Document KmaGEvXe7jRx7jGM5Bwq9580

however, both ingestion and skin with talc. Dust may be formed and contact arc of rclatively-minor impor dispersed when solid materials are tance in industrial poisoning inso . reduced to small sizes in processes far ns dusts, fumes, and mists arc con cerned. such as grinding, crushing, blasting, shaking, and drilling. In these proc- Origin and Properties of Particulate Matter ` esses, the mechanical action of the grinding or shaking device supplies a source of energy to* disperse the 9. The dust normally present in dust formed (Figure 1). (he atmosphere has a beneficial 12. When a solid such as a metal clfect in screening out some of the is heated to a temperature high harmful rays of the sun. Inhalation of enough to volatilize it. the volatil - this dust may not be harmful because ised matter later condenses in cooler . cither the dust may be nontoxic or air to form a fume (Figure 2). The body mechanisms capture, remove solid panicles that make up a fume and eliminate or isolate the small arc extremely fine, usually less than amounts of dust trapped in the lungs. 0.5 micron in size. In some eases, the Air pollution, radioactive fallout, hot material reacts with the air to pollens, and similar conditions may form an oxide. Examples arc lead have an adverse effect on some indi oxide fume from smelting and iron viduals. Also, when the air breathed oxide fume from arc welding. Also, a contains excessive amounts of dust, fume can be formed when a material the body has difficulty in handling such as magnesium metal is burned ' the load and dust may remain in the or when welding or gas cutting is lungs. done on galvanized metal. Sources 10. The term dust.as used in in dustry is generally applied to air' home solid particles that range in si/e from 0.1 micron to 25 microns (one micron ss I / 10.000 centimeter = I 25.000 inch I. Process dusts below- 0.5 micron in size arc rare. Ousts above 5 microns in size usually will not stay air-borne long enough to present an inhalation problem. 11. Dust may enter the air from various sources. It may be dispersed when a dusty material is handled, such as when lead oxide is dumped into a mixer or a product is dusted 13. A mist is formed when a finely divided liquid is suspended in air. An example is the oil mist pro duced during cutting and. grinding operations. 14. Smoke may be formed by the incomplete combustion of organic materials. Smoke generally contains droplets as well as dry particles. Tobacco, for instance, produces a wet smoke composed of minute tarry droplets. The-size of the particles contained in tobacco smoke is about 0.25 micron. 15. Radioactive dust may be dis persed in the same ways as other in dustrial dusts. Radium, thorium, and other radioactive elements arc pres ent in extremely minute amounts in the atmosphere. Fig*** 1. Owt* f'Offl Mftrf it g**'Ol*tf dw'ixg tfc* tSotf Ovi of ceoingt. JK otocfconical ec'iox of h ikeW'Ou* meettino tfiip*nt it>* dull. PclFi laktn by dut* portiUot at fby Of* drawn into the hood thowt lb* ftticiancv of ll< local atiewil ty,liri. (Court*ly AmofMOA Foundry***'* So<i*ty1 Magnitude of particles 16. When a solid is broken ,into finely divided particles, its surface area is increased many times. For ex ample. I cubic centimeter (0.061 cubic inch) of quartz in the form of a cube when crushed into I-micron cubes will give 10*" (1.000.000.000.000 or one trillion) particles with a total surface area of 6 square meters (9.300 square inches), as compared with 6 square centimeters (0.930 square inch) for the original cube. 17. When a solid is broken into finely divided particles, the volume occupied by the mass is also in creased because of the voids between the particles. A dust concentration of 50 million particles per cubic foot of air (mppcf), resulting from 1 cubic centimeter of material reduced to particles 1 cubic micron in size, will occupy an air space of 20.000 'cubic feet. 18. Even smaller amounts of toxic dusts, fumes, and mists, will make a workroom atmosphere hazardous. For example, the threshold limit value for lead, as adopted by the Amcfican Conference of Govern mental Industrial Hygienists, is 0.2 milligram per cubic meter of air (mg/cu m), which is 0.0000002 ounce per cubic foot. Therefore, the dispersion of only 0.002 ounce of lead will be enough to give the threshold limit value of 0.2 mg/cu m of dust or fume in an air space of 10,000 cubic feet (280 cubic me. ters). The concentrations that may be present in the workroom without harm to health are different for differ ent substances. 19. A person with normal eye sight can delect dust particles as small as SO microns in diameter. Smaller air-borne particles can be detected individually by the naked eye only when strong light is reflected from them. Dust of respirable size (below tO microns) cannot be seen without the aid of a microscope. 20. Most industrial`dusts consist of particles that vary widely in size, with the small panicles greatly out numbering the large ones. Conse quently. with few exceptions, when dust is nqticeable in the air around an operation, probably more invi sible dust particles than visible ones are present. Separation In air-borne dust 21. Oust in the air may or may not have the same composition as its parent material. The determining factors arc the particle size and density of each component in the original mixture, and the hardness of the materials (hard.materials will resist the pulverizing action of. a mechanical device.) 22. For example, foundry mold ing sand contains a large percentage of free'silica (quartz) with a lower percentage ofclgys. Most of the clays consist of fine particles that can be air-borne, but most of the quartz particles arc too large to be air borne. The atr-bornc dust, there fore. as compared with the original mixture, may contain a much higher percentage of days and a much 90 National Safety Newt, June 1949 lower percentage of free silica. 23. Dust particles are, of course, attracted by gravity. Their settling rate through stilt air will vary with their size, density, and shape. Mi croscopically smalt particles settle out more slowly than larger particles be cause of their relatively minor densi ty and because of their being in fluenced by Brownian movement. Mineral particles larger than 10 mi crons will settle out relatively fast. The estimated settling rates for silica dusts in still air'are given in Table I. TABLE I. SETTLING RATES FOR SILICA OUSTS Size in Microns 0.25 0.50 1.00" 2.00 5.00 Time to Fall 1 Foot (minutes) 590.0 167.0 54.0 , 14.5 2.5 24. Most of the particles io air borne industrial dusts are small. Bccausc'of air currents, the fine pani cles in dust clouds at an operation will remain suspended in the work room air for relatively long periods of time. The smaller dust particles, moreover, will travel farther away from their point of origin than will the larger particles so that the far ther dust is from its source, the greater the percentage of small par ticles it contains. Inhalation of Dusts* Fumes, and Mists 25. With the exception , of such fibrous materials as asbestos, dust .particles must usually be smaller than 5 microns in order to enter the alveoli or inner recesses of the lungs. Al though a few particles up to 10 microns in size may enter the lungs occasionally, nearly all the larger particles are trapped in the nasal passages, throat, larynx, trachea, and bronchi, from which they arc expec torated or swallowed into the diges tive tract.. 26. When larger particles of cer tain toxic dusts arc trapped in the upper respiratory passages, they can be absorbed by the body fluids in the nasal passages and in the digestive tract before they are elimi nated. Hence the-final toxic effects , of larger dust particles may be de layed. The larger particles of irri tant dusts can cause immediate effects in the upper respiratory system. 27. Ragweed pollen, which var- ies from 18 to 25 microns in diameter can cause hay fever from its action in the upper respiratory system. This type of dust and other allergenic types, as well as bacterial and irritant dusts, can cause difficulty even In the larger air-borne sizes. 28. When dust-laden air b in haled, some of the larger particles are trapped by. the hairs in the nose. Other dust particles are removed from the air as' it passes over the moist mucous membranes of the nose, throat, and ether portions of the upper respiratory system. . 29. The bronchi aitd other re spiratory passages are covered with a large number of tiny, hairlike cilia or microscopic whiplashes, which aid in the removal of dust trapped on these moist surfaces. The cilia, all beading in one direction, make a fast stroke toward the mouth and a slower return stroke. This actioo tends to push mucous and deposited dust upward to the mouth so that the particles can be ex pectorated or swallowed. Retention of dust 30. Many studies have been made in an effort to determine the amount of.dust that is retained in the lungs, but there is no simple answer to this question. It has been shown that the size of the dust particles, the rate of respiration, the density of the dust in the air, the efficiency of the dust-catching mechanism, and probably many other factors are in volved. Sizes of particles inhaled 31. Although an occasional dust particle of larger size will enter the lungs, particles jess than 3 microns in diameter are the most likely to do so and thus have the greatest oppor tunity to cause a physiological re action. In sfiicotic lungs, for example, dust particles under 3 microns greatly outnumber larger ones, and many particles are less than 1 micron. 32. In the case of very fine fibrous asbestos dust, an exception occurs in the size of particles in haled. Many fibers up to 100 micronslong have been found in the lungs figvr* a. M**d volofAsod by lb* boot of vWing Igttr <andiMt to form o f*a. On Alt bawdvotlding tnifoitotion, ftnti oro romoood ef tbaif point oI origin by o property locst*4 loco! *kett InitcflatloA. (Court**? Aatoricon Faundryman't Sadat?) of asbestos workers at autopsy. 'A typical fibrosis caused by asbestos is produced by fibers ranging from 20 to 50 microns in length, but only a few microns wide. Physiological offocts 33. The physiological reactions caused by the inhalation of air borne particulate matter will vary with different types of dusts, fumes, and mists. The reactions include: a. The cardiopulmonary reaction which consists of the pneumoco nioses. such as silicosis and asbtstosis. In certain cases, specific types of lung pathology result, and the heart may be affected (cor .pul monale) when the fibrosis is ad vanced. In other cases,' there is mainly just an accumulation.of a relatively inert dust in the lungs. b. The systemic reactions which are caused by toxic dusts of such ele ments as lead, manganese, cad mium. and mercury, by their com pounds. and by certain organic compounds. c. Metal fume . fever which results from the inhalation of finely divid- ed and freshly generated fume of zinc or possibly of magnesium or of their oxides. This is a transient condition. d: Allergic and sensitization reactions which may be caused by inhala tion of. or skin contact with, such materials as organic dusts from flour, grains, arid some woods and dusts of a few organic and inor ganic chemicals. c. Bacterial and fungus infections which occur from inhalation of dusts containing active organisms, such as wool or fur dust contain- Notional Saftfy New*. Juoa 1969 91