Document EmmKgE6Dn5G38z9OGk8927MKj

Elements of Industrial Toxicology 1320 TABLE 42-B THRESHOLD LIMIT VALUES FOR 1968 (Continued) additive In the above example the limit for 20 per cent quartz is 10 mppcf For another mixture of 25 per cent quartz 25 per cent amorphous silica and 50 per cent talc 1 TLV = 025 025 05 = 73 mppcf 2 5 + 20 + 20 The limit for 25 per cent quartz approxi mates 8 mppcf Appendix C BASES FOR ASSIGNING LIMITING "C" VALUES By definition in the Preface, a listed value bearing a "C" designation refers to `ceil ing* value that should not be exceeded, all values should fluctuate below the listed value In genera) the bases for assigning or not assigning a "CM value rest on whether excursions of concentration above a pro posed limit for periods up to 15 minutes may result in a) intolerable irritation, b) chronic, or irreversible tissue change, or c) narcosis of sufficient degree to increase accident proneness, impair self rescue or materially reduce work, efficiency In order for the Committee to decide whether a substance is a candidate for a "C** listing, some guidelines must be formulated on the permissive fluctuation above the limit in terms of the seriousness of the re sponse in the categories a, b, c, given above For this the factors given in the table be low have been used by the Committee For both technical and practical reasons. the factors have been pegged to the con centration in an inverse manner It will be noted that as the magnitude of the TLV in creases a correspondingly decreased range of fluctuation is permitted not to decrease the factor for TLVs of increasing magni tude would permit exposures to large ab solute quantities, an undesirable condition, a condition that is minimized at low TLV's Moreover, larger factors at the lower TLV's are consistent with the difficulties in ana lyzing and controlling trace quantities TLV RANGE ppm or mg/cu m Whichever applicable unit is Test TLV Factor Examples 0 to 1 1 + to 10 10 + to 100 3 Toluene dmocyanateTLV, 0 02 ppm, if per mitted to nse above 0 06 ppm may result in sen sitization in a single sub sequent exposure *`C' listing recommended on category b 2 Manganese-TLV, 5mg/ cu m, contains little or no safety factor All values should fluctuate below 5mg/cu m **C ` listing recommended on cate gory b 15 Methyl styrene-TLV 100 if encountered at levels of 150 ppm will prove intensely irritating, "C" listing recommended on category a 100 + to 1000 1 25 Methyl chloroform- TLV 350ppm, at 438 ppm for periods not exceeding 15 minutes is not expected to result m untoward effects relating to cate gory c No C' listing recommended PERMISSIBLE EXCURSIONS FOR TIMEWEIGHTED AVERAGE (TWA) UMITS As stated in the preface, the same factors may be used as guides for reasonable ex cursions above the time-weighted average applies The time-weighted average im plies that each excursion above the limit is compensated by a comparable excursion below the limit Thus, a value of 6-ppm HF is permissible for periods not exceed ing 15 minutes, provided an equivalent decrease below the limit of 3-ppm obtains Appendix D Some "Inert" or Nuisance Particulates9 Alundum (Al203) Calcium carbonate Cellulose Portland Cement Corundum (Al*Oj) Emery Clycenn Mist Graphite (synthetic) Gypsum Limestone Magnesite Marble