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NOISE-INDUCED HEARING LOSS
This is deafness caused by too much noise. Loud sound destroys the tiny hairlike cells in the inner ear that do the actual hearing.
Loud noise is one of the most common causes of
deafness. As many as 5% of adults have been diagnosed with this kind of hearing problem, countless others suffer without seeking medical attention. This is not surprising as noise induced deafness is permanent and
incurable. Hearing aids can help, but they can't fully correct it.
This kind of hearing loss can be prevented by staying away from loud and sustained noises.
HOW LOUD ARE THOSE SOUNDS THAT HURT?
You may be exposed, at work or through lifestyle; to noise that hurts your hearing. If you have to shout when you talk to a co-worker or friend who is standing next to you, the noise
level is at a dangerous level.
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Common Noises That Might Hurt Your
Ears Include:
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Firearms
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140 to 170 decibels
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Pain threshold
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130 decibels
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Jet aircraft taking off (heard from runway)
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120 to 140 decibels
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Chain saw, rock concert
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110 to 120 decibels
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Personal stereo players, home and commercial music systems
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100 decibels
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Motorcycle, lawnmower
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95 decibels
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Both the loudness and the length of time you hear the noise are important. Sound is measured in decibels. Eight hours of suffering noise at 85 decibels could hurt your hearing. At higher sound levels,
you could lose hearing in even less time. Some sounds take only minutes to damage your hearing for life.
By UK law, employers must start to take measures to save the hearing of their
workers in workplaces where noise reaches 85 decibels or more. This means that the noise has to be monitored, and hearing protection provided for those who
request it. After 90 decibels the noise exposure has to be reduced in addition to providing free hearing protection devices to workers. See HSE leaflets for more
information.
HOW TO RECOGNISE NOISE INDUCED DEAFNESS
This usually happens slowly. There is no pain. After being in noise, you may notice a "ringing" sound in your ears. You might have trouble hearing people talk. After several hours or even a few days, these symptoms usually go away.
However, damage has already been done and when you are exposed to this kind of noise again, you could get a hearing loss that lasts forever. Each noise assault adds to the previous one to produce permanent deafness.
Early signs of noise-induced deafness include the following:
- Having trouble understanding what people say, especially in crowded rooms
- Needing to turn the TV sound higher (others tell you of this!)
- Having to ask people to repeat what they just said to you (sometimes
three times and then you give up because its embarrassing)
- Not being able to hear high-pitched sounds, like a baby crying or a
telephone ringing in another room
Along with the hearing loss, you may also have ringing in the ears, called tinnitus.
The only way to find out if you have a hearing loss is to have your hearing tested by a trained professional.
HOW TO PREVENT NOISE INDUCED DEAFNESS
- Make the health of your ears a part of your lifestyle. Stay away from loud
or prolonged noise. Turn down the music volume. Buy power tools that have sound controls.
- When you must be around noise, either at work or at play, use something
to protect your hearing.
- Hearing protection devices, like earplugs, earmuffs and canal caps, are sold
in chemist shops and hardware stores. Different brands offer different amounts of protection. If you are not sure which kind is best for you, or
how to use it correctly, ask your doctor. Often the best kind is the one that you feel comfortable in so you can wear it when you need it.
- Keep your hearing protectors handy and in good condition.
- Inform your family and friends how important it is to stay away from too
much noise and to use hearing protection.
- If you think you have a hearing loss (or if someone suggests that you
have), it is important to have your hearing tested.
INFORMATION ON DECIBELS
The unit of power ratio, the Bel, was named after Alexander Graham Bell, inventor
of the telephone who wanted to measure the loss of signal over long phone wires. Technically, it is a logarithmic scale used to compare sound intensity or
electric current levels. A Bel is a ratio of one number to another. In measuring sound, the pressure waves can be recorded by a sensitive detector. If the
pressure required at a given frequency to reach the threshold of normal hearing is increased by tenfold then that second sound pressure is a Bel above the first.
The human ear can detect sounds with an intensity as low as a million-millionth of a Watt per square metre, and as high as 1 Watt per square metre. This is a
huge range of intensity; and is why we don't perceive loudness as proportional to intensity. To produce a sound that seems to humans about twice as loud requires a sound wave that has about ten times the intensity.
The Bel is an unwieldy and large unit, and the decibel (dB), a tenth of a Bel, is more convenient. The decibel is used to express power, but it doesn't measure
power. It is in fact a ratio of two power levels. A ratio of 3 decibels means a doubling of sound pressure. 6 decibels is a doubling of the doubling and is
therefore an increase of 4 times. 9 decibels means an increase of 8 times and so on. By the time you reach 80 decibels the sound pressure has increased by 100
million times. Another 3 decibels to 83 doubles this again to 200 million times the original threshold pressure.
Noise is measured in decibels and anything 80 decibels or higher is potentially
damaging, particularly with sustained exposure. The louder the sound, the less exposure is needed to cause damage. A lawn mower producing a 95 decibel
sound level will cause hearing loss in four hours, while a rock concert or amplified sound producing 110 decibels can cause damage in half an hour. At 160 decibels instant hearing loss occurs.
Sources:
Dr. Ronald Hoffman, Medical Director of the Hoffman Centre, New York
http://www.drhoffman.com
American Academy of Family Physicians May, 2000
http://www.aafp.org/afp/20000501/2749.html
Further reading:
Health & Safety Executive demonstration
Royal National Institute for the Deaf
BUPA
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