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n
Path: Reducing noise levels along the path involves using sound-absorbing materials to
reduce noise as it travels from the source to the listener. Examples include adding soundabsorbing materials to the room surfaces (e.g., ceiling, walls), building barriers around noisy
areas, installing noise-reducing curtains, and enclosing the worker in a sound-treated
room/booth.
n
Receiver: Controlling noise at the receiver involves reducing the noise at the listener’s ear.
Examples include using HPDs and using administrative controls to modify work schedules to
limit workers’ noise exposure.
Types of Hearing Protection
Reducing noise levels at the source or along the path can be expensive. Therefore, use of HPDs is the
most common method for reducing noise exposure. There are many types and styles of HPDs available.
The primary styles are earplugs, earmuffs, and banded earplugs, but special protectors with additional
features are available within these categories. The main types of HPDs include user-molded foam
earplugs, premolded earplugs, push-to-fit (hybrid) earplugs, banded earplugs (semi-inserts or canal
caps), passive earmuffs, flat (uniform) attenuation earplugs, nonlinear-level dependent (amplitudesensitive) devices, devices with amplification (earplugs or earmuffs), noise-isolating entertainment
devices, and communication headsets. Table 8–2 describes advantages and disadvantages of each type
of HPD.
AUDIOLOGY NUGGET
Traditional earplugs and earmuffs attenuate high frequencies more than mid
and low frequencies (Chasin, 2009). This can interfere with speech understanding and music perception. Flat attenuation earplugs and earmuffs (also
called uniform attenuation, high fidelity, or musician plugs) are designed to
provide approximately even attenuation across the frequency range, thus preserving the natural balance between the low-frequency fundamental energy and
the high-frequency harmonic energy. Therefore, flat attenuation earplugs can
be beneficial, not only for music listening but also for situations where speech
understanding is important.
HPD Fitting, Care, and Cleaning
HPDs must be properly worn and cared for in order to achieve the desired noise reduction/attenuation.
The fit of an HPD can be checked visually or acoustically.
n
Visual check: When earplugs with stems are fit properly, only the stem should be visible when
looking at the wearer from the front. Earplugs without stems should not be visible when
viewed from the front. Earmuffs should be worn with the ear cushions surrounding the ears,
pressing tightly against the head.
n
Acoustic check: The fit of earplugs can be checked by having the wearer insert the earplugs
and then cover the ears with his or her hands. If the earplugs are properly inserted, this should
TABLE 8–2. Advantages and Disadvantages of Different Types of Hearing Protection Devices
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TYPE ADVANTAGES DISADVANTAGES
Nonelectronic
User-Molded
Foam Earplugs
Premolded
Earplugs
Push-to-Fit
(Hybrid)
Earplugs
Custom
Earplugs
Inexpensive
Comfortable for longer wearing times
Cooler than earmuffs in hot weather
Range of sizes
Can provide good attenuation if properly
worn
Reusable/washable
Comfortable for longer wearing times
Cooler than earmuffs in hot weather
Range of sizes and shapes
Stem or tab for easier insertion and
removal
Easy to insert
Hygienic to remove/reinsert when hands
are dirty
More comfortable
Better fit
Can be easier to insert
Reusable
— Designed to last an extended
period of time
Can be made for attachment to noise-isolating
entertainment and communication headsets
Not reusable
Easier to lose
Inconvenient for intermittent use
Must wash hands before reinserting
Can be difficult to properly insert
Attenuation varies depending on fit
Slightly more expensive than user-molded
foam earplugs
Must be cleaned after each use
May have to reinsert/adjust fit after
talking/chewing
Attenuation varies depending on fit
Slightly more expensive than user-molded
foam earplugs
Attenuation varies depending on fit
More expensive
Attenuation depends on quality of the
impression and manufacturing
Banded Earplugs
(Semi-Inserts or
Easy to insert and remove
Convenient for intermittent use
Canal Caps)
Passive Earmuffs Easier to fit than earplugs
Comfortable in cold temperatures
Less variability in attenuation
Convenient for intermittent noise
Easier to monitor use because of high
visibility
Special types available for wearing with
other personal protective equipment (e.g.,
back-band earmuffs with welding helmets,
earmuff–hard hat combinations, face
shields, etc.)
More expensive than user-molded foam
earplugs
Greater occlusion effect
Causes an annoying sound when the
band is bumped or hit
Less attenuation than most other types of
earplugs
Higher cost than earplugs (except
custom-molded)
Can be uncomfortable over long periods
of time
Uncomfortable in hot temperatures
Reduced comfort and attenuation when
worn with safety glasses
continues
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not cause any significant change in the subjective noise level perceived by the wearer. The fit of
earmuffs and earplugs can be generally checked by determining if loud sounds become softer
and if the wearer’s voice sounds muffled or hollow.
HPDs must also be appropriately maintained and cleaned. It is important to follow the recom-
mendations specific to each type of HPD.
TABLE 8–2. continued
TYPE ADVANTAGES DISADVANTAGES
Flat (Uniform)
Attenuation
Earplugs
Non-Linear
Level
Dependent
(AmplitudeSensitive)
Devices
Devices with
Amplification
(Earplugs or
Earmuffs)
Equal attenuation for low- and highfrequency noise, creating more natural
sound
Allows for better speech understanding
and music appreciation
Good for environments with moderate
noise levels
Beneficial for workers with hearing loss
Available in noncustom and custom
options
Good for intermittent noise
Allow the wearer to hear soft speech and
warning sounds while attenuating loud
noise
Available in passive (nonelectronic) or
active (electronic) options
Electronic
Allows for better speech understanding
and situational awareness by amplifying
soft sounds and attenuating loud sounds
Especially helpful for impulse noise
May be beneficial for workers with hearing
loss
Slightly higher cost than other earplugs
Less attenuation than other types of
earplugs
More expensive than other earplugs
Only appropriate for specific
environments (e.g., gunfire)
More expensive than nonelectronic
devices
May not be waterproof
Batteries must be replaced
Noise-Isolating
Entertainment
Devices
Communication
Headsets
Appropriate for environments with low
noise levels
May result in greater acceptance and wear
time
Allows for radio communication and noise
attenuation
Improves situational awareness/safety
More expensive than nonelectronic
devices
Not appropriate for all noise
environments
May interfere with situational awareness/
cause safety risks
More expensive than nonelectronic
devices
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n
Foam earplugs: Foam earplugs can only be used two to three times before replacing and should
not be washed. They should be replaced when they do not return to their original shape.
n
Premolded earplugs: Premolded earplugs can be washed using warm water and mild soap
and used for days to weeks. They should be replaced when the flanges are damaged or are no
longer soft.
n
Push-to-fit (hybrid) earplugs: Push-to-fit earplugs can only be used two to three times before
replacing and should not be washed. They should be replaced when the foam does not return
to its original shape.
n
Custom earplugs: Custom earplugs can be washed using warm water and mild soap and used
for years. However, they can shrink and harden over time. The fit can also change due to the
listener’s weight gain or loss.
n
Earmuffs: The earmuff manufacturer’s specific instructions should be followed. The outside
of the earmuff can be cleaned with soap and water. Solvents should not be used, and earmuffs
should not be stored at high temperatures. Earmuffs should be inspected for cracked or
hardened earcup seals and to confirm that headband tension is adequate to maintain adequate
noise reduction.
395
HPD Attenuation
To reduce the risk of developing NIHL, HPDs must provide an appropriate amount of noise reduction/attenuation. The amount of noise reduction/attenuation provided by a person’s HPDs can be
estimated using formulae that incorporate the noise reduction rating (NRR) or directly measured using
different types of field attenuation-estimation systems (FAESs), colloquially referred to as “fit-test”
systems (Voix et al., 2022).
Methods of Estimating HPD Attenuation
The NRR is a single number designed to estimate the amount of attenuation provided by a particular
HPD. In the United States, the Environmental Protection Agency (EPA, 1979) requires the NRR to
be included on HPD packages. The NRR for a particular type of HPD is derived from experiments
where the hearing protector is fit by the experimenter. Open ear and occluded thresholds are obtained
in soundfield using one-third octave band noise. The difference between the occluded and unoccluded
thresholds is the rear ear attenuation at threshold (REAT). Data from at least 10 subjects are collected,
and the NRR is calculated using a formula that involves mean attenuation and standard deviation
across different frequencies. Refer to Rawool (2012) for the NRR formula and an example showing
its calculation.
The NRR can be used in various ways to estimate a person’s noise exposure when wearing a
particular type of HPD. According to the EPA, the adequacy of hearing protection is estimated by
subtracting the NRR of the hearing protector from the worker’s C-weighted TWA noise exposure.
However, OSHA (1983) and NIOSH (1998) require workers’ noise exposure to be measured in dBA.
To account for possible differences between the A-weighted and C-weighted noise exposure values,
OSHA and NIOSH specify that 7 dB should be subtracted from the NRR when it is used with
A-weighted noise exposure values (as shown in the formulae below). OSHA (1983) described both a
required method and a recommended method of estimating HPD attenuation. OSHA (1983) requires
using the following methods of estimating HPD attenuation.
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Q & A
Question: Does the NRR accurately estimate the amount of attenuation
workers receive when wearing hearing protection in the real world?
Answer:
No. Research shows that the attenuation workers receive when wearing
hearing protection in the real world is much less than the labeled NRR (Schulz
& Madison, 2014). On average, the actual attenuation was about one third
to one half of the labeled NRR. Much greater variability across workers is also
seen, with standard deviations being two to three times greater in the real world.
Lower attenuation and greater variability may be seen in the real world because:
n
Workers in real-world settings tend to not fit earplugs as deeply in the
ear canal as when experimenters fit the earplugs for NRR calculation
studies.
n
Earplugs may work themselves loose during a typical work shift as a
worker chews and talks.
n
Earmuffs may not fit as tightly and therefore may provide less
attenuation when worn with safety glasses, goggles, or other personal
protective equipment.
n
When the TWA is measured in dBC: Estimated protected exposure (in dBA) = Unprotected
TWA (in dBC) − NRR
n
When the TWA is measured in dBA: Estimated protected exposure (in dBA) = Unprotected
TWA (in dBA) − (NRR − 7)
However, OSHA (1983) recommends (but does not require) using a more conservative method
in which the NRR is derated to more accurately estimate real-world attenuation.
n
When the TWA is measured in dBC: Estimated protected exposure (in dBA) = Unprotected
TWA (in dBC) − [NRR × 50%]
n
When the TWA is measured in dBA: Estimated protected exposure (in dBA) = Unprotected
TWA (in dBA) − [(NRR − 7) × 50%]
NIOSH (1998) specifies its own recommendations designed to prevent the overestimation of
noise attenuation that can occur when using the NRR. When possible, NIOSH recommends using
subject fit (instead of experimenter fit) data. If subject fit data are not available, NIOSH recommends
using the following deratings of the NRR. Different derating values are recommended for different
types of hearing protection.
n
Foam earplugs
When the TWA is measured in dBC: Estimated protected exposure (in dBA) =
Unprotected TWA (in dBC) − (NRR × 50%)
When the TWA is measured in dBA: Estimated protected exposure (in dBA) =
Unprotected TWA (in dBA) − [(NRR − 7) × 50%]
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n
Other types of earplugs
397
When the TWA is measured in dBC: Estimated protected exposure (in dBA) =
Unprotected TWA (in dBC) − (NRR × 30%)
When the TWA is measured in dBA: Estimated protected exposure (in dBA) =
Unprotected TWA (in dBA) − [(NRR − 7) × 30%]
n
Earmuffs
When the TWA is measured in dBC: Estimated protected exposure (in dBA) =
Unprotected TWA (in dBC) − (NRR × 75%)
When the TWA is measured in dBA: Estimated protected exposure (in dBA) =
Unprotected TWA (in dBA) − [(NRR − 7) × 75%]
In some situations, noise levels can be so high that wearing one type of HPD is not enough to
attenuate the noise to a safe level. Wearing double (dual) hearing protection (e.g., wearing earplugs and
earmuffs simultaneously) is one possible solution. Different organizations have different recommendations for when double hearing protection should be used.
n
OSHA: The OSHA (1983) noise regulation states that employers can require double hearing
protection if there is evidence of progressive NIHL.
n
MSHA: For workers in the mining industry, MSHA requires double hearing protection when
exposure is equal to or greater than a TWA of 105 dBA.
n
NIOSH: To best protect hearing, NIOSH (1998) recommends using double hearing
protection when noise exposure is equal to or greater than a TWA of 100 dBA.
n
Military: The U.S. Marine Corps (n.d.) requires all personnel to wear double hearing
protection when noise exposure exceeds an 8-hour TWA of 100 dBA. The U.S. Army (2015)
requires double hearing protection for those exposed to greater than an 8-hour TWA of
103dBA, whereas the U.S. Navy (2020) requires use of double hearing protection when
noise reaches 104 dBA or greater.
Wearing double hearing protection typically only adds 5 to 10 dB to the maximum attenuation
provided by a single hearing protector. OSHA recommends that to estimate a worker’s noise exposure
when wearing double hearing protection, the previously described formulae are used, but 5 dB is added
Q & A
Question: Does OSHA require employees with hearing loss to wear hearing
protection?
Answer: Although not addressed in OSHA’s (1983) Occupational Noise
Standard 29 CRF 1910.95, OSHA provided clarification on this issue through
an interpretation letter (Fairfax, 2004). The letter states that the noise regulation
applies to all employees, with no exception for those with hearing loss. Hearing
aids worn in the OFF position cannot satisfy the requirement for wearing
hearing protection. OSHA states that employees with hearing loss should wear
their hearing aids with earmuffs that provide sufficient attenuation to reduce
workplace noise to below 85 dBA.
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to the NRR of the HPD with the higher NRR. Therefore, if earmuffs with an NRR of 30 dB and foam
earplugs with an NRR of 20 dB are worn simultaneously, dual protection will provide an estimated
35dB of attenuation if both are worn properly. An NRR of 35 dB could then be used in the previously
described equations to more accurately estimate real-world attenuation.
Measuring the Personal Attenuation Rating (PAR)
When HPD attenuation is estimated, the amount of attenuation a particular person experiences may
be overestimated or underestimated. To best protect hearing, individuals should undergo individual fit
testing to measure the PAR, the amount of attenuation actually provided by an individual’s HPDs as
they are wearing them. The calculated PAR is a more realistic estimate of attenuation provided to an
individual in “real-world” use, rather than predicting attenuation from laboratory data as derived using
the NRR. Results of HPD fit testing can be used to train employees on proper HPD fit, teach people
how to train employees on proper HPD fit, help ensure HPDs are providing enough attenuation,
provide documentation of HPD attenuation, and help with selection of appropriate HPDs.
Different types of HPD fit testing are available (Hager, 2011). Some test methods allow the individual to wear their own HPDs, and others require the individual to wear HPDs that are specifically
designed to be used with the fit test equipment.
n
REAT: This method involves measuring thresholds in soundfield with and without the listener
wearing their HPDs. One-third octave bands of noise are typically used as the stimulus signal.
The amount of attenuation provided by the HPDs is calculated as the difference between
the thresholds obtained with and without the HPDs. REAT is considered the gold standard
for HPD fit testing, and it can be performed using any type of earplug or earmuff. However,
REAT can be more time-consuming than the other methods of HPD fit testing.
n
Field microphone-in-the-ear (F-MIRE): For F-MIRE testing, a probe microphone is placed in
the ear canal, and real ear insertion gain is measured in the unoccluded condition (i.e., without
hearing protection) and the occluded condition (i.e., with hearing protection). Attenuation
is represented by negative deviation from 0 dB. One disadvantage of commercially available
F-MIRE systems is that they require use of special earplugs with the probe built in, which are
not available for many earplug models.
n
Loudness balance systems: With loudness balance systems, the listener wears headphones and
adjusts the volume until the sound is of equal loudness in both ears. This process is completed
in the unoccluded condition (i.e., without hearing protection), in the occluded right ear
condition (i.e., with hearing protection only worn in the right ear), and in the occluded left
ear condition (i.e., with hearing protection only worn in the left ear). The amount the level
had to be increased in the occluded ear to be perceived as equally loud to the unoccluded
ear is the calculated PAR, which estimates the attenuation provided to the individual being
tested. Some disadvantages of loudness balance fit testing include that it can only be used with
earplugs and can be difficult for workers with hearing loss to perform.
Audiometric Monitoring
The purpose of audiometric monitoring is to identify signs of NIHL early so that steps can be taken
to prevent the hearing loss from progressing. For nonoccupational noise exposure, hearing screening is
often recommended for children and adults. However, it is possible to pass a hearing screening and still
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399
have permanent NIHL. For example, in the early stages of NIHL, hearing thresholds can still be within
normal limits, despite having a noticeable “noise notch” that would only be seen if a threshold puretone evaluation is performed. In other cases, the noise notch may occur at a frequency not included
in a typical hearing screening (e.g., 3000 or 6000 Hz). Therefore, best practice is to recommend an
annual audiological evaluation for any child or adult exposed to high noise levels to monitor their
hearing sensitivity.
For occupational noise exposure, different organizations have different regulations/recommendations related to audiometric monitoring. OSHA (1983) and NIOSH (1998) both state that
audiometric monitoring should:
n
Be available for/provided to all employees exposed to an 8-hour TWA of 85 dBA or greater
n
Be performed by a licensed audiologist, a physician, or a technician certified by the Council
for Accreditation in Occupational Hearing Conservation (CAOHC), working under the
supervision of an audiologist or physician
n
Include air-conduction, pure-tone audiometry at 500, 1000, 2000, 3000, 4000, and 6000 Hz
There are some differences between the OSHA (1983) and NIOSH (1998) audiometric monitoring requirements/recommendations. For example, while OSHA will allow someone without training to
use a microprocessor audiometer, NIOSH has strongly recommended against this practice. In addition,
OSHA does not require testing 8000 Hz, but NIOSH considers inclusion of 8000 Hz to be a best
practice option since it is a useful source of information about the etiology of a hearing loss (i.e., the
presence of “noise notches” at 6000 Hz) for audiologists and physicians in their review of audiograms
for determination of NIHL and work-related hearing loss.
Test Environment and Equipment
Occupational standards do not require that audiometric monitoring be performed in a sound booth.
However, in order to help ensure valid results, background noise levels in rooms where audiometric
testing is performed must not exceed specified limits. As shown in Table 8–3, OSHA (1983) allows
higher levels of ambient background noise than those allowed by ANSI S3.1–1999 (as cited in Frank,
2000). Previous research has shown that in audiometric test rooms where ambient noise levels are at
the OSHA MPANLs, hearing thresholds cannot be accurately measured down to 0 dB HL (e.g., Berger
& Killion, 1989, as cited in Frank & Williams, 1994).
OSHA and NIOSH also require that audiometers (whether manual or microprocessor) meet
certain requirements (Danielson, 2014). OSHA requires that the operation of the audiometer be
checked before each day’s use with a daily (biological or bioacoustic) calibration check and functional
TABLE 8–3. Maximum Permissible Ambient Noise Levels (Measured in dB SPL) in Audiometric Test
Rooms Allowed by OSHA (1983) and ANSI (S3.1–1999)
125 Hz 250 Hz 500 Hz 1000 Hz 2000 Hz 4000 Hz 8000 Hz
OSHA (1983) 40 40 47 57 62
ANSI
(S3.1–1999)
49 35 21 26 34 37 37
Difference 19 14 13 20 25
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(listening) check. The audiometer must also meet ANSI S3.6–1969 requirements for calibration,
which includes an annual acoustical check and an exhaustive calibration every 2 years. NIOSH recommends that audiometers meet ANSI S3.6–1996. Calibration should include a daily functional check,
an acoustical check when the daily check shows a threshold difference greater than 10 dB in either
headphone at any frequency, and an exhaustive calibration every year or when the acoustic check
indicates the need.
Baseline and Annual Audiograms
The baseline audiogram is meant to document a worker’s hearing thresholds prior to being exposed to
noise at a particular job. These baseline thresholds are used in comparisons with results of subsequent
periodic audiograms.
n
OSHA (1983) requires that the baseline audiogram be performed within 6 months of
exposure at or above a TWA of 85 dBA or within 1 year if testing is conducted using a mobile
test van. The baseline audiogram must be preceded by at least 14 hours without workplace
noise exposure (i.e., noise-free period), but if this is not feasible, the worker can wear hearing
protection instead.
n
NIOSH (1999) recommends that the baseline audiogram be performed before employment
or within 30 days of employment for workers exposed to a TWA of 85 dBA or greater.
The baseline audiogram must be preceded by at least 12 hours of quiet, and use of hearing
protection cannot be substituted.
Each year the annual audiogram is compared to the baseline audiogram to determine if the worker
has experienced a decline in hearing that could be due to occupational noise exposure.
n
OSHA (1983) requires that annual audiometric testing be performed for all employees with
noise exposure at or above a TWA of 85 dBA. The annual audiogram can be obtained any
time during the work shift, but testing at the end of the work shift to account for the exposure
is encouraged.
n
NIOSH (1998) recommends that the annual audiogram (i.e., the monitoring audiogram)
be performed for all employees with noise exposure at or above a TWA of 85 dBA. The test
should be scheduled at the end of or late in the work shift to detect any TTSs.
Threshold Shift
A worker’s baseline audiogram is compared to the annual audiogram to determine if a significant change
in hearing has occurred. Although there are some similarities, OSHA (1983) and NIOSH (1998)
differ in some of the specific requirements/recommendations for determining whether a significant
change in hearing has occurred and what the subsequent actions should be.
n
OSHA (1983) refers to a significant change in hearing as a standard threshold shift (STS).
An STS is defined as an average change of 10 dB or more at 2000, 3000, and 4000 Hz
in either ear when compared to the baseline audiogram. The results must be reviewed by
an audiologist or physician, and a retest can be performed within 30 days. If the annual
audiogram showing an STS is determined to be valid, it becomes the worker’s new baseline.
An employee who is identified as having an STS must be notified in writing of the test
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results within 21 days. OSHA permits use of age corrections when determining if an STS has
occurred (i.e., a portion of the change in hearing is attributed to age and subtracted from the
STS calculation).
If an STS is identified, the following actions are required: fit, train, and require HPD
use; refit and retrain employees who have previously worn hearing protection; refer
for evaluation by an audiologist or otolaryngologist if a medical pathology of the ear is
suspected; and notify employees when an otologic exam is needed for an ear problem that is
nonwork related.
OSHA requires that a hearing loss be recorded in the OSHA 300 Log of Work-Related
Injuries and Illnesses when an STS is present (age corrections are allowed); the current
audiogram shows hearing thresholds of an average of 25 dB HL or greater at 2000, 3000,
and 4000 Hz (in the same ear that showed the STS); and the shift in hearing is related to
occupational noise exposure (Wells, 2014).
n
NIOSH (1998) refers to a significant change in hearing as a significant threshold shift, defined
as a change of 15 dB or more in either ear at any of the following frequencies: 500, 1000,
2000, 3000, 4000, or 6000 Hz. The results must be reviewed by an audiologist or physician,
and a retest can be performed immediately or within 30 days. The annual audiogram with
the significant threshold shift becomes the new baseline. If a significant threshold shift is
identified, the employee must be notified within 30 days. NIOSH recommends that age
corrections not be used when calculating a significant threshold shift.
401
If a significant threshold shift is identified, a minimum of the following actions is
recommended: reinstruct and refit hearing protection, retrain on worker responsibilities for
hearing conservation, and/or reassign the worker to work in a quieter area.
Threshold Shift Case Example
A 40-year-old male has worked at a tire manufacturing plant for 15 years. At his current annual
audiometric evaluation, a change in hearing is seen in both ears. The first two lines of Table 8–4 show
the worker’s right ear thresholds at the baseline and current audiometric evaluations. The first two lines
of Table 8–5 show his left ear thresholds for the baseline and current audiometric evaluations. OSHA
(1983) defines an STS as an average change of 10 dB or more at 2000, 3000, and 4000 Hz in either
ear compared to the baseline audiogram. As shown below, the change in hearing in each ear meets the
criteria for an STS.
n
Right ear
Baseline average of 2000, 3000, and 4000 Hz = 11.67 dB
Current average of 2000, 3000, and 4000 Hz = 25 dB
Shift = 13.33 dB
n
Left ear
Baseline average of 2000, 3000, and 4000 Hz = 13.33 dB
Current average of 2000, 3000, and 4000 Hz = 25 dB
Shift = 11.67 dB
Given that the shift in the average of 2000, 3000, and 4000 Hz is at least 10 dB in each ear, the
employee would be considered to have had an STS. However, OSHA (1983) allows use of age correction
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