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NOISE The invisible pollutant |
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What is the meaning of noise? The definition
of this very ubiquitous phenomenon is a very subjective one. After all what is one man's
Mozart may be another's dub music. Perhaps the best definition would be sound energy that
causes annoyance. Of course this only takes into account the fact that noise can cause
psychological and physiological upsets. This is true for sound at any intensity.
To illustrate, let us consider passengers in a moving train. To a man reading his newspaper the sound of the train is almost calming but to two people trying to hold a conversation it can be infuriating. This then is one aspect of noise - the sound that irritates. The other more alarming but far more insidious aspect is the physical damage that noise can product. This is a function of its intensity. There is now irrefutable evidence that loud noise damages the delicate mechanism of the ear, and when such damage has occurred it s irreversible. The end organ of hearing located within the delicate snail shell of the cochica is the Organ of Corti. Simply, it contains millions of hair like cells embedded in a jelly. These hairs bend when sound waves strike them. High frequency sounds stimulate the Organ of Corti near the base of the cochiea and low frequency sound near its apex. The range is from 60Hz to 20,000Hz. The intensity of sound or its loudness will dictate how much these hair cells bend and thus the intensity of the electrical signal reaching the brain. It is therefore easy to see that sounds of large intensity constantly striking these delicate hairs will eventually damage them and that since the high frequency receptors are first in the path of the sound wave they are the first to go. Noise damage is a function of intensity (measured in decibels - db) times length of exposure (measured in hours). The decibel scale is a logarithmic scale so that an increase of 20dbs is a tenfold and 40dbs a hundredfold increase in sound pressure. To illustrate what is meant by sound intensity some everyday examples are shown below. 0 db Threshold of hearing 10 db Normal breathing 20 db Leaves rustling in a breeze 30 db Empty movie house 40 db suburban residential neighbourhood at night 50 db Quiet restaurant 60 db Two-person conversation 70 db Busy traffic 80 db Vacuum cleaner 90 db Water at the foot of Niagara falls 100 db Subway train 120 db Steel band at close range 130 db Rock Band at 100 yards 140 db Military Jet at take off 160 db Wind tunnel 180 db Space rocket 0 decibels of near absolute silence can only be achieved in an echo free chamber but it is the level at which a normal ear will just pick up sounds in the range of 250Hz to 4000Hz. The speech frequencies incidentally are 500, 1000 and 2000Hz with 1000Hz being the frequency at which hearing is most accurate. Above 120db noise is so intense that it can be felt as a ticking sensation in the ear, and beyond 130db the sensation changes to pain and will damage the unprotected ear. In the early part of the century in the U.K. noise induced hearing loss was recognized in workers who used pneumatic riveters to rivet steel plates. It was given the name 'boilermaker's deafness'. Oddly enough it was the Russians in 1929 who first classified noise induced deafness as an industrial disease and offered compensation. Nowadays most industrialized countries have set safety standards for maximum noise to which workers can be exposed during a working shift through Occupational Safety and Health Acts. For example the U.S. O.S.H. Agency recommends eight hours at 90db six hours at 92db, four hours at 95db and so on. Scandinavian countries use even lower levels viz eight hours at 85db etc. In addition to the damage they can do to hearing, loud sounds have several other effects. For instance a sound of 140db can produce unpleasant bodily sensations: a felling of vibration in the head, a pain in the middle ear, loss of equilibrium, nausea and sweating. Sudden sounds of lower intensity like the sound of a small firecracker going off unexpectedly can cause the blood pressure to rise, the pulse to quicken, the mouth to dry up and digestion to be upset. If noise produces so many unpleasant side effects is it any wonder that rock musicians who are constantly exposed to sound at 130dbs need recreational drugs to "calm their nerves"?; or nearer home that schoolchildren exposed to loud music in the confines of a maxi taxi are aggressive when they get to school? And these are just the physiological and psychological aspects! Think of the damage that is being done to their delicate hearing apparatuses. We are slowly producing a generation of deaf children and deaf musicians Now if you think that this is all a bit far fetched and alarmist, then think of the last Carnival fete you went to. Do you remember how, as you left the fete your ears were ringing? And maybe even hurting a bit? Do you remember as you walked to your car you and your companions spoke to each other in raised voices? Do you recall that when you were in your car you had to turn up the car radio's volume in order to hear it? What had just happened was you had suffered temporary deafness. Your threshold of hearing had shifted downwards. In other words if you started off with a hearing average of 10db you could be now down to 15db. Not much you might think but this means that you will now require sounds to be four times as loud if you are to hear them. Of course this is only temporary and your hearing will be restored by the next day. But think of this happening everyday or even say three times a week - it is not difficult to imagine what the final outcome will be. And the bad news is that once you've lost it you can never get it back. You then will probably end up wearing a hearing aid. We can now identify the sources of noise with the potential to damage your hearing … what has often been referred to as Invisible pollution. Noise in the Work Place….. machinery, engines, turbines, steam valves, lathes, grinders, jackhammers, pneumatic tools - the list goes on. Also at risk are workers at airports, tractor drivers and railway workers.….. machinery, engines, turbines, steam valves, lathes, grinders, jackhammers, pneumatic tools - the list goes on. Also at risk are workers at airports, tractor drivers and railway workers. Recreational Noise There is no doubt that loud music in public transport vehicles should be banned. Besides the deleterious effect on the passengers it is distracting to the driver. This is a matter of some urgency and can easily be carried out by the relevant licensing authority. Musicians should wear ear defenders, D.J.s should keep headphone sound down to a minimum (suggested maximum of 80 db for a six hour stink with several days rest in between); Revelers should wear ear plugs when attending noisy fetes and attendees at concerts should do the same. Ear plugs will attenuate sound by up to 25db still allowing you to enjoy the music. It is very important that our musicians heed this advice for the very people who represent the creative talent in our society now have endangered hearing acuity. And if you can't hear you can't create (Not everyone is a Beethoven!!). And of course there's the eternal nuisance created by noisy fetes. All public fetes should require a license and none should be granted to promoters who desire to hold it within 500 yards of a residential area. Ambient Noise This can be reduced by enacting strict laws governing noisy auto and motor bike mufflers; the use of car horns in residential areas; the siting of factories and workshops; the licensing of bars and nightclubs. Enviornmental Noise There is always the debate as to which came first the airport or the residential area and similarly the industrial complex and the housing estate. If a residential area existed before then no planner should put in an industrial complex slap bang in the middle of it. Besides the noise nuisance there's also the obvious danger of industrial accidents (remember Five Mile Island and Bhopal). Airports with low flying aircraft landing and taking off present a very real nuisance. Airports should be as far away from residential areas as possible. Of course both examples with their large employment capacity attract home buyers to their vicinity so that there should be good policing of developers by the Town and Country Planning Division. Finally, here is a sobering fact… in 1975 in the U.S.A., there were more people afflicted with hearing problems that were permanent than all the people afflicted with blindness, multiple sclerosis, tuberculosis, kidney, liver and venereal disease combined!!!! In a world full of sound the intensity is reaching deafening proportions. Our hearing is fast becoming an endangered sense. Let us opt more for the sound of silence.
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