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The Bay Area Rapid Transit System Finally Gives Real Numbers On Time To Filter Farts From Subway Cars

Illustration for article titled The Bay Area Rapid Transit System Finally Gives Real Numbers On Time To Filter Farts From Subway Cars
Illustration: Jason Torchinsky

I’m pretty sure anyone who’s ever ridden on a subway, anywhere, would find this valuable information: how long can a subway car’s air filtration system filter a fart from the air? As far as I can tell, no major subway system has provided such information. Until now.

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Yes, the Bay Area Rapid Transit System (BART), the system that serves the San Francisco Bay area, an area well-known for its prodigious and committed flatulators, has publicly given an official estimate regarding how long a fart will linger in a BART subway car:

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So, there you go— one minute and ten seconds. This also, I believe, is the first time an official missive from a municipal mass transit system has included the word “sharted.”

The discussion seems to have stemmed from a larger discussion regarding the air filtration systems in BART cars, noting that constant airflow is crucial to preventing the spread of airborne COVID-19 viruses:

Here’s a larger version of that diagram:

Illustration for article titled The Bay Area Rapid Transit System Finally Gives Real Numbers On Time To Filter Farts From Subway Cars
Graphic: SFBART
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Each car appears to have an independent HVAC unit under the car floor, which sends air into the cabin via ceiling-mounted vents. Fresh air—making up 30 percent of the air in the car—is pulled in through exterior vents just below the car’s beltline, and is mixed with recirculated air.

This system allows for all the air in a cabin to be refreshed every 70 seconds, which, as the original tweet suggested, would carry away any lingering farts.

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Of course, if the source of the stench is continual—as in the aforementioned shart situation—even with the whole cabin air being replaced every 70 seconds, it could still be contaminated by the shart material as long as its present on the car.

Illustration for article titled The Bay Area Rapid Transit System Finally Gives Real Numbers On Time To Filter Farts From Subway Cars
Photo: NASA
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According to my copy of NASA’s Bioastronautics Data Book, humans can generate up to 2800 ml of farts per day, about one and a half two-liter soda bottle’s worth, but the odds of someone unloading the maximum daily volume of flatus in one go on a subway is pretty minimal. It would also probably blow them out of their seat.

Still, it’s good to have this sort of information. I guess it’s useful for COVID-19 reasons, but I like knowing how rapidly farts can be whisked out of the car.

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Once, on the LA subway, a dude on the car I was on lit his hair on fire. That smell took a hell of a lot longer than 70 seconds to go away.

Senior Editor, Jalopnik • Running: 1973 VW Beetle, 2006 Scion xB, 1990 Nissan Pao, 1991 Yugo GV Plus, 2020 Changli EV • Not-so-running: 1977 Dodge Tioga RV (also, buy my book!: https://rb.gy/udnqhh)

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DISCUSSION

I’m afraid the BART discussion and your NASA documentation are taking about different things. NASA here is looking at flatus, the gaseous part of farts, where for us, the key component is that ever-so-faint whiff of hydrogen sulfide. Many of those gases aren’t going to behave like the dominant gases in the atmosphere. And filtration will not remove them. That’s why an N95 mask only provides marginal protection against flatus.

BART is talking about farticulate matter, the other component of farts, which can involve aerosols of fecal matter and, inter alia, SARS-CoV-2. These farticles add not just notes to the aroma, but give SBDs their namesake lethality.

Ultimately, experimentation will resolve the issue. Unfortunately, I will not be available to participate.