ENVIRONMENTAL SCIENCE : HUMAN POPULATION AND ENVIRONMENT 239
(iii) Filtration: Different varieties of filters are used to purify the water at domestic
level.Chemical methods for water sterilization
(i) Aluminium sulphate: It is largely used to purify muddy water.
(ii) Chlorine: Chlorine gas or tablet is added to destroy disease-producing germs. It
is a very cheap and convenient method.
(iii) Potassium permanganate: It oxidises the organic matter and destroys 98% of
the microorganisms in four to six hours.
(iv) Purification by the use of ultra-violet rays: Ultra-Violet rays have the power
of destroying microorganisms from the water without any chemical change. They
exert their action only when the water is fairly clear and bright.VENTILATION
Ideal ventilation is possible only when there is sufficient pure air. Ventilation is defined
as the “Science of maintaining atmospheric conditions which are comfortable and suitable
to the human body.” Ventilation incorporates comfortable and appropriate balance of gases,
also optimum temperature adequate humidity, movement or flow of air and free from disease
producing microorganisms.
(a) Internal Ventilation
Proper ventilation of the rooms is known as ‘internal ventilation. Lack of efficient and
adequate ventilation leads to many discomforts and diseases. When the carbon-dioxide
concentration exceeds 0.04% and reaches 0.06% then the air in the room gets suffocating.
Every person needs 3000 cu feet of air every hour and if the impurities in the air exceed
0.02%, the air is regarded as impure and unhealthy.
(b) External Ventilation
Fresh air flows into the house from the surroundings and open space. This type of
ventilation is known as external ventilation. This is ensured by making the streets wide and
straight, providing open space, parks and gardens.
Artificial Ventilation
Artificial ventilation is easily controlled and, installed. The means of artificial ventilation
are coolers, air conditioner, which are more frequently, used equipments. Humidifiers and
dehumidifiers are used where there is problem of humidity. Exhaust fans also play an
important role in bringing in fresh air and flushing out polluted and impure air.
Inadequate Ventilation and Health
Inadequate ventilation has following effect on the occupants of the room:
(i) Lack of oxygen leads to early fatigue and reduces alertness.
(ii) Results in sweating, heat exhaustion and faintness.
(iii) Foul odours from skin, mouth, stomach and clothes produces uneasiness, sickness
etc.