WPE: 407

Environmental Studies

Chapter-3: Noise Pollution

Mohammad Shohag
Lecturer, DoWPE
BUTEX
Chapter Contents
• General terminology
• Noise Pollution.
• Sound Meter.
• Sources of Industrial Noise Pollution.
• Hazards of Noise Pollution.
• Control of Noise Pollution In Textile Industries.
• Standard sound intensity Level.
 General Terminology
Sound: Sound is a form of energy which is emitted by a vibrating body and on reaching the ear causes the
sensation of hearing through the nerves system. The frequency limits of audibility are from 20Hz to 20,000Hz.
The sound of human speech mainly 300 to 3000Hz.
Noise: Any undesired or unwanted sound that causes disturbance. Sound level above 75 dB is called noise.
Intensity: Amount of sound energy received per sec is known as intensity of sound. Its unit is decibel(dB).
Frequency: The number of complete waves passes from source per unit time. Its unit is cycle/sec or Hz.

Decibel: The intensity of sound waves produces a sound pressure level, which is commonly measured in a unit
called the decibel.
𝐼
1. decibel (dB) = 10 log10 (𝐼 ) [Where, I = Measured intensity, I0 = 10−12 W/m2.]
0
𝑃
2. SPL (dB)= 20 log10 [Where, P = Measured pressure, P0 = 2x10−5 N/m2.]
𝑃0
Thus decibel measures how much intense is the sound as compared to reference intensity.
 What is Noise Pollution?
Any undesired or unwanted human or machine created sound that disrupts the activity or balance of human
or animal life means the Noise pollution.

The most significant two attributes of noise is

i. Loudness.
ii. Duration.

Generally, Intensity level above 75dB is termed as noise pollution. Human ear can tolerate up to 120dB
noise.
 SOUND METER
Sound level meters(SLM) are useful for
measuring, monitoring, and controlling
noise levels.
They are utilized in multiple scenarios in
factories and other industrial plants and
on construction sites. They are also used
in urban environments to monitor noise
levels from car, rail, and air traffic, public
events, and other sources of sound.
 HOW SOUND METER WORKS?
• The basic parts of most SLMs consist of a microphone, pre and post amplifier, weighting network,
rectifier and a display meter reading in decibels.
• At the microphone, the sound wave energy is converted into an electrical signal of low-magnitude
voltage that is boosted in magnitude at the preamplifier.
• The electrical signal may be modified by the weighting network followed by a further boosting in
magnitude through the amplifier.
• The rectifier converts the electrical signal from alternating current (AC) to direct current (DC) to
cause the display meter to register the sound pressure level directly in decibels.
• An output jack may exist to record or analyze the measured signal whenever desired.
 Sources of Sound
There are two types of sources of noise pollution in general.
• Primary Sources: Many primary sources of noise exist in industrial situations. Common
primary sources are interacting parts such as gear teeth and bearings, motion of pistons
between end-stops in hydraulic and pneumatic actuators, air and gas jets, combustion
processes and vibrating components.
• Secondary Sources: However, noise from primary sources is frequently reflected from
various boundaries in the environment. Each such boundary becomes a secondary noise
source and often results in a standing wave, such that sound is nullified in some positions
but reinforced in others.
 Possible Sources of Noise Pollution and their intensity level
in Textile Industry.

1. Noise Zone in Textile Spinning Section:

• Blow room Area Noise Level

• Carding Ginning 88-92

Blow room 80-83
• Draw frame
Carding 84-89
• Combing Draw Frame 84-88
• Simplex Combing 82-86

• Ring frame Simplex 84-88

Ring Frame 86-90
• Open end/ Rotor
Rotor 85-100
• Winding Winding 82-86
2. Noise zone in Fabric Manufacturing Section: Area Noise Level (in dB)
• Sizing Warping 80-86
• Weaving- Sizing 73-86
o warping,
Shuttle loom 99-104
o cheese/cone winding,
o shuttle loom, Auto Loom 94-99
o auto loom Cheese/Cone 88-92
• Knitting. Winding
Knitting 85-90

3. Noise zone in Wet Processing Section:

• Yarn Dyeing- soft winding & hard winding machine.
• Printing- high speed automated printing machine.

4. Noise zone in Utility Section: Area Noise level (in dB)

• Boiler Boiler 95-100
• Generator
Generator 110-115
 HAZARDS OF NOISE POLLUTION

1. Workers consistently exposed to the noise levels above 75 to 90 dB result in-

a) May reveal permanent hearing loss.
b) Prevalence of noise induced hearing loss was highest in the workers working in weaving area,
followed by the spinning workers and the workers working in TFO, doubling area.

2. In addition to hearing loss, exposure of workers to noise levels of 90-119 dB was also found to result in-
a) Cardiovascular and psycho physiologic problems.
b) Sleep disorders and headache,
c) Mental fatigue, Annoyance, speech interference and reduced alertness,
d) Increased blood pressure, deep body temperature and pulse rate,
e) Speed of performance was impaired significantly by noise.
 CONTROL OF NOISE POLLUTION IN TEXTILE INDUSTRY
1) Proper maintenance: It is observed that malfunctioning or improperly 1
maintained parts produces more noise than well maintained one like,
1. Loosely held bearings and belts.
2. Torn belts.
3. Worm gears.
4. Imbalanced rotating masses.
5. Missing guards or shields.
6. Improperly adjusted cams and linkages.
3
It is recommended that a good preventive maintenance practice should
be adopted to reduce the noise level and also follow scheduled check list
for lubrication to reduce the wear and tear of parts and maintain the same.

2
5

4
2) Operating procedures and equipment replacement technique: This technique is totally in the
hand of administration where provision of job rotation and purchasing of new equipment’s or tools is the
main priority.
3) Relocation of equipment: Noise level drops off when the distance from the noise source is increase.
1. Noisy equipment should be as far as possible from employees.
2. Do not put noisy parts at corner to avoid noise reflection.
4) Simple machine treatments: Many simple modifications in the machine show significant reduction in
the noise level.
1.Reduce the dropping height of parts from the ground.
2.Enclose or damping with rubber base material to absorb the noise
3.Keep optimum pressure when working with pneumatics and hydraulics
5) Room treatments: One of the basic principles of
noise control is to reduce the reflecting sound, for that
use of absorbent materials in between the
departments.
6) Proper operation of machine: As we know any increase in speed will prone to develop more noise
so run the machines with manufacturer recommendation.
a) Enclosures: These are like boxes covered with sound and heat absorbable coatings simple
used to control the machines parts which are moveable especially in case of motor panels where
both heat and noise generation are the key parameters to be performed.
b) Shields and barriers: These are sound absorbable materials which are used to control high
frequency noise and they should be as thick as possible.
c) Ducts and pipes: vibrating duct is the common cause of noise. The source of noise is the fan
and is depend on
1) Proper fan size and type
2) Speed of the fan
Generally the backward curved fan produces low level of noise than forward curve due to the low
air turbulence.
a b c
 Sound Intensity Level

In Bangladesh the sound intensity standard is set by the Department of Environment

(VIDE RULE 12) as below:

ZONE CLASS DAY (6am -9pm) NIGHT (9pm-6am)

Silent zone 45 dB 35 dB

Residential zone 50 dB 40 dB

Mixed zone 60 dB 50 dB

Commercial zone 70 dB 60 dB

Industrial zone 70 dB 70 dB