The LIGHT Center, T-90, College of the Redwoods (476-4290)

Regardless of which jungle one works or lives in, noise is an inherent element of the environment. For the most part, we consider noise to be an irritation and distraction. However, noise has a far more dangerous side to it. Approximately 10 million Americans suffer from hearing loss which is attributable to noise exposure.

Understanding noise induced hearing loss (NIHL) dictates that one must first have some appreciation for the functioning of the ear. The ear has three main components: the outer ear, middle ear, and inner ear. The outer ear is what you can see, plus the ear canal leading up to the eardrum. The eardrum and the closed cavity which houses the three small bones of the ear comprise the middle ear. Beyond the middle ear lies the inner ear; the most vulnerable part of the ear when noise is involved. A component of the inner ear is the cochlea, which looks like a snail. Inside the cochlea are hair cells, which wave back and forth in fluid when it receives auditory stimuli. When that stimuli is either too strong (loud), or persistent (for too long a duration), the hair cells can be injured and die. Once they die, the sounds that they were responsible for transmitting to the brain can no longer be sent. Noise exposure can cause two types of injury:

This is damage to the hair cells resulting from exposure to a sudden or intense sound, like a gunshot or explosion. Not only can such noise kill the hair cells in the inner ear, but it can also rupture the eardrum.

Moderate exposure to noise creates a temporary hearing loss, like that experienced when attending a loud concert. This is called a Temporary Threshold Shift. Typically, in a couple of hours one’s hearing level returns to normal. However, when this exposure is ongoing, there comes a point at which the shift in threshold is no longer temporary, and remains as a permanent hearing loss. Once these hair cells no longer function, they are not replaceable.

How does one know when noise is too loud? Sound is measured in two dimensions. The level of the sound is measured in decibels, and can be translated into "how loud" the sound is. However, the loudness is not the only critical factor. The pitch or frequency of the sound is also important and this dimension is measured in Hertz. The frequency is less critical when one considers exposure to noise. So, what level of sound is safe?

(House Ear Institute-Research and Education 1999)

January 18, 2000

It is interesting to consider the loudness of very common sounds in our environment. When one compares these to sounds more typically considered to be "loud", it is no wonder that 10 million Americans have some form of noise induced hearing loss. Consider the following:

• Dripping Faucet – 20 dB
• Conversation – 60-70 dB
• Power Tools – 100 dB
• Earphones (volume 5) – 110 dB
• Thunder – 120 dB
• Gunshot – 140 dB

A good rule of thumb to use if you are wondering if your environment is too noisy for your hearing health is:

There are four main types of ear protection, which are considered effective if you are in a noisy environment.

1. Foam Ear Plugs

These need to be soft and springy. They can’t be worn for more than a day or two without being replaced.

2. Pre-molded Plugs

These are typically made of wax or a similar substance. They should not be hard or sticky.

3. Ear Muffs

Make sure you have removed any hair or jewelry which might be stopping a good seal.

4. Custom-Molded Plugs

Made for you by an audiologist.

Comments? Questions? mailto:trish-blair@redwoods.edu