Document 7MjmprYq07n0ONoJb0pBNR20R

TABLE 42--B THRESHOLD LIMIT VALUES FOR 1968 (Concluded) Pentaerythntol Plaster of Pans Rouge Silicon Carbide Starch Sucrose Tin Oxide Titanium Dioxide Vegetable oil mists (except castor, cashew nut, or similar lrntant 01 Is) `When toxic impunties are not present Appendix E Some Simple Asphyxiants -- ' Inert" Cases and Vapors Acetylene Argon Ethane Ethvlene Helium Hvdrogen Methane Neon Nitrogen Nitrous Oxide Propane Requests for permission to republish or reprint these Threshold Limit Values should be directed to Secretary-Trea surer, ACCIH, 1014 Broadwav, Cincinnati, Ohio 45202 bnef excursion of concentration beyond the acceptable ceiling There are many sub stances where such excursions would be quite acceptable, if the remaining exposure is otherwise limited to the acceptable ceiling and acceptable time-weighted average The Z37 Standards also include any other level or levels considered by experts to be pertinent to a particular substance under consideration Many individuals refer to a published TLV or AC as a "go" or "no go" value -- something to be used m a specific situation --and over look the important qualifications of these values set forth by the organizations estab lishing them The preface to the annual list of TLV's and the introduction to each of the ASI Z37 series of AC's provide a basic ex planation of the concepts on which these values are based To use the values intelli gently, their definitions should be understood before they are applied to a specific situation Knowledge of the type of injury which would result from dangerous overexposure is also needed As mentioned previously, toxic effects may be broken down into four major classifications ' 1 Acute toxicity, 2 Chronic toxicity, 3 Narcosis, and 4 Discomfort The time-weighted average concentration would be the appropriate guide where chronic toxic effects result from overexposure When protection against narcosis is required, the concentration should never exceed some ceiling value To minimize discomfort, the instantaneous excursions or peak concentra tions are of interest Both the ASI and ACCIH, in defining their respective values, point out that an understanding of the criteria on which the values are established is necessary in decid ing how to use the values It should be remembered that TLV's and AC's are, even though applied as intended, relative values The concentration that just approaches the threshold limit is just as haz ardous or safe as the one that slightly exceeds it, and conversely There is no fine line that can be drawn to provide complete safety for all individuals In general, it is desirable to limit air con tamination to the lowest possible level -- consistent with efficient plant operations Probably the greatest misuse of both the TLV's and the AC's is the practice of com paring toxic substances by a ratio of their respective AC or TLV It should also be re membered that neither the TLV nor AC should be considered the sole criterion of sus pected occupational disease The ASI and ACGIH specifically state that their values are intended to serve as guides for good engi neering practice and are not intended to be 1321