Noise PollutionNoise Pollution

Ms Noor Rosyidah Binti Sajuni

School of Engineering

rosyidah@ucsi.edu.my

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Content

• Definition,

• sources of noise pollution,

• unit measurement,

• effects of noise pollution to environment and human,

• major noise monitoring devices,

• control and preventive action.

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Definition

• Sound:

Sound, a manifestation of vibration, travels in wave patterns through solids, liquids and gases. The waves, caused by vibration of the molecules, follow sine functions, typified by the amplitude and wavelength (or frequency)

Sound waves of equal amplitude with increasing frequency from top to bottom

• Noise Pollution:

Any unwanted sound that penetrates the environment is noise pollution.In general noise pollution refers to any noise irritating to one's ear which comes from an external source.

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Sound propagation

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Level and the Decibel• Unit measurement: Decibel (dB, or tenth (deci) of a Bel)). The decibel is named after Alexander

Graham Bell, the Canadian pioneer of the telephone who took great personal interest in the

problems of deaf people.

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Power / Intensity / Pressure

Intensity & pressure – measured using instruments

Power is calculated

Power is basic measure of acoustic energy it can produce & is independent of surroundings

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Power / Intensity / Pressure ???

Sound Power: for noise rating of machinesunique descriptor of noisiness of sourceW=4πr2I

Sound Pressure: evaluation of harmfulness and annoyance of noise sources

Sound Intensity: location & rating of noise sourcesrate of energy flow per unit areaI=P2/ρc

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Sound power and intensity

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Sound pressure level

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Effect of multiple sound sources• Average Sound power

• Average Sound pressure

• Equivalent continuous equal energy level

1010

1

10log 10nLpN

totn

Lp

N Li

p NL

1

20101

log20

))(10(log101

10i

N Li

eq tL

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How sound is measured

•Pressure, P, usually Pascals

•Frequency, f, usually Hertz

•Intensity, I, usually W/m2

•Bels, L’, derived from logarithmic ratio

•Decibels, L, derived from bels

P = 1/f

I = W/A

L’ = log (Q/Qo)

L = 10*log (Q/Qo)

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- The following photos show two differentThe following photos show two different kinds of kinds of decibel metersdecibel meters::

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Sources of noise pollution

• Street traffic

• Rail roads

• Airplanes

• Constructions

• Consumer products

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Sound and human hearing – Frequency

Humans are less sensitive to low frequency sound and more sensitive to high frequency sound. Therefore, sometimes the dB scale is adjusted to take this into account:

A-weighting (db(A)): adjusts overall scale so it better matches what the human ear would hear

C-weighting (dB(C)): adjusts scale for loud or low frequency sounds

B-weighting (dB(B)): adjusts by factors that are “in between” the A-weighted factors and C-weighted factors (rarely used)

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Effect of Noise Pollution

• There are about 25000 hair cells in our ear which create wave in our ear, responding to different levels of frequencies.

• With increasing levels of sound the cells get destroyed decreasing our ability to hear the high frequency sound.

• Constant exposure to loud noise → temporary / permanent hearing loss depending on:– volume– Duration– Repetition of exposure

• Irreversible hearing loss.• Blood pressure rise of 5 to 10 mmHg on 8 hrs of exposure to even 70 dV of sound

level.• Hearing loss begins at 80- 90 dBA. 140 dbA is painful and 180 dB can even kill a

person.• Most of the electronic vehicles and motors are above 80 dB level.• High noise levels may interfere with the natural cycles of animals, including feeding

behavior, breeding rituals and migration paths.

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Impact of Noise• Annoyance:

– It creates annoyance to the receptors due to sound level fluctuations. The periodic sound due to its irregular occurrences causes displeasure to hearing and causes annoyance.

• Physiological effects:

– The physiological features like breathing amplitude, blood pressure, heart-beat rate, pulse rate, blood cholesterol are effected.

• Loss of hearing:

– Long exposure to high sound levels cause loss of hearing. This is mostly unnoticed, but has an adverse impact on hearing function.

• Human performance:

– The working performance of workers/human will be affected as they'll be losing their concentration.

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Impact of Noise (continue)

• Nervous system:

– It causes pain, ringing in the ears, feeling of tiredness, thereby effecting the functioning of human system.

• Sleeplessness:

– It affects the sleeping there by inducing the people to become restless and loose concentration and presence of mind during their activities

• Damage to material :

– The buildings and materials may get damaged by exposure to infrasonic / ultrasonic waves and even get collapsed.

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Symptoms of occupational hearing loss• Feeling of fullness in the ear.

• Sounds may seem muffled.

• Cannot hear high frequency sounds.

• Ringing in the ears while listening to the high frequency sounds.

• Loud noise for a long period of time, or sudden burst of sound can cause occupational hearing loss.

• Hearing that does not return after an acute noise injury is called a permanent threshold shift.

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• Factories And Machinery (Noise Exposure) Regulations 1989

Legislation/Regulatory guidelines

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Guidelines for Environmental Noise Limits and Control, DOE

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Noise Management Strategy

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Noise Control Plan

i. design stage - design out or minimise noisy work;

ii. organizational stage - plan how the site will be managed and the risks controlled;

iii. contractual stage - ensure that contractors meet their legal requirements; and

iv. building phase - assess the risks, eliminate or control them, and review the assessment.

Before work starts on site:

i. implement a low-noise procurement policy (purchase and hire) for machinery and work equipment;

ii. set desired noise-control requirements in the tender specifications;

iii. plan the work process to minimize worker exposure to noise; and

iv. implement a noise-control programme (for example, by planning, training, induction, site layout, maintenance activities).

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Noise Control at Source• Reducing the noise levels from domestic sectors:

– The domestic noise coming from radio, tape recorders, television sets, mixers, washing machines, cooking operations can be minimized by their selective and judicious operation. By usage of carpets or any absorbing material, the noise generated from felling of items in house can be minimized.

• Maintenance of automobiles:

– Regular servicing and tuning of vehicles will reduce the noise levels. Fixing of silencers to automobiles, two wheelers etc., will reduce the noise levels.

• Control over vibrations:

– The vibrations of materials may be controlled using proper foundations, rubber padding etc. to reduce the noise levels caused by vibrations.

• Low voice speaking:

– Speaking at low voices enough for communication reduces the excess noise levels.

• Prohibition on usage of loud speakers:

– By not permitting the usage of loudspeakers in the habitant zones except for important meetings / functions. Now-a-days, the urban Administration of the metro cities in India, is becoming stringent on usage of loudspeakers.

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• Selection of machinery:

– Optimum selection of machinery tools or equipment reduces excess noise levels. For example selection of chairs, or selection of certain machinery/equipment which generate less noise (Sound) due to its superior technology etc. is also an important factor in noise minimization strategy.

• Maintenance of machines:

– Proper lubrication and maintenance of machines, vehicles etc. will reduce noise levels. For example, it is a common experience that, many parts of a vehicle will become loose while on a rugged path of journey. If these loose parts are not properly fitted, they will generate noise and cause annoyance to the driver/passenger. Similarly is the case of machines. Proper handling and regular maintenance is essential not only for noise control but also to improve the life of machine.

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Control in the transmission path

• Installation of barriers:

– Installation of barriers between noise source and receiver can attenuate the noise levels. For a barrier to be effective, its lateral width should extend beyond the line-of-sight at least as much as the height (See Fig. 5).

– The barrier may be either close to the source or receiver, subject to the condition that, R <<D or in other words, to increase the traverse length for the sound wave. It should also be noted that, the presence of the barrier itself can reflect sound back towards the source.

– At very large distances, the barrier becomes less effective because of the possibility of refractive atmospheric effects. Another method, based on the length of traverse path of the sound wave is given at Fig. 6.

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• Design of building:

– The design of the building incorporating the use of suitable noise absorbing material for wall/door/window/ceiling will reduce the noise levels.

– The approximate reduction of outside noise levels using typical exterior wall construction is given at Table 6. The reduction in noise levels for various frequencies and the A-weighted scale are shown.

– Variations in spectrum shape may change this A-weighted value by as much as +/- 3 dB.

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• Installation of panels or enclosures:

– A sound source may be enclosed within a paneled structure such as room as a means of reducing the noise levels at the receiver.

– The actual difference between the sound pressure levels inside and outside an enclosure depends not only on the transmission loss of the enclosure panels but also on the acoustic absorption within the enclosure and the details of the panel penetrations which may include windows or doors.

– The product of frequency of interest and surface weight of the absorbing material is the key parameter in noise reduction through transmission loss.

– With conventional construction practices, the high-frequency transmission loss of a panel becomes limited to around 40 dB, owing to the transmission of sound through flanking paths other than the panel itself.

– Examples of such flanking are structural connections or ducts joining the two spaces on either side of the panel of interest. Procedures for detailed design examples.

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• · Green belt development:

– Green belt development can attenuate the sound levels. The degree of attenuation varies with species of greenbelt.

– The statutory regulations direct the industry to develop greenbelt four times the built-up area for attenuation of various atmospheric pollutants, including noise.

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• Using protection equipment

– Before employing the use of protective equipment, the various steps involved in the noise management strategy are illustrated.

– Protective equipment usage is the ultimate step in noise control technology, i.e. after noise reduction at source and/or after the diversion or engineered control of transmission path of noise.

– The first step in the technique of using protective equipment is to gauge the intensity of the problem, identification of the sufferer and his exposure to the noise levels.

– For the Regulatory standards pertaining to time of exposure vs. maximum noise levels permitted in a workspace environment.

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• The usage of protective equipment and the worker's exposure to the high noise levels can be minimized by -

– Job rotation: By rotating the job between the workers working at a particular noise source or isolating a person, the adverse impacts can be reduced.

– Exposure reduction: Regulations prescribe that, noise level of 90 dB (A) for more than 8 hr continuous exposure is prohibited. Persons who are working under such conditions will be exposed to occupational health hazards. The schedule of the workers should be planned in such a way that, they should not be over exposed to the high noise levels.

– Hearing protection: Equipment like earmuffs, ear plugs etc. are the commonly used devices for hearing protection. Attenuation provided by ear-muffs vary widely in respect to their size, shape, seal material etc. Literature survey shows that, an average noise attenuation up to 32 dB can be achieved using earmuffs .