Protect Your Hearing:
Understanding Hearing Loss
CDR David C. Byrne, MS, CCC-A
NIOSH/DART - Cincinnati, OH
Robert F. Randolph, MS
NIOSH/OMSHR – Pittsburgh, PA
Disclaimer: The findings and conclusions in this report are those of the author(s) and do not necessarily
represent the views of the National Institute for Occupational Safety and Health (NIOSH). Mention of company
names or products does not constitute endorsement by the Centers for Disease Control and Prevention or NIOSH.
Topics
•
•
•
•
•
•
•
Scope of the NIHL problem
Basic anatomy
Hearing protectors
NRR regulation revision
Earplug fit-testing
Chemical exposures
Earplug fitting practice
Occupational Hearing Loss
Our o i e i on e wel
loor
Occupational Hearing Loss
Our office is on the twelfth floor
What is the problem?
Noise-induced hearing loss is:
PAINLESS
• PROGRESSIVE
• PERMANENT
•
...but it is also PREVENTABLE
Why should you care?
Noise-induced hearing loss is:
A potentially major liability when your
job depends upon your sense of
hearing.
• A seriously disabling condition
(psychologically and socially)
•
Occupational Hearing Loss
• Cross-cutting issue, affects workers
in nearly every sector
• Currently no recovery; severely
impairs quality of life
• One of most common workplace
illnesses/injuries
• Significant $costs$ associated with
high noise levels in the workplace.
Scope of the problem
How many workers are exposed to
hazardous noise levels at work?
▫ OSHA: 5.2 million (manufacturing only)
▫ EPA: 9 million (all sectors)
▫ NIOSH: 30 million
▫ Tak et al, 2009: 22 million (self-report)
Prevalence of noise-exposure
NHANES, 1999-2004
Tak et al., 2009
Scope of the problem
How many workers are exposed to
other auditory hazardous agents at work?
▫ Morata et al., 1994: 10 million (solvents)
Unknown number exposed to other ototoxicants
• metals (mercury, lead, trimethyltin)
• asphyxiants (carbon monoxide)
• endocrine disrupters (acrylonitrile)
Scope of the problem
How many workers have experienced
a hearing loss due to their exposure?
▫ NIDCD: 22 million US workers
▫ Tak & Calvert (2008): 24% of hearing loss in US
▫ BLS: 11% of all occupational illnesses
▫ WHO: 16-24% of hearing losses worldwide
Occupational hearing loss (OHL) is the most
commonly-reported non-fatal work injury in US
Prevalence of hearing difficulty
NHIS, 1997-2003
Tak & Calvert, 2008
Incidence of threshold shifts
BLS, 2004-2008
http://www.caohc.org/updatearticles/spring2010/hearing_loss_data.php
Hearing Loss Types
• CONDUCTIVE
▫ Outer and Middle Ear
▫ Usually low frequency, correctable
▫ Ex: earwax, hole in eardrum, headcold
• SENSORI-NEURAL
▫ Inner Ear
▫ Usually high frequency, not correctable
▫ Ex: aging, diseases, medications, noise
Noise-Induced Hearing Loss
Noise-induced hearing loss is a sensori-neural
hearing loss.
It typically starts at 4000 Hz, and as it gets
worse, it spreads to the adjacent frequencies
(3000 and 6000 Hz).
The amount of hearing loss depends on the
amount of noise exposure.
Noise-Induced Hearing Loss
Typical progression of noise-induced
hearing loss:
• Temporary Threshold Shift
• Permanent Threshold Shift
This is your ear…
Healthy
...this is your ear
on Noise.
Damaged
NIOSH Hearing Loss Simulator shows what a noiseinduced hearing loss sounds like.
Normal
Click to play sound
Impaired
25 years of 95 dB(A) exposure, 55-year old
worker – noise “notch” at 4,000Hz
Click to play sound
Severely Impaired
Click on picture for sound
25 years of 105 dB(A) exposure, 55-year old
worker – noise “notch” at 4,000Hz
Click to play sound
Click to stop sound
Simulated effects of exposure, age, sex based on ANSI
S3.44 method
Use the NIOSH Hearing Loss Simulator
to hear more effects of noise exposure
On the web:
http://www.cdc.gov/niosh/mining/products/product47.htm
Download from: www.CDC.gov/niosh/mining/products/product47.htm
Warning Signs of too
much noise
• Feeling of “fullness” in ears
• Ringing in ears
• Huh? What?
• Blasting radio/TV
• Tired, stressed
Exposure Limits:
OSHA (PEL)
NIOSH (REL)
dB(A)
85
90
95
100
105
110
115
dB(A)
82
85
88
91
94
97
100
Time
16 hours
8
4
2
1
30 min.
15 min.
Time
16 hours
8
4
2
1
30 min.
15 min.
Exposure Limits
• Depends on overall
sound level
• Depends on time
Noise
1
+Time
+1
Hearing
2
loss
Estimated Risk of Developing
a Hearing Loss
Reporting Org.
Avg. Daily Exposure
Excess Risk
EPA
90 dBA
85 dBA
80 dBA
90 dBA
85 dBA
80 dBA
22%
12%
5%
29%
15%
3%
NIOSH
NOTE: There is a wide variability in susceptibility to NIHL across individuals. Extrapolation of
estimates of NIPTS to other populations (e.g., children and adolescents) exposed to nonindustrial
sound exposures (e.g., music) is therefore questionable. From Table 3-1 in the NIOSH 1998
Criteria Document.
Hearing Protectors
Standard Types:
• Earplugs
• Earmuffs
• Canal Caps
http://www.cdc.gov/niosh/topics/noise/hpcomp.html
“The science of hearing protector technology is
mature. There is no need to fund additional
research on hearing protectors.”
Col. George Mohr
Aerospace Medical Division, 1979
Hearing Protectors
Special Types:
• Moderate attenuation
• “Flat” attenuation
• Impulse noise
• Communication
• Active Noise Reduction
Hearing Protectors
Hearing protector performance:
Noise Reduction Rating (NRR)
• Laboratory test conducted on humans
(REAT)
• Single-number rating
• Required by EPA
Hearing Protection Devices
Noise Reduction Ratings
• A limitation of the NRR is that attenuation values
tend to over-estimate the amount of protection
received by individuals during daily use.
• The NIOSH Criteria for a Recommended Standard:
Occupational Noise Exposure, published in 1998
suggests de-rating the NRR on HPDs as follows:
EAR MUFFS by 25%
FOAM PLUGS by 50%
MOLDED(flanged) PLUGS by 70%
Hearing Protectors
Factors that compromise performance:
•Comfort
•Readjustment
•Utilization
•Deterioration
•Fit
•Abuse
•Compatibility
•Wearing time
Hearing Protection Devices
Advantages & Disadvantages
• There is NO single “best” type for all individuals or
situations.
• Varies with individual comfort, size of canals, noise
environments, work activities & environmental
conditions.
Ear Plugs
Advantages


Small, inexpensive, portable, &
comfortable
Worn effectively without interference
from glasses or hair
Disadvantages

Can be hard to fit

Can introduce dirt into the canal

Protection level can vary

May interfere with other PPE
Hearing Protection Devices
Advantages & Disadvantages
• There is NO single “best” type for all individuals or
situations.
• Varies with individual comfort, size of canals, noise
environments, work activities & environmental
conditions.
Ear Muffs
Advantages
Disadvantages

Easy to fit properly


Provide constant attenuation


Less time & effort applying/fitting
Uncomfortable in hot environments
May be cumbersome & restrict head
motion
Wrong:
Hair interfering
with seal
Wrong:
Band too loose
Wrong:
Ear interfering with seal
Wrong:
Hat and sunglasses
interfering with seal
Wrong:
Drilled holes allow
noise to pass
Right:
Good fit
Wrong:
Inserted too deep
Wrong:
Not inserted
deep enough
Wrong:
Inserted backwards
(stem in)
Hand-formed Foam Earplugs
• Polyvinyl foam –
cylindrical shape
• Universal (one size
fits most)
• Yellow, white, or twocolor
Improper
Hearing protection
NIOSH Compendium of HPDs:
Searchable database by noise level, desired NRR,
device type, features, etc.
http://www2a.cdc.gov/hp-devices/hp_srchpg01.asp
HPD labeling
Problems with current regulation:
▫
▫
▫
▫
▫
▫
Based on outdated standard
Experimenter-fit device
Not representative of field performance
Based on C-weighted noise levels
Does not address variation across individuals
Does not deal with more sophisticated HPDs
Proposed new regulation
Proposed regulation addresses these issues by:
▫ Basing rating on updated standard (ANSI S12.62008)
▫ Using an “informed-user” fit
▫ Basing the calculations on A-weighted levels
▫ Providing a range of noise reduction values for
each device
▫ Including methods for testing level-dependent
devices and evaluating suitability for impulsive
noise environments
Current HPD label
EPA proposed labels
71
Types of protectors Covered
• EPA – 1979 40 CFR 211 B
▫ Earplugs, Earmuffs, Canal Caps
• EPA – 2009 40 CFR 211 B
▫ Active Noise Reduction (ANR)
 Earmuffs & Earplugs
▫ Impulsive performance
 Nonlinear Attenuation
 Sound Restoration
72
Current Noise Reduction Rating
• NRR – ANSI S3.19
▫ Experimenter Fit Data
 98% protection factor
 Small standard deviations (<3 dB)
73
Proposed NRR Label for General Use
74
Proposed NRR Label for General Use
80% Lower
Limit
of
Attenuations
Achieved by
Test Panel
20% Upper
Limit
of Attenuations
Achieved by
Test Panel
Proposed NRR Label for General Use
75
A worker is in a noise environment of 97 dBA. What is the
range of exposures received when wearing this protector?
Proposed NRR Label for General Use
76
80% of users will achieve this level
97 dBA – 18 dBA = 79 dBA
20% of Users will achieve this level
97 dBA – 32 dBA = 65 dBA
77
How do you deal with other noises?
• The Protector is tested with 1/3rd Octave
bands of noise to determine its performance
with frequency.
• When a protector is used in different types of
noise, the attenuation changes as a function
of the noise spectrum.
• ANSI S12.68 codified a graphical method to
determine the variability.
78
Spectral Variability
Using the Graphical Method
• Measure the C-weighted Noise:
LC = 95
• Measure the A-weighted Noise:
LA = 87
• Compute the difference:
LC – LA = 8 dB
• Look up attenuation on graph:
8 dB yields about 8 dB noise
reduction for 80th percentile.
8 dB yields about 14 dB noise
reduction for 20th percentile.
79
80
Estimating Exposure with Graphical NRR
• A-weighted exposure level was 87 dB(A)
• LC-LA = 8 dB yielding 8 dB NRR at 80th
Percentile
• Estimated Exposure with Protectors:
87 – 8 = 79 dBA
• Note that this is a more accurate estimate for
that specific noise
81
Noise Reduction Rating for Active HPDs
• Passive NRR – ANSI S12.6 / S12.68
▫ Experimenter-Trained REAT
▫ Passive NRR from ANSI S12.68
• Active NRR – ANSI S12.42
▫ Microphone in Real Ear (MIRE) modified
Active Noise Reduction devices
 Measure with ANR turned ON and OFF.
▫ Passive REAT + Active MIRE
 NRR determined with ANSI S12.68
82
Noise Reduction Rating for Active HPDs
• Active NRR – MIRE Testing Muffs
▫ Miniature microphone centered in ear canal
 Measure with the muff turned OFF
 Measure with the muff turned ON
 The difference in the octave band measurements
will be used to estimate NRR Active.
83
Noise Reduction Rating for Active HPDs
• Active NRR – MIRE Testing Plugs
▫ Need to be tested on a mannequin.
 Measure with the plug turned OFF
 Measure with the plug turned ON
 The difference in the octave band measurements
will be used to estimate NRR Active.
84
NRR Label for Active Noise Reduction
NRR Label for Active Noise Reduction
Passive HPD
Rating
80 and 20%
protection
85
Active HPD
Rating
80 and 20%
protection
86
A pilot is exposed to low frequency noise while flying.
What is the expected protection with the device turned ON?
What is the protection when the batteries fail?
87
NRR Label for Active Noise Reduction
When the device is ON: protection 22 – 35 dBA
When the batteries fail: protection 20 – 32 dBA
88
Impulsive Noise Reduction Rating
• No ANSI or ISO acoustic standards exist
• Passive NRR – ANSI S12.68 / S12.6
▫ Experimenter-Trained
• Acoustic Test Fixture for Impulse Tests
▫ Range of impulse levels:
130-134, 148-152, 166-170 dB Peak SPL
▫ Multiple tests will be used to identify the lower
and upper range of impulse noise reduction
89
NRR Label for Impulse Noise Reduction
90
NRR Label for Impulse Noise Reduction
Passive HPD
Rating
80 and 20%
protection
Impulsive
HPD Rating
80 and 20%
protection
91
A carpenter uses a pneumatic nail gun which has peak
impulse levels of 135 decibels. What is the expected
exposure level?
92
A carpenter uses a pneumatic nail gun which has peak
impulse levels of 135 decibels. What is the expected
exposure level?
135 dBA – 22 dBA = 113 dBA
135 dBA – 35 dBA = 100 dBA
93
Retesting and Relabeling
• Proposed rule will have required retesting of the
HPD.
▫ Retested product will be evaluated against the
current label
▫ If significantly lower: Relabel the product with the
lower NRR.
94
Can We Live With the Revision?
• The rule has not yet been completed.
• EPA’s institutional resources for noise are
limited to the EPA authors.
• The original rule was promulgated Sept 28,
1979, over 30 years ago.
• This revision will last for many years to come.
Fit-testing
Enables us to know how much protection an
individual worker receives from a protector
Utility:
▫ Provides feedback to workers regarding fit
▫ Useful training tool
 Motivate workers to fit HPDs better
 Check worker understanding of training
▫ Helps assign appropriate HPD
▫ Documents adequate protection
Why Fit-Test?
•
•
•
•
•
Visual inspection doesn’t guarantee a good fit.
Cupped hands over ears is not quantitative
Tactile tests are not quantitative
Some persons cannot wear a particular protector.
High-level exposure requires high attenuation.
The shoe that fits one person pinches another;
there is no recipe for living that suits all cases.
Carl Jung
Fit-testing
Methods of fit-testing:
▫ REAT technique - Difference in occluded vs.
unoccluded thresholds
e.g., Fit-Check (Michael & Associates)
▫ MIRE technique – Difference in simultaneous
sound measurement inside/outside the HPD
e.g., E·A·Rfit (Aearo Technologies)
▫ Loudness balance technique – Adjusted difference
in perceived loudness with HPD
e.g., VeriPro (Sperian)
Fit-testing
Work needed to implement routinely
in field settings
▫ Requires specialized equipment
▫ Most systems will not work with all HPDs
▫ Takes additional time
Current research
▫ Minimum frequencies required
▫ Use unoccluded test as annual audiogram
First Fit-Test System
 Paul Michael et al. (NIOSH 76-181)
 Ear muffs with speaker.
 Racks of equipment
99
Michael and Bloyer, NHCA conference 1999
Effect of Training on HPD Rating
Joseph et al., Int. J. Aud. 2007
Why Fit-Test?
•
•
•
•
•
•
•
Train workers in proper HPD use
Train the trainer
Satisfy OSHA requirements
STS follow-up: Good or bad fit?
Demonstrate HCP effectiveness
HPD selection for hearing critical jobs
HPD selection for newly hired workers
Fit-Testing Increases Self-Efficacy
If co-workers asked me, I could show them the
right way to fit and wear hearing protectors.
Stephenson et al., Noise & Health 2010
The Five C’s of Hearing Protection
1.
2.
3.
4.
5.
Comfort: Uncomfortable HPDs will not be worn
Convenience: Inconvenient HPDs will not be used
Communication: Communication is critical need
Compatibility: HPDs must not disrupt other PPE
Cost: What value can be placed on Hearing?
“An ounce of prevention is worth a pound of cure.”
Benjamin Franklin
Testing Methods
• Physical Fit-Test
▫ Microphone in Real Ear
 E•A•Rfit, SafetyMeter, QuietDose
• Psychophysical Fit-Test
▫ Loudness Balance
 VeriPRO
▫ Pass/Fail
 QuickFit, WebFit
▫ Real Ear Attenuation at Threshold
 FitCheck, HPD Well-Fit, INTEGRAfit, Multi-Fit 4
Fit-Test Solutions
Microphone in Real Ear (MIRE)
106
REAT Fit-test Systems
107
NIOSH MultiFit
Michael & Associates
FITCHECK
NIOSH HPD Well-Fit
NIOSH QuickFit earplug tester
Inexpensive, reliable design uses off-the-shelf components
MP3 player containing test
sounds
Housed in earmuff
Fit-Test Solutions
Loudness Balance / In-ear Dosimeter
109
Pitfalls & Problems
• REAT methods:
▫ Background Noise
▫ Subject’s hearing threshold
• Loudness Balance:
▫ New testing paradigm
▫ Subject’s hearing thresholds
• MIRE
▫ Surrogate estimate of attenuation
▫ Performed with a modified protector
111
Fit-Test System Output
• Personal Attenuation Ratings
▫ E-A-Rfit, SafetyMeter, VeriPRO, MultiFit, HPD
Well-Fit, FitCheck, IntegraFit
• Daily dose
▫ QuietDose
• Pass/Fail
▫ QuickFit, VeriPRO QuickCheck
112
Personal Attenuation Ratings
•
•
•
•
•
•
•
E-A-Rfit: NRSA50 (7 frequencies)
SafetyMeter NRR (7 frequencies)
VeriPRO: NRRSF (1, 4 or 5 frequencies)
FITCHECK: A-weighting (1-7 frequencies)
HPD Well-Fit: A-weighting (1-7 frequencies)
INTEGRAfit: Attenuation @ 500 Hz.
MultiFit: Attenuations @ 7 frequencies
The Role of Fit-Testing in a
Comprehensive Hearing
Conservation Program
•Initial HPD selection and training of HPD wearers
in correct fitting procedures
•Random field sampling of protector effectiveness
•Documentation that proper protection was
provided to the employee with personal training in
fit technique
•Identification of failing or deteriorating protectors
and changes in ear physiology
Steel Industry Study
• 389 workers individually fit-tested as part of annual
audiometric testing
• Workers selected HPDs
• 192 wearing flanged re-usable
plugs (NRR = 27)
• 85 wearing urethane foam
plugs (NRR = 33)
• Others wearing variety of types
FIgure 1. Distribution of PARs, 1998
50
Percent
40
30
20
10
0
<5
>5,<10
>10,<15
>15,<20
>20,<25
PAR in dB
Silicone reusable
Urethane foam
>25
Example of Fit-Testing:
Two male HPD wearers:
•Both with large ear canals
•Both wearing identical foam-type insert HPDs
•Both inserting plug fully into canal
Two male HPD wearers:
Conclusions
• The best hearing protector is the one
that is worn properly whenever exposed
to hazardous noise.
• Several Fit-Test systems are available
and meet a range of needs.
• As a Hearing Conservation Provider,
you have the responsibility to work with
your customers to facilitate Best
Practices.
NHCA Fit-test workshop (February 2011)
• Elimination
▫ Design hazard out of product/process.
• Substitution
▫ Reduced noise product/process.
• Engineering/maintenance
▫ Properly maintain.
▫ Retrofit existing equipment.
▫ Barriers/Enclosures.
• Administrative
▫ Limit exposure, medical surveillance,
improved work practices.
• Personal Protective Equipment
▫ Ear Plugs/muffs…
More Effort
Preferred
Hierarchy of Controls
121
Impulse noise
The Problem and the Ideal
Solution
“Earplugs
or muffs appear to be counter-indicated,
with regard to speech communication in the situation
where they are probably needed most – namely, in
the presence of intermittent, impulsive noise, such as
gunfire. Here, the wearer of earplugs or muffs
cannot hear weak speech during silent intervals
between impulses. The ideal solution would be a
nonlinear device that would let weak sounds through
at full strength but would attenuate intense sounds.”
pp. 68-69
K.D. Kryter, The Effects of Noise on
Man (1970) Academic Press
U.S. ARMY CENTER FOR HEALTH PROMOTION AND PREVENTIVE MEDICINE
The Solution and the Science
“The acoustic resistance through the
orifice increases with peak level.”
Sivian, L.J. (1935). Acoustic impedance of small orifices. Journal of
the Acoustical Society of America, 7 (2), 94-101.
U.S. ARMY CENTER FOR HEALTH PROMOTION AND PREVENTIVE MEDICINE
Plate
Hole
Cavity
Figure 5
Schematic representation of the ISL “filter” (overall length: 3.7mm,
outside diameter: 3.0mm, inside diameter: 2.0mm). The thickness
of the perforated plates is 0.1-mm and the diameter of the holes is
0.30mm. After Dancer.
U.S. ARMY CENTER FOR HEALTH PROMOTION AND PREVENTIVE MEDICINE
Problems with the NRR…
126
• Designed for Continuous Noise
• Typical protectors exhibit nonlinear response
at high levels >140 dB SPL
• Nonlinear orifice protectors provide
increased attenuation with increasing peak
Sound Pressure Level (peak SPL).
• Electronic Protectors are designed to limit
output to levels below about 82 dB peak SPL.
127
Project: Impulse Noise Reduction
• Measure the Performance for protectors for
levels from 130 to 170 peak SPL.
• Measure performance over a range of levels
(130-134), (148-152) and (166-170) dB.
• Measure the device on an Acoustic Test Fixture
(ATF) to limit human subject exposure.
• Measure both Free-field and ATF waveforms
and apply signal processing to the determine the
impulse rating.
Measurement
Equipment
Blast Probe
ISL Acoustic
Test Fixture
128
129
Experimental Configuration
Colt AR-15 0.223 caliber rifle
130
131
Experimental Design
• Three peak pressure levels (AR-15 rifle) 130,
150, 170 dB at 1, 3, 20 meters
• Five models of hearing protectors
 EAR Pod Express
 Etymotic EB1
 EAR Combat Arms Open (Nonlinear)
 EAR Combat Arms Closed (Linear)
 Bilsom 707
• Five samples of each model; Five insertions
of each sample; Three shots per insertion
How IMPULSE Labels Might Look
OPEN
Open
CLOSED
Closed
Project Summary
Create an annual Award to recognize organizations that uphold
effective hearing loss prevention and document measurable
achievement.
Goals
 To obtain information on successful hearing loss prevention strategies
currently in use in industry.
 To disseminate leading edge and best practices information to
encourage and enable other groups to effectively advance hearing
loss prevention practice.
Funding
Construction, Manufacturing and Services Sectors.
www.safeinsound.us
Earplug Fitting
Practice
Let’s try it...
Let’s try it...
Let’s try it again...
ROLL the earplug into a
small, thin “snake” between
your fingers
PULL the top of your ear up
and back with your opposite
hand; insert the plug
HOLD the plug in place while
counting to 20 to give the plug
time to expand
What we’ve learned…
Training is essential and makes a
difference in the amount of protection a
worker will receive
Workers do not insert their earplugs the
same way experimenters do when they
test the earplugs
All earplugs do not fit all people
Hearing is important
Ray Charles
1930-2004
“I can’t imagine being deaf…
To me it’s the worst thing in
the world. Imagine never
being able to hear music.
Most people expect me to
help the blind, but I don’t
think they need help. After
all, I’m blind and I’m doing
all right.”
Time Magazine, 2004
Questions or
Comments?
David Byrne
Research Audiologist
NIOSH - Cincinnati
▫ Dbyrne@cdc.gov
▫ 513-533-8414
Bob Randolph
Research Psychologist
NIOSH - Pittsburgh
▫ RRandolph@cdc.gov
▫ 412-386-4660