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Hearing Protection & Noise Reduction Rating (NRR): What Have You Heard?

construction construction hearing products ear muffs ear plugs Ear protection hearing Hearing Protection loud noise noise reduction noise reduction rating NRR

Everyone has little quirky anecdotes about their spouse. My husband, Zachariah, doesn't read this blog. That's cool, because then I get to use him to tell dumb stories to illustrate whatever point I'd like to make.
 
One evening in 2013, shortly after we'd been married, I went to dinner at The Lowry in Minneapolis with Zach and one of his oldest friends. Both served deployments to the Middle East in the mid-aughts, and have subsequently experienced hearing damage and loss from IED explosions and gunfire. (Zach's is also because he likes to stand next to speakers at house music concerts with his ear protection in his pocket. I'd say no judging, but I totally judge him for this. He is going to live longer because I selectively judge. He'll be deaf, but, the love of all my lives, he'll be old and deaf.)

Photo by anna-m. w. from Pexels

Woo. 

 
Zach's biggest issue is with his right ear; I can remember this easily because he can never hear me in the car. And his buddy's hearing damage is worse in his left ear. And if you've ever been to The Lowry, you know it’s not a quiet place. There's music and lots of conversational noise and the acoustics sort of amplify everything. The place is delicious, so it really bustles during rushes. And my only ever complaint with it is that my husband and his goofy pal sat on the wrong side of one another at dinner and just yelled, "WHAT?" at each other the whole time, because Frick couldn't hear what Frack was saying. They thought this was hilarious and mostly wouldn't change seats because they could see it was making me crazy.
 
In addition to their hearing loss, both men experience tinnitus (TIN-ih-tus), which can be loosely described as a ringing in the ears. The Mayo Clinic describes it as a symptom to some other underlying condition, be it age-related damage, injury to the ear, or a disorder of the circulatory system. Over 50 million Americans are reported to suffer from tinnitus, and of them, 1 in 5 have bothersome tinnitus, defined as having a negative impact on their quality of life or functional health.

Dilbert, by Scott Adams

The human body is a remarkable and odd thing. Equilibrium keeps our bodies in a state of normalcy, or homeostasis. And so when things are working properly, we tend not to notice much. But when things get out of whack, especially in a fundamental sensory system like being able to hear sounds that we might tend to take for granted on a daily basis, it can be a very big deal. Hearing damage can be temporary, but it can also deepen in severity as time goes on, becoming an intermittent lifelong irritation, or worse, permanent.
 
Certainly, we can adapt to a new normal, and medical technology continues to improve, but, as the saying goes, an ounce of prevention is worth a pound of cure. Doubly so when the cure isn't really a cure. So, it's important to know how to protect our hearing, and perhaps the best place to start is to understand how our ears works. And to do that, we need a brief lesson in anatomy. So fun!

THE EAR

The Outer Ear

Pretty obviously, the outer ear is the part of the ear stuck to the sides of your head. It's called the pinna or auricle, and it's job is to funnel sounds to the organs and bones protected by the skull for processing and interpreting. The ear canal is also included as part of the outer ear. This is where earwax is produced. Earwax is often seen as something nasty to be removed, but it actually performs an immunological function. Made of chemicals that help fight infection, it coats the ear canal to protect it from pathogens, and is tacky to collect unwanted debris and dirt.

Ear anatomy https://beltonetristate.com/ear-anatomy-and-hearing-loss/

The Middle Ear

Things get a bit more complicated in the middle ear. In a nutshell, the middle ear transforms the sound waves funneled through the ear canal into vibrations that can be delivered to the inner ear. The eardrum sits at the end of the ear canal, and as sound waves bump into the ear drum, it vibrates to move three tiny bones on the other side called the ossicles--the malleus (hammer, in Latin), incus (anvil), and stapes (stirrup). These bones are the smallest in the human body. When they receive vibrations from the eardrum, the ossicles move in a chain reaction, one tapping the next, to send the signal to the inner ear. The last and smallest of these, the stapes, sits behind a membrane within the porous bony structure that separates the middle from the inner ear.

The Inner Ear

On the other side of the membrane surrounding the stapes sits the cochlea of the inner ear. This is considered to be the sensory organ of hearing. The vibrations of the stapes generate waves within the fluid of the cochlea. The surface of the cochlea is coated with tiny cells that project microscopic hairs. Vibrations and the wave-like response of the fluid within the cochlea move these hairs, causing nerve signals to be sent to the brain and interpreted as sound by the auditory cortex. 

HEARING LOSS 

Hearing loss can be attributed to a number of factors -- aging, physical damage to the outer, middle or inner ear, a ruptured eardrum, an abnormal buildup of earwax in the ear canal, a virulent untreated ear infection, tumors or abnormal bone growth in the ear, and even certain medications.

There are over 40 million Americans currently suffering from hearing loss. About a quarter of sufferers have noise-induced hearing loss. What is so striking about that number is that noise-induced hearing loss is largely preventable. Understanding the measurement of sound, knowing the risks of dangerous decibels and the proper protection for certain exposures is key.

MEASURING SOUND

Sound is physical, physiological, and psychological. Physics defines sound as the movement or vibration of molecules through some medium (solid, liquid, or gas) as an audible wave of pressure. When this wave of pressure reaches human ears, it is physiologically interpreted by the brain, and psychologically interpreted by the mind and the mental and emotional factors governing thoughts and feelings.

There are two factors to rating sound -- pressure and frequency. Sound volume (loudness) is measured in decibels (dB), specifically measuring the sound pressure level. The greater the pressure, the louder the sound, the higher the decibel rating will be. Sound frequency refers to the pitch of the sound, whether it is high or low. Frequency is measured in hertz (Hz), and refers to how many vibrations occur per second. The higher the frequency in hertz, the higher the pitch of the sound.

Sound must reach a certain volume before it can be heard by human ears, known as the auditory threshold. While it can vary from ear to ear, for consistency's sake the auditory threshold is measured at 0 dB. Similar to a temperature scale, the decibel scale goes below zero for sounds that humans can't hear.

The decibel scale is logarithmic, which means that at 10 dB, a sound is 10 times the pressure (louder) than the auditory threshold. At 20 dB, a sound is 100 times louder than the auditory threshold. At 30 dB, the sound is 1,000 times louder than the auditory threshold, and so on. 

The image below does a nice job visually explaining the dB scale. Both the sound pressure level in dB and the duration a person is exposed to it will impact how much damage it will cause. Anything over 85 dB is considered to be harmful when exposed over long periods of time.


Decibel ScaleImage: trgrowth, Adobe Stock

 

Here is my favorite fact of the post--Orfield Labs in Minneapolis has created a Quiet Chamber. Remember that the auditory threshold at 0 dB doesn't mean that there is no sound, it simply means that anything with a negative dB rating is below the threshold of human hearing. A regular room in a quiet home is measured around 30 dB. The Quiet Chamber is rated at -9 dB. This degree of silence causes your ears to attune more acutely to the noises of your own body--stomach, heart, lungs--and this experience can be so disorienting that with the exception of members of the media, all visits must be booked in advanced and supervised.

NOISE REDUCTION RATING (NRR)

The Noise Reduction Rating (NRR) system measures the level of decibel exposure reduction a device is capable of providing to the wearer. The higher the rating, the more robust the sound protection. The highest NRR rating for earplugs is 33, and the highest rating for earmuffs is 31.
 
It seems intuitive that the NRR rating would be a decrease in decibels by the number of the rating, but it's actually the rating, minus 7, divided by 2. So, for earplugs with an NRR of 33, it would be (33 - 7) / 2 = 13. That means realistically, the best you're going to get from hearing protection is a reduction of 13 dB.
 
So, remember our dB scale above? Say you're working construction. A jackhammer is rated at about 100 dB. Worn properly, ear plugs with an NRR of 33 would reduce dB exposure of your ears to right around 87 dB. To further protect your ears, you should wear those ear plugs with earmuffs over them. This can increase the NRR to 36. Using our equation, (36 - 7) /2 = 14.5 dB. Now you're down to an exposure of about 85.5 dB of sound pressure. At 100 dB, you are exposed to sound pressure that is ten billion times the auditory threshold. The reduction to 85.5 dB brings the pressure down into the millions. Your ears are still being exposed to damage-causing pressure, but remember that the dB scale is also logarithmic, so it's much, much less than it would be with no ear protection at all.
 
Anecdotally, I have to just drop this in here because it's interesting. Theoretically, there is a threshold of sound loud enough to kill a human. You can see above that the threshold of pain is 140 dB. 150 dB is loud enough to rupture the eardrum. Death would most likely occur between 185-200 dB, likely due to an embolism in the lungs, or possibly cause the lungs to burst due to the increase in air pressure.
 
All this to say, understanding the anatomy of your ears, the nature and measurement of sound, and the relationship therein can help you manage the protection you need for a given occupation or activity. Certain industries require proper NRR rated hearing protection as their workers are exposed to 85 dB or more for an eight hour period. The ANSI guideline S3.19-1974 details this for the workplace.
 
There are plenty of other activities loud enough to warrant wearing hearing protection. Going shooting? Wear hearing protection. Setting off fireworks? That's a yes, too. Working with loud tools? Yep. Riding a motorcycle? I'd argue that you really should be going for head protection, but a lot of helmets have noise-cancelling properties. So, yes. Going to a concert? Yes. Standing next to the sound system? For the love of… Ugh. YES.
 
I'd be remiss if I didn't mention that if you're looking for hearing protection, we've got a selection of NRR hearing protection available for purchase. This is not our comprehensive collection, so if you're not finding what you're looking for, call our office at (952) 890-1321 and one of our trained representatives can help you find what you need.

Brian Gordon FowlLanguageComics.com

In conclusion, this is my actual life.


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