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FILE NAME: National Safety Council (NSC) DATE: 1963 DOC#: NSC128 DOCUMENT DESCRIPTION: NSC - Dust, Fumes & Mist in Industry o Ce // e y -y N~ / DATA SHEET 531 MUiq DUSTS, FUMES, AND MISTS IN INDUSTRY Published by N a tio n a l S a fe ty C o u n cil 425 North Michigan Avenue, Chicago 11 PLAINTIFFS EXHIBIT Is AHC- 115 Introduction 1. Industrial dusts, mists, and fumes, their hazards and their con trol, are discussed in this data sheet.* The general principles presented can be applied to evaluate most in dustrial situations involving these air contaminants and to determine the need for controls. This data sheet is intended to guide employers, plant safety engineers, personnel man agers, and supervisors. 2. A plant manager who believes that he has a toxic or irritating dust problem should consult a competent industrial hygienist. Such help may be obtained from his own company, insurance carrier, private consul tants, or state health or labor agency. 3. To protect the health of em ployees who work where a dust, fume, or mist created by a manufac turing process is released into the at mosphere, a control program may be required. In such a case, three steps must be taken: a. The properties o f the specific dust, fume, or mist and its possible physiological effects on employees must be ascertained. '"This data sheet covers toxic and irri tating air contaminants encountered in industry. It does not include a discussion of the explosive properties of such air borne particulate matter. This data sheet is one of a series published by the National Safety Council, reflecting experience from many sources. Not every accept able safety procedure in this field is necessarily included. This data sheet should not be con fused with American Safety Stand ards, federal laws, insurance re quirements, state laws, rules, reg ulations or municipal ordinances. b. The particular exposure must be evaluated by dust counts or by chemical analyses of air samples, and a step-by-step analysis of the operations must be made to find the areas where employees are ex posed to hazardous amounts of the material. The operational anal ysis also should determine how the dust, fume, or mist is dispersed. c. Appropriate methods of control must be provided where indicated. The type and extent of controls will depend upon the physical, chemical, and toxic properties of the dust, fume, or mist, the evalua tion made of the exposure, and the operation that disperses the con taminant. The extensive controls needed for lead oxide dust, for example, would not be needed for limestone dust, since much greater quantities of limestone dust can be tolerated. 4. Except for the skin diseases, most occupational diseases are ac quired by inhalation of material. Lung tissue is by far the most efficient medium the body possesses for ab sorbing materials. In addition, the surface area of this lung tissue aver ages 55 square meters or about 590 square feet. 5. Certain dusts that reach the lungs can pass directly into the blood stream and be absorbed over a long period of time. Others may stay in the lungs and set up local irritant or dam aging action. 6. Toxic and irritant dusts can also be ingested in amounts that may cause trouble. If toxic dust swal lowed with food or saliva is not sol uble in body fluids, it is eliminated directly through the intestinal tract. Toxic materials that are readily sol uble in body fluids can be absorbed in the digestive system and picked up by the blood. 7. A third way in which toxic and irritant substances may enter the system is skin absorption. Many or ganic compounds, such as TNT, cy anides, and most aromatic amines, amides, and phenols, can produce systemic poisoning by direct contact with the skin. Contact of toxic and irritant dusts with the skin also may result in skin irritation. 8. As compared to inhalation, N A T IO N A L S A F E T Y C O U N C IL 1963 however, both ingestion and skin contactare of reM yeiy minor impor tance in industrial poisoning inso far as dusts, fumes, and mists are con cerned. Origin and Properties of Particulate Matter 9. The dust normally present in the atmosphere has a beneficial effect in screening out some of the harmful rays of the sun. Inhalation of this dust may not be harmful because either the dust may be nontoxic or body mechanisms capture, remove and eliminate or isolate the small amounts of dust trapped in the lungs. Air pollution, radioactive fallout, pollens, and similar conditions may have an adverse effect on some indi viduals. Also, when the air breathed contains excessive amounts of dust, the body has difficulty in handling the load and dust may remain in the lungs. Sources 10. The term dust as used in in dustry is generally applied to air borne solid particles that range in size from 0.1 micron to 25 microns (one micron = 1/10,000 centimeter = 1/25,000 inch). Process dusts below 0.5 micron in size are rare. Dusts 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 Figure 1. Dust from foundry sand is generated during the shake-out of castings. The mechanical action of the shake-out machine disperses the dust. Path taken by the dust particles as they are drawn into the hood shows the efficiency of the local exhaust system. (Courtesy American Foundrymen's Society) with talc. Dust may be formed and reduced to small sizes in processes such as grinding, crushing, blasting, shaking, and drilling. In these proc esses, the mechanical action of the grinding or shaking device supplies a source of energy to disperse the dust formed (Figure 1). 12. When a solid such as a metal is heated to a temperature high enough to volatilize it, -the volatillized matter later condenses in cooler air to form a fume (Figure 2). The solid particles that make up a fume are extremely fine, usually less than 0.5 micron in size. In some cases, the hot material reacts with the air to form an oxide. Examples are lead oxide fume from smelting and iron oxide fume from arc welding. Also, a fume can be formed when a material such as magnesium metal is burned or when welding or gas cutting is done on galvanized metal. 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 are pres ent in extremely minute amounts in the atmosphere. Magnitude of particles 16. When a solid is broken into finely divided particles, its surface area is increased many times. For ex ample, 1 cubic centimeter (0.061 cubic inch) of quartz in the form of a cube when crushed into 1-micron cubes will give 1012 (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 cpfeic.. 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 American 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 detect dust particles as small as 50 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 10 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 particles greatly out numbering the large ones. Conse quently, with few exceptions, when dust is noticeable in the air around an operation, probably more invissible dust particles than visible ones are present. Separation in air-borne dust 21. Dust in the air may or may not have the same composition as its parent material. The determining factors are 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 of clays. Most of the clays consist of fine particles that can be air-borne, but most of the quartz particles are too large to be air borne. The air-borne dust, there fore, as compared with the original mixture, may contain a much higher percentage of clays and a much lower percentage of free silica. 23. Dust particles are, of course, attracted.. by.. g f a v ity r T h e 'ir s e ttlin g rate through still air will vary with their size, density, and shape. Mi croscopically small particles settle out more slowly than larger particles be cause of their relatively minor densi ty and because of their being in fluenced b y . 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 DUSTS Size in Microns 0.25 0.50 1.00 2.00 5.00 Time to Fall 1 Foot (minutes) 590.0 187.0 54.0 14.5 2.5 24. Most of the particles in air borne industrial dusts are small. Be cause of air currents, the fine parti 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 ihicrons 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 are expec torated or swallowed into the diges tive tract. 26. When larger particles of cer tain toxic dusts are 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:3rger 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 is 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 other portions of the upper respiratory system. 29. The bronchi and 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 bending in one direction, make a fast stroke toward the mouth and a slower return stroke. This action 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 less 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 silicotic 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 microns long have been found in the lungs Figure 2. Metol volatilized by the heat of weld ing later condenses to form a fume. On this bench-welding installation, fumes are removed at their point of origin by a properly located local exhaust installation. (Courtesy American Found rymen's Society) of asbestos workers at autopsy. A typical fibrosis caused by asbestos is produced by fibers ranging from 2 0 to 5 0 microns in length, but only a few microns wide. Physiological effects 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 asbestosis. 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 o f magnesium or o f 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, and some woods and dusts of a few organic and inor ganic chemicals. e. Bacterial and fungus infections which occur from inhalation of dusts containing active organisms, such as wool or fur dust contain- ..................... ................. ..................... Substance TABLE II. SELECTED INDUSTRIAL MINERAL DUSTS ............................ ............................... ......................................... ...... ...... Threshold Limit In Million Particles Description and Uses per Cubic Foot of Air* Chalcedony Chert Cristobalite Flint Jasper Quartz Tridymite Tripoli (Rottenstone) CRYSTALLINE FREE SILICA (Si02, including microcrystalline forms) A heat-resistant, chemically inert form of macrocrystalline quartz. A decorative material. Rare in industry. A microcrystalline form of silica. An impure form of flint used in abrasives. A crystalline form of free silica, extremely hard and inert chemically; very resistant to heat. Quartz in refractory bricks and amorphous silica in diotomaceous earth are altered to cristobalite when exposed to high temperatures (cal cined). Cristobalite is extensively used in precision casting by the hot wax process, dental laboratory work, and certain specialty ceramics. A microcrystalline form of native quartz, more opaque and granular than chalcedony. Used as an abrasive and in ceramics. A microcrystalline impure form of silica similar to chert. Used for decorative purposes. Rare in industry. Vitreous, hard chemically resistant free silica, the most common form in nature. The main constituent in sandstone, igneous rocks, and common sands. Vitreous, colorless form of free silica. Formed when quartz is heated to 870 C (1,598 F). A porous, siliceous rock, resulting from the decomposition of chert or siliceous limestone. Used os a base in soap and scouring powders, in metal polishing, as a filtering agent, and in wood and paint fillers. A cryptocrystalline form of free silica. Calculate from formula:** 250 % S0,,2 + 5 Diatomoceous earth Silica gel AMORPHOUS FREE SILICA (Noncrystalline) A soft, gritty amorphous silica composed of minute siliceous skeletons of small aquatic plants. Used In filtration and decolonization of liquids, insulation, filler in dynamite, wax, textiles, plastics, paint, and rubber. Calcined and flux-caldried diatomoceous earth contains appreciable amounts of cristobalite, and dust levels should be the same as for cristobalite. A regenerative absorbent consisting of the amorphous silica manufactured by the action of HCI on sodium silicate. Hard, glossy, quartz-llke in appearance. Used in dehydrating and in drying and as a catalyst carrier. Amorphous = 20 mppcf Calcined = use formula: 250 % sio2 4* 5 20 mppcf Asbestos Clays Feldspar SILICATES (Compounds made up of silicon, oxygen, and one or more metals with or without hydrogen. These dusts cause nonspecific dust reactions, but generally do not interfere with pulmonary function or result in disability.) A hydrated magnesium silicate in fibrous form, The fibers are believed to be the more hazardous component of asbestos dust. A great variety of aluminum--silicate bearing rocks, plastic when wet, hard when dry. Used in pottery, stoneware, tile, bricks, cements, fillers, and abra sives. Kaolin is one type of clay. Some clay deposits may include appreciable quartz. Commercial grades of clays may contain up to 20 per cent quartz. Most abundant group of materials, composed of silicates of aluminum with sodium, potassium, calcium, and rarely barium. Most economically important mineral. Used for ceramics, glass, abrasive wheels, cements, insulation, and fertilizer. 5 mppeft 50 mppeft 50 mppeff `These threshold limit values were adopted by the American Conference of Governmental Industrial Hygienists in 1962. " Threshold limit values obtained from formula apply to all the substances in "Crystalline Free Silica" group. (Threshold limits given for substances in "Silicates" group are for compounds containing less than 1 per cent crystalline silica. For compounds containing more than 1 per cent silica, calculate threshold limit from formula: 250 % Si02 + 5 TABLE II. SELECTED INDUSTRIAL MINERAL DUSTS (Continued) ..................................................................SILICATES..*............... ................... .......-............... .... (Compounds made up of silicon, oxygen, and one or more metals with or without hydrogen. These dusts cause nonspecific dust reactions, but generally do not interfere with pulmonary function or result in disability.) Fuller's earth Kaolin /Area Portland cement Silicon carbide (Carborundum) Talc Vermiculite A hydrated silica--alumina compound, associated with ferric oxide. Used as a filter medium and as a catalyst and catalyst carrier and in cosmetics and insecticides. A type of clay composed of mixed silicates and used for refractories, ceramics, tile, and stoneware. A large group of silicates of varying composition, but similar in physical proper ties. All have excellent cleavage and can be split into very thin sheets. Used in electrical insulation. Fine powder containing compounds of lime, alumina, silica, ond iron oxide. Used as construction material. Bluish-black, very hard crystals. Used as abrasive and refractory material. 50 mppeff 50 mppeff 20 mppeff 50 mppeff 50 mppeff A hydrous magnesium silicate used in ceramics, cosmetics/ paint/ and phar maceuticals, and as a filter in soap, putty, and plaster. An expanded mica (hydrated magnesium-aluminum-iron silicate). Used in light weight aggregates/ insulation, fertilizer, and soil conditioners, as a filler in rubber and paints, and as a catalyst carrier. 20 mppeff 50 mppeff fThrcshold limits given for substances in "Silicates" group are for compounds containing less than 1 per cent crystalline silica. For compounds containing more than 1 per cent silica, calculate threshold limit from formula; 250 % Si02 + 5 ing anthrax spores or wood bark or grain dust containing parasitic fungi. f. Irritation of the nose and throat, which is caused by acid, alkali, or other irritating dusts or mists. Some dusts such as soluble chromate dusts may cause ulceration of the nasal passages or even lung cancer. g. Damage to internal tissues, which may result from inhaled radioac tive materials such as radium and its daughter products and from other radioisotopes that emit highly ionizing radiation. Pneumoconioses 34. Pneumoconiosis comes from three Greek words that mean "lung," "dust," and "abnormal condition." The present generally accepted meaning of the word is merely "dusty lung." The kind of dust inhaled determines the type of condition or injury. A number of organic dusts are capable of producting lung dis eases, but not all these diseases are classified as pneumoconioses be cause they are not all a "dusty con dition" of the lung. 35. In very rare cases, enough dust had been inhaled to cause mechanical blockage of the air spaces. Flour dust has been known to cause this condition. Some dusts may be essentially inert and remain in the lungs indefinitely with no recognizable irritation, and a few like limestone dust may be gradually dissolved and eliminated without harm. Silicosis 36. The most important lung dis ease caused by the inhalation of mineral dust is silicosis--well-known in industries where crystalline free silica dust is present, such as foun dries, glass manufacturing, granite cutting, mining, and tunneling in quartz rock. It is found throughout the world, and in the past it has had many names, such as miner's asth ma, grinder's consumption, miner's phthisis, potter's rot, and stone mason's disease. The same occupa tional disease, however, is meant by all these names, and it is caused by dust from crystalline free silica, us ually quartz (see Table I I ) . 37. Although considerable prog ress has been made in dust control in industry, men still develop sili cosis in plants and on jobs where dust control is not adequate. Engi neering control is still the basic means of preventing this disease, and dust control equipment and proce dures must be carefully maintained. 38. Definition. Silicosis has been defined as "a disease due to breath ing air containing silica (Si02) characterized anatomically by gener alized fibrotic changes and the de velopment of miliary nodulation in both lungs, and clinically by short ness of breath, decreased chest ex pansion, lessened capacity for work, absence of fever,, increased suscep tibility to tuberculosis (some or all of which symptoms may be present), and by characteristic X-ray find ings." * 39. Factors of influence. Sili cosis, has been known to manifest itself after widely differing periods of exposure to silica dust. Appar ently, development of the disease depends upon: a. The amount and kind of dust in haled. b. The percentage of free silica con tained in the dust. c. The form of the silica. d. The size of the particles inhaled. e. The duration of the exposure. "R e p o rt (Jo in t) of th e C om m ittee on Pneumoconiosis and the Committee on Standard Practices in Compensation of Occupational Diseases," Year Book, 1933, American Public Health Association, 1790 Broadway, New York 19. p 100. f. The powers of resistance of the .....individual concerned^...... g. The presence or absence of a com plicating process such as infection. 40. Many theories have been ad vanced over the years to explain why crystalline free silica acts as it does in the lungs. Theories have been based on the hardness of the material and the effect of sharp edges, solubility phenomena, elec trochemical action of the crystals, and immunological reactions. 41. It is believed now that the fibrosis produced is caused not by the hardness or sharpness of the particles, but by a combination of slight solubility with a physiochemical effect and an immunological effect--but no one is certain of the exact mechanism of the disease. Ex perimental work on the reasons for the development of silicosis is still going on in various parts of the world. If the precise mechanism of silicosis could be determined, better medical preventive measures might be developed and possibly a cure could be found. 42. Three stages. Silicosis is gen erally classified in three separate stages by medical authorities. More sophisticated classifications are some times used for the various X-ray stages and complications of the dis ease, but for a basic understanding the three stages give a good break down. 43. The first stage of the dis ease produces no disability. The affected man can carry on his work as well as ever. Frequently, the in dividual is not aware that anything is wrong, and the disease is revealed only by opaque nodular shadows on a chest X-ray coupled with a known exposure to crystalline free silica. 44. In the second stage, respira tion may be affected in some persons but not in all by any means. Labored breathing on heavy exertion usually is noted first, and a dry cough also may be present. 45. The third stage can develop after the second stage even though the individual has been removed from ex posure to silica dust. However, the progress of the disease will be slow er without continued dust exposure. Breathing may become severely labored. The worker is far below nor mal physically and is susceptible to respiratory diseases. Chest X-rays roav show an enlarged heart as a result of the body's attempts to over come the resistance of restricted blood vessels in the lungs. Pulmonary tuberculosis is a frequent complica tion and occasionally results in death. 46. Detection and development. Silicosis may be detected by chest X-rays in each of the three stages. However, X-rays alone are not sufficient for a positive diagnosis, for the shadows may be due to a variety of other conditions, includ ing infection or another type of pneumoconiosis. The individual must have had a definite exposure to free silica, because only it can cause sil icosis. The complete occupational and medical history of the employee must therefore be evaluated before a conclusion can be reached. The cor relation of chest X-ray findings and physical disability may be poor in many cases. 47. From most industrial expe rience, silicosis seldom develops in less than five years and in many cases may take 20 years or longer to become disabling. 48. The development of silicosis in its earliest stage is not perceived by the individual. The disease cannot be cured by any means yet known. Tuberculosis is more prevalent in persons with silicosis, but the inci dence is decreasing, as it is in the general population. 49. Men with early signs of sili cosis are able to perform their duties and are not a menace to other em ployees, for it is not a contagious disease. A perceptible X-ray change is not grounds for assuming disability because most people show chest changes with advance in age even without exposure to dust. Where there is a known exposure to silica dust, however, men with early signs of silicosis should be seen periodi cally by a physician. 50. Action of silica on the lungs: At the points in the lung where silica dust is deposited and accumu lated, a fibrous tissue develops and grows around the particles. This fibrous tissue is tough like scar tissue. It is not as elastic as normal lung tissue, does not permit the ready passage of oxygen and carbon diox ide, and as it proliferates, cuts down the amount of normal lung tissue. As a result, the available functional volume of the lung is reduced. 51. In some advanced cases, the fibrous tissue will slow down or even prevent the diffusion of oxy gen from the lung to the blood in the capillaries, and the blood in the area will not be completely oxy genated. The fibrous tissue can also affect the blood vessels by oblitera ting them or cutting down the flow of blood. All these effects tend to limit the rate at which oxygen is supplied to the body tissues. Emphy sema is the most obvious symptom. 52. As the inhalation of silica continues over the years, the amount of fibrous tissue will, of course, in crease, with the ultimate result that the lungs will not readily oxygenate sufficient blood for the body's needs. Then when the oxygen demand of the body is increased by exertion, the individual will feel distress with shortness of breath. 53. Amorphous free silica differs from crystalline free silica in physical structure and in physiological effects. In the amorphous state, molecules of silica exist in random orientation, which may be caused by natural forc es to form opal and diatomaceous earth (kieselguhr). Amorphous silica may be converted by artificial proc esses into such forms as silica gel, silica fume, and fused silica or quartz. 54. If amorphous silica is heated to a high temperature, as in calcining, forms of crystalline free silica called cristobalite and tridymite result. These intermediate forms of amor phous silica are known as crypto crystalline (ultra-microcrystalline. ) Inhalation of these crystalline forms can readily cause diatomite pneu moconiosis. 55. When diatomaceous earth is calcined, particularly in the pres ence of a trace of alkaline flux, appreciable quantities are converted to cristobalite. As a result of studies made by the U. S. Public Health Service, it has been recommended that the threshold limit value for crude or amorphous diatomite be placed at 20 mppcf (see Table II), but that the atmospheric concentra tion for dust containing cristobalite be kept under 5 mppcf. 56. Various commercial products containing particles of silica under 1 micron in size are available. The physiological effects of these prod ucts have not been well defined. ...........Until' iriore experience with 'human beings is available, it is believed J these products should be handled with care. 57. Free silica and silicates. Free silica is uncombined silicon dioxide (S i02). Silicates contain silicon and oxygen combined with other ele ments in a more complex molecule. Analyses of minerals, particularly in geological reports, are sometimes re ported as percentages of oxides, which may include Si02, A1203, K20, Fe20;). The Si02 reported in such chemical analyses is the total of the silicon dioxide present, both the free silica (if present), and the silica combined in the mineral. Such analyses are not reliable indications of the silicosis potential of the material. 58. It is uncombined or free silica that is most important in industrial dust exposure. So that an exposure can be properly evaluated, the per centage of uncombined silica must be determined by petrographic analysis using a polarizing microscope or, preferably, by X-ray diffraction analyses and special analytical chemical procedures. 59. There has been some experi mental evidence that some dusts may tend to inhibit the action of silica on the body, but this inhibiting action is so slight and uncertain that it must be discounted in practice. In fact, there also is evidence that the nonsiliceous components of a dust mixture containing free silica may provoke a disabling condition more severe than that caused by the silica acting alone. 60. With the exception of asbes tos and some talcs, the silicate dusts do not ordinarily cause a serious disabling lung condition such as is produced by free silica. Much higher levels of silicate dusts than of free silica dust can be tolerated. 61. In many industries,'men have worked with silicate dusts that con tained no free silica without devel opment of disability or of nodulation in the lungs. The X-ray may show shadows indicating dust deposits in the lungs, but the pneumoconiosis is essentially harmless. However, par tially disabling pneumoconioses have been reported where men have worked for long periods of time in very high concentrations of certain silicate dusts. .....627 Disabling ... pneumoconioses ' from exposure to abnormally high concentrations of mica, tremolite talc, and kaolin dusts have been de scribed in the literature. The clinical signs are not the same for these sili cate dusts as for free silica, but the symptoms can be marked. 63. The body does not have ade quate defense against indiscrimi nate amounts of dust of any kind. Therefore, although specific symp toms have not been described for many mineral dusts, the general ex perience would indicate that dust levels should be kept within thresh old limit values or below (Table II). Asbestosis 64. Asbestos is a general term ap plied to several minerals having a fibrous character. These asbestos minerals are hydrated silicates of magnesium with variable amounts of iron, calcium, sodium, potassium, and aluminum present as impurities. 65. Asbestos when inhaled pro duces fibrous tissue in the lungs of both men and animals. It has been shown that fibers of asbestos must be present for the production of asbestosis. Other silicate minerals of the same chemical composition but nonfibrous in form produce no re action or a relatively mild reaction, but not the severe reaction of fibrous asbestos dust. 66. These facts lead to the con clusion that asbestosis is mainly the result of physical irritation of the lung tisssue and not of a chemical action, which is thought to be one of the causes of silicosis. It is suspected that lung cancer may be induced by asbestos. However, there is no im pressive amount of evidence to sup port this assumption. 67. The fine air-borne fibers of asbestos can pass through the upper respiratory tract to the lower parts of the lungs to cause irritation and to form "asbestos bodies" where the fibers are encapsulated. This diffuse fibrosis probably begins as a "collar" about the terminal bronchioles. There is evidence that other min erals having a fibrous character can produce a reaction similar to that of asbestos. Fiber glass, however, does not produce such a reaction. 68. Following a study by the U. S. Public Health Service of the asbestos textile industry,* it was recommended that the dust concentratibh" be kept at less than' 5 mppcf to prevent asbestosis. Evaluation of an exposure to abestos dust is based on the total amount of dust because it has proved out in practice that if the fine dust is kept below the suggested threshold limit, the concen tration of injurious fibers will also be kept within safe limits. Talcosis 69. As used in industry, "talc" is a very general term. To the geolo gist, talc is a hydrous magnesium sili cate, which may be a relatively pure mineral or may be mixed with tremo lite or with dolomite depending upon where it is mined. The term "talc" is applied commercially- to carbonate mixtures that have the same general feel and physical properties; it also is applied to pyrophyllite, a hydrous aluminum silicate, which frequently is mixed with a high percentage of quartz. The free silica generally found with pyrophyllite can cause silicosis. It is therefore essential to know which talc is being used in order to evaluate a specific dust ex posure. 70. Talcosis is usually associ ated with tremolite talc. This disease produces changes in the lungs and symptoms similar to those of as bestosis.' Anthracosilicosis 71. A nthracosilicosis, a complex form of pneumoconiosis, is a chronic disease caused by breathing air con taining dust that has free silica as one of its components and that is generated in the various processes involved in mining and preparing anthracite (hard coal)** and, to a lesser degree, bituminous coal. 72. The disease is characterized anatomically by generalized fibrotic changes throughout .both lungs and by the presence of excessive amounts *Dreesen, W. C., Dalla Valle, J. M., Edwards, T. I., Miller, J. W., and Sayers, R. R,, A Study of Asbestosis in the As bestos Textile Industry, U. S. Public Health Bulletin No. 241, U. S. Public Health Service, Washington 25, D. C. 1938. **Anthracosilicosis among Hard-Coal Miners, U. S. Public Health Bulletin No. 221, U. S. Public Health Service, Wash- ! of carbonaceous and siliceous ma terial.Such lungs on autopsy are coal" black. ................ .......... 73. Symptoms found in early stages of the disease are shortness of breath, cough with a coal-black sputum, pain in the chest, and in some cases physical weakness. In the advanced stages, there are loss of weight and decreased capacity for work, partly caused by pulmonary infection (frequently bronchitis), and in some cases there may be heart failure. 74. Experiments with animal's showed that mixtures of coal and quartz produced more fibrosis than did quartz alone. The harmful effects of coal dust do not come only from the silica in the dust. Coal dust alone in very heavy concentrations over a period of many years can cause breathlessness and ventila tory impairment. Miscellaneous pneumoconioses 75. Even though a dust is classi fied as harmless, excessive amounts of it can lead to trouble by causing a pneumoconiosis or simply by me chanically irritating the walls of the respiratory system. Moreover, even though there is no chemical or physi cal irritation, mechanical plugging of the lungs and interference with their ordinary processes can result. Mica dust and kaolin dust are two good examples of dusts that ordinarily are considered benign but in excessive amounts can cause a troublesome pneumoconiosis. 76. Mica pneumoconiosis has been observed in grinding operations where mica dust, but no free silica was present. There were marked changes in the X-ray pictures of the lungs and some disability. The cases occurred where the dust exposures were massive over many years. 77. Kaolinosis has been described as a condition induced by inhalation of dust released in the grinding and handling of kaolin (china clay). Where the cases occurred, dust levels of several hundred million particles per cubic foot of air were common. 78. Aluminum dust is not consid ered to be harmful except where exposures are massive. Without ad verse effects, aluminum dust inhala tion has been used as part of an endeavor to prevent silicosis. Also without adverse effects, extensive exposures to aluminum dust have oc TABLE III. SELECTED TOXIC DUSTS AND FUMES Substance Description and Effects Threshold Limit in MiUigroms per Cubic Meter of Air* Antimony Arsenic Barium (soluble compounds) Beryllium Chromic acid and Chromates Cyanide (as CN) Dinitrobenzene Fluorides Hydroquinone Iron oxide fume Lead Lead arsenate Magnesium oxide fume Gray metal often associated with lead and arsenic. Hazardous from Inhala tion and ingestion. Soluble salts may cause dermatitis. Silvery brittle crystalline metal. Haz ardous from inhalation and ingestion. Usually encountered as arsenic trioxide. Soluble barium chloride and sulfide are toxic when taken by mouth. Light weight, gray metal. The metal, low-fired oxides, soluble salts, and some alloys are toxic by inhalation. Red, brown, or black crystals. Caustic action on mucous membranes or skin. Nonvolatile cyanides are ingestion haz ards. Cyanides inhibit tissue oxidation upon inhalation and cause death. Yellowish crystal. Hazardous from skin absorption, inhalation, and ingestion. Inorganic fluorides are highly irritant and toxic. Colorless hexagonal crystals. Contact with the skin may cause sensitization and irritation. Excessive exposure to dust may cause corneal injury. Major sources are cutting and welding. Lead fumes and lead compounds cause poisoning after prolonged exposure. Most important means of entry into body is inhalation. Skin absorption is of significance only from such organic compounds as lead tetraethyl. White crystals--highly toxic. White powder. Inhalation of freshly generated fume may cause metal fume fever. 0.5 0.5 0.5 0.002 0.1 5.0 (skin**) 1.0 (skin**) 2.5 2.0 15.0 0.2 0.1:5 15.0 ` These threshold limit values were adopted by the American Conference of Govern mental Industrial Hygienists in 1962. curred in the grinding of aluminum parts and castings. It can therefore be concluded that reasonably good control will prevent harm from alu minum dust. 79. Bauxite pneumoconiosis (Sha ver's disease) has been found only in workers exposed to fumes contain ing aluminum oxide and minute or ultramicroscopic silica particles aris ing from smelting bauxite in the manufacture of corundum, an im pure form of aluminum oxide. It is essentially a diffuse interstitial fi brosis and marked associated emphysenia, with a complete absence of any nodular fibrosis. It definitely does not occur from the use of cor undum grinding wheels or from other forms of aluminum oxide. 80. Some pneumoconioses may show marked shadows on an X-ray film; these shadows, without the nec essary information on the exposure TABLE III. SELECTED TO XIC DUSTS AND FUMES (Continued) the lungs are somewhat similar to the shadows from silicosis. Because of Substance Description and Effects Threshold Limit in Milligrams per Cubic Meter of Air* `IKiFTimilanty^ differefitiM' diagnosis is often difficult, and heavy exposures to iron oxide dust and fume may lead to medicolegal problems. It is there Manganese Pentachlorophenol Silvery gray metal. Hazardous from inhalation of fumes or dust. Dark-colored flakes. Harmful dust. Emits toxic fumes when heated. 5.0 0.5 (skin**) fore important to control iron oxide exposures even though siderosis is not disabling. 83. Limestone, marble, lime, gyp sum, and poTtland cement dusts ap Phosphorus (yellow) Poisonous mainly by inhalation. Severe 0.1 burn hazard from skin contact. parently have no serious effect even after long exposures. Also, many sili Picric acid Selenium compounds Yellow crystals or liquid. Explosive-- particularly metallic salts. Emits toxic fumes on decomposition. Toxicity varies somewhat according to the solubility of the specific com pound. Often causes contact dermatitis. 0.1 (skin**) 0.1 cates and other minerals have not caused impairment in individuals in haling the dusts, and the resulting pneumoconioses are generally classed as benign. Toxic Dusts and Fumes Sodium hydroxide Tellurium Titanium dioxide White, deliquescent pieces or lumps. 2.0 Has severe action upon all body tissue. Similar to selenium chemically and in 0.1 physiological effects. White to black powder. Considered in 15.0 the nuisance category. 84. Systemic reactions are caused by toxic dusts and fumes of various elements and their compounds and by certain organic compounds. All metallic fumes are irritating, especi ally when freshly generated. Indus trially important metals and their Trinitrotoluene Colorless to yellow monoclinic crystals. Emits toxic fumes of oxides of nitrogen when heated to decomposition. Highly poisonous explosive. 1.5 (skin**) compounds that can have a toxic effect when the dust or fume is in haled include arsenic, antimony, cad mium, chromium, lead, manganese, mercury, selenium, tellurium, thall Uranium Highly toxic and a radiation hazard that requires special consideration. 0.05 (soluble com pounds) 0.25 (insoluble com pounds) ium, uranium, and a few others.* 85. The effect of some metals, such as magnesium and zinc, appears to be transient. Only limited data Vanadium pentoxide Zinc oxide fume Yellow to red crystals. Acts chiefly as an irritant to the conjunctiva and re spiratory tract. Amorphous white or yellow powder. The powder is essentially nontoxic, but freshly generated fume may cause metal fume fever. 0.5 (dust) 0.1 (fume) 5.0 are available on the exotic and rare earth metals. 86. Although the dusts and fumes from metals with low toxicity do not need as much attention as the dusts and fumes from highly toxic metals, they should not be neglected or disregarded. The metals with low Zirconium compounds Most compounds are insoluble and 5.0 have low toxicity. toxicity are controlled more readily because greater amounts can be tol erated, but their dusts, and fumes ` These threshold limit values were adopted by the American Conference of Govern mental Industrial Hygienists in 1962. " The word "skin" in this table indicates that the substance can penetrate the skin to contribute to the exposure. should be kept at reasonable levels since excessive amounts of any of them can be harmful (Table III). Lead poisoning of the individual, may be alarming in a general X-ray screening pro gram. On clinical examination of in dividuals showing the X-ray mark ings, however, often no disability or example, can show very marked shadows on X-ray films without pro ducing signs of significant pathology (barium dust that is soluble in the body fluids can give a toxic reaction), 87. Although extremely severe cases of lead poisoning are rare in industry today, lead exposures must be controlled to prevent even the moderate symptoms, which can be symptom can be found. 81. These shadows are frequently encountered w hen the dusts contain atoms of relatively high molecular weight because the heavier atoms are fairly opaque to X-rays. Insoluble barium dusts and tin oxide dusts, for 82. Iron oxide, particularly ex cessive fume from welding opera tions, may produce siderosis with a pigmentation of the lungs (black in welders and red in iron ore miners) without disability. The X-ray shad ows produced by the iron oxide in See the following National Safety Council Data Sheets: Antimony and Its C o m p o u n d s , 4 0 8 ; Arsenic and Its inor ganic Compounds, 499; Cadmium, 312; Lead, 443; Magnesium, 426; Manganese, 306; Mercury, 203; Titanium, 485; Zinc and Zinc Oxide, 267; Zirconium Powder, 382. troublesome.. Inhalation of the dust of lead compounds is the most com mon mode of entry ffdTh'le system. Ingestion of lead compounds can add to the problem if personal hygiene is poor. Workers should therefore be encouraged to wash thoroughly before eating, and lunch rooms should be segregated from work areas. 88. It should be recognized that lead is a normal constituent of plants and animals. People ingest and ex crete lead daily even though they are not exposed to lead in their daily work. The body can handle and eliminate small amounts without harm. When intake rates exceed the normal excretion level, build-up oc curs in the body. There is a safe level of absorption, and if the. con centration of lead dust in the air of work areas is kept below the threshold limit, there should be no difficulty. 89. The importance of maintain ing the concentration of air-borne lead at a very low value stems from lead's high toxicity and its tendency, in small amounts, to accumulate in the human system. When lead ab sorption in the body reaches a suf ficient degree, symptoms of poison ing or intoxication appear. Beryllium intoxication 90. Beryllium intoxication is a severe systemic disease that can re sult from the inhalation of dust or fume of metallic beryllium, beryl lium oxide, and soluble beryllium compounds. 91. There are two forms of the disease. One is an acute form of chemical pneumonitis with cough, pain, difficulty in breathing, cyano sis, and loss of weight. In the chronic type, known as berylliosis, there may be loss of appetite and weight, weakness, cough, extreme difficulty in breathing, cyanosis, and cardiac failure. Formerly, mortality was high in chronic beryllium intoxica tion, and many who survived suffer from pulmonary distress. 92. Individual susceptibility ap parently is an important factor in the development of the disease. In many instances, one employee has developed the severe symptoms while other employees doing the same work have shown no signs of disability. 93. Beryllium intoxication has never been demonstrated in individ uals mining or handling ore only. There is"ho evidenceof intoxication from the ingestion of beryllium oxide, beryllium metal, or any of the beryllium alloys. Only the in halation of beryllium-bearing dusts or fumes produces systemic disease. Accordingly, control of such dusts and fumes at or below concentra tions specified by ACGIH threshold limit values* is to be recognized as a basic protective measure. 94. When the soluble salts of beryllium, especially beryllium fluo ride, come in contact with cuts or abrasions on the skin, deep ulcers may be formed that heal very slowly. Complete surgical excision of the ul cer is sometimes required in order to effect healing. Metal fume fever 95. Metal fume fever is an acute condition of short duration caused by a brief high exposure to the freshly generated fumes of metals such as zinc or magnesium or their oxides. Symptoms appear from four to twelve hours after exposure and consist of fever and shaking chills. There is complete recovery usually within one day, and ordinarily the employee can return to the same job without recurrence. However, after a period in which there has been no contact with the fume, for example, after a layoff, resumption of exposure is likely to bring on an attack. 96. To cause metal fume.fever, heavy concentrations of fumes are required. Zinc oxide fume is the most common source, but cases caused by the inhalation of fumes from magnesium oxide, copper oxide, and other metallic oxides have also been reported. The condition does not occur from the handling of these oxides in powder form. Apparently, it results only from the inhalation of extremely fine particles freshly formed as fume (nascentfume). 97. Nickel, mercury, and other metals may also produce a fever fol lowed by the toxic effects of the element. Allergic Reactions 98. When in the form of dust, a large number of materials may cause various allergic reactions in suscep *Threshold Limit Values for 1962, published by American Conference of Governmental Industrial Hygienists, 1014 Broadway, Cincinnati 2, Ohio. tible individuals. Examples of such agents are certain animal products, '`T55asT"dffiiS;`'^a^hB iH tea3r." The bodily systems usually involved in allergic reactions, which may be quite severe, are the skin, respiratory sys tem, and gastrointestinal system. Oc casionally, two or more systems are involved. Some of the allergic reac tions are dermatitis, hay fever, asth ma, and hives. 99. Usually, the victim is subject ed to a series of exposures without any reactions during which sensiti zation is built up. These exposures may occur continuously for years. Then, at the end of the "incubation period," which varies according to the individual, a reaction is pro duced. 100. For a true allergic reac tion two factors are required: a. A history of prior exposure to the material involved (sometimes not known by affected employees). b. A "challenge dose" o f the mate rial, which provokes the allergic re action. 101. Continuous exposures may act as "desensitizing doses," and under these conditions an allergic individual may work without incident for long periods of time only to find that re-exposure after removal from the sensitizing material ( such as after a vacation) causes an allergic re sponse to recur. 102. Medical and engineering rec ommendations to prevent allergic reactions are based on prevention of exposure by means of personal pro tective equipment, ventilation meth ods, or removal of sensitized individ uals from the exposure. Infections Infection and pneumoconiosis 103. The- presence of pulmonary disease that significantly interferes with the natural defenses against foreign particles may increase sus ceptibility to pneumoconiosis. Con versely, a pneumoconiotic lung is more prone to infection. For exam ple, tuberculosis occurs more fre quently among silicotics than among normal persons. Severe disability or death of a silicotic, when caused by pulmonary conditions, usually results from complicating tuberculosis either alone or combined with other infec tions. Bacteria and fungi 104. The possibility of lung in- fections from the inhalation of bac teria and fungi exists in several jn-, dustries. Pulmonary anthrax from the inhalation of dust containing an thrax spores has occurred among em ployees engaged in the handling of wool and the crushing of bones from infected animals. 105. Fungi (molds) growing on grain have been found in sputum of workmen shoveling the grain and are believed to be the cause of out breaks of respiratory disorders. Fungi found in sugar cane residues (bagasse) are believed to be part of the cause of bagassosis. Fungal spores formed under the bark of some trees have been blamed for respiratory difficulties among em ployees who debark dry logs. 106. Although the incidence of occupationally related bacterial and fungal infections is found to be relatively low, the respiratory effects can be troublesome and, in the case of pulmonary anthrax, even fatal. The basic methods of control are the same as those for the pneumoconio sis producing dusts, but sterilization and disinfection must be added. Radioactive Dusts* 107. A radioactive contaminant may offer a chemical toxicity hazard in addition to an ionizing radiation exposure, and it may be present as a gas, dust, fume, or mist. 108. Radioactive contaminants taken into the body may be deposited in various organs where they consti tute sources of internal radiation. The chemical characteristics of the radioactive contaminant or isotope determine the organ in which it will be deposited. The excretion rate is also dependent upon the chemical nature of the isotope, because the radioactive isotopes of an element follow the same metabolic process as do the stable isotopes of that ele ment. 109. If a radioisotope has been deposited in the body, the internal exposure is regarded as continuous until the isotope is lost by radiologi cal or biological decay. In some cases, exposures may last a lifetime. "For a detailed discussion of radio activity and an extensive bibliography, see the chapter entitled "Ionizing Radia tion" in the Accident Prevention M'antutl for Industrial Operations, published by the National Safety Council. 110. Since radioisotopes are selectively taken up__in..jndry]dji^jy;-_i_ gans, they may cause only localized irradiation. The radiosensitivity of the organ dictates the extent of the hazard of a particular radioactive substance. Solubility and particle size determine how much of the ac tive material will gain access to and remain in the blood stream and var ious organs. 111. If radioactive air-borne con tamination is known to be present, control measures are mandatory. If the presence of contamination is un known but suspected, sampling must be done to determine whether or not air-borne concentrations of the ra dioisotope are below the threshold limit value. 112. Good personal hygiene and good operating techniques are much more important in the handling of radioactive materials than in the han dling of most other materials used in industry. 113. Engineering controls for radioactive dusts are similar to those for other dusts and depend primarily upon capture at the point of genera tion. The difference lies in the fact that controls for radioactive dusts must be extremely efficient. Thresh old limit values for radioactive par ticulate matter are very low, and in some cases 100 per cent efficiency in capture and retention is required. Permissible Dustiness 114. Threshold limit values of mineral dusts and toxic dusts--that is, time-weighted average concentra tions considered permissible for ex posures of eight hours per day, five days per week--have been pub lished by the American Conference of Governmental Industrial Hygien ists. These values have been obtained from the experience of many groups in industry and from laboratory studies on animals. They are re viewed annually and changed as nec essary on the basis of experience. 115. These values are set only as guides for the best practice and are not to be considered absolute values. There is reasonable assur ance that occupational disease will not occur if exposures are kept be low these levels. On the other hand, occupational disease is likely to de velop in some people if the recom mended levels are exceeded consis tently. 116. The currently recommended threshold..limits of particular dusts can be found in the most recently published ACGIH list, or the ACG1H can be consulted directly. Information on threshold limits also can be obtained from the National Safety Council, state occupational health agencies, the American Indus trial,Hygiene Association, and com pensation insurance carriers. 117. No one knows the exact concentration at which men will start to develop silicosis, asbestosis, or lead poisoning. With some toxic dusts, however, experience has been wide enough to establish the present threshold limits as fairly reliable. 118. For example, if the level of lead in a workroom is kept below 0.2 mg/cu m, experience has shown that cases of lead intoxication will not. occur. Experience also has shown that many men can tolerate lead levels well above 0.2 mg/ cu m without signs of trouble. Mineral dusts 119. In the United States, the threshold limits for mineral dusts are expressed in millions of par ticles per cubic foot of air (mppcf). The concentration of a mineral dust is determined by counting dust par ticles that are less than 10 microns in size in an aliquot sample after sampling a known volume of air in a known volume of liquid. In some European countries, mineral dusts are weighed, and permissible levels are expressed as milligrams of dust per cubic meter of air (mg/ cu m ). In England and some other areas, the number of particles per cubic centimeter is the current basis of measurement. 120. In comparing United States and foreign dust counts, it is helpful to keep in mind that 100 particles per cubic centimeter is equivalent to approximately 3 million particles per cubic foot. 121. It is difficult to compare dust counts with results obtained on the basis of weight. However, with either type of measurement, a thresh old limit can be set as an objec tive. Experience has shown that maintaining dust levels below the recommended threshold limits has resulted in a great decrease in the incidence of occupational diseases. 122. Threshold limits are based on the percentage of free silica where this substance is the impor- tant constituent of the dust. If sili, cosis is..tp be prevented, these limits must not be exceeded. Concentra tions of dusts containing less than 5 per cent free silica should not exceed 50 million particles per cubic foot (mppcf). Concentrations of dusts containing from 5 per cent to 50 per cent free silica should not exceed 20 mppcf. Dusts containing more than 50 per cent free silica should be kept at concentrations below 5 mppcf. 123. As more experience accu mulates, original threshold limits sometimes can be modified. In some cases, it has been necessary to lower the limits, for the objective is to protect the more susceptible indi viduals. In a few cases, experience has shown that the limits were too stringent, and it has been possible to raise the limits to allow for more reasonable controls. Toxic dusts 124. In all countries, threshold limits for toxic dusts are expressed in milligrams per cubic meter of air. With toxic dusts, the average levels must be kept below the sug gested threshold limits. In fact, it is advisable to keep the levels of toxic dusts as low as practical in the specific circumstances. Little in the way of experience or data will be developed if the levels are kept unusually low, but few if any cases of occupational disease will occur from these dusts. Nuisance dusts 125. Even though a dust may be considered generally innocuous and not be recognized as the direct cause of a serious pathological condition, its level should be kept as low as is practical. Dust levels well below the suggested threshold limits aredesirable. 126. A concentration of 50 mppcf is suggested as the threshold limit for a number of nuisance dusts. With good engineering prac tice, there is no need for this level to be exceeded. Any reduction be low this level will increase the com fort of employees and improve plant housekeeping. Methods of Control 127. Various methods of con trolling dusts, mists, and fumes are available. Basic engineering dictates where possible an operation should Figure 3. Each of these grinding wheels is partially enclosed by an exhaust hood. Efficient local exhaust is achieved by drawing the dust into the hoods, through branch ducts, and Into a central duct which leads to the collection point. (Courtesy American Foundrymen's Society) be made dustless through control at foundry and the use of water in the source. This method is always drilling. the most effective, for it either com e. Local exhaust systems may be in pletely prevents the contaminant stalled with virtually full or partial from entering the workroom atmos enclosure. Examples are an ex phere or limits to safe levels the haust hood on a grinding wheel amounts that do escape. In addi (Figure 3) and an exhaust hood at a bagging or filling operation. tion, this method is generally the least expensive. f. General room ventilation can be used to dilute the dust by adding 128. When control at the source large quantities of air and thus is not possible, other methods may preventing build-up of dust con have to be considered. Any one or centrations. Examples of this meth a combination of the following types od are roof fans and roof moni of dust control may be needed to tor windows. But it generally is limit the exposure. inefficient and expensive to attempt a. The dusty operation may be en closed, with or without a local exhaust system. An enclosed op to control contaminants by dilu tion. g. The dusty work may be performed eration generating large quantities at night or on week-ends to reduce of dust usually needs to be ex the number of employees exposed. hausted, or the dust will leak into the surrounding atmosphere. Ex amples are sandblast cabinets or sandblast rooms and the dry boxes used to handle radioactive materials. b. The dusty work may be performed Cleaning dust accumulations from overhead beams, for instance, is preferably done during a weekend. The employees who are exposed should wear appropriate type of respiratory protective equipment. in a separate building or may be h. The number of working hours at isolated by partitions to reduce the the particular exposure ctin be re number of employees exposed to duced. However, other methods of the dust. The employees who are control are preferable. still being exposed should be pro i. Use of respiratory protective equip tected by respiratory protective ment approved for the exposure equipment. by the U.S. Bureau of Mines can c. A less hazardous material may be give excellent protection against substituted. For instance, steel shot all types of dust, but in most cases may be used instead of silica sand should be considered as a tem in abrasive cleaning. porary c o n tro l m e a s u re . In a d. Keeping the materials moist may sandblast room, however, air-sup be a practical means of control. plied helmets usually are required Examples are the careful and prop continuously during operations. er wetting down of aisles in a Respiratory protective equipment. b. Ducts, to carry the contaminated 138. Enough air must be sup air to a central point. plied to the room from the outside to c. Dust anti fume collectors, to clean replace ~iKe"~air that"TrTem5ved~tiy' the air before it is discharged. the exhaust system. Otherwise, d. A fari and motor to keep the air there will be interference with other moving through the system. exhaust systems in the area or with 133. While each of these parts gas or oil flames in nearby furnaces. should be designed and installed to Great difficulty has occurred where perform its required function with an exhaust system caused a slightly respect to the system as a whole, negative pressure in a room con design of the exhaust hood demands taining a gas furnace. As a result the greatest care. The degree of air came down the furnace flue, control of dust at the point of gen and the area became contaminated Figure 4. Since this swlng*frome grinder is used eration or dispersion is determined with carbon monoxide from the fur in o variety of positions, the local exhaust sys tem must be adjustable. The flexible duct (A) by the shape of the hood or degree nace. permits movement of the exhaust hood (B) as of enclosure, the location of the 139. With small exhaust systems, needed. (Courtesy American Foundrymen's So hood and its distance from the dust air that is removed usually can be ciety) source, and the rate of flow of air replaced by infiltration flow, but into the hood. A poorly designed larger exhausts may need a positive hood can make an exhaust system air supply (Figure 7 ). An adequate nevertheless, should not be con sidered as a universal substitute ineffective. 134. There is no standard hood. supply of make-up air, tempered when necessary, is one of the most for adequate local exhaust re moval, elimination of the con In every case, the hood must be frequently overlooked fundamentals taminant, or containment. designed to fit the specific opera of ventilation. Air always should be 129. Many states and municipal tion and to make the exhaust effec supplied in quantities equal to or ities have dust control codes of or tive without interfering with the slightly in excess of the amounts dinances with which employers operation (Figure 4). Among the exhausted. must comply. In a few states, for factors to be considered are the nat 140. The size of the ducts, the instance, written approval of plans ural air currents in the room and type and size of the dust collectors, must be obtained before a local other exhausts or windows in the and the type and size of the fan exhaust system is installed. Each area. and motor (explosion-proof where employer should therefore know his 135. The hood should be shaped necessary) are among the other fac state and municipal dust control re to conform to the shape of the area of dust production so as to secure tors which must be considered in the design of an exhaust system. Pre quirements. reasonably uniform air velocity over venting ignition of a combustible 130. Each type of exposure must be considered separately. For ex this area. A hood which does not en ample, a local exhaust system suit close the process should be placed able for welding or cutting of steel with its opening as close as possible might not be satisfactory for weld to the point of generation of the ing or cutting steel coated with red dust or fume (Figure 5) because lead. the velocity of the air in the zone of the hood influence is inversely Local exhaust systems proportional to the square of the 131. A local exhaust system for distance from the face of the hood. the control of an industrial dust or 136. The hood opening, or part fume traps the air contaminant of it, should be located so as to re near its source so that an operator ceive directly dust that is thrown standing at the process is not ex off along a well-designated path posed to harmful concentrations. (Figure 6). The directional energy The system should be designed to of the material can thus be used enclose the process as completely for its own capture. Air movement as possible. This method usually is must always be past the employee, preferred to general ventilation, then over the dust source, and di but should be used only when the rectly into th face of the hood. contaminant cannot be controlled 137. The fan should be of suffi by isolation, process revision, or cient capacity to maintain the re substitution of less harmful mate quired air capture velocity at the rials. Even though a process has point of generation of the dust. In been isolated, it may still require ternal baffles should be installed to a local, exhaust system. 132. A local exhaust system con sists of four principal parts: a. Hoods or other inlets, into which the air-borne contaminant is guide the air flow where it is most needed. Flanges should be provided wherever possible to reduce the air flow from areas where no dust is produced; that is, air-flow contours Figure 5. To achieve the proper exhaust air v e lo c ity , th e h o o d s fo r th e se b a rre l fu rn a c e s can be positioned as dose to the furnace spouts as practical. Such positioning is made possible by mounting the hoods on a trolley suspended from an overhead track. (Courtesy American drawn. ' should be controlled. Brake Shoe Co.) contaminant is a prime safety con sideration... Since.discussion of.. the.. subject of exhaust system design is beyond the scope of this data sheet, an experienced ventilation engineer should be consulted. 141. Also, information can be secured from several excellent pub lications, one of which is the current edition of Industrial Ventilation-- A Manual oj Recommended Prac tice, published by the American Conference of Governmental Indus trial Hygienists. Another is the chapter entitled "Local Exhaust Systems and Ventilation" in the Accident Prevention Manual for Industrial Operations, published by the National Safety Council. General ventilation 142. Where it is impossible, im practical, or too expensive to con trol dust entirely by local exhaust systems, general ventilation must be used as a supplement or a substitute. It should be noted, however, that where local exhaust systems can be used, they will always do a better job than general ventilation. 143. General ventilation requires the introduction of enough clean air from the outside to dilute the con taminated atmosphere to a safe level. This method requires larger volumes of. air than local exhaust systems to accomplish the same con trol, and will not be effective uni formly over a large room. It should be considered only when local ex haust systems require such assis tance. This is usually where the sources of dust are widely dispersed and each is small. 144. General room exhaust and supply fans must be carefully in stalled. Eddy currents, which will interfere with local exhaust systems, must be avoided. Employees must not be exposed to excessive con centrations of dust as the dust-laden air moves away from the point of generation, and sufficient makeup air from the outside must be sup plied to the room to replace the air that is exhausted. The location and design of the source of supply are important. It is becoming common practice to supply clean, tempered air to the work zone 'for controlled dilution. Wet methods 145. Wet dust is not dispersed as readily as dry dust-- advantage of this fact should be taken whenever possible. *~CarloaHi" r in some cases may be wetted down before they are unloaded. Aisles in foundries should be wetted down to prevent dispersal of the dust by traffic. Water sprays can be used at some operations. Wet drilling methods can be used for rock drill ing to wet the dust as it is formed. Personal protective equipment 146. Respirators of various de signs are available which will give protection against toxic and pneu moconiosis-producing dusts by fil tering out the contaminant from the air. The U. S. Bureau of Mines has set up performance standards for dust respirators and gives approval to respirators that meet these stand ards. It is important that a respirator be used only for the particular dust exposure for which it has been approved. 147. Although approved respira tors will give excellent protection when properly fitted, they should be used only as supplements to other methods of control or for short or occasional exposures and not as primary controls. 148. Proper fitting of a mechani cal filter respirator to the face of the individual is most important because a small space between the facepiece and the face will permit dustladen air to bypass the filter. 149. Respirators must be in spected and cleaned daily. Filters should be replaced before they be come so plugged with dust as to seriously increase resistance to breathing. Proper filters for replace ment should be available. Medical program 150. An effective medical con trol program will help prevent cases of occupational disease. Such a program can also serve as a check on the engineering controls because symptoms of exposure in a group of workers will indicate a failure that must be corrected. The extent of the medical program will depend upon the seriousness of the expo sures. 151. An industrial hygiene pro gram should parallel the medical program. Both are essential to pro tect the health of employees. 152. The physical examination for new employees should include a thorough pre-employment history with the occupational background given in'detail: Chest' X-raysshould be made of all new employees who will be working in dust exposures that could produce disabling pneu moconiosis. The examining physi cian should decide on placement of those who have pneumoconiosis, active or significant past tubercu losis, abnormally low timed vital capacity, or serious pulmonary dis eases. 153. Periodic physical examina tions, including chest X-rays, should be made of employees exposed to toxic dusts, fumes, and mists. Such checks can help find incipient cases of poisoning in which symptoms are slight, and the X-rays can pick up early symptoms of lung condi tions. Suitable preventive measures can then be taken. 154. Routine periodic clinical examinations, stipple cell counts, porphyrin determinations, and propperly evaluated blood and urine lead level measurements, are prac tical methods for checking em ployees exposed to lead. If unsafe exposures are found, further en vironmental control is mandatory. Affected employees should, of course, be given proper medical treatment. 155. Medical controls for em ployees who work with radioactive dusts must be more stringent than the medical controls for most dusts. An extensive bioassay sampling program is nearly always required. Other control measures 156. Although the most effective method of control is to prevent con tamination of workroom air and thus prevent inhalation of harmful Figure 6, The centrifugal force created by this grinding wheel causes tire generated dust to travel in a well-defined path. To prevent disper sion of the dust, the exhaust hood is placed di rectly in the dust stream, close to Its source. (Courtesy American Foundrymen's Society) dusts, the importance of personal hygiene should not be overlooked. Th" periodic medical examinations' provide a good opportunity for in struction of employees in various personal hygiene measures. 157. Good washing facilities, clean lunchrooms, and clean work clothes can help prevent additional, even though minor, exposure to toxic materials. Also, contaminated work clothes should not be taken home where a toxic dust could contaminate the home or expose other members of the family. These recommendations become manda tory where such materials as beryl lium and radioisotopes are handled. Figure 7. In this foundry, local exhaust hoods are Installed over each station machine and glue press. Adequate make-up air is supplied from ventilating molding machines and presses. (Courtesy American Foundrymen's Society) having a shell-molding d u d situated between BIBLIOGRAPHY Public Health Service, Washington 25, 2nd Edition, 1958, and Volume II, Accident Prevention Manual for Industrial Operations, National Safety Council, 425 N. Michigan Ave., Chi cago 11. Anthracosilicosis Among Hard-Coal D . C. 1938. Drinker, Philip, and Hatch, T. F., Industrial Dust, 2nd Edition. Mc Graw-Hill Book Co., Inc., 330 W. 42nd St., N ew York 36. 1954. 2nd edition (in preparation). Interscience Publishers, 250 Fifth Ave., New York 3. 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No. 499, Arsenic and Its Inor Prevost, Detroit 27. ganic Compounds Beryllium (in preparation) No. 312, Cadmium No. 443, Lead No. 426, Magnesium No. 306, Manganese No. 203, Mercury No. 485, Titanium No. 267, Zinc and Zinc Oxide No. 382, Zirconium Powder Industrial Ventilation-- A Manual of Recommended Practice, 7th Edition. American Conference of Governmen tal Industrial Hygienists, Committee on Industrial Ventilation, Box 453, Lansing, Michigan. 1962. Johnston, R. T., and Miller, S. E. , Occupational Diseases and Indus trial Medicine. W. B. Saunders Com pany, Philadelphia. 1960. ACKNOWLEDGMENT The text of this data sheet, which re places Health Practices Pamphlet No. 4, was prepared by the Health Committee of the Chemical Section, National Safety Council. The content has been extensively reviewed by members of the National Safety Council, representatives of chapters Dreesen, W. C., Dalla Valle, J. M., Edwards, T. I., Miller, J. W., and Sayers, R. R., A . Study of Asbestosis in Lanza, A. J., Silicosis and Asbes tosis. Oxford University Press, New York. 1938. of the American Society of Safety Engi neers, medical authorities, and industrial hygienists. The data sheet has been ap proved for publication by the Publications the Asbestos Textile Industry, U. S. Patty, F. A., editor, Industrial H y Committee of the Industrial Conference, Public Health Bulletin No. 241, U. S. giene and Toxicology, Volume I, National Safety Council. V l 13M66309 P rin ted in U .S.A. Stock N o. 123.04-531