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-Improved communicat~on hygienic standards for daily inhalation' HENRY FIELD SMYTH. JR.,Ph.D. Mellon Institute a n d Union C a b i d e a n d C a h o n Corporation, Pittsburgh, Pennsylvania EXHlBlt Experience convinces us that we humans are unique in the universe. Because of our ability to communicate, we may be well o n t h e 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 a n d goals, still retaining his own individuality. Real progress in this direction h a s been made during the past ten thousand years through developments of recording, duplicating and retrieval techniques. Despite brief back-sliding, there has hrthermore been real spiritual progress, a n d a n increase in the proportion of men of good will. The next ten thousand years should bring substantial achievements in communication upon higher levels, perhaps even through inarticulate contact of mind with mind. There a r e hints that what s o m e 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 Bacon,whom today wecall a scientist,could live a full life investigating the secrets of nature, feeling n o need and finding no opportunity to communicate his discoveries a n d his conclusions t o a living soul.H e could bury his achievements in code, making them difficult for posterity to unravel. We d o not have such people and such situations today. Each o n e of u s benefits h-om current division of labor, of experience, and ofknowledge. Each o n e of u s is a unique specialist, depending upon a multitude of other unique specialists for the achievement of our aims, for our very existence. If nothing else 1~10tivates us, simple self-interest should dictate that each o n e of u s ought to make publicall that h e has learned, in order that his fellow specialists may use it to help LIS all. Communication A year ago Sterner"' expressed the situation in more concrete terms. We comprise persons separately trained in highly specialized fields,led after training t o cooperate in the common aim of providing m e a n s by which technological developments in occupation may be utilized in a manner compatible with complete health. H e said, "We must provide a fluid a n d effective means ofcommunication between the chemIsl, the engfneer, the physicist, the toxicologist, thephysician, a n dthe otherspecialists brought into industrial hygiene. There must result from this interchange ofideas not onry a n appreciation of each team member's contrlbutlon, but a n ability actually to bridge the gap between the disciplines, to synthesize, from the offerings of each of the fields, the solutions to the ever more complicatedproblems. Each memberspeclalist must not only contribute the information he Ls most qualifled to give, but also must encouragesympathetic, intelligent, and mutual understanding." In this matter of mutual understanding, we are very much like the inhabitants of Looking Glass l a i d . You remember that the White Queen to:d Alice, "Mow here, you see, it takes all t h e running you can do, to keep in the same place. If you want t o get somewhere else,you must run a t least twice as fast a s that." With the entry of new people into our profession a n d the recognition of new constituent specialties such as health physics and atmospheric pollution control, each with a tendency to keep to itself,are we running fast enough The Donald E. Cummlngs Memorial Lecture presented a t t h e Seventeenth Annual Meeting of the American Industrial Hygiene Association, April 25, 1956, Philadelphia. Published in Am. Ind. flyg.Assoc. Q. 17129-136 (1956). i k p r inted by permission of Atneriwn Industrial Hygiene Associa tiori. i Page 93 Thirty-five Years of TLVs even to stay in the same place? We all feel there are too many conferencesand too many committees to leave u s time to do our daily work. On the other hand, if w e a r e t o do our work a s well a s it can be done,we must be in constant communication with related specialists, because each o n e of us fully knows only o n e facet of his own problems. Communication is not a simple process. It requires a n informed speaker or writer who can express himself a t the level of comprehension of his audience. It requires a n audience which wishes to receive communication. It must be carried on with words, those abstract symbols for reality, each of which h a s a different meaning to each individual, shaded by his entire past experience. Only a newly coined word is free from ambiguity, a n d it remains new for only a brief interval. Most important of all, successhl communication requires what is today known as feed-back. By this, the speaker hears his audiences' impressions. He can correct and amptify his words until he thinks his audience truly perceives his meaning. A Ieisiircly conversation can be effective communication through feed-back; a n article in ajournal 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 is a t least acceptable. Success is by n o means as great in helping those people who d o not recognize their need for help. Once more communication cannot 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. During what may be called the age of chaos, every experienced industrial hygienist had a fewvalues uniquely his own,drawn from his own experience. For less familiar substances, he borrowed more or less judiciously from the values cherished by his professional colleagues. Some degree of unanimity was brought about when the United States Public Health Service values, based on its long-time collective experience in industrial hygiene, were published in a manual.(2) Further unanimity followed publication of the values collected and extended by Cook.':'' In 1947 the American Conference of Governmental Industrial Hygienists published its first list in the fndustrial Hygiene N e ~ s l e t t e r . ' ~In' the next two years revised lists were privately circulated to the members of the Association.'".'' Then publication took place in a scientific j~urnal,'~a'n d each year thereafter a revised list of threshold limit values h a s appeared in the scientific literature, and h a s been generally accepted."-'" The contributions of Cook'3' in unifying opinion, and in weighing threshold limitvalues then in use, judging new data a n d proposing a list of 129 values, a r e worthy of high regard. Among the 238 values for substances other than mineral dusts in the ciirrcnt list''3) of established a n d tentative thrtshold limit values are 54 of those which were first proposed in Cook's list, s o m e a s definitely established, others to be used cautiously until verified by actual experience. Not since Cook has anyone published a summary of the data which serve a s bases for the selection of specific threshold limits. The privately circulated documents'14-'6'which give s o m e of these data cannot b e considered to be publication, although they are freely available to any person. Threshold limits are, and must continue to be the products ofjudgment, important if true. Some few truly represent their definition and are approximations of the maximum concentrations which can be inhaled continuously and repeatedly without injury to health. These may possibily be fit parameters for incorporation into codes and regulations. Many of the threshold limits are well below concentrations which can injure health. They represent currentjudgment a s to concentrations to which, good practice dictates, men may be expected to subject themselves. These do not seein fit parameters for regulations. I n a particular operation, if possible, it is desirable to maintain concentrations below the bench-mark by reasonableventilation and precaution. It isalways best to reduce exposure to chemicals to the lowest practical level. Page 94 Smyth: Improved Conimunication Previous suggestions for improvement comes known and referred to by a brief name, a During the Ninth Annual Congress on Industrial Health, the writer was chairman of the Committee on Chemical Agents. The report of the 16-man ~ o m m i t t e e " d~e'voted considerable attention to praising the development of threshold limits, and to suggesting ways in which their presentation could be made more useful. Since that report, two developments have taken place alonglines desired by the Committee. The annual table of the Thresh- catch-word. Most persons who learn of the concept hear the catch-word name, and do not go back to the original presentation. The meaning they attach to the name comes from their previous experience with the particular words. I t may be, but is usually not, exactly what the originator of the idea intended. The more carefullyone chooses the name h e assigns to a concept, the more likely a r e others t o interpret the concept as h e himself does. J -old Limits Committee ofthe American Conference The values now known as threshold limits are ofGovernmenta1 Industrial Hygienists is now pub- usually identified by phrases containing the word*s lished in the Archives of Industrial Health, removing the earlier implication of quasi-legal status arising from its appearance in the lndustrial Hygiene Mewsletter of the Division of Industrial Hygiene, U S . Public Health Setvice. In 1954, the Committee on Threshold Limits of that Association began to supplement i t s table of accepted values with a list of tentative values. allowable or permissihlP-T hese two words have .connotations of legal regulations. Such c o n r u b tions cannot properly attach to the iudament ofa voluntary professional association. The identifying phrases may also contain the words maximum, threshold and limit. These words all imply that below the concentration specified, human response is negligible, above the concentration it Three other suggestions of the Committee on Chemical Agents deserve reiteration and discussion. It w a s urged that the bases for the selection of each value should be published, that the name should be changed to hygienicstandard, and that the particular concept of permissible human response behind each value should be clearly indicated. There is such a multitude of factors involved in the protection of health in our complex civilization that n o o n e person o r group of persons is competent to weigh them all with assurance. N o oracular or ex cathedra statement on health deserves serious attention. Only when the facts upon which a decision a r e based are furnished for general scrutiny and evaluation can the decision be considered even tentatively sound, and only after t h e r e has been adequate opportunity for is dangerous. Actually, it is more than a n implica- tion. It is definitelystated. In the introduction to its 1956list the Committee on Threshold Limits says, "Values are giuen . . . for the maximum average atmospheric concentrations of contaminants to which workers may be exposed for a n eight-hour working d a y without iwury to health.""3'_CarefuL study of the data which support the currently accepted values suggests that no such description can be truthtullyattached to most of them. trial hygienists recognize this. They are accus- tomed to empnasize that the values should be regarded simply as bench-marks, guides to good practice. Indeed, the Threshold Limits CommiLts itself confusinglv s "Threshold l l m k . . should not be regarded as fine lines between safe and dangerous concentratlons."`" The term maximum acceptable concentration criticism and modification can it be considered established. All toxicological facts should be published, a n d all decisions upon the facts should be accompanied by a summary of the reasoning being used in revisions of standards by the American Standards Association 2-37 Committee is objectionable only because itwill be abbreviated M.A.C. Many will interpret this abbreviation a s under which they were derived, before anyone should be expected to act upon the decisions. Any publication ofstandards for maintenance of health maKimurn allowable concentration, and nothing will have been gained by the change from allowable to acceptable. ought to include reference to the underlying data. I conclude that the names mavImum allowab(e The second suggestion referred to the name b y --c `sleadinL which t h e values are known.Semantics is more l h e y convey a wrong impression to those w h o are than a sport for the idle. N o matter how thoroughly not already familiar with the concepts behind the a concept is orig-inally. p. resented, it always be- values. The name sug_ g- ested in 1949, hI_jgi.enic .4nn. Am. Coni Ind. Hyg..Vof.9(19&lJ) Page 95 Thirty-fiveYears of TLVs .I standard, is not misleading. Standards of good practice a r e familiar to all of u s in many fields. Looking toward the future provision of a variety of hygienic standards, a series of values should be selected, to be known as hygienic standards for daily inhalation. The third suggestion is more far-reaching. The Committee on Chemical Agents pointed out that there has been no simple or uniform relation between the effectsof a substance and the numerical value chosen for tab~lation!'~T' he Committee concluded that concentrations have been selected o n the basis of o n e of four concepts of the level 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 or mlnus:The maximal time-weighted average concentration which produces only minor injury, a n d that in a very small proportion of exposed workmen. b. Safe: The maximal time-weighted average concentration which sound evidence leads o n e to believe will cause n o demonstrable iilness o r other symptom of toxic effect in anyworkman duringa lifetime of industrial exposure. c. Bench-mark: A concentration based on -the belief that any unnecessary exposure is undesirable a concentration lowcr than that of a o r b, o n e as low a s is consistent with practical engineering control. d. Comfort: A concentration lower than a o r b, representing the maximum which in a short time is not objectionable t o 9 out of 10 of a group of persons not accustomed to inhalation of the substance. Note well that these four concepts were judged t o be those already used for the selection of hygienic standards for daily inhalation. All four werejudged consistent with the goals of industrial hygiene. Hygienic standards for daily inhalation The subject of hygienic standards for daily inhalation should be re-examined, the coricepts represented by the values should be restated in more realistic toxicological terms, and more consistent and more informative standards should be prepared. Such a s t e p will not undo any of the accomplishments of the profession of industrial hygiene o r of any organization. Rather, it will supply informative standards to supplement the accumulation of naked numbers now accepted, some ofwhich have not been criticallyre-examined for a decade. It is certainly imperative that the inhalation of substances during the working'day shall not be allowed t o result in any injury to the physical well-being ofworkmen. I t is furthermore imperative that inhalation shall not increase the probabilityof accidentsthrough the mental distress occasioned by objectionable eye, n o s e o r throat irritation, transient though it may often be, nor through the impaired judgment a n d delayed reaction time of light narcosis. It is desirable that inhalation shall result in n o degree of discomfort whatsoever. On the other hand, when it is impractical to avoid all discomfort, then such inhalation is certainlyjustified, provided there results n o injury to workmen and n o increase in the probability of accidents. Tables of hygienic standards do not now carry indications of t h e nature and of the magnitude of the effects to be expected from inhalation of greater concentrations. It is only by a rather thorough study of the available data that o n e can decide whether or not a particular substance can safely be inhaled a t a greater concentration. With most substances, it is quite practical to set two standards,o n e a n inoffensive level, another a concentration which cannot safely b e exceeded under any pressure of practicality. Administrative expediency may be served by a table of numbers which constitute a part ofofficial regulations. Regulations need not be defended, they need not cite 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 greater degree of 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 specify twoconcentrations,together with a description of the human response t o be expected from Page 96 Ann. Am. ConL Ind. tlyg., Vol. 9 ( 1984) Sniyth: lmproued Communication inhalation of each. One concentration should be Chronic toxicity low enough so that n o injurious effect can be The most dangerous effect of s o m e substances expected in any workman, but it may cause a is a progressive systemic iqjury, increasing in detectable odor, it may cause a detectable eye, severity with continuing inhalation. Benzene, car- nose or throat irritation.The second concentration bon disulfide, carbon tetrachloride and lead a r e should produce somewhat more severe, but still the most familiar examples. The lower standard reversible and non-progressive effects. From these for these substances should be a concentration two concentrations, o n e can a t once see how believed not to produce any effectin anyworkman, strictly the standard should be observed, the and n o considerations of practicalityare sufficient steepness of the dosage-response curve, the to justify inhalation in excess of the standard. breadth of the plateau of non-injurious concentra- Close medical supervision isrequired for safe u s e tions. Despite the wide range in individual sus- of these toxic substances. The standard for chron- ceptibilities of workmen, such values can be ically toxic substances should refer to the time- selected for most, if not all, substances. J Adequate data for preparing this sort ofstandard consist of appropriate human experience, or repeated medical examinations of workmen in at- weighted average concentration throughout a working day. Brief peaks of a few times the standard have n o significance, save as they increase the average. mospheres whose concentration has been frequently estimated. Sterner'" discussed this point Acute toxicity in detail. Experiments upon animals, verified by Some substances do not produce a n injury biochemical a n d physiological studies in humans, progressing with repeated inhalation. Such sys- may demonstrate conclusively that a substance temic injury as they may cause takes place as the has a n effect duringone period of inhalation which result of o n e excessive inhalation, o r not a t all. does not progress during off-repeated inhalation. Familiar examples are carbon monoxide and For such a substance, satisfactory data can be hygrogen cyanide. The standards for acutely toxic obtained from objective study and secretly re- substances should be interpreted in the s a m e i corded subjective effects of a group of huinatis light as those for chronically toxic substances. inhaling known concentrations for substantially eight hours.Anylesser body ofdatashould result in Narcosis a hygienic standard being designated a s tentative. The most dangerous effect of s o m e substances is narcosis, which becomes anesthesia in i t s extreme state.At a rather low concentration they Categories of objectionable action induce accidents by impairing judgment and delaying reaction time. Familiar examples are ethyl Judgments should be m a d e to determine which alcohol, ethyl ether and gasoline. The lower stan- hygienic standards for daily inhalation must be dard for a narcotic substance should be a concen- carehilly observed, and which may be exceeded tration which produces n o detectable effect upon when it is impractical to observe them. These judgment and reaction time after eight hours in- judgmentswill be most consistent ifwe first decide halation. It should refer to the average concentra- for each substance what objectionable action w e tion existing during s o m e appreciable period of are guarding against by the standard. Every toxi- time, the length of which can be estimated from cologistwill realize that the action at a lowconcen- absorption and elimination data. N o considera- tration which it is most important to guard against, tions of practicality can just@ exceeding the stan- may not be the s a m e as the menace to life to be dard for a narcotic substance. expected a t a high concentration. In a tentative fashion, the writer h a s made these decisions for Im'tation the 238 substances, exclusive of the mineral dusts, The most dangerous effect of s o m e substances included in the 1956tables of proposed accepted is irritation. Eye, nose and throat a r e irritated a t a and tentative standards.""' The decisions can be low concentration,the bronchi a t a higher concen- divided into the following nine categories on the tration, and fatal lung edema may be the result of basis on the nature of human response. inhaling an extremeconcentration. The aldehydes, h t n . Am. Conl. Ind. Hyg.. Vol. 9 (1981) Page 97 Thirty-five Years of TLVs halogens a n d 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 wliich is detectable, but is not objectionably irritating to the majority of unhardened subjectswho are exposed for a substantial part of a working day. The higher standard should be s e t a t a concentration which is well under o n e injuring bronchi o r lungs, and which isjustifiable when it is impractical to keep concentrations a t the lower standard. Standards for irritating substances should refer to concentrations existing for even a brief period during a work day. Asphyxia ti on S o m e substances are inert in the body a n d can injure only by asphyxia a t extremely high concentrations, excluding the oxygen of the atmosphere. Familiar examples are the fluorochloro refrigerants. Thc lowcr standard for tlicse asphyxiatits should be a nominal bench-mark of good c i i gineering practice, such a s the 1000ppm concentration now quoted. The inert nuisance dusts like iron oxide might well be placed in this s a m e catagory, a n d the currently used bench-mark of 15 mg./cu.m. s e e m s a n appropriate level. The standard should refer to the concentration existing duringany brief period, but it should be recognized that higher concentrations are justified when it is impractical to keep below the standard. Fume fever The most important effectofsome substances is a transient influenza-like condition known a s 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 menacingconditiorl in any workman, and it should apply to a n appreciable period, such a s half an hour. N o consideratiorls of practicality can justify exceeding the standard for fume fever producing substances. Eye pigmentation The most important effect of two substances, quinone and hydroquinone, appears to be a slowly developing pigmentation ofthe sclera, which may reduce visual acuity, or even lead to blindness. The lower standard for these substarices should be a concentration which produces n o pigmentation after years of exposure, and it should refer to the ti m e-weighted average concentration throughout the day. For a few days a t a time, conditions of practicality should justitj, exceeding the standard. Cancer One substance is reasonably well established a s a cause of respiratory tract cancer.This is nickel 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 has already been done for nickel carbonyl, and n o considerations can justib allowing the inhalation of any concentration which is avoidable. Allergy Some substances are known to sensitize an appreciable proportion of exposed workmen. They tiiay produce distressing and menacing asthmalike attacks wlien a sensitized person itihalcs a low concentration. Exampies are ethylene diamine and the diisocyanates. At this time there is no rational experimental basis for defining a concentration which will not sensitize a susceptible workman, o r o n e to which n o 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 t o sensitization, 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 particular group includes no susceptible workmen, no considerations canjustify allowing inhalation of anyconcentratiori which is avoidable. ( t iiit(>r'sn o t e The tablewliicliliststlie238valuesaswellas the discussion that followed this portion of Dr. Smyth's paper is not reproduced in this publication due to space liniitatioiis. T h e interested reader may find the table along \\itti the discussionsand rcfcrcncescited on pp. ISG-185of the A n i . hid. ilgg. Assoc. Q., Vol. 17. The l 9 5 B rccoiiiriierided threshold litnit values appear i n this volurnc. The Doctoneritation of the Threshold Umlf Valites, 4th ed.. proLides more up to date information regarding the predictcd effects of a given substance. This publication is mailable from ACQIH, Publications Office, 6500 Glenway Aie.. Bldg. D-5,Cincinnati, OH 45211.) Page 98 Smyth: Improved Commitnication References 1. Sterner, J.H.: The Experimental Animal - Man - i n Iridustrial Hygiene. Am. Ind. Hyg. h o c . Q. 16:103-107( 1955). 2. U.S.Public Health Service:Manual oflndusfrial Hygir!ze. p. 264. W.M. Gafaler, Ed. Saunders, Philadelphia (1913). 3. Cook, W.A.: Maximum Allowable Concentratiorls of Iiidirstrial Atmospheric Contaminants. Ind. Ned. 14:936-946( 1945). 4. ACGlH: 1947 M.A.C.Values. Ind. Hyg. Newsleffer 7: 15-16 1ALrgust 1947). 5. ACGIH: Threshold Limit Values adopted a t April 1918 meeting (privatelycirculated) ( 1948). 6. ACGIH: Threshold Limit Values adopted at April I949 nieetiilg (privatelycirculated) (1949). 7. ACGIR: Threshold Limit Values for 1950.Arch. Ind. Hyg. &Occup. Med. 2:98-100 (1950). 8. ACGIH: Threshold Limit Values for 1951. /bid. 4:398-400 (1951). 9. ACGIH: Threshold Limit Values for 1952. /bid. 6: 178-180 i1952). 10. ACGIH: Threshold Limit Values for 1953. /bid. 8296-298 (1953). 11. ACGIH: Threshold Limit Values for 1954. Ibld. 9530-534 (1954). 12. ACGIH: Threshold Limit Values for 1955. AMAArch. 1nd. Health JI:521-524 (1955). 13. ACGIH: Proposed Threshold Limit Values for 1956, presented April 23,1956to Philadelphia annualmeeting. Privatelycirculated i n advance of publication. 14. ACGIH: Privately circulated document giving support for many earlier adopted threshold limits. and those proposed in 1953 (1953). 15. ACGIH: Privatelycirculated document givingsupportfor threshold limits newly proposed in 1954 (1954). 16. ACGIH: Privatelycirculated document givingsupportfor threshold limits newly proposed in 1955 (1955). 17. Committee on Chemical Agents: Report of the Panel of Environmental Agents, Ninth Annual Congress on Industrial Health. Chicago. January 18-19. 1949. Arch. Ind. Hyg. & Occup. Med. 1;601-624 { 1950). Ann. .4m. Conf. 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