Civil Engineering Reference
In-Depth Information
Table 5 Radom concentration (Bq/m
3
) due to radon exhalation from floor material according to
the ventilation rate (Chen et al.
2010
)
Radon exhalation rate (Bq/m
2
d)
Air changes per hour (ACH)
3
1
0.3
0.15
0
5
0.03
0.09
0.3
0.6
5
10
0.06
0.2
0.6
1.2
25
50
0.3
0.9
3.0
5.9
123
100
0.6
1.8
6.0
12
246
300
1.8
5.5
18
35
737
C
¼
E
A
ð
k
0
þ
k
v
Þ
V
where E is the radon exhalation rate (Bq/m
2
/d) of the material installed, A the area
(m
2
) of the material exhaling radon, V the air volume (m
3
) of the room, i.e., the
room volume minus the volume occupied by room contents, k
0
the radon decay
constant (0.181/d), and k
v
the air removal rate due to ventilation.
Anjos et al. (
2011
) analyzed the radon exhalation rate of several Brazilian
granites, concluding that 91 % can be used inside homes without any concern in
respect to health issues. They based their conclusions on the fact that 91 % of the
granites were responsible for an indoor concentration below 300 Bq/m
3
for low
ventilation conditions and 100 Bq/m
3
for good ventilation conditions. These
conclusions seem to forget that recent epidemiological findings demonstrate a lung
cancer risk from exposure to indoor radon at levels of the order of 100 Bq/m
3
.
The radon exhalation rate is influenced, not only by the content of radionuc-
lides, but also by the physical properties of the granites (Tuccimei et al.
2006
;
Shweikani and Raja
2009
; Ujic et al.
2010
).
Marochi et al. (
2011
) mentioned that the radon exhalation rate is influenced by
the granite porosity and that higher porosity is associated with a higher exhalation
rate. Hassan et al. (
2011
) reported that specimens in a dry condition show an
exhalation rate 2-5 times lower when compared to specimens with just 1 % of
absorbed water.
Allen et al. (
2010
) studied the exhalation rate of granite countertops reporting a
higher dispersion. These authors mention that the use of small granite specimens
does not allow for extrapolations concerning the exhalation rate of the countertops.
Other studies (Sahoo et al.
2011
) criticize previous estimations on radon
exhalation rate made on construction material specimens, because they under
evaluate, by as much as seven times, the exhalation rate of the material when used
in a wall. Results are influenced by the size of the specimens and also by the wall
thickness.
These authors present a model to help predict the wall exhalation rate.
According to Sahoo et al., the solution of 1D radon diffusion equation is com-
monly used to determine radon flux from building surfaces (such as walls and
ceiling). However, one limitation in the 1D solution is the requirement of several
