> "about five teaspoon" should not wreak too much damage
Well, using a little WolframAlpha magic[1][2], it looks like the energy would be equivalent to about 200 grams of TNT. The internet tells me that that's about equivalent to a hand grenade. The internet also tells me that this video is only 50 grams of TNT, but take that with a grain of salt: https://www.youtube.com/watch?v=7rE-8o9NDZk
Point is, be wary of scoffing at small amounts of gasoline. That stuff is potent.