Noise-Induced Hearing Loss

What is Noise Induced Hearing Loss (NIHL)?

Noise-induced hearing loss (NIHL) is a type of sensorineural hearing loss (read this article to understand the different types of hearing loss) that results from exposure to loud sounds This condition develops gradually from chronic exposure to high noise levels or suddenly from a single intense noise event. NIHL affects the delicate structures of the inner ear, specifically the hair cells and auditory nerve, leading to permanent damage that cannot be reversed

Understanding Noisy Environments

To get a sense of what constitutes a "noisy environment," we need to understand decibels (dB). A decibel is a logarithmic unit used to measure sound intensity. In a logarithmic scale, a small increase in decibels represents a drastic increase in sound intensity. To give you a idea of this concept:

• Each 10 dB increase represents a tenfold increase in sound intensity.
• Each 3 dB increase represents doubling in sound intensity.

Here's a more detailed scale of various environments and their approximate dB levels:

Sounds at or below 70 dB are generally considered safe. The risk of hearing damage increases with both the intensity of the sound and the duration of exposure.

❗Prolonged exposure to noises above 85 dB can lead to permanent hearing loss.

 

Types of Noise Exposure

There are two main types of noise exposure that can cause NIHL:

1. Impact noise (acoustic trauma): This is a short, intense sound like a gunshot, explosion, or firecracker. These sudden, powerful noises can cause immediate and permanent damage to the inner ear structures. They can rupture the eardrums, dislocate the hearing bones (ossicular chain) and cause irreversible damage to the inner ear. This type of noise usually causes ear pain, and depending on the harm done, can lead to bleeding from the ear.

2. Chronic noise exposure: This involves prolonged or repeated exposure to high levels of noise, such as working in a noisy factory, frequently attending loud concerts, or regularly using power tools. Over time, this type of exposure can gradually damage the hair cells in the inner ear. This type is silent in the sense that you don't notice the damage being done over time until you begin to notice the hearing loss.

What Are the Noise Standards for Quebec Workers?

Quebec's standards for noise exposure for workers are outlined in the Regulation Respecting Occupational Health and Safety (Règlement sur la santé et la sécurité du travail), which falls under the Act Respecting Occupational Health and Safety. As of June 16, 2023, significant changes have been implemented to better protect workers from noise-induced hearing loss.

Key Points of Quebec's Noise Exposure Standards

1. Exposure Limit: The maximum noise exposure level for an 8h workday has been reduced from 90 dBA to 85 dBA.

2. Identification of Risk: Employers have one year from June 16, 2023, to identify work situations that may exceed the new exposure limit values.

3. Assessment Frequency: After the initial assessment, employers must repeat the noise exposure assessment every five years.

4. Measurement Standards: Noise measurements must follow the international standard ISO 9612:2009 for determining occupational noise exposure,

5. Exposure Duration: The regulation provides a sliding scale of maximum exposure times for higher noise levels. For example:

   • 85 dBA: 8 hours of exposure is allowed
   • 88 dBA: 4 hours of exposure is allowed
   • 91 dBA: 2 hours of exposure is allowed

   • 94 dBA: 1 hour of exposure is allowed

6. Employer Responsibilities: Employers must take reasonable measures to reduce noise at the source, isolate noisy areas, or provide appropriate hearing protection when noise levels exceed the limits.

7. Implementation Timeline: Employers have five years to implement necessary measures to reduce noise exposure after identifying high-risk situations.

These updated standards aim to align Quebec's noise exposure regulations with those of other Canadian provinces and international best practices, significantly improving worker protection against the harmful effects of occupational noise.

How Noise Damages the Ear

Loud noises overstimulate the delicate hair cells (the cells responsible for hearing) in the cochlea, the snail-shaped organ in the inner ear that converts sound waves into electrical signals. This overstimulation can lead to:

1. Mechanical damage: Excessive vibrations from sound noises can physically damage or destroy the hair cells and their stereocilia (hair-like projections at the top of the hair cells that are most important for the detection of sound).

2. Metabolic exhaustion: Prolonged stimulation can consume all the hair cells' energy reserves, leading to the death of those cells.

3. Excitotoxicity: Overstimulation can cause a rupture in the connection between hair cells and hearing nerve fibers, disrupting signal transmission.

4. Cochlear synaptopathy: Also known as "hidden hearing loss," this involves damage to the synapses (the connections) between inner hair cells and hearing nerve fibers, affecting the transmission of the nerve signal to the brain.

Once these hair cells or their connections are damaged or destroyed, they cannot regenerate, resulting in permanent hearing loss.

Diagnosing Noise-Induced Hearing Loss

NIHL is typically diagnosed through a complete hearing evaluation. For more information on hearing evaluations, read this article.

1. Pure tone audiometry: The audiogram pattern for NIHL typically shows better hearing at low frequencies, a significant drop (notch) at 3000-6000 Hz, and some recovery at 8000 Hz. The characteristic "notch" at high frequencies is usually around 4000 Hz, and is really unique to noise damage and NIHL. 

2. Speech audiometry: This assesses the ability to understand speech, which will be impaired in NIHL.

3. Tympanometry: This checks the middle ear function to rule out other causes of hearing loss. This is typically normal in NIHL.

4. Otoacoustic emissions: This test can detect damage to outer hair cells even before it's apparent on an audiogram. It would be a early predictor of NIHL.

Risk Factors For Noise-Induced Hearing Loss

Several factors can exacerbate the risk of NIHL. It is important for patients that have some of those risk factors to be even more vigilant if they are chronically exposed to noise in their workplace or during leisure activities:

1. Chemical solvents: Exposure to certain organic solvents (such as toluene and ethylbenzene) can make the inner ear more susceptible to noise damage. These solvents are usually present in factories producing plastic, rubber, certain textiles and paints).

2. Cardiovascular diseases: Conditions that affect blood flow can increase vulnerability to noise-induced damage (diabetes for example).

3. Smoking: Tobacco use may increase the risk of hearing loss when combined with noise exposure.

4. Genetic predisposition: Some individuals may be more susceptible to NIHL due to genetic factors.

5. Age: Older individuals may be more susceptible to noise damage.

6. Pre-existing hearing loss: This can make the ear more vulnerable to further noise damage.

Preventing Noise-Induced Hearing Loss

Prevention is crucial in managing NIHL. In fact, I would say it's more important than its treatment. Here are some detailed strategies:

• Follow the 85/8 rule: Limit exposure to 85 dB to no more than 8 hours per day. For every 3 dB increase, cut the exposure time in half. As we saw above, this is because for every 3 dB increase in noise, the sound intensity doubles.
  
  
• Use hearing protection: Custom earplugs provide the most effective combination of noise reduction and comfort. The Noise Reduction Rating (NRR) indicates how many decibels a hearing protector reduces noise by when worn correctly. This article provides more information on the NRR and on the types of noise protection available, and can help you determine which noise protection is best suited for your situation.
  
  
• Take listening breaks: When exposed to loud noises, take regular breaks to allow your ears to recover.
  
  
• Lower the volume: Keep personal listening devices at 60% of maximum volume or lower (or 85 dB).
  
  
• Regular screening: Workers in noisy environments should undergo annual hearing tests to detect any changes early.
  
  
• Education: Raise awareness about the dangers of noise exposure and proper use of hearing protection.

Treating Noise-Induced Hearing Loss

While there is no cure for NIHL, several management strategies can help:

1. Hearing aids: Modern digital hearing aids can be programmed to amplify specific frequencies affected by NIHL.

2. Assistive listening devices: These can help in specific listening situations, such as watching TV or talking on the phone.

3. Cochlear implants: For severe to profound hearing loss, these devices can bypass damaged portions of the inner ear and directly stimulate the auditory nerve.

4. Tinnitus management: Techniques such as sound therapy or cognitive behavioral therapy can help manage tinnitus often associated with NIHL.

5. Auditory training: This can help improve speech understanding, especially in noisy environments.

Remember, protecting your hearing is crucial. If you suspect you have NIHL, consult an ENT or audiologist promptly. Early intervention can help prevent further damage and significantly improve quality of life.