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Noise-Induced Hearing
Loss (NIHL)
Of
the roughly 40 million Americans suffering from
hearing loss, 10 million can be attributed to
noise-induced hearing loss (NIHL). NIHL can be
caused by a one-time exposure to loud sound as
well as by repeated exposure to sounds at various
loudness levels over an extended period of time.
Damage happens to the microscopic hair cells
found inside the cochlea. These cells respond to
mechanical sound vibrations by sending an
electrical signal to the auditory nerve.
Different groups of hair cells are responsible
for different frequencies (rate of vibrations).
The healthy human ear can hear frequencies
ranging from 20Hz to 20,000 Hz. Over time, the
hair cell's hair-like stereocilia may get damaged
or broken. If enough of them are damaged, hearing
loss results. The high frequency area of the
cochlea is often damaged by loud sound.
Sound pressure is measured in decibels (dB). Like
a temperature scale, the decibel scale goes below
zero. The average person can hear sounds down to
about 0 dB, the level of rustling leaves. Some
people with very good hearing can hear sounds
down to -15 dB. If a sound reaches 85 dB or
stronger, it can cause permanent damage to your
hearing. The amount of time you listen to a sound
affects how much damage it will cause. The
quieter the sound, the longer you can listen to
it safely. If the sound is very quiet, it will
not cause damage even if you listen to it for a
very long time; however, exposure to some common
sounds can cause permanent damage. With extended
exposure, noises that reach a decibel level of 85
can cause permanent damage to the hair cells in
the inner ear, leading to hearing loss. Many
common sounds may be louder than you think…
A typical conversation occurs at 60 dB - not loud
enough to cause damage.
A bulldozer that is idling (note that this is
idling, not actively bulldozing) is loud enough
at 85 dB that it can cause permanent damage after
only 1 work day (8 hours).
When listening to music on earphones at a
standard volume level 5, the sound generated
reaches a level of 100 dB, loud enough to cause
permanent damage after just 15 minutes per day!
A clap of thunder from a nearby storm (120 dB) or
a gunshot (140-190 dB, depending on weapon), can
both cause immediate damage.
In fact, noise is probably the most common
occupational hazard facing people today. It is
estimated that as many as 30 million Americans
are exposed to potentially harmful sounds at work.
Even outside of work, many people participate in
recreational activities that can produce harmful
noise (musical concerts, use of power tools, etc.).
Sixty million Americans own firearms, and many
people do not use appropriate hearing protection
devices.
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