the problem originates from america, where the pumps dont need to be manned, you can lock them on... then people can sit back in there car... where they would make a call and gain static from the rubing of the plastic against their clothes/hair... then when they went to stop the fuel, a small arc would spark between the users hand and the bare metal or the handle, igniting the fumes escaping from your filler pipe... then they would normally pull the nozzle out in a panic and essentially have a flamethrower in there hand... sparting everything within 3 feet or so in flaming fuel...

so as a rule in general, no engines are allowed to run and you are not meant to use your phone... its not that it will be guaranteed, its that you cannot guarantee when it will happen and how people will react...

(if it does ever happen, you are meant to leave the nozzle in and smother the cap to remaove all the air... therefore stopping the fire! (fuel cannot burn without air)