<%@ Page Language="vb" AutoEventWireup="false" Codebehind="hhlp.aspx.vb" Inherits="HCP.hhlp"%> <%@ Register TagPrefix="user_control" TagName="leftnav" Src="\hcp\user_controls\leftnav.ascx"%> <%@ Register TagPrefix="user_control" TagName="bottomfooter" Src="\hcp\user_controls\bottomfooter.ascx"%> Hearing and Hearing Loss Prevention Print Page
HCP Logo
Hearing and Hearing Loss Prevention


Preventing hearing loss due to hazardous noise exposure
The best way to prevent hearing loss due to noise exposure is to eliminate or reduce the noise level so that it is not hazardous. When noise cannot be eliminated, individuals must be protected from the noise by wearing hearing protection. Other ways to prevent hearing loss due to noise exposure is to limit the amount of time around noise, or increase your distance from the source of the noise.

Noise hazards are not only found on the job they can also be found at home and when participating in recreational activities. Ensure the same hearing loss prevention techniques are practiced at home and on the job.

Commanders and Supervisors must provide a hearing conservation program to protect the hearing of workers exposed to hazardous noise levels on the job. Employees must wear hearing protection when working around noise hazards. Military personnel exposed to noise hazards are required to wear hearing protection when working in industrial settings and during training. It is the responsibility of the employee/soldier to practice hearing loss prevention. It is also important to remember to practice hearing loss prevention off the job as well.

Personnel exposed to noise must also receive an annual hearing test to monitor their hearing.


How the ear hears
(Print-friendly version)
The anatomy of the ear is divided into three parts. The outer ear, middle ear and inner ear.



Outer Ear
(Print-friendly version)
The outer ear consists of the pinna and the ear canal. Sound waves are collected by the pinna and travel through the ear canal to the tympanic membrane (eardrum). Sound waves striking the eardrum cause it to vibrate. The eardrum separates the outer ear from the middle ear.



Middle Ear
(Print-friendly version)
The middle ear is made of the eardrum, three small bones (malleus, incus and stapes) collectively called ossicles, the space that encloses the ossicles and the Eustachian tube. Sound waves hitting the eardrum are transferred by the ossicles to the inner ear. The middle ear acts like an amplifier, increasing the intensity of the vibrations to overcome the difference between the air filledouter ear and the fluid filled inner ear. The Eustachian tube does not help one hear directly. Its function is to keep the pressure equal on either side of the eardrum.



Inner Ear
(Print-friendly version)

The inner ear can be divided into three parts: the semicircular canals, vestibule and the cochlea all of which are located in the temporal bone of the skull. Vibrations from the ossicles are transmitted to the cochlea via the stapes bone. The inner ear changes mechanical vibrations from the middle ear into electro-chemical impulses by stimulating hair cells inside the cochlea.


Inside The Cochlea
(Print-friendly version)

Movement of the fluid in the inner ear cause the hair cells to move. Hair cell movement sends electro-chemical impulses to the auditory nerve and the auditory nerve sends the impuses to the brain where they are interpreted as sound. This cochlear mechanics animation shows the movement of haircells.
    



How noise affects hearing
(Print-friendly version)
Exposure to loud noise destroys the hair cells in the inner ear. Once destroyed the hair cells cannot be replaced. Destroyed hair cells equate to loss of hearing. The loss of inner ear hair cells can also result in a loss of lateral inhibition whereby surviving adjacent hair cells and nerve endings are no longer "controlled" by the missing hair cells and fire spontaneously. This is one explanation for an acompanying condition to a noise-induced hearing loss called.
For more information on tinnitus visit the sites below:







Hearing loss due to exposure to noise usually occurs in the high frequencies. Because speech sounds that give meaning to words (ch, th, sh, f, p) are high frequency sounds, hearing loss due to noise exposure causes difficulty understanding speech.


Adapted from Northen, Jerry L. and Downs, Marion P. Hearing In Children (Third Edition) Baltimore, MD: The Williams and Wilkens Co. 1984.)


Hearing loss due to noise exposure is Progressive. It occurs over a long period of time and is called noise induced hearing loss. Loss of hearing due to noise exposure is Painless. By the time hearing loss is noticed, damage to hearing has been done. Hearing loss due to noise exposure is Permanent. Hearing that is lost cannot be regained.

Hearing loss due to noise exposure can also occur as a result of a one time very loud, very short duration noise such as an explosion. Hearing loss of this nature is called acoustic trauma. Acoustic trauma may permanently damage the inner, middle and or outer ear instantaneously.

Exposure to loud noise can also have what is called non auditory effects. Non auditory effects of noise induced hearing loss include, stress, high blood pressure, and increased anxiety levels.

When is sound harmful?
(Print-friendly version)
When steady state sounds (sounds lasting longer than .5 ms) reach a level of 85 dB(A) and the length of exposure is 8 hours or longer, hearing loss can occur if the ear is not adequately protected. The chart to the right shows the relationship between sound level and exposure time limit. Notice that as the sounds get louder the exposure time gets shorter.

Most people do not walk around with a device to measure noise levels so it might not be obvious when sound is hazardous. A good rule of thumb to use is the "three foot rule," which says, "if you must shout above the noise to be heard by someone standing three feet away then the noise could be damaging your hearing."

Also, if after leaving a potentially noise hazardous area, you experience tinnitus (ringing in the ears) or people talking to you sound as though they are mumbling, you could be experiencing temporary hearing loss due to noise exposure. Over time, temporary hearing losses may lead to permanent hearing loss.

Impulse or impact noise such as the discharge of a weapon or explosion can damage hearing instantly When impulse noise reaches a level of 140 dB (P) hearing loss can occur if the ear is not adequately protected.

 Sound Level
Exposure Limit
 85 dB (A)
 8 hours
88 dB (A)
 4 hours
 91 dB (A)
 2 hours
 94 dB (A)
 1 hour
 97 dB (A)
 30 minutes
 100 dB (A)
 15 minutes
 103 dB (A)
 7.5 minutes
106 dB (A)
 3.75 minutes