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Elements of Industrial Toxicology 1316 TABLE 42-B THRESHOLD LIMIT VALUES FOR 1968 (Continued) Mineral Dusts, Notice of Intended Changes, and Appendix A MINERAL DUSTS NOTICE OF INTENDED CHANGES Substance mppc I" SILICA Crystalline ** Quartz. Threshold Limit calculated from the formula 250* SiO, + S ** Cnstobalite Amorphous including natural diatomaceous earth Tremolite 20 5 SILICATES (less than 1 % crystalline silica) Asbestos 5 Mica 20 Soapstone 20 Talc 20 Portland Cement 50 GRAPHITE (natural) 15 "Inert" or Nuisance Particulates SOforlSmg/m5 whichever is See Appendix 0 the smaller) Conversion (actors mppcf x 35 3 -- million particles per cubic meter = particles per cc e> Millions of parlulis per cubic foot of air. based on tmpiiigcr sjtnplcs counted h> light-field techniques n The percentage of crystalline silica in the formula is the ainnimt determined from air borne samples, except in those instances in which other methods have been shown to be applicable See "Notice of Intended Changes These substances, with their corresponding values, compose those for which either a limit has been proposed for the first time, or for which a change in the Recommended* listing has been proposed In both cases, the proposed limits should be considered trial limits that will remain in this listing for a period of at least two years During this time, the previously Recom mended Limit will remain in effect If, after two years no evidence comes to light that questions the appropriateness ol the values herein, the values will be placed in the ' Recommended" list Documentation is available for each of these substances Substance ppm* mg/cu m1 Abate Boron tnbromide Bromine pentafluonde 4 Butyl mercaptan *C Cadmium oxide fume (as Cd) Camphor Chlorine Cyanogen 44C Dichloroacety- lene C Diethylene C Diethylene tnamine- Skin Diphenyl amine 44 Endosulfen (Thiodan) Skin * Ethyl mercaptan Fibrous glass 10 01 05 2 1 10 01 10 - 05 - 15 01 10 01 $ Heptane Indene Indium and com pounds, as In Iron salts, soluble, as Fe Methyl isoamyl ketone Methyl mercaptan Methyl silicate Octane Oil mist (particulate) Oil vapors Pentaerythritol (tetra- methylomethane) Pentane Petroleum distillates Propargyl alcohol-Skin RDX-Skm Stoddard solvent Styrene Tetraethyl lead (as Pb)-- Skin Tetramethyt lead (as Pb) --Skin Tnmethyl benzene Tungsten and com pounds, as W Soluble Insoluble Uranium, sol and insol compounds as U 500 10 100 0! 5 400 biAa . 500 "A* 1 - 200 50 . 25 * 2,000 01 1 475 1,900 5* 15 1,500 15 0100* 0150" 1 5 02 Parts of vapor or gas per million parts oi con taminated air by volume at 25 C and 760 mniHg pressure