Can Farts Catch Fire?
The flaming fart is one of humanity's most enduring party tricks — and unlike most legends, this one is grounded in real chemistry. Intestinal gas contains hydrogen and methane, both of which are genuinely flammable. Whether your particular fart will actually ignite depends on concentration, oxygen availability, and a healthy dose of luck. Science has something to say about all of it.
The Flammable Ingredients
Human intestinal gas is a mixture of nitrogen (~59%), carbon dioxide (~21%), hydrogen (~9%), methane (~7%), and oxygen (~3%), with trace amounts of hydrogen sulfide and other compounds responsible for odor. Of these, hydrogen and methane are the only truly flammable components. Hydrogen has a lower flammability limit of 4% in air, while methane ignites at concentrations above 5%. Since both can be present in intestinal gas at meaningful concentrations, the chemistry for combustion is theoretically achievable — provided the other conditions are met.
The Blue Flame Experiment
The so-called 'blue flame' phenomenon — igniting a fart with a lighter — is a real, reproducible (if inadvisable) event. When methane burns, it produces a blue flame, while hydrogen burns with a nearly invisible pale-blue flame. Witnesses of successful ignitions typically report a brief, small blue or blue-orange flame lasting a fraction of a second. The hydrogen sulfide present adds a yellowish tinge. The effect is brief because the total volume of flammable gas expelled in a single flatulence event is small — typically a few milliliters at most — and disperses quickly in open air.
Why Most Farts Don't Ignite
Despite the chemistry being technically favorable, most flatulence events will not ignite even with an open flame nearby. The main reason is dilution: gas expelled into open air mixes rapidly with atmospheric nitrogen and oxygen, dropping the concentration of flammable components below their ignition thresholds almost immediately. Timing is also critical — the window between expulsion and dispersion is measured in milliseconds. Additionally, methane production varies enormously between individuals: roughly one-third of people harbor significant populations of methanogenic archaea in their gut, meaning only some people produce methane-rich gas at all.
Myth vs. Reality and Safety
The internet is full of claims about fart ignitions causing serious burns or hospitalizations. These are largely exaggerated — the gas volume is far too small to sustain a significant flame. However, attempting to ignite intestinal gas is genuinely not risk-free: clothing can catch fire, burns to sensitive skin are possible, and the act requires positioning a lighter in proximity to the body in ways that are objectively undignified. More importantly, the real danger of flammable intestinal gas arises in clinical settings: surgical diathermy (electrosurgery) in the colon can ignite residual bowel gas, a well-documented surgical complication that has led to strict bowel preparation protocols in colonic surgery worldwide.
Did You Know?
- Approximately 30% of people produce methane in their gut — the rest produce mostly hydrogen.
- Hydrogen has a lower explosive limit of 4% in air, meaning it ignites more easily than methane.
- Surgical bowel electrocautery igniting intestinal gas is a real, documented medical complication.
- A methane flame burns at approximately 1,957°C — hot enough to melt iron, if only there were enough of it.
Fun Fact
In 1978, a paper in the journal Gastroenterology confirmed that hydrogen concentrations in rectal gas can exceed 69% in certain individuals after a lactulose challenge — well above the 4% ignition threshold (Levitt et al., 1978).
Sources
- Levitt, M.D. et al. (1978). H2 excretion after ingestion of complex carbohydrates. Gastroenterology, 75(4), 786–796.
- Powar, S.L. & Bhattacharya, S. (2005). Colonic gas explosion during colonoscopy. Journal of Postgraduate Medicine, 51(1), 48–49.
- Strocchi, A. & Levitt, M.D. (1993). Maintaining intestinal H2 absorption capacity and the factors responsible for this. Gastroenterology, 105(2), 383–390.
- Bond, J.H. & Levitt, M.D. (1972). Quantitative measurement of lactose absorption. Gastroenterology, 70(6), 1058–1062.