Document RGbBmKVaMqbwYV4G7r3L6x1a

FILE NAME: National Safety Council (NSC) DATE: 1980 DOC#: NSC129 DOCUMENT DESCRIPTION: NSC Data Sheet - Dust, Fumes & Mists in Industry National Safetym::. Council Data Sheet c k 1-531-Rev 80 i Dusts, Fumes, and Mists in Industry I n d u s t r ia l d u s t s , fumes, and b. The particular exposure 5. Certain dusts that reach the mists, their hazards and their con must be evaluated by dust counts or lungs can pass directly into the trol, are discussed in this data sheet.* by chemical analyses o f air samples, blood stream and be absorbed over The general principles presented can and a step-by-step analysis o f the a long period o f time. Others may be applied to recognize and evaluate operations must be made to find the stay in the lungs and set up local most industrial situations involving areas where employees are exposed irritant or damaging action. these air contaminants and to deter to hazardous amounts o f the mate 6. Toxic and irritant dusts can mine the need for controls. This data sheet is intended to guide em ployers, plant and safety engineers, rial. The operational analysis also should determine how the dust, fume, or mist is dispersed. also be ingested in amounts that may cause trouble. If toxic dust swallowed with food or saliva is not personnel managers, and super c. Appropriate methods of soluble in body lluids, it is elimi visors. control must be provided where in nated directly through the intestinal 2. A plant manager who believes that he has a toxic or irritating air borne particulate problem should consult a competent industrial hy gienist. Such help may be obtained from his own company, insurance carrier, private consultants, and from state and federal agencies.3 3. To protect the health o f em ployees who work where a dust, fume, or mist created by a manufac turing process is released into the work environment, an evaluation dicated. The type and extent o f con tract. Toxic materials that are read trols will depend upon the physical, ily soluble in body fluids can be ab chemical, and toxic properties o f the sorbed in the digestive system and dust, fume, or mist, the evaluation picked up by the blood. made o f the exposure, and the na 7. Contact of toxic and irritant ture o f the operation that disperses dusts with the skin also may result the contaminant. The extensive con in skin irritation. trols needed for lead oxide dust, for example, would not be needed for limestone dust, since greater quantities o f limestone dust can be tolerated. 8. As compared to inhalation, however, both ingestion and skin contact are of relatively minor im portance in industrial poisoning insofar as dusts, fumes, and mists 4. Except for the skin diseases, are concerned. most occupational diseases are con and a control program may be re tracted by inhalation o f material. quired. In such a case, three steps Lung tissue is by far the most effi must be taken: cient medium the body possesses for a. The properties o f the spaeb sorbing materials. In addition, cific dust, fume, or mist and its pos the surface area o f this lung tissue sible physiological effects on em averages 55 square meters or about This data sheet covers toxic and irri tating air contaminants encountered in in dustry. It does not include a discussion o f the ~ explosive properties of such airborne par ployees must be ascertained. 590 square feet. ticulate matter. 444 North M ichigan Avenue Chicago, Illinois 60611 312-527-4800 PLAINTIFF'S EXHIBIT After U Origin and Properties of Particulate Matter Sources 9. The term dust as used in dustry is generally applied to air borne solid particles that range in size from 0.1 micrometer (pm) to 25 micrometers (one micrometer = 10"6 meter = 1/10,000 centimeter = 1/25,400 inch). Process dusts below 0.5 pm in size are rare. Dusts above 5pm in size usually will not stay airborne long enough to present an inhalation problem. 10. 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 with talc. Dust may be formed and dispersed when solid materials are reduced to small sizes in processes such as grinding, crushing, blasting, shaking, and drilling. In these proc esses, the mechanical action o f the grinding or shaking device supplies a source of energy to disperse the dust formed (Figure 1). 11. When a solid such as a metal is heated to a temperature high enough to volatilize it, the volatil ized matter later condenses in cooler air to form a fum e (Figure 2). The solid particles that make up a fume are extremely fine, usually less than 0.5 pm 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 mate rial such as magnesium metal is burned or when welding or gas cut ting is done on galvanized metal. 12. 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. 13. Smoke may be formed by the incomplete combustion o f organic materials. Smoke generally contains droplets as well as dry particles. Tobacco, for instance, produces a wet smoke composed o f minute tarry droplets. The size o f the par ticles contained in tobacco smoke is about 0.25 pm. 14. Radipactive dust may be dis persed in the same ways as other in dustrial dusts. Radium, thorium, Will give 1012 (1,000,000,000,000 or .r.85iMrJ!lton} particles with a total `.surface area of 6 square"`meters" (9,300 square inches), as compared with 6 square centimeters (0.930 in square inch) for the original cube. 16. 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 o f air (mppcf), resulting from 1 cubic centimeter o f material reduced to particles 1 cubic micrometer in Figure 1. Dust from foundry sand is generated during the shake-out of castings. The mechanical action of size, will occupy an air space of 20,000 cubic feet. 17. Even smaller amounts of the shake-out machine disperses the dust. Path taken by the dust par ticles as they are drawn into the hood shows the efficiency of the local exhaust system. (Courtesy American Foundrymen's Society) toxic dusts,"fumes, and mists will make a workroom atmosphere haz ardous. For example, the Threshold Limit Value for lead, as adopted by the American Conference of Gov ernmental Industrial Hygienists, is 0.15 milligram per cubic meter of air (m g/m 3), which is 0.00000015 and other radioactive elements are present in extremely minute amounts in the atmosphere. ounce per cubic foot. Therefore, the dispersion o f only 0.0015 ounce of lead will be enough to give the Threshold Limit Value of 0.15 Magnitude of particulates m g/m 3 o f dust, or fume in an air space o f 10,000 cubic feet (280 m3). 15. When a solid is broken into finely divided particles, its surface area is increased many times. For example, 1 cubic centimeter (0.061 cubic inch) of quartz in the form of a cube when crushed into 1 pm cubes The concentrations present in the workroom without harm to health differ for different substances. 18. A person with normal eye sight can detect dust particles as small as 50 pm in diameter. Smaller airborne particles can be detected individually by the naked eye only when strong light is reflected from them. Dust o f respirable size (below 10 pm) cannot be seen without the aid of a microscope. 19. Most industrial dusts consist o f particles that vary widely in size, with the small particles greatly out numbering the large ones. With few exceptions,, when dust is noticeable in the . air around an operation, probably more invisible dust par ticles than visible ones are present. Figure 2. Metal volatilized by the heat of welding 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 Foundrymen's Society) Separation in airborne dust 20. Dust in the air may or may not have the same composition as its parent material. The determining factors are particle size, density o f; each component in the original mix ture, and hardness of materials (which will resist th pulverizing ac tion o f a mechanical device). -2- TABLE I. SETTLING RATES FOR SILICA DUSTS gestive tract before they are elimi nated. Hence the final toxic effects occurs in the size o f particles in haled. Many fibers up to 100 pm .......... Time t o .... of. larger dust particles, may.be de long have been found in the lungs Fall 1 Foot layed. The larger particles o f irri o f asbestos wbffs at autopsy.' A Size in Micrometers (minutes) tant dusts can cause immediate ef typical fibrosis caused by asbestos 0.25 590.0 fects in the upper respiratory system. is produced by fibers ranging from 0.50 187.0 20 to 50 pm in length, but only a 1.00 54.0 26. Ragweed pollen, which var few micrometers wide. 2.00 14.5 ies from 18 to 25 ju.m in diameter, 5.00 2.5 can cause hay fever from its action in the upper respiratory system. This Physiological effects type of dust and other allergenic 32. The physiological reactions types, as well as bacterial and irri caused by the inhalation o f air 21. For example, foundry mold tant dusts, can cause difficulty even borne particulate matter will vary ing sand contains a large percentage in the larger airborne sizes. with different types o f dusts, fumes, of free silica (quartz) with a lower 27. When dust-laden air is in and mists. The reactions include: percentage o f clays. Most o f the haled, some o f the larger particles clays consist of fine particles that are trapped by the hairs in the nose. a. The cardiopulmonary re can be airborne, but most of the free Other dust particles are removed action, which consists o f the pneu silica particles are too large to be from the air as it passes over the moconioses, such as silicosis and airborne. The airborne dust, there moist mucous membranes o f the asbestosis. In certain cases, specific fore, as compared with the original nose, throat, and other portions of types o f lung pathology result, and mixture, may contain a much higher the upper respiratory system. the heart may be affected (cot pul percentage of clays and a much lower percentage o f free silica. 28. The bronchi and other res piratory passages are covered with monale) when the fibrosis is ad vanced. In other cases, there is 22. Dust particles are, o f course, a large number o f tiny, hairlike cilia mainly just an accumulation o f a attracted by gravity. Their settling or microscopic whiplashes, which relatively inert dust in the lungs. rate through still air will vary with aid in the removal of dust trapped b. The systemic reactions their size, density, and shape. The on these moist surfaces. The cilia, that are caused by toxic dusts or estimated settling rates for silica all bending in one direction, make a fumes o f such elements as lead, dusts in still air are given in Table I. fast stroke toward the mouth and a manganese, cadmium, and mercury, 23. Because o f air currents, the slower return stroke. This action by their compounds, and by certain fine particles in dust clouds at an tends to push mucus and deposited organic compounds. operation will remain suspended in dust upward to the mouth so that c. Metal fume fever, which the workroom air for relatively long the particles can be expectorated or results from the inhalation of finely E? periods of time. The smaller dust swallowed. divided and freshly generated fume : particles, moreover, will travel farther away from their point o f o f zinc or possibly o f magnesium or of their oxides. This is a transient fi origin than will the larger particles Retention of dust condition. so that the farther dust is from its 29. Many studies have been made d. Allergic and sensitization source, the greater percentage of in an effort to determine the amount reactions, which my be caused by small particles it contains. of dust that is retained in the lungs, inhalation of, or skin contact with, but there is no simple answer to this such materials as organic dusts from Inhalation of Dusts, Fumes, and Mists question. It has been shown that the size of the dust particles, the rate of respiration, the density o f the dust flour, grains, and some woods and dusts o f a few organic and inor ganic chemicals. 24. With the exception o f such in the air, the efficiency o f the dust- e. Bacterial and fungus in fibrous materials as asbestos, par catching mechanism, and probably fections which occur from inhala ticulates must usually be smaller many other factors are involved. tion o f dusts containing active or than 5 /mm in order to enter the al ganisms, such as wool or fur dust veoli or inner recesses o f the lungs. Although a few particles up to 10 Sizes of dust particles inhaled containing anthrax spores or wood bark or grain dust containing para pm in size may enter the lungs oc 30. Although an occasional dust sitic fungi. , casionally, nearly all the larger particle o f larger size will enter the f. Irritation o f the nose and particles are trapped in the nasal lungs, particles less than 3 pm in throat, which is caused by acid, al passages, throat, larynx, trachea, diameter are the most likely to do so kali, or other irritating dusts or and bronchi, from which they are and thus have the greatest oppor mists. Some dusts, such as soluble expectorated or swallowed into the tunity to cause a physiological reac chromate dusts, may cause ulcera digestive tract. tion. In silicotic lungs, for example, tion o f the nasal passages or even 25. When larger particles o f cer dust particles under 3 pm greatly lung cancer. tain toxic dusts are trapped in the upper respiratory passages, they outnumber larger ones, and many particles are less than 1 pm. g. Damage to internal tis sues, which may result from inhaled can be absorbed by the body fluids 31. In the case o f very fine fi radioactive materials such as radium in the nasal passages and in the di brous asbestos dust, an. exception and its daughter products and from iilP llII -3- Substance Chalcedony Chert Flint Jasper . Quartz Tripoli (Rottenstone) Cristobolite Tridymite Diatomaceous earth Silica gel TABLE J). SELECTED INDUSTRIAL MINERAL DUSTS ....... ...............-- -- ......................... Description, and. Uses-. . .................. ...... ........... ......._......... CRYSTALLINE FREE SILICA (S i03, including microcrystalline ______________________________________ forms)_______ A heot-resistant, chemically inert form of microcrystalline quartz. A decorative material. Rare in industry, A microcrystalline form of silica. An impure form of flint used in abrasives. A microcrystalline form of native quartz more opaque and granular than chalcedony. Used as an obrosive 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. A porous, siliceous rock, resulting from the decomposition of chert or siliceous limestone. Used as a base in soap and scouring powders, in metal polishing, os o filtering agent, and in wood and paint fillers. A cryptocrystolline form of free silica. A crystofline form of free silica, extremely hard and inert chemically; very resistant to heat. Quartz in refractory bricks and amorphous silica in diatomaceous earth are altered to cristobolite when exposed 16 high temperatures (calcined). Cristobolite is extensively used in precision costing by the hot wax process, dental laboratory work, and certain specialty ceramics. Vitreous, colorless form of free silica. Formed when quartz is heated to 870 C (1598 F). AMORPHOUS FREE SILICA. (Noncrystalline) A soft, gritty amorphous silico composed of minute skeletons of small aquatic plants. Used in filtration and decolorization of liquids, insulation, filler in dynamite, wax, textiles, plastics, paint, and rubber. Calcined and flux-calcined diotomoceous earth contains'appreciable amounts of cristobolite, and dust levels should be the same os for cristobolite. A regenerative absorbent consisting of the amorphous silica manufactured by the action of HC1 on sodium silicate. Hard, glossy, quartz-like in appearance. Used in dehydrating and in drying and as a catalyst carrier. .. Ihi.eshoid Ljm it Va lues* Calculate from formula: ** 300 % Si02 *t- 10 mppcf Total dust: 30 mg/m 3 % quartz + 3 Respirable dust: 10 m g/m 3 % quartz + 2 Use respirable dust quartz formula. One-half the value calculated from the first formula for quartz. Amorphoui = 20 mppcf Calcined: ------222------ mppcf % SiOj + 10 20 mppcf other radioisotopes that emit highly ionizing radiation. Pneumoconioses 33. Pneumoconiosis comes from three Greek w ords 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 o f pro ducing lung diseases, but not all these diseases are classified as pneu moconioses because they are not all a " dusty condition" of the lung. 34. 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 rec-. ognizable irritation, and a few like limestone dust may be gradually dissolved and eliminated without harm. Silicosis 35. The most important lung dis ease caused by the inhalation of mineral dust is silicosis -- wellknown in industries where crystal line free-silica dust is present, such as foundries, glass manufacturing, granite cutting, mining, and tunnel ing in quartz rock. It is found throughout the world, and in the past it has had many names, such as miner's asthma, grinder's consump tion, miner's phthisis, potter's rot, and stonemason's disease. The same occupational disease, however, is meant by all these names, and it is caused by dust from crystalline free silica, usually quartz (see Table II). 36. Although considerable prog ress has been made in dust control in industry, workers still develop sili cosis in plants and on jobs where dust control is not adequate. En-.. gineering control is still the basic means o f preventing this disease, and dust control equipment and procedures must be carefully se lected and maintained. 37. Definition. Silicosis has been defined as " a disease due to breath ing air containing silica (S i0 2) char acterized anatomically by general ized fibrotic changes and the devel- -4 Substance TABLE II. SELECTED INDUSTRIAL MINERAL DUSTS (Continued) Description and Uses SILICATES (Compounds made up of silicon, oxygen and one or more metals with or without hydrogen. These dusts cause nonspecific dust reodlons, but generally do not interfere with pulmonary function or result in disobility.) Threshold Limit Voiuesf Asbestos A hydrated magnesium silicate in fibrous form. The fibers are believed to be the more hazardous component of asbestos dust. 8 hr T.W.A. 5 fibers/ml >5pm in length Clays A great variety of aluminum -- silicate beoring rocks, plastic when wet, hard when dry. Used in pottery, stoneware, tile, bricks, cements, fillers, and abrasives. Kaolin is one type of cloy. Some clay deposits may include appreciable quartz. Commercial grades of cloys may contain up to 20 percent quartz. 30 mppcf *j* or 10 m g/m 3 of total dust, or 5 mg/m3 of respirable dust Fuller's earth A hydrated silica-alumina compound, associated with ferric oxide. Used as a filter medium and as a catalyst and cotalyst carrier and in cosmetics and insecticides. 30 mppcf Kaolin A type of clay composed of mixed silicates and used for refractories, ceramics, tile, and stoneware. 30 mppd Mica A large group of silicates of varying composition, but similar in physical properties. All excellent cleavage and can be split into very thin sheets. Used in electrical insulation. 20 mppd Portland cement Fine powder containing compounds of lime, oiumina, silica, and iron oxide. Used as construction material. 30 mppd Silicon carbide (Carborundum) Bluish-black, very hard crystals. Used as abrasive and refractory material. 30 mppd Talc (nonabestiform) Vermiculite A hydrous magnesium silicate used in ceramics, cosmetics, paint, and pharmaceuticals, and as a filler in soap, putty, and plaster. An expanded mica (hydrated magnesium-aluminum-iron silicate). Used in lightweight aggregates, insulation, fertilizer, and soil conditioners, os a filler in rubber and points, and Os a catalyst carrier. 20 mppd 30 mppd These Threshold Limit Values (TLVs) were adopted by the American Conference of Governmental Industrial Hygienists in 1979. Threshold Limit Values obtained from formula apply to all the substances In "Crystalline Free Silica" group. (Threshold limits given for substances in "Silicates" group for compounds containing less than 1 percent crystalline silica. For compounds containing more than 1 percent silica, calculate threshold limit from crystalline free silica formulas. opment of miliary nodulation in both lungs, and clinically by short ness o f breath, decreased chest ex pansion, lessened capacity for work, absence of fever, increased suscp-' tibility to tuberculosis (some or all of which symptoms may be present), and by characteristic X-ray find ings." * 38. Factors of influence. Silicosis has been known to manifest itself after widely differing periods o f ex posure to silica dust. Apparently, development of the disease depends upon: a. The amount and kind of dust inhaled. b. The percentage of fr.ee silica contained in the dust. c. The form o f the silica. d. The size o f the particles inhaled. e. The duration o f the ex posure. f. The powers of resistance of the individual concerned. g. The presence or absence of a complicating process such as infection. 39. Many theories have been ad vanced over the years to explain why the crystalline form of 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. 40. It is believed now that silicotic fibrosis is caused not by the hard ness or sharpness o f the particles, but by a combination o f slight solu bility with a physiochemical effect and an immunological effect--but no one is certain of the exact mech anism o f the disease. Experimental work on the reasons for the develop ment of silicosis is still going on in various parts of the world. If the precise mechanism o f silicosis could be determined, better medical pre ventive measures might be devel oped and possibly a cure could be found. " Report (Joint) of the Committee on Pneumoconiosis and the Committee on Standard Practices in Compensation of Occupational Diseases." Year Book, 1933. American Public Health Association. 1015 18th St. NW, Washington, DC 20036, p. 100. -5 - 41. The clinical signs of silicosis are not-unique. Symptoms may be progressive with continued exposure lo quantities o f dqst containing free silica, with advancing age, and with continued smoking habits. 42. Three stages. Silicosis is gen erally classified in three separate stages by medical authorities. More sophisticated classifications are sometimes used for the various X-ray stages and complications o f the disease, but for a basic under standing the three stages give a good breakdown. 43. The first stage of the disease produces no disability. The affected person can carry on his work as well as ever. Frequently, the individual 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 ex posure to crystalline free silica. 44. In the second stage, respira tion may be affected in some per sons but not in all by any means. Labored breathing on heavy exer tion 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 exposure to silica dust. How ever, the progress of the disease will be slower without continued dust exposure. Breathing may become severely labored. The worker is far below normal physically and is sus ceptible to respiratory diseases. Chest X rays may show an enlarged heart as a result of the body's at tempts to overcome the resistance of restricted blood vessels in the lungs. Pulmonary tuberculosis is a fre quent complication and occasionally results in death. 46. Detection and development. Silicosis may be detected by chest X rays in each o f the three stages. However, X rays alone are not suf ficient for a positive diagnosis, for the shadows may be due to a variety of other conditions, including in fection or another type o f pneu moconiosis. The individual must have had a definite exposure to free silica, because only it can cause sil icosis. The complete occupational and m edical h isto ry o f the em ployee must therefore be evaluated before a conclusion can be reached. The correlation o f 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 o f silicosis in its earliest stage is not perceived by the individual. The disease can not be cured by any means yet known. Tuberculosis is more prev alent in persons with silicosis, but the incidence is decreasing, as it is in the general population. 49. People with early signs of sili cosis are able to perform their duties and are not a menace to otfier em ployees, for it is not a contagious disease. A perceptible X ray change is not grounds for assuming disa bility 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, persons with early signs o f silicosis should be seen periodically by a physician. 50. Action of silica on the lungs. At the points in the lung where silica dust is deposited and accumulated, a fibrous tissue develops and grows around the particles. This fibroustissue is tough like scar tissue. It is not as elastic as normal lung tissue,. does not permit the ready passage of oxygen and carbon dioxide, and asit proliferates, cuts down the amount o f 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 oxygen from the lung to the blood in the capillaries, and the blood in the area will not be completely oxygenated. The fibrous tissue can also affect the blood vessels by obliterating 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. Emphysema 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 de mand o f 'the body is increased by exertion, the individual will feel dis tress with shortness o f breath. 53. Amorphous free silica differs from crystalline free silica in physi cal structure and in physiological effects. In the amorphous state, molecules o f silica exist in random orientation, which may be caused by natural forces to form opal and diatom aceous earth (k ieselgu h r). Amorphous silica may be converted by artificial processes 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 calcin ing, forms of crystalline free silica called cristobalite and tridymite re sult. These intermediate forms of amorphous silica are known as cryptocrystalline (ultra-microcrys talline). Inhalation o f these crystal line forms can readily cause diatomite pneumoconiosis. 55. When diatomaceous earth is calcined, particularly in the pres ence o f a trace of alkaline flux, appreciable quantities are converted to cristobalite. 56. Various commercial products containing particles o f silica under 1 micrometer in size are available. The physiological effects of these products have not been well defined. Until more experience with human beings is available, it is believed these products should be handled with care. 57. Free silica and silicates. Free silica is uncombined silicon dioxide (S i0 2). Silicates contain silicon and oxygen combined with other ele ments in a more complex molecule. Analyses o f minerals, particularly in geological reports, are sometimes reported as percentages of oxides, which may. include S i0 2, A120 3, K20 , Fe2Q 3 . The S i0 2 reported in such chemical analyses is the total o f the silicon dioxide present, both the free silica (if present), and the silica combined in the mineral. Such analyses are not reliable indications o f the silicosis potential o f the ma terial. 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 o f uncombined silica musi be determined by petrographic anal ysis using a polarizing microscope or, preferably, by X-ray diffraction -6 - analyses and special analytical chem icaljprocedures. 59. There has been some experi mental evidence that some dusts may tend to inhibit the action o f 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 o f 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 o f 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 o f silicate dusts than o f free silica dust can be tolerated. 61. In many industries, people have worked with silicate dusts that contained no free silica without de velopment o f disability or o f nodula tion in the lungs. The X ray may show shadows indicating dust deposits in the lungs, but the pneu moconiosis is essentially harmless. However, partially disabling pneu moconioses have been reported where people have worked for long periods of time in very high con centrations of certain silicate dusts. 62. 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 o f dust o f 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, pages 4 and 5). Asbestosis 64. Asbestos is a general term ap plied to several minerals having a Fibrous character. These asbestos minerals are hydrated silicates o f magnesium with variable amounts of iron, calcium, sodium, potas sium, and aluminum present as im purities. 65. Asbestos when inhaled pro duces fibrous tissue in the lungs o f both humans and animals. It has been shown that fibers of asbestos must be present for the production of asbestos. Other silicate minerals o f the same chemical composition but nonfibrous in form produce no reaction, or a relatively mild re action, but not the severe reaction o f fibrous asbestos dust. 66. These facts lead to the con clusion that asbestosis is mainly the result o f physical irritation o f the lung tissue and not of a chemical action, which is thought to be one o f the causes of silicosis. It is suspected that lung cancer may be induced by asbestos. However, there is no im pressive amount o f evidence to sup port this assumption. 67. The fine airborne fibers o f 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 bronchi oles. There is evidence that other minerals having a fibrous character can produce a reaction similar to that of asbestos. Glass fiber, how ever, does not produce such a reac tion. Talcosis 68. As used in industry, " talc" is a very general term. To the geolo gist, talc is a hydrous magnesium silicate, which may be a relatively pure mineral or may be mixed with tremolite or with dolomite depend ing upon where it is mined. The term " talc" is applied commercially to carbonate mixtures that have the same general feel-and physical prop erties; it also is applied to pyrophyllite, a hydrous aluminum silicate, which frequently is mixed with a high percentage o f 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 exposure. 69. Talcosis is usually associated with tremolite talc. This disease pro duces changes in the lungs and symptoms similar to those o f as bestosis. Anthracosilicosis 70. Anthracosilicosis, a complex form o f p n eu m o co n io sis, is a -7 - chronic disease caused by breathing air containing dust that has free silica as one of its components and that is generated in the various proccesses involved in mining and pre paring anthracite (hard coal) and, to a lesser degree, bituminous coal. 71. The disease is characterized anatomically by generalized fibrotic changes throughout both lungs and by the presence of excessive amounts of carbonaceous and siliceous ma terial. Such lungs on autopsy are coal black. 72. 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. 73. Experiments with animals showed that mixtures o f coal and quartz produced more fibrosis than did quartz alone. The harmful ef fects o f coal dust do not come only from the silica in the dust. Coal dust alone in very heavy concentrations over a period o f many years can cause breathlessness and ventilatory impairment. Miscellaneous pneumoconioses 74. Even though a dust is classi fied as " harm less," excessive amounts o f it can lead to trouble by causing a pneumoconiosis or simply by mechanically irritating the walls o f the respiratory system. Moreover, even though there is no chemical or physical irritation, mechanical plug ging o f the lungs and interference with their ordinary process can re sult. Mica dust and kaolin dust are two good examples o f dusts that ordinarily are considered benign but in excessive amounts can cause a troublesome pneumoconiosis. 75. Mica pneum oconiosis has been observed in grinding opera tions where mica dust, but no free silica, was present. There were marked changes in the X-ray pic tures o f the lungs and some disa bility. The cases occurred where the dust exposures were massive over many years. 76. Kaolinosis has been described as a condition induced by inhalation o f dust released in the grinding and handling, of. kaolin..(ch in a .cig y ). Where the cases occurred, dust levels of several hundred million particles per cubic foot o f air were common. ' 77. 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 occurred in the grinding o f alumi num parts and castings. It can therefore be concluded that reason ably good control will prevent harm from aluminum dust. 78. Bauxite pneum oconiosis (Shaver's disease) has been found only in workers exposed to fumes containing aluminum oxide and minute or ultramicroscopic silica particles arising from smelting bauxite in the manufacture o f co rundum, an impure form o f aluinum oxide. It is essentially a dif fuse interstitial fibrosis and marked associated emphysema, with a com plete absence o f any nodular fibrosis. It definitely does not occur from the use o f corundum grinding wheels or from other forms o f alu minum oxide. 79. Some pneumoconioses may show marked shadows on an X-ray film; these shadows, without the necessary information on the expo sure o f the individual, may be alarming in a general X-ray screen ing program. On clinical examina tion o f individuals showing the X-ray markings, however, often no disability or symptom can be found. 80. These shadows are frequently encountered when the dusts contain atoms o f relatively high molecular weight because the heavier atoms are fairly opaque to X rays. Insol uble barium dusts and tin oxide dusts, for example, can show very marked shadows on X-ray films without producing signs of signif icant pathology (barium dust that is soluble in the body fluids can give a toxic reaction). 81. Iron oxide, particularly ex cessive fume from welding opera tions, may produce siderosis with a pigmentation o f the lungs (black in welders and red in iron ore miners) without disability. The X-ray shad Substance TABLE HL SELECTED TOXIC DUSTS AND FUMES Description and Effects ...... Threshold.Limit.. in Milligrams per Cubic Meter of Air* Antimony' Gray metal often ossocioted with lead and 0.5 arsenic. Hazardous from inhalotlon and in gestion. Soluble salts may cause dermatitis. Arsenic Silvery brittle crystalline metal. Hazardous 0.5 from inhalation and ingestion. Usually en countered as arsenic trioxide. Barium (soluble Soluble borium chloride ond sulfide are 0.5 compounds) toxic when taken by mouth. Beryllium Light weight, gray metal. The metal, lowfired oxides, soluble salts, and some alloys are toxic by Inhalation. 0.002 Chromic acid Red, brown, or black crystals. Caustic action 0.05 and Chromates on mucous membranes or skin. Cyanide (os CN) Nonvolatile cyanides are ingestion hazards. Cyanides inhibit tissue oxidation upon in halation and cause death. 5.0 (skin**) Dinitrobenzene Yellowish crystal. Hazardous from skin a b sorption, inhalation, and ingestion. 1.0 (skin**) Fluorides Inorganic fluorides are highly irritant and 2.5 toxic. Hydroquinone Colorless hexagonal crystals. Contact with 2.0 the skin may cause sensitization and irrita tion. Excessive exposure to dust may cause corneal injury. Iron oxide fume M ajor sources are cutting and welding. 5.0 Lead Lead fumes and lead compounds cause 0.15 poisoning after prolonged exposure. Most important means of entry into body is in halation. Skin absorption is of significance only from such organic compounds as lead tetraethyl. Lead orsenate White crystals-- highly toxic. 0.15 Magnesium oxide White powder. Inhalation of freshly gen 10.0 fume erated fume may cause metal fume fever. *These Threshold Limit Voiues were odopted by the American Conference of Governmental Industrial Hygienists in 1979. **The substance can penetrate the skin to contribute to the exposure. ows produced by the iron oxide in the lungs are somewhat similar to the shadows from silicosis. Because o f this similarity, differential diag nosis is often difficult, and heavy exposures to iron oxide dust and fume may lead to medicolegal prob lems. 82. Limestone, marble, lime, gypsum, and Portland cement dusts apparently have no serious effect even after long exposures. Also, many silicates and other minerals have not caused impairment in in dividuals inhaling the dusts, and the resulting pneumoconioses are gen erally classed as benign. However, because some limestones contain significant amounts of quartz, a quartz determination is advisable. Toxic Dusts and Fumes 83. Systemic reactions are caused by toxic dusts and fumes o f various -8 - TABLE III. SELECTED TOXIC DUSTS AND FUMES (Continued) Substance Description and Effects Threshold Limit In Milligrams per Cubic M eter of Air* Manganese Silvery gray metal. Hazardous from inhalotion of fumes or dust. .C-5.0*** toxicity are controlled more read ily because greater amounts can be- tolerated, but their dusts and fumes should be kept at reasonable levels since excessive amounts of any of them can be harmful (Table III). fentachlorophenol Dark-colored flakes. Harmful dust. Emits toxic fumes when heated. 0.5 (skin**) Phosphorus (yellow) Poisonous mainly by inhalation. Severe burn 0.1 hazard from skin contact. Picric acid Yellow crystals or liquid. Explosive-- partic ularly metallic salts. Emits toxic fumes on decomposition. 0.1 (skin**) Selenium compounds Toxicity varies somewhat according to the 0.2 solubility of the specific compound. Often causes contact dermatitis. Sodium hydroxide White, deliquescent pieces or lumps. Has severe action upon all body tissue. 2.0 . Tellurium Similar to selenium chemically and in physi 0.1 ological effects. Titanium dioxide White to black powder. Considered in the nuisance category. 10.0 (total dust < 1% quartz or 5.0 mg/m3 respirable dust) Trinitrotoluene Uranium Vanadium pentoxide Zinc oxide Colorless to yellow monodinic crystals. Emits toxic fumes of oxides of nitrogen when heated to decomposition. Highly poisonous explosive. Highly toxic and a radiation hozard that requires special consideration. Yellow to red crystols. Acts chiefly os an irri tant to the conjunctiva and respiratory tract. Amorphous white or yellow powder. The powder Is essentlolly nontoxic, but freshly generated fume may cause metal fume fever. C-0.5*** 0.2 0.5 (dust) C-0.05 (fu m e )*** 5.0 Zirconium compounds Most compounds are insoluble and hove 5.0 low toxidty. These Threshold Limit Values were adopted by the American Conference of Governmental Industrial Hygienists in 1979. " The word "skin" in this table indicates that the substance can penetrate the skin to contribute to the exposure. ***C --Indicates that this limit should not be exceeded at any time. elements and their compounds and by certain organic compounds. All metallic fumes are irritating, espe cially when freshly generated. In dustrially important metals and their compounds that can have a toxic effect when the dust or fume is inhaled include arsenic, antimony, cadmium, chromium, lead, man ganese, mercury, selenium, tellu rium, thallium, uranium, and a few others.* 84. The effect o f some metals, such as magnesium and zinc, ap pears to be transient. Only limited data are available on the exotic and rare earth metals. 85. 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 Lead poisoning 86. 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 troublesome. Inhalation o f the dust o f lead compounds is the most com mon mode of entry o f lead into the system. Ingestion o f lead com pounds can add to the problem if personal hygiene is poor. Workers should therefore be encouraged to wash thoroughly before eating, and lunchrooms should be segregated from work areas. 87. It should be recognized that lead is a normal constituent o f plants and animals. People ingest and excrete lead daily even though they are not exposed to lead in their daily work. The body can handle and eliminate small amounts with out harm. When intake rates exceed the normal excretion level, buildup occurs in the body. There is a safe level of absorption, and if the con centration o f lead dust in the air o f work areas is kept below the threshold limit, there should be no difficulty. 88. The importance o f maintain ing the concentration o f airborne 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 89. A worker can be exposed to two types of beryllium: a. Elemental beryllium and compounds and alloys o f beryllium that may be released into the work environment as particulate matter. See the National Safety Council Data Sheets listed in the Bibliography. -9 - b. Bulk forms o f berylliuImt increases the resistance o f copper that pose a skin hazard to employ to corrosion, improves its machin- ees. These..Torms"incluae'r16raHB' ability, and raises its-annealing -tem beryllium compounds or solid forms perature. (for example, crystals, chips, or shavings) of soluble or insoluble beryllium that could penetrate the skin. 96. Arsenic and its compounds require intelligent handling. Em ployees must be completely familiar with the potentially hazardous na 90. Beryllium intoxication is a ture of such materials. Employee severe systemic disease that can re training must include thorough in sult from the inhalation o f dust or doctrination in the use of personal fume o f metallic beryllium, beryl protective equipment. lium oxide, and soluble beryllium compounds. 97. Where arsenic fumes may be present, such as in the sintering and 91. There are two forms o f the roasting o f arsenic-bearing ores, disease. One is an acute form of complete enclosure and exhaust ven chemical pneumonitis with cough, tilation o f the operation is needed. pain, difficulty in breathing, cyano If respirators are required for pro sis, and lo ss o f w eight. In the tection against arsenic and its com chronic type, known as berylliosis, pounds, a respirator approved by there may be loss o f appetite and the National Institute for Occupa weight, weakness, cough, extreme tional Safety and Health (NIOSH), difficulty in breathing, cyanosis, for protection against fumes not and cardiac failure. Formerly, mor significantly more toxic than lead, tality was high in chronic beryllium or a similarly approved air-line res intoxication, and many who sur pirator, should be used. vived suffer from pulmonary dis tress. 98. The effects of chronic poi soning by arsenic or arsenic com 92. Individual`susceptibility ap pounds first show themselves oh the parently is an important factor in skin, on the mucous membranes of the development o f the disease. In the eyes, and upper air passages, in many instances, one employee has the gastrointestinal tract, and in the developed the severe symptoms nervous system. Often symptoms while other employees doing the such as weakness, loss o f appetite, same work have shown no signs of and occasional nausea develop slow disability. ly, with the eyes, skin, and respira 93. Beryllium intoxication has tory system being affected later. never been demonstrated in individ 99. Dusts on the skin, especially uals mining or handling ore only. where there are folds, as around the There is no evidence of intoxication mouth, or where the surfaces are from the ingestion o f beryllium ox moist, as in the armpits, set up an ide, beryllium metal, or any o f the eruption or eczematous condition beryllium alloys. Only the inhalation which, if not treated, will lead to ex of beryllium-bearing dusts or fumes tensive ulceration. Inhalation of ex produces systemic disease. Accord cessive amounts o f dust will lead to ingly, control o f such dusts and perforation o f the nasal septum. fumes at or below concentrations specified by ACGIH Threshold Lim it Values'" is to be recognized as a Metal fume fever basic protective measure. 100. Metal fume fever is an acute 94. When the soluble salts of condition o f short duration caused beryllium, especially beryllium fluo by a brief high exposure to the ride, come in contact with cuts or freshly generated fumes o f metals abrasions on the skin, deep ulcers such as zinc or magnesium or their may be formed that heal very slowly. oxides. Symptoms appear from four Complete surgical excision o f the to twelve hours after exposure and ulcer is sometimes required in order consist o f fever and shaking chills. to effect healing. There is complete recovery usually within one day, and ordinarily the Arsenic poisoning employee can return to the same job without recurrence. However, after 95. Elemental arsenic is utilized a period in which there has been no in the production o f various alloys. contact with the fume, for example, after a layoff, resumption of expo sure is likely to bring on an attack. l'OT. To cause metal fume fever, heavy concentrations o f fumes are required. Zinc oxide fume is the most common source, but cases caused by the inhalation o f fumes from magnesium oxide, copper ox ide, and other metallic oxides have also been reported. The condition does not occur from the handling of these oxides in powder form. Ap parently, it results only from the inhalation o f extremely fine parti cles freshly formed as fume (nascent fume). 102. Nickel, mercury, and other metals may also produce a fever fol lowed by the toxic effects o f the element. Welding fumes 103. Welding fumes cannot be classified simply. The composition and quantity of both are dependent on the alloy being welded and the process and electrodes used. Reli able analysis of fumes cannot be made without considering the nature of the welding process and system being examined; reactive metals and alloys such as aluminum and tita nium are arc welded in a protective, inert atmosphere such as argon. Al though these arcs create relatively little fume, they do produce an in tense radiation which can produce ozone. 104. Similar processes are used to arc weld steels, also creating a rela tively low level of fumes. Ferrous alloys also are arc welded in oxi dizing environments which generate considerable fume, and can produce carbon monoxide. Such fumes gen erally are composed o f discrete particles o f amorphous slags con taining iron, manganese, silicon, and other metallic constituents de pending on the alloy system in volved. 105. Chromium and nickel com pounds are found in fumes when stainless steels are arc welded. Some coated and flux-cored electrodes are 'Threshold Limit Values fo r Chemical Substances and Physical Agents in the Work room Environment, " published by American Conference of Governmental Hygienists, 2205 South Road, Cincinnati, Ohio 45238. -10- formulated with fluorides and the fumes associated with them can contain significantlym ore., fluorides than oxides. 106. Because o f these factors, arc welding fumes frequently must be tested for individual constituents that are likely to be present to de termine whether specific TLVs have been exceeded. Conclusions based on total fume concentration are generally adequate if no toxic ele ments are present in welding rod, metal, or metal coating and con ditions are not conducive to the formation o f toxic gases. Most welding does not produce expo sures inside the welding helmet above 5 m g/m 3. Allergic Reactions 107. When in the form o f dust, a large number o f materials may cause various allergic reactions in suscep tible individuals. Examples o f such agents are certain animal products, foods, drugs, and chemicals. The bodily systems usually involved in allergic reactions, which may be quite severe, are the skin, respira tory system, and gastrointestinal system. Occasionally, two or more systems are involved. Some of the allergic reactions are dermatitis, hay fever, asthma, and hives. 108. Usually, the victim is sub jected to a series o f exposures with out any reactions during which sensitization is built up. These ex posures may occur continuously for years. Then, at the end o f the " in cubation period," which varies ac cording to the individual, a reaction is produced. 109. For a true allergic reaction two factors are required: a. A history of prior ex posure to the material involved (som etim es not known by af fected employees). b. A " challenge dose" of the material, which provokes the allergic reaction. 110. Continuous exposures may act as " desensitizing doses," and under these conditions an allergic individual may work without in cident for long periods of time only to find that reexposure after re moval from the sensitizing material (such as after a vacation) causes an allergic response to recur. 111. Medical and engineering recommendations to prevent,allergic reactions are based on prevention of exposure by means o f personal protective equipment, ventilation methods, or removal of sensitized individuals from the exposure. Infections Infection and pneumoconiosis 112. The presence o f 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 re sults from complicating tuberculosis either alone or combined with other infections. Bacteria and fungi 113. The possibility o f lung in fections from the inhalation o f bac teria and fungi exists in several in dustries. Pulmonary anthrax from the inhalation of dust containing an thrax spores has occurred among employees engaged in the handling o f wool and the crushing of bones from infected animals. 114. Fungi (molds) growing on grain have been found in sputum of workers shoveling the grain and are believed to be the cause o f out breaks o f respiratory disorders. Fungi found in sugar cane residues (bagasse) are believed to be part o f the cause o f bagassosis. Fungal spores formed under the bark of some trees have been blamed for respiratory difficulties among em ployees who debark dry logs. 115. Although the incidence of occupationally related bacterial and fungal infections is found to be relatively low, the respiratory ef fects can be troublesome and, in the case of pulmonary anthrax, even fatal. The basic methods o f control are the same as those for the pneu moconiosis-producing dusts, but sterilization and disinfection must be added. Radioactive Duets* 116. A radioactive contaminant may offer achemlcahtoxidt'yhaza'rd in addition to an ionizing radiation exposure, and it may be present as a gas, dust, fume, or mist. 117. Radioactive contaminants taken into the body may be depos ited in various organs where they constitute sources of internal radia tion. The chemical characteristics o f the radioactive contaminant or iso tope determine the organ in which it will be deposited. The excretion rate is also dependent upon the chemical nature of the isotope, be cause the radioactive isotopes o f an element follow the same metabolic process as do the stable isotopes of that element. 118. 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. 119. Because radioisotopes are selectively taken up in individual or gans, they may cause only localized irradiation. The radiosensitivity o f the organ dictates the extent of the hazard o f 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 vari ous organs. 120. If radioactive airborne con tamination is known to be present, control measures are mandatory. If the presence o f contamination is un known but suspected, sampling must be done to determine whether or not airborne concentrations o f the radioisotope are below the Threshold Limit Value. 121. Good personal hygiene and good operating techniques are much more important in the handling of radioactive materials than in the handling o f most other materials used in industry. 122. Engineering controls for radioactive dusts are similar to those for other dusts and depend primarily For a detailed discussion of radio activity and an extensive bibliography, see the chapter entitled " Ionizing Radiation" in the Fundamentals o f Industrial Hygiene man ual, published by the National Safety Coun cil. -11 - upon capture at the point o f generation. The, cljfferenc Hes 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 percent efficiency in capture and retention is required. Permissible Dustiness 123. 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 published by the American Conference of Governmental Industrial Hygienists. 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 necessary on the basis of experience. Permissible exposure limits are set by OSHA regulations. 124. These values are set only as guides for the best practice and are not to be considered absolute values. There is reasonable assurance that occupational disease will not occur if exposures are kept below these levels. On the other hand, occupa tional disease is likely to develop in some people if the recommended levels are exceeded consistently. 125. The currently recommended threshold limits of particulate dusts, fumes, or mists can be found in the most recently published ACGIH list (see Bibliography), or the ACGIH can be consulted directly. Informa tion on threshold limits also can be obtained from the National Safety Council, state occupational health agencies, the American Industrial Hygiene Association, and compen sation insurance carriers. 126. No one knows the exact con centration at which workers will start to develop silicosis, asbestos, or lead poisoning. With some toxic dusts, however, experience has been wide enough to establish the present threshold limits as fairly reliable. For example, if the level of lead in a workroom is kept below 0.15 m g/m 3, experience has shown that cases of lead intoxication will not occur. Mineral dusts 12-7; In..the United- States, the threshold limits for mineral dusts are expressed in millions of particles per cubic foot of air (mppcf) or m g/m 3 . The concentration of a mineral dust is determined by count ing dust particles that are less than 10 microns in size in an aliquot sam ple after sampling a known volume o f air in a known volume o f liquid, or by weighing a collection filter before and after a sample is taken. In England and some other areas, the number o f particles per cubic centimeter is the current basis of measurement. 128. 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. 129. It is difficult to compare dust counts with results obtained on the basis o f weight. However, with either type of m easurement, a threshold limit can be set as an ob jective. Experience has Shown that maintaining dust levels below the recommended threshold limits has resulted in a great decrease in the incidence o f occupational diseases. 130. Threshold limits are based on the percentage of free silica where this substance is the impor tant constituent o f the dust. If sili cosis is to be prevented, these limits must not be exceeded. 131. As more experience accumu lates, original threshold limits some times can be modified. In some cases, it has been necessary to lower the limits, for the objective is to pro tect the more susceptible individ uals. 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 132. In all countries, threshold limits for toxic dusts are expressed in milligrams per cubic meter o f air. With toxic dusts, the average levels must be kept below the suggested threshold limits. In fact, it is advis able to keep the levels o f 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 o f occupational disease will occur from these dusts. Nuisance dusts 133. Even though a dust may be considered generally innocuous and not be recognized as the direct cause o f a serious pathological condition, its level should be kept as low as is practical. Dust levels well below the suggested threshold limits are desirable. 134. A concentration o f 30 mppcf (10 m g/m 3) is suggested as the threshold limit for a number of nuisance dusts. With good engineer ing practice, there is no need for this level to be exceeded. A ny reduction below this level will increase the comfort o f employees and improve plant housekeeping. Toxic mists 135. Spray painting operations should be examined for the possi bility o f hazards from inhalation and skin contact with toxic and irritating mists of solvents and pig ments. The solvent vapor evaporat ing from the sprayed surface is also a health hazard. 136. Electroplating processes in volve risk of skin contact with strong chemicals and, in addition, may present a respiratory hazard if mist or gases from the plating solutions are dispersed into the workroom air. 137. Oil mist is a problem in shops where oil is used as a coolant. Condensation on walls and ceilings increases the fire hazard. Methods of Control 138. Various methods of con trolling dusts, mists, and fumes are available. Basic engineering dictates where possible an operation should be made dustless through control at the source. This method is always the most effective, for it either com pletely prevents the contaminant from entering the workroom atmo sphere or limits to safe levels the amounts that do escape. In addi tion, this method :is generally the least expensive. -12- 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) Respiratory protective equipment, nevertheless, should not be con sidered as a universal substitute for adequate local exhaust removal, elimination o f the contaminant, or containment. 140. Many states and municipal ities have dust control codes or or dinances with which employers must comply. In a few stateSjjfor instance, written approval o f plans must be obtained before a local exhaust system is installed. Each employer should therefore know his state and municipal dust control re quirements. 141. Each type of exposure must be considered separately. For ex ample, a local exhaust system suit able for welding or cutting o f steel might not be satisfactory for weld ing or cutting steel that is coated with red lead. 139. When control at the source is not possible, other methods may have to be considered. Any one or a combination o f the following types o f dust control may be needed to limit the exposure. a. The dusty operation may be enclosed, with or without a local exhaust system. An enclosed opera tion generating large quantities of dust usually needs to be exhausted, or the dust will leak into the sur rounding atmosphere. Examples are sandblast cabinets or sandblast rooms and the dry boxes used to handle radioactive materials. b. The dusty work may be performed in a separate building or may be isolated by partitions to re duce the number o f employees ex posed to the dust. The employees who are still being exposed should be protected by respiratory protec tive equipment. c. A less hazardous mate rial may be substituted. For in stance, steel shot may be used instead o f silica sand in abrasive cleaning. d. Keeping the materials moist may be a practical means of control. Examples are the careful and proper wetting down o f aisles in a foundry and the use o f water in drilling. e. Electrostatic precipita tion is also a means o f removing harmful or nuisance dusts from the atmosphere. f. Local exhaust systems may be installed with virtually full or partial enclosure. Examples are an exhaust hood on a grinding wheel (Figure 3) and an exhaust hood at a bagging or filling operation. g. General room ventilation can be used to dilufe the dust by adding large quantities o f air and thus preventing buildup o f dust concentrations. Examples o f this method are roof fans and roof monitor windows. But it generally is inefficient and expensive to at tempt to control contaminants by dilution. h. The dusty work may be performed at night or on weekends to reduce the number o f employees exposed. Cleaning dust accumula tions from overhead beams, for in stance, is preferably done during a weekend. The employees who are exposed should wear appropriate type of respiratory protective equip ment. i. The number o f working hours at the particular exposure can be reduced. However, other meth ods of control are preferable. j. Use o f respiratory pro tective equipment certified by NIOSH can give excellent protec tion against all types o f dust, but in most cases should be considered as a temporary control measure. In a sandblast room, however, air-sup plied helmets usually are required continuously during operations. Local exhaust systems 142. A local exhaust system for the control of an industrial dust or fume traps the air contaminant near its source so that an operator stand ing at the process is not exposed to harmful concentrations. The system should be designed to enclose the process as completely as possible. This method usually is preferred to general ventilation, but should be used only when the contaminant cannot be controlled by isolation, process revision, or substitution o f less harmful materials. Even though a process has been isolated, it may still require a local exhaust system. 143. A local exhaust system con sists o f four principal parts: a. Hoods or other inlets, in to which the airborne contaminant is drawn. b. Ducts, to carry the con taminated air to a central point. c. Dust and fume collectors, to clean the air before it is dis charged. d. A fan and motor to keep the air moving through the system. 144. Although each o f these parts should be designed and installed to perform its required function with respect to the system as a whole, design o f the exhaust hood demands the greatest care. The degree o f con trol of dust at the point o f genera tion or dispersion is determined by the shape o f the hood or degree of -13- Figure 4. Since this swing-frame grinder is used in a variety of posi tions, the local exhaust system must be adjustable. The flexible duct (A) permits movement of the exhaust hood (B) as needed. (Cour tesy American Foundrymen's So ciety) enclosure, the location o f the hood and its distance from the dust source, and the rate of flow of air into the hood. A poorly designed hood can make an exhaust system ineffective. 145. There is no " standard hood." In every case, the hood must be designed to fit the specific opera tion and to make the exhaust effec tive without interfering with the operation (Figure 4). Among the factors to be considered are the nat ural air currents in the room and other exhausts or windows in the area. 146. The hood should be shaped to conform to the shape o f the area o f dust production so as to secure reasonably uniform air velocity over this area. A hood that does not en close the process should be placed with its opening as close as possible to the point o f generation of the dust or fume (Figure 5) because the velocity o f the air in the zone o f the hood influence is inversely propor tional to the square of the distance from the face o f the hood. 147. The hood opening, or part o f it, should be located so as to re ceive directly dust that is thrown off along a well-designated path (Figure 6). The directional energy o f the material can thus be used for its own capture. Air movement must always be past the employee, then over the dust source, and directly into the face of the hood. 148. The fan should be o f suffi cient capacity to maintain the re quired air capture velocity at the point o f generation o f the dust. In ternal baffles should be installed to guide'the air-flow-where -it -is mostneeded. Flanges should be provided wherever possible to reduce the air flow from areas where no dust is produced; that is, air-flow contours should be controlled. 149. Enough air must be supplied to the room from the outside to re place the air that is removed by the exhaust system. Otherwise, there will be interference with other ex haust systems in the area or with maintaining gas or oil flames or ade quate combustion in nearby fur naces. Great difficulty has occurred o f ventilation. Air always should be supplied in quantities equal to or slightly in excess, o f the amounts ex, hausted. 151. The size of the ducts, the type and size of the dust collectors, and the type and size o f the fan and motor (explosion-proof where nec essary) are among the other factors that must be considered in the design o f an exhaust system. Pre venting ignition of a combustible contaminant is a prime safety con sideration. Discussion o f the sub ject o f exhaust system design is beyond the scope o f this data sheet; consultation with an expe rienced ventilation engineer may be necessary. 152. Also, information can be secured from several excellent pub lications, one o f which is the current edition o f Industrial Ventilation-- A Manual o f Recommended Prac tice, published by the American Conference o f Governmental Indus trial Hygienists. Another is Part IV of Fundamentals o f Industrial H y giene, 2nd ed., published by the National Safety Council. Figure 5. To achieve the proper ex haust air velocity, the hoods for these barrel furnaces can be posi tioned as close to the furnace spouts as practical. Such position ing is made possible by mounting the hoods on a trolley suspended from an overhead track. (Courtesy American Brake Shoe Co.) General ventilation 153. General ventilation should be used to supplement local exhaust systems, not to replace them. It should be noted, however, that where local exhaust systems can be used, they will always do a better job than general ventilation. 154. General ventilation requires the introduction o f enough clean air where an exhaust system caused a slightly negative pressure in a room containing a gas furnace. As a result air came down the furnace flue, and the area became contaminated with carbon monoxide from the furnace. 150. With small exhaust systems, air that is removed usually can be replaced by infiltration flow, but larger exhausts may need a positive air supply (Figure 7). An adequate supply o f makeup air, tempered when necessary, is one o f the most frequently 'overlooked fundamentals Figure 6, The centrifugal force cre ated by this grinding wheel causes the generated dust to travel in a well-defined path. To prevent dis persion of the dust, the exhaust hood is placed directly In the dust stream, close to Its source. (Cour tesy American Foundrymen's So ciety) -14- Figure 7. In this foundry, local exhaust hoods are installed over each station having a shell-moulding machine and glue press. Adequate make-up air is supplied from ventilating duct situated between molding machines and presses. (Courtesy American Foundrymen's Society) from the outside to dilute the con taminated atmosphere to a safe level. This method requires larger volumes o f air than local exhaust systems would to accomplish the same control, and will not be effec tive uniformly over a large room. It should be considered only when local exhaust systems require such assistance. This is usually where the sources o f dust are widely dispersed and each source is small. 155. 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 o f 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 o f supply are important. It is becoming common practice to supply clean, tempered air to the work zone for controlled dilution. Wet methods 156. Wet dust is not dispersed as readily as dry dust--advantage of this fact should be taken whenever possible. Carloads of dry minerals 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 traf fic. Water sprays can be used at some operations. Wet drilling meth ods can be used for rock drilling to wet the dust as it is formed. Personal protective equipment 157. Respirators o f 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. NIOSH has set up performance standards for dust respirators and gives approval to respirators that meet these standards. It is important that a respirator be used only for the particular dust exposure for which it has been approved. Respirators for use in mines are certified by the Mining Safety and Health Admin istration. 158. Although approved respira tors will give excellent protection when properly fitted, they should be used only as supplements to other methods o f control or for short or occasional exposures and not as primary controls. 159. Proper fitting of a mechani cal filter respirator to the face of the individual is most important be cause even a small space between the facepiece and the face will permit dustladen air to bypass the filter. 160. Respirators must be in spected and cleaned daily. Filters should be replaced before they be come so plugged with dust as to seri ously increase resistance to breath ing. Proper filters for replacement should be available. Medical program 161. An effective medical con trol program will help prevent cases o f occupational disease. Such a pro gram can also serve as a check on the engineering controls because symptoms o f exposure in a group o f workers will indicate a failure* that must be corrected. The extent o f the medical program will depend upon the seriousness o f the exposures. 162. An industrial hygiene pro gram should parallel the medical program. Both are essential to pro tect the health of employees. 163. The physical examination for new employees should include a thorough preemployment history with the occupational background given in detail. Chest X rays should be made o f all new employees who will be working in dust exposures that could produce disabling pneu moconiosis. The examining physi cian should decide on placement o f those who have pneumoconiosis, active or significant past tubercu losis, abnormally low timed vital capacity, or serious pulmonary dis eases. 164. Periodic physical examina tions, including chest X rays, should be made o f 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 o f lung condi tions. Suitable preventive measures can then be taken. 165. Routine periodic clinical examinations, stipple cell counts, porphyrin determ inations, and properly evaluated blood and urine lead-level measurements are prac tical methods for checking employ ees exposed to lead. If unsafe ex posures are found, further environ mental control is mandatory. A f fected employees should, o f course, be given proper medical treatment. 166. 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 pro gram is nearly always required. Other control measures 167. Although the most effective method o f control is to prevent con tamination of workroom air and thus prevent inhalation o f harmful dusts, the importance o f personal hygiene should not be overlooked. The periodic medical examinations provide a good opportunity for in -15- struction o f employees in various p e r se n a lh y g ie n e -m e a su r e s.^ ...... ..... 168. 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 con taminate the home or expose other members of the family. These rec ommendations become mandatory where such materials as beryllium and radioisotopes are handled. BIBLIOGRAPHY Anlhracosilicosis Among Hard-Coal Miners, U.S. Public Health Bulletin No. 221, U.S. Public Health Service, Washington, DC 20201.1935. Brandt, A. D., Industrial Health Engineering. John Wiley and Sons, Inc., 605 3rd Ave., New York, NY 10022.1947. Data Sheets, National Safety Coun cil: No. 408, Antimony and Its Com pounds No. 499, Arsenic and Its Inorganic Compounds No. 562, Beryllium No. 312, Cadmium No. 443, Lead No. 241, Lime No. 426, Magnesium No. 306, Manganese No. 203, Mercury No. 578, Selenium and Its Com pounds No. 612, Handling and Storage of Solid Sulfur No. 267, Zinc and Zinc Oxide No. 382, Zirconium Powder Dreesen, W. C., Dalla Valle, J. M., Edwards, T. I., Miller, J. W., and Say ers, R. R., A Study o f Asbestosis in the Asbestos Textile Industry, U.S. Public Health Bulletin No. 241, U.S. Public Health Service, Washington, DC 20201. 1938. Drinker, Philip, and Hatch, T. F., IndustrialDust, 2nd Edition. McGrawHill BookCo.,lnc., 330 W.42hdSL, New York, NY 10036.1954. Elkins, H. B., Chemistry o f Indus trial Toxicology. John Wiley and Sons, Inc., 605 3rd Ave., New York, NY 10022.1969. Fundamentals of Industrial Hygiene, 2nd ed. National Safety Council. 1979. Hunter, Donald, The Diseases of Occupations, 5th Edition, Little Brown and Company, 34 Beacon St., Boston, MA 02108.1975. "Hygienic Guide" Series, American Industrial Hygiene Association, 475 Wolf Ledges Parkway, Akron, OH 44311. Industrial Ventilation--A Manual of Recommended Practice, Latest Edition. American Conference of Governmental Industrial Hygienists, Committee on Industrial Ventilation, P.O. Box 453, Lansing, MI 48902. Johnston, R. T., and Miller, S. E., Occupational Diseases and Industrial Medicine. W. B. Saunders Company, Philadelphia, PA. 1960. Lanza, A. J., Silicosis and Asbes tosis. Oxford University Press, New York, NY. 1938. Patty, F. A., editor, Industrial Hy giene and Toxicology, Volume I, 3rd Edition, 1978, and Volume II, 2nd Edition, 1963. Interscience Publishers, 605 3rd Ave., New York, NY 10022. "Report (Joint) of the Committee on Pneumoconiosis and the Committee on Standard Practices in Compensa tion of Occupational Diseases." Year Book. American Public Health Asso ciation, 1740 Broadway, New York, NY 10019.1933. Review of Literature on Dust, U.S. Department of the Interior, Bureau of Mines, Bulletin 478, U.S. Government Printing O ffice, W ashington, DC 20025.1950. "Threshold Limit Values for Chem ical Substances and Physical Agents in the Workroom Environment," Amer ican Conference of Governmental In dustrial Hygienists, 2205 South Road, Cincinnati, OH 45238. (Annually.) U.S. Department of Health, Educa- tion and Welfare, National Institute for Occupational Safety and Health, 4676 Columbia-Parkway, Cincinnati-,- OH 45226. /' Abrasive Blasting Operations: Engi neering Control and Work Prac tices, NIOSH Pub. No. 76-179. Criteria for a Recommended Stand ard fo r Occupational Exposure to Crystalline Silica, NIOSH Pub. No. 75-12. Guide to Industrial Respiratory Pro tection, NIOSH Pub. No. 76-189. ACKNOWLEDGMENT This revision was prepared by the Council Staff. The original data sheet 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, representa tives of chapters of the American Society of Safety Engineers, medical authorities, and industrial hygienists. The data sheet has been approved for publication by the Publications Com mittee of the Industrial Division, Na tional Safety Council, 444 N. Michigan Ave., Chicago, IL 60611. COPYRIGHT 1080 NATIONAL SAFETY COUNCIL ALL RIGHTS RESERVED The Information and recommendations contained In this publication have been compiled from sources believed to be reliable and to represent the best current opinion on the subject No warranty, guarantee, or representation is made by the National Safety Council as to the absolute correct ness or sufficiency of any representation contained in this and other publications, and the National Safety Council assumes no responsibility in con nection therewith; nor can It be assumed that all acceptable safety measures are contained In this (and other publications), or that other or additional measures may not be required under particular or exceptional conditions or circumstances. An Alphabetical Index of all Ind ustrial Safety D ata Sheets (Stock No. 123.09) is a v a ila b le from the Council on request. Rev. 3M0780 Printed In U.S.A. /is Stock No. 123.04-531