As a plant maintenance engineer, you are required to purchase a 3,500 L tank of liquid butane to heat a maintenance building during the winter. You are concerned about the tank rupture and the possibility of a vapour cloud explosion of all the butane. How far (in metres) must the tank be from the maintenance building to ensure that it will receive only partial demolition in the event of an explosion? The specific gravity of liquid butane is 0.6, and the energy of explosion for butane is 510 kcal/gm-mol. Assume the explosion efficiency is 10 % in this case.