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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 uncombincd silicon dioxide (SiOj). Silicates contain silicon and oxygen combined with other ele ments in a more complex molecule. Analyses of minerals, particularly in geological reports, arc sometimes re ported as percentages of oxides, . which may include SiO-y. A120,t, K20. FcjO*,. The SiOj 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. 5$. It is uncomhined or free silica that is most important in industrial dust exposure. So that an exposure can tv properly evaluated, the per centage of uncomhined 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, (here also is evidence that the nonsiliceous components of a dust mixture containing free silica may provoke a disabling condition more severe than that caused by the silica acting alone. 60. With the exception of asbes tos and some tales, 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 dusi 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 nodulalion in the lungs. The X-ray may show' shadows indicating .dust deposits in the lungs, but the pneumoconiosis is essentially harmless. However, par tially disabling pneumoconioses have been reported where men have worked for long periods of time in very high concentrations'of certain silicate dusts. 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 arc not the same for these sili cate dusts as for free silica, but the symptoms can be marked. 63. The body docs not have ade quate defense ' against indiscrimi nate amounts of dust of any kind. Therefore, although specific symp toms have not been described for many mineral dusts, the general ex perience would indicate that dust levels should be kept within thresh old limit values or below (Table II). Asbestoili 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 us 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 tisssuc 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 (he upper respiratory tract to the lower parts of the* lungs to cause irritation and to form "asbestos bodies'' where the fibers are encapsulated. This diffuse fibrosis probably begins as a "collar" about the terminal bronchioles. There is evidence that other min erals having a fibrous character can produce a 'reaction similar to that of asbestos. 'Fiber glass, however, does not produce such a reaction. 68. Following a study by the U. S. Public Health Service of the asbestos textile industry,* it was recommended that the dust 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. Talc&li 6#. As used in industry, "talc" is a very general term! To the geolo gist, talc is a hydrous magnesium sili cate, which may be a relatively pure mineral or may be mixed with tremo lite or with dolomite depending upon where it is mined. The term "talc" is applied commercially to carbonate mixtures that have the same genera) feel'and physical properties; it also is applied to pyrophyllite. a hydrous aluminum silicate, which frequently is mixed with a high percentage of quartz. The free silica generally found with pyrophyllite can cause silicosis. It is therefore essential to know which talc is being used in order to evaluate a specific dust ex posure. 70. Talcosis is usually associ ated with tremolite talc. This disease produces changes in the lungs and symptoms similar to those of asbestosis. AnfhrocotiNcoM 71. Anthracostlicosis, 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 Dreewn. W. C,, Oalta Valle. J. M.. Edwards. T. 1- Miller, J. W,, and Sayers. R. R.. A Study of Asbestosis in the As bestos Textile Industry, U. S. Public Health Bulletin'No. 241. U. S. Public Health Service. Washington 25. D. C. 1958. nihraeositkosis among Hard-Coal Miners. U. S. Public Health Bulletin No. 221. U. S. Public Health Service, Wash* ingion 25. D. C..'I935. 94 Notional Safety Nun, Jvne 1)83 of carbonaceous and siliceous ma terial. Such lungs on autopsy are coal black. . . 73. Symptoms found in early stages.of the disease are shortness of breath, cough with a coal-black sputum, pain in the chest, and in some eases physical weakness. In the advanced stages, there are toss of weight and decreased capacity for work, partly caused by pulmonary infection (firequcndybronchiiU),and in some eases there .may be heart failure. -T< Experiments with animals showed (hat mixtures of coal and quartz produced more fibrosis than did quartz alone. The harmful effects of coal-dust do not come only from the silica in the dust. Coal dust alone in very heavy concentrations over a period of many years can cause breathlessness and ventila tory impairment. Miscellaneous pneumoconioses 75. Even though a dust is classi fied as harmless, excessive amounts of it.can lead to trouble by causing a pneumoconiosis' or simply by me chanically irritating the walls of therespiratory system. Moreover, even though there is no chemical or physi cal, irritation; mechanical plugging of the lungs and interference with their ordinary processes can result .Mica dust and kaolin dust are two good examples of dusts that ordinarily are considered benign but in excessive amounts can cause a troublesome pneumoconiosis; 76. Mica pneumoconiosis has been observed in grinding operations where mica dust, but no free silica was present. There were, marked changes in the X-ray pictures of the lungs and some disability. The cases occurred where the dust exposures were massive over many years. , 77. Kuolinosis has been described as a condition induced by inhalation df dust.released in the grinding and handling of. kaolin (china clay). Where the cases occurred, dust levels of several hundred million panicles per cubic foot of air were common. 78. Aluminum dust is not consid ered to be harmful except where exposures are massivc. Wiihout ad verse effects,' aluminum dust inhala tion has been used as pan of an endeavor to prevent silicosis. Also without adverse effects, extensive exposures to aluminum dust have oc curred in the grinding of aluminum pans and castings. It can therefore be'concluded that reasonably good control will prevent harm from alu minum dust. 79. Bauxite pneumoconiosis (Sha ver's disease) has been found only in workers exposed to fumes contain ing aluminum oxide and minute or ultramicroscopic silica panicles aris ing from smelting bauxite in the manufacture of corundum, an im pure form of aluminum oxide. It is essentially a' diffuse interstitial fi brosis and marked associated em physema. with a complete absence of any nodular fibrosis. It definitely does not occur from the use of cor undum grinding wheels or from other forms of aluminum oxide. 80. Some pneumoconioses may show marked shadows on nn X-ray film; these shadows, without the nec essary information on the exposure of the individual, may be alarming iri 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 , (hat is. soluble in the body fluids can give a toxic reaction). 82. Iron oxide, particularly ex cessive fume from welding opera tions, may produce siderosis with a pigmentation of the lungs-(black in welders and red in iron ore miners) without disability.-The X-ray shad ows produced by the' iron .oxide in the lungs arc somewhat similar to the shadows from silicosis. Because of this similarity, differentia} diagnosis is often difficult, and heavy exposures to iron oxide dust and 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 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 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 mctais 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 arc controlled more readily because greater amounts can be tol erated, but their dusts and fumes should be kept at reasonable levels sinqe excessive amounts of any of them can be harmful (Table III). leod 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 troublesome. Inhalation of the dust . of lead compounds is the most com mon mode of entry of lead into the system. Ingestion of lead compounds can add to the problem if personal hygiene- is poor. Workers should therefore be encouraged to wash thoroughly before eating, and lunch rooms should be segregated from work areas. 88. It should be recognized that lead is a normal constituent of plants and animals. People ingest and ex crete lead daily even though they ' are not exposed to lead in their daily work. The body can handle See the following National Safety Council Data Sheets; Antimony and Its Compounds, 408; Arsenic and Its Inor ganic Compounds. 499; Cadmium. 312; Lead. 443: Magnesium. 426; Manganese. 306; Mercury. 203; 7'i/<mii//n.'48S; Zinc and Zinc Oxide, 267; Zirconium Powder, 382. National Safety Nows, Juno 1963 97