Transcript Hearing Conservation and Noise Measuring Equipment

Noise Measurement
Training Module
1
© 3M 2013. All Rights Reserved.
Table of Contents
 Physics of Sound (Hearing loss, terminology)
 OSHA (Regulations)
 Sound Level Meters
 Noise Dosimetry
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© 3M 2013. All Rights Reserved.
Noise Measurement and Dosimetry
Learning Objectives
 Explain sound pressure level, frequency & respective units of
measure
 Describe level average, time weighted average & dose
 Explanation of criterion, threshold & exchange rate
 Proper placement & care of microphones and instrumentation
 Explain hearing conservation regulations & OSHA
requirements as it pertains to noise measurement
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 Hands on calibration, function & measurement with the noise
dosimeter, sound level meter and octave band analyzers
Section I
Physics
of
Sound
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1-20
Sound vs Noise?
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Why Measure Noise?
I.
Determine if the employee(s) are at risk for
Noise Induced Hearing Loss (NIHL) & should
be in a Hearing Conservation Program (HCP)
II.
Differentiate between on-the-job & off-the-job
noise exposure
III. Determine most effective hearing protection
IV. Engineering Controls
V. Administrative Controls
VI. Compliance with applicable Standards
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© 2009 3M Company. All Rights Reserved.
Why Measure Noise?

Prolonged exposure to noise causes permanent and
debilitating hearing loss
 Mostly between 4 – 8 kHz
 Lose ability to understand speech in many situations
 Typically affects consonant reception
 Individual losing hearing is often the last to know!
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Why Measure Noise?
 Long term health effects due to adrenaline release
 More accidents in high noise environments
 Measurable decrease in productivity
 Measurable decrease in work accuracy
 Increased fatigue
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Noise Induced Hearing Loss
 Intensity + Duration
 Damage occurs in the cochlea
 Results in loss of
comprehension, not loudness
 Permanent
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Definition of Sound
Fig. I-3 Compression & Rarefaction of air molecules
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What does Sound look like?
Adapted from Acoustics Animations – Dr. Dan Russell – Kettering University Applied Physics
http://www.kettering.edu/~drussell/Demos/waves/wavemotion.html
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Compression & Rarefaction of
Air Particles in a Sine Wave
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Four Characteristics Of Sound
 Frequency
(measured in Hz)
 Intensity
(measured in dB)
 Speed
(measured in feet or meters/second)
 Wavelength (measured in feet or meters)
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Frequency
 Measured in Hertz (Hz)
 kHz for 1000xHz
 Relates to the pitch of the signal
 Is a measure of the cycles completed in one second
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Frequency – (Pitch)
Fig. I-4 1Hz and 10Hz Sine Waves
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Typical Frequency Examples
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 Lathe
50 to 1100 Hz
 Compressed air
500 to 8000 Hz
 Circular saw
300 to 12000 Hz
 Cars
8 to 1100 Hz
 Violin
300 to 9000 Hz
Frequency Response & Weighting
 The human ear is capable of responding to frequencies ranging

from 20 Hz to 20 kHz
 The ear is less efficient at high and low frequencies
 In the range from 500 Hz to 4 kHz a normal human ear is very
sensitive
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Frequency Response & Weighting
Fig. I-6 “A” and “C” Weighting Curves
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Sound Pressure Level
Fig. I-7 Sine Waves with different sound pressures
Measured in decibels (dB)
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2 Sine Waves:
Same Frequency
Same Time Duration
Different Intensity
One is TWICE as
loud as the other
Understanding deciBels (dB)
 deciBels S P L
dB SPL
 deciBels H L
dB HL
 Sound
Pressure
Level
 Hearing
Level
 Relates to intensity of
 Relates to measurements of
audiometric test tones
the environment
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Doubling Sound Source
100 dB
100 dB
+
 Add 3 dB
 10 dB  perceived as “twice” as loud
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= 103 dB
Addition of Decibels
If the difference between two levels to be added is:
- 0 to 1 dB,
then add 3 dB to the higher number
- 2 to 3 dB,
then add 2 dB to the higher number
- 4 to 7 dB,
then add 1 dB to the higher number
- 8 dB or more, then add 0 dB to the higher number
 Decibels are logrithmic values
 They can not be directly added or subtracted
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Changing Distance From Source
 Outside
 Doubling distance
 Decrease SPL 6 dB
 Room
 Very Near Source
 Twice the distance decreases
SPL by 6dB
 Far from source
 No change with change in
distance
NOTE: These are general
guidelines. Each case may vary.
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Octaves
Fig. I-11 Octave Bands
 Focus on the frequency content of the overall noise signal
 Important for noise control efforts
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Occupational Noise Characteristics
Fig. I-12 Mixture of Source Signals
 In the real world of occupational noise the overall sound is a mixture of
many simultaneous sources with a variety of frequencies and intensities.
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Types or Characteristics of Sound
“Measure all continuous, variable and impact/impulse sound”
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Response Time
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 Slow
1 second rise and fall
 Fast
0.125 second rise and fall
 Impulse
35 millisecond rise
1.5 second fall
 Peak
50 microsecond rise and fall
Various time responses
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Types of Hearing Protectors
 Muffs
 Plugs
Foam formable
Pre formed
Custom
 Others
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Plugs on a head band
Noise cancellation
Hearing Protection
NRR
Noise Reduction Rating
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NRR Devaluation
 NRR
- 7 dB
Adjusted
Attenuation
then divide this value by 2
to determine if hearing protector’s are adequate
to forego noise control
 The OSHA method is described well on the OSHA
Noise & Hearing Conservation e-Tool website
http://www.osha.gov/dts/osta/otm/noise/hcp/attenuation
_estimation.html
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Hearing Protection
2
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NRR
- 7
NIOSH subject fit Model
 Muffs
NRR less 25%
 Formable Plugs
NRR less 50%
 All Other Plugs
NRR less 70%
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GRAPHIC ILLISTRATION
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 Assume you need 10 dB
reduction
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35
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Muff
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 Assume NRR is 24 for all
 De-rate muff by 25%
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Formed
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Others
10
6
 De-rate formable by 50%
5
 De-rate anything else by 70%
0
Net Protection
NRR
Plugs + muffs
 REMEMBER:
 Earmuffs over earplugs provide a maximum of 5dB
additional attenuation no matter what the muff rating.
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Critical Terminology
Criterion - If exposed to SPL on average for eight hours, it
would result in a maximum allowable exposure. [90dB for 8
hrs]
Threshold – dB level below which, all SPL’s are assigned a
value of zero. [80dB]
Exchange Rate - Results in a doubling or halving of the
maximum allowable exposure.
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Critical Terminology
Average Level (LAVG and Leq) - If present continuously, would
generate the same amount of energy as the varying levels that
are present in the environment measured in decibels.
Time Weighted Average (TWA) - A level average with an
assumed fixed sample period of eight hours measured in
decibels.
Dose - The allowable daily exposure value. A maximum
allowable exposure is equal to 100% dose. [90dB x 8hrs = 100%
Dose]
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A Basic Concept…
 TWA = Lavg @ exactly 8 hours
 DOSE = Follows the same line!
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Dose / Lavg over time
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Exercise I
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Exchange Rates
 SOUND LEVEL METERS
 3dB exchange rate
 When averaged, Leq (level equivalent)
 NOISE DOSIMETERS
 5dB exchange rate

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When averaged, Lavg (level average)
Criterion and 5 dB Exchange rate
 90dB x 8hrs = 90dB TWA = 100% Dose
 95dB x 8hrs = 95dB TWA = 200% Dose
 100dB x 8hrs = 100db TWA = 400% Dose
 100dB x 4hrs = 95dB TWA = 200% Dose
 100dB x 2hrs = 90dB TWA = 100% Dose
 100dB x 1hr = 85dB TWA = 50% Dose
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Section II
OSHA
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21-25
The Occupational Noise Exposure Standard
 Derived from the Walsh-Healey Public Contracts Act.
 1971 adopted under the Occupational Safety and
Health Act.
 Permissible Exposure Level (PEL) of 90 dBA.
 Noises with a higher level than 90 dBA can be
sustained for periods of less than 8 hours.
 Sounds with average levels less than 90 dBA can
persist for periods of more than 8 hours.
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Permissible Noise Exposure
Hours per Day
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Sound Level dBA slow
response
8
90
6
92
4
95
2
100
1.5
102
1
105
0.5
110
0.25 or less
115
Hearing Conservation Amendment
 Published in the Federal Register on March 8, 1983.
 The Hearing Conservation Amendment requires the employer to perform
five key tasks:
 Measure Noise
 Audiometric Tests
 Hearing Protectors
 Education & Training
 Record Keeping
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Table G-16a (abbreviated)
Measuring Threshold
H.C. Action Level (50% exp.)
8 Hour Criteria
Minimum Upper Range
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24
85
A-Weighted
Sound Level
Duration
(Hours)
80
16
90
95
100
105
110
115
120
125
130
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8
4
2
1
0.5
0.25
0.125
0.063
0.031
Section II
Measuring Method for OSHA Surveys
Original Rule
H.C.A.
A/Slow
A/Slow
Exchange (Doubling) Rate
5 dB
5dB
Criterion (LC=100%)
90dB
90dB
Threshold (Cut Off)
90dB
80dB
Weighting/Response
Limit
90dB/100%
(PEL)
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85dB/50%
Action
Level
Conclusion
 The focus of the Occupational Noise Exposure Standard and the Hearing
Conservation Amendment, is to set minimum requirements to protect
hearing for those workers in a noisy environment.
 The Keys to Success
 Positive attitude on the part of the management
 Clear communication of the value of hearing
 Hearing protection takes care of the problem of noise for the short term, but the
key to real hearing protection is education and communication.
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Section III
Sound Level Meters
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26-39
Components of a Sound Level Meter
Fig. III-1 Block Diagram of a Typical Sound Level Meter
Microphone
Amplifier
Range
Control
Frequency
Filter(s)
C
A
Fast/Slow
F
S
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Display
Classification of Sound Level Meters
 Three types of SLM’s established by ANSI, and IEC Standards:
 Class 0 Laboratory grade instrument
 Class 1 Precision instrument
 Class 2 General purpose instrument
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Types of Microphones
Random
Incidence
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Direct
Incidence
Pressure
Microphone
Acoustical Calibrators
1) Loudspeaker
1
2) ON/OFF switch
3) Battery indicator
4) Microphone adapter
2
4
3
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SoundPro SE/DL series
Understanding the KeyPad
Enter key ~
The center key is primarily used to
execute an action from the menu
displays or in measurement and
logging displays.
Arrows ~
The left/right arrows and up/down
arrows are used to navigate in the
direction you select. These are used
often as you are moving through the
menus or toggling through logged
sessions.
Alt f key ~
Alternate functions. Pressing this key
toggles the contents in the Softkey
Region.
On/Off/Esc ~
Triple function key. Its function
depends on the circumstances at
that time. Press it to apply power
and switch the instrument on. Press
it to power down . Press it to
Escape (or exit) from a data field or
a screen.
Run/Pause key ~ Press to start and pause studies
depending upon whether a study
was running at that time or not.
Stop key ~
Press to stop (or close) the session.
Backlight key ~ If you have Backlight set to
“Manual,” press this key to manually
turn the backlighting on or off.
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SoundPro Exercise I – Calibration & Battery Check
 Page 32 – In workbook
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SoundPro Exercise 2: Measurement of Noise Sources
 Pages 33 & 34 – In workbook
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Sound Level Meter Placement Keys
 Location, Location, Location
 Reflection
 Vibration
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60
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Section IV
Noise Dosimeters
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Noise Dosimeter Components
Microphone
Amplifier
Range
Control
Frequency
Filter(s)
C
Fast/Slow
F
S
A
Display
Computer
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Storage
Printer
Calculator
Clock
Meter
Environmental Concerns
 Temperature
 Humidity
 Atmospheric Pressure
 Wind
 Radio Frequency Interference
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 Magnetic Interference
How To Do A Noise Survey
 Check Battery
 Leave It Alone
 Reset Unit
 Work
 Check Set Up
 Check It
 Calibrate Unit
 Observe
 Inform Worker
 Remove Unit
 Unit Placement
 Record or Download Data
 Microphone Placement
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© 2009 3M Company. All Rights Reserved.
Survey Techniques
I.
Individual Full Exposure Assessment
II.
Representative Sampling
III. Task-Based Exposure Assessment Modeling
(T-Beam)
IV. Area Mapping
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© 2009 3M Company. All Rights Reserved.
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© 2009 3M Company. All Rights Reserved.
Survey Methods
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Managing Mobility and Variability
 5 day , 40 hour evaluation
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Infrequent Exposures
 The day OSHA inspects
is reality
 Use informative signs
 Use HPD’s
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Re-monitoring
 Change in process or procedure that affects
inclusion and/or hearing protection
effectiveness
-production rates
-material processed
-production technique
-machine placement
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Survey Pitfalls!!!
 Microphone Placement
 Employee
 Project Assumption
 Threshold Distortion
 Wind
 Battery & Calibration
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What To Record In Addition To Sound Levels
 Dates and Times
 Model and Serial Numbers
 Pre and Post Survey Calibration Levels
 Workplace Descriptions
 Task Descriptions
 Environmental Factors
 Instrument Settings
 Unusual Conditions
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Noise Dosimeters
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NoisePro Dosimeter Key Pad Functions
The RUN/PAUSE button is pressed to Start and
Stop integration and data logging.
The Enter key is used to accept values or actions
in the Setup menu.
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The RUN/PAUSE button is pressed to Start
and Stop integration and data logging.
The ON/OFF ESCAPE key has two functions. It is
used to turn the instrument on and off. If also
serves as an escape key in the instrument setups
Microphone Placement
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Proper Mounting
Typically Belt
Mounted
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Middle of Shoulder
NoisePro: Exercise I - Calibration
 Page 54 in Workbook
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NoisePro: Exercise 2 – Noise Measurement for
OSHA Compliance
 Pages 55 & 56 in Workbook
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© 3M 2013. All Rights Reserved.
Measuring Dose

Using the 5 dB exchange rate (doubling rate), we can conclude the
following:
80
95 dB for
8 hours
equals
200%
dose
100 dB for
8 hours
equals
400%
dose
105 dB for
8 hours
equals
800%
dose
110 dB for
8 hours
equals
1600%
dose
NoisePro: Exercise 3 – Effects of Exchange Rate &
Criterion
 Pages 55 & 56 in Workbook
81
© 3M 2013. All Rights Reserved.
Tim Bailey
3M Detection Solutions
Phone: (800) 245-0779, ext. 152
Fax: (262) 567-4047
[email protected]
Customer Service: Heidi Tunak, ext. 106
Tech Support: Randy Sleggs, ext. 123
Mark Scherer, ext. 158
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What We Measure
Fig. I-13 RMS (Root-Mean-Square)
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Crest Factor
Fig. I-14 Crest Factor - Impulse/Impact Noise
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