Document nkYZz5V5kpkNday0nnz7D6XaR

ACCIDENT PREVENTION MAN UAL for Industrial Operations DATE DUE EDITION PtE-SE C: 01 ; t- ; iE:cOd ".c-a c-,7" : . ? NATIONAL SAFETY COUNCIL CH.ccgc, lUi^o-s 606 3na 3iva r ifti. Radier radloac- extremely ly dtiv<ded cased many 061 cu In.) cube when give 10" i) particles {9.300 an (0.930 fly divided < (be mass voids bencentrelion ft of alr of matedi size, will ixic dusts, rlcroom si mple, the idopted by vemmcntal per cu m per cu ft. ' 0.00- ot threshold of durt or ru ft (250 can detrvf i diumetrr. e drtrrted anlv when , Du.t of cannot be ope. Me* *tV.V* t?i^J U partielf* ee>\ Cmwhen rf:uf Operaf/iUfc. ' 1 -- fK^s to iisnnrr " ;h IS DUSTRIAL HYGIENE Joeity. Tkii type of dijperjion ii known u dynamic projection and ii * result of the kinetic energy of the particle's motion. As Ac i"" of the particle decreases, however, a point will be reached when Its kinetic aaergy (which is one-half the mass times the squire of the velocity) is too small to overcome air resistance. The particle's for ' vird velocity is thus minimized and it revaiu suspended Is the cootainisg Air mass. As i rough approximation, macroscopic panicles (those visible to the salted eye) are considered to be dispersed by dynamic pmiectioo. Microscopic particles (those visible oaly through a microscope) are coodered to have a mast so small that their movement is dependent on the containing tb mass. Contaminants such as the Uiger dost particles, mists, aod sprays, which are dispersed by dynamic projection, can cause ererea] injury such as acid bums, eye damMt, aod dermatitis- The microscopic partitio are dangerous to health if inhaled. Stparaiion in airborne dusts Du in the air may or may not have the composition as its parent material. 7* determining factors are the particle *** d density of each component in the ^Ciaal mixture, the hardness of the ^trials (hard materials will resist the M'crizing action of a mechanical device). For example, foundry molding sand con- 1 Urge percentage of bee silica with cr percentage of clays. Most of the P Co,lr`st ( fin* particles that can be but most of the free silica parti *** loo large to be airborne. The air- dust, therefore, as compared with the ^aj mixture, may contain a much high* Percentage of clays and a much lower *^=^56 of free silica. particles are, of course, attracted by settling rate tlirough still vary with their size, density, and 4**) k CT0'CP'C Parriclcs settle out more i n.kfScr particles hccausc of their density and because of their .n^ucr,ccd by Bruwnian movement C, Particles larger than 10 u will setfelatjvcly fast. The estimated set tles i *5? Jor ,^JC^ dusts in still air are ^InTjblc 39-A. Particle? in airbomc indus- ^llj afc small, hit.tuic of air curc 6c particles in dust clouJs at an TABLE 39-A SETTLING RATES FOR SILICA DUSTS IN STILL AIR Size (M) 0.25 0.50 1.00 2.00 5.00 Time to Fell 1 ft (minutes) 500.0 187.0 54.0 14.5 2.5 operation will remain suspe&ded in the workroom air for relatively ioog 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 nasal passages, throat, larynx, trachea, and bron chi, from which they are expectorated or swallowed into the digestive tract. When larger particles of certain tone dusts are trapped in the upper respiratory passages, they can be ahsorbed by the body fluids in the nusj) passages and in the digestive tract before they are eliminated. Hence die final toxic effects of larger dust particles may be delayed. The larger particles of irr.tant dusts can cause immediate effects in the upper respiratory s>jlcm. Ragweed pollen, which varies from IS to 25 t* in diameter can cause hay fever from its action in the upper respiratory system. This fype of dust and other allergenic OP^s, as well as bacterial and irritant dusts, can cause difficulty even in tb** larger airborne sizes. When dust-lad*, n air u inhaled, some of 39-5 'I sr- th h m ""i1! i m i'T |i i r j '>ii^ T w, iqiwmKTWTWr i n , i nu' i iU W W W P ^ w r .. i; i < i \ I* i "7VV ^'2*- s1'--- ----. _ . r^&SBpreri-^'.. ^rftir-^., <*.^ya-a,. r - ,-^r rt igrfar ................. - - .- .. --..........................*-r p- i- i (i!M H I w m 1 'Mn iiqi' i asts. Ridler ndlosc. extremely ty divided cased many .061 eu in.) cube when Jive 10 0 particln m (9.300 cm (0.930 sly divided t the msu void] beneentratlon ft of air of nuterti lire, will use dusts, rfcroom *<npfe. the idopN.il by eemmcntal per eu re per cu ft 0.002 os ; threshold of diilt or ru ft (2S0 can detf'"* , ii.ime'er. e detects ,nk *hf*t n. D^ cannot ^ \* t tK*; CtT' , rf^ r.iti* iK^s /WDUSm/AL HYGIENE vdodty. Ttii type of dispersion is known TABLE 39-A. u dynamic projection and i] a result of the boetic energy of the particle's motion. As of the particle decreases, however, SETTLINC BATES FOR SILICA DUSTS IN STILL AIR a point will be reached when its kinetic merxy (which b one-haIf the mass times Size Time to the aQuare of the velocity) b too small to erereome air resistance. The particle's for (*0 Fell 1 ft (minutes) * ward velocity b thus minimized and it re* maiBJ suspended in the containing air mass. As a rough approximation, macroscopic particles (those visible to the naked eye) in considered to be dispersed by dynamic 0.25 0.50 1.00 2.00 5.00 590.0 187.0 54.0 14.5 2.5 prejcct>OQ. Microscopic particles (those liable only through a microscope) are coo* . ddcred to have a mass so small that their movement is dependent on the containing t 'ah bus. Contaminants such as the larger dost particles, mists, and sprays, which are dispersed by dynamic projection, can cause eternal injury such as acid bums, eye damaie, and dermatitis. The microscopic parti te are dangerous to health if inhaled. operation wtfll remain suspended in the worlaoom 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 panicles so that the farther dust is from its source, the Reparation in airborne dusts Dust in the air may or may not have the greater the percentage of small particles it contains. me composition as its parent material. Mechanism of inhalation 7* determining factors are the particle tee and density of each component in the mixture, and the hardness of the loials (hard materials will resist the Wveruing action of a mechanical device). Tor example, foundry molding sand con- With the exception of such fibrous mate rials as asbestos, dust panicles 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 pf** Urge percentage of free silica with a few panicles up to 10 u in size may percentage of clays. Most of the enter* the lungs occasionally, nearly all Tj* of fine panicles that c&o he the larger panicles are trapped in the nasal V^me, but most of the free silica parti passages, throat, larynx, trachea, and bron ?* *** too large to be airborne. The air chi, from which they are expectorated or yTM* oust, therefore, as compared with the swallowed into the digestive tract. When ^Ca*l i&ixtuxe, may contain a much high- larger panicles of certain toxic dusts are ^ P^ceotagc of clays and a much lower trapped in the upper respiratory passages, *^Ugeof free silica. they can be absorbed by the body fluids in particles are, of course, attracted by "^le*r **ttUng rate through still \v^ry their si2Ct density, anc* ^^7* Microscopic particles settle out more 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 *UUv*l " ^r^cr Part*cUs hccause of thrir dusts can cause immediate effects in the lm-.g yminor density and because uf their upper respirator)' s> >t. m. l0uenccd by Brownian movement. Ragnecd pollen, which varie from IS to Oki* ^aft^c^cs larger than 10 u will set' 25 u in diameter can cause hay fever from relatively foLSt. The estimated set* its action in the upper respiratory system. Cw i ,*0f s^ic3 dusts in still air are This type of dust and other allergenic types, 1,1 Table 39-a. as well a< Lwetcn.d and irrit.mt dusts, can ^ie particles in airbnmc indus* cat2$c difficulty even in ihr larger airborne ^.4lScarc Sfr,all. Rccjaim: rv( air cut sizes. e fine particles in dust clouds at an When dust-laden air is inhaled, some of 39-5 '=zrrm iv ; 1i ! . *I 1 11 1 . 1, y mult, (cor puldvueti |ust an 1 dust tn Jt ctuscd s as lead, muy, by a organic from the i fmHIv aibiySf Hus is a is which . or skin organic t woods ^organic rial and tom ine organoUioing jt grain See the her Ot is chap- . which irriut* such as ulceraso lung :h may ulerials rodnCU at emit Chapter Cfn^ id *ab-ocraft' merely led de,,rv. A of P^ se dl*m rl .dtion INDUSTRIAL HYGIENE la %eO' tare cases, enough dust has been fahsled to cause mechanical blockage of the sir spaces. (Flour dust has been known to this .condition.) Some dusts may be essentially inert and remain in the lungs ^definitely with oo recognizable irritation, sad 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 dun. It is well-known in industries where eystalline free silica dust is present such u foundries, glass manufacturing, granite mttisg, mining, and tunneling in quartz rock. It is found throughout the world, and b the past it has had many names, such as iner*s asthma, grinder's consumption, felaer's phthisis, potter's rot, and stone*to*on*s disease. The same occupational disoae, however, is meant by all these names, ad it is caused by dust from crystalline free silica, usually quartz. SilicosU has been defined as "a disease to breathing air containing silica char acterized anatomically by generalized fitou changes and the development of milifJF adulation in both lungs, and clinically S' shortness of breach, decreased chest ex- lessened capacity for work, absence * ;ever* increased susceptibility to tubercu I?* ^*me or ell of which symptoms may tooupirgejs*e*nt), and by characteristic X-ray ^Silicosis has been known to manifest itr*f "ter widely differing periods of expo rt to silica dust. Apparently, develop * the disease depends upon: The amount and kind of dust inhaled. "* percentage of free silica contained * the dust. ^ Th* form of the silica, j of the particles inhaled. ^ duration of the exposure. The powers of resistance of the indi- 7 Vld`ul concerned. Th* presence or absence of a complicat- 4 Process such as infection. jj^4y theories have been advanced over ^Ciyears l0 etpljin why crystalline free 4S't docs in tlic lungs It is now ^ tJut die fibrosis produced is caused Y the hardness or sharpness of the particles, but by a combination of slight solubility with a physiochemical effect aod 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 io various parts of the world. If the precise mechanism of silicosis could be determined, better medical preventive measures might be developed and poscibly a cure could be found. Amorphous free silica differs from cry stalline free silica in physical structure and Is physiological effects. In the amorphous state, molecules of silica are rar ' mly ori ented and may be naturally ci .reed to opal and diatomaceous earth (* .etguhr) or artificially converted into sucli forms as silica gel, silica fume, and fused silica or quartz. * If amorphous silica , is heated to a high temperature, ss in calcining, forms of cry stalline free silica called cristobalite and tridvmite result, intermediate forms of amor phous silica are lmowa as crypto-crystalline (ultra-microcrystalline). Inhalation of these crystalline forms can readily cause diatomite 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 dintomite be placed at 20 mppcf (million particles per cubic foot), but dial the atmospheric con centration for dust containing cristobalite be kept under 5 mppcf. Various commercial products containing particles of silica under 1 it in sire are available. The physiological effects of these products have nnt b*en well defined. Until more experience with human b*inct is avail, able, these products should be handled with core. # American Public Health Association, 1790 Broadway. New York City. "Heport (Joint) of the Committee on Pneumoconi osis ami the Committee no StanJard Prac tice* in Compensation of Occupational Dis eases.** Year Bool, 1913. ill m .