First find the volume of the room:
convert m to ft first:
15.7m * 3.28084ft/m = 51.5092 ft
2.9m *3.28084ft/m = 9.5144 ft
Calculate the volume of the room:
V= 9.5144 ft* 6.9ft*51.5092 ft= 3381.5580 ft^3
find the 22% of the room:
3381.5580 * 0.22= 743.9428 ft^3
Find the flow of gas that has LFL,
3.5 ft^3/min* 0.021 = 0.0735 ft^3/min
Then divide the volume by flow rate:
743.9428 ft^3 / (0.0735 ft^3/min) = 10121.67 minutes or 168.69 hours