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The American Ceramic Society February 15,1993 I hereby certify that the attached copies of Journal of the American Ceramic Society, Volume 16,1933, are true and accurate copies, which are maintained in the normal course of business at the American Ceramic Society, 735 Ceramic Place, Westerville, Ohio 43081. Ceramic Information Center i 735 Ceramic Place Westerville, Ohio 43081-8720 614 890 4700 TWX: 7101109409 Journal of the American Ceramic Society VOLUME 16, 1933 A Monthly Journal Devoted to the Arts and Sciences Related to the Silicate Industries Editorial and Advertising Offices: 2525 North High Street, Columbus, Ohio. Publication Office: 20th and Northampton Streets, Easton, Pa. Editor: Ross C. Purdy; Assistant Editor: Emily C. Van Schoick. Committee on Publications: Louis Navias, Chairman; M. F. Beecher, L. J. Trostel, R. M. King, Ross C. Purdy. dust elimination in the pottery industry* By Edward Schramm ABSTRACT pust counts were made in different parts of a pottery with and without natural and duced ventilation. The hoods installed at the benches of the finishers and setters >nthe remodeled stoveroom air-circulating system are described and illustrated. 9,^e effectiveness in reducing the dust count is given quantitatively. I. Introduction There have been two generally recognized health hazards in the manu facture of pottery, one due to the use of lead, the other to the breathing 0f air containing silica dust. The former is more easily dealt with since 0 most potteries the use of lead is localized to dipping and glaze making. \t has been found that "fritting" the lead, i.e., smelting it into a glass before grinding into the glaze mixture, removes the danger of lead poisoning if the lead silicates or borosilicates are compounded to be only slightly soluble in acids so that they are not readily absorbed by the system. The practice of "fritting" and other precautionary measures have been adopted by many potteries in which lead poisoning is almost unknown today. The dust problem, however, is more difficult; it is a problem not confined to the potteries and in fact is more serious in various other industries. The writer, therefore, was sufficiently concerned with it to undertake an experi mental study of conditions in the plant to serve as a guide to remedial measures. II. Dust Particle Count In initiating this work, the writer was fortunate in having the assistance 0f Dr. Leonard Greenburg of the United States Public Health Service. Dr. Greenburg had been instrumental in the development of a convenient and efficient apparatus for dust determinations known as the impinger (Fig- 1). /D Imoineer In this machine, air is forced at high velocity through a II " nozzle under water, striking a brass plate, and is broken into many bubbles. Due to the inertia of the dust particles, the impinging serves to free them of the adhering air film so that they are wetted and retained by the water in the flask. Note: A demonstration of the principle can be given with tobacco smoke in an ordinary pipette. If the smoke-laden air be blown slowly through water in a beaker or flask, the smoke can be seen to emerge. If, however, the end of the pipette be placed close to the bottom of the beaker and the smoke-laden air sharply ejected, the extremely fine tobacco smoke particles are absorbed and the air comes through clear. The impinger machine is provided with a flow meter of the Venturi type which is calibrated against a gas meter. In operation air is sucked through at the rate of one cubic foot per minute and the time of sampling can be varied at will, 15 or 30 minutes being usual. The sample in the flask is diluted to 500 or 1000 cubic centimeters according to the time of sampling; 1 cubic centimeter portions are examined in a counting cell for the dust count at a magnification of 100X, objective and eyepiece each 10 X. A factor is used to convert results to the number of particles per cubic centi- * Presented at the Annual Meeting, American Ceramic Society, Pittsburgh, Pa.. February, 1933 (Materials and Equipment Division). Received February 24, 1933. 205 206 SCHRAMM meter of air. The remainder of the sample is filtered through a Gooch ; crucible to give the total weight of dust collected. 1 (2) Dust Count To c^iec^ the technique, two half-hour samples were and Dust Weight ta^en unc*er different atmospheric conditions. These were each divided in two and worked separately giving the results in Table I. DUST The number of large pa fraction of the total, nor astandpoint, so that in latei counts are fairly consiste appear less satisfactory bu; Check on Sample 1 1 2 2 3 3 4 4 Machine A B A B A B A B ties are being considers appear more reliable thai case is probably reversed filtration and weighing s. Fig. 1. Sample la lb 2a 2b Table I Check on Laboratory Work Dust count per cc. air Total Over 10m 119 2.3 125 2.1 61 1.7 51 1.1 Dust weight (mg.) 0.8 0.6 0.3 0.3 As a further check simultaneous samples were taken with two machines, the results being recorded in Table II. follows that the counts a double method gives a ro (1) Jigger Shop ^ briefly described as follov crews, consisting of a jigg DUST ELIMINATION IN POTTERIES 207 The number of large particles, over 10ju diameter, is not an important fraction of the total, nor are these larger particles important from a health standpoint, so that in later work this observation was omitted. The dust counts are fairly consistent throughout; the checks on the weighings appear less satisfactory but it must be remembered that very small quanti- Sample 1 1 2 2 3 3 4 4 Table II Check on Sampling and Laboratory Work Machine A B A B A B A B Total 244 274 224 228 48 54 56 58 Dust count >10m 3.4 3.5 4.1 3.4 Dust weight (mg.) 3.2 2.1 1.4 1.9 1.4 0.8 0.8 0.8 ties -are being considered. With low dust concentrations the counts appear more reliable.than the weighings; with high concentrations the case is probably reversed since the counts become more difficult and the filtration and weighing subject to less error. It will be seen in what Fig. 2. follows that the counts and weighing are generally in agreement and the double method gives a rough check on the work. HI. Shop Studies (1) Tieeer Shoo These determinations were begun in the jigger shop. J &b F The situation when the work was started may be briefly described as follows: In each unit there were three or four working crews, consisting of a jiggerman, a batter-out, and a finisher. The jigger- 208 SCHRAMM man and batter-out making the ware handled only wet day. The finisher, usually a girl, removed the dried ware from the molds, trimming, dusting, and arranging it in bungs. Evidently in this set-up, the finishing was the chief source of dust. The stove room for drying ware was at the workers' back and was provided with a series of slides with shelves (Fig. 2). Heat was supplied by a hot-air blast entering the back of the stove room, traveling forward, and escaping between the slides at the front, whence it was supposed to enter an overhead suction duct to be recirculated through the heating coils and stove room. During the summer Shop condition Wintdi ows clostted, faan oan tt tt tt tt tt tt tt Windows closed, fan off, and stairway screened Windows open, fan on Table III Clay Shop Survey Description of sample Shop, early morning (blank) Shop, crew working Stove room Hot-air supply duct Shop, early morning (blank) Shop, crew working Shop, crew working Dust count 57 132 103 44 43 144 97 Dust (mg.) 0.1 1.95 0.5 0.1 0 2.5 0.5 months windows were kept open, making the atmospheric condition different from that of the winter period. The first undertaking was a survey of the actual dust content of the jigger-shop air covering the range of operating conditions. A large number of tests was made (30-minute samples) with the surrounding details noted. The general averages are recorded in Table III. The data in Table III serve to show the average amount of dust as compared to normally pure air and to indicate the effect of ventilating conditions. The detailed data brought out more clearly than the averages the effect of air currents. Thus in one day there was obtained an appre ciable count in the morning with the outside air quiet and a negligible Table IV Dust Tests in Closed-Off Room Conditions of test Early morning (blank) Ordinary working conditions Exhaust hoods for finishers Exhaust hoods and no air escape from driers Dust count 40 156 99 60 Dust (mg.) 1.9 1.0 0.8 count in the afternoon with a sharp breeze blowing through the windows. A reversed effect was obtained by pulling out the stove-room slides, allowing the hot blast to sweep direct into the room. It will be noted in Table III that the hot-air supply duct gave low dust counts and that considerable dust was picked up by the air in traveling through the stove rooms. Because of the impossibility of eliminating entirely stray air currents in the regular working units, one section of the shop was boarded off to serve as a testing laboratory for further studies in dust elimination. Tests were made daily over a period of a month or more under each of the fol lowing conditions: (a) ordinary working conditions; (b) with special The iming, ishing ras at helves of the it the to be mmer i ust Ug.) .1 .95 .5 .1 0 .5 .5 dition >f the large nding ist as lating :rages -PPreigible >g) lows, lides, ed in that stove rents off to Tests e fol>ecial DUST ELIMINATION IN POTTERIES 209 exhaust hoods for the finishing operation; (c) with special exhaust hoods ^jjd with stove-room circulation arranged to prevent escape of hot air into the working room. The general averages are recorded in Table IV. (2) Separate These experiments for eliminating dust from the jigger- shop air. Since the finishing was a pjain source of trouble, it was de cided to reorganize the whole jigger- shop procedure by centralizing that operation in two rooms. This change made it possible and economical to provide adequate suction hoods for the finishers. Details of the finishing hood are shown in Fig. 3 and a Fig. 3. battery of hoods in Fig. 4. The following tests made close to the finisher show the efficiency of the system. Table V Dust Tests near Finisher Conditions of test Dust count Old finishing; no suction fjew finishing bench; suction 228 129 Dust (mg.) 5.9 1.2 stove Rooms The dust survey proved the necessity of stopping the ' ' air leakage from the stove rooms. Placing the whole drying system under suction was not feasible and accordingly a closed-circuit pressure system was next established. The escape of air was observed by taking anemometer readings at the top and bottom of slides at two points, A and B, at the front of the stove room. The original drier (Fig. 5) with air blast at the back and overhead external suction duct gave anemometer readings as follows: A top 774 A bottom 715 B top 831 B bottom 884 The first modification consisted in closing the main suction duct to the room air while connecting it to the Fig. 4. drier by a series of narrow vertical flues placed between the slides. With this arrangement it was possible to reverse the air flow, supplying the blast through the vertical flues and taking the discharge from the back. Anemometer readings corresponding to the above under this system were as follows: 210 SCHRAMM A top 330 A bottom 151 B top 198 B bottom 278 (draft in) The altered system had two serious defects (a) the vertical supply flues constituted an excellent radiator and caused overheating of the shop and (b) drying of the ware in different parts of the slide was very unequal. With the same construction, it was decided to return to the air supply through distributing screens at the back, obtaining the following readings; A top A bottom B top B bottom 362 181 264 116 This method gave more even drying Old Stovf Room fig. 5 New Sro^E Room Fig.6 but there was still excessive heating from the vertical flues. Further consideration of the problem led to the conclusion that better control over air leakage and at the same time improved drying would be obtained by substituting a rising vertical column for the horizontal air movement. There was very little space available between the slides, but it appeared possible to install a system of narrow horizontal supply ducts in place of the guard rail between the slides at the bottom. The system finally adopted is shown diagrammatically in Fig. 6. The main pressure duct at the back of the stove room supplies air to the system of horizontal ducts whence it rises to a new suction chamber extending across the entire top of the stove room. By providing properly spaced take-off's from this suction chamber an even distribution of air is obtained giving improved drying as well as economies in power and steam. This system has been installed throughout the plant. Typi cal anemometer readings are as follows: A top 215 A bottom 0 B top 218 B bottom 0 (4) Kiln The discussion so far has Placing been confined to the jig- Rooms er shoP' In the manu` facture of vitreous china tableware there are other sources of dust in the "bedding" or placing operation and in cleaning the ware after the first or biscuit fire. These problems are less acute in most semi- vitreous and in true porcelain plants where a supporting bed is not em ployed. Flint is the cheapest and most commonly used bedding Fig. 7. material, and, unfortunately, silica is the most harmful of the common mineral dusts. This situation has been a source of much concern in England where flint is largely used for bedding bone china. An interesting discussion is found in a paper by Moore.1 Two methods of mitigation referred to are (a) elimination of the fines from the placing flint, thereby removing the harmful portion, and (b) substitution of other 1 Trans. Ceram. Soc. [Eng.], 31, 153.(1932). DUST ELIMINATION IN POTTERIES 211 materials, especially bone ash and alumina. For a great many years this offlpany has used kaolin instead of quartz for placing. The operation Cf claying up the bungs of ware is carried out under a hood with strong Hraft (Fig- 7)- Similar precautions are taken in cleaning the ware after the fire (Fig. S). IV. Medical Aspect It is not within the scope of the present report to consider in detail the j^edical aspects of the subject. Much valuable work has been done by Fig. 8. the United States Public Health Service, some of which will be briefly reviewed. Any mineral dust entering the lungs causes the formation of a fibroid tissue reducing the area of effective lung tissue, a condition known as fibrosis. The development is gradual and a long period of years may elapse before marked physiological effects, notably a shortness of breath, become apparent. There is a lowered resistance to respiratory diseases, colds, bronchitis, pneumonia, and tuberculosis. It has been dearly established that silica dust is especially harmful, and the resulting condition is known as silicosis. It was thought at first that the bad effect of silica was due to the hard 212 SCHRAMM character of the mineral. This view, however, is inconsistent with the observation that a still harder dust, silicon carbide, does not produce the same physiological effects, and especially the same susceptibility to tuberculous infection. The specific effect of silica is thought to be associated with its solution and the formation of colloidal silicic acid, which apparently tends to destroy the phagocytes or natural scavenging cells, which normally attack and absorb poison, or tubercle bacilli. Studies in South Africa and in this country indicate that practically no particles over lO/i diameter enter the lungs, and very few over 5n, so that the dangerous dust is the finer, microscopic fraction. Particles below 0.1m are of the order of size of the body colloids and probably harmless in the case of inert minerals. If, however, the chemical theory of the toxicity of silica is accepted, there can be no lower limit to the particle size which will be harmful. One of the most complete correlations between dust exposure and medical histories is contained in a study of the granite industry by the U. S. Public Health Service.2 This is particularly interesting since granite dust contains 35% free quartz, about the average content of pottery bodies. Some of the more important conclusions will be quoted from Health News, a release of the Public Health Service. It was possible, by differentiating occupations on the basis of the amount of dust exposure, to determine within broad limits how much dust of the composition studied can be tolerated by workers without serious deleterious effects. A maximum of dust exposure falling somewhere between 10 and 20 million particles per cubic foot of air is a desirable limit (for dust containing 35% free silica). Exhaust velocities at the ventilating hoods of 1500 feet per minute served to keep the dust exposure of the operator below 10 million particles per cubic foot of air. The limit established was not found to prevent entirely the occurrence of silicosis, but there seemed to be no particular liability to tuberculosis within this limit. Case histories of men working in the granite industry brought out the following salient points: () The long period of service (20 years or more) before the liability to tuberculosis becomes manifest. () The sharp correlation between length of exposure to dust and the prevalence of tuberculosis and also the death rate from this disease. (c) The close relation between the extent of dust exposure and the health of the men. V. Maximum Dust in Potteries below Dangerous Minimum in Granite Quarries Conditions in the potteries have never approached, to the knowledge of the writer, those prevailing in granite quarrying as set forth in the fore going. It is to be noted that a dust count of 10 to 20 million particles per cubic foot is described as a desirable condition. This corresponds to 352 to 704 particles per cubic centimeter. Before the work described in this report was begun, the average dust count in the clay shop was about 150 or less than half the strictest requirement of the Public Health Service. Through the measures described this low figure has again been cut in two. The count of about 130 near the hoods in the finishing rooms is misleading, for nearly all of this consists of kaolin sprinkled on the ware and the equivalent count in terms of 35% free quartz is too low for measurement. It therefore appears that conditions have been improved to a point ' Public Health Bull., No. 187 (1929). D where the dust hazard no longer exists. (1) Final Report, M Africa, Govt. Printing and (2) A. Mavrogordato ses," S. African Inst, for > 1922. (3) R. R. Sayers, Mines, 1925. (4) "Health of Worki Industry),'' U. S. Public 1 (5) "Silicosis among Based on the Study of " [Feb.] (1929). The word "phthisis" 1* t with the iroduce the y to tuber, associated apparently h normally ctically no on, so that cles below ' ^armless in he toxicity size which ; osure and ry by the i ice granite if pottery ited from : unt of dust .ion studied :um of dust >ot of air is : red to keep f air. The but there e following uberculosis prevalence alth of the ium nowledge the fore particles ponds to cribed in as about i Service, t in two. sleading, and the urement. ) a point | DUST ELIMINATION IN POTTERIES 213 where the dust hazard formerly associated with the manufacture of pottery no longer exists. Bibliography (1) Final Report, Miners' Phthisis* Prevention Committee, Union of South Africa, Govt. Printing and Stationery Office, Pretoria, 1919. (2) A. Mavrogordato, "Studies in Experimental Silicosis and Other Pneumoconio ses," S. African Inst, for Medical Research, Publication, XV, Johannesburg, March 31, 1922. (3) R. R. Sayers, "Silicosis among Miners," U. S. Dept, of Commerce, Bur. Mines, 1925. (4) "Health of Workers in Dusty Trades, II: Exposure to Siliceous Dust (Granite Industry)," U. S. Public Health Bull., No. 187. (5) "Silicosis among Rock Drillers, Blasters, and Excavators in New York City, Based on the Study of 208 Examinations," Jour. Industrial Hygiene, 9 [2], 37-81 [Feb.] (1929). * The word "phthisis" is here used to mean "silicosis" complicated by tuberculosis