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SAFETY FOCUS

Noise Induced Hearing Loss

By Mitch Kruse,

Manager of Environmental Health and Safety

In the United States, hearing loss is the third most common physical condition after high blood pressure and
arthritis. It occurs naturally as you age, as result of a health condition such as diabetes, and can even occur from tak-
ing certain medications or being exposed to certain chemicals which are ototoxic. The most common cause of hear-
ing loss is noise induced hearing loss from over exposure of loud noise. Approximately 22 million U.S. workers are
exposed to hazardous levels of noise at work. Not surprisingly, hearing loss is one of the most common work-related
illnesses. Unlike other injuries or illnesses, almost all work-related hearing loss is permanent. When your hearing is
damaged from overexposure to noise, there is no way to repair it. This is why it is critically important to understand
how this injury occurs and how to protect yourself.
When the human ear is exposed to the sound waves created by noise, the wave passes through the outer ear
into the tympanic membrane. This membrane, also known as the ear drum, separates the outer ear from the middle
ear. When the sound wave vibrates this membrane, the vibrations are picked up by sensory hair cells in the inner ear
and translates them into electrical signals that the brain can interpret and distinguish as sound. Exposure to loud noise
can overwork the hair cells in the ear, which can cause these cells to die. For example, after leaving a very loud event,
such as a concert or football game, you may notice that you don’t hear as well as before. You might not hear whis-
pers, sound might seem muffled, or you may hear ringing in your ears. Normal hearing usually returns within a few
hours to a few days. This is because the hair cells, similar to blades of grass, will bend more if the sound is louder. But
they will become straight again after a recovery period. The risk of damaging your hearing from noise increases with
the sound intensity. If loud noise damaged too many of the hair cells, some of them will die. Repeated exposures to
loud noises will over time destroy many hair cells. This can gradually reduce your ability to understand speech in
noisy places. Eventually, if hearing loss continues, it can become hard to understand speech even in quieter places.
You can typically tell if the noise around you is too loud even without a specific device to measure the sound.
If you or others need to shout in order to be heard or cannot understand each other even at arm’s length away, the
sound is too loud and may damage your hearing. The table below shows the sound level of common sources and how
they may affect your hearing.
The best way to protect yourself from noise is to minimize your exposure. Although it cannot always be
achieved, reduction of the noise is always the best control. Make sure equipment is being maintained by replacing
worn, loose, or unbalanced machine parts. Keeping equipment well lubricated and maintained reduces noise genera-
tion potential. Decreasing the total time of exposure will also help minimize potential of hearing loss. Work should
be planned to reduce the time spent in noisy environments or to isolate noise to specific locations. Finally, if the noise
source or exposure time cannot be reduced, hearing protection devices such as earplugs and earmuffs must be worn.
Make sure that you keep hearing protection in a convenient place and are wearing it properly. Hearing protection
that does not fit properly will not protect your hearing. Always plan on having hearing protection on you or nearby in
case you need it. Using all methods of protection listed above will give you and your crews the best possible chance
of avoiding damage to your hearing.

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