Sound pollution leads to Noise Induced Hearing Loss (NIHL)
Pollution is a contaminant created by people and introduced into the environment. Noise pollution in many Indian cities including Hyderabad has been witnessing soaring decibels, way above medically permissible limits. It is time we observe this and correct it before it leads to Noise-induced hearing loss (NIHL).
The permissible limit of noise during the day is 55 decibels (dB) in residential areas and 50dB in silent zones like schools as per environment protection rules, 1986. The peak permissible level in industrial areas including other work areas and festivals like Diwali has been fixed at 140dB.
NIHL is one of the disorders which has been dramatically on the rise with civilization of the society. NIHL results from exposure to high-intensity (loud) sound, especially over a long period of time. It is a preventable hearing disorder that affects people of all ages.
Hearing mechanism: NIHL occurs when too much sound energy is transmitted into the ear and reaches the auditory system (system which converts the sound waves into signals which pass through nerves to the brain where they are perceived and interoperated).
A sound signal from an energy source, such as a radio, enters into the ear and is funneled through to the tympanic membrane (eardrum) and vibrates it. It is followed by the complex system of ear drum and ossicles (bunch of small bones in the ear) that transmit the mechanical energy to the inner ear called cochlea. Cochlea is the organ which converts this mechanical energy into signals and transmits these signals to the central auditory system within the brain.
When the ear is exposed to excessive sound levels or loud sounds over time, the overstimulation of the hair cells leads to heavy production of reactive oxygen species, leading to oxidative cell death. NIHL is therefore the consequence of overstimulation of the structures which converts the mechanical energy into signals which can transmit to the brain.
Types of NIHL
The ear can be exposed to short periods in excess of 120 dB without permanent harm — except with discomfort and possibly pain; but long term exposure to sound levels over 80 dB can cause permanent hearing loss.
There are two basic types of NIHL:
NIHL is caused by acoustic trauma which gradually develops into NIHL.
Acoustic trauma: sudden exposure to very loud sounds like – gun fire, bomb blasts, firecrackers can cause permanent irreversible damage to the cochlea.
Gradual developing of NIHL: It can lead to permanent cochlear damage from repeated exposure to loud sounds over a period of time.
NIHL usually occurs in people who are constantly exposed to noisy surroundings, traffic places, factories, bursting of fire crackers during Diwali festival. The U.S. Department of Labor's Occupational Safety and Health Administration (OSHA) states that exposure to 85 dB (A) of noise, known as an exposure action value, for more than eight hours per day can result in permanent hearing loss.
Daignosis is done by evaluating hearing capacity. Audio logical tests show some characteristic findings specific for NIHL. NIHL is generally observed to affect a person's hearing sensitivity in the higher frequencies, especially at 4000 Hz. Sometimes it can even affect 3000Hz or 6000Hz.
Who are at risk for NIHL?
People who develop NIHL usually complain of some disturbing sound in the ears all the time, decreased hearing especially in some frequencies, head ache, mood irritability etc.
“NIHL can easily be prevented through the use of some of the most simple, widely available and economical tools. This includes, but is not limited to ear protection (i.e. earplugs and earmuffs), education, and hearing conservation programs. Earplugs and earmuffs can provide the wearer with at least 5 to 10 dB SPL of attenuation,” says Dr. Satish Chandra, ENT, Head & Neck specialist.
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