Document 6BVRZMkvZqn2oJnXgJVorGMod

'-.-f -31 a/ DUSTS, FUMES, AND MISTS IN INDUSTRY Published by National Safety Council 425 North Michigan Avenue, Chicago 11 17 introduction -I- Industrial dusts, mists, and fumes, their hazards and their coo* trol, are discussed in this data sheet.* The general principles presented can be. applied to evaluate most in* dustriai 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 (hat 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 ils possible physiological effects oo employees must be ascertained. `This data thcct covert toxic end irri* (lint sir contaminants encountered in industry. It docs not include e discussion of the explosive properties of such air. borne particulate sutler. This dot* sheet Is ene ef a series published by the Notional Safety 'Council, reflecting experience from May sources. Net every accept able safety procedure in this Md b necessarily included. This data Asst should nut be con fused until Amortcon Safety Stand ards. federal taws. in$4ifiic f* putreieentx. Hale lews, rules, rag. uleftam or municipal ordinances. S''** . 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, e. Appropriate methods of control must be provided where indicated. The type and extent of controls will depend upon the physical, chemical, and toak 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 pf 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 53 square meters or about 590 square feet. 5. Certain dusts that reach the lungs can pass directly into the blood stream and be absorbed over a long period of time. Others may stay in the lungs and set up local irritant or dam aging action. 6. Toxic and irritant dusts can also be ingested in amounts that may cause trouble. If toxic dust swal lowed with food or saliva is not sol uble in body fluids, it is eliminated directly through the intestinal tract. Toxic materials that are readily sol uble in body fluids can be absorbed in the digestive system and picked up by the blood. 7. A third way in which toxic and irritant substances may enter the system is skin absorption. Many or ganic compounds, such as TNT, cy anides, and most aromatic amines, amides, and phenols, can produce systemic poisoning by direct contact with the skin. Contact of toxic and irritant dusts with the skin also may result in skin irritation. 8. As compared to inhalation. C MATtOUXI. axrCTV COUUCIL INI J3- 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 particles 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 particles larger than 10 mi crons will settle out relatively fast. The estimated settling rates for silica dusts in still air are given in Table L table i. settling rates FOR SILICA OUSTS Size in Micron* 0.23 0.30 1.00 2.00 3.00 ' Time to Fall 1 Foot (minutes) 390.0 187.0 34.0 U4 2J 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, wiH travel farther away from their point of origin than wfll the larger panicles so that the far ther dust is from hs source, the greater the percentage of small par ticles it contains. \ Inhalation of Ousts, Furnas, and Mists 23. With the exception of such fibrous materials as asbestos, dust panicles must usually be smaller than 3 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, larynx, trachea, and bronchi, from which they are expec torated or swallowed into the diges tive tract. 26. When larger panicles 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 * *........ ............ --m* %.... *" nated. Henc* the SnaJ toxic effect of larger dust particles may be de layed. The larger pirticles of irri tant dusts can cause immediate effects in the upper respiratory system. 27. Ragwe-d pollen, which var ies from 18 to 23 microns in diameter can cause hay fever from iu actioa in the upper respiratory system. This type of dust and other allergenic types, as wfl as bacterial and irritant dusts, can cause difficulty even in the larger air-borne sixes. 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, all bending in one direction, make a fast stroke toward the mouth and a slower return stroke. This actioa (ends to push mucous and deposited dust upward to the mouth so that tite panicles can be ex pectorated or swallowed. Retention ef duet 30. Many studies have been made in an effort to determine the amount of dust that is retained in the lungs, but there is no simple answer to this question. It has been shown (hat tile 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. Sixes ef particles Inhaled 31. Although an occasional dust particle 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 panicles in haled. Many fibers up to 100 microns long have been found in the lungs I. *) by its* Isoat | *+14. for* U*#. Q* rt rcitd tfc+i# pmimt pt fcy pfpmtiy Weal * inifaUati**. {Caw**ir Saciafyj of asbestos workers at autopsy. A typical fibrosis caused by asbestos is produced by fibers ranging from 20 to 30 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 ty pes of dusts, fumes, and mists. The reactions include: a. The cardiopulmonary reaction which consists of the pneumoco nioses. such as silicosis and asbtsiotit. In cenatn cases, specific types of lung pathology result, and the hean 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 arc caused by toxic dusts of such ele ments at 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 finds divid ed and freshly generated fume of zinc or possibly of magnesium or of their oxides. This is a transient condition. d. Allergic and sensitization reactions which may be caused b> inhala tion of. or skin contact wnh. such materials as organic dusts from flour, grains, and some woods and dusts of a few organic and inor ganic chemicals. e. Bacterial and fungus infections which occur from inhalation of dusts containing active organisms, such as wool or fur Just contain- Sll.ICA.Tt5 (Compounds mod* up of silicon, osygtft, and one or mart metolt with or witkout kydregen. Tkete dusts caww nantpecific dux reactions. bur generally da aat interfere with pulmonary function at result ia disability.) PvJtor'! wife KeeGts Mka PmiWnd comoot * sake* 1 carbide ICetbetunduw) Tale Ydrafeyfei A hydrated silica--alumina compound, associated --irK ferric aside. Used es e filler medium and os a catalyst and catalyst carrier end in coimefict and insecticides. A lyp* of day competed of nlid ificsfvt and vttd for nrfocloio, tiramiQ, tflp. and ilMtwofts A largo group of liKcetot of varying competition, but dmilof m pfcytkaJ prop#* Hot. AJI Kvt twtlUm doavago ond con bo tpftt into *ory tfein Attn. Utod In iboficd intwlation. fina powfi containing compound! of 6mo, alumina, dSca, ond iron aid*. Utod conatrvotion moforioi. Bfofek-bfoofco vary Kord oyifok Utod o obrotivo ond n/rodofy moltfiol. 3C mppeft 1 90 mppeft 20 mppeft SO mppeft SO mppeft A feydmm mognodum iSkflta u*od In Mminio, tsmaiia, point, and pfcor* mocowfkoU, ond m c fflor in wop, putty, ond plotter. An upended mica fhydrated megnesrunvaturmnum-ron tSicote). Used in light weight aggregates. imuletien. fertiliser, and saZ cendtlianers, as a inter irt rubber and paints, and as a catalyst carrier. 20 mppeft SO mppeft (Threshold limits given for substance* in "Silicnai' (roup arc for compound! containini leu than I per cent crystalline tilica. For mmpoundi containing more than 1 per cent silica. calculate threahold limit from formula: ' 230 . * SiOj + J Tng anthrar iporei or wood bark or grain dutt containing paraaitic fttagi. C IrritatiM of the DOM and throat, which b caused by acid, alkali, or other irritating dusts or mists. Soma dusts such at soluble chromate may be essentially inert and remain in the lungs indefinitely with no recognizable irritation, and a few Eke limestone dust may be gradually dissolved and eliminated without harm. dusts may causa ulceration of tho nasal passages or even lung cancer, g Damage to internal tissues, which may result from inhaled radioac tive materials such as radium tnd Its daughter products and from other radioisotopes that emit highly waiting radiation. Saicosis 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 u foun dries, glass manufacturing.' granite Pnoumoconiesos cutting, mining, and tunneling in quartz rode. It is found throughout 34. Fncumocomosis comes from the world, and In the past it has had three Creek words that mean 'lung,'* many names, such as miner's asth "dust." and "abnormal condition." ma, grinder's consumption, miner's The present generally accepted phthisis, potter's rot, and stone meaning of the word is merely "dusty mason's disease. The same occupa lung." The kind of dust inhaled tional disease, however, is meant by determines the type of condition or all these names, and it it caused by injury. A number of organic dusts dust from crystalline free silica, us are capable of producting lung dis ually quartz (sec Table II). eases, but not all these diseases 37. Although considerable prog are classified as pneumoconioses be* ress has been made in dust control cause they are not all a "dusty coo* In industry, men stiD develop sili ditioa"of the lung. cosis m plants and on jobs when 33. In very rare cases, enough dust control is not adequate. Engi dust had been inhaled to cause neering control is sull (he basic 'mechanical blockage of Use air ~ means of preventing this disease, and spaces. Flour dust has been known dust control equipment and proce to cause this coodiiion. Some dusts dures must be carefully maintained. 38. Definition. Silicosis has been defined as "a disease due to breath ing air containing silica (SiOs) characterized anatomically by gener alized fibrotic changes and the de velopment of miliary nodutation in both lungs, and cUnicaUy by short ness of breath, decreased chest ex pansion. lessened capacity for work, absence of fever, increased suscep tibility to tuberculosis (some or all of which symptoms may be present). and by characteristic X-ray find ings."" . 39. Factors of influence. Sili cosis has been known to manifest itself after widely differing periods of exposure to silica dust. Appar ently. development of the disease depends upon: a. The amount and kind of dust in haled. b. The percentage of free silica con tained in the dust. c. The form of the silica. d. The size of the panicles inhaled, c. The duration of the exposure. "Report (Joint) of the Committee on Pneumoconiosis and the Committee on Standard Practices in Compensation of Occupational Diseases.* free Bool. 19JJ. American Public Health Association. 1790 Broadway, New York 19. p 100. pin siological 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. Fret silica and silicates. Free silica is uncombined silicon dioxide (SiO-). 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*. AI303, KSQ, Fe-O^. 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 analysts using a polarizing microscope or. pra&zbly. 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 (hat h/ must hr discounted fat practice. In\ fact, there also is evidence that the onsiBceous components of a dust mixture containing free silica may provoke a disabling condition more severe than that caused by the silica acting alone. 50. 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 siHca 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 nodulatioa in the lungs. The X-ray may show shadows indicating dust deposits in he lungs, but (he pneumoconiosis is essentially harmless. However, par tially disabling pneumoconioses have been reported where men have worked for long periods of time in very high canccnirauor.s of certain silicate dusts. 62. Disabling pneumoconioses from exposure to abnormally high concentrations of mica, tremoliie 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 iha( dust levels should be kept within thresh old limit vaiues or below (Table II). /fab*tol 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 Iiron, calcium, sodium, potassium, land aluminum present as impurities. I 65. Asbestos., when inhaled pro puces fibrous tissue in the lungs of xxh men and animals. H has been ihowii that fibers of asbestos must te present for the production of tsbestosis. 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 facta lead to the con clusion that asbestosis is mainly the result of physical irritation of the lung tisssyc and nor of a chemical action, which is thought to be one of the causes of silicosis, h is suspected that lung cancer may be induced by asbestos. However, there is no im pressive amount of evidence to sup port this assumption. 67. The fine air-borne fibers of asbestos can pass through the upper respiratory tract to the lower parts of the lungs to cause irritation and to form "asbestos bodies" where the fibers are encapsulated. This diffuse fibrosis probably begins as a "collar" about the terminal bronchioles. There is evidence that other min erals having a fibrous character can produce a reaction similar to that of asbestos. Fiber glass, however, does not produce such a reaction. 68. Following a study by the U. S. Public Health Service of the asbestos textile industry.* it iJS recommended that the dust concen tration be kept at lest than 5 mp'pei 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 Emits. 'Yolcosla ' 69. As used in industry, "talc" is a very general term. To the geolo gist. talc is a hydrous magnesium sili cate, which may be a relatively pure mineral or. may be mixed with tremolite or with dolomite depending upon where it is mined. The term "talc" is applied commercially io carbonate mixtures that have the same general feel and physical properties; it also is applied to pyrophyllite. a hydrous aluminum silicate, which frequently is mixed with a high percentage of quartz. The free silica generallyfound 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 tremolitc talc. This disease produces changes in the lungs and symptoms similar to those of as bestost*. AnlhrecotilUutit 71. A niMroeositicosis, 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 "Drccscn. W. C, Dills Valle. I. MEdwards. T. 1- Miller. J. W_ and Sajtrs. It. It. A Study of Atbttteut * bttiel Ttttilt tnduury. U. I Public Health Bulletin No. HI. U. S. Public Health Service. Washington 23* D- *- 19)*. * *Artfiroeotil!cout ament HarCAToal Minrn. U. S. Public Health Bulletin No. 221, U. S. Public Health Sen-.ee. Withififtoi 23. D. G 1335.  ' t*u* III. ScLJOEO TOXIC OUSTS AND fUMtS (Csnfinv^t Substance 0*t<rp*ion and Effects Threshold limit n Miitifrsm per Cvbk Meter ef Air* Mofigonete fm fffo<hlorap hunol fhosphorvs (yellow) Picric acid Selenium compound* Savory gray metal. Hatardout from inhalation of fumes or dud. Darfc^olord flakes. Harmful . dim. Emits lank fume* when heated. faitaftowi molfity by inhalation. Severe bum hasord from thin contact. Yellow crystal* or liquid. Explosive-- portkvlarly metallic wiftw Emin task fumes on decomposition. Toiicity vari lome-rhat according fa tfca tolwbSiiy of tfc. ip.cdk (M. so 0J Wlin--) 0.1 0.1 (skin**) 0.1 Sodium hydroesde Tellurium Titanium dietide Trinitrotoluene "4- ' Uranium Vanadium pentetide Zn< aside fume Zirconium compounds White, deliquescent pieces nr lumps. Has severe actinn upon all body tasua. SbnSar ta aeJeniwin chemically and in physiological affects. 2.0 0.1 White to black powder. Considered in the nuhence category. 130 Colorless fa yellow monoclinic crystal, Emin tank fumes of ooidos of nitrogen when headed fa decompdsfrinn. Highly poisonous eaplotiea. IJUkin") . Highly Inic and . iWatiw Inwd tfiat requirat sptcid ca.sidw.tiM. 0.03 ttflwht. tarn* pounds) 003 OiualiMa com pounds) TcRow t. tad crystals. Acts chiefly as M irritant ra the CMj.nctit. and toigiratary trad. OJ IduU) at (fume) Amorphous white nr yoVow powder. The powder is essentially aonteak. but freshly generated luma may causa metal fume lent. 10 Most compounds ore insoluble and hoes low toekity. SO "Time threshold limit value! were adopted by the American Conference of Govern mental Industrial Hygienist in 1942. "The vwg "shin" in this table indicates that the substance can penetrate the skin to contribute to tbc exposure. of the individual, may be alarming in a genera! 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 encouniered 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 sips 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 ridtroiis with a pigmentation of the lungs (black in welders and red in iron ore miners) without disability. The X-ray shad ows prodoced by the iron oxide io liie lungs are some* hat similar io the shadows from silicosis. Because of this similarity, differential diagnosis is often difficult, and heavy exposures to iron oxide dust and fume mav 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 Dusts 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 ean have a toxic effect when (he 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 mapesium 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 low toxicity 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 III). Iced 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 ean be See the (olTo'-jng National S*f> Council Daia Sheets: An>.mofr\ / Compoundi. <01: A fifnit end lit l"Of taiut Compound). 499; Cadmium 3II. Ltod. 44); Mafntiium. 416. Munfunrit. 306. V/rriMV, 203. Titanium. 415. Ztm and Zint OliJt. 267; Zutonium Foudtf. 362. 'J.' .-a frw.ii the of t.c- tofia' and' fungi exists in several in dustries. Pulmonary anthrax from the inhalation of duit containing an thrax spores has occurred among em ployees encaged in the handling of *ooI and the crushing of bones from nfected animals. 105. Fungi (molds) growing on grain have been found in sputum of workmen shoveling the grain and are believed to be the cause of out breaks of respiratory disorders. Fungi found in sugar cane residues (bagasse) are believed to be pan of the cause of bagassoth. Fungal spores formed under the bark of some trees have been blamed for respirator)' difficulties among em ployees who debark dry togs. 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 (hose for the pneumoconio sis producing dusts, but sterilization and disinfection must be added. Radioactive Ousts* 107. A radioactive contaminant nay 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 diwimion of radio* activit) and an extensive bibliography, see the chapter entitled "Ionizing Radia tion" in the Ziiii/rni Prr\rntian Stanaai fur huht uriul Oprrations, published by the National Safety Council. 110. Since rid':uisotc;-zs ire se lectively uken 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 particle size determine how much of the ac tive material will gain access to and remain in the blood stream and var ious organs. > 111. If radioactive air-borne con tamination is known to be present, control measures are mandatory. If the presence of contamination is un known but suspected, sampling must be done to determine whether or not air-bome concentrations of the ra dioisotope are below the threshold limit value. 112. Good personal hygiene and good operating techniques are much more important in the handling of radioactive materials than in the han dling of most other materials used in industry. 113. Engineering controls for radioactive dusts are similar to those for other dusts and depend primarily upon capture at the point of genera tion. The difference lies in the fact that controls for radioactive dusts must be extremely efficient. Thresh old limit values for radioactive par ticulate matter are very low, and in some cases 100 per cent efficiency in capture and retention is required. Permissible Dustiness 114. Threshold limit values of mineral dusts and toxic dusts--that is, time-weighted average concentra tions considered permissible for ex posures of eight hours per day, live 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 i'ceomm-d. J threshold limits of particular qu,(, can be found in the most reeentU published ACG1H list, or the ACGIH can be consulted directlv Information on threshold limits a"lw* 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 ar which men will start to develop silicosis, asbestosi*. or lead poisoning. With some toxic dusts, however, experience has been wide enough to establish the present threshold limits as fairly reliable. IIS. 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 panicles per cubic centimeter is equi\ alent 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 limns has resulted in a great decrease m the incidence of occupational diseases. 122. Threshold limits are based on the percentage of free tihca where this substance is the impor- (CaiKiHf Imriwii S nevanhclesx, should got be con sidered as a universal wbuitatc 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 dinance* with which employers must comply. In a few states, lor instance, written approval of plans must be obtained before a local exhmnt system, is installed. Each employer should therefore know his state and municipal dust control re- uiremeats. 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 weldbig or cutting steel coated with red lead. teeuf exhaust systems ' 131. A local exhaust system for the eootrol of an industrial dust or fume traps the air contaminant near Hs source so that an operator standing at the process ir not ex posed to harmful concentrations. The system should be designed to enclose the process as completely as posable. 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 airborne contaminant is drawn. b. Ducts, to carry C.e cuRtaminated air to a central point. ' c. Oust and fume collectors, to clean the air before it is discharged. d. A fan and motor to beep the air moving through the system. 133. While each of these parts 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'generalion or dispersioa is determined by the shape of the hood or degree of enclosure, the location 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. . 133. 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 hs opening as dose as possible to the point of generation of the dust or fume (Figure 5) because die 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 h, 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 hs own-capture. Air movement must always be past the employee, then over (he 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 flow from areas where no dust is produced; that is. air-flow contours should be controlled. I3S. E^-T-^h sir Must be sup plied to the room from the outside to 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 its 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 R|im S. Tt KUm A# Aa.,1 ai* ^lily, A, SailA, I, W., A W pavAia-ad M dAM At *,., IMAA m ptaadnl. $--<k pat^'a-.-e ., --d. *a,xkla --a.-a-s Aka kaad, -- a Malta, I.IA.-A.A kaa aa a--,k-ad Naab. A--aiaa laaka Skaa C*J fr.c-U r.ot be o.ci'.ooVed. TVe 'periodic medical examinations provide a good opportunity for in struction of employees in various personal hygiene measures. 157. Good washing facilities, clean lunchrooms, and dean work dothes can help prevent additional, even though minor, exposure to toxic materials. Also, contaminated work dothes should not be takes 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. aiauoeaAFMY Accident Ftevention Manual for Industrial Operations. National Safety Council, 425 N. Michigan Avc., Chi cago |i. Amhraeosilicosix Among Hard-Cool 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, lnc,, 440 4th Ave,, New York 21. 1941. 6au Sheets, National Safety Coun cil: No. 408, Antimony and lu Com pounds No. 499, Arsenic and Its ganic Compounds Beryllium (in preparation) No. 312. Cadmium No. 443. Lead No. 426, Magnesium No. 300, Manganese No. 203, Mercury No. 485, Titanium Ncl 267. Zinc and Zinc Oxide No. 382, Zirconium Powder Inor Dreescn. W. C.. Della Valle. J. M, Edwards, T. L. Miller, 3. W,, and Say ers, R. R., A. Study of Asbestotis 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. Mc Graw-Hill Book Co.. Inc.. 330 W. 42nd St.. New York 36. 1954. Elkins. H. B-, Chemistry of Indus trial Toxicology. 2nd Edition. John Wiley and Sons. Inc., 440 4tfa Ave.. New York 21. 1939. 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 VrntUaiion--A Manual of Recommended Practice. 7th Edition. American Conference of Governmen tal Industrial Hygienists, Committee oo Industrial Ventilation, Box 453. Lansing. Michigan. 1962. Johnston. R- T- and Miller. S. E_ Occupational Diseases and Indus trial Mrdicine. W. B. Saunders Com pany, Philadelphia. 1960. Lanza, A. J., Silicosis and Ashestods. Oxford University Press. New York. 1938. Patty, F. A., editor. Industrial Hy giene end Toxicology. Volume I. 2nd Edition. 1938, and Volume II. 2nd edition (in preparation). Inter science Pubtiibers. 230 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." Tear 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-. 1930. ACXNOWUMMINT The ten of this data sheet, which re places Health Practices Pamphlet No. I, was prepared by the Health Committee of the Chemical Section. National Safety Council. The content hat been estensivcly 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 hat been ap proved for publication by the Publications Committee of the Industrial Conference. National Safety Council.