EPA/600/A-97/013
AN EVALUATION OF INDOOR RADON REDUCTIONS
POSSIBLE WITH THE USE OF
DIFFUSION-RESISTANT FLEXIBLE CONSTRUCTION MEMBRANES
David C, Sanchez
U.S. Environmental Protection Agency
National Risk Management Research Laboratory
Research Triangle Park, NC
Robin Minga and Cephas Sloan
Eastman Chemical Company
Kingspoil, TN
ABSTRACT
The importance of foundation construction design and materials used is recognized as critically important to the radon
resistance of buildings. Some states have adopted "standards" or guidelines which prescribe methods and materials of
construction. This paper provides a modeling assessment of the indoor radon reductions possible through the use of
"improved" radon resistant membranes. The analysis focuses on quantifying the impacts on indoor radon concentrations
of using "improved radon diffusion resistant membranes" for a typical experimentally determined range of membrane radon
diflusion coefficients. The evaluation considers the application of radon resistant membranes to slab-on-grade construction
typical of Florida and source strengths and site conditions typical of Florida. Guidance for the extrapolation of findings to
non-Florida construction and site conditions is discussed.
ACKNOWLEDGMENT
The inspiration for this paper is derived from a jointly sponsored research effort, CRADA No. 0122-95 of the U.S.
EPA and Eastman Chemical Company of Kingsport, Tennessee, intended to develop methods and data on the radon difiusion
barrier resistance of construction membranes. The modei, RAETRAD 4.1, used for assessing the radon resistance of possible
radon barriers, was provided by Rogers and Associates Engineering Corporation of Salt Lake City, Utah. Finally, the
assistance of Richard Snoddy of Acurex Environmental Corporation, Research Triangle Park, is acknowledged in exercising
the RAETRAD analysis.
INTRODUCTION
Government and private sector responses to dealing with the public health risk of indoor radon are well developed.
Federal and state programs of problem assessment, control technology development and demonstration, and the transfer of
guidance reached their zenith of effort in the period 1988 to 1995 (EPA88,EPA91,EPA93,EPA94,DCA95). Government
efforts are now focassed on outreach programs and privatization of certification programs for radon testing and mitigation
(RRTC95). Private sector efforts now play a major role in addressing the remaining problematic aspects of indoor radon.
The current state of the art of radon control technology, as indicated by formalized guidance and extensive
demonstrations (Henschel88, Fowler91, Leovic94, Tyson95, Hintenlang95, Najafi95, and Fowler96), indicates that an
adequate technical basis exists for dealing with most indoor radon problem situations found in new construction and existing
buildings. Yet there are problem situations (e.g., buildings built over high radon potential lands) where more effective or
robust control technologies are needed. An early expression of this concern, focused on one control strategy, is found in
the proceedings of a workshop on innovative radon barriers sponsored by EPA and held at the National Association of Home
Builders headquarters in Wasliington, DC, on July 21,1992. Some of the above referenced control technology evaluations
1
-------
of new construction teclmiques (Tysoo95, Hintenlang95, Najafi95, and Fowler96) also support consideration of the use of
passive controls (such as vapor burners) employed and required in all Florida new construction- This paper addresses this
technical issue, in die context of all Florida construction (DCA95), by using (I) a computer model (Nielson94) developed
and enhanced in support of the Florida Radon Research Program (Sancliez91) and (2) existing literature data on the radon
diffusion resistance performance of classes of flexible membranes. The following assessment provides an analytical method
for evaluating the indoor radon impacts of newly developed radon resistant construction membranes.
ASSESSMENT APPROACH
Approach
This paper is an applications paper; i.e., it uses tools and information developed within the Florida Radon Research
Program and research findings specific to the radon diffusion characteristics of selected flexible membranes as input for a
computer model simulation and estimation of resultant indoor radon impacts. The following discussion presents a
description of the main teclmical aspects and data input needed for background and understanding of the context in which
the computer simulations are undertaken.
Radon Diffusion Through Flexible Films
The study of gas diffusion as a mass transport process has been well defined since 1855 (Pick 1855), and its
application to contemporary problems is evidenced by the development of American Society for Testing and Materials
(ASTM) standards (ASTM82, ASTM84, ASTM95a, ASTM95b) and research specific to radon transmission through plastic
films (Jha82, Hafez86, Nielson96) including ongoing research (Perry96, Mosley96). Table I presents the diffusion
coefficients determined by this research and some of the characteristics of these research tests. This research defines the
difiiision coefficient range relevant to an assessment of the impact on radon entry of the use of improved diffusion barriers.
Of special note is die variability of test results, for nominally the same materials, between researchers. This variable result
is largely explained by the uncertainty introduced by the quality of test materials and the use of different test methods.
Florida Standard for Passive Radon Resistant New Residential Building Construction
The Florida Standard for Radon Resistant New Residential Construction was the result of a concentrated research
effort, undertaken by the Florida Radon Research Program (FRRP) (1989-1995). The FRRP's initial effort was directed
at indoor radon problem assessment and the development of diagnostic measurement and assessment tools. This effort was
followed by an extensive effort directed at developing a quantitative basis for rank ordering the efficacy of selected radon-
resistant construction techniques and control approaches. The results are individually reported in "new house evaluation
studies" (Najafi95, Hintenlang95, Tyson95, and Fowler96) and presented in summary in Nielson96 and Nielson95. Tables
2, 3, and 4 present house parameters and site conditions encountered at the study houses. The studies present the typical
range of house parameters (e.g., house dimensions and house shell openings) and house conditions (e.g., radon soil gas
concentrations and house ventilation rates) which influence radon soil gas entry into a house and which are entered as default
values into the RAETRAD simulation model which is later discussed.
-------
Table 1« Comparison of Test Results and Conditions
for Radon Diffusion Coefficient Measurements
Publication =>
Units =*•
Jha82
m's-'
Hafez86
mV
Nielson96
mV
Material 1-
Natural Rubber
Cellulose Nitrate
Cellulose Acetate
Polyvinylchloride
Polyethylene
Polyethylene
terephthalate
Polyester
Polycarbonate
Mylar
6.36x10-"
1,24x10-"
5.00x10-"
1.95x10-"
3.82x1 0-"
8.36xlO'u
7.5x10'"
5.8xlO'IJ
7.8x10'"
3.0x10'"
2.4x10-"
5.5x10-"
3.36x10-"
Test Conditions $
Exposure Time
Radon Source
Monitor
Steady State
Thickness
to equilibrium
ore, Ra@
1730pCi/g
alpha
yes
not reported
30 d
not reported
alpha track
yes
0.5,1,3 mil*
to equilibrium
mill
tailings
alpha
not reported
6 mil*
* 1 mil = 25 urn
-------
Table 2. House Parameters by Study Cohort
Ref.
Nielson Mean
95 ±S.D.
Mean
±S,D.
" Mean
±S.D.
Mean
±S.D.
Nielson Mean
96 ±S.D.
" Mean
±S.D.
H Mean
±S.D,
" Mean
±S.D.
Base
Area
(m2)
233
±59
212
±35
268
±108
207
±33
217
±43
201
±21
199
±81
258
±52
Occup,
Vol.0
(m3)
683
±198
645
±141
908
±364
618
±103
623
±181
579
±93
602
±286
750
±170
Inside
Height
(m)
2.9
±0,3
3.0
±0.2
3.6
±1.2
3.0
±0.2
2,8
±0.3
2.9
±0,2
3.1
±1.0
2,9
±0.3
Equiv.
Wid.6
(m)
10.0
±2.9
13.3
±1.5
17.6
±5.0
16.4
±1,5
10.7
±1.0
10.3
±0.6
10,0
±2.1
11.6
±1.1
No.
Stories
1.4
±0.5
1.1
±0.2
1.7
±0,4
1
±0
NR
NR
NR
NR
House •
Const.c
BL
FR
BR
BL
FR
BR
BL
FR
BR
BL
FR
BR
BL
FR
BR
BL
FR
BR
BL
FR
BR
BL
FR
BR
Floor Slab
Edged
Detail
SSW
Mono
SSW
Mono
SSW
Mono
SSW
Mono
SSW
Mono
SSW
Mono
SSW
Mono
SSW
Mono
Slump
(cm)e
20
±1
19
±2
11
±1
13
±2
15
±3
10
±0.0
16
±4
17
±4
Super-
plast/
Y
N
Y
N
Y
N
Y
N
Y
N
Y
N
Y
N
Y
N
Rein-
force,*
W
F
PT
W
F
PT
W
F
PT
W
F
PT
W
F
PT
W
F
PT
W
F
PT
W
F
PT
SSV
Syst*
WP
SP
VM
WP
SP
VM
WP
SP
VM
WP
SP
VM
WP
SP
VM
WP
SP
VM
WP
SP
VM
WP
SP
VM
"Volume of the occupied space in the house.
*Width of the equivalent rectangular area of the house footprint.
^Construction: block (BL), frame (FR), or brick (BR).
''Slab edge detail: slab poured into stem wall (SSW) or monolithic slab (Mono).
^Concrete slump.
•'Super plasticizer used in slab concrete (Yes or No).
*Slab reinforcement: wire mesh (W), glass fiber (F), or post-tensioned (PT).
*Sub-slab ventilation system: well point (WP), suction pit (SP), or ventilation mat (VM).
NR = Not Reported
-------
Table 3. House, Soil, and Ventilation Measurements by Study Cohort
Ref.
Nielson
95
H
H
H
Nielson
96
H
Nielson
95
«
House
ID
Mean
±S.D.
Mean
±S.D.
Mean
±S.D.
Mean
±S.D.
Mean
±S.D.
Mean
±S.D.
Mean
±S.D.
Mean
±S.D.
Soil Air
Permeabil-
ity (cm2)
2.3x1 0-7
il.lxlO'7
l.lxlO'7
±1.2x10"'
7.4x10-*
±7.8x1 0-*
l.lxlO'7
±1.2x10-'
NA
NA
9.1xlO'7
±1.9x10"*
9.0x1 0'7
±1.7xlO-6
Soil*
Moist.
(%dry)
7.2
±5.4
8.6
±3.6
7.3
±2.5
8.3
±3.3
9.3
±5.4
20.0
5.2
±3.5
3.6
±1.1
Fill"
Moist.
(%dry)
5.7
±3.1
5.6
±2.1
7.2
±2.9
7.4
±1.9
NA
NA
0
±0
NA
Fill
Depth
(cm)
35
±15
33
±16
28
±5
28
±5
NA
NA
NA
NA
House
Perm.*
(ach50)
5.2
±1.2
5.8
±1.2
NA
NA
NA
NA
5.6
±1.3
5.8
±1.2
Reported^
Nat, Vent.
(ach)
0.29
±0.07
0.31
±0.08
0.20
±0.07
0.18
±0.02
0.33
±0.10
0.27
±0.12
0.31
±0.13
0.17
±0.04
Slab**
Crk. Area
(cm2)
50.
±67.
92.
±200.
94
±104
330
±240
57
±130
32
±22
0.015
±0.005
0.014
±0.004
Soil
Density
(g/cm3)
1.60*
1.60*
1.60s
1.60e
1.59
±0.11
1.79
NA
1.60
±0.13
1.63
±0.09
"Moisture percentage, dry-weight basis.
^Infiltration air changes per hour at 50 Pa pressure, from blower-door test.
Tassive-condition air infiltration rate.
^Total area of observed slab cracks.
'Assumed typical soil densities, since none were reported,
NA = Not Available
-------
Table 4. Sub-slab and Indoor Radon Measurements in Study Houses (Nielson 96)
Statistical Summary
Mouse
ID
F-01
F-04
F-05
F-06
F-07
F-09
F-12
F-13
F-02
F-03
F-08
F-10
F-ll
F-14
1
2
3
4
5
7
9
10
11
12
JKMl
Radon
(pCi I'1)
5,510
5,180
19,900
3,050
2,690
14,300
5,700
5,990
1,480
2,630
1,310
11,500
2,760
2,510
1,680
2,940
1,190
911
2,900
921
1,300
1,060
10,700
6,980
indoor
Radon
(pCi L'1)
1.6
4.1
1.5
1.6
1.4
2.7
2.5
1.6
3.8
3.3
8.0
1.9
3.1
2.3
3.0
2.2
2.7
2.5
1.2
10.9
2.8
uutaoor
Radon
(pCiL-1)
0.4
1.3
0.1
0.5
0.3
0.6
0.7
0,6
0.3
0.3
1.3
0.4
1.3
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
SuDslat) •
Radon
(pCiL")
4,310
12,100
4,490
4,520
4,240
6,480
6,210
886
5,990
4,000
5,580
4,180
8,270
730
970
488
809
1,220
722
3,870
8,480
Soil
Statistic Radon
(pCiL'1)
G.M., 6,230
GSD 1.99
G.M., 2,720
GSD 2.17
G.M., 2,070
GSD 2.38
Indoor Outdoor
Radon (pCi Radon
I'1) (pCiL-1)
2.0 0.4
1.49 2.23
3.1 0.6
1.77 1.97
2.8 0.5
1.86 1.00
Subslab
Radon
(pCi I'1)
5,640
1.46
4,000
2.19
5,840
1.46
The Florida Standard for Passive Radon-Resistant New Residential Building Construction (DCA95) is a
performance based standard requiring the installation of passive construction features. It contains quantitative requirements
to ensure a standard quality of construction; e.g., requirements specifying slump of concrete, and the use of ASTM rated
sealants and vapor barriers. Figures 1 and 2 show examples of how the Florida standard addresses certain important radon-
resistant construction features (Shanker93).
The RAETRAD Model
The RAETRAD (Radon Emanation and Transport into Dwellings) model (Nielson94, Rogers96) is a public-
domain computer simulation model developed and refined within the FRRP. It has been used extensively in support of the
Florida standard development, especially in evaluations of (1) radon contributions of foundation soils and fill materials,(2)
advective and diffusive radon transport, (3) geographic distributions of radon potential in Florida, and (4) the development
of simplified models for the assessment of the radon resistance of building features. This paper describes the use of the
RAETRAD model to evaluate the indoor radon reduction potential of two distinct vapor membranes on the difiusive entry
of radon into a typical Florida standard house built over three distinct radon potential sites. Table 5 presents the scenarios
evaluated using the RAETRAD model.
-------
Table 5. Model Simulation Matrix
Scenario
1
2
3
4
5
6
7
8
9
Soil Parameters Site Parameters
House Parameters Soil Ra Content Vapor Barrier Diffusion
(see Table 6) (pCiL'1) Coefficient (mV)
Set to Default * 5.0 none
10.0 none
20.0 none
5.0
10.0
20.0
5.0
10.0
20.0
.00x10-"
.OOxlO'"
.00x10'"
.00x10'"
.00x10'"
.00x10'"
* See Table 6
MODELING SCENARIOS RESULTS
Introduction
The purpose of the RAETRAD evaluation presented below is to identify the significance of improvements in
moisture barrier radon diffusion resistances to the resultant indoor radon. The belief before this evaluation was that
technically feasible enhancements to the diffusive resistance of vapor barriers should produce cost effective reductions in
indoor radon, especially where (1) small reductions, though hard to come by reductions, in indoor radon are needed or (2)
radon source variability is such that more robust passive controls are a prudent addition to the Florida standard. For
example, the results of the "new house evaluation projects" identified exceptions to the adequacy of the Florida standard's
passive controls, on high radon potential sites, to always produce indoor radon concentrations below EPA's 4 pCiL"1 action
level (Tyson95, Hintenlang95, Najafi95, and Fowler%).
Baseline Conditions
Table 6 presents the baseline or reference house input parameters used in the RAETRAD model. These conditions
are common to all scenarios listed in Table 5. Tables 7 and 8 present the foundation and soil (1) physical characteristics
and (2) radiological characteristics input into the baseline (no barrier) and vapor barrier analysis runs. Vapor barrier
thicjcnesses of 6 mils (150 um) are used for all vapor barrier runs with the only parameter changing among runs being the
radial and vertical diffusion coefficients. The diffusion coefficient values used, though hypothetical, are representative of the
range of values shown in Table 1.
-------
Table 6, Home Parameter Value* Used in Model Runs
Dimensions: 28.4 x 54.3 ft. (8.6 x 16.5 m)
Area: 1542ftJ(143 ma)
Fill Thickness: 1 unit (0.9 ft.) (0.27 m)
Footing Depth: 3 units (2.9 ft.) (0.88 m)
Indoor Pressure: -2,4 Pa
Outdoor Pressure: 0 Pa
Outdoor Radon Cone.: 0 pCuV
Floor Openings: Eliplical Crack at Slab Edges, 1 cm width
Utility Penetrations, 2 at 13 ft. (3.9m) from edge
Table 7. Foundation and Soil Characteristic*
Materials: Sand, Concrete, Membranes
Layers: Soil, Floor, Footing
Parameters: Density, Porosity, Saturation Fraction, Particle Diameter
Table 8. Foundation and Soil Radiological Characteristics
Materials: Sand, Concrete, Membranes
Layers: Soil, Floor, Footing
Parameters: Radium Content, Emanation Fraction, Diffusion
Coefficient, Permeability Coefficient, Adsorption
Coefficient
Results
Table 9 presents the indoor radon concentrations predicted by RAETRAD for the selected soil radon potential and
radon barrier diffusion coefficient test conditions. Those are compared with the baseline no barrier case.
-------
Table 9. Comparison of Baseline (No Barrier) and Flexible Membrane
Barrier Effects on Indoor Radon Concentration
Indoor Radon Concentration (pCiL"')
for Selected Barrier Conditions
Soil Radon Potential:
Soil M6Ra Content (pCig'1)
5.0
10.0
20.0
No Barrier
17.4
34.8
69.5
Diffusion
1 x 10'"
0.121
0.219
0.414
Coefficient (mV)
1 x 10-"
0.073
0.077
0.085
Figure 3 presents the above results on a semilog plot to show the overall relationship of indoor radon concentrations
to building site radon potentials (soil radium content) for the no barrier (soil) and barrier (10'" and 10"") conditions. This
figure shows clearly the non-linear nature of the radon entry process with respect to diffusion limiting processes (comparing
the 10"" and 10"" plots) and the proportionality of indoor radon concentrations to source strength for advective and high
diffusion coefficient conditions (as shown by the no barrier and 10"" plot).
CONCLUSION
Placement of an integral impermeable flexible membrane (vapor barrier) under slab-on-grade construction can
produce significant (100 x) reductions in indoor radon concentration from the no barrier case.
In most cases, even for floating slab-on-grade construction, on moderately high radon potential (1 OpCig"1,226Ra) sites,
currently available and diffusion resistant membranes can keep indoor radon concentrations below 4 pCiL"1.
Enhanced radon diffiision limiting membranes (e.g., going from I x I0""tol x 10"" mV diffusion coefficients) may
become cost effective on high radon potential sites; i.e., sites greater than 20 pCig"1226Ra.
The placement of a completely intact vapor barrier is critical to limiting radon entry into new and existing structures
even at the well-balanced indoor/outdoor pressure differential condition (-2.4 Pa) used in this analysis.
Comparison of the performance of new house evaluation study results with RAETRAD model predictions indicates
the potential for enhanced radon entry limiting performance of vapor barriers, perhaps through enhanced placement
practices.
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Haines City, FL.
Mosley96 Mosley, R.B. "Description of a Method for Measuring the Diffiision Coefficient of Thin Films to 222Rn
Using a Total Alpha Detector." Prepared for Presentation at the 1996 AARST International Radon
Symposium, September 30- October 2, 1996. Haines City, FL.
Nielson95 Nielson, K.K., Holt, R.B., and Rogers, V.C. "Lumped-Parameter Model Analyses of Data from the 1992
New House Evaluation Project Florida Radon Research Program." EPA-600/R-95-090 (NTIS PB95-
243077), U.S. Environmental Protection Agency, Research Triangle Park, NC.July 1995.
Shanker93 Shanker, A. "Guidelines for Radon-Resistant Residential Construction in the State of Florida." Final
Report to the State of Florida, Department of Community Affairs. University of Florida. Gainesville, FL.
August 1993.
Rogcrs% Rogers, V,, Nielson, K.K., and Rogers, V.C. "RAETRAD Version 4.1 User Manual." RAE-G1R/33-2,
Rogers and Associates Engineering Corporation. Salt Lake City, UT. June 1996.
11
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Fig. 1 Monolithic Slab,
Vapor Barrier Installation
In monolithic slab construction, slab edges are thickened around the
perimeter to form a monolithic concrete beam. The soil cover membrane
should extend beyond the outer edge of the monolithic slab (see Figure 1).
Monolithic slab is recommended for radon resistant construction.
A. 4" (0,10m) thick concrete slab with
monolithic edge.
B. 6 mil (152 urn) s°«' cover membrane
continues beyond outside edge of slab.
Fig.2 Slab Poured into
Stem Wall Vapor Barrier
Installation
When a slab is poured into a stem wall, concrete header blocks (see
Figure 2, part A) serve as forms for the concrete slab. The soil cover
membrane should extend at least 1" (0.025m) into the header block. The
slab extends to the inside surface of header blocks. The cores of header
blocks should be completely filled with concrete.
A. Concrete header blocks.
B. Fill header block cores along perimeter to
form 8" (0.20m) thick cap.
C. 4" (0.10m) nominal concrete slab.
D. 6 mil (152|jm) vapor barrier at least 1"
(0.025m) into the header block.
E. Compacted fill soil.
F. Undisturbed soil.
G. Grade.
12
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100
Fig. 3 RAETRAD Model Results
soil
10 —
o
a.
c
o
•O
<0
o:
i_
O
O
•o
1 —
1E-11
20pCi/L
4pCi/L
1
0.1 +-
1E-13-
0.01
8
10 12
Soil Radium (pCi/L
14
16
18
20
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NRMRL-RTP-P-153
TECHNICAL REPORT DATA
(Please read Instructions on the reverse before complei
1. REPORT NO.
EPA/600/A-97/013
4. TITLE AND SUBTITLE
An Evaluation of Indoor Radon Reductions Possible
with the Use of Diffusion-resistant Flexible Construc-
tion Membranes
5. REPORT DATE
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
D. C. Sanchez (EPA) and R, Minga and C. Sloan
(Eastman)
8. PERFORMING ORGANIZATION REPORT NO.
S. PERFORMING ORGANIZATION NAME AND ADDRESS
Eastman Chemical Company
Kingsport, Tennessee 37662
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
EPA CRADA 0122-95
12. SPONSORING AGENCY NAME AND ADDRESS
EPA, Office of Research and Development
Air Pollution Prevention and Control Division
Research Triangle Park, NC 27711
13. TYPE OF REPORT AND PERIOD COVERED
Published paper; 7-8/96
14. SPONSORING AGENCY CODE
EPA/600/13
is. SUPPLEMENTARY NOTES APpCD project officer is David C. Sanchez, Mail Drop 54, 919/
541-2979. Presented at ARRST Int. Radon Symp., 9/30-10/2/96, Haines City, FL.
16. ABSTRACT
paper gives results of a modeling assessment of the indoor radon re-
ductions possible through the use of improved radon resistant membranes. The analy-
sis focuses on quantifying the impacts on indoor radon concentrations of using impro-
ved radon diffusion- resistant membranes for a typical experimentally determined
range of membrane radon diffusion coefficients. The evaluation considers the applica-
tion of radon resistant membranes to slab-on-grade construction typical of Florida
and source strengths and site conditions typical of Florida. It discusses guidance for
the extrapolation of findings to non-Florida construction and site conditions. The im-
portance of foundation construction design and materials used is recognized as criti-
cally important to the radon resistance of buildings.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTlFIERS/OPEN ENDED TERMS
cos AT I Field/Group
Pollution Foundations
rladon
Membranes
Piffusion
Slab-on-Ground Construction
Blabs
Pollution Control
Stationary Sources
Indoor Air Quality
Diffusion Resistance
13 B
07B
11G.06P.06C
14G
13 M
13 C
18. DISTRIBUTION STATEMENT
Release to Public
19. SECURITY CLASS (ThisReport)
Unclassified
21. NO. OF PAGES
20. SECURITY CLASS (This page)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
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