Noise Pollution In Residential Areas Biology Essay

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Twenty six sites power looms industries were selected in the nine sectors of Mohalla Gorakhnath in Gorakhpur city. Out of twenty six industries selected, one industry is having two power looms, six numbers of industries are having 2 to 4 power looms, ten numbers of industries are having 4 to 8 power looms and twelve numbers of industries are having more than 8 power looms. These small scale power loom based industries are located in the heart of residential colonies of Gorakhnath area of the Gorakhpur city. Photographs of some of power loom based textile industries are given in Appendix-A. People in these areas are suffering from the noise pollution generated by the operation of power looms. So, it was decided to measure the noise produced by power loom industries in these areas with an aim to suggest suitable measures for their control.

For understanding the noise effect, noise levels (db) were recorded at three time slots viz. 9:00 AM, 12:00 PM and 9:00 PM. 24-hour data was also recorded at few sites for understanding the noise pattern for full day. The propagation of noise to outside from the industry was also studied. The measured data for different power looms are given in Appendix-B.

Generation and propagation of noise depend on many factors like quality and type of machine, its foundation, enclosure and barrier around it. It also depends on texture or surface finishing of wall and ceiling. All these factors have been taken into consideration while collecting data and its analysis.

The weather data was also collected from the Indian Meteorological Department, Gorakhpur. The average monthly weather conditions are given in Table-3.1 for reference.

Table: 3.1 Summary of Weather Condition

Month

Average Rainfall

Average Temp. (°C)

Average Relative Humidity

24 hrs

Seasonal

Max.

Min.

Max.

Min.

June (2008)

15.82

132.19

32.93

24.75

84.40

65.66

July (2008)

23.56

878.05

31.41

24.92

87.58

71.74

August (2008)

14.69

1433.74

32.70

25.21

86.58

65.12

September (2008)

7.86

1755.14

33.29

24.22

86.10

58.27

October (2008)

0.81

20.40

32.03

20.38

86.90

48.61

November (2008)

0

25.20

29.17

14.05

85.26

38.60

December (2008)

0

25.20

22.59

11.71

85.90

57.61

January (2009)

0

0.43

21.74

9.36

86.16

53.96

February (2009)

0

0.60

27.08

11.62

73.35

29.89

March (2009)

0.03

0.071

32.32

15.54

68.25

21.38

April (2009)

0

1.10

38.42

21.31

51.50

15.00

May (2009)

5.82

39.51

36.51

23.87

71.42

35.64

June (2009)

1.65

26.43

37.56

25.67

76.80

37.03

3.2 Variation of Noise Pollution (Level) with Time

The noise level data collected from all 26 power looms based industries (irrespective of number of power looms) were plotted (Fig; 3.1) in order to understand the variation of noise with three time slots viz. 9:00 AM, 12:00 PM and 9:00 PM. It is evident from Fig. 3.1 that the noise pollution (level) is higher at night and lower at 12:00 noon (irrespective of number of machines).

The sound intensity is given by the following formula (source: Sharma, 1996):

I = 2π2n2a2ρv ……….. (3.1)

Where I=intensity of sound

n= frequency

a= amplitude of the wave

ρ= density of medium

v = speed of the wave

For a given machine, since the other factors are constant,

I ρ

Thus, the noise intensity will increases with the increase in density of medium. During day, the temperature of earth increases and density decreases, leading to reduction in sound velocity and consequently reduction in noise intensity (I). Similarly, the air is denser at night due to reduction in temperature causing increase in density and consequently increase in intensity.

Fig. 3.1: Average Noise Level Graph (at 9:00 AM, 12:00 PM and 9:00 PM)

3.3 Variation of Noise Pollution (Level) with Number of Power Looms

The relationship between the number of machines and average noise level (for eight sites) is shown in Fig. 3.2.

It is evident from Fig. 3.2 that number of machines does not have much effect on average noise level.

Trend Lines

Fig. 3.2: Graph showing relation between number of machines and noise level

As we know summation of noise level from different sources does not follow rule of arithmetic summation as sound pressure levels in decibels (dB) or A-weighted decibels [dB (A)] are based on a logarithmic scale. If one machine emits a sound level of 90 dB, and a second identical machine is placed beside the first, the combined sound level is 93 dB, not 180 dB.

If there are two sound sources in a room - for example a machine producing an average sound level of 62.0 dB, and another machine producing a sound level of 73.0 dB, then the total sound level is a logarithmic sum i.e.

Combined sound level = 10 x log (10^ (62/10) + 10^ (73/10))

= 73.3 dB

For two different sounds, the combined level cannot be more than 3 dB above the higher of the two sound levels. However, if the sounds are phase related there can be up to a 6dB increase in SPL.

3.4 Effects of Building Structure on the Noise Pollution

The power loom based industries varies not only by number of machines but also by the structure type e.g. plastered or unplastered wall, with or without windows, R.C.C. or G.I. ceilings etc. A typical workshop of power loom based industries is shown in Fig. 3.3. The noise data with respect to the structure type are summarized in Table 3.2. The average noise level/unit area with respect to observation time is also calculated and summarized in Table 3.3. The average noise level for 24 hour is given in Table 3.4.

Unplastered wall

Meshed wall

GI Sheet

Fig. 3.3: A Typical Power loom Workshop

Table 3.2: Variation in Noise Level Due to Texture and Types of Ceiling

(a) GI Roofing with Unplastered wall (GI UP)

S.No.

Area (sq. ft)

Reading (dB)

Divided by area

9:00AM

12:00PM

9:00PM

9:00AM

12:00PM

9:00PM

1

6000

92.84

92.79

98.54

0.01547

0.01546

0.01642

2

6400

95.94

97.25

103.65

0.01492

0.01519

0.01619

3

4900

98.02

97.67

99.59

0.0200

0.01993

0.02032

4

6400

96.19

96.69

98.69

0.01502

0.0151

0.01542

5

5600

96.42

98.17

96.16

0.01721

0.01753

0.01717

6

1200

98.96

99.90

102.27

0.08246

0.0830

0.00852

7

6000

100.64

98.62

98.58

0.01677

0.016436

0.01643

8

3600

102.68

102.25

102.33

0.02850

0.02840

0.02842

9

900

98.89

98.43

99.73

0.10987

0.10936

0.11081

10

1600

103.22

103.00

111.32

0.06451

0.06437

0.06957

11

225

94.17

96.40

99.08

0.41853

0.42844

0.44035

12

375

91.79

92.23

93.91

0.24477

0.245947

0.25043

13

1750

93.82

94.02

95.64

0.05361

0.053726

0.05465

14

2400

97.80

97.89

100.12

0.04075

0.040788

0.04172

15

1500

101.21

101.34

101.58

0.06747

0.06756

0.06772

Average Noise Level

0.08066

0.081416

0.07828

(b) GI Roofing with Plastered wall (GI P)

S.No.

Area (sq. ft)

Reading (dB)

Divided by area

9:00AM

12:00PM

9:00PM

9:00AM

12:00PM

9:00PM

1

800

101.72

102.41

109.74

0.12715

0.128013

0.13718

2

2000

101.32

101.74

110.58

0.05066

0.05087

0.05529

3

150

95.65

96.74

101.42

0.63767

0.644933

0.67613

Average Noise Level

0.27183

0.274605

0.28953

(c) RCC Roofing with Unplastered wall (RCC UP)

S.No.

Area (sq. ft)

Reading (dB)

Divided by area

9:00AM

12:00PM

9:00PM

9:00AM

12:00PM

9:00PM

1

1000

99.99

102.56

103.16

0.09999

0.10256

0.10316

2

150

97.13

98.26

113.62

0.64753

0.655067

0.75747

3

1000

102.25

102.41

103.68

0.10225

0.10241

0.10368

4

500

92.25

92.56

101.77

0.1845

0.18512

0.20354

5

600

101.06

111.6

118.84

0.16843

0.186

0.19807

Average Noise Level

0.24054

0.246231

0.27318

(d) RCC Roofing with Plastered wall (RCC P)

S.No.

Area (sq. ft)

Reading (dB)

Divided by area

9:00AM

12:00PM

9:00PM

9:00AM

12:00PM

9:00PM

1

10000

97.59

97.27

101.85

0.00976

0.009727

0.01019

2

225

96.18

99.5

100.34

0.42747

0.442222

0.44596

3

2000

94.73

94.59

95.15

0.04737

0.047295

0.04758

Average Noise Level

0.16153

0.166415

0.16791

Table 3.3: Average Noise Level vs. Structure Type

Structure Type

Observation time

9:00 AM

12:00 PM

9:00 PM

GI UP

0.08066

0.08142

0.07828

GI P

0.27183

0.27461

0.28953

RCC UP

0.24054

0.24623

0.27318

RCC P

0.16153

0.16641

0.16791

Where, GI UP = Galvanized Iron unplastered

GI P = Galvanized Iron plastered

RCC UP = Reinforced Cement Concrete unplastered

RCC P = Reinforced Cement Concrete plastered

The bar graph between structure type and noise level/area at 9:00AM, 12:00 PM and 9:00 PM are plotted in Figures 3.4, 3.5 and 3.6 respectively. From these graphs, it is clear that unit noise level is lowest in case of GI UP (G.I. Unplastered) and maximum in case of GI P (G.I. Plastered). However, RCC UP (RCC Unplastered) is in close agreement with GI (P). The same trend is observed in Fig. 3.7. Thus it may be recommended that GI Unplastered structure is more suitable structure for power loom based textile industries.

RCC P

Types of ceiling

RCC UP

GI P

GI UP

Fig. 3.4: Noise Level/unit area at 9:00 AM

Types of ceiling

RCC P

RCC UP

GI P

GI UP

Fig. 3.5: Noise Level/unit area at 12:00 PM

GI P

RCC UP

RCC P

GI UP

Types of ceiling

Fig. 3.6: Noise Level/unit area at 9:00 PM

Table 3.4: Average Noise Level with respect to Structure Type

Structure Type

Average Noise Level (db)

GI UP

0.08012

GI P

0.27866

RCC UP

0.25332

RCC P

0.16528

Types of ceiling

GI UP

GI P

RCC UP

RCC P

Fig. 3.7: Final average reading taken at 9:00 AM, 12:00 PM, &9:00 PM

Following are the other factors which influences the noise level:

Room Parameters: In smaller rooms noise level is more because sound continues to travel in the room even after multiple reflections. On the other hand in larger rooms energy of sound waves is dissipated while travelling from one surface to other, and hence reflections will be less and this results into lesser noise level.

Wall Texture: Sound absorption occurs when some or all of the incident sound energy is either converted into heat or passed through the absorber.

A room with good absorbing surfaces will have lesser noise level. An open window is a perfect absorber; as it absorbs all the acoustical energy incident on it, but here insulation will be poor as more noise energy is transferred outside the room.

3.5 Relationship between Theoretical and Measured Noise Level

Decibel readings of a sound spectrum need to be added and converted to a single reading. The total decibel level corresponding to a sound spectrum may be given by the formula (Sincero and Sincero, 1996)

……….. (3.2)

Using the above equation, the theoretical noise level based on the data of single machine was used to find out the theoretical noise level for 8 machines. The same was compared with the measured noise level for 8 machines and % error was calculated and the complete data is given in Table 3.5. No particular trend between the theoretical and measured noise level was observed but it was found that the theoretical noise level was less than the measured noise level.

Table 3.5: Relationship between Theoretical and Measured Noise Level

S. No.

Noise Recorded 1 Machine

Noise Recorded 8 Machine

Noise Theoretical 8Machine

C=10 log (10^(C3/10) + 10^(C4/10)….)

Error %

1

85.2

96.8

94.23

2.65

2

87

97.3

96.03

1.30

3

87.2

99.3

96.23

3.09

4

90

99.8

99.03

0.77

5

87

99.1

96.03

3.09

6

86.7

98.4

95.73

2.71

7

86.7

98.9

95.73

3.20

8

87.1

99.4

96.13

3.28

9

86.8

98.6

95.83

2.80

10

86.9

98.6

95.93

2.70

11

85.3

98.9

94.33

4.61

12

87.1

98.4

96.13

2.30

13

87.3

97.9

96.33

1.60

14

90.1

99.9

99.13

0.76

15

87.2

98.5

96.23

2.30

16

85.6

98.2

94.63

3.63

17

85.4

98.4

94.43

4.03

18

87.6

98.8

96.63

2.19

19

87.8

98.3

96.83

1.49

20

88.9

99

97.93

1.07

21

85.6

98.8

94.63

4.21

22

87.2

98.6

96.23

2.40

23

87.3

98.5

96.33

2.20

24

88.4

98.2

97.43

0.78

25

88.5

98.9

97.53

1.38

26

85.3

98.4

94.33

4.13

27

85.4

98

94.43

3.64

28

86.5

98.2

95.53

2.71

29

86.3

98.8

95.33

3.51

30

84.9

99

93.93

5.12

31

84.3

98.4

93.33

5.15

32

85.8

98.4

94.83

3.62

33

86

98.8

95.03

3.81

34

86.2

98.6

95.23

3.41

35

85.8

98.4

94.83

3.62

36

87.1

98.5

96.13

2.40

37

87.2

97.4

96.23

1.20

38

86.3

98.8

95.33

3.51

39

87.4

98.8

96.43

2.39

40

83.3

98.6

92.33

6.35

3.6 Variation of Noise Level with Distance

In order to understand the variation of noise with the distance away from the source of noise generation, first the noise data was collected within the workshop, then at the door of the workshop, and then at the distances of 10 m, 20 m and 25 m away from the workshop. Collected data is given in Table 3.6 and related graph is shown in Fig. 3.8. It is observed from the Fig. 3.8 that the noise level decreases with increasing distance.

Table 3.6: Variation of Noise Level with Distance

Distance (m)

Average Noise Level (db)

1 Machine

% Reduction

Multiple Machine (8)

% Reduction

Inside Workshop (0m)

86.6925

0

98.54

0

At the door of the Workshop (2m)

83.7725

3.48

87.79

12.29

At 10 m

78.6525

10.22

80.35

22.60

At 20 m

67.0575

29.29

68.19

44.49

At 25 m

61.775

40.33

62.55

57.53

Fig. 3.8: Graph showing variation of noise level with distance

The percent reduction is plotted in Figure 3.9

Fig. 3.9: Graph showing percent reduction in noise level

The sound intensity I at a distance r from a point noise source radiating uniformly in all directions in the surrounding is Pw / 4 πr2, where 4 πr2 is the spherical area receiving the noise. Hence sound intensity at a distance r from the source may be written as (Sincero, 1996).

………… (3.3)

Where Q = coefficient of directivity (a constant)

Pw = power (constant for a source)

4 πr2 = a spherical area equivalent to receiving the noise

So, sound intensity I 1/r2 ………. (3.4)

It is clear from equation (3.4) that the sound intensity decreases with the distance r from source.

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