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Appendix A DEFINITIONS3 Aerosol; An assemblage of small particles, solid or liquid, suspended in air. The diameter of the particles may vary from 100 microns down to 0.01 micron or less, e.g., dust, fog, smoke. Air Cleaner; A device designed for the purpose of removing atmospheric airborne impurities such as dusts, gases, vapors, fumes, and smokes. (Air cleaners include air washers, air filters, electrostatic precipitators, and charcoal filters.) Air, Dry; Air containing no water vapor. Air Filter; An air cleaning device to remove light particulate loadings from normal atmospheric air before introduction into the building. Usual range; Loadings up to 3 grains per thousand cubic feet (0.003 grains per cubic foot). Note; Atmospheric air in heavy industrial areas and in-plant air in many industries has higher loadings than this, and dust collectors are then indicated for proper air cleaning. Air Horsepower; The theoretical horsepower required to drive a fan if there were no losses in the fanâthat is, if its efficiency were 100 percent. Air, Standard; Dry air at 70Â° F and 29.92 inches (Hg) barometer. This is substantially equivalent to 0.075 Ib/cu ft. Specific heat of dry air = 0.24 Btu/lbÂ°F. Air-to-Cloth Ratio; The volumetric rate of capacity of a fabric filter; the volume of air (gas), in cubic feet per minute, per square foot of filter media (fabric) . Anemometer; An instrument for measuring the velocity of air or gas. Aspect Ratio of an Elbow; The width (W) divided by depth (D) in the plane of the bend. AR = W (see Figure 3-9) D Aspiration; The movement of air by suction. a Compiled in part from Industrial Ventilation; A Manual of Recommended Practice, 25th Edition, American Conference of Government Industrial Hygienists, Lansing, 1978 and "Fundamentals of Fabric Collectors and Glossary of Terms," Publication No. F-2, Industrial Gas Cleaning Institute, Inc., Stamford, 1972. 89