Wising up about Noise Induced Hearing Loss (NIHL)

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Noise Induced Hearing Loss

 

Henwasin Sweety Lorin

Audiologist & Speech Pathologist, CIHSR


As one of the cause of hearing impairment, Noise Induced Hearing Loss (NIHL) is next to Presbycusis (age related hearing loss); yet it is preventable. One of the insidious cause of all occupational and environmental hazards is noise, causing severe hearing loss in every country in the world. Avoiding excessive exposure to noise is one of the major preventable ways to avoid permanent hearing impairment. 


Noise can be described in terms of frequencies (perceived as pitch) and intensity (perceived as loudness). Both the intensity and duration of noise exposure determine the potential damage to the hair cells of the inner ear. Sounds which are perceived as “comfortably” loud can also be harmful with repeated and continuous exposure over a period of time.


Sound level is measured in decibels dBA. Exposures to steady or fluctuating noise less than 85 dBA averaged over an 8-hour day pose little risk of hearing damage over a lifetime. Whereas repeated exposure to noise even at a permissible limit can develop a gradual NIHL where there is a repeated temporary threshold shift in hearing which fail to come back to normal baseline. In contrast to NIHL, acoustic trauma results in immediate permanent hearing loss due to impulsive noise (eg, gunfire or explosive blasts) or short durations of exposure to sound levels exceeding 115 dBA. Both NIHL and acoustic trauma are permanent sensorineural hearing losses. It is bilateral and symmetrical, usually affecting the higher frequencies (3k, 4k or 6k Hz) and then spreading to the lower frequencies (0.5k, 1k or 2k Hz). Impairment of hearing at high frequencies will initially cause a loss of clarity in speech and then interfere with daily activities as hearing loss progresses. Hearing loss-related symptoms, such as trouble in normal and telephonic conversation, turning up the radio/television volume and tinnitus, usually occur in the early stages of NIHL. Other major health effects due to the noise pollution are lack of concentration, irritation, fatigue, headache, sleep disturbances, etc. The risk of hearing loss and injury to the ears increases with the sound intensity, the length of time exposed to noise and the individual susceptibility to NIHL.


We are at all times exposed to noise through our daily living environment (nonoccupational noise) or at our workplace (occupational noise). 

 

Nonoccupational Noise

Nonoccupational noises may not be something that most people are exposed to frequently enough and long enough to incur NIHL, but there are potentially damaging noise sources including gunfire, fireworks, chain saws, power tools, woodworking equipment, and attendingsporting events, motor races, and loud concerts etc. Personal stereo players can be hazardous if the user wears the device regularly enough at high in-ear sound levels. Children are susceptible to acoustic trauma if they activate sound sources (eg; a bicycle horn or cap pistol) close to their ears. Some type of toys for children can produce sounds capable of causing permanent hearing damage.


Occupational Noise

In India, the occupational permissible noise exposure limit is 90 dBA  8 hours per day. The major industries responsible for excessive noise and exposing workers to hazardous levels of noise are textile, printing, saw mills, mining, etc. Studies carried out by the National Institute of Occupational Health in India, showed that the sound pressure levels were very high in various industries of India.


The noise levels in different industries is given in the Table

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Since 1948 in India, under the Employees State Insurance Act (1948) and the Workmen's Compensation Act (1923), NIHL has been a compensable disease. But still there is very little awareness regarding this fact. Nearly 3 billion dollars has been paid as compensation for NIHL in the USA in the last two decades. In India, it was only in 1996 that the first case got compensation, and about 250 workers received compensation for NIHL. Thus the need for educating the public and spreading awareness on its prevention and management is an important factor in the present Indian scenario.


How are you going to prevent noise induced hearing loss?
•    What is Noise Induced Hearing Loss (NIHL)?
NIHL is a permanent hearing loss due to long duration exposure to noise or a sudden short duration loud noise, eg; gunfire or explosive blasts. One of the common causes of nerve deafness.

 

•    How do I know if noise could be hurting my ears?
You maybe exposed to noise that hurts your ears through your hobbies or at your workplace. If you have to shout when you talk to a coworker who is standing just an arm’s length away, than the noise level at your workplace may be hurting your ears.

 

•    How do I know if I am getting Noise Induced Hearing Loss (NIHL)?
NIHL is usually gradual and occurs with no pain. After exposure to harmful noise, you may notice “ringing” sounds in the ear. You might have trouble hearing people talk, especially in crowded rooms and difficult in hearing high pitched sounds, like a baby crying or a telephone ringing in another room. These symptoms will usually go away after several hours or few days. However, when you are continuously exposed to this kind of noise again, you could get a hearing loss that could last forever.

 

•    What can I do to prevent Noise Induced Hearing Loss?

    Make “hearing health” part of your lifestyle. Stay away from loud and prolonged noises and turn down the music volume. Buy power tools that have sound controls. Invest on good quality headphones and earpiece which has the proper frequency balance.


    When you must be around noise, use Hearing Protection Device to protect your hearing.


    Hearing Protection Devices, like earplugs, earmuffs and canal caps are sold in drugstores and hardware stores. Different brands and different styles offer different amount of protection. If you are not sure which kind is best for you, or how to use it correctly, ask your audiologist or a professional in that  area.


    Keep your Hearing Protection Devices handy and in good condition.


    If you think that you have a hearing loss and is experiencing the signs and symptoms of a NIHL at your workplace and daily living environment, it is important to have your hearing tested.

 

"Blindness cuts us off from things, but deafness cuts us off from people,”     -Hellen Keller

 

References; 
Indian Journal of Occupational and Environmental Medicine (IJOEM); North Carolina Medical Journal of health policies analysis and debate(NCMJ).