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Indoor and Built Environment
http://ibe.sagepub.com/content/21/3/452
The online version of this article can be found at:
DOI: 10.1177/1420326X11410583
2012 21: 452 originally published online 28 June 2011Indoor and Built Environment
S.U. Rahman, F. Malik, Matiullah, T. Nasir and J. Anwar
Monitoring of Indoor Radon Levels Around an Oil Refinery Using CR-39-Based Radon Detectors
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Case Report
Indoor and B
uil
tuilt
Environment
Indoor Built Environ 2012;21;3:452–457 Accepted: April 19, 2011
Monitoring of Indoor Radon
Levels Around an Oil
Refinery Using CR-39-Based
Radon Detectors
S.U. Rahman
a,b
F. Malik
c
Matiullah
c
T. Nasir
d
J. Anwar
b
a
Department of Medical Physics, Nuclear Medicine, Oncology and Radiotherapy Institute (NORI),
Islamabad, Pakistan
b
Department of Physics, COMSATS Institute of Information Technology (CIIT), Islamabad, Pakistan
c
Physics Division, PINSTECH, P.O. Nilore, Islamabad, Pakistan
d
Department of Physics, Gomal University, D.I. Khan, Pakistan
Key Words
Internal dose ENatural radiation sources EEffective
dose ECR-39-based radon detector
Abstract
Contribution of radon and its decay products towards
the total effective dose has been reported to be more
than 50% and is a second leading cause of the lung
cancer after cigarette smoking. It is an established fact
that besides soil and rocks, naturally occurring radio
nuclides are also associated with the petroleum
extracted from the sedimentary deposits. Therefore,
radon measurement around oil refineries is desirable.
In this regard, an indoor radon measurement study was
carried out in 40 dwellings which were situated in the
vicinity of an oil refinery in the Rawalpindi district using
CR-39-based radon detectors. For comparison, indoor
radon levels were also measured in 40 dwellings
situated at a greater distance (42 km) from the refinery.
The maximum measured indoor radon concentration
was found to be 190 6Bqm
3
whilst the minimum
recorded concentration was 12 7Bqm
3
. The mean
radon concentration in the dwellings surveyed was
57 29 Bqm
3
. No significant difference was observed
in the average indoor radon levels in the dwellings
situated near the oil refinery premises when compared
with those further away. From the measured radon
concentrations, an annual effective dose was calculated
to be 0.9 0.1 mSv which is below the ICRP recom-
mended value.
Introduction
Radon (
222
Rn) is a radioactive noble gas and is
generated from the decay of
238
U. It is a colourless,
odourless, electrically uncharged gas but hazardous. It
emits alpha radiation and decays with a half-life of 3.824
days. Radon is present in trace amounts almost every-
where in the earth’s crust. Its concentration in the
atmosphere varies, depending on the place, time, height
above the ground and meteorological conditions. Radon
production rate from the soil depends upon the geological
ßThe Author(s), 2011. Reprints and permissions:
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DOI: 10.1177/1420326X11410583
Accessible online at ibe.sagepub.com
Saeed-ur-Rahman,
Department of Medical Physics, Nuclear Medicine, Oncology and Radiotherapy
Institute (NORI), Islamabad, Pakistan. Tel. þ92 3008309821, Fax þ92 51 9260616,
E-Mail snori66@yahoo.com
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characteristics of the soil itself and its underlying
geological strata. A fraction of radon emanated from the
soil (and sometimes also from water, in which it may be
dissolved) can find its way into the buildings through
cracks in the foundations. After entering into the indoor
atmosphere, it accumulates in poorly ventilated rooms to
levels which may pose a significant health risk to the
occupants [1–9]. Rates of radon emission from the soil
may vary markedly over time, even for a single location. In
addition to the daily variations, radon levels in buildings
are also season-dependent. Some of the influential factors
on indoor radon include content and porosity of the soil,
building structure, whether the house has a basement,
insulation and heating system of the house and ventilation
habits [10–12].
As radon is a human carcinogen, extensive data are
available extending into the range of general population
exposure [13–16]. Risk projections imply that radon is the
second leading cause of lung cancer after smoking.
Inhalation of radon decay products has been linked to
an increased risk of lung cancer. As mentioned above, over
85% of human total annual dose, averaged over the world
population, stem from natural sources, with about half of
it coming from radon decay products [17–23]. A survey of
120 schools situated in four districts of the Punjab
Province in Pakistan has been reported [24].
This article reports the measurements of indoor radon
levels in 80 selected houses in the vicinity of and at some
distance remote from an oil refinery located in the district
of Rawalpindi. The dwellings selected, which were within a
radius of 1 km from the main installations of the refinery,
were considered to be in the vicinity of oil refinery.
Dwellings located at a radius of 2 km or more from the
main refinery installations were considered as being
remote for comparison purposes. An increase in the
indoor radon level in the vicinity of the refinery was
expected due to the fact that the petroleum deposits would
usually occur in the areas consisting of sedimentary,
igneous and metamorphic rocks. The sedimentary and
igneous rocks would contain
238
U in varying quantities
and therefore act as sources of
222
Rn. Hence, it was
expected that crude oil will contain considerable amount
of the dissolved radon which in turn will result in higher
radon levels in the vicinity of the refinery.
Type of Houses
The types of houses surveyed were approximately
similar in both locations. Most of the houses in the
surveyed area were built from baked bricks, sand and
concrete with roofs made of concrete. These included both
single- and double-storey houses; however, most were
double storied. Each house contained at least two rooms
and one kitchen. CR-39-based radon detectors were
installed in bedroom and living room of each house. In
the case of double-storey houses, dosimeters were installed
at the ground floor. All the houses surveyed were detached
and semi-detached houses. The sizes of the rooms were
approximately 3.7 3.7 3.5 m
3
with one or two windows
and a door. Usually, the windows are not operational and
remained closed especially in living rooms with no
additional exhausting fans, which resulted in poor
ventilation conditions.
Climate
Rawalpindi is located at a latitude of 348200N and a
longitude of 738060E and at an altitude of 507 m above the
sea level. Map of the studied area is shown in Figure 1.
Weather of the Rawalpindi is highly variable due to its
location. The average annual rainfall is 990 mm, most of
which falls in the summer monsoon season. However,
frontal cloud bands also bring quite significant rainfall in
the winter. The temperature begins to rise in the area from
early April and reaches around 478C in June. The period
from December to February is cold and temperature drops
to a minimum of 48C.Table 1 gives the temperature and
rainfall monthly averages recorded [25].
Materials and Methods
In order to carry out indoor radon measurement in
dwellings in the vicinity and remote from the oil refinery,
CR-39-based radon detectors were used. In this regard,
introductory brochures were distributed amongst the
inhabitants wherein instructions about installation and
safety of the radon detectors were explained. Occupancy
factor plays an important role in the dose calculation.
Therefore, information regarding the indoor occupancy
was obtained by interviewing the dwellers during the
installation/collection of the dosimeters. Based on these
interviews, an average occupancy factor 0.5 was estimated.
Large sheets of CR-39 having 500 mm thicknesses,
supplied by the Page Mouldings, Ltd., UK were cut into
small pieces of size 1.5 1.5 cm
2
. These small-sized CR-39
detectors were fixed by double-sided solo tape at the
bottom of the dosimeters of National Radiological
Protection Board (NRPB, UK), now called the
Radiation Protection Division of the Health Protection
Agency for radon measurements. From these detectors,
some samples were kept in refrigerator for background
Radon Levels Around an Oil Refinery Indoor Built Environ 2012;21:452–457 453
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purpose. Radon detectors were then installed in dwellings
at various locations in the vicinity of the oil refinery. All
the detectors were installed at head height and exposed for
a period of 6 months. After exposure, the detectors were
removed and subjected to a chemical etching process in
25% NaOH solution at 808C for 16 h. The tracks
produced in CR-39 were counted under an optical
microscope. The measured track densities were related to
the indoor radon concentrations (Bqm
3
) using calibra-
tion factor 2.7 trackscm
2
h
1
kBqm
3
[6,26,27]. The
minimum detection limit was 2rof the background
divided by the minimum acceptable sensitivity of the
CR-39 detector. In this study, the average minimum
detection limit was found to be 4 Bqm
3
.
The NRPB dosimeters were also calibrated and our
values were within 16% of the above-mentioned factor. In
this regard, ore with known uranium content was locally
obtained. The secular equilibrium was confirmed by
determining
226
Ra content of the ore samples using a
coaxial HPGe detector. The dried ore was placed in three
polyethylene terephthalate containers each having a
volume 5.4 10
3
cm
3
. The NRPB radon detectors were
then placed in the above-mentioned ore-containing con-
tainers at a distance of 25 cm from the ore and the
containers were then hermetically sealed. The detectors
were exposed to radon for 3 weeks. After exposure, the
CR-39 detectors were chemically etched and counted
under an optical microscope. The observed track density
was divided by the radon concentration, as shown in
Equation (1), to provide a calibration factor as follows.
CF ¼Tracks cm2h1
CRn kBq m3
ð1Þ
where his the effective exposure time in hours which was
obtained from Equation (2) of the following relation:
Teffective ¼t1et
ð2Þ
where ‘‘’’ is the mean life of radon, i.e., 5.5 days, ‘‘t’’ the
total exposure length (days) and ‘‘’’ the
222
Rn decay
Fig. 1. Map showing the studied area of the district Rawalpindi.
Table 1. Monthly recorded average temperature and precipitation
in the district of Rawalpindi
Month Temperature Average
precipitation
(mm)
Average
minimum
(8C)
Average
maximum
(8C)
January 3 18 56
February 5 19 74
March 10 24 90
April 15 30 62
May 20 35 39
June 24 39 62
July 24 35 267
August 24 33 310
September 21 34 98
454 Indoor Built Environ 2012;21:452–457 Rahman et al.
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constant. The radon concentration ‘‘C
Rn
’’ was obtained
using Equation (3) of the following relation.
CRn kBq m3
¼
F0A1eA=VþðÞt
AþVð3Þ
where C
Rn
is the
222
Rn concentration in void space of the
container (Bqm
3
), F
0
the exhalation rate (Bqm
2
s
1
), a
the correction term for back diffusion and is equal to x
(ms
1
), xthe thickness of the layer of ore sample in
container (m), Athe surface area of the sample (m
2
), Vthe
volume of the air space of the container (m
3
), the
222
Rn
decay constant (s
1
), tthe exposure time (s). The radon
exhalation rate ‘‘F
0
’’ in Bqm
2
s
1
is obtained from
Equation (4) showing the following relation:
F0Bq m2s1
¼CRa Exð4Þ
where C
Ra
is the specific activity of
226
Ra (i.e. 1 ppm of
238
U¼12.3 Bqkg
1 226
Ra), qthe bulk density of the ore
sample (kgm
3
), Ethe emanation coefficient of the
sample and xthe thickness of the ore sample (m).
Results and Discussion
As mentioned earlier, indoor radon activity concentra-
tions have been measured at 160 locations (i.e. bedrooms
and living rooms) in 80 dwellings in the vicinity of and at a
distance remote from the oil refinery in the Rawalpindi
district. The results obtained are listed in Table 2.
Mean, minimum and maximum values are given in this
table. The radon levels in the bedrooms are seen to vary
from 12 7 to 161 11 Bqm
3
with an average activity
value of 51 24 Bqm
3
in the refinery environment and
remote from the oil refinery premises. The indoor radon
levels in the living rooms varied from 16 5to
190 6Bqm
3
with an average value of 62 34 Bqm
3
.
There is no significant difference in the radon concentra-
tion when comparing houses in the vicinity of the refinery
with those at a distance further away. The overall mean
average value was 57 29 Bqm
3
. The values of indoor
radon concentration for each of the houses in the vicinity
of and at a distance remote from the oil refinery are given
in Table 3.
The values obtained in these investigations are in good
agreement with the values reported in the earlier study
[22–24]. The average radon concentration in living rooms
and bedrooms of the studied area is above the world
average 40 Bqm
3
. Different reference levels have been
recommended by different countries for indoor
222
Rn
concentrations. ICRP recommends a maximum limit of
600 Bqm
3
[1], whereas the action level recommended by
US-EPA is 150 Bqm
3
[28]. In this study, the indoor
radon levels are within the acceptable limits of the ICRP
limits. Indoor radon levels of a few dwellings are above the
recommended limits of the US-EPA. The highest radon
levels were observed in living rooms. This may be due to
the fact that most of the time living rooms are closed and
only used when some relatives or family friends visit the
dwellers. This results in poor ventilations in the living
rooms and therefore radon concentrations in living rooms
are higher.
Figures 2 and 3 comprise frequency distributions of
indoor radon concentrations in surveyed bedrooms and
living rooms, respectively. As may be observed in Figure 2,
most bedrooms (i.e. 60% and 65%) have indoor radon
levels ranging from 0 to 50 Bqm
3
in either location with
respect to distance from the oil refinery, whereas 27.5%,
10%, 2.5%, 22.5%, 10% and 2.5% bedrooms have indoor
radon levels in the ranges 51–100, 101–150 and 151–
200 Bqm
3
in the vicinity of and at a distance away from
the oil refinery, respectively. In the living rooms (Figure 3),
measured indoor radon levels of the ranges 0–50, 51–100,
101–151 and 151–200 Bq m
3
have been observed in 55%,
27.5%, 10%, 7.5% and 52.5%, 30%, 12.5% and 5% of
the houses situated in the vicinity of and at a distance
remote from the oil refinery premises, respectively.
Table 2. Indoor radon concentrations in bedrooms and living rooms in the vicinity of and at a distance remote from the oil refinery
Location Type of
rooms
Dosimeters
installed
Radon concentration (Bqm
3
) Annual effective
dose (mSvy
1
Min Max A.M
Vicinity of the oil refinery Bedrooms 40 12 7 159 75323 0.8 0.4
Living rooms 40 16 5 190 66135 1.0 0.6
Mean 14 6 174 65729 0.9 0.5
Remote from the refinery Bedrooms 40 15 6 161 11 49 25 0.8 0.4
Living rooms 40 17 5 176 76232 1.0 0.5
Mean 16 5 168 95628 0.9 0.4
Radon Levels Around an Oil Refinery Indoor Built Environ 2012;21:452–457 455
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Dose Estimation
From the measured indoor radon concentration,
expected annual effective doses received by the residents
of the area surveyed have been calculated using Equation
(5), the UNSCEAR model [20]
E¼CFHTDð5Þ
where Cis the
222
Rn concentration (Bqm
3
), Fthe
equilibrium factor (0.4), Hthe occupancy factor (0.5 was
estimated for the studied dwellers), Tthe hours in a year
(8760 hy
1
) and Dthe dose conversion factor
(9.0 10
6
mSv Bqm
3
h
1
). Substituting the measured
average radon concentration values in Equation (5), the
annual effective doses due to the indoor radon were
estimated to be 0.8 0.4 and 1.0 0.5 mSv for bedrooms
and living rooms, respectively. The mean annual effective
dose was 0.9 0.1 mSv for the inhabitants living in the
studied area.
Conclusion
To conclude, indoor radon levels have been measured
in houses in the vicinity of and at a distance remote from
an oil refinery situated in the district of Rawalpindi. No
significant difference was observed in the indoor radon
levels in dwellings from either location. In this study,
higher indoor radon levels have been observed in living
rooms as compared to the bedrooms. From the measured
indoor radon concentrations, an annual effective dose
was calculated using UNSCEAR model with occupancy
factor 0.5 for the studied houses. The doses expected to
be received by the inhabitants of the studied area were
found to be less than the ICRP recommended values
3–10 mSvy
1
.
Table 3. Indoor radon concentrations in the houses surveyed in the
vicinity of and at a distance remote from the oil refinery
House no. Indoor radon
concentration (Bqm
3
)
Vicinity of
the refinery
Remote from
the refinery
H1 59 16 27 5
H2 32 8618
H3 23 11 68 16
H4 67 9368
H5 48 7387
H6 29 8257
H7 94 10 76 11
H8 44 12 81 13
H9 53 7276
H10 22 5485
H11 32 79319
H12 16 6399
H13 86 11 69 8
H14 21 9264
H15 45 13 88 12
H16 33 4297
H17 173 17 59 10
H18 25 61813
H19 61 15 31 7
H20 104 19 57 10
H21 30 7285
H22 27 11 137 14
H23 19 5 107 12
H24 64 8309
H25 154 16 98 13
H26 36 11 45 14
H27 134 15 28 3
H28 126 14 52 9
H29 27 84711
H30 81 10 146 13
H31 40 11 24 9
H32 68 93412
H33 41 5308
H34 14 7 118 12
H35 48 13 22 5
H36 109 17 42 6
H37 39 8216
H38 54 12 19 3
H39 22 5 151 12
H40 74 93711
0
2
4
6
8
10
12
14
0-10
11--20
21-30
31-40
41-50
51-60
61-70
71-80
81-90
91-100
101-110
111-120
121-130
131-140
141-150
151-160
Radon concentration (Bq m-3)
Number of observations
Bedrooms around an oil
refinery
Bedrooms away from an oil
refinery
Fig. 2. Frequency distribution of radon in bedrooms.
0
2
4
6
8
10
12
0-10
11--20
21-30
31-40
41-50
51-60
61-70
71-80
81-90
91-100
101-110
111-120
121-130
131-140
141-150
151-160
161-170
171-180
181-190
Radon concentration (Bq m-3)
Number of
observations
Living rooms around an oil
refinery
Living rooms away from
an oil refinery
Fig. 3. Frequency distribution of radon in living rooms.
456 Indoor Built Environ 2012;21:452–457 Rahman et al.
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