When I was a kid, my Dad was burning some trash in the backyard of our house. Old wood and such as I recall. To get it started, he tossed on some gasoline (much as suggested by Hoke). He was safe about it. He tossed on some gasoline, let it soak in a bit, and set the gas can a good 10+ feet away next to the back porch stairs (more about that 10 foot estimate in a moment). He lit up a match and tossed it onto the pile and it went up with a satisfying whoosh! Great stuff as a kid! Fire! Cool!
Gasoline fumes are flammable. As the fuel evaporates out of the gas can, the fumes tend to drop to the ground and spread. Then came the second whoosh! I just happened to be in the right place, at the right time, looking at the right spot, to see a flame move from the fire, travel across the ground towards the porch, and finally go up in a blaze over the gas can, sitting next to the wooden steps. I have to hand it to my Dad. As he told my Mom to call the fire department, he reached out with a garden rake he was using to tend the fire (about a five foot handle), hooked the handle on the flaming gas can, and slowly swung the can over to the fire (hence, the ten foot estimate). Since the can didn't have a cap on it, there was no build up of pressure or explosion. The gas continued to burn from the can until it was gone. The wood pile burned down to coals. My Dad told my Mom to cancel the call to the Fire Department.
It was an formative experience in how gasoline can be ignited from a source of ignition more than ten feet away from nothing but the fumes coming off the can.
Dave