A good friend saw matches in my bag and asked, “Do you smoke Wendy?” “No,” I replied sheepishly, not wanting to reveal the true purpose of the matches. He looked at me quizzically. There was silence. I eventually spoke, “If you light a match it takes away the smell from a fart.” There was even more silence. I knew the only way to get out of this awkward situation was going to be discussing science, because what better way to end an uncomfortable moment than whipping out the periodic table?
What is a fart?
A fart (or flatus in the science terminology) is gas from our intestines. Gas gets into our intestine through several sources: when we swallow air, the chemical reactions in our guts (from when we breakdown food), and gas made from bacteria living in our intestine.
How the gas entered our belly (and out of our bottom) will determine what type of chemicals our fart is made of, and how badly the fart smells. Flatus that came to our intestine from the air we swallow is mostly made of nitrogen (because the oxygen in air is absorbed by the body before it gets into the gut). Farts made from gas in bacteria are mostly made from hydrogen, methane and carbon dioxide.
Why are farts smelly?
The wonderous odour of flatus mainly comes from hydrogen sulphide gas. Sulphides get into your intestine through the foods you eat and are picked up by the gases already going through your intestine. A study performed in the Minneapolis Veterans Affairs Medical Center in 1998 found that the smelliest farts, from 16 healthy subjects, had around 0.04mg/L of smelly hydrogen sulphide. Our threshold for smelling hydrogen sulphide is around 0.03mg/L. (So if you release a flatus a little at a time, you increase your chances of your fart going undetected).
Foods jam-packed with sulphur, like cauliflower, eggs and meat, are the usual suspects for a smelly fart. Contrary to popular belief, beans, whilst notorious fart-producers, don’t have a lot of sulphur in them, so thaey actually don’t create smelly farts.
Why can you burn farts?
Methane and hydrogen are flammable gases, and they are both found in flatus. Just like you can burn gas from the stove, you can burn a fart. But, watch out! Before putting a flame to your butt spare a thought for my mum’s Peruvian friends who in primary school burnt their pyjama pants in a bid to burn a fart (science tycoons of the 1960’s – bless them).
Does burning a fart really remove the smell?
Hell yeah! Just give it a go! Smelly sulphur will ignite at around 250 degrees Celsius, which is around the same as the ignition temperature of phosphorus (the ingredient in a match head). When you light a match the hydrogen sulphide will decompose to form to form water (vapour) and sulphur dioxide. This means no more hydrogen sulphide, and no more smell! Even more exciting is that sulphur dioxide has the odour of a burnt match. So while many people think that the fart smell is merely masked by the smell from the match – it isn’t! There’s a completely new chemical substance in the air.
While carrying around a lighter to burn our farts might not be the most subtle way to remove the smell – it’s surely better than looking around the room and noticing that “look” on everyone’s face as the smell slowly hits them. It’s a look of disgust, suspicion and ultimately, it’s a cold hard look at you. Pre-empting these events, I suggest that after you fart, quickly light a match, and then whip out the periodic table. Hopefully, through the confusion of these events the people around you will have forgotten that you just farted and lit a match and will simply wonder why you carry around a periodic table.