Document evydaqywRyKEryojj1z10YkBE

FILE NAME: Engineering (ENG) DATE: 1944 June DOC#: ENG014 DOCUMENT DESCRIPTION: Dust as an Industrial Hazard A MONTHLY MAGAZI NE TOR E N G I N E E R AND CONTRACTORS CONCERNED WITH 4I Heating V entilating COMMERCIAL. INDUSTRIAL AND INSTITUTIONAL AIR CONDITIONING. REFRIGERATION, PIPING, HEATING. VENTILATION )-.<-mU h&l THE INDUSTRIAL PRESS President ROBERT E. L'JCHARS Vice-President and Treasurer EDGAR A. BECKER Secretory ERIK O EERG Zdiio iia l Editor CLIFFORD STROCK Asscclcte Ed-far N. N. V/CLFERT HEATING AND VENTILATING is c.-blished rrc-rhly b> The Industrial Press a : !4E Laroyette Street, New Yc'< 13. N. Y. Yearly sub scription Ir ~he Ur.i+ed States, Spam, Sou*". America, Mexico, and Canada, $2.00; in a" other coun ties, $3.C0. Slnaie copies 30 cents. Entered, os second class matter, rorii 18. 925, ct the Post Office, New Ycr't, N. v., under the act ot Mo th 3, I 79. r,VW'tiCf. esyieteniaiiiiei. Eastern Reoresentctives DV/'G-" COOK HARRY J. TV/INE 1 4* Lcfc/e-ie Street Ne* Yor< ! 3, N. Y. V.'estern Reoresentative GEDRGE G.TURNER 22c Nortn La Ss^e Street v-^lCOCO CONTENTS F O R J UNE , 1 9 4 4 V O L U M E 41 NUMBER 6 D u s t Collecting S y s t e m in G u n stc c k P l a n t .................. Benjamin 5. Mziir. G rinding W h eel Q uality Im proved by C ontrolled Air I. C. Baker D u s t as an In d u s tria l H e a lth H azard . ........................ F. II'. Hutchinson Ventilation for Welding Booths V. Ii. Ringquii: Ventilation for Radium Dial Storage . . .......................... Off Again, On Again .............................................. John ], 1Voo'jer.dcn Blueprint of Post-W ar Realities-- Coal for H eating and S te a m G en eratio n ..................................................................... Irxin R. IIofrr.cn S o m e N otes on R a d ia n t H eating ........................................... T. !!'. Reynold: W e a t h e r O b se rv e rs H av e Difficulties ................................... C en tra! P l a n t H eats 45 Buildings ............................................ F. A'. Hollingtxorth . Building B razil ................................................................................. W a s h in g to n News ........................................................................... Boring F. Overman N e w s of th e Month ........................................................................ B rief R ev iew s ................................................................................... N e w s of E q u ip m e n t a n d M a t e r ia ls ....................................... D egree-D ays f o r A pril, 1944 ...................................................... W it h th e M a n u f a c tu r e r s ............................................................. R e feren ce D ata 271-272 ............................................................... P e rs o n a ls a n d P ers o n n el ............................................................. G ettin g P e rs o n a l ............................................................................. A rm y-Navy " E " A w ard s ............................................................. N ew C atalo gs ................................................................................... in d u s tria l D egree-D ays for April, 1944 .........' .................... Coming E v e n ts ............................................................................. 51 55 , . 64 ,. 64 . . 65 . . 81 . . 81 .. 82 84 . 86 . . 88 . 90 92 100 . 104 .. 104 . 107 . 110 . 110 . 111 . 113 . 113 Cccyr-ght. 1aa, oy The Industrial Preis MEMBER Audit Bure o? Circulation Associated Business Papers L 1i NEXT MONTH'S ISSUE Process pii-mz is a subject that readies out into many industries. Startina v. :;!i our July issue- Harry D. Unwin, of Albert Kahn Assodai' il A-ihitocts & Knginoors. Inc., will present the first of a si-ni- ii a.-iu-b-s on and layout of process piping in stallation!- Dust as an Industrial Health Hazard F. W. HUTCHINSON Assistant Professor of Mechanical Engineering, University of California, Berkeley, Calif. ^ i t r i h e a l t h problem inline irom dust in Indus try is one cf increasing seriousness. Socially, ec'r.omicallv and legaliv it has become evident that immediate steps must be taken to combat the hazard represented bv wholesale industrial exposure to the pr.eumoconiosis-rroducinp dusts. Pneumoconiosis, in rr.snv of its forms, is incurable. Thus consideration c: the problem which it represents is based largely <-' methods of dust reduction and removal and is therefore as much a responsibility of the engineer as it is of the physician. Fortunately, medical knowledge and engineering ecuinmcnt have progressed to such a point that rvropnition cf hazardous conditions and availability of methods for correcting them will now permit a ccmrlete. practical and economical solution of the emblem. Un:ortur.ateiv. prejudice and fear have surrounded the entire subject with such an aura of suspicion and distrust that neither workmen nor emoltvers have until recently been willing to acknowltdre the hazard or recognize the need for preventive ~.a?\:res. In addition, the slew action of the disease ' c.ed with failure or. the part of many physicians aenusint themselves with the proper diagnostic m-nhods has made it difficult for the worker to es tablish his claim for compensation in the event of Iniurv and equally difficult for the employer to : ;"r j iumself neair.st fraudulent claims; it has been aid -hat silicosis claims constitute 'one of the. most v j.C"preae of .ecru rac/tci>. Workmen have bitterly opposed adoption of the exacting emolovment qualifications and periodical nhvsicai examinations of those exposed to dust which art essentia! to medical control. "Vet, t is essential >--* --.e-'sons having a predisposition to tuberculosis c' a :ow nasal filtering efficiency be excluded from the ustv trades. Similarly, protection of the worker ue be removed from exposure at tne f-it indication of iung damage. v __ .'ivers. on the cth.er hand, have adopted the , , -* of view that most claims of silicosis are unfair and ar ur.scrupu'ous attemot to take advantage of them. Tl-e exrlanaticr. behind an employer's unwillingness .. acknowledge ti.e hazard is not unreasonable. The diseasesarc almost invariably of long duration . j f-eQ-jcmlv are not discovered until many years exposure has ceased. Thus many employers ; r.ow in the ci.fhcu'.t and alarming position of fac:r. claims for disease which is a result of exposure re"ccr.cvtior.s *"nt existed in their plants 10 or 15 U - :; aco; at ci.r.t time they were unaware of the maith* hazard associated with dusty atmospheres :.'d zor.seque*:lv. though, tb.ey might have had every desire to furnish their employees with full protection from occupational injury, they cid not take the "special care" which is now known to be necessary. Wilson states: "Most well-intentioned employers may be said to have used `reasonable care' in past years and--considering their lack of knowledge-- this is now their best defense in damage suits. How ever. from now on, with tne spread o f . . . available know ledge... only `special care' will safeguard the interests of employer and workman alike. Recent interest in dust diseases has built up an extensive literature; theories have been confirmed with experimental evidence and innumerable case histories c: individuals and of entire groups are available. In contrast to the widespread ignorance of ten vears ago. it would probably be difficult at the present time to find a worker in the dusty industries who lias net at least heard of silicosis, or an employ er who is unaware of the crippling damage suits which will face him if his employees, through failure on his par. to take the necessary preventive mea sures, contract the disease. The cost of dust control is often far less than the cost of one damage suit. Jury awards in silicosis cases of '*0,000. $17,000, 22,500. 25,000 and like sums are matters of record. In the St. Louis area alone there were, some time ago. over 2000 suits pending. A Missouri mining company, as another example, faced claims aggregating 5.000,000 and spent 500,000 in out-of-court settlements of a few of them. _ The purpose of this article is to review the liter ature on the physiological enects of some of the haz ardous industrial dusts and to summarize present- day criteria acceptable as a basis ior the design pf dust control sv'tems. Silicosis Silicosis ci>ease of *.!';e 1ur.zrs cai:sed by the inhalador, [ dus t contain 'Vrr f 51:ica. Some authorises eh eve. but tills :act has not peeri estab- hiked, tha- .he ini;lalation cf sill cates is also a caus- ative factor. Jjuurcb!i ar*d Progress'.', e. The important facts a b o u t t h i s d i s e a s e a r e t h a t . :for p r a c t i c a l p u r p o s e s , it is progress:ive a n d in cu rab le . T h e q u alification " for practica, r jrpotes is n e c e s sa r y b e c a u se recent in* v e s t i g a t i o n -- s u g g e s t t h a t u n c o m p l i c u t c u sih e o si? not pre ure - iv e : h o w ev e r, ti ,e c o n tin u e d ex isten ce of a c a s i k : ' ; c o - i s w i t h o u t : ::c o n - e t c : c o m p l i c a t i o n s is so r a :e time, from the st:n d p o in : o f social c o n sc o n e r i -. ti .v: d i s e a s e c a n in it s e i f b e r e g a r d e d a s p r o Jic- . ! : t h e m e d i c a ! h u ratnre t h e " p r o g r e s s i v e " C7 viewpoint 5 the one which has been most w:d< y Metallica" and. with reference to dust, warned ids i adopted out the possmie futtire* significance of t .c reader to beware because it ""penetrates into the I recent findings is promising. _ windpipe--eats away the lungs--implants consump- ' With reference to the "incurability** of silicosis, lion in .the body." He called attention to the fact ' ccent work has also indicated the possibility of a hat the death rate among Carpathian miners was solution but it is as yet too soon to Iio.g out oi great that a wife could often outlive six husbands. for savsiartnrv mcdicai Treatment. One promising The passage ot time has done little to alleviate the medic.: consists in the administration of thyroxer.c: hazard. The development of pneumatic tools has lea the investigators report Uiat: \r a great increase in the dust concentrations at "Thvroid therapy may possibiv not on:y prevent tending the grinding, polishing and cutting of stone. the development of silicosis, hut may also arrest The death rate among Barre granite cutters, for ex its further prepress and possibly reduce to some ample. increased from 1.5 per 1.000 in the year 1890 extent the degree of fibrosis already existing." to 19.6 per 1.000 in 1924, an increase attributable to The above remarks cn the "progressiveness and the introduction of pneumatic equipment. When one incurability*' of silicosis have been included because realizes that a threshold concentration of 5 miliion thev show how very far the medical profession has particles per cubic loot is required to constitute a vet to go to achieve a solution of the silicosis prob silicosis hazard (for dust made up of 100% free lem. In terms of concrete present-day gain, the sum .-ica). it is then evident that there are many indus iota! of the best that medicine can now offer is not trial operations today which represent health haz ,f much vr.iuc. When dealing with contagious dis ards that did not exist prior to the introduction of eases such as smallpox and Spanish influenza, it mechanical equipment. has been possible to achieve a satisfactory treatment Manv estimates have been made of the number as a first step toward the elimination of the disease of persons exposed to hazardous concentrations of itself; in the ease of silicosis, a non-contagious dis silica Just, but such estimates arc usually based only ease, the only advance of real significance which i nn industrial exposure. When account is taken of possible is an advance which must be brought about the fact that 60% of the earth's crust consists of pv tiic application of basic engineering principles-- silica the likelihood seems great that such estimates the reduction of dust concentrations at the breaming n:c conservative. Lanza and Vane estimated that zone to a point such that a health hazard no longer the number of industrial workers exposed to the exists: only in this way can silicosis be eradicated. silica dust hazard is in excess of half a million in If permitted to run its course without complica those industries in which the processing or handling tion. silicosis will lead to death by suffocation--the of siliceous material is of basic importance; this esti luncrs becoming incapable of maintaining a gas trans mate docs not take account of the many workers fer sufficient to sustain life. Usually, however, ter exposed as a result of the industrial use of silica as mination occurs as a result of complications such as a filtering agent. tuberculosis or heart disease: a definite correlation In one other respect the silicosis hazard has not has been established between silicosis and tubercu v e t been evaluated. As already mentioned there is losis. but an explanation is, as yet, lacking. a definite relationship between silicosis and tubercu With reference to tuberculosis a study of axe losis. This fact leads to the probability that in any grinders and polishers showed a death rate of 1,900 community in which there is a large number of sili 'per 100.000 from tuberculosis as contrasted with 15C cotic there will be a decided familial tuberculosis per 100,000 for the general population of the same hazard. Fortunately, however, this danger is some state. In this study the death rate of all workers in what lessened as a result of the long incubation the dusty trades investigated was used. More strid period which is found with silicosis-- by the time a ing figures and more significant ones were obtamec workman's lungs have reached the stage at which from a Massachusetts investigation in which the tuberculosis is most likely to set in it is more than tuberculosis death rate of 9ol silicotic quarry work p-obabic that his children will have grown past the ers was compared with that for the general popu.a- nee at which the danger of their contracting the dis tion and found to be forty times as great. ease is greatest. Ilacheround and Extend. The name silicosis :s c: That silicosis is definitely related to a particular lelativeiy recent origin, but the existence oi me kind of occupational risk is dcmonstiated by the health hazard associated with dusty work has beer, data fiom examinations (X-ray) of 2500 workmen i ,,'cognized by medical men for many centuries. from all departments of a typical "heavy industry '; l*iom the literature of the period we find that m: : 8 9c had silicosis, but 90.0% of those affected were Ptolemics knew of it. Pliny the Elder referred m foundry workers. The great importance of the silica mc "stone cutters' disease" and devised a crude hazard is clearly indicated from the following com respirator for the protection of miners: Aristom parative mortality figures (from a 1933 publication warr.ea Greek workmen against the inka'.aoon o: <,i Hollis and ^ ulo) ! dust. Hippocrates, three centuries before Christ, 1000 for standard population (all causes for noticed that his surgical knives were dulled by c..s: age? 20-63) in th.e !ungs of stone workers. In the 16th cent..:;- l"n4 lor idea group (roice- Agricola. a mining engineer, wrote "He K- l/67 for non-silica group 58 J U N E , 1944. H E A T I N G A N D V E N T I L A T I N G The silica uiuup (above) showed only three enures c: death (diabetes appendicitis, digestive diseases) which did r.r; differ significantly from the general cro;:n. The significance of these figures is at once apparent when it is considered that an estimated ] ;0.003 wcikers in the United States have silicosis ir. some decree. Dcz-cieminent o' the Disease. The time required :acaoaeitatloit due to smco-is has been the sub* iect of a ercat deal cl attention, but as yet no generaliv accepted conclusions have been reached. Aprarcr.tlv th.e period of exposure preceding contrac tor. of the disease is a function of the dust concen tration. nature of the dust, nature of the work and individual physical idiosyncrasies. From a study of 9.c00 stone-cutters in the Ruhr it is concluded that 15 vears exposure are required to show slight sili cosis and 20 vears to cause incapacitation. This s.-.rr.c studv reveals that 63% of the deaths among silicotic? occur fiom tuberculosis complications. In porcelain workers silicosis develops slowiy but pro gress!vclv: nice second stage is usually not reached until after 10 years. Among sandstone workers the minimal exposure has been found to be 11 years while for iron miners an exposure of 4 to 5 years mav be responsib'e for the appearance of lung chance* 4 to 5 vears after the exposure has ceased. !r. contrast to the above relatively long incubation periods arc those found among workers engagedin sand-blasting and in the manufacture of abrasive ;_ros: in these occupations on!}' 3 or 4 years may vcctic the onset of the disease. Likewise, an exam.nation of 175 men engaged in rock drilling showed that 50% were affected in less than ope year. There is a good reason for believing that under rarticularlv heavy dust concentrations silicosis takes r.r. acute form a.nd may appear after an exposure of -::lv ?. few months.' Not soon forgotten will be the case of the Hawk's Nest Hydro Plant on the New River. Some 4000 workers, mostly negroes, were employed for wages of 3.00 for a la-hour day; in a relatively short time after completion of the tunnel v.crk 475 of them were dead and an estimated 1500 ethers incurably ill. This case was investigated by a committee in the House of Representatives before ',vhnm witnesses testiiied that, In the tunnel 10 dri!!' were ir. operation at once and you could not *ee Ten feet ahead of you even with the headlight of the conkey engine-'. Workmen were so thoroughly covered with a silica dust that "you could not tell a white man from a colored man, 15 feet away . It wa> this case that a senator from West Virginia de scribed as "the most horrible industrial disaster in the history of the world". It was of this case that Representative Marcantonio of New York charged .hat 169 workers had been buried unidentified be cause the undertaker had "lost" his records. On the basis of all evidence which has yet been brought for ward it would seem to the impartial investigator th.jt the Hawk's Nest Tunnel should remain a tragic -minder tc the engineer of the need for consider- WFATtNO ANH VC-NTII 4TIN IIINC 1AAA ation o f human values in the solution of engineering problems. The above case is'only one of a number of similar but less sensational cases which have shown that there is a real pr -sibility of contracting an acute form of shicosis if work " in an atmosphere having an extremely high concentration of siliceous dust. Experimcr.tallv the possibility of acute silicosis has been demonstrated bv laboratory tests on animals; for exposures of eight hours a day to concentrations of 200 midion particles per cubic foot or more it has been shown that the last stage of silicosis may be expected in a relatively short time. Size- of Hazardous Dust. The importance of par ticle size in determining the hazard associated with dusts has received a great deal of attention. Par ticles 25 to 30 microns in size will usually settle out rapidlv and are therefore not likely to be breathed in quantities sufficient to constitute a hazard. How ever. particles of this magnitude (such as pollen of the Giant Ragweed or wood dust in carpenter shops) mav be responsible for hay fever or for various types of asthma. In general, particles greater than 10 mi crons are caught in the trachea, large bronchi and mucous membrane. Particles around 5 microns go to the respiratory tract, but few of them reach the alveoli where the l micron particles arc most numer ous. Policard mace a detailed examination of the lungs of two silicotic miners and found that 50% of the particles were less than .4 micron and 75% less than l micron; his findings should be used with care, however, because it is very probable that the dust distribution in the ungs is a function of the distribu tion of particle size in the inhaled dust--thus Poli- card's findings may be applicable only for the con ditions under which the men whose lungs he examined had worked. The smaller particles are obviously the most dangerous since, on a weight basis, they offer a much iarger surface than do the larger ones. For this reason dust counts are of more value in evaluating the hazard associated with a dusty environment than are gravimetric dust de terminations. . The dust particles that are most effective in the causation of silicosis arc of a magnitude so small that they are not perceptible to the human eve. A micron is l/ 1000 of a millimeter or about 1/25.000 of an inch. As has beer, shown, the particles most important in silicosis are in the neighborhood of .5 micron o: 1/50,000 of ar. inch--this represents a di mension c: the same order of magnitude as the wave lercih of that form of radiant energy which we recognize as light. I? one cubic inch of quartz were broker, into cubes .5 micron on a side enough par ticles would be formed to create a silicosis hazard in a 2 30,0X) cubic space. The determination of mean dust sizes was the purpose of a series of comprehensive studies con ducted bv the 1'. S. Public Health Service: examina tion of 15.000 outdoor dust particles showed the media:! *.ze lo be .5 niemn--nearly all were less SO than 1.0 micron: in contrast. only 21c/c of 6/KK1 in dustrial dust particles were less than 1.0 micron, the majority being between 1 and 3 microns and me mean 1.5 microns. Hatch and Moke investigated foundry dusts and found that composition is a function of particle rizs: the proportion of combustible matter and acid sol uble iron, carbonates, etc., increase with dccreat.ng size; the proportion of clay and other silicates \a..cs without a definite trend with size; the quartz be comes less as the size decreases and for particles un der 2 microns (which comprises 907c of the tctal number) it is from 1/5 to 1/25 of that found in the particles greater than 10 microns. These findings emphasize the necessity of taking dust samples di rectly from the contaminated air and not utilizing "rafter" or any other kind of settlement sample which does not contain a representative size distri bution. Hazardous Concentration. Permissible concentra tions of dust vary with size, composition, and the dust retention characteristics of the individual, lh e latter factor is one which offers some hope from the standpoint of preventive medicine. Practically aL thm ; known of the dust retaining characteristics of the human nose is attributable to the work o: one man--G. Lehmann. This experimenter has shown that the dust fixation in the nose varies from 2^c to 7 5 7 and 1S almost completely independent o: such factors as the condition of the nasal secreuon, the rate of air currents, the degree of concentration or chemical composition of the dust, the widtu or narrowness of the nasal passages; seemingly, r.xariou is a function of the vortex formation and re after ra'fsce through a restriction. 'o'iow from the tV.lowinz tests: 0: 4o s'or.< ..........n...\ c .: .. - * - tv." hrr; nave smcosis: o : cj store tions*less"ihan 29% only 2 were healthy. After ex aminin'.: the above data Lehmann concludes ir.a._ "applicants for work with poor dust fixation capacity >r.ouL! not be allowed to work where a menace o: rihcOMS CXIStS . . A> a result of 418 experiments with magnesium oxide and calcium carbonate. Carlton F.. Brown e:ve? die following relationships between dust re tention and other factors: P c Cent Retention is inversely proportional to 1. Re'pirati.m rate for rates below 2U per minute. An increase above 20 per minute i> apparently jolioucd oy no changes ... per amt retention. __ 2. Minute-volume of air breathed. Imp ; ably results from increase in respiration rate with minute-volume. Per Cent Retention is unaffected by 1. Volume per respiration. 2. Vital capacity. a. Relative humidity. llte same investleator found mat the peici,..*^-^ 60 inaenesium oxide retained during norma: breattutf ..p: while at rest varied little from about 60/c at a cco- ^ centration of 10 mg. Above 10 mg. the retenti* changed but little, but as the concentration dropped ; f.. below 10 mg. the retention rapidly approach . A; 1007. .. ^ The relation between dust concentration ar.d t u - ? incidence of silicosis has been studied b\ man. is- .. ^ vestigators, but no general empirical relationship ... has as yet been established. One commonly used \ rule (proposed by Drinker) recommend^ the acccp- tance of 5 million particles per cubic foot ar tit minimal permissible dust concentration tor pert . - silica and 50 million particles per cubic foot for dot: - - 1 that are very low in silica. Some evidence >uzrrti r that this rule is unduly conservative for dusts which 7 ; contain little silica and an alternative which is w-idy 'p* used is to limit the total dust count to a value ~ * that the product of the dust concentration by \'zt . percentage of silica be less than 5,000.000; tmi r.'.r , cives 100,000,000 particles per cubic foot a< :h minimal concentration for non-siliccous dust'. Physiological Ejject. The lung condition kr.cn " as silicosis results only from the inhalation m n..:- V bearing dusts. Why silica possesses the ai i ::y bring about this condition has been the mrur:: H much investigation and theories of silico?;- <:r at present responsible for considerable corn: '-roy _' Physiologically--excluding the effect ot o tions--silicosis affects the normal functi"n:i.; : ; body in the same way that the formal.or. <: car affects the efficiency of a heat transfer dev..--. It the heat exchanger the hot and cold fluids me sepa rated by an exchange surface and the depo-r. scaic on this surface reduces its effeciivene.-s as it ] :;x.e btccrr.e stilficier.t r iiea'. y it will be impos-ibic to secure the transfer r: -r, arccrr.r'.isr. the rurrese for which the 'cr wis iirntisriy. ir*c unij is 1 su.* face through which oxygen is transferred iiom the air to the blood. Tire formation of scar tissue re duces the effective transfer area and eventually tr.e lung is unable to accomplish its purpose--death from suffocation is the result. Asbestosis Asbestos dust is second only to free silica in the magnitude of health hazard which it represen.5. Asbestos is a fibrous material of varying compos.tion. but is usually made up of approximately 43 7 macnesia, 40 c/c silica and 147o water. Oxide of iron is frequently present and appears as dark particles aniniie the translucent fibers--the fibers are of such lenuth and fineness that cloth weighing less than 8 oz. per square yard has been made from them. The lung condition resulting from the inhalation of this dust 5 known as asbestosis and resembles silicosis in its main clinical aspects, but differs djt to the enhanced rate of development. Under a\ craze industrial conditions the length of employment in fatal cases is only about one-half that which i- usual J U N E , 1944, H E A T I N G A N D V E N T I L A T I N G for skicosi-s. It is estimated that there are in the United States approximately 10,000 men exposed to this hazard as a result of work in the insulating, asbestos cloth, and similar industries. As is true of the silicosis exposure estimates, this figure does not take into account the number of persons exposed as a result of employment in the process industries where asbestos finds use. under various trade names, as a hirer aid. In one respect asbestosis is less dead ly than silicosis--that is. there is seemingly a lower susccrtibilitv the supervention of pulmonary tu berculous. The danger of contracting the disease is aoparemlv n t influenced by cither age or sex. Like silicosis, it is incurable and progressive; a case is re ported of a patient who was exposed to asbestos dust for one vear and whose sputum showed the presence c: asbestosis bodies fourteen years later. \ erv few data are available on the relation of dust concentration to the incidence of the disease. No rmrimnl safe concentrations have yet been set up and information is scant as to the conditions in those niar.ts where n hazard is known to exist. It has been determined. However, tnat tire asbestos dust en countered ir. tabncatir.cr plants is free of ;uica when air is floated at the breathing level and that the car.crcr of the dust increases as the quality or length cf the fibers increases. Miscellaneous Siliceous Dusts Many siiiceou- dusts other than quartz and asbes:s have beer, carefully investigated. Talc-- a siii, c containin'." 62% silica--has been shown to be -..-consib'e a form <<f pneumoconiosis wnen in haled in lame quantities. One group of investigators report that SOT, of the talc workers whom they ex : --ined were affected and about 12% had tubercuo.ij; The same report snows that talc containing OT tremoiite -is much more dangerous than talc containing 40 T trcmclite, but an explanation is lacking. . The action of cement on the lungs is not definitely known. German investigators say that it produces cniv an inert deposit in die lungs, but American re ports show that the frequency of disability from respiratorv diseases in cement plants is about double that found among employees :n non-dusty manu __r;r r. plants: absence from work was also twice ^ f ^ c r . *. "dct experiments snew tns.t ce- **:ke, limestone or.d srypsum produces an ad sorptive reaction; the dust disappears from the -mV-neai cav.tv witnout tr.c production of scar 0.55US. Slate ( i / 3% quartz) in concentrations of 700 million particles per cubic foot produces a fibrosis and pneumoconiosis, but few cases have been known to progress seriously. On the other hand, there is -easen for bc.icvmg that clay and slate dusts are responsible for a high incidence of tuberculosis. I '-'ian >r-v*_c'"eators have studied trie oust hazard i- spin:...ns nulls and report that the silicos,:, 'm-wrnrd is apparently negligible. Mineralogic analy H E A T IN G A N D V E N T IL A T IN G , J U N E , 1M4 sis of such dusts brought to light the interesting fact that their composition is similar to that of the soil in which the cotton was grown. Non-Siliceous Dusts * Apparcndy there is a great difference of opinion as to whether or not non-siliceous dusts are harmful cither to normal or tubercular persons. The data are so scar.: that a review of the literature must con sist essentiallv of a catalogue of the few and scat tered investigations that have been made of particu lar dusts. General conclusions can not be drawn and an extension of available data to dusts of even the same mineral family is hazardous. German investigators have studied a number of different carbon dusts and rate them in the order of hazard which they represent: lignite, coal, graphite, charcoal, soot. _ A statistical studv of the health hazard in a large American company which manufactures artificial abrasives led to the conclusion that persons who have had pulmonary tuocrculosis should not be al lowed to work where they will be exposed to dust from abrasives. The dust in this particular plant was aluminum oxide combined with silicon carbide and the incidence to tuberculosis was 1 1/2 times as crcat in the dusty departments as in the non-dusty. In this connection it is interesting to note tnat other investigators hac prcviouslv reported aluminum ox ide as not bcinz a "factor in the production of silicosis --thus a distinction must be drawn between the fibrosis-forming ability of a particular dust and its dancer throuoh increased susceptibility to pulmonary tuberculosis. This leads to the conclusion that, the claim is unwarranted that a dust is not harmful merely because its reaction on lung tissue is inert. The U. S. Public Health Service has grouped dusts (siliceous as well as non-siliccous) in three classifi cations: _ t 1. Those causing an inert reaction, the amount of dust in the peritoneal cavity remaining approxi mately constant: soapstone, carborundum, jewel er's rouge, anthracite coal, bituminous coal and precipitator ash. _ 2. Those causing a proliferative reaction, nod ules cor.tinuino to increase in size: quartz, chat and fiir.L _ 3. Those causing an absorptive reaction, dust disappears from the peritoneal cavity, but scar tissue is not formed; calcite limestone, precipitat ed calcium carbonate, gypsum and cement. A simi'ar list of dusts has been prepared by Haynes who carried on a long scries of animal ex periments. He arranges them in order of toxicity as follows: precipitated silica, flint, slate, hydroxide, precipitated chalk, magnesium carbonate, carborun dum. caispar, emery, colloidal coal (m massive amounts). _ All of the respiratory disorders discussed above, together with many others which are caused by the inh.'dr.rion o: fibrosis-forming dusts, are grouped un der the or.c broad term Pneumoconiosis. 61