Why you should switch off engine while refueling
 

bros please always turn off your engine and not using mobile devices while refueling...

http://paultan.org/2015/10/05/video-...st-refuelling/

If you are filling gas, and if conditions are right, the spark that could start the fire could be due to someone sitting in a car and making electricity sparks just moving in the seat. Also, don't turn off the engine just for the fire hazard, be careful leaving your engine running when someone could just drive off in front of your face with family or friends still inside.