Document a4rDg15e58xJmkxRoLkdpV2LB

HEATING VENTILATING AIR CONDITIONING GUIDE 1943 a classic example in the history of gaseous air pollution. Released in a rare combination of atmospheric calm and dense fog, it is believed that sulphur dioxide and other toxic gases from the industrial region of the valley caused 63 sudden deaths, and injuries to several hundred persons. Carbon monoxide from automobiles and from chimney gases consti tutes another important source of aerial pollution in busy cities. During heavy traffic hours and under atmospheric conditions favorable to con centration, the air of congested streets may contain enough CO to affect those exposed over a period of several hours, particularly if their activities call for deep and rapid breathing. In open air under ordinary conditions the concentration of CO in city air is insufficient to affect the average city dweller or pedestrian. : Occlusion of Solar Radiation The loss of light, particularly the occlusion of solar ultra-violet light due to smoke and soot, is beginning to be recognized as a health problem in many industrial cities. Measurements of solar radiation in Baltimore13 * by actinic methods show that the ultra-violet light in the country was 50 per cent greater than in the city. In New York City4 a loss as great as 50 per cent in visible light was found by the photo-electric cell method. The aesthetic and economic objections-to air pollution are so definite, and the effect of air-borne pollen can be shown so readily as the cause of hay-fever and other allergic diseases, that mearts and expenses of pre vention or elimination of this pollution are justified. SMOKE AND AIR POLLUTION ABATEMENT Successful abatement of atmospheric pollution requires, the' combined efforts of the combustion engineer, the public health officer, and the public itself. The complete electrification of industry and railroads, and the separation of industrial and residential-communities would aid materially in the effective solution of the problem.. In the large cities where the nuisance from smoke, dust and cinders is the most serious, limited areas obtain some relief by the use of district heating. The boilers in these plants are of large size designed and oper ated to burn the fuel without smoke, and some of them are equipped with dust catching devices. The gases of combustion are usually discharged at a much higher level than is possible in the base of buildings that operate their own boiler plants. In general, time, temperature and turbulence are the essential require ments for smokeless combustion. Anything that can be done to increase any .one of these factors, will reduce the quantity of smoke discharged. Especial' care must be taken in hand-firing bituminous coals. (See Chapter 8.) : Checker or alternate firing, in which the fuel is fired alternately on separate parts of the grate, maintains a higher furnace temperature and thereby decreases, the amount of. smoke. . 1Effects of Atmospheric Pollution Upon Incidence of Solar Ultra-Violet Light, by J. H. Shrader, M. H. Coblentz and F. A. Kor(American Journal of Public, Health, p. 7, Vol. 19, 1929). . - 4Studies in Illumination, by J. E. Ives (/. S. Public Health Service Bulletin No. 197, 1930).' 560 CHAPTER 28. AIR POLLUTION Coking and firing, in which the fuel is first fired close to the firing door and the coke pushed back into the furnace just before firing.again, pro duces the same effect. The volatiles as they are distilled thus have to pass over the hot fuel bed where they will be burned if they are mixed with sufficient air and are not cooled too quickly by the heat-absorbing surfaces of the boiler. , Steam or compressed air jets, admitted over the fire, create turbulence in the furnace and bring the volatiles of the fuel more quickly into contact 'with the air required for combustion. These jets are especially helpful for the first few minutes after each firing. Frequent firings, of small charges shorten the smoking period and reduce the density. Thinner fuel beds on the grate increase the effective combustion space in the furnace, supply more air for combustion, and are sometimes effective in reducing the smoke emitted, but care should be taken that holes are not formed in the fire. A lower volatile coal or a higher gravity oil always produces less smoke than a high volatile coal or low gravity oil used in the same furnace and fired in the same manner. The installation of more modern or better designed fuel burning equip ment,, or a change in the construction of the furnace', will often reduce smoke. The installation of a Dutch oven which will increase the furnace volume and raise- the furnace temperature often produces satisfactory results. In the case of new installations, the problem of smoke abatement can be solved by the selection of the proper, fuel-burning equipment and furnace design for the particular fuel to be burned and by the proper operation of that equipment. Constant vigilance is necessary to make certain that the equipment is properly operated. In old installations the solution of the problem .presents many difficulties, and a considerable investment in special apparatus is often necessary. - Legislative measures at the present time are largely concerned with the smoke discharged from the chimneys of boiler plants. Practically all of the ordinances limit the number of minutes in any one hour that smoke of a specified density, as measured by comparison with a Ringelniann Chart (Chapter 35) .may be discharged. These'ordinances do not cover the smoke discharged at low levels by automobiles, and, although they have been instrumental in reducing the smoke emitted by boiler plants, they, have, in many instances, increased the output of chimney dust and cinders due to the use of more excess air and to greater turbulence in the furnaces. Legislative measures in general have not as yet covered the noxious gases, such as sulphur dioxide, nor sulphuric acid fog,-which are dis charged with the gases of combustion. Where high sulphur coals are burned, these sulphur gases present a serious problem, DUST AND CINDERS The impurities in the air other than smoke come from so many sources that they are difficult to control. Only those which are produced in large quantities at a comparatively few points, such as the dust, cinders and fly-ash'discharged to . the atmosphere along with the gases of com bustion from burning solid fuel, can be readily controlled. 561