With the engine running you have an open ignition source in the Alternator
Here are the explosive limts for gasoline UEL: 7.6% and LEL: 1.4%.
The conditions for an explosion have to be just right but why take a chance?
If you have spilled gasoline on hot concrete under your car you could have a problem with electrical sources or static electricity.
Why do you think all the electrical conduit around gas pumps is in "seal off" Class 1 Div 1 conduit?
Guidelines for Fueling Vehicles (From Chevron)
http://www.chevron.com/products/prod...e_safety.shtml
Turn off your engine. Disable or turn off any auxiliary sources of ignition such as a camper or trailer heater, cooking units or pilot lights.
Put your vehicle in park and/or set the emergency brake.
Do not smoke, light matches or use lighters while refueling
Use only the refueling latch provided on the dispenser. Never jam the refueling latch on the nozzle with any object (i.e. gas cap, etc.)
Never leave the nozzle unattended.
Do not overfill or top-off your vehicle tank ? it can cause spillage.
Do not allow children to fuel and /or assist fueling vehicle.
Never use a cell phone or other personal electronic device while refueling (for example, laptops, PDAs and electronic games).</B> These items should be left in your vehicle.