered by four
change orders for which the construction contractor charged $5,300
additional cost. Thus the system cost $1.03/m* of floor space,
Specifications had already called for 10 cm of aggregate under the
slab, and there was no charge for the change in aggregate size
used. The other three change orders covered installation of the
suction pit and stack: to the roof, sealing of all pour and control
saw joints with a polyurethane caulking, and installation of the
fan and warning system. A recent study of costs of mitigation in
eight new schools recently built gave costs from $3.00 to $11.00
per ma. (See reference 5.) Hence, the installed mitigation system
cost only a fraction of the cost of systems currently being
installed in new schools in the U.S.
CONCLUSION
A low cost, single point ASD system, installed during
construction, has lowered radon levels in a new 5,500 m2 single
story hospital building to near ambient levels of less than 18
Bq/ma , the detection limit of the radon test used. Levels as high
as 1950 Bq/m3 were measured in the building with both the HVAC and
ASD systems off and as high as 360 Bq/m3 with the HVAC system
operating and the ASD system off. Ingredients of the radon
mitigation system are:
1. Slab-on-grade post and beam construction with no barriers
to soil gas flow below the slab.
2. Continuous layer of coarse, narrow particle size range crushed
aggregate a Minimum of 10 cm thick.
3. Careful sealing of all slab cracks and penetrations and the
use of a 0.022 mm plastic film between the slab and the
aggregate.
4. Low permeability layer beneath the aggregate. (In this
case, the clay itself was low permeability.)
5. A specially designed subslab suction pit having a void to
aggregate interface area of 0.5 to 0-7 m* and a 15 cm stack
to the roof.
6. An exhaust fan (on the stack) capable of exhausting a
minimum of 240 L/sec.
6
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Incremental cost for the mitigation system was $1.03/ar
compared to a cost range of $3,00 to $ll,00/u2 for eight schools
recently built in the U.S. with more complicated radon mitigation
REFERENCES
1. Craig, A* B. , K. W. Leovic, D. B. Harris, and B, I. Pyle,
Radon Diagnostics and Mitigation in Two Public Schools in
Nashville, Tennessee. Presented at The 1990 International
Symposium on Radon and Radon Reduction Technology, Atlanta,
Gh, February 19-23, 1990.
2. Craig, A. B., K. W. Leovic, and D. B. Harris, Design of Radon
Resistant and Easy-to-Mitigate New School Buildings.
Presented at The 1991 International Symposium on Radon and
Radon Reduction Technology, Philadelphia, PA, April 2-5,1991,
3. Gadsby, K. J., T. A. Reddy, D. F. Anderson, R, Gafgen, and A.
B. Craig, The Effect of Subslab Aggregate Size on Pressure
Field Extension. Presented at The 1991 International
Symposium on Radon and Radon Reduction Technology,
Philadelphia, PA, April 2-5, 1991.
4, ASTM-33-86 "standard Specifications for Concrete Aggregate,"
May 1986,
5. Craig, A. B., K, W, Leovic, and D. W. Saurn, Cost and
Effectiveness of Radon Resistant Features in Mew School
Buildings, Healthy Buildings—IAQ'91, Washington, D. C.,
September 4-8, 1991.
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Section A
J
- - -n
l
20 cm Plastic pipe
_
_. 1
1.2 m x 1.2 m x 2 cm
Treated plywood
20x20x20 cm
Concrete block
Section A,
Figure 1
Subslab suction pit
8
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100-—_-—^
6
o
o
CO
o
r-.
O
in
SUBSLAB PRESSURE, Neg. pascals
Figure 2,
Pressure field extension
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AEERL-P-826
TECHNICAL REPORT DATA
(Please read Instructions on the reverse before complet'
i. REPORT NO.
EPA/600/A-92/272
2.
4. TITLE AND SUBTITLE
Design of New Schools and Other Large Buildings
Which Are Radon Resistant and Easy To Mitigate
S. REPORT DATE
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
A. B. Craig, K. W. Leovic, and D. B. Harris
B. PERFORMING ORGANIZATION REPORT NO
9. PERFORMING ORGANIZATION NAME AND ADDRESS
10. PROGRAM ELEMENT NO.
See Block 12
11. CONTRACT/GRANT NO.
NA (Inhouse)
12. SPONSORING AGENCY NAME AND ADDRESS
EPA, Office of Research and Development
Air and Energy Engineering Research Laboratory
Research Triangle Park, North Carolina 27711
13. TYPE OF REPORT AND PERIOD COVERED
Published paper; g/9Q-8/9l
14. SPONSORING AGENCY CODE
EPA/600/13
15.SUPPLEMENTARY NOTES AEERL project officer is Alfred B, Craig, Mail Drop 54, 919/541-
2824. Presented at 5th International Symposium on the Natural Radiation Environ-
ment. Salzburg. Austria, 9/22-28/91.
s. ABSTRACT
paper discusses the recent incorporation of radon mitigation design re-
commendations in the construction of a hospital in Johnson City, TN. The recom-
mendations resulted in the mitigation of a 5, 500 square meter building with only
one suction point at an incremental cost of $1,03 per square meter. Extra-
polation of the pressure field extension (PFE) measurements indicates that a much
larger building could have been mitigated with the system used. A search is under-
way for larger buildings to be built in radon prone areas of the U. S. in order to de-
termine the effectiveness of this mitigation system in reducing radon in even larger
buildings. As a prelude to the preparation of a new construction technical guidance
document for schools, architectural drawings of all schools research by EPA, to
date, were carefully studied to determine which building characteristics affect radon
entry and ease of mitigation. Results of the study were presented at an international
symposium on radon in Philadelphia, PA, in April 1991. EPA's radon mitigation re-
search, development, and demonstration program started in 1985 with existing and
new houses. In 1988, the program was expanded to include mitigation programs in
existing schools.
7.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFlERS/OPEN ENDED TERMS
c. COSATI Field/Group
Pollution
Radon
Hospitals
Building Codes
Schools
Pollution Control
Stationary Sources
13 B
07B
06L
13M, 05D
051
8. DISTRIBUTION STATEME1
Release to Public
19. SECURITY CLASS (This Report)'
Unclassified
21. NO- OF PAGES
2O. SECURITY CLASS (This page}
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
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