Document KGq5yB1GeDKmOzZq6dE0eRGLx

FILE NAME: Foster Wheeler (FW) DATE: 1946 Nov DOC#: FW002 DOCUMENT DESCRIPTION: Trade Journal Article - Industrial Hygiene Importance of Dust - Southern Power & Industry P fol Industrial Hygiene Importance of Dust By N.- V. Hendricks Chief Engineer Industrial Hygiene Service, Georgia Department of Public Health N early all types of m odern industry a r e concerned with dust and its control. Courtfiey M. B. A. Co. i ), T H E M ID G E T IM P IN G E D U SED FO R C O LLEC T IN G A T M O S PHERIC DUST SAMPLES. tiate between the o r i g i n of these materials, a defi nition of them is in order. annual cost to industry DUSTS are formed by the re om u n c o n t r o l l e d dust duction of earthy materials and its to a staggering figure. In are usually produced by such ope cases the problem of dust is sed by management as only isance. In other plants, the /ery of certain dusts is eco- rations as crushing, grinding, buffing, etc. The particle size of dusts may vary considerably, ranging from sub-microscopic to ically sound, especially where articulate matter may conMrecious metals or may carry ||b le processing stock. Aside 'any nuisance or economic Resulting from the escape of Kthere are certain dust ex es which may result in acute ! h hazards. This is especialfee of dusts containing a high ntage of free silica, asbestos, flther toxic materials. Where !h considerations are involv- such exposures, legal aspects |ifet themselves. In most states visible. FUMES are formed by conden sation and sublimation. Chemi cally, they are metallic and are usually the oxides of such metals as zinc, and lead. The particle size is usually below one micron. Smoke comes from the burning of organic material and its par ticle size is usually less than one- half micron. Mists and Fogs result from the condensation of water vapor on suitable nuclei, and the particle size will vary with given con 'e occupational diseases are ditions. iensable, specific coverage is J to those disabilities result- General Properties jfttom the inhalation of silica As a substance is reduced in m Definitions particle size, there are certain general properties of the material which are changed. On breaking iny times true dusts are conwith fumes, smokes, mists, ':fogs. In order to differen up a solid into finely divided par ticles, the surface area is greatly enlarged and therefore the space occupied is greatly increased. As an example, a piece of quartz one centimeter on each side when crushed to where the particles of one micron in size will present a system containing 10" number of particles. The total surface area will be 6 square meters. If these dust particles are dispersed onto the atmosphere in such manner that the concentration will be 100 million particles per cubic foot, the space occupied by this dis persed system will be 10 thousand cubic feet. The chemical activity of a solid is considerably increased by a reduction in particle size. Thus the rate of oxidation is increased as is evidenced by occasional dis astrous dust explosions. The phe nomena of adsorption becomes more important as gases are more easily adsorbed on the surface of the smaller particle. From the standpoint of health hazards resulting from dust ex posures, the physiological proper ties of dust vary somewhat with the particle size. It is an accepted fact that with exposures to silica dust, the smaller the particle size, the greater the hazard. Physiological Response Drinker has summarized the re actions resulting from the inhala- tion of dust by classifying the re sponse into four groups. These are: (a) Pneumoconiosis---The dusts producing this type reaction are harmful only when inhaled. The principal materials producing this type reaction are free silica and asbestos dust. On inhalation, these two materials produce specific lung pathology and from the standpoint of disability, present the most important of the dust ex posures. (b) Toxic Reaction--(As poison ing by lead, cadmium or radium) These materials produce harmful effects when taken into the body both by inhalation and ingestion. With reference to lead and its compounds which may be present in the atmosphere as particulate matter, it has been fairly well established that entrance into the body oy inhalation is more im portant mode of entry than the same material taken by mouth. This is primarily due to the fact that when such materials are tak en into the body by inhalation, the major portion is taken into the blood stream, whereas, a consider able part of that taken by mouth is removed by certain organs of the body. (c) Metal Fume Fevers--These conditions result from the inhala tion of finely divided fume partides. The importance of metal fume fever has been brought to the attention of industry by the great amount of welding which has been an important industrial tool for the past few years. Where burning or welding is done on sur faces which have been galvanized, the problem of metal fumes be comes immediately important. F I6 . 2. T H E ELE C T R O ST A T IC P R E C IP IT A T O R A S U S E D FO R C O LLEC T IN G ATM OS. P H E R IC SA M P L E S OF DUST A N D FUM ES. IN SER T SHOW S RATE OF SETTLIN G OF OUST. where the pouring done. (d) Allergy--This type r is in general produced by and certain organic dusts. Common Industrial Carbonates are usually ei ed with either calcium or nesium. They normally nature as calcite and ma or as dolomite, which both magnesium and calci the carbonate. Limeston marble c o n t a i n consid amounts of these earbona do the materials from wh ment is made. Due to the solubility in fluids, these materials are ed when taken into the b inhalation. The presence o bon dioxide in such fluids, important factor influencing solubility. The same thing to the presence of carbon in water which comes into c with these materials. In ence of carbon dioxide th bonate is converted to the soluble bicarbonate, thus a to the ease with which it is r ed by solution. Experimental and practic servations on carbonate d dicate that these materials ar harmful when taken into the by inhalation. This is pro due to the fact that they are ly removed due to their solub Sulfates are common ind; materials and this general may be illustrated by which is calcium sulfate, a common material and is w, used in many industrial o tions. It is generally consi that this type material is no ic and does not present anj& ticular problem from a " standpoint. Oxides vary considerab their physiological reactio general the nature of the r will be dependent on the metal from which the oxide rived. Where such me1 specifically toxic, as would case with arsenic or lead, cific toxic' reaction could ; pected from the inhalation oxide. However, other oxi pear to be relatively hi particularly where the _ of a non-specific type. This of iron oxide. The mining results in the exposure of number of men to the oxi ictical dust ils are i the pro) ' are solubi indi eral FIG. 4. Q U ARTZ D U ST (S I 0 2> M A G N IF IC A . T IO N I30X. FIG. 5. C A LC IU M C A RB O N A TE D U ST M A G N IF IC A T IO N I30X. fenetal. However, it appears >exposure to the dust of iron | | {,not produce pathology ungych exposure is accompanied ire pressure of free silica, mining of coal results in jjtire to coal dust which con|i'a high percentage of carbon, lied studies of exposure to jfBdst have been made by the 'Public Health Service and agencies. It has been found jj|; in general, coal dust is re " ;in the lungs only when dust contains a high per- ||age of free silica. Although j|dust may be deposited in the 9 of exposed individuals, the |tion resulting is usually not jjiidered disabling unless silica resent. ' icates make up an important l of industrial materials and f/'Used principally in the pro t o n of ceramics and similar trials. Talc, kaolin, mica, etc., are chemically silicates Itheir widespread industrial ap- ifttion results in a great number ^employees being exposed to type dust. With the excep- ifrof asbestos, which is a silicate, |J|eneral class of materials does appear to produce a disabling lotion, except in isolated cases, ifen taken into the body by in- |tion. Sbests is the only silicate at the present time which luces a lung pathology com mie with that resulting from figure td silica dust. all the dust found in indusgfprobably the most important fee silica or silicon dioxide. It ,, js in the form of quartz, flint, Wtone, and chert; and is as- sociated with many other miner als and ores. The disabling con dition resulting from the inhala tion of free silica is known as silicosis and has long been a problem with industries such as stone cutting, granite, foundry, abrasive, and the like, where sili ca is used in processing. There are relatively few industrial ope rations which might result in di rect exposure to pure silica dust. The importance of silica lies in its association with other materials. As an example, in foundry opera tions the dust generally will con tain clay and materials of a nonsilicious character, so that the ac tual percentage of free silica may be relatively low. This is also true in exposures to coal, iron oxide, and the mining of ores. When hard rock or silica is present, these dusts become important mainly due to the presence of silica rather than to the inherent properties of the parent material. Factors Influencing Hazards In evaluating the exposure to a dust there are several factors which should be taken into con sideration. The duration of ex posure is important, as it will in dicate in a general way the total amount of dust which might be expected to have entered the body. Obviously other factors enter into such an evaluation of total dusti ness, and these will be discussed later. History, of past exposure is important. This is particularly true where an individual is ex posed to silica dust. This point is of extreme importance to industry due to the fact that a worker may have contracted silicosis under a previous employment. Where such a condition exists, the desirability of preemployment examination is obvious. The c o n c e n t r a t i o n of dust breathed is important as this, within certain limits, will deter mine the possibility of develop ment of dust diseases. Consider able research and practical obser vations have been made in the field of dust exposures to corre late clinical findings with atmos pheric concentrations. For free silica, asbestos, and some of the other materials, fairly definite standards have been established. The nature of dust is important primarily from the standpoint of free silica content. This is par ticularly true of mixed dusts which constitute the majority of industrial exposures. The volume of air breathed enters into the picture as it directly influenc es the amount of dust which will be taken into the body. The rate of respiration or amount of air breathed in general will be de termined by the physical effort required on the particular job. Where heavy work is being done, naturally an individual will re quire more ventilation than where less physical effort is involved. Dust Measurements In addition to the factors in fluencing dust hazards, it is neces sary to make direct dust measure ments in order to obtain a true evaluation of any dust exposure. Such measurements are made by the actual collection of dust sam ples, the counting of the dust par ticles, and by the identification of the materials making up the dis- r i t - . . ________ __ ______ . . . . . persed system. For the collection oi dust samples, several instru ments may be employed. Much of the early work done on the control of silicosis in the mining areas of South Africa was carried out with the Konimeter. This instrument has been used some in this country, however, it has not met with the popularity which is enjoyed by certain other methods. From the standpoint of collecting efficiency, the electro static precipitator is probably the choice instrument, however, most of the work done on correlating atmospheric dust concentrations with medical findings has been based on samples collected and counted by the Greenburg-Smith technique. The collecting device employed is an impinger unit which samples at the rate of one cubic foot per minute. Counting by this technique is done under light field. The per centage of free silica in a dust sample is usually determined by either chemical or petrographic methods. Permissible concentrations of dust havg been established for free silica, asbestos, and other ma terials. For both silica and asbes tos, 5 million particles per cubic foot is considered as maximum working concentration. The U. S. Public Health Service has suggest ed a procedure by which the total dust concentration in millions of particles per cubic foot is multi plied by a percentage of free sili ca. If the resulting figure is more than 5 million particles per cubic foot, the condition is considered unsafe. If less than 5 million, the condition is considered safe. There should be considered certain limits of dustiness for any type of dust, whether it be merely a nuisance two 15-foot fans are instaf value or health consideration. To which handle 500 thousand most industrial hygienists, 50 mil feet per minute each. Actua lion particles per cubic foot is the maximum atmospheric concentra tion of dust under which an em ployee should work. It should be pointed out that the only way of determining both the nature of the dust and the actual concentration is by direct sampling and similar procedures for the counting of dust. the material removed by these ! is made up principally of snifj rather than true dust. Two electric arc furnaces operated and these are equip! with roof fans located immediatj above the units. These fans hat 60 thousand cubic feet per mil each. Again, the major portion! Case History the material coming from the; furnaces is smoke rather than MANY industries having prob dust, and comes from the _ lems of dust control recog and flux material charged int| nize the existence of such problemfusrnaces. to varied degrees. Some take pass A problem of dust control inj ive attitudes, while others apply foundry is the shakeout operatijpj s o u n d engineering procedures This is particularly true whl which result in a real job of dust s h a k e o u t is mechanical control. Such modern engineering handled on a vibrating screen! methods are used by the Le grate. Here, a line conveyor i Tourneau Company of Toccoa, Georgia. This particular plant manufac tures heavy road grading equip ment and its major dust problem lies in operation of a foundry for the protection of basic steel parts. It is interesting to note that this Company considers the control of dust as a part of the general over all production schedule and as a result has its control methods inte grated into general plant opera tions. Although there are several methods which can be used for control of dust, ventilation, both in the form of general and local exhaust, probably offers the most satisfactory method and it is this approach which has been used by the LeTourneau Company. For general ventilation in the foundry, tern is used to bring the cast! directly to the shakeout grate,' canopy type hood is installed mediately over the grate addition to canopy, side enclos are provided which prevent;; leakage. The fan serving this l delivers 35 thousand cubic ieet-| minute, which results in a capturing velocity at the entr and discharge ports. An i job of dust control results on particular operation. Sand conditioning in mfl foundries is a dusty job. With; LeTourneau Company this.; handled by means of local es ventilation and three bag typ.? ters handling 6 thousand cubic; per minute each. Tumbling Pi tions for cast cleaning are also I vided with local exhaust vent (Continued on page 80) F ie . 6. LO C A L E X H A U S T ON T U M B L E R S FOR CAST C LEA N IN G . F IG . 7. B A G H O U S E A N D S A N D B L A S T U N I T F O R O A S T C L E A N IN G Courtesy Le'flou? Igf; /m i t i irnu n nrM/C * ikiniicTDv t~ . kinvPMBER. at least 75%. Figure 2 shovys the condition of the tube that .failed: , Other tubes were found eroded adjacent to U bolts holding baffle tiles. The U bolts provided sufflcient interruption in las flow to cause eddy currents ai|d localized impingement. (Fig. 3.) Erosion by partieleskof fly ash and unburned fuel has also been found in stoker-fired boilers. At the time of each shutdown for cleaning and preventitive main tenance (at least once every four months), all areas vulnerable to erosive attack should be examined. Areas mot susceptible are: . / 1. Where- flow of gasefs makes a \ tu rii throwing out par.ficles'of v dolhfc: ; T i -. / v 2. Behind any cracks, breaks, or y g&lW bi a gas baffl., 3 Adjacent to any! pnojecfipn that might divert normal flow of gases. .Should the boiler be provided with an induced draft fan, observe the condition of the blading. Ab normal wear may be indicative of erosive attack in the boiler. Careful attention by all engi neers to the problem of erosion may well prevent a serious acci dent. in the plant. The modernization prothe Brock Candy Comp " ing place at a time w' any product, regardless'! or cost, can be sold. Tnei tlenecks today are shortag materials and skilled However, progressive bujjj know that these condi only temporary and that few years, companies w not garantee quality ahlq tp sell their prod Brock Candy Company tinue to be a leader in itg cause it has refused to ' | quality of its products days when consumer de greater than the supply of terials and because it has inaugurated a program and research which will constant improvements. . Candy Making* (Continued from pkge 60) not be taken for granted, a chemi cal laboratory is essential. ,, The Brock Candy Company is now in tfce process of constructing a modern chemical laboratory and training a technician to perform control analyses. The laboratory, which is located in a large air con ditioned room' near the candy' cooking operations, is equipped with modem stone-topped labora tory benches, the latest chemical glassware, and such special analyt ical instruments ., as.; balances, vacuum oven, refractometer, and pH meter. Provision has been made for such analyses as moisture, in vert sugar, viscosity, pH, melting point, and refractive index. Many of the control tests have been de veloped specifically for the Brock Candy Company, and new pro cedures will be added from time to time as the need arises. The Industrial Research Institute of the University of Chattanooga has cooperated . with the Brock Candy Company in selecting the equipment, outlining and develop ing. analytical procedures, and training a technician to operate the control laboratory. A research 1 project on improvement of the quality of candy has been sponsor ed by the Brock Candy Company at the Industrial Research Institute of the University of Chattanooga. Since all raw materials will be analyzed and tested in the com pany laboratory, variation in prop erties will be detected before the material is used. This procedure will assure products of uniform quality, since inferior raw ma terials will be discarded and form ulations will be based on the ac tual analysis of high grade raw materials rather than on standard procedure which do not make al lowance for variation in the in gredients. Analysis and testing will assure high quality of finished products and permit any difference in quality to be detected. In this way, any unavoidable errors in manufacture can be corrected and adequate controls instituted to pre vent their reoccurrence. The facilities of the control lab oratory will also be available for the evaluation of research and de velopment work being carried out in the factory. In addition to main taining the production of uniform high quality products, the person nel and equipment of the control laboratory will be available for many other technical, assignments Dust (Continued, from page' tion and dust arrestors as in the photograph. Note haust is applied through trunnion of the tumbler. In foundry operations or other industrial type proce housekeeping is an important^ tor influencing the general! dust. This foundry employs five horsepower vacuum cl for floor maintenance. By cedure loose dust, sand, and like, is removed from the floQ.fi is not projected into the a phere by the movement of.; chinery, scuffing of feet, an like. This is one impressive' in the operation of this parti foundry. Excellent housek' is combined with a good proc for materials handled. In all of the attempts at dust trol at the LeTourneau Corn; employee cooperation is obt Employee c o o p e r a t i o n i through planned program of ployee education and em] participation in affairs invi the health of the worker P erio d ic d u st sam ples colli in the LeTourneau foundry cate atm ospheric concentratr various operations well w h at is considered as max safe w orking limits.