Replies to LegCo questions
LCQ8: Impact of magnetic fields on human health
Following is a question by the Hon Patrick Lau and a written reply by the
Secretary for Health, Welfare and Food, Dr York Chow, in the Legislative Council
today (July 6):
Question :
Some members of the public have complained to me that the magnetic fields inside
their flats are strong enough to divert the needle of a compass to a particular
direction. They suspect that this phenomenon may be attributable to the
reinforcement bars inside the walls or the high voltage power lines in the
vicinity of their buildings. In addition, some medical experts have suggested
that magnetic fields generated by high voltage power lines are hazardous to
health. It has also been reported that, according to a study by a cancer
research group of the Oxford University in the United Kingdom, the incidence of
leukemia among children living within 200 metres of pylons is 70 per cent higher
than ordinary children. In this connection, will the Government inform this
Council whether it knows if:
(a) any studies have been carried out in Hong Kong or other countries on the
impact on human health of magnetic fields generated by reinforcement bars inside
the walls of buildings, high voltage power lines in the vicinity of residential
buildings or other environmental factors; if so, of the study results;
(b) there are any stipulations regarding the minimum distance between high
voltage power lines and residential buildings in Hong Kong or other countries;
and
(c) there is a set of monitoring indicators in Hong Kong or other countries for
assessing whether the levels of magnetic fields in the living environment meet
the safety standards and for regulatory control purposes; if so, of the details;
if not, the reasons for that?
Reply :
Madam President,
(a) As far as the Administration is aware, no local study has been conducted on
the impact on human health of magnetic fields generated by reinforcement bars
inside the walls of buildings, high voltage power lines in the vicinity of
residential buildings or other environmental factors. The Administration however
notes that the link between cancer development and the electromagnetic fields
generated by overhead high-voltage power lines has been a subject of scientific
studies worldwide. As far as we understand, the studies have not provided
conclusive evidence that electromagnetic field exposures would increase
leukaemia risks. As regards reinforcement bars in building structures, they do
not produce any magnetic fields and we are not aware that any studies has been
conducted in other places about the link between cancer development and such
reinforcement bars.
We are aware that some UK researchers have recently conducted the largest study
of childhood cancer and power lines to date. While the study has identified,
inter alia, greater leukaemia risks for children born close to pylons, the
authors of the study consider that the relation may be due to chance and may not
be supported by scientific explanations. They also do not regard their findings
as establishing a definite causal association between childhood leukaemia and
exposures to electromagnetic fields from power lines. Moreover, the Health
Protection Agency of the United Kingdom considered that studies conducted so
far, including the one in question, were unable to establish a conclusive link
between childhood leukaemia and exposure to electromagnetic fields as they
failed to address other possible factors that might affect the study outcomes,
like representativeness of the control groups, and demographic factors that
differ between those who live near pylons and those who live further away etc.
(b) With advice from Electrical and Mechanical Services Department (EMSD) and
other relevant departments, Chapter 7 of the Hong Kong Planning Standards and
Guidelines (HKPSG) issued by the Planning Department require, on electrical
safety considerations, that minimum safety clearance be provided between
conductors (including overhead power lines) and adjacent buildings/structures.
The respective minimum safety clearances for various voltage levels of
conductors are set out below -
Voltage Level (kV)
Minimum Safety Clearance (m)
400
5.5
132
3.7
66
3.2
33
2.9
11
2.9
HKPSG also require that, for electrical safety considerations, adequate vertical
ground clearance be provided in the design of overhead power lines. In
determining the minimum vertical ground clearance, reference should be made to
the relevant statutory requirements as laid down in the Electricity Supply
Regulations (Cap. 406A). The specific requirements, as set out in HKPSG, are as
follows -
Voltage Level (kV)
Minimum
Vertical Ground Clearance (m)
400
7.6
132
6.7
66
6.1
33
6.1
11
6.1
In setting the above clearance requirements, reference has been made to relevant
standards and guidelines in other places, particularly those in the United
Kingdom.
Apart from the electrical safety considerations, the HKPSG also set out the
environmental and health considerations with regard to the overhead power lines.
Although there is no conclusive scientific evidence to date to support the
hypothesis of adverse health effects arising from exposure to power frequency
electric and magnetic fields (EMF), the EMF exposure limit promulgated in the
guidelines issued by the International Commission on Non-ionizing Radiation
Protection (ICNIRP) in 1998 are adopted by EMSD as a prudent avoidance against
the influence of power frequency EMF.
In line with the guidelines issued by ICNIRP, the following standards on the
continuous public exposure limits for power frequency electric and magnetic
fields are recommended to the power companies by EMSD when the erection of
permanent overhead power lines is planned -
(i) electrical field strength not exceeding 5 kV per metre; and
(ii) magnetic flux density not exceeding 0.1 millitesla.
The power companies should seek further advice from EMSD at the design and
planning stages of the overhead power lines.
A preferred working corridor for overhead power lines which provides the
physical separation and makes allowance for environmental, safety and health
considerations has been set. The preferred working corridor for 400 and 132 kV
overhead power lines on pylons are 50 m and 36 m wide respectively. At the early
planning stage of the overhead power lines, the power company concerned should
provide the necessary information to EMSD for consideration.
(c) The EMF emanating from overhead power lines, known as power frequency EMF,
are at extremely low frequency. That said, in the interest of public health, and
to protect citizens from the influence of power frequency EMF, we have adopted
the relevant EMF exposure limits promulgated in the guidelines issued by the
ICNIRP. In planning permanent overhead power lines, the two power companies in
Hong Kong must comply with relevant standards set out in HKPSG regarding the
continuous public exposure limits for power frequency EMF.
EMSD carries out regular on-site measurement of EMF near overhead power lines
throughout the territory. So far, the EMF levels measured are below the exposure
limits promulgated in the ICNIRP guidelines. In addition, EMSD will also carry
out on-site inspection and measurement of EMF near overhead power lines if
requested by the public.
As mentioned in part (a), reinforcement bars in building structures do not
produce any magnetic fields, and monitoring indicators are therefore not
developed in Hong Kong. We are also not aware of such indicators being adopted
in other places.
Ends/Wednesday, July 6, 2005
Issued at HKT 13:52
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