Document rppz226N05mKgj2p13NKr51mV

FILE NAME: BF Goodrich (BFG) DATE: 1939 DOC#: BFG036 DOCUMENT DESCRIPTION: Article - Industrial Dust - NSC Health Practices [V i ri V \ a'-*. : industrial Dust Health Practices Pamphlet No. 4 Published by National Safety Council, Inc. 20 North Wacker Drive, Chicago 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 lung pathology. Silicosis may be followed by 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 a b s o r b e d through the skin. c. A transient disorder known as metal fume fever, from the inhalation of finely divided metallic dust or fume particles such as zinc oxide. d. A reaction, allergic in nature, caused by breathing organic dusts such as pollen, flour, certain pulverized woods. e. An increase in bronchitis a n d o t h e r acute respirator}' infections by breath ing inert, non-fibrosis-producing dust such as coal, emery, limestone, marble, etc. 3. In each of the above cases, the inhalation of dust can be the sole cause This pamphlet is a compilation of ex perience in accident prevention, and is one of a series of more than 150 Safe Practices and Health Practices pamphlets. It should not be assumed, however, that it includes every acceptable procedure in the field covered. It must not be con fused with federal, state or insurance requirements, or with American Standard safety codes. of disability. With the toxic dusts, trouble may result from swallowing or more rarely from skin absorption, as well as from inhalation. Nevertheless, inha lation is usually considered far more dangerous. 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 "pneumonoconiosis" 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. Dust 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 than 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 immediate area where men or 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 9. Dust is formed by reducing solid materials to small sizes. Processes like (Copyright, 1939, National Safety Council, Inc. All rights reserved. Printed in U. S. A.) / 2 HEALTH PRACTICES PAMPHLET NO. 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 particle 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, crushing, 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 par ticle of quartz may be seen when the particle 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 0.25 microns. Chemical 15. The chemical and mineralogical 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, there will be 1012 (1,000, 000,000,000 or one trillion) particles 16. The following classification of with total surface areas of six square meters (9300 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 material will occupy an air space of 10,000 cubic feet. 4 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-viafale particles which may or may not be either toxic or irritant, but nevertheless have effect on the human organism. 1. Toxic or Irritant Dusts. 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, horns, hoofs, bones, etc. Diphtheria, tuberculosis, typhoid and other bacillus-produced diseases may result from exposure to infected dusts. Bacterial-sensitized dust can also be the cause of allergic diseases, as asthma, hay fever, eczema, migraine headaches, etc. 2. 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 and/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,, 12. With the exception of such fi brous material as asbestos, the dust par ticles must be smaller than 10 microns np micron equals one twenty-fifth Figure 3. Granite surfacer in operation, without and with dust control provided. 1NDUSTR1AL DUST 3 2. Fibrosis - Producing Dusts. The most important of these are the inor ganic, slightly soluble dusts, which cause fibrosis in the lungs, of which quartz is the outstanding example. 3. -Von - 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 are aluminum oxide, coal, corundum, emery, limestone, magnesite, marble, plaster paris, polish of rouge, etc. pectorated. Dust particles which reach the inner recesses of the lungs are also 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. The Respiratory System Retention of Dust 17. In 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 tion of common silica dust is about SO 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 IS 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 particles are removed from the respiratory tract has been described by Dr. A. E. Barclay, British spedalist on X-ray. The bronchi or respiratory passages, are covered with a number of tiny, hairlike cilia or mi croscopic whip lashes. These cilia 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 cilia bend so that the particles may be ex Sizes of Particles 20. Microscopic dust particles are, of course, attracted by gravity, but be cause of the high resistance of the air, the smaller dust particles settle out more slowly. The settling motion of a dust particle through still air will vary with the size and shape of the particle. 21. In order that dust particles be inhaled, they must be small enough to float about in the air or be carried by air currents. In the light of present information, it is probably best to con sider all dusts as somewhat injurious re gardless of size. Nevertheless it has been stated that most injurious dusts lie be tween y i and 3 microns and that possi bly between 5 and 10 microns is the upper limit of danger. McCrae showed that 70 per cent of the particles in sili cotic lungs were found to be less than one micron and that the largest particles 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 particles may be found in the lungs simply because smaller par ticles remain suspended longer and in greater amounts. Particles above five microns will not remain floating in the air for any great length of time. The air cells of the lungs are large enough to admit particles possibly up to 200 mi crons in length. However, according to Clark and Drinker, the most represen tative particle size in the lungs of men who have died of silicosis is one micron. 23. The finer particles of dust re main suspended in a still atmosphere for Figure 4. Ground silica dumped onto the apron of a conveyor. Note the en closed conveyor exhaust hood and the use of an approved respirator by the operator. 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 particles settle out very quickly, the farther away from the dust source, the greater will be the percentage of smaller particles. 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." (See Health Practices Pamphlet No. 20 "Silicosis" and Safety Instruction Card No. 408 "Silicosis-- What the Worker Should Know About It.") 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 clinically by a paucity of symptoms and physical signs that usually appear only in the late stages of the disease and by 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." 27. The International Silicosis Con ference in 1930 defined silicosis as a 4 HEALTH PRACTICES PAMPHLET NO. 4 ``pathological condition of the lungs due to the inhalation of free silica (S iO J." 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 ers and Jones at the Saranac Symposium on Silicosis in 1935 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." Factors of Influence 28. Silicosis becomes noticeable after widely differing periods of exposure to silica dust, apparently depending on: a. The amount of dust inhaled. b. The percentage of free silica con tained therein. c. The size frequency, or fineness of the particles inhaled. d. The nature and source of such other substances (including vapors and gases) as may be inhaled simultane ously or otherwise. e. The powers of resistance of the indi vidual concerned. 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. Physiological Effects 29. In earlier years it was believed that the physiological action of quartz on the lungs was caused by the hardness of the material. In fact, it was claimed 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 aluminum oxide, both of which are harder than quartz, had practically neg ative physiological effects when inhaled. Dr. Gardner also showed that dust from the diamond, the hardest substance known, was practically inert when in haled. 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 carry on his operations as well as ever. Second Stage: Respiration is affected. The victim may be bothered by labored breathing. Third Stage: This stage may develop following the second stage even if the victim has been removed from the dusty atmosphere. Here labored breathing be comes severe and the injured person is susceptible to pulmonary tuberculosis, frequently with fatal results. The work cosis, in the opinion of the Saranac Sili cosis Symposium, are not disabled and are not a menace to their fellow em ployees. The fact that barely percepti ble X-ray change is visible is not er is now far below normal, and a possi grounds for assuming disability, since ble victim to respiratory diseases. most persons over 40 show some chest 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 35. 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-ray upper respiratory tract, it reaches the findings before a conclusion is reached^ terminal air sacs of the lungs where the exchange of gases between the blood and air takes place. At this point, as the dust is a foreign matter, it is ingested by what are known as "scavenger" cells which carry it through the walls of the air sacs to the lymph drainage canals located outside the air sacs. This re sults in a rapid increase of tissue cells which narrows the lymphatic channel, hampering elimination, as it is along these canals that foreign substances are removed. Also, when silica is being re moved, the particle may kill the scaven ger cell by which it is being transported, with the result that all dust particles are Figure 5. An automatic bag loader han dling finely powdered silica dust. An effective local exhaust system is in oper ation. not removed from the lung. Instead, they may remain along the course of the drainage canal. Apparently, these small particles of silica dust are toxic in this 32. From most industrial experience the development of silicosis may not be anticipated short of five years. A few cases have been claimed 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 location and the tissue cells in the im mediate vicinity are altered and re placed by what is known as scar or fibrous tissue. The ultimate result is larger areas of tissue or lung volumes in which capillary action is definitely re duced -- through which a normal ex change of gases between the blood and inhaled air cannot take place. ment of silicosis, but this has not been 36. As the inhalation of silica con substantiated in recent experience. tinues, the amount of fibrous tissue will, 33. Silicosis is a disease of which the victim may be unaware in the early stages. Its development is usually slow and unperceived. Inasmuch as silicosis cannot be cured by any means yet known and in its advanced stages is frequently complicated by tuberculosis of course, increase, with the ultimate re sult that the lungs will not readily oxy genate sufficient blood for the body need. This produces a shortness of breath in the affected individual in pro portion to the amount of scar tissue in his lungs. or other infections, the importance of Free Silica vs. Silicates 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 of pneumatic tools. 37. With the exception of asbestos, all inorganic dusts other than free silica that have been studied, including a num ber of silicates, seem to behave alike. The particles are ingested by phagocytes or dust cells and slowly transported into the lymphatic system. Experiments 34. Men with early first stage sili have indicated that even very large INDUSTRIAL DUST 5 quantities of such dusts have little irri tating effect. There is little evidence that any of them have caused a progres sive fibrosis, and only a few have ex cited more than a transitory inflamma tion. However, when a small amount of uncombined silica is mixed with such dusts, the lymphatic changes tend to become fibrous. When the silica is in excess, generalized nodulation develops. Asbestosis 38. Asbestos is the only silicate at present recognized as causing pathology, and even its reaction is definitely differ ent from that due to silica alone (Drink er). Its behavior is the exception to the rule that silicates are inert, at least in uninfected tissues. Asbestos, when in haled, produces fibrous tissues in the lungs of both men and animals. .As bestos is made up of hydrated silicates of magnesium with variable amounts of iron, calcium, sodium, potassium, and aluminum replacing portions of the mag nesium. The property common to all of this group is the fibrous structure, and it is probable that this physical structure may be more important than the chem ical composition. Further studies will undoubtedly throw more light on this subject. 39. There are other silicates which resemble asbestos chemically, such as shale, talc, kaolin, feldspar, and pure mica, all of which have been given con siderable study. These have generally proved to be inert with the exception of biotite, a species of mica, which has produced some definite tissue changes in recent, uncompleted animal materials. Infection 40. In the opinion of most investi gators, the factor of infection is most important. I t 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. Tuberculosis frequently devel ops in a silicotic lung, and many cases of advanced silicosis terminate in a tu berculous infection. 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 hopeless. Silicosis is gradually being brought under control. The time is not far distant when dangerous concentra tions of silica dust will no longer be per mitted in American industries. Periodic examinations of those already employed will detect new infections in persons now silicotic. Prompt institution of treatment will eliminate most of the hopeless cases of silico-tuberculosis. Pre employment examinations will insure placement of men in positions that they can fill without damage to their health." 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 of anthracosilicosis 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 an thraco-silicosis among the entire group of employees was found to be about 23 per cent. Among all except rock work ers, less 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 35 per cent free silica the prevalence of anthraco-silicosis va ried from 10 to 72 per cent depending on length of exposure and dust concen 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. 46. According to A. E. Russell, the disability rate among anthracite miners from respiratory tuberculosis is about 6 '.ALTH PRACTICES PAMPHLET NO. 4 gree. It is possible for one worker to be an early victim, while the man work ing beside him remains comparatively free. This angle of the problem indi cates a need for further research. arbitrarily set at five million particles per cubic foot of air as determined by the United States Public Health Serv ice standard light field count." Toxic Dusts Figure 7. A method of receiving dust into trucks and auxiliary collecting equip ment. 4 l/> times 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. 48. A study of 2500 post-moriem examinations made in Pittsburgh hos 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 per haps a predisposition to colds, pneu monia, bronchitis and similar physical ailments. 49. Also, Dr. Greenburg 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 ing in the same plant, at the same task and in the same work place, frequently do not develop silicosis to the same de 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 most metal mining operations, it is of importance at least because of the number of work men concerned. 51. The hazard of silicosis 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 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 atm.ospheres were unusu ally susceptible to respiratory infection. The incidence of influenza, disabling colds and pneumonia was not high. No cases of clinical tuberculosis were dis covered, and the incidence of healed or latent foci 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 injury from cement plant dust, even after pe riods of long exposure, maximum con centrations in dusty areas should be re duced to 100 million particles per cubic foot (light field count, impinger tech nique) as rapidly as economically feasi ble. High concentrations may not be dangerous, but they are not compatible with good housekeeping standards. "An exception to the general rule is indicated by the discovery of two cases of non-clinical dust reaction in this group of 2,000 persons. These men had been exposed to quartz dust (usu ally in the form of sandstone) used in the manufacture of special cement. While possible inhibitory effects of other components of cement mill dust seem to have protected all other per s o n s s im i l a r l y exposed, these isolated individuals apparently reacted because of abnormalities peculiar to themselves. Although it is known that protective action becomes less effective as the relative amounts of silica in the dust increase, the limits of toleration have not been defined. Therefore, the limit for silica particles less than 10 microns in diameter at the breathing zone was Breathing 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 part 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 furnacemen, 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. Unfortunately this has sometimes been done under a physician's advice. It must never be Figure 8. View in an iron foundry show ing bench grinders with exhaust hoods. INDUSTRIAL DUST 7 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.) 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. 58. 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 bring about the symptoms more quickly. 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. 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 dividuals are born with their particular types of hyper-sensitivity. While this is probably so, according to Dr. May R. Mayers, 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 hyper-sensitive first comes in contact with the substance, he is not aware of his condition. An "incubation period" is required, during which time repeated contacts perhaps sensitize him to a point where subsequent contacts may result in immediate allergic reac tion. This waiting period may vary from a week or two to several months or even years. However, the allergic tendency must have been in the indi vidual to begin with, and then there must be continuous or intermittent con tacts with the substance in question in order that the latent allergic tendency can be brought out. Figure 9. Dust collector units mounted on the roof. 63. It has been claimed that once a person has become sensitized to a given substance, he may, more readily than before, become sensitive 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 viewpoint of prevention, it seems logical that workingmen who have be come allergic to certain substances in the course of their occupations should be encouraged to go into other lines of work, for in most cases the tendency is to become more sensitive as exposure continues. Permissible Dustiness - 64. Generally, we lack data for de fining rigidly permissible dustiness. The point has not been reached where a man ufacturer can be told the exact concen trations at which, for instance, his men will start developing cases of silicosis, asbestosis, or lead poisoning. He can only 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 of 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 is now known commonly as "the South African standard." In 1934, L. G. Irvine stated that no miner who had entered the industry since this low con centration had been maintained had, as yet, contracted silicosis. 66. It was stated by I). E. Cum mings in a paper presented at the 4 with 13% quartz, and o,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: Lead: As the result of an extensive investigation in the storage battery in dustry it was concluded that less than 0. 15.mg. per cubic meter is safe. The American Public Health Association Committee on Lead Poisoning stated that more than 0.5 mg. per cubic meters constitutes a condition of lead ex posure. 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.). Manganese: 50 mg. per cubic meter is safe (Drinker & Hatch). Control of Dustiness 70. There are various ways in which dust diseases and annoyances may be avoided*: Figure 10. Portable industrial vacuum cleaner. 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 years without impairing his health if the concentration did not exceed five million particles per cubic foot of air." 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 other components 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 tion of protector substances to warrant the recommendation that they be em ployed to prevent silicosis in industry. Our aim should be to reduce existing dust concentrations rather than to in crease them by adding more dust. I would very strongly oppose the recom mendation that protector dust be used to attempt to prevent silicosis at the present time. But I do believe that we should attempt to discover more about their action. Some, like gypsum, seem to combine with silica in the atmos phere, forming clumps which are too heavy to remain suspended in air and too large to pass the barriers of the nose and upper respiratory tracts. With such information at hand, it may be possible to apply the knowledge in a practical manner." 68. Other threshold limits for spe cific dusts have been stated as follows: Asbestos--(Dreessen, 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 1. The avoidance of exposure furnishes the first and most important defense 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 con taining no quartz, for wheels made from natural sandstone, which is about 95 per cent quartz. 4. The substitution of wet methods for original dry methods has ex erted considerable control over dusty atmospheres. Dry drilling is the cause of considerable dustiness in mining, which may be greatly re duced by wet drilling. This is also true in many construction and quarry jobs. T he eight methods of prevention given here are listed in this order in "In dustrial Medi cine" by Clark and D rinker, published by the National Medical Book Company, Inc., New Y ork, N. Y. INDUSTRIAL DUST 9 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 be most effective. The air should be 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. Periodical counts of air samples are a great help in showing whether or not there is need for further control. 7. In some cases, the application of general rather than local exhaust ventilation is desirable. There are instances where the source 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. 8. A final method of protection is the wearing of special protective equip ment by workers. This step is fre quently the last resort and 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 for the Protection of Heads, Eyes and Respiratory Organs.) 71. In many localities codes or or dinances for the 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 b. Piping or ducts c. Air cleaning plant d. Source of suction C ourtesy, K irk and Blum M anufacturing Company Figure 11. Exhaust system for removal of lead dust and fumes. 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 and economic aspects entirely be yond the limitations of those industries in which the production of dust has been 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-filled 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 exhaust 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- Courtesy, K irk and Blum M anufacturing Company Figure 12. Adjustable exhaust hoods for polishing wheels. ment, all air motion around the source of dust production must be under ab solute control. 77. Proper design and location of the suction opening 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 as-1completely as possible and provide internal baf fles to guide the air flow where it is most needed 2. An exhaust hood which does nof 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 witli 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 capture. ' "Design of Exhaust Hoods for Dust-Control Systems" by Theo dore Hatch, Harvard Graduate School of Engineering and School of Public Health, Boston, Mass. The Journal of Industrial Hygiene and Toxicology, November, 1936. Figure 13- Dust from rock drilling operations, uncontrolled and controlled by dust trap. W et vs. Dry D rilling 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, but if reasonable precautions are taken with wet drilling, and suitable precautions are also taken as to ventilation, as to the wetting of the muck pile, as to the time in which blasting is done, as to drilling is done in class 1 rock, dust counts must be below 100 million per cubic foot, and below 10 million par ticles if the rock falls in class 2. "This means, in effect, that dry drill ing can only be used with local ex giene and Engineering Research, Zurich General Accident and Liability Insur ance Company, and Edward R . Granniss, Staff Engineer, National Safety Council. It has been reviewed by the hausts and adequate air cleaning. It Safe Practices Conference Committee, happens, also, that wet drilling without ventilation will not achieve adequate air cleanliness in the case of the high quartz or class 2 rock." the Health Advisory Committee, and ap proved by the Executive Committee of the National Safety Council. In writing this pamphlet, the authors have reviewed 80. The situation is well summed up carefully the literature already in the the precautions which are taken after in an editorial that appeared in "Chem 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." ical Engineering and Mining Review" (Melbourne). "W hatever the ultimate findings as to the cause and development of pneu 79. Prof. Philip Drinker, in com menting on the adoption of the New York State Code governing dustiness in 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 rock drilling, stated: remove unavoidable dust as rapidly as "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. J f possible. In this latter respect, a logi cal forward step has been taken in the adoption of means to collect the dust at certain points of production instead of relying upon the general ventilation current to dilute and transport the in field, and grateful acknowledgment is made to the numerous publications. The United States Department of Labor has ; contributed many of the illustrations used herein. Appreciation is expressed also to all others who reviewed and submitted sug gestions for the improvement of this work. Outstanding among those giv ing the pamphlet their personal atten tion are: W. T. Cameron, United States Department of Labor; A. J. R. Curtis, Portland Cement Association; Philip jurious material. Small units are now Drinker, Harvard University; Dr. Le 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 Roy U. Gardner, Saranac Laboratory for the Study of Tuberculosis ; Daniel Har rington, United States Bureau of Mines; Dr. M. H. Kronenberg, Illinois Depart ment oj Public Health; Dr. A. J. Lanza, Metropolitan Life Insurance Company; Dr. Carey P. McCord, Chrysler Corpo sion of change house and other facili ties, and many minor but important factors can also contribute to a reduc tion in the incidence of silicosis." ration; Dr. R. R. Sayers, United States Public Health Service; Dr. C. D. Selby, General Motors Corporation; R. C. Stratton, Travelers Insurance Company ; ACKNOWLEDGMENT and Dr. C. E. A. Winslow, Yale Uni versity. Figure 14. Sweeping with the use of oiled sawdust to allay dust. This pamphlet was prepared by War ren A. Cook, Division oj Industrial H y 4-39-3M