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lit A T ION A l SAFETY COUNCIL, INC. 10 NO. MOCKER DRIVE OHICASO S, ILL. SCF-ALLF-00955 Automotive and Machine Shop Section Executive Committee 1947-1948 General Chairman--}. E. MOORE. Director of Safety, Corporate Service Incurported, Detroit. Mich. riee-Chairman-L. B. LOOMIS, Safely Engineer. Fisher Body--Tentstcdt Division. Ceneral Motors Corporation, Detroit. Mich. C. A. DeMONGE. Safety Director. Kdsey-Hayes Wheel Company, Detroit, Mich. Secretary--D. L. McCULLY, Safety Supervisor, Weuinghouse Air Brahe Company, Wilmerdiog. Pa. Program Ccmmhteo ., Chairman: CEO. F. NUEK.SBEB.GEiK, Safety Engineer. A. B. Dick Company, Cnicago, 111. R. D. HARVEY, Safety Engineer, The Murray Corporalion of America, Detroit. Michigan C. O. ENOCHS. Safety Director. Chevrolet Flint Division of Ccnetal Motors-Corporation. Flint. Michigan `. F. H. HUMPHRIES. Manager Safety and Claims Division. American Car and Foundry Company, New York, N. Y. V .. Engine Bring CnmmttMi . Chairman: F. W. FISEE, Safety Director. The Brewer Titchner Corporation. Cortland. New York ' ' .. BARNEY J. POVOLNY. Safety Director, Detroit Diesel Engine Division, General Motors Corporation. Detroit. Michigan ._ WM. SMITH, Director of Safety, Ford Motor Company of Dearborn. Michigan ` MamheriMp Comndtlee " Chairman: PAUL J. BLACK. Safety Supervisor. Westinghouse Electrics Corporation,Lima, Ohio ARTHUR E. EWING. Lacrobc Electric Steel Company, Latrobe, Pa. FRED C. YELTO.V, Safety Director, Deico Remy Division. General Motors Corporation. Anderson, Indiana Newi Letter Cooxaittee Chairman: PAUL F. BUNGER, Safety Diteaor, Frigidaire Dirision. Ceneral Motors Cor poration, Dayton, Ohio LOUIS A. CALANTUCCI. Safety Engineer. Cenetal Electric Company, Bloomfield, N. J. G, W. YEMM. Safety Director. Otis Elevator Company. Harrison, N. J. Heahh Committee Chairman: A. L. BROOKS, MJD, Medial Divuion. Fuber Body Division. General Motors Corporation, Detroit, Michigan C. F. ENGEL, M.D, Assistant Medial Director. Westinghouse Electric Corporation. East Pittsburgh, Pa. FRANK A. FATTY, Director of Industrial Hygiene, Ceneral Motors Corporation, De troit. Michigan / v$* ' fjtSgS :SS! 3: ..:U M] swissy t- V-ss&H 6 35th. National Safety Congress]'"1947 ......................... ..... PobBcitr Committed Chairman: O. C. BOILEAU, Supervisor of Safety, Health and Retirement, R.C-A. Vidor Cor poration of America. Camden, N. J. ' GERALD C. SQUIER, Assistant Director of Personnel, Bulldog Electric Products, Detroit, Michigan EDWARD C. HOLTZMAN, Director o( Safety and Medial Depan menu, Wagner Electric Corporation. St. Louis, Missouri Statistical Committed Chairmen; H. J. JENNINGS, Safety Engineer, Genera! Electric Company, West Lynn. Mamachusetts W. E. BROWN, JR., Safety Director. The City Auto Stamping Company, Toledo, Ohio LOYLE DAVIS, Director of Personnel and Industrial Relations. MuelleT Company, De catur. Illinois Ofr&d-Job Committed Chairman: M. F. B IANCARDI. Safety Engineer, Health and Safety Department. Industrial Relations. Div, Allis Chalmers Company, Milwaukee. Wis. ROBERT C BENSON. Director of Personnel and Safety, Lansing Stamping Company, Ijnsing. Michigan E. CLARK WOODWARD, Director of Safety, A-O Smith Corporation, Milwaukee, Wis consin Podtet Committed . Chairman: CARL PETERSON, Safety Supervisor. Plymouth Motors Division of Chrysler Corporation, Detroit, Michigan CARLTON* R. REID, Safely Engineer, Westinghouse Electric and Manufacturing Com pany, Springfield, Masachusetu HAROLD M. ERICKSON. Dirtaor of Safety, Nash Motors, Kenoaha. Wis, Mtmben-al-Large--*J. W, YOUNG, International Harvester Co, Chicago, 111.: *0. F. LEH MAN, Chrysler Corp, Detroit, Mich.; *\V. A, BECHILL, Chrysler Carp, Detroit. Mich.: J. C BOWER, io*i Mifflin Ave., Pittsburgh. Pa.; *M. A. CLARK, S537 Dcionsbire Road. Crone Pointe, Mich.; *H. B. DUFFUS. Wotingbousc Electric Corp, East Pltuburgh. Pa.; HOYT L. FRACHER, Detroit Steel Products Co, Detroit, Mich.; *0. A. KUECHENMEISTER, Dominion Forge fc Stamping Co, Walkerville, Ont, Canada; *M. J. MC CARTHY, Fisher Body Detroit Div, General Motor* Corp, Detroit. Mich.; ROBERT A. SHAW, Detroit Diesel Engine Div, General Motors Corp, Detroit, Mich.; LT. COMDR. PAUL S. STRECKER; *R. F. THALNER, Buick Motor Div, General Motor* Corp, Flint, Mich.; *V. 1, TROTTER: *C. E. WOOL1EVER. A. O. Smith Corp, Milwaukee, Wis. Staff .Representative--ARTHUR S. KELLY. National Safety Council, Chicago. ID. Indicates Past Cencral Chairman Automotive ami Machine Shop Section 7 MONDAY AFTERNOON SESSION October 6, 1947 ^ Presiding: Da. A. I.. flaookS. Mcdital Director. Fisher Body Division. General Motors Cot* poration Recognition and Control of Fume and Dust Exposure By V. J. CASTROP Research Laboratories Division, General Motors Corporation [linen which can he attributed m the oc cupation may occur in the automotive and allied industries. While occupational disease cues are much fewer in number than those resulting from accidental injury, there Mill accepted opinion as to their effea on health. Many conditions are corrected or improved because of reasons other than their effect upon the health of the employees. Better products, hater employee relationship, reduc remains the need [or vigilance in maintaining a healthful working environment. The revjionsibi'liiy for employee health is delegated tion in maintenance of equipment may be cited as justification for management's de cisions for such correction or improvement. hy management to the medical director with ttve safety director charged with matters per taining to safety. For the smooth functioning Generally speaking there are two means of . entrance of toxic compounds into the human body under industrial conditions, namely, by uf either department it it necessary that these ingestion or via the respiratory iraa through individuals work in clove harmony with each the inhalation of fumes, dusts, misu or gases.' other. Ingestion is of importance if toxic materials A safety engineer who it capable of recog- which have a systemic effect are used and niting conditions which may be detrimental adequate washing facilities are not provided, ; to the health of the employee it an excellent or, where the employees are slovenly in their - teammate (or the doctor in any employee (rersonat habits. Inhalation is considered the health maintenance program. The safety en tnost important portal of entry of fumes gineer need not be capable of actually sam or dusts and the particle site, therefore, be- pling air in the environment or dewigning a coma significant in evaluating an exposure. ventilation system for the control of toxic The panicles which cause the, physiological materials. He should, however, have knowl changes are those which are smalt enough to edge of the materials which have been proved ictruiu suspended In the air and rvot those harmful, should be fairly well informed of which immediately fall to the floor. Flying how these materials may be used safely, have particla, which are of concern to a safety some undemanding ol luvic control measures nun and for which he advocates (he use of which are normally recommended when such goggles, are not of hygienic significance since materials are used. they are hot of respirable sire. To judge the The intention is not to present a highlv -criouvncss of an exposure hy the quantity technical discussion of fume and dust ex uf detritus adjacent to an operation is often posures or detailed information, regarding misleading. This is especially true where ventilation systems, as such matters are of mechanical ventilation has been provided interest to the professional industrial hygien which will remove the fine material but is ists and of comparatively Utile value to safety inadequate to trap or convey the larger engineers. This discussion will be limited to particles. the more basic principles of industrial hy In evaluating an exposure it is necessary giene as they relate to fume and dust ex to consider the toxicity ol the material, the posures, to indicate what control measures duration of the exposure, the average concen are available or used to protea. the em tration of the contaminant with special atten ployee's health, and, to call to your attention tion being paid to those operations which operations and materials which Sre commonly produce high concentrations at some phase used in the automotive and allied Industrie--, of an operating cycle, and the measures which at the tame time `indicating the generally have been provided to control the exposure. 8 35th National Safety Congress, 1947~ Medial record* of ihe individual* subjected to the exposure may be ol value if (he examjnations are thorough and frequent and not of a cunory type. .It must be remembered that occupational rliwsun are slow in develop ment and in some instances lasting in ettea.Slow changes may not be detected and the mere fact that cases have not occurred is no definite assurance that exposures to known toxic materials may be ignored. The determination of the concentration of the toxic material in the air is important in evaluating the exposure. Tests of this type are not only indicative of the degree of con* Lamination but in some instances which op eration is the major offender. The apparatus used in collecting the con taminant and the method used in estimating the amount present in the atmosphere vary with the type of material Tests of this type are specialised in nature and are beset with many pitfall* which can lead to very errone ous results and conclusions if done by other than exjsericnced personnel In a discussion pertaining to tonic ma terials it is generally necessary to quote per missible concentrations or as it b sometimes expressed -- maximum allowable concentra tions--permissible limits, or threshold limits. Thee terms are used extensively by industrial' hygienists to indicate concentrations of a substance in the air which are considered compatible with good health. The limit usu ally applies to exposures of eight hours dura tion (or a prolonged period. The limit* are, (or the most part, advisory standards or bench marks which are prac tical to men. In general, Lhoe Limits are de rived from three types of evidence all ol which have value and limitations. t. Animals have been exposed at different concentrations and the effects noted, s. A few experiments have been made on human subjects (or short periods of time. j. Safe limit* have been arrived , at by measuring the concentrations of sub stance in the workroom air and corre lating this information with result* of medical examinations of workmen. There is no magic connected with these limits and the mere fact that they are ex ceeded does not necessarily mean that some one will definitely become ill, but there it a good probability that someone will suffer ill effects if the limit is greatly exceeded for a considerable period. There remains much to be learned regarding the toxicity of many substances used in industry, axsd it U hoped that with more research and wudy that the answers will be found. - So much for the general picture. Now let's take a look at some specific operation!, Welding--Welding processes max common ly used can be divided into three types, arc. gas, and resistance. The safety' measures per taining to doihing, goggles, and helmets are of common knowledge and therefore, shall not be considered in this discusaioa. . Arc welding when performed on uncoaled steel doo not produce a condition which is considered harmful to the welder provided it is accomplished in a comparatively large open area. The fumes which result from welding consist essentially of the oxides of Iron and oxides of metals which may comprise the steel or coating of the welding rod. Some In vestigators have found characteristic mark ings on chest x-rays of men who have welded under seven conditions (or long periods of time. Them markings axe presumably due to the deposition of iron fumes-within the lungs, but it has dm been demonstrated that such fumes have caused physiol impairment. A frequently suggested limit tor welding fume b 15 milligrams of iron oxide per cubic meter of air. Concentrations of this magnitude existing in the workroom would, materially reduce visibility and thereby become a nui sance or an unsafe condition requiring cor rection. - Welding within confined areas such is unkr, inside michinny or equipment, or in small rooms presents a condition which on be of concern. The concentration of fume b materially higher under these cootlitioos as there b little opportunity for dilution by natural air currents normally present io a large shop. Nitrogen oxides formed by the dearie arc when inhaled in sufficient qtsan*. lilies causes fluids to form In the lung--edema -with the resultant failure of the respiratory system. While welding in large open -.areas these toxic gases are normally dm present in sufficient quantities to cause harmful efioct*However, when welding b done in confined areas, the nitrogen oxides may reach a con centration which will be harmful. . Gaa welding generally is not productive of harmful fumes. There are. however. In brat; ing two potentially harmful exposures. While boric add or borate* generally are used In 10 35th Motional Safety Congress, 1947 grinding of numuxic metals which are free of sand is generally considered a nuisance and U not harmful per sc. Despite this fact some state taws require griding o[tention' to be ventilated. This requirement has probably been a hold over from the days when sand stone wheels were prevalent and also to pre vent the crettion of a nuisance condition. Grinding wheels in use in industry love ar tificial abrasives such as aluminum oxide or silicon carbide. Emery, which is a natural product composed of osemially aluminum and the magnetic oxide of iron, may also be used. A permissible limit of 50 million par ticles per cubic foot of air for aluminum oxide and silicon rarbide was recently ac cepted by the members of the American Con ference of Governmental Industrial Hygien ists. Such a limit is liberal and concentrations of such magnitude are normally not cn-' countered. * When lead, silica, or some similar toxic material comes in contact with the grinding wheel the exposure to the abrasive matter may be ignored and the exposure evaluated on the basis of the toxic material. If this Uuer material U controlled the nuisance will also be eliminated. VentiUtion systems for grinding wheels have been fairly well standardized and gen erally are satisfactory to present a nuisance. Roods should enclose (he wheel as completely as is practicable. Air volumes should be pro vided which are sufficient to cause an inward flow into the hood when using the smallest wheel. This is especially true where toxic materials are involved. Wet Grinding--Baffles, hoods, and guards are generally located near wet grinding wheels to prevent dispersion of the liquid used u a cooUnt. These devices are usually sufficient to control the dust if it is nontoxic In nature. If the dust liberated is toxic. me< chanical exhaust ventilation may be required. Buying and potiihing--The buffing com pound applied to wheels used ' for buffing and polishing vary in composition. Waxes and various types of abrasive are (he major components. These - materials plus lint and fibers from the wheel are the essential in gredients of the airborne dust. The toxicity is dependent upon the type of abrasive. Generally ventilation is provided so as to improve housekeeping and reduce the num ber of complaints and not because of (he hazard to health. . Machining-Smoke from oily parts is the prevailing source of air contamination at machining operations. Ulncst has not been attributed to this type of exposure. As it the case with mast fumes and dusts of the nui sance variety little is known as to what ef fect such materials have on already existing physial abnormalities. Machining operations on steel produce large chips or turnings; consequently, dust is not a problem. Operations involving the machining of high lad alloys have been studied, and signifiant quantities of air borne lad have not been demonstrated. Graphite which becomes airborne during the machining of cast iron is not considered to be physiologically signifiant, ami there fore is classified as a nuisance dust. Frequent ly management considers it advisable to pro vide ventilation for the machines which are productive of the most dust, as graphite on the clothing and person and surrounding machinery is conducive to many complaints. Ventilation systems for the machining, drill ing, and so forth, of cast iron should in clude hoods looted av near the cutters or drills as is practicable. Many of thee hoods are in use on production machinery and are doing an excellent job.of dust control. . Abmive Cleaning--Since silica is recog nized the most harmful of mineral dusu, an adequate ventilation system is normally provided at the time of installation of com mercially built sand blast equipment. Con tinuous usage and lack of maintenance result in a breakdown of adequate control. Visible escape of dust is (he belt evidence Out this has occurred and it is advisable to correct such a condition without undue delay. Employees who are stationed in blast rooms are dependent upon personal respiratory equipment. It is of utmost importante that such deviea are of a type which will provide the necessary proteaion. Devices of this type are of the supplied-air variety, and it is neces sary that the air provided be free of harmful contaminants. The air compressors should be located in an area free of contamination otherwise the contaminant will be transmitted to (he helmet and the breathing tone of the worker. * Normally, ventilation within the room is provided so as to improve visibility and to help prevent the escape of dust to the sur rounding areas not to reduce the concentra tion of silica dust to a safe level. Automotive and Machine Shop Section . 11 - Tiimblaii or rotating table type of sand Practically all industrial plants have opera blast units should be provided with sufficient tions which involve the use of leading base ventilation to prevent the escape o( silica bearing metal or solder. Babbitt bearing dust. Leakage due to excessive Wear should metal containing approximately 75 per cent i>e remedied. lead has been encountered. The composi Small sand blast cabinets, where the open* tion of solder metal is variable and de tor controls the blast notila from outside the pendent upon the purpose Cor which it is cabinet, frequently have faulty seals around used, with ordinary 10ft solder containing a the doors or the rubber gauntlets are loose comparatively high percentage of lead. . or tom. The dust which escape Irotn the Assuming that the babbitt or solder in cabinet through these openings is in dose use is one containing a significant amount of. proximity to the breathing rone of the cm- - lead, the question then arise as to.whether ployce and in many instances exceeds the per or not the employees working with this ma missible limit for silica. This leakage should terial will become ilL'Thc answer to such a lie corrected and the men should not lie re question could be given by a qualified in-, quired to use respirators. .dustrial hygienist after he had seen the opoa-' If the articles being blasted are free of tion and considered such factors as the tea-' silica or other toxic material, the dust result perature to which the metal is heated,' the ing from grit or tbot blasting is classified in method of removing excess solder, the length' the nuisance category. It follows that (he of exposure, and the effectiveness of the con maintenance of ventilating wmctu' (or grit trol measures provided. - blasting, although desirable, is not always It is a well known fact that lead causes ' *o necessary as for sand blasting. illness if absorbed in excessive amounts, and - The inc of steel grit or shot in blasting therefore operations wherein" lead .is.-used ? rooms produce excessively high concentra have received considerable attentionv and ~ tion* of tlust within the enclosure. It is there study. Out of this experience certain prac-j fore. necetsary to protect the worLcr within tices arc known to produce excessive exposure, the room. The remarks included in the sec whereas other practices have been proved Dpt.{ tion devoted to and blasting rooms ate there to be harmful. It is generally conceded that, fore. pertinent when considering rooms in excessive concentrations do not route from. which steel grit or shoe are used as the abra operations where solder is applied by means' sive. ' of an electric soldering iron. This is probably Vapor blasting, a variation of sand blasting, due to the small amounts of solder used and is of comparatively recent development. This the comparatively low heat of the {metal. procedure involves the use of fine silica and When an iron is used which is heated.in a water under pressure. The silica used in vapor small gas fired furnace, the exposure may be blast units varies in site and may even be as of greater consequence. Solder which retuins small as iijo mesh (approximately to mi on the iron coming- into contact with' the crons), It is generally believed that airborne flame or heat is vulnerable for volatiliration.^ silica panicles below 5 microns are most sig Small amounts of solder drop from the iron nificant in causing silicosis. It then follows ' onto the hot floor of the furnace where It is* that operations involving the use of silici readily volatilized or oxidized. The oxidized abrasive whote initial particle sue approaches material may become airborne due to tits-, that ordcT of magnitude are more hazardous, turbances created by the flame or by remov-: and require continual vigilance in maintain ing or pladng the soldering'iron in the fur ing good control. It is. therefore, essential that nace. Frequently industrial hygienists recom the vapor blast cabinets be maintained so mend that ventilation be provided tor heating that leakage of mist does not occur. Good units of this type thereby removing lead housekeeping is also essential as spillage of fumes and dust bom the environment. This the sand and water sludge upon the floor, is particularly true in small rooms or where will acate a source for dust dissemination many units are in use. . ' when the water evaporates. Likewise, con The atmospheric contamination occasioned tainers of the dried sludge should not be al by the use of cither gas <>r electrically heated lowed to stand in the factory where they pots containing solder is dependent on a cin be influenced by air current* of high number of factors. With higher temperatures velodly. more volatilization will occur and the greater .'5th Xolional Safety Congress, 1947 wit] be .the exposure. _\Vith the htj'hnMcmperature the mcul it more readily oxiditcd to produce a dross consisting of a high iwrreniage of lead oxide. The droa may provide a protective coating to reduce the volatilization of the lead: however, disturbance of this coat ing will create ait exposure. As a safeguard against excessive contamination, pots contain ing solder or babbitt are usually ventilated. Wherever possible it is advisable to enclose the pot as completely as possible and provide sufficient air volume to overcome the thermal effects of (he molten metal. Attempt.* have been made to use natural draft ventilation systems to control these fumes and in (hove instances where the dint* were not of suffi cient diameter (lie system was inadequate A preferable method i* the u*e of mechanical systems. The removal of excess solder with poweT driven tools, such as grinding wheels, discs, or wire wheels, creates airborne dust which may contaminate large areas of the factory if (he operation is extensive. Diligent use of abrasive doth will also result in exceaivc concentration* of lead dust. Filing, however, is not productive of small panicles and t* preferred over the tvc of power driven tools. If filing is not practicable or feasible it will be nrcessarv to provide some type of me chanist ventilation system (or the solder re moval operation* involving the use of power tool*. Since the permissible limit generally accepted for lead is 1.5 milligrams per 10 cubic meter* of air (355 cubic feet) it will be nrccssarv to have an effective *>'slem to pro vide adequate control. F.nginecrs experienced in designing ventilation systems to control toxic material* should he consulted, other wise a comIv *wtcm might lie erected and later discovered 10 lie entirely ineffective. Fre quently solder removal operation.* require the use of portable tools on large objects and a local exhaust system would not be effective. a is the case in the fabrication of automobile bodies. General contamination of the factory with lead dust has been eliminated by endcu ing the entire operation in a large booth and exhausting a sufficient quantity of air from the enclosure to insure a constant inward flow of air from (he factory into the booth. Under these circumstances no practical amount of air. could be removed from the booth to reduce the lead concentration to a safe level, and therefore it is necessary that the men working therein be provided with adequate personal protective device*. Heat_Trraiing-High temperatures are 1 frequent source of'complaTnt''Crbra'employees in heat treat departments but such condi tions and their control are not within the subject matter under discussion. Fumes disseminated from cyanide ]>ou are often assodated with cyanides used as fumi gants or as the lethal agent in death cham bers and supervision as wdl as the employee become apprehensive. Fumes from such a source are irritating and because of this property should be adequately vcnulatcd. The irritant nature of the fume is cau*ed by alkali formed upon decomposition of the cyanide. . Molten lead is sometimes used as a harden ing medium for metals. Frequently charcoal or hoc similar material is placed on the surface of the metal to conserve heat and prevent oxidation. A covering of this type reduces the volatilization of lead while the bath is quiescent, but has no effect while the, bath is in use. Adequate ventilation should' therefore be provided (or baths of this type. As complete an enclosure as 'a practical (or the operation being performed is advisable with air quantities dependent upon the open areas in the hood. To prevent contamination resulting from volatilization of lead accumu lating in the combustion chambers the prod ucts of combustion from gas fired lead pots should be vented to the outdoors and not be allowed to dissipate into the workroom. Iron Foundries--The principal ingredient* of foundry dusu are lilia, tea coal, clays, and parting compounds. The predominant ma terial will be dependent upon which phase of the foundry operation is being studied and what operation is being performed. The control of dust is the major prohlem. whereas fume is of secondary importance. A discussion of all the aspects of the in dustrial hygiene problems in such plants would require a separate treatise. For the present discussion it should be sufficient to state that all obvious sources o< dust dis persion should be reduced to a minimum by adequate localized exhaust system*. In a mechanized foundry such places would be sand conditioning and mixing equipment, tumbling mills, shakeouts, core removal and knockout stations, transfer points of . dry sand, abrasive blasting operations, and all grinding operations performed on castings containing appreciable quantities of sand. Automotive and Machine Shop Section 13 Maintenance of ventilation equipment is Expcrience has shown that frequently pro a_jMjor_item_m.foundjiia_beQ.ux_of the. . teclive. devices-havelm-issued-which-do- not------- abrasive action'of the dust. ft ii imperative provide adequate protection. Upon inquiry that a good program be maintained to as to keep the equipment functioning at maximum efficiency. ' information was generally offered that the safety engmror was not too well informed as to what should have been provided. Because of the heat associated with large The U. S. Bureau oi Mina at their experi Kale foundry activities it Li a common tight mental station in Pittsburgh tats equipment to tee pedestal fans or air cooling ducts di of this type and studio the protection of rected in such a manner as to create cron fered to the wearer. If the device is satisfac drafts which interfere with the efficient re tory in perform nee. they issue an approval moval of the dust dispersion. Better discre 'number to the manufacturer which appars tion in the placement of these farts or ducts on the device as well as the container in will go far in reducing dust concentrations which it Li received from the manufacturer!. in the areas where they are used. The approval granted by the Bureau also ` After the obvious has been corrected, it is stipulates that type of materials for which advisable that a survey of the foundry be it is approved. made by an industrial hygienist so that an accurate evaluation of the exposure may be obtained. It has become general practice in the field of industrial hygiene to recommend the use of only those respirators which hare been ap- . Respiratory Protective Devices -- As has prosed by the Bureau. Safety engineers . been stated, the atmospheric concentration should likewise insist that such devices be of dust and fume and other materials mar procured and acquaint themsdvs with the be reduced to a safe level by adequate ex type of protection afforded by each device haust ventilation. In some oses it is possible and thereby provide adequate control for the. to correct the condition by substituting a individual wearing thp equipment. Some cn- ' less toxic material. If these measures are not gineers prefer to stock only that type of res- practical respiratory protective devices may pirator which Will protect against the more be used. They may also prove valuable in harmful dusts or fumes, since a respirator of giving protection during an emergency or to this type will also gf** adequate protection provide protection (or intermittent exposures for malerials of lower toxicity. The advan or to supplement other methods of control. tage of such a procedure has merit as it re-* They should, however, not be considered as .duces the types of devices needed in stock the desirable moms of controlling a health and likewise insures the correct device for hanrd. the more serious exposures. Metal Cleaning By THOMAS MOONEY , Med-Fac Industrial. Hygiene Laboratories The complete finishing of metals by elec troplating may indude: i. Geaning by abrasives. i. Polishing the base metals. j. Geaning with solvents. Geaning with alkaline solutions. 5. Geaning with adds often referred to as "Pickling." 6. Metal deposition or elcaroplating. 7. Buffing the deposits. S. Lacquering the finished product. In abrasive cleaning, sand or steel shot is used under pressure. The potential health haardi in this type of dcaning are exposure. to dust of a high free silica (SiOJ content caused by the sand and also to metallic dusts where metals capable of produdng toxic dusts are cleaned by shot and sand blasting. Steel shot blasting Is a much less severe health huard than sand blasting; consequently, steel shot abrasive desning methods should be used wherever possible. , ' - The maximum allowable concentraLions (M.A.C.) for free silica are five million parii- l