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Mining Engineering Mine Ventilation Difficulty: Medium

While measuring average air velocity of air flowing through a circular duct using precise traversing with equal area method, the radii r 1 , r 2 and r 3 , in mm, as shown in the figure of the three circles should be Ores useually occurs in Dust plan shall be maintained in every mine having working below ground plan on a scale having representative factors of not less than . . . . . . . . clearly, showing by distinctive colours, code letters and numbers. At what percentage of black damp, the mine atmosphere becomes non explosive irrespective of % of fire damp. A back sight on a bench mark of RL 100m on the floor of tunnel is 3.25m. The inverse staff reading on a roof station of the tunnel is 1.25m. The RL of the roof station is . . . . . . . .