Question: How much is fart smell affected by clothing?
Short answer: Surprisingly little.
Long answer: Today’s question is one that we at the College are frequently asked. Although we have undertaken highly precise measurements of fart diffusion and velocity, we have to concede that these measurements are indirect, being filtered through one or more layers of clothing. Such uncontrolled variables are troubling to experimental scientists.
Our first stab at addressing this problem was to simulate farts with commercially available fart spray, as shown below:
This solved the problem of the clothing barrier, but introduced a new problem, namely that the product is unrealistically potent. Even small amounts of fart spray typically saturated our VOC meters, often for several hours after administration. Thus we had little choice but to attack the problem directly, by performing controls that removed the variable in question.
At this point, it should be mentioned that the faculty of the College are all highly regarded members of their communities, with impeccable reputations for their exemplary conduct.
The exception is our intern, Cletus, who came to the College after losing his job at a nearby carnival. Although we were wary of his rough and rowdy past, his passion for flatology was unmistakable, and we agreed to accept him into our internship program. His first assignment was to perform the decisive experiment, producing a series of farts with and without intervening material.
Below is a fart-triggered average of fart smell (VOC) at different times and distances relative to the point of release. As in previous plots, each line shows the time-course of fart smell at a specific distance along our experimental collection tube. Each plot comprises an average of 34 farts.
There is surprisingly little difference in overall smelliness in the conditions, and the flatodynamics do not appear to be obviously different. However, careful scrutiny reveals that the fart smell reaches the deeper reaches of the collection tube more rapidly when there is no barrier to propulsion (plot on the right). Indeed, within a few seconds, the air quality meter located 4” from the top of the tube (purple line in each plot) reacts to the fart, and the meters closer to the bottom of the tube react strongly within 20 seconds (green and cyan lines). This indicates that velocity is somewhat faster when farts are unimpeded. Indeed, by fitting these data to the diffusion equation, we find that clothing decreases the average velocity of farts from 4.4 in/min. to 3.1 in/min, a difference of 43%.
However, since the speed of farts is quite slow in either case, we conclude that clothing has little role in preventing or redirecting fart stink. Indeed, the typical indoor air velocity is on the order of 200 in./min., or about 50 times the speed of an unimpeded fart. So outside of a laboratory environment, the movement of farts is entirely at the mercy of circulating air.
That doesn’t mean that it’s entirely safe to fart naked, as other materials might very well be released, but it does mean that there is potentially some value in underwear that offers “flatulence filtration”, given that standard clothing does not. This flatulence blocking underwear does not try to trap the fart, which is impossible, but rather adds a layer of carbon that removes the smell. Previous work provides experiment validation that these products can be effective (Ohge et al., Am J Gastro, 2005).
Reference (Highly recommended) Ohge, Hiroki, et al. “Effectiveness of devices purported to reduce flatus odor.” American Journal of Gastroenterology 100.2 (2005): 397-400.