Step 1: A little delicate work.
Use a hammer and a nail to punch a hole in the middle of the lid and the bottom of the tin. Use the same hammer to flatten the sharp bits (health and safety, don'tcha know).
Step 2: Just do it!
Stand the tin on something that lets air get to the hole underneath (if you don't have a tripod in your laboratory, or you don't have a laboratory of your own, use two bricks side-by-side with a gap between).
Wave a lighter over the top hole. The gas will light.
Watch the flame. As long as you can see the flame, it will just burn like a lamp. Eventually, though, the flame will turn blue, shrink, and disappear down into the tin.
At that point... >>>BANG!<<<