The equipment for tanker ops is provided with failsafe, see #61. The ignition source must be provided by someone deliberatly.
In a consumer filling station... The hose and nozzle are grounded. If the person does not connect the nozzle to the car by first touching the car with the other hand at any point other than the metal fill port; there's a possibility that a spark will occur that can ignite any vapors that might be exiting the fill port.
The nozzle should never be placed in the fill port, w/o first touching the car at a point adjacent to the fill port while holding the nozzle.