CCCH9008 Noise Pollution and Control in HK Two important characteristics of sound or noise Frequency of Sound Sound is the quickly varying pressure wave travelling through a medium. When sound travels through air, the atmospheric pressure varies periodically. The number of pressure variations per second is called the frequency of sound, and is measured in Hertz (Hz) – cycles per second. Loudness A loud noise usually has a larger pressure variation and a weak one has smaller pressure variation. Pressure and pressure variations are expressed in Pascal (Pa) – Newton per square metre (N/m2). The human audible range Human ear can perceive a very wide range of sound pressure. |?? |Sound Pressure expressed in | |?? |Pa |??Pa | |Softest Noise just Heard by a Human Ear (the Threshold of |20 x 10-6 |20 | |Hearing) | | | |Launching of the Space Shuttle |2,000 |2 x 109 | To express sound or noise in terms of Pa is quite inconvenient because we have to deal with numbers from as small as 20 to as big as 2,000,000,000. Response of the human ear to sound – audible range ?? A normal human ear is able to hear sounds with frequencies from 20 Hz to 20,000 Hz. The range of 20 Hz to 20,000 Hz is called the audible frequency range. The sounds we hear comprise of various frequencies. ?? The response of the ear to sound is dependent on the frequency of the sound.
The human ear has peak response around 2,500 to 3,000 Hz and has a relatively low response at low frequencies. Audible range – There is a remarkably wide range of frequencies and sound pressure levels over which the human ear can detect. Noise Problems in HK Major causes of noise pollution in later 1980s * A high-rise and high density living environment * The high volume of surface traffic * The prevalence of high-rise flatted factories The close interface between noise sensitive premises and noise sources, such as factory buildings and roads, due to the scarcity of land for development * The almost incessant construction activities dictated by the fast pace of development * An increasingly busy international airport situated in the centre of the populated area * The sub-tropical climate which renders noise insulation and expensive option due to the need to provide air-conditioning. A four-pronged approach is adopted by the Government to tackle environmental noise in HK.
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The four prongs are as follows : * planning – proactive participation in the planning and policy making process, * abatement – formulating abatement strategies and implementation of noise abatement measures, * control – control on noise by enforcing of the Noise Control Ordinance, and * partnership – promoting partnership with various stakeholders. a. planning The Government has been taken a more active environmental participation in the land-use and infrastructure planning process since the mid-1980s to pre-empt noise problems.
The Government has prescribed standards with due regards to noise in planning new development or redevelopment projects. All new major development projects are required to go through the Environmental Impact Assessment process to ensure that existing and planned noise sensitive receivers such as residential dwelling and schools are protected from excessive noise. Where the predicted noise impacts exceed the applicable noise criteria, direct mitigation measures as shown below shall be considered and evaluated in an appropriate manner: * alternative land use arrangement alternative siting * screening by noise tolerant buildings * setback of buildings Mitigation of Noise Impacts * alternative alignment * treatment of source * open-textured road surfacing * decking over * building orientation * extended podium * special building design * architectural features/balcony * noise barrier/enclosure b. Abatement * Abatement is one of the means to resolve existing noise problems. * Examples of these problems are : * busy highways running through residential districts; * schools affected by noise from aircraft or road traffic. The Government has implemented noise abatement programmes such as * the School Insulation Programme, * the Quiet Road Surfacing Programme and * the Retrofit Noise Barrier Programme to reduce impact of traffic noise on existing noise sensitive receivers. c. Control * Many forms of environmental noise have already been put under statutory control. A key instrument for control is the Noise Control Ordinance, which commenced in 1989. other related ordinance: * The Civil Aviation (Aircraft Noise) Ordinance and Road Traffic Ordinance contain provisions for the control of environmental noise.
References Hong Kong Environmental Protection Department’s Educational Package on Environmental Noise: http://www. epd. gov. hk/epd/noise_education Environmental Protection Department website: Hong Kong’s Environment: Noise: http://www. epd. gov. hk/epd/english/environmentinhk/noise/noise_maincontent. html Environmental Protection Department (1989) Environment Hong Kong 1989??: A Review of 1988, Hong Kong Government. The Normal Equal-loudness Contours of a normal human ear. [pic] [pic]