Document QJXVm4gaoExoNzQeJwRnzrgmR

FILE NAME: National Safety Council (NSC) DATE: 1963 June DOC#: NSC223 DOCUMENT DESCRIPTION: NSC - National Safety News - Dust, Fumes & Mists in Industry Men's clothes were going to pieces That man is cleaning out a diesel fuel tank. To finish the job, he has to squirm into the tank where there's a mixtute o f oil ami water. Trouble was the oil softened his work sun ami boots, caused the rubber coating to peel oil at the slightest snag. This was the situation until H.F.(ioodrich came up with protective slothing that solved this costlv problem. The B I G work suit is n u d e of a special nvlon fabric that is four tunes stronger than the fabric used in orbinary protective clothing. 'Hus is then coateb with a special oil-resisting rubber compound. O n many industrial jobs. B }'.( "rood ru h oil resisting b uns have shown tlu v oin stand rtie most punis hing weai ami tear --outiast ordinary work suits by as much .as 2 to 1. In spire of being tar stronger, the BL'G suit weighs much less than regular waterproof clothing, and it 's softer and more com fortable. too. T h e B.T .Goodrich Xtratuf b o o t, sh ow n here, is ideal for use wherever oil and grease are encountered. Ir has a nonskid m o ld e d o u ts td e cli.it gives terrific traction on the slipperiest surfaces. Long-lasting BFG gfoves have m.inv features, t o o . th a t make them easv to wear as well as protective. To find out more about B.F.Goodrich protective clothing, boots and gloves, see your supplier or write for free catalogs. In .f u s i r t .t i / V o / m A C .V . / V>/ A k r o n 1 S, ().}>; C.i>:Jj;Ktr. h e n e r j 68 C IR CLE 34 O N REA D ER CARD A NATIONAL SAFETY COUNCIL TECHNICAL SERVICE DATA SHEET 531 DUSTS, FUMES, AND MISTS IN INDUSTRY * Copies oi this data sheet will he available for purchase within 30 days. Subscribers to the Council'sdlata sheet maintenance service will receive a copy in - the next quarterly mailing. Introduction 1. Industrial dusts, mists, and fumes, their hazards and their con trol. are discussed in this data sheet.* The general principles presented can be applied to evaluate most in dustrial situations involving these air contaminants and to determine the need for controls. This data sheet is intended to guide employers, plant safety engineers, personnel man agers. and supervisors. 2. A plant manager who believes that he has a toxic or irritating dust problem should consult a competent industrial hygienist. Such help may be obtained from his own company, insurance carrier, private consul tants. or state health or labor agency. d. To protect the health of em ployees who work where a dust, tunic, or mist created In a manulaeturing process i> released into the at mosphere. a control program may be required. In such a ease, three steps must be taken: ;i. !'hc properties of tiro qvcilic diM. fume, or mist and h possible ph\Mologica! clleeN on employees must he ascertained. This U,it.i sh ee t e e \ e r s n ix ie .un i nri iainn: .m eonl.miin.inis eneonniei\ni m im liisiix. It li ne s n o t in eli ul e a Uiseu ss in n ol the e x p l o s i w p i o p e i l i e s ut Mich a i r borne pat lieukiie niattei This d ata sheet is one of a series published by the N atio nal S a fety Council, reflecting experience from many sources. Not every accept ab le safety procedure in this field is necessarily included. This d ata sheet should not be con fused with American Safety Stand ards, federal laws, insurance re quirements, state laws, rules, reg ulations or municipal ordinances. -b. The--particular exposure must he evaluated by dust counts or by chemical analyses of air samples, and a step-by-step analysis of the operations must be made Jo Find the areas where employees are ex posed to hazardous amounts of the material. The operational anai- . y>is also should determine how die dust. fume, or mist is dispelled, c. Appropriate methods of control must be provided where indicated. The type ami extent of controls will depend upon the physical, chemical, and toxic properties ol the dust. tume. or mist, the c\.dila tion made ol the exposure, am! the opeiation that disperses the con taminant. Hie extensive controls needed tor lead oxide dust, lor example, would not he needed tor limestone dust, since much greater quantities ol limestone Just can be tolerated Notional Safety News. June 1963 4. Except for the skin diseases, most occupational diseases are ac quired by inhalation of material. Long tissue is by far the most efficient medium the buck possesses for ab sorbing materials. In addition, the surface area of this lung tissue aver ages 55 square meters or about 590 square feet. 5. Certain dusts that reach the lungs can pass directly into the blood stream and be absorbed over a long period of time. Others may stay in the lungs and set up local irritant or dam aging action. 6. Toxic and irritant dusts can also be ingested in amounts that may cause trouble. If toxic dust swal lowed with food or saliva is not sol uble in body fluids, it is eliminated dircctlx through the intestinal tract. Toxic materials that arc readily sol uble in body fluids can be absorbed in the digestive system and picked up by the blood. 7. A third way in which toxic and irritant substances may enter the system is skin absorption. Many or ganic compound'-, such as TNT. cy anides. and most aromatic amines, amides, and phenols, can produce systemic poisoning by direct contact with the skin. Contact of toxic and irritant dusts with the skin also may result in skin irritation. S. As compared to inhalation. 89 however, both ingestion and skin eontaet arc ot rclatocU nmu'i impor tance in industrial poisoning inso far as dusts, fumes, and mists are con cerned. Origin and Properties of Particulate Matter T The dust normally present in the atmosphere has a beneficial elTect in screening out some of the harmful rays of the sun. Inhalation of this dust may not be harmful because . either the dust may be nontoxic or body mechanisms capture, remove and eliminate or isolate the small amounts of dust tripped in the lungs. Air pollution, radioactive fallout, pollens, and similar conditions may have an adverse etfeet on some indi viduals. Also, when the air breathed contains excessive amounts of dust, the body has dillieulty in handling the load and dust may remain in the lungs. * Sources 10. The term Just as used in in dustry is generally applied to air borne solid particles that range in --sue. from 0.1 micron to 25 microns (one micron 1 10.000 centimeter 1 25,000 inch). Process dusts below (f5 micron in si/c are rare. Dusts above 5 microns in size usually will not stay air-borne long enough (o present an inhalation problem. 11. Dust may enter the air from various sources. It may be dispersed when a dusty materia) is handled, such as when lead oxide is dumped into a mixer or a product is dusted F ig u re 1,-D ust from fo u n dry sand is g en eratoci during the shake-out of cosiiegs. The m echanical action of the shake-out m achine disperses the dust. Path token by the dust particles as they o re d ra w n into the hood shows the e ffic ie n cy of the local exhaust system. iC ourtosy A m erican Fouruirym en's Society' with tale. Dust may be fotm ed and dispersed when solid materials arc reduced to small sizes in processes such as grinding, crushing, blasting, shaking, and drilling. In these proc esses. the mechanical action of the grinding or shaking device supplies a source of energy to disperse the dust formed (P'igurc 1). 12. When a solid such as a metal is heated to a temperature high enough to volatilize it. the volatil iz e d matter later condenses in cooler air to form a inu- (P'igurc 2 ). The solid particles that make up a fume arc extremely line, usually less than 0.5 micron in size. In some eases, the hot material reacts with the air to form an oxide. P.xamples are lead oxide fume from smelting and iron oxide fume from are welding. Also, a fume can be formed when a material Such as magnesium metal is burned or when welding or gas cutting is done on galvanized metal. 15. A /ni.\f is formed when a finely divided liquid is suspended.in air. An example is the oil mist pro duced during cutting and grinding operations. 14. S/n<>kc may be formed by the incomplete combustion of organic materials. Smoke generally contains droplets as well as dry particles. Tobacco, for instance, produces a wet smoke composed of minute tarry droplets. The size of the particles contained in tobacco smoke is about 0.25 micron. 15, Radioactive dust may be dis persed in the same ways as other in dustrial dusts. Radium, thorium, and oilier radioactive elements are pres ent in extremely minute amounts in the atmosphere. Magnitude of particles lb. When a solid is broken into finely divided particles, its surface area is increased many times. P'or ex ample. 1 cubic centimeter (0.0b! cubic inch) of quartz in the form of a cube when crushed into 1-micron cubes will give 101- (1,000.000,000.000 or one trillion) particles with a total surface area of b square meters (0.3(H) square inches), as compared with b square centimeters ( 0 .03() square inch) tor the original cube. 17. When a solid is broken into finely divided particles, the volume occupied In the mass is also in creased because of the voids between the panicles. A dust concentration of .''0 million particles per cubic toot ot air tm ppef), resulting bom 1 cubic ceminjeter of material reduced to particles 1 cubic micron in size, will occupy an air space of 20.000 cubic feet. 1S. Iv e n smaller amounts of toxic dusts, fumes, and mists, will make a workroom atmosphere hazardous, l-'or example, the threshold 'limit value for lead, as adopted b\ the American Conference -of Govern mental Industrial Hygienists. is 0.2 milligram per cubic meter of air (mg cu m>. which is 0.0000002 ounce per cubic foot. Therefore, the dispersion of only 0.002 ounce of lead will be enough to give the threshold limit value of 0.2. mg eu m of' dust or fume in an air space of 10,000 cubic feet (2S0 cubic me ters). The concentrations that nun be preset^ in the workroom without harm to health are different for differ ent substances. IT A person with normal eye sight can detect dust particles as small as 50 microns in diameter. Smaller air-borne particles can. be detected iridividuallv by the naked eve only when strong light is reflected from them. Dust of respirable size (below 10 microns) cannot be seen without the aill of a microscope. 20. M ost`industrial dusts consist of particles that vary widely in size, with the small particles greatly out numbering the large ones. Conse quently, with few exceptions, when dust is noticeable in the air 'around an operation, probably more invissible dust particles than visible ones are present. Separation in air-borne dust 21. Dust in the air may o r may* not have the sam e'com position as its parent material. The determining factors are the particle size `and density of each component in the original mixture, and the hardness of the materials (hard materials will resist the pulverizing action of a mechanical device.) 22. Tor example, foundry mold ing sand contains a large percentage of free silica (quartz) with a lower percentage of clays. Most of the cla\s consist of fine particles that can he air-borne, but most of the quartz particles are too large to he air borne. The air-borne dust, there fore. as compared with the original mixture, mav contain a much higher pereentaee *ol ela*vs and a much 90 Notional Safety News, June 1963 lower percentage of free silica. 3. Dust particles arc. of course, attracted by gravity. Their settling rate through still air will vary with their size. density, and shape. M i croscopically small particles settle out more slowly than larger particles be cause of their relative!) minor densi-* t\ and because of their being in fluenced by Brownian movement. Mineral particles larger than IU mi crons will settle out relatively fast. The estimated settling rates for silica dusts in still air are given in Table 1. T A B L E 1. S E T T L IN G R A T E S FOR SILICA DUSTS Size in M icrons 0 .2 5 0 .5 0 1.00 2 .0 0 5.00 Tim e to Fall 1 Foot (m inutes) 5 9 0 .0 1 8 7 .0 54 .0 1 4 .5 2.5 34. Most of the particles in air borne industrial dusts are small. Be cause of air currents, the line parti cles in dust clouds at an operation will remain suspended in the work room air for relatively long periods of time. The smaller dust particles, moreover, will travel farther away from their point of origij) than will the larger particles so that the far ther dust is from its source, the greater the percentage of small par ticles it contains. Inhalation of Dusts, Fumes, and Mists 25. With the exception of such fibrous materials as .obc-aos. dust particles must usually be smaller than 5 microns in order to eu:,-' :'v . o' , or inner recesses of the lungs. \1- though a few panicles up to '0 microns in si/e mav enter the lungs occasionally, nearly all the larger particles are trapped in she n.o.i! passages, throat. Ian n\. trueuoa. ..ad bronchi, from which ,oe e\;v c torated or swalloueJ ;u:o the tivc tract. 2b. When larger pennies o; ce: tain toxic dusts arc i:.;pp. J oi the upper respiraton v - . e o , :he\ can be absorbed h\ ;h, :\>b\ 'h.el- in the n.isal passages ,uid in the digesti\e tract before thc\ .a. . nated. Hence the final to\;c c f.v ,- of larger dust particles m.i\ oe .a laved. The larger particles ot , tant dusts can cause immediate c h e .. in the upper respiratory system. 27. Ragweed pollen, which '.a ies from 1S to 25 microns in diameaa can cause hav fever from its action in the upper respiratory system. This type ol dust and cither aljergeme types, as well as bacterial and irritant dusts, can cause ditheulty even in the larger air-borne sizes. 28. When dust-laden air is in haled. some of the larger particles are trapped by the hairs in the nose. Other dust particles are removed from the air as it passes over the moist mucous membranes of the nose, throat, and other portions of the upper respiratory system. 7 29. The bronchi and other re spiratory passages are covered with a large number of tiny, hairlike cilia or microscopic whiplashes, which aid in the removal of dust trapped on these moist surfaces. The cilia, all bending in one direction, make a fast stroke toward the mouth and a slower return stroke. This action tends to push mucous and deposited dust upward to the mouth so that the particles can be ex pectorated or swallowed. Retention of dust 30. Many studies have been made in an elfort to determine the amount of dust that is retained in the lungs, but there is no simple answer to this question. It has been shown, that the size of the dust particles, the rate of respiration, the density of the dust in the air. the efficiency of the dust-catching mechanism, and probably many other factors arc in\ olved. Sizes of particles inhaled 3 1 V;;;ough an occasional dust :\>r:';c1c of larger si/e will enter the lun;>. particle'' less than 3 microns in diameter arc the most likely to do so and thus ha\c the greatest oppora;-a:\ to cause a phvsiological re- In okconc lungs, for example, dust particles under 3 microns greatly .minumber larger ones, and many ['articles arc less than 1 micron. 3 2. In the case of very fine [hums asbestos Just, an exception occurs in the size of particles inh.dcd Main libers up to 100 microns long have been found in the lungs Notional Safety News, June 1963 Fig u re 2 . M eU il \ ...1 r.:,. t-:l L'y the heat of w e ld in g later conoi-n-!'- v form o fume. O n thi> bench -w eldin g i u .;o " . 1'..' fu i'U's ore rem iVed a t th eir point ot c rig v i by a p-operly located lo cal exhaust inUoUot.o-'. .Courtesy Am erican Foondrym en's Society of asbestos workers at autopsy. A typical fibrosis caused by asbestos is produced by fibers ranging from 20 to 50 microns in length, but only a few microns wide. Physiological effects 33. The physiological reactions caused by the inhalation of air borne particulate matter will vary w ith different types of dusts, fumes, and mists. The reactions include: a. The cardiopulmonary reactionwhich consists of the pneumoco nioses. such as silicosis and ashesrosis. In certain cases, specific types of lung pathology result, and theheait may be affected (cor pul monale) when the fibrosis is ad vanced. In other cases, there is mainly just an accumulation of a relativelv inert dust in the lungs. b. The systemic reactions which arc caused bv toxic dusts of such ele ments as lead, manganese, cad mium. and mercury, by their com pounds. and by certain organic compounds. c. Metal fume fever which results from the inhalation of finely divid ed and freshly generated fume of zinc or possibly of magnesium or of ihcir oxides. This is a transient condition. d. Allergic and-sensitization reactions which max be caused by inhala tion of. or skin contact with, such materials as organic dusts from flour, grains, and some woods and dusts of a few organic and inor ganic chemicals. c. Bacteria! and fungus infections which occur from inhalation of dusts containing aetbe organisms, such as woo) or !ur dust contain- 91 fr*a`ziac J Substance Chalcedony Chert C risto b a lite Flint Jasper Q u a rtz Tridym ite Trip o li (Rottenstonet Diatom aceous earth Silica gel Asbestos C lays F e ld s p a t I' V . I . iillH llfflW m TABLE II. SELECTED IN D U STRIA L M IN ERAL DUSTS r Description and Uses * CRYSTALLIN E FREE SILIC A ftiO in clu d in g ' m icrocrystalline fo rm st A heat-resistant, chem ically inert fortii of m icrccrystallirsc q uartz. A decorative m a te ria l. R a re in industry. A m icrocrystalline form of silica. An im pure form of flint used in ab rasives. A crystalline form of free silica, extrem ely h ard and inert ch em ically; very resistant to h e a t. Q u a rtz in re fra c to ry b ricks a n d a m o rp h o u s silica in diatom aceous earth a r e alte re d t& c risto b a lite w h e n e x p o se d to high tem p ero tures tealc in e d k C risto b alite is e x te n siv e ly used in p recisio n ca stin g b y the hot w a x process, dental lab o rato ry w o rk, and certain specialty ceram ics. A m icrocrystalline form of native q uartz, more o paq u e and g ranu lar than ch a lce d o n y . Used as an a b ra s iv e a n d in c e ra m ic s. A m icro crystallin e im pure ta rm of silic a sim ila r to ch ert. Used for d eco ra tiv e p urposes. R a re in in d ustry. V itreo us, h a rd ch e m ic a lly resista n t fre e s ilic a , the most com m on form in n atu re. Th e m ain constituent in san d sto ne , ig n e o u s ro cks, a n d com m on sa n d s. V itreo us, co lo rless form o f-fre e silic a . Fo rm e d w h e n q u a rtz is h ea ted to 8 7 0 C (1 ,5 9 8 F). A porous, siliceous rock, resorting from the decom position of chert or siliceous lim estone. Used os a b a se in so a p a n d sco u ring p o w d ers, in m etal p olish in g , a s a filtering a g e n t, a n d in w o o d a n d p a in t fille r s . A c ryp to crysta llin e form of free silica. Thresho ld L' mit in M illion Pa rticles per C ubic Foot of Ait ` C alcu late from formult'* " 250 % SiO . f 5 AM O RPHO US FREE SILIC A (N oncrystallinel A soft, gritty omorphous silica com posed b f m inute siliceous skeletons of sm all a q u a tic p la n ts. Osed in filtra tio n a n d d e c o lo riz a tio n o f liq u id s, in su latio n, fille r in d yn a m ite, w a x , textile s, p la stic s, p a in t, a n d ru b b e r. C a lc in e d a nd flu x -ca l cined diatom aceous earth contains ap p reciab le am ounts of cristobalite, and dust levels should be the sam e as fo r cristo b alite. A regenerative absorbent consisting of the am orphous silica m anufactured by the action of HC! on sodium silic a te . H a rd , g lo ssy, q u a rtz-lik e in a p p e a ra n c e . Used in d e h yd ra tin g a nd in d ry in g a n d a s a c a ta ly s t ca rrie r. Amorphorus : - 20 mppcf C a lc in e d use form ula: 250 o S iO , -f 5 20 mppcf SILIC A TES iC o m p ou nd s m ade up of silico n , o x y g e n , a n d one or m ore m etals with or without hydrogen. These dusts cause nonspecific dust reactions, but g enerally do not in terfere with p u lm o n a ry fu nction or result in d isab ility.'' A h yd ra te d m agnesium silica te in fib ro u s fo rm . Th e fib e rs a re b elieved to be the more hazardo us component of asbestos dust. A a n \if variety of when d ry. Used in -;v i .\.io lin i-. one d . ru cilurninum --s ilica te b e a rin g rocks, p lastic when wet, h ard potter v, stonew are, tile, bricks, cem ents, fillers, and abtat\p<- of elav Som e c la y dep o sits m ay in clu d e a p p re c ia b le .u a d u s ot c la y s m a y co nta in up to 20 per cent q u a r t z % Most a b u n d a n t gro up of m a te ria ls, co m p o sed o f silicate s of alum inum with ad>. n . ' t . >. : \ ' a.1.1 r a r e l y b a r iu m . M o st e c o n o m ic a lly im p o rt a n t1 m in e ral. Used tor c e ra m ics, g la ss, a b ra s iv e w h e e ls, cem en ts, in su latio n , and) fe r tiliz e r. 5 m pp cf1 * 50 m ppcfj " i 50 m ppcft Imiu-nl.il le,:: : '< r s s t .iiliiie I I i v s I or 92 National Safety News, J u n e 1963 TABLE II. SELECTED INDUSTRIAL MINERAL DUSTS (Continued) SILICA TES Compounds m ade up of silicon, o xy g e n , a n d one o r m ore m etals with or without hydrogen. These dusts cause nonspecific dust reactions, but generally do not in terfere with p ulm on ary function or result in d is a b ility .) Fuller's earth Kaolin M ica Portland cement Silicon c a rb id e (Carborundum ) Talc V erm iculite A h yd ra te d s ilic a --a lu m in a co m p ound , filter medium and as a catalyst and insecticides. associoted with fe rric catalyst carrier and o xid e. Used as a in cosmetics and A typ e of c la v com posed of m ixed silicates a n d used fo r refrcfcctories, ceram ics, file, and stonew are, A larg e group of silicates of varyin g com position, but sim ilar in physical proper ties. A ll h ave exce llen t c le a v a g e a n d can be split into v e ry thin sheets. Used in electrica l insulation. Fine p ow d er co ntaining com pounds of time, a lu m in a , silic a , a n d iron oxide. Used as construction m ateria). Bluish-block, very hard crystals. Used as ab rasive and refracto ry m aterial. 50 mppcft 50 m ppcft 20 m ppcft 50 m ppcft 50 mppcft A hydrous m agnesium silicate used in cera m ics, cosm etics, p a in t, and p h a r m a ceu ticals, and as a fille r in so a p , p u tty, a n d p la ste r. An e xp a n d e d m ica shydrafed m agnesium -oJum inum -iron silica te ). Used in light w eig ht a g g re g a te s, in su latio n, fe rtiliz e r, a nd soil co n d itio n ers, as a fille r in rubber and paints, and as a catalyst carrier. 20 m ppcft 50 m ppcft 'T h r e s h o ld lim it s g iven fo r su b sta n ces in ` 'S ilic a te s " g ro u p a rc f o r c o m p o u n d s c o n ta in in g /<\vv than ] per c c n t 'c r \ s t a l)in e s ilic a . F o r com pounds co ntaining m ore than l per cent silica, calcu late threshold lim it fro m fo rm u la: :?o "sib- -f 5 ing anthrax .spores or wood bark or grain dust containing parasitic fungi. f. Irritation of the nose and throat. which is caused by acid, alkali, or other irritating dusts or mists. Some dusts such as .soluble chromate dusts may cause ulceration of the nasal passages or even lung cancer. g. Damage to interna) tissues, which may result from inhaled radioac tive materials such as radium and its daughter products and from other radioisotopes that emit highly ionizing radiation. Pneumoconioses 34. Pneumoconiosis comes from throe Greek words that mean "lung." 'dust," and "abnormal condition.*' The present generally accepted meaning of the word is merely "dusty lung." The kind of dust inhaled determines the type of condition or injury. A number of organic dusts are capable of produeling lung dis eases. ' but not all these diseases are classified as pneumoconioses be cause they are not all a "dusty con dition" of the lung. 35. In very rare eases, enough dust had been inhaled to e.a :v mechanical blockage of the air spaces. Hour dust has been known may be essentially inert and remain in the lungs indefinitely with no recognizable irritation, and a few like limestone dust may be gradually dissolved and eliminated without harm. Silicosis 36. The most important lung dis ease caused hv the inhalation of mineral dust is silicosis--well-known in industries where crystalline free silica dust is present, such as foun dries. glass manufacturing, granite cutting, mining, and tunneling in quartz rock. It is found throughout the world, and in the past it has had manv names, such m iners asth ma. grinder's consumption, miner's phthisis, potter's rot. and stone mason's disease. I he same occupa tional disease, however, is meant by all these names, and it is caused by dust from crystalline free silica, us ually quartz (see Table II). 37. Although considerable prog ress lias been made in dust control in industry, men still develop silico'iv in plants and on jobs where JuM control is not adequate. T'ngineevine control is still the basic memo of prewming this disease, and dust control equipment and proeevimc'- must be carefully maintained. 38. Definition. Silicosis has been defined as "a disease due to breath ing air containing silica ( SiO-_. > characterized anatomically by gener alized fibrotic changes and the de velopment of miliary noduhuion in both lungs, and clinically by short ness of breath, decreased chest ex pansion. lessened capacity for work, absence of fever, increased suscep tibility to tuberculosis (some or all of which symptoms may be present}. and bv characteristic X-ray find ings."* 39. Doctors of influence. Sili cosis has been known to manifest itself after, widely differing periods of exposure It) silica dust. Appar ently. development of the disease depends upon: ;i. The amount and kind of dust in haled. h. The percentage of free silica con tained in the dust. c. The form of the silica. d. The size of the particles inhaled. e. The tluratii'n of the exposure. -- Continual on page 95 ` R ep ort ( J o i n t ! o f the C o m m itte e on Pneum oco niosis a n d the C o m m ittee on Sta n d a rd P ra c tic e s in C o m p o n sa iio n of O c cu p a tio n a l D isease s. >cn/ Iy .'.\ .A m e rican P u b lic M ca lih .A sso cia tio n. 17s>0 B ro a d w a \ . N e w Y o r k !9 . p lOU. Notional Safety News, June 1963 93 H ow one of the w orld's m o st important insurance companies cliose th is sym bol...and why Sitre, Wausau lias landmarks more impressive than this depot. And gs, for trademarks, Em ployers M utuals' handsome office in Wausau would be a far better reflection of our coast to coast operations and our $325 million assets. But there's another dim ension to Em ployers M utuals of W ausau. And when we set. out to define it and describe it, we find the depot does it best. Back in 1874, the first train puffed its way through the W isconsin timberlands, sum m oned north to Wausau by the thriving lumber' in dustry. From then on, the depot, stood as proof t hat t his commit nit y was no longer the " faraway plaee,'' as the early t 'h ip p e w a s had d e scribed it in giving Wausau its name. This Wisconsin com munity is an integral part of the operating phi losophy of Employers M utuals of Wausau, just as if has been through out the 52 years since this mutual insurance company was founded. Call this neighborly concern or " Main Street" friendliness and co operation. It's a way of doing busi ness our policyholders seem to like and we don't want to lost'. E m p lo y e r s M u tu a ls o f W a u sa u is a la rg e n u n p a in n o w . h u t th e W a u sa u W a y is e v id e n t in o u r rotatio n s h ip w ith | m lii-y h o h lo rs < '\u tv w h o re . W o d o h u s m o s s in a ll tin ' p r it i* ` ip.-11r i l i r s o l t in ' n a t i o n ( h r o u g h l -In o l lic o s W o ; i t v o lio i ' l t h o la t g ust a n d m ost u vp u nu n uu d u n d c ru ritiT ;- C IRCLE 40 ON REA D ER C A R D in the fipld of workmen's compensa tion. We w rite group h ealth and accident., fid e lity b on d s, and- all forms of fire and casualty insurance, including autom obile. We write only nonassessable policies. WVre proud of our unbroken record o f dividend- savings. And, as a mutual company, we're dedicated1't o the prevention of loss. c 1business' Mutuals w olUmisiHi t. 1he powers of resistance of the mdi\idual kOivomod : 1he presence or-Mb-wiicc of a c om plicating process such a ' mtcciion. 40. Many theories have been ad vanced o\cr the years to explain win crystalline free silica acts as it Joes in the luni:$. 1'heorics have been based on the hardness of the nutenal and the effect of sMari' edges. solubility phenomena, elec trochemical action of the crystals, and imnumologicaUvactions. 41. U is believed now that the fibrosis produced is caused not by the hardness or sharpness of .the particles, but hv a combination of slight solubility with a physiochcmical effect and an immunological effect--hut no one is certain of the exact mechanism of the disease. K \perimental work on the reasons for the development of silicosis is still going on in various p arts'of the world. If- the precise mechanism of silicosis could be determined, better medical preventive measures might he developed and possibly a cure could be found. 42. Three stages. Silieosis is gen-, orally classified in three separate stages bv medical authorities. More sophisticated classifications arc some times used for the various X-ray stages and complications of the dis ease, but for a basic understanding the three stages give a good break down. - 45. The lirsr stage of the d is ease produces no disability. The affected man can carry on his work as well as ever. Frequently, the in dividual is not aware that anything is wrong, and the disease is revealed only by opaque nodular shadows on a chest X-ray coupled with a known exposure- to crystalline free silica. 44. In the second stage, respira tion may be alleeted in some persons but not in all by any means. Labored breathing on heavy exertion usually is noted first, and a dry cough also max be present. 45. The third stage can develop after the second stage even though the individual has been removed from ex posure to silica dust. However, the progress of the disease will be slow er without continued dust-exposure. Breathing max become severely labored. The worker is far below nor mal plixsieallx and is susceptible to C n<o*u K lou/c lim p 1 9 A 3 respiratory diseases. Chest X-rays may show an enlarged heart as a re sult of the body 's attempts to over come the resistance of restricted blood vessels in the lungs. Pulmonary tuberculosis is a frequent complica tion and occasionally results in death. 4b. Dcrccrnm and development. Silieosis may be detected by chest X-rays m each of the three stages. `However. X-rays alone are not sufficient for a positive diagnosis, for the shadows mav be due to a variety of other conditions, includ ing infection or another type of pneumoconiosis. The individual must have had a definite exposure.to free silica, because only it can cause sil icosis. The complete occupational and medical history of the employee must therefore be evaluated before a conclusion can be reached. The cor relation of chest X-ray findings and phvsieal disability may be poor in many eases. 47. From most industrial expe rience. silieosis seldom develops in less than five years and in many eases may take 20 years or longer to ` become disabling. 4S. The development of silieosis in its earliest stage is not perceived by the individual. The disease cannot be cured by any means yet known. Tuberculosis is more prevalent in persons with silieosis. but the inci dence is decreasing, as it is in the general population. 49. Men with early signs of sili eosis are able to perform their duties and are not a menace to other em ployees. for it is not a contagious disease. A perceptible X-ray change is not grounds for assuming disability because most people show chest changes with advance in age even* without exposure to dust. Where there is a known exposure to silica dust, however, men with early signs of silieosis should be seen periodi cally by a physician. 50. Action <>/ silica on the lungs. At the points in the lung where silica dust is deposited and accumu lated. a fibrous tissue develops and crows around the particles. This fibrous tissue is tough like sear tissue. It is not as elastic as normal lime (issue, does not permit the ready passage of oxvgen and carbon diox ide. and as it prolilerates. cuts down the amount of normal lung tissue. As a result, the available functional volume of the lung is reduced. 51. In some advanced cases, the fibrous tissue will slow down or even prevent the diffusion of oxy gen from the lung to the blood in the capillaries, and the blood in the area will not be completely oxy genated. The fibrous tissue can also aiTeei the blood vessels by oblitera ting them or cutting down the How of blood. All these effects lend to limit the rate at which oxygen is supplied to the body tissues, Timphysetna is the most obvious symptom. 52. As the inhalation of silica continues over the years, the amount of fibrous tissue will, of course, in crease. with the ultimate result that the lungs will not readily oxygenate sufficient blood for the body's needs. Then when the oxygen demand of the body is increased by exertion, the individual will feel distress with shortness of breath. 55. Amorphous free silica differs from cry stalline free silica in physical structure and in physiological effects. In the amorphous state, molecules of silica exist in random orientation, which may be caused by natural forc es to form opal and diatoniaceous earth (kiesclguhr). Amorphous silica mav be converted by artificial proc esses into such forms as silica gel. silica fume, and fused silica or quartz. 54. If amorphous silica is heated to a high temperature, as in calcining, forms of crystalline free silica called eristobalitc and tridymite result. These intermediate forms of amor phous silica are known as, cryptocrystalline ( uhra-microerystalline.) Inhalation of these crystalline forms can readily cause diatoimtc pneu moconiosis. 55. When diatoniaceous earth is calcined, particularly in the pres ence of a trace of alkaline ffux. appreciable quantities are converted to eristonalite. As a result ol studies made bv the U-. S. Public Health Service, it has been recommended that the threshold limit value lor crude or amorphous diatomite be placed at 20 mppcf (see Table 11). but that the atmospheric concentra tion for dust containing eristobalitc be kept under 5 mppcf. 5n. Various commercial products containing particles of silica under 1 micron in m / c are available. 1he 95 physiological effects of these pn\tucts have not been well defined. Until more experience with humart beings is available, it is believed these products should be handled with care. 57. Tree silica and silicates, l ive silica is uneomhined silicon dioxide (SiO._>). Silicates contain silicon and oxygen combined with other ele ments in a more'complex molecule. Analyses of minerals, particularly in geologicabreports, are sometimes re ported as percentages of oxides, which may include SilT... A D O -. K.-d), Fe.>0;{. The SiO-j repotted in such chemical analyses is the total of the silicon dioxide present, both the free silica (if present), and the -silica combined in the mineral. Such analyses are not reliable indications of the silicosis potential of the material. 58. It is uiteombined or free silica that is most important in industrial dust exposure. So that an exposure can he properly evaluated, the per-' eentage of uneomhined silica must be determined by petrographic analysis using a polarizing microscope' or. preferably, by X-ray diffraction analyses and special analytical chemical procedures. 5l). There lias been some experi mental evidence that some dusts may tend to inhibit the action of silica on the body, but this inhibiting action is so slight and uncertain that it must be discounted in practice. In fact, there also is evidence that the tionsiliceous components of a dust mixture containing free silica mav provoke a disabling condition more severe, than that caused by the silica acting alone. 60. With the exception of asbes tos and some talcs, the silicate dusts do not ordinarily cause a serious disabling lung condition such as is produced by free silica. Much higher levels ol silicate dusts than of free silica dust can be tolerated. h [. In many industries, men have worked with silicate dusts (hat con tained no free silica without devel opment of disability o; of nodul.ition in the lungs. 1he \ - r a \ ina\ show shadows indicating dus; deposits in the lungs. Pa; the pneumoconiosis is V'scnli ol 1v hartnk.`sv l lo w e v e i. pat tiullv ,li'-ubliU'' pn eilMlo, a;i , v , !i.i\ , been icpoi led vvhcie men have uorkci0 for long periods ol tune in wry high concentrations of certain silicate dusts. 62. Disabling pneumoconioses from exposure to abnormally high concentrations of mica, trcmolite talc, and kaolin dusts have been de scribed in the literature. The clinical signs are not the same for these sili cate dusts as for free silica, but the symptoms can be marked. bo. The body docs not have ade quate defense against indiscrimi nate amounts of dust of any kind. Therefore, although specific symp toms have not been described for many mineral dusts, the general cx`perienee would indicate that dust levels should be kept within thresh old limit values or below (1'able 11). Asbestosis 64. Asbestos is a general term ap plied to several minerals having a fibrous character. These asbestos minerals are hydrated silicates of magnesium with variable amounts of iron, calcium* sodium, potassium, and aluminum present as impurities. 65. Asbestos when inhaled pro duces fibrous tissue in the lungs of bojh men and animals. U has been shown that fibers of asbestos must be present for the production of asbestosis. Other silicate minerals of the same chemical composition but nonlibrous in form produce no re action or a relatively mild reaction, but not the severe reaction of fibrous asbestos dust. 66. 'These facts lead to the con clusion that asbestosis is mainly the . result of physical irritation of the lung tisssue and not of a chemical action, which is thought to he one of the causes of silicosis. It is suspected that lung c ancer may be induced by 'asbestos. However, there is no im pressive amount of evidence to sup port this assumption. 67. `The line ait'-borno libers of asbestos can pass through the upper respiratory tract to the lower parts of the lungs to cause irritation and to form "asbestos bodies" where the libers are e n ca p s u la te d . This diffuse libiosis piobablv begins as a "collar" about the iermin.il bronchioles. 1here is e vid e nce ih.it othei min erals li.ivme a hbious character can pioduec a reaction similar to that ol asb e sto s I ilv r class, however. m e | mi -a m e s u c h u i eaet i o n . oS. hollowing a study by the 1\ S. Public Health Smviee of the 'asbestos textile industrv,* it was recommended that the dust concen tration he kept at less than 5 mppei to prevent asbestosis. Evaluation of an exposure to abestos dust is based on thc'total amount of dust because it lias proved out in practice that if the tine dust is kept below the .suggested threshold limit, the concen tration ol ijunoas tilvrs will also be kept within safe limits. Talcosis (d). As used in industry, "tale" is a very general term. To the geolo gist. tale is a hydrous magnesium sili cate, which may be a relatively pure mineral or may be mixed with tremolite or with dolomite depending upon where it is mined. 'The term "talc" is applied commercially to carbonate mixtures that have the same general feel and physical properties; it also fs applied to pyrophyllite, a hydrous aluminum silicate, which frequently is mixed with a high percentage of quartz. The free silica generally foun'd with pyrophyllite can cause silicosis. It is therefore essential to know which talc is being used in order to evaluate a specific dust ex posure. 70. Talcosis is usually . associ ated with trcmolite talc. This disease produces changes in the lungs and symptoms similar to those of asbestosis. Anthracosilicosis 71. Anthracosilu-osis. a complex form of pneumoconiosis, is a chronic disease caused by breathing air. con taining dust that has free silica as one of its components and that is generated in the various processes involved in mining and preparing anthracite (hard coal)** and. to a lesser degree, bituminous coal. 72. The disease is characterized anatomically by generalized tibrotic changes throughout both lungs and by the presence of excessive amounts H i ecson. W . n u lla V a lle . T V ,. I Jv \ a u K . \ . 1.. M i l l e r . 1. W . . a n d S a > e r \ K. K.. I i 't .1 0>( -w.' in t he ;w . ' ! < m :L n b . S . P ub lic I k '.ih h B u lle tin N o M l . T . S. Public H e a l t h V m k u Wi i sl uii Ji i on 11. C in ;n i <,'w/i< c'w' "ic I hn < l( >'>il \ h ui'^ v I ' . S P u b lic H e a lth B u lle t in No. \ M . I' S P u b lic H ea lth S o iv ic e . W a d i Nn fi ii p ol SrOr-' v Nrvss l i m e 1963 of carbonaceous and siliceous ma terial. Such lungs on. autopsy arc coal black. Tv' Symptoms found in early stages of the disease arc shortness of breath, cough with a .coal-black sputum, pain in the chest, and in some eases physical weakness. In the advanced stages, there'are loss of work, partly caused by pulmonary infection ( frequently bronchitis'), and in some eases there may be heart failure. 74. Fxporiments with animals showed that mixtures of coal and quartz produced more fibrosis than did quart/ alone. The harmful ctTects of coal dust do not come only from the silica in the dust. Coal dust alone in very heavy concentrations over a period of many years can cause breathlessness and ventila tory impairment. Miscellaneous pneumoconioses 75. Even though a dust is classi fied as harmless, excessive amounts of it can lead to trouble by causing a pneumoconiosis or simply by me chanically irritating the walls of the respiratory system. Moreover, even though there is no chemical or physi cal irritation, mechanical plugging of the lungs and interference with their ordinary processes can result. Mica dust and kaolin dust arc two good examples of dusts that ordinarily are considered benign but in excessive amounts can cause a troublesome pneumoconiosis. 7b. Mica pneumoconiosis has been observed in grinding operations where mica dust, but no free silica was present. There were marked changes in the X-ray pictures of the lungs and some disability. The eases occurred where, the dust exposures were massive over many years. 77. Kdolinosis has been described as a condition induced by inhalation of dust released in the grinding and handling of kaolin (china d a y ). Where d iseases occurred, dust levels of several hundred million particles per cubic foot of air were common. 78. Aluminum dust is not consid ered to he harmful except where exposures are massive. Without ad verse effects, aluminum dust inhala tion has been used as part of an endeavor to prevent silicosis. Also withoul adverse effects, extensive exposures to aluminum dust have oc Nationol Safety News, June 1963 curred in the grinding of aluminum parts and castings. It can therefore be concluded that reasonably good control will -prevent harm from alu minum dust. 74. Bauxite pneumoconiosis (Sha ver's disease) has been found only in workers exposed to fumes contain ing aluminum oxide and minute or ing from smelting bauxite in the manufacture of corundum, an im pure form of aluminum oxide. It is essentially a diffuse interstitial fi brosis and marked associated em physema. with a complete absence of any nodular librosis. It definitely does not occur from the use of cor undum grinding wheels or from other forms of aluminum oxide. SO. Some pneumoconioses may show marked shadows on' an X-ray him; these shadows, without the nec essary information on the exposure of the individual, may be alarming in a general X-ray screening pro gram. On clinical examination of in dividuals showing the X-ray mark ings, however, often no disability or symptom can be found. 81. These shadows are frequently encountered when the dusts contain atoms of relatively high molecular weight because the heavier atoms are fairly opaque to X-rays. Insoluble barium dusts and tin oxide dusts, for example, can show very marked shadows on X-ray films without pro ducing signs of significant pathology (barium dust that is soluble in the body fluids can give a toxic reaction ). 82. Iron oxide, particularly ex cessive fume from welding opera tions. may produce v/V/mw.v with a pigmentation of the lungs (black in welders and red in iron ore miners) without disability. The X-ray shad ows produced by the iron oxide in t:ie lungs are somewhat similar to the shadows from silicosis. Because of this similarity, differential diagnosis is often difficult, and hdavy exposures to iron oxide dust and fume may lead to medicolegal problems, it L there fore important to control iron oxide exposures e\en though siderosis is not disabling. 83. Limestone, marble, lime, gyp sum. and portland cement dusts ap parently have no serious ofleet even after long exposures. Also, many sili cates and other minerals h a w not caused impairment in individuals in haling the dusts, and the resulting pneumoconioses are generally classed as benign. Toxic Dusts and Fumes 84. Systemic reactions arc caused by toxic dusts and fumes of various elements and their compounds and by certain organic compounds. All metallic fumes are irritating, especi ally when freshly generated. Indus trially important metals and their compounds that can have a toxic elTeet when the dust or fume is in haled include arsenic* antimony, cad mium. chromium, lead, manganese, mercury, selenium, tellurium, thall ium. uranium, and a few others.* 85. The effect' of some metals, such as magnesium and zinc, appears to be transient. Only limited .data are available on the exotic and rare earth metals. 86. Although the dusts and fumes from metals with low toxicity do not need as much attention as the dusts and fumes from highly toxic metals, they should not be neglected or disregarded. The metals with low toxicity are controlled more readily because greater amounts can be'tolerated. but their dusts and fumes should be kept at reasonable levels since excessive amounts of any of them can be harmful (Table 111). Lead poisoning 87. Although extremely severe cases of lead poisoning are rare in industry today, lead exposures must be controlled to prevent even the moderate symptoms, which can be troublesome. Inhalation of the dust of lead compounds is the most com mon mode of entry of lead into the system. Ingestion of lead compounds can add to the problem if personal hygiene is poor. Workers should therefore be encouraged .to..-wash thoroughly before eating, and lunch rooms should be segregated from work areas. 88. It should be recognized that lead is a normal constituent of plants and animals. People ingest and ex crete lead daily even though they are not exposed to lead in their dailv work. The body can handle "Sec the follow ing N ational Safety C o u n c i l D ata S h ee t s : .1 n n n u m y and h s C o m p o u n d s . -JOS; A r u m n an d I n Innr<panu C o m i 'o iu n h . 4 ' N ; C a d m i u m , ?1 2 ; I.tad. 44V Mauiu'siitrn. 420; Manganese. ' (H>; Wr 'iMM 21Vv I il amn m. 4S5; /.im anil / o n (>\n/t. 2<w. / u i o n n u n /'o i r j i v , 97 and eliminate small amounts without harm. When intake rates exceed the normal excretion Icsel. InuM-up oc curs in the body. There is a safe level of absorption, and if the con centration of lead dust in the air of work areas is kept below the threshold limit, there should be no ditlieulty. ST The importance of maintain ing the concentration of air-borne lead at a verv low value stems from lead's high toxicity and its tendency, in small amounts, to accumulate in the human system. When lead ab sorption in tl\e body reaches a suf ficient degree. symptoms of poison ing or intoxication appedr. Beryllium intoxication *>0. Beryllium intoxication is a severe systemic disease that can re sult from the inhalation of massive doses of dust of metallic beryllium, .beryllium oxide, and some soluble beryllium compounds. There are two forms of the disease. One is an acute form of chemical pneumonitis with cough, pain, ditlieulty in breathing, cyanosis, and loss of weight. In the chronic type, known as berylliosis, there may be loss of appetite-and weight, weakness, cough, extreme' diiTiculty in breathing, cyanosis, and cardiac failure. Mortality is high in chronic beryllium intoxication, and many who survive stiller from pul monary distress. 91. Individual susceptibility ap parently is an important factor in the development of the disease. In many instances, one employee has devel oped the severe symptoms while oth er employees doing the sam e work have shown no sinus of disabilitv. 92. Beryllium intoxication lias never been demonstrated in indivfduals mining or handling ore only. There is no evidence of intoxication from the ingestion of bcrvllium oxide, beryllium metal, or any of the beryl lium alloys. Only the inhalation of beryllium dust produces systemic disease. 93. Because of the severe nature of the disease and because there is no way of predicting' who will de velop it. extreme care must he taken to control the dust and fume that arise in the handling of beryllium, its alKns. and its compounds. Berylhum is toxic in such -small quantity as to t v considered the most toxic of all elements w i investigated. TABLE III. 5 U U .D lO X -v - W ' ,'M tS Substance Description and Effects Threshold Limit in M illig ia ms per Cubic Meter of Air ' Antim ony A rse n ic Barium \soluble compounds' Beryllium Chrom ic acid and Chromates C yan id e las CN) D in itro b e n ze n e F lu o rid e s H ydroquinone Iron o xid e fume Lead Lead arsenate M agnesium oxide fu m e G ra y m etal often associated with iead 0.5 arid arsen ic. H a 'a rd o u s fr^m in h a la tion a n d in g estion . S o lu b le salts m av cause der matitis. Silvery brittle crystalline m etal. H a z 0.5 ardous from inhalation and ingestion. U su a lly e n co u n te re d a s . a rse n ic trio xid e . Soluble barium chloride and sulfide 0.5 are toxic when taken by mouth. Light w eight, g ra y m etal. The m etal, low-fired oxides, soluble salts, and some a llo ys a re toxic try in halatio n . 0.002 Red, brow n, or black crystals. Caustic 04 action on mucous m em branes or skin. N onvolatile cyan id es are ingestionhaza rd s. C ya n id es inhibit tissue o xid ation upon inhalation and cause death. 5.0 ;skin* *) Yellow ish crystal. H a za rd o u s from skin absorption, inhalation, and ingestion. 1.0 (skin* *' Inorganic fluorides are highly irritant 2.5 and toxic. Colorless h exag on al crystals. Contact 2.0 with the skin m ay cause sensitization a nd irrita tio n . E xcessiv e e x p o su re to dust m ay cause co rneal injury. M ajor sources a re cutting and w elding. 15.0 Lead fumes and lead compounds cause 0.2 poisoning afte r prolonged e xp o su re .- M ost im p o rta n t m ean s o f e n try into b o d y is in h a la tio n . S k in a b so rp tio n is of sig nificance only from such organic compounds as lead tetraethyl. W hite crystals--highly toxic. 0 .1 5 W hite pow der. Inhalation of freshly generated fum e m ay cause metal fume fever. 15.0 These iln eshoTU lim it v a lu e s w e re a d o p ted b y the A m e r ic a n i C o n f re n c e o f G o v e rn mental Industrial Hygienists in 19(->2. 94. When the soluble .salts of bcrvllium. especially bcrvllium fluo ride. come in contact with cuts or abrasions on the skin, deep ulcers may he formed that heal very slowly. Complete surgical excision of the ul cer is sometimes required in order to ctTccl healing. Metal fume fever 95. Metal fume fever is an acute condition of short duration caused by a brief high exposure to the freshly generated fumes of metals such as zinc or magnesium or their oxides. Symptoms appear from four to twelve hours after exposure and consist of fever and shaking chills. There is complete recovery usually within one day. and ordinarily the employee can return to the same job without recurrence.- However, after a period in which there has been no contact with the fume, for example. 98 National Safety News, June 1963 Substance TABLE III. S E LEC T ED TO X IC D USTS A N D PUMES (Continued) Description and Effects Threshold lim it in M illig ra m s p er Cubic Meter of A ir* M anganese Pentachlorophenol Phosphorus vyellow' Picric a cid Selenium compounds Sodium hydroxide Tellurium Titanium dioxide Trinitrotoluene Vanadium pentoxide Zinc o xid e fume Zirconium compounds S ilve ry g ra y m etal. H azardous from 5.0 irrhalation of fumes or dust. Dark-coioied flakes. Harmful Emits toxic fumes when heated. dust. 0 .5 Vskin * Poisonous m ainly by inhalation. Severe 0.1 burn h aza rd from skin contact. Yello w crystals or liquid. p a rticu larly metallic salts. fum es on decomposition." E xp lo s iv e -- Emits toxic 0.1 (skin* T o xicity v a rie s som ew hat acco rd in g to 0.1 the solubility of the specific com pound. O ften causes contact dermatitis. W h ite, deliquescent pieces or lumps. H a s se v e re actio n upon a ll body tissue. S im ila r to selenium ch em ically a nd in physiological effects. W h ite to b la c k p ow d er. C onsidered in the nuisance category. 15.0 Colorless to yello w m onoclinic crystals. Emits toxic fum es of oxides of nitrogen when heated to decomposition. Highly poisonous explosive. 1.5 (skin **' Highly toxic and a radiation hazard that requires special consideration. 0.05 0.25 (soluble com pounds' (insoluble com pounds) Ye llo w to red crystals. Acts chiefly as an irritant to the conjunctiva and re spiratory tract. 0 .5 (dust) 0.1 (fume) Am orphous white or yellow powder. Th e p o w d e r is essen tia lly n ontoxic, but freshly generated fume m ay cause m etal fum e fever. Most com pounds a re insoluble and have low toxicity. *These threshold limit values were adopted by the American Conference of Govern mental Industrial Hygienists in B>h2. **The word "skin'* in this table indicates that the substance can penetrate the skin to contribute to the exposure. after a layoff, resumption of exposure is likely to bring on an attack. 96. To cause metal fume fever, heavy concentrations of fumes are required. Zinc oxide fume is the most common source, but eases caused by the inhalation of fumes from magnesium oxide, copper oxide, and other metallic oxides have also been reported. 'The condition does not occur from the handling of these oxides in powder form. Apparently. it results only from the inhalation of extremely tine particles freshly formed as fume (nascent fume). 97. Nickel, mercury, and other metals may also produce a fever fol lowed by the toxic effects of the element. Allergic Reactions OS. When in tlie form of du-d. a large number of materials may cause various allergic reactions in suxeep- National Safety News. June 1963 tible individuals. Examples of such agents are certain animal products, foods, drug's, and chemicals. The bodily systems usually involved in allergic reactions, which may be quite severe, are the skin, respiratory sys tem, and gastrointestinal system. Oc casionally. two or more systems are involved. Some of the allergic reac tions are dermatitis, hay fever, asth ma, and hives. 99. Usually, the victim is subject ed to a series of exposures without any reactions during which .sensiti zation is built up. These exposures may occur continuously for years. Then, at the end of the ''incubation period," which varies according to the individual, a reaction is pro duced. 100. For a true allergic reac tion two factors are required: a. A history of prior exposure to the material involved (sometimes not known by alfectcd employees). b. A 'challenge dose" of* the mate rial. which provokes the allergic re action. 101. Continuous exposures may act as "desensitizing doses.'' and under these conditions an allergic individual may work without incident for long periods of time only to find that re-exposure after removal from the sensitizing material (such as after a vacation) causes an allergic re sponse to recur. 102. Medical and engineering rec ommendations to prevent allergic reactions are based on prevention of exposure by means of persona) pro tective equipment, ventilation meth ods. or removal of sensitized individ uals from the exposure. Infections Infection and pneumoconiosis 103. The presence of pulmonary disease that significantly interferes with the natural defenses against foreign particles may increase sus ceptibility to pneumoconiosis. Con versely. a pneumoconiotic lung is more prone to infection. For exam ple. tuberculosis occurs more frequentlv among silicotics than among normal persons. Severe disability or death of a silicotic, when caused by pulmonary conditions, usually results from complicating tuberculosis either alone or combined with other infec tions. Bacteria and fungi 104. The possibility of lung in- 99