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Mine Sealing and Recovery                                         407





























           Figure 24.1 R-Index versus the dimensionless ratio of residual gas to oxygen (Rg/O 2 ).

           Table 24.2 Litton Ratio for a Dying Mine Fire

            Day         O 2 %         CH 4 %        C 2 H 6 (ppm)      Ratio, R
            1           13.89         0.38          740                4.45
            10          12.69         2.61          700                3.68
            30          9.45          3.93          660                1.19
            60          5.81          5.23          440                0.16
            80          2.25          5.42          410                0.04

           Adapted from Timko RJ, Derick RL. Methods to determine the status of mine atmosphere e an overview. In: Paper
           presented at 2006 SME annual meeting e mine fire prevention; 2006. p. 9.


              It is prudent to wait until R values stabilize at a point below 1.00 for 30 days or so
           before reopening the mine.


           24.3.3.2 Hydrocarbon Ratio (HR)
           Justin and Kim [8] developed the hydrocarbon ratio based on their finding that low mo-
           lecular weight hydrocarbons desorbed from coal in direct proportion to increasing tem-
           perature. Methane is liberated first followed by CO 2 , CO, H 2 ,C 2 H 4 ,C 3 H 6 , and C 2 H 2 in
           that sequence.
              The HR is defined by Eq. (24.10) below:
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