To get this effect, I let a can of liquid nitrogen stand for about 10 minutes. In doing so, the nitrogen condensed oxygen from the air around it, trapping it at the bottom, and when the nitrogen had boiled off, liquid oxygen was left behind. The candle wax provides fuel, the flame provides heat, and the liquid oxygen provides so much oxygen that the entire candle is completely consumed within seconds. The metal can got hot enough that it melted and exploded within seconds as well.