Even with the motor off, the transfer system causes gasoline to build friction in the transer process.
Portable fueling is simply dumb.
The fuel supply tank tank is grounded. The pipes connect the nozzle to the tank, via metal wires in the hose. The metal nozzle should rest on the metal fill plat. The metal fill plate should go to the vessel's bonding system. No spark possible.
Filling from a plastic container does not create a ground. One spark - boom.