The effect of dust on health has been properly emphasized by competent medical authorities. The normal human breathes about 17 times a minute. The air taken into the lungs may contain large quantities of dust, soot, germs, bacteria, and other deleterious matter. Most of this solid matter is removed in the nose and air passages of the normal person. However, if these passages are dry and permit the passage of these materials, colds and respiratory diseases result. Air-conditioning apparatus remove these contaminants from the air and further provide the correct amount of moisture so that the respiratory tracts are not dehydrated, but are kept properly moist. Among the airborne diseases are mumps, measles, scarlet fever, pneumonia, colds, tuberculosis, hay fever, grippe, influenza, and diphtheria.
Dust is more than just dry dirt. It is exceedingly complex, with variable mixtures of materials, and, as a whole, is rather uninviting, especially the type found in and around human habitation. Dust contains fine particles of sand, soot, earth, rust, fiber, animal and vegetable refuse, hair, chemicals, and compounds, all of which are abrasive, irritating, or both. The U.S. Weather Bureau estimates that there are 115,000 particles of dust per cubic inch of ordinary city air, and that each grain of this dust at breathing level contains from 85,000 to 125,000 g. The proximity of factories using oil or coal-burning equipment and the presence of considerable street traffic will aggravate this condition and increase the dust and germ content.
The Mellon Institute of Industrial Research conducted a series of experiments to determine dust precipitation in three large cities. The measurements published were the average amounts measured in more than 10 stations in each of the cities and were for a period of 1 year. It was observed that precipitation was considerably greater in the industrial districts. It is certainly plain that filtered air is almost a necessity, especially in large buildings where number of individuals are gathered. Hotels, theaters, schools, stores, hospitals, factories, and museums require the removal of dust from the atmosphere admitted to their interiors, not only because a purer product is made available for human health and consumption, but also so that the fittings, clothing, furniture, and equipment will not be damaged by the dust particles borne by the fresh airstream.
The air filter is one part of the air-conditioning system that should be operated the year around. There are times when the air washer (the cooling and humidifying apparatus) is not needed, but the filter is one part of the system that should be kept in continuous operation, purifying the air.
