Environment & Health

Water pollution: Chemical Polution

A diverse nature of chemical pollutants are derived from industrial and agricultural wastes. These wastes are more commonly finding their way to water supply systems. These pollutants include cyanides, detergent solvents, organic acids and minerals, organ phosphorus compounds, dyes, bleaching agents, pigments nitrogenous substances, ammonia, sulphides, toxic and biological organic compounds. Chemical Pollutants can effect men’s health directly and indirectly (by accumulating in aquatic life like fish, which are consumed as food). The main concern of water pollutants (chemical) is their long term effects that can occur even if present at small level and exposed to prolonged periods of months and years. Their long term effects are also non-specific and difficult to detect and determine. Some new chemical pollutants are difficult to remove with conventional water treatment methods. In developed countries, water-borne communicable disease are now rare and they are now focusing on chemical pollutants of water.

The water is associated to the following problems in addition to the above:

(1) Cardiovascular disease: Hardness of water have beneficial effect on cardiovascular system. Soft water can cause cardiovascular problems if consumed for prolonged period. Example of soft water is rain water.

(2) Dental health : The presence of fluoride (fluorine) at around 1mg per liter is essential in drinking water for dental and bone health. Fluorides below the above level causes dental caries and if it is in excess it causes dental fluorosis.

(3) Cyanosis in infants: High nitrate concentration in water can cause methemoglobinemia. This is rare but can occur if water from farmland gain access to public water supply.

(4) Some diseases are due to insects which carry the organism and they breed in water or nearby water. They are malaria, filarial, dengue fever, dengue hemorrhagic fever, onchocerosis, African trypanosomiasis, and arboviruses etc.

(5) Some diseases are transmitted due to inadequate filtration of water like, ascariasis, shigellosis etc. Some diseases are transmitted due to inadequate use of water, like scabies, trachoma, conjunctivitis.

Water Related Diseases

Human Health can be affected by drinking contaminated water through food or directly as drinking water and also by use of contaminated water for personal hygiene or recreation (swimming pools for swimming and diving and other water sports). The term water related disease include water borne disease also. Developing countries carry a heavy burden of water borne diseases due to lack of safe drinking water supply. Among the water borne and water related diseases diarrhea is most important. Water related disease can be biological (water borne disease) and chemical.

Biological: They are two types those caused by the presence of infective agents in water and those due to presence of aquatic host in water.

(1) Due to Infective agents:

These can be subdivided by the type of the infective agent present in water-

(a) Viral: Viral hepatitis (due to hepatitis A virus, Hepatitis E virus) poliomyelitis and rotavirus diarrhea in infants.

(b) Bacterial: Typhoid fever, paratyphoid fever, Escherichia coli (E. coli) diarrhea, cholera, bacillary dysentery, Travelers diarrhea etc.

(c) Protozoal: Amoebissis (antameba histolytica), giardiasis (giardia lamblia).

(d) Helmintic: Worm infestation like round worm, thread worm and hydrated disease.

(e) Leptospiral: Weill’s disease

(2) Due to presence of aquatic host:

(a) Snail: Schistosomiasis.

(b) Cyclopes : guinea worm, fish tape worm.

Water Pollution

Pure uncontaminated water dose not occur in nature. The natural water contain impurities both natural and man made. The natural impurities are not dangerous like man made impurities. The natural impurities are dissolved gas (nitrogen, carbon dioxide, hydrogen sulphide which are picked up during rain), and dissolved minerals (salts of calcium, magnesium and sodium). The minerals are due to contact of water with soil. Natural water also contain suspended impurities (clay, sand, mud, silt etc.) and microscopic organisms (bacteria, virus, planktons, fungi etc). All the natural impurities are derived from the soil, catchments area and atmosphere.

Water pollution by man made containments are more serious which is generally due to human actives mainly urbanization and industrialization. The sources of man made water pollution are

(1) Sewage: This contain pathogenic organism and organic (decomposable) matter. Main constituents of sewage is human excreta with water.

(2)Industrial and trade wastes: These contain toxic agents from synthetic, organic compounds to metals and metal salts.

(3) Agriculture pollutants: These are mainly chemical fertilizers and pesticides. In many parts of the world like India and Kazakhstan due to uncontrolled use of pesticide and fertilizers(chemical) their content in soil and water has crossed normal acceptable limits, which is not harmful to health of general population.

(4) Physical pollutants: Heat (thermal pollution) and radioactive substance are present in water.

Indicators of water pollution:

The following are the indicators of water pollution, the total amount of suspended solids, concentration of chlorides, BOD (Biological Oxygen Demand) at 20 degree centigrade, nitrogen, Phosphorus and absence of dissolved Oxygen.

In presence of high quality treatment (purification) of water, pollution of water may still be there due to corrosion of pipelines, leaky joints and due to cross connection of water supply pipe with that of sewage drain. That is why surveillance is required at every point in the water supply system to ensure safe drinking water to the consumer.

Effects of Heat on Humans

Effects of Heat: There are 14 documented disorders which can be due to excess exposure to heat. Some of the common and important disorders are discussed below:

1. Heat stroke: Also known as sunstroke. This is due to failure of heat regulating mechanism of human body . The main feature of heat stroke is very high body temperature of about 110 degree Fahrenheit(43⁰ Centigrade). High temperature is accompanied by convulsion, delirium and partial or complete loss of consciousness. Skin is usually dry and hot. Sweating is absent or very scanty. Death rate is high (about 40%) even it quick medical attention is provided. Treatment of heat stroke consists of rapidly cooling the body in ice water till rectal temperature falls blow 102 degree Fahrenheit. Rectal temperature should be continuously monitored. It indicate the progress of treatment as well as guard against hypothermia, that may occur if cooling is continued for very long . Further treatment of heat stroke is supportive & symptomatic. The patient should be hospitalized for several days, till temperature control & regulatory mechanism become stable.
2. Heat Hyperpyrexia: This is due to impairment of heat regulating mechanism of human body. It generally have temperature above 106 degree Fahrenheit. It may be seen before heat stroke /sun stroke.
3. Heat exhaustion: It is not because of failure of heat regulating mechanism ,unlike heat stroke and heat hyperpyrexia. It is less severe than heat stroke and due to imbalance or inadequate replacement of water and salts lost by perspiration due to excess heat. Body temperature may be normal or slightly higher but generally do not cross 102 degree Fahrenheit. It is seen after several days of high temperature. Symptoms of heat exhaustion are dizziness, weakness, and fatigue. Elderly people with heat exhaustion may require hospitalization. Treatment is correction of fluid and electrolyte imbalance.
4. Heat cramps: It is seen in people engaged in heavy work and muscular activity at high temperature and humidity, mainly those who are not adopted to muscular activities at high temperature and humidity. Heat cramp is due to loss of sodium and chlorides in blood and it causes painful and spasmodic contraction of skeletal muscles.
5. Heat syncope: Heat syncope is quite common problem . In typical form of heat syncope, person standing in sun suddenly become pale, his blood pressure falls and he collapses. Body temperature is normal. This is due to pooling of blood in legs due to dilatation of blood vessels in legs. This results in reduced venous return to heart and fall in blood pressure and lack of blood supply in brain. The treatment is very simple. The patient is made to lie down in shade with the head slightly down . Patient recovers in 5 to 10 minutes. This type of problem is very common in soldiers standing in sun for parade.

Preventive Measures: The effects of heat can be prevented by following measures.

• Replacement of water : People working under high temperature and humidity should encouraged to drink lots of cool water. In hot climate a person requires about one liter of water per hour during physical work and a sedentary worker need half liter of water. There is no need of extra salt in water because sweat contain very less salt, contrary to popular belief that extra salt is required. But if a person is not acclimatized he should take extra salt for first 10 days.

• Clothing: The cloth used should be loose fitting and of light color

• Regulation of work: Duration of work at hot and humid condition should be reduced. There should be periods of rest in between intense work. If symptoms of effect of heat like headache, dizziness appear the worker should be removed to a cooler place and adequate treatment given.

• Protective Devices: protective goggles, helmets and shields should be used where practicable.

• Proper ventilation should be provided and air-conditioning done where practicable.

Effects of Radiation on Humans

The biological effects of radiation on human can be divided into two groups, somatic effects and genetic effects.

(1) Somatic effects: A dose of 600 to 700 roentgen is invariably fatal in humans and a dose of 400 to 500 roentgen can kill up to 50% of people. Those who are not killed, also suffer from severe damage and radiation sickness. If a person is exposed to 25 to 50 roentgen of radiation it effects white blood cells (corpuscles) and produce lassitude and softening of the muscles. Somatic effects of radiation can be immediate and delayed. Immediate effects are radiation sickness and acute radiation syndrome. Delayed effects take time to develop and can take from few weeks to few years to develop. Delayed effects of radiation are mainly leukemia (blood cancer), malignant tumors ( cancer) shortening of life and fetal developmental abnormalities.

(2) Genetic effects: Somatic effects are seen during ones lifetime of the person exposed to ionizing radiation genetic effects generally manifest in the life of off-spring . Genetic effects of radiation are mainly due to point mutation and chromosomal mutation. Chromosomal mutation generally is involved with sterility and point mutation effects the genes .

Protection from Radiation: The amount of radiation received from outer space is about 0.1rad per year and at present it is not considered a hazard. The additional permissible dose from man made sources is about 5rad per year. Out of all the man made sources x-ray constitute the greatest hazard. In routine fluoroscopy a dose of 4rad is delivered to a part in one minute, which means unnecessary x-ray examination should be avoided, mainly in pregnant woman an children.

There is requirement of adequate control & surveillance of x-ray installations, protection of workers, improvement of techniques to reduce dose of radiation.

Effective protective measures include use of lead shields, and lead rubber aprons by radiographers .Lead aprons of 0.5mm thickness of lead reduces the intensity of scattered x-rays up to 90% and all workers should use them who are associated with x-rays. Worker also should wear a dosimeter or a film badge that shows accumulated exposure to radiation. Besides all the above periodic medical cheek up, regular working hours & recreation should be provided to the health workers who are exposed to x-rays.

Radiation hygiene is one of the latest branch of hygiene. International agencies like WHO(World Health Organization), IAEA(International Atomic Energy Agency) and International Commission on Radiological Protection (ICRP) are active in the field of radiation hygiene. The ICRP has recommended that the genetic dose to the whole population from man made sources (other than natural sources) should not exceed 5rems per year over period of 30 years. Many countries in the world have adopted the ICRP recommendation . The main concern is to promote peaceful use of atomic energy with out any problem on heath.

There is growing concern throughout the world in recent times for codes of practice for the safe operation of nuclear power plants and safe disposals of nuclear waste which is generated from nuclear power plants.

Types of radiation

Ionizing radiation is the radiation which can penetrate tissues and deposit its energy within them. They are of three types of electromagnetic radiation: alpha particles, beta particles (electron) and protons.

Alpha particles are 10 times more harmful than X-rays, beta particles or gamma rays but they have very little penetrating force. But they are dangerous it enters the body by inhalation or wound. X-rays & gamma rays are of short wave length and can penetrate deep.

Alpha particles can penetrate 4cm in air, 0.05mm in tissue and no penetration in lead. Beta particles can penetrate 6 to 300cm in air, 0.06-4mm in tissue and 0.005 to0.3 mm in lead. Gamma rays can penetrate 400 meters in air, 50cm in tissue and 40mm in lead. X-rays can penetrate 120-240 meters in air 15 to 30cm in tissue and 0.3 mm in lead.

“Non ionizing radiation” in compare to ionizing radiation have longer electro magnetic wave length. As the wave length becomes longer the energy of the electro magnetic wave decreases. So all the non-ionizing radiation have lesser energy than ionizing radiation. In order of increasing wave length that means lesser energy, non ionizing radiation include ultraviolet rays (UV), visible light, infrared rays, microwave radiation and radio frequency radiation.

Units of Radiation

The activity of radioactive material is the number of nuclear disintegration per unit of time. The unit of radioactive activity is Becquerel(Bq). 1 Bq is equal to one disintegration per second. Formerly unit of radiation was curie (Ci).

The potency of radiation is measured in three ways. Roentgen: It is the unit of exposure. . It is the amount of radiation absorbed in air at a given point, that is the number of ions produced in one ml of air . Rad: It is the unit of absorbed dose of radiation, that is the amount of radioactive energy absorbed per gram of tissue in humans or in any material. 1mrad (milliard ) is equal to 0.001rad of radiation. Rem: This is the product of absorbed dose and modifying factors, that means the effects of modifying factors are deducted from absorbed dose and we get the rem. Due to high speed and high penetrating power of x-rays and gamma rays the rem and rad of these are equal. This means the entire dose which is absorbed and modifying factors have no effect.

The above radiation units (roentgen, rad & rem) have been replaced by the new SI units (International System of Units). They are of three types

(1) Coulomb per kilogram(c/kg)has replaced Roentgen unit. 1 roentgen unit is equal to 2.58×10⁴ C/kg. This is the unit for exposure.

(2) Gray(GY): It has replaced rad. It is the unit of dose of ionizing radiation that imparts 1 joule of energy to one kilogram of absorbed material. 1rad is equal to 0.01Grey (GY).

(3) Sievert (sv) has replaced rem. It is the unit of dose equivalent. 1 seivert (Sv) is equal to 100rem.

Dose equivalent(H): The concept of dose equivalent has been introduced due to the fact that all types of radiation do not produce same biological effect per unit of energy absorbed. The dose equivalent (H) of seivert, which is equal to the absorbed dose (D) of grays, multiplied by a quality factor Q, which depends upon the density of ionizing radiation produced in the tissue by the radiation.

H = DQ

The quality factor (Q) of X-ray, gamma ray and electron is equal to 1 (one), whereas for a particle it is 20. From this fact it is clear that particles like ? rays are 20 times more harmful than X-ray or gamma ray.

Radiation: a Discussion

Radiation is a part of man’s environment. Man is exposed from two sources of radiation natural and man made.

Natural sources of radiation are cosmic rays internal rays like carbon-14 and Potassium-40, atmospheric and terrestrial. Man made sources of radiation are medical & dental X-rays, radioisotopes for treatment of killer disease like cancer, radioactive fall out from nuclear explosions. Miscellaneous man made radioactive sources are television sets, radioactive dial matches, luminous markers, isotope tagged products. They are too small a source of radiation to be significant at present.

Natural sources:

Man is exposed to radiation throughout life continuously. Cosmic rays originate in outer space and become weak as they pass through atmosphere. Generally a person is exposed to about 35mrad of radiation a year. At higher attitude of about 20 km cosmic radiation becomes important. A commercial jet pilot receives about 300mrad of radiation a year compare to normal 35mrad.

Terrestrial radiation: Radioactive elements like thorium, uranium, radium and radioactive isotopes are present in man’s environment e.g. soil, rocks, buildings. Man derives about 50mrad of radiation from terrestrial sources. Some areas like Kerala in India, rock formations contain uranium, where radiation exposure may be as high as 2000mrad per year. Radiation from radioactive gases like radon contribute about 2mrad of radiation per year.

Internal radiation: Man is exposed to internal radiation from radioactive materials stored in body tissues. These include minute quantities of uranium, thorium, radioactive isotopes of carbon(C14), Potassium(K40), strontium(Sr90). From these sources radiation is about 25mrad per year but it may be as high as 70 to 80. it is estimated that a person is exposed to about 0.1rad of radiation per year from natural sources.

Man made sources:

Man is exposed to man made sources of radiation in addition to natural sources.

X-ray: this is the largest source of man made radiation. Two groups of people are exposed to X-ray radiation, patients and radiologists & radio technicians and radiotherapists. When optimum radiographic techniques are used a single X-ray film can give more than 0.02rad.

Radioactive fallout:

Nuclear explosions release tremendous amount of energy in the form of heat, light, radiation and also it releases many radioactive substances like carbon (C14), iodine (I 131), cesium (Cs 137) and strontium (Sr 90). Cesium and strontium are very important because they are released in large quantities and their half lives are 30 years and 28 years respectively. They float for few years and due to air current the particles are distributed throughout the world. Miscellaneous sources contribute too small am out of radiation to be important.

Ventilation

Ventilation is replacement of vitiated indoor air by fresh supply of outdoor air. Modern concept of ventilation includes quality of incoming air in terms of air temperature, humidity and purity of air with a view to provide an environment that is comfortable and free from risk of infection.

To decide the standard of ventilation is a tough job. Standard of ventilation takes into account certain things like cubic space of the occupied room , air change and floor space. Cubic space: requirement of a minimum cubic space per person was considered important but modern ventilation standard gives more importance to air change.

Air change: it is the most important factor in the modern standard of ventilation. It is recommended that in the living rooms there should be 2 to 3 air changes in one hour, that is if cubic capacity of a room is 1,000 cubic feet than 2,000 to 3,000 cubic feet of fresh outdoor air should enter the room every hour. In work rooms there should be 4 to 6 air changes in one hour. If air change is more than 6 times per hour it may produce drought, which should be avoided. Based on this principle it is now considered that 1,000 to 1,200 cubic feet per person is sufficient.

Floor space: Floor space is more important than cubic space. Heights more than 12 feet are not important from ventilation point of view due to the fact that products of respiration accumulates in the lower levels. The optimum floor space requirement per person is 50 to 100 per head. While calculating cubic space for ventilation, heights above 12 feet are not taken into consideration.

Types of ventilation:

Natural ventilation: this is the simplest way of ventilation and used in schools, houses and small offices. Natural ventilation is due to certain forces that play in nature. The wind: it is the most active force in ventilation. When wind blows through a room it is called perflation. When wind meets an obstruction it bypasses the obstruction and causes a suction action at its tail end, called aspiration. Doors and windows facing each other provides cross ventilation. Ideally every house should be constructed in such a way that it provides enough cross ventilation. Back to back houses do not provide cross ventilation, so this type of houses are not allowed. Diffusion: this can occur through smallest of the openings, but it can not be relied upon as only source of ventilation, because this process is very slow. Temperature difference: hot air is lighter than cold air and air flows from higher density (heavier) to lower density (lighter). When temperature of rooms rises the air becomes light and escapes through openings and cooler air enters. The greater the temperature difference the higher the velocity of the incoming air. Due to higher outside temperature in the tropics the above process can reverse and cooler room air may go out and hotter outside air may come in. the biggest flaw of natural ventilation is that incoming air, temperature and humidity can not be regulated.

Mechanical ventilations are of four types, exhaust ventilation, plenum ventilation, balanced ventilation and air conditioning.

1. Exhaust ventilation: in this system, air is driven out by exhaust fans. As air is removed a vacuum is created and fresh air enters inside through doors, windows and other inlets. This type of ventilation is used for large rooms and halls to remove vitiated air. Ventilation may be adjusted by adjusting the speed of the fans. This is widely used in industry to remove dust, fumes and other contaminants.
2. Plenum ventilation: in this system fresh outside air is blown into the rooms and vitiated air is replaced. The air is delivered through inlets at desired points. This is of limited use.
3. Balanced ventilation: it is combination of both exhaust and plenum ventilation.
4. Air conditioning: “It is simultaneous control of those factors affecting both physical and chemical condition of air within a confined space. These factors are temperature, humidity, air movement, distribution, dust, bacteria, odor and toxic gases most of which affect in greater or lesser extent human health and comfort”. Air conditioning is popular in large institutions, hospitals and dwellings. It is used in operation theaters in hospitals and of particular value in control of pathogenic bacteria. Air is filtered when drawn into the air conditioning system. Excess humidity is removed and the air is circulated back into the room after cooling or heating it so that the temperature of the room come to comfort zone. Mixing of fresh air with re circulated air is controlled.

When temperature difference is large between outside and air conditioned room, some times transition room is provided which maintain temperature between the two and prevent sudden exposure to high or low temperature.

Air conditioning is very costly. It uses certain chemicals like CFC (chlorofluorocarbon) which causes depletion of ozone layer. Ozone layer is the layer of ozone high in atmosphere which prevent harmful cosmic rays and gamma rays from entering the atmosphere. Cosmic rays and gamma rays can give rise to skin cancer and can raise the temperature of the world (global warming).

Effects and Control of Noise Pollution

Noise pollution can cause two types of pollution, auditory and non auditory.

1. Auditory problems: Auditory fatigue can appear in the region of 90 dB and it is greatest at 400 Hz. It is generally associated with buzzing, whistling and ringing in the air. Deafness is the most serious problem of noise pollution. Temporary deafness or hearing loss can be seen after exposure of specific types of noise. Temporary hearing loss disappear 24 hours after stoppage of exposure to noise. Most commonly, temporary hearing loss occurs in frequency between 4000 to 6000 Hz. Continuous or repeated exposure to noise of approximately 100 dB can result in permanent hearing loss. At the beginning of hearing loss patient may not be aware of hearing loss. Permanent hearing loss may vary from minor change in inner ear to complete destruction of organ of Corti. When permanent hearing loss occurs as a result of occupation in industries it is called “occupational hearing loss”. Exposure to noise above 160 dB can cause rupture of tympanic membrane (ear drum) and cause permanent hearing loss.
2. Non auditory effects: There may be interference with speech and interfere with communication. Most disturbances of speech communication occurs in between 300 to 500 Hz in everyday life. These type of frequencies are produced by road and air traffic. For a good intelligibility of speech the sound should ideally exceed the Speech Interference Level (SIL) by approximately 12 dB.

Annoyance is a psychological response to noise. Neurotic people are more sensitive to noise and get annoyed easily than normal balanced people. People who are constantly exposed to noise are more short tempered, irritated, impatient and more likely to resort to agitation and violence. Noise pollution can reduce efficiency at work place, especially where mental concentration is required.

Body physiological changes like rise in blood pressure, rise in intracranial pressure (rise in cerebrospinal fluid pressure, which is present inside brain and can cause headache), rise in heart rate, rise in respiratory rate and sweating can occur. Symptoms like nausea, giddiness and fatigue can occur in noise pollution. It ca also interfere with sleep. Noise can cause narrowing of pupils, affect color vision and reduce night vision.

Economic loss due to occupational hearing loss is quite significant to the industry. This is more common in the Armed forces mainly in the Regiment of Artillery, where troops are regularly exposed to artillery gunfire which can be more than 150 dB of intensity. The number of troops with loss of hearing and hard of hearing is very large in the regiment of artillery.

Control of noise pollution:

Careful city planning can reduce noise pollution. Residential areas should be separate from industrial areas. Widening of main street will reduce noise penetration into the houses. House front should ideally be at least 15 meters from street and planted with thick bushes and trees. Green belt should be planned in between residential and industrial areas which can reduce air pollution in addition to reducing noise pollution.

Heavy vehicles should not be allowed in the residential areas and indiscriminate use of horns should be prohibited. Acoustic insulation of the building should be done. Wherever required building should be made soundproof. Protection should be given to all the workers who are exposed to more than 85 dB. Workers should be regularly rotated from noisy areas to less noisy environment. Regular audiogram check up and use of air plugs and air muffs should be made compulsory.

Legislation should be made to control noise pollution as well as for provision of compensation to workers who suffer from hearing loss due to occupational exposure. Loud speakers should be banned in certain areas like hospitals and schools.

Finally people should be educated about the effects of noise pollution. Nothing can succeed without the participation of people with adequate knowledge about that particular subject.

Noise Pollution: an Understanding

Noise can be defined as “unwanted sound”, but this is a subjective definition due to the fact that one person’s sound may be another person’s noise. So a better definition of noise is “wrong sound, in the wrong place, at the wrong time”.

The 20^th century has been described as the “century of noise”. It has become a very important stress factor. The term ‘noise pollution’ is of recent origin and signify a vast cacophony of sounds that are produced in modern life that leads to health hazards like deafness, sleepless ness, annoyance etc.

Sources of noise: Sources of noise are plenty. Noise may arise from automobiles, factories, industries, aircrafts, trains, loud speakers etc. Noise levels are particularly much more than normal near airports, railway stations and railway lines, near traffic signals. Use of electric horns, pressure horns, loud speakers during festivals, specially festivals like Diwali in India can cause noise pollution much more than acceptable limit.

Noise has two properties. First one is loudness or intensity of noise and the second one is frequency.

(1) Loudness or intensity: It depends in the amplitude of the vibration which initiate sound/noise. The loudness is measured in unit called decibels (dB). If a sound is 50 decibels, it means that it is 50 times louder than the smallest distinguishable (audible) sound or the ‘reference’ sound pressure. The smallest audible sound have a sound pressure of 0.0002 micro bar or dyne/cm².A dyne is one millionth of normal atmospheric pressure which is 760 mm of mercury at sea level. Normal conversation produce a noise of 60-65 dB, whispering produces 20-30 dB, boiler factories produce 120 dB, busy streets produce 60-80 dB of noise.

Human ear responds in a non uniform way to different sound pressure levels. It responds to the perceived intensity of the sound not to the loudness of sound. That means at different places and different situations some person will have different perception to same loudness of sound. For example in a house acceptable noise level is approximately

40dB. But in hospitals it is 20 to 30dB and in industrial area it is 40dB to 60dB.

(2)Frequency: The unit of frequency in use is Hertz (Hz). One Hz is equal to one wave per second. The human ear is made to hear and can hear frequencies from 20 Hz to 20,000 Hz. This range is reduced with age and certain factors. Many animals like dogs & cats can hear sounds which are not audible to humans. If frequency is less than 20 Hz they are infra audible to humans and those above 20,000 per seconds are ultra-sounds. In ultrasounds machines these above 20,000 frequency sound waves are used for diagnostic purpose. These are also used in sonar technique in submarines and ships to detect any object which may be present in front of a submarine . These ultrasonic waves are also used in breaking down of kidney stones and gall stones.

Noise is also expressed in psycho acoustic term called the phon. The phon is a psycho acoustic index of loudness. Intensity and frequency are taken in to consideration in calculating phon.

The basic instruments used in the study of sound and noise are: (1) The Audiometer to measure the hearing ability. Zero line at the top represent normal hearing. A characteristic dip in the curve is seen at 4000Hz.(2) The ‘sound level meter’ measures the intensity of sound in dB. (3) The Octane Band Frequency analyzer measures noise in octane bands. The resulting plot shows the sound spectrum and indicate characteristics of noise, whether it is high pitched, low pitched or variable pitch.

The sound levels of some common noises are given below: