Control
in Basic Guide
Industry:
A
Target Audience
This guide is for workers, supervisors, health and safety
committee members, health and safety representatives,
industrial hygienists, occupational health and safety
nurses and others with an interest in hearing
conservation. The technical level of this guide meets the
needs of the target audience.
Summary
Noise is a major occupational hazard. Short term effects
of noise exposure include temporary hearing loss, stress,
annoyance, difficulty in verbal communication, and
safety hazards. The primary long-term health effect of
noise exposure is permanent hearing loss. Both short-
term and long-term effects can be prevented by timely
recognition, evaluation and control of noise exposure.
This guide provides an overview of the methods of
recognition, evaluation and control of workplace noise
exposure. Topics covered include: a review of the units
and measures of noise; methods of measuring noise level
and noise exposure; instruments used to measure noise;
the relationship between noise exposure and risk of
hearing loss; noise exposure limits; engineering methods
of noise control; and the effectiveness of hearing
protectors. Basic components of a hearing conservation
program are outlined.
Table of Contents
Introduction
Section I Why do we worry about noise
Health Effects: Auditory Effects . . . . . . . . . . . . . . . . 2
Health Effects: Non-Auditory Effects . . . . . . . . . . . . 3
Physiological Effects . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Performance Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Effect on Pregnancy . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Section II Basics of Noise
What is noise? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
How do I know if I have noise problem
in my workplace ? . . . . . . . . . . . . . . . . . . . . . . . . . 8
Production and Transmission of Noise . . . . . . . . . . . 9
Units and Measures of Noise . . . . . . . . . . . . . . . . . . 10
Frequency. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Sound Pressure. . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Units and Measures of Workplace Noise. . . . . . . . . 12
A-Weighted Noise Levels . . . . . . . . . . . . . . . . . . . 13
Sound Pressure Level and Sound Energy . . . . . . 14
Continuous, Variable, Intermittent
and Impulse Noise . . . . . . . . . . . . . . . . . . . . . . . . 17
Sound Power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Relationship Between Sound Pressure Level
and Sound Power Level . . . . . . . . . . . . . . . . . . . . . . 18
Section III Measures of Workplace Noise
Workplace Noise Level . . . . . . . . . . . . . . . . . . . . . . 20
Noise Exposure Level of an Employee . . . . . . . . . . 20
Relationship Between Noise Exposure Level
and Noise Level . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Time Weighted Average (TWA) Noise
Exposure Level . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Comparison: TWA based on 3-dB and
5-dB exchange rates (rules). . . . . . . . . . . . . . . . . 22
Evaluation of Noise Exposure Level . . . . . . . . . . . . 23
Section IV Instruments and Methods of Measuring Noise
Identifying Noise Problem . . . . . . . . . . . . . . . . . . . . 26
Planning Noise Measurement . . . . . . . . . . . . . . . . . 27
Selecting Noise Measuring Instruments . . . . . . . . . 28
Sound Level Meter . . . . . . . . . . . . . . . . . . . . . . . . 30
Integrating Sound Level Meter . . . . . . . . . . . . . . 31
Noise Dosimeter. . . . . . . . . . . . . . . . . . . . . . . . . . 31
Octave Band Analyzers . . . . . . . . . . . . . . . . . . . . 33
Effects of Environmental Conditions
on Noise Data. . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Correction for Background Noise . . . . . . . . . . . . 35
Conducting Noise Measurements . . . . . . . . . . . . . . 36
Noise Survey. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
Measuring Equivalent Noise Using An
Integrating Sound Level Meter . . . . . . . . . . . . . . 38
Noise Dosimetry. . . . . . . . . . . . . . . . . . . . . . . . . . 39
Measuring Impulse/Impact Noise . . . . . . . . . . . . 41
Documenting Noise Levels Data . . . . . . . . . . . . . . . 42
Section V Evaluating the Risk of Noise-Induced Hearing Loss
Types of Hearing Loss . . . . . . . . . . . . . . . . . . . . . . . 46
Permanent Hearing Loss . . . . . . . . . . . . . . . . . . . 46
Hearing Loss Due to Aging . . . . . . . . . . . . . . . . . 47
Other Causes of Hearing Loss. . . . . . . . . . . . . . . 47
Measures of Hearing Loss . . . . . . . . . . . . . . . . . . . . 47
Hearing Disability . . . . . . . . . . . . . . . . . . . . . . . . 48
Relationship Between Noise Exposure
And Hearing Loss . . . . . . . . . . . . . . . . . . . . . . . . 49
Section VI Occupational Noise Exposure Limits
Noise Exposure Limits. . . . . . . . . . . . . . . . . . . . . . . 54
Exposure Limits for Impulse/Impact Noise . . . . . 55
Noise Exposure Limits for Extended Workshifts . . . . . 56
Deciding Exposure Limits
for Extended Workshifts . . . . . . . . . . . . . . . . . . . . 57
Canadian and U.S. Noise Regulations . . . . . . . . . . . 58
Synergistic Effects: Ototoxic Chemicals . . . . . . . . . 61
Office Noise Levels . . . . . . . . . . . . . . . . . . . . . . . . . 61
Section VII Managing Workplace Noise Problems
Hearing Conservation Program Components . . . . . 64
Noise Monitoring: Hazard Identification. . . . . . . . . 65
Noise Reduction: Engineering Controls . . . . . . . . . 67
At the Source . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
Along the Path . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
Hearing Protection . . . . . . . . . . . . . . . . . . . . . . . . . . 78
Advantages and Limitations of Earplugs
and Earmuffs . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
Standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
Noise Reduction Rating (NRR)
of Hearing Protectors . . . . . . . . . . . . . . . . . . . . . . 81
Hearing Measurement . . . . . . . . . . . . . . . . . . . . . . . 85
Administrative Controls . . . . . . . . . . . . . . . . . . . . . . 86
Employee Training . . . . . . . . . . . . . . . . . . . . . . . . . . 87
Program Evaluation and
Continuous Improvement. . . . . . . . . . . . . . . . . . . 88
Section VIII Occupational Health and Safety Legislation
Canadian Legislation . . . . . . . . . . . . . . . . . . . . . . . . 92
What Does the OH & S Legislation Say . . . . . . . 92
Workplace Hazardous Material Information
System WHMIS) . . . . . . . . . . . . . . . . . . . . . . . . . . 96
U.S. Legislation . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
Section IX Information Sources
In Canada. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108
In the U.S.A. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114
Appendix A Sound Pressure Level Calculations . . . . . . . . . . . . 118
Definition of Decibel (dB) . . . . . . . . . . . . . . . . . . . 118
Convert Dose to Equivalent Sound Level (Leq) . . 119
Appendix B Relevant Noise Standards . . . . . . . . . . . . . . . . . . . 121
Canadian Standards Association . . . . . . . . . . . . . . 121
American National Standards Institute (ANSI) . . . 122
Appendix C Further Reading . . . . . . . . . . . . . . . . . . . . . . . . . . . 124
Appendix D Sound Absorbing and Sound Attenuation
of Some Building Materials and Furnishings . . . . 125
3. Production and Transmission of Noise
Noise (or sound) comes from vibrating objects. Vibration
can result from air flow, high speed rotating machines,
friction or mechanical impacts involved in machine
operation. From the source, noise spreads out as a series
of air pressure fluctuations known as sound waves. The
spread of sound waves from the source to other locations
occurs via the surrounding air or other media such as
water and solids. This process of sound transmission or
propagation is similar to the spread of ripples on the
surface of a lake when a rock is dropped into in the water.
The following example illustrates the production and
transmission of sound waves. Imagine striking a drum
surface with a stick. As a result of the impact, the drum
surface vibrates back and forth. As it moves forward, it
pushes the air in contact with the surface and produces a
dense (high pressure) region in contact with the drum.
When the surface moves in the opposite direction, it
creates a rarified (low-pressure) region by
decompressing the air in contact with the drum. As the
drum surface vibrates, it creates alternating regions of
high and low pressure.
PRODUCTION AND TRANSMISSION OF SOUND WAVES
Air Air
Compression Compression
High
Distance
from the
Variation in air pressure
source
Low
9
Typical A-Weighted Sound Levels
NOISE SOURCE dB(A)
pneumatic chipper at 1 metre 115
hand-held circular saw at 1 metre 115
textile room 103
newspaper press 95
power lawn mower at 1 metre 92
diesel truck (50 km per hour at 20 metres) 85
passenger car (60 km per hour at 20 metres) 65
conversation at 1 metre 60
quiet room 40
Sound Pressure Level and Sound Energy
The sound pressure level is related to the sound energy
entering the ears of exposed persons. The following table
gives some useful relationships between changes in
decibel level and corresponding changes in the sound
energy.
Sound Pressure Level and Sound Energy:
Basic Rules
CHANGE IN dB CHANGE IN SOUND ENERGY
3 dB increase Sound energy doubled
3 dB decrease Sound energy halved
10 dB increase Sound energy increased by factor
of 10
10 dB decrease Sound energy decreased by factor
of 10
20 dB increase Sound energy increased by factor
of 100
20 dB decrease Sound energy decreased by factor
of 100
14
As a person ages, hearing may worsen because
T
"age-related hearing loss" adds to the existing noise
induced hearing loss.
Both ears are equally affected except in cases when
T
one ear is exposed to a higher noise level than the
other.
Hearing loss is a cumulative process; both level of
T
noise and exposure time are important factors.
Hearing Loss Due to Aging
Hearing sensitivity naturally declines as people become
older. Like noise-induced hearing loss, everyone is not
affected equally. Age-related hearing loss adds to noise-
induced hearing loss and therefore hearing ability may
continue to worsen even after a person stops working in
a noisy environment.
Other Causes of Hearing Loss
Exposure to ototoxic chemicals (eg. toluene, lead,
manganese), certain medications and diseases may also
cause hearing loss. Generally, it is not possible to
distinguish hearing loss due to noise from hearing loss
due to other causes. Judgement in such cases is based
on the noise exposure history.
2. Measures of Hearing Loss
Hearing loss is measured as threshold shift in dB units
using an audiometer. The 0 dB threshold shift-reading of
the audiometer represents the average hearing threshold
level of a young adult with disease-free ears. The
threshold shift as measured by audiometry is the dB
level of sounds of different frequencies barely audible to
that individual. A positive threshold shift represents
hearing loss, and a negative threshold shift means better
than average hearing.
47
Mufflers
A muffler is an acoustic filter. Its performance varies
with the sound frequency. A muffler reduces the
transmission of sound and allows the free flow of gas.
Mufflers are installed to reduce noise where large
quantities of high pressure gas, liquid, steam or air are
discharged into the open air.
Reducing air exhaust noise by installing muffler.
Open Air
Discharge
Noisy Flow
High Pressure Air,
Steam or Vapor
Exhaust Lines
Silencer
Quiet Flow
Selection Criteria for Mufflers
Acoustical Criterion: Noise reduction capability
measured as insertion loss.
Insertion Loss (dB) =
SPL before muffler 鈥? SPL after muffler
Aerodynamic Criterion: Maximum acceptable pressure
drop through the muffler.
Geometrical Criterion: Maximum allowable volume
and restrictions on the shape.
Mechanical Criterion: Durability, maintenance, and
environmental conditions.
73
|