osha
TRANSCRIPT
NOISE & HEARING (KAS 3501) Year 3 (II) 2014/2015
Group 18May 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 SOOK YEEN U K 2 9 5 6 3
NABILA BT MD HANIF U K 3 0 1 0 4
NUR FARHANA BT MAT NOH U K 2 9 5 6 1
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.
REGULATIONSo Factories and Machinery (Noise Exposure)
Regulation1989o Aim at protecting employees while they workso 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)
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. OVERALL NOISE CONTROL PROCEDURE
o Appropriate control measures includes;o Change in plant design and layouto Substitution of a less hazardous work methodo Reduction of the hazard at its sourceo 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)
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.
CONTROL BY SUBSTITUTIONa) 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.
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.
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
Generated Noise
• Reduction or elimination of the impact and generation of noise• Modification of equipment which reduce the metal-to-metal contact
(eg: blade,gear etc)
Radiated Noise
• Move the machine to new place far from the exposed employees• Apply vibration isolation to machine housing
CO
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CO
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PATH
Directly Transmitted Noise
• Use sound absorptive material• Construct and acoustical barrier to shield, deflect or absorb noise
energy
Reverberant Noise
• Use sound absorptive material (eg: fiberglass, acoustic tiles on wall, ceiling etc)
• Reduce reflection by move the machine far from corner or walls
Structure-borne Noise
• Use duct lines with sound-absorptive material• Use wrapping on pipe to increase their sound insulation
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.CO
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REC
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REDUCING GENERATED NOISE
• Reduce Impact Noise• Reduce or Eliminate
Aerodynamically Generated Noise
• Reduce Vibration
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.
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
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
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
CHANGE THE SOURCE DIMENSIONS SUCH THAT NOISE IS CANCELLED OUT ATTHE 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
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.
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
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
USE SILENCERSAbsorptive 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.
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
CONTROLLING NOISE IN ROOMS
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.
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.
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.
PERMISSIBLE NOISE EXPOSURES
Duration per day, in hours
Sound level in dB* - Decibel
level8 906 924 953 972 100
1.5 1021 105
0.5 1100.25 or less 115
DECIBEL LEVELS OF ENVIRONMENTAL SOUNDS
Source--Dangerous Level dBA SPL
Produces Pain (120-140dB)
Jet Aircraft During Takeoff (at 20 meters) (130dB)
SnowmobileTractor Without Cab (120dB)
Rock Concert (110dB)
Die Forging HammerGas Weed-WhackerChain SawPneumatic 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)
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.
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)