Document LZ1VYmx5NemGZ8L8J5yEax3w

-Improved communication hygienic standards for daily inhalation' HEf'iRY FIELD SMYTH. JR, Ph.D. Melion lnstlhtte and Union Cabide and Carbon Corpomtlon,plttrrburgh. Pennsylvania Experience convinces us that we humans are unique in the universe. Because of our ability to communicate, we may be well on the way toward emerging into a new level of biological existence. Each individual may eventually share completely all past and present experiences of the species. Each may act in concert with his fellows toward common ideals and goals, still retaining his own individuality. Real progress in this direction has been made during the past ten thousand years through developments of recording, duplicating and retrievaltechniques. Despitebriefback-siiding, therehas furthermorebeen real spiritualprogress, and an increase in the proportion of men of good will. The next ten thousand years should bring substantialachievementsin communication upon higher levels, perhaps even through inarticulate contact of mind with mind. There are hints that what some have called the world mind may come into being before the present human species evolves physically into whatever new species its body is tending toward. However, until the world mind develops, we are forced to depend upon more prosaic means of communication. Not so many generations ago, a natural philosopher like Roger B9con,wbom today we call a scientist,could livea full life investigating the secrets of nature, feeling no need and flnding no opportunity to communicate his discoveries and his conclusions to a livingsoul. H e could bury his achievements in code,making them difftcult for posterity to unravel. We do not have such people and such situations today. Each one of u s beneflts from current division of labor, of experience, and of knowledge. Eachone of us isa unique specialist, depending upon a multitude of other unique specialists for the achievement of our aims, for our very existence. if nothing else m e h t e s us, simple self-interest should dictate that each one of us oughtto make publicail thathe has learned, in order that his fellow specialists may use it to help us all. co~unication A year ago Sterner"' expressed the situation in more concrete terms. We comprise persons separatelytrained in highlyspectalizedflelds,led &r training to cooperate in the common aim of providing means by which technological developments in occupation may be utilized in a manner compatible with complete health. He said, . "We must provide a fluid and effcctfue means ofcommunicationbetween the chemIst, the engineer, the physicist, the tardcolOglst,thephgsiclan,and the otherspecialists brought into industrial hggiene. There must resultfromthis interchange ofideas not only an apprecfatfonofeach team member's contribution,but an ability actuallg tobtidge the gap between the dwpilnes, to SynChcslzc, from the ofierlngs of each of the fields,the sdutionsto the euermore compiicatedprob- iems. Each memberspeclaifst must not onlg contribute the information he Is mast qual[fledtoglue, but also must encouragesympathetk Intefllgent,and mutual undetstandfng." In this matter of mutual understanding, we are very much like the inhabitants of Looking Qlass Land You remember that the White Queen told Alice, "Nowhere, you see,it takes all the running you can do, to keep in the same place. If you want togetsomewhere else,you must run atleasttwice as b t as that"Wth the entry ofnew people Into our proftssion and the recognition of new constituent specialties such as health physics and atmospheric pollution control, each with a tendencyto keep to itself, arewe running fastenough The Donald E CummingsMemorial Leduep m t e d at the Sexenteenth Annual Meeting of the American Industrial w e n e kwciation, April 25, 1956,Philadelphia Pubtishod in Am Ind. H&&j.Assoc Q. 1Z129-136(1956). Reprinted by permission of American indusMal ttygkne Assodation. Thirty-fiveYearsof TLVs ewmtostayin the sameplace?We all feel thereare toomany conferences and too many committees to leave us time to do our dallywork. On the other hand, if we are to do our work aswell as it can be done,we must be in constantcommunication with related specialists, because each one of us fully knows only one facet ofhis own problems. Communication is not a simple process. It requires an informed speaker or wrlter who can express himself at the level of comprehension of his audience. It requires an audiencewhichwishes to receive communication. it must be carried on with words, those abstract symbols for reality, each of which has a different meaning to each individual, shaded by his entire past experience Only a newly coined word is free from ambiguity, and it remains new for only a brief intern. Most important of all, successful communication requires what is today known as feed-back. By this, the speaker hears his audiences' Impressions. He can correct and arnplifjr his words until he thinks his audiencetrulyperceiveshis meaning A leisurely conversation can be effective communication through feed-badu an article in ajoumal is likely to be poor communication because feed-back is inadequate. The relatively new specialty of industrial toxicology has already contributed to the equally new profession of industrial hygiene by means of communication. The toxicologists are doing an acceptable Job for those people who recognize their need for toxicological information and opinion. TheJob could be done better, but it isat least acceptable. Success is by no means as great in helping those people who do not recognize their need for help. Once more communicationcannot succeed unless the audience desires to receive communication. Acceptable concentrations The most important communication within industrial hygiene, and between our profession and others, may be the collection ofjudgments upon acceptable concentrations of contaminants in working atmospheres. Duringwhat may be called the age of chaos, every experienced industrial hygienisthad a fewvaluesuniquelyhis own,drawn from his own experience. For less familiar substances, he borrowed more or less judiciously from the values cherished by his professional colleagues.Somedegreeof unanimitywas brought aboutwhen the United StatesPublic Health Service values,based on I t s long-timecollectiVeexperience in industrialhygiene,werepublished in a manual.@' Further unanimity followed publication of the values collected and extended by Cook.'3' In 1947 theAmerican ConferenceofQovemmental Indus- trial Hygienists publishtd its first list in the In- dlcstrlal Hygfene rJewslctter!" In the next two years revised lists were privately circulated to the members of the Then publication took place in a scientificjournal!" and each year thereafter a revised list of threshold limit values has appeared in the sdentific literature, and has been generally accepted!8-'2' The contributions of Cook'3' in unifying opinion, and in weighingthreshold limitvalues then in use, judging new data and proposing a list of 129 values, are worthy of high regard. Among the 238 values for substances other than mineral dusts in the current list"3' of established and tentative threshold limit values are 54 of those which were first proposed in Cooks list, some as definitely established, others to be used cautiously until verified by actual experience. Not since Cook has anyone published a sum- mary of the data which serve as bases for the selection of specfficthreshold limits.The privately circulated which give some of these data cannot be considered to bepublication, although they are freely available to any person. Threshold limits are, and must continue to be the products ofjudgment, Important If true. Some fewtrulyrepresenttheirdefinitionand areapproximations of the maximum concentrations which can be inhaled-continuously and repeatedly with- out injury to health. These may posslbily be fit parameters for incorporation into codesand reg- ulations. Many of the threshold limits are well below concentrations which ca-n iqjure heatfh. They represent currentjudgment asto concentrattions towhich, goadpractice dictates,men msybe expected to subJect themselves. These do not seem fitparameters for regulations. In a particular operation, if possible, it is desirable to maintain concentrations below the bench-mark by reasonableventilationand precaution. I t isahuaysbestto reduce exposure to chemicals to the lowest practical level. Smyth: improued Communiation Revbus suggestions for improwmmst Duringthe NinthAnnual Congresson lndustrlal Health. the writer was chairman of the Commlttee on Chemical Agents. The report of the 16-man committee"" devoted considerable attention to praising the development of threshold limits, and to suggesting ways in which their presentation could bemade more useful. Sincethatreport, two developmentshavetaken placealonglinesd d r e d by theCommittee.Theannual tableoftheThreshold UrnitsCommittee of theAmerican Conference of Ckwernmental Industrial Hygienists isnowpublished in the Archfves of industrial Health, removingtheearlier implication of quasi-legal status arising from its appearance In the industrial Hggkne IYewsktter of the Division of industrial Hygiene, U.S. Public Health Service.In 1954,the Committeeon Threshold Limits ofthatAssodation began to supplement its table ofaccepted values with a list of tentative values. Three other suggestions of the Committee on Chemical Agents deserve reiteration and discussion. It was urged that the bases for the selection ofeach value should be published, that the name should bechanged to hggfenfcstandarda,nd that the particular concept of permissible human response behind each value should be clearly indicated. There is such a multitude of factors involved in theprotection of health in our complexcivilization that no one person or group of persons is competent to weigh them all with assurance. No oracular or ex cathedra statement on health deserves serious attention. Only when the facts upon which a decision are based arefurnishedfor general scrutiny and evaluation can the decision be considered even tentatively sound, and only after there has been adequate opportunity for criticism and modification can it be considered established. All toxicological facts should be published, and all decisions upon the fadsshould be accompanied by a summary of the reasoning under which they were dertved, before anyone should be expected toad upon the decisions.Any publication ofstandardsfor maintenanceofhealth ought to include reference to the underlying data. The second suggestion referred to thename by which the values are known. Semantics is more thana sport for the idle.No matter how thoroughly a concept is originally presented, it always be- comes known and referred to by a brief name, a catchword. Hostpersons wholearnof theconcept hear the catch-wordname, and do not go back to theoriginal presentatlon.ThemeaningtheyaUach tothenamecomesfromtheirpreviousexperlence with the particular words. I t may be, but is usually not, exactly what the originator of the Idea intended. The more carefullyonechoosesthe name he assignsto a concept,the more likelyare others to interpret the concept as he himself does. The values now k n m as threshold limits are usuallyidentlfied by phrases containing thewords alloukable or pennlrs;Ible.These two words have connotations of legal regulations. Such connotations cannot properly attach to thejudgment ofa voluntary professional association. The &dent& ing phrases may also contain the words maximum, threshold and limit. These words all imply that below the concentration specifled, human response is negligible, above the concentration it is dangerous. Actually,it is more than an implication. lt isdefinitelystated. in theintroduction toits .1956listthe CommitteeonThreshold Umitssays, "Valuesare given . .for the maximum average atmospheric concentratfons of contarnfnantsto which workers maybe exposed foran elght-hour working dag without i$uW to health."''3'Carefbl study of the data which support the currently acceptedvaluessuggeststhatno suchdescription can be truthfullyattached to most of them. Industrial hygienists recognize this. They are accustomed to emphasize that the values should be regarded simply as benchmarks, guides togood .practice. Indeed, the Threshold LimitsComdttee Itself confusingly warns "mreshold lfmfts . . should not be regarded asfrne lfnesbetweensafe and dangerous concentratfons.""S' The term m a m u m acceptable concentratfon being used in revisions of standards by the American StandardsAssodation 2-37Committee isobjectionableonlybecause itwill beabbreviated MAC. Many will interpret this abbreviation as maxfmumallowable concentratfon,and nothing wlll have been gained by the change from atlow able to acceptable. I condude that the names mawlmum allowaWe concentratfonand threshold lfmfat remislslccading. They conveya wrong impression to thosewho are not already famillar with the concepts behind the values. The name suggested in 1949,h&&e?Ilc Thirty-fiveYears of TLVs standard, is not misleading. Standards of good practice are familiar to all of us in many fields. Lookingtoward the future provision of a Varietyof hygienic standards, a series of values should be selected, to be known as hysfenfc standards for daUa fnhalatfon. The third suggestion is more far-reaching. The Committee on Chemical Agents pointed out that there has been no simple or uniform relation between theeffectsof a substance andthe numericalvalue chosen fortabulation!'"~he Committee concluded thatconcentrationshave been selected on the basis of one of four concepts of the I d best suited to hygienic control of inhalation, the choice having been governed by the nature of the toxic response and by the degree of organoleptic response. The Committee's four concepts follow a. Plus orminu:Themaximaltimeweighted averageconcentralionwhichproduces only minor iqjury, and that in a m y small proportion of exposed workmen. b. Safe:The maximal timeweighted average concentration which sound evidenceleads one to believe will cause no demonstrable illness or other symptom of toxic effect in anyworkman duringa lifetimeof industrial exposure. c. Bench-mark A concentration based on -the belief that any unnecessary exposure is undesirable a concentration lower than that of a or b, one as low as is consistent with practical engineering control. d. Cornfork A concentration lower than a or b, representing the m d m u m which in a shorttime is not objectionable to 9 out of 10of a group of persons not accustomed to inhalation of the substance. Note well that these four concepts werejudged to be thosealready used for the selection of hygienic standards for dailyinhalation.All fourwerejudged consistent 4 t h the goals of industrial hygiene. Hygienic standards for daily inhalation The subjea of hygienic standards for daily inhalation should be re-examined, the concepts represented by the values shoutd be restated In more realistic toxicological terms,and more con- sistentand more informathrestandardsshould be prepared. Such a step will not undo any of the accomplishments of the profession of industrial hygiene or of any organization. Rather, it wlll supply informative standards to supplement the accumulation of naked numbers now accepted, someofwhichhavenot been criticallyreexamined for a decade. I t is certainly imperative that the inhalation of substances during the working day shall not be allowed to result in any iqjury to the physical well-beingofworkmen.I tisfurthermore imperative that inhalation shall not increasetheprobabilityof accidentsthrough the mental distressoccasioned by obJectIonaMe eye, nose or throat irritation, transient though it may often be,nor through the impaired judgment and delayed reaction time of light narcosis. It is desirable that inhalation shall result in no degree of discomfort whatsoever. On the other hand, when it is impractical to avoid all discomfort, then such inhalation iscertainlyjudfied, provided there results no iqjur'yto workmen and no increase in the probability of accidents. Tables of hygienic standards do not now cany indications of the nature and ofthe magnitude of the effects to be expected from inhalation of greater concentrations. I t is only by a rather thorough study ofthe availabledata that one can decide whether or not a particular substance can safely be inhaled at a greater concentration. wfth most substances, it is quite practical to set two standards,onean inoffensivelevel, another a con- centration which cannot safelybe exceeded under any pressure of practicality. Administrative expediency may be served by a tableofnumbers which constitute a part ofoficial regulations. Regulations need not be defended, they need not dte justifications. However, it is a minority of the profession of industrial hygiene who have regulatory responsibilities. Most of our colleagues act through obtaining voluntary cooperation with their judgments. They would be aided by a gre%ter degree 6f explanation in a tabulation of standards. They could then show that their recommendations are quite defensible, that they are not arbitrary decisions having no regard for the realities of competitive industrial existence. A hygienic standard for daily inhalation should spedfytwoconcentrstiOns,togetherwithadescrlg tion of the human response to be expected from Page 96 Sm#& lmproocd Communication inhalation of each.One concentration should be low enough so that no iqjurious effect can be expected in any workman, but it may cause a detectable odor, it may cause a detectable eye, nose orthroat irritation.Thesecund concentration should produce somewhat more severe, but still reversibleand non-progressiveeffects.From these two concentrations, one can at once see how strictly the standard should be observed, the steepness of the dosageresponse curve, the breadth of the plateau ofnon-iqjuriousconcentrations. Despite the wide range in individual susceptibilities of workmen, such values can be selected for most, If not all, substances. Adequatedataforpreparingthissortof standard consist of appropriate human experience, or repeated medical examinations of workmen in atmospheres whose concentration has been frequently estimated. Sterner"' discussed thispoint in detail. Experiments upon animals. verified by biochemical and physiological studiesin humans, may demonstrate conclusively that a substance hasan efFectduring one period ofinhalationwhich does not progress during &-repeated Inhalation. For such a substance, satisfactory data can be obtained from obkctive study and secretly recorded subjecthe effects of a group of humans inhaling known concentrations for substantially eighthours. Anylesser body ofdatashouldresultin a hygienicstandard being designated astentative. Categories of&$ectionable action Judgments should be made todetermine which hygienic standards for daily inhalation must be carefully observed, and which may be exceeded when it is impractical to observe them. These judgments will be most consistentffwe firstdecide for each substance what obkctionable action we are guarding against by the standard. Every toxicologist will realize thattheaction ata lowconcentration which it ismost important to guard against, may not be the Same as the menace to life to be expected at a high concentration. In a tentathe fashion, the writer has made these decisions for the 238substances, exclusiveofthe mineraldusts, included in the 1956tabtesofproposed accepted and tentative standard^."^' The decisions can be divided into the following nine categories on the basis on the nature ofhuman response. CIVonic azricity The most dangerouseffectof some substances is a progressive systemic iqjury, increasing in severitywith continuing inhalation. Benzene, carbon disulfide, carbon tetrachloride ahd lead are the most familiar examples. The lower standard for these substances should be a concentration believednottoproduceanyeffcctinanyworkman, and no considerations of pradicality aresufficient to justify inhalation in excess of the standard. Closemedical supervision isrequired forsafeuse of thesetrbxicsubstances. Thestandard forchroni d l y toxk substances should refer to the tlmeweighted average concentration throughout a working day. Brief peaks of a few times the standard have no significance, save as they increase the average. Acute W C i Q - -- Some substances do not produce an iniUry progressing with repeated inhalation. Such sys- temic iqjury as they may causetakes place asthe result of one excessive inhalation, or not at all. Familiar examples are carbon monoxide and hygrogen cyanide. The standards for acutelytoxic substances should be interpreted in the same light as those for chronically toxic substances. Narrcosis The most dangerous effectofsome substances is narcosis, which becomes anesthesia in its extreme state.At a rather low concentration they induce accidents by impairingjudgment and delaying reaction time. Familiar examples are ethyl alcohol, ethyi ether and gasoline. The lower standard for a narcotic substanceshould bea concentration which produces no detectableeffect upon judgment and reaction time afbr eight hours inhalation. It should refer to the average concentration existing during some appreciable period of time, the length of which can be estimated from absorption and elimination data. No considerations of practicalitya njustify exceeding the standard for a narcotic substance. Inftation The most dangerous effect of some substances is irritation. Eye,nose and throat are irritated ata lowconcentration,the bronchi ata higher concentration, and fatal lung edema may be the result of inhalingan extremeconcentration.Thealdehydes, lhirty-fiveYears of TLVs halogens and acids are familiar examples. Highly odorous substances may also be considered in this catagory. The lower standard for an irritant substance should be a concentration which is detectable,but isnot objectionablyirritatingtothe mqjorityof unhardened subjectswhoare exposed for a substantial part of a working day. The higher standard should besetata concentration which is well under one injuring bronchi or lungs, and which isjustifiable when it is impractical to keep concentrations at the lower standard. Standards for irritating substances should refer to concentrations existing for even a brief period during a work day. Asphyxiation Some substances are inert in the body and can iqjure only by asphyxia at extremely high concentrations, excludingthe oxygen of the atmosphere. Familiar examples are the fluorochloro refrigerants. The lower standard for these asphyxiants should be a nominal bench-mark of good engineering practice,such asthe 1000ppm concentration now quoted. The inert nuisance dusts like iron oxide might well be placed in this Same catagoty,and the currentlyused bench-mark of15 mg./cu.m. seems an appropriate level. The standard should refer to the concentration existing duringanybrief period,but itshould berecognized that higher concentrations arejustified when it is impractical to keep below the standard. Fume fever The most important effect of some substances is a transient influenza-like condition known as fume fever. A familiar example is zinc oxide fume. The lower standard for a fume fever producer should be a concentration which will not produce that distressing but not menacing condltion in any workman, and it should apply to an appreciable period, such as half an hour. No considerations of practicality can justiw exceeding the standard for fume fever producing substances. Eye pigmentation The most important effect of two substances, quinoneand hydroquinone,appearsto be a SIdevelopingpigmentation of the sdera, which may reducevisual acuity,or even lead to blindness. The l o w r standard for these substances should be a concentration which produces no pigmentation after years ofexposure, and it should refer to the time-weighted average concentration throughout the day. For a few days at a time, conditions of practicality should justifyexceeding the standard. Cancer One substance is reasonably well established asa cause ofrespiratorytractcancer.This isnickel carbonyl. It appears probable that the minimum cancerigenic exposure will never be defined. At this time it is prudent to set the standard for a cancerigenic substance substantially at zero, as hasalready been done for nickel carbonyl,and no considerations canjustifyallowing the inhalation ofany concentration which is avoidable. Aliergg Some substances are known to sensitize an appreciable proportion of exposed workmen.They may produce distressing and menacing asthmalike attacks when a sensttized person inhales a lowconcentration. Examplesare ethylenediamine and the diisocyanates. At this time there is no rational experimental basis for defining a concentration which will not sensitize a susceptible workman, or one to which no previously sensitized workman will respond. Control of exposure to allergenic substances must rely heavily upon industrial medicine. After experience has allowed withdrawal of workmen susceptible to sensftization, the remaining resistant individuals can be protected by a hygienic standard for daily inhalation based upon irritation or systemic injury. Until it has been demonstrated that a p a r h l a r group includes no susceptible workmen, no considera- -tions canjustifyallowing inhalation ofanyconcen- tration which is avoidable. (Editor'snote: Thetablewhichliststhe 238valuesaswcilas the discussion that followed this pnrtion of Dr.Smyth's paper is not reproduced In this publication due to space limitations.The Interestedreader may find the tablealong With thediscussionsand referencesdted on pp.136-185of the Am. tnd. Hw. AESOC. Q., Vol. 17. The 19% recommended threshold limitvalues appear In this volume.The m e n t a t i o n of the n t r u h d d Umlt Values, 4th cd.. provides more up to date Information regarding the predicted effects of a given substance. This publication Is available from ACOIH, Publications Office,6500 Olenway Aw., Bldg. D5,Cincinnati,OH 45211.) S m m Impmud Corrtmuniation Rceetcncccs - -1. stana,J.H.: Thr Experimental Animal Man in lndustrlol Hygknc. Am. Ind. H a . h o c 4.16:103-107 (1959). 2 u~puwkntrftbsavict:~nurlo~industrlr~n~~ncp.2~. W.R. olfakr, Ed.slundcrs,PhiWphii (1943). 3. codr. WA: Maximum Ntombk concentrations of indtlstrial Atmospheric CMltaminants. Ind. tkd. 14956-946 (1945). 4. ACGIH: 1947 MACValuts.Ind. Hw.Nt!Imkftt!r7:15-16(krguSt 1947). 5. ACCYH: ThmhoM Umit Wues adopted at April 1948 meeting (prluawydrcubtcd) f 1948). 6. M W H : Thrclhdd Umit Wues adopted at &ril 1949 meeting (privately circulrted) (1949). 7. ACQm:pcshold UmitValucsfor 195O.ArchInd. H@.&&xup. rJed. 2Bs-loo(1950). 8. ACW:ThmhobdUmit Wuesfor 1951. Md. 4398uw) (1951). 9. ACQIII: 'fhruhold Umit Wucsfor 1952. MI.6:178-1W (1952). Annals of the American Conference of @ v m e n t a i Industrial Hygienists Volume 9 -Threshold Wt Values Discussion and Thirty-five Year Index with Recommendations AMERIW CONFERENCE OF QOVERPIMENTAL INDUSIRW, HYQIEPilSTS ammn OHIO u)(w f L' f i I -3