Hearing Loss Prevention

Our ability to hear can help us connect with others, experience music, learn, and live a social lifestyle.  Protecting our hearing is crucial in order to take advantage of all the amazing things our ears have to offer.  Let's learn about hearing loss prevention.

Workplace Noise Exposure

Did you know that hearing loss is the third most common chronic physical condition in the United States.  Furthermore, occupational work related hearing loss is the most commonly reported work-related injury in the United states.  Noise-induced hearing loss is the second most common cause of acquired deafness, right behind age-related hearing loss.

The formula for calculating damage to your ears from noise is simple, think D = D+D, which stands for Damage equals Decibels plus Duration.  In other words, damage to your hearing is equal to how loud the noise your listening to is and for how long your listening to this noise.  The National Institute for Occupational Safety and Health (NIOSH) has developed a maximum recommended noise exposure for people working in a noisy environment.  The maximum noise exposure they developed is a sound level of 85 decibels (A) for an 8 hour daily shift.  If the noise level increases, the exposure time should be less.  Specifically, every 3 decibel increase in noise level cuts the "safe" noise exposure time in half.  For example, at 88 decibels, workers should only be exposed to this noise level for 4 hours.  Exposures above this level are considered hazardous to hearing.  You can find out the decibel level of something by using sound level meter (SLM).  Simple sound level meters can be purchased online or in some department stores.

Why is noise so bad for our hearing?

Excess noise will affect the part of your inner ear known as the cochlea.  The cochlea is a spiral shaped, fluid filled shell, often referred to as your "organ of hearing".  Inside the cochlea are tiny sensors, called outer hair cells, that move when they come in contact with sound waves.  Regular cochleas have thousands of these outer hair cells, and each hair cell is responsible for sensing different pitches of sound.  The hair cells closest to the entrance of the cochlea are responsible for sensing high pitch sounds, whereas the hair cells deep in the cochlea spiral are responsible for sensing low pitch sounds.

When noise levels are moderate, hair cells move nicely, and can transmit information up to the brain with ease.  However, when the noise level is very high, hair cells can actually get damaged.  Many long term exposures of excessive noise can permanently damage outer hair cells, affecting their ability to send sound information up to the brain.  Usually, the first sign of noise-induced hearing loss is a drop in hearing at 4 kHz.  Why 4 kHz? Well, the hair cells responsible for sensing 4 kHz sounds are right in the 'pummel-zone' for all incoming sound waves.  That means, when sound waves enter the cochlea, sounds will need to bounce off the section for 4 kHz before it gets to where it is sensed in the cochlea.  This constant wear and tear causes the hair cells to weaken and damage over time.

Shortly after the 4 kHz drop in hearing, higher pitches like 6 kHz and 8 kHz drop in hearing ability.  Why are the high pitches more affected by noise than the low pitches?  This has to do with the amount of hair cells located in each region of hearing.  There are fewer hair cells in the high pitch range of hearing relative to the amount of hair cells in the low pitch range of hearing.  For example, there are roughly the same amount of of outer hair cells between 125Hz to 250Hz and 4000Hz to 8000Hz.  So, loosing some hair cells in this low pitch range will not have a major effect on hearing, but loosing some hair cells in this high pitch range will likely affect hearing thresholds.

So, what can be done to protect from noise-induced hearing loss at the workplace?

NIOSH has developed "Noise Controls" to help reduce worker's noise exposure, which is a hierarchy of decisions used to control noise in a workplace.

At the top of the hierarchy are the best methods to reduce noise related hearing loss, and at the bottom of the list are the least effective methods to reduce noise related hearing loss.  Physically removing the noise tops this list, but most of the time isn't possible as the noisy equipment is likely performing an important job at the workplace.  Replacing the noisy equipment with quieter equipment is a common strategy to prevent noise induced hearing loss.  For example, switching from propane forklifts to electric forklifts can significantly reduce the amount of blanket noise in a busy warehouse.  Installing baffles around machinery can also significantly reduce ambient workplace noise.  Sometimes, these replacements and adjustments are not possible.  One suggestion could be move the noisy equipment to a place more isolated from people.  Having a separate generator room can reduce noise levels in common work areas.

Near the bottom of the noise control hierarchy is reducing the exposure time limits of workers with noisy machinery.  Finally, using ear protection can also be used as a strategy for reducing noise related hearing loss.  Unfortunately, ear protection is often not worn correctly, reducing it's effectiveness.   Earplugs are one of the most common varieties of ear protection.  They're inexpensive and easy to store.  It is important to actually insert the earplug into your ear canal correctly to get the maximum hearing protection benefit.  First roll the ear plug between your fingers into a compacted rod.  Then slide the ear plug into your ear canal.  By pulling your ear back, you will be able to better insert a earplug into your ear.