Acetylene + Chlorine Gas = Spontaneous Combustion
This is the kind of science demonstration that Walter White would've taught in his chemistry class or used to escape a perilous situation. From io9: "Acetylene is not a gas to be played with, as it supplies the fuel for welding torches. It generally needs a flame, or excessive heat nearby, to ignite. If chlorine is around, it ignites without any further help. Acetylene is pretty simple. it has two hydrogen atoms and two carbon atoms. Those two carbon atoms are bound together in what's called a triple bond. Six electrons are all invested in keeping the two carbon atoms together. That's a lot of energy, and when chlorine comes in and starts ripping the atoms apart--kaboom."