Document 7O22B8EpJGjKVdrzxM8q5QmBR

DU5TRIAL HYGIENE 200 days old, and it appears that tS? difference in activity was associated with the exposure of the experimen group to an atmosphere containing1 high concentration of light nega ions. by natural and by mechanical methi Jour. Sect., Keating, Piping and Conditioning, 1931, S, 866. _ 5. Herbinoton, L. P.: The influent ionized air upon normal subject? Clin. Invest., 1935, 14, 70. 6. Loeb, L. B.: The nature of ions in air and their possible physiolq effects. Jour. Sect., Heating, Pi, and Air Conditioning, 1934, 6, 437.' 7. Petirsin, W. F.: The patient and w-nher. Vol. 2. Nervous and Diseases. Edwards Bros.,' \100r, Michigan, 1934. THE MINERALOGY OF ASBESTOS DUST* Cornelius S. Hurlbut, Jr. Instructor in Mineralogy, Harvard University, Cambridge, Mass. AND Charles R. Williams Petrograpker, Engineering Laboratory, Liberty Mutual Insurance Co., Boston, Mass. HE term asbestos has no defi operations in both spinning and mold Tnite mineraiogical significance, but is applied to several min ing of asbestos were obtained. Micro scopic examination of the dusts erals which, under certain circurmev ealed a most startling condition, stances, occur in fibrous form. The namely that asbestos fibers in respir hydrous magnesium silicate "chryso- able sizes make up only a very small tile" (or serpentine asbestos) is the percentage of the various dusts. most widely used of these asbestos The generally accepted maximum minerals. According to recent figures size for dust particles which can pene s of the U. S. Bureau of Mines (1) over trate into the lungs is about 10 90 per cent of the asbestos fabricated microns. As a result of animal ex in the United States comes from mines perimentation with asbestos dust, how I near Thetford, Quebec. These mines ever, Gardner and Cummings (2) are the leading producers of chrysotile. state: "The experiments demonstrate Other forms of asbestos are "Croci- that fibrous structures at least as long jdolite," soda-iron silicate; "amosite" as 200 microns can pass the protective `'and "anthophyllite," iron-magnesium mechanism of the upper respiratory silicates, but all are of minor impor- tract and enter the lungs." This is ^tance from a quantitative point of confirmed by human lung sections of iView. asbestosis victims which the writers Dusts generated in the processing have seen. Thus the percentages ft asbestos are known to be harmful given in the following tables represent jphen inhaled in sufficient quantities, the number of particles less than 10 the mineraiogical composition of microns in maximum dimension for ?wh dusts is an important factor in all minerals except asbestos. In the problem uf the effects uoinr the case of that mineral, fibers as long as 3piratory system. During the past 200 microns are included as respirable r the writers secured for petro- providing their maximum thickness Paphic analysis dusts from six as- does not exceed 5 microns. In none of 3 plants in various parts of the the dusts examined was there present Jountry. Samples of rafter dust more than a trace of asbestos with the ted by many of the different maximum dimension less than 10 f *,Received for publication October 7, microns. The mineral particles which make 289 V i \) h * <jIENE [17, no. 6' microns in maximum di a.< found to be essentially the hat below 10 microns, with m of asbestos, the fibers of y in length from 50 to 300 id average about 15 microns mineralogy of asbestos dust BIBLIOGRAPHY j. Bowles, 0.: Asbestos--domestic and foreign. U. S. Bur. Mines Inf. Cir. No. 6790, June, 1934. 2. GaRonbr, L. U., and Cbmminos, D. C.: Studies on experimental pneumonokoniosis. VI. Inhalation of asbestos losis infection. This Jour., 1931, IS, 65, 97. ' See also: Ladoo, R. B.: Non-metallic minerals. McGraw-Hill: New York, 1925. Merewethbr, E. R. A.: The occurrence dust: its effect upon primary tubercu- of pulmonary affections in asbestos workers. This Jottr., 1930, 12, 198. .....g. A portion of a hair-like % nany smaller fibers. Note the by crushing. (Crossed nicol* vjfz Summary phic analyses of rafter dust ^ sbestos processing plants, j molding and weaving of losed that in the respirable^ stos is a relatively twin* istituent. Talc, serpentine, and magnetite predominate :he dusts examined. Tie ises as to the importance f ayed by these minerals to ?e resulting from dust e**. the asbestos industries. ii 290 THE JOURNAL OF INDUSTRIAL HYGIENE [17, no. 6 up the bulk of the respirable portions operation, but they were largely con p-r :a these dusts are the impurities found fined to the sizes above 200 microns. in raw asbestos. Figure 1 shows the The amount of respirable materia! in pnnrity of asbestos fibcrj in the drift- I this dust was smaller than in the other and the relative abundance of granular two, for most of it is apparently material. As the composition of dusts liberated in operations preceding the from similar operations in all plants (spinning. was analogous, only two groups of Because cement is used in the manu data are necessary to illustrate the facture of many molded asbestos prod existing conditions. Moreover, all of ucts, calcite (calcium carbonate) is Fig. 1.--Photomicrograph of dust from preparation room. The black grains are msg nettite, while the lig_ ht ones are mostl.y carbonate and talc with some serpentine. A few fibers of asbestos can be seen. The large white fiber to the left of the picture is organic. (Crossed nicols 175 X) the plants included in the investiga tion use chry 'tile as the raw material. The dust produced by the prepara tion of the asbestos contained a higher percentage of respirable asbestos fibers than any of the other dusts examined.' The carding dust consisted of some coarse (25 to 300 microns) asbestos fibers and abundant respirable grains of other minerals. Asbestos fibers dominated the dust from the spinning generally the chief constituent of the dusts from such operations. Thus, all of the samples examined from this type of work contained a iarge per centage of acid soluble (1:10 HC1) material by weight. The lowest was 64.8 per cent. Asbestos in long fibers is an im portant constituent of the dusts from the mixing and pulverizing operations but is relatively unimportant in DL'STRIAL HYGIENE [17, no. 6 odi m, but they were largely coa-f 1 to the sizes above 200 microns. _ . amount of respirable material in this dust was smaller than in the other two, for most of it is apparently liberated in operations preceding the pinning. - Because cement is used in the manu- acture of many molded asbestos prod-Jj cts, calcite (calcium carbonate) is; >n room. The black grains are n d talc with some serpentine. A r to the left of the picture is orga illy the chief constituent of tfiS from such operations. Thus,MJ samples examined from Udfl >f work contained a large e of acid soluble (1:10 H< ll by weight. The lowest,* r cent. stos in long fibers is an; constituent of the dustr ing and pulverizing Of relatively unimportant i yfov., 1935] MINERALOGY OF ASBESTOS DUST 291 spirable sizes. Dust from the cutting room showed almost no asbestos. The small percentage of respirable asbestos is even more impressive when it is con sidered that 90 per cent of the total number of particles of all the dusts were respirable. In most of the samples asbestos is present in sizes varying from 20 to -TABIrfi- fibers while still retaining its original length. The processing, therefore, splits the asbestos finer and finer with little tendency to shorten it. More over, inasmuch as the fibers tend to mat together they are less likely to be picked up by air currents. Gran ular particles, such as the foreign material present in these dusts, are easily dispersed. The talc, serpentine, magnetitite, Dust Produced in the Manufacture of and carbonate so abundant in the " Asbestos Textiles dusts are all impurities in the asbestos PREPA- lCAROtNolsHXNING las mined. Figure 2 shows the raw RATIOS 1 ' material with these minerals clinging |to the long fibers of asbestos. In all Talc.......... Carbonate. Magnetite. Serpentine. Asbestos Iv Others. rases where the Canadian raw material examined microscopically, the ^ mineral assemblage of impurities is Essentially the same. Talc is a mica-like hydrous mag nesium silicate, and its platy character TABLE 2 . Dust Produced in Molding Operations in the Manufacture of Asbestos Building Bricks, etc. permits it to be dispersed easily and stay suspended in the atmosphere. Serpentine is chemically identical with asbestos (chrysotile); it is the material iriRcorn mo MIXING RULYER- ROOK ROOK composing the rock in which asbestos veins are found. Unlike asbestos, per cent per cent percent however, it breaks into equidimen- Talc......................... 4 Carbonate............... 75 Magnetite................ trace 8erpentine............... 4 Aabestoa.................. trace 1 17Others..................... trace 70 4 10 3 13 trace 70 9 6 trace 15 sional grains that have no tendency to mat together. Magnetite is an iron oxide which also forms granular par ticles. Carbonate as listed in the analyses includes three carbonates-- calcite (CaCOj), dolomite [(Ca, [f.500 microns in length and from i to 50 F.microns in diameter. Practical-/ all [.particles, however, are over 100 mi crons in their longest dimension. The jfcason for the scarcity of asbestos in porter fibers is no doubt due to its physical nature. Asbestos is bounded parallel to its elongation by perfect [planes of cleavage which permit it to ;>reak into almost infinitely slender Mg)C03], and magnesite (MgCOs)-- all having similar physical properties; and, like serpentine and magnetite, they break into roughly equidimensional particles. The physical nature, then, of all these impurities permits them to be liberated from the asbestos during processing operations and thus find their way into the plant at mosphere. 292 THE JOURNAL OF INDUSTRIAL HYGIENE [17, no. 6 Gardner and Cummings of the Saranac Laboratory have for some time been carrying on experimental work in asbestosis (2). They sub jected guinea pigs, white rats, and rabbits 8 hours a day, for as long as 2jj years, to air laden with asbestos than 10 microns in maximum di mension was found to be essentially the same as that, below 10 microns, with the addition of asbestos, the fibers of which vary in length from 50 to 300 microns and average about 15 microns in diameter. . ! ] ] 4 Fig. 2.--Photomicrograph of raw asbestos used in spinning. A portion of a hair-like asbestos fiber is shown after it had been separated into many smaller fibers. Note the abundance of granular impurities that have been set free by crushing. (Crossed nicols TABLE 3 Respirable Material in King's Floats Serpentine-- 40% Carbonate____ 185? Magnetite----- 12% Talc................. 12% Asbestos........ 14% Others.............. 4% dust. The material used for these! experiments is called King's Floats an asbestos dust obtained from the Thetford producers. A petrographic analysis of this material is given in Table 3. The material in King's Floats larger Summary Petrographic analyses of rafter dust from six asbestos processing plants, including molding and weaving of asbestos, disclosed that in the respirable sizes, asbestos is a relatively unim portant constituent. Tale, serpentine, carbonates and magnetite predominate in ail of the dusts examined, 'the question arises as to the importance of the part played by these minerals in lung damage resulting from dust ex posures in the asbestos industries.