Gasoline vapors are pretty bad. A long time ago I had a little ski boat, and was pretty concerned about running out of gas. So I put a gallon jug of emergency gas in the boat. Now, the boat was completely open to the breeze. No matter how tightly I closed the cap on that jug (and it was a standard gas can) the fumes made me nauseous. I finally gave it up.

The same goes for filling a gas can at the station to transport to the boat to fill its tank. I would not spill a drop of gas, and driving it home I'd have all the windows open on the car and drive with my head out the window and it would still make me sick.