NOISE CONTROL IN

WORKPLACE

NOISE RISK ASSESSMENT MODULE

DOSH
SCOPE
• 1.0 Basic Concepts in Noise Control
• 2.0 Hierarchy of Noise Control Measures
• 3.0 Noise Control Strategies
• 4.0 Principles of Noise Engineering Control
• 5.0 Administrative Control
• 6.0 Personal Hearing Protector

NOISE RISK ASSESSMENT MODULE 2

OBJECTIVE
At the end of the course, participant will be able to:
• Explain the basic concept of noise control.
• Understand and utilise the hierarchy of noise control.
• Determine appropriate noise control strategies.
• Elaborate six (6) engineering noise control principles.
• Determine the important aspect of administrative
control and personal hearing protection.

NOISE RISK ASSESSMENT MODULE 3

1.0 Basic Concepts in Noise Control

• Employer shall ensure, nobody is allowed to be exposed to :-

▪ Daily Noise Exposure Level > 85dB(A) or Daily Personal Noise Dose >
100%
▪ Maximum SPL > 115dB(A) at any time
▪ Peak SPL > 140dB(C)

If exposed to excessive noise exceeding NEL, the employer shall

reduce the excessive noise.

NOISE RISK ASSESSMENT MODULE 4

1.0 Basic Concepts in Noise Control

Key Action of Noise Control

• prioritising and tackling the immediate risks

• identifying possible methods
• assessing the reduction levels that can be achieved by
introducing cumulative controls
• assigning responsibilities
• monitoring controls and performance.

NOISE RISK ASSESSMENT MODULE 5

1.0 Basic Concepts in Noise Control

Utilising Noise Monitoring Result

NOISE RISK ASSESSMENT MODULE 6
1.0 Basic Concepts in Noise Control
Utilising Noise Mapping Result
• Noise contours/zoning will
indicate the noise sources.
• Noise sources with the higher
noise level could be identified and
action to be prioritized.
• Priority given to higher
machines or process emitting
higher noise levels.
NOISE RISK ASSESSMENT MODULE 7
1.0 Basic Concepts in Noise Control

Key Action of Noise Control

• prioritising and tackling the immediate risks

• identifying possible methods
• assessing the reduction levels that can be achieved by
introducing cumulative controls
• assigning responsibilities
• monitoring controls and performance.

NOISE RISK ASSESSMENT MODULE 8

1.0 Basic Concepts in Noise Control

Other effective
measures Administrative
Control

Engineering &
Administrative
Control
Engineering Control

Noise Control Practicability Assessment

NOISE RISK ASSESSMENT MODULE 9
1.0 Basic Concepts in Noise Control
• To adequately define the noise problem and set a good
basis for the control strategy, the following factors
should be considered:
▪ type of noise
▪ noise levels and temporal pattern
▪ frequency distribution
▪ noise sources (location, power, directivity)
▪ noise propagation pathways, through air or through
structure
▪ room acoustics (reverberation).

NOISE RISK ASSESSMENT MODULE 10

1.0 Basic Concepts in Noise Control

11
NOISE RISK ASSESSMENT MODULE
1.0 Basic Concepts in Noise Control

NOISE RISK ASSESSMENT MODULE 12

1.0 Basic Concepts in Noise Control
Directivity Factor, Q

Source Position Q SPL at 1 m

In Air 1 X dBA
On Hard Floor 2 X + 3dBA
Near Hard Wall 4 X + 6dBA
At Corner 8 X + 9dBA

NOISE RISK ASSESSMENT MODULE 13

1.0 Basic Concepts in Noise Control

NOISE RISK ASSESSMENT MODULE 14

1.0 Basic Concepts in Noise Control

NOISE RISK ASSESSMENT MODULE 15

2.0 Hierarchy of Noise Control Measures

NOISE RISK ASSESSMENT MODULE 16

2.0 Hierarchy of Noise Control Measures

• Noise Reduction
– Substitution
– Engineering Control

• Exposure Reduction
– Administrative Controls
– Use of Personal Hearing
Protection

NOISE RISK ASSESSMENT MODULE 17

2.0 Hierarchy of Noise Control Measures
• Are plant, process or equipment that minimizes the exposure to excessive
noise, suppress the level of exposure or limit the area of exposure.
• Types of engineering control include absorption, insulation, damper, silencer
and vibration insulation.
Engineering
Control • The type of engineering control measures that will be installed should be
assessed according to suitable methods, use and effectiveness, and
maintenance of equipment.
• Employer should refer to acoustic experts or noise control supplier if
necessary.

• Are the way work is organised to reduce either the number of workers who
Administrative are exposed or the duration of time they are exposed to noise.
Control • Should be used when it is not possible to reduce noise exposure through
engineering noise control measures

• If it is not practicable to reduce excessive noise by engineering control or

Other control administrative control, the employer shall take other effective measures
including personal hearing protector.
NOISE RISK ASSESSMENT MODULE 18
2.0 Hierarchy of Noise Control Measures

• Substitution
– Change to quieter methods of work
– Replacing equipment with less noisy ones for both production
& material handling

• Engineering Controls (the use of engineering principles

to reduce noise levels)
– Reduce noise at source
– Prevent or reduce propagation

NOISE RISK ASSESSMENT MODULE 19

2.0 Hierarchy of Noise Control Measures

NOISE RISK ASSESSMENT MODULE 20

Noise Elimination/Substitution: Buy Quiet

NIOSH Power Tool

Database

http://www.hse.gov.uk/n
oise/buy-quiet/index.htm

NOISE RISK ASSESSMENT MODULE 21

 Noise Elimination/Substitution: Buy Quiet

New gen set during purchase New compressor heatless dryer –

built in silencer (reduce no intermittent purging (reduce
<85dB) <70dB)

NOISE RISK ASSESSMENT MODULE 22

Video: Buy Quiet

NOISE RISK ASSESSMENT MODULE 23

 Noise Reduction: Substitution

Replace high impact

impulsive force (i.e.,
mechanical power) used
for pile driving in building
and construction with
hydraulic power.

NOISE RISK ASSESSMENT MODULE 24

 Noise Reduction: Substitution

Replace acoustically ‘live’ materials with acoustically ‘dead’ (highly internal damped)
materials.

NOISE RISK ASSESSMENT MODULE 25

 Noise Reduction: Substitution

Replace metal cold work with hot work process.

NOISE RISK ASSESSMENT MODULE 26

 Noise Reduction: Substitution

Installation of centralize vacuum

pump at facilities plant building
complete with noise absorption
material (rockwool with cement
board). Noise level reduce to avg <
Individual vacuum pump install at 70 dBA
production machine (40 units) .
Noise level (90 dBA)
NOISE RISK ASSESSMENT MODULE 27
Engineering Control- New Plant & Places of
Work
• The purchase of new plant, the design of the area in which it is to be installed &
the design of new place of works generally, will provide opportunities for cost-
effective noise control measures.
• The maximum acceptable level of noise shall be specified in invitation tender.
Without tender, noise level information shall be obtained from suppliers.
• New places of work and installation sites for new plant in existing places of work,
shall be designed and constructed to ensure that exposure to noise is as low as
practicable.
• If new plant is likely to expose workers to excessive noise, design features shall
incorporate effective engineering control measures to reduce noise to level as low
as practicable.

NOISE RISK ASSESSMENT MODULE 28

 Engineering Control – Existing Plant &
Places Of Work
• Once a noise risk assessment has been carried out and the necessity to
reduce the noise exposure of employees is established, the task of
controlling the noise can be addressed.
• Priority to noise sources that contribute to the highest noise exposures
affecting the largest number of people.
• Noise exposure levels shall be reduced below the NEL.
• Machinery which emits lower level of noise should be considered to be
replaced if available and suitable.

NOISE RISK ASSESSMENT MODULE 29

2.0 Hierarchy of Noise Control Measures

• Noise Reduction
– Substitution
– Engineering Control

• Exposure Reduction
– Administrative Controls
– Use of Personal Hearing
Protector

NOISE RISK ASSESSMENT MODULE 30

Video : Controlling Noise

NOISE RISK ASSESSMENT MODULE 31

3.0 Noise Control Strategies
• Noise control efforts should be approached according to the hierarchy of
control strategies:

source path receiver

• The best way to reduce is to tackle the problem at the source.

• Reduction at path would generally involve adding barriers or enclosing the
equipment, but may also involve adding sound-absorbent materials.
• Reduction at receiver is achieved by either removing the employee from the
sound field, limiting his working time in the area, or through the use of hearing
protective devices (HPD).

NOISE RISK ASSESSMENT MODULE 32

3.0 Noise Control Strategies

NOISE RISK ASSESSMENT MODULE 33

3.0 Noise Control Strategies

Control At
Source

NOISE RISK ASSESSMENT MODULE 34

 Engineering Control – At The Source
✓Engineering control at the source is the
preferred method .
✓An understanding of the operation of the
machine or process is necessary in
considering the possible control of the noise
at source.
✓General noise control solutions :
✓ Eliminate or replace the machine or its
operation by a quieter operation with
equal or better efficiency.
✓ Replace the noisy machinery by
installing newer equipment designed
for operating at lower noise levels.

NOISE RISK ASSESSMENT MODULE 35

Engineering Control – At The Source

NOISE RISK ASSESSMENT MODULE 36

 Engineering Control – At The Source
➢General noise control solutions :
✓ Correct the specific noise source by minor design changes.
✓ A high standard of plant and equipment maintenance.
✓ Correct the specific machine elements causing the noise by a
local source approach, rather than by consideration of the
entire machine as a noise source.
✓ Separate the noisy elements that need not be an integral part
of the basic machine.
✓ Isolate the vibrating machine parts to reduce noise from
vibrating panels or guards.

NOISE RISK ASSESSMENT MODULE 37

Engineering Control – At The Source

NOISE RISK ASSESSMENT MODULE 38

Engineering Control – At The Source

NOISE RISK ASSESSMENT MODULE 39

 Engineering Control – At The Source
➢In addition to engineering changes to
machinery and parts, processes can be
modified to reduce noise.
• Specific means of modification include
the use of processes that are inherently
quieter than the alternatives.

NOISE RISK ASSESSMENT MODULE 40

 Engineering Control – At The Source

• Material handling
processes, in
particular, can also
be modified to
ensure that impact
& shock during
handling and
transport are
minimised as far as
possible.

NOISE RISK ASSESSMENT MODULE 41

Control At Path

NOISE RISK ASSESSMENT MODULE 42

 Engineering Control – At The Transmission
Path
➢ Engineering control at the noise transmission path
includes
✓ isolating the noise-emitting object(s) in an
enclosure, or
✓ placing them in a room or
✓ building away from the largest number of
employees, and
✓ acoustically treating the area to reduce noise
to the lowest practicable levels.
➢ Alternatively, it may be desirable to protect the
employee instead of enclosing the noise sources.
✓ design of the soundproof room or
✓ sound-reducing enclosures to the employee
shall still follow the same principles.

NOISE RISK ASSESSMENT MODULE 43

Control At Path

NOISE RISK ASSESSMENT MODULE 44

Control At Path

NOISE RISK ASSESSMENT MODULE 45

Engineering Control – At The Transmission
Path
The principles to be observed in carry out engineering control of the noise transmission
path:

DISTANCE is often the cheapest solution. But not effective in reverberant conditions.

Erect A NOISE BARRIER between the noise source and the receiver; in some instances, a
partial barrier can be used.

Once the acoustical barrier is erected, FURTHER treatment, such as the addition of absorbing material
on surfaces facing the noise source, may be necessary.

Walls and machine enclosures must be designed to MINIMIZE RESONANCES which will transmit
acoustical energy at the resonant frequency to the protected area.

Reduce the REVERBERATION of the room where noise is generated by the introduction of acoustically
absorbent material(s).

NOISE RISK ASSESSMENT MODULE 46

Engineering Control – At The Transmission
Path

Example for Controlling Noise by Distance

NOISE RISK ASSESSMENT MODULE 47

Engineering Control – At The Transmission
Path

NOISE RISK ASSESSMENT MODULE 48

 Source/Path/Receiver Model
Basic treatment strategies using
engineering controls.

"Typical" noise reductions associated with

each strategy are listed below :-

SOURCE INDIRECT
DIRECT PATH RECEIVER
PATH

10 to 25 dB & 10 to 25 dB &
6 to 8 dB 4 to 6 dB
up up

NOISE RISK ASSESSMENT MODULE 49

Video : Noise Path

NOISE RISK ASSESSMENT MODULE 50

4.0 Principles of Engineering Control

• Absorption
• Insulation
• Distance
• Silencer
• Vibration isolation
• Damping

NOISE RISK ASSESSMENT MODULE 51

 4.1 Absorption
• Sound energy is absorbed
whenever sound meets a
porous material.
• Porous materials
intended to absorb sound
is called absorbents.
• Absorbents usually
absorb 50-90% incident
sound energy.

NOISE RISK ASSESSMENT MODULE 52

 4.1 Absorption
• Machines that contain cams, gears,
reciprocating components and metal
stops are often located in reverberant
areas.
• Absorbent materials are employed in
several applications including muffler
linings, wall, ceiling and enclosure linings,
wall fill and absorbent baffle construction
to reduce noise level.
• The type, amount, configuration and
placement of absorption material
depends on the specific application.

NOISE RISK ASSESSMENT MODULE 53

 Sound Absorption Coefficient
• The effectiveness of an
acoustically absorbent material
is measured by the absorption
coefficient.
• An absorption coefficient of
(1.0) means the material will
absorb all sound impinging
randomly on the surface, while
an absorption coefficient close
to (0) means the material will a = 0.75 means 75% sound absorption
absorb little acoustic energy. (The remaining 25% is sound reflection)

NOISE RISK ASSESSMENT MODULE 54

 Sound Absorption Coefficient of Surface Materials
Frequency (Hz)
Material
125 250 500 1000 2000 4000
Brick: Glazed 0.01 0.01 0.01 0.01 0.02 0.02
Unglazed 0.03 0.03 0.03 0.04 0.05 0.06
Unglazed, painted 0.01 0.01 0.02 0.02 0.02 0.03
Carpet: Heavy (on concrete) 0.02 0.06 0.14 0.37 0.60 0.65
On 40 oz. hairfelt or foam rubber (carpet has coarse 0.08 0.24 0.57 0.69 0.71 0.73
backing)
With impermeable latex backing on 40 oz. hairfelt or 0.08 0.27 0.39 0.34 0.48 0.63
foam rubber
Concrete block: Coarse 0.36 0.44 0.31 0.29 0.39 0.25
Painted 0.10 0.05 0.06 0.07 0.09 0.08
Poured 0.01 0.01 0.02 0.02 0.02 0.03
Fabrics: Light velour: 10 oz/yard2 0.03 0.04 0.11 0.17 0.24 0.35
Medium velour: 14 oz/yard2 0.07 0.31 0.49 0.75 0.70 0.60
Heavy velour: 18 oz/yard2 0.14 0.35 0.55 0.72 0.70 0.65

NOISE RISK ASSESSMENT MODULE 55

 Sound Absorption Coefficient of Surface Materials

Frequency (Hz)
Material
125 250 500 1000 2000 4000
Floors: Concrete or terrazo 0.01 0.01 0.015 0.02 0.02 0.02
Linoleum, asphalt, rubber or cork tile on concrete 0.02 0.03 0.03 0.03 0.03 0.02

Wood 0.15 0.11 0.10 0.07 0.06 0.07

Wood parquet in asphalt on concrete 0.04 0.04 0.07 0.06 0.06 0.07
Glass: Ordinary window glass 0.35 0.25 0.18 0.12 0.07 0.04
Large panes of heavy plate glass 0.18 0.06 0.04 0.03 0.02 0.02
Glass fibre: Mounted with impervious backing, 3 0.14 0.55 0.67 0.97 0.90 0.85
lb/ft3, 1 in. thick
Mounted with impervious backing, 3 lb/ft3, 2 in. 0.39 0.78 0.94 0.96 0.85 0.84
thick
Mounted with impervious backing, 3 ib/ft3, 3 in. 0.43 0.91 0.99 0.98 0.95 0.93
thick
Gypsum board: ½ in. thick nailed to 2” x 4”, 16” on 0.29 0.10 0.05 0.04 0.07 0.09
centre
NOISE RISK ASSESSMENT MODULE 56
 Sabine Absorption Coefficient of Common Acoustic
Materials
Frequency (Hz)
Material
125 250 500 1000 2000 4000
Fibrous glass
4 lb/ft3, hard backing
1 inch thick 0.07 0.23 0.48 0.83 0.88 0.80
2 inch thick 0.20 0.55 0.89 0.97 0.83 0.79
4 inch thick 0.39 0.91 0.99 0.97 0.94 0.89
Polyurethane foam (open cell)
¼ inch thick 0.05 0.07 0.10 0.20 0.45 0.81
½ inch thick 0.05 0.12 0.25 0.57 0.89 0.98
1 inch thick 0.14 0.30 0.63 0.91 0.98 0.91
2 inch thick 0.35 0.51 0.82 0.98 0.97 0.95
Hairfelt
½ inch thick 0.05 0.07 0.29 0.63 0.83 0.87
1 inch thick 0.06 0.31 0.80 0.88 0.87 0.87

NOISE RISK ASSESSMENT MODULE 57

 Sabine Absorption Coefficient

NR = 10 log (A2/A1) The total absorption in a room can be

expressed as;
Where;
A = S1α1 + S2α2 +...+ Sn αn
• NR = Noise reduction (NR) a reverberant A = ∑ Si αi
sound level between two different
conditions of room absorption, dB
Where,
• A1 = Total absorption of original room
• A = the absorption of the room
condition, m2 sabine
(m2 Sabine)
• A2 = Total absorption after adding the
• Sn = area of the actual surface (m2)
absorbent of room condition, m2 sabine
• αn = absorption coefficient of the
actual surface

NOISE RISK ASSESSMENT MODULE 58

 Sabine Absorption Coefficient – Example

Question :

For a room 8m long x 6m wide x 4m high, determine the noise

reduction using the Sabine approach when the absorption
coefficient before treatment for the floor is 0.02, for the walls 0.04,
and for the ceiling 0.01, and after treatment with an acoustic panel
which is attached to the walls using 0.08 absorption coefficient.

NOISE RISK ASSESSMENT MODULE 59

 Sabine Absorption Coefficient – Example

Answer:
Area of walls = 2 x [(8 x 4) + (6 x 4)] = 112 m2
Area of floor and ceiling = 48 m2
Total area = 208 m2

Before Treatment After Treatment

Item Surface Area, S
α A1 α A2
Walls 112 0.04 4.48 0.08 8.96
Floor 48 0.02 0.96 0.02 0.96
Ceiling 48 0.1 4.8 0.1 4.8
Total 10.24 14.72

Noise reduction, NR = 10 log (14.72 / 10.24) = 1.58 dB

NOISE RISK ASSESSMENT MODULE 60

 Absorption - Case Study
Problem

• The production room in a confectionary factory

contains 38 coating pans.
• The operators move around the entire room
attending to all the pans and the average noise
level was 93dB (A).

Solution

• A lay in acoustically absorbent ceiling was installed across the entire room.
• The average reverberant noise level was reduced by 6dB to 87dB and the operators noise
exposures were reduced by 4dB.

https://www.hse.gov.uk/noise/casestudies/coatingpans.htm

NOISE RISK ASSESSMENT MODULE 61

Video : Absorption

NOISE RISK ASSESSMENT MODULE 62

Absorption vs Insulation

NOISE RISK ASSESSMENT MODULE 63

 4.2 Insulation
• Sound insulation is a technique that is used
to restrict sound from travelling between
separate spaces through walls, ceilings and
floors.
• When sound meets a wall or partition, only
a small proportion of sound energy passes
through, most are reflected back.
• Sound insulation can be used to prevent
transfer of :
– Airborne sounds such as voices,
airplanes or traffic.
– Impact noises such as footsteps or
vibrating appliances.

NOISE RISK ASSESSMENT MODULE 64

 Insulation – Sound Transmission Loss

• The sound isolation properties of

materials are stated in terms of
transmission loss.
• Transmission loss is 10 log (incident
energy) / (transmitted energy).

STL = 10 log (1/τ),

where τ = I Transmitted / I Incident

NOISE RISK ASSESSMENT MODULE 65

 Insulation – Sound Transmission Class
• As a result of the search for a single number to indicate the average full
transmission loss, the concept of sound transmission class (STC) was
developed.
• It is useful specifically in assessing the degree to which intelligible speech is
prevented from being transmitted through a wall.

NOISE RISK ASSESSMENT MODULE 66

Insulation – Sound Transmission Class

NOISE RISK ASSESSMENT MODULE 67

 Barrier

NOISE RISK ASSESSMENT MODULE 68

 Barrier

NOISE RISK ASSESSMENT MODULE 69

Insulation : Examples

NOISE RISK ASSESSMENT MODULE 70

Insulation : Examples

NOISE RISK ASSESSMENT MODULE 71

Insulation : Examples

NOISE RISK ASSESSMENT MODULE 72

 Insulation – Case Study
Problem
• Noise from pellets passing rapidly through
transfer pipes and also moving within cyclones
often create levels of noise.
• Typically the noise is due to the internal
"scratching" noise breaking out through the pipe
walls, but also to the resonant ringing of the
pipes.

Solution
• Thermally lag the pipes with a conventional system consisting of a 30 to 50mm mineral
wool jacket and a 1mm thick aluminium outer skin.
• Noise was reduced by over 15dB.
https://www.hse.gov.uk/noise/casestudies/pneumaticbreak.htm
NOISE RISK ASSESSMENT MODULE 73
Video 1 : Insulation

NOISE RISK ASSESSMENT MODULE 74

Video 2 : Insulation

NOISE RISK ASSESSMENT MODULE 75

 4.3 Distance
Drop Height
• Reduce impact noise mechanical and material handling devices commonly
produce noise from impact.

Reducing the dropping height of goods Using soft rubber or plastic to receive and absorb hard impacts,
collected in boxes or bins. such as where panels are likely to be struck by materials during
processing
NOISE RISK ASSESSMENT MODULE 76
 4.3 Distance
Turbulence Noise
• Reducing fluid turbulence by
straightening bends and
transitioning diameter changes in
fluid flow.

NOISE RISK ASSESSMENT MODULE 77

 4.3 Distance
Turbulence Noise

• Reducing ductwork fan

noise by shifting fan to
low turbulence
region.

NOISE RISK ASSESSMENT MODULE 78

 4.4 Silencer
• Silencers or mufflers can be classified into two fundamental groups :
• Dissipative (sometimes also called absorptive)- governed primarily by the
presence of sound absorbing material that dissipates acoustic energy.
• Reactive - governed primarily by its internal configuration and reduction of
flow velocity by abrupt changes in shape and resonance of added branches or
cavities to a pipe or duct.

• They are made to reduce noise while permitting the flow of air or gas.
• Absorptive silencers contain porous or fibrous material and use absorption to
reduce noise.
• The basic mechanism for reactive silencers is expansion or reflection of sound
waves, leading to noise cancellation.

NOISE RISK ASSESSMENT MODULE 79

Video 1 : How silencer works

NOISE RISK ASSESSMENT MODULE 80

 Silencer - Application
Exhaust Silencer
• Come in standard and custom made to fit to various type internal
combustion engines.
• Installed after engine exhaust outlet with manifold or pipe connection in
order to reduce noise level emitted by high flow rate exhaust gas.
• Commonly known as muffler and designed with multiple chambers and
perforated tubes.

NOISE RISK ASSESSMENT MODULE 81

 Silencer - Application
Duct Silencer
• Designed to efficiently reduce noise
for generator sets, compressors,
pumps, blower and all system that
require air intake and outlet for this
equipment to operate.

• A duct silencer needs to be installed

in the plant room and as close to the
noise source as possible.

NOISE RISK ASSESSMENT MODULE 82

 Silencer - Application
Steam Vent Silencer
• Reduce the noise produced by the
expansion of gas or steam from elevated
pressures to atmospheric pressure.
• These absorptive silencers are used to
suppress noise generated by high velocity
gas streams such as steam vents, safety
relief valve outlets, system blow downs
and purge outlets.
• Typically used in oil and gas processing,
chemical processing and heat recovery
steam generators or boilers.

NOISE RISK ASSESSMENT MODULE 83

Silencer - Application

NOISE RISK ASSESSMENT MODULE 84

Silencer - Application

NOISE RISK ASSESSMENT MODULE 85

 Silencer - Case Study
Problem
• A knife system, which cuts roof tiles to shape,
was producing 92dB at 1m from the operator's
side.
• Most of the noise arose from the exhaust on the
pneumatic cylinders used to move the knives up
and down. There was also a contribution from
the solenoid valve exhaust.

Solution
• 6 pneumatic exhausts were piped to a manifold which in turn was piped to a straight
through silencer.
• The noise levels were reduced by 12dB.
https://www.hse.gov.uk/noise/casestudies/pneumaticex.htm
NOISE RISK ASSESSMENT MODULE 86
Video 2 : Silencer Application

NOISE RISK ASSESSMENT MODULE 87

 4.5 Vibration Isolation
• The application of
vibration isolation is
generally required to
silence structure-borne
noise.

• A relatively small vibrating

machine, pipe, or other
mechanism, when closely
coupled to a floor or panel
and then radiates the
vibration acoustically, can
often produce
objectionable noise levels.

NOISE RISK ASSESSMENT MODULE 88

 4.5 Vibration Isolation
• Machinery noise is created by a
vibrating source coupling to a
large radiating surface.
• When possible, large radiating
surface should be detached from
vibrating sources.
• Reinforcing the floor structure to
provide a stiffer solid base, or
mounting the machine on pillars
founded directly in the ground.

NOISE RISK ASSESSMENT MODULE 89

 4.5 Vibration Isolation

• Vibration isolation may not

be completely effective
when noise is transferred
through piping or conduits
from the equipment.

• Flexible connectors to
mount the tubing to the
building must also be
considered.

NOISE RISK ASSESSMENT MODULE 90

 Vibration Isolator

Four resilient materials that are most used as vibration isolators:

Cork

Rubber Metal Spring Felt

NOISE RISK ASSESSMENT MODULE 91
 Vibrator Isolation - Case Study
Problem
• A high speed strip-fed press used to blank
electrical trip-catch components generated
operator noise levels of 101dB.

Solution

• The press legs were found to be welded construction and thus with little inherent
damping. Consequently, they respond strongly to the vibration generated in the press
frame (to which they are bolted).
• The press frame was isolated from the fabricated legs by inserting 6mm composite pads
between frame and legs.
• Noise reduction of 9dB at the closest operator position was achieved.
https://www.hse.gov.uk/noise/casestudies/highspeed.htm

NOISE RISK ASSESSMENT MODULE 92

Video : Vibration Isolation

NOISE RISK ASSESSMENT MODULE 93

 4.6 Damping
• Damping is any mechanism, occurring either within or
between the components in a vibrating system which lead to
the conversion of vibrational energy into heat energy and
reduction in vibration amplitude.
• If a panel is set into vibration, the level of vibration, hence
noise level will diminish with time
• Reducing the amplitude of vibration reduces resonance peaks
hence reducing the noise radiated
• Stiffening the vibrating surfaces with metal, spray-on damping
material, hardboard.

NOISE RISK ASSESSMENT MODULE 94

4.6 Damping

NOISE RISK ASSESSMENT MODULE 95

 Damping - Case Study
Problem
• Power presses are commonly used
in most metal industries.
• Noise from the flywheel is
frequently a significant source of
noise, produced 88dB at the
operator's position.

Solution
• A soft compressible sheet of rubber was glued to the flywheel of the press.
• The noise levels were reduced by 2dB.
https://www.hse.gov.uk/noise/casestudies/pressflywheel.htm

NOISE RISK ASSESSMENT MODULE 96

 Damping - Case Study
Problem
• A manufacturer of tube fittings used conveyors to
transport components through the manufacturing
process, and to deposit components into hoppers.
• The metal products would drop through some 3m,
partly along a metal delivery chute, before landing
in the hopper. The noise level associated with this
was 96dB.

Solution
• The angle of the conveyor was reduced, to reduce the drop height and the section of the
delivery chute was removed.
• The face of the chute was lined with a sheet of plastic.
• The noise level was reduced by 7dB to 89dB.
https://www.hse.gov.uk/noise/casestudies/metalchute.htm
97
NOISE RISK ASSESSMENT MODULE
 Damping - Case Study
Problem
• Noise from pellets passing rapidly through transfer
pipes and also moving within cyclones often create
noise.
• Typically the noise is due to the internal "scratching"
noise breaking out through the pipe walls, but also to
the resonant ringing of the pipes.

Solution
• Analysis showed that the resonant ringing part was dominant.
• The pipes and cyclones were covered with a self-adhesive pitch-based damping sheet to
eliminate the ringing.
• This is not an insulation - it is damping down pipe ringing. Pipes prone to ringing are usually
circular, thick walled and often welded.
• Noise was reduced by at least 6dB
https://www.hse.gov.uk/noise/casestudies/pneumatic.htm
98
NOISE RISK ASSESSMENT MODULE
NOISE RISK ASSESSMENT MODULE 99
Video : Damping

NOISE RISK ASSESSMENT MODULE 100

Video : Acoustic Enclosure

NOISE RISK ASSESSMENT MODULE 101

5.0 Administrative Control

NOISE RISK ASSESSMENT MODULE 102

 5.0 Administrative Control
How?

Job rotation Scheduling rosters

NOISE LEVEL DAILY EXPOSURE DURATION

dB(A) LIMIT Distance Quiet areas
82 16 hrs
83 12 hrs 42 mins
84 10 hrs 5 mins
85 8 hrs
86 6 hrs 21 mins
87 5 hrs 2 mins
88 4 hrs
89 3 hrs 10 mins
90 2 hrs 31 mins
91 2 hrs
92 1 hr 35 mins
93 1 hr 16 mins
94 1 hr
95 48 mins
NOISE RISK ASSESSMENT MODULE 103
 Job Rotation

Noise Duration of Noise Duration of Noise Duration of

Level Exposure Permitted Level Exposure Permitted Level Exposure Permitted
(dB (A) per day (dB (A) per day (dB (A) per day
– slow) (hours – minute) – slow) (hours – minute) – slow) (hours – minute)
82 16 hrs 93 1 hrs 16 mins 104 6 mins
83 12 hrs 42 mins 94 1 hrs 105 5 mins
84 10 hrs 5 mins 95 48 mins 106 3 mins 45 sec
85 8 hrs 96 38 mins 107 3 mins
86 6 hrs 21 mins 97 30 mins 108 2 mins 22 sec
87 5 hrs 2 mins 98 24 mins 109 1 mins 30 sec
88 4 hrs 99 19 mins 110 1 mins 3 sec
89 3 hrs 10 mins 100 15 mins 111 1 mins 11 sec
90 2 hrs 31 mins 101 12 mins 112 56 sec
91 2 hrs 102 9 mins 113 45 sec
92 1 hrs 35 mins 103 7 mins 30 sec 114 35 sec
115 28 sec
NOISE RISK ASSESSMENT MODULE 104
 Distance

• Sound that propagates from a

point source in free air
attenuates by 6dB for each
doubling of distance from
source.

• For indoors, attenuation is less

due to contributions to the
total sound level from
reverberant sound brought
about by reflection from walls
and ceilings.

NOISE RISK ASSESSMENT MODULE 105

 Distance -Example

Examples: DISTANCE

Example:
Noise level is 90 dB (SPL1) at 1meter
(r1). Calculate noise level (SPL2) at
distance 2 meter (r2)?

Simple Method of knowing SPL2 = 90dB – 20 log (2/1)

how much sound
is reduced by DISTANCE = 83.97 dB

NOISE RISK ASSESSMENT MODULE 106

 6.0 Personal Hearing Protection (PHP)
Employer shall ensure PHP
provided to the employee -

• suitable & efficient

• properly inspected,
maintained and made
available at all time
• will reasonably attenuate the
employee’s personal noise
exposure below NEL
• approved by Director General
of DOSH
NOISE RISK ASSESSMENT MODULE 107
 PHP – NOISE REDUCTION RATING (NRR)
Single protection
• For single protection (only ear muffs or
ear plugs are used) use the following
formula:

Where;
• LEX,8h is daily noise exposure level;
• 2 is de-rating factor (to lower the rating of a
device, especially because of a deterioration in
efficiency or quality).
NOISE RISK ASSESSMENT MODULE 108
 PHP – NOISE REDUCTION RATING (NRR)
Dual protection

• For dual protection (ear muffs and plugs are used

simultaneously), use the following formula to
determine the Estimated Exposure:

Where;
• NRRh is NRR for the higher rated protector;
• LEX,8h is daily noise exposure level.

Note : Employer may use any recognized method to calculate noise reduction rating such as Single
Number Rating (SNR), Sound Level Conversion (SLC80).

NOISE RISK ASSESSMENT MODULE 109

 PHP – NOISE REDUCTION RATING (NRR)

• The NRR describes the average sound level

reduction (attenuation) provided by a hearing
protection device (HPD) in a laboratory test.

• It doesn’t take into consideration on:

– the loss of protection that occurs when
hearing protectors are not fit properly
– they are not worn for the entire time that the
wearer is exposed to noise

NOISE RISK ASSESSMENT MODULE 110

 PHP – SINGLE NUMBER RATING (SNR)
SNR VS NRR
• There is currently no exact formula
to convert the rating values from
NNR to SNR or vice versa but SNR
values tend to be about 3 dB higher.
• Eg: PHP with NRR 25 will have an
SNR of about 28.

https://www.hse.gov.uk/noise/goodpractice/
hearingoverprotect.htm

NOISE RISK ASSESSMENT MODULE 111

 Conclusion - Key Points
• Excessive exposure to noise can cause loss of hearing

• Eliminate / reduce the excessive noise levels based on

Hierarchy of Noise Control Measures

• Effective noise controls in the workplace will benefit both

employers & employees

• Attitude – New mindset (Do not purely rely on PPE)

NOISE RISK ASSESSMENT MODULE 112

 THANK YOU
FOR LISTENING

NOISE RISK ASSESSMENT MODULE 113