Noise-​induced hearing loss

November 15, 2011 by Michèle Veilleux

La surdité liée à l’exposition au bruit

Several people suffer from noise-induced hearing loss, whether it’s due to a noisy workplace or a noisy hobby. This type of hearing loss often remains mysterious and is considered taboo.

Hearing loss and the mechanisms of hearing

To better understand the effects of noise on hearing it’s important to understand how hearing works. Sounds are captured by the auricle and are directly sent to the ear canal making the eardrum vibrate. When it vibrates, the auditory ossicles (three ear bones), which are linked to the eardrum will move to finally press on the oval window, which is located at the beginning  of the inner ear. The pressure will move the fluid and the little ear cells in the inner ear. A nerve impulse is then transmitted to the brain via the auditory nerve.

Hearing loss

Noise-induced hearing loss affects the ear cells of the inner ear. These resemble little hairs and with time they become less abundant and some of them get damaged. Hearing loss then fallows with all that it entails.

Hearing loss is often preceded by the appearance of tinnitus, this infernal echo that is continuously heard, making silence inexistent. It becomes like a signal of alarm. Also, one of the first symptoms of hearing loss is auditory fatigue, a sensation similar to what we experience when we leave a noisy bar. After our ears have rested, our hearing will return to its usual state. Over time, if the noise exposures are repeated, the hearing loss can remain.

We often use the ‘grass’ analogy to describe this type of hearing loss. In the summer time, when we leave things on the grass for a long period of time, the grass underneath will lay flat. If we leave them there for several days, the grass will turn yellow, but will eventually go back to normal. If we leave them there all summer, the grass will eventually die
Factors of influence

Hearing loss will depend on the noise’s intensity level. Higher is the noise level, greater are the risks of hearing loss. Also, the length of noise exposure will be influential, longer is the time of exposition, greater is the risk of hearing loss. In fact, the CSST considers it safe to be exposed to noise levels of maximum 90 dB for a period of 8 hours, but the World Health Organisation (WHO) determines that a maximum of 75 dB for a period of 8 hours is safer.

In addition, certain personal predispositions, a form of vulnerability, will have an affect, such that even with the same work environment and length of exposure, one may have more hearing damage than the other.

Finally, to preserve hearing, the use of hearing protection is recommended.