9.1.1
When electricity is used, electric fields (ELF)
are
produced by the voltage in a conductor and magnetic fields are produced by the
current or flow of electricity in a conductor. In a modern society that depends
on electricity, electromagnetic fields (EMF) are a fact of life. ELF and EMF are
produced by virtually all consumer appliances, computer terminals, wiring in
homes, offices and power lines.
9.1.2
Over the past few decades, the issue of possible
health effects of EMF has generated a number of studies and reports. However,
no conclusive scientific evidence showing health hazard from ELF
and EMF has been found. The weight of the evidence from those studies indicates that CLP Power’s present power delivery methods are safe and no changes
are warranted.
9.1.3
This section is to address whether there is any
potential adverse impacts to arouse health concern of the surrounding residents
or workers arising from the operation of existing overhead pole lines and to
recommend mitigation measures to reduce the impacts, if any, to acceptable
standards.
9.1.4
According to the latest development area boundary,
the overhead cables and pylons are situated at and/or are close to the southern
portion of the San Hing Road (SHR) Site, SHR Site Extension and Hong Po Road
(HPR) Site. As such, the potential ELF and EMF impacts to the future
development at this portion of the development area (Site) have been evaluated
and discussed in the following sections.
9.2
Environmental
Legislation and Guidelines
9.2.1
Guidelines on limits of exposure to power frequency ELF
and EMF were issued by the International Commission on Non-ionizing Radiation
Protection (ICNIRP) in 1998. The guidelines were recognised by both the World
Health Organisation and the Hong Kong SAR Government. ELF and EMF generated
from the overhead line and underground cables shall comply with the guidelines
(see Table 9.1).
Table 9.1 Guidelines on
Limits of Exposure to 50Hz Power Frequency Electric and Magnetic Fields Issued
by ICNIRP
|
Exposure Characteristics |
Electric Field Strength V/m (rms) |
Magnetic Flux Density Microtesla
(rms) |
|
General Public Continuous |
5,000 |
100 |
|
Occupational Continuous |
10,000 |
500 |
Note: The
standards stipulated in Chapter 7 of Hong Kong Planning Standards and
Guidelines following the ICNIRP limits for 50 Hz electric and magnetic fields.
9.3.1
In order to investigate the potential health hazard
to humans due to exposure by overhead lines, ELF and EMF measurement have
been
carried out in accordance with the ELF and EMF standards
stipulated in Chapter 7 of the Hong Kong Planning Standards and Guidelines and
the guidelines issued by the ICNIRP in 1998, as well as the
requirements of the Study Brief issued by Environmental Protection Department.
9.3.2
The strength of electric and magnetic field
which are generated by the existing overhead lines have been measured on-site
and evaluated with reference to the stipulated standards.
Electric Field Strength Measurement Procedures
9.3.3
The electric field adjacent to a conducting
surface is normal to the surface. Therefore, the horizontal component of the
electric field, particularly where it is generated by overhead lines, can be
ignored close to the ground surface. Single-axis measurement (vertical
component) is therefore sufficient near the ground at
a height of 1.0 m above the ground under overhead lines.
9.3.4
In order to take electric field level
measurements representing the unperturbed field at a given location, the area
should be free as far as possible from other overhead lines, towers, trees,
fences, tall grass, or other irregularities. It is preferred that the location
should be relatively flat. It should be noted that the influence of vegetation
on the electric field level can be significant. In general, field enhancement
occurs above individual items of vegetation and field attenuation occurs near
the sides. The distance between the measuring probe and the object should be at
least 1.0 m.
9.3.5
To reduce perturbation of a measured electric
field, the distance between the electric field measurement instrument and the
operator should be at least 3.0 m. This can be achieved using a fibre optic
cable between the monitor and the probe with the latter on a non-conductive
support.
Magnetic Field Strength Measurement Procedures
9.3.6
Magnetic field measurements should be made with
three-axis instruments and should be of the resultant field.
9.3.7
Non-permanent objects containing magnetic
materials or nonmagnetic conductors should be at least three times the largest
dimensions of the object away from the point of measurement in order to measure
the unperturbed field value. The distance between the measuring probe and
permanent magnetic objects should be at least 1.0m in order to accurately
measure the unperturbed field.
9.3.8
The presence of the operator does not affect
the magnetic field. Consequently, the measuring instrument is hand-held device.
In the same way, most objects, which may perturb the electric field, do not
affect the magnetic field.
Position Electric and Magnetic
Fields Measurement Procedures
9.3.9
The largest electric/magnetic field level is
found under conductors at the point on the span where the conductors are
closest to the ground. Therefore, to find the position where the field level is
the maximum, the electric/magnetic field level should first be measured at 1.0
m above the ground along the path parallel to the overhead line under
conductors where possible at appropriate intervals (longitudinal profile).
Then, to discover whether another peak occurs, measurement should be performed
at 1.0 m above the ground along the path perpendicular to the overhead line, at
the point of the longitudinal profile maximum (lateral profile). When the
position where the field level is a maximum is already known in the area of interest,
a single-point measurement should be performed at that position.
9.3.10
Figures 9.1a and 9.1b show the measurement locations
within the project site boundary. The selection criteria of the sampling
locations are based on potential risk of human exposure to ELF and EMF during
operation of the housing development. As a result, twelve (12) sampling points
are proposed which cover the proposed public transport interchanges (PTI),
school sites, housing sites and sewage pumping station (SPS) within the proposed
development area as shown in Table 9.2. No
sampling point for ELF and EMF measurement was selected at or/and nearby the
infrastructure works due to infrastructure works are mainly for installation of
water mains, drainage and sewerage works and junction improvement works. The chance
for human to expose ELF and EMF generated by overhead cable would be low within
infrastructure works boundary during construction and operation phases (please
refer to Figure 9.1a and
Figure 9.1b).
Table 9.2 ELF and EMF
Measurement Locations
|
No. |
Easting |
Northing |
Description |
|
1 |
814967 |
831070 |
HPR Site – Proposed Housing Development Area |
|
2 |
815068 |
831037 |
HPR Site – Proposed PTI |
|
3 |
815129 |
831047 |
HPR Site – Proposed PTI |
|
4 |
815155 |
831067 |
HPR Site – Proposed PTI |
|
5 |
815462 |
831174 |
SHR Site Extension – Proposed Housing Development
Area |
|
6 |
815608 |
831041 |
SHR Site – Proposed Housing Development Area |
|
7 |
815734 |
830974 |
SHR Site – Proposed School Site |
|
8 |
815813 |
830781 |
SHR Site – Proposed SPS |
|
9 |
815764 |
830870 |
SHR Site – Proposed PTI |
|
10 |
815815 |
830828 |
SHR Site – Proposed PTI |
|
11 |
815866 |
830786 |
SHR Site – Proposed PTI |
|
12 |
815933 |
830793 |
SHR Site – Proposed Housing Development Area |
9.4.1
The existing 400kV overhead cables run from the hillside near Tsing Shan
firing range boundary and then have sharp bend near Po Tong Ha, and run then across
the Hong Po Road, open storages area, brownfield sites and San Hing Tsuen areas
(as shown in Figure 9.1a). People living in these
areas and the workers work in the open storage areas, and brownfield sites would
expose to ELF and EMF associated with the overhead lines for certain extends.
9.5.1
The measurement of overhead cables in relation to ELF and EMF were
carried out at the measurement locations as shown in Table
9.2. For measurement locations nos.
2-4 and 9-11, they are located within the proposed PTI boundaries. For remaining
measurement locations nos. 1, 5-8 and 12, they are located within the the proposed
housing development areas, school sites and SPS boundaries. The results for ELF
and EMF are summarised in Table
9.3 and Table
9.4 respectively.
Table
9.3 ELF Measurement Results
|
No. |
Description |
Electric Field Strength V/m (rms) |
ICNIRP Standard V/m (rms) |
Compliance |
|
Proposed
PTI |
|
|||
|
2 |
At HPR Site |
50 |
5,000 |
Yes |
|
3 |
At HPR Site |
148 |
||
|
4 |
At HPR Site |
288 |
||
|
9 |
At SHR Site |
49 |
||
|
10 |
At SHR Site |
52 |
||
|
11 |
At SHR Site |
281 |
||
|
Other
Proposed Development/Works |
|
|||
|
1 |
HPR Site – Proposed Housing Development |
2 |
5,000 |
Yes |
|
5 |
SHR Site Extension – Proposed Housing Development Area |
10 |
||
|
6 |
SHR Site – Proposed Housing Development |
88 |
||
|
7 |
SHR Site – Proposed School Site |
3 |
||
|
8 |
SHR Site – Proposed SPS |
34 |
10,000 |
|
|
12 |
SHR Site – Proposed Housing Development |
124 |
5,000 |
|
Table 9.4 EMF Measurement
Results
|
No. |
Description |
Magnetic Flux Density µT (rms) |
ICNIRP Standard µT (rms) |
Compliance |
|
Proposed
PTI |
|
|||
|
2 |
At HPR Site |
2.63 |
100 |
Yes |
|
3 |
At HPR Site |
4.88 |
||
|
4 |
At HPR Site |
3.51 |
||
|
9 |
At SHR Site |
1.46 |
||
|
10 |
At SHR Site |
2.02 |
||
|
11 |
At SHR Site |
2.24 |
||
|
Other
Proposed Development/Works |
|
|||
|
1 |
HPR Site – Proposed Housing Development |
0.58 |
100 |
Yes |
|
5 |
SHR Site Extension – Proposed Housing Development Area |
0.48 |
||
|
6 |
SHR Site – Proposed Housing Development |
0.60 |
||
|
7 |
SHR Site – Proposed School Site |
0.44 |
||
|
8 |
SHR Site – Proposed SPS |
1.29 |
500 |
|
|
12 |
SHR Site – Proposed Housing Development |
1.24 |
100 |
|
9.5.2
On-site measurement results indicated that ELF
and EMF arising from the existing overhead cables to the proposed PTIs and
proposed development/works will be only a fraction of the guideline limits (i.e.
ranging from 0.04% to 6% of ELF guideline limits; ranging from 0.3% to 5% for EMF
guideline limits). Thus, the overhead cables locating within the proposed PTI
and proposed development/works will not pose a hazard to human health.
9.6.1
The assessment results demonstrate that the exposure
of the public to the ELF and EMF generated from the existing 400kV overhead
cables do not exceed (far below) the values laid down under the guidelines
issued by the ICNRP in 1998. Moreover, there is no concrete scientific evidence
to demonstrate that exposure of low-level ELF and EMF generated from overhead
cables is harmful to human health. As a result, no mitigation measure is
required.
9.7.1
Some sections of the existing 400kV overhead
cables run across the Hong Po Road and San Hing Tsuen areas. In order to
investigate the potential health hazard to humans due to exposure to EMF
generated by overhead lines, an on-site measurement have been conducted at
the selected locations which represent the proposed locations of PTIs, housing
development areas, school sites and SPS.
9.7.2
The assessment results confirmed that the strength
of the ELF and EMF generated from the 400kV overhead cables are well below the
stipulated guideline limits issued by the ICNIRP in 1998. As such, the overhead
cables locating within the proposed PTI and proposed development/works will not
pose a hazard to human health.