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Значение термина air в knolik

air - Air
air - As applied to the atmosphere we breathe the word denotes a mixture of gases surrounding the surface of the earth. Fresh country air consists of approximately 20.93 p.c. oxygen, 79.04 p.c. nitrogen. There is also present a small quantity of carbon dioxide which amounts to 0.03 p.c. in country air and approximately 0.04 p.c. in town air. A variable amount of water vapour is also present, the actual amount depending upon climatic conditions and on the locality. In addition there may be present in the air very small quantities of ammonia, sulphuretted hydrogen, sulphurous acid gas, and floating organic and inorganic matter, such as dust. See Atmosphere.

air and public health

An abundant supply of pure air is of the greatest importance in maintaining health. If the lungs are weakened by the effect of continually breathing impure air, they are apt to become the seat of tuberculosis or other disease.

Air may be vitiated or rendered unsuitable for breathing mainly by the following causes: (1) in rooms, by respiration and the burning of gas for heat or light; (2) in factories arid workshops, by certain trade processes; (3) in towns, by smoke from chimneys and dust from streets.

air in rooms

It was long believed that the injurious effects of ill-ventilated rooms were due to diminution of oxygen owing to its absorption in the process of breathing and the respiration of carbon dioxide gas. The air expired by human beings contains approximately 4.5 p.c. of carbon dioxide. In one hour an average man will exhale 0.6 cubic feet of carbon dioxide, so that in a closed gas-tight compartment measuring 10x10x10 ft. the air would be vitiated by one individual to the extent of 6 parts of carbon dioxide per 10,000 of air at the end of an hour. This led to the old-standing recommendation that the carbon dioxide in room air should not exceed 0.06 p.c.

It follows that if the carbon dioxide in the air of a room is kept down to this level there must be a good supply of fresh air ventilating the room. It must not be thought, however, that carbon dioxide itself is harmful in such small concentrations. In fact, it has been shown by Prof. Leonard Hill that a man can breathe 2 p.c. carbon dioxide in the air without experiencing discomfort. Usually, however, a high concentration of carbon dioxide in a room indicates stagnation of the air, which Prof. Hill showed to be the chief cause of discomfort experienced in a badly ventilated room. Satisfactory air conditions in a room are not only a question of the purity of the air in respect of a low concentration of carbon dioxide. A human being is continually producing heat which must be lost to its surroundings if the body temperature is to be kept normal. Heat is lost by radiation to cool surroundings, by conduction (warming the air near the skin), and by evaporation of sweat. Hence the temperature, movement, and humidity of the air affect our bodies by virtue of their cooling effect.

Air in factories

Government regulations in regard to the purity of air in factories are strict. Provision must be arranged for securing and maintaining a suitable air temperature and effective ventilation. The air should be changed sufficiently often by the admittance of fresh air, impurities, unpleasant odours, and dust being intercepted. A satisfactory rate of air movement in the vicinity of a worker tends to ward off oppressive conditions and the relative humidity to create a feeling of comfort.

Special requirements apply to various types of manufacture. For example, all woodworking machines should be installed with mechanical exhaust fans, ducts, and hoods, by which sawdust and shavings are picked up at the machines and delivered at a point where they can be collected and used or destroyed. Grinding and polishing machines require to be treated in a similar manner so that dust is carried away from the worker and deposited in a settling tank or receiver. Fumes from galvanising tanks, type-casting machines, and cellulose spray-painting also require to be exhausted by fans so that the workers shall not inhale dangerous particles or fumes.

Air in towns

In industrial towns the air is most likely to be vitiated by solid particles, sulphurous acid and noxious gases contained in smoke from factories and private houses, and fumes from motor traffic. The regulations in regard to emission of smoke from factory chimneys are very definite, as shown by the following extracts from the Public Health (Smoke Abatement) Act:

"A chimney (not being the chimney of a private dwelling house) sending forth smoke in such quantities as to be a nuisance shall be deemed to be a nuisance liable to be dealt with summarily in manner provided by the Act, notwithstanding that the smoke is not black smoke...

"The expression 'smoke' shall include soot, ash, grit and gritty particles...

" The expression 'chimney' shall include structures and openings of any kind whatsoever capable of emitting smoke...

"Any local authority may, and if so required by the Minister of Health, shall, make by-laws regulating the emission of smoke of such colour, density or content as may be prescribed by the bylaws, and where such by-laws are in force the emission of smoke of the character so prescribed for such period as may be prescribed in the by-laws."

Contamination of the air by smoke has been considerably reduced by many factories now being provided with electric power for driving the machines, thus allowing the number of solid fuel burning boilers to be reduced. Smoke from private houses would be much reduced if central heating were adopted, as less fumes pass to the chimney through a well-designed hot water boiler using coke or anthracite as fuel.

By L. J. Overton, M.I.H.V.E.

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