A “blue angel”, or “blue dart”, also known in Australia as a “blue flame”, is flatus ignition. Flatus ignition is also known as pyroflatulence, or fart lighting. Yes, fart lighting.
Fart lighting is the practice of igniting the gases produced by human flatulence. It produces a flame of a blue hue. The fact that flatus is flammable, and the actual combustion of it through this practice, gives rise to much humorous derivation. Other colors of flame such as orange and yellow are possible with the color dependent on the mixture of gases formed in the colon. In order to “fire fart”, one must have a fart prepared in the anal cavity, and a lighter at the ready. Then they fart onto the lighter.
The composition of farts varies dramatically among individuals. Flatulence produces a mixture of gases with the following six as major components: carbon dioxide, hydrogen, hydrogen sulfide, methane, nitrogen, oxygen.
Methane burns in oxygen forming water and carbon dioxide often producing a blue hue (ΔHc = −891 kJ/mol), as:
CH[sub]4/sub + 2 O[sub]2/sub → CO[sub]2/sub + 2 H[sub]2[/sub]O(g)
Hydrogen sulfide also combusts (ΔHc = −519 kJ/mol) to
2 H[sub]2[/sub]S(g) + 3 O[sub]2/sub → 2 SO[sub]2/sub + 2 H[sub]2[/sub]O(g)
The odor associated with flatus is due to hydrogen sulfide, skatole, indole, volatile amines and short-chain fatty acids. These substances are detectable by olfactory neurons in concentrations as low as 10 parts per billion, hydrogen sulfide being the most detectable.
“Cite?”, you may ask? About 40 some odd years ago as a young teen, I personally confirmed that I could light my own farts. Fortunately I didn’t get injured, as I’ve heard can happen.
Cite 2 is, I kid you not, Wikipedia’s page on fart lighting: Fart lighting - Wikipedia
I am confident there are YouTube demonstrations on this topic. It is left as an exercise to the reader to view them.
(And I pat myself on the back for all those [sub]SUBS[/sub] in those chemical equations.)