Exposure Assessment of Electromagnetic Fields in Malaysian Public

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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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, cost-effectiveness 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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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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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 air-conditioners. 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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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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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.

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C:\student\srj(c)damansara\060303t.lines2.mbk

Broadband ResultantBroadband X - ComponentBroadband Y - ComponentBroadband Z - Component

2.0Mar/06/200311:59:18 AM

258.0

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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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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.

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Broadband Resultant

2.0Feb/22/200312:13:40 PM

196.0

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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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Badminton court (next to football field)

Water tank and TNB substation (Looking from the football field)


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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.

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C:\Program Files\Enertech Consultants\EMCALC 2000\Data\dsara school 22feb03 f ball f ield.mbk

Broadband Resultant

0.3Feb/22/200311:20:39 AM

648.9

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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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P ole 1

X 4 5X 40

X 34

X 2 9.4 X 2 8

X 29 .7

X 2 8.3

X 3 1

X 2 5

X 58 .8

X 1 01

X 9 3

X 53 .1

X 3 9

33 k

V

mar

kers

scho

ol fe

nce

com

pact

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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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1 1 3 m

1 5 0 m

2 5 0 m

P ow er linesM ain R o ad

School ga te

en trance

To Kuala

Lumpu r

To

Kaj

ang

S u bs ta tio n

S c h o o lB u ild in g s

L o w v o l tag esu b st a tio n

T ran s m iss ion l ine s

H o u s e s

H o u s e s

Subs

tatio

n's

fenc

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ol's

back

fen

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T itle : M e a su re m e n t o f su b sta tio n b e h in dL e fte n a n A dn a n P rim a ry S c ho o l

*0 .4 m G

*0 .2 m G

*0 .1 m G

*0 .2 m G

*0 .2 m G

*0 .2 m G

*0 .2 m G* 0 .3 m G

*0 .1 m G

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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L o w v o l ta g e s u b s ta t io n ( 4 1 5 V )

S u b s ta t io n

9 .3 m GX

7 .9 m GX

4 .6 m GX

7 .5 m GX

1 0 .1 m GX

X1 3 .2 m G

X1 3 .5 m G

X1 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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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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2.0 mG2.2 mG

1.4 mG1.5 mG

1.2 mG1.4 mG

0.4 mG0.4 mG

1.7 mG1.8 mG

F

v

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0.9 mG1.0 mG

0.9 mG1.0 mG

0.9 mG1.1 mG

2.0 mG2.0 mG

1.2 mG1.3 mG

0.7 mG1.1 mG

0.9 mG1.4 mG

1.0 mG1.3 mG

1.4 mG1.6 mG

0.5 mG0.9 mG

0.8 mG1.5 mG

0.9 mG1.2 mG

0.5 mG0.7 mG

0.3 mG1.3 mG

1.0 mG1.5 mG

0.3 mG0.9 mG

0.3 mG0.5 mG

1.7 mG2.0 mG

1.2 mG1.8 mG

0.7 mG0.9 mG

1.9 mG2.5 mG

1.7 mG2.9 mG

3.6 mG3.6 mG

3.7 mG3.7 mG

1.8 mG2.5 mG

1.7 mG1.8 mG

1.6 mG1.7 mG

1.6 mG2.9 mG

3.4 mG3.4 mG

1.4 mG2.0 mG

3.4 mG3.4 mG

1.1 mG1.5 mG

3.6 mG3.6 mG

F

F

6.1

m 3.8

m

18.

7 m

Wall

School Brick Fence

Transmission Lines

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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to under the 275 kV line. The picture taken below also shows the location of the lines and tower near the school fence.

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C:\Program Files\Enertech Consultants\EMCALC 2000\Data\SMKSRIINDAH240403.mbk

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2.0Apr/24/200301:19:38 PM

336.0

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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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Path taken for measurement of the school building

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1962.0

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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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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

6.5 mG6.6 mG

14.4 mG16.4 mG

4.7 mG5.5 mG

5.0 mG5.8 mG

4.5 mG4.5 mG

FF F

3.1 mG 3.7 mG 3.6 mG

9.14m7.

47m

Mean Magnetic Field ValueOFF = 7.02 mGON = 7.76 mG

Dis

trib

utio

n pa

nel

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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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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Physics Lab #1

Tea

cher

'sT

able

0.5 mG0.5 mG

0.5 mG0.5 mG

0.5 mG0.5 mG

0.5 mG0.5 mG

0.3 mG0.4 mG

FF F

0.5 mG 0.5 mG 0.5 mG

F F

OHP

OHP

C

T

C

T

Osilloscope

Van De Graff Machine

9. 1

7 m

14.7 m

Switchboard


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.

6.2 mG15.0 mG

1.8 mG1.8 mG

3.9 mG18.4 mG

20.5 mG20.5 mG

1.4 mG2.5 mG

Computer Lab #1

7.1

5 mF FF

9.1 m

F

Air-cond#1

F

4.1 mG14.8 mG

0.6 mG0.9 mG

0.9 mG1.0 mG

6.5 mG2.5 mG

4.5 mG6.2 mG 3.9 mG 3.6 mG 2.2 mG2.6 mG2.7 mG3.3 mG

Air-cond #2

2.0 mG 1.7 mG 1.7 mG


Sketch of a computer lab measured in Serdang Baru (2) (C) Primary School


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Computer Room #2Computers (Single Row, NEC PC)

VR

VR

VR

3.6 m

0.60

m

X0.6mG

X1.2mG

X0.8mG

10.8mGX

X8.5mG

X19.1mG

X4.4mG

X4.1mG

X1.7mG

X6.8mG

X5.2mG

X0.4mG

X0.8mG

9.4mGX

X0.8mG

X0.8mG

X1.5mG

X1.2mG

X1.7mG

X8.3mG

X10.8mG

5.2mGX

X1.9mG

X1.9mG

X0.7mG

X1.9mG

X1.2mG

7.2mGX

VRLegend:

Voltage Regulator

Wall

X7.0mG

X3.2mG

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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Administrative Office

1.0 mG1.9 mG

0.1 mG0.1 mG

0.2 mG1.3 mG

0.1 mG0.1 mG

0.1 mG0.1 mG

FF

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F

F

FF

Principal's Office

S2

S1S3

0.2 mG 0.2 mG0.2 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

0.1 mG0.1 mG

0.1 mG0.1 mG

0.2 mG1.3 mG

0.1 mG1.4 mG

0.1 mG0.1 mG F

4.75 m

2.4

m


Photocopier

Desk

Sketch of the principal’s office in Leftenan Adnan Primary School Kajang


21

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.


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a. Tropicana Damansara (C) Primary School

Average Field (mG) % of Areas No. of areas 0.2 48.57 17 0.5 20.00 7 0.6 17.14 6 0.8 8.57 3 0.9 2.86 1 1.0 2.86 1

Table 1: Number of Classrooms with Magnetic Fields Exceeding Given Values

Average Field (mG) % of areas No. of areas 0.1 34.17 27 0.4 30.38 24 0.6 21.52 17 0.8 6.33 5 1.0 2.53 2 1.2 2.53 2 1.5 1,27 1 2.0 1.27 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) % of Areas No. of areas 0.3 55.55 20 0.6 19.44 7 0.8 11.11 4 1.0 11.11 4 1.5 2.77 1



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Average Field (mG) % of areas No. of areas

0.3 26.38 19 0.5 20.83 15 0.8 16.66 12 1.1 15.27 11 1.2 12.50 9 1.5 4.16 3 2 4.16 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 No. of areas 0.3 34.48 10 1.0 17.24 5 1.6 17.24 5 2.0 13.79 4 3.0 10.34 3 4.0 3.45 1 7.0 3.45 1


Average Field (mG) % of areas No. of areas 0.2 25.86 15 0.6 22.41 13 1.1 17.24 10 1.8 12.07 7 3.0 12.07 7 4.0 6.90 4 9.0 3.45 2

12.0 3.45 2 Table 6: Number of School Areas with Magnetic Fields Exceeding Given Values


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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) % of Areas No. of areas

0.1 53.3 8 0.11 – 0.19 40.0 6

0.2 6.67 1 Table 7: Number of Classrooms with Magnetic Fields Exceeding Given Values


0.1 43.75 14 0.11 – 0.19 28.10 9

0.2 12.50 4 0.5 12.50 4 1.0 3.13 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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e. Bandar Baru Bangi Jalan (2) Primary School, Bangi

Average Field (mG) % of Areas No. of areas 0.1 33.33 6 0.2 38.88 7

0.21 – 0.29 6.67 5 Table 9: Number of Classrooms with Magnetic Fields Exceeding Given Value


0.1 43.8 14 0.2 25.0 8

0.21 – 0.29 21.9 7 0.4 6.25 2 1.0 3.13 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.

Fig. 1. Box and Whiskers Plots of the Distribution of Average Fields in Different Types of School Areas

281344060133N =

Categories of areas

All AreasOutdoor Staff Area Indoor areasClassrooms

Mea

n M

agne

tic F

ield

(m

G)

8

6

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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) % of Areas No. of areas 95% C.I.

0.1 30.83 41 24.0 – 41.84 0.3 16.54 22 6.75 – 20.43 0.5 14.29 19 2.94 – 16.49 0.6 11.28 15 1.97 – 15.53 0.8 8.27 11 0.745 – 14.35 1.0 6.76 9 0.002 – 13.64 1.5 5.26 7 -0.998 – 12.71 2.0 3.01 4 -1.501 – 12.24 3.0 2.25 3 -2.006 – 11.78 5.0 1.50 2 -2.412 – 11.42 Table 11: Number of Classrooms with Magnetic Fields Exceeding Given Values

Fig. 2. Distribution of Classroom Average Magnetic Field

Distribution of Mean Magnetic Field in Classrooms

-10

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20

30

40

50

0.1 0.3 0.5 0.6 0.8 1 1.5 2 3 5

Mean Magnetic Field (mG)

Per

cent

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%)


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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.

Distribution of Mean Magnetic Field in Classrooms

-5

0

5

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15

20

25

0.1 0.3 0.5 0.6 0.8 1 1.5 2 3 5


Per

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Average Field (mG) % of areas No. of areas 95% C.I.

0.1 27.76 78 21.16 – 40.19 0.3 16.73 47 5.28 – 19.88 0.5 14.23 40 1.764 – 16.16 0.6 11.03 31 0.861 – 15.25 0.8 8.89 25 -0.279 – 14.14 1.1 7.12 20 -1.223 – 13.23 1.5 4.63 13 -1.900 – 12.59 2.0 2.85 8 -2.368 – 12.15 3.0 2.49 7 -2.838 – 11.72 4.0 1.78 5 -3.074 – 11.503 5.0 1.42 4 -3.216 – 11.373 10.0 1.07 3 -3.500 – 11.114

Table 12: Number of School Areas with Magnetic Fields Exceeding Given Values

Fig. 4. Distribution of All Areas Average Magnetic Field

Distribution of Mean Magnetic Field in All Areas

-10

-5

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25

30

35

40

45

0.1 0.3 0.5 0.6 0.8 1.1 1.5 2 3 4 5 10


Per

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)


29

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.

Distribution of Mean Magnetic Field in All Areas

-6

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0.1 0.3 0.5 0.6 0.8 1.1 1.5 2 3 4 5 10


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REFERENCES [1] William F. Horton, Saul Goldberg. Power Frequency Magnetic Fields and Public Health. CRC Press. [2] Leonard A. Sagan, MD. 1996. Electric and Magnetic Fields: Invisible Risks? Gordon and Breach Publishers. [3] Electric and Magnetic Field Exposure Assessment of Powerline and Non-Powerline Sources for California Public School Environments. Internet: http://www.dhs.ca.gov/ps/deodc/ehib/emf. [4] Review of Powerline EMF Health Effects and the Role of Electric Power Utility Companies. Presentation of 3rd TNB Technical Conference 6th-8th August 2001. [5] Electromagnetic Fields Explained. Internet: http://www.aaronline.com/documents/1114-aspx. [6] Anthony J.Hayter.1996. Probability and Statistics for Engineers and Scientists. PWS Publishing Company. [7] A.S Farag, M.M Dawoud, T.C Cheng, Jasen S. Cheng, “Occupational Exposure Assessment for Power Frequency Electromagnetic Fields”, Energy Conversion Engineering Conference, 1997. IECEC-97 Proceedings of the 32nd Intersociety, Vol:3, 27 July – 1Aug 1997. pp. 2107 – 2113. [8] Maruthi, R., Karunakara, K.; Kumari, M.K.; Srinivasa, K.M., Channakeshava; “Computation and measurement of AC electric and magnetic field lateral profiles and longitudinal contours under transmission lines”, Energy Management and Power Delivery, 1995. Proceedings of EMPD '95., 1995 International Conference on , Volume: 1 , 21-23 Nov. 1995, pp. 209 – 214 [9] Desai, R., Shah, D.T., “Electromagnetic fields: can't live without them, can't live with them”, Southcon/96. Conference Record , 25-27 June 1996, pp. 233 - 235

http://www.dhs.ca.gov/ps/deodc/ehib/emf.

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Exposure Assessment of Electromagnetic Fields in Malaysian Public