United States
Environmental Protection
Agency
National Kisk Management
Research Laboratory
Cincinnati, OH 45268
Research and Development
EPA/600/SR-96/022
March 1996
& EPA Project Summary
Technical Basis for a Candidate
Building Materials Radium
Standard
Vern C. Rogers and Kirk K. Nielson
The Florida Radon Research Program
(FRRP), sponsored by the Environmen-
tal Protection Agency and the Florida
Department of Community Affairs, is
developing the technical basis for a
radon-control construction standard.
Results of the research conducted un-
der the FRRP are presented in several
technical reports. This report is a sum-
mary of the technical basis for a candi-
date building materials radium stan-
dard. The report contains the standard
and a summary of the technical basis
for the standard.
This Project Summary was developed
by the National Risk Management Re-
search Laboratory's Air Pollution Pre-
vention and Control Division, Research
Triangle Park, NC, to announce key
findings of the research project that is
fully documented in a separate report
of the same title (see Project Report
ordering information at back).
Introduction
Residential building materials, principally
concrete, can contain small amounts of
radium, which generates radon gas that
can migrate into residences. Furthermore,
radon daughters trapped in concrete emit
gamma radiation that can cause expo-
sures to building occupants. This portion
of the standard defines acceptable limits
for the concentration of radium in building
materials.
Candidate Building Materials
Radium Standard
The candidate building materials radium
standard is:
No material used in concrete for the
construction of habitable structures shall
have a total radium concentration that ex-
ceeds 10pCi/g, as measured in accor-
dance with procedures contained in "Stan-
dard Measurement Protocols, Florida Ra-
don Research Program." The radium con-
centration in concrete used in the con-
struction of habitable structures shall not
have a total radium concentration that ex-
ceeds 5 pCi/g.
Radiation exposures from building ma-
terials to people can occur either from
indoor radon or from external gamma ra-
diation. Both the concentration of indoor
radon and the level of gamma radiation
from the building materials depend prima-
rily on the total radium concentration in
the materials. Thus, limiting the radium
concentration in the building material lim-
its the amount of potential exposure to
building occupants from both indoor ra-
don and gamma radiation. For typical con-
crete thicknesses (tens of centimeters),
the gamma radiation exposures yield about
the same radium concentration limits in
building materials as do exposures to in-
door radon from the materials.
Technical Analysis Supporting
the Candidate Standard
The technical analysis supporting the
building materials standard consists three
steps:
1. Determine building material perfor-
mance objectives for potential radon
and gamma exposures.
2. Calculate radium limit for indoor ra-
don exposures.
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3. Calculate radium limit for external
gamma radiation exposures.
Performance objectives were selected
according to their consistency with other
Florida Radon Research Programs. Spe-
cifically, the performance objectives are a
selected fraction of the U.S. Environmen-
tal Protection Agency's (EPA) indoor ra-
don (as radon-222) concentration guide-
line of 4 pCi/L and the EPA's external
gamma radiation criterion of 20 uR/hr for
cleanup of off-pile lands associated with
uranium milling.
Indoor radon and gamma exposures to
occupants of residences can come from
many sources in addition to the building
materials. Soils under building structures
constitute the major source. Accordingly,
a reasonably conservative value of 25%
has been selected as the fraction of the
radon guidance and gamma radiation cri-
terion attributed to building materials. Thus,
the building material performance objec-
tives are:
1. Indoor radon-222 concentration limit -
1 pCi/L
2. External gamma radiation limit - 5 uR/
hr.
The calculations of indoor radon
concentration from a concrete slab
use an established procedure and
equation. Rearranging the
equation gives
F
Ra=-
tanh(,/x75xc)
where:
Ra = radium-226 concentration limit in
the concrete (pCi/g)
F = radon flux (pCi/cm2 s)
p = concrete density (g/cm3)
E = radon emanation coefficient (unit-
less)
X = radon decay constant (2.06x10"6/s)
D = radon diffusion coefficient of con-
crete (cm2/s)
Xc = thickness of concrete slab (cm).
A simple approximation for F is available:
F = ChXV(3.6x106)
(2)
where:
C
h
= indoor radon concentration
(pCi/L)
= average indoor height of
building (cm)
Xv = dwelling ventilation rate (air
changes/hour)
3.6x106 = units conversion (cm3 s/L hr)
Combining Equations (1) and (2) gives:
Ra=-
Xcj
(3)
The following values were used in the
calculations:
C = 1 pCi/L (performance objective)
h = 240 cm
Xv = 0.25 air changes/hour
p =2.1 g/cm3
E = 0.11
Xc = 10cm
D = 2x10-3cm2/s
Substituting these values into Equation
(3) gives a radium limit of 4 pCi/g in the
concrete.
This is rounded to 5 pCi/g in the Stan-
dard.
The radium concentration limit in con-
crete readily converts to radium concen-
tration limits in concrete constituents. Since
aggregate comprises about 49% of Florida
residential concrete, the concrete aggre-
gate radium limit can be estimated as
4 pCi/g/0.49, or 8 pCi/g in the aggregate.
A similar limit for sand is 10 pCi/g.
Exposures from gamma-emitting radio-
nuclides in the concrete were estimated
by a slab with the same characteristics as
given in the full report. A 6x6-m area was
assigned to the slab, and the gamma-
radiation exposures were calculated with
the MICROSHIELD computer code.
The MICROSHIELD calculations gave
a value of 0.95 uR/hr per pCi/g of total
radium in the concrete. Thus, a radium
limit of about 5 pCi/g for the concrete gives
a potential exposure of 5 uR/hr. The cor-
responding total radium limit in the aggre-
gate is 10 pCi/g, and that for the sand is
approximately 13 pCi/g.
Conclusions from Technical
Analysis
Potential exposures from building mate-
rials to occupants of dwellings occur from
external gamma radiation and from indoor
radon. The extent of these potential expo-
sures is mainly determined by the radium
concentration in the materials. Both in-
door radon exposure limits and external
gamma exposure limits yield a 5 pCi/g
radium concentration limit in concrete and
a 10pCi/g radium limit in the aggregate
for the concrete.
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V. Rogers and K. Me/son are with Rogers and Associates Engineering Corp., Salt
Lake City, UT 84110.
David C. Sanchez is the EPA Project Officer (see below).
The complete report, entitled "Technical Basis for a Candidate Building Materials
Radium Standard," (Order No. PB96-157565; Cost: $17.50, subject to change)
will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Air Pollution Prevention and Control Division
National Risk Management Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
United States
Environmental Protection Agency
National Risk Management Research Laboratory (G-72)
Cincinnati, OH 45268
Official Business
Penalty for Private Use $300
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POSTAGE & FEES PAID
EPA
PERMIT No. G-35
EPA/600/SR-96/022
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