COURSE CODE: 72542 COURSE NAME: MINE ENVIRONMENTAL

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COURSE CODE: 72542

COURSE NAME: MINE ENVIRONMENTAL ENGINEERING

CREDITS: 3

COURSE INSTRUCTOR: Dr. Sumant Mohanto

Department of Mining Engineering

Malla Reddy Engineering College, Telangana

MODULE II:

AIR POLLUTION, NOISE AND VIBRATION

LECTURE:NOISE AND VIBRATION: BASIC CONCEPTS,

SOURCES, MONITORING AND CONTROL

MEASURES

NOISE POLLUTION: DEFINITION

• Noise: Unwanted sound pollutant producing undesirablephysiological and psychological effects in an individual, byinterfering with one’s social activities like work, rest,recreation, sleep, etc.

• Noise of sufficient intensity and duration: induce health problems:temporary and permanent hearing loss

• Other effects of noise pollution: annoyance, irritation, disturbance,headaches, insomnia, fatigue, mental torture, nausea, high bloodpressure, high pulse rate, greater perspiration, etc.

SOUND: CHARACTERISTIC AND MEASUREMENT

• Sound: Alternating pressure changes inthe air and caused by vibrations of solidobjects or separation of fluids, as theypass over, around, or through holes insolid objects

• Surrounding air undergo compression,followed by rarefaction, thencompression, then rarefaction, and so on

• Results in sound waves propagating insinusoidal path

Period (P)

Wavelength


• Period (P): Time between successivepeaks or troughs of oscillation

• Frequency (f): Number of times a peakarrives in a second

P = 1/fHuman ear: 20 – 20000 Hz

• Wavelength ( ): Distance betweensuccessive peaks or troughs

= C. (1/f)

where C = velocity of the sound wave

Period (P)

Wavelength


• Power of sound (W): Energy transmittedby a sound wave in the direction of itspropagation

• Sound intensity (I): Sound poweraveraged over time per unit area normalto direction of propagation of sound wave

P = 1/f

• Relation between W and I:

I = W/where I = intensity of the sound wave (watt/m2),W = power of sound wave in watts = unit area perpendicular to the direction ofwave motion

Period (P)

Wavelength

LEVELS OF NOISE and TYPES OF SOUND

▪ Sound pressure: varies in the range of 20 μPa – 200 Pa

▪ Thus, sound pressure expressed on a scale based on the log of the ratio of themeasured sound pressure ‘P’ and a reference standard pressure ‘Pref’, also calledsound pressure level ‘SPL’ or noise level (decibel)

SPL= 20 log [P/Pref] (dB)

P = measured sound pressure (N/m2)Reference/standard sound pressure Pref= 2 × 10-5 N/m2


• TYPES OF SOUND✓ Continuous noise: uninterrupted sound level that varies less than 5 dB during entire period of

observation. e.g. running fan

✓ Intermittent noise: noise which continues for more than 1 second and is then interrupted formore than 1 second (> 30 dB). e.g. drilling machine used by a dentist

✓ Impulse noise: change of sound pressure of atleast 40 dB within 0.5 second with a duration ofless than one second. e.g. firing of a weapon

SOURCES OF NOISE POLLUTION

1. Traffic Noise:• Air traffic• Road traffic, and• Sea-shore and inland water traffic

• Amount and type of noise produced bytraffic is largely dependent upon type oftraffic


2. Industrial Noise:• Noise: essential by-product of industry

• Intensity and nature depends on the typeof the industry.

• Industrial noises produced by rotating,reciprocating or any other types ofmachinery, or by high pressure highvelocity gases, liquids or vapour involved inthe industrial processes

• Usual noise level of the industries of theorder of 60 to 95 dB


3. Noise produced by other sources:

• Blaring of loudspeakers and sirens

• Shouting of hawkers

• Ringing bells

• Playing of children

• General life activity

• Fire crackers in festive seasons andcelebrations

SOURCES OF SOME NOISE AND THEIR INTENSITY

Source Intensity Source Intensity

Quiet conversation 20 – 30 dB Radio music 50 – 60 dB

Loud conversation 60 dB Traffic noise 60 – 90 dB

Lawn mower 60 – 80 dB Heavy truck 90 – 100 dB

Aircraft noise 90 – 120 dB Space vehicle 140 – 180 dB

Beat music 120 dBJet Engine 140 dB

Motor cycle 105 dB

Instantaneous rapture of the membrane occurs at the decibel of 150. Threshold of pain is caused at the decibel of 146. If the noise level increased to 150 decibels than within no time there will be an instantaneous rupture of membrane occurs.

EFFECTS OF NOISE POLLUTION

1. Auditory effects:

▪ Auditory fatigue -- Whistling & buzzing in ears( noise level - 90dB)

▪ Deafness -- Permanent hearing loss ( noise level- 100dB)

2. Non-auditory effects:

▪ Interference with speech communication - 50dB

▪ Annoyance, ill temper, bickering

▪ Loss in working efficiency - tiredness, deterioration or complete loss of ability to work


3. Physiological disorders:

▪ Neurosis, anxiety, hypertension, increased sweating, giddiness,nausea, fatigue, visual disturbance, reduces depth and quality of sleep,peptic ulcers, Increases cholesterol level resulting in constriction of blood vessel,Low weight children to mothers

Noise (dB) Health hazards80 Annoyance90 Hearing damage95 Very annoying

110 Stimulation of reception in skin120 Pain threshold130 Nausea,vomiting140 Pain in ear150 Burning of skin160 Rupture of tymphonic membrane180 Permanent damage


3. Other effects:

▪ Even the nonliving things such as buildings undergo physical damage by cracks,breakage of windows, doors, and glasses etc. by sudden and explosive sounds

NOISE POLLUTION: CONTROL

1. At source level:• Designing and fabricating silencing devices in air craft engines, automobiles industrial

machines and home appliances• By segregating the noisy machines

2. During transmission:• Achieved by adding insulation and sound-proofing to doors, around industrial

machinery• Zoning urban areas to maintain a separation between residential areas and zones of

excessive noise✓Acoustillite : made up of compressed wood pulp, wood fibers and is available in theform of tiles✓Acoustical blanket : Prepared from mineral wool or glass fibres✓Hair Felt: Consists of wool fibres, coarse cotton fibres.✓Fibre Glass

NOISE POLLUTION: CONTROL

2. During transmission:

✓Cork Carpet: Prepared out of pieces of corks treated with linseed oil and is used for

covering floors.

✓Acoustic Plaster: Mainly consists of gypsum in the form of plaster

3. Protecting the exposed person

4. Creating vegetation cover:

✓ Plants absorb and dissipate sound energy and thus act as Buffer Zone

✓ Trees should be planted along highways, schools and other places

PERMISSIBLE AMBIENT NOISE LEVEL IN DIFFERENT AREAS

Area Code CategoryNoise level (dB)

Day time Night time Area Industrial Area 75 70

B Commercial Area 65 55C Residential Area 55 45D Silence Zone 50 40

▪ Silence zones near schools, hospitals.▪ Indiscriminate use of loudspeakers at public places should be banned/restricted by laws▪ Restriction on unnecessary use of horns and vehicles plying without silencers


▪ Thus, sound pressure expressed on a scale based on the log of the ratio of themeasured sound pressure ‘P’ and a reference standard pressure ‘Pref’, also calledsound pressure level ‘SPL’ or noise level (decibel)

SPL= 20 log [P/Pref] (dB)

P = measured sound pressure (Pa)Reference/standard sound pressure Pref= 2 × 10-5 Pa

▪ Since SPL are based on log scale, they cannot be added directly. If there are i numberof sources, the total sound pressure level SPLT is calculated by:


▪ Average sound pressure level Lavg produced by single source:

𝐿𝑎𝑣𝑔 = 20 𝑙𝑜𝑔10 (1

𝑛) [10

𝐿𝑖

20]

Where n is number of sound observationsand Li is the SPL of the source at a particular time interval

NUMERICALS: NOISE POLLUTION

1. If sound pressure is 0.02 Pa, what is the sound pressure level?

2. Given two machines producing 80 dB each, what is the total SPL?

3. Given four machines producing 100 dB, 91dB, 90 dB, and 89 dB respectively, what is thetotal sound pressure level?

4. The sound pressure level of a jet plane with sound pressure of 2000 bar should be:(a) 60 dB(b) 100 dB(c) 140 dB(d) 180 dB

1 bar = 105 Pa


5. A source emits 80 dB, 60 dB and 100 dB at different times in a day. What is the averagenoise produced by the source in the day?


1. If sound pressure is 0.02 Pa, what is the sound pressure level?Ans: 69.5 dB

2. Given two machines producing 80 dB each, what is the total SPL?Ans: 83 dB

3. Given four machines producing 100 dB, 91dB, 90 dB, and 89 dB respectively, what is thetotal sound pressure level?Ans: 101.2 dB

THANK YOU

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COURSE CODE: 72542 COURSE NAME: MINE ENVIRONMENTAL