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164 FRANK A. PATTY tration standards until we learn through experience, or research, the true maxi, mum safe limit, and then, if necessary, change our standards accordingly. V. Standards for Permissible Atmospheric Contamination and How They Are Set "I;. '.use... Our present standards of practice regarding atmospheric contaminants are very helpful bench marks, as long as we regard them for what they are and do npt, try to set them up as absolute safe limits to be regarded as established facts com* parable to, or in the same class with, flammable limits, flash points, or othe^ properties that can be determined accurately. Rather, the idea should be fostere that the limits are flexible and are to be adjusted to conform with any new, propeft. weighted, evidence of facts regarding physiological effects. It must also be remem| bered that just as all of us are subject to occasional ill health regardless of! ou"' work environment, so are we at one time more easily affected by foreign material than at another. There are probably too many uncontrollable factors for us to set^a positively safe limit, applying to all people at all times, and still have the linn appreciably different from that of pure air. No matter how carefully our standard are established, if they are maintained at a level compatible with industrial pra' tice, there may be occasional ill health in the especially susceptible individual!,ily* shall always need periodic medical examinations by thorough and compete physicians. The United States Public Health Service has been the outstanding contribut|: tb-bur'knowlb3'ge bl` maximum permissible li`mits~for atmospheric contaminants' and some of the states have co-operated in the toxicological and chemical studre required to establish such limits. The United States Bureau of Mines, the Umi* States Department of Labor, and a few universities and other schools of higji learnings as well as private research organizations, have added to the stoi'ef information. ')' Some of the states have set up "safe" standards of their own, some of wBich', have developed'into safe practice codes enforceable by law, but for the most,,l|a they have been restricted to advisory standards. A survey conducted by the author in 1943, including thirty-four states, revealed a wide range of figures adopted^ these states as maximum safe concentrations. This wide variation indicate^t he'ed'for ,a oop?al-lR^,vlsQyy; body,.whether it' b'e'th"e''Uhited''StaC6'S''Public7l|^ Service, Association, the American industrial Hygjoh' Association, the'American Conference of Governmental Industrial Hygienist^ some other qualified and representative body, to take the initiative in establisKm permissible concentrationsr-More-recently several- states -ha-ve adopted the-rec|m- mendations of the Committee on Threshold Limits of the American Conferences), Governmental Industrial Hygienists. This group reviews the information availaBl'1 to them and publishes yearly a list of "Threshold Limit Values and Tentati Threshold Limit Values." Even though this list may have several shortcoming pP ENTRY AND ACTION OF TOXIC MATERIALS 165 Mitt. wfflpregarded as the most reliable information on permissible contamination or environment and, therefore, serves a very useful purpose. The 1957 ||||||re above committee is reproduced here in its entirety. Threshold Limit Values for 1957" prafabpted at the Nineteenth Annual Meeting of the American Conference of "lllpi Government Industrial Hygienists, St. Louis, April iO-SS, 1967 ||||l|are given in the following tabulation for the maximum average atmospheric j|pf contaminants to which workers may be exposed for an eight-hour working 1 |injury to health. nfciy41ues are based on the best available information from industrial experience, j^Tpr^expeimental studies, and, when possible, from a combination of the two. They are not SwSlh'vTfl^y^butiiare reviewed annually by the Committee on Threshold Limits for changes, wpjpiitions as further information becomes available. Threshold limits should be the control of health hazards and should not be regarded as fine lines between concentrations. They represent only conditions under which it is .felt that aSWMTO repeatedly exposed, day after day, without adverse effect on their health. The ^latgdwefer to weighted average concentrations of an eight-hour working shift rather Sashlramum which is not to be exceeded even momentarily. The amount by which these m^^j^xceeded for short periods during the workday depends upon a number of factors, BMatore .of the contaminant, whether very high concentrations even for short periods whether the results are cumulative, the .frequency with which high J^^^^gHlfor what periods of time. All must be taken into consideration in arriving at ^M^^^^^'ffhether a hazardous situation is deemed to exist. ^ji^^^^iues are not intended for use, or for modification for use, in ,the evaluation or ^ifipfvy/mmunity air pollution or air-pollution i IjlnJJiJViTinittee welcomes the suggestion of substances to be added to the list and also arae^^r^lliehces, or reports of experience with these materials. % Recommended Values " "Plfj*--' OASES AND VAPORS p.p.m." Approx; mg. per cu. m.b IP K^Kid? j^3]|fflw|lisulfide................................................. ;............................ ^^>^&j^^l|f(itoamyl alcohol) .......................... ims**m *'.............................. 200 10 5 1,000 0.5 20 5 5 2 100 200 100 5 0.05 360 25 20 2,400 ..................12 45 12 15 12 70 1,050 360 19 02 sfflL (continued) J|||leman et al, A.MA. Arch. Ind. Health, 16, 261-65 (Sept., 1957). sv,, SmS