gistfile1.txt

The theme of my research is NIHL - Noise Induced Hearing Loss, which refers to the field of auditory organ's problems.
Noise induced hearing loss is defined as permanent hearing impairment arising from prolonged exposure to excessive levels of noise. 

One in 10 Americans has a hearing loss that affects his or her ability to understand normal speech. People working before the mid1960s may have been exposed to higher levels of noise where there were no laws governing hearing problems. Recent studies show an alarming increase in hearing loss in youngsters.

There are two different kinds of hearing loss:
1. Irreversible hearing loss
2. Noise can also cause a reversible hearing loss, called a temporary threshold shift. This typically occurs in individuals who are exposed to gunfire or firecrackers, and hear ringing in their ears after the event.

First, we have to define noise. Sound can be measured scientifically in two ways — intensity and pitch. Both of these affect the degree to which sound damages hearing.
Intensity of sound is measured in decibels (dB). Decibels are measured logarithmically, being 20 times the log of the ratio of a particular sound pressure to a reference sound pressure. Thus, 20 decibels is 10 times the intensity of 0 decibels, and 40 decibels is 100 times as intense as 20 decibels. 
Many experts agree that continual exposure to more than 85 decibels may become dangerous.

The following table illustrates some common sounds and their intensity. (Table &1)

Pitch is measured in frequency of sound vibrations per second, called Hertz (Hz). Generally noise induced hearing loss occurs at a pitch of about 2000-4000 Hz. Young children, who generally have the best hearing, can often distinguish sounds from about 20 Hz, such as the lowest note on a large pipe organ, to 20,000 Hz, such as the high shrill of a dog whistle that many people are unable to hear.

The duration of noise is also very significant: the longer you are exposed to noise the more damaging it could be. 
The next table illustrates how long we can be exposed to sounds of any intensity without having our hearing easily destructed. (Table &2) 

Let's take a look at the inside of an ear. If anything makes a sound, that sound enters the head through the earcanal and hits the eardrum, which vibrates when the sound waves hit it. Behind the drum, in the middle ear cavity, there are three tiny bones: stirrup, the anvil, and the hammer. They vibrate too. And actually they amplify the sound. They send the amplified sound vibrations to the cochlea, which looks sort of like a snail.
These sound waves travel around and around inside the cochlea and bend over tiny nerve endings called haircells. Much like wind pushes around the field of grain.
These haircells are the ends of nervecells, and the movement of the haircells sends electrical signals to the brain.
The brain decodes those signals and by such a way we can hear.
So that is how our hearing works.

But what happens when an ear is subjected to hazardous noise?
Let's go back to those hair cells. If those haircells get bent over to the point they can spring back, that's when hearing loss occurs. 

It's like blades of grass: imagine that they are haircells in our ears and the wind is the sound. Here comes a moderately loud sound and the wind just pushes the grass to the ground but after an exposure all of the grass bounces back.

And then here comes an extremely loud sound: the grass is pressed down to the ground but it never springs back.
Extremely loud sound causes permament damage, but so can moderately loud sounds if they continue over ,an extended period of time. Long exposures of the moderately loud sounds can do just as much harm as one really loud sound.
Both situations are hazardous. Fortunately, the grass grows back or it can be replaced; not so for your ears: the haircells never grow back and they can't be replaced. But noise-induced hearing loss is different in one important way – it can be reduced or prevented altogether.

For the sake of avoiding NIHL we can use earmuffs and earplugs. Both of them must tightly cover our ears for the optimum protection.

Noisy cities, listening to loud music, infrastructure sound emission: nowadays our life is overflowing with the harmful impact of sounds. In my research I came to understand that it is burning necessity to protect our ears and the problem of NIHL takes one of the first places by its importance.
My research shows that now it is clear that almost the whole planet should assume measures to investigate and prevent such impairments at governmental level. Clinics should be equipped with specific appliances, medical cabinets should be created. People should pay attention to their environment, because the environment has a direct influence on our health, and we are responsible for the welfare of nations.