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FILE NAME: Engineering (ENG) DATE: 1935 Apr DOC#: ENG004 DOCUMENT DESCRIPTION: Trade Journal Article - Prevention of Occupational Diseases: Other Than Those That Are Caused by Toxic Dust Cl8 256529 C/Yr MECHANICAL ENGINEERING Published by The American Society of Mechanical Engineers V o l u m e 57t N umbbr 4 ' Contents for A pril, 1 9 3 i THE E N G IN E E R AS A C IT IZ E N .......................................... C A V IT A T IO N R E S E A R C H .......................................... A . R . Cullimore J . C. Hunsaker E N G IN E E R IN G METHODS IN M ED ICAL RESEARCH..................................................... ..............................................C. M. G ratz and S. N . Blackberg o i l b u r n e r s a n d b o i l e r s ............................................................... L . E. Seeley DEFLECTION OF A LONG HELICAL GEAR TOOTH . . C. W . MacGregor STUDY OF THE FLOW OF AIR W ITH A STROBOSCOPE . H . E. Edgerton PR E V E N T IO N OF OCCUPATIONAL D I S E A S E S ............................................................... ...................................... R . R . Sayers and J . Ai. D alla V a lle c o r r e c t i n g o u r e c o n o m y ..................................................... R . E. Freeman s e l l i n g o n e ' s s e r v i c e s ...........................................W illia m M cClellan co r r o sio n of b e a r in g surfaces . . . . C. H . Bierbaum BU RN IN G OF CRACKED-RESIDUE FUEL OILS . . . M . J . Hanlon 209 211 217 221 225 228 230 235 237 239 241 EDITORIAL . . E N G IN EER IN G PROGRESS LETTERS AND COMMENT DISPLAY ADVERTISEMENTS w h a t 's NEW . . . 205 . 244 . 257 A .S.M .E . BOILER CODE . . . REVIEWS OF BOOKS . . . w h a t 's GOING ON ... . 260 . 262 . 265 . 1 PROFESSIONAL SERVICE . . . . 29 . 14 CLASSIFIED ADVERTISEMENTS . . 30 : 0 ADVERTISERS . . . 32 OFFICERS OF THE SOCIETY: Ralph E. Flanders, President E r ie O bhro, Treasurer C . E . D avies, Secretary PU B L IC A T IO N STAFF! G boeos A . Stetson, Editor Frederick L a sk , Advertising M p . COM MITTEE ON PUBLICATIONS: S. W. D udley, Chairman $, F. Voorhbbs G. F. Bateman W. F. Ryan M. H. R oberts A D V ISO RY MEM BERS OF THE CO M M IT TBB E. L. Ohls, St. Louis, Mo. E. B. N orris, Blacksburg, Va. Junior Member, O. B. Schibr, 2d ON PUBLICATIONS. A. J. D ickie, San F rancisco, Cal. a**aqu4ran Ol Uie owjcij. " f' ,, ,, qTM St so/Wduional. the cents Change of add** moat be received i t Society Headquart* two weeits oaurc ttuhceyy Prevention of OCCUPATIONAL DISEASES t h r Than Those T h at Are Caused by Toxic D u st By R. R. SAYERS a n d J. M. DALLAVALLE u n ite d states pu blic h ea lth service Th e USE of volatile chemicals has increased greatly durum n chPea m a S ^ ^ W ^ and ,, I f au re of Palnts> ia dry-cleaning processes and as solvents m various industrial processes, to mention but a few of their common uses. In fact.so great hasTeen the dc- mand for volatile solvents both by industry and the general ! u j i C' dh a tj eW appllCadons for ilem arc constantly8 being developed and commercialized.- The volatile solvents L f o r t f fnieellddsfassnn^ew uses for them^ aredfisicno(vWereida. I ^ - s i o n L fo new Partly as the result of the increased use of new chemicals in industry, it is now well recognized that the hazards of certain occupations are important factors in the causation of sickness and even death. Dublin (1). has evaluated the effect o fth e industrial environment on the well being of a large number of s is w th' * 1-- Z l i . J p ' Cary and occupational surveys* (T) merhan.v t h o d , co,,Pr mg , " cj j ^ ^ san1' periodic medical examinations and surveys Each J t h methods is discussed in the paragraphs which follow SANITARY a n d occupational SURVEYS ated. In studies made by the Public Health Service (3) it has X ^m aV eafnem dyThme ^ g rm d from 1922 to 1924, i n c l u s i v e . ^ ^ 'r c o l p a r S w h h " the hygienic items which enter into the worker-* 1 * 11 similar study made over a similar period from 1911 to 1913 The groups studied constituted a fairly representative sociai timeXXsprnds S x ^ s k M ^ ^ nd economic class and were considered as an urban earning r ,, ? r TM 7 T i population. Dublin has shown by an analysis of the data o tf tamed, that adult males engaged in industrial pursuits h a d ^ higher mortality and a shorter longevity than those in other S types of work such as professional, clerical, etc. In the more " d d" f - f a which recent study, it was further shown that the mortality rates for the industrial workers were more than double the rates " " in"' 1 sanitary ~ m r choold ioclodc Z Z oon-hazardous occupations. In terms of life expec tancy, the picture presented was impressive. The industrial worker at the age of 20 had an expectancy of 42 yearn as com nffrheW1i ^ f 49 yCafS- In ther words, the life iogsemee; -.-cching Lcn?tdv^y of the mdustrial worker in 1924 was shortened by approxi- ccspiior and - J - e n years, while the data for 1911 to 1913 showed the decrease m_ 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, vapo, W s and g ses, radiant heat, etc., explains the difference in longevity fctween industrial and non-industrial workers. Since fur thermore, there are some 900 separate occupations w kh ex posure to occupational-disease hazards (2), the magnitude of he preventive probiem should merit considerable attention Several methods arc at present available for the prevention of occupational diseases due to exposure to substances which are injurious to health. Some of these methods have already been extensively discussed in the literature of industrial hygiene 4.; ^ s s ^ z d z liat pro'f`i'j >"* * It may be seen from the foregoing list of ireme th,* fairly complete picture of the conditions existing in a plant is s ; A. r * i f , h' o o ^ i ". ,1o i L r item at once heips the investigator to form a general conception I v r___i_ ... - _ S . * 1" " fa " " S ? f i f c * S t e SOOTTY op M hchanicai, Engineers. " * '-- *1 f a , avaliabiXtt0o h) i1X!? aa d^ailed amo*u*nt of inform*atfiuornthwcrh"icahkcis* thrX y " X"1' SuCh 1 SUrvCy ma-y indicate whether or not ' 3 ' *T Amhrican 5 5 VoSdcsmPFnr CC Wlt^ Vafi0Uu StaCC 01 0ther ind" - / CJCample> on the tasis of the number of em ployees found m a given room, it may be determined whether 230 231 April, 1935 there is ample per capita space, or whether sufficient toilets have been provided. . . . . Occupational Analysis. 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 field investigations has attempted by such a procedure to establish what may be considered the safe conditions under which work ers may be exposed indefinitely without injury to 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 other 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 arc given in Table 1. From an analysis of this table, 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 w- flammation of the mucosa and more than 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 table 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 not possible to correlate engineering and medical data 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 plumbism), physical examinations, and blood and urine analysis. The medical 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 medical data 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 indicated 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 that concentration of lead for which a minimum number of workers had found it necessary to visit the clinic. Hence, except for prolonged exposure, it ta nr F l OCCUPATIONAL HISTORY AND CLINICAL FINDINGS TAB OF WORKERS N CHROMIUM-PLATING PLANTS was shown in this manner that the safe limit of exposure of lead dust and fumes was less than 1.5 mg per 10 cu m of air. The foregoing examples show the importance of a carefully 1 B |: t IO 06 t! o & ,o5.9** ?o>>ruifrsSi 3 CU CU S a. D a +5 x* 2a.f9l u3 K na X T 0 m r ,, 3 H<4 8 11 2 g-i | Occupation D 1 Chromium plater 6V* 4 15.0 + + -- 2 Chromium plater 20 4 28.0 + + -- } Foreman plater 7 2 25.0 -- +4- 4 Foreman plater 87* 3 25.0 -- + + 5 Chromium plater 37* 4 56.0 -- 6 Chromium plater 7 Chromium plater V* 7 7 7 1.2 1.2 -- -- -- -- 8 Chromium plater 9 Chromium plater 7 3 7 1.2 --` 7 1.2 -- -- 10 Chromium plater 36 4 2.0 -- -- 11 Chromium plater 5 6 1.2 -- --* 12 Chromium plater 7 , 6 1.2 -- -- 13s Chromium plater 12 4 28.0 '-- -- 28.0 -- -- 14 Chromium plater 15 Nickel plater 7* 2 17* o 0 ) .. + + 16 Racker 8 0 0) + -- + 7 0 (*> -- -- + 17 Racker 18 Racker 7< o -- -- + 19 Wiper u / i o (*) -- -- + 20* Foreman 0 00 -- + 21* Foreman 0 00 0 00 --. + -- -- 22* Clerk 23* Inspector O 0 0 /-- - + + -- 4- - 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) * detailed list of occupations and the number of workers exposed; 0 ) 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 applicable 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 p e a t assistance in diagnosing ailments which may not be entirely attributed to his present work; 00 physical examinations of all workers with particular emphasis on the characteristic symptoms of the contaminant to which they are exposed. Careful present and past medical histories must also be taken; 0 0 quantitative determinations of the contaminant present m the air; and a correlative analysis of the medical and engineering findings with a view to establishing threshold or safe limits of exposure. Threshold Lim its. T hus far th e steps necessary to evaluate a given hazard have been outlined. It is d e a r th a t the starting point of a preventive program hinges upon the safe lim it of air contam ination w hich th e worker may breathe continuously w ith o u t injury to h is h e a lth . U nfortunately, extensive field studies of th e type discussed above have been few and there are still many practical data w anting. However, both in this country and abroad, laboratory experiments have been carried o u t on anim als and hum ans, and it has been possible to deter i marked; -(-slight; -- negative'; * U nknown;* Used vaseline m ine approxim ately th e safe lim it o f exposure to various suh- in nose; *Cyanide bums; Work in other departments of factory. v- , . a u`V . * * " * * - r u i i \^ 4 U 4 ^ < fe U M M U E W i& ): Substance Chlorine........................... Bromine.................... Rr* Oiat)c .................. " Hydrocyanic acid ......... Formula Qi o3 HCN Hydrogen chloride.......... Hydrogen fluoride............ Sulphur dioxide................. Nitrogcti tetraoxide......... Ammonia........................ Carbon A ioxidc ......... ** CarboD monoxide............. Hydrogen sulphide........... ^ m!- ............................. Fhosphcoe........................ Phosphorus trichloride.. . HC1 HF SOj NO* or NHa CO* CO H*S AsH, pHj PCI* NjO* Phosphorus pcntachloride PCI* Arsenious chloride........... AsCl* ............................ Z \ u c *c , ........ ........... Xylene (-xylene)........... MctlxarooJ......................... CsHs CsHsCH, CsH* (CH*)* CH3OH ............................ CiHsOH Aceronc. ..................... CHCO-CH, rormaldchydc.................. Methyl chloride.............. Ethyl ebbtide ................ Carbon tetrachloride....... H*CHO CH3CI CtHsCI CCU Trichloroethylene............ CHC1CCI, Carbon disulphide........... CS* -Amyl acetate............... CHa-COOCsHu -Butyl acetate............... CHaCOOCiH Nitrobenzene.................. CoHsNO* An`Il'l c -........................ -Toluidrne...................... Turpentine........................ Phosgene........................ CsHs-NH* CHaCsHs-NH* CtoHi* COC1* Gasoitoe-'......................... C,,H2 +2 0 Calculated. 6 Based on animal tests. e Computed as NO*. Solid Liquid Liquid Liquid Liquid Liquid Liquid Liquid Gas Gas Gas or liq. Liquid ' Liquid Liquid Liquid Liquid Liquid Liquid Liquid Liquid Gas Liquid Si TABLE 2 PHYSICAL AND TOXIC PROPERTIES OF COMMON VAPORS AND GASES Si Spec. gr. Least of gas or Inflammable Physio amount detectable Phyjiulogica! response to various concentration, (ppn. Maximum Amounts causing limirs (per cent) logical action by odor (ppm) Kills in very short time Dangerous for J/ j f l hr exposure concentration for exposure of V *-l hr slight symptoms after several hours' exposure Maximum allow able concentration for prolonged exposure Non-inflamm. Non-inflamm. Non-inflamno. Strong irritant 3.5 (2) Strong irritant No data Strong irritant 0.5-1 0 (3 ) 900(3) at 550 (3) 14-21 (3) at 6-9 (3) 3-5(3) at 3-5 (3) 0 35(3) < 0 35 (3) Non-inflamm. Irritant No data No data 270 (3) 5(3)6 No dara 0 3-0 45 (3) 0.8-1.8 (3) 0.15-0 3 (3) Asphyxiant 110-135 (3) 45-54 (3) 18-36 (3) < 0.8 Non-inflamm Non-inflamm. Strong irritant No data Strong irritant No data 1250-1750 1000-1350 (3) 40-90(3) <18(3) Non-inflamm, ~ Strong irritant 3-5 (5) 660(3)6 535-650 (3) 50-250 (4) 10(4) No data 10 ( 3)6 0 0 (3) Non-inflamm. 16-27 (7) Strong irritaot No data Strong irritant 5 3 (2 ) 320-530 (3 )c 5000-10.000 (8) H1570--I15940 ((63)) 50-100 (3) 105-21C (3) e 5205-04)060) 3(4) 10(3) Non-mflamm. 12 5-74 0 (7) Rcsp. scira. Asphyxiant No data No data 50,000-67,000 (3) 2500-4500 (9) 33,500-44,500 (3) 300-500(9) 33,500-39.000 (3) 146(3) 39(6) 85(3) 4 3-46.0(7) Asphyxiant 0 .7 5 (H ) >4000(8) 420-600 (3) 1500-2000 (8) 600-700 (8) 11,000-16,700 (3) 500(10) 5,550 (3) Inflammable Inflammable Asphyxiant Asphyxiant No data 1 .4-2.8 250 (3) 360-500 (3) 15-5(3) 200-300 (8) 6 25 (3) 100-150 (8) 100 (8 ) 85-130 (3) Nou-mflamm. Strong irritant 400-600 0 ) 652 (12) 290-430 (3) 50-90 (12) 100-190 (3) 3 .1 0 ) 7 0) < 3 .1 <7 - Non-inflamm. Strong irritant 2-4 (12) 0.7 0)6 0.7(12) Non-inflamm. Strong irritant Analogous to phosphorus trichloride (3), (8) 1-4-7.0(7) 1-4-7.0(7) Asphyxiant Asphyxiant 19,000 (14) Analogous to phosphorus trichloride (3) (8) 3,000 (15^) 3,130-4,700 (14) Inflammable Asphyxiant Analogous to benzene (3) , (8) 1,570-3,130 (14) ICO (16) 7.45-26.5(17) 4-19 (7) Anesthetic Anesthetic 290,000(3)6 No data A4n-a1logous to b' enzene (3), (8y] No data " 3- 11 (7) Anesthetic No data 46.000 (3)6 No data 1380-5000 (19) No data Non-inflamm. 8-19 (7) Irritant Anesthetic No data >6500 (20)6 75,000 0 ) 6 No data No data No data 3370-4220 (3)6 No data No data 4- 15 (7) Anesthetic 150.000- 300,000 ( 21)620.000-40,000 (21) 6 150.000-300,000 (21)6 7000(21)6 2 0 0 (20)6 500(21)6 No data Non-inflamm. Non-inflamm. 1.50(7) Anesthetic Anesthetic 10.000 0 5 ) 7800 (3)6 60.000- 100,000(21)6 317(22) No data 40,000 (21)6 <1000(22) 20,000 (21)6 No data <500 < < 21000,0(0202) Inflammable Anesthetic Anesthetic 4,800 (3) 3200-3850 (3) 3700 (3)6 960-1.600 (3) No data No data 1 7(7) Anesthetic No data No data 900(23) No data 320-390 (3) No data No data loflammablc Inflammable Inflammable Narcotic Narcotic Narcotic No data > 420 (24) No data 19,000(3)6 No data No data No data 1 0 (8) 105-160 (8) 5000 (3)6 0 2-0 4 (8) 7-26 (8) No data No data < 0.2 Inflammable Non-inflamm. 1.4-6.0(7) Irritaot Strong irritant Anesthetic 5-6(2) No data 2900 ( 25)6 90(3) 30-40 m g /l (3) No data 540-720 (25)6 12.5(3)* 91-140 (8) No data No data 6-23(8) 720-1100 (25) 1 (2) <7 <6 No data 25-30 m g /l (3) 10-20 m g /l ( 3) 5-10 m g /l (3) <1 10 mg/l (3) M e c h a n ic a l E n g in e e r : OO TM > -Il. "irfodcrQe0ecwerbii-hCnv rCatf linS Apparatus by Gascs K an sas-- Vapors," A. C. Fieldner H Katz and ^rCp U,?f Staatia^ s*U- s - Department of Commerce, 1918 1886, vol. 5, p .l. .espunse aci Treasury Department, 1929. it iS } * " " * i B:.hh-- . W - f c . 4 . GaSCUDdDampfc** *" . p. 962. K. B. Lehmann. CXXXII-XXXUI). voi. 70, p. 217. _____________ Service, U. S. 2 0 tfHIHki April, 1935 233 stances. Shell data have, therefore, been tabulated and are presented in Table 2. In this table are given the principal physical characteristics of various gases and vapors and the physiological response on exposure to them. The last column in the 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 the problem of exposure to any of the substances given in the table, it devolves upon the engineer to determine methods which will keep the concentration below the given safe limit, that is, the value in the last column of the table. acid mist in the breathing zone of the worker, it was found that the air movement in the plane of the opening, necessary to produce a safe concentration of mist, was approximately 1500 fpm. Some variations were found when the current den sity in the plating process was increased, since turbulence due to gas formation at the electrodes was increased correspond ingly. However, the 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 the shape of the hoods used, it is necessary to study each method of control separately. There arc, however, some data on the characteristics of most EN G INEERIN G METHODS OF PREVENTION hoods which arc not obstructed in the zone of influence which Until recently, the methods of controlling occupational dis ease hazards met w ith 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 the 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, the control of a hazard by engineering methods can be achieved in several ways, namely: (<*) by isolation of the haz ardous process; ( i) by exhaust ventilation; (c) by means of personal-protection devices, such as respirators and canister- type masks. , Isolation Methods. 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 arc not connected with it, but who work close by. An example of such a condition has been given in connection w ith the five 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 closed 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 arc often the simplest and most practical approach in eliminating most occupational-disease hazards. A more ex tensive use of these methods, however, is often limited because of the 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 the 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 at 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 the threshold limit established by an occupational analysis previously discussed (4). The chromium-plating tanks de scribed in the study utilized lateral exhaust. By varying the air flows handled and making determinations of the chromic- may prove convenient (8). These characteristics express the conditions of air flow forward of an opening and thus allow some estimate of the performance of a particular hood. For the approximate calculation of the flow at any point along the axis of a hood without any surrounding barrier, the following formula has proved useful (8): V -- 0.1 Q / ( x 2 0.1 A), where V is the velocity of the air in fpm at a point along the axis; x is inches from the opening; Q is the volume of air handled in cfm; and A is the area of the opening in square inches. If overhead hoods are used for lighter-than-air vapors or gases, the air velocity at the edge of the tank or basin from which they issue is given by the formula (9): V = 0.71 QJPD Here V and Q are as in the former equation, w hileD is the dis tance from the hood opening to the edge of the tank in feet and P is the tank perimeter in the same unit. Thus, if the air movement necessary to control a given hazard at a point is known for one hood, the amount of air necessary to 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 the hood, while the operator stands just outside the opening. In such cases, the air flow necessary to secure safe limits of exposure is ex pressed in feet per minute at the opening. From studies made of the benzol hazard in various industries, it has been found that air flows of from 100 to 200 fpm are required to keep the concentration of benzol below the 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 to 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 it 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 that the tendency of a vapor such as ben zol is to form into dense layers which sink gradually downward. Lighter-than-air gases or vapors, on the other hand, are best handled with vertical exhaust, taking advantage of their natural tendency to rise. The importance of utilizing the characteristics of a given gas lies not only in the fact that it simplifies the problem of control, but also it prevents any accumulation of gas in such concentrations that they may be accidentally ignited and cause explosions. For this reason there are given in Table 2 the inflammable limits of various gases 234 M ech a n ica l E n g in e e r in g 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 Respiratory-Protection Methods. Personal respiratoryprotection apparatus are widely used, especially when isolation and mechanical methods cannot be properly designed or when workers are exposed for very brief periods of time. Such ap paratus cannot be worn continuously because of the incon College of Surgeons (15), 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. venience incurred in wearing them. Consequently, they form SUMMARY a method of protection when other preventive measures arc 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 fits 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 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 dusts 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 w ith medical examinations. In this way, it is shown to be possible to determine the safe or Mines (12). This Bureau has recently prepared a schedule of tests for respirators which attempts to standardize the procedure for determining the effectiveness of various res threshold limits of exposure. The toxic limits of common industrial gases and vapors are included in table form. With regard to the engineering methods of prevention, there is dis pirators (13). Heretofore, much confusion has resulted with reference to the claims made by the various manufacturers on respirator efficiencies. cussed the comparative features of three methods in present use, namely, isolation, local exhaust, and personal respiratory protection. "Hie value of medical supervision and periodic For the prevention of hazards due to exposure to gases and physical examination as a method of increasing the longevity vapors, canister masks have been developed. These masks of workers is shown to form an integral and important part in a are made of special fabrics and cover the face completely. A preventive program. 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 w ith a variety of absorbing materials arranged in layers and REFERENCES (1) "The Mortality Trend in the Industrial Population," Louis I Dublin, Jour. Pub. Health, May, 1929, vol. 19, no. 5. ' (2) "Occupational Hazards and Diagnostic Signs," Louis I. Dublin and Robert J. Vane, Bui. 582, Bureau of Labor Statistics, 1933 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 5 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 'i!rf 1irnirj?rXI vys of the Industrial Environment," J. T. p"blrlc Health Reports, Nov. 3,1933, vol. 48, no. 44. J William Blumth, PDuabu ltircd Humea,l^thh rR mepiourmts , PSIaedpnt.S7- " , 1J-92J8- Bdldoom23f3ie0l-d21a4n7d or Public Health Reprint No. 1245,1928. P ' PP' 3 7, (5) "Lead Poisoning in a Storage Battery Plant," A E Russell H T n J -J loomfieTld>R- H - Britten, and L. R. Thompson, Public Health Bulletin No. 205, Tunc, 1933. r * (6) "The Occupational History and How to Make It," R. R. Sayers Am. Rtv. of TuberculosisyJanuary, 1934, vol. 29, no. 1. * 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. * (7)c ',Cnj Cria k ^ d u s t n a l Exhaust Systems," J. J. Bloomfield,Jour. , at- " d Veat- f a c e r s , July, 1934, vol. 6, no. 7. __W velocity Characteristics of Hoods Under Suction," J. M. Dalla- Valle, Jour. Am. Soc. Heat, and Vent. Engineers, May, 1932, vol 4 no. 5. * ** T ,,T*" Importance of Velocity Characteristics in the Design of toT I s m T l1 H 0d5'" J- DallaVal,e. Jour. of Ind. Hyg,, Jan., 1933, 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. M ED ICAL ASPECTS OR P R E V E N T IO N 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 (10) Final Report of the Committee on Benzol. Chemical and Rub ber Sections of the National Safety Council, May, 1926. (11) " Ventilation of Heavier Than Air Vapors," P. W Gumaer Transactions of the Nineteenth Annual Safety Council, National Safety Council, Chicago, 111., 1930. 7 (12) "Dust Respirators," S. H. Katz, G. W. Smith, and E. G. Meiter Bureau of Mines, Technical Paper 394, 1926. ' 0 3 ) "Procedure for Testing Filter-Type Dust, Fume and Mist Respiratorsfor 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. attention to the specific occupations which are dangerous. In this connection, as has been pointed out by the American 0 5 ) "Medical Service in Industry and Workmen's Compensation Laws, N. M. Newquist. Prepared for and published by the American College of Surgeons, 1934.