NOISE AND HEARING

1. NOISE & HEARING
(KAS 3501)
Year 3 (II) 2014/2015
Group 18
May 13th 2015
MUHAMMAD NUH B SULAIMAN U K 3 0 0 0 6
WAN HAFIZAH BT WAN ZAKARIA U K 3 0 0 5 8
LEE SOK YEEN U K 2 9 5 6 1
NABILA BT MD HANIF U K 3 0 1 0 4
NUR FARHANA BT MAT NOH U K 2 9 5 6 3

2. 1. INTRODUCTION
 Noise is unwanted or offensive sounds that
unreasonably intrudes into our daily activities.
 Classified as physical hazard.
 May lead to permanent and irreversible damage to
hearing.
REGULATIONS
o Factories and Machinery (Noise Exposure)
Regulation1989
o Aim at protecting employees while they works
o Regulation 5 – Permissible Exposures Limit
o No employee shall be exposed to noise level exceed
continuous sound level of 90dB (A)
o No employee shall be exposed to noise level exceed
115dB (A) at any time
o No employee shall be exposed to impulsive noise exceed
a peak sound level of 140dB (A)

3. NOISE CONTROL - CONCEPT
AND BASIC PRINCIPLE
 As in all hazard control, noise control efforts should
be approached according to the hierarchy of control
strategies, i.e. using the paradigm:
 Noise from most equipment comprises mainly waste
energy.
 The best way to reduce noise is to tackle the
problem at the source.
 At the other end, reduction at receiver (i.e. affected
employee) is achieved by either removing the
employee from the sound field, limiting his working
time in the area.

4. 4. OVERALL NOISE CONTROL
PROCEDURE
o Appropriate control measures includes;
o Change in plant design and layout
o Substitution of a less hazardous work method
o Reduction of the hazard at its source
o Reduction of the hazard at its path of transmission.
Thus the recommended method of approach is
outlined below;
 Plant planning (design and layout)
 Substitution (equipment, process, material)
 Engineering control
 Control at source (modification of noise generator)
 Control at path (modification of sound wave)

5. CONTROL BY PLANT
PLANNING
Successful planning for noise control involves:
 Knowledge of the noise characteristics of each machine
and process;
 Proposed location of each noise source, operator, and
maintenance man;
 Selection of design criteria based on employee exposure
time.
It is important to consider the following:
 The building's load-bearing structure
 Powerful noise sources should be enclosed by structures
 Rooms where there are sound sources and where
personnel are present continuously should be provided
with ceiling
 Office areas should be separated from building elements
where vibrating equipment is installed by a joint of elastic
material.

6. CONTROL BY SUBSTITUTION
a) Use Quieter Equipment
 The first step in providing quiet workplace equipment is to make a
strong effort to have equipment purchase specifications include noise
emission limits. When acquiring new equipment, its type and speed
should be selected on the basis of the applicable noise criteria.
b) Use Quieter Processes
 In many cases, changing the process can be one way of getting to
grips with noise generation. This would in turn involve cooperation
between the employer, supplier, process designer and OSH
professional.
 In most building and construction work, Hazardous local noise levels
are generated both by the impact on the pile and from the explosion,
and annoyance may be caused at distances of up to a few miles.
c) Use Quieter Material
 Materials from which buildings, machinery, piping and containers are
constructed have a vital relation to noise control. Some materials have
high internal damping and are called 'dead' materials, while others
called 'live' materials have little internal damping and cause a ringing
sound when struck.

8. ENGINEERING NOISE CONTROL
Existing Equipment
a) Once generated, noise can transmit through;
i. Direct sound field
ii. Reverberant sound field
iii. Structure-borne path
b) Reduce amount of work hour in the sound field.
c) Proper maintenance of equipment.

9. ENGINEERING NOISE CONTROL
Systematic Approach
o Control noise from existing equipment by applying
engineering principal.
Generated
noise
Radiated
noise
Control at
source
Directly
transmitted
noise
Reverberant
noise
Structure-
borne noise
Control at
path
Control at
receiver

10. • Reduction or elimination of the impact and generation of noise
• Modification of equipment which reduce the metal-to-metal
contact (eg: blade,gear etc)
Generated Noise
• Move the machine to new place far from the exposed
employees
• Apply vibration isolation to machine housing
Radiated Noise
CONTROLAT
SOURCE
CONTROLAT
PATH
• Use sound absorptive material
• Construct and acoustical barrier to shield, deflect or absorb
noise energy
Directly Transmitted Noise
• Use sound absorptive material (eg: fiberglass, acoustic tiles on
wall, ceiling etc)
• Reduce reflection by move the machine far from corner or walls
Reverberant Noise
• Use duct lines with sound-absorptive material
• Use wrapping on pipe to increase their sound insulation
Structure-borne Noise

11.  Use enclosure or control room to house the
employee.
 Reduce the amount of time the employee is
allowed to work in a high noise area.
 Provide HPE to the employee.
CONTROLAT
RECEIVER

12. REDUCING GENERATED NOISE
• Reduce Impact Noise
• Reduce or Eliminate
Aerodynamically Generated
Noise
• Reduce Vibration

13. REDUCE IMPACT NOISE
Mechanical and material handling devices-
produce noise from impact
 Reducing the dropping height of goods collected in
boxes or bins
 Using soft rubber or plastic to receive and absorb
hard impacts
 Increasing the rigidity of containers receiving
impact goods and adding damping material —
especially to large surfaces.
 Regulating the speed or cycle time of conveyors to
prevent collisions and excessive noise.

14. REDUCE OR ELIMINATE
AERODYNAMICALLY GENERATED
NOISE
• Change the character of the noise
• Reduce the surface area of the source
• Change the source dimensions such that
noise is cancelled out at the edges
• Reduce or remove interrupted-wind tonal
noise
• Reduce turbulence in fluids
• Reduce fan noise
• Use silencers
• Reduce Vibration

15. CHANGE THE CHARACTER OF
THE NOISE
 Replacing a noise source with one of higher
noise frequency may reduce the sound
level at typical property-line distances

16. REDUCE THE SURFACE AREA
OF THE SOURCE
 When large surfaces vibrate they will
produce high sound levels. Consider
replacing solid plates, wherever possible,
with expanded metal, wire mesh or
Perforated

17. CHANGE THE SOURCE DIMENSIONS SUCH
THAT NOISE IS CANCELLED OUT AT
THE EDGES
 At the edges of large vibrating plates, the
compression and rarefaction sound waves
tend to cancel each other out using long
narrow surfaces instead of square or
approximately square surfaces

18. REDUCE OR REMOVE
INTERRUPTED-WIND TONAL NOISE
 When tonal noise is produced by machinery due to this
effect, it maybe possible to eliminate the wind (i.e. the air
flow) by filling out any hollow space, thus removing the
noise created by it.

19. REDUCE TURBULENCE IN
FLUIDS
• Fluid noise is due to turbulence. The more turbulent
the flow, the greater would be the noise.
• Vapour bubbles can be created by abrupt changes in
the flow of fluids. Providing
 gradual transition in cross-sectional area reduces the
likelihood of these bubbles
 forming

20.  Turbulence at the walls of ducts or pipes is always
present. To reduce noise;
 Interior walls should be smooth, free of protrusions at joints,
and sharp bends at 'tees' (T junctions) and 'wyes' (Y
junctions) should be avoided.
 Turning vanes can be placed inside ductwork when
construction methods utilise sharp bends.
 Straightening vanes can be used to smoothen the flow
downstream of any change in direction, diameter, or
branching

21. USE SILENCERS
Absorptive silencer:
 Simplest form: lined duct
 considered for cooling and exhaust air
whenever sources are to be enclosed
Reactive silencer:
 simplest form: single expansion chamber
 the expansion and contraction in pressure
cause reflection of sound waves.
 The reflected wave added to the incoming
sound wave results in destructive
interference, leading to noise reduction.

22. REDUCE VIBRATION
• Shifting instrument panel to wall
• Putting damping on flexible panel
• Obtaining maximum isolation by stiffening the floor
structure; or mounting the machine on ground-
founded pillars
• Placing heavy vibrating equipment on inertial block
with vibration isolators and dampers.
• Flexible connectors for preventing vibration
transmission to building structure.
• Isolation of pipe work on refrigeration plant by use
of flexible couplings
• Shifting small service machinery onto isolators on a
solid floor
• Reducing resonance in a circular saw blade

23. CONTROLLING NOISE IN
ROOMS

24. DEFINING SOUND FIELDS
Near Field The region close to a sound source usually defined
as 1/4 of the longest wavelength of the source.
Near field references can pertain to both indoor and
outdoor environments.
Far Field Sound field beyond the near field limits described
above where the sound pressure level (SPL) drops
off at the theoretical rated of 6 dB for every
doubling of distance from the source.
Direct Field To describe far field conditions that follow the
Inverse Square Law SPL loss rate of 6 dB for every
doubling of the distance.
Diffuse Field There are so many reflections contributing to the
total sound field that sound levels measured
virtually anywhere in the sound field are the same.
Diffuse fields usually pertain to indoor environments
Reverberant
Field
Essentially the same as the diffuse field.
For indoor sound field discussions it is used to
contrast direct fields.

25. NOISE REDUCTION OBTAINED
FROM USE OF NOISE BARRIER
 If a sound source is in a room with a large amount
of absorption present, blocking the direct path with
a partial barrier may provide adequate noise control.
 Indeed, this technique is more often used outdoors,
since even a modest amount of reverberation will
destroy the effectiveness of a shield.

26. OSHA DECIBEL LEVELS – HEARING
PROTECTION
Employee exposure to excessive noise depends
several factors including;
 The loudness of the noise as measured in
decibels (dB)
 The duration of each employee’s exposure to the
noise
 Whether employees move between work areas
with different noise levels (decibel levels)
 Whether noise is generated from one or multiple
sources
 Generally, the louder the noise, the shorter the
exposure time before hearing protection is
required.

27. PERMISSIBLE NOISE
EXPOSURES
Duration per
day, in hours
Sound level in
dB* - Decibel
level
8 90
6 92
4 95
3 97
2 100
1.5 102
1 105
0.5 110
0.25 or less 115

28. DECIBEL LEVELS OF
ENVIRONMENTAL SOUNDS
Source--Dangerous
Level dBA SPL
 Produces Pain
(120-140dB)
 Jet Aircraft During
Takeoff (at 20
meters) (130dB)
 Snowmobile
Tractor Without
Cab (120dB)
 Rock Concert
(110dB)
 Die Forging
Hammer
Gas Weed-
Whacker
Chain Saw
Pneumatic Drill
(100-105dB)
 Home Lawn
Mowers (95 to
100dB)
 Semi-trailers (at
20 meters) (90dB)
Source--dBA SPL
 Discomfort Level
Above (80dB)
 Heavy Traffic
(80dB)
 Automobile (at 20
meters) (70dB)
 Vacuum Cleaner
(65dB)
 Conversational
Speech (at 1
meter) (60dB)
 Quiet Business
Office (50dB)
 Residential Area
at Night (40dB)
 Whisper, Rustle of
Leaves (20dB)
 Rustle of Leaves
(10dB)
 Threshold of
Audibility (0dB)

29. TYPES OF HEARING
PROTECTION
Some types of hearing protection include:
 Single-use earplugs are made of waxed cotton, foam, silicone
rubber or fiberglass wool. They are self-forming and, when
properly inserted, they work as well as most molded earplugs.
 Pre-formed or molded earplugs must be individually fitted by
professional and can be disposable or reusable. Reusable plugs
should be cleaned after each use.
 Earmuffs require a perfect seal around the ear. Glasses, facial
hair, long hair or facial movements such as chewing may reduce
the protective value of earmuffs.

30. REFERENCES
Health, N. I. (2014, August 08). Center for Disease Control and
Prevention. Retrieved from USA.gov:
http://www.cdc.gov/niosh/topics/noisecontrol/
Industrial Noise Control Manual, Revised Edition, National
Institute of Occupational Safety and Health (USA)