Noise pollution


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Noise pollution

  1. 1. NOISE POLLUTION By Bibhabasu Mohanty Assistant Professor Department of Civil EngineeringSAL Institute of Technology & Engineering Research
  2. 2. CONTENTMeasurement of sound, Sources,Effects and control of noise pollution
  3. 3. 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.
  6. 6. 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).
  7. 7.  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
  8. 8. 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)
  9. 9. 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)
  10. 10.  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)
  12. 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.
  13. 13.  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.
  14. 14.  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.
  15. 15. 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.
  16. 16. 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.
  18. 18. HUMAN HEARING AND FREQUENCY0 16 Hz 20 kHz 5 MHz
  19. 19. 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.
  20. 20. 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
  21. 21. 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
  23. 23. EFFECTS OF NOISE POLLUTION Loss of hearing Annoyance Health effects Interference with communication Working efficiency
  24. 24. 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.
  25. 25. 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.
  26. 26. 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.
  27. 27. 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.
  28. 28. 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:
  29. 29.  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.
  30. 30. 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.
  31. 31.  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.
  32. 32. Noise barrier: Highway in Melbourne, Australia