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Control of Air Borne Microorganisms

	Control of Air borne Microorganisms - Various methods for the removal or destruction of microorganisms have been employed and found to be practicable. Airborne microorganisms are controlled through the application of physical techniques or chemical agents. Air merely represents a special environment for their application. Under certain conditions disinfection or sterilization of air is desirable. Several general methods are available for the control of microorganisms in the air of rooms and buildings, and are described in the following paragraph.
Dust control: Dust found in homes, offices, schools, factories and hospitals arises from airborne sand, ash, and soot, soil and lint from bedding, clothing and carpets. Most dust particles are laden with a variety of microorganisms, and have been studied particularly in relation to infections of respiratory tract and skin, and secondary infections of burns and wound. Suppression of dust in room cleaning operations is therefore, extremely important. Oiling floors, bedclothes, and other textiles is a highly effective method for the control of dust.
Use of dry vacuum pick up, followed by the application of an appropriate disinfectant-detergent solution has been recommended for dust removal. Where vacuum cleaning facilities are not available, some material such as oiled saw dust should be applied before sweeping. This prevents the scattering of dust. Ultraviolet radiation: The lethal effect of ultraviolet radiation on microorganisms is discussed in the chapter 'Microbial control'. Application of this killing effect has been made in the irradiation of air with ultraviolet light using a wavelength of 254 nm, which is microbicidal but not too irritating.
These radiations are effective only when they make direct contact with the particles carrying the organisms, as they have little peneterating power. Secondly ultraviolet 91Ys are irritating to human eyes arid skin. Practical application, therefore, requires skillful installation of the lamps. Rooms which are either unoccupied, or occupied for short periods of time, are exposed to direct irradiations.
	When the rooms are not occupied, ultraviolet lights are left on. In occupied rooms indirect irradiations ate used, and the occupants are shielded from direct exposure to the rays. In some situations air can be treated apart from the room or space. In air -circulating systems, air is first filtered and then passed through a tube, where it is irradiated by powerful ultraviolet sources. Bactericidal vapours: Many airborne microorganisms are killed when certain chemical substances are vaporised or sprayed into the air of a room. Germicidal substances are dispersed as aerosols. Vapours of propylene glycol and triethylene glycol are strongly germicidal. These are colourless, tasteless, non-irritating, nontoxic, and not explosive or corrosive.

The vapour from as little as 0.5 mg of propylene glycol can kill nearly all the microorganisms in a liter of heavily contaminated air within 15 seconds. Triethylene glycol is nearly 10 times as germicidal.

Laminar air flow system: In this system air passes through high efficiency particulate air, (HEPA) filters. These consist of cellulose acetate (filter medium) pleated around aluminium foil. Particles as small as 0.3 µm are removed by this filter system. Air is passed through a bank of these filters and into the enclosure, so that the entire body of air moves with uniform velocity along parallel flow lines. Many other methods and practices are useful in controlling microorganisms in air.

Ventilation is one such method which is very effective in controlling airborne diseases indoors. With extensive development in space technology, electronics, and the aerospace industry an extremely high degree of cleanliness is required. In recent years much attention is DOW paid to aerobiology, particularly air hygiene.

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