Document Rr9yDmBV53NwOBNpjdnOxMjV

i L.'. ..f .31 PLAINTIFF'S EXHIBIT NSC-26 DUSTS, FUMES, AND MISTS IN INDUSTRY Published by National Safety Council 425 North Michigan Avenue, Chicago 11 7 Introduction -I- 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 of the specific dust, fume, or mist and its possible physiological effects on employees must be ascertained. 'This data sheet covers toxic and irrilaiini air contaminants encountered in indutiry. It docs 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. Net every accept able safety procedure in this field is necessarily included. This data sheet should not be canfused with American Safety Stand ards, federal lews, insurance re quirements. slate taws, 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. 3. 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. C3n 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, C NATIONAL SAFETY COUNCIL IMS 12. Dust particles are, of course, attracted by gravity. Their settling rate through still air will vary with their size, density, and shape. Mi croscopically small panicles settle out more slowly than larger panicles be cause of their relatively minor densi ty and because of their being in fluenced by Brownian movement. Mineral panicles larger than 10 mi crons will settle out relatively fast. The estimated settling rales for silica dusts in still air are given in Table I. TA8LE I. SETTLING RATES FOR SILICA OUSTS Size in Microns 0.25 0.50 1.00 2.00 5.00 Tim* to Fall 1 Foot (minutes) 590.0 187.0 54.0 14.5 2.5 24. Most of the panicles 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 panicles, moreover, will travel farther away from their point of origin than will the larger panicles so that the far ther dust is from its source, the greater the percentage of small par ticles it contains. Inhalation of Ousts, Furnas, 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 panicles up to 10 microns in size may enter the lungs occasionally, nearly all the larger panicles are trapped in the nasal passages, throat, lary nx, 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 nated. Hence the final toxic effects of larger dust particles may be de layed. The larger particles of irri tant dusts can cause immediate effects in the upper respiratory system. 27. Rag-weed 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 panicles 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, ail 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 panicles can be ex pectorated or swallowed. Retention of dust 30. Many studies have been made in an efTon 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 panicles, 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 particle* inhaled 31. Although an occasional dust panicle of larger size will enter the lungs, panicles 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 panicles under 3 microns greatly outnumber larger ones, and many panicles 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 luags FTgw't 2. M#pl opJpfiKgvd br * Wat irtg (ptpr fp form fgm* On mu fumat arc Pt fkpir ppinf p/igirt by property latd fpyftdrjmp* % Soc>ry) of asbestos workers at autopsy. A typical fibrosis caused by asbestos is produced by fibers ranging from 20 to 50 microns in length, but only a few microns wide. Physiological effects 33. The physiological reactions caused by the inhalation of air borne paniculate 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 asbeslosit. In certain eases, 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 toxie 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 line or possibly of magnesium or of their oxides. This is a transient condition. d. Allergic and sensitization reactions which may be caused b\ 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 acti'e organisms, such as wool or fur Just contain- SILICATES (Compounds mad** up of sit-eon, oxygen, and on* or mar* metals with or without hydrogen. These dusts cout nonspecific dust reactions, but generally do not interfere with pulmonary function or result in disability.! Fuller's earth Kaolin Mien Portland cement Silicon carbide (Carborsindum) Talc Varmicufita A hydrated silica--alumina compound, associated with ferric ox-de. Used as a filter medium and as a catalyst ond catalyst carrier and in cosmetics and insecticides. A type of day composed of mixed silicates and used for refractories, ceramics, tile, ond stoneware. A large group of silicates of varying composition, but similar in physicol proper* ties. All have excellent deavege and can be split into very thin sheers. Used in electrical insulation. Fine powder containing compounds of lime, alumina, silica, ond iron oxide. Used as construction material. Bluish-black, very hard crystols. Used as abrasive and refractory material. 50 mppeft 50 mppeft 20 mppeft 50 mppeft 50 mppeft A hydrous magnesium silicate used in ceramics, cosmetics, paint, and pharmoceulicals. and as a filler in soap, putty, and plaster. An expanded mica (hydrated mognetrummluminum-inon silicate). Used in lightweight aggregates, insulation, fertiliser, and sail conditioners, as a filler in rubber and paints, and as a catalyst carrier. 20 mppeft 50 mppeft IThreshold limits given for substances its "Silicates' group are for compounds containing fru than I per cent crystalline silica. For compounds containing more than I per cent silica, calculate threshold limit from formula: 250 * SiO- + 5 Int anthrar spores or wood bark or (rain dust containing parasitic Aingi. L 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 Ihe 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 a* foun dries, giass 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 II). 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 baisic meaTi? of preventing this disease, and dust conuoi equipment and proce dures must be carefully maintained. 38. Definition. Silicosis has been defined as "a disease due to breath ing air containing silica (SiO-..) 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 ail 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. Report (Joint) of ihe Committee on Pneumoconiosis and ihe Commune on Standard Practices in Compensation of Occupational Diseases." Ytar Soot 19)3. American Public Health Association. 1790 Broadway, New York 19 p 100. physiological effects of these prod ucts 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 (StO_.). 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 SiO.j. A1202, K.O, Fe.jO,. The SiO- 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 nonsiCceous 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 he 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. 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 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 11). 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 pans 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.* u recommended that the dust concen tration 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 w ith 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 pyrophyllice. 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. AnthrocosHicosit 71. Anthracosilicosis, 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 `Oreeven. W. C_ Dalta Valle. 1. M.. Edwards. T. I- Miller. J. W.. and Sa>ers. 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. 193*. Anthracosilicosis among Hj'dATjai Miners. U. S. Public Health Bulletin No 221. U. S. Public Health Service. Wash ington 23. D. C- 1935. Substance Ta&LE III. SELECTED TCXlC DUSTS AND FUmES (Csnnnved) Description and Effects Threshold Limit in Milligrams per Cubic Meter of Air* Mongonese Silvery grey metoJ. Hazardous from inhalation of fume* or duel. 5.0 Pentochforpphenol Phosphorus (yellow) Pkric ocid Slflium compounds Sodium hydroside Tellurium 0ark<otord Hokes. Hormful dust. Emits toxic fumes when heated. Poisonous moiniy by inhaiotion. Severe burn hozord from skin contact. Yellow crystals or liquid. Explosive-- particularly metallic softs. Emits toxic fumes on decomposition. Toxicity varies somewhat according to ike solubility of tbe specific com* pound. Often couses contact dermatitis. White, deliquescent pieces or lumps. Has severe action upon oil body tissue. Similar to selenium chemically and m physiological effects. 0J (skin**) 0.1 0.1 (skin**) 0.1 2.0 0.1 Titanium dioside White to block powder. Considered in the nuisonce cotegory. 15.0 Trinitrotoluene Colorless to yellow monoclinic crystals. Emits toxic fumes of oxides ef nitrogen when heeted to decomposition. Highly poisonous explosive. 1_J (skin**) Uranium Vanadium pentoxide Highly toxic and 0 radiation hazard that requires special consideration. 0.05 (soluble com pounds) 0.25 (insoluble com pounds) Yeltow to red crystals. Acts chiefly as on irritant to the conjunctive and re* spirotory tract. 0.5 (dust) 0.1 (fume) Zinc oside fume Amorphous white or yellow powder. The powder is essentially nontoxic, but freshly generated fume may cause metal fume fever. 5.0 Zirconium compounds Most compounds are insoluble and have law toxicity. 5.0 `These threshold limit values were adopted by the American Conference of Cavernmental Industrial Hygienists in 1962. "The word "skin* in this table indicates that the substance can penetrate the skin to contribute to tbe exposure. 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 symptom can be found. 81. These shadows are frequently encountered when 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 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). 82. Iron oxide, particularly ex cessive fume from welding opera tions, may produce riderosis 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 trie lungs are somewhat similar to the shadows from silicosis. Because of this, similarity, differential diagnosis is often difficult, and heavy exposures to iron oxide dust 3nd fume may lead to medicolegal problems. It is there fore important to control iron oxide exposures even though siderosis is not disabling. 83. Limestone, marble, lime, gyp sum, and portland cement dusts ap parently have no serious effect even after long exposures. Also, many sili cates and other minerals have not caused impairment in individuals in haling the dusts, and the resulting pneumoconioses are generally classed as benign. Toxic Ousts and Fumes 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 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 ium. uranium, and a few others.* 85. The effect of some metals, such as magnesium and zinc, appears to be transient. Only limited data 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 lowtoxicity are controlled more readily because greater amounts can be tol erated. but their dusts and fumes should be kept at reasonable levels since excessive amounts of any of them can be harmful (Table 111). Lead poisoning 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 See the following Nuonal S-a fet > Council Data Sheet*: Ar.t.mony and In Compounds, <0S; Arsenic and In Inor ganic Compounds, <99; C-sdmmm 3 I 2. Lead, 4^3, Afagnesiu/n, <16. Munfunrj<. 306. \4f*curx, 203. Titanium. Zmt and Zinc Oxide, 267, Zirconium Fodder 312. _.-s fr-.n the . .hale;,or: of t.Ctcna 2fid funci exists in several in dustries. Pulmonary anthrax from the inhalation of dust containing an thrax spores has occurred among em ployes encaged in the handling of wool and the crushing of bones from nfected animals. 105. Fungi (molds) growing on grain have been found in spurura 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 bagassoui. 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 Ousts* 107. A radioactive contaminant ,iay 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 radioacti\it> and an extensive bibliography, see (he chapter entitled "Ionising Radia tion* in (he An idem Pre\emion Sfunitul for hulusiriul Operations, published by the National Safely Council. NO. bine; radioisotopes arc se lectively taken up in individual or 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 panicle size determine how much of the ac tive material will gain access to and remain in the blood stream and var ious organs. 1 111. 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 w hether or not air-borne concentrations of the ra dioisotope are below the threshold limit value. 112. Good persona] 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. TTiresh- 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 du'N can be found in the most recentiv published ACGIH list, or the ACGIH can be consulted directly. Information on threshold limns iNo 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 panicles 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 panicles 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 >n the incidence of occupational diseases. 122. Threshold limits are based on the percentage of free s.hca where this substance is the mpor- Rff 4. Sm4 HJi gn'ndtf r% <nd Sal mi pBoitiaat, tfca !( a*hwf iy* tmm m*it b 4|vavbl. TXa ffaaiVa 4w0 (A) permit* movement mi ftie a*Rwt hoed (1) ea woodid. (CMdiiy AiMriaan Foundrymoo'i defy) nevertheless, should not be con sidered as a universal substitute for adequate local exhaust re moval, elimination of the Con taminant, or containment. 129. Many states and municipal ities have dust control codes or or dinances with which employers must comply. In a few states, for instance, written approval of plans must be obtained, before a local exhaust system- is installed. Each employer should therefore know his state and municipal dust control re- uiremenu. 130. Each type of exposure must be considered separately. For ex ample. a local exhaust system suit able for welding or cutting of steel might not be satisfactory for weld ing or cutting steel coated with red lead. local exhaust systems 131. A local exhaust system for the control of an industrial dust or fume traps the air contaminant near its source so that an operator standing at the process is not ex posed 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 of less harmful mate rials. Even though a process has been isolated, it may still require 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 draws. b. Duels, to carry the contaminated air to a central point, e. Dust and fume collectors, to clean the air before it is discharged, d. A fan and motor to keep the air moving through the system. 133. While each of these pans should be designed and installed to perform its required function with respect to the system as a whole, design of the exhaust hood demands the greatest care. The degree of control of dust at the point of'gen eration or dispersion is determined by the shape of the hood or degree of enclosure, the locatioa of 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. 134. 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. 135. The hood should be shaped to conform to the shape of the area of dust production so as to secure reasonably uniform air velocity over this area. A hood which does not en close the process should be placed with its opening as close as possible to the point of generation of the dust or fume (Figure 5) because the velocity of the air in the zone of the hood influence is inversely proportional to the square of the distance from the face of the hood. 136. The hood opening, or pan of 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 of the material can thus be used for its own-capture. Air movement must always be past the employee, then over the dust source, and di rectly into the face of the hood. 137. The fan should be of suffi cient capacity to maintain the re quired air capture velocity at the point of generation of the dust. In ternal baffles should be installed to guide the air flow where it is most needed. Flanges should be provided wherever possible to reduce the air Sow from areas where oo dust is produced; that is, air-flow contours should be controlled. 13S. E:>c-.;gh air must be sup plied to the room from (he outside io replace the air that is removed by the exhaust system. Otherwise, there will be interference with other exhaust systems in the area or with gas or oil flames in nearby furnaces. Great difficulty has occurred where an exhaust system caused a slightly negative pressure in a room con taining a gas furnace. As a result air came down the furnace flue, and the area became contaminated with carbon monoxide from the fur nace. 139. 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 of make-up air, tempered when necessary, is one of the most frequently overlooked fundamentals of ventilation. Air always should be supplied in quantities equal to or slightly in excess of the amounts exhausted. 140. The size of the ducts, the type and size of the dust collectors, and the type and size of the fan and motor (explosion-proof where necessary) are among the other fac tors which must be considered in the design of an exhaust system. Pre venting ignition of a combustible P**## $. bcR:#*# fb# hood ft * OBA b at Him 'a *> *n'*at ipaw* by oiBMftfiAf tba bedt a* a *ally fppai an a*rk*o4 track. (Cwr**y a <<<* Itaka Sfr*a S. tho-id r.ot be u.urioo'sed. The -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 borne 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. FTfvr* 7. In Ifcit fnwndfy. local vchavtt hood* arn inttaltad avar roch Italian having a thvll.moldlng madtinn and glwa prau. Adaewaf* ntakn-wp a if i ivppiivd tram -fiftlating d-CT wfvaivd bf*n maiding machines and prasnat. (Cavrtotr American Powndiymen'i Society) IKUOGIAPHY Accident Prevention Manual for Industrial Operations. National Safety Council. 425 N. Michigan Ave., Chi cago 11. Anthracosilicosis Among Hard-Coal Miners, U. S. Public Health Bulletin No. 221, U. S. Public Health Service, Washington 25. D. C. 1935. Brandt, A. D., Industrial Health Engineering. John Wiley and Sons, Inc., 440 4th Ave., New York 21. 1948. Data Sheets, National Safety Coun cil: No. 408, Antimony and Its Compounds No. 499, Arsenic and Its 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 Inor Dreesen, W. C.. Dalla Valle, J. M.. Edwards, T. 1.. Miller, J. W., and Say ers, R. R., A. Study of Asbestosis in the Asbestos Textile Industry. U. S. Public Health Bulletin No. 241, U. S. Public Health Service, Washington 25. D. C. 1938. Drinker, Philip, and Hatch, T. F.. Industrial Dust. 2nd Edition. MeGraw-Hill Book Co.. Inc.. 330 W. 42nd St., New York 36. 1954. Elkios. H. B., Chemistry of Indus trial Toxicology. 2nd Edition. John Wiley and Sons. Inc., 440 4th Ave., New York 21. 1959. Hunter. Donald. The Diseases of Occupations. 2nd Edition. Little Brown and Company. 34 Beacon St., Boston. 1957. Hygienic Guide Series. American Industrial Hygiene Association, 14125 Prevost, Detroit 27. 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. Lanza, A. J., Silicosis and Asbes tosis. Oxford University Press, New York. 1938. Patty, F. A., editor. Industrial Hy giene and Toxicology, Volume 1, 2nd Edition, 1958, and Volume II. 2nd edition (in preparation). Interscience Publishers, 250 Fifth Ave., New York 3. "Report (Joint) of the Committee on Pneumoconiosis and the Commit tee on Standard Practices in Com pensation of Occupational Diseases.'* Year Book. American Public Health Association. 1790 Broadway, New York 19. 1933. Review of Literature on Dust, U. S. Department of the Interior. Bureau of Mines. Bulletin 478. U. S. Government Printing Office Office, Washington 25, D. C., 1950. ACKMOWUDGMCNT 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 exiensively reviewed by members of the National Safety Council, representatives of chapters 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 Committee of the Industrial Conference, National Safety Council.