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Environmental Engineering
Lecture # 6
Chemical Engineering Department UET Lahore
Synopsis
Noise Pollution Noise & Our Hearing Level of Noise Measurement of Noise Classification of Noise Sources of noise Impacts of noise Control of noise pollution Conclusion
What is Noise?
Noise is unwanted sound.Sound is a form of energy which is emitted by a vibrating body and on reaching the ear causes the sensation of hearing through nerves. Or we can say when the effects of sound are undesirable it termed as NOISE
Noise Pollution and Our Hearing
The inner ear of humans contains a snail-shaped structure called a cochlea that is lined with thousands of microscopic hairs. When sound vibrations enter the cochlea, they cause the tiny hairs to move back and forth. If strong vibrations blast into the cochlea, the hairs can be flattened and damaged.
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.
The response of the human 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.
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. A simpler way is to use a logarithmic scale. As such, the loudness of sound is commonly expressed in decibel (dB).
Levels of Noise in the Environment
Sound Levels and Human ResponseCommon sounds Noise Level [dB] Effect
Rocket launching pad, (no ear protection) 180 Irreversible hearing lossCarrier deck jet operation, Air raid siren 140 Painfully loud
Thunderclap 130 Jet takeoff (200 ft), Auto horn (3 ft) 120 Maximum vocal effort
Pile driver, Rock concert 110 Extremely loudGarbage truck, Firecrackers 100 Very loud
Heavy truck (50 ft), City traffic 90 Very annoyingHearing damage (8 Hrs)
Alarm clock (2 ft), Hair dryer 80 AnnoyingNoisy restaurant, Freeway traffic, Business
office 70 Telephone use difficultAir conditioning unit
Conversational speech 60 IntrusiveLight auto traffic (100 ft) 50 Quiet
Living room, Bedroom, Quiet office 40 Library, Soft whisper (15 ft) 30 Very quiet
Broadcasting studio 20 10 Just audible 0 Hearing begins
Measurement of Noise
Sound Power
Sound Intensity
Sound Pressure
IrW 24
c
pI
2
010log20p
pLp
Example
If a sound source has a pressure of 2000µPa at 10m distance, compute:
a) The sound pressure level in dB,
b) The sound intensity in W/m2,c) The sound power in W.
Answers
a) Lp = 40dBb) I = 9.9x10-9 W/m2
c) W = 12.5x10-6 W
Classification of Noise
1) Community Noise/Environmental Noise
2) Occupational Noisea) Continuous Noiseb) Intermittent Noisec) Impulsive Noise
Community Noise
It is also known as, Environmental Noise Domestic Noise Residential Noise
Sources: Road, Rail, Air traffic Construction and Public works Restaurant, cafeteria etc. Sporting events like motor
sports Play grounds Parks
Occupational Noise
Sources: Industrial Machinery
includes, Rotors, gears, electrical
machines. Combustion engines Drilling, crushing Pneumatic equipment
Occupational Noise
Continuous Noise
Impulsive Noise
Intermittent Noise
Continuous Noise
It is produced by the machinery that operates without interruption e.g.
Pumps, Compressors and Processing equipments
Intermittent Noise
Impulsive Noise
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