Question: Is there any way to predict how smelly a fart will be?
Short answer: Yes.
Long answer: We have previously seen that the fart smelliness is correlated with sound frequency and volume. So it might be possible to detect a smelly fart by ear, even before the smell reaches one’s nose.
But is it possible to predict fart smelliness before the fart occurs? This kind of prediction might be analogous to the challenge of predicting an earthquake before it occurs, a notoriously difficult problem in seismology. As far as we know, it has not been attempted in the field of flatology.
As part of our experimental protocol, data is typically recorded for some time before each fart arrives. This is meant to provide a baseline measure of air quality, but it also allows us to examine whether such measures predict the smelliness of the subsequent fart.
The figure below illustrates the average flatodynamics for 76 farts recorded from one subject. As in previous figures, each line indicates the level of VOCs detected by air quality meters located at various distances from the release point. By aligning all 76 data records at the time of fart onset and averaging the data from each one, we obtain the following fart-triggered average of VOCs in space and time.
The blue rectangle indicates a baseline period from about 30 to 5 seconds before the fart. If we zoom in on this data, we obtain the following:
Here it can be seen that the baseline levels of VOCs hover between about 0.2 and 0.4 ppm, with values that decrease with distance from the subject. This suggests that a miasma of smelliness might be emanating from the subject during this pre-fart time period, even in the absence of an overt fart. To quantify this miasma, we computed the baseline VOC level for each fart, by subtracting the VOC levels at the bottom of the collection tube from those at the top. (This removes any offset due to general environmental smelliness, leaving only the gradient attributable to the subject). Plotting this value against the mean VOC levels observed after the fart yields the following relationship:
There is a highly significant correlation (p < 0.0000004) between baseline miasma and fart smelliness, with the regression line having a slope of 28.896, plus a small intercept of around 3. This suggests that a fart will be about 30 times as smelly as the baseline miasma that precedes it. Moreover, given the data shown in the first figure, the baseline miasma will often be above the olfactory threshold of 0.1 ppm. It should therefore be detectable to the human nose at a distance determined by the flatological constant, so that it could serve as an early warning system.