Encyclopedia of Health and Medicine

nose 37
Most hearing experts agree that exposure to
sounds louder than 85 dB begins to damage the
hair cells in the COCHLEA, which activate the nerves
that translate sound waves into NERVE impulses.
Sounds at higher frequencies (2,000 Hz and
above) do more damage at the same decibel level
than sounds at lower frequencies (under 800 Hz).
Much of human conversation takes place between
2,000 Hz and 4,000 Hz. Damage to the hair cells
responsible for sound translation in this frequency
range is particularly devastating.
Noise Exposure
Nearly everyone faces exposure to noise at levels
capable of causing damage to the hair cells and
ultimately hearing loss. The sounds of city traffic,
a noisy restaurant, and a flushing toilet all measure
in at about 85 dB. The US Occupational Safety
and Health Administration (OSHA) has established
regulations limiting noise exposure in the
workplace. These regulations stipulate the amount
of time an employee may experience noise exposure
at certain decibel levels, prohibit exposure
without protection to sounds over 115 dB, and
prohibit exposure of any kind to sounds over 140
dB. The OSHA Web site (www.osha.gov) publishes
current noise regulations and guidelines.
Musicians face the unique conundrum of needing
to hear the full range of pitch while protecting
their hearing from its intensity, particularly in
group settings such as playing in a band or orchestra.
Yet musicians playing in a rock concert may
experience bursts of exposure at 150 dB, as loud
as a jet taking off, which causes permanent damage
to the inner ear after only a minute or two.
The audience at a symphony concert experiences
a sound level of 110 dB, equivalent to a car horn,
and peaks near 140 dB. Musicians playing the violin,
flute, and trombone face continued exposure
to 110 dB or greater at frequencies above 2,000
Hz, among the most damaging of exposures. People
who work in construction, steel working, mining,
air travel, manufacturing, and public safety
also face increased exposure to noise that threatens
hearing.
Noise exposure exists in personal environments
as well. Appliances such as hair dryers, blenders,
coffee grinders, and even coffee makers can generate
90 dB of sound or louder. The decibel level of
movies on television or in theaters can exceed 120
dB. Stereos played beyond the halfway point on
the volume indicator, especially when using headphones,
quickly pass the 100 dB mark. Children’s
noise-making toys can reach 110 dB to 140 dB.
Ear Protection
The most effective protection against noise exposure
is to avoid it. As this is not always practical or
possible, health experts recommend (and in the
workplace OSHA requires) wearing hearing protection
for exposure to sound at 90 dB for longer
than eight hours and for any exposure that
exceeds 90 dB. There are two kinds of ear protection:
ear plugs and ear muffs.
Ear plugs fit snugly into the auditory canal and
block sound waves from traveling to the middle
and inner ear. They are available in various materials
and in different sizes and shapes; finding ear
plugs that fit properly and comfortably can take
some experimentation. Custom ear plugs are also
available, made specifically to fit an individual’s
ears. A common complaint about ear plugs is that
they block so much sound that conversation is difficult.
This dampening of the sound is called attenuation.
Some designs of ear plugs contain
channels that allow sounds at certain frequencies
to pass through. This improves the ability to hear
and understand speech. Customized ear plugs for
musicians can block selected sounds so the musician
can hear the tones and pitches necessary to
play or sing.
Ear muffs fit over the ears with a strap that holds
them in place. They form a seal around the ear,
which prevents sound waves from traveling into
the auditory canal. As with ear plugs, there are various
designs that offer different levels of effectiveness
and comfort. Ear muffs tend to muffle all
sound, though ear muffs and ear plugs have comparable
ability to block noise, about 30 dB. People
exposed to noise louder than 100 dB to 110 dB
should use both ear plugs and ear muffs, which in
combination can block up to about 45 dB.
See also AUDIOMETRIC ASSESSMENT; COCHLEAR
IMPLANT; HEARING AID; OCCUPATIONAL HEALTH AND
SAFETY.
nose The facial structure that serves as the organ
of smell as well as the portal through which air