Comment by oxymoron
9 years ago
I once took a university course called "Chemical Equilibrium" which required some lab time. The labs were about examining solutions with unknown ions and figuring out what they were. A common tool in doing so is by bubbling hydrogen sulfide gas through the solution, which will cause the precipation of certain cations.
Needless to say, we were warned about the dangers of H2S, and told that if it ever escaped the fume hood we would know immediately by the smell and should evacuate the premises before we succumbed to olfactory fatigue and poisoned ourselves. Another fun gas used in the same course was HCN. All in all, A very solid lesson in not fooling around outside the fume hood, and from the anecdote above a possibly life saving lesson which can't be said for most university courses...
For those who do not know, H2S is also a key part of the vile smell in flatulence, so strictly speaking it's a rather common substance in nature albeit in "safe" concentrations.
>"For those who do not know, H2S is also a key part of the vile smell in flatulence, so strictly speaking it's a rather common substance in nature albeit in "safe" concentrations."
Funny story and probably TMI.
I used to work in aviation maintenance on large military aircraft. We regularly had to enter into "confined spaces" (fuel tanks, wings, ect) and were required to take a hand-held "air sniffer" with us that would alarm if any of about 5 or so monitored gases got too high.
I would always fart into the thing to see what would happen and it would always read 0 on all monitored gases. However on one day, I had perhaps the worst smelling "flatulence" ever and while inside the center fuel tank of a P3, I let one rip right into the sniffer. H2S went from 0 to 1ppm, but strangely carbon monoxide (CO) went from 0 to 7ppm. I always expected the H2S, but I don't know what the heck CO was doing in my bowels..
CO is produced by bacteria in your gut, just like H2S.
The short version is more likely CO2, not CO, and the detector was probably fooled by methane. In more detail:
I was motivated to google, and much like radioactivity or electric current its possible to measure "scary" things to low levels that don't usually matter, and according to a 1982 gastroenterology paper that I found, aerobic fecal fermentation will produce an irrelevent yet measurable extremely low CO output while the anerobic fecal bacteria find CO to be a yummy fuel and will rapidly consume it. Unfortunately they cannot consume CO fast enough to scavenge your blood clean if you're suffering from CO poisoning, which is too bad. Carbon monoxide being known as that thing that gives you massive gas would be far preferable to being known as that poison that kills people, but thats how it goes, can't win em all, so despite our helpful fecal bacteria CO does kill people. The paper theorized the anerobes protect the host by eating the extremely small level of CO that normal aerobic gut flora output.
From fooling around with chemical sensors in my youth, quite a few work by heating up an oxidation catalyst and measuring its temp very closely given the carefully measured outside air temp and electricity fed into them. So feed it a fuel like carbon monoxide and it gets microscopically, yet measurably, hotter. You can play molecular weight games to get a catalyst that preferentially responds to light stuff like methane or CO, or heavy stuff like vaporized wax. My semi-educated guess is the aviation CO sensor got fooled by methane in the guy's gas. Methane isn't a serious threat in an airplane fuel tank so its unlike bowel gas analysis was a high priority in the specs. This is in the class of proving things by ruling them out, and you can't rule out a heated oxidation catalyst sensor getting fooled by low molecular weight methane, its a believable scenario.
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So if 999 other men were in there farting with you, you might have all died?
It occurs in deep wells that cave divers swim into as well. They often have to swim through an H2S layer, which can numb their lips and any exposed skin. It's generally a race to get through this layer and into the caves below as fast as possible.
so holding your breath doesn't help against H2S very well?
If I remember correctly, a fatal concentration of H2S is actually lower than HCN (hydrogen cyanide).
Many people each year succumb to H2S poisoning. It's a pretty insidious poison.
And for those interested, H2Se has an LC50 about an order of magnitude lower than H2S. Fortunately S/Se in crude oil is likely to be >10000. It smells like garlic.
I just wanted to add an evolutionary perspective on why H2S might smell so bad for us. Sure it's dangerous, but so are many gases that don't smell. However:
https://en.wikipedia.org/wiki/Permian%E2%80%93Triassic_extin...
It can also be produced by bacteria that would would normally emit H2O, as in an oxygen deprived environment they can produce H2S instead.