Is your hearing shot?
Noise from firearms carries a very high risk of noise injury.The use of high powered weapons and high velocity ammunition involves intensely high noise levels and an even greater risk.
Although the ear is only exposed to loud noise from the firearm for a fraction of a second, there is a very high risk of noise injury to hearing. This is due to:
The very loud level of noise
Firearms can produce noise in excess of 150 dB, sometimes up to 165 dB, i.e. above the pain threshold.
The impulsive nature of the noise
The sound emitted consists of a single, distinct pressure peak. An impulse reaches a high level in a very short period of time and can cause considerable damage to the ear and hearing - even with one exposure. Under conditions of continuous loud noise, a reflex is triggered causing the middle ear muscle to tighten and act as a dampener to excessively high levels of noise. This protects the inner ear (nerve of hearing) from damage. This reflex does not operate effectively in response to impulse noise.
The amount of protection required to protect your hearing is determined by the loudness of the sound and the length of time that you a e exposed. However, sudden intense sounds such as rifle fire can cause instantaneous damage to your hearing. Therefore, adequate protection form impulse noise, such as explosive fastening tools and firearms, can be obtained from good quality ear muffs with a hearing protector rating of 5. Prior to 1998 this rating was called an SLC80 rating and to adequately protect your hearing using protectors rated using this system, an SLC80 rating of 25dB or more would be recommended. The best protection can be obtained from a combination of ear plugs and ear muffs. (Find out more about the classification system on our "Hearing Protection" Fact Sheet—3.1).
Hearing protection should always be worn when you are exposed to noise from firearms. Noise injury may occur from very short periods of exposure but damage is permanent.
The result ?
Need More Hearing
Ear plugs and ear muffs worn together provide greater protection than either device worn alone. This dual protection also provides the wearer with an additional safety factor as each device is a backup for the other in the event of failure or inadequate seal. This is particularly important in the case of impulsive noise.
The resulting noise reduction is not the total of the two devices combined. The total level of noise reduction provided is limited by the skull itself. Sound waves are all around us and the skull acts as a conductor of sound. The two cochlear, or nerves of hearing, are encased in bone in the skull. Therefore, sound can be conducted through the bone to the hearing nerve by vibration. Evidence suggests that the maximum probable protection is equivalent to 35-40 dB.
When using a combination of plugs and muffs it is the quality of the plug that determines the effectiveness of the combination. Similar levels of protection are obtained for plugs in combination with muffs which have both large and small protection ratings. Note however, muffs with lower protection ratings are generally less bulky and more comfortable to wear.
It essential that the ear plug is inserted deeply enough to avoid contact with the ear muff. NOTE: Ear plugs are not recommended if wax, ear infection or any other medical condition relating to the ears is present.
Hearing protection should always be worn when you are exposed to noise from firearms.
ACKNOWLEDGMENT: Attenuation of Hearing Protectors, eighth edition, Australian Hearing Services, (National Acoustics Laboratories), 126 Greville Street, Chatswood, NSW, 2067.
Copyright © 1998 Farm Noise & Hearing Network