Occupational Noise-Induced Hearing Loss

Occupational noise-induced hearing loss is a type of hearing loss that affects workers who are exposed to excessive noise levels over a long period of time. In Quebec, it is the second most common occupational disease in terms of the number of cases compensated by the Commission des normes, de l’équité, de la santé et de la sécurité au travail (CNESST).

In most cases, occupational noise-induced hearing loss occurs when a worker is exposed to excessive and repetitive noise levels in the workplace over a long period of time.

In Quebec, the CNESST has established that over an 8-hour period, noise levels are considered excessive and may be harmful if they exceed 85 dB. As for the World Health Organization (WHO), they recommend that noise levels not exceed 75 dB for the same period of exposure.

Hearing loss can also occur as a result of acoustic trauma, i.e., a single exposure to excessive noise levels that can cause permanent hearing damage (see the article on acoustic trauma on pages 12 to learn more).

Some workers are also exposed to chemicals that can damage the inner ear. Exposure high noise levels or chemicals classified as “ototoxic” increases the risk of developing occupational noise-induced hearing loss. In terms of the auditory system, this exposure can cause irreversible damage to the sensory cells of the inner ear (outer and inner cilia).

Many signs can point to occupational noise-induced hearing loss. For example, workers in noisy environments will often tend to ask the people around them to repeat themselves outside working hours. They might find it hard to follow conversations in group or noisy settings, and turn up the volume of the TV to understand better. Auditory symptoms such as tinnitus are also common among workers exposed to noise.

Typically, for workers with occupational hearing loss, pure-tone audiometry results show a more pronounced hearing impairment at high frequencies (from 3,000 Hz to 6,000 Hz). In other words, the ability to detect low intensity high-pitched sounds is diminished. It should be noted that those sounds make all the difference between “hearing” and “understanding” what is being said.

Interestingly, while audiograms may show “normal” results, this doesn’t necessarily mean that there is no noise-induced hearing damage. Several recent studies actually show that exposure to noise can cause hearing damage that cannot be measured by pure-tone audiometry. This type of damage is called “cochlear synaptopathy”. It may appear before the hearing loss can be measured by pure-tone audiometry, and may make it hard for a person to follow conversations when there is background noise.

According to the Regulation respecting occupational health and safety, employers should, where possible, take the necessary steps to reduce noise at the source, if they cannot comply with noise exposure limits. For example, they must replace or properly maintain equipment to reduce noise levels (caused by squeaking, rubbing, vibrations, etc.).

Employers must also put measures in place to reduce noise propagation, either by enclosing noisy machinery, soundproofing rooms or workstations, or installing noise-absorbing acoustic panels.

Reducing the duration of noise exposure can reduce the risk of hearing damage. The truth is, workers with shifts more than 8 hours long don’t benefit from the 16-hour auditory rest period that would allow them to recover from hearing fatigue, thereby increasing their risk of hearing damage.

If it is still impossible to comply with the standards for preventing excessive noise levels, employers must make hearing protectors available to workers. Bear in mind, however, that hearing protectors are only effective if they are properly fitted and worn for the entire duration of exposure. For people who need to communicate with colleagues despite the surrounding noise, we recommend filtered earmolds that will make understanding one another easier. To enhance comfort and efficiency, earmolds can be custom-made.

If you think you may have work-related hearing loss, don’t hesitate to book a free** hearing consultation, including a brief evaluation of your hearing*.

*Permanent offer. 18 and over.