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Respirable Dust Sampling and Measurement                          207

           Table 12.8 The Variation of Quartz Percentages in Respirable Dust Samples on Consecutive
           Working Days

                                     Quartz Percentage
            Mine A    Mine M    Mine C    Mine N   Mine G    Mine O    Mine K
            3.39      0.2       5.77      5.93     14.3      8.0       1.0
            3.10      4.05      4.80      4.78     10.2      3.5       1.2
            2.88      3.91      2.14      7.00     7.0       3.4       0.9
            19.88     3.84      3.75      10.35    13.6      5.8       0.9
            17.85     2.88      9.69      5.25     11.7      1.7       1.1
                      3.75                         16.2      0.0       2.1
                                                             0.3       3.4
                                                             0.0       3.0
                                                             0.0       4.0
                                                             0.8       0.6


                         Table 12.9 The Minimum Number of Samples Needed
                         to Obtain a Quartz Percentage Within 20% of the Mean
                         Value at a 90% Confidence Level

                          Mine                  Number of Samples
                          A                     46
                          M                     13
                          C                     16
                          N                      6
                          G                      5
                          O                     86
                          K                     28



           12.6   Threshold Limits for Various Dusts Prevailing in
                  Mines

           Besides coal, silica, and DPM (diesel particulate matter), there are other dust clouds in
           mines that can create a health hazard. The American Congress of Governmental Indus-
           trial Hygienists (ACGIH) has set a threshold limit value (TLV) for each of them. A
           short list is provided in Table 12.10 to illustrate the relative pathogenicity of various
           dust particles.
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