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Occupational Hearing Loss

The modern-day world we live in is a noisy one. Everywhere you go there is loud noise: driving down the street, school cafeterias, gymnasiums, restaurants and large sporting venues. Outside of our recreational activities, some people always work within a noisy environment. Our first responders, factory positions, pilots, aircraft attendants, construction workers, military and so many other work positions complete their forty-hour work week around constant, loud noise. How does this affect our ears and hearing? This article will dive deeper into occupational noise exposure and what we can do to protect our ears from occupational hearing loss.

What causes Occupational Hearing Loss (OHL)?

Occupational Hearing Loss (OHL) is hearing loss that is caused by exposure to noise within your work environment. Most often this is long-term noise with repeated exposure. The Occupational Safety and Health Administration (OSHA) helped create noise exposure guidelines, with their rule of thumb being 85 decibels of noise for an 8-hour workday. As noise gets louder than this guideline, the amount of time you can safely spend in that environment becomes shorter. This rule does not take into account sudden loud noises though. Sudden sounds, although very short in duration, can often reach levels of up to 120 decibels. Even one exposure to such a high sound intensity can cause damage to our inner ear of hearing, causing occupational hearing loss. For these reasons, it is important to protect your ears while working within environments that have excessive noise.

How can noise damage our hearing?

To explain occupational hearing loss further, we first need to understand what is happening within our ears. Our ear has three parts: the outer, middle, and inner ear. Our outer ear is made up of our pinna, the portion of the outside of our head, and our ear canal. Our ear canal leads to our eardrum, which is the start of our middle ear. Sound is funneled into the ear canal by the pinna and travels to the eardrum. When sound hits the eardrum it causes it to vibrate back and forth. Behind the eardrum is an air-filled cavity and three tiny ear bones, the ossicles. As the eardrum vibrates back and forth, the ossicles rotate in a similar motion. The ossicles are attached to our inner ear, the cochlea, can be found on the other side. As the ossicles rotate, they push and pull on the cochlea. The cochlea is shaped like a snail, filled with fluid, and has one side for hearing and one side for balance. When the cochlea is being pushed by the ossicles, the fluid will start to travel through the snail shaped portion. Within this snail shaped portion are tiny hair cells that contract in response to this fluid movement. When these hair cells contract, they trigger a neural response on our auditory nerve. This neural response is the signal that travels up our auditory nerve to the auditory center within our brain. This is how we hear and understand sounds around us! There are many things that can cause sound to not travel through the entire system. For occupational noise induced hearing loss our damage occurs within the inner ear. The outer ear and middle ear all remain intact and fully functional, but more specifically, the hair cells in our cochlea become damaged beyond repair. Let’s repeat our hearing process from above again, but this time with a very loud sound. A very loud sound will be funneled into the ear canal and reach the eardrum. The eardrum will vibrate excessively causing the bones to rotate in a large arc and at a faster speed. This causes a larger push on the cochlea, creating a big rush of fluid through the snail shaped structure. I picture it like a big surfing wave in the ocean. As this wave travels, it will activate the hair cells. Such a large wave though will cause the hair cell contraction to be very tight. This contraction is changing the structure of the hair cell. Often, the hair cells cannot open back up to their original state. The signal is sent to our brain, which sends us a warning to react and cover our ears. This was just for one single sound. Imagine if this happened over and over, everyday while you were at work. As the hair cells continue to be exposed to loud sounds, they will contract more and more. At some point, your hair cells will stop opening again completely and die or break off. With no hair cells, there is no triggered neural response to send to the auditory nerve and brain. This lack of signal causes noise induced hearing loss.

What are the signs of noise induced hearing loss and how does this differ from other types of hearing loss? This is a great question!  Differentiating the cause of your hearing loss and varying symptoms can be difficult. Occupational noise induced hearing loss will be preceded by a history of working within a loud noisy environment. Often these environments provide yearly hearing screenings to monitor the effects of the noise. Please note, these are hearing screenings and the person performing the testing is not looking for hearing loss in general, but a threshold shift from baseline. What does this mean? When you see an audiologist for a full diagnostic evaluation, they will perform multiple tests. They will review your medical history and discuss your concerns with you. They will look into your ears with an ear light and otoscope, to see if you have a buildup of earwax; and to determine the health status of your eardrum. They will then perform pure-tone air and bone conduction testing to determine your threshold of hearing for low, middle, and high frequency sounds. Air testing is using over the ear headphones or insert earplugs to test all three parts of our ear. Bone conduction testing uses a bone oscillator that is placed on the mastoid bony process directly behind your pinna and tests the inner ear of hearing only. This allows us to determine where the site of damage is and what type of hearing loss you have. The audiologist will, next, perform speech testing.  This is to determine the thresholds,softest levels, you can hear words at and an additional test at louder levels to determine what percentage of correct word understanding you have. The appointment is then completed by reviewing your results, classifying any hearing loss into a severity level, type, and discussing treatment options. When seeing an audiologist hearing loss can be classified into five severity levels: mild, moderate, moderately severe, severe, and profound. The workplace hearing screenings only use pure tone air threshold testing to get a baseline or starting point of your hearing, and they do not classify any pre-existing hearing loss. If you have hearing loss, they will make note of that, but not provide any intervention. What they are looking for is a significant threshold shift.  This means that your hearing ability has changed by 15 decibels or more at three consecutive frequencies. This is a significant shift and can bump you into a higher severity of hearing loss. If this criterion is not met, then you do not qualify for occupational hearing loss under their screening standards. These screening standards are to help prevent further damage from occurring, and your employer provides these screenings because it is mandated by law and helps protect them from any potential lawsuits. Therefore, they do not always have the employee’s best health and hearing safety in mind. Since the hearing screenings provided are not as thorough as a diagnostic evaluation performed by an audiologist, it is important to seek professional care if you have concerns for occupational hearing loss.

There are some common symptoms to look for if you are concerned about occupational noise induced hearing loss. The first step would be to list your noise history, specifically as it is pertaining to your work environment. Next there are three common symptoms that accompany occupational noise exposure and hearing loss. Tinnitus, which is the presence of a sound without a physical external auditory stimulus, is often associated with occupational hearing loss. When you are first exposed to noise, you might notice that the tinnitus comes and goes. It may come immediately following your workday, and only last a few minutes. After more noise exposure though, the tinnitus will start to last longer and may even become louder. This mechanism is your ears’ way of warning you about the noise exposure. Another common symptom is that you are able to hear that people are talking but often cannot understand exactly what they are saying. Noise induced hearing loss commonly affects our high frequency sound hair cells first, as these hair cells are at the start of our inner ear. Therefore, noise reaches them first before traveling through the rest of the snail shape. When we have hearing loss in the high frequencies, we lose some clarity aspects of speech. This may make you feel like you are constantly playing a game of hangman. You may hear one or two words of the sentence but have to guess using context the rest of the sentence. You also may perceive that sounds or speech seem distorted. This only becomes worse in background noise as well, as background noise covers the lower and middle frequencies where you have better hearing. You may, also, feel a pressure or fullness in your ears from noise induced hearing loss. This is often another way for our ears to tell us something has changed. This fullness, although it feels like it is coming from our outer or middle ear, is actually our inner ear not having access to those high frequency sounds anymore. If you are experiencing any of these symptoms, make sure to report them to your manager and seek professional care from an audiologist.

What can be done to reduce the hazard from noise?

At this point we have thoroughly discussed what noise exposure is and how it can damage our ears and cause occupational hearing loss. Although this may seem scary, there are things we can do to prevent noise induced hearing loss. The greatest prevention method is wearing hearing protection. There are many types of hearing protection including a one-size-fits-all foam insert earplugs, over the ear headphones, and custom made hearing protection. Each of these have what is called a noise reduction rating (NRR), which describes the level of sound that helps block and give protection to your ears. For example, if they have a 20 dB NRR, they can block up to 20 decibels of sound. These large numbers can fool people though as it is dependent on how they are inserted and how long they are used. Most commonly, foam earplugs are what workplaces provide to their employees to use within the workplace. These foam inserts usually have an NRR of anywhere between 15-30 dB. This is only when they are inserted correctly into your ear. Most cases they are not inserted correctly. There are four essential steps for inserting foam earplugs correctly: 1) roll into a small snake like structure, 2) pull back on the pinna of your ear with your opposite hand, 3) push the earplug into your ear canal, and 4) hold until it expands and stays in place. Often employees are not given these instructions, therefore the insertion of their foam earplugs are poor and allow for more sound to escape protection. Using over the ear headphones can help with this insertion issue. These headphones can be very easy to use and have an average NRR of 30-45 decibels. You can even combine the foam earplugs and headphones for double protection. The problem with these two options though is often safety. Yes, you are protecting your ears from noise exposure, but can you hear important work calls or signals? Therefore, workers often opt to wear no hearing protection in order to prioritize safety and be able to perform their job correctly. The best solution is to have custom made hearing protection. Custom hearing protection requires getting earmold impressions taken of your ear canals, as to ensure a perfect fit. Custom hearing protection has many sound attenuation options available and can even include vents. These vents can allow certain sounds to pass, like speech, meaning workers can wear them to protect their hearing and still be able to effectively complete their job duties. You are also less likely to lose custom hearing protection as they stay securely within your ear canals and can include a connecting chord that can lay over your shoulders. There are also things you can do within your work environment to reduce the effects of noise. There are two main changes that can be made: administrative changes and engineering changes. Administrative changes involve changing your work rotation, length of noise exposure, or anything related to the scheduling of your job. This often requires you talking with management about your concerns for noise induced hearing loss. If you work within a large factory that is noisier on one end of the building compared to the other, you could ask to rotate through different job responsibilities throughout your work week. This will allow you to vary the amount of noise you are exposed to. You can also request breaks or lunches to be held within a quiet break room, which will give your ears a break, even if only for a little bit of time. Engineering changes are often more difficult to do, as this requires changes to the physical equipment you are using. There are equipment and power tools on the market that operate at quieter levels and are advertised for their hearing safety capabilities. Unfortunately, these machines also cost more than the traditional ones. Therefore, it is less common for workplaces to purchase the sound safe equipment because of budgets and revenue. Overall, you should always start with hearing protection and then work your way into changing your work environment as necessary, and if even at all possible.

Occupational noise induced hearing loss is a very serious condition, but if caught in enough time can be managed and prevented. It is important as a worker to take your own initiative and fight for your hearing safety. You can start by setting a meeting with your managers, request custom hearing protection, and schedule an appointment with an audiologist to get a full diagnostic evaluation. From there, this team can help keep your ears healthy and safe from damage due to noise exposure.

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