Document MMJXv9a2pexwjKNL25ON3dmrM

HEATING VENTILATING AIR CONDITIONING GUIDE 1940 !lj In some instances it may be important to record not only the movement :j' and temperature of the air at various levels, but also the temperature of jj each wall and window, of the flooring, and of the ceiling, and to measure i|j the totaleffective radiation of the surroundings in 6 directions; in order to trace the exact causes of defects in the building which have an unk favorable influence on the heat exchanges of its inhabitants. Facts of ij' this type are of great practical importance. C; In all fundamental studies of air conditions records should be obtained, Vj therefore, showing: 1. True air temperature (free from radiation effects), ff 2. Air movement. j 3. Humidity. | 4. Mean radiant temperature ofsurrounding surfaces. Ij In interpreting theresults of such studies, the clothing and the physical I activity of the subjects are of primary importance. 76 Chapter 4 AIR POLLUTION Classification of Air Impurities, Dust Concentrations, Air Pollution and Health, Occlusion of Solar Radiation, Smoke and Air Pollution Abatement, Dust and Cinders, Nature9s Dust Catcher THE particulate impurities which contribute to atmospheric pollution include carbon from the combustion of fuels, particles of earth, sand, ash, rubber tires, leather, animal excretion, stone, wood, rust, paper, threads of cotton, wool, and silks, bits of animal and vegetable matter, and pollen. Microscopic examination of the impurities in city air shows that a large percentage of the p&rticles are carbon. CLASSIFICATION OF AIR IMPURITIES The most conspicious sources of atmospheric pollution may be classified in various ways; as dusts, fumes and smoke. In Fig. 1, the classification is by particle size, but recent practice favors differentiation by method of formation. Thus, dusts are composed of particles produced by disintegration of larger material, as by crushing or grinding, whereas fumes are produced by condensation, and smoke consists of the finer carbon particles resulting from incomplete combustion. Similarly, mists are formed by the breaking up of liquids and fogs by condensation of vapors. There is as yet, however, no general agreement on these terms. Dusts tend to settle without agglomeration, fumes to aggregate and smoke to diffuse. Particles which approach the common bacteria in size--from 1 to 10 microns--are difficult to remove from air and are apt to remain in suspension unless thay can be agglomerated by artificial means. The term fly-ash is usually applied to the microscopic glassy spheres which form the principal solid constituent of the effluent gases from powdered-coal fired furnaces. Cinders denote the larger solid constituents which may be entrained by furnace gases. Particles larger than 10 microns are unlikely to remain suspended in air currents of moderate strength. Only violent air motion will sustain them in air long enough for them to be breathed. This means that, in hygenic problems, the engineer is concerned mostly with suspensions of particles comparable to the common bacteria in size.- A notable exception to this size limitation is the common hay-fever producing pollen such as that from rag-weed. Pollen grains may be anything from fragments 15 microns in diameter to whole pollens 25 microns or more in size. 77