Document KzqgV5NVgdyEjngNxo8e8wMK

HEATING VENTILATINC AIR CONDITIONING CUIDE 1944 Dusts and cinders in flue gas may be caught by various devices on the market, such as fabric filters, dust traps, settling chambers, centrifugal separators, electrical precipitators, and gas scrubbers, described in Chapter 29. The cinder particles are usually larger in size than the dust particles; they are gray or black in color, and are abrasive. Being of a larger size, the range within which they may annoy is limited. The dust particles are usually extremely fine; they are light gray or yellow in color, and are not as abrasive as cinder particles. Being ex tremely fine, they are readily distributed over a large area by air currents. The nuisance created by the solid particles in the air is dependent on the size and physical characteristics of the individual particles. The difficulty of catching the dust and cinder particles is principally a function of the size and specific gravity of the particles. Lower rates of combustion per square foot of grate area will reduce the quantity of solid matter discharged from the chimney with the gases of combustion. The burning of coke, coking coal, and sized coal from which the extremely fine coal has been removed will not as a general rule produce as much dust and cinders as will result from the burning of non-coking coals and slack coals when they are burned on a grate. Modern boiler installations are usually designed for high capacity per square foot of ground area because such designs give the lowest cost of construction per unit of capacity. Designs of this type discharge a large quantity of dust and cinders with the gases of combustion, and if pollution of the atmosphere is to be prevented, some type of catcher must be installed. NATURE'S DUST CATCHER - Nature has provided means for catching solid particles in the air and depositing them upon the earth. A dust particle forms the nucleus for each rain drop and the rain picks up dust as it falls from the clouds to the earth. However, it was found in recent studies5 tha't rain-was not a good air cleaner of the material below about 0.7 micron. ffeott*IB^CNoIll2MnMLrcSei936).CitieS f0r yea" 193M933' by K * > <* & REFERENCES Bulletins, Industrial Hygiene Foundation, Inc., Pittsburgh, Pa. Determination and Control of Industrial Dust, by J. J. Bloomfield and J. M. Dalla Valle (V. S. Public Health Bulletin, No. 217, 1935). Journal of Industrial Hygiene and Toxicology, Harvard School of Public Health, Boston, Mass. Reports of the National Silicosis Conference, Washington, D. C. (To be published by the U. S. Department of Labor.) Symposiums on Silicosis, 1937 and .1939, Saranac Laboratories, Saranac Lake, N. Y. Symposium on Tuberculosis, 1941, Saranac Laboratory, Saranac, N. Y. Industrial Dust, by Philip Drinker and Theodore Hatch, McGraw-Hill Co., N. Y. Noxious Gases, by Y. Henderson and H. Haggard, Chemical Catalog Co., N. Y. Occupation and Health, International Labour Office. Preventive Medicine and Hygiene, by Milton J. Rosenau, D. Appleton-Century Co., N. Y. , 552 CHAPTER 29 :r C^-ieaninq. ^j)euiced Air Cleaners, Dust and Lint, Classifiestion of Air Cleaning Media, Viscous Impingement Type Cleaners, Automatic Viscous Filters, Dry Air Filters, Electric Precipitators, Per formance and Testing, Selection and Maintenance, Safety Requirements, Odor Adsorption F)R the purposes of this discussion, an air cleaner is defined as a device for capturing and removing solid matter from a stream of air. This solid matter includes fibrous material such as lint as well as particulate matter such as dust, fumes, smoke, cinders, etc. Air cleaning is distinct from air purification in that the latter consists of removing harmful or unpleasant gases, vapors, or bacteria from an occupied space. Air pollution and purification are discussed in Chapters 2 and 28. In general, air cleaners are not installed in buildings for the specific purpose of improving the health of the occupants. However, in some cases air borne solid matter does affect health and the removal of such matter from the air by means of cleaners is, beneficial, such as pollen, house dust, and similar allergens which motivate attacks on persons having allergeric sensitivity1. The toxic elements in some war gases are in reality fine particles capable of air flotation. It is known by experience that air cleaners greatly reduce the rate of dirt accumulation in buildings, but, in the present state of knowledge, an exact numerical expression for the cleaning effect of the filter cannot be given on account of the many unknown or variable factors involved. For this reason air cleaners are usually selected on a basis of experience or judgment, guided by the results of various test procedures. \ AIR CLEANERS \ A typical air cleaner consists of a frame, which may be metal, wood, cardboard, etc., and a filtering medium. The frame is designed to support, the medium in a duct or chamber forming part of the air conditioning or ventilating system, so that the air passes through the medium while en route to spaces to be veptilated. Unit Air Cleaners or Filters Many air cleaners are available in the form of units of convenient size for handling during installation, cleaning or replacement, where required. 'Bronchial Asthma and Allied Allergic Disorders, by S. S. Dmpold. and C. S. Leopold (.Journal of the American Medical Association, March 7, 1925, Vol. 84, p. 731*734). , 553