Download Industrial Audiology lectures handout

Industrial Lectures
Page 1
Card number_____ 1
card fld "card field id 3"
Ramazzini in 1700, "De
Morbus Artificium Diatriba"
morbus:
"disease"
artificium:
a trade or profession
diatriba:
•a discourse or dispute
•also, a wasting away
"Those hammering copper had their ears so injured by that perpetual
din that workers of this class became hard of hearing and, if they
grow old at this kind of work completely deaf."
-noise exposure results in hearing loss
-damage is a function of exposure level and duration
-correlation with aging
Some terms:
-NIHL: chronic exposure; most exposures are ≤ 100 dBA.
Exposures.
-tinnitus: common symptom associated with NIHL, often a symptom of
temporarily or permanently damaged sensory or neural tissue.
-acoustic trauma: brief duration exposure
-occupational hearing loss: NIHL from employment, "boilermaker's
deafness"
-sociocusis: hearing loss from non-occupational noise exposure
(music, airplanes, subways, firearms, lawnmowers, powertools,
snowmobiles, etc.)
-presbycusis: hearing in the elderly, hearing loss associated with
aging; primary variable confounded with NIHL. The issue of
◊employer culpability
◊combination of factors affecting handicap
-nosoacusis (GR nosos, disease): hearing loss from accident,
trauma, ototoxicity, etc.
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For an introduction to the main components of a hearing
conservation program, click HCPs
card fld "Info…"
Towards the end of the semester, some concepts…
•Be sure you are very familiar with the OSHA regulations for
occupational noise exposure.
◊I will be picky & specific
-go card Regulations
•The story of the Mabaan tribe and presbycusis
-regarding hearing loss: maybe its not growing old per se, but
how we grow old
-go card Mabaan
•Calculating the fence (onset of material impairment) or %HL for
each ear and binaural weighting (5:1)
-go card Fence
•Probability of crossing the fence from exposure to the PEL
-29% without noise exposure ammendment, 5% risk with Jan '81
-go card Risk
•Interaction of pre-existing permanent hearing loss with daily TTS
-more hearing loss, less TTS
-go card TTS
•Cochlear electrophysiology and mechanics
-go card Cochlea
•Major theories regarding mechanism of hearing loss from noise
exposure
-go card Effects
•Dose and TWA calculation
-Done for you by the dosimeter
-go card Dose
•For a pink noise exposure, which formula, HPD attenuation,
paragraph (j), predicts greater HPD attenuation (or estimated Alevel TWA exposure, Est-A)?
◊Est-A = A-weighted TWA - (NRR - 7)
◊Est-A = C-weighted TWA - NRR
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-go card Regulations
•Ambient noise in test suite can affect validity of the baseline
audiogram
-this limits ability of the annual audiogram to detect changes in
threshold produced by noise exposure
-go card Ambient
card fld "HCPs"
•Administration
√Initial
√Ongoing Evaluation & Re-evaluation
•Exposure Measurements
√Initial Survey
√Noise Monitoring
•Noise Controls
√Administrative
√Engineering
•Hearing Protector Devices (HPDs)
•Audiometry
√Baseline
√Annual
•Training & Education
•Medical Evaluation
Card number_____ 2
card fld "Stressor"
•increased noise levels
produce peripheral
vasoconstriction
•resulting in increased
heart action,causing
increased blood pressure
•increased secretion of
corticosteroids (adrenal
steroids, catecholamines)
•fight or flight mechanism
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card fld "Performance"
•vigilance tasks boring, may help
•hinders more complex tasks
card fld "Absenteeism"
•Noisy jobs generally less attractive, more dangerous
Card number_____ 3
card fld "Elasticity"
An elastic deformation: a
deforming force causes a
body to change shape. When
the deforming force is
removed, body returns to
original size.
•eg, a spring moving a
distance when a mass is
suspended from it
•stiffness: the ratio of the applied force to the displacement
•compliance: the inverse of stiffness
card fld "Pascal"
Blaise Pascal (1623-1662)
French philospher and mathematician. Invented an adding machine,
developed modern theory of probability, worked in field of
hydrodynamics.
•Physical unit, Pascal
•Programming language
card fld "Ambient"
Ambient denotes "resting" or "initial" conditions, i.e., of the
atmosphere which (usually) serves as the propagating medium…
•The molecules of the atmosphere are uniformly distributed.
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•Each molecule (particle) is connected to its neighbor. If one
particle is disturbed, its neighbor is disturbed, as if they were
connected by springs (i.e., elastic elements).
Statistics about the atmosphere
•The ambient density (ro) is…
1.21 kg/m^3
0.00121 gm/cm^3
•The ambient pressure is…
1 atmosphere (atm)
101,300 N/m^2
1,013,000 dyne/cm^2
14.7 psi
760 mm of Hg
almost 30 inches of Hg
•1 N/m^2 is 1 Pascal (Pa)
•A Pascal is a relatively large unit. The softest sound we can
hear is about 2*10^-5 Pa (0.00002 Pa), so units expressed in
millionths of a Pascal are common (µPa)
2*10^-5 Pa = 20 µPa
•Sound waves propagate as tiny fluctuations above and below
atmospheric pressure
•For example, the typical rms** pressure in average conversational
level speech is about 0.036 Pa.
ACL = 101,300 Pa ± 0.036 Pa
**more about rms later
•Fluctuations in atmospheric density (r) create fluctuations in
pressure
Pressure = r * c^2
•Fluctuations in atmospheric pressure (p) create fluctuations in
sound intensity
Intensity = p^2 / (ro* c)
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card fld "Power"
Sound Power
•Power has the units of "Watts."
is being used, or consumed.
Power is the rate at which energy
•1 Watt = 1 joule/s
Sound Intensity
•Intensity is measured in Watts/m^2. Intensity is the "rate at
which energy is being radiated over a given surface area."
Intensity = Power / m^2
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Card number_____ 5
card fld "Speed"
The tine of the tuning fork
moves to the right:
•compressing the atmosphere
(increasing density &
pressure)
pressure = r * c^2
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•when the tine moves to the left it expands or "rarefies" the
atmosphere (decreasing density & pressure)
•each molecule influences its neighbor
•causing the area of compression (or rarefaction) to propagate away
at the speed of sound, c
Speed of sound is influenced only by the physical properties of the
propagating medium (not by the characteristics of the vibrating
body, such as frequency):
•temperature
-increased T increases c
•density
-increased density reduces c
•elasticity
-increased stiffness increases c
•Generally, sound travels faster in solids, slower in liquids,
slowest in gases
-mainly due to differences in stiffness (not density)
•At room temperature the speed of sound is about 344 m/s
Sound waves are longitudinal
•Each particle oscillates back & forth in the same direction that
the wave travels; each particle…
-moves very little
-with a relatively small
mean velocity
Card number_____ 6
card fld "SHM"
Simple harmonic motion…
•Motion with one degree of freedom; repetitive, cyclical motion
Examples…
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•Tine of a tuning fork (produces a pure tone, a tone of a single
frequency)
•A swinging pendulum, a metronome, the pendulum on a cuckoo clock
•A mass on the end of a spring
•Beavis swinging a dead rat on a string about his head
•The diaphragm of a headphone while its delivering a 1000 Hz tone
during a hearing test
•A spinning top, water swirling through a lavatory
•The spinning wheel of a bicycle
•The air inside your mouth while you are whistling
Cycles, phase, period, frequency
•After 1 complete cycle, the vibrations associated with SHM are
repetitive, like going around a circle (0° to 360°)
•Phase describes what part of the cycle the vibrating body is in…
-or where in the cycle it begins, or
-the difference between two bodies vibrating simultaneously
•The duration of one complete cycle is defined as the period (T)
-seconds
-milliseconds (1000ths of a second)
•Frequency (Hz, named after Heinrich Hertz) is defined as the
number of cycles completed in 1.0 second (f)
-Hz (cycles/sec)
-kHz (1000nds of cycles/sec)
Amplitude
•Instantaneous amplitude is the displacement from the position of
rest at any instant in time.
•Peak amplitude (Ap) is the absolute value of the maximum deviation
from the position of rest (to either the right or left, + or -).
•Peak-to-peak amplitude (Ap-p) is the absolute value of the
deviation between the maximum excursions (right to left, or + to ).
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Card number_____ 7
card fld "Concepts"
Harmonic Motion Stack
•Illustrates SHM via a
simple spring-mass system (a
mass oscillating on the end
of a spring)
•Shows the linear projection
of the SHM into a sine wave
•Shows the analogy between
projected SHM and circular motion — projected uniform circular
motion
•Describes why the waveform is called a sine wave — the anatomy of
a triangle is defined.
Oscilloscope Stack
•This stack allows us to synthesize pure tones by defining the
frequency, amplitude and phase.
•We can define complex tones (i.e., sounds that have more than one
frequency)
•Illustrates how complex tones are built from simple tones by
addition
•Tones of the same frequency can be added, but phase is important
-A 180° phase difference ("out of phase") causes cancellation.
-A 0° phase difference ("in phase") causes reinforcement.
•Periodicity, the repetitiveness of complex, periodic waves is
illustrated.
•Defines period and wavelength relative to the waveform
•Describes the mathematical relationships between period,
frequency, wavelength, and speed of sound
•Defines peak amplitude (Ap), peak-to-peak amplitude (Ap-p),
instantaneous amplitude (ai), and the rms amplitude (Arms)
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•Defines the relationship between Ap and Arms.
And…
When complex sounds are composed of frequencies that bear simple
numerical relationships to one another, the result is aesthetically
pleasing. Nice visual and auditory patterns result, as in Leonardo
da Vinci's ideas of beauty in symmetry.
card fld "Ordinate"
The ordinate of the graph can represent…
•The instantaneous displacement of the vibrating body (relative to
"0," its position of rest)
•The corresponding changes in density, pressure, or intensity
occurring in the propagating medium
•A measured analog of these changes, like voltage on an
oscilloscope)
The abscissa of the graph, for example, when displaying density…
•Can represent time. Changes in density occurring at a point in
the atmosphere as a function of time (as the wave moves through).
•Can represent distance. Strike the tuning fork, allow a few
cycles to propagate, "freeze" time. Changes in density in the
atmosphere can be plotted as a function of distance from the sound
source.
Card number_____ 8
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Card number_____ 10
card fld "Info…"
•A 10 volt peak sine wave delivered to a resistor, causes the
resistor to generate heat (i.e., energy).
•The same amount of heat would be generated by delivering a 7.07
volt dc signal to the same resistor.
•The rms value measures the amount of energy contained within the
signal.
Card number_____ 11
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Card number_____ 12
card fld "Decibel"
The decibel scale
•Decibels are
"dimensionless" units. In
the process of calculating
dB, the units cancel. So
always specify the type of
dB, i.e., dB SPL, dB IL, dB
HL, etc.
•All decibel scales have a
reference. The reference defines what 0 dB is. The reference for
the hearing level scale (dB HL) is the average sound pressure
needed to reach threshold for normal hearing people. This pressure
varies with frequency.
•The reference for the SPL scale is…
CGS
MKS
0.0002 dyne/cm^2
2*10^-4 dyne/cm^2
0.00002 Pa
2*10^-5 Pa
20 µPa
Note: These are the same pressures, just expressed in different
units
•The reference for the dB IL scale is…
MKS
10^-12 Watt/m^2
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•A sound with a pressure of 20 µPa has an intensity of 10^-12
Watt/m^2. This means that the dB SPL for a sound will always equal
its dB IL.
Procedures for calculating decibels
Sound pressure
1. Identify the sound pressure that you wish to convert to a sound
pressure level.
2. Divide the pressure by the reference to obtain a ratio.
the reference that has the same units.
3. Take the logarithm of the ratio.
to get the dB SPL.
Choose
Multiply the logarithm by 20
Intensity
1. Identify the intensity that you wish to convert to an intensity
level.
2. Divide the intensity by the reference (10^-12 Watt/m^2) to
obtain a ratio.
3. Take the logarithm of the ratio.
to get the dB IL.
Multiply the logarithm by 10
Constant Proportions
•Every time the pressure increases 10 times, the SPL increases by
20 dB.
•Every time the sound pressure doubles, the SPL increases by 6 dB.
•Every time the intensity increases 10 times, the IL increases by
10 dB.
•Every time the intensity doubles, the IL increases by 3 dB.
•Every time the sound pressure doubles, the intensity increases 4
times. The SPL increases by 6 dB, and the IL increases by 6 dB.
Finding dB differences
•You can find the dB difference between any two values, provided
they have the same units.
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•Example: What is the dB difference between a pure tone that has
an Ap = 7 Volts, and one that has an Ap = 3.2 Volts?
dB = 20*log( 7/3.2) = 6.8 dB
Should I multiply by 10 or 20?
•For pressure, force, voltage multiply the ratio by 20.
•For intensity, power, energy multiply the ratio by 10.
Card number_____ 13
Card number_____ 14
card fld "card field id 1"
0 Softest audible sound
10 Normal Breathing
20 Rustling leaves
30 Very soft whisper
40 Quiet residential
community
50 Department store
60 Average speaking voice
(65 dB)
70 Inside moving car
80 Loud music from radio
90 City traffic
100 Subway train
110 Loud thunder
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120
130
140
180
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Amplified rock band
Machine gun fire (close range)
Jet engine at takeoff
Space rocket at blastoff
Card number_____ 15
card fld "Spectrum"
The sound spectrum
•The sound spectrum is…
-a description of which
frequencies are contained
within a sound, and the dB
level of each frequency
-a plot of amplitude as a
function of frequency
(amplitude spectrum), phase is usually ignored
•Given the waveform (a plot of amplitude as a function of time)…
-the spectrum can be calculated using a mathematical procedure
developed by Fourier
-Fourier analysis, the FFT
-the FFT converts the waveform into an amplitude spectrum
-the inverse FFT converts the amplitude spectrum into the
waveform
•Spectrum analyzer: a device which determines and displays the
spectrum of a sound
Line spectrum
•Complex periodic sounds are composed of discrete frequencies,
their amplitudes can conveniently be graphed as lines
Continuous spectrum
•Complex aperiodic sounds are continuous in the frequency domain,
they are graphed as a continuous spectrum
Sonogram
•The sonogram is useful for displaying sounds whose spectra change
with time, such as speech
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•The sonogram displays…
-frequency along the ordinate
-time along the abscissa
-amplitude by the darkness (more intense) or lightness (less
intense) of the display
Card number_____ 16
Card number_____ 17
Card number_____ 18
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Card number_____ 19
card fld "Continuous"
Noise… complex & aperiodic
classified as continuous or
impulse
Continuous
•steady state
•fluctuating
•intermittant
Impulse
•type A
-Pmax (peak pressure) usually large
-Tr relatively short
-rapidly expanding gases
•type B (impact)
-Pmax lower
-Tr longer
-often contain more energy than type A
-collision of two masses
card fld "Noise"
•Noise results from a vibrating body undergoing random motion.
•The waveform is not repetitive; it is aperiodic.
are present so noise is "complex and aperiodic."
Many frequencies
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•Completely random motion results in all frequencies being present
at the same level (there are statistical fluctuations).
-This is broad band noise,
-white noise (by analogy with visible light),
-Gaussian noise (the normal curve),
-Thermal noise (from amplifying the random voltage fluctuations
in a resistor)
•Transient (temporally brief) sounds have a spectrum that is white.
-clicks
Card number_____ 20
Card number_____ 21
Card number_____ 22
Industrial Lectures
Card number_____ 23
card fld "The Point"
When you are in an
environment that contains
multiple sound sources, the
overall SPL is determined
primarily by the single
source with the highest SPL.
If you want to reduce the
employee's exposure,
identify the highest level
source and eliminate it.
Card number_____ 24
Card number_____ 25
card fld "card field id 1"
Page 19
Industrial Lectures
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A method for finding the total SPL resulting from the combination
of two sources (A and B)
1.
Identify a frequency from source A, display its waveform
2.
Find the same frequency from source B
3. Add the two sine waves, taking into account amplitude and phase
differences. Call the result p1 (p1 is the rms value of the pure
tone that is the sum of the two waves).
4.
pn
Repeat #1 thru #3 for all frequencies.
The result is p1 thru
5. Find the total sound pressure by summing p1 thru pn.
pTotal.
6.
Call it
Find the dB SPL associated with pTotal.
An alternative method
1.
Find the intensity Ia associated with source A.
2.
Find the intensity Ib associated with source B.
3.
Find Itotal = Ia + Ib
4.
Find the dB IL associated with Itotal
Note: This method is much simpler. It simulates the process of
combining all frequencies of complex sources. The procedure
assumes:
•There are many frequencies present
•The average phase relationship is 90°
The End
Card number_____ 26
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Card number_____ 27
card fld "Dosimeters"
Dosimeters… a lot like sound
level meters
•personal, wearable device
•continuously samples the
worker's environment
(microphone on shoulder)
•very useful when
employee's exposure is
-fluctuating, or
intermittant
-contains impulse noise
•often has the capability to save samples
-gives a time related profile (histogram) of worker's exposure
-to identify "problem times" in the workday
-accessible via personal computer
•integrates dBA or dBC levels according to a formula
•computes dose (and TWA), Leq
•this information used in hearing conservation program
Dosimeter 1
Dosimeter 2
Dosimeter 3
card fld "Ballistic"
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•The fast and slow settings provide a more "sluggish" response to
time varying sound, so the eye can follow the variations.
•The fast setting has a time constant of 1/8 sec; the slow setting
has a time constant of 1 sec.
•For a rapid increase in dB level, the meter needle will reach
63%** of its steady state value in one time constant. The OSHA
standard specifies dBA levels with a slow response.
•Some SLMs have an impulse setting (rise time of 35 msec, decay
time of 1.5 sec). This does not give the true peak SPL.
___________________________________
**The increase in amplitude (y) varies with time (t) according to:
y = Yo*(1 - exp(-k*t))
where Yo is the steady state value, k is a constant, and k*t is the
"time constant." For y/Yo = .63, k*t = 1. This is,
coincidentally, the same formula for describing how TTS approaches
ATS.
Card number_____ 28
card fld "card field id 1"
Frequency
50
63
80
100
125
160
200
A-Weight
-30
-26
-22
-19
-16
-13
-11
C-Weight
-1
-1
-1
0
0
0
0
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250
315
400
500
630
800
1000
1250
1600
2000
2500
3150
4000
5000
6300
8000
10000
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-9
-7
-5
-3
-2
-1
0
1
1
1
1
1
1
1
0
-1
-2
0
0
0
0
0
0
0
0
0
0
0
0
-1
-1
-2
-3
-4
Card number_____ 29
card fld "Filters"
•The shape of the filter is
given by its frequency
response. Individual
frequencies, all at the same
level, are input to the
filter. The output for each
frequency is measured. The
difference (dBout minus
dBin) is plotted as a
function of frequency.
•The corner frequencies are defined as the "half-power" points, the
output is 3 dB less than the input.
f1 (or fl): low frequency cut-off
f2 (or fh): high frequency cut-off
fo (or fc): center frequency
•The bandwidth (BW) is f2 - f1.
2.
For an octave-band filter, f2/f1 =
•The filter does not change the output frequency from what it was
at the input or add additional frequencies.
•The filter only changes the level (dB) of the frequency.
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•The filter doesn't care what the absolute input level is or the
absolute output level. It only controls the difference between the
two.
•Multiple frequencies at the input respond the same as if each were
input individually.
•A filter shapes the spectrum. If white noise was the input to the
filter, the spectrum of the noise at the output of the filter would
equal the frequency response of the filter.
•By doing an octave-band analysis, you get an idea of where in the
spectrum energy predominates. This could help with choosing
engineering controls.
Card number_____ 30
card fld "Bandwidth"
Octave-band filters…
•The bandwidth of each
filter doubles as the center
frequency of the filter
doubles
Consider the following
experiment where white noise
is being measured. The
octave-band filter set of a
SLM is set to 250 Hz. The octave band SPL is measured at 94 dB.
•At a
◊at
◊at
◊at
center frequency of 500 Hz, the octave band SPL is 97 dB
1000 Hz, 100 dB SPL
2000 Hz, 103 dB SPL
4000 Hz, 106 dB SPL
•What is the overall level of the noise?
level?
What is the A-weighted
•What would have been the result of this experiment if pink noise
had been used?
Card number_____ 31
Industrial Lectures
Card number_____ 32
Card number_____ 33
card fld "Phon"
Psychoacoustics
•The study of our internal
representation of external
stimuli
•Don't ask a guy who has
been operating a jack hammer
for 15 years — without HPDs
— if he's exposed to loud
noise.
Loudness (phons & sones)
Phon scale
Page 25
Industrial Lectures
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•Loudness level in phons (Lp) used for making relative loudness
judgements
√Compare loudness of a car horn to the loudness of a 1000 Hz
tone, say 82 phon
√Compare loudness of a door bell to the loudness of a 1000 Hz
tone, say 63 phon
√Compare loudness of a door bell to the loudness of a car horn
(19 phon difference)
•reference: A 1000 Hz tone at 40 dB SPL has a loudness level of 40
phons
-a 57 dB SPL 1000 Hz tone = 57 phons
-a 80 dB SPL 1000 Hz tone = 80 phons
•Equal loudness contours (related to weighting networks on SLM)
-The 80 phon contour, for example, shows all combinations of
frequency/SPL judged to be equally loud
-Loudness contours are like isobar maps used in meteorology, or
elevation contours around mountains
-The A-weight is a (inverse) 40 phon contour, the B-weight is a
(inverse) 70 phon contour, the C-weight is a (inverse) 100 phon
contour — approximately.
-The C-weight is intended to provide a flat response from 25 to
8000 Hz
•The 0 phon contour is usually described as the threshold
sensitivity curve, assuming 0 dB SPL is threshold at 1000 Hz — but
it isn't.
•The 4.2 phon contour is approximately the threshold senstivity
curve (binaural) in the sound field (MAF). The equivalent contour
under headphone is the MAP curve. The MAP curve defines normal
hearing and is used to calibrate audiometers.
•One goal of a successful hearing aid fitting is to restore normal
loudness perception for as large a frequency range as possible.
card fld "Sone"
Sones
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•The sone scale is used for making absolute loudness judgements
•The reference is… a 1000 Hz tone, 40 dB SL re: threshold for a
normal hearing person has a loudness of 1 sone
-SL is sensation level (the number of dB above threshold)
•How does loudness change with SPL?
-For every 10 dB increase in SPL the loudness doubles
(approximately)
___________________________________
Loudness phons
Loudness in sones
Lp
Ls
___________________________________
20
0.25
30
0.5
40
1
50
2
60
4
70
8
80
16
90
32
100
64
Ls = 2^((Lp - 40)/10)
•This is useful for performing a listening check of the calibration
of an audiometer
•Also notice how rapidly loudness is changing between 80 and 100 dB
SPL (PEL = 90 dBA, AL = 85 dBA)
Recruitment
•Recruitment is usually described as an abnormal rate of loudness
growth that is associated with cochlear pathology (i.e., damage to
the hair cells)
•For example, compare the results for a normal hearing person, a 40
dB HL conductive hearing loss, and a 40 dB HL cochlear hearing
loss. Each person judges the tone to be equally loud
Normal
80 dB HL
Conductive 120 dB HL
Cochlear
80 dB HL
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•Ears with recruitment don't hear soft sounds very well, but hear
more intense sounds normally
-This makes it difficult to fit hearing aids. Amplification that
makes the soft sounds audible makes the more intense sounds too
loud.
Card number_____ 34
card fld "Pitch"
Pitch: the psychoacoustic
analog of frequency
•Pitch can be measured in
units called "mels"
•1000 mels is defined as the
pitch associated with a 1000
Hz, 40 phon tone
-a 2000 mel tone would be
judged as being twice as high in pitch as the reference tone
•Below
pitch,
-100
-500
1000 Hz there is a linear relationship between frequency and
i.e.
Hz ≈ 100 mels
Hz ≈ 500 mels
•Above 1000 Hz, the relationship is not linear
-to increase the pitch of a 1000 Hz tone by a factor of 3 (3000
mels), the frequency must be increased to 9000 Hz)
Card number_____ 35
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Card number_____ 36
card fld "card field id 1"
Most Industrial noise
exposures are:
•red to pink to white, or
"light blue"
•riveting, chipping,
planing, saws, steam or air
hiss, grinders, welders,
lathes, etc.
So why is hearing loss
usually localized to the octave band surrounding 4000 Hz?
•For pure tone exposures, most of the hearing loss occurs about
1/2-octave above the stimulus frequency
•Results are similar for complex stimuli, except there are more
frequencies
•The resonant characteristics of the external ear are primarily
responsible for the 4 kHz notch
Noise Control Techniques
General principle: Energy flows most efficiently from one medium to
another when the impedances of the two media are equal. So, reduce
the efficiency of energy flow by making impedances unequal.
√Source Control
√Path Abatement
√Receiver Abatement
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Typical source control procedures:
•maintenance
•substitution of quieter machines/processes
•check noise level specifications for new equipment
•modify equipment
•reducing vibration via damping material
•decoupling vibrating equipment from surrounding structures
•reducing fluid (or gas) flow noise (i.e., mufflers, reduce
velocity)
Path Abatement Procedures:
•Sound absorbing material
•Enclosures for equipment
◊reduced access to controls
◊generates heat
•Segregate noisy operations from quiet
•Barriers
◊reflections can increase other worker's exposures
Receiver Abatement techniques:
•HPDs (muffs, plugs, semi-aural)
•Personal enclosures
•Control rooms
Card number_____ 37
card fld "Info…"
Valsalva (Italian anatomist,
1666-1723) credited with
dividing ear into 3 major
divisions:
•Outer (external): pinna &
canal
•Middle: eardrum, ossicles,
middle ear spaces,
Eustachian tube, middle ear
muscles
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•Inner ear: cochlea, vestibule, and semicircular canals
Some points:
•Outer ear/middle ear are the conductive portion of the system
√funnels acoustic energy to drum
√transduces acoustic energy to mechanical
•Cochlear portion is the sensory system
√Four rows of ≈3500 sensory cells (hair cells) each, over a
distance of 35 mm
√motion detectors, changing mechanical energy to electrical
energy
√an ADC
•Vestibular system monitors linear and angular accelerations of the
head
√automatically controls eye movements, vestibulo-ocular reflex
(VOR)
√maintains posture (orientation relative to the gravitational
field, while stationary or moving)
√intense low frequency noise may produce vertigo
Card number_____ 38
card fld "Info…"
External Ear
•Protective function
√S-shaped curve keeps
objects from directly
hitting drum
•External ear resonance
√3.2 cm tube closed at one
end
√maximum of 17 dB at 2700
Hz
√results in the 4 kHz notch (1/2 octave above 2700 Hz)
•Cerumen
√produced by apocrine and sebaceous glands located in
cartilaginous portion of canal
√dark and bitter tasting?
√moistens and lubricates canal tissue
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√probably has no insect repellent properties
√normally externalized by TMJ movements, growth pattern of
epidermis
√motion of the condyle of the mandibule increases size of the
anterior canal at the first bend, causes plugs to extrude
•Otitis externa
√accumulation of cerumen aggravated by HPDs (plugs defeat normal
removal mechanism), increases moisture in canal
√increased moisture, higher pH associated with fungal, bacterial
infections
√dirt, chemicals, etc. from hand while inserting can contribute
to HPDs as a source of external otitis
√surprisingly, external otitis and cerumenosis do not seem to be
a major problem with industrial workers
√earplugs seem to help with cerumen management
Card number_____ 39
Card number_____ 40
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Card number_____ 41
card fld "Protocols"
Audiometric Test
Protocols
•Ascending procedure
(Hughson-Westlake)
+ the level is decreased
by 10 dB
- the level is increased
by 5 dB
•Descending procedure
+ the level is decreased by 5 dB
- the level is increased by 10 dB
•Combined procedure alternate between ascending/descending
Threshold is defined as lowest level where tone is detected 50% of
the time, on at least three presentations.
card fld "Procedures"
Audiometric Test Procedures
•History
AMA criteria for medical referral…
◊visible congenital, traumatic deformity
◊history active drainage (90 days)
◊sudden, rapidly progressive loss (90 days)
◊acute/chronic dizziness
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◊unilateral loss of sudden, recent onset (90 days)
◊ABG ≥ 15 dB @ 500, 1000, 2000 Hz
◊significant cerumen accumulation, foreign body
◊pain or discomfort
•Otoscopic exam
◊collapsed canal
◊cerumenosis, foreign body
◊perforation
◊inflammation, anything abnormal
•Patient instructions (before putting headphones on)
◊tell them what they will hear (tone)
◊emphasize that tones will be soft, they must listen carefully
◊they should guess if necessary
◊indicate how they should respond (press button, raise hand, or
finger, anything unambiguous)
•Headphone placement
◊remove eyeglasses, ear rings if large
◊red on RE, blue on LE (during testing, stop to check, you will
eventually make an error)
◊allign cone of loudspeaker with canal
◊put cords in back of patient
•Patient placement
◊at right angles so you can see them, they cannot see you
◊do not allow them to watch you, people can pick up subtle cues
•Select an ear to test
◊test better ear, or
◊test RE (for consistency)
◊test all frequencies for ear before moving on to next ear
•Select a frequency to test
◊begin at 1000 Hz
◊then 2000, 3000, 4000, 6000, 500 Hz
◊order of frequencies tested will not affect validity of
threshold, but consistency will avoid errors
•Present tone
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◊first tone should be clearly audible
◊40 dB HL, or higher (60, 80 dB) if no response
◊this presentation defines what you meant by "tone" in your
instructions
◊their response validates that they understand instructions
•Choose a protocol (Hughson-Westlake)
◊see "Protocols" button
◊particular protocol does not affect validity of threshold, but
consistency will avoid errors
•Duration of tone
◊present tone for 1 second (0.5 to 1.5 sec is OK)
◊longer presentations will create more false positives (believing
a random response was really heard)
•Response characteristics
◊note response latency, this varies with patient, but is usually
less than 1 second
◊latency increases slightly as you get nearer to threshold, but
◊do NOT accept a response longer than the normal latency
•Stupid tendencies we all have
◊when close to threshold, you present the tone longer, and push
the button harder (to squeeze out a few extra dB?)
◊when close to threshold, you wait too long for a response,
thereby increasing false positive responses
•Faking a hearing loss (pseudohypacusis)
Malingerers…
◊usually have something to gain (money, or attention)
◊often feign a unilateral hearing loss
◊often give a flat audiogram configuration
◊may respond inconsistently over a wide range of presentation
levels
◊may respond to conversation better (or worse) than their
"audiogram" indicates
◊may make an exaggerated show of effort at listening
◊you can often "smell them a mile away"
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•Inconsistent responses
◊abnormal behavior can be related to drugs, alcohol, etc.
◊FM modulation of tone, or presenting 3 beeps (tell the patient
to respond when you hear 3) can be useful when tinnitus interferes
with audibility of tone
----The End---card fld "Audiometers"
Microprocessor-Based Audiometers
•Utilize software that simulates the decision making a human would
go through when using the Hughson-Westlake protocol.
•Sometimes the software gives up with inconsistent responses, and
you must intervene manually. The audiometers have a manual mode.
•You must carefully monitor the equipment and patient to make sure
the results are valid. Sometimes the software can be fooled.
•Most audiometers interface with a PC (via the RS232 serial port)
for maintaining an audiometric database, facilitating
recordkeeping.
Automatic (Self-Recording) Audiometers
•Automatic audiometers sometimes called "Békésy audiometers," after
the first one developed.
•Automatic audiometers have a servo-mechanism that automatically
controls the dB HL of the tone…
◊When the patient response button is pressed, the signal
decreases in level. When the button is released, the tone
increases in level.
◊The patient is instructed to "press the button when you hear,
release when you don't."
◊A pen records the level changes on an audiogram form.
Disadvantages of Automatic Audiometers
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•They cost as much as 4 times what a manual audiometer will cost,
and there are more parts to go wrong. Microprocessor audiometers
seem to be replacing automatic audiometers.
•It is easier to malinger with an automatic audiometer. In one
study of a plant with poor worker morale, Gosztonyi et al. (1971)
found that whereas all office worker audiograms were judged valid,
only 27% of the shop employees were judged valid.
◊Company performed self-recorded audiograms vs. audiologist
performed manual ranged from -18 dB to 53 dB.
◊Manual and self-recorded audiograms performed by the audiologist
differed by only 10 dB.
•Automatic has difficulties with older employees, those with
physical limitations, limited education, language barriers, those
lacking attention or motivation (drugs & alcohol).
•The idea that "it takes care of itself,"
◊people with little training perform the test
◊noise levels are not monitored
◊patient motivation is not monitored
◊quality of the audiogram is not monitored, amplitude of tracings
Advantages of Self Recording
•Speed, you can test up to 4 employees at one time (maybe more),
but
◊Manual is quicker for testing one employee
•It is easier on the tester, less fatigue at end of day.
less likely to take shortcuts.
Examiner
•Applied properly, a valid audiogram can be obtained either
manually, or automatically.
Card number_____ 42
card fld "About Patient…"
Patient History
•21 yr old male
•Handgun
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•Head injury 2x, MVA, coma
Card number_____ 43
card fld "About Patient…"
Audiogram of Ruben Gonzales,
a virtuoso violinist who has
played with the Chicago
Symphony Orchestra
•He has played for 30-35
years, 60+ hours per week
with a powerful Bergonzi
which previously was owned
by Itzaac Pearlman
•The 8 hour Leq = 105 dBA
•From Killion, "The parvum bonum, plus melius fallacy in earplug
selection."
-ER-15 flat attenuation, musician's earplug
Card number_____ 44
Card number_____ 45
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Card number_____ 46
Card number_____ 47
card fld "Info…"
•The middle ear serves as an impedance matching device
•The stapedius muscle offers limited protection from noise exposure
•Otitis media is a common cause of middle ear pathology
•Otosclerosis is a common cause of conductive hearing loss in early
to middle adult life
•Conductive hearing loss serves roughly the same function as a HPD
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Card number_____ 48
card fld "Info…"
Cochlear electrophysiology &
mechanics (in brief)
•The stria vascularis
generates a +80 mV potential
in scala media.
◊This is the cochlear
energy source or "battery."
•Scala media contains
endolymph, a fluid rich in
potassium ion, K+.
•Motion of the stapes footplate delivers energy to the fluid of the
inner ear. This initiates a traveling wave which propagates from
the basal end of the organ of Corti towards the apical end.
◊See the traveling wave movie.
•The wave crests after traveling a certain distance. Higher
frequencies crest sooner (toward the base); lower frequencies
travel further and crest more toward the apex. Each frequency "has
its place" along the organ of Corti.
◊The central auditory nervous system "knows" which frequencies
are present in the stimulus by the place being "touched" — much
like our body's surface area is mapped onto the somatosensory
cortex.
•As the wave moves down the organ of Corti, a shearing force is
created between the tectorial membrane and the reticular lamina.
The shear is maximum at the crest and causes bending of the cilia
of the outer and inner hair cells (OHCs and IHCs).
•Bending the OHC cilia causes K+ to flow into the interior of the
cell, depolarizing the cell, causing a length change (shortening)
of the OHC. This effectively amplifies the sound, generates
additional shearing force, causing increased bending of the IHC
cilia.
◊Typical industrial noise exposures damage the OHCs and their
stereocilia, causing less stimulation of the IHCs (i.e., bending of
their cilia).
◊The mechanism of the damage is related to "mechanical stress"
and/or "metabolic exhaustion."
◊Completely eliminating the OHC amplifier results in a 40 - 50 dB
HL hearing loss.
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•Bending IHC cilia causes K+ current to flow into the hair cell,
releasing the neurotransmitter (glutamate) onto the dendrites of
the neurons of the auditory nerve. Depolarization of the neurons
sends afferent information to the central auditory nervous system.
Card number_____ 49
Card number_____ 50
Card number_____ 51
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Card number_____ 52
Card number_____ 53
card fld "card field id 1"
The Effects of Noise on
Cochlear Physiology
Metabolic Exhaustion: damage
to hair cells & nerve
endings
•Inability to convert
nutrients to energy to match
biologic demands
•Vasoconstriction of
strial capillaries
•Accumulation of waste products
Mechanical stress: damage to hair cells (outer to inner)
•Loss of ciliary stiffness
•Fusion of cilia
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•Cilia dissolving into cuticular plate, occasional formation of a
giant cilium
•Microfractures in cuticular plate allowing entrance of endolymph
into fluid bathing hair cells
•Swelling of hair cell
•Extrusion of cytoplasm, destruction of hair cell
•Hair cell missing, phalangeal scar
•At high levels, rips & tears in organ of Corti, entire organ
missing for large distances
Card number_____ 54
Card number_____ 55
card fld "card field id 1"
Hearing
and Hearing Loss
The ear is composed of three
systems:
•outer or external ear
•middle ear
•inner ear
-contains hair cells
which act as biologic
transducers, converting mechanical to electrical energy: damaged
from noise exposure
NIHL is temporary and permanent
•TTS: recovers in about 14 hours
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•ATS: reached within about 6-8 hours, or sooner
•PTS (NIPTS)
-ATS approximates future PTS (5 to 10 years)
NIHL is a sensorineural hearing loss; "nerve damge"
•SN hearing loss is (with some execptions) not reversible
•contrary to conductive lesions, it cannot be helped medically, or
surgically
-rehabilitation is the main option
-the hearing aid
•hearing aids offer much benefit, but there are limitations…
•they do not simulate normal hearing in the same way that
eyeglasses simulate normal vision
•SN hearing loss is not just an attenuation, but a distortion
•speech is audible, but loses clarity
•hearing aids amplify speech, but also (unwanted) noise
Estimating magnitude of damaging effect caused by noise
•impairment…change in structure or function
•handicap…disadvantage imposed by impairment on activities of
everyday living
•disability…loss in earning power
The 25 dB HL fence…onset of material impairment
•.5, 1, 2 KHz: AAOO, 5:1 weight for binaural
-created for medico-legal purposes (compensation)
–never intended for preventative purposes
•.5, 1, 2, 3 KHz: AAO, 5:1 weight for binaural
•1, 2, 3 KHz: NIOSH fence adopted by OSHA
Effects of NIHL on speech perception
•there is a difference between hearing and understanding speech
•vowel sounds… lower frequencies
•consonant sounds… higher frequencies
•NIHL, by removing higher frequencies, reduces intelligibility of
speech, not its audibility
Other effects of hearing loss
•depression, isolation, suspicion, withdrawal from social contacts
•feelings of inadequacy, insecurity from constant misunderstanding
Areas often mentioned
•self
•family
•social
•vocational
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Ramsdell's psychological levels of hearing
•symbolic… speech communication
•warning… sounds signaling danger
•primitive… fundamental attachment to real world
Presbycusis… major variable confounded with noise exposure
•hearing loss is a function of age
•there is a gender effect, race effect
•There are different types: strial, sensory, central
•factors other than pure physiological aging may be confounded with
presbycusis
Exposure and Hearing Loss
•Hearing loss builds rapidly and is almost complete within the
first 10 years (5 years, actually)
-protect people early
•Hearing loss is a positively accelerated function of exposure
level
-increasing exposure by 5 dB (95 to 100 dBA) can produce 20 dB
extra hearing loss
Who is exposed, and at what levels?
•over a third of the workers receive significant exposures (doses
exceeding .5)
•most people have exposures ≤ 100 dBA
•Are HPDs capabable of providing protection?
-yes and no, depending upon how they are used
Card number_____ 56
card fld "The model"
About the model…
The buildup and decay of
TTS at each frequency is
calculated according to a
combination (that I have
made) of the mathematical
models described by John
Mills (The Effects of Noise
on Hearing) and John Macrae
(JSHR 34, 661-670, 1991).
There is also an ISO standard 1999 which deals with this issue.
Industrial Lectures
Terms:
L:
Page 46
a frequency dependent level (dB SPL) that needs to be
exceeded before TTS will occur:
L=
500 Hz
93 dB
1000 Hz
2000 Hz
4000 Hz
89 dB
80 dB
75 dB
(see note at end)
SPL:
ATS:
the octave-band SPL for each frequency
asymptotic threshold shift (dB)
ATS = 1.7 * (SPL - L)
T:
TTS:
the duration of the exposure (or post exposure) in hours
temporary threshold shift (dB) at a frequency. The ear
begins with normal hearing (0 dB HL)
a constant used for calculating buildup of TTS= 0.476
where T is duration of exposure in hours:
TTS = ATS * (1 - exp(-k1 * T)
a constant used for calculating recovery of TTS= 0.141
where T is duration following exposure in hours:
TTS = ATS * exp(-k2 * T)
k1:
k2:
HTL:
the threshold for an ear with pre-existing hearing loss,
and also exposure to noise (dB HL). HTL, as calculated,
represents the hearing loss that occurs from a
combination of noise exposure and pre-existing hearing
loss
NIPTS: the noise induced permanent threshold shift (estimated
by using calculated TTS)
SNHL: pre-existing sensorineural hearing loss (dB HL)
P:
a power used in calculating HTL= 0.15
HTL = 10*LOG( ( (10^(NIPTS/10))^P + (10^(SNHL/10))^P - 1)^1/P)
Note…
•The model predicting TTS is essentially the one developed by
Mills. I have substituted Mills values for L with those given by
Macrae.
•The method for calculating HTL is from Macrae. I use TTS in place
of NIPTS when calculating HTL.
•With regard to the relationship between TTS and NIPTS. I assume
that, very nearly, one can substitute "years of exposure" for
"hours of exposure" and use TTS to predict NIPTS. The ATS is
essentially NIPTS after 10 years of exposure.
------The End------
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Card number_____ 57
Card number_____ 58
card fld "Info…"
To compute binaural hearing
loss…
Let
BE = %HL for better ear
PE = %HL for poorer ear
BHL= binaural hearing loss
BHL = (BE*5 + PE)/6
If BE is 50% and PE is 100%
then
BHL = (50*5 + 100)/6 = 58.33%
Card number_____ 59
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Card number_____ 72
card fld "1910.95"
1910.95 - Occupational noise
exposure.
* Standard Number:
1910.95
* Standard Title:
Occupational noise exposure.
* SubPart Number:
G
* SubPart Title:
Occupational Health and
Environmental Control
Produced by USDOL OSHA - Directorate of Safety Standards &
Directorate of Health Standards
Maintained by USDOL OSHA - OCIS
-----------------------------------------------------------------(a) Protection against the effects of noise exposure shall be
provided when the sound levels exceed those shown in Table G-16
when measured on the A scale of a standard sound level meter at
slow response. When noise levels are determined by octave band
analysis, the equivalent A-weighted sound level may be determined
as follows:
FIGURE G-9 - Equivalent A-Weighted Sound Level
(Figure G-9 is not shown, see card
"Weighting Networks")
Equivalent sound level contours. Octave band sound pressure levels
may be converted to the equivalent A-weighted sound level by
plotting them on this graph and noting the A-weighted sound level
corresponding to the point of highest penetration into the sound
level contours. This equivalent A-weighted sound level, which may
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differ from the actual A-weighted sound level of the noise, is used
to determine exposure limits from Table 1.G-16.
..1910.95(b)
(b)(1) When employees are subjected to sound exceeding those listed
in Table G-16, feasible administrative or engineering controls
shall be utilized. If such controls fail to reduce sound levels
within the levels of Table G-16, personal protective equipment
shall be provided and used to reduce sound levels within the levels
of the table.
(2) If the variations in noise level involve maxima at intervals of
1 second or less, it is to be considered continuous.
TABLE G-16 - PERMISSIBLE NOISE EXPOSURES (1)
______________________________________________________________
|
Duration per day, hours
| Sound level dBA slow response
____________________________|_________________________________
|
8...........................|
90
6...........................|
92
4...........................|
95
3...........................|
97
2...........................|
100
1
1/2 ......................|
102
1...........................|
105
1/2 ........................|
110
1/4 or less................|
115
____________________________|________________________________
Footnote(1) When the daily noise exposure is composed of two or
more periods of noise exposure of different levels, their combined
effect should be considered, rather than the individual effect of
each. If the sum of the following fractions: C(1)/T(1) + C(2)/T(2)
C(n)/T(n) exceeds unity, then, the mixed exposure should be
considered to exceed the limit value. Cn indicates the total time
of exposure at a specified noise level, and Tn indicates the total
time of exposure permitted at that level. Exposure to impulsive or
impact noise should not exceed 140 dB peak sound pressure level.
..1910.95(c)
(c) "Hearing conservation program." (1) The employer shall
administer a continuing, effective hearing conservation program, as
described in paragraphs (c) through (o) of this section, whenever
employee noise exposures equal or exceed an 8-hour time-weighted
average sound level (TWA) of 85 decibels measured on the A scale
(slow response) or, equivalently, a dose of fifty percent. For
purposes of the hearing conservation program, employee noise
exposures shall be computed in accordance with appendix A and Table
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G-16a, and without regard to any attenuation provided by the use of
personal protective equipment.
(2) For purposes of paragraphs (c) through (n) of this section, an
8-hour time-weighted average of 85 decibels or a dose of fifty
percent shall also be referred to as the action level.
(d) "Monitoring." (1) When information indicates that any
employee's exposure may equal or exceed an 8-hour time-weighted
average of 85 decibels, the employer shall develop and implement a
monitoring program.
(i) The sampling strategy shall be designed to identify employees
for inclusion in the hearing conservation program and to enable the
proper selection of hearing protectors.
..1910.95(d)(1)(ii)
(ii) Where circumstances such as high worker mobility, significant
variations in sound level, or a significant component of impulse
noise make area monitoring generally inappropriate, the employer
shall use representative personal sampling to comply with the
monitoring requirements of this paragraph unless the employer can
show that area sampling produces equivalent results.
(2)(i) All continuous, intermittent and impulsive sound levels from
80 decibels to 130 decibels shall be integrated into the noise
measurements. (ii) Instruments used to measure employee noise
exposure shall be calibrated to ensure measurement accuracy.
(3) Monitoring shall be repeated whenever a change in production,
process, equipment or controls increases noise exposures to the
extent that:
(i) Additional employees may be exposed at or above the action
level; or (ii) The attenuation provided by hearing protectors being
used by employees may be rendered inadequate to meet the
requirements of paragraph (j) of this section.
..1910.95(e)
(e) "Employee notification." The employer shall notify each
employee exposed at or above an 8-hour time-weighted average of 85
decibels of the results of the monitoring.
(f) "Observation of monitoring." The employer shall provide
affected employees or their representatives with an opportunity to
observe any noise measurements conducted pursuant to this section.
(g) "Audiometric testing program." (1) The employer shall establish
and maintain an audiometric testing program as provided in this
paragraph by making audiometric testing available to all employees
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whose exposures equal or exceed an 8-hour time-weighted average of
85 decibels.
(2) The program shall be provided at no cost to employees.
(3) Audiometric tests shall be performed by a licensed or certified
audiologist, otolaryngologist, or other physician, or by a
technician who is certified by the Council of Accreditation in
Occupational Hearing Conservation, or who has satisfactorily
demonstrated competence in administering audiometric examinations,
obtaining valid audiograms, and properly using, maintaining and
checking calibration and proper functioning of the audiometers
being used. A technician who operates microprocessor audiometers
does not need to be certified. A technician who performs
audiometric tests must be responsible to an audiologist,
otolaryngologist or physician.
..1910.95(g)(4)
(4) All audiograms obtained pursuant to this section shall meet the
requirements of Appendix C: "Audiometric Measuring Instruments."
(5) "Baseline audiogram." (i) Within 6 months of an employee's
first exposure at or above the action level, the employer shall
establish a valid baseline audiogram against which subsequent
audiograms can be compared. (ii) "Mobile test van exception." Where
mobile test vans are used to meet the audiometric testing
obligation, the employer shall obtain a valid
baseline audiogram within 1 year of an employee's first exposure at
or above the action level. Where baseline audiograms are obtained
more than 6 months after the employee's first exposure at or above
the action level, employees shall wearing hearing protectors for
any period exceeding six months after first exposure until the
baseline audiogram is obtained.
(iii) Testing to establish a baseline audiogram shall be preceded
by at least 14 hours without exposure to workplace noise. Hearing
protectors may be used as a substitute for the requirement that
baseline audiograms be preceded by 14 hours without exposure to
workplace noise.
(iv) The employer shall notify employees of the need to avoid high
levels of non-occupational noise exposure during the 14-hour period
immediately preceding the audiometric examination.
..1910.95(g)(6)
(6) "Annual audiogram." At least annually after obtaining the
baseline audiogram, the employer shall obtain a new audiogram for
each employee exposed at or above an 8-hour time-weighted average
of 85 decibels.
(7) "Evaluation of audiogram." (i) Each employee's annual audiogram
shall be compared to that employee's baseline audiogram to
determine if the audiogram is valid and if a standard threshold
shift as defined in paragraph (g)(10) of this section has occurred.
Industrial Lectures
This comparison may be done by a
audiogram shows that an employee
shift, the employer may obtain a
the results of the retest as the
Page 56
technician. (ii) If the annual
has suffered a standard threshold
retest within 30 days and consider
annual audiogram.
(iii) The audiologist, otolaryngologist, or physician shall review
problem audiograms and shall determine whether there is a need for
further evaluation. The employer shall provide to the person
performing this evaluation the following information:
(A) A copy of the requirements for hearing conservation as set
forth in paragraphs (c) through (n) of this section;
(B) The baseline audiogram and most recent audiogram of the
employee to be evaluated;
..1910.95(g)(7)(iii)(C)
(C) Measurements of background sound pressure levels in the
audiometric test room as required in Appendix D: Audiometric Test
Rooms.
(D) Records of audiometer calibrations required by paragraph (h)(5)
of this section.
(8) "Follow-up procedures." (i) If a comparison of the annual
audiogram to the baseline audiogram indicates a standard threshold
shift as defined in paragraph (g)(10) of this section has occurred,
the employee shall be informed of this fact in writing, within 21
days of the determination.
(ii) Unless a physician determines that the standard threshold
shift is not work related or aggravated by occupational noise
exposure, the employer shall ensure that the following steps are
taken when a standard threshold shift occurs:
(A) Employees not using hearing protectors shall be fitted with
hearing protectors, trained in their use and care, and required to
use them.
(B) Employees already using hearing protectors shall be refitted
and retrained in the use of hearing protectors and provided with
hearing protectors offering greater attenuation if necessary.
(C) The employee shall be referred for a clinical audiological
evaluation or an otological examination, as appropriate, if
additional testing is necessary or if the employer suspects that a
medical pathology of the ear is caused or aggravated by the wearing
of hearing protectors. ..1910.95(g)(8)(ii)(D)
(D) The employee is informed of the need for an otological
examination if a medical pathology of the ear that is unrelated to
the use of hearing protectors is suspected.
(iii) If subsequent audiometric testing of an employee whose
exposure to noise is less than an 8-hour TWA of 90 decibels
indicates that a standard threshold shift is not persistent, the
employer:
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(A) Shall inform the employee of the new audiometric
interpretation; and (B) May discontinue the required use of hearing
protectors for that employee.
(9) "Revised baseline." An annual audiogram may be substituted for
the baseline audiogram when, in the judgment of the audiologist,
otolaryngologist or physician who is evaluating the audiogram:
(i) The standard threshold shift revealed by the audiogram is
persistent; or
(ii) The hearing threshold shown in the annual audiogram indicates
significant improvement over the baseline audiogram.
(10) "Standard threshold shift." (i) As used in this section, a
standard threshold shift is a change in hearing threshold relative
to the baseline audiogram of an average of 10 dB or more at 2000,
3000, and 4000 Hz in either ear.
..1910.95(g)(10)(ii)
(ii) In determining whether a standard threshold shift has
occurred, allowance may be made for the contribution of aging
(presbycusis) to the change in hearing level by correcting the
annual audiogram according to the procedure described in Appendix
F: "Calculation and Application of Age Correction to Audiograms."
(h) "Audiometric test requirements." (1) Audiometric tests shall be
pure tone, air conduction, hearing threshold examinations, with
test frequencies including as a minimum 500, 1000, 2000, 3000,
4000, and 6000 Hz. Tests at each frequency shall be taken
separately for each ear.
(2) Audiometric tests shall be conducted with audiometers
(including microprocessor audiometers) that meet the specifications
of, and are maintained and used in accordance with, American
National Standard Specification for Audiometers, S3.6-1969.
(3) Pulsed-tone and self-recording audiometers, if used, shall meet
the requirements specified in Appendix C: "Audiometric Measuring
Instruments." (4) Audiometric examinations shall be administered in
a room meeting the requirements listed in Appendix D: "Audiometric
Test Rooms."
(5) "Audiometer calibration." {i} The functional operation of the
audiometer shall be checked before each day's use by testing a
person with known, stable hearing thresholds, and by listening to
the audiometer's output to make sure that the output is free from
distorted or unwanted sounds. Deviations of 10 decibels or greater
require an acoustic calibration. [Image]
..1910.95(h)(5)(ii)
{ii} Audiometer calibration shall be checked acoustically at least
annually in accordance with Appendix E: "Acoustic Calibration of
Audiometers." Test frequencies below 500 Hz and above 6000 Hz may
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be omitted from this check. Deviations of 15 decibels or greater
require an exhaustive calibration. {iii} An exhaustive calibration
shall be performed at least every two years in accordance with
sections 4.1.2; 4.1.3.; 4.1.4.3; 4.2; 4.4.1; 4.4.2; 4.4.3; and 4.5
of the American National Standard Specification for Audiometers,
S3.6-1969. Test frequencies below 500 Hz and above 6000 Hz may be
omitted from this calibration.
(i) "Hearing protectors." (1) Employers shall make hearing
protectors available to all employees exposed to an 8-hour timeweighted average of 85 decibels or greater at no cost to the
employees. Hearing protectors shall be replaced as necessary.
(2) Employers shall ensure that hearing protectors are worn:
(i) By an employee who is required by paragraph (b)(1) of this
section to wear personal protective equipment; and
(ii) By any employee who is exposed to an 8-hour time-weighted
average of 85 decibels or greater, and who:
..1910.95(i)(2)(ii)(A)
(A) Has not yet had a baseline audiogram established pursuant to
paragraph (g)(5)(ii); or
(B) Has experienced a standard threshold shift.
(3) Employees shall be given the opportunity to select their
hearing protectors from a variety of suitable hearing protectors
provided by the employer.
(4) The employer shall provide training in the use and care of all
hearing protectors provided to employees.
(5) The employer shall ensure proper initial fitting and supervise
the correct use of all hearing protectors.
(j) "Hearing protector attenuation." (1) The employer shall
evaluate hearing protector attenuation for the specific noise
environments in which the protector will be used. The employer
shall use one of the evaluation methods described in Appendix B:
"Methods for Estimating the Adequacy of Hearing Protection
Attenuation."
(2) Hearing protectors must attenuate employee exposure at least to
an 8-hour time-weighted average of 90 decibels as required by
paragraph (b) of this section.
..1910.95(j)(3)
(3) For employees who have experienced a standard threshold shift,
hearing protectors must attenuate employee exposure to an 8-hour
time-weighted average of 85 decibels or below.
(4) The adequacy of hearing protector attenuation shall be reevaluated whenever employee noise exposures increase to the extent
that the hearing protectors provided may no longer provide adequate
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attenuation. The employer shall provide more effective hearing
protectors where necessary.
(k) "Training program." (1) The employer shall institute a training
program for all employees who are exposed to noise at or above an
8-hour time-weighted average of 85 decibels, and shall ensure
employee participation in such program.
(2) The training program shall be repeated annually for each
employee included in the hearing conservation program. Information
provided in the training program shall be updated to be consistent
with changes in protective equipment and work processes.
(3) The employer shall ensure that each employee is informed of the
following:
(i) The effects of noise on hearing;
..1910.95(k)(3)(ii)
(ii) The purpose of hearing protectors, the advantages,
disadvantages, and attenuation of various types, and instructions
on selection, fitting, use, and care; and
(iii) The purpose of audiometric testing, and an explanation of the
test procedures.
(l) "Access to information and training materials." (1) The
employer shall make available to affected employees or their
representatives copies of this standard and shall also post a copy
in the workplace.
(2) The employer shall provide to affected employees any
informational materials pertaining to the standard that are
supplied to the employer by the Assistant Secretary.
(3) The employer shall provide, upon request, all materials related
to the employer's training and education program pertaining to this
standard to the Assistant Secretary and the Director.
(m) "Recordkeeping" - (1) "Exposure measurements." The employer
shall maintain an accurate record of all employee exposure
measurements required by paragraph (d) of this section.
(2) "Audiometric tests." (i) The employer shall retain all employee
audiometric test records obtained pursuant to paragraph (g) of this
section:
..1910.95(m)(2)(ii)
(ii) This record shall include:
(A) Name and job classification of the employee; (B) Date of the
audiogram;
(C) The examiner's name;
(D) Date of the last acoustic or exhaustive calibration of the
audiometer; and
(E) Employee's most recent noise exposure assessment.
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(F) The employer shall maintain accurate records of the
measurements of the background sound pressure levels in audiometric
test rooms.
(3) "Record retention." The employer shall retain records required
in this paragraph (m) for at least the following periods.
(i) Noise exposure measurement records shall be retained for two
years. (ii) Audiometric test records shall be retained for the
duration of the affected employee's employment.
(4) "Access to records." All records required by this section shall
be provided upon request to employees, former employees,
representatives designated by the individual employee, and the
Assistant Secretary. The provisions of 29 CFR 1910.20 (a)-(e) and
(g)-(i) apply to access to records under this section.
..1910.95(m)(5)
(5) "Transfer of records." If the employer ceases to do business,
the employer shall transfer to the successor employer all records
required to be maintained by this section, and the successor
employer shall retain them for the remainder of the period
prescribed in paragraph (m)(3) of this section.
(n) "Appendices." (1) Appendices A, B, C, D, and E to this section
are incorporated as part of this section and the contents of these
appendices are mandatory.
(2) Appendices F and G to this section are informational and are
not intended to create any additional obligations not otherwise
imposed or to detract from any existing obligations.
(o) "Exemptions." Paragraphs (c) through (n) of this section shall
not apply to employers engaged in oil and gas well drilling and
servicing operations. (p) "Startup date." Baseline audiograms
required by paragraph (g) of this section shall be completed by
March 1, 1984.
(Approved by the Office of Management and Budget under control
number 1218-0048)
card fld "STS"
From Federal Register 2-2-96
(c.) Hearing loss. Employers would record any work-related case
resulting in an average shift of15 decibels or more at 2000, 3000
and 4000 hertz in one or both ears as measured from the employee's
original baseline established under 29 CFR Part 1910.95
Occupational Noise Exposure. The hearing test may be adjusted for
aging and the recorded case may be removed if a retest performed
within 30 days does not confirm the original shift. A presumption
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of work-relatedness is used for hearing loss occurring to employees
covered by the Occupational Noise Exposure standard, i.e. those who
are exposed to noise levels in excess of an 85 dB 8 hour time
weighted average.
The lowest action level in the noise standard is an average shift
of 10 decibels or more at 2000, 3000 and 4000 hertz. OSHA is
proposing the 15 decibel criteria for recordkeeping purposes to
account for variations in the reliability of individual audiometric
testing results.
OSHA asks for input on which level of a shift in hearing should be
used as a recording criteria; 10 decibels? 20 decibels? 25
decibels? For each level, what baseline should be used?
Preemployment (original) baseline? Audiometric zero? Is adjusting
for presbycusis appropriate?
Card number_____ 73
card fld "card field id 1"
1935
•Congress passes the
Walsh-Healey Public
Contracts Act
•DOL now has authority to
impose regulations on
companies having contracts
with the federal government
1969
•DOL issues a standard
requiring noise exposures to be limited to 90 dBA, or less
•Engineering controls, feasible administrative controls must be
employed.
•HPDs used as a last resort
1970
•Occupational Safety and Health Act passed by congress
1971
•Walsh-Healey noise standard becomes OSHA standard 29 CFR 1910.95
(a)-(b)
1981
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•Hearing Conservation Amendment to standard was issued: 29 CFR
1910.95 (c)-(p)
•this outlined an effective hearing conservation program
•"January version" of the standard
1981
•in August, due to industry lobbying, an administrative stay was
issued on several paragraphs (and portions of paragraphs) of the
standard
•"August version" of the standard
1983
•In March the final rule went into effect
•"March version" of the standard
1984
•November 8, 1984 the United States Court of Appeals for the Fourth
Circuit issued an opinion in the Forging Industries Association and
National Arborist Association v. Secretary of Labor vacating the
hearing conservation ammendment
Allegations:
•OSHA had exceeded its authority
√hearing loss is an effect or result, not a hazard; therefore
OSHA cannot regulate it
√the standard requires the employer to take action when the cause
may not have been in the workplace
•December 28, 1984 DOL petitioned for a rehearing and eventually
the ammendment was reinstated
------The End?-----Card number_____ 74
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January 1981 (Original) Version
29 CFR 1910.95, March 1983
a) same as original adopted in
May of 1969
a) Permissable Exposure Limit
(PEL)
•TWA of 90 with a 5 dB timeintensity trade; Dose = 1
•See next card for sample
calculations
•Impulses shall not exceed 140
dB peak pressure. Otherwise
impulse noise is integrated
into the dose same as other
noise.
(b) same
(b)(1) Controls
•when PEL is exceeded,
"feasible" engineering or
administrative controls shall
be utilized
•exposure reduced to ≤ PEL
•when controls fail, use HPDs
(b)(2) Fluctuations
•when time interval between
successive peaks is ≤ 1 sec,
it's continuous noise
(c) same
(c) Hearing Conservation
Program
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•provided (free) for all
employees with exposures
exceeding action level (AL)
•TWA = 85 (Dose= .5)
(d) major compromises
•used to have an initial
determination
(d) Monitoring
(1) Do it when "any
information" indicates
exposures exceed AL
•more precise definition of how
to sample, how to use SLM or
dosimeter
•a "sampling strategy" should
identify employees with
significant exposures
√help in selecting HPDs
•area monitoring is Ok
•use personal (dosimeter)
measurements when area sampling
in not appropriate
√fluctuating noise levels
√high worker mobility
•all sound between 80-130 dBA
should be included in exposure
•no precise statements for
calibrating dosimeters/SLMs
•all equipment used in taking
exposure measurements should be
calibrated
•no time limit within which
monitoring has to be done, used
to be 60 days
•repeat monitoring when there
is a change that could
√increase number of employees
exposed ≥ AL
√render HPDs inadequate
•no provisions for repeat
monitoring, used to be every 2
years
•goal is to obtain an exposure
measurement for each employee
(e) similar
(e) Employee Notification
•employer must notify each
employee exposed to levels ≥ AL
(f) similar
(f) Observation of Monitoring
•employee, or their
representative can observe
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monitoring
(g) major changes
(g) Audiometric Test Program
(1) for all exceeding AL
(2) no cost
(3) tests performed by
•licensed/certified audiologist
•ENT, other physician
•certified technician
•anyone who has demonstrated
competency
√audiometric testing
√calibration
(4) audiometer must meet
appendix C requirements
•specifications for selfrecording audiometers
•baseline had to be taken
within 4 months
(5) Baseline audiogram
•obtained within 6 months of
first exposure ≥ AL
•no exemption for van
•obtained within 1 year if
using mobile van
√HPDs used for last 6 months
•HPDs were no substitute for
quiet
•preceded by 14 hours of "no
exposure to workplace noise"
√HPDs may substitute for
quiet
√employer must tell employee
to avoid non-occupational noise
(6) Annual audiogram
•for each employee ≥ AL
•STS was "significant" not
"standard"
•audiologist/ENT/physician had
to evaluate audiograms for STS
(7) Evaluate audiograms for STS
•the technician can do this
•if STS the employer can redo
audiogram within 30 days
•audiologist/ENT/physician
shall review "problem"
audiograms
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√copy of 29
√baseline &
√background
√audiometer
records
CFR 1910.95
annual audio
noise levels
calibration
(8) Follow-up regarding STS.
•notify employee in writing (21
days)
-->If STS, (assuming a
physician has not determined it
to be non-work related)
•fit employee with HPD
•train them in their use & care
•they are required to use HPD
•already using HPD?
√re-train
√re-fit, perhaps with HPD
with greater attenuation
•possible medical pathology?
√refer for ENT evaluation, or
√audiologic evaluation
√even if unrelated to HPD
use, or occupational exposure
•STS was "permanent" not
"persistent"
(9) Revise baseline when
•STS is persistent, or
•hearing has improved
•used to have objective
criteria for baseline revision
•audiologist/ENT/physician
should make subjective decision
•STS used to have a more
stringent definition,
especially as hearing became
poorer
•You don't have to report STS
until it is ≥ 15 dB
(10) Standard threshold shift
•STS exists when annual changes
≥10 dB (relative to baseline)
for (2K + 3K + 4K)/3
(h) same except for quiet
environment
(h) Audiometric test
requirements
(1) minimum frequencies
.5, 1, 2, 3, 4, 6 kHz
•you can correct for
presbycusis using appendix F
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•used to use ANSI standard, now
too much background noise is
allowed
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(2) ANSI S3.6-1969
(3) appendix C (self-recording)
(4) Quiet test environment,
appendix D
(5) How often to calibrate?
•biologically, daily, with a
stable hearing person,
deviations ≥ 10 dB then do
acoustic calibration
•acoustic calibration annually
√SPL (audiometric zero)
√linearity
if deviations ≥ 15 dB then do
exhaustive calibration
•exhaustive calibration every 2
years
√complete ANSI calibration
(i) same, basically
•used to require warning signs
where TWA = 85, HPDs required
(i) Hearing protectors
•for everyone who wants one,
regardless of exposure (no
cost)
•employer ensures they are worn
by
√everyone ≥ PEL
√all who ≥ AL if
-STS been documented
-waiting for the van
(baseline)
•employee has a the right to a
choice in selecting HPD
•employer must ensure
√HPDs worn properly
√employee trained in use &
care
(j) same
(j) HPD attenuation
•estimated A-weighted TWA
= TWA - (NRR - 7)
= TWA (C-weighted) - NRR
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•reduce exposure to:
√PEL, or
√AL if STS exists
•re-evaluate HPD if dose
changes
(k) different
•used to have to include a lot
more, almost too much
(k) Training program
•all people in HCP
•repeated annually
•areas covered
√effects of noise on hearing
√purpose of HPDs, advantage,
disadvantages, attenuation of
various types, instructions on
selecting, fitting, use & care
√purpose of audiometric
testing
(l) same
•they eliminated a paragraph
requiring posting warning signs
√AL exceeded
√PEL exceeded
√HPDs required
(l) Access to information &
training materials
•the employer should make
copies of standard available,
post in workplace
•make available anything
supplied by assistant secretary
•assistant secretary can have
access to your training
materials
(m) similar, but
•details of how exposure
measurement were taken are not
included, used to have to keep
track of who the representative
individual was
•most records had to be
retained longer
√audiograms, employment
duration plus 5 years
(m) Recordkeeping
•all exposure measures (2
years)
•audiograms (keep for duration
of employment) including
√date
√examiner's name
√date of last calibration
√employees last noise
exposure
√background noise levels
•access to records by employee,
former employee, his
representative, asst. secretary
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(n) similar, left out a
horrendous one dealing with SLM
sampling strategies, fine with
me
(n) Appendicees
•mandatory
√exposure computation
√HPD attenuation
√audiometers
√test room
√acoustic calibration
•informational
√presbycusis
√monitoring noise levels
(o) no oil & gas exemptions
(o) Exemptions
•oil & well drilling/servicing
(p) startup date had to change
(p) Startup date
•baseline audiograms completed
by March 1, 1984
------The End------
card fld "Table G-16"
Table G-16 — Permissable Noise Exposures.
Duration per day,
8 . . . . . . . .
6 . . . . . . . .
4 . . . . . . . .
3 . . . . . . . .
2 . . . . . . . .
1.5 . . . . . . .
1 . . . . . . . .
1/2 . . . . . . .
1/4 or less . . .
hours
. . .
. . .
. . .
. . .
. . .
. . .
. . .
. . .
. . .
Card number_____ 75
Sound Level, dBA
slow response
. . . 90
. . . 92
. . . 95
. . . 97
. . . 100
. . . 102
. . . 105
. . . 110
. . . 115
------The End------
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Card number_____ 76
Card number_____ 77
card fld "Standards"
All the standards define what is meant by "normal hearing,"
audiometric zero (0 dB HL), or RETSPL (reference equivalent
threshold SPL)
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•The ASA-1951 standard was based upon a US Department of Public
Health survery (late 1930s). It describes hearing of the "typical
man on the street." Test booths were set up at state and county
fairs.
◊geographically diverse
◊people of different ages, gender
◊may have included individuals with ear pathology, noise exposure
◊testing environment was not optimal (noisy)
•The ISO-1964 standard was a "laboratory standard."
compiled from European and US researchers.
Results were
◊Young (18-24 yo), otologically normal adults.
◊Well-defined test protocols
◊Quiet conditions
•ANSI-1969 standard is the ISO-1964 standard using a different set
of headphones (TDH-39 vs. WE 705A). Current revision is ANSI-1996.
Points:
•Hearing is about 10 dB better using ANSI-1969 as compared to the
ASA-1951 standard. A 30 dB HL threshold (ANSI-1969) is a 20 dB HL
threshold (ASA-1951).
•Some compensation laws reference the older standard, reducing the
magnitude of hearing loss.
Card number_____ 78
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Card number_____ 80
Card number_____ 81
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