There are many different recognized causes of hearing loss. Certain medications, otologic medical conditions, head trauma, age, and noise exposure are all possible reasons for the loss of hearing. As a result, there are some occupations or fields of work that put people at greater risk of experiencing noise induced hearing loss–particularly if the individual finds themself in a field of work where they are frequently exposed to loud noises as part of their daily occupation.
Occupations often responsible for increased risk of occupational hearing loss include (but are not limited to) the U.S. military, agricultural positions, mining, construction work, manufacturing/utilities, and transportation positions. These industries are regulated by safety agencies like the Occupational Safety and Health Administration (OSHA) and the National Institute for Occupational Safety and Health (NIOSH). Annually, it has been estimated that as many as 22 million U.S. workers are exposed to hazardous levels of occupational noise, potentially leading to occupational noise induced hearing loss.
What Are The Mechanisms Of Noise-Induced Hearing Loss?
Noise induced hearing loss occurs when several important functions within the auditory system are damaged. The ear and auditory system are complicated little structures, with many different well-balanced, well-oiled parts. When one or several of these parts are damaged or not functioning, the processes described below are interrupted, and temporary or permanent hearing loss can result.
The ear is split into three separate parts: the outer ear, middle ear, and inner ear. The outer ear collects sound waves in the air, and effectively funnels those sounds toward the middle ear. The middle ear functions as a mechanical sound booster, and helps to increase the audibility of soft sounds as they travel along the middle ear bones to reach the inner ear for sound processing.
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The inner ear, or cochlea, is the organ of hearing and is full of fluid rich in potassium, sodium and calcium which help to transform the mechanical energy of sound into electrical energy along the sensory hair cells and auditory neurons so that the brain can interpret it as sound.
Occupational hearing loss, often caused by exposure to loud noise, involves complex molecular mechanisms beyond the simple notion that loud sounds damage the inner ear’s tiny hair cells. The reality is that multiple pathways contribute to hearing impairment. Some of these involve the auditory system’s metabolic processes, where various receptors may change, hindering the inner ear’s function. Others result from the direct physical harm to the hair cells. The outcome can range from temporary to permanent hearing loss, with the former typically associated with transient inhibition of metabolic pathways, while the latter results in enduring noise-induced hearing damage.
Under What Conditions Does Noise Induced Hearing Loss Occur?
As briefly discussed above, noise induced hearing loss is not always a simple matter, with clear-cut causes and triggers. While loud noise is obviously the culprit in this type of hearing loss, the noise exposure itself can significantly impact the reach of noise induced hearing loss. To understand how noise exposure and decibel level impact hearing and hearing health, you must first understand the manner in which sound is measured. While measures frequently operate on a linear scale–think 1, 2, 3, 4–sound is measured in terms of logarithmic scales, or scales with a more complicated rating or measuring system than a simple stack of addition or subtraction. This is important largely because of the way that the auditory system takes in and interprets sound; while one sound may be technically similar to another in terms of sound, the way that our brain measures, takes in, and processes those loud noises will determine whether it seems like excessive noise and leads to hearing issues, or whether it easily fades into the background.
One way to more fully understand how excessive noise is calculated in the human auditory system is to look at it in terms of a time/intensity tradeoff. When looking at the trade off of time and intensity, consider the following questions:
- How loud is the sound? Is the sound a deafening one? Whether a jackhammer or a loud sound system, the louder the sound, the greater the likelihood that hearing damage will occur (though the nature of the noise can also come into play).
- How long are you listening to it? Are you listening to the sound all day, every day? Loud noise that continues for hours each day is far more likely to lead to occupational hearing loss than a loud noise exposure that is only experienced periodically.
These two things together determine your noise dose. There are “allowable” amounts that are determined to be safe, and some amounts of sound cross the threshold for what is safe and are known to cause a greater risk for occupational hearing loss that can affect one or both ears.
Occupational noise induced hearing does not guarantee complete hearing loss or permanent hearing impairment; instead, you can take a close look at the loud sounds and how frequently you are being exposed to them to determine how great the likelihood is that you will experience hearing impairment as a result of occupational noise exposure.
Regulations Regarding Occupational Noise Induced Hearing Loss
The ability of loud noises to jeopardize hearing has not gone unnoticed by healthcare professionals and those in leadership positions. Ultimately, OSHA developed a hearing conservation program that is mandated for workers exposed to sounds at or above 85 dB averaged over 8 hours. The same exposure limit recommendations exist through NIOSH, in order to reduce the likelihood of experiencing damage to the auditory nerve pathway that leads to hearing loss and preserving remaining hearing ability.
As we discussed above, the way that sound is measured differs from standard linear measurements. That means that the way sound is looked at to determine the maximum job noise exposure levels takes more than one measure into account; instead, the safety limits are developed only after weighing the average of sound over time and its subsequent impact on the hearing system. These safety limits were developed to reduce the likelihood of occupational noise exposures leading to hearing loss, and to prevent excessive noise exposure in situations in which loud noises are unavoidable.
Primary Characteristics Of Noise Induced Hearing Loss (NIHL)
There are many varieties of hearing loss, and each of them is characterized by different causes, configurations, and severities of those losses. NIHL is characterized by bilateral sensorineural hearing loss, with a notched pattern, typically around 3000-4000-6000 Hz. What this means is that in the initial stages of this type of hearing loss, changes may only be readily distinguishable at certain Hz, making it difficult to detect. Many people with this type of hearing loss incorrectly assume they may be experiencing changes to hearing primarily as a result of aging. This means that a proper diagnosis can go undetected, until the loss progresses past this initial threshold.
Although NIHL is often detected in both ears, there can be asymmetries if noise exposure is consistently greater on one side. This should also be noted in any consultations or meetings with hearing health professionals, along with any ringing in the ears (called tinnitus), as noise exposure is a risk factor for tinnitus development.
Regardless of the type of hearing loss experienced by an individual, hearing healthcare professionals unanimously agree that reducing loud noise exposure is a good way to protect yourself from further hearing damage. Although not all noise exposure can be prevented, as in the case of sudden loud noise exposures, many recreational and occupational noise exposures can be avoided or at least reduced with the use of hearing protective devices like earplugs and earmuffs.
Preventing Noise Induced Hearing Loss
Prevention is key when risk factors for NIHL are present. OSHA has implemented a hearing conservation program for people with regular exposure to loud noises at work–think those working in construction, those with regular exposure to aircraft noise as might be the case with air force workers, and more. Hearing conservation programs typically include at least some of the following components:
- Audiometric monitoring (baseline testing + subsequent monitoring on an annual basis)
- Measurements of noise levels
- Hearing protection devices (including assessments related to their effectiveness)
- Education and training related to how to reduce the impacts of hazardous noise exposure
- Scheduling to account for maximum noise doses
While these cannot, of course, guarantee that occupational hearing loss does not occur, it does significantly lessen the likelihood of acoustic trauma in response to loud noise exposure. Taking care in personal pursuits and hobbies to avoid noise exposure is also recommended for anyone, but especially those at risk of developing occupational hearing loss.
Treating Noise Induced Hearing Loss
Whether NIHL develops as a result of occupational hearing loss or damage to the inner ear of one or both ears following recreational noise exposure, occupational work exposures, or accidental noise exposure, there are ways to address hearing loss and resulting tinnitus. Tinnitus treatment and hearing loss treatment can differ, but often intersect, including the following:
- Hearing aids. Hearing aids are often considered one of the first interventions for damages to hearing health, including hearing loss caused by occupational noise exposure and tinnitus.
- Cognitive Behavioral Therapy (CBT). When hearing loss is not repairable, CBT can be useful to address the emotional effects of losing hearing and the potential fallout, including difficulty in social situations.
- Cochlear implants. Cochlear implants can be used to address hearing loss from occupational noise exposure when standard interventions like hearing aids are not sufficient to successfully amplify hearing.
Treating NIHL focuses on restoring missing input to the brain through the use of devices like hearing aids, to help facilitate better communication and improve quality of life. Unfortunately, there is no treatment to restore the permanent damage to the delicate inner ear structures that has occurred. However, with modern hearing aid technology, and the support of a hearing health care provider thousands of those with NIHL are hearing the world around them again, and experiencing tinnitus relief. If you work in a loud environment or like to enjoy loud recreational hobbies, it is important to take preventative measures for your hearing health now and wear hearing protective devices when exposed to loud sounds.
This means that preventive measures, like wearing hearing protection and adhering to OSHA guidelines, and supportive measures, like hearing aids, are the primary means used to address NIHL and successfully mitigate the effects of hearing loss caused by regular or severe exposure to loud sounds.