Document DvBJgoV7MO9MzR1QNp1GakdeN

The foundation ofmodern sdence and modem Haldane, Henderson and Haggard. Experiments technique is the process ofwighing, measuring on human beings (experiments on the author andcountJng.Thestcpfromtheemplri~~~tr,himself) are rarely re&red to. An extension and modem sdence, &om skilled handhrork to me- completion ofthistable maybe found in the book, chanical performance waa possible only after Ndous Qascs, by Ruryand Zernik.@' methodafor spedfkweighingandmeasuringhad been found Exact examinations of air and its contaminants in hctorieswere great raritieseven 20 and 15 years ago; indeeddeterminaUons of dust concentrations were the only such measurements made to any appredable extent and these were done in English speaking countries alone. No other instruments were available for investigations In factories except those for determtnlng the dust contents. (In the United States, the sugar-tube, Palmer apparatus, QeenburgSmith impinger; in England W e n s dust counter; in South AM-, Kotze k0ntmeter.JThe methods and instruments used in laboratories have also been used in factories, instruments dlfflcult to handle and transportoftennotaccurate.All thisis difkrent today. The table, "MaximumAllowableConcentrations," compiled by BOWI~~C~"w'' as especially meritorious as it included tabulation of regulations of other governmental authorities in addition to t h e suggested for Massachusetts. These had been referred foruiticism to more than a score of the leadlngauthorities in this countryand abroad prior to their promulgation. This table has been revlsed and extended by himself, CK Drinker, P. Drinker, H.H. Haggard and A Hamilton!" By formulating the problem into "allowableconcentratlons" it has been taken out of the fleld of theoretlcal.reSearchand transfemd to the practical frtdustrfalhygiene. But the ready avallabillty of apparatuseasy to handle and oftablesoftoxic llmits~edbywlellknownscienUststowtrich the results can be referred for interpretation may We now have various instruments suitable for lead tothe undesirable situation that men notwell use in factories, although the truly exact instru- trained in industrial hygiene will underestimate m a t and the predse method is still lacking for the dilkulties of obtaining truly representative certain purposes. On the contrary we even suffer results. In addition there is the danger that they from too many offers of instruments made by will employ these results beyond thelr limits of flrms and sdentlsta Their only small devlatlon usetblncss and sodraw UqpUiabk conclusions. from already existinginstruments makes it more difllcult to compare the results, since the new instruments often do not -tee any greater accuracy. RR published In 1927data about the most important poisons, briefly summarlzing them. AS fiwas I know, mnggefl' in 1928waa the firstauthor to compile a table "about the effictof lrrltant and poisonous gases and vapors.' For many gaww he sptdfled the exact concentration in m l U I g r a m perUterwhichwould MU immcdlately or be htai&r 03to 1.0hour. He defined which Therefbre the wlue of the U m l t s , the practical purpuse and the limltatlons of their use may be discussed in the followinglines A sharp disthctlon must be drawn between acute and chronic d o n which must be applkd espe&Uytothot~~ma~rlalswhichproduceacute andchronic occupational potsontpg (benzol,toluene, xylene, carbon disulfide, trtchloroethylene, anlllne,ozone, e)Th.e "allowableconcentration" is much higher where there b danger of acute poisoning than under condltlons where there is concentration may be borne with large, small or no damaging e&ct for a period of tlme. The compilation is supported for the largest part by anlmal experiments, made by KB.khmann and hb collaborators, m e r , US. Bureau of Mlncs. Thirty-five Y a m of TLVs continuous inhalation for a long time. It is evident it was caused by a larger recent absorption of that it wuld be out of place to demand the same benzol. limitingvalueof contaminationwhere theworkers Manyanimal experimentsare at hand concern- are only accaslonally exposed to the danger of acute poisoning (transferring benzol. trichloroethyIene,carbon bfsulflde,etc,orsimilarintermit- tent work puformed at extended inttrvzrls)as in places where there is danger of continuous inhalationfora period ofweeks or months. -ing concentration and duration of air mtamina- tions which cause temporary or lasting iqjury but their application to man iseither not feasible orto be done onlyverycautiously. There are important differences between the dilfierentsped- of animals. The fatal concentra- The Massachusetts publication quoted above tion of carbon monoxide poisoning at 32% is seems to give the "allowableconcentrations" for above 0.12% by volume for the rat. above 0.25%, those adtonswhich are most important in indus- forthe guinea pig and aboveO S forthe rabbit mi hygtgne the chronic influence ofbenzol and its homologues, the acute poisoning by CO.AIthough the expert knows or isable to find out for which situation the given value is applicable. It would be expedknt to spccffb In Ute table the Umltsforacute and thosefor chmnkjwlsonlngs. If that is not possible or not necessaty for some substances,itshouldbe stateddearlywhetherthe quoted value refersto acute orchronicaction. Pluryand Zernlk@t'ell usthatcats,mice, rats are very sensithe to phosgene;dog8arelesssensitive, rabbit still less. Horses are less sensithte than human beings.When thedrhrerdied in gasattacks during the World War, the horses sometimes showed only slightsymptomsof poisoning. Our condusions therefore on acute poisonings havetobebasedpreferablyontheexpertenceswe have had with man. For chronic poisoning and Of course, the conceptions of "acute" and damages the animal experiments fail entirely to "chronic"are not sharply differentiated. But gen- be useful forour purpose becauseitisimpossible erallywe may call poisonings and damages acute to determine the comparability of the tlme re- whenth~canCakeplacewithinawo~ng~and quired for injuryto develop in animal and in man. -we maycall them chronicwhen they need a longer tlme to develop usuallyweeksor even years. Asftrdyofconditonswhichmayproducechronlc poisonings presents a number of difffcultles. The A specifleation of the concentration fatal in a contaminationoftheair canbedeterminedduring halfhourorless,althoughsdenUflcallyinterdng, the wbole working shift very well, but is it impos- is of little value for pracUcal industrial hygiene as sibleto ascertain the circumstances undcr which polntedout below. theinjurousmaterlalwasabsorbedduringmonths As -pies of the damages which arise after and years gone by. harmful actlon of years or decades may be men- If it is admitted that the conditions afftdlng tlonedstlicoais.bladder cancer ofanilineworkers. the symptoms of chronic alcoholism, certain damages by X-rays and radium, some serlous industrial health have impraved in the courstof -years which istrue in general, but not in every -s i n e case orthatthewwkingtimeisshorttncd. forms of carbon bisullide poisonings, mercury then theamountofidurlousmaterialabsorbedin shakes, the changes of the vessels and as a rule a Workingday was larger in formertimes than it is the paresesasa result oflead poisoning. now. But it mayalsobe thatthedamaBingmateria1 But if a man working wlth lead for many years falls ill Mth lead colic, Le., the subacute form of lead poisoning,it is wrrect to suspectthat he has recentlyabsorbed an exceptionallylargeamount --e same cause a larger amount of absorbed -poison may also be considered in casea man warking wlth mercury for many years acquires gingMtisanddhnhca.andifserlousblooddrange in a man working many years with be-molis not started by inftctious disease, it is possible that is not used such a long time, as the case history may tell us, or that its concentration has been Increasedrecen~suchasunnoti~s~~Uon ofbenzolforbenzine orabenzine-benzolmixture, or substitdon oflead for color containing littleor no lead. Therefore itmust berememberedthatall results are approximatevalues only.But the most important materials,espcdaUyin regardtothdrchronic poisonings (benzol, carbon disulfide, lead) have been studied with suchthoroughness and skill by our best industrial hygienists that the obtained flsunsare actudly practlCaMe as limits. But the obsenmtions about some other substances (cadmium, chlorine (chronic),dichioroethylene and many others) are too limited in number and not clear and reliable enough to makeevenpartlysafeconclusiorw.Ifflguresabout such substances are included in the list at all a mark of lntemgatbn has tobe added. The limitsare approximate,notonlyonaccount of the drrrtculty of most of the observations, but also on account of differences in SensiMty of individual persons and on a w u n t of dUbent amounts of the contaminated air absorbed by the worker under different circumstances For instance, the worker when working hard Inhales much more of the contaminated air (up to 5040 liters per minutej than when doing light work (8-10liters per minute). But these lists of toxic limits give the practical industrial hygtenist essential data for his work. they m e laborious studies ofliterature and give him the results obtained by those carrying on resemch and basic Investigation. Thcnforewe haue to be htaw for the compuatlons of Ute Zfmlts by thelr authors. How are the "limits" to be utilized? For which purposes may they be used? What is their immediate practical actvantage and when may they be applied? Firstofall:Thelimitsstronglysupportthe indusMal hygienist in anMng at an opinion as to whether the exposureisorisnot excesshe,and,if so,in convincingincredulous employers and englrteers (under certain clrammncca) that the contaminated air in their rooms is infurlouseven though the contamination cannot be readilyseen or smelled.The data on the exposures,lfproperly substantiated,actasimpartialarbitrators beween the man recommending control measures and the man persisting in thepresent situation. Thelimitsareuseful in constructionand testing exhaust systems. Naturallyyou will hy to remove every contamination of the air, becauseonly that givescomplete security.Ifthat isnot possible,you must insistthattheventilation hasatleastsuchan effect aa to reduce the exposure to lesa than the "allowableconcentration"in thebreathingzone. If that is impossible, you have to hy to bring about hysltnic conditions by changingthe operation or byabnd~thcuseoftbepoisonoussubstance. I might indicate that exhaustventilation seems tobecrmsMcredtoomuchasfheprindpelremedy n<rwadays,asthereLIpiratorwascodderedsome ytars ago though with much less foundatSon. Other p d u r e s mentioned above are m e timesforgottentoday, although theyhaveattained greatsuccess in industrialhygiene. If the limits are used, it must be ddnitely ascertained that the euafuaUonofthc contarnlnatlon lnthe alr Isrellabte. Because the testing devices are reasonably priced, easy to handle and because the methods ofesamination in laboratories are fkequentlysimplifIed,there is (asmarked previously)the danger of unqualifiedmen using them. Thereforethe follavlnghastobestressed: -Striousacute poisonings,expeclallyfatalones, arfse through unforeseen a d d e n t s as leaking ofvessels,pipe lines, or by unexpected formation of in larger amounts or by other abnormal events. Also,by exceptional atmospheric condftiorwwhcretheremovalofgasesisnot e&ctedby strongmechanicallydrhen exhaustsvstemip. Alodwmith wasfounddeadbesidehisforgeflre where he had been seen working 20 minutes befbre. As an exhaust pipe has been installed in thisplace and the manhadworked here form y -yeam, the tLchnlcian thought a CO poisoning im- possible the blood of the dead man however w ~fobund tobe saturatedwith CO.Abnormal cold and severestormshadinterfered with thenatural up-draft existing at other times. I have seen CO pohonlngwith unconsdousnesein someworking places of a large plant in presence of such a b normal weather; the workers had worked in these placesWithoutdietwhnce ofhealth for months. I have seen poisonings by arsine as a result of using too strong an add so that the solution was not neutralized: as a result of too much zinc powder being added;and asa result ofan exhaust pipe being obstructedby the formation of foam. Such circumstances caused by abnormal accidental events cannot be investigated by air examination because he do not know all contrlbutlng factors and therefore we are not able to reproduce thesedrcummm(tosaynothing of hgc 39 Thirty-five Years of TLVs the danger to the investigator). Therefore, as mentioned above, data about the deadlyconcentratlon would be oflittle practicalvalue In all other ctrcumstanasit is sdf evident that numeroussamples ofair give a true picture of the exlsting conditions, if taken at dylcrcnt tfmesand duringdkrentworking processesand in theexactworkingplaceatthe brcaUILng le& of the worker. Sample8 taken off-hand are without anyvalue. Theinvestigatorhastobecertainthattheworking processes during the Ume ofexaminationare the same as at other times. The investigator can be mlded intentionally or unintentionally. The occurrenceof illnessshouldofcourse induce the improvement ofthe workingconditions.When we investigatewe have to knowif such changeshave taken place or not I t iss o m d m e s difftcult to flnd that out Another ditiicultywhichmay be overcome only - -by patience isthe fktthat all persons concerned even involuntmlly work more "accordfng to presdptlon" if observers and supervfsors are prescnt In addition it must be taken into consideration -that little variation8 produced intentionally or -not areableto change thewhole picture small changtshardlydetectableinthe processproduce considerable difpercnces in the amount of contamination in the air; season (open or closed windows),and weather alsoinlluena the plcture. An electrol@lcnickel platingbath deliversmore h y d r e j c add gas,achrome platingbath more chromic acid mist when thecurrent is h d e r or the treated ob- larger. The amount of lead fumcsdepends,among other fixtom,on the tempaature ofthe lead bath,the zinca i d e hmeson the temperature of the molten alloy. More vapor cdlcapcs in an apparatus fix dagrtadng by trichloratirylene if the trkhlomethylene is heated more and if it is not cooled W o r e empQ4ng. The quantftyofexcapingvaporschanges in the usual degreaslngapparatuswtth the tempe!ature ofthe mte: used in the cooling coil, with thesize ofthe and their number and with the frequency andspeedwithwhichthcyaretakenout Ball mllls pulverizing rock have dtcn been submittedtomyinspecUonandIwasahownthcy were u~orkingWithout escape of dust-- it was soon after loading large rock. But half an hour hter,when the material has been reduced to flne powder, much dust was escaping into the breathing zone. Togive some examplesofnmericaldifferences: Dust concentrationsfound In my investigationsin grindlngshopsminthesummer bytheOwensdust counter have averaged between 600 and ls00 particla per cm3in the same room, at the same speed of rotation of the sandstone wheels but grindingdiffkrent kindsof knhm. In winter, when the windows were dosed,the flgures ran up to 5700 atthe breathing level oftheworker. In theair ofthemom in general thedustflguresaveragedto 560In summertime,3900in winter. Bowditchand Elklns''' found in the coating room ofan artlfldal leatherfactoryon different daysin March 130-200 parts per million of benzol; concentrations of 300-1300 ppm of naphtha vapor were detected during the work done by one worker in a factory using rubber cement Qeenburg and corroboratorsfound in a rotogravure printingplant50-1060 ppm ofbenzol in Merent partsofthe press room. I think it is not necessary to stress that all the ditffcultlesmentioned above have to be regarded especially if there is a compcnsaton case,or if there isa question ofnegligence. -s- A well-halned industrial hygknist onlyisableto make invesUgaUons in industrial hyglene and especiallyfor anmeting the question, If, when or haw often limitsare and besides he can answer only after a long-lastlng and exact examinatSon. It should never be forgotten,that all our limits have their d g t n from health examination of workers and that only from comparlson between the resultsof thesephysicalexraminationsand the content of contamination in the air do the limits result All the mentioned uncertainties and diftlcultiescan be avoided in manyCBBeSifw referto thborigtn. Ifthereisadangerofchronicpoisoning thethorough invesdgatlonand examination ofthe workers especially for early symptoms gtve us a sure answer in caseswherethe time is longenough foracquiring symptomsofchronic poisoning W e may alsosee ifthe contaminationisable to produceacutepoisoningbyewrminingtheworkers attheendofthedailymrkhgtlme. Tdeky:T d c limits A special consideration must be m e n to the question if and how far the results of air examinations and their relation to the limits are able to contribute in determing the occurence of an occupational d h w . Thequestlon ofwhetherthereisanoccupational diacase presents itself as a medical q d o n . A physrcign onlyisabletoansweritafterconsidering all the clinical symptoms and after a thorough medical examination executed 4 t h all necessary ai& The clinical pictures (and the pathological one in the autopsy) of the more frequent occupatonal disease3 (chronic poisonings-by lead, mercury, benzol, silicosis,to some extent carbon disulfide, and certain acute poisonings as CO)have been studied so carefully and are so well established -that the diagnosis can be made with greatest certainty bya physicianexperienced In thisfleld asis the casewith every other medical diagnosis. We have mentioned above the difRculUes and uncertaintiesof airexaminations.We cannotguarantee that the air contamination during the investigation was the same as in the time before the poisoning occurred. Therefore negative findings in air contaminationsor flndingsbelow the limits are never able to shake such a posithre mcdlcal diagnosis though under certain circumstances it 1s possible that a former occupation may have been responsible forthe disease.Positivefindings on the other hand are able to support i t %arthermore ifwe havea clinicalpicture thataccordingto medical opinion does not correspond with the well knownpicture of this poisoning norwith signs of its rare Meties and therefore the physician deniesan occupational disease,then thefindings of aircontamination abovetirelimitsisno proofof a causal connection between the illness and the contamination; the illness may have originated entirely independently of the contamination becauseof an internal or another externalcause. But there is another method which gives us an insight into the circumstances under which the ill man worked prior to his disability and which should be practiced in chronicpoisonings if itcan be done shortly after the beginning of his illness The physid examination of the feliow-workers (still working, disabled and dismissed). If the symptoms of the same illness are found, it confirmsour diagnosis ofthe case in questlon. Nega- tive findingsare of small value, because the sick man many hanbeen more exposed to the damaghgsubstance or may be more sensitive. In acute poisonings the examination of the fellowworkersshould be made at the end ofthe shut There is however, a long list of less explored substances (most at present rarety used), the -clinical pictures of which are not clearly worked out asyet nor are their toxic limits. We are able to conclude that there is a causal connection if certain substances are found in the air and contemporarilysymptoms of illness determined in a worker and if these symptoms agree with those mentioned in the literature as a consequence of this poison or if simllar pictures are to be seen among the fellow-twrkers. But cases occur when a positive medical diagnods alone is not sufficient For compensation cases and for prophylaxis it may be of greatest imporlance to know through which kind of work the illness isacquired. If the examination of the air falls to give exact proof, then all chemical and other processes shouM be s u b w e d to the opinion of apede n d expertsin technology,chemistryand industrial hygiene. In such cases all the impurities possible present in the substancesused are to be considered. I wrote about "experienced physicians." The universities (medical schools)should gIve better instructions to students of medicine in Industrial hygiene and in occupational diseases.EspeCially in the latter fleld, there should be established shortcoursesfor physicians also.The leglslatlon. the indusMal commissions, the insurance companies, the employers and the employeesshould take advantage flrst of all suchtrained physicians and thus give them occasion toacquire still great experience. Surnmnrv 1.To d d n e toxic limits of the greatestsdenU f k and ofthegreatest practical value. 2. It should be made evident whether the toxic limit applies to acute or chronic poisoning,if It Iswell founded ordoubtful. 3.The limitsarevaluablehelp in showingthe Thirty-fiveYears of TLVs necessity of prophylacUc measures in a plant for the construction of new and for testing and existing Installations But the examinations should be made very carefullyand byexpertenced Indusblal h@enis& In determining the severity of exposura resulting &om cxlatlng installations, the medical examination ofworken oftengives a better insight 4. It is the field ef medical diagnosis to a% certain the presence or absence ofan occupational disease.This dlagnosis made by an expert physician cannot be shaken by a contrary result of air examinaton, but if this result is certainly represehtive of the workefs exposure,it may point to the desirabilityoffurther investlgatlons. References ' 1. Spyem, RR: lnkrnatlonal Critical Tables of Numerical Data. Tarlaology f@ aesu and Vapom Vol. It, pp. 318-521. lktioml R-Kh COUnCil ofthe U.S. MCQfaW-HillBodr Ca.inC. NGW YO& (1927). 2. &ng@r, H.: flwyzilnagcr Lchrbuch der Todkologlc. p. 256. Jullw Springer. Berlin (1928). S. nury, F. and r, tanik: schadllcnc p. 453. Julius Springer, Bedin (1931). 4. Bawdltch, M.: MaxlmumMlouroble Concenttatton.Dhr. of Oceup. Hygiene. Mass, ocpt of Labor Cy Industtles, Boaton (kbruay 1937). 5. Elkha, H.R: Toltlc Fumes in NasachwtttsIndustries. Ind. Mcd a426432 (Octobu 1959). 6. Bowdltch,M, CK,Ikhrkcr.P. Make?d al: Code for Safe Concen- bationsof CertainCommon Toxic SubstancesUsed in Industry. J. Ind. Hgg Cy Tar 22251(1940). 7. Tddry, L. 1. Iacbtkcmper, E Roacn~-Dcusstnand Derdach: Staubg@ahrdungund StauhxhadfgungenderMetaUshkljrr.R Hobing BeItln(1928). 8. Ikwdltcb. M. a d H.R clkinr: Chronic Exposun to Benzene (knzol). Ind. /Qg. Cy Tar 21:321-w0 (1939). 9. Wabuq, L.M.R Myem, L (kldwaterand L R Smlth: Benzene (BcNoo Poisoning in the Rotbgravun Printing Industy in N m Yo* city. Ibld, pp. 395420. Annals of the American CoIlference of G S V ~ e n t a i Industrial Hygicaists Volume 9 -Threshold Limit Values Discussion and Thirty-fiveYear Index with Recommendations i f I t