Description Of NIHL:
When an individual is over-exposed to excessive sound
levels, sensitive structures of the inner ear can be damaged. This can
result in permanent noise-induced hearing loss (NIHL). These structures
can be injured by exposure to a brief but intense sound, such as an
explosion, or from regular exposure to excessive sound levels over time.
NIHL can be prevented through the control of sound levels or proper use of
hearing protection devices (HPDs), such as earplugs or earmuffs.
Measurements That Determine Which Sounds Cause NIHL:
Sound pitch or frequency is measured in Hertz (Hz).
Although the human ear collects sounds ranging from 100Hz to 20kHz, the
2kHz to 5kHz frequency range is where most of the spectral cues for speech
are found. Sound pressure levels are measured in decibels (dB). Normal
conversation is measured at a moderate noise level of 50dB to 70dB, while the
extreme noise level of a rock concert might be measured at 100dB to 120dB.
Over-exposure to high intensity sound is a leading cause of damage to
sensory ("hair") cells. Prolonged exposure to sounds above 85dB
may cause permanent hearing loss. Some examples of loud sounds that can
cause NIHL are:
Normal inner ear "hair" cells
Motorcycle/Hair dryer/Lawn mower/Leaf blower
Wood shop/Chainsaw/Firecrackers (small)
Ambulance Siren/Jet Engine at Take-Off/Pneumatic Drill
Effects Of NIHL:
Damaged inner ear "hair" cells
When damage first occurs, it usually affects the part of
the ear corresponding to the mid-frequency range of 3kHz to 5kHz. On an
audiogram, this type of hearing loss configuration is commonly referred to
as a "noise notch." These frequencies correspond to the region
where our consonant sounds are heard. A person with this type of hearing
loss may have trouble understanding speech because the speech sounds
"muffled." It is common for individuals with this type of
hearing loss to report "I can hear you; I just can’t understand
you." This is because the louder, lower frequency vowels are audible
but the softer high frequency consonants are made even more difficult to
hear, due to reduced hearing sensitivity in that spectral region.
Hearing loss may or may not be accompanied by tinnitus
– a ringing, buzzing or fluttering in one or both ears. While normal
hearing people may also have tinnitus, it is usually symptomatic of some
sort of high frequency hearing loss. Sometimes short duration exposure to
sound may only cause temporary hearing loss. Temporary hearing loss is
called a temporary threshold shift. This means that if a sound was
first heard at some level of intensity, after over-exposure to loud
sounds, that same sound would need to be louder in order to be heard. A
temporary threshold shift usually disappears within 14-16 hours after
over-exposure to loud sound. Cumulative over-exposure to loud sounds will
eventually result in a "permanent threshold shift," e.g. a
permanent hearing loss.
|Warning Signs And
Symptoms of NIHL:
Temporary threshold shift
Ear discomfort after exposure
Ringing or buzzing sensation in the ears
Difficulty hearing in noise
Evidence Of Over-Exposure:
Tinnitus or head noise
High frequency hearing loss
|Tips For Preventing
Noise Becomes A Hazard:
Intensity of the sound signal
Prolonged exposure to sound levels greater than 85dB
or cumulative exposure
Avoid hazardous sound environments.
If you are in an environment where you must raise your voice to be heard,
you are in a potentially hazardous environment for your hearing. This
includes loud music performances (regardless of musical genre), and
activities such as operating power tools, driving loud vehicles, or
driving with the windows down, etc.
Use hearing protection devices (HPDs) - such as foam earplugs, earmuffs or
custom earplugs - whenever possible.
Custom-molded earplugs offer "flat" attenuation and may make
listening to loud music more enjoyable than standard earplugs that may
filter more high frequencies than low frequencies.
Musicians should avoid practicing at "concert hall levels" as
much as possible.
Monitor sounds in excess of 85 dB.
Take 15-minute "quiet" breaks every few hours.
Move away from on-stage monitors or amplifiers, or reposition yourself so
you are not directly in front of the speaker while performing or
|Safe Sound Levels:
National Institute for Occupational Safety and Health (NIOSH) guidelines
are stated in terms of the maximum time that you can safely be exposed to
different time-weighted averages (TWAs) of sound pressure on a daily basis
over a 40-year period.
TWA Decibel Levels Max. Exposure
85dB . . . . . . . . . .
. . . . . . 8 hours
88dB . . . . . . . . . . . . . . . . 4 hours
91dB. . . . . . . . . . . . . . . .. 2 hours
94dB . . . . . . . . . . . . . . . . 1 hour
97dB . . . . . . . . . . . . . . . . 30 minutes
100dB . . . . . . . . . . . . . . . . 15 minutes
103dB . . . . . . . . . . . . . . . . 7-1/2 minutes
106dB . . . . . . . . . . . . . . . . 3-3/4 minutes
Exposure to 115+dB or greater
may pose a serious health risk.
|Public Awareness Of
More than 20 million Americans of all ages are regularly exposed to
dangerous levels of sound. Exposure occurs at work, home and in
recreational activities. We can damage our ears while listening to stereos
or attending movies, concerts, bars, and health clubs where music and
other sounds are amplified. Even wearing headphones can be dangerous if
the volume is too loud.
the 28 million Americans who have some degree of hearing loss, about
one-third have damaged their hearing from excessive exposure to sound.
Not all hearing
loss is caused by exposure to loud sound. Some types of hearing loss are
reversible with medical intervention.
of hearing loss may be signs of a medical condition.
notice a change in your hearing you should have an evaluation by an ear
specialist, such as an otolaryngologist (ENT), otologist, neurotologist,
of your hearing sensitivity and changes over time.
constantly work around high levels of sound, you should have your hearing
tested by a licensed audiologist at least once a year.
tests include pure tone threshold testing (the traditional hearing test),
tests of middle ear function, otoacoustic emissions testing, and the
"Hearing In Noise Test" ("HINT"), which assesses
speech perception in noise, similar to an everyday listening situation.
Otoacoustic emissions have been reported to be more sensitive to subtle
damage in the inner ear than the pure tone threshold test. The HINT is
better than pure tone threshold audiometry for indicating how well an
individual hears in real-world situations. These tests together, however,
can give your hearing care provider important information for assessing
your hearing health.