2. Definition
• Noise is derived from the Latin word “nausea”
implying ‘unwanted sound’ or ‘sound that is
loud, unpleasant or unexpected’.
• The noise originates from human activities,
especially the urbanization and the development
of transport and industry.
• For environmental noise pollution, decibel (dB) is
used as a measure of sound power level, sound
intensity level and sound pressure level.
4. MEASUREMENT OF NOISE
• Sound Level Meter
• At the microphone, the sound wave energy is converted into an electrical
signal 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.
5. • Dosimeter
• A noise dosimeter is a convenient means of
assessing the risk of having hearing damage.
• It can be worked easily by the employee
throughout their work-day.
• The instrument gives an accurate indication of
the total noise dose the worker receives while
working and during breaks.
• At the end of the day, the accumulated noise
dose is read directly from a digital display.
• It indicates whether the permissible noise dose
has been exceeded or not.
6. NOISE CONTROL
• The noise exposure of plant personnel can be reduced in three
general ways.
1. Reduction or elimination of the causes of noise at the source
2. Attenuation of the noise in the source-to-receiver pathways
3. Limiting the noise-exposure duration to workers by
administrative controls.
7. MEASURES TO REDUCE NOISE AT SOURCE
• Lubricating of noisy parts
• Replacing worn-out parts
• Fitting silencers on noisy exhaust systems
• To avoid vibration, mounting noisy machinery on rubber or thick
plastic pads
• Lining of vibrating parts with antivibration materials
• Significant reduction in noise level can be achieved by regular
maintenance of machinery
8.
9. Hierarchy of Noise Control Measures
• The following hierarchy of control for reduction of hearing
loss to personnel.
• Elimination
• Substitution
• Engineering controls
• Administrative controls
• Personal protective equipment
10. Noise Survey
• The noise survey is essential before initiating any administrative,
engineering and remedial measures.
• They help in identifying the noise sources and quantifying the
exposure risk of workers.
• The most commonly used methods to assess health impacts are;
1. Area surveys: noise levels are measured at different sites throughout
the plant.
2. Dosimetry: cumulative exposure of personnel to noise over a period
of time is measured with a dosimeter.
3. Engineering surveys: noise is measured using a range of instruments.
11. Green Streets for Noise Reduction
(A)Stretch of Diagonal Avenue, where a
greenery barrier 500 m long (on the right of
the image) was used for acoustic
measurements
(B)Transverse detail of the concrete wall with
the external vegetated layer
(C)Internal face
12. Sound Absorption by Vegetation
• Many studies have been done to determine the absorption of sound
by vegetation. Horoshenkov et al. (2013) studied the effect of leaf
morphology and area on the acoustic absorption coefficient in an
impedance tube to quantify the ability of absorption of a series of low
growing plants with a relatively high leaf area density, and with and
without a soil substratum. The larger leaf area density and dominant
angle (defined as the angle of the leaf orientation from the vertical
direction), the higher values of the acoustic absorption coefficient.
The type of soil in which a plant is growing also affects the ability of
the plant to absorb sound. Soils with high permeability and low
density are more effective.
13. Sound Absorption by Vegetation
• Lacasta et al. (2016) performed in situ measures on the same type of
module-based green wall. The absorption coefficient had an average
value of 0.7 and frequency dependent values higher than those
previously obtained in the laboratory. In any case the values are
higher than other buildings’ materials and furnishings.
