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Elements of Industrial Toxicology 1318 TABLE 42-B THRESHOLD LIMIT VALUES FOR 1968 (Continued) made when there is good reason to believe that the chief effects of the different harm ful substances are unt tn fact additive, but independent as when purely local effects on different organs of the body are produced by the various components of the mixture In such cases the threshold limit ordinarily is exceeded only when at least one member <C. C etc) of the series jr+or-f^j itself has a quering, certain foundry operations, diesel exhausts, etc (Example 2 ) THRESHOLD LIMIT VALUES FOR MIXTURES EXAMPLES 1A General case, where air is analyzed for each component value exceeding unity, (See Example 1A b) . Antagonistic action or potentiation may occur with some combinations of atmos pheric contaminants Such cases at present must be determined individually Po tentiating or antagonistic agents are not necessarily harmful by themselves Po tentiating effects of exposure to such agents by routes other than that of inhalation is also possible, e g , imbibed alcohol and in haled narcotic /trichloroethylene) Po tentiation is characteristically exhibited at high concentiations, less probably at tow a ADDITIVE EFFECTS I C: j Cj j T, T, T, CN _ j Tn Air contains 5 ppm of carbon tetra chloride (TLV, 10), 20 ppm of ethyl ene dichloride (TLV, 50) and 10 ppm of ethylene dibronude, (TLV, 25) 5 20 10 65 10 + 50 + 25 _50-13 When a given operation or process char acteristically emits a number of harmful dusts, fumes, vapors or gases, it will fre quently be only feasible to attempt to evalu ate the hazard by measurement of a single substance In such cases, the threshold limit used for this substance should be reduced by a suitable factor, the magnitude of which will depend on the number, toxic ity and relative quantity of the other con taminants ordinanlv present Threshold limit is exceeded b INDEPENDENT EFFECTS Air contains 0 15 mg/tu m of lead . (TLV, 0 2) and 0 7 mg/cu m of sul furic acid (TLV, 1) 015 020 - 075, 07 I =7 Threshold limit is not exceeded Examples of processes which are typi cally associated with two or more harmful atmospheric contaminants are welding, automobile repair, blasting, painting, lac Special case when source of contami nant is a mixture and atmospheric com position is assumed similar to that of original material, i e vapor pressure of each component is the same at the observed temperature n ADDITIVE EFFECTS, approxi mate solution 1 A mixtme of equal parts (I) tri chloroethylene (TLV, 100), and (2) methyl chloroform (TLV, 350) C. -C.s 100 * 350 T Solution appli cable to "spot" solvent mixture usage, where all or nearly all, solvent evaporates c, = c, = |c,, c, C, 2C, 100 350 " Tm 7C, 2C, 2C, 700 + 700 Tm Tm = 700 x - = 155 ppm 1B b General Exact Solution for Mixtures of N Components With Additive Effects and Different Vapor Pres sures <1>c1+c, T, Tj c, T,, ' (2) C, + C2 + -t C,, = T,