Why are mobile phones not allowed in petrol pumps?

We all know that mobile phones are banned in petrol pumps. Usage of mobile phones at petrol station can cause explosions or fires? Whenever we go at the petrol station we generally saw a warning board which tells us to switch our mobile phones off. So the main reason behind this is

How much will it cost to open a petrol pump in a small city in Pakistan?

We conducted a short feasibility study to open petrol station in Sialkot in 2014. We were considering franchise of PSO & Byco.They both had slightly different parameters/standards based on location/area, like mandatory snack shop, mandatory oil change area etc.They charge a large sum of money that is used for