Proceedings of the International Conference on Non-Ionizing Radiation at UNITEN (ICNIR 2003)
Electromagnetic Fields and Our Health
20th –
22nd October 2003
Exposure Assessment of Electromagnetic Fields in Malaysian
Public Schools Environment
A.S. Farag, T. Juhana Hashim, H. Hussain, I. Said, N. Abdul Rahman
University Tenaga Nasional
Selangor, Malaysia
ABSTRACT
Electromagnetic fields (EMFs) health issue have been traced and believed to have been
developed over the past 30 years when the possibility that EMF could cause health effects
was considered totally implausible to the present. Universiti Tenaga Nasional (UNITEN)
started a project for recommending policies for managing possible health risks posed by
power-frequency electromagnetic fields in Malaysian public schools. UNITEN is in the
process to develop a thorough program of measurements, modeling, and simulation tools to
estimate the exposure assessments, exposure reduction, if needed, health risk, costeffectiveness associated with various electric and magnetic field standards.
This paper discusses the research that has been carried out in 5 Malaysian public schools in
the state of Selangor, which consists of 4 primary schools and one secondary school. This
paper discusses particularly the measurement protocols and the data collections that have
been done in order to determine the level of electromagnetic fields in different areas selected,
to present, laboratories, classrooms and offices. Several aspects of EMF that have been
focused on the power frequency electric and magnetic fields are field levels and field sources.
The internal and external field sources located within the school buildings are defined.
Statistical analysis and comparison between different sources and field level categories are
also done and presented.
INTRODUCTION
Public concern over electromagnetic fields (EMFs) exposure is growing. People living under
transmission lines, or working in close proximity to equipment generating EMF radiation, or
using electric equipment and electrical appliances are concerned about the potential health
effects of these EMF exposures[1-2]. The research on the effects of electromagnetic fields
human health has been ongoing for the past 30 years. However, scientists are still far from
making a conclusion whether electromagnetic do pose health hazard to the people either at
home, in schools or in the workplace. This research is focused on schools for several reasons.
First of all, the disease that first brought the issue of EMF to the widespread attention of the
public and the scientific community was the childhood cancer study, leukemia, which is
believed to be associated with EMF, although it is considered conclusive by some scientific
review panel [3].
Secondly, the society has historically set high standards for safety in schools and has shown a
higher willingness to pay for to protect their children than to protect adults [3]. Finally, the
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Proceedings of the International Conference on Non-Ionizing Radiation at UNITEN (ICNIR 2003)
Electromagnetic Fields and Our Health
20th –
22nd October 2003
public school environment is governmental managed, so the government has more direct
institutional responsibility to manage EMF risks in schools compared to EMF risks in other
areas [3]. The goal of this project is to help policy makers evaluate alternative countrywide
policies to address EMF exposure standards for schools. This research was done in 4 primary
schools and one secondary school which are located in close proximity to external sources of
magnetic fields, for example, transmission lines, distribution lines and substation. Several
important aspects of EMF have been focused on in order to obtain accurate information about
the degree of which students in Malaysian schools are exposed to power system electric and
magnetic field (EMF) while attending school.
EQUIPMENT USED
Measurements were carried out for both the indoor and outdoor areas including the lateral
profile for the transmission lines. For the outdoor areas, measurements were done using the
LINDA wheel together with the EMDEX II meter. The EMDEX II meter was attached to the
wheel and the data that was recorded was uploaded in the computer once the measurements
for each area were done. For the indoor areas, the EMDEX SNAP meter was used in taking
the data. Measurements were done at about one meter from the ground at the 4 corners and at
the center of each room.
A. EMDEX II System
The EMDEX II/LINDA was used to measure broadband magnetic fields during an extended
walk down the areas of the school. Though not specific to any given EMF source, the
recorded provide a basic characterization of field levels around the different areas of the
school. These data can be used to make very general comparisons of the field levels at the
school areas. After a walkthrough was completed, the data was downloaded to a laptop
computer for storage and analysis. Each file was given a unique name. Field versus distance
3D field contour plots can be generated from this data with the EMCALC Software supplied
with the unit. The software also provides a 2 dimensional plot of the path that was followed.
The EM DEX II displays the RMS vector magnitude of the ELF magnetic field, the primary
exposure metric in most health studies. It measures broadband resultant magnetic field from
40 to 800 Hz and was used to characterize the magnetic field levels in this frequency range
around this source measured by the MultiwaveTM System as well as on a walk-through survey
of most areas. It is mounted on a surveyor’
s wheel (Enertech LINDA System), which
provided a distance triggered to the recording device. The spatial distribution of magnetic
fields was characterized by measurements recorded along the path taken. The EMDEX II
simultaneously records magnetic field and distance traveled at 1.5 seconds intervals. The
median and maximum of the RMS vector magnitudes from each walkthrough are simple
metrics that might predict EMF exposures in different areas. The profiles are contour maps
generated by the LINDA system indicate the location and extent of EMF sources. The plots
of field versus distance and tables of statistical measures for the measurements were reviewed
to confirm the validity of the measurements. There are however, a few limitations to the use
of the EMDEX II/LINDA System. As the protocol indicates, the results of this survey can
depend on the utilization of the magnetic field source. Hence, the ideal source survey would
be during the time the equipment is fully utilized, that is during normal school hours.
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Proceedings of the International Conference on Non-Ionizing Radiation at UNITEN (ICNIR 2003)
Electromagnetic Fields and Our Health
20th –
22nd October 2003
B. EMDEX SNAP
Spot measurements have been done on the identified sources particularly the operator sources
such as office equipment. The measurement was taken around the source identified and one
meter away from it using the EMDEX SNAP meter. This was done in order to characterize
the spatial distribution of magnetic fields in various areas. Other than that, the temporal and
spatial characteristics of magnetic fields near identified sources in the school could also be
assessed. The temporal nature of the magnetic fields present at areas was determined by the
operation of the principal source.
MEASUREMENTS IN SCHOOLS
Basically, there are two types of EMF sources that can also be classified as internal and
external sources. There are the internal operator sources such as the computers, overhead
projectors, and other office equipment. The internal area sources include the electrical panels,
fluorescent ceiling lights, power cables, transformers (in-house substation) and airconditioners. On the other hand, the external sources of EMF for the area sources are the
transmission lines, the distribution lines and the nearby substation. Internal and external
sources are those located within and outside the school building respectively. Operator
sources are sources that are used by one individual at a time (the operator) for which the EMF
exposure is generally limited to the period of use. Area sources are all sources, both internal
and external, that are not operator sources [3].
Exposure assessment in this project was carried out in 4 primary schools and one secondary
school. The selection of the school was based on 3 factors:
1. School location –
whether it is located near the external area sources which include
the transmission lines, distribution lines and also substation.
2. The level of the schools –
whether it is a primary, secondary or kindergarten school.
3. The electrical appliances available in the schools, depending on the area of the school
location whether it is located in the area of high, middle-class or low-class areas.
All of the schools that were involved in the measurements are governmental-managed; hence
there are not much of differences in EMF levels obtained for the measurements that were
carried out for the indoor areas since the electrical appliances that are also the EMF sources
are quite the same for most of the schools involved. Measurements in schools can be
categorized mainly into two areas, the outdoor areas and also the indoor areas. Measurement
in the outdoor areas was mainly done in order to get the schools’
profiles. This was done by
getting the profile of the transmission lines and distribution lines and performing
measurements for the other areas that can be categorized as the school outdoor areas, namely
the school’
s fence, football field, basketball court and others. Measurements were also carried
out based on the measurements protocols that has been developed and reviewed by the other
EMF researchers who are experienced in the EMF field.
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Proceedings of the International Conference on Non-Ionizing Radiation at UNITEN (ICNIR 2003)
Electromagnetic Fields and Our Health
20th –
22nd October 2003
MEASUREMENT PROTOCOLS
1. Get the profile of the school. Measure the distance of the school fence to the distribution
lines, transmission lines and the nearest substation.
Sketch the area that is to be measured.
2. Get the plan view of the school. Do spot measurements or use LINDA for profile at the
fences around the school.
3. Identify the area of the schools that are to be involved in the EMF measurements. For
example, classrooms, staff occupied indoor areas; other student occupied indoor areas and
outdoor areas. Sketch and measure the dimensions of each area.
4. Upon entering an area (e.g. a classroom), identify all the sources responsible for each
magnetic field in each area, including the internal and external sources. Ask questions to
the teacher or staff in the area on the equipment that is used in the area to ensure that
there is no hidden equipment.
5. State the time of measurements. Do spot measurements for each area (e.g. classrooms or
other indoor areas).
If there are no panels nearby, do spot measurements at the four corners and the center of
the rooms.
If there are panels nearby, do spot measurements at the four corners and the center of the
rooms, but now also do spot measurements at the areas outside the rooms and the room
next to it.
6. The spot measurements are to be carried out in 3 conditions:
i.
All the internal sources are switched off. (This is to take into consideration the
contributions of all the external sources only).
ii.
All the sources are measured separately.
iii.
All the sources (external and internal) are combined on.
7. Systematic magnetic field measurements at a large number of points for each area using
LINDA that is the perimeter and area scan.
8. Documentation (sketches, photos and special measurements) of the area sources
identified during the survey is to be done. Measurements of the magnetic field
characteristics of the selected operator sources are also to be done.
9. 50 Hz and harmonic magnetic field at the center of all classrooms.
10. Measurements of the magnetic field lateral profile of all power lines adjacent to the
school. Sketches photos of the lines, including details of the conductor attachment of each
structure.
The 5 schools that were involved in the EMF measurements are in the vicinity of major
external sources of magnetic fields, transmission lines, distribution lines and substation. The
5 schools which were involved in the measurements are Tropicana (C) Primary School,
Serdang Baru (2) (C) Primary School, Leftenan Adnan Primary School, Bandar Baru Bangi
Jalan (2) Primary School and Sri Indah Secondary School. Most of the measurements that
have been performed focused on the outdoor areas and results and discussion in this paper
will be mainly based on the results of the EMF measurements for the outdoor areas.
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Proceedings of the International Conference on Non-Ionizing Radiation at UNITEN (ICNIR 2003)
Electromagnetic Fields and Our Health
20th –
22nd October 2003
1. Measurements for the outdoor areas of Tropicana (C) Primary School Damansara
The 132/275 kV transmission lines is located perpendicular to the school, which is about 65
feet or 20 meters from the school fence, This distance is the standard distance approved by
Tenaga Nasional Berhad (the main electric utility company in Malaysia) for a building to be
built in the vicinity of transmission lines. The distance of the transmission lines to the nearest
school building, block C is about 225 feet or 68 meters. Located at the east side of the school
is a substation that is about 15 meters from block C of the school and distribution lines which
is also in the range of 65 feet or 20 meters from the school fence and about 200 feet or about
63 meters from the school building. Given below is the transmission lines profile that was
generated using the EMCALC software.
school to house
50
Broadband Resultant
Broadband X - Component
Broadband Y - Component
Broadband Z - Component
Event 4
Event 3
20
Event 2
30
Event 1
Magnetic Field (mG)
40
10
0
20 40 60 80 100 120 140 160 180 200 220 240
Distance (ft)
2.0
Mar/06/2003
11:59:18 AM
C:\student\srj(c)damansara\060303t.lines2.mbk
258.0
Transmission lines profile for 132/275 kV tower near Tropicana (C) Primary School
From the magnetic field versus distance plots of the transmission lines profile obtained
shown above, it can be seen that for Event 1 that was recorded under the 132 kV line, the
magnetic field value recorded reaches 17 mG and the maximum value that was recorded is
46.3 mG.
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Proceedings of the International Conference on Non-Ionizing Radiation at UNITEN (ICNIR 2003)
Electromagnetic Fields and Our Health
20th –
22nd October 2003
View of the transmission lines looking from the school football field area
The other measurement on the external EMF source was carried around the fence of the TNB
substation which is located near the football field and beside the water tank. The magnetic
field versus distance plot of this measurement is given below.
ss
1.6
1.5
1.4
1.3
1.2
Magnetic Field (mG)
1.1
1.0
0.9
0.8
Broadband Resultant
0.7
0.4
Event 3
0.5
Event 2
Event 1
0.6
0.3
0.2
0.1
0.0
10
2.0
Feb/22/2003
12:13:40 PM
20
30
40
50
60
70
80
90 100 110 120 130 140 150 160 170 180 190
Distance (f t)
196.0
C:\Program Files\Enertech Consultants\EMCALC 2000\Data\220203perimeters.mbk
From the plot obtained above, it can be seen that the value of magnetic field ranges from 0.96
mG to 1.52 mG. The higher value of EMF is obtained along the path between Event 2 to 3.
This is where the door of the substation is located and indicates that the door did not provide
a good shielding.
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Proceedings of the International Conference on Non-Ionizing Radiation at UNITEN (ICNIR 2003)
Electromagnetic Fields and Our Health
20th –
22nd October 2003
Badminton court (next to football field)
Water tank and TNB substation (Looking from the football field)
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Proceedings of the International Conference on Non-Ionizing Radiation at UNITEN (ICNIR 2003)
Electromagnetic Fields and Our Health
20th –
22nd October 2003
Besides the measurement that was carried out for obtaining the transmission lines profiles,
measurements were also performed for other outdoor areas, for examples the football field
and badminton court, basketball court, car park, and canteen area. From the pictures above, it
can be seen that the football field and together with the badminton court which are located
next to each other is near the school’
s fence and transmission lines. As can be seen from the
plot that was obtained, the maximum magnetic field value measured was 5.16 mG and the
lowest value was 1.13 mG. The location of the football field that is perpendicular to the
school fence and the transmission lines makes the exposure of magnetic fields higher
compared to the other outdoor areas measured. From the plot, the value of magnetic field
increases and decreases according to the path taken. As the LINDA was moved nearer to the
transmission lines, the values recorded are higher and vice versa. The Tenaga Nasional
Berhad (TNB) substation is also located beside the field. Next to the substation is the water
tank which is about 11 meters away from the field.
Football Field & Badminton Court
6
5
3
Event 3
Event 4
2
Event 2
Broadband Resultant
Event 1
Magnetic Field (mG)
4
1
0
100
0.3
Feb/22/2003
11:20:39 A M
200
300
400
500
Distance (m)
600
648.9
C:\Program Files\Enertech Consultants\EMCALC 2000\Data\dsara school 22feb03 f ball field.mbk
2. Measurements of the outdoor areas of SK Leftenan Adnan Kajang
Measurements for the outdoor areas of this school were performed mainly to identify the
effect of the substation that is located behind the school as well as the compact substation
located near the main gate of the school. The route of the underground cable going into the
school was also traced and the value of magnetic field was recorded by spot measurements
using the EMDEX SNAP. The sketch below shows the tracing of the underground cable in
Leftenan Adnan Primary School. The cable was traced from the 33 kV underground cable
markers to the lighting pole number 1.
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Proceedings of the International Conference on Non-Ionizing Radiation at UNITEN (ICNIR 2003)
Electromagnetic Fields and Our Health
20th –
22nd October 2003
33 kV
markers
X 53 .1
X 93
X 1 01
X 58 .8
X 25
school fence
X 31
X 2 8.3
X 28
X 34
compact
substation
X 29 .7
X 2 9.4
X 39
X 40
X 45
ma in
g a te
P o le 1
Tracing of underground cable in Leftenan Adnan Primary School
The 33 kV underground cable markers
The sketch below shows the results of the spot measurement that was done behind the school
in order to determine the magnetic field level caused by the substation that is located more
than 100 meters from the school building. As can be seen in the sketch, the magnetic field
value obtained is quite low as the distance from the substation is increased. The value of 0.4
mG obtained at the fence of the substation is decreased to as low as 0.1 mG when the
EMDEX SNAP meter is used to measure the magnetic field level at the fence behind the
school. The values of spot measurement were taken every 3 feet and the result that is shown
in the sketch below is the average of the values that is obtained.
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Proceedings of the International Conference on Non-Ionizing Radiation at UNITEN (ICNIR 2003)
Electromagnetic Fields and Our Health
20th –
22nd October 2003
T itle : M e a s u r e m e n t o f s u b s ta tio n b e h in d
L e fte n a n A d n a n P rim a ry S c h o o l
*0 .2 m G
*0 .2 m G
School
B u ild in g s
fence
Substation's
S u b s ta tio n
*0 .1 m G
*0 .2 m G
School's
150 m
*0 .4 m G
back fence
113 m
Houses
*0 .2 m G
* 0 .3 m G
M a in
R oa
* 0 .1 m G
250 m
d
Pow
in e
er l
s
Sc
te
ga
ol
ho a nce
tr
en
la
ua r
K pu
T o um
L
L o w v o l ta g e
s u b s t a tio n
To Kajang
Houses
*0 .2 m G
T ran s m ission line s
The transmission substation located behind the Leftenan Adnan Primary School
The level of magnetic field of the compact substation located near the main gate of Leftenan
Adnan Primary School was also measured by performing spot measurements outside and
around the fence of the substation.
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Proceedings of the International Conference on Non-Ionizing Radiation at UNITEN (ICNIR 2003)
Electromagnetic Fields and Our Health
20th –
22nd October 2003
L o w v o l ta g e s u b s ta t io n ( 4 1 5 V )
4 .6 m G
X
7 .9 m G
X
9 .3 m G
X
7 .5 m G
X
S u b s ta tio n
1 0 .1 m G
X
X
1 3 .2 m G
X
1 3 .5 m G
X
1 0 .2 m G
Spot measurement results at the surrounding fence of the compact substation
The spot measurement carried out at the compact substation
3. Measurements in Serdang Baru 2 (C) Primary School and Sri Indah Secondary
School, Serdang
The measurements for both primary and secondary schools are more focused on the
transmission lines profile and the effect of it to the level of magnetic field on the schools. For
Serdang Baru 2 (C) Primary School, the 275 /132 kV transmission lines is located about 17
meters or 56 feet away from the school fence and about 23 meters or 75 feet to the nearest
school blocks buildings. Due to the distance that is quite near to the school, the level of the
magnetic field near the fence and at the school blocks is quite high. From the results of the
spot measurements that were carried out along the school fence located near to the
transmission lines, the values of the magnetic field recorded are around 5 mG to 6 mG.
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Proceedings of the International Conference on Non-Ionizing Radiation at UNITEN (ICNIR 2003)
Electromagnetic Fields and Our Health
20th –
22nd October 2003
275/132 kV transmission lines located parallel to the school
Measuring the distance of the transmission lines to the school fence
Since the school canteen is located near to the school’
s fence, detailed spot measurements
were also done in the canteen areas for two conditions, first, when all the lightings in the
canteen are switched off and second, when all the lightings are switched on. Below are given
the results of spot measurements for the school canteen. As can be seen from the results, the
highest magnetic field value obtained is around 3.7 mG and the value decreases as the
distance increases from the school’
s fence and transmission lines.
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Proceedings of the International Conference on Non-Ionizing Radiation at UNITEN (ICNIR 2003)
Electromagnetic Fields and Our Health
20th –
22nd October 2003
Transmission Lines
18.7 m
6.1 m
3.8 m
School Brick Fence
1.9 mG
2.5 mG
2.0 mG
2.2 mG
1.7 mG
2.9 mG
3.6 mG
3.6 mG
v
0.9 mG
1.0 mG
F
0.9 mG
1.0 mG
F
0.9 mG
1.1 mG
1.4 mG
1.5 mG
1.8 mG
2.5 mG
F
1.7 mG
1.8 mG
F
1.6 mG
2.9 mG
v
F
2.0 mG
2.0 mG
3.7 mG
3.7 mG
v
0.7 mG
1.1 mG
F
F
0.9 mG
1.4 mG
F
1.0 mG
1.3 mG
v
1.4 mG
1.6 mG
1.6 mG
1.7 mG
1.4 mG
2.0 mG
1.1 mG
1.5 mG
3.4 mG
3.4 mG
3.4 mG
3.4 mG
3.6 mG
3.6 mG
v
F
1.7 mG
1.8 mG
F
0.8 mG
1.5 mG
0.5 mG
0.9 mG
v
0.9 mG
1.2 mG
0.5 mG
0.7 mG
v
F
1.2 mG
1.3 mG
1.2 mG
1.4 mG
v
0.3 mG
1.3 mG
1.7 mG
2.0 mG
F
F
1.0 mG
1.5 mG
1.2 mG
1.8 mG
F
0.3 mG
0.9 mG
0.7 mG
0.9 mG
v
0.3 mG
0.5 mG
0.4 mG
0.4 mG
Wall
Spot measurements results of Serdang Baru 2 (C ) Primary School.
Serdang Baru 2 (C) Primary School canteen.
Measurements for the outdoor areas of Sri Indah Secondary School also involved the
measurement as have been done for the Serdang Baru 2 (C) Primary School. The
measurement of 275/132 kV transmission lines profile and the other outdoor areas
measurement results are given as below. The transmission lines is located approximately 20
meters from the school fence and about 25 meters to the school’
s canteen, computer lab
building and nearest school block building, Block D. As can be seen from the plot that is
obtained below, the highest value of magnetic field obtained 71.70mG and as low as
2.16mG. The value increases as the LINDA/EMDEX II is moved from under the 132 kV line
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Proceedings of the International Conference on Non-Ionizing Radiation at UNITEN (ICNIR 2003)
Electromagnetic Fields and Our Health
20th –
22nd October 2003
to under the 275 kV line. The picture taken below also shows the location of the lines and
tower near the school fence.
school to lines
80
70
Magnetic Field (mG)
60
50
40
Broadband Resultant
Event 6
20
Event 5
Event 2
1
Event 3
Event 4
30
10
0
100
2.0
Apr/24/2003
01:19:38 PM
200
Distance (ft)
300
336.0
C:\Program Files\Enertech Consultants\EMCALC 2000\Data\SMKSRIINDAH240403.mbk
Magnetic Field versus Distance Plot for 275/132 kV transmission lines near Sri Indah Secondary School
275/132 kV transmission lines view looking from school
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Proceedings of the International Conference on Non-Ionizing Radiation at UNITEN (ICNIR 2003)
Electromagnetic Fields and Our Health
20th –
22nd October 2003
Path taken for measurement of the school building
school building
2.4
2.2
2.0
1.8
1.4
1.2
Broadband Resultant
Ev ent 26
Ev ent
ent 28
27
Ev
Ev ent 24
Ev ent 25
Ev ent 22
Ev ent 23
Ev ent 20
Ev ent 21
Ev ent 18
Ev ent 19
Ev ent 16
Ev ent 17
Ev ent 14
Ev ent 15
0.6
Ev ent 12
Ev ent 13
Ev ent 1
Ev ent 2
0.8
Ev ent 10
9
Ev ent 11
1.0
Ev ent 3
Ev ent 4
Ev ent 5
Ev ent 6
Ev ent 7
Ev ent 8
Magnetic Field (mG)
1.6
0.4
0.2
0.0
200
2.0
Apr/24/2003
01:49:40 PM
400
600
800
1000
1200
1400
1600
Distance (ft)
1800
1962.0
C:\Program Files \Enertec h Cons ultants\EMCALC 2000\Data\SMKSRIINDAH240403.mbk
Magnetic field versus distance plot for school building perimeter measurement
The school building perimeter measurements was also carried out in order to identify which
location of the school building with the highest magnetic field value. From the plot that is
shown above, the highest magnetic field value obtained ranges from as low as 0.42mG to as
high as 2.31mG. The highest value of magnetic field of 2.31mG is obtained at Block D of the
school, which is also the nearest location to the transmission lines.
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Proceedings of the International Conference on Non-Ionizing Radiation at UNITEN (ICNIR 2003)
Electromagnetic Fields and Our Health
20th –
22nd October 2003
MEASUREMENT IN INDOOR AREAS
Measurements in the indoor areas were also performed for all the 5 schools that were
involved in the measurements. The indoor areas are categorized into 3 different categories,
which are classrooms, other indoor student areas such as libraries, laboratories, workshops
and etc, teacher and staff areas such as offices and meeting rooms.
Altogether 133 classrooms, 60 other indoor student areas, 54 teacher and staff areas and 34
outdoor areas which totals up to 281 areas were involved in this project. The most common
sources that can be found are the switches for the fluorescent lights and fans, overhead
projectors and computers. Some of the indoor areas which were involved in the
measurements are having the same sources of magnetic field; hence the mean magnetic field
value obtained is low and around 0.1 to 0.2mG. The exception occurs for some areas which
the higher mean magnetic field values are contributed by external sources such as
transmission lines and distribution lines, which is the case for Serdang Baru (2) (C) Primary
School. A few examples of the results of the measurements for the indoor areas, particularly
on the areas with high average magnetic field values and also the spot measurements that
were carried out mainly on the operator sources such as overhead projectors, switches for the
fluorescent lights and fans and computers are given next.
Classroom - 1I/3I
3.1 mG
Mean Magnetic Field Value
OFF = 7.02 mG
ON = 7.76 mG
3.7 mG
3.6 mG
9.14m
5.0 mG
5.8 mG
Distribution panel
6.5 mG
6.6 mG
4.5 mG
4.5 mG
F
F
7.47m
F
4.7 mG
5.5 mG
14.4 mG
16.4 mG
Sketch of a classroom measured in Serdang Baru (2) (C) Primary School
The sketch above is an example of the measurement that was performed in one of the
classrooms in Serdang Baru (2) (C) Primary School. The values which are marked in red are
when all the internal sources are switched on whereas the values marked in blue are when all
the internal sources are switched off. From the sketch, spot measurements were done at the 4
corners and at the center of the room. The only internal source that is available in the
classrooms and most of the classrooms which were involved in the measurements is the
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Proceedings of the International Conference on Non-Ionizing Radiation at UNITEN (ICNIR 2003)
Electromagnetic Fields and Our Health
20th –
22nd October 2003
lightings and fans switches, except for the Standard One classrooms in Tropicana Damansara
(C) Primary School, one of the significant operator source available is the projector which is
used as one of the teaching tool for Standard One students. The dimensions of the room was
also measured and recorded in the sketch. Spot measurements were also done at the corridor
of the classroom. It can also be seen here that the mean magnetic field value obtained is quite
high due to the distribution panel which is located outside the classroom.
Projector used in Standard One classroom of Tropicana Damansara (C) Primary School
One of the classrooms in Serdang Baru (2) (C) Primary School
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Proceedings of the International Conference on Non-Ionizing Radiation at UNITEN (ICNIR 2003)
Electromagnetic Fields and Our Health
20th –
22nd October 2003
Physics Lab #1
0.5 mG
Mean Magnetic Field Value
OFF = 0.48 mG
ON = 0.48 mG
0.5 mG
0.5 mG
14.7 m
0.5 mG
0.5 mG
0.5 mG
0.5 mG
OHP
F
F
F
F
F
9. 17 m
Teacher's
Table
Switchboard
0.3 mG
0.4 mG
OHP
Osilloscope
C
C
T
T
Van De Graff Machine
0.5 mG
0.5 mG
0.5 mG
0.5 mG
Sketch of a laboratory measured in Sri Indah Secondary School
The sketch above is one of the Physics laboratories that were measured in a secondary school
in Serdang. There are a few operator sources which are also considered sources of magnetic
fields available in this laboratory. The sources are the overhead projectors, the Van De Graff
machine, the oscilloscope and also the switchboard. Spot measurements were done for the
sources mentioned. Other than that, the measurement for the lab was carried out as have been
done for the other indoor areas according to the measurement protocols.
Mean Magnetic Field Value
OFF = 4.66 mG
ON = 9.04 mG
6.2 mG
4.5 mG
3.9 mG
3.6 mG
3.3 mG
9.1 m
2.7 mG
2.2 mG
2.0 mG
1.7 mG
6.5 mG
2.5 mG
6.2 mG
15.0 mG
F
1.7 mG
1.8 mG
1.8 mG
F
F
4.1 mG
14.8 mG
3.9 mG
18.4 mG
2.6 mG
F
F
0.9 mG
1.0 mG
1.4 mG
2.5 mG
Air-cond#1
0.6 mG
0.9 mG
Air-cond #2
20.5 mG
20.5 mG
Sketch of a computer lab measured in Serdang Baru (2) (C) Primary School
18
7.15 m
Computer Lab #1
Proceedings of the International Conference on Non-Ionizing Radiation at UNITEN (ICNIR 2003)
Electromagnetic Fields and Our Health
20th –
22nd October 2003
Computer Room #2
Computers (Single Row, NEC PC)
3.6 m
Wall
X
7.0mG
X
8.5mG
X
3.2mG
X
19.1mG VR
X
5.2mG
VR
X
6.8mG
X
X
X
0.6mG 0.8mG 1.2mG
X
X
X
4.4mG 4.1mG 1.7mG
X
0.4mG
X
0.8mG
7.2mG
X
5.2mG
X
9.4mG
X
VR
X
8.3mG
X
1.9mG
X
10.8mG
X
1.2mG
X
X
X
1.5mG 1.7mG 1.2mG
0.60 m
10.8mG
X
X
X
X
1.9mG 1.9mG 0.7mG
X
0.8mG
X
0.8mG
Legend:
VR Voltage Regulator
Spot measurements for computers in the lab
Computer lab in Serdang Baru (2) (C) Primary School
The sketch above is an example of the measurements that was performed in a computer lab
that is located in a building that is parallel to the transmission lines on the second floor of the
building. As can be seen, the mean magnetic field value obtained is 9.04mG which is also
quite high for the lab especially when all the internal sources are switched on. When the all
the internal sources are switched off, the mean magnetic field value drops to a value of
4.66mG and is still considered high. Note that the spot measurements are carried out also at
the 4 corners and at the center of the room, but this time the spot measurements were also
done at the center of each wall since to get a more detail and precise measurements. Spot
measurements were also done at every 3 feet at the corridor of the computer lab to obtain the
magnetic field level outside the lab.
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Proceedings of the International Conference on Non-Ionizing Radiation at UNITEN (ICNIR 2003)
Electromagnetic Fields and Our Health
20th –
22nd October 2003
Administrative Office
Mean Magnetic Field Value
OFF = 0.3 mG
ON = 0.7 mG
0.2 mG
0.2 mG
0.2 mG
24.38 m
1.0 mG
1.9 mG
0.1 mG
0.1 mG
S2
S3
S1
F
F
F
7.3 m
F
0.1 mG
0.1 mG
F
F
F
Principal's Office
0.1 mG
0.1 mG
0.2 mG
1.3 mG
Sketch of the administrative office in Leftenan Adnan Primary School Kajang
Other than the indoor student areas, the school offices in the category of teacher and staff
areas are also one of the examples that is shown above. As can be seen here, the
administrative office consists of a few rooms such as the principal’
s office and the assistant
principal’
s offices. Below is given the sketch of the principal’
s office. There are some
magnetic field sources which are available in the room such as the photocopier machine and
computer.
Principal's Office
Mean Magnetic Field Value
OFF = 0.12 mG
ON = 0.6 mG
4.75 m
0.1 mG
0.1 mG
0.1 mG
1.4 mG
2.4 m
F
Desk
0.1 mG
0.1 mG
Photocopier
0.1 mG
0.1 mG
0.2 mG
1.3 mG
Sketch of the principal’
s office in Leftenan Adnan Primary School Kajang
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Proceedings of the International Conference on Non-Ionizing Radiation at UNITEN (ICNIR 2003)
Electromagnetic Fields and Our Health
20th –
22nd October 2003
Administrative Office
Principal’
s Office
STATISTICAL ANALYSIS
The data that have been collected are analyzed by using statistical methods and tools to
summarize the level of overall exposure of the schools which are involved in the
measurements to magnetic fields. Statistical analysis is done for each 5 schools to determine
the percentage of areas and its magnetic field levels. Given below are the tables of the mean
and percentage of areas for all 5 schools involved.
21
Proceedings of the International Conference on Non-Ionizing Radiation at UNITEN (ICNIR 2003)
Electromagnetic Fields and Our Health
20th –
22nd October 2003
a. Tropicana Damansara (C) Primary School
Average Field (mG)
0.2
0.5
0.6
0.8
0.9
1.0
% of Areas
48.57
20.00
17.14
8.57
2.86
2.86
No. of areas
17
7
6
3
1
1
Table 1: Number of Classrooms with Magnetic Fields Exceeding Given Values
Average Field (mG)
0.1
0.4
0.6
0.8
1.0
1.2
1.5
2.0
% of areas
34.17
30.38
21.52
6.33
2.53
2.53
1,27
1.27
No. of areas
27
24
17
5
2
2
1
1
Table 2: Number of School Areas with Magnetic Fields Exceeding Given Values
Table 1 and Table 2 above show the percentages of areas and the average magnetic field
values for the classrooms and the all the school areas respectively for Tropicana Damansara
(C) Primary School. From Table 1, it is clearly seen that the total number of classrooms with
average magnetic field of 0.2mG to 0.5mG is the largest with 48.57 %. The number of
classrooms decreases with the increasing value of average magnetic field and from the table;
the number of classrooms obtained is only one for mean magnetic field values of more than
0.9mG and 1.0mG.
The same case happens in Table 2, where the number of school areas decreases with the
increasing value of magnetic field. However, the number of areas obtained for average
magnetic field of more than 0.1mG and 0.4mG does not vary much, with a total of 27 and 24
areas each. The number of areas can be seen decreasing greatly as the magnetic field value
reaches more than 1.0mG. Only four areas of the school are having mean magnetic field
values of more than 1.0mG.
b. Sri Indah Secondary School Serdang
Average Field (mG)
0.3
0.6
0.8
1.0
1.5
% of Areas
55.55
19.44
11.11
11.11
2.77
No. of areas
20
7
4
4
1
Table 3: Number of Classrooms with Magnetic Fields Exceeding Given Values
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Proceedings of the International Conference on Non-Ionizing Radiation at UNITEN (ICNIR 2003)
Electromagnetic Fields and Our Health
20th –
22nd October 2003
Average Field (mG)
0.3
0.5
0.8
1.1
1.2
1.5
2
% of areas
26.38
20.83
16.66
15.27
12.50
4.16
4.16
No. of areas
19
15
12
11
9
3
3
Table 4: Number of School Areas with Magnetic Fields Exceeding Given Values
Table 3 and Table 4 above represent the percentage of areas with mean magnetic field
exceeding given values for Sri Indah Secondary School in Serdang Selangor. From Table 3,
55.55% or 20 classrooms are having mean magnetic field of more than 0.3mG. For mean
magnetic field values of more than 0.8mG and 1.0 mG, both are accumulating 11.11% of the
total areas of classroom. Only one classroom in this school is having mean magnetic field
value of more than 1.5mG.
From Table 4, the number of areas is seen to be decreasing proportionally with the
decreasing value of magnetic field. The number of areas with the average magnetic field
value of more than 0.3mG is 26.38% and decreases to 15, 12, 11 and 9 areas for mean
magnetic field values of more than 0.5, 0.8, 1.1 and 1.2mG respectively. Both magnetic field
values of more than 1.5mG and 2.0mG are accumulating 8.32% or 8 areas of the total school
areas.
c. Serdang Baru (2) (C) Primary School, Serdang
Average Field (mG)
% of Areas
0.3
34.48
1.0
17.24
1.6
17.24
2.0
13.79
3.0
10.34
4.0
3.45
7.0
3.45
No. of areas
10
5
5
4
3
1
1
Table 5: Number of Classrooms with Magnetic Fields Exceeding Given Values
Average Field (mG)
0.2
0.6
1.1
1.8
3.0
4.0
9.0
12.0
% of areas
25.86
22.41
17.24
12.07
12.07
6.90
3.45
3.45
No. of areas
15
13
10
7
7
4
2
2
Table 6: Number of School Areas with Magnetic Fields Exceeding Given Values
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Proceedings of the International Conference on Non-Ionizing Radiation at UNITEN (ICNIR 2003)
Electromagnetic Fields and Our Health
20th –
22nd October 2003
For Serdang Baru (2) (C) Primary School, the mean magnetic field values for the areas
measured is higher compared to the other 4 schools which were involved in the
measurements. As can be seen from the tables obtained above, the number of areas is still
decreasing proportionally with the increasing values of magnetic fields, but only the level of
mean magnetic field is high. For the classrooms, the number of areas with average magnetic
field of more than 0.3mG is 10 or 34.48% of the total 29 classrooms measured. Both mean
magnetic field values of more than 1.0mG and 1.6mG are also accumulating 34.48% or 10
classrooms. 4 and 3 classrooms are having mean magnetic field of more than 2.0 and 3.0mG
respectively. One classroom is having average magnetic field value of more than 4.0mG.The
same case goes for the mean value of more than 7.0mG. This high value of more than 7.0mG
of magnetic field is due to the location of the classroom that is close to the underground
cables connecting to the distribution panel room located next to the classroom.
From Table 6, the number of areas with means magnetic field value of more than 0.2 mG is
about 25.86% or 15 areas. The number of areas is still high with 13 and 10 areas each for
both magnetic field of more than 0.6 and 1.1mG respectively. Both 1.8mG and 3.0mG are
having 7 areas each. 4 areas are having magnetic field value of more than 4.0mG while both
mean value of more than 9.0 and 12.0mG are having 2 areas each.
d. Leftenan Adnan Primary School, Kajang
Average Field (mG)
0.1
0.11 –
0.19
0.2
% of Areas
53.3
40.0
6.67
No. of areas
8
6
1
Table 7: Number of Classrooms with Magnetic Fields Exceeding Given Values
Average Field (mG)
0.1
0.11 –
0.19
0.2
0.5
1.0
% of areas
43.75
28.10
12.50
12.50
3.13
No. of areas
14
9
4
4
1
Table 8: Number of School Areas with Magnetic Fields Exceeding Given Values
The average magnetic field values obtained for the classrooms and all areas in this school is
quite low, with the average of 0.1mG accumulating more than 50% of the classrooms areas
and more than 43% of the school areas. For average values from 0.11 to 0.19mG, the number
of classrooms is still high since it represents 40% of the total classrooms and more than 28%
of the total areas. Only one classroom is having mean value of more than 0.2mG whereas
12.5% of the total areas are having mean value of more than 0.2mG. 12.5% of the total areas
are also having average magnetic field values of more than 0.5mG. Only 1 area of the whole
school is having mean magnetic field value of more than 1.0mG.
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Proceedings of the International Conference on Non-Ionizing Radiation at UNITEN (ICNIR 2003)
Electromagnetic Fields and Our Health
20th –
22nd October 2003
e. Bandar Baru Bangi Jalan (2) Primary School, Bangi
Average Field (mG)
0.1
0.2
0.21 –
0.29
% of Areas
33.33
38.88
6.67
No. of areas
6
7
5
Table 9: Number of Classrooms with Magnetic Fields Exceeding Given Value
Average Field (mG)
0.1
0.2
0.21 –
0.29
0.4
1.0
% of areas
43.8
25.0
21.9
6.25
3.13
No. of areas
14
8
7
2
1
Table 10: Number of School Areas with Magnetic Fields Exceeding Given Values
Both Table 9 and Table 10 above represent the statistics for the measurements that has been
carried out in a primary school located in Bandar Baru Bangi, Selangor. The mean values
obtained are quite low and is about the same as in Leftenan Adnan Primary School. A total of
6 classrooms and 14 areas are having average magnetic field value of 0.1mG. 7 out of the
total of 18 classrooms measured and 8 out of 32 areas are having mean values of 0.2mG.
6.67% of the total classrooms and 21.9% of the total areas are with average values from 0.21
to 0.29mG. The increasing value in magnetic fields resulted in only 2 areas with more than
0.4mG and only one area with mean value of more than 1.0mG.
The distribution of average fields was calculated separately for all types of school areas. The
results are given graphically in the form of box and whiskers plots in Figure 1.
Mean Magnetic Field (mG)
8
6
4
2
0
N=
133
60
40
34
281
Classrooms
Indoor areas
Staff Area
Outdoor
All Areas
Categories of areas
Fig. 1. Box and Whiskers Plots of the Distribution of Average Fields in Different Types of School Areas
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Proceedings of the International Conference on Non-Ionizing Radiation at UNITEN (ICNIR 2003)
Electromagnetic Fields and Our Health
20th –
22nd October 2003
The average magnetic field in the 5 schools classrooms is a statistical quantity described in
Figure 2. The figure shows, for example that 24% of the classrooms of the 5 schools have
average field greater than 0.2mG. The 95% confidence interval of the estimated percentage is
from 15% to 31%. Since the results corresponding to the lowest percentages are of greatest
interest, the same data are plotted with an expanded vertical scale in Figure 3. From this
figure it is possible to read, for instance, that 7.5% (95% C.I. from 0.3% to 14%) of
classrooms have average field greater than 0.9 mG. Table 11 shows the estimated number of
the 5 schools classrooms with fields exceeding a given value.
Average Field (mG)
0.1
0.3
0.5
0.6
0.8
1.0
1.5
2.0
3.0
5.0
% of Areas
30.83
16.54
14.29
11.28
8.27
6.76
5.26
3.01
2.25
1.50
No. of areas
41
22
19
15
11
9
7
4
3
2
95% C.I.
24.0 –
41.84
6.75 –
20.43
2.94 –
16.49
1.97 –
15.53
0.745 –
14.35
0.002 –
13.64
-0.998 –
12.71
-1.501 –
12.24
-2.006 –
11.78
-2.412 –
11.42
Table 11: Number of Classrooms with Magnetic Fields Exceeding Given Values
Distribution of Mean Magnetic Field in Classrooms
Percentage of Areas Exceeding Given Values (%)
50
40
30
20
10
0
0.1
0.3
0.5
0.6
0.8
1
1.5
2
-10
Mean Magnetic Field (mG)
Fig. 2. Distribution of Classroom Average Magnetic Field
26
3
5
Proceedings of the International Conference on Non-Ionizing Radiation at UNITEN (ICNIR 2003)
Electromagnetic Fields and Our Health
20th –
22nd October 2003
Distribution of Mean Magnetic Field in Classrooms
Percentage of Areas Exceeding Given Values (%)
25
20
15
10
5
0
0.1
0.3
0.5
0.6
0.8
1
1.5
2
3
5
-5
Mean Magnetic Field (mG)
Fig. 3. Distribution of Classroom Average Magnetic Field. Same data as Figure 2, but with an expanded vertical
scale
The average magnetic field in the 5 schools school area (classroom, other indoor student
occupied areas, offices, outdoor areas) is a statistical quantity described in Figure 4. The
figure shows, for example, that about 22% of school areas have average field greater than
0.2mG. The 95% confidence interval of the estimated percentage is from 13% to 30%. Since
the results corresponding to the lowest percentages are of greatest interest, the same data are
plotted with an expanded vertical scale in Figure 5. From this figure it is possible to read, for
instance, that 10% (95% C.I. from 0.1% to 14.8%) of school areas have average field greater
than 0.7mG. Table 12 shows the estimated number of all the 5 schools areas with fields
exceeding a given value.
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Proceedings of the International Conference on Non-Ionizing Radiation at UNITEN (ICNIR 2003)
Electromagnetic Fields and Our Health
20th –
22nd October 2003
Average Field (mG)
0.1
0.3
0.5
0.6
0.8
1.1
1.5
2.0
3.0
4.0
5.0
10.0
% of areas
27.76
16.73
14.23
11.03
8.89
7.12
4.63
2.85
2.49
1.78
1.42
1.07
No. of areas
78
47
40
31
25
20
13
8
7
5
4
3
95% C.I.
21.16 –
40.19
5.28 –
19.88
1.764 –
16.16
0.861 –
15.25
-0.279 –
14.14
-1.223 –
13.23
-1.900 –
12.59
-2.368 –
12.15
-2.838 –
11.72
-3.074 –
11.503
-3.216 –
11.373
-3.500 –
11.114
Table 12: Number of School Areas with Magnetic Fields Exceeding Given Values
Distribution of Mean Magnetic Field in All Areas
45
40
Percentage of Areas Exceeding Given Value (%)
35
30
25
20
15
10
5
0
0.1
0.3
0.5
0.6
0.8
1.1
1.5
2
3
-5
-10
Mean Magnetic Field (mG)
Fig. 4. Distribution of All Areas Average Magnetic Field
28
4
5
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Proceedings of the International Conference on Non-Ionizing Radiation at UNITEN (ICNIR 2003)
Electromagnetic Fields and Our Health
20th –
22nd October 2003
Distribution of Mean Magnetic Field in All Areas
24
Percentage of Areas Exceeding Given Value (%)
19
14
9
4
-1
0.1
0.3
0.5
0.6
0.8
1.1
1.5
2
3
4
5
10
-6
Mean Magnetic Field (mG)
Fig. 5. Distribution of All Areas Average Magnetic Field. Same data as Figure 4, but with an expanded vertical
scale
CONCLUSION
Exposure assessment of electromagnetic fields in Malaysian public schools environment is
going on successfully. The level of magnetic fields in the sample of five different schools
with different types of internal and external sources have been thoroughly measured and
evaluated. The values that have been obtained vary from school to school due to the different
sources, especially external sources of magnetic fields available around the school areas. The
data presented are useful for understanding the levels of magnetic fields that can be
encountered in different environment of schools and also for estimating exposure levels to
students and instructors while attending school.
ACKNOWLEDGEMENT
The authors like to acknowledge the financial support of IRPA (Ministry of Science,
Technology and Environment), principals of schools and support given by UNITEN and
TNB to facilitate measurements.
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Proceedings of the International Conference on Non-Ionizing Radiation at UNITEN (ICNIR 2003)
Electromagnetic Fields and Our Health
20th –
22nd October 2003
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[1]
William F. Horton, Saul Goldberg. Power Frequency Magnetic Fields and Public
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[2]
Leonard A. Sagan, MD. 1996. Electric and Magnetic Fields: Invisible Risks? Gordon
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[3]
Electric and Magnetic Field Exposure Assessment of Powerline and Non-Powerline
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for
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[4]
Review of Powerline EMF Health Effects and the Role of Electric Power Utility
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Anthony J.Hayter.1996. Probability and Statistics for Engineers and Scientists. PWS
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A.S Farag, M.M Dawoud, T.C Cheng, Jasen S. Cheng, “
Occupational Exposure
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Maruthi, R., Karunakara, K.; Kumari, M.K.; Srinivasa, K.M., Channakeshava;
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1995. Proceedings of EMPD '95., 1995 International Conference on , Volume: 1 , 21-23 Nov.
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[9]
Desai, R., Shah, D.T., “
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, Southcon/96. Conference Record , 25-27 June 1996, pp. 233 - 235
30