A rectangular face of 2.0 m x 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,
$t = 2.303 \frac{V_m}{Q} \log \frac{q}{V_m c} + \frac{V - V_m}{Q}$,
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.