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Sound
& Noise
Sound is caused by pressure variation in an elastic medium,
usually air, with characteristics of frequency measured in
cycles/second or Hertz (Hz, perceived as pitch), and intensity
measured in decibels (perceived as loudness). Noise is considered
to be unwanted sound. While the human ear can hear from about
50-20,000 Hz, the speech range is between 1000 and 3000 Hz. Noise
induced hearing loss typically occurs at about 4000 Hz, but with
continued exposure spreads above and below. The bulk of hearing
loss resulting from noise occurs in the first decade of exposure.
Other
characteristics may influence the effects of sound. Noise can be
continuous, intermittent, impulse or impact and may be for a short
or long duration. Temporary hearing loss may follow a noise
exposure. If exposure is continued, permanent loss may result.
Experience
has shown extreme exposure up to 80 dB of sound causes insignificant
hearing deficits except in sound-sensitive individuals. At 85 dB
however, more and more people may have injury. If you need to
shout to communicate at 2-3 feet, you have probably been exposed to
enough noise to cause damage in the majority of people. Prolonged exposure may cause hearing loss that is permanent and
untreatable. Initially higher
frequency consonants, greatest 4000 to 6000 MHz are lost or confused making for example
“bark” sound like “shark” or “ark”. As hearing loss
continues, vowels begin to be confused as well. Sometimes hearing
loss is accompanied by just the opposite - Tinnitus - or hearing
sounds, ringing, chirping that is not really there. This is
subjective and so not measurable, but can be very distracting and
irritating.
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Examples
of Noise Exposure:
| chain
saw |
100-115
dB |
| snow
machine with wind effects |
85-110
dB |
| vacuum
cleaner |
60-85
dB |
| food
blender |
62-85
dB |
| heavy
truck at 50 ft |
78-90
dB |
Regulations
The Occupational Safety and Health Administration (OSHA) and the
Mine Safety Health Administration (MSHA) have regulations
concerning noise exposure in industry, construction, and mining.
The Federal Railroad Administration (FRA) and Federal Aviation
Administration (FAA) define hearing criteria for engineers, and
pilots. For more information on the regulations concerning your
job, please speak with your company safety officer.
Audiogram
Testing
Audiogram testing is a screening method that tests pure sounds
with an arbitrary zero reference level. If you can hear these
tones up to 25 dB, your hearing is considered to be normal. This
testing does not discriminate between causes of loss, and if your
levels are significantly above 25 dB, or one ear is significantly
worse than the other, you may be referred to a specialist to
determine other causes of hearing loss or ear disease. MOMC does
hearing testing using a standard
technique to help to get the best test available and allows
comparison of your tests year to year to eliminate errors. Our
technicians are certified by the Council For Accreditation In
Occupational Hearing Conservation (CAOHC), our equipment is
approved by the National Institute for Occupational Safety and
Health (NIOSH), and our booth is OSHA certified. To avoid any
effects of temporary hearing loss, we suggest that you precede
your testing with a 14 hour noise free period, and avoid testing
when you have recently traveled or had a head cold. Your ears will
be examined to detect wax buildup and other diseases and you will
be asked to complete a hearing questionnaire so we can interpret
your audiogram more accurately.
Hearing
Protectors
Hearing protection is optional for an employee exposed to noise
levels below 90 dB, but you might want to consider using
protection anyway if you perceive your work area as loud.
Employees must use hearing protection if they are exposed to
levels greater than 90 dB or they have been shown to have a loss
of hearing with annual surveillance. Although hearing protection
can reduce noise exposure, they can also interfere with hearing
ability and communication needs. Equipment should be compatible
with other safety equipment, comfortable, and used and cared for
properly. Various types of hearing protection include earplugs,
canal caps, ear muffs, non-linear protectors, and noise
cancellation devices. Look for the Noise Reduction Rating (NRR) of
your selected hearing protection. This is the amount of noise
reduction in ideal circumstances. To determine “real world
values”, we recommend you divide the number by 2. For example,
if you are in an environment with 90 dB ambient noise exposure and
you are wearing ear plugs with an NRR of 16, your exposure is 90 -
8 = 82 dB. If you wear a second type of hearing protection, for
instance earplugs + muffs, you should divide the NRR of the higher
device by 2, then add 5 for the second device. (Two are not twice
as good.) The best hearing protector is one that is used
consistently.
Non-Occupational
Exposure
Non-occupational noise exposure can also lead to hearing loss.
Saws, snow-machines, loud vacuum cleaners, power tools, etc. may
all contribute to your hearing loss.
OSHA
regulation
(opens
in new window):
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http://www.osha-slc.gov/OshStd_data/1910_0095.html
CAOHC (opens
in new window):
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http://www.caohc.org/
ACOEM (opens
in new window):
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http://www.acoem.org/guidelines/article.asp?ID=53
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