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196** N a tio n a l S a fe ty C ouncil ACCIDENT PREVENTION MAN UAL | for Industrial Operations i ii EDITION f : PLEASE DO f-.'Or REVOVE THIS C-:"J rrr--- -rr-'-T Tsxsod I'joaj oiivs si-ii r.:.C:a 1-V * >*" ^ NATIONAL SAFETY COUNCIL Chicago, Illinois 606^ 3fia 31VQ & +iil dusts. Radlther radloac. n extremely re. inely divided teased many 1.061 cu in.) cube when 3 give 10" an) particles >q m (9,000 1 cm (0.900 inely divided by the maw le voids bc-oncentration u ft of air ,m of materiin size, will : ft. toxic dusts, vorkroom atcample, the ; adopted by tovemmcntal g per Cu m I - per cu ft. | lly 0.002 ox he threshold i a of dust of ) cu ft (950 INDUSTRIAL HYGIENE velocity. This type of dispersion is known is dynamic projection and is a result of the kinetic energy of the particle's motion. As the mass of the particle decreases, however, l point will be reached when its kinetic energy (which is one-half the mast times the square of the velocity) is too small to I overcome air resistance. The particle's for' wird velocity is thus minimized and it re mains 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 contidered to have a mass so small that their movement is dependent on the containing 'air mass. Contaminants such as the larger inst particles, mists, and sprays, which are dispersed by dynamic projection, can cause external injury such as acid burns, eye damte, and dermatitis. The microscopic parti te* are dangerous to health if inhaled. Separation in airborne dusts Dust in the air may or may not have the 2"ne composition as its parent material. V* determining factors are the particle and density of each component in the *iginal mixture, and the hardness of the aterials (hard materials will resist the Wverizing action of a mechanical device). For example, foundry molding sand con- a large percentage of free silica with *t wcr percentage of clays. Most of the consist of fine particles that can be ?~orne. but most of the free silica parti- are too large to be airborne. The airrf.e dust, therefore, as compared with the ^Siaal mixture, may contain a much high- Percentage of clays and a much lower * ''"oatage of free silica. Dust particles are, of course, attracted by er'a^'li "^eir settling rate through still *"! vary with their size, density, and Microscopic particles settle out more **> / "lan larger particles because of their % . minor density and because of their .J ,n3uenccd by Brownian movement. ^ Particles larger than 10 n will set O2 Lrelrel>-lfasjtt. The estimated set- u n? ,1f1r ss^ilicc:a dusts in still air are ^ T--awbl.et 3ja9--A. lost of the particles in airborne indusT~ dusts are small. Because of air cur- the gne particies jn dust `clouds 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 Fall 1 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 p 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 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 toxic dusts axe 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 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 t i' r - f i! i ir i ' / \ , !j I: !ii i. : dusts. Radlther radioaca extremely -re. inely divided reised many 3.061 cu in.) cube when .'3 give 10" on) particles oq m (9,300 ! cm (0.930 Inely divided by the mass ,'ie voids be.XJncentration -u ft of air m of matcri> in size, will ft. i toxic dusts, workroom atxample, the i adopted by ^ovemniental , * ocr cu to per cu It aly 0.002 or :he threshold of dust or cu ft (2S0 ec. :ted hr*> t of be velocity. This type of dispersion is known as dynamic projection and is a result of the kinetic energy of the particle's motion. As die 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 overcome air resistance. The particle's for' ward velocity is thus minimized and it re mains 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 visible only through a microscope) are con. ridered to have a mass so small that their movement is dependent on the containing `air mass. Contaminants such as the larger dnst particles, mists, and sprays, which are diipersed by dynamic projection, can cause external injury such as acid bums, eye damage, and dermatitis. The microscopic partida are dangerous to health if inhaled. Separation in airborne dusts Dust in the air may or may not have the tme composition as its parent material. The determining factors are the particle *** and density of each component in the original mixture, and the hardness of the Merials (hard materials will resist the Etherizing action of a mechanical device). For example, foundry molding sand cona large percentage of free silica with *, "wer percentage of clays. Most of the consist of fine particles that can be but most of the free silica partitoo large to be airborne. The airdust, therefore, as compared with the ^Baal mixture, may contain a much highPercentage of clays and a much lower lrTCetoge of f,-ee s;lica. particles are, of course, attracted by yV,'ai "^eir settling rate through still ^ *ul vary with their size, density, and Microscopic particles settle out more I j an larger particles because of thrir .F minor density and because of their V,rK !n"Uenced by Brownian movement. Particles larger than 10 p will set- gj. relatively fast. The estimated set^or sihea dusts in still air are ^ to Table 39-A. of the particles in airborne indus- sma^- because of air curc "ne 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 1 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 p. 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 p 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 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 tiact 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 IS 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 K :"il :Ir S' - t' "1 J I I i j - - - f 'gy result, (cor putadvanced. Jy just an :rt dust in ire caused :s as lead, rcury, by in organic : from the id freshly pssibly ^of This is a ons which if, or skin ;.s organic me woods inorganic terial and 1 from inive organrontaining or grain (See the Dther Ochis chap- at, which er irritats such as se ulcera:ven lung hich may material* products that emit : Chapter INDUSTRIAL HYGIENE In 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 essentially inert and remain in the lungs indefinitely with no recognizable irritation, ind a few (like limestone dust) may be r gradually dissolved and eliminated without harm. ter 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 is foundries, glass manufacturing, granite cutting, mining, and tunneling in quartz rock. It is found throughout the world, and b the past it has had many names, such as miner's asthma, grinder's consumption, miner's phthisis, potter's rot, and stone mason's disease. The same occupational dis ease, however, is meant by all these names, *ad it is caused by dust from crystalline free silica, usually quartz. Silicosis has been defined as "a disease ue to breathing air containing silica char acterized anatomically by generalized fi brous changes and the development of miliJty nodulation in both lungs, and clinically by shortness of breath, decreased chest exPansion, lessened capacity for work, absence fever, increased susceptibility to tubercu*~* (some or all of which symptoms may h.' he present), and by characteristic X-ray ^dings."* Silicosis has been known to manifest itafter widely differing periods of expo- *ore to silica dust. Apparently, developB'et of the disease depends upon: The amount and kind of dust inhaled. -- The percentage of free silica contained 10 the dust. The form of the silica, j The size of the particles inhaled. ' duration of the exposure. The powers of resistance of the indi- ^ vtdual concerned. The presence or absence of a complicat- ln8 process such as infection. ij^laoy theories have been advanced over . years to explain why crystalline free befi3 iCtS aS ^ocs 'n l^e lunS*- 1* *s now l^ej'ed that 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 state, molecules of silica are rar ' -nly ori ented and may be naturally cl :rted to opal and diatomaceous earth (1 selguhr) 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 cristobalite and tridymite result, intermediate forms of amor phous silica are known 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 diatomite be placed at 20 mppcf (million particles per cubic foot), but that the atmospheric con centration for dust containing cristobalite be kept under 5 mppcf. Various commercial products containing particles of silica under 1 p in size are available. The physiological effects of these products have not been well defined. Until more experience with human beings is avail able, these products should be handled with care. American Public Health Association, 1790 Broadway, New York City. "Report (Joint) of the Committee on Pneumoconi osis and the Committee on Standard Prac tices in Compensation of Occupational Dis eases." Year Booh, 1933. 39-7 it i :t i .) . :I INDUSTRIAL HYGIENE I silicon dioxide The fine airbo: ilicon and oxy- pass through th icments in more the lower parts >'iOa reported in . tion- and to foi d and geological the fibers are : silicon dioxide fibrosis probabl :a (if present), the terminal bri le mineral. Such that other mine idications of the ter (except gla: terial, because it tion similar to tl is me unconiouieu ilica that i--s mo~st important in industrial dust exposure. So that an exposure can be properly evaluated, the percentage of uncombined silica must be determined by petrographic analysis using a polarizing microscope or, preferably, by X-ray diffraction analyses and special ana lytical chemical procedures. There has been some experimental evi dence that some dusts may tend to inhibit Following a Health Service of the asbestos textile try, it was recommended that the dust eo*. centration be kept at less than 5 mpptf ^ - prevent asbestosis. Evaluation of an er-o. sure to asbestos dust is based on the amount of dust, since the concentration of injurious fibers will be kept within limits if the fine dust is kept below A, 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 condition more severe than that caused by the silica Miscellaneous pneumoconioses. Even though a dust is classified as haralr*, amounts above the TLV can lead to tzoui, by causing a pneumoconiosis, mechanicaSr irritating the walls of the respiratory tyttei, or interfering with ordinary lung proctoeL Mica dust and kaolin dust are two good a. acting alone. With the exception of asbestos and some talcs, the silicate dusts do not ordinarily rame a serious disabling lung condition such amples of dusts that ordinarily are corral, ered benign but amounts above the TLV on cause a troublesome pneumoconiosis. Mia pneumoconiosis has been observed in grind- CUSdUUII^ ----------------- ^ where men have worked for long periods of time in very high concentrations of certain silicate dusts. Disabling pneumoconioses from exposure to abnormally high concen- trations of mica, tremolite talc, and kaolin dusts have been described in the literature. The clinical signs are not the same for these silicate dusts as for free silica, but the symp- toms can be marked. ____ their compounds and hy certain organic cca** pounds. All metallic fumes are irritating. * pecially when freshly generated. IndustriiSy important metals and their eompoundi tW can have a toxic effect when the dust fumes are inhaled include arsenic, antbsooff. cadmium, chromium, lead, manganese, cun', selenium, tellurium, thallium, unsiaok and a few others. - \'t 39-8