A rectangular face of 2.0 m×2.5 m dimension is blasted with 20 kg explosive in a 1000 m long drive. One kilogram of explosive produces 2200 cm³ of nitrous fumes. The face is ventilated with a duct, located 10.0 m away from the face, to dilute the fumes. The quantity of air, in m³/s to be circulated for reducing the concentration of nitrous fumes to 5 ppm within a period of 5 minutes, is (round off up to 2 decimals)
[Use the relation, t=2.303V_m/Qlogq/V_mc+V-V_m/Q where t=time, V_m= volume of the tunnel over which the mixing of the gases produced at the face, and air delivered by the fan occurs, c= concentration at time, t, V= volume of tunnel, Q= quantity of air flow, q= total volume of nitrous fumes produced ]