Today just about anyone participating in a sport or hobby involving a rifle, pistol or shotgun is aware of Hearing Protection Devices (HPD’s), more broadly called earplugs. HPD’s are personal safety devices worn in or over the ears to reduce the harmful or annoying effects of sound. OSHA has set the level for hazardous noise at 90dB, which is also the level at which hearing protection is required. The Department of Defense and all branches of the Armed Services have reduced that number to 85dB in order to give their personnel even greater protection. Furthermore, the use of double hearing protection is required anytime continuous noise is greater than 104dB. HPD’s are required in excess of 140dB(peak) for impulse/impact noise such as shooting. Just to give you an idea, a .22 rifle is about 136-140dBp at ten feet. Heavier calibers can reach 170dBp. Therefore, any rimfire or centerfire requires HPD’s.
Why bother to use hearing protection? If you don’t, over a period of time or even from as little as one loud (explosive) episode, you could suffer the effects of acoustic trauma or noise induced hearing loss which results in permanent, irreversible nerve damage. I have prescribed and fitted a considerable number of hearing aids that could have been completely avoided. Noise induced hearing loss occurs slowly over a period of years, however, by the time it is noticed, there is already significant permanent nerve damage, and it can only get worse.
How do hearing protection devices work? Basically, for sound to heard it must pass through the outer and middle ear in order to get into the inner ear where nerve cells then transmit the message to your brain where sounds are interpreted. When you cover the outer ear or place an earplug into the outer ear canal it creates a conductive or temporary hearing loss. The HPD interrupts or cuts down the amount of sound that can be transmitted to the inner ear which is measured in decibels. In fact, all HPD’s are given a rating that gives you an idea of how effectively they can, under excellent fitting conditions, reduce the sound level reaching your inner ear. This is referred to as the Noise Reduction Rating (NRR). This number will be found on the HPD or on its package. The higher the number, the more protection the HPD provides. This can assist to some extent in choosing the level of hearing protection to use, but your choice should not be based solely on the NRR, but rather performance factors for the occasion and at the time of use. Remember, hearing loss can be a significant social handicap.
Some people who do not use HPD’s as they should say the sound is still loud even when they do, and falsely assume that there is no point. While this is true in a very narrow sense, they are missing a very significant point. If the sound level is 100 dB and you use a set of earplugs with an NRR of 20 dB your inner ear would now in theory be receiving a sound level of 80 dB (100 dB minus 20 dB). Is that loud? Yes. Is it damaging? No. Why do so many people not use hearing protection when necessary? I can only recall a remark by the rock star, Frank Zappa who once said, “The two most common things on earth are hydrogen and stupidity.”
Hearing protection devices are many and varied, but all fall within a few categories such as inserts, canal caps, head muffs, and custom molded types. There is no one type of HPD that is best. Within each type of HPD there will also be a wide variety of NRR values. Please note: wearing a head-phone or muff type HPD in combination with an insert type does not double your protection, and it does not result in the total decibel protection of adding the NRR of each type used. Decibels cannot be directly added. So, if a 30dB NRR muff type is placed over a 20 dB NRR set of insert plugs it does not give a total of 50dB noise reduction. However, be of good cheer since using double hearing protection does produce significantly greater protection (attenuation of noise) than the use of single hearing protection, especially if both types have high NRR values. Contrary to popular belief, cigarette filters or cotton balls inserted into the ear canal are acoustically transparent and offers essentially no hearing protection.
Insert type earplugs come in a myriad of materials, shapes, colors, and NRR values. They are available in single units, on connecting strings and some are made as headbands and neckbands. These should be chosen with consideration for the NRR needed, but the most important thing is getting a correct fit, otherwise you will not get the protection you paid for. Many types can be reused if washed with soap and water. Insert earplugs are usually quite inexpensive.
Muff type HPD’s can offer some of the highest NRR numbers, but can be difficult to use with a rifle or shotgun. This type is heavy and among the most expensive. Also, earmuff effectiveness can be reduced by hair and eyeglasses due to the small channel caused by the temples.
Custom molded earplugs are made individually for each ear by a professional. They “lock” into the ear and fit the same (correct) way each time. The quality of this type is dependent on the skill of the fabricator, they are comfortable, but will not last forever.
There has been much more research and study of HPD’s than can be presented in this article. However, one of the most important facts that have been proven beyond doubt is that hearing loss caused by noise exposure can be prevented. That’s right! All you have to do is select an HPD that is comfortable and easy for you to wear…and it is never too late to start. Are you using them?
Mr. Lewis can be contacted for further information or questions at slewis@mar.med.navy.mil
