Things no one talks about: Flatulence and Indoor Air Quality

Have you ever wondered if the gases we produce as humans are toxic to those who live with us?

It is a taboo but I think we all have thought about it at one moment in our lives. Scientifically known as flatus but commonly known as a fart, many of us even use funny expressions to cope with this uncomfortable situation they create like Acid-rain maker, After the thunder comes the rain, Baking brownies, Death Breath, Fire a stink torpedo, pass the gas, etc…

Let’s take a step back and analyze the chemical composition of a flatus. More than 99% of the volume of flatus is composed of non-smelly gases. These include oxygen (O2), nitrogen (N), carbon dioxide (CO2) hydrogen (H) and methane (CH₄), keep in mind, methane is a colorless, odorless gas and nitrogen is not produced in the gut, but it is a component of environmental air. The remaining trace (<1% volume) compounds give flatus its smell which comes from a combination of volatile sulfur compounds. Hydrogen sulfide (H₂S), methyl mercaptan (CH₄S), dimethyl sulfide (C₂H₆S), dimethyl disulfide (C₂H₆S₂), and dimethyl trisulfide (C₂H₆S₃).

Diet plays an important role in the composition of a flatus, and a diet rich in protein, especially sulfur-containing amino acids (eggs), have been demonstrated to significantly increase the percentage of volatile sulfur compounds and consequently the smell of flatus.

Undoubtedly, all indoor air quality monitors with a VOC sensor are able to detect the presence of the “toxic human gases”. Why? Simple because most of them are carbon bases gases that trigger the VOC sensors.

What science says about theses gases.

hydrogen sulfide (H₂S)

Hydrogen sulfide is a poison that affects nervous system the most. The toxicity of H₂S is comparable with that of carbon monoxide as it binds with iron and it prevents cellular respiration.

ethyl mercaptan (CH₄S)

It is a colorless but flammable gas with an extremely strong and repulsive smell (rotten egg). At very high concentrations it is highly toxic and affects the nervous system. It is used as an additive in natural gas in order to detect leakage.

dimethyl sulfide (C₂H₆S)

It is flammable and an eye and skin irritant. It has an unpleasant odor at even extremely low concentrations.

Are the concentrations of these gases in a flatus able to affect human health?

It won’t kill you but it will definitely affect the mood of people around you! It is hard to estimates vary on how much of every gas is in every flatus in order to determine the health effects. For example, it may contain from 1 ppb to 1000 ppb of H₂S. A prolongued exposition of more than 1 hour to H₂S above 1000 ppb is a health hazard and deadly at doses of more than 700 ppm (700,000 ppb). However, the gases inside a room are getting diluted and it is unlikely to breathe concentrations that high.

I would suggest to keep rooms well ventilated and bathrooms too.

Fun fact: The human odor threshold for the H₂S is above 0.0047 ppm (4.7 ppb).

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