Document V34VDVwYZkmxvYV6wJM1mw27q

FILE NAME: Engineering (ENG) DATE: 1933 Apr DOC#: ENG029 DOCUMENT DESCRIPTION: Trade Journal Article - Dust in Industry: The Sampling and Analysis of Industrial Dusts MECHANICAL ENGINEERING Published by The American Society of Mechanical Engineers V olume 55 N um ber 4 Contents for A pril, 1933 TH E B A L A N C IN G OF ECO NO M IC FQ&CES- (P A R T i ) .........................................................2 1 1 e l i h u Th o m s o n ....................................................................................K . T. Compton 2 2 5 d u s t i n i n d u s t r y ........................................................................... J . J . Bloomfield 229 s o c i a l t r e n d s - .......................................................................................................E. E. Hunt 2 3 4 t h e f e r m i- d ir a c sta t ist ic a l t h e o r y of g as d e g e n e r a t io n -- I . . Vladimir Karapetoff 2 3 7 a t h e r m o d y n a m i c t h e o r y f o r s t e a m ? . . . . H. E. Longiuell 2 4 3 s i g n i f i c a n c e o f s p e e d s t a n d a r d i z a t i o n J. Decker and W . P. Acres 2 4 6 CHARLES M acC A U G H E Y s a m e s , 1 8 6 6 - 1 9 3 3 .................................................................. 2 4 9 E D IT O R IA L .... ... 250 A .S .M .E . BOILER CODE . . SURVEY OF E N G IN E E R IN G PROGRESS . 2 5 2 POW ER TEST CODES . . . . C O R R E S P O N D E N C E ............................................. 2 6 3 t BOOK REVIEW S A N D LIBRARY NOTES W H A T S G O IN G O N ................................................................................................................................... 2 7 1 1 . 266 . 268 . 2 6 9 ** DISPLAY ADVERTISEM ENTS PROFESSIONAL SERVICE . 1 CLASSIFIED ADVERTISEM ENTS ... 16 14 IN D E X TO ADVERTISERS . . . .1 8 O FFICE R S OF TH E SO C IE T Y : A. A. P o t t e r , President C.R1K O b e r g , Treasurer C a l v i n W . R ic e , Secretary P U B L IC A T IO N STA FF: G eorge A. Ste t so n , Editor F r e d e r ic k L a s k , Advertising Mgr. CO M M ITTE E ON P U B L IC A T IO N S : L . C. M o r r o w , Chairman S. W . D u d l e y S. F. V o o r h ebs, Vice-Chairman M. H. R oberts \V. F. R y a n C. E. D a v ie s , Secretary to Committee on Publications -olishcd m onthly by The American Society o f Mechanical Engineers. Publication office at 20th and N ortham pton Streets, Easton, Pa. Editorial and Advertising departments a t the head quarters of the Sociery, 29 West T h irty -N in th Street, New Y ork, N. Y. Cable address.'U yaatm c," New York. Price 60 cents a copy, $5 00 a year; to members and affiliates, 50 cents a copy. H 00 a year. Postage to Canada, 75 cents additional, to foreign countries. $1.50 additional. Changes of address rnusrbe received a t Society headquarters tw o weeks before they are to be -"'tetive on the m ailing list. Please send old as well as new a d d ress.. . . By-Law: The Society shall not be responsible for statem ents o r opinions advanced in papers or . . , printed in its =-oiicatiooj (BZ. Par. 3). . . . Entered as second-class m atter at the Post Office a t E aston, Pa., uadcr the Act of March 3, 187?. . . . Acceptance for m ailing at special rare of postage provided or in section 1103. Act of October 3 ,1917. autnorized on January 17.1921____ Copyrighted, 1933, by The American Society o f M echanical Engineers. DUST in INDUSTRY The Sampling and Analysis of Industrial D usts B y J. J. BLOOMFIELD1 THE abundant evidence at hand showing that the inhalation of certain industrial dusts is an impor tant factor in the causation of pulmonary disease iias emphasized the significance of the quantitative as pects of this problem. A knowledge of the dust content of the industrial atmosphere is required not only for the purpose of determining the extent of the hazard involved in various manufacturing processes, but is also useful in measuring the efficiency of protective devices which may be used in the elimination of the dust hazard. The object of the present contribution is to describe the under lying factors involved and the technique employed in the study of the quantitative phases of the industrial dusts w hich may produce injury to the respiratory sys tem. Such dusts are produced by the numerous indus inhaled dust gain access or are retained by the human lung. For this reason it is essential to determine the size of the dust particles present in the industrial atmos phere. With reference to the quantity of dust present in the air of a workroom, it is apparent that when the dust concen tration is high the exposed person w ill inhale a greater quantity in a given period of time than he w ill when it is relatively low, and since the rate of production of the disease is partially dependent upon the total amount of dust inhaled, this latter fact plays an important role in determining the time of onset of the end result. The need for the evaluation of the quantity of dust in the in dustrial atmosphere is obvious. trial operations involving the drilling, crushing, and N ATU RE OF DUST - grinding of mineral matter such as talc, quartz, granite, slate, and cement. Research on the problem of industrial-dust inhalation has demonstrated that so far as their fibrosis-producing The properties of a given dust which determine its capacity to produce pulmonary pathology are the nature of the dust, that is, irs chemical and mineralogical com position, its particle size, and finally the quantity of the dust dispersed in the atmosphere. One of the outstanding results of the last zo years of research in the field of dust inhalation is the demonstra tion of the fact that, in general, the degree of health hazard associated w ith the inhalation of any dust, all other factors remaining constant, is dependent upon the qualities are concerned, dusts may be divided into three groups: ( i ) those composed completely of combined silica, that is, silicates, such as pure asbestos; (x) those containing free silica in the crystalline form known as quartz (granite contains approximately 35 per cent of quartz), and lastly, (3) dusts containing free silica in a non-crystalline form such as diatomaceous eartli. In general it has been found that the harmfulness of a quartz-containing dust is in direct proportion to its quartz content. For this reason in attempting to evalu composition of the dust. For example, it is now w ell established that the inhalation of certain tvpes of dust, such as granite dust, w ill in time produce fibrosis of the lungs, frequently associated w ith tubercu losis. In other cases exposure to dust may result in the production of a far lesser degree of fibrosis without sub sequent tuberculosis; this is true of cement dust. And anally, there are certain types of dusts w hich produce uttle or no lung fibrosis, as typified by marble dust. In general, it has been found that those dusts which are high in quartz content are the ones which produce a disabling fibrosis of the lungs most readily. Hence the necessity for knowledge concerning the chemical and mineralogical composition of a dust is obvious. So far as the size of the dust particles is concerned, it is apparent that in order for any given dust to produce in jury to the lung it must gain access to the parenchyma oi the lung, the site where the harmful effects of the dust mke place. It is known that not all of the particles of p Sanitary Engineer, U. S. Public Healrh Service, Washington, D. C. [ L resentei ac the NatIonal Process Meeting arranged by the Proces; h , n C2 e? C mnutt? of rhe A.S.M.E., and held under the auspices ol ne uuttaio Section or the Society, Buffalo, N. Y. J u n e 6 to S 1 Q32 ate the harmfuiness of a dust it is of the utmost impor tance to ascertain its quartz content. This should be done by a chemical and mineralogical analysis. We find in practice that samples of dust settled out of the atmosphere at the breathing level of the worker serve admirably for these chemical and mineralogical determinations. It is our practice to have such analyses made by an expert geologist. Only in this way is it possible to determine accurately the amount of "quartz present in a given sample. Table 1 presents the quartz TABLE 1 PERCENTAGE OF QUARTZ PRESENT IN VARIOUS INDUSTRIAL DUSTS Kind of dust Percentage of quartz Rock-drilling dust (bituminous-coal mine). .. Granite-cutting dust........................................ Rock-drilling dust (anthracite mine)................. Brass-foundry dust.................................................. Dust from raw mills in cement plant................. Slate-mill dust (Vermont red slate).................... Silverware-polishing dust..................................... Anthracite dusc...........................................1 3 Bituminous-coal dust................................... . Cement dust............................................................. Slate-mill dust (Vermont green slate)............. Talc-mill dust.......................................................... Marble-cutting dust............................. .... 54.0 35.2 31 0 19.0 6.5 3.0 17 12 less chan 1 . 0 trace none n0ne 229 230 S r btaiaed " VariOUSindUStrieSwbicbwe It is quite evident that, judged by quartz content, rockdriiling occupations in the coal-mining indusm and certain occupations in the granite-cutting industry and in brass foundries may be considered as hazardous h, h l* true ls evtdenced by the high rates of illness ?n d u sS es.?0m SlllC SiS ^ tUbcrCUl0S" the" PARTICLE SIZE OP DUST It has been demonstrated that particles of a size greater than xo to ia microns m the longest dimension are very dom found m the lungs. Thi? absence of larger Pa"ticrns is partly due to the fact that the number of such particles greater than io microns in size present in indus at a high magnification (1500 to 2 5 0 0 diameters)- from his cither an enlarged print may be made, or & rive may be enlarged by means of a stereooncon. The particles revealed on the enlarged print or screen mav be measured by means of a millimeter scale. The particle size dimensions are grouped in classes accord in g^ size from which a percentage distribution curve Is eashy of ta"lcl udusstt ffrroomm tthhreeSaimr Sofftha wPoarnkirdoeo-mSlziendwishtriicbhuttiaolnc IS tiveij small, and, due to gravity and the protective action of the mucous surfaces of the upper respiraton tract ppoorrtdioonnssTof/tthhee"re10s1p^iradtorny0ttrapcet.netHraetne cet0wteheneteedrmoinnlavl concern ourselves w ith those dust particles that are less han io microns m the longest dimension iiss ccaapmabblek no?f gaa' mCeirntagmacWcehsesthtoerthre nluont gasn, iintdiussntreicaelsdsaursyt HG. 2 PHOTOM ICROGRAPH OF TALC DUST O BTAIN ED W ITH t h e OW ENS JET DUST COUNTER. X 6 5 0 FIG . I f a r t ic l e -s iz e d is t r ib u t io n o f t a l c d u st don inPr ' S12e StUdlS 0f the dust under considera- obtained h ^ S/ mples for Such studies mav be Th s a t 7 C USC f th WCns i counter * 0^ a apparatus prIects the atmospheric dust directly on a microscope cover slip. This cover slip may then be properly mounted and examined by any one of sev scooppiiccaHlilyv,dUS'sinSgUCah mSaamgnpikfiscatmioanp obfe 1s0tn00dieddiammeicterors- (oil-immersion objective), and the horizontal diameter of a representative number of narrickf TM j by means of a calibrated filar ocular m ic ro m e te r^ H _nother method a photomicrograph o f the dust is made j V B io o ^ ia , j. TThher mmtelansgurgemreUnntsd, frrom2 VwChryichfintheStdataetaofforsutbhdisivifsigiounre were obtained, were made by means of a filar cella r 2 maS'nification o f 1000 diameters. With small as o f micn " " ,P Ssible to mea^ re particles as than o s micron lndla" >while particles smaller ion aL *TT Y dlsnn^uIshed at this magnifica- corded dFn! Ug " 0t measured= rheir presence is reorded. _ For routine particle-size measurements the photomicrographic method as described bv Green5 has a decided advantage over the direct m i c r o s i o S " easee- ments, that the task is less tedious and the B rtid e s are measured with more ease and accuracy. However ^ u ld S 'S 'r e S 'L S : mcth0<1' major portion (6, p ,, cent) being between" and , m b S,mm S T i' m' dia" si2c of thc dust was found a a m e ' s ' p S r S d n ^ - 1 " * P1-- ^ of the April, 1923, p. 522. - D Countmg Apparatus/' Jl, Hyytm, the ^artkie^Si'^ProTCrric^^Non3!! Description of n . Franklin Ins,., M a r S . iWS W U n iIO r m Partku1 ' Substances," QU AN TITY OF DUST _As_pomted out earlier, a knowledge of the quantity of r io n ^ n c le 'of P a K d ^ u b b ^ 1P'Mcth d .f r thc *- voi. 192, no. 5, p. 637 N o" 1921. ^ ^ e n t s , " Jl. Fr.nU.n Ins,., A p r il , 1933 231 dust dispersed in the industrial atmosphere is very im portant, since w ith any given dust the rate of production or the injury w ill be dependent upon the total quantity of dust inhaled. " The author feels that from the hygienic viewpoint the particle count is at present the best index of the degree of atmospheric pollution. The decision as to the size range of the particles which should be included in the dust count is a question requiring careful consideration. Ob viously the size of the smallest visible particle w ill de pend on the magnification and type of illumination used m the microscope, the refractive properties of the dust, and, to some extent, on the visual acuity of the observer. We must bear in mind that our chief interest in this prob lem is in its industrial and hygienic aspects. Primarily we are interested in differentiating between the dust content in ordinary normal atmospheres, not known to be harmful, and certain industrial dusts w hich are known to be associated w ith lung damage. This difference is sharply marked as far as the dust particles between ap proximately y , and 10 microns in diameter are con cerned; but the difference between such normal and ab normal air is masked and lost when we include in our determination the particles of ultramicroscopic size which are present in vast numbers in all air. So far as the upper lim it of particle size is concerned, it has been demonstrated by the South African studies that particles greater than io microns in the longest dimension are of negligible importance. The data con cerning the lower size limit of potentially hazardous dust is not so conclusive. The only available data which throw some light on this point are found in the work of M oir,6*8of South Africa, w ho examined microscopically n o dust particles obtainedfrom two specimens of silicotic lung and found that only 13 per cent of the particles were less than 0.5 micron and about 36 per cent of the particles less than 1 micron in diameter. The majority of the panicles (60 per cent) were between 1 and 3 microns in size. The median size o f the dust was found to be 1.2. microns in diameter. Practically the same results were obtained by Watkins-Pitchford,7 who examined and measured the silica particles in sections of silicotic lungs illuminated by polarized light. Drinker,8in comparing the size frequency of the particles measured by Moir w ith the particles found by him in the sputum of men employed in ore mills, found a close correspondence. The findings of M oir and Watkins-Pitchford have also been corroborated by Mavrogordato,9 who examined dust both w ith light and dark ground illumination, in sections of human and animal silicotic lungs as well as 6 Moir, J., "Report on a Specimen of Dust From Silicotic Lungs," General Report of the Miners' Phthisis Prevention Committee, Pretoria, 1916, Appendix 9, pp. 138-140. ` Watkins-Pitchford, W., "The Situation, Outline and Dimensions of Mineral Particles Visible by Polarized Light in Sections of Silicotic Lungs, Mounted in Canada Balsam." General Report of the Miners' P h th isis P rev en tio n C o m m itte e , P re to ria , 1916, A p p e n d ix 8, pp. 135 138. s Drinker, Philip, "The Size-Frequency and Identification of Certain Phagocytosed D u sts," //. Ind. Hygiene, vol. 7, no. 7 , July, 1925. 9 Mavrogordato, A ., "The Value of the Kommeter," Publication of the South African Institute of Medical Research, no. 17. the dust recovered from these lungs. As a result of his work and that of his colleagues in South .Africa, M avro gordato says: " In the damaged lungs, as far as simple silicosis is concerned, the lesions are discreet, localized, and associated w ith visible particles; whereas, if the ultramicroscopical particles were an important agent, one would expect the simple disease to be generalized and to show no particular association between lesions and visible particles." In connection w ith the lower limit of particle size of dust of pathologic significance, the following pertinent question arises: Aside from the evidence direct or indirect of the non-retention of minute particles of dust by the lungs, w hat evidence is there that appreciable per centages of ordinary industrial dusts ever fragment into those minute sizes less than 0.5 micron in diameter? It is a well-known fact that in most of the fine-grinding operations in use today, such as in the preparation of paint pigments, considerable energy must be expended to obtain a product the particle size of which is less than 0.5 micron in average diameter, and this not in an industry where dust is an evil by-product but where finely divided dust is the chief aim of the whole indus trial process. The best answer to the question just raised, namely, What is the particle-size distribution of industrial dust? would be data of actual measurements of such dust. Unfortunately we have but scant published data to date on the particle-size frequency of dusts in the air of in dustrial establishments. In 1 9 Z 9 , Fehnel10 reported some particle-size dust measurements in connection w ith a dust study of hard-rock drillers in New York City. As a result of his study, Fehnel reported the findings on three samples, which showed the dust, which was less than one micron in size, to vary from 1 to 15 per cent. Most of the dust in these hard-rock drilling operations was, according to- Fehnel, between 2. and 5 microns in size. Badham,11 in studying the dust hazard among sand stone workers in Sydney, measured some 16,000 particles of dust in the air of work places and found that 67 per cent of these particles were about 1.5 microns in size. From his study Badham states: "It would appear that below xo microns there is no selective action by the dust cells of the lung, and that the particles found in the lung have the same size-frequency as those in the air breathed.. . . " In a particle-size study of 10 samples of aerial industrial dusts made by the filar-micrometer method at a mag nification of 1000 diameters, rhe author found that prac tically all of the dust was less than 5 microns in size. Only 1 per cent of the particles was less than 0.5 micron, 18 per cent wxre less than 1 micron, and the m ajority of the dust (73 per cent) was found to be between 1 and 3 microns in diamerer. From all of rhe evidence just presented and in the ab- 10 Fehnel, William J., "A Study of Silica Dust in Hard Rock Drilling in New York C ity," / / . Ind. Hygiene, vol. 11, no. 2, Feb., 1929. u Badham, Charles, Reyner, H. E. G., and Broose, H. D ., "Dust Sampling in Svdney Sandstone Industries," Report of the DirectorGeneral of Public Health, New South Wales, Dec., 1927, p. 74. 232 M e c h a n ic a l E n g in e e r in g sence of conclusive proof to the contrary, it is apparent that we need only be concerned w ith those dust particles between >/, and 5 microns in size, and from a practical standpoint the lower limit of particle size may well be taken at about one micron. The method of dust count ing which we nave used, the description of which fol lows, is capable of revealing particles as small as one micron quite readily, and in the hands of a trained person smaller particles may be enumerated. M any methods have been devised and used for the a glass plate which is kept beneath the surface of the water or other suitable fluid in the collecting flask. The dust is momentarily arrested, wetted bv the collecting fluid, and m this manner trapped. ' The impinger apparatus consists essentially of two portions: first, a source of sufficient suction to"draw the air to be sampled through the sampling device; and second, the sampling device or impinger itself, which consists of a container and the impinger tube and plate. As a source of suction one may use either an electrically driven pump or a compressed-air ejector device. Fig. 3 depicts the essential portions of the apparatus, which consists of a straight piece of Pyrex glass tubing 13 mm m outside diameter and approximately 3 1 5 mm in length. I he tube is drawn down in streamline form at its lower end to a tip w ith a 1.3-mm orifice. A circular glass impinging plate approximately 3 mm in thickness and 2.5 mm in diameter is attached to the lower end of the impinger tube at a distance of 5 mm from the orifice bv means of three glass rods. The collecting medium (distilled water) m the sampling flask is of sufficient volume to keep the impinger plate immersed at a depth of approximately 3 cm. In sampling, the outlet or suction elbow of the sampling flask is connected w ith the source of suction by means of a suitable length (2.3 ft) of non-collapsible rubber tubing. The duration of the samp ing period should be such as to yield a satisfactory suspension of dust for analysis, and is thus dependent on the concentration of dust in the atmosphere. Under the usual industrial conditions, samples of from 1 0 to 30 cu ft of air yield sufficient suspended dust for analysis. Since a sampling rate of 1 cu ft per min is maintained, this wiH require a sampling period of from 1 0 to 3 0 min. The collecting efficiency of the apparatus is dependent upon adherence to the previously cited impinger-tube dimensions and the sampling rate of 1 cu ft of air per mig. Experimental tests of this instrument against suspensions of finely divided silica dust in air have con- purpose of determining the quantity of dust in air. These methods have already been fully discussed in an excellent review of this subject by Dr. Greenburg.12 Suffice it to say that for the purpose of dust sampling in either high or low dust concentrations, the GreenburgSmith impinger apparatus now finds universal favor." ih is instrument has been used by the United States Pub lic Health Service m all of its dust studies during the past DthKnisen-ye^ldrubothl * h1eSre2]aSn0d baebirnogadu.scd b>T otller workers in In this instrument, the air to be sampled is drawn through a glass tube and impinged at a high velocity on ^0nar^> "Studies on the Industrial Dust Problem " b lic Health Reports, vol. 40, no. 16, April 1 7 1925. ' Greenburg, Leonard, and Bloomfield, T. I `The Imoinp-er n.isr W1cc,^ *ePuubbihicc lHiceaalltthh RRe p^o rts, vboyl,. 47=, Un on.ir1c2d, M^ aa r'tcesh P18u,b1li9c3`2H. eflth Se" Sedgwick-Rafter Cell Whipple Disk FIG. 4 SED GW ICK -RAITER CELL AN D W HIPPLE PIECE FOR USE IN C O U N TIN G D U ST PARTICLES M ICR O SCO PE DISK E Y E UNDER A sistcntly yielded efficiencies of 98 per cent at the specified sampling race. Since practically all dusts are, to some extent, soluble in water, it is good practice to analyze the samples as soon as possible. Such practice tends to prevent any undue flocculation as well as any solvent action on the dust par ticles. In the laboratory14 the dust suspension in the 14 For a more detailed description of the dust-counting technique the March 18,ri932Cd " 2 COntnbuclon ln the PuWic H eflth Reports of \PR X L , l S 3 3 233 sampling fluid is filtered through a 315 -mesh screen and then diluted so that the number of dust particles in the microscope field is equal to approximately 50 to 75. Two or more i-cc portions are placed in SedgwickR.iirer cells for counting (see Fig. 4). The microscope :s of the ordinary type, provided with a suitable eyepiece and objective and fitted w ith an Abb condenser. A Whipple disk-eyepiece micrometer (Fig. 4) is placed in the microscope eyepiece and the microscope tube length s adjusted so that the side of the ruling in the eyepiece is 1 mm in length. (We employ a 7.5 X eyepiece, 16:um objective, and a tube length of 178 mm.) As a source of illumination we use an ordinary type of micro scope lamp w ith the iris of the Abb condenser system aaiusted so as to provide a high degree of visibility, in making counts the microscope should be focused throughout the depth of the cell since some of the dust particles may remain in suspension. Since the counting cell is 1 mm deep and the area in the microscopic field is 1 sq mm, each count represents the amount of dust in a cubic millimeter of the sampling fluid. Knowing the original dilution of the sample and the number of cubic teet of air sampled, it is an easy matter to compute the number of dust particles in the sample per cubic foot of .ur. It is of course necessary to make control dust counts on the sampling fluid. In Table 1 a summary is presented of the average dust content of the air in certain dusty industries. This table shows that the highest dust exposure was in the TABLE 2 AVERAGE DUST COUNT IN CERTAIN DUSTY TRADES Dust count in millions of Industry cubic foot of air Slaue-tinishing mills: Floormen . . . . . . . 1598.0 Loaciers........................... Disk-crusher operators. . Taic mimne: . . 1276.0 . . 312.8 jack-hammer drillers. . Muckers........................................ 2159.8 ................. 44 3 Talc-finishing mills: Crushers and cylindermen............................................. 14.0 Packers.......... . 50.1 Marble cutters. Marble carvers.. , ................................................... 3 2 .g 39 1 Granite quarrying: Leyner drillers.................................................................. 1 4 4 , 4 Jack-hammer drillers.. . 112.1 _ Plug drillers............. . . . . 36.9 Cement mill, average of all operations.. Granite cutting: .26.0 Hand pneumatic-tool operatives . . 59.2 Machine pneumatic-tool operatives. 35.9 Attendant labor............................................................... 17 0 Anthracite mining: Miners and miners' helpers........................................... 2 3 1 . 5 Attendant labor........................ . . 31 i Bituminous-coal mining: Coal cutters and coal loaders........................................ ,, Attendant labor............................................... . 112.3 39 Silverware manufacturing: Dusty processes. ... ... 5.2 Non-dusty processes............. .. 1.7 Municipal dust iscreet cleaners): Congested district................... ,, Residential district.... . Cotton industry: 4.1 . . . . 1.8 Carding room. . . . 86 W eaving and spinning ro o m ... 4 .5 slate mills, talc and coal mining, and in the granite cutting industry. Owing to the high percentage of quartz (35 per cent) present in granite, as compared w ith the dusts in the other industries listed in Table a, gran ite cutting is revealed to be the most hazardous of the occupations we have studied. A test of the value of any technique is in the results obtained in its practical application to a definite prob lem. Such a test was offered to us in the study of the health hazards of granite cutters in Vermont. In this study the following investigations were conducted for a period of slightly more than two years on a large group of workers: (1) Examination of the workers to determine 70 60 .) ANNUAL FREQUENCY OF ABSENTEES FROM TUBERCULOSIS 50 40 c 30 0 14) 20 a. o 10 0 vQi__ "o ZQ OL 5 10 A B G ra n ite 0 C D W orkers 100 / j Hard Rock Gold Cement /4 /.5 Iro n General and Sick 5 0 A 3 C J) Rural 36* 4* I* Vermont Deaths Deaths Deaths Age 20*59 'z From Beginning o f Study to Working Up o f Report -- aoout Three Years - among 972 W o r k e r s A , 614:3, 04 ; C, 14$;1)JQ&. FIG. 5 ( a ) A N N U A L FREQUENCY OF ABSENCES FROM T U BERCULOSIS (E IG H T D AYS A N D M O R E ). ( ) A N N U A L D EA TH RA TE PER IOOO PERSONS FROM TUBERCULOSIS their general physical condition; (a) special physical examinations to determine the prevalence of specific diseases of the respiratory system and the lung pathology resulting from exposure to granite dust; (3) record of the nature and severity of disabling illnesses; (4) occupa tional mortality statistics; (5) autopsies; and lastly (6), detailed studies of the nature and quantity of the dust exposure in each occupation. Let us briefly examine the results of this study. The whole group of workers was divided into four sub groups, depending on their average dust exposure. Fig. 5 shows the annual frequency of absences due to tuberculosis and the annual death rate per 1000 persons from tuberculosis among the workers in these four groups. This figure also compares this data w ith simi lar information for other industrial groups. In group A, w hich included hand pneumatic-tool operators and in w hich the exposure averaged about 59 (Continued on -page zt>i) 262 M e ch an ical E n g in e e r ^ g and 4 parts o potassium carbonate, which is boiled for 5 min and then rapidly cooled. The fabric is then stentered on a hot-air stentering machine in such a way that it is dried at a low temperature, being afterward heated for two minutes at 170 C and finally soaped. A catalyst is generally required in the formation of formalde hyde synthetic resins, and this may be acidic or alkaline. The process adds weight to the material and is claimed to increase the dry strength by 30 to 50 per cent and the wet strength sometimes as much as 100 per cent. This is par ticularly important for rayon fabrics because of their weak strength when wet. (Plastics and Molded Products, vol. 8, no. 11, Nov.. 1931, pp. 417, 432- 433. d) 6 Self-excitation, or optional separate excitation from am d-c source. ' 7 Weight and cost low; less than one-half the usua; d-c machine; comparable to 60-cycle transformer equipments 8 Three-phase loading of power lines as comparte tc single-phase 60-cycle transformer sets. 9 Rugged construction of rotor; no windings: no com mutator; no brush wear. 10 Optional direction of rotation. (G. A. Johnstone, Great Lakes Electric Mfg. Co., Chicago 111., in Electrical Engineering, vol 52, no. 1,Jan., 1933, pp l- - lf 6 figs., d) ` T H E R M O D Y N A M IC S (See Power-Plant Engineer ing: Boilers and Heat Pumps j W ELDING Articles appearing in the Survey are classified as c compart live; d descriptive; e experimental; g general; h historical m mathematical; p practical; s statistical; t theoretical Articles of especial merit are rated A by the reviewer H igh Frequency for A rc W elding Dust in Industry EXPERIMENTS with induction generators operating at frequencies ranging from 500 to 9000 cycles per second have shown that currents of such relatively high frequencies (Continued from -page 233) million particles per cubic foot of air, it was found tha: have important advantages for use in metal arc welding and practically 100 per cent developed an established sili for other arc applications of heat. cosis within 10 years from the time o f beginning em There are no surges of more than 10 per cent above normal in either voltage or current when short-circuits are made and broken by wiping the welder's rod holder quickly across the edge of the grounding base. The voltage and current curves (Fig. 5 in the original article) show practically normal con ditions immediately after the short-circuit is broken or made. The machine which the author describes consists of a gen erator of the double-core type designed to operate at 3600 rpm to produce welding currents at a frequency of 900 cycles per ployment. Also, in this group the highest rate was found for cases diagnosed on physical examination as having active tuberculosis. Furthermore, a definite relation was established between length of service in the industry and the prevalence of tuberculosis. In group B were included those workers other than hand pneumatic-tool operators who were also exposed to more than the average plant dustiness. Taking the second. The machine is said to have **the simplicity and group as a whole, the average dust concentration was ruggedness of a squirrel-cage motor, although the length of nearly 45 million particles per cubic foot of air. This the air gap is almost twice that usually employed in an induc group showed the same reflection of a dust hazard as tion motor. The relatively high speed enables direct connec group A. tion to gasoline engines of similar speeds, resulting in portable sets, compact and light in weight, and this machine makes S* practical welding generator with which metal arcs are easy to strike and hold, and good penetration is obtained. It is particularly good where new heavy-coated rods are used and in other work where reversed polarity of direct current is recommended. With a carbon torch this high-frequency In group C, consisting of those occupational groups exposed to the average plant dustiness (about 2.0 million particles per cubic foot of air), silicosis developed much more slowly than in the groups just discussed, and there appeared to be very little excess in the rate for tuberculo sis, w ith no tendency for an increase according to length current is also useful. The arc projects so well away from the of service. Analysis of occupational m ortality over a carbons that it is almost as handy to the work as is a gas period of 2.5 years, however, indicated th at some of the flame. In the case of the carbon arcs the no-load voltage used occupations in this group may have been exposed to a real is the same as for metal arcs. The carbon arcs operate at from dust hazard. 45 to 50 volts, with correspondingly lower current per circuit. It should be noted that this generator is operated at low opencircuit voltage, and is comparable to d-c machines in this respect. Metal arcs are easy to strike and hold at from 65 to 70 volts. Arcs of smallest current values can be held successfully with open-circuit voltages below 100. Among the features of this high-frequency generator that command attention are: Group D was made up of those occupations in which the dust exposure was less than that of th e average plant dustiness. The average exposure for the group was less than 10 million particles per cubic foot of air. Although a certain amount of silicosis wras found even in this group, there was no indication of serious results, even when the workers had been employed for manv years. 1 Multiple circuits for more than one generator; adjustment of circuits. 2 No transients that affect the welding operation. 3 Low open-circuit voltage. simple It is clear from these data that there exists a high corre lation between the dust counts and the effects of this dust exposure on the health of the granite workers. It is obvious, therefore, that the technique o f dust analysis 4 Inherent regulation, no external reactance or resistance described in this paper constitutes a valuable index of the required. hazardousness of dust inhalation, and one from which the 5 High efficiency. degree of hazard may be judged w ith practical certainty 262 and 4 parts of potassium carbonate, which is boiled for 5 min and then rapidly cooled. The fabric is then stentcred on a hot-air stentering machine in such a way that it is dried at a o " temperature, being afterward heated for two minutes at 170 C and finally soaped. A catalyst is generally required in the formation of formalde hyde synthetic resins, and this may be acidic or alkaline. The process adds weight to the material and is claimed to increase the dry strength by 30 to 50 per cent and the wet strength sometimes as much as 100 per cent. This is par ticularly important for rayon fabrics because of their weak strength when wet. (P lastics and Molded Products, vol. 8 no. 11, Nov.. 1931, pp. 417, 432- 433. d A ) ' M ec h a n ic a l E n g in e e r ^ ,g 6 Self-excitation, or optional separate excitation from an d-c source. m 7 Weight and cost low; less than one-half the usual d_, machine; comparable to 60-cycle transformer equipments 8 Three-phase loading of power lines as comparec - single-phase 60-cycle transformer sets. ` 9 Rugged construction of rotor; no windings; no cor. mutator; no brush wear. " 10 Optional direction of rotation. CO. A. Johnstone, Great Lakes Electric Mfg. Co., Chicagc 111., m Electrical Engineering, vol 52, no. 1,Jam, 1933,'pp l-S-V 6 figs., ' T H E R M O D Y N A M IC S (See Power-Plant Engineer ing: Boilers and Heat Pumps) W ELDING Articles appearing in the Survey are classified as c comnan uve; d descriptive; e experimental; g general; h histories' m mathematical; p practical; s statistical; t theoretical Articles of especial merit are rated A by the reviewer. H igh Frequency for A rc W elding J--('RPERIMEKTS with induction generators operating at ~ ' frequencies ranging from 500 to 9000 cycles per second have shown that currents of such relatively high frequencies have important advantages for use in metal arc welding and for other arc applications of heat. There are no surges of more than 10 per cent above normal m either voltage or current when short-circuits are made and broken by wiping the welder's rod holder quickly across the edge o. tne grounding base. The voltage and current curves fhig. 5 m the original article) show practically normal con ditions immediately after the short-circuit is broken or made. The machine which the author describes consists of a gen erator of the double-core type designed to operate at 3600 rpm to produce welding currents at a frequency of 900 cycles per secn The machine is said to have "the simplicity and ruggedness of a squirrel-cage motor, although the length of the air gap is almost twice that usually employed in an induc tion motor. The relatively high speed enables direct connec tion to gasoline engines of similar speeds, resulting in portable sets, compact and light in weight, and this machine makes ** practical welding generator with which metal arcs are easy to strike and hold, and good penetration is obtained. It is particularly good where new heavy-coated rods are used and m other work where reversed polarity of direct current is recommended. With a carbon torch this high-frequency current is also useful. The arc projects so well awav from the carbons that it is almost as handy to the work as is a gas name. In the case of the carbon arcs the no-load voltage used is the same as for metal arcs. The carbon arcs operate at from t 1 , 7 CS' Wuh C0ITPcmdinglv lower current per circuit, t s ould be noted that this generator is operated at low open- circuit voltage, and is comparable to d-c machines in this respect. Metal arcs are easy to strike and hold at from 65 to 70 volts. Arcs of smallest current values can be held successfully with open-circuit voltages below 100. Among the features of this high-frequenev generator that command artenrion arc: ' ,1 MultiPle circuits for more than one generator; simple adjustment of circuits. * 2 No transients that affect the welding operation. 3 Low open-circuit voltage. 4 Inherent regulation, no external reactance or resistance required. 5 High efficiency. Dust in Industry (Continued from page 23s') million particles per cubic foot of air, it was found that practically 100 per cent developed an established sih costs within 10 years from the time o f beginning em ployment. Also, in this group the highest rate was found for cases diagnosed on physical examination as having active tuberculosis. Furthermore, a definite relation was established between length o f service in the industry and the prevalence of tuberculosis. In group B were included those workers other than hand pneumatic-tool operators who were also exposed to more than the average plant dustiness. Taking the group as a whole, the average dust concentration was nearly 45 million particles per cubic foot of air. This group showed the same reflection of a dust hazard as group A. In group C, consisting of those occupational groups exposed to the average plant dustiness (about 10 million particles per cubic foot of air), silicosis developed much more slowly than in the groups just discussed, and there appeared to be very little excess in the rate for tuberculo sis, w ith no tendency for an increase according to length of service. Analysis of occupational m ortality over ?. period of 15 years, however, indicated th at some of the occupations in this group may have been exposed to a real dust hazard. Group D was made up of those occupations in which the dust exposure was less than that of th e average plant dustiness. ^ The average exposure for the group was less than 10 million particles per cubic foot of air. Although a certain amount of silicosis was found even in this group, there was no indication of serious results, even when the workers had been employed for many years. It is clear from these data that there exists a high corre lation between the dust counts and the effects of this dust exposure on the health of the granite workers. It is obvious, therefore, that the technique o f dust analysis described in this paper constitutes a %7aluable index of the hazardousness of dust inhalation, and one from which the degree of hazard may be judged w ith practical c e rta in ty