Document XOOD959Mq2Dmy21d07NE8vzKx

PLAINTIFF'S EXHIBIT TPI-684 Prevention of OCCUPATIONAL DISEASES Other Than Those That Are Caused by Toxic Dust By R. R. SAYERS and J. M. DALLAVALLE UNITED STATES PUBLIC HEALTH SEEVICE HE LJSE of volatile chemicals has increased greatly during with reference to dust hazards, and, in general, the ideas there Tthe past few years. They have become indispensable in the manufacture of paints, in dry-cleaning processes, formulated have a very general application in other related fields. Briefly, these methods of prevention include: (a) sani and as solvents in various industrial processes, to mention buttaary and occupational surveys; (i) mechanical and personal few of their common uses. In fact, so great has been the de methods of controlling a hazard at the point of origin; and (r) mand for volatile solvents both by industry and the general periodic medical examinations and surveys. Each of these public, that new applications for them are constantly being methods is discussed in the paragraphs which follow. developed and commercialized. The volatile solvents perform a large and important part of industrial expansion into new SANTTAXT AMD OOCUVATIOMAL IOTLVXTS fields as new uses for them are discovered. Sanitary Surveys. No estimate of a hazard can be made until Partly as the result of the increased use of new chemicals in the conditions of the worker's environment have been evalu industry, it is now well recognized that the hazards of certain ated. In studies made by the Public Health Service (3) it has occupations are important factors in the causation of sickness been customary, as a first step in its field investigations, to make and even death. Dublin (l)1 has evaluated the effect of the detailed sanitary surveys. These surveys include a study of che industrial environment on the well being of a large number of various items with which the worker comes in daily contact. workers in a mortality study among more than three million The sanitary survey is, in other words, an "inventory" of all white, male wage earners. The study covered a three-year the hygienic items which enter into the worker's environment, period from 1922 to 1924, inclusive, and is compared with a the manner in which he conducts his work, and the length of similar study made over a similar period from 1911 to 1913. time he spends at each task. As a rule, such a study is carried The groups studied constituted a fairly representative social out for each room and for the various occupations in a given and economic class and were considered as an urban earning plant. This procedure, when completed, gives at once perti population. Dublin has shown by an analysis of the data ob nent information as to the types of hazards which are likely to tained, that adult males engaged in industrial pursuits had a exist and the number of workers which may possibly be af higher mortality and a shorter longevity than those in other fected. types of work such as professional, clerical, etc. In the more The items which enter into a sanitary survey should include recent study, it was further shown that the mortality rates che following: for the industrial workers were more than double the rates for the non-hazardous occupations. In terms of life expec tancy, the picture presented was impressive. The industrial (1) Physical characteristics of building and room in which the survey is made: coostructioa of building; locaaoa and sin of room; number of workers; cype of iiluminadon; type of venrilation. worker ac the age of 20 had an expectancy of 42 years as com pared with the Qormal of 49 years. In other words, the life of the industrial worker in 1924 was shortened by approxi mately seven years, while the data for 1911 to 1913 showed the (2) Sanitary facilities for workers: refuse cans; cuspidor and sweep ing service; washing facilities; type of toilets; drinking-water facilities; eadng facilities; type of care and miinwimig given to sanitary facili ties. O) Hazards: safety hazards; dust, vapors, fumes, or gaaes present; decrease in longevity to be even greater. Considering the characteristics of the groups studied, Dublin was led to the conclusion that in the industrial environment, exposure to abnormal conditions such as toxic dusts, vapors, fumes and gases, radiant heat, etc., explains the difference in longevity between industrial and non-industrial workers. Since, fur thermore, there are some 900 separate occupations with ex posure to occupational-disease hazards (2), the magnitude of exposure of workers to any sources of radiation or to abnormal tempera tures. (4) Analyses of types of employment: list of various operations and umber of workers employed us each; materials handled; absenteeism and labor turnover. (3) Preventive methods in use: isolation methods; local exhaust and general ventilation; personal respiratory-protection apparatus. (6) Medical services: cype of medial service provided and records kept; prirdif merlirsl nnmiiminM the preventive problem should merit considerable attention. It may be seen from the foregoing list of items that a Several methods are at present available for the prevention of fairly complete picture of the conditions existing in a plant is occupational diseases due to exposure to substances which are recorded. A record of the existence or non-existence of any injurious to health. Some of these methods have already been item at once helps che investigator to form a general conception extensively discussed in the literature of industrial hygiene of the line of study which must be adopted. It further makes 1 Numbers in parentheses refer to similarly numbered references at the back of the paper. Contributed by the Safety Committee and presented at the Annual Meeting, New York, N. Y., December 3 to 7, 1934, of Tn AatsaictM Soasrr o> Mksumical ENonrasa. available to him a detailed amount of information which is extremely useful. Such a survey may indicate whether or not there is compliance with various state factory or other indus trial codes. For example, oa the basis of the number of em ployees found in a given room, it may be determined whether 230 April, 1935 231 there is ample per capita space, or whether sufficient toilets have been provided. Occupational Analytic. Following the sanitary inspection of a plant, it is then necessary to study the various occupations. The occupational analysis includes an extensive study of the workers' immediate environment wherever a hazard is found to exist. It also entails a correlative study of the health of the workers. One is supplementary to the other and the omission of either cannot be expected to yield results which can be con sidered satisfactory. The Public Health Service in all its held investigations has attempted by such a procedure co establish what may be considered the safe conditions under which work ers may be exposed indefinitely without injury co health. Two examples of the methods used will aptly illustrate the technique employed in making occupations surveys. In a study of chromium-plating hazards, Bloomfield and Blum (4) examined 23 men, four of whom were not chromium platers and were selected as controls. Five ocher workers were not actually engaged in chromium plating, but were engaged at various duties at a distance of about ten feet from the plating tanks. The length of service of the workers was carefully determined from the individual occupational his tories and varied from zero to seven years. Since some of the workers were affected by acid mist, it was important to obtain data on the severity of the exposure. Accordingly, determinations of the amount of chromium mist present in the atmosphere were made. The amounts found varied from less than 1 mg to about 56 mg of chromic-acid mist per 10 cu m of air. The tabulated results showing the period of employment, the degree of exposure, and the findings on physical examination of the workers are given in Table 1. From an analysis of this able, it may be seen that 3 of the 19 persons employed in the plating rooms had perforated septa, 21 per cent had ulcerated septa, 47 per cent had marked in- TABLE1 OCCUPATIONAL HISTORY AND CLINICAL FINDINGS OF WORKERS IN CHROMIUM-PLATING PLANTS 1 Chromium placer 2 Chromium plater 3 Foreman plater 4 Foreman plater 5 Chromium plater 6 Chromium 7 Chromium 8 Chromium plater 9 Chromium pliter 10 Chromium plater 11 Chromium plater 12 f^hfnmtyfn places' 13* Chromium 14 Chromium plater 15* Nickel placer 16 Racket 17 Racket 18 Racket 19 Wiper 20* Foreman a* Foreman 22* Clerk 23* Inspector 6`/t 4 15.0 4-4- -- ++ 4- 4- 20 4 28.0 4-4- -- + 4- 4- 7 2 25.0 -- 4-4- ++ 4- -- 8`/s 3 25.0 -- 4-4- 4-4- 4- -- 3l/s 4 56.0 -- 4-4- 4-4- 4- 4- `/ 7 1.2 -- -- 4-4- 4- 4- Vs 7 1.2 -- -- ++ 4- -- 7 7 1.2 -- -- 4-4- 4- -- 3 7 1.2 -- 4-4- -- 4- 36 4 2.0 -- -- 4-4- -- -- 5 6 1.2 -- -- 4- 4- 4- V. 6 1.2 -- -- 4- -- -- 12 4 28.0 V. 2 28.0 lVt 0 (*) + 4- 4- -- 8 0 Cv + -- + 4- -- / 0 w -- -- 4- -- -- V. 0 to I1/* o to -- -- -- -- 44- -- -- ---- 0 00 -- -- 4- -- -- 0 00 -- -- 4- -- -- 0. 0 0 0 00 ---- 4- -- -- 1++marked; 4* slight; --negative; 'Unknown; ' Used vaseline in nose; ` Cyanide barns; Work in other departments of factory. damnation of the mucosa and more rhan half were subject to frequent nose bleeds. From these data it is possible to dis cover those occupations which require immediate attention. Together with the occupational analysis, the able further shows that the safe limit of concentration of chromic-acid mist in the air is probably under 1 mg per 10 cu m of air. The occu pational analysis thus often establishes the permissible limit of a contaminant for prolonged exposure. Frequently, it is nor possible to correlate engineering and medical daca in an occupational analysis. Thus, in a study of the lead hazard in a storage-battery plant (5), the Public Health Service adopted a special method of determining the permissible limit of lead dust. The investigation included a sanitary sur vey as outlined above and an occupational analysis which in cluded a determination of the lead dust and fumes present in the air, a record of employment and of disabling sickness (mostly compensation cases of plumbum), physical examinations, and blood and urine analysis. The medial examinations, because of the nature of lead poisoning, were necessarily extensive. With each worker, subjective symptoms such as colic, weak ness, loss of appetite, constipation, nervousness, etc., were noted. Similarly, the important objective symptoms were recorded, including pallor, jaundice, tremor, reflex and patho logical changes in the blood and urine. However, although a large number of engineering and medial daa were available, it was found to be inconclusive due to the large labor turnover which the plant had experienced during the course of the study. This had already been indiated by the sanitary survey, and as a result a careful record had been kept of the workers who had reported to the plant clinic for various complaints, characteris tic of lead poisoning. From the knowledge of the lead con centration to which these workers had been exposed, it was then possible to estimate approximately chat concentration of lead for which a minimum aumber of workers had found it necessary to visit the clinic. Hence, except for prolonged exposure, ic was shown in this manner chat the safe limit of exposure of lead dust and fumes was less chan 1.5 mg per 10 cu m of air. The foregoing examples show the importance of a carefully conducted occupational analysis. Not all conditions found in practice can be similarly treated, but a few facts stand out and are generally common in most surveys of occupational-disease hazards; these are; (a) a derailed list of occupations and the number of workers exposed; (4) a careful occupational history of each worker. This is most important as has already been pointed out with regard to dust hazards (6), but it is equally appliable to all types of hazards. The occupational history which is a list of all the previous occupations of the worker and his time spent in each is frequently of great assistance in diagnosing ailments which may not be entirely attributed ro his present work; (0 physical examinations of all workers with particular emphasis on the characteristic symptoms of the contaminant to which they are exposed. Careful present and past medial histories must also be taken; (d) quantitative detetminations of the contaminant present in the air; and (<) a correlative analysis of the medial and engineering findings with a view to establishing threshold or safe limits of exposure. Thnskoli Limits. Thus far the steps necessary co evaluate a given hazard have been outlined. It is clear that the starting point of a preventive program hinges upon the safe limit of air contamination which the worker may breathe continuously without injury to his halth. Unfortunately, extensive field studies of the cype discussed above have been few and there are still many practical data wanting. However, both in this country and abroad, laboratory experiments have been carried out on animals and humans, and it has been possible to deter mine approximately the safe limit of exposure to various sub- 232 i S, aESaI C- "0S * sS&s-s=:a ii* VOW V 5s*sB5-W-o- 99O -- o O 9 oON O - a 22ZwV2222VVV2V" Sfl rS4f=1S-,.S3,, o* 8.. 3 |ft'i I -?t* 'SSSStsf0'5'3 J<-; JSSSi S2sS2=t^6 sfaSossgscrssa a ihzhz&ilzzzhz ^Sss -.525 -.axlas a iSiirSS^mS .ii|sa|p fcslaltedz AA -.xsSs-. a I oegsgo^ca asvlagcg0 IS! s$ ilSlli=iI 38~.a~a. c ^ = la35- - o8a?-S3g3 cC - -II | s aiaa-, if si. Iff < `, 3 5 2?** 2*J? ^I 'jj-sa-s^aa i 82?;a*Il! < _a_-,_ --, aN Sfol s z540 z^f0l ^^>z0fl.Sz.03z^O2o^89Z0TT- * s t e s s.s j s.s's 3 3 I s-i-S H a aji.*jiji .!:.;..ysiii|.i iitltEJiA gASIiiii-s-S-S ii -is.* ifjijjmmj ijmiiiiiiijiijJlJljfl gii aaaa JUM^Hl IJssiiJ 5! 11rs si s ISfi.S a .slsl^lv*|ia "af"gsSSISS*"Siai Zzzz Mechanical Engineering 111 ^ 5. I IIS }JjJ M *] *i JI 1ii=si r | in*!?]5 i 1Ih55U*1'*ii 3I |8 mm * slim? "*1121 55 *1 *-rJI a *"3 1*1 ii sh !i isi s' L tM M: S" m _? 3a Has SilsIlsIiSs. ls>pasj.is,!,Ij.iviVi>ii?.M. O -- O m m o - O *" * XS2S S2S5Sr2*S88X,,*_7 --SSi,. Z i i i ii m ii i 12dS2=a=23Rsi i ~B*2=!5a25 3-- TJ .^ - . }:T.S TT3 TS T fT r T 7 T rs t t* "* 8 1 villi'*!! ^ 5 s ir a r <5 OJOJ 3 33333333.7 OJOOOOOOOISJ S'asrssssisis i 33 3 ?;;OXwz iz.8 , isSiigssiiS* .3 5 - 5$ _1 , 33=130 - 8 8lig..; 2SSS3l3sag5S^SS3Si533 r?A :1 4111 7-3 5 .: iSH1 1 i: .- .2a3 i: i: II ? "mS. ; . : u: 1v<Jt --S^J g 2 : : : : April, 1935 233 stances. Such daca have, cherefore, been cabuiaced and are presented in Table 2. In this cable are given the principal physical characteristics of various gases and vapors and the. physiological response on exposure to them. The last column in che table represents the concentration of a gas or vapor which is considered safe (according to information at present available) and which should not be exceeded.. Hence, given che problem of exposure to any of che substances given in the cable, it devolves upon the engineer to determine methods which will keep che concentration below the given safe limit, that is, che value in the last column of the cable. BNOINHBJUNO METHODS OF PUVENT10K Until recently, the methods of controlling occupational dis ease hazards met with little attention. Since, however, the use of substances injurious to health has been associated with a subsequent rise in the number of persons affected by continuous exposure to them, the preventive aspects of che problem have seriously engaged the attention of industrial physicians and engineers. The methods which have been developed differ widely due to the varying ways in which processes and opera tions are conducted. Detailed information, therefore, cannot be given with respect to the design of control apparatus. In general, che control of a hazard by engineering methods can be achieved in several ways, namely: (a) by isolation of the haz ardous process; (A) by exhaust ventilation; (c) by means of personal-protection devices, such as respirators and canistertype masks. Isolation Mtthads. The object of this method of prevention is to segregate a particular hazard so that a minimum number of workers are exposed. Frequently, a hazardous occupation may affect workers who are not connected with it, but who work close by. An example of such a condition has been given in connection with the Eve workers in the foregoing chromium study who had ulcerated septa, but who were not engaged in plating operations. Isolation methods have been successfully used in plants where dust hazards exist, such as the modern sand-blast room and the hydraulic shake-out in foundries, which not only tend to localize the hazard within a definite dosed area, but also expose few workers who are adequately pro tected by masks or helmets. Similar developments have also taken place in the spray-painting industries. Thus, spray painting and cabinets have been developed which are automati cally operated and require only limited attention by the worker. The same is true of paint-drying rooms and tunnels. Isolation methods are often the simplest and mosc practical approach in eliminating most occupational-disease hazards. A more ex tensive use of these methods, however, is often limited because of che complex operations found in many plants which require frequent handling of objects and hence necessitate the exposure of a large number of workers. Exhaust Ventilation Methods. The use of exhaust methods near che source of a hazard has grown rapidly in recent years. Briefly, the control of any industrial hazard by local exhaust is based on the principle that sufficient air motion must be created by a hood or opening ac the source of the hazard to reduce the concentration below the threshold limit. The amount of air motion necessary cannot always be estimated di rectly but depends upon a careful study of the relation between the amount of air contaminant present and the airflows han dled (7). Bloomfield applied this procedure with regard to the degree of ventilation required to keep chromic-acid mist below che threshold limic established by an occupational analysis previously discussed (4). The chromium-placing canks de scribed in the study utilized lateral exhaust. By varying the air flows handled and making determinations of che chromic- acid mist in che breathing zone of che worker, ic was found that che air movement in che plane of che opening, necessary co produce a safe concentration of misc, was approximately 1500 fpm. Some variations were found when the current den sity in che placing process was increased, since turbulence due to gas formation at che electrodes was increased correspond' ingly. However, che air movement produced a safe concentra tion for most conditions encountered. Since in any case the amount of ventilation required depends on the operations performed and on che shape of che hoods used, it is necessary to study each method of control separately. There are, however, some daca on the characteristics of mosc hoods which are not obstructed in che zone of influence which may prove convenient (8). These characteristics express the conditions of air flow forward of an opening and thus allow some estimate of che performance of a particular hood. For the approximate calculation of che flow ac any point along che asds of a hood without any surrounding barrier, che following formula has proved useful (8): V ~ 0.1 QJix1 -- 0.1 A), where V is che velocity of che air in fpm at a point along the axis; x is inches from the opening; Q is che volume of air handled in cfm; and A is the area of the opening in square inches. If overhead hoods are used for lighcer-chan-air vapors or gases, che air velocity at the edge of che tank or basin from which chey issue is given by the formula (9): V * 0.71 QJPD Here Vand Q are as in the former equation, while D is the dis tance from the hood opening to the edge of che tank in feet and P is the tank perimeter in che same unit. Thus, if che air movement necessary to control a given hazard at a point is known for one hood, the amounc of air necessary co be handled by a hood of different size may be approximately determined. In the case of hoods used in spray-painting operations where solvent vapors are found, it is customary, from the nature of the work, to place the object to be sprayed within che hood, while the operator stands just outside che opening. In such cases, che air flow necessary co secure safe limits of exposure is ex pressed in feet per minute at che opening. From studies made of the benzol hazard in various industries, it has been found chat air flows of from 100 to 200 fpm are required co keep the concentration of benzol below che safe limit of 100 parts per million (10). Here again, however, data on the air movements required to control hazards caused by the use of other substances are lacking, and the investigator must devise special studies and apply the data of Table 2. While no-attempt is made in this paper to discuss the various designs of hoods in use, it is necessary co point out a few im portant factors in design which must be considered. First, a careful study of the operation to which a hood is to be applied must be made. A hood should be so designed that ic offers a minimum amount of hindrance to the operator. Secondly, due consideration must be given to the nature of the substance to be collected. In Table 2, the principal properties of a number of gases and vapors are given. The type of hood design used, therefore, must utilize the fact that if a gas or vapor is heavier than air, it is preferable to use downward or lateral exhaust. This point has been aptly illustrated by Gumaer (11), who has shown chat the tendency of a vapor such as ben zol is to form into dense layers which sink gradually downward. Lighter-chan-air gases or vapors, on che ocher hand, are best handled with vertical exhaust, taking advantage of their natural tendency to rise. The importance of utilizing che characteristics of a given gas lies not only in the fact that it simplifies che problem of control, but also ic prevents any accumulation of gas in such concentrations chat chey may be accidentally ignited and cause explosions. For this reason there are given in Table 2 the inflammable limics of various gases 234 Mechanical Engineering and vapors when data pertaining to them have been available. Finally, the third factor to be considered is the frequent testing and care of the ventilation apparatus. Exhaust systems should always be operated at their maximum efficiency and periodic checks should be made to see that the concentration of air con taminant is kept below the threshold limit. Personal Rctpirattry-Pmtctiam Methods. Personal respiratoryprotection apparatus are widely used, especially when isolation and mechanical methods cannot be properiy designed or when workers are exposed for very brief periods of time. Such ap paratus cannot be worn continuously because of the incon venience incurred in wearing them. Consequently, they form a method of protection when other preventive measures are impracticable. Nevertheless, personal respiratory-protection apparatus form an important part in many preventive programs and a proper knowledge of their uses and limitations is ex tremely important. The simplest form of respiratory-protection device is the res pirator. Respirators consist of a face piece covering the nose and mouth, with a filter medium to restrain dust or mist on in halation. A special valve is provided to facilitate expiration. Respirators are used for protection against injurious dusts, such as silica, asbestos, lead, and cadmium oxides. Their effectiveness depends upon the type of filter medium used and the manner in which it fin the wearer. A large number of respirators of various types have been developed. Many of these have been tested and reported upon by the Bureau of Mines (12). This Bureau has recently prepared a schedule of tests for respirators which attempts to standardise the procedure for determining the effectiveness of various res pirators (13). Heretofore, much confusion has resulted with reference to the claims made by the various manufacturers on respirator efficiencies. For the prevention of hazards due to exposure to gases and vapors, canister masks have been developed. These masks are made of special fabrics and cover the face completely. A flexible hose connection extends from the lower portion of the mask to a small canister containing an absorbing medium. Thus, the inhaled air is made to pass through the canister and insures pure air to the wearer. Universal canisters are supplied with a variety of absorbing materials arranged in layers and can be employed against most of the commoner gases and vapors found in industry. Canister masks, however, cannot be used where the gases or vapors are in high concentration. A range of 2 to 3 per cent of a given contaminant appears to be the maximum limit in which a canister-type mask can be used (14). It is important to remember that canister-type masks cannot be employed in an atmosphere deficient in oxygen. Further more, great care should be taken to refill canisters at regular intervals to insure high absorption efficiencies. Still another type of mask used to protect the worker is the positive-pressure mask. Such masks are supplied with a con tinuous flow of compressed air from a clean source. This method of protection is finding increasing use in many indus tries because of the high efficiencies which can be obtained. A chief fault to be found with such masks, however, is the in convenience experienced by the wearer who is compelled to carry about with him an air-supply hose. MBDICAL aspaers OP PUVXNTION The industrial physician is in a position to estimate the success or failure of a preventive program. He is the first, by virtue of the workers who report to his clinic, to discover the characteristic symptoms of an occupational disease and to call attention to the specific occupations which are dangerous. In this connection, as has been pointed out by the American College of Surgeons (13), the periodic medical examination of workers is of immense value. Only in this way is it possible to secure and maintain the physical fitness of employees and to help increase their longevity. Workers exposed to the hazards of volatile solvents, such as benzol, carbon disulphide, etc., and to such gases as carbon monoxide and hydrogen sulphide, re quire medical examinations at frequent intervals to insure them against serious chronic ailments. Workers showing symptoms of poisoning should be given other jobs, and should be re examined at later dates to determine their improvement. SUMMAZr This paper points out the decreased longevity of industrial workers in comparison with workers of similar social and eco nomic status. The importance of possible exposure to occu pational-disease hazards as a contributing cause in the decreased longevity is stressed, and methods of their prevention with particular reference to substances other than toxic doses are discussed. These methods include the preliminary plant sur vey and occupational analysis and engineering and medical methods of prevention. The plant survey consists of a listing of all the hygienic facilities for the purpose of determining those occupations in a plant which require further study. This is followed by an occupational analysis, which is intended to show the severity of the exposure of various occupational groups and to correlate the findings with medical examinations. In this way, it is shown to be possible to determine the safe or threshold limits of exposure. The toxic limits of common industrial gases and vapors are included in able form. With regard to the engineering methods of prevention, these is dis cussed the comparative features of three methods in present use, namely, isolation, local exhaust, and personal respiratory protection. The value of medical supervision and periodic physical examination as a method of increasing the longevity of workers is shown to form an integral and important part in a preventive program. REFERENCES (1) "The Mortality Trend in the Industrial Population,'' Louis I. Dublin, Jew. Pot. Health, May, 1929, vol. 19, no. 5. (2) "Occupational Hazards and Diagnostic Signs," Louis I. Dublin and RobertJ. Vane, Bui. 382, Bureau ofLibor Statistics, 1933. (3) "Preliminary Surveys of the Industrial Environment," J. J. Bloomfield, Public Health Reports, Nov. 3,1933, vol. 48, no. 44. (4) "Health Hazards in Chromium Plating," J. J. Bloomfield and William Blum, Public Health Reports, Sept. 7, 1928, pp. 2330-2347, or Public Health Reprint No. 1243,1928. (3) "Lead Poisoning in a Storage Battery Plant," A. E. Russell, R. R. Jones, J. J. Bloomfield, R. H. Britten, and L. R. Thompson, Public Health Bulletin No. 203, June, 1933. (6) "The Occupational History and How to Make It," R. R. Sayers, dm. K#v. tf TahtraUttis, January, 1934, vol. 29, no. 1. (7) "Criteria for Industrial Exhaust Systems,"J. J. Bloomfield,Jour. Am. Soc. Heat, and Vent. Engineers, July, 1934, vol. 6, no. 7. (8) "Velocity Characteristics of Hoods Under Suction," J. M. DallaVallc.Jour. Am. Soc. Heat, and Vent. Engineers, May, 1932, vol. 4, no. 3. (9) "The Importance of Velocity Characteristics in the Design of Local Exhaust Hoods," J. M. DallaValle, Jttn. tf bed. Hji., Jan., 1933, vol. 13, no. 1. (10) Final Report of the Committee on Benzol. Chemical and Rub ber Sections of the National Safety Council, May, 1926. (11) "Vendlatioo of Heavier Than Air Vapors," P. W. Gumaer, Transactions of the Nineteenth Annual Safety Council, National Safety Council, Chicago, 111., 1930. (12) "Dust Respirators," S. H. Katz, G. W. Smith, and E. G. Meiter, Bureau of Mines, Technical Paper 394,1926. (13) "Procedure for Testing Filter-Type Dust, Fume and Mist Respi rators for Permissibility," Schedule No. 21, Bureau of Mines, 1934. (14) "Gas Masks for Gasoline and Petroleum Vapors," S. H. Katz and J. J. Bloomfield, Bureau of Mines, Technical Paper 348,1924. (13) "Medical Service in Industry and Workmen's Compensation Laws," N. M. Newquist. 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