Document q65JoyvJoELZ2gy95En3vYRj

*X < 3O O t o 33 3 C 3o CO P 3C o zn \J O ^ c* <3 > O in cO T3 O O o<j 'js\ < rs -o t Ot i i "b LU or: j-LJ CQ ACCIDENT PREVENTION MAN UAL for Industrial Operations : EDITION ; PLEASE CO :.QT r$vv.s 7> 'ijNOOd 'A'Cdi CLi7 7 S'-;; r t .- "V NATIONAL SAFETY COUNCIL JChicago, Illinois 606, 3na ma rr *0- U-// dusts. RidU her radioac. 3 extremely ne'y divided reased many 5.061 cu in.) cube when 1 give 20" id) particles -t\ n> (9,"00 \ cm (0.030 flely divided by the mi : voids be'oncentrntion n ft of air m of rTUteri- dc dus!J. /orlcroom atample, the ; adopt'd by <3\ emnu'nul - per cu m ' per cu ft;!y 0.002 0* of dust or cu ft ( .* can detect a d.'.ifflc-.er. fee detect* only ,-m. Ou.<tJ c.innof h* -Pc. M*-; uU par^*^ 00e"' = *h** r to is 5ci<m< cr,*lf UgSb ' ~`4 INDUSTRIAL HYCIESE rtlocity. This type of dispersion is known u dynamic projection and is a resuit of the tactic energy of the particle's motion. As the mass of the particle decreases, however, s point will be reached when its kinetic eergy (which is one-half the mass times the square of the velocity) is too small to twcKome air resistance. The particle's for th,. ' nrd velocity is thus minimized and it re^ tuias suspended in the containing air mass. As a rough approximation, macroscopic particles (those visible to the naked eye) ire considered to be dispersed by dynamic projection. Microscopic particles (those risible only through a microscope) are conddered to have a mass so small that their movement is dependent on the containing ih mass. Contaminants such as the larger dt particles, mists, and sprays, which are dirpersed by dynamic projection, can cause eternal injury such as acid bums, eye dam- *te, nd dermatitis. The microscopic parti ed are dangerous to health if inhaled. Separation In airborne dusts j Dust in the air may or may not have the 1 *e composition as its parent material. ' TV determining factors are the particle v **e and density of each compooent in the original mixture, and the hardness of the r materials (hard materials will resist the ^slveriaing action of a mechanical device). For example, foundry molding sand con* . a Urge percentage of free silica with 'lower percentage of clays. Most of the consist of fine particles that can be > ^ut mQst of the free silica partiF fr* are too large to be airborne. The. air- l dust, therefore, as compared with the I. ^dcal mixture, may contain a much high- J Percentage of clays and a much lower . ^"-cnLige of free silica. Particles are, of course, attracted by "^eir Mining rate through still . . %dl vary with their size, density, and jbe. Microscopic particles settle out more y than larger particles because of their xj^*vtly minor density and because of their influenced by Brownian movement. -<rU particles larger than \0 p will set- relatively fast. The estimated set* C rates for silica dusts in still air are _ n Table w.\% bul6? :. particles in airborne indus* JmaH. Because of air cur "n* particles in dust clouds at an TABLE 39-A. SETTLING RATES FOR SILICA DUSTS IN STILL AIR Size (n) 0.25 0.50 1.00 2.00 5.00 Time to Fall I ft (minutes) 590.0 187.0 54.0 14.5 2.5 operation will remain suspended in the workroom air for relatively long periods of time. The smaller dust particles, moreover, will travel farther away from their point of origin than will the larger particles so that the farther dust is from its source, the greater the percentage of small particles it contains. Mechanism of inhalation With the exception of such fibrous mate rials as asbestos, dust particles must usual ly be smaller than 5 u ia order to enter the alveoli or inner recesses of the lungs (see illustration of the bronchia! tree in Chap, ter 42, "Ionizing Radiation"). Although a few particles up to 10 jt in size may enter the lungs occasionally, nearly ail the larger particles are trapped in the oasal passages, throat, larynx, trachea, and bron chi, from which they are expectorated or swallowed into the digestive tract. When larger particles of certain toxic dusts are trapped in the upper respiratory passages, they can be absorbed by the body fluids in the nasal passages and in the digestive tract before they are eliminated. Hence the final toxic effects of larger dust particles may be delayed. The larger particles of irritant dusts can cause immediate effects in the upper respiratory,system. Ragweed pollen, which varies from 18 to 25 p in diameter can cause hay fever from its action in the upper respiratory system. This type of dust and other allergenic types, as well as bacterial and irritant dusts, can cause difficulty even in the larger airborne sizes. . When dust-laden air is inhaled, some of ''*.** I * t j i i .--Y*-- . .*> f~* : . Y- >xxw.-- ' `* 1. . -' ViuiV*'''"li--. '-..-^?L-v - * ` `^ ****&."; -;- "' *: tfl^x **.* Wr- * -' ;-- * - ^:.'r-'^-`:^`:''\-.- *; 'yC-y^ r Pi!Nrm'.;*:C`*;V^;^.5v*:'/? / T^HierrF'S ..*'* * * * *'*". ^# . . *,>'V.^"*d'.s*''* '- *H4^. .. \. '* . s** ' r . . < 'k ' * v`,#!* w* ** dusts. Radi.her radioscn extremely Te. '.aely divided ."eased many X061 eu in.) cube when - give 101-* '.n) particta q m (9.100 l cm (0.930 nely divided by the mm ie voids bcroncentr.ttion ii ft of air 31 mated* i will oxie dusts, orkreom at* ample, the adopted by jvemmenfaJ ; per cu m per cu ft. !y 0.002 ox ie thfosbeid of dust of cu St (ISO :<vt ef. rted h<m t of S' L INDUSTRIAL HYCIENZ tdocity. This type of dispersion is known u dynamic projection and is a result of the Hcetic energy of the particle's motion. As tie mass of the particle decreases, however, a point will be reached when its kinetic energy (which is one-half the mass times the square of the velocity) is too small to gertomc air resistance. The particle's for1 vird velocity is thus minimized and it re mains suspended io the containing air mass. As a rough approximation, macroscopic particles (those visible to the naked eye) w considered to be dispersed by dynamic projection. Microscopic particles (those risble only through a microscope) are eon . adered to have a mass so small that their movement is dependent oo the containing 'dr mass. Contaminants such as the large* dart particles, mists, and sprays, which are dispersed by dynamic projection, can cause external injury such as acid bums, eye damUft lad dermatitis. The microscopic parti tas are dangerous to health if inhaled. Separation in airborne dusts &Jst in the air may or may not have the *me composition as its parent material. determining factors are the particle **< and density of each compooent in the ori^ant mixture, and the hardness of the aterials (hard materials will resist the Wvenxing action of a mechanical device). For example foundry molding sand con- a large percentage of free silica with \ 1*tf percentage of clays. Most of the consist of fine particles that can be rPonie, but most of the free silica parti- V? *** f(x> large to be airborne. The. air* *^e dust* therefore, as compared with the mixture, may contain a much high . Percentage 0f days and a much lower >namugeoffree silica. Du# particles are* of course, attracted by ^le`r settling rate through still ^with their size, density, and Microscopic particles settle out more ^" larger particles because of their s, .y m*nor density and because of their if'** !n"unced by Brownian movement. ^ Particles larger than 10 n will set* ' relatively fast. The estimated set- *dica dusts in still air are to Table 39*a. of tlie particles in airborne indus* **0. it^e4*0 sma^* of air cur- one particles in dust clouds at an TABLE 39-A. SETTLING RATES FOR SILICA DUSTS IN STILL AIR Size (f*) 0.25 0.50 1.00 2.00 5.00 Time to Fail I ft (minutes) 590.0 187.0 54.0 14.5 2.5 operation will remain suspended in the workroom air for relatively long periods of time. The smaller dust particles, moreover, will travel farther away from their point of origin than will the larger particles so that the farther dust is from its source, the greater the percentage of small particles it contains. Mechanism of inhalation With the exception of such fibrous mate rials as asbestos, dust particles must usual ly be smaller than 5 u in order to enter the alveoli or inner recesses of the lungs (see illustration of the bronchial tree in Chap ter 42, "Ionizing Radiation**). Although a few particles up to 10 u in size may enter the lungs occasionally, nearly all the larger particles are trapped in the oasal passages, throat, larynx, trachea, and bron chi, from which they are expectorated of swallowed into the digestive tract. When larger particles of certain toxic dusts are trapped in the upper respiratory passages, they can be absorbed by the body Quids in the nasal passages and in the digestive tract before they arc eliminated. Hence the final toxic effects of larger dust particles may be delayed. The larger particles of irritant dusts can cause immediate effects in the upper respiratory system. Ragweed pollen, which varies from 13 to 25 n in diameter can cause hay fever from its action in the upper respiratory system. This type of dust and other allergenic types, as well as bacterial and irritant dusts, can cause difficulty even in the larger airborne sizes. When dust-laden air is inhaled, some of 39-5 35r= V* g i i i i Sy reiuif, (cor pui3dvanced. y just an rt dust in ire caused s as lead, rcury, by in organic from tKe td freshly assibly'~of This is a ans which >f, or skin s organic me woods inorganic terial and (jf in* n* ,n. -n? or grain (See the Dther Oc* his chap* at, which er irritats such ai se ulceniveo lung hich may material* products that etTM1 Chat'ff -rot "jberuKy ,crcb' i dc* v. A ' r di** s b*: INDUSTRIAL HYGIENE la very rare cases, enough dust has been inhaled to cause mechanical blockage of the sir spaces. (Flour dust has been known to cause this condition.) Some dusts may be tfsenrially inert and remain in the,lungs indefinitely with no recognizable irritation, tod a few (like limestone dust) may be gradually dissolved and eliminated without harm. Silicosis is the most important lung dis ease caused by the inhalation of mineral dust. It is well-known in industries where crystalline free silica dust is present, such u foundries, glass manufacturing, granite cutting, mining, and tunneling in quartz reck. It is found throughout the world, and fe the past it has had many names, such as miner's asthma, grinder's consumption, ainer's phthisis, potter's rot, and stone mason's disease. The same occupational dis cs*, however, is meant by all these names, wd it is caused by dust from crystalline free silica, usually quartz. Silicosis has been defined as "a disease due to breathing air containing silica charjKteTed anatomically by generalized fiweus changes and the development of miliwy ooduhtion in both lungs, and clinically by shortness of breath, decreased chest exJBflsion, lessened capacity for work, absence *Jever, increased susceptibility to tubercu- (some or all of which symptoms may rv present), and by characteristic X-ray *Boings.''* Silicosis has been known to manifest ItJ(fer widely differing periods of expo* 10 silica dust. Apparently, developthe disease depends upon: I* amount and kind of dust inhaled. - ** Jhe percentage of free silica contained *n the dust. form of the silica. j size of the particles inhaled. ' "^e duration of the exposure. ^bc powers of resistance of the indi* ^ 'ndual concerned. * TJ1* Presence or absence of a comph'cat* g procesi such as infection. tiieVany theories have been advanced over ^ years to explain why crystalline free 1 ,. ac{* a* it does in the lungs. It is now ^e'ed drat the fibrosis produced is caused y the hardness or sharpness of the particles, but by a combination of slight solubility with a physiochemical effect and an immunological effect--but no one is cer tain of the exact mechanism of the disease. Experimental work on the reasons for the development of silicosis is still going on in various parts of the world. If the precise mechanism of silicosis could be determined, better medical preventive measures might be developed and possibly a cure could be found. Amorphous free silica differs from cry stalline free silica in physical structure and in physiological effects. In the amorphous st3te, molecules of silica are rar : -nly ori ented and may be naturally cl .rted to opal and diatomaceous earth (1 -elguhr) or artificially converted into such forms as silica gel, silica fume, and fused silica or quartz. If amorphous silica is heated to a high temperature, as in calcining, forms of cry stalline free silica called cristobaljte and tri. dymite result, intermediate forms of amor phous silica are known as crypto-crystalline (ultra-microcrystalline). Inhalation of these crystalline forms can readily cause diatoniite pneumoconiosis. When diatomaceous earth is calcined, par ticularly in the presence of a trace of alka line flux, appreciable quantities are con verted to cristobalite. As a result of studies made by the U.S. Public Health Service, it has been recommended that the threshold limit value for crude or amorphous diatomite be placed at 20 mppcf (million particles per cubic foot), but that the atmospheric con centration for dust containing cristobalite be kept under S mppcf. Various commercial products containing particles of silica under l 11 in size are available. The physiological effects of these products have not been well defined. Until more experience with human hoinzs is avail able. these products should be handled with American Public Health Association, 1790 Broadway, New York City. "Report (Joint) of th Committee on Pneumoconi osis and the Committee on Standard Prac tices in Compensation of Occupational Dis eases." Year Book, 1931. mm* 1 'i j u j w r !\ w fj w w m u u i u u u w m h W - T O f .'it: j : v- i j^T ^pr I'M r '/: . y>i jk-. .ii'' f;->- *.*v '"V I- - *;> !> INDUSTRIAL HYCIZSE Free silica is uncombined silicon oioxide The fine airborne fibers of (SiOt). Silicates contain silicon and oxy pass through '.lie upper respiratory .. gen combined with other elements in more the lower parts of the iuegs to cjur il_ complex molecules. The SiOs reported in tion- and to form "asbestos bodif*" 1. chemical analyses for mineral and geological the fibers arc encapsulated. ^? reports is the ford of the silicon diov'de fibrosis probably begins as a "cellar" ' present, both the free silica (if present), the terminal bronchioles. There is and the silica combined in the mineral. Such that other minerals having a fibrous fv analyses are not reliable indications of the ter (except glass fiber) can produce silicosis potential of the material, because it tion similar to that of asbestos. is the uncombined or free silica that is most Following a study by the U.S s . important in industrial dust exposure. So Health Service of the asbestos teral? ul that an exposure can be properly evaluated, try,* it was recommended that the d^g*- the percentage of uncombincd silica must be eentration be kept at less than 5 -n~^- determined by petrographic analysis using a prevent asbestosis. Evaluation of ao ^ polarizing microscope or, preferably, by sure to asbestos dust is based oq the X-ray diffraction analyses and special ana amount of dust, since the concentration lytical chemical procedures. injurious fibers will be kept within There has been some experimental evi dence that some dusts may tend to inhibit limits if the fine dust is kept be!<r%- ' suggested threshold limit. the action of silica on the body, but this in hibiting action is so slight and uncertain that it must be discounted in practice. In fact, there is also evidence that the nonsiliceous components of a dust mixture containing free silica may provoke a disabling conditioo more severe than that caused by the silica acting alone. Miscellaneous pneumoconioses. , though a dust is classified as hard amounts above the TLV can lead to trx by causing a pneumoconiosis, mechanic irritating the walls of the respiratory r>-c or interfering with ordinary lung procw Mica dust and kaolin dust are two gcod amples of dusts that ordinarily are cm With the exception of asbestos 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 of silicate dusts than of free silica dust can be tolerated. In many industries, men have worked with silicate dusts that con tained no free silica without development of disability or of nodulation in the lungs. The ered benign hut amounts above the TLV cause a troublesome pneumoconiosis. ' pneumoconiosis has been observed in p ing operations where mica dust, but no silica was present. There were uu. changes in the X-ray pictures of the : and some disability. The cases occv where the dust exposures were missive many yean. X-ray may show shadows indicating dust deposits in the lungs, but the pneumoconiosis Toxic dusts and fumes is essentially harmless. However, partially Systemic reactions are caused by disabling pneumoconioses have been reported dusts and fumes of various elements where men have worked for long periods of their compounds and by certain organic time in very high concentrations of certain pounds. All metallic fumes are irriiatin; silicate dusts. Disabling pneumoconioses pecially when freshly generated. Indue from exposure to abnormally high concen important metals and their compounds trations of mica, tremoiite talc, and kaolin can have a toxic effect when the du dusts have been described in the literature. fumes are inhaled include arsenic, antis The clinical signs are not the same for these cadmium, chromium, lead, manganese, silicate dusts as for free silica, but the symp cury, selenium, tellurium, thallium, utu toms can be marked. and a few others. Asbestosis. Several minerals having a fibrous character are classed as "asbestos"-- hydrated silicates of magnesium with vari able amounts of iron, calcium, sodium, potas sium, and aluminum present as impurities. U.S. Public health Service, Washis. D.C. Study of Asbcstosis in the Ash Textile Industry." Bulletin No. 241.192 39-6