NOISE POLLUTION By Bibhabasu Mohanty Assistant Professor Department of Civil EngineeringSAL Institute of Technology & Engineering Research
CONTENTMeasurement of sound, Sources,Effects and control of noise pollution
THE NATURE OF SOUND Sound is a physical phenomenon that stimulates the sense of hearing. Sound, a manifestation of vibration, travels in wave patterns through solids, liquids and gases. Sound waves of equal amplitude with increasing frequency from top to bottom.
BASIC TERMINOLOGY Frequency: Frequency is the no of cycles repeated in unit time duration. Its unit is cycle/sec or Hz(1Hz=1Cycle/sec) Intensity: Amount of sound energy received / sec is known as intensity of sound. Its Unit is decibel(dB).
Decibel: Decibel is define as the logarithm to the base 10 to ratio of two intensities Lt =10log10(I/I0)dB Where, I=Measured Intensity I0=Reference Intensity Lt=Level of noise in dB
SOUND NOISE Pleasant to hear Unpleasant to hear Constant pitch Constantly varying pitch Regular periodic motion No regular periodic motion Produces meaningful Produces no meaningful communication communication Unit is Hertz (Hz) Unit is decibel (dB) Hz= cycle/sec. dB=10 log(intensity measured/reference intensity)
LEVELS OF NOISEL = log10 Q/Q0 (bels) Q=Measured Intensity Q0=Reference Intensity L=Level of sound in Bels1dB= 1/10 BHence, L = 10 log10 Q/Q0 (dB)
When sound pressure is measured, Q0= 20 μPa.Lp= 10 log10(Prms/ 20μPa)2sound pressure is computed by squaring r.m.s valueor Lp= 20 log10(Prms/ 20μPa) When sound power is measured, Q0= 10 – 12 watts Lw = 10 log 10 (W/10– 12) When sound intensity level measured , Q0= 10 – 12 W/m2 LI = 10 log 10 (I/10– 12)
Sound level meters (SLMs) measure sound pressure level and are commonly used in noise pollution studies. Positioned in desired location with no obstruction from source and sound is taken. Basic parts include microphone, amplifiers, weighting networks and display reading in dB.
This device performs three basic operations: - First, microphone to convert the energy in the sound into an electrical signal. When a sound wave hits the microphone, it causes a diaphragm. To vibrate, electronic signals, which are proportional to the sound pressure causing the vibration. Thirdly, this electronic network then provide meaningful results transmitted through a visual display.
Internationally accepted three weighing scales adopted. A,B and C.A for human intensity to low intensity sound.B for medium intensity sound.C for human response to high intensity sound.
Rule of thumb when measuring noise levels The noise source being measured should be at least 10 dB above the background (ambient) noise. Keep the sound level meter as far away from any large reflecting surfaces as you are from the source that you are measuring. Allmeasurements are to be made with the microphone at least 3 feet above the ground.
SOUND AND HUMAN HEARING People generally hear sounds between the “threshold of hearing” and the “threshold of pain”. In terms of pressure, this is 20 μPa – 100 Pa. The decibel scale was developed from this fact and makes numbers more manageable. The decibel scale generally ranges from approximately 0 to 130.
HUMAN HEARING AND FREQUENCY0 16 Hz 20 kHz 5 MHz
WHAT IS NOISE POLLUTION ??? unwanted sound that penetrates the environment any noise irritating to ones ear which comes from an external source in relatives terms one’s enjoyment may be pollution to other. sound which pleases the listeners is music and which causes pain and annoyance is noise. noise affect us in hearing, ability to communicate and behavior.
SOURCE OF NOISE POLLUTION Street traffic Rail traffic Road traffic Airplanes Constructions Indoor source (Radio, TV, AC, home appliances) Less maintained vehicles produce more sounds
NOISE STANDARDS Area code Category of area Limits in dB Day time Night time A Industrial area 75 70 B Commercial area 65 55 C Residential area 55 45 D Silence zone 50 40 Day time: 6 am to 9 pm Night time: 9pm to 6 am
EFFECTS OF NOISE POLLUTION Loss of hearing Annoyance Health effects Interference with communication Working efficiency
Loss of hearing – due to exposure of noise, which termed as artificial hearing loss.1. Noise induced temporary threshold shifts (NITTS)- due to exposure to loud noise like bursting of crackers. Recovered in a short period of time.2. Noise induced permanent threshold shifts (NIPTS)- because of exposure to loud noise for long period time.
Annoyance – subjective matter for sound/noise. Someone may like classical music, it may annoy others. Annoyance is felt about 75 to 85 dB. Blood vessel get constricted, breathing rate affected.Health effects –Effects on physical health. Auditory effects- short time and long time effects. Acoustic trauma due to high intensity impulsive noise of about 150 dB or more. Non-auditory effects- exposure to loud noise increase pulse rate and blood pressure change.
Effects on mental health- lack of conc. at high noise level and mental disturbance.Interference with communication – background noise affect the efficiency of offices, schools and other places where communication is vital importance. External sound also interfere with conversation and use of telephone as well as enjoyment of radio and TV. Maximum acceptable limit of noise 55dB.
Working efficiency – decrease the working efficiency drastically. Experiments indicate that irregular bursts of noise are more disruptive than steady noise. Sound levels of 90 dB may interfere with the performance of a task.Other effects Sleep interference Personal comfort interference Effects on wild life Increased industrial accidents.
CONTROL OF NOISE POLLUTION Can never be eliminated completely, but it can be controlled. Noise pollution can be controlled by paying attention to one or all of the three elements involved:
Source :- can be modified by changing in design, treatment of machine surface, noise source could be stopped or operation limited to certain times. Transmission path :- sound insulating enclosure, construction of noise barrier, absorbing materials along the path. Receiver :- altering the work schedule, by provision of ear protection.
Others steps to control noise pollution Noise pollution (Regulation and control) Rules, 2000. Vehicular noise can be controlled by proper maintaince. Industrial noise controlled under the factory act, 1948. Legal laws to control blaring loudspeakers, playing of music system at loud level. Use of better technology in design of systems like fan, AC, washing machines and refrigerators.
Proper town planning can help in avoiding noise pollution (construction from major noise sources). Proper zoning and separation of buffers. Thick and high vegetation can absorb much noise. Aerodrome should be located away from the city. Aeroplanes should take off in direction readily away from the city.
Noise barrier: Highway in Melbourne, Australia