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Measurement of radon concentration for assessment of the radiological hazard in the
Chakwal coalmines of the Salt Range, Pakistan
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IOP PUBLISHING JOURNAL OF RADIOLOGICAL PROTECTION
J. Radiol. Prot. 31 (2011) 353–367 doi:10.1088/0952-4746/31/3/004
Measurement of radon concentration for assessment of
the radiological hazard in the Chakwal coalmines of
the Salt Range, Pakistan
Arif Mahmood1
and M Tufail2
1 Department of Physics, University of the Punjab, Lahore, Pakistan
2 Pakistan Institute of Engineering and Applied Sciences, Nilore 45650, Islamabad, Pakistan
E-mail: mtufail@pieas.edu.pk and dr92tufail@yahoo.com
Received 1 February 2011, in final form 17 July 2011, accepted for publication
27 July 2011
Published 24 August 2011
Online at stacks.iop.org/JRP/31/353
Abstract
Radon and its progeny are prevalent everywhere on the lithosphere especially
in the mining environment. Coal exists in the Salt Range that passes through
Pakistan. The aim of the present study was to measure radon concentration
and assess the associated radiological hazard in the coalmines developed in
that portion of the Salt Range which passes through the district of Chakwal
in Pakistan. Among the various coalmines in the coalfield, five were selected
for radon survey. A passive integrated technique consisting of SSNTDs (solid
state nuclear track detectors) was employed for the measurement of radon
concentration in these coalmines. Box type dosimeters containing CN-85
detectors were placed for three months at six locations in every selected
coalmine. After removing the dosimeters, the CN-85 detectors were etched
in alkaline solution to enlarge the alpha tracks in the detectors and counted
under an optical microscope. The track densities were converted to radon
concentration. The average concentration of radon in the coalmines varied in
the range 50–114 Bq m−3
. Radon exhalation rates from the samples of coal
and shale collected from the coalmines were determined to be respectively
934 (830–1010) and 1302 (1020–1580) mBq m−2
h−1
. The radiation dose and
corresponding health risk for the mine workers were also estimated.
1. Introduction
The discovery of a high incidence of lung cancer among the people working in the uranium
mines of Schneeberg in Germany and Joachimsthal in Czechoslovakia has diverted much more
attention to the measurement of radon in non-uranium mines and caves and indoors (Durrani
and llic 1997, Bodansky et al 1987). Radon (222
Rn) is found all over the world in almost all
0952-4746/11/030353+15$33.00 © 2011 IOP Publishing Ltd Printed in the UK

354 A Mahmood and M Tufail
environments. It comes from the natural decay of uranium (238
U) in soil, rock and water and
gets into the air (Hopeke 1987). Radon moves from its sources in the Earth’s crust through
cracks, voids and fractures (Nazaroff and Nero 1988). It is trapped in confined places and
attains equilibrium between its build-up and decay. People working in enclosed environments
and in underground mines are inevitably exposed to radon and its decay products (Lubin et al
1994). It is very evident that prolonged exposure to the alpha emitting decay products of
radon increases the risk of lung cancer among underground miners (NRC 1988, 1999). Due to
the increasing evidence of the carcinogenic potential of inhaled radon, occupational standards
for radon progeny concentrations in mines have been implemented in many countries of the
world. The International Commission on Radiological Protection (ICRP) in its publication 65
recommended the range of 500–1500 Bq m−3
as the action level for radon in workplaces (ICRP
1993).
Coal is one of the major sources of energy production in the world (UNSCEAR 1988). It
is usually extracted from underground mines. Radon accumulates in coalmines through cracks,
sumps and drains in the surrounding rocks (Hopeke 1987, Nazaroff and Nero 1988, Lubin et al
1994). The workers at coalmines are exposed not only to radon and its progeny but also to dust
and coal gases (Qureshi et al 2000). Members of the public may be affected by radon present
in the exhaust air of coalmines (UNSCEAR 1988).
The lung cancer risk varies directly with the alpha dose received by lung tissues from
inhalation of radon and its decay products (NRC 2006). The concept of effective dose was
launched by the ICRP (1991) in place of effective dose equivalent. This quantity makes an
allowance for differences in radio-sensitivities of various organs or tissues irradiated. The
worldwide average effective dose to the general public from natural airborne alpha particles
from radon and its decay products is 1.26 mSv y−1
, i.e. 52% of the total dose from all sources
(UNSCEAR 2000). The large share of this dose is due to the damage produced to human tissues
by alpha particles (NRC 2006).
Coal plays a significant role for energy production in Pakistan and is mined from various
coalfields present in different areas of Pakistan (Shah 1977, Ahmad 1969). A little information
is available in the literature about the concentration of radon in the coalmines of Pakistan (Tufail
et al 1998, Qureshi et al 2000, Mahmood et al 2000). The purpose of this study was to
determine the radon concentration level in the coalmines of the Salt Range in the district of
Chakwal in Pakistan, and to assess the radiological hazard for the mine workers. To achieve
these goals, the radon concentration was measured in the coalmines with CN-85 etched track
detectors placed in box type dosimeters. Annual effective dose and excess lifetime cancer risk
were calculated from the exposure of the mine workers to radon daughters in the coalmines
under study.
2. Materials and methods
2.1. The coalfield under study
The major coalfields of Pakistan lie in the Hyderabad, Quetta, Kalat, Sargodha and Rawalpindi
divisions (Ahmad 1969). We are concerned with the coalfield of the district of Chakwal in the
Rawalpindi division of Pakistan. The coalfield is situated in the Salt Range passing through
Pakistan. The city of Chakwal is located in the foothills of the Salt Range and lies at the
southern slope of the Potohar Plateau. The atmosphere of the district of Chakwal is arid
and the terrain is mainly hilly, covered with scrub forest in the southwest, and levelled plains
interspaced with dry rocky patches in the north and northeast (www.wikipedia.org). The soil of
the levelled plains and the climate are not very suitable for cultivation; therefore coal mining is

Radon in the Chakwal coalmines of Pakistan 355
Figure 1. The location of Chakwal city (shown by ) along the Salt Range on a portion of the
global map.
one of the major professions of the people of the district. The location of the area under study
is shown on a portion of the global map presented in figure 1.
The Salt Range is intersected by number of faults, gorges and erosion valleys forming
blocks that have necessitated the opening of numerous small outcrop workings. Most of the
coalmines in the area have commenced from outcrops and their production is restricted to
shallow depths. The coalfields of the Salt Range are found within the Patala Shale formation of
the early Eocene age (Shah 1977, Ahmad 1969). The coal seam ranges in thickness from a few
centimetres to about 2 m and is characterised by lateral variation in thickness and composition.
It is difficult to predict how far the seam of workable thickness extends (Ahmad 1969).
The coalfields of the Salt Range passing through the Punjab province of Pakistan are the
property of the province. The assets of coal in the province are regulated by the Punjab Mines
and Mineral Department, Government of the Punjab, Pakistan. The coalmines are allotted on
lease to the contractors who employ mine workers to extract coal from the mines. Among the
various coalmines, only five were selected for the purpose of radon concentration measurements
in coalmines of the Salt Range, which lie in the district of Chakwal in Pakistan. The selection
of the mines was based on their length and workability. Relatively longer mines expectedly
having higher radon concentrations were selected. All the selected mines were in working
condition and naturally ventilated. The inclined length and vertical depth from the mouth of
the mines were 90–210 m and 90–105 m respectively. The geology of the coalfield leads to a
large number of small outcrop workings; therefore these mines are smaller than others around
the world. In addition to the five functioning mines, one training coalmine at Katas village was
also included in the study. The training mine operates under the auspices of the Punjab Mines
and Mineral Department. The village of Katas is a historical place due to the temples of the

Figure 2. A sketch of the box type dosimeter with CN-85 detectors installed in the dosimeter and
the dosimeter enclosed in a thin polyethylene bag.
Hindu religion, most of which were built during the reign of Hindu kings. The temples were
built more than 900 years ago, although the earliest of the Katasraj temples date back to the
latter half of the 6th century AD (www.wikipedia.org).
2.2. Measurement of radon concentration
A passive integrated technique was employed for the measurement of radon concentration in
the coalmines. This method involves the registration of alpha tracks in the SSNTDs from radon
and its decay products, and counting of the etched tracks under an optical microscope (Durrani
and Bull 1987, Flesicher et al 1975).
Two pieces of cellulose nitrate CN-85, as etched track detectors, were fixed in a plastic
box. The box along with the detectors was enclosed in a thin polyethylene bag as shown in
figure 2. The polyethylene bag protects the detectors from humidity and dust, and blocks radon
daughters while allowing 222
Rn to permeate into the bag (Tommasino 1988, Tufail et al 1991).
This arrangement is called a box type dosimeter. At each sampling point, two dosimeters were
hung on the mine wall. The dosimeters were kept at six different points in every coalmine,
starting from the mouth of the mine up to the coalface at the end of the mine.
The distance between each dosimeter placed in a coalmine varied from 20 to 30 m
depending upon the length of the coalmine. For the determination of radon concentration in
the outer vicinity of each mine, 2–3 dosimeters were also placed near the mine mouth in the
open environment. In this way 75 dosimeters with 150 CN-85 detectors were employed for
this study. All the dosimeters were placed at the specified places in the coalmines within one
day, therefore the detectors were exposed to radon almost simultaneously in every mine. The
dosimeters were installed on 11 March and removed on 10 June 2008 after an exposure of three
months. The detectors were detached from the dosimeters and etched in 6 M NaOH solution
at 50 ± 1 ◦
C for 90 min. The detectors were washed in an ultrasonic cleaning bath. After
drying, the tracks in the detectors were counted under an optical microscope at a magnification
of 400×. In order to decrease the readout uncertainty of the microscope to 10% and to follow
Poisson statistics, 100 fields of view were scanned and averaged.
The mean track density of the two detectors in a dosimeter was converted to radon
concentration using the conversion factor of 0.009 tracks cm−2
h−1
/Bq m−3
(Tufail et al
1991). This factor has been experimentally verified by exposing the box type dosimeters
loaded with CN-85 track detectors in a radon reference chamber at Physikalisch-Technische

Figure 3. The closed can arrangement for the measurement of exhalation rate.
Bundesanstalt (PTB) (National Institute for Science and Technology for the Field of Metrology
and Physical Safety Engineering), Braunschweig, Germany. The estimated calibration
factor was in the range 0.0097–0.012 tracks cm−2
h−1
/Bq m−3
with an arithmetic mean of
0.010 ± 0.009 tracks cm−2
h−1
/Bq m−3
. The estimated factor is not much different from
0.0092 tracks cm−2
h−1
/Bq m−3
. The small difference in calibration factor is due to statistical
fluctuations in the measurement and uncertainty in the radon concentration. Radon exposure in
WLM was calculated from the measured concentration of radon.
2.3. Determination of radon exhalation rate
In order to observe the contribution of coalmine material towards the growth of radon in the
mine, radon exhalation rates from coal and shale samples from the coalmines were measured
using the closed can technique. This technique has been widely used for the determination
of time related radon exhalation rates using SSNTDs (Abu-Jarad et al 1980, Somogyi et al
1986, Tufail et al 2000). In this technique, a material sample is kept inside a closed can and the
exhaled radon is measured by an SSNTD fixed inside the can. In the present study, a plastic box
loaded with two CN-85 detectors, enclosed in a thin polyethylene bag (as shown in figure 2)
was fixed to the upper side of the closed container as is shown in figure 3. The polyethylene bag
not only protects the detectors from humidity and dust but also blocks radon daughters while
allowing 222
Rn to pass through the plastic. This arrangement makes the dosimeter independent
of the contributions of radon progeny outside the dosimeter because only radon emerging from
the sample can permeate through the plastic cover enclosing the dosimeter. After an exposure
of 33 days, the detectors were detached from the boxes and etched in 6 M NaOH. The radon
exhalation rate of the material under investigation was determined using the following relation
(Tufail et al 2000):
E =
ρ
η

(λV/A)
t + 1
λ
(e−λt − 1)

(1)
where ρ is the track density (tracks cm−2
) due to radon build-up inside the container, η is the
track detection efficiency (tracks cm−2
h−1
/Bq m−3
), V is the volume of the closed container
(m3
), t is the exposure time (h), A is the area covered by the can (m2
) and λ is the decay

constant of 222
Rn (=7.56 × 10−3
h−1
). The detection efficiency in the present measurement
was taken as 0.0092 tracks cm−2
/Bq m−3
(Tufail et al 2000).
2.4. Assessment of radiological hazard
Absorbed radiation dose is the fundamental dosimetric quantity used for the assessment of
radiological hazard (UNSCEAR 2000). The risk of lung cancer from exposure to radon can
be estimated by means of the effective dose from the exposure to radon progeny (Nazaroff and
Nero 1988). The conditions of exposure to radon in mines are different from those in homes
due to the lower unattached fractions and higher breathing rates in mines than in homes and in
an open environment. Therefore, the conversions of radon daughter exposure to effective dose
in mines and homes require different dose conversion factors (ICRP 1993).
2.4.1. Radon daughter exposure. The annual exposure of mine workers to radon daughters
can be determined using the following relation given by ICRP (1993) and UNSCEAR (2006):
ER = CR F(2.7 × 10−4
)

T
170

(2)
where ER is the radon daughter exposure (WLM y−1
), CR is the concentration of radon
(Bq m−3
), F (=0.5) is the equilibrium factor (Qureshi et al 2000), the figure 2.7 × 10−4
is
the conversion factor (WL/Bq m−3
) (UNSCEAR 2006), 170 represents the working hours per
month in a mine (h M−1
), and T is the working time (h) in the mines.
Studies of caves and mines have shown a wide variation in the equilibrium factor F, from
as low as 0.04 to right up to 1 (Rao et al 2001, Lario et al 2005, Alberigi et al 2011), with the
higher values being found in poorly ventilated areas (Rao et al 2001). Normally, F is taken as
0.4, the default value adopted by the ICRP (1993), and decreases with increase of ventilation
rate (Islam et al 1996). The mines studied here are naturally ventilated and the slow ventilation
favours a high value of F. Therefore, F = 0.5 was used in the present study, as was adopted
by Qureshi et al (2000) for the coalmines in Pakistan.
The wages of the mine workers are determined from the number of tonnes of coal extracted
from the mine. To earn more money, the workers spend up to 9 h in a day and work for 26 d
in a month. In this way, they spend around 2880 h y−1
, i.e. about one third of the year, in coal
mines, with an occupancy factor of 0.33 (Qureshi et al 2000).
2.4.2. Annual effective dose. The annual effective dose to the personnel exposed to radon
while working in a mine is estimated using the following relation (ICRP 1993):
DE = kER (3)
where DE is the annual effective dose (mSv y−1
), ER is the radon daughter exposure
(WLM y−1
), k is the conversion factor (mSv/WLM), 5 mSv/WLM as recommended by ICRP
(1993).
2.4.3. Excess lifetime cancer risk. The excess lifetime cancer risk (ELCR) due to exposure of
the mine workers to radon can be found using the following relation (EPA 2003):
ELCR = ERT FR (4)
where ER is the radon daughter exposure in WLM y−1
, T is the average life expectancy;
according to the UNICEF (United Nations Children’s Fund), the average life expectancy in
Pakistan is about 67 years (www.unicef.org). FR is the nominal risk coefficient for exposure to
222
Rn gas in equilibrium with its progeny; based on the recommendations of ICRP (2009) it is
taken as 5 × 10−4
per WLM.

Figure 4. Radon concentration versus distance from the mine mouth in two coalmines (Punjab
Mine-13 and Wah Stone-13) in the Chakwal area of the Salt Range, Pakistan.
3. Results and discussion
3.1. Radon concentration
The radon concentration at a sampling point was the mean value from two dosimeters placed at
that point in the coalmine. The concentration of radon increased down the mine. This increase
in radon concentration towards the ends of the mines is shown graphically in figures 4–6. In
view of the increasing radon levels down the mines, the average radon concentration for each
mine is presented in table 1. The radon concentration level given for a coalmine is the average
value ± standard deviation, and the minimum–maximum values (within parentheses) from
six sampling points in the mine. The radon concentration is higher in the mines of greater
length except in the training coalmine. This is perhaps due to the poor ventilation and greater
emergence probably of radon in longer mines.
In the training coalmine, the radon concentration of 1100 ± 191 (803–1367) Bq m−3
is the
highest among the individual mean values given in table 1. The mine was bored at Katas, a
village in district Chakwal. During inclined boring, water leakage was observed at a depth of
about 15 m from the ground surface. The inclined boring was stopped and vertical boring was
started to make a shaft to reach the buried coal. During the time of the radon measurements,
the mine was augured up to about 60 m. Two water pumps were installed to drain the water out
of the mine so that boring could be carried out up to the buried coal. The mine shaft was lined
with steel to protect it from collapse due to heavy water coming into it. Accumulation of water
in the shaft can be a major contributor to raising the concentration of radon in the training mine.
Water on the way towards the shaft may have transported radon from the rock pores. Owing to
the high values of radon concentration in the training mine, radon concentration measurement
was carried out again after about six months, from 7 December 2008 to 6 March 2009. The level

Figure 5. Radon concentration versus distance from the mine mouth in two coalmines (Punjab
Mine-3 and Punjab Mine-21) in the Chakwal area of the Salt Range, Pakistan.
Figure 6. Radon concentration versus distance from the mine mouth in the Katas area of the Salt
Range, Pakistan (∗ indicates the post-repair measurements).
of radon dropped to 562 ± 296 (218–911) Bq m−3
, almost half of its previous concentration.
This reduction in radon concentration might be due to the control of water accumulation in the
mine.

Table 1. Radon concentration averaged at six points in every coalmine in the district of Chakwal
in Pakistan.
Radon concentration (Bq m−3)
Name of coal mine Mine length (m) Inside Outside
Punjab Mine-3 215 114 ± 45 (66–186) 13
Punjab Mine-7 180 104 ± 28 (62–141) 12
Punjab Mine-13 165 103 ± 34 (59–154) 13
Punjab Mine-21 100 50 ± 12 (33–67) 11
Wah Stone-13 130 75 ± 21 (43–99) 11
Training Mine (Katas) 60 1100 ± 191 (803–1367) 14
Training Mine (Katas)a 88 562 ± 296 (218–911) 10
Rangeb 100–215 50–114 11–13
a Post-repair measurements.
b
Range values are obtained by excluding the post- and pre-repair values of the training coalmine at
Katas.
The second highest radon concentration level of 114 ± 45 (66–186) Bq m−3
was observed
in the Punjab Coalmine-3. This coalmine is relatively older among the mines under study. The
mine’s length is approximately 215 m and it has a slope of about 45◦
from the horizontal. The
ventilation conditions of the mine are not very good due to the long length of the mine. It can
be speculated that radon accumulation may have risen due to the presence of more soil gas at a
greater depth in the Earth’s crust. A large number of cracks and a significant amount of water
leakage in some portions of the mine were also observed. All these factors contribute towards
the relatively higher average radon concentration observed in the Punjab Coalmine-3.
The lowest of the average concentration values, 50 ± 12 (33–67) Bq m−3
, was observed in
the Punjab Coalmine-21. The length of this coalmine is about 100 m. The mine has good
ventilation conditions due to its relatively shorter length. The atmosphere of the mine is
relatively cleaner than that of the other coalmines under investigation. The mine was properly
maintained, water leakage and the number of cracks in the mine walls were relatively small.
The concentration of radon in the outer atmosphere of the coalmines, given in table 1,
is almost consistent and low. The observed radon level is significantly higher in the mine
atmosphere than outside the mines.
The pre- and post-repair concentration levels of radon in the training coalmine are
exceptionally higher than those in the other five coalmines. The significantly different and
raised radon levels in the training coalmine distort the data for the other mines; therefore this
mine was treated separately. The radon concentration range in the remaining five mines given
in table 1 is 50–114 Bq m−3
.
The average concentration levels of radon in the five mines under study are below the action
level of 500–1500 Bq m−3
recommended by the International Commission on Radiological
Protection (ICRP 1993). The radon concentration of 1100 ± 191 Bq m−3
in the training
coalmine (before repair) exceeded the ICRP (2009) recommended value of 1000 Bq m−3
. This
value however reduced to 562±296 Bq m−3
, about half of its previous value, within six months
after repair to control water accumulation in the mine. The radon concentration levels in the
coalmines under study (except the training coalmine) are comparable to those observed in the
dwellings of most European countries (UNSCEAR 2006). The observed radon concentrations
in the coalmines are higher than those for most Asian and regional countries, described in the
UNSCEAR (2006) report.
Annual/seasonal variation of radon levels has not been measured in the coalmines under
study and the seasonal correction factor for Pakistani coalmines was not available. The effect

Table 2. Radon exhalation rates form coal and shale samples collected from the coalmines under
study.
Radon exhalation rate (mBq m−2 h−1)
Name of coal mine Shale Coal
Punjab Mine-3 1580 960
Wah Stone-13 1390 970
Mean ± Std 1302 ± 209 934 ± 70
Range 1020–1580 830–1010
of seasonal variation on radon concentration in coalmines and dwellings has been studied by
many investigators (Rao et al 2001, Pinel et al 1995, Font 2009, Groves-Kirkby et al 2006).
There are many common factors between India and Pakistan related to coalmining. Therefore,
to accommodate the seasonal variations in the measured radon concentrations in the mines
under study, the correction factors for Indian coalmines were a better choice. The seasonal
variation of radon concentration for all the seasons in Indian coalmines has been reported by
Rao et al (2001). Using the methodology of Pinel et al (1995), and the data of Rao et al
(2001), the seasonal correction factors for radon derived for some Indian coalmines have the
values 1.08 for March–May, 0.83 for June–August, 0.83 for September–November, and 1.26
for December–February. The seasonal correction factor of 1.08 for March–May suits the data
for the five working mines and 1.26 for December–February the data for the training coalmine.
By applying these correction factors, the concentration of radon in the five working coalmines
under study will increase by 8% and that of the training mine will be enhanced by 26%.
3.2. Radon exhalation rate
Radon exhalation rates from the samples of coal and shale collected from the study mines
were determined using equation (1) and the results are given in table 2. The measured
exhalation rates from shale and coal samples are statistically significant as the p-values are
less than 0.05 (within the 0.05 significance level). The average radon exhalation rate of
1302±209 mBq m−2
h−1
from the shale samples is more than the rate of 934±70 mBq m−2
h−1
from the coal samples, which may be due to the higher radium content in shale as compared to
that in coal in the area under study. The results confirm those of Jamil et al (1998), and suggest
that, on average, there is more radium in shale than in coal.
The radon in the coalmines under study is not merely due to the small amount of 226
Ra
in the samples of shale and coal from the mines under investigation, its accumulation in an
underground mine depends upon several other factors such as air pressure, rock conditions,
ventilation conditions in a mine, moisture content, mine temperature, etc (Nazaroff and Nero
1988, Mahmood et al 2000, Xue et al 2010). The design, construction and ventilation of the
mine also affect the radon level in a mine.
Radon is transportable in ground water, moving in response to gravity within saturated
fractured bed rock and surficial deposits. The gas is also mobile in air within the fractured
work of the bedrock and pore space of the surficial deposits. Here it moves by a combination of
flow and diffusion, and is sometime called ‘soil gas’ in levels near the surface of the Earth.
In some cases, radon in ground water can be exchanged into the air in soil and fractured
rock by evaporation. Radon bearing air is also capable of migration directly into an unsealed
environment.

Table 3. Radon concentration and effective dose in some coalmines of the world.
Country
Radon concentration
(Bq m−3
)
Effective dose
(mSv y−1
) Reference
Australia 68–220 2.9 Hewson and Ralph (1994)
Brazil 1650 (170–6100) 10.7 (1.0–36.0) Veiga et al (2004)
Germany 105 (up to 400) — Eicker and Zimmermeyer (1982)
India 144–315 — Rao et al (2001)
Iran 320 (146–520) 2.0 (0.91–3.24) Ghiassi-Nejad et al (2002)
Iran 230 (630–90) 0.5 (0.3–0.7), 0.4 (1.0–2.0) Fathabadi et al (2006)
Poland 740 (0–7000) — Chruscielewski et al (1984)
Poland — 0.31 (up to 7.2) Skowronek (1999)
Taiwan 88.5 Chen (1992)
Turkey (31–185) (0.99–4.16) Yener and Kucuktas (1998)
Turkey 117 (49-223) 1.24 Baldik et al (2006)
Turkey 15–78 0.06–0.31 Emirhan and Ozben (2009)
Turkey (Zonguldak) 678 (656–705) 4.89 (4.72–5.08) Fisne et al (2005)
United Kingdom 65–613 — Page and Smith (1992)
United Kingdom 74 (22–518) — Duggan et al (1970)
United Kingdom 220–733 (0.95–5.0) Dixont et al (1991)
Pakistan
Sor Range 192 (121–408) 2.19 (1.38–4.67) Qureshi et al (2000)
Salt Range (Khushab) 105 (72–140) — Mahmood et al (2000)
Salt Range (Chakwal) 50–114 0.57–1.30 Present study
3.3. International comparisons
The radon concentration in the coalmines of the Salt Range in the district of Chakwal in
Pakistan and some other mines of the world along with previous measurements in coalmines
of Pakistan are given in table 3. The radon concentration range of 50–114 Bq m−3
in the
working coalmines under study is lower than the values of 72–140 and 121–408 Bq m−3
respectively measured in the coalmines of the Salt Range (Khushab district) by Mahmood et al
(2000) and the Sor Range (Baluchistan province) by Qureshi et al (2000). The concentration
remains smaller even if the seasonal correction factor of 1.08 is applied to the measured radon
concentration. The lower radon concentration in the coalmines of Chakwal is due to the
relatively good ventilation conditions in these mines as compared with those in the coalmines
of the Khushab district and the Sor Range. The concentration levels of radon in coalmines vary
from one country to another. A worldwide comparison of radon concentration in coalmines
may not be justified because the methods of measurement and mine parameters may not be the
same in all of the studies.
The radon concentration in non-uranium mines of some countries of the world has been
discussed in the report of UNSCEAR (1988). The minimum value (8 Bq m−3
) of radon
concentration is in the Saline Salt Mines of the Federal Republic of Germany and the maximum
value (29 000 Bq m3
) is in the Feldspar Mines of the same country. The radon concentration
found in the coalmines under study is higher than the minimum value and far lower than the
maximum value, but lies on the lower side if compared with the overall radon concentration in
non-uranium mines given in that report.
3.4. Health hazards
The annual exposure to radon daughters was derived from the average radon concentration
in a mine by applying equation (2) and the results are given in table 4. The exact position
of the miners in the mines was not known, therefore the total time spent by the miner and

Table 4. Annual exposure, effective dose, and cancer risk from radon daughters for personnel
working in coalmines in the district of Chakwal in Pakistan.
Name of coal mine
Radon daughter
exposure
(WLM y−1)
Effective dose
(mSv y−1)
Excess lifetime
cancer risk
(×10−3)
Excess lifetime
cancer risk (%)
Punjab Mine-3 0.26 1.30 8.73 0.87
Punjab Mine-7 0.24 1.19 7.97 0.80
Punjab Mine-13 0.24 1.18 7.89 0.79
Punjab Mine-21 0.11 0.57 3.83 0.38
Wah Stone-13 0.17 0.86 5.75 0.57
Training Mine (Katas) 2.51 12.57 84.20 8.42
Training Mine (Katas)a 1.29 6.43 43.06 4.31
Rangeb 0.11–0.26 0.57–1.30 3.8–8.73 0.38–0.87
a Post-repair measurement.
b The range values are obtained by excluding the post- and pre-repair values of the training coalmine at Katas.
average radon level in the mine were used in these calculations. The exposure to potential
alpha energy from radon progeny in five coalmines has the range 0.11–0.26 WLM y−1
and in
the training mine the exposure value is 1.29 WLM y−1
. International radiation protection and
regulatory agencies have given their recommendations to limit radon progeny exposure in the
workplace. A limit of 4 WLM y−1
due to radon progeny has been adopted by NRC (1991),
EPA (1988) and USDOE (1989, 1993) An annual limit of 10 WLM of radon progeny exposure
in the workplace has been recommended by NCRP (1993), IAEA (1994) and ICRP (1994). The
results of the present investigation are lower than those recommended by the above mentioned
radiation protection agencies.
Based on the exposure to radon progeny, the annual effective dose was determined using
equation (3) for the workers of every mine and the results are presented in table 4. The
estimated average effective dose to the mine workers from the exposure to radon daughters
lies within 0.57–1.30 mSv y−1
in five of the mines and is 6.43 mSv y−1
in the training mine.
The average effective dose given in table 4 for most of the coalmines is greater than the limit
of 1 mSv y−1
recommended by the ICRP (1991) for the general public. The present estimated
annual effective dose in every coalmine except Punjab Mine-21 is higher than the world average
dose of 0.7 mSv for coalminers (UNSCEAR 2006). The estimated annual effective dose for
the present study, however, is well below the effective dose of 20 mSv y−1
(the reference level
recommended by ICRP in its publication 103) due to radon in workplaces (ICRP 2007). The
annual effective dose estimated for the workers at the Chakwal coalmines and most other
countries are listed in the table 3. The effective dose range of 0.57–1.30 mSv y−1
in the
coalmines under study is lower than those of previous estimates for Pakistani coalmines. The
annual effective doses of 10.7 and 4.89 mSv, estimated in Brazil (Veiga et al 2004) and Turkey
(Fisne et al 2005) respectively, are much higher than the dose received by the miners in the
coalmines of Chakwal in the Salt Range of Pakistan.
The ELCR (excess lifetime cancer risk) has been derived from the annual exposure to
radon daughters using equation (4) and the results are presented in table 4. The ELCR due to
radon progeny for the Chakwal coalminers has the range (3.8–8.73)×10−3
for the five working
coalmines. The ELCR estimated for the personnel working in the coalmines under study is less
than the estimated lifetime cancer risk of 1.3% due to a radon exposure of 148 Bq m−3
(action
level of EPA) for the entire population (EPA 2003).
All of the calculations for the determination of health hazard were performed without
applying the seasonal correction for radon in the coalmines under study. The seasonal

correction factor of 1.08 estimated for these working mines will enhance the values of annual
effective dose and risk by 8% compared with those given in table 4.
The level of radon in the coalmines under study may not be high enough to cause
abnormally high lung cancer rates in the miners but the presence of coal dust and gases (CO2,
CO, SO2, etc) and automobile smoke increases the risk of lung cancer. The lung cancer risk
due only to radon is multiplied by the risks of other cancer causing factors in the mine. Among
non-uranium mines, coalmines have an adversely large impact on the health of mine workers
due to the additional hazards of coal dust and gases in coalmines.
4. Conclusions
This study on measurements of the radon concentration in Chakwal coalmines has shown that
one mine had raised radon levels and moderate levels of radon were present in the others, and so
a comprehensive survey of radon levels in the longer mines is justified. The range of averaged
radon concentrations from the five working coalmines was lower than those determined in other
coalfields of the Salt Range and the Sor Range passing respectively through the Punjab and
Baluchistan provinces of Pakistan. The cracks in the walls and floor, and water seepage may be
the sources of radon in the coalmines under study. The poor ventilation and greater emanation
may be the causes of elevated radon concentration in relatively longer and deeper coalmines.
The higher radon exhalation rate determined in shale than that in coal is due to relatively higher
radium content in shale of the geological formation under study. The estimated average annual
effective dose to the workers in all coalmines except one was higher than the world average dose
value 0.7 mSv y−1
in coalmines. The annual effective dose received by the miners working in
the Chakwal coalfields of the Salt Range, Pakistan is well below the annual reference dose of
20 mSv for workplaces, given by ICRP-103. The estimated excess lifetime cancer risk for the
workers at the coalmines under study was found to be comparable to the estimated lifetime
cancer risk of EPA for the entire population. The application of a seasonal correction factor
enhances the measured radon concentration and the derived health hazard by 8% in the five
working coalmines and 26% in the training mine. The risk of lung cancer in the coalmines is
multiplied by the risks of other carcinogens in the mines.
The study led to the following recommendations: (a) a separate study should be carried
out to estimate the seasonal variations of radon in the coalmines under study and the seasonal
correction factor for these coalmines should be determined, (b) a work plan should be designed
to measure 226
Ra and 222
Rn concentrations in water seeping into the coalmines, (c) the longer
and deeper mines should be properly ventilated not only naturally but also artificially, and
(d) mechanical ventilation and regular monitoring of radon levels in the training coalmine at
Katas should be accomplished.
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