Noise is defined as the sound which is unwanted or undesired for a particular community in a particular place. Sound is the form of energy which gives the sensation of hearing. It is produced by longitudinal mechanical waves in the matter and is transmitted by the oscillations of atoms and molecules of matter. Noise is basically a form of unwanted sound with a specific pitch, intensity, frequency, amplitude and other characteristics. The description of noise as an unwanted sound indicates that it has an unpleasant effect on human beings and their environment including land structure and domestic animals, also affecting wildlife and ecological cycles.
Units of measurement:
The unwanted sound or noise can be physically determined as a quantity with the unit called decibel (dB). Decibel is audio loudness measurement. It is the logarithmic unit that describes the ratio between sound intensity values or sound pressure values. 0dB is nominally the “threshold of hearing” and 85-90dB is nominally the “threshold of pain” while levels near 120dB may disturb normal body functioning.
Noise and our hearing:
The auditory function of the ear consists is the conduction of sound through the external and middle ears or cranial bones and their reception by the spiral organ of corti, the receptor of the auditory analyzer. The external and middle ear make up the sound conducting apparatus, while the internal ear, specially the organ of corti, makes up the sound perceiving apparatus.
The auricle in man plays a role in collecting sound and determining their direction.
Sound waves striking the tympanic membrane set it into vibrations. The drum being connected to the handle of malleus, these vibrations are transmitted to the ossicular window of the labyrinth, rocks in and out of the oval window according to the phase of sound vibration. The vibration of the foot plate of the stapes in the oval window sets up vibrations in the perilymph. These vibrations are transmitted to the basilar membrane, and the organ of corti which it supports.
The vibration of the basilar membrane causes the hair cells of the spiral organ of corti to get in touch with the overhanging tectorial membrane. At the same time, the mechanical energy of excitation, which is conveyed to most delicate receptors of the auditory nerve to be passed further to its nuclei into the medulla to the temporal brain lobes where nerve impulses are interpreted as sounds heard.
Normal hearing depends on the normal condition of the apparatus for sound perception and conduction. Human being can hear external sounds with a frequency of 16-20,000 cycles per second.
When sound vibrations enter into the cochlea; the tiny hairs in the cochlea to move back and forth. If vibrations with a great intensity blast into the cochlea, these hairs, especially the stereocilia, can be flattened and damaged.
Noise pollution is the pollution caused when the unwanted sound is dumped into the environment without taking concern of its adversaries it may have. It causes health hazards (auditory + non-auditory effects) to the people and also affects the surrounding environment as well as wildlife.
PARAMETERS FOR NOISE POLLUTION MEASUREMENT:
For noise emission measurement, change in several sound characteristics is determined for detecting and recording the accurate values in dB. Some of these measuring parameters are:
It is defined as the energy of sound per unit time and is given by:
W= E/t (j/s or Watts)
Whereas, sound power level can be described as:
Lw= 10 log (W/W0)
Where: W= measured power from the sound source
W0= reference power level (10-12 Watts)
It is defined as the amount of energy per unit area in unit time that is perpendicular to the direction of travelling sound waves. It is also defined as the sound power transmitted per unit area and is given by:
I = W/A (W/m2)
The dynamic range of sound intensity for human hearing ranges from 10-12W/m2 to 10-100 W/m2. The highest sound intensity possible to hear is 10,000,000,000,000 times as loud as the quietest. The usage of intensity for describing human ear response over a linear scale is very difficult as it gives such large values. Therefore, a logarithmic scale is used instead of linear scale in which the intensity level is given by 10 times the logarithmic ratio of the actual intensity to the reference intensity value. The threshold of audible sound is 10-16 W/cm2; which is considered as “0 dB”. Sound intensity level is given by:
Lt= 10 log (I/I0)
Where: I= intensity value measured (W/m2)
I0= reference intensity (10-16W/m2)
Sound pressure is defined as the force of sound per unit area perpendicular to the direction of sound waves. It is given by:
P= F/A (N/m2 or Pa)
The range of human hearing is 0.00002-20 Pa. the sound pressure level is given by:
SPL= 20 log (P/P0)
Where: P= measured sound pressure (Pa)
P0= reference power level (2A-10-5 Pa)
Table 1.1- Showing relationship between sound pressure and intensity level
CLASSIFICATION OF NOISE POLLUTION
Depending on the source of generation, the pollution due to several types of noises can be divided into following types:
COMMUNITY NOISE POLLUTION:
Community noise pollution is mainly spreading in the environment due to various community noises. These community noises can be further sub-divided into:
Road traffic noise:
With rapid increase in number of road vehicles, traffic noise is increasing day by day. The noise is spreading mainly due to traffic speed as the volume of the noise enhances with the traffic speed, and as modern high ways and traffic systems encourage speed, the noise pollution phenomenon is raising rapidly.
There is maximum noise pollution during morning and evening hours in urban areas. Heavy engine-trucks are the noisiest vehicles on road having at least 80-85dB level of noise.
This type includes all types of noises that are common in residential areas i.e. the noise of music players, television, burglar alarms, dog barking, residential construction noise etc. depending on its intensity and volume, residential or domestic noise can be source of annoyance to anyone. The noise level in residential areas ranges from 35-45dB and does not cause serious auditory disorders.
The noise which is spreading in the environment mainly due to aviation activities i.e. phases of a flight including take off, landing and flying on a path. These aerodynamic activities have an adverse effect on the people associated with the flight processes but also the people residing near airports. These noise levels are much higher in ultra-flight aircraft having a peak near 100dB which is extremely hazardous to the health.
Fig. 1.1- Aircraft noise pattern from a jet engine
OCCUPATIONAL NOISE POLLUTION:
Occupational noise pollution is the pollution which is present in the environment due to noises on work places, factories, and industries i.e. the noise of machines, tools, and other working equipment at work. Depending on the time of exposure, these noises have been divided into following three types:
It is defined as the noise whose maxima (highest levels) occur more often than once per second. It is produced by the machinery that operates without interruption e.g. pumps, compressors and processing equipments etc.
The noise that is not continuous with time i.e., taking alternating periods of start and stop is called intermittent noise e.g. drill machines.
House in a quiet street
Electrically amplified music
Table 1.2-Sound sources and their intensities
It is the noise that gives rise to instantaneous sharp sound for a small time duration and then diminishes e.g. blasting. The sound pressure in this type may be from 40dB (minimum) to 200 plus dB (sufficient to destroy internal organs).
Fig 1.2- intermittent noise from blasting
HAZARDOUS EFFECTS OF THE NOISE POLLUTION
Health effects on human beings:
Noise pollution is being considered as one of the leading environmental hazards nowadays. From a simple ceiling fan to a heavy traffic sight, the sound affects our lives somehow. But it is the relative loudness that is hazardous to the man and the other life forms. Noise pollution affects the human beings in two ways which are: 1) auditory effect: when it interferes with the functions of hearing mechanism. 2) Non-auditory effects: where it interacts with the health and bodily functions other than our hearing organs.
Fig.1.3- a brief chart description of noise pollution hazards on human health
The first organ that gets affected by the noise is the ear. More than 50% of our working community complains of tinnitus (continuous ringing noise) in the ear. Continuous exposure may lead to deafness or permanent loss of hearing. It is because of the complete destruction of the organ of corti that transmits sound from ear to brain. The levels at which a person can get affected by the noise exposure are given below:
Sensorineural hearing loss, neural hearing loss is due to damage to auditory nerves, sensory hearing loss is due to damage to inner ear or cochlea resulting from repeated loud noise exposure.
High noise levels can result in excessive ear-wax secretion, a damaged ear-drum or fluid in the inner ear.
More serious affects include permanent deafness, pain and ringing in the ears.
Non-auditory effects can be defined as “all the effects on health and welfare due to the noise exposure apart from the effects on the hearing organs.” they affect the social behaviour of the objects also altering the normal biological functioning of the body. When the noise pollution is considered to cause hazards other than hearing disorders, annoyance is the most basic level by which it affects people’s actions and communication, which leads to stress showing further symptoms and thus showing illness. On the other hand, noise may not always cause annoyance first and can directly affect health. The degree to which it may affect the health depends on the parameters including the intensity, pressure, volume, duration and the nature of the noise.
It is the most prevalent and well documented subjective response to the noise, including fear and mild anger. Noise is also seen as interfering into personal privacy, while its meaning for any individual is important in determining whether the person will be annoyed by it. Annoyance reactions are associated with the degree of interference that any noise causes in everyday activities, which probably precedes and leads on to annoyance. In both traffic and aircraft noise studies, the noise levels have been found to be associated with annoyance in a dose-response relationship. on the whole, it seems that the speech communication activities are most disturbed by aircraft noise while traffic noise is most disturbing for sleep,if present at night.
Noise pollution and sleep interference:
Exposure to the noise for a long duration disturbs sleep resulting in raised anxiety levels. Habituation is likely to occur with the continual exposure of the noise. Objective sleep disturbance will develop if more than 50 noise events per night with a maximum level of 50 dB are at indoors or more. But, for the outdoor noise levels the value is quite low for sleep disturbance. Noise exposure during sleep may elevate blood pressure, heart rate, pulse amplitude and affect body movements. Following disturbed sleep, there may also be after-effects during the day; perceived sleep quality, short temper and daily performance levels are decreased due to sleep disturbed by road traffic noise.
Effects on performance:
It has been concluded from the laboratory studies, that noise exposure impairs routine performance. If a speech is played in front of a person who is learning a particular subject, it will cause performance impairment. Such impairment is independent of the meaning or subject of the speech but depends on the relative loudness.
Noise exposure also slows down the rehearsal and the of selectivity processes in memory, and the choice of strategies for a particular tasks. It has also been observed that noise may reduce helping behaviour, increase violence and reduce the obedience of social cues.
The continuous exposure to noise causes numerous short-term physiological responses as transmitted through the nervous system. Exposure to noise causes physiological activation including elevated heart rate and blood pressure, peripheral vasoconstriction and increased peripheral vascular resistance. There is habituation to brief noise exposure but to the prolonged noise, habituation is less certain.
Studies have suggested that individuals continually exposed to continuous noise of at least 85 dB have higher blood pressure than those not exposed to noise. Noise exposure is also an indicator of exposure to physical and psycho-social factors, associated with high blood pressure. Aircraft noise pollution is found related to heart trouble and hypertension, more cardiovascular drug use and higher blood pressure. The effects of noise have been shown on systolic blood pressure (but not diastolic pressure), total cholesterol, total triglycerides, blood viscosity, platelet count and, glucose level. However, it was found that the prevalence of hypertension was higher among people exposed to aircraft noise levels of at least 55 dB or maximum levels above 72 dB around. There is some evidence from community studies that environmental noise is related to hypertension and there is also evidence that environmental noise may be a minor risk factor for coronary heart disease. A sudden exposure to noise may stimulate catecholamine secretion and precipitate cardiac dysrhythmias.
It has been found that persistent exposure to noise causing annoyance may lead to psychological disorders. Early studies showed that regular exposure to high levels of noise to the factory workers and inhabitants of overpopulated areas complain about nausea, headache, anxiety, restless nights, and edgy tempers. But recent studies do not confirm this association between air-craft and road noise and psychiatric disorders; and the weak association was established between road-traffic noise and mental depressiveness. Hence, it is now believed that environmental noise may seem related with certain psychological symptoms, but does not result in serious psychological disorders. However, enhanced noise levels may increase the possibility of such disorders.
Effects on cognitive behaviour in children:
It is of the common knowledge that children belong to a group which is especially vulnerable and sensitive to environmental pollution and all of its types. Their cognitive structure is developing and they lack the well-developed strategies to coop-up. Studies have found the Effect of environmental noise activities on the cognitive structure. The research shows that noise pollution does not affect all cognitive structures uniformly; affecting mainly central processing and understanding of the language. Difficulties have been found in concentration and visual attention. The reports describe that noise exposed children show more difficulty in concentrating than those who are less exposed. The test performed on primary school children living in over-populated areas showed them having poor auditory distinction and speech perception; affecting their reading ability, as well as their school performance than those living in quiet areas.
Effect of noise pollution on wildlife:
Noise pollution can be harmful to the animals. High enough levels of the noise pollution may interfere with the natural cycles of the animals, which may change their migration paths to avoid the sound; moreover, masking which is the inability to perceive sound of ecological cues and animal signals.
Exposure of Desert Kangaroo Rats to dune buggy sounds (95 db at 4 meters, on and off for 500 seconds) caused a major reduction on detection distance for its principal predator the Rattlesnake. When the distance for the normal sand kicking response to the snake’s presence was reduced from 40 cm to 2 cm, and it took three weeks for the rat to recover.
Plenty of evidences exist to prove that serious damage is occurring to the wild animals. Long-term effects from medium to low level noise intrusion need much more study, with emphasis on threatened and endangered species.
NOISE POLLUTION COUNTROL
All the sources of noise including road traffic, heavy vehicles, airplanes, factory machines etc. contribute towards noise pollution in one way or another. Some of these sources may have tolerable noise levels but when combined together, these can cause serious risks. According to World Health Organization, noise pollution control is easiest among all kinds of pollution the world is facing today Several steps are needed to be implemented so as to improve environmental conditions and to attain healthy “noise free” environment. Some of these steps are following
Public awareness measures are required to make people understand about noise pollution and to guide them about permissible noise levels by using print media and electronic media properly.
Noise exposure may be reduced on personal level by usage of protective ear plugs and also steps are required to reduce of exposure time to noise.
Engineering techniques such as altering and modifying the designs to reduce noise, construction of sound barriers and sound absorbers might be helpful.
Academic institutions and hospitals can be shifted away from the noisy roads, railway stations and airports. Similarly, the heavy industries and factories ought to be formed away from residential areas.
The usage of pressure horns and record players among all means of transportation must be banned by the government in order to reduce the noise intensity.
Monitoring of sound levels should be carried out by the traffic police. Legal action should be taken against violators by the government.
Law formation and implementation is required to lessen the hearing problems among factory workers.
Vegetation programmes along the roads should be initiated as plants absorb and dissipate high energy sound waves.