This Fact Sheet Courtesy Of
House Ear Institute and
Drew Daniels, Electroacoustics Engineer
NOISE-INDUCED HEARING LOSS
(NIHL) FACT SHEET 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 100-20,000 Hz, the 2-5 kHz
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 50-70 dB, while the extreme noise level of a rock
concert might be measured at 100-120 dB. Over-exposure to high intensity sound
is a leading cause of damage to sensory ("hair") cells. Prolonged
exposure to sounds above 85 dB may cause permanent hearing loss. Some examples of loud sounds that can cause NIHL are: · Motorcycle/Hair dryer/Lawn mower/Leaf blower 85-90 dB · Wood shop/Chainsaw/Firecrackers (small) 100-110 dB · Rock concerts 110-120
dB · Ambulance Siren/Jet Engine at Take-Off/Pneumatic Drill 119-140 dB
EFFECTS
OF NIHL: When damage first occurs, it usually affects the part of
the ear corresponding to the mid-frequency range of 3 to 5 kHz. 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.
SAFE
SOUND LEVELS:
The 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. Exposure to 115+ dB or
greater may pose a serious health risk. 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 ·
Hypersensitivity ·
Loss of sensitivity PUBLIC AWARENESS OF NIHL: THINGS TO CONSIDER 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. ·
Of 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. ·
Some types of hearing loss may be signs of a medical
condition. ·
If you notice a change in your hearing you should have an
evaluation by an ear specialist, such as an otolaryngologist (ENT), otologist,
neurotologist, or audiologist. ·
Keep track of your hearing sensitivity and changes over
time. ·
If you constantly work around high levels of sound, you
should have your hearing tested by a licensed audiologist at least once a year. ·
Hearing 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. TIPS FOR PREVENTING NIHL: WHEN NOISE BECOMES A HAZARD: ·
Intensity of the sound signal ·
Prolonged exposure to sound levels greater than 85 dB ·
Repeated or cumulative exposure ·
Individual susceptibility CONSERVATION TIPS: ·
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 listening. CONTACT INFORMATION: Marilee
Potthoff Marketing Department House Ear Institute Phone: 213- 483-4431 /FAX:
213 483-8789 E-mail: soundpartners@hei.org © House Ear Institute
See also: Ear Plug Infohttp://www.etymotic.com/ |
