Question

i. Identify and discuss methods used to control noise pollution.
ii. Discuss how noise pollution level is measured and calculated.
iii. A machine with an overall noise level of 80 dB is placed in a room with another machine putting out 90 dB.
a. What will be the sound level in the room?
b. How long should workers be in such a room in one working day, based on the permitted noise levels criteria?

Answer 1

i) There are several ways to control noise pollution. a few of these are listed below:

1. Controlling at receiver's end: This includes wearing headphones, earplugs etc.

2. Source suppression: This includes adding infrastructure that reduces noise at the source and placing padding arround the machinery to reduce noise.

3. Acoustic zoning: This means placing the machinery in zones where the sound produced is less likely to disturb residential areas, hospitals and other places that might be specially sensitive to noise pollution.

4. Sound insulation during construction: This includes measures taken to reduce sound while construction a building such as padding doors and walls.

5. Planting of trees considerably reduces sound .

6. Legislative measure: Include prohibition of sounds above certain levels past certain hours of the day and banning usage of machinery and bursting of firecrackers etc that might emit these sound levels past certain times

ii) Noise pollution is measured using a microphone attached to a decibelmeter. A decibel is the standard unit for measurement of noise. deciBels are measured on a logarithmic scale, so that an increase of 10dB means that the sound inensity has increased by a factor of 10.

iii) The two intensities are 80dB and 90dB.

The intensity of 80dB is 10⁸W and 90dB is 10⁹W. Thus, the total intensity is 11x10⁹W . Taking log, we get 10.04. Thus, the dB level is 10x10.04 = 100.4dB (dB = 10log₁₀W)

At these levels, workers can stay for only 15 minutes without it affecting their hearing.