NOISE POLUTION

Background

   Sound is a form of energy. It is that external physical cause which produces the sensation of hearing in our ears. Sound is produced only when some material body is made to vibrate. It requires material medium for its propagation and cannot travel in vacuum because there are no material particles which can vibrate and propagate energy. The vibrations travel through the medium in form of waves with a certain speed depending on the density and elasticity of the medium. When vibrations reach our ear, sound is heard. Our ears are sensitive only to a limited range of frequencies 20 Hz to 20,000 Hz. This range of frequency is, therefore, called the audible range of sound. The sound of frequency above 20,000 Hz is called the ultrasonic, while the sound of frequency below 20 Hz is called the infrasonic. Ultrasonic and infrasonic both are inaudible to human beings. Ultra sound used in medical diagnosis. Infra sound produced in earthquakes.

   Different animals have different ranges of audible frequencies. A dog can hear sounds of frequencies up to nearly 50 kHz, a bat up to about 100 kHz, while Dolphins can hear sounds of even higher frequencies up to 150 kHz. The animals can also produce ultrasonic sounds and can communicate in them. Elephants and Whales produce sounds of frequencies less than 20 Hz. Some fishes can hear sounds of frequencies in the range of 1 Hz to 25 Hz.

Frequency Ranges for Hearing and Speaking by Human and Animals

Loudness, Intensity and dB

	Loudness is the property by virtue of which a loud sound can be distinguished from a faint one, both having the same quality. Loudness is an aural sensation, i.e., a physiological rather than a physical phenomenon;
	The louder a sound is, the more energy its sound waves carry. Loudness is measured in decibels(dB).Sound of 0 dB are just audible to the human ear, while sound of 130 dB or more cause pain;
	Loudness of sound depends on intensity of the wave, however, loudness is not the same as intensity. Intensity is a measurable quantity, while loudness is a sensation;
	Experimentally, Weber and Fechner established a relationship between the loudness L and intensity I which is given as: L = K log10I, where K is a constant of proportionality. Thus, loudness is proportional to the logarithmic value of the intensity, but not in the same proportion. Relation between the two is not linear.
	The intensity at any point of the medium is measured as the amount of sound energy passing per second normally through unit area at that point. Its unit is microwatt per metre² (which is equal to 10-6 joule per second per metre²).
	The intensity of normal sound is nearly 10µW m-2 while minimum intensity of sound audible to ears is 10-6µW m-2. Greater the energy carried by a sound wave, greater is the intensity of sound, hence louder it seems to us. The intensity of a sound wave in air is proportional to (i)the square of the amplitude of vibration,(ii)the square of the frequency of vibration and(iii)the density of air.
	The sound level is usually expressed in decibel(dB).If at a given frequency, I1 and I0 are intensities of two sounds, which loudness are L1 and L0 then difference in loudness of the two sounds L is: L = L1 - L0 = K(log10I1 – log10I0) or L = K log10 I1 I0 If, I0 is taken as reference intensity (10-12µW m-2), the minimum intensity of audible sound intensity at frequency 1 kHz, then L is called the sound level. Taking K = 1, the sound level is L = log10 ( I1 I0 ) ForI1 = I0, sound level L = 0 dB, sound of intensity 10-12µW m-2 at 1 kHz has loudness zero dB.    For an increase in intensity at a point by 100 times the initial value, the increase in sound level will be 10 log10 100 = 20 dB. For an increase in intensity at a point by 100,00 times the initial value, the increase in sound level will be 10 log10 100,00 = 40 dB. It means that for 100 times increase in intensity, the loudness get doubled.
	the inventor of telephone. the scientist Alexander Graham Bel,
	1 dB is defined as the change in level of loudness when the intensity of sound changes by 26%.

Sound Pressure, Sound Pressure Level
Sound Power, Sound Power Level

   Intensity is the energy/time/area; and since the energy/time ratio is equivalent to the quantity “power” , hence, intensity is simply the power/area.

   Therefore, sound strength is measured as sound pressure, sound pressure level or sound power, sound power level (in decibels).

Sound Pressure

	The Sound Pressure is the force (N) of sound on a surface area (m2) perpendicular to the direction of the sound. The SI-unit for the Sound Pressure is N/m2 or Pa.
	Sound is usually measured with microphones responding proportionally to the sound pressure - p. The power in a sound wave goes as the square of the pressure.
	The lowest sound pressure possible to hear is approximately 2 10-5 Pa (20 micro Pascal, 0.02 mPa), 2 ten billionths of an atmosphere.
	It is therefore, convenient to express the sound pressure as a logarithmic decibel scale related to this lowest human hearable sound - 2 10-5 Pa, 0 dB.

Sound Pressure Level

        Where,

        L_p = sound pressure level (dB)

        p = sound pressure (Pa)

        p_ref = 2 10^-5 - reference sound pressure (Pa)

        If the pressure is doubled, the sound pressure level is increased with 6 dB (20 log (2)).

Sound Power

        Sound power is the energy rate - the energy of sound per unit of time (J/s, W in SI-unit) from a sound source.

Sound Power Level

Sound power can more practically be expressed as a relation to the threshold of hearing - 10^-12 W - in a logarithmic scale named Sound Power Level - L_w, expressed as:

L_w = 10 log (N / N_o)

Where,

L_w = Sound Power Level in Decibel (dB)

N = sound power (W)

N_o = 10^-12 - reference sound power (W).

Human hearable Sound Power spans from 10^-12 W to 10 - 100 W, a range of 10/10^-12 = 10¹³.

Sound Level in dB of Some Common Sound

HOW DO WE HEAR

The Human hear consist of three main parts; the outer ear, middle ear and inner ear.

The outer ear consists of:

	The ear lobe (pinna or auricle)
	The ear canal, through which sound waves pass to the ear drum
	The ear drum (Tympanic membrane that separates the outer ear from the middle ear)

   The ear lobe and the outer ear canal, which delivers sound to the middle ear, make up the outer ear. Within the outer ear canal are wax- producing glands and hairs that protect the middle ear.

The ear drum is a thin, semitransparent, oval-shaped membrane that separates the middle ear from the outer ear. Its purpose is to vibrate according to the frequency and amplitude of sounds that strike it.

The Purpose of the middle ear is to:

	Transmit and amplify sounds from the eardrum to the oval window.
	Act as a dampener on loud sounds that may damage that inner ear (cochlea).

   The middle ear acts as an impedance matching device and has three small bones operating as a set of levers. These bones transfer the vibration to the inner ear which consists of two separate systems, the semi-circular canals for controlling balance and cochlea.

The inner ear consists of:

Two chambers called the vestibular labyrinth and the cochlea.

	The vestibular labyrinth consists of elaborately formed canals (3 semicircular tubes that connect to one another), which are largely responsible for the sense of balance.
	The cochlea, which begins at the oval window, curves into a shape that resembles a snail shell. Tiny hairs line the curves of the cochlea. Both the labyrinth and cochlea are filled with various fluids.

   The cochlea is a fluid-filled, snailed-shaped tube which is divided longitudinally into two parts by the basilar membrane.
In response to an acoustic stimulus the fluid in the cochlea is disturbed and this distorts the basilar membrane on whose upper surfaces are thousands of bery sensitive hair cells. The hair cells register this distortion and transform it into nerve impulses which are transmitted to the brain. Brain is sent these messages (translated from vibrations by the cilia) through the auditory nerve. Our brain then translates all that and tells what we are hearing. Neurologists don’t yet fully understand how we process raw sound date once it enters the cerebral cortex. In the brain.

Sound and Noise

   Sound is that part of energy which excites in us, the sensation of hearing. This is because some type of energy originating from the source and is entering our ear. Sound becomes unwanted when it either interferes with normal activities such as sleeping, conversation, or disrupts or diminishes one’s quality of life and such sound is known as unwanted sound, hence we call it sound pollutant or Noise. The traditional definition of noise is also “unwanted or disturbing sound”. A sound might be unwanted because it is:

	Loud
	Unpleasant
	Intrusive or distracting

   A constant hearing of sound of level above 120 dB can cause headache and permanent damage to the ears of the listeners. The sound of level 30 dB to 10 dB has the soothing sensation, while the level 0 dB of loudness of sound represents the limit of hearing. We should not confused about the limit of hearing with the limit of audibility. The limit audibility refers to the frequency of sound 20 Hz to 20 kHz which a man can hear, while the limit of hearing is the level of loudness (=0 dB) which a man can hear. Noise is also considered a mixture of many different sound frequencies at high decibels levels.

Type of Noise

Classification of Noise

Noise Pollution

  Noise Pollution refers to sound in the environment that are caused by humans and that threaten the health or welfare of human or animal inhabitants.
The most common source of noise pollution by far, the one that affects the most people on the planet, is loudspeaker, siren, motor vehicles. Aircraft and industrial machinery are also sources. Additional noise pollution is contributed by office machines, sirens, power tools, and other equipment.
The response of ear to sound is very dependent on the frequency content of the sound. The ear has a peak response around 2.5-3 kHz and has a relatively low response at low frequencies.
Threshold of Pain: sound level at which the ear starts to feel pain. The threshold of pain is different for sound of different frequencies.

NOISE AND ITS IMPACT

7.1 Human health

   Noise health effects are other health and behavioural in nature. The unwanted sound is called noise. This unwanted sound can damage physiological and psychological health. Noise pollution can cause annoyance and aggression, hypertension, high stress levels, tinnitus, hearing loss, sleep disturbances, and other harmful effects. Furthermore, stress and hypertension are the leading causes to health problems, whereas tinnitus can lead to forgetfulness, severe depression and at times panic attacks.

   High noise levels can contribute to cardiovascular effects and exposure to moderately high levels during a single eight hour period causes a statistical rise in blood pressure of five to ten points and an increase in stress. Noise health effects are the health consequences of elevated sound levels. Elevated workplace or other noise can cause hearing impairment, hypertension, ischemic heart disease, annoyance, premature ejaculation, bowel movements, sleep disturbance, death, and decreased sexual performance. Changes in the immune system and birth defects have been attributed to noise exposure, but evidence is limited. Beyond these effects, elevated noise levels can create stress, increase workplace accident rates, and stimulate aggression and other anti-social behaviour. The most significant causes are vehicle and aircraft noise, prolonged exposure to loud music, and industrial noise.

Hearing Damage:

	Well established effect, caused by prolonged exposure to intense sound.
	Impairs ability to understand speech.
	Permanent and irreversible, even with hearing aids.

7.2 Animal Health:

   In general, a noise impact to wildlife can be determined by the degree to which the noise disrupts a functioning ecosystem. Noise has the potential to affect wildlife in a variety of ways, varying between different types of animals. Research shows that the degree of reaction to noise often varies with age, sex, season, situation, previous exposure to noise (habituation), noise level, and frequency spectrum. Potential noise effects on wildlife include; auditory damage, physiological changes and behavioural alterations. These effects are further characterized into primary and secondary effects. Primary effects are direct physical effects to the animal. Secondary effects are indirect changes which occur between the animal and its environment.

Physiological Effects- Physiological effects, such as metabolic and hormonal changes, are often associated with stress. Stress in wildlife in their natural setting is typically a difficult response to quantify. For wildlife, stress reactions are part of survival and a routine occurrence. Stress reactions involve what is commonly referred to as the “fight or flight” response. When this reaction is inappropriate, such as fleeing from a non-threaten noise, impacts begin to occur. Inappropriate reactions unnecessarily to deplete an animal’s energy resources which can increase susceptibility to predators, disease, and starvation.

Behavioural Effects- Changes in normal behavioural patterns are the most apparent effects of noise on wildlife. When noise becomes an objectionable intrusion on wildlife habitat, these changes include alterations in habitat locations and migration patterns, and abnormal behaviour that can cause difficulty in mating and survival.

AIR ACT & NOISE RULES

8.1 AIR ACT & NOISE RULES

   Under section 2(a) of Air (Prevention and Control of Pollution) Act, 1981 noise is defined as air pollutant “Air pollutant” means any solid, liquid or gaseous substance [(including noise)] present in the atmosphere in such concentration as may be or tend to be injurious to human beings or other living creatures or plants or property or environment.” Increasing ambient noise level in public places from various sources, inter-alia, industry activity, construction activity, generators sets, loud speakers, public address systems, music systems, vehicular gowns and other mechanical devices have deleterious effects on human health and the psychological well being of the people. Therefore, it is considered necessary to regulate and control of noise producing and generating sources with the objective of maintaining the ambient air quality standards in respect of noise.
   Central Government notified the Noise Pollution (Regulation and Control) Rules, 2000 as it is published in the Gazette of India, Extraordinary, Part-II – section 3 (ii), vide S.O 123 (E) dated 14.2.2000. In reference to above mentioned rules following responsibilities are vested with State Governments. District Magistrate, Police Commissioner, or any other officer not below the rank or Deputy Superintendent of Police:

Ambient Air Quality Standards in Respect of Noise is notified under Noise Pollution (Regulation and Control) Rules, 2000.

Note:

NOISE STATUS

Ambient Noise Level of Patna Town during year 2010-2011

[Note: dB(A) Leq represents the time weighted average of the level of sound in decibels on scale A which is relatable to the human hearing]

NOISE LEVEL ON DIWALI

A Report on Ambient Noise Level Monitoring is carried out as per CPCB Protocol given for Ambient Noise Level Monitoring in Patna town at Boring Road Crossing in normal day as well as on Diwali day, 2011.

     Diwali is one of the important festivals of India and bursting of crackers and noise generating fireworks are integral part of its celebration. So generation of noise pollution and air pollution during the festival cannot be denied. Though the Hon'ble Supreme Court has banned the bursting of crackers or any noise generating fireworks of high decibels to control the noise pollution but unfortunately, the same is not being followed in letter and spirit. Therefore, an unbearable noise pollution creates severe problem to the common people during Diwali Festival.

Ambiant Noise Pollution Survey procédure:

     Firecrackers generate instantaneous impulsive noise, which when measured in free field condition in impulsive mode, gives peak sound pressure level. It is quite obvious that a number of crackers when bursting serially can easily form a band of continuous noise in the presence of reflecting surfaces. The reverberation of sound wave due to repeated reflection in the surfaces prolongs the time interval of prevailing sound intensity. The continuous band of noise, thus formed, definitely affects the ambient level in close proximity.

     The Integrating Sound Level Meter along with Microphone fitted with windscreen was placed 1.3m above the ground on the Tripod stand in the free field at Boring Road Crossing location. The site was appeared like free field. The monitoring point was away from obstacles. Data recorded at the said location for one-hour equivalent continuous noise level in Leq dB(A). The above procedure was repeated for 06 hours i.e.18:00 hours to 24:00 on normal day i.e. 19.10.2011 and the Diwali day i.e. on 26.10.2011 on the same location.

     Bihar State pollution Control Board has conducted ambient noise level monitoring hourly at Boring Road Crossing, Patna for two days for 6 hours from 18:00 hours to 24:00 hours on normal day 19.10.2011 and on Deepawali day 26.10.2011 to observe the environmental impact of bursting of crackers. The observations were taken hourly. The observations of the monitoring are given in table below:

Ambient Noise Level at Boring Road Crossing in Patna during Normal and Diwali day in the year 2011

            [Note: Monitoring site was commercial area.]

Findings of Ambient Noise Level Monitoring – Diwali- 2011

	The ambient noise level during day & night time at Boring Road Crossing on Diwali day- 2011 was found increased as comparedto normal day.
	The average ambient noise levels in day time for normal day were ranging from 72.97 to 90.98 in Leq dB(A) and on the eve of Diawali day 73.36 to 86.14 in Leq dB(A).
	The average ambient noise levels in night time for normal day were ranging from 63.20 to 78.55 in Leq dB(A) and on the eve of Diwali day 68.65 to 84.68in Leq dB(A).

Overall Conclusion:

     Ambient Noise levels during day & night time on the occasion of Diwali Day, 2011 were found higher value with respect to the normal day, because of bursting of increased number of bursting crackers as well as from trade activities, the transport system and various domestic activities.

Recommendations:

Protecting The Common & Contribute to Peace and Quiet

     A number of public complains are being made to the state pollution control board and local authority every month specially due to D.G. Sets, pressure horns and community hall for party & function. The following noise sources in the community can disturb quality of life:

»   Music concerts and clubs.
»   Car and home stereos.
»   Personal music players.
»   Bus, Truck, car, motor cycles and their pressure horn etc. and
»   Transportation: subways, traffic, garbage trucks.

There are several steps one can take to reduce noise in our community and protect us

► Turn down the volume: Today, many people play their television sets and personal stereos unnecessarily loud. keep the sound       at safe level.

► Reduce your exposure: Some situations are inherently noisy, but you can decrease the risk of damage in several ways. Try to       avoid going to loud bars, restaurants, or clubs for hours at a time. Limit the time you spend in noisy area;

► Protect yourself: Earplugs can be used to protect from noise and don’t be afraid to speak up for better hearing. Politely ask to       turn it down.

► Remember your neighbors: Noise from your personal recreation affects not only you but everyone around you. Be a good       neighbor and lower the volume. This is true whether at home, the beach, or a shopping mall—anywhere your loud noises could interfere       with others’ peace

► Use silent generator only, and

► Educate your children: Educate and talk to your children about what is noise and their health hazards.

To learn more please visit the following external links:

₪   NoisePollution:Sources,Effectsand Control

₪   DecibelTable − Loudness Comparison Chart

₪   Conversion of sound units (levels)

₪   Sound (music) and noise (bang)

₪   The Relation of Sound Quantities-their Levels and References. Conversions, Calculations and Formula