Document 6DLmmr25dn0oaGXmJmmbBb39

P-NSC-32 Health Practices Pamphlet No. 4 Industrial Dust Published by National Safety Council, Inc 20 North Wacker Drive, Chicago 6 Industrial Dust 1. The literature on hazardous ef fects of dust- is so extensive that no at tempt has been made here to cover the subject in all of its ramifications, but to assemble only the outstanding data on several of its aspects. This pam phlet is intended for employers, plant safety engineers, personnel managers, and supervisors generally. The subject has been approached from the prevention angle, giving general information on oc cupational diseases caused by dust and on methods of control. No reference is made to the economic and legal aspects of dust -diseases in industry and none (.of the uncommon dusts as, for instance, might be found in the pharmaceutical industry, are discussed. There is a short section on dust explosibility. Physiological Effects of Dust 2. The inhalation of dust may pro duce different types of reactions in hu man beings: a. Pneumoconioses (silicosis and asbestosis) which result in specific long pathology. 2a. Silicosis increases susceptibility to tuberculosis. b. The systemic reaction caused by such toxic dusts as lead, radium, man ganese. cadmium and mercury com pounds, when either breathed or swallowed or possibly absorbed through the skin. - ^ c. A transient disorder known as meta! fume fever, from the inhalation of finely divided metallic dust or fume -particles such as line oxide. d. A reaction, allergic in nature, caused by breathing organic dusts such as pollen, flour, certain pulverized woods. e. An increase in bronchitis and other acute resp'ti'oO' infections by breath ing inert, non-fibrosis-prodttcing dust such as coal, emery, limestone, marble. 3. In each of the above cases, the inhalation of dust can be the sole cause This pamphlet is one of more than ISO Safe Practices and Health Practices Pamphlets. It is a compilation of experi ence in accident prevention from many sources, it should not be assumed, how ever, that it includes evert- acceptable procedure in the field covered. It must not be confused with American Standard safety codes; federal laws; insurance re quirements; state laws, rules and regula tions; and municipal ordinances. Addi tion*} topitt of tbit pamphlet ere treat*b!t. Member price, 3J centt eecb. Quom thy mf non-member prices on request. of disability. With the toxic dusts, trouble may result from swallowing or more rarely from skin absorption, as well as from inhalation. Inhalation, how ever, is by far the most important means of absorption of industrial dusts.' 4. Irritation and ulceration of skin and mucous membranes may be caused by such dusts as lime and chromium compounds. Pneumoconiosis 5. Zenker applied the name "pneumonoconk>sisn to the various changes in the lungs caused by the inhalation of dust. The term has now been shortened to "pneumoconiosis." It represents three words from the Greek, which mean Figure 1. Dun counting by standard light field methods. "lung," "dust" and "abnormal condi tion." The present generally accepted meaning of the word involves the con cept merely of "dusted lung." The kind of dust inhaled determines the type of injury noted in the lungs. However, there is one pathological process which underlies lung disease caused by dust This consists of a fibrosis or a replace ment of the elastic tissue of the lungs by an impervious scar tissue. 6. Research on pneumoconioses has been carried on in the North American continent more actively in the past decade han in any other period. The hysteria with regard to silicosis and other occupational diseases has now largely subsided, and the subject is be ing more carefully considered and more soberly judged. The Problem 7. Modem manufacturing methods are, in many instances, creating consid erable dust Much of this dust is often released in the area where men o women are working, and this fact compels a practical solution of the problem. 8. The first step in the prevention of injury to health by dust is the control of its concentration so that workers will not be exposed to injurious amounts. In order to obtain wide spread control of dust throughout industry, it is necessary that information be developed and dis seminated on the effect of various kinds and amounts of dust to which workers are exposed Origin and Properties Physical T 9. Dust is formed by reducing solid materials to small sizes. Processes like (Copyright, 1939, i9&. National Safety Council, tnc. All rights reserved. Printed in U. S. A.) 2--H.P.P.-4 HEALTH PRACTICES PAMPHLET NO. 4 thousandth of an inch) in their longest dimensions in order to enter the inner recesses of the lungs where the damage is caused. It was formerly believed that the hardness and sharpness of quartz particles were deciding factors in the injurious properties of dust, but this view has been generally disproved. (See paragraphs 20 and 29). Hay fever and other allergic types of disease from or ganic dusts or larger partide sizes can be caused by breathing particles into the Figure 2. left: Operator in monument shed using pneumatic banker. Neither dust control nor respirator has been pro vided. Right: The same operation with goggles and dust-control hood in use. nose and not having them reach the lungs at alL Ragweed pollen is from 18 to 25 microns in diameter. 13. By comparison a healthy red blood cell is about 7.8 inches, and a grinding, crashing, blasting and drilling produce dust particles of sizes from the microscopic to the visible, their composi tion being the same as that of the parent materials if not altered chemically dur ing the subdivision. Frequently the percentage of some hard mineral such as quartz in the fine dust may be less than that in the parent material Common examples are the mineral or inorganic white cell up to about 16 microns. A person with normal eyes can see an ob ject 50 microns in diameter. However, the reflection of light from a shiny partide of quartz may be seen when the partide is as small as 20 microns in di ameter. It is to be realized, therefore, that individual dust particles small enough to reach lung tissue are essen tially invisible to the naked eye- dusts derived from the disintegration of rock and the organic dusts like wheat and flour. 14. Fumes may result from any of several chemical or physico-chemical changes such as zinc oxide, formed when 10. Smoke from burning carbonace ous fuels--coal, oil, wood, etc.--con tains droplets as well as dry particles. Tobacco, for instance, produces a wet burning zinc vapors arise from molten brass, or lead occurring in the exhaust of a motor car burning gasoline contain ing tetra-ethyl lead. smoke composed of minute tarry drop lets. The particle size of tobacco smoke is about 0.2S microns. Chemical 15. The chemical and mineralogicat make-up of the dust are the deciding 11. When a solid is broken into fine factors in determining its injurious ly divided particles and released in the properties. It has been shown that sili air, one of the important changes that con dioxide (free silica) in the form of take place is that the space occupied quartz may produce a disabling fibrosis, by the broken material and also the sur whereas little or no fibrosis is produced face areas are increased many times by the equally hard and sharp cornered from that of the original mass. For ex aluminum oxide (emery). ample, if one cc. (.061 cu. in.) of quartz -is crushed into particles one cubic Classification of Dusts micron in size, these will Lc 10la,vt7$CC7~': 000,000,000 or one trillion) particles l The following dassification of with total surface areas of six square meters (93CO sq. in.) as compared with six square centimeters (.930 sq. ,in.) for the original block. If we assume a dust concentration of 100 million particles to each cubic foot of air, the one cc. of materia! will occupy an air space of 10,000 cubic feet. dusts, according to their physical char acteristics and physiological effects has been arranged by Dr. R. R. Sayers: ^ ORGANIC DUSTS " ' ' A. Non-Living Organic Dusts As the name implies, these are com prised of non-viable particles which may or may not be either toxic or irritant. .. but nevertheless have effect on the human organism. 1. Toxic or Irritant Dtutt. These are organic dusts which produce un toward,symptoms either systemic or lo cal. Those producing local symptoms are described as irritants, while those producing general symptoms are termed toxic. A dust may be both toxic and irri tant. 2. Allergic. (See paragraph 59.) B. Living Organic Dusts ' These dusts contain particles capable of reproduction or multiplication, such as bacteria and fungi. They are usually found in low concentrations and asso ciated with non-living dusts in the air. 1. Bacteria. One of the most im portant is the anthrax bacillus, which is found in the dusts from skins, furs, wool, and animal hair, boms, hoofs, bones, etc. Diphtheria, tuberculosis, typhoid and other bacillus-produced diseases may result from exposure to infected dusts. Bac- J lerial-sensitized dust can also be the J cause of allergic diseases, as asthma, hay fever, eczema, migraine headaches, etc. Z Fungi. Dusts containing parasitic fungi may cause annoyance and discom fort. Mould on straw, hay, grass, vege table debris is typical of this type of dust. C Inorganic Dusts These are of mineral origin not re quiring a living organism to produce them. Many dusts not classed as toxic come under this classification. Classified under inorganic are toxic and/or irritant, fibrosis-producing and non-fibrosis-pro ducing dusts. 1. Toxic end/or Irritant. These are inherently toxic when inhaled, ingested or otherwise absorbed. Among them are the dusts from heavy metals and their compounds, such as lead, mercury,--* arsenic, cadmium, zinc. 12. .With the exception of such fi brous materia] as asbestos; the dust partides must be smaller than 10 microns (one micron equals one twenty-fifth Figure 3. Granite lurfarrr in operation, without and with dust cootrol provided. INDUSTRIAL DUST H.P.P.-4--J 2. Fibrosis - Producing Dusts. The mosi important of these are the inor ganic. slightly soluble dusts, which cause Abrnsis in the lungs, of which quartz is the outstanding example. J Son - Fibrosis - Producing Dusts. These are inert, and by themselves sel dom if ever cause fibrous tissue, but may lie free in the tissues or be absorbed. Included arc aluminum oxide, coal, corundum, emery, limestone, magnesite, marble, plaster paris, polish of rouge, etc. removed by means of dust valves (phagocytes) which ingest the dust par ticles and carry them to a system of fine drainage canals called the lymphatics. Both the cells and their contents are transported through these canals to sed imentary reservoirs known as lymph nodes, r- Sizes of Particles The Respiratory System Retention of Dust 17. Id the human respiratory sys tem, there are complicated moist pass ages, on the walls of which dust particles will stick. Also, the nose contains hairs which catch some dust. However, the respiratory system can become over loaded with dust, and when this hap pens, the dust catching mechanism functions poorly. 18. C. E. Brown has estimated the average amount of dust a normal man will retain. Breathing at the rate of 20 respirations a minute, for example, he will inhale about 10 liters a minute and retain 60 per cent of the inspired dust it is estimated roughly that the reten Jtion of common silica dust is about 50 per cent, but the way this dust may be divided between the upper and lower respiratory passages has not been dear ly defined. Drinker has observed in the case of metal fume fever that slow, deep breathing, possibly five or six breaths a minute, is much more likely to produce a fever than the normal rate of about 15 breaths a minute. This is supposed ly due to the higher retention of dust re sulting from deep breathing. However, we cannot select by any known exami nation the men best suited to dust ex posure, although some men show them selves obviously unfitted for dusty at mospheres. 19. The way in which dust partides are removed from the respiratory tract has been described by Dr. A. E. Barclay, British specialist or. X-ray. Toe b.*suchi or respiratory' passages, are covered with a number of tiny, hairlike cilia or mi croscopic whip lashes. These dlia make a fast stroke in one direction and a slower return stroke. They cover the passages leading to the lungs, and all keep in time with each other. This tends to push any foreign particles of dust up ward in the direction in which the dlia bend, so that the particles may be ex pectorated. Dust particles which reach the inner recesses of the lungs are also 20. Microscopic dust particles are, of course, attracted by gravity, but be cause of the high resistance of the air, the smaller dust partides settle out more slowly. The settling motion of a dust particle through still air will vary with the size and shape of the partide. 21. In order that dust partides be inhaled, they must be small enough to float about in the air or be carried by air currents. It has been shown by research that dust partides must be smaller than 3 microns in diameter to cause silicosis. However, since all at mospheric dusts include a majority of particles smaller than this size, the partide size distribution of dust in the air is of little significance. McCrae showed that 70 per cent of the partides in sili cotic lungs were found to be less than one micron and that the largest partides did not exceed 10.5 microns in their greatest dimensions. Results since ob tained by other investigators have served to substantiate this comparative ly early statement. 22. In silicotic lungs, dust particles under 3 microns greatly outnumber those of larger dimensions. Some have be lieved that the human respiratory mechanism is responsible for this size grading. It must be realized, however, that considerable size grading is done in the air before the dust comes into con tact with the respiratory organs. An excess of small partides may be found in the lungs simply because smaller partides remain suspended longer and in greater amounts. Partides above five rnkrons.-sill not remain floating in the air for any great length of time. The air cells of the lungs are large enough to admit panicles possibly up to 200 mi crons in length. However, according to Clark and Drinker, the most represen tative particle size in the lung; of men who have died of silicosis is one micron. 22a. Fine asbestos dust particles have been shown to product only the inert reaction on the lungs characieristics of other silicate dusts.' It is. con?equently, believed that the asbestos Figure 4. Ground silica damped onto the tproo of a conveyor. Note tbc en closed conveyor exhaust hood and the use of an approved respirator by the operator. fibers are the cause of the physical irri tation resulting in asbestosis. 23. The finer partides of dust re main suspended in a still atmosphere for relatively long periods of time. Their chances of being inhaled are, therefore, greatly increased. The smaller dust par ticles also travel farther away from their point of origin, and inasmuch as the larger partides settle out very quickly, the farther away from the dust source, the greater will be the percentage of smaller partides. 24. Neither upper nor lower size limits have been suggested for toxic sub stances, as lead, etc. It is the opinion of Drinker and Hatch that no physio logical size limits exist for these sub stances. Silicosis 25. Undoubtedly the most important kind of lung disease caused by the in halation of dust is that which has been named "silicosis." Definition 26. Dr. Gardner's definition of sili cosis is as follows: "Silicosis is a chronic disease of the lungs resulting from pro longed inhalation of fine particulate sil ica. It is manifested anatomically by formation of sharply defined fibrous nodules not over four to six mm. in di-.. ameter, which in most cases are uniform ly distributed throughout all portions of both lungs; and dinically by a paucity of symptoms and physical signs that usually appear only in the late stages of the disease and bv a tendency to be come complicated by tuberculosis. In some cases, nodulation is concentrated in certain parts of the lungs, in which cases symptoms may be marked." 2 7. The International Silicosis Con ference in 1*1.10 defined silicosis as a 4 HEALTH /A'.KT/C/IV r.lMl'JJLET NO. A "pathological condition of the lungs due to the inhalation of free silica (SiOs)." Other authorities have given various definitions. That given by the American Public Health Association includes the statement that silicosis is "a disease due to breathing air containing silica." Say following the mci'oiiiI siaitr run if the victim has been removed from tin- dusty atmosphere. Here labored breathing he-, comes srvrrr and the injured p-r.nn is susceptible to pulmonary tuhrrrnlnsi., frequcntly with fatal results Thr urkFt is now far beloii normal, .'ni1 .t blc victim to respiratory !ica-<< cosis, in the opinion of the Saranac Sili cosis Symposium, are not disabled and are not a menace to their fellow em- f ployees. The fact that barely percepti-3 ble X-ray change is visible is not grounds for assuming disability, since most persons over 40 show some chest ers and Jones at the Saranac Symposium on Silicosis in 193 S stated that, "From the viewpoint of etiology, the harmful ness of a given dust containing free sil ica is directly influenced by the number of particles of free silica less than 10 microns in diameter that it contains." 31. Silicosis may be detected by X-- changes regardless of dust inhalation. ray in each of the three stages. How Action of Silica on the Lungs ever. X-ray appearances alone are not sufficient for a diagnosis of silicosis. The 33. The theory of the action of silica complete occupational and medical his on the lungs is as follows: Where quartz tory- of the employee should be care dust is inhaled and is passed through the fully evaluated and related to the X-rav upper respirator}' tract, it reaches the Factors of Influence findings before a conclusion is reached. terminal air sacs of the lungs where the exchange of gases between the blood and 28. Silicosis becomes noticeable after air takes place. At this point, as the widely differing periods of exposure to dust is a foreign matter, it b ingested silica dust, apparently depending on: by what are known as "scavenger" cells a. The amount of dust inhaled. which carry it through the walk of the h. The percentage of free silica con tained therein. air sacs to the lymph drainage canals located outside the air sacs. Thb re c. The sire frequency, or fineness of the particles inhaled. I. The nature and source of such other substances (including vapors anil gases) as may be inhaled simultane ously or otherwise. c. The powers of resistance of the indi vidual concerned. sults in a rapid increase of tbsue cells which narrows the lymphatic channel, hampering elimination, as it is along these canals that foreign substances are removed. Also, when silica b being re moved, the panicle may kill the scaven ger cell by which it is being transported, f. The presence or absence of a compli cation by an infective process. g. The presence of complicating condi tions such as high temperatures or humidity, and unfavorable postures. Figure 1. An automatic bag loader han dling finely powdered silica dust. An effective local exhaust system is in nper- with the result that all dust panicles are not removed from the lung. Instead, f they may remain along the course of the ' drainage canal. Apparently, these small particles of silica dust are toxic in this Physiological Effects 32. From most industrial e.\[)erience 29. In earlier years it was believed (hat the physiological action of quartz on the lungs was caused by the hardness of the malerial, in fact, it was daimed that men who worked on sandstone were harmed not only by the silica particles, but also by sharp bits of steel. These ideas were contradicted by Dr. L. U. Gardner, of Saranac Laboratory, who showed that silicon carbide and fused the development of silicosis may not be anticipated short of five years. A few cases have been daimed to develop in as short a period as one and one-half years, but these were under extreme and un usual conditions. There has been evi dence that alkaline materials, such as soap powder, accelerate the develop ment of silicosis, but this has not been substantiated in recent experience. aluminum oxide, both of which are 33. Silicosis is a disease of which the harder than quartz, had practically neg victim may be unaware in the early ative physiological effects, "hen -inhaled*. =utages.'TCs development is usually slow Dr. Gardner also showed that dust from and unperceived. Inasmuch as silicosis the diamond, the hardest substance cannot be cured by any means ye; known, was practically inert when in haled. known and in its advanced stages is frequently complicated by tuberculosis location and the tbsue cefls in the im mediate vicinity are altered and re placed by what b known as scar or fibrous tissue. The ultimate result b larger areas of tbsue or lung volumes in which capillary action b definitely re duced-- through which a normal ex change of ga.vs between the blood and inhaled air cannot take place. 36. As the inhalation of silica con tinues, the amount of fibrous tissue will, of course, increase, with the ultimate re sult that the lungs will not readily oxy genate sufficient blood for the. body__ need. Thb produces a shortness of breath in the affected individual in pro portion to the amount of scar tissue in hb lungs. 30. Silicosis is considered in three separate stages by medical authorities: First Stage: The disease here pro duces no disability and does no apprecia ble harm The affected man can carri on his operations as well as ever. Second Stage: Respiration is affected. The victim may be bothered by labored breathing or other infections, the importance of prevention is apparent. Also, in many industries, new developments have greatly increased the dust output In granite stone cutting, for instance, and in rock drilling, dust production in creased tremendously with the introduc tion ol pneumatic tools. Free- Silica vs. Silicates 37. With the exception of asbestosis. the silicate ^dus-ts have not been shown to cause a disabling lung condition such as b produced, by free silica. Experimeats conducted both by causing animab to inhale dust over a long period of time and by injecting dust in their ^ Third Slice: This suge may develop 34 Men with earlv first stapi- silj. peritoneal tissues have shown that sili- INDUSTRIAL DUST H.P P .4--5 cate dusts are inert and do not cause the characteristic nodulation produced pay free silica. In addition to the animal /experimentation, men who are exposed to silicate dusts containing no free silica have been x-rayed, and in a number of cases there has been opportunity for examination of their lungs. The nodular appearance on the x-ray and the actual nodules on the lungs, both of which are characteristic of silicosis, have not been found when exposure has been limited to silicates. Gardner has stated that evidence so far available indicate that, where a disabling lung condition is alleged to result from exposures to sili cate dusts (other than asbestos), there is either an unsuspected presence of free silica in the dust, the victim has had a previous undisclosed exposure to free silica dust, or there has been inadequate interpretation of the x-ray. On the other hand, Dreeson et al. have reported pneumoconiosis in workers exposed to high concentrations (ISO million par ticles per cubic foot of air) of clean washed mica. Greenburg and his co workers found fibrosis associated with such symptoms as dyspnea and chronic cough in 14.5% of Z21 tremolite talc J miners and millers. These men were all employees of 10 or more years ex Asbestosis 38. Asbestos is the only silicate at present recognized as causing pathology, posure and the reported dust concentra and even its reaction is definitely differ tions are as high as 1300 million par- ent from that due to silica alone (Drink tides per cubic foot of air. In two er). Its behavior is the exception to the mines in this area, Gardner had found rule that silicates are inert, at least in quartz ranging from 12 to 20 per cent, uninfected tissues. Asbestos, when in- but in the mills, where all rock is mixed baled, produces fibrous tissues in the and crushed, the dust showed low quartz lungs of both men and animals. As percentages both in Gardner's studies bestos is made up of hydrated silicates and those of Greenburg. This subject of magnesium with variable amounts of of the possible action of silicate dust iron, calcium, sodium, potassium, and on the lung tissue is being further in aluminum replacing portions of the mag vestigated, and any indications that nesium. The property common to all certain silicate dusts may be causing a of this group is the fibrous structure. disabling lung condition should be It has been shown that the presence of given thorough study before conclusions fibers of asbestos are necessary for the are reached. production of asbestosis and this fact, coupled with the observation that one Mixed Dusts 3 7a. Where free siiica'is nuxea wuK other dust, the greater the percentage of free silica, the less the dust exposure required to cause silicosis. Since some dusts such as gypsum have ar. inhibit ing effect, there is an increasing tend asbestos dust is analoguus in its inert xeactioB-on- the lungs to that of other silicate dusts leads to the conclusion that asbestosis U the result of physical irritation of the lung tissue and not of chemical action as in (he case of sili cosis. ency to evaluate the extent of the hazard presented by mixed dust on the basis of the individual dust exposure. More data are constantly being ac 39. Following a study by The United States Public Health Service of the asbestos textile industry, it has been recommended that the dust concentra cumulated on the actual effects of vari tion be kept ai les< (han 3 million par- ous types of mixed dusts. ticle-N |<rr cubic f* I of air if a.-brMn-i-, is to be avoided. The use of a standard based on the number of fine particles result from the use of dust determina tion technique developed for the study of silica dust exposures. Although fu ture research will undoubtedly set up a standard based on the number of as bestos fibers in air, keeping the fine dust at less than the suggested standard will keep the concentration of injurious fibers within sale limits. Infection 40. In the opinion of most investi gators, the factor of infection is most important. It has been observed in guinea pigs with chronic pneumonia that in an infected area which developed before exposure to dust, the local branches of the lymphatic system were not so efficient as those in the rest of the lung. Silica inhaled into tissue thus damaged appeared to accumulate in un usual amounts. 41.. Since men with silicosis are more susceptible to tuberculosis than are normal men. there is often an excessive Incidence of tuberculosis among such workers. "Usually disability and death of a silicotic, when due to pulmonary conditions, results from the complicat ing tuberculosis For this reason, it is especially important to have a re-em- 6--H.P.P.-4 HEALTH PRACTICES PAMPHLET NO. 4 ployment and periodic x-ray program ried from 10 to 72 per cent depending monia, bronchitis and similar physical among workers exposed to silica dust. on length of exposure and dust concen ailments. 42. Gardner states as follows: "At the present time the treatment of tuber culosis in silicotic subjects is comparable to that for ordinary consumption 50 years ago. The prospects are far from tration--the higher percentages of in cidence being found among workers ex posed more than 25 years to concentra tions greater than 300 million particles per cubic foot of air. 49. Also, Dr. Greenljurg reminds us\ that there is an important factor other' than the one of environment, which is that of individual susceptibility. In vestigators have noticed that men work hopeless. Silicosis is gradually being 46. According to A. E. Russell, the ing in the same plant, at the same task brought under control. The time is not disability rate among anthracite miners and in the same work place, frequently far distant when dangerous concentra from respiratory tuberculosis is about do not develop silicosis to the same de tions of silica dust will no longer be per gree. It is possible for one worker to mitted in American industries. Periodic be an early victim, while the man work examinations of those already employed ing beside him remains comparatively will detect new infections in persons free. This angle of the problem indi now silicotic Prompt institution of cates a need for further research. treatment will eliminate most of the hopeless cases of silico-tuberculosis. Preemployment examinations will insure placement of men in positions that they can fill without damage to their health." 50. It is well, nevertheless, to con sider all coal mining as involving a risk to some degree, depending upon the type of rock being drilled. While the hazard may not be as severe as in roost metal Coal Mining 43. Anthraco-silicosis is a term used for a form of pneumoconiosis commonly called "miners' asthma." According to Public Health Bulletin No. 221, "Anthraco-Silicosis Among Hard Coal Min ers," it is a chronic disease due to breathing air containing dust generated in the various processes involved in mining and preparing anthracite coal. It is characterized anatomically by gen eralized fibrotic changes throughout both lungs and with the presence of ex cessive amounts of carbonaceous and siliceous materials. 44. Symptoms found in early stages are shortness of breath, cough, pain in the chest, and possibly physical weak ness. In the advanced stages of the disease there is loss of weight and de creased capacity for work, due partly to pulmonary infection. 45. In studies conducted by the United States Public Health Service in Pennsylvania,_no cases af_ aothracos. silicosis were found in the controlled group of hard coal mining employees whose dust exposure averaged less than five million particles per cubic foot of air. However, the prevalence of anthraco-silicosis among the entire group of employees was found to be about 23 per cent. Among all except rock work er?., le<- than two per cent of the men were affected when the duration of em ployment was less than 15 years, regard less of the amount of dust in the air. Among rock workers, who were exposed to dust averaging 3S per cent free silica the n^valffir, r\f anthraro-*ilirneie va Figure 7. A method of receiving dust into trucks and auxiliary collecting equip ment. 4times the rate for general manufac turing. The pneumonia rate is less than one-third of general manufacturing. Bronchitis, however, is a rather common complaint. 47. S. L. Cummins and S. F. Sladden conducted an examination of a large number of coal miners' lungs in South Wales. As a result, they made the statement--"Coal is retained in large amounts only when there is a really high silica content." They added, "We be lieve that in the absence of the silica factor, there would be, under modem mining conditions, no serious degree of anthracosis." E. L. Collins and J. C. Gilchrist have claimed that workers who have had considerable exposure in trim ming coal ships where there is practi cally no silica exposure, but nevertheless a very heavy dust condition, showed some fibrosis which, however, was not considered disabling. 4S. A study of '500 |>ost-monem examinations made in 1`iitsburgh ho pitals shows that city air which may contain an unusually large amount of coal dust may cause lungs to become darkly pigmented but yet produce no pathology of importance other than perhaD? a nredlsDosition to colds, pneu mining operations, it is of importance at least because of the number of work men concerned. 51. The hazard of sQicosis seems to be practically absent in the manufacture of cement. A recently completed survey of 2000 cement plant employees in all sections of the country by Dr. LeRoy U. Gardner and staff of the Saranac / Laboratory for the Study of Tuberculo- V sis, has failed to demonstrate that the inhalation of cement plant or quarry dust has a significant effect on the res piratory tract. Neither did it appear that men who had spent their industrial lives in such atmospheres were unusu ally susceptible to respiratory infection. The incidence of influenza, disabling colds and pneumonia was not high. No rave of clinical tuberculosis were dis covered, and the incidence of healed or latent fod as revealed in the roentgeno grams is the same as that found in the general adult population; namely, 4.5 to 5 per cent. Dr. Gardner has stated: "Although the medical examinations re veal no evidence of respiratory injuryfrom cement plant dust, even after jreriods of long exposure, maximum con centrations in dusty areas should be re duced to 100 million particles per cubic foot (light field count, irapinger tech nique) as rapidly as economically feasiblc. High concentrations may not be dangerous, but they arc not eonipatiblf with good housekeeping standards. "An exception to the general rule iindicated by the discovery of two rase-. ( of non-clinieal dust reaction in this V group of 2,000 persons. These men had been exposed to quart* dust (usu ally in the form of sandstone) used in_ the manufacture of special cement. While possible inhibitory effects of INDUSTRIAL DUST H.P.P.-4--7 other components of cement mill dust seem to have protected all other per* sons similarly exposed, these ix-Kited individual* apparently reacted Ihtuiisc a* abnormalities jnenliar t ilnni'l\r Allhouk'b it * kii<ivn that jf "Un'liv c action becomes Ion lTcciive a* the relative amounts ni silica in the duM increase, the limits ot mlcration linvf not been defined. Thcrciore, the limit for silica particles less than 10 microns in diameter at ilie breathing /> was arbitrarily set at five million particle* per cubic foot of air as determined by the United States Public Health Serv ice standard light field f'liiii.*' Toxic Dusts .Breaching vs. Swallowing 52. Generally, workers may be poi soned by toxic dusts much more quickly through inhaling them than by swallow ing them. Dust swallowed with food goes into the stomach from which the major pan of it is directly eliminated. Some may be picked up in the blood cir culation and then moved on to the liver. The liver, however, is an effective filter and detoxifier, and it is only the poison that gets beyond this point that enters general circulation. On the other hand, dusts that reach the lungs can pass di rectly into the blood stream, to the heart and then to all parts of the body. 53. Alice Hamilton, in "Industrial Toxicology" (Macmillan Company) points out the distinction between the two ways in which poisonous dust can be taken into the body in the following paragraph--"A great deal of money has been wasted by well-meaning em ployers who sought to protect lead fur- nacemen, white lead grinders, etc., against poisoning, by providing bath and lunch rooms, clean overalls, mouth washes, and such, instead of preventing the escape of lead into the air the men were obliged to breathe. I'niortunatelv this has sometimes been done under a physician's advice. It must never be forgotten that the great majority of in dustrial poisons enter the body with the inspired air and that while a workman eats only, three times a day, he breathes 16 times a minute during the eight or ten hours of the working day." 54. Numerous authorities give evi dence that there is far more danger of being poisoned by inhaling toxic dusts than by eating them with food or taking them in liquids. But all precautions should be taken to prevent toxic dusts from entering or even coming into direct contact with the body. Lead 55. The practical problem in con nection with lead poisoning is the pre vention of serious lead exposure. The problem consists of two phases: one, the determination of the limits of safe ex posure, (see paragraph 68) and, two, the reduction of lead exposure below these limits. 56. We must recognize however that lead is a normal constituent of a living animal and that there is a level of lead absorption which is safe. Lead intoxi cation and lead absorption can be pre vented by engineering methods. (See Health Practices Pamphlet No. 3 and Safety Instruction Card No. 116 on this subject.) Figure 9. Dun collector units moumt.l on the nml. Allergic Diseases 59. Conditions arising from allergic disturbances of an occupational origin are coming more into prominence, from the compensation point of view. 60. Persons said to be allergic are those who are particularly susceptible to certain substances with which they come in contact These substances may in clude foods, drugs, and vapors and dusts of various kinds. A wide variety of substances may, therefore, be responsi ble for allergic reactions in various in dividuals, which substances may have no effect on others or, in some cases, may even be of positive benefit. The types of reactions experienced by affected in dividuals to given substances may also vary greatly both in nature and in de gree. A single substance may, in one case, cause intestinal disturbances, in another case develop asthmatic attacks, and in a third case cause a skin eruption. Still another person may be affected in all three ways. Fi^urc H Virw in an iron ftnjnjrv me hcPiK eniuii rx Metal-Fume Fever 57. Metal-fume fever may be one of the results of breathing dust from metal sources. This malady usually follows contact with a heavy concentration of magnesium oxide, copper oxide, lead, zinc oxide, and possibly lead oxide and -manganese dioxide. 5S. The symptoms are chills fol lowed by a malaria-like fever which usu ally passes off within 24 hours, allowing the worker to return to his job on the following day. The first attack usually immunizes the victim so that attacks are not experienced consecutively. How ever, after a lay-off or an absence from contact with the dust, a further attack is likely. Slow, deep breathing, accord ing to Drinker and Hatch, seems to brine about the symptoms more quickly. 61. Dusts of various kinds sometimes cause attacks of asthma. Asthma may be suffered by stablemen from exposure to horse dander and by furriers from exposure to fur dust. Other persons cannot work near animals or, in fact, keep pets or sleep on feather pillows without suffering acute attacks. Hay__ fever is another type of reaction to dust on the part of certain individuals. These dusts are frequently in the nature of pollen, as from plants. Hay fever, it is claimed, however, may also be caused by other types of dust. In any event, the precise manner in which an allergic in dividual may react to a substance to which he has become sensitized cannot be predicted 62. Many believe that allergic in dividual* are horn with their particular 8- -H.l'.l* > HEALTH I'K.MTH'ES TAMI'HLET NO. A be told that the maintenance of certain degrees of air cleanliness represents the best known practice. Moreover, while such standards would undoubtedly be of value for a single industry,'"under differ ent conditions and in other industries there would be a question of their appli cability. \ 65. As the result of many years-cf practical experience in dust control in the South African gold mines, a concen tration of one mg. of dust per cubic meter of air was accepted as standard and 'L*'no\v known commonly as "the South African standard." In 193-1. I.. G. Irvine stated that no miner who had entered, the industry since this low con centration had been maintained had. ayet, contracted silicosis. 66. It was slated by I). E. Cum mings in a paper presented at the Second Symposium on Silicosis at Sar anac Lake-- ". . . Information from field studies made in many parts of the world indi cated that a normal man might work in pure crystalline silica dust for many yean without impairing his health if the concentration did not exceed five million particles per cubic foot of air." tyj^e? 'ii' hyiwr-jensiiiviiy. While this is probably so. according 10 Dr. May R. Mayer.-, individuals do not become sen sitive to substances which later cause the trouble until they have had sufficient contact to become sensitized. When a person who is hvjser-sensitive first comes in comae: with the substance, he is not aware >,i hi- condition. An "incubation period" - required. durme which time repea u-'i voMtact? perhap- sensitize, him to a po.n; v.here subsequent contacts may rt-u'r :r. iiiinu-riiaie allergic reac tion 1 hi- wailing |>crio< 1 may varv from a week or two to several months or e\en yc.tr- However, the allergic teniii-r.i , have been in the imii- vidiKi! cut with, an.] then there no.'-' I" i '." r.t.-u;- or iminimii-ni cun- tat'- -ub-n.imo in qae-'iiun in ortn.: latent nlli-reu tendency c.m in- lirni:.-,: out. !' i i -1 11 11.mni'd that once a substance. he may , more rtadily than Iteiure. bet..me sen.-ilivt to other sub stances. Occasionally, too, it has been suggested certain individuals are capable of developing a certain degree of im munity as time goes on. However, from the viewjxiint of prevention, it seems logical that workingmen who have be come allergic to certain substance- in the lour-e of their occupations should be i-n. i.urai'i-'t to go ini" other lines of work, tor irt Min-1 u;r- the tendency i- l,i lieioiiii- tiioii- -i-n-;:i\i- a- i-spi-urtloiinnue- I'er-ini'siltle Dustiness I,- < . : i.i11 v . wc kick ittita lor tie;:1111;r.- ;t\ |n-rmi'-ib'e 'iu-1itie-.- I he pnir. ita- |,-a liren rc.uhvl whi rr a tnanmacture: c.in be told the e\au conccniraii"n- a' which, tor in-ianu-, hi- men will -i.in 'lev elopinc ra-e- of -then-is, as1 n -1 * - -1 - ' li-.nl pn-i-ning lb-ian only 67. Dr. L. U. Gardner states, con cerning the permissible dustiness where silica is present: "The evidence now available makes it seem improbable that a silica hazard is defined solely by the number and size of the silica particles in industrial atmospheres. The oiher component of a dust modify its action. Some may inhibit, others retard, and perhaps some will be found to prevent its in jurious effect. Because these possibil ities are recognized, it becomes diffi cult to set up definite standards of per missible dustiness in industrial atmos pheres. Dr. Gardner continues further: "Not enough is known about the ac lion of protector substances to.warrant the recommendation that they be efii ployed to prevent silicosis in industry Our aim should be to reduce existtnc dust concentrations rather than to in crease them by adding more dust. 1 would very strongly oppose the recom mendation that protector dust be usd to attempt to prevent silicosis at tinpresent time. But 1 do believe that w> should attempt to discover mure abrun their action. Some, like gypsum, seem fo. combine with silica in the atmopherel forming clumps which are too heavy to remain suspended in air am1 too iarge to pass the barriers of lb* nose and upper respiratory iractv Will such information at hand, it mav I" possible to apply the knowledge in a practical manner." INDUSTRIAL DUST Manganese: 50 mg. per cubic meier is safe (Drinker & Hatch). H.r.!'.-4-- y 68. Other threshold limits for spe cific dusts have been stated as follows: Asbestos--(Drecssen, et al. United States Public Health Service) five mil lion particles per cu. ft. Coal dust--(R. R. Sayers, et al.) 50.000,000 particles per cubic foot for coal dust containing not over 5% quartz. 10.000,000 to 15,000,000 particles for dust with 1.1% quartz, and 5,000.000 to 10.- 000.000 particles for hard rock workers exposed to dust containing 35% free silica. Lead--(Legge and Duckering) more than .5 mg. per cubic meter is hazar dous and (A. E. Russell et al), less than .15 mg. per cubic meter is safe. Zinc oxide--(P. Drinker, et al.) 14 mgs. of zinc oxide per cubic meter for 8 hours of exposure or 45 mgs. for short exposures. 69. Of the metals, the following suggestions have been made: The American Public Health Associa tion Committee on Lead Poisoning state in their comprehensive 1943 Report that "when the air of workrooms regularly contains more than 1.5 milligrams of lead lrr 10 cuhir meters of air, rases of dis abling lead intoxication do not occur among men who work regularly in such workrooms, ami cases of qncslicnabte or minor intoxication are rare. In practice the attempt is made to maintain the lead content of the air within such limits a will yield an average of not more than 1.5 milligrams of lead per 10 cubic meters throughout the working day. while pre venting the occurrence of materially higher concentrations (5 milligrams per 10 cubic meters or more)." Zinc Oxide: To avoid metal fume fever the concentration should be kept below 14 mg. per cubic meter for 8 hours' exposure or 48 mg. for short ex posures (P. Drinker et al). Ccunety. Kirk utd Blum Manu/ikcturtnf Company t'icufr II. kxruubi system fr removal <>f Ic-jtl duw arvj /umr*. Control of Dustiness 70. There are various ways in which dust diseases and annoyances may be Tvoided*: 1. The avoidance of exposure furnishes the first and most important <)<fcnsc against industrial disease. Jobs should be performed in clean air as far as possible. It is not necessary, however, to prohibit all exposure to a toxic substance, as the human sys tem can protect and cleanse itself to a certain degree. 2. Exposure can be limited by reduc ing working hours where dust con centrations cannot be sufficiently re duced to constitute an otherwise safe condition. 3. Safe processes may sometimes be substituted for those of an unsafe nature. An example of this is the substitution of abrasive wheels made from synthetic abrasives containing no quartz, for wheels made from natural sandstone, which is about 93 per cent quartz. 4. The substi.ution of wet methods for original dry methods has exerterl considerable control over dusty atmospheres. Dry drilling is the cause nf considerable dustiness in mining, which may he greatly re duced by wet drilling. This is also true in many construction and quarry jobs. 5. An effective method for preventing the escape of undesirable dust into the working atmosphere is the local exhaust hood. It should be placed close to the source of pollution to he most effective. The air should he discharged through a dust col lector to prevent contamination of neighboring areas or return of the dust through open windows into the plant. 6. The routine recording of dusty con centrations is a valuable check on the existing exposure. Periodica! counts of air samples are a great help in showing whether or not there is need for further control. 7. In some eases, the application of general rather than local exhaust ventilation is desirable. There are instances where the soorce of pol luting materials is constantly chang ing position- and local exhaust be comes difficult and impracticable Here a general ventilating system may be the only answer. The eirhi methods ot prevention given listed in this order In "Industml Medi cine" by C!krk *nd Drinker, published by th> National Mnrtiral B<^k Company. Inc N**w Trrk. N. T Courtesy. KJrk and Stum Manutaeturing Company Figure 12. Adjustable exhaust hoods for polishing wheels. 8. A final-method of protection is the -wearing of special protective equip ment by workers. This step is fre quently the last resort amt is used only in an emergency or for jobs of short duration, but it is never theless of considerable importance. (See American Standard Safety Code (or the Protection of Heads, Eves ami Respiratory Organs.) 71. In many localities codes or or dinances for tie control of dustiness are in effect which should be investigated and followed by employers seeking to improve working conditions. Local Exhaust Systems 72. Local exhaust ventilation for the control of industrial dusts and fumes consists of four principal parts: a. Exhaust hoods h. Piping or ducts c. Air cleaning plant d. Source of suction 73. While each of these parts should be designed and installed to perform its required function with respect to the system as a whole, the exhaust hood probably demands the most careful de sign, inasmuch as the degree of control secured depends to a larger extent upon the shape and location of the hood--and the rate of air flow to it--than upon any other single factor. 74. Hoods have to a considerable ex tent followed the design first employed in such industries as woodworking and metal grinding. However, as noted by Theodore Hatch, in recent years the in dustrial dust problem has assumed hy gienic anil economic aspects entirely be yond the limitations ui those indu-tricin which the f*rfiini<-n oi riu-t has hrrn_ io n.r.r.-4 HEALTH PRACTICES PAMPHLET NO. 4 a nuisance rather than a serious health hazard. Occupational diseases have come to mean so much to industry in medical costs and compensation as well as the health of workers, that there is ample justification for extensive research and investigation in the development of the best possible design in control equip ment. 75. To maintain a safe concentration of dust in the vicinity of dust generating equipment it is necessary to introduce sufficient clean air from the outside to dilute the dust-fllled atmosphere to the degree necessary for safety. In the util ization of general ventilation systems, care must be taken to avoid excessive exposure of workers as dust is removed from its source. Especially where local dust systems are being supplemented by general ventilation, it should be seen that eddy currents are not set up to in terfere with proper functioning of the local exhaust. 76. Undoubtedly, the best method of ventilation is the control of contami nated air at its source. To do this, there must be sufficient movement of air toward the exhaust opening to counter act any tendency of the dust-laden air to escape into the surrounding atmos phere. Proper hood design will make this possible with the least possible flow of txhaust air. The object of an ex haust system is to trap the contaminated air and not to remove the harmful dusts from it. It is suggested that the scat tering of large particles may be pre vented by the erection of suitable bar riers or, of course, by causing them to flow into the collecting duct. For effi cient operation of dust collecting equip ment, all air motion around the source of dust production must be under ab solute control. 77. Proper design and location of the suction 0|>ening and the rate of air flow into it is a matter of utmost importance. Laws governing the flow of air into ex haust openings have been given in "In dustrial Dusts" by Drinker and Hatch:* 1. Enclose the process ns completely as possible and provide internal bat tles to guide the air flow where it is most needed. 2. An exhaust hood which docs not enclose the process should be placed with its opening as close as possible to the point of dust generation since the air velocity in the zone of hood influence decreases approximately with the square of the distance from the face of the hood. 3. Shape the hood to conform with the shape of the area of dust pro duction so as to secure reasonably uniform air velocity over this area. For a given required air velocity at the point of dust generation, the velocity at the hood opening should be as low as possible. This is con trary to the common idea that the hood suction should be high. 4. Provide flanges wherever possible to reduce the air flow from inef fective areas where no dust is pro duced. 5. Locate the hood opening, or part of it, so as to receive directly any dust that is thrown off along a welldefined path, thus utilizing the di rectional energy of the material for its own captnrr. "Design of Exhaust Hoods for Dust-Control Systems" by Theo dore Hatch. Harvard Graduate School of Engineering and School of Public Health. Boston, Hass. The Journal of Industrial Hygiene and Toxicology, November, 1936. Figure 14. Sweeping with the use of oiled sawdust in allay dust. Wet vs. Dr)- Drilling 78. On the matter of drilling, Har rington says: "Dry drilling is. of course, very much more of a dust producer than wet drill ing--possibly in the ratio of 10 to 1. Wet drilling produces some dust, bin if reasonable precautions are taken with wet drilling, ami snitable precautions are also taken as to ventilation, as to the welting oi the mock pile, as to the time in which blasting is done, as to the precautions which are taken after going back to the face after blasting ... there need be no particular harm to workers in those places, as far as dust diseases are concerned." 79. Prof. Philip Drinker, in com menting on the adoption of the New York State Code governing dustiness in rock drilling, stated: "This code divides all rock formation into two classes, class 1 being those with less than 10 per cent free silica, by weight, and class 2 being those with more than 10 per cent free silica. If drilling is done in class 1 rock, dust counts most be below 100 million per cubic toot, and below 10 million par ticles if the rock tails in class 2. INDUSTRIAL DUST H.P.P.-4-- "Thu means, in effect, that dry drill ing can only be used with local ex hausts and adequate air cleaning. It happens, also, that wet drilling without ventilation will not achieve adequate air cleanliness in the case of the high quartz or class 2 rock." 80. The situation is well summed^ip in an editorial that appeared in ''Chem ical Engineering and Mining Review" (Melbourne). "Whatever the ultimate findings as to the cause and development of pneu moconiosis, the task of the mining en gineer is indicated clearly; the first es sential is to minimize the formation of dust, and the second is to collect or remove unavoidable dost as rapidly as possible. In this Utter respect, a logi cal forward step has been taken in the adoption of means to. collect the dost at certain points of production instead of relying, upon the general ventilation current to dilute and transport the in jurious material. Small units are now being installed in some mines at load ing stations and orepass tipplers, the installation and maintenance costs of which are low and a high efficiency is developed. "More efficient rock drilling practice, an improved general standard of health, reduced working hours, provi sion of change house and other facili ties. and many minor but important factors can also contribute tola reduc tion in the incidence of silidosis." ACKNOWLEDGMENT. Thu pamphlet was prepared by War ren A. Cook, Division of Industrial Hy giene and Engineering Research, Zurich General Accident and liability Insur ance Company, and reviewed by Floyd A. Van Atta, Industrial Hygienist, Na tional Safety Council. It has been re viewed by theSafe Practices Conference Committee, the Health Advisory Com mittee, and approved by the Executive Committee of the National Safety Coun cil. In writing this pamphlet, the au thors have reviewed carefully the litera ture already m the field, and grateful acknowledgment is made to the numer ous publications. The United States Department of Labor has contribut many of the illustrations used here. Appreciation is expressed also to c . others who reviewed and submitted su geslions for the Improvement of tk work. Outstanding among those gi. ing the pamphlet their personal alia lion are: W. T. Cameron, United State Department of Labor; A. J. P Portland Cement Association; Phil; Drinker, Harvard University; Dr. Lt Roy U. Gardner, Saranac Laboratory fc the Study of Tuberculosis; Daniel Her mgton, United States Bureau of Mines. Dr. M. H. Kronenberg, Illinois Depart ment of Public Health; Dr.A.J. Lanza. Metropolitan Life Insurance Company, Dr. Carey P. McCord, Chrysler Corpo ration; Dr. R. R. Sayers, United States Public Health Service; Dr. C. D. Selby, General Motors Corporation; JL C. Stratton, Travelers Insurance Company; and Dr. C. E. A. Winslow, Yale Uni versity. Rep. IM--'VHP