Document wKq30xanQgOgn9YawQpM4gKxB

FILE NAME: CERAMICS (CER) DATE: 1933 Apr DOC#: CER004 DOCUMENT DESCRIPTION: Journal Article - Dust in Industry MECHANICAL ENGINEERING Published by The American Society of M.echanical Engineers V o l u m e 55 N um ber 4 Contents for April, 1933 T H E BA L A N C IN G OF ECONOM IC FORCES- (PA R T i ) ..................................................... 211 e l i h u T h o m s o n ...................................................................... K . T. Compton 225 d u s t i n i n d u s t r y ...................................................................... J. J. Bloomfield 229 s o c ia l t r e n d s - ...................................................................... . . E. E. Hunt 234 T H E FE R MNI-D I--R A C STATISTICAL TH EO RY OF GAS D E G E N E R A T IO N ----1 . . Vladimir Karapctoff 237 A TH ER M O D Y N A M IC TH EO RY FOR STEAM? . . . . H . E. LongWlll 243 SIG N IFIC A N C E OF SPEED ST A N D A R D IZA TIO N J . Dtckir and W . P. AcrtS 246 Ch a r l e s m a c c a u g h e y s a m e s , 1866-1933 ......................................... 249 EDITORIAL . . . . ... 250 A .S.M .E . BOILER CODE . SU RVEY OF E N G IN E E R IN G PROGRESS . 252 POW ER TEST CODES . . . . CORRESPONDENCE . . ... 263 BOOK REVIEW S AND LIBRARY NOTES w h a t ' s g o i n g o n ...........................................................................................................................271 . 266 . 268 . 269 DISPLAY ADVERTISEM ENTS . . . . 1 CLASSIFIED ADVERTISEM ENTS . . . 16 PROFESSIONAL SERVICE . ... 14 IN D EX TO ADVERTISERS . . .1 8 O FFIC E R S OF TH B S O C IE T Y : A. A. PoiT ii, President E * ir O bbro, Treasurer Ca lv in W . R ice, Secretary PU B L IC A T IO N ST A FF: G eohoh A. Stetson, Editor Frederick L ast, Advertising M jr. C O M M IT T E B O N P U B L IC A T IO N S : L. C. M orrow, Chairman S. W . D udley S. F. Vo o r h u s, Vice-Chairman W. F. Ryan M . H . R oberts C. E. D avies, Secretary tv Committee on Publications -bliihed monthly by The American Society of Mechanical Engincera, Publication ofict at 20ch ta d Northampton Socco, Easton, Pa. Editorial aad Advertising d e p u ta ta a at the head:ia r tm o f the Society. 29 West Thirty-Ninth Street. New York, N. Y. Cable addms,"Dynamic," New York. Price 60 cents a copy, S5JX * year; to members aad a fill i , 30 ce sa i copy. s4/30 a year. Postage to Canada, 75 ceno additional, to foreign coontncs. SI.SO additional. Chances of address m atr be received i t Society headquarters cwo ceka before they arc co be -=ccttve oo the mailing list. Please ceod old as well as ocw address.. . . By-Law: The Society shall not be responsible for statements o r opmioos advanced in papers o r . . . printed ta to =colicatioos (B L Par. >X . . . Entered aa aecood<Uas matter at the Poac Ofice at Easton, Pa., ander the Act of March J. 1179------ Acceptance for mailiof at special rate of p o m p provided `or in section 1103, Act of October 3,1917, a u th o re d on January 1 7 ,1 9 1 1 .... Copyrighted, 1933 by The American Society o f Mechanical Engincera, I A d vertising Section April, 193: THE quantity and the quality of the welding to be done by The Babcock & Wilcox Company in fabricating 14,500 feet of plate-steel pipes for Hoover Dam require the exercise of those abilities constituting welding leadership. This undertaking includes shaping 50,000 tons of steel . . . welding more than 400,000 linear feet of seams . . . stress-relieving the largest pipes ever constructed . . . and the examination of welds with 300,000 volt x-ray equipment that will consume a quantity of film exceeding that produced to date in this country for all industrial purposes. Details of this project, contained in a new bulletin now available, provide further evidence of the resourcefulness of The Babcock & Wilcox Company. . . an organization with every, facility for the production of superior fusion-welded pressure vessels of every size and type. Two publications, one describing the com plete fusion-w elding technique . . . an d the other, containing o brief description of the Hoover Dam protect as a whole ond featu r ing the port to be com pleted by this Com p an y , will be sent upon req u est. Sim ply ask fo r Bulletins S-4 a n d S-10. The Babcock & Wilcox Company . . . 85 Liberty Street. . . New York G-3* BABCOCK ScWlLCDX M echanical E ngineering DUST in INDUSTRY The Sampling and Analysis of Industrial Dusts 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 has emphasized the significance of the quantitative as inhaled dust gain access or arc 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. pects of this problem. A knowledge of the dust content With reference to the quantity of dust present in the air of the industrial atmosphere is required not only tor the of a workroom, it is apparent that when the dust concen purpose of determining the extent of the hazard involved tration is high the exposed person w ill inhale a greater in various manufacturing processes, but is also useful quantity in a given period of time than he w ill when it is in measuring the efficiency of protective devices which relatively low, and since the rate of production of the may be used in the elimination of the dust hazard. The disease is partially dependent upon the total amount of object of the present contribution is to describe the under dust inhaled, this latter fact plays an important rle in lying factors involved and the technique employed in determining the time of onset of the end result. The the study of the quantitative phases of the industrial need for the evaluation of the quantity of dust in the in dusts which may produce injury to the respiratory sys dustrial atmosphere is obvious. tem. Such dusts arc produced by the numerous indus trial operations involving the drilling, crushing, and grinding of mineral matter such as talc, quartz, granite, slate, and cement. The properties of a given dust which determine its capacity to produce pulmonary pathology are the nature of the dust, that is, its 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 10 ytars of research in the field of dust inhalation is the demonstra tion of the fact that, in general, the degree of health hazard associated with the inhalation of any dust, all other factors remaining constant, is dependent upon the mineralogical composition of the dust. For example, it is now well established that the inhalation of certain types of dust, such as granite dust, w ill in time produce fibrosis of the lungs, frequently associated with 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 finally, there arc certain types of dusts which produce little or no lung fibrosis, as typified by marble dust. In general, it has been found that those dusts which arc NATURE OF DUST Research on the problem of industrial-dust inhalation has demonstrated that so far as their fibrosis-producing qualities are concerned, dusts may be divided into three groups: ( i ) those composed completely of combined silica, that is, silicates, such as pure asbestos; (z) 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 earth. 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 ate the harmfulncss 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 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 of the lung, the site where the harmful effects of the dust mke place. It is known that not all of the particles of ` Sanitary Engineer, U. S. Public Health Service, Washington, D. C. Presented at the National Process Meeting arranged by the 7rocas "tries Committee of the A.S.M.E., and held under the aus-ices of 'he Buffalo Section of the Society, Buffalo, N. Y.. June 6 to 8.1932. TABLE 1 PERCENTAGE OF QUARTZ PRESENT IN VARIOUS INDUSTRIAL DUSTS Percentage Kind of dim of quartz Rock-drilling dust (bituminous-coal mine)__ 34.0 Granite-cutting dust........................................... 35.2 Rock-drilling dust (anthracite mine)................ 31.0 Brass-foundry dust.............................................. 19.0 Dust from raw mills in cement plant................ 6.5 Slate-mill dust (Vermont red slate).................. 3 0 Silverware-polishing dust................................. 1.7 Anthracite dusc.................................................... 1.5 Bituminous-coal dust.......................................... 1.2 Cement dust......................................................... less than 1.0 Slate-mill dust (Vermont green slate)............ trace Talc-mill dust...................................................... none Marble-cutting dust............................................ none 229 230 content of dusts obtained in various industries which we have studied. , Is ^U` te ev^ ent r^at. judged by quartz content, rock drillmg occupations in the coal-mining industry and certain occupations in the granite-cutting industry and in brass foundries may be considered as hazardous Tliat this is true is evidenced by the high rates of illness and death from silicosis and tuberculosis in some of these industries.* PARTICLE SIZE OF DUST It has been demonstrated that particles of a size greater than 10 to i z microns in the longest dimension are very seldom found in the lungs. This absence o f larger par ticles is partly due to the fact that the number of such particles greater than io microns in size present in indus trial air is as compared with the lower sizes, compara tively small, and, due to gravity and the protective action of the mucous surfaces of the upper respiratory tract, these larger particles do not penetrate to the terminal portions of the respiratory tract. Hence we need onlv concern ourselves with those dust particles that are less than io microns in the longest dimension. In order to ascertain whether or not an industrial dust is capable of gaining access to the lungs, it is necessary M ech anical E n g in eer in g at a high magnification (1500 to zjo o diameters); from this either an enlarged print may be made, or the nega tive may be enlarged by means of a stcreopticon. The particles revealed on the enlarged print or screen may be measured by means of a millimeter scale. The particlesize dimensions are grouped in classes according to size from which a percentage distribution curve is easily obtained. Fig. i presents the particle-size distribution of talc dust from the air of a workroom in which talc f ig . Z PHOTOM ICROGRAPH OF TALC DUST OBTAINED W ITH T H E O W E N S J E T D U S T C O U N T E R . X 650 F IG . I PARTICLE-SIZE D ISTRIBU TIO N OF TALC DUST to make particle-size studies o f the dust under considcration. In practice the samples for such studies may be obtained by the use of the Owens jet dust counter. ih is apparatus projects the atmospheric dust directly SLr,?"0S'SUCt"mplES bLen purnop^erlySCm0oPuCnCtedJCarnSdi ipex` amminsed Cb0yVCaInsyliPon"e *o7f tsheevn- scopically, using a magnificat"ioVn o f 1000 diammeitoeors(oil-immersion objective), and the horizontal d ia m e S of a representative number of particles measured by means of a calibrated filar ocular micrometer < In another method a photomicrograph of the dust is made T.'^ h e H ^ h was being ground to a very fine state of subdivision The measurements, from which the data for this figure were obtained, were made by means of a filar ocular micrometer at a magnification of 1000 diameters. With this magnification ir is possible to measure particles as smaiJ as 0.5 micron m diameter, while particles smaller than 0.5 micron are easily distinguished at this magnifica r ' a t :'aithough not measured, their presence is re corded. For routine particle-size measurements the photomicrographic method as described by Green* has a decided advantage over the direct microscopic measure ments, in that the task is less tedious and the particles arc measured with more case and accuracy. However f?r 1j PurPoscs the filar-micrometer method should fulfil the required needs. An examination of Fig. 1 shows that only 16 per cent of the particles were found to be less than 1 micron the major portion (65 per cent) being between 1 and' 2.. microns m size. The median size of the dust was found to be 1.5 microns. Fig. z is a photomicrograph o f the same specimen o f dust. P QUANTITY o f DUST As pointed out earlier, a knowledge of the quantity of " A. Pbotomicrogr.phic Method for the Determina- m i Rubber P,gmrats;' " * "- April, 1933 231 dust dispersed in the industrial atmosphere is very im portant, since w ith any given dust the rate of production of 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 in 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 which arc known to be associated with lung damage. This difference is sharply marked as far as the dust particles between ap proximately '/: and io microns in diameter arc 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 limit 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,8of South Africa, who examined microscopically 12.0 dust particles obtained from 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 particles (60 per cent) were between 1 and 3 microns in size. The median size of the dust was found to be i.z 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,* in 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 Moir and Watkins-Pitchford have also been corroborated by Mavrogordato,' who examined dust both w ith light and dark ground illumination, in sections of human and animal silicotic lungs as well as ' Moir, J., "Report on a Specimen of Duit 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' Phthisis Prevention Committee, Pretoria, 1916, Appendix 8. pp. 135 138. ... . . * Drinker, Philip, "The Size-Frequency and Identification of Certain Phagoeytosed D u sts,"//. Ind. H jtitnt, vol. 7, no. 7, July, 1925. ' Mavrogordato, A., "The Value of the Kooimcccr," 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, Mavro 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, what 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 1919, Fchnel15 reported some particle-size dust measurements in connection with a dust study of hard-rock drillers in New York City. As a result of his study, Fchnel 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 dusc in these hard-rock drilling operations was, according to Fchnel, between 1 and 5 microns in size. Badham,11 in studying the dust hazard among sane 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 10 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 chose in the air breathed.. . . " In a particle-size study of xo samples of aerial industrial dusts made by the filar-micrometer method at a mag nification of 1000 diameters, the author found thac prac tically all of the dust was less than 3 microns in size. Only 1 per cent o f the particles was less than 0.5 micron, 18 per cent were less than 1 micron, and the majority of the dust (73 per cent) was found to be between 1 and 3 microns in diameter. From all of the evidence just presented and in the ab- > Fchnel, William J., "A Study of Silica Dust in Hard Rock Drilling in New Y o rk G ty ," //. Ind. H jiiau, vol. 11, no. 2, Feb., 1929. u Badham, Charles, Rcyoer, H. E. G., and Broose, H. D., Dust Sampling iu Sydney Sandstone Industries," Report of the DirectorGeneral of Public Health, New South Wales, Dec., 1927, p. 74. 232 M ech anical E n g in e e r in g scncc 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 have used, the description of which fol lows, is capable of revealing panicles as small as one micron quite readily, and in the hands of a trained person smaller panicles may be enumerated. Many 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 by the collecting fluid, and in 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 electricallv 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 in outside diameter and approximately 315 mm in length. The tube is drawn down in streamline form at its lower end to a tip with 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 by 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 with the source of suction by means of a suitable length (15 ft) of non-collapsible rubber tubing. The duration of the sampling 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 10 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 w ill require a sampling period of from 10 to 30 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 min. Experimental tests of this instrument against suspensions of finely divided silica dust in air have con- riG . 3 e sse n t ia l p o r t io n s o f t h e g r e e n b u r g -s m it h IM PIN G ER APPARATUS FOR DUST SAM PLING 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. Green burg.12 Suffice it to say that for the purpose of dust sampling in either high cr low dust concentrations, the GrcenburgSmith impingcr apparatus now finds universal favor." This instrument has been used by the United States Pubbc Health Service in all of its dust studies durin** the past nine years. It is also being used by other workers in this field both here and abroad. In this instrument, the air to be sampled is drawn thiough a glass tube and impinged at a high velocity on " Greenburg, Leonard, "Studies on the Industrial Dust Problem " Public Health Reports, vol. 40, no. 16, April 17,1925 ' * Greenburg, Leonard, and Bloomfield, 1. J., "The Impingcr Dust Sampling Apparatus as Used by the United States Public Health Ser vice," Public Health Reports, vol. 47, no. 12, March IS, 1932 Sedgwick-Rafter Cell Whipple Disk FIG . 4 SEDGW ICK-RAFTER CELL A N D W H IPPLE DISK EYE PIECE FOR USE IN CO U N TIN G DUST PARTICLES U N D E R A MICROSCOPE sistently yielded efficiencies of 98 per cent at the specified sampling rate. Since practically all dusts arc, 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 laboratory" the dust suspension in the " For a more detailed description of the dust-counting technique, the reader is referred to a contribution in the Public Health Reports of March 18, 1932. April- 1933 233 sampling fluid is filtered through a 315-mesh screen and :hen 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 SedgwickRarrer cells for counting (see Fig. 4). The microscope is of chc ordinary type, provided with a suitable eyepiece and objective and fitted with an Abb condenser. A Whipple disk-eyepiece micrometer (Fig. 4) is placed in :nc microscope eyepiece and the microscope tube length s adjusted so that the side of the ruling in the eyepiece is i ram in length. (We employ a 7.5 X eyepiece, 16:nm objective, and a tube length of 178 mm.) As a source of illumination we use an ordinary type of micro scope lamp with the iris of the Abb condenser system ai)usted 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 feet of air sampled, it is an easy matter to compute chc number of dust particles in the sample per cubic foot of air. It is of course necessary to make control dust counts on the sampling fluid. In Table i a summary is presented of the average dust contenc of the air in certain dusty industries. This cable shows that the highest dust exposure was in the 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 with 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 TABLE 2 AVERAGE DUST COUNT IN CERTAIN DUSTY TRADES Dust count in millions of Industry cudic toot of air Slitc-rimshing mills: Floormcn.. . 1598 0 Loaders.................. 1176 0 Disk-crusher operators. J1..8 Talc mining: Jack-hammer drillers.. 2159.8 Muckers.................. . . 44 8 Talc-Hmshing mills: Crushers and evlindermen. . . 14.0 Packers......... ' . . 50.1 Marble cutters.. Marble carvers............... . }2 8 ... . 19.1 Granite quarrying: Leyner drillers.......... . . . 144.4 Jack-hammer drillers........ 112.1 Plug drillers........................................ . 36.9 Cement mill, average of all operations........................ 26.0 Granite cutting: Hand pneumatic-tool operatives.......................... 59.2 Machine pneumatic-tool operatives......... 35.9 Attendant labor....................................................... 17 0 Anthracite mining: Miners and miners' helpers........................................ Attendant labor....................................................... 2)1.5 }1.1 Bituminous-coal mining: Coal cutters and coafloaders..................................... 112.3 Attendant labor......................................................... 3.9 hi'verware manufacturing: Dusty processes....................... . . .. . 5.2 Non-dusty processes....................... ... 1.7 Municipal dust (street cleaners). Congested district................................................... 4.1 Residential district................................................ 18 Cotton industry: Carding room.............................................................. 3.6 Weaving and spinning room ... ... . 4.5 Deaths Deaths Deaths gt 20*5$ From Beginning o f Study to Working Up o f Report - about Three Years - among 972 W orkers. A., FIG . 5 (_a) A N N U A L f r e q u e n c y o f a b s e n c e s f r o m t u b e r c u l o s is ( e ig h t DAYS AND m o r e ) . ( ) A NN U AL DEATH RATE 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 with simi lar information for other industrial groups. In group A, which included hand pneumatic-tool operators and in which the exposure averaged about 59 (Centm ud m psf? - 'i- '.it- 262 M ech anical E n g in eer ^ and 4 pans of potassium carbonate, which is boiled for 5 min and then rapidly cooled. The fabric is then stentered on a 6 Self-excitation, or optional separate excitation from Jn, d-c source. ' hot-air stentering machine in such a way that it is dried at a 1 Weight and cost low; less than one-half the usua, <j.( I low temperature, being afterward heated for two minutes at machine; comparable to 60-cycle transformer equipment: 170 C and finally soaped. 8 Three-phase loading of power lines as comparte ,, A catalyst is generally required in the formation of formalde single-phase 60-cycle transformer sets. hyde synthetic resins, and this may be acidic or alkaline. 9 Rugged construction of rotor; no windings; no com The process adds weight to the material and is claimed to mutator; no brush wear. increase the dry- strength by 30 to 50 per cent and the wet 10 Optional direction of rotation. strength sometimes as much as 100 per cent. This is par ticularly important for rayon fabrics because of their weak (G. A. Johnstone, Great Lakes Electric Mfg. Co., Chicaec strength when wet. (Plastics and Molded Products, vol. 8, 111., in Electrical Engineering, vol 52, no. l.Jan ., 1933, pp N -V no. 11, Nov., 1932, pp. 417, 432-433, <M) 6 figs., ) ' TH ERM O D YN A M ICS (See P ow er-P lant Engineering: Boilers and H eat Pum ps) W ELD IN G Articles appearing in the Survey are classified as c compara tlVC; d descriPtlve; ` experimental; g general; h histonca! m mathematical; p practical; s statistical; t theoretical Articles of especial merit are rated A bv the reviewer ' High Frequency for Arc Welding L'XPERIMENTS with induction generators operating at ' frequencies ranging from 500 to 9000 cycles per second Dust in Industry ( Conttnutd from fa^e 2jy ) have shown that currents of such relatively high frequencies m illion particles per cubic foot of air, it was found tha: 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 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 practically roo per cent developed an established sii; cosis w ithin ro years from the tim e of beginninc em ploym ent. Also, in th is group the highest rate wa> found for cases diagnosed on physical exam ination a: having active tuberculosis. F urtherm ore, 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 thar erator of the double-core type designed ro operate at 3600 rpm hand pneum atic-tool operators w ho w ere also exposed to produce welding currents at a frequency of 900 cycles per to more than the average p lan t dustiness. T aking the second. The machine is said to have the simplicity and group as a w hole, the average dust concentration w 2< 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 a 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 nearly 45 m illion particles per cubic foot of air. T.n: group showed th e same reflection of a dust hazard a: 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 in other work where reversed polarity of direct current is appeared to be very little excess in th e rate for tuberculo recommended. With a carbon torch this high-frequency 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 o f occupational m o rta lity over a carbons that it is almost as handy to the work as is a gas flame. 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 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. period of z j years, however, indicated th a t some of the occupations in this group may have been exposed to a reel dust hazard. Group D was made up of those occupations in which the dust exposure was less than th a t of th e average plan; dustiness. The average exposure fo r th e group w as less th an 10 m illion particles per cubic foot o f air. A lthough 2 certain amount of silicosis was found even in this group Among the features of this high-frequency generator that there w as no indication of serious results, even w hen the command attention are: workers had been employed for many years. 1 Multiple circuits for more than one generator; simple I t is clear from these d ata th a t there exists a h ig h corre iK. adjustment of circuits. lation between the dust counts and th e effects of this 2 No transients that affect the welding operation. dust exposure on th e h ealth of th e g ranite w orkers. It is I 3 Low open-circuit voltage. obvious, therefore, th at the technique of dust analysis lI' 4 Inherent regulation, no external reactance or resistance described in th is paper constitutes a valuable index of the t required. hazardousness of dust inhalation, and one from w hich the i 5 High efficiency. degree of hazard may be judged w ith practical certainty p 1M ki