
Detecting Methane from Miles Away - gukov
https://cires.colorado.edu/news/detecting-methane-miles-away
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teddyh
Since humans don’t exhale methane, it’s weird of the article to use “¼ of a
human exhalation” as a measure of volume.

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anonytrary
I think they missed a great title opportunity. A "fart detector that works a
mile away" seems to be great way to phrase it; it's concise, easy to imagine,
relatable and comical. The article could then go into the specifics of what
the detector actually picks up (e.g. CH4).

I find the diffusion of the smell of flatulence to be a better comparison,
because it invokes a visceral reaction ("eww", "yuck", etc.). Imagining a
device which does this seems easier. I have a worse idea of what "1/4 of a
human exhalation" means.

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evrydayhustling
Unfortunately for the fart detector (but fortunately for us!), human farts
average around 100ml [1], whereas an adult male breath averages about 500ml
[2]. That could still be sorted out for your title, but we also have to
consider that a fart is only about 7% methane [3]. This suggests the one mile
sensitivity is going to be at around 18 simultaneous average farts, or 5 at
the record-breaking end of the scale -- conditions which might indeed justify
further surveying the region _at altitude_.

If we're willing to get closer than a mile (questionable in the above
scenario), we can apply an inverse law for gas diffusion [4] (I was surprised
it wasn't inverse square!) and find that the apparatus can can detect a single
average fart at a distance of around 30 feet -- easily covering most
elementary school classrooms and automating away the "whom smelt it dealt it"
dilemma.

[1] [https://www.chemistryworld.com/news/explainer-the-
chemistry-...](https://www.chemistryworld.com/news/explainer-the-chemistry-of-
farts/2500168.article) [2]
[https://en.wikipedia.org/wiki/Tidal_volume](https://en.wikipedia.org/wiki/Tidal_volume)
[3]
[https://en.wikipedia.org/wiki/Flatulence](https://en.wikipedia.org/wiki/Flatulence)
[4]
[https://physics.stackexchange.com/questions/290059/inverse-s...](https://physics.stackexchange.com/questions/290059/inverse-
square-law-equivalent-for-concentration)

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craftyguy
Well, that's a terrifying device for finding humans.

~~~
candiodari
Terminator: a thousand humans. Tracking.

Terminator: Acquiring target. Distance 200m.

150m

100m

50m

Cow: MOOOOOOOOOO!

Terminator struggles 30 seconds to eject head from cow butt.

~~~
skocznymroczny
[https://en.wikipedia.org/wiki/People_sniffer](https://en.wikipedia.org/wiki/People_sniffer)

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meatsock
headline should read "a mile away"

also i don't think that methane comes out when a human exhales.

~~~
amelius
Perhaps a tiny fraction, and that's detected (?)

~~~
simias
I'm not entirely sure about it but I guess they used "human exhalation" as a
somewhat relatable unit of volume for a gas but the actual system has nothing
to do with detecting humans? That's the only way that makes sense to me,
although if that's the case that's really needlessly confusing.

