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And within a pretty tight range, too. I've heard that if O2 is more than 25% of the atmosphere, things would catch fire spontaneously; if less than 15%, they wo

And within a pretty tight range, too. I've heard that if O2 is more than 25% of the atmosphere, things would catch fire spontaneously; if less than 15%, they wouldn't be able to burn at all.

zaarn 7y ago
Not with oxygen but flourine (and some of it's compounds) will actually cause spontaneous combustion in a wide range of things such as burnt coal and asbestos.
masklinn 7y ago
> I've heard that if O2 is more than 25% of the atmosphere, things would catch fire spontaneously Oxygen reached 35% during the Carboniferous. This lead to lifeforms taking advantage (e.g. giant invertebrates outside the seas) as well as rainforest wildfires as the oxygen levels significantly increased flammability of flammable materials (most of our coal dates back to these days, where rainforests would grow quickly, burn down to 10~20% charcoal by volume, and that charcoal would fossilise over time). Somewhat oddly, very few things are hypergolic with oxygen, even LOX (which is as full of oxygen as you can get) or 100% oxygen atmosphere. Fuel will readily ignite, but it needs an ignition source of some sort. This is in contrast with fluorine-based oxidants like ClF3, which is hypergolic with sand, asbestos, or water.
- bonzini 7y ago
  ... or test engineers!
  - dredmorbius 7y ago
    Production engineers too.
  - lmilcin 7y ago
    I see what you did here, you In the Pipeline reader.
- arethuza 7y ago
  Isn't liquid ozone even more "full of oxygen" than LOX?
  - masklinn 7y ago
    I guess, I was using "oxygen" as a shortcut for "O2" which does make me technically wrong. Though ozone is as toxic as fluorine and tend to spontaneously explode, according to Ignition! it can be made safer by mixing it with LOX but to reach safe use levels you apparently need to get down to ~25% O3, at which point it's just a harder to handle LOX. It seems (I didn't remember this passage) folks also tried out mixing ozone with fluoride, which strikes me as a very Cave Johnson idea.
- memling 7y ago
  > This is in contrast with fluorine-based oxidants like ClF3, which is hypergolic with sand, asbestos, or water. Speaking of things that 'splode, there's a lovely article that makes the rounds here every so often by Dr. Derek Lowe on the onomatopoeically named FOOF (dioxygen diflouride)[1], one of his "Things I won't work with."[2] [1]: https://blogs.sciencemag.org/pipeline/archives/2010/02/23/things_i_wont_work_with_dioxygen_difluoride https://blogs.sciencemag.org/pipeline/archives/2010/02/23/th... [2]: https://blogs.sciencemag.org/pipeline/archives/category/things-i-wont-work-with https://blogs.sciencemag.org/pipeline/archives/category/thin...
littlestymaar 7y ago
It's not that extreme. Things don't catch fire spontaneously even when the atmosphere is 100% oxygen (you still need an activation energy) but a fire that starts in this conditions is incredibility fast: some things even becomes explosive because of that. See the Apollo 1 accident [1]. [1] https://en.m.wikipedia.org/wiki/Apollo_1 https://en.m.wikipedia.org/wiki/Apollo_1

And within a pretty tight range, too. I've heard that if O2 is more than 25% of the atmosphere, things would catch fire spontaneously; if less than 15%, they wouldn't be able to burn at all.

zaarn 7y ago

Not with oxygen but flourine (and some of it's compounds) will actually cause spontaneous combustion in a wide range of things such as burnt coal and asbestos.

masklinn 7y ago

> I've heard that if O2 is more than 25% of the atmosphere, things would catch fire spontaneously Oxygen reached 35% during the Carboniferous. This lead to lifeforms taking advantage (e.g. giant invertebrates outside the seas) as well as rainforest wildfires as the oxygen levels significantly increased flammability of flammable materials (most of our coal dates back to these days, where rainforests would grow quickly, burn down to 10~20% charcoal by volume, and that charcoal would fossilise over time). Somewhat oddly, very few things are hypergolic with oxygen, even LOX (which is as full of oxygen as you can get) or 100% oxygen atmosphere. Fuel will readily ignite, but it needs an ignition source of some sort. This is in contrast with fluorine-based oxidants like ClF3, which is hypergolic with sand, asbestos, or water.

bonzini 7y ago
... or test engineers!
- dredmorbius 7y ago
  Production engineers too.
- lmilcin 7y ago
  I see what you did here, you In the Pipeline reader.
arethuza 7y ago
Isn't liquid ozone even more "full of oxygen" than LOX?
- masklinn 7y ago
  I guess, I was using "oxygen" as a shortcut for "O2" which does make me technically wrong. Though ozone is as toxic as fluorine and tend to spontaneously explode, according to Ignition! it can be made safer by mixing it with LOX but to reach safe use levels you apparently need to get down to ~25% O3, at which point it's just a harder to handle LOX. It seems (I didn't remember this passage) folks also tried out mixing ozone with fluoride, which strikes me as a very Cave Johnson idea.
memling 7y ago
> This is in contrast with fluorine-based oxidants like ClF3, which is hypergolic with sand, asbestos, or water. Speaking of things that 'splode, there's a lovely article that makes the rounds here every so often by Dr. Derek Lowe on the onomatopoeically named FOOF (dioxygen diflouride)[1], one of his "Things I won't work with."[2] [1]: https://blogs.sciencemag.org/pipeline/archives/2010/02/23/things_i_wont_work_with_dioxygen_difluoride https://blogs.sciencemag.org/pipeline/archives/2010/02/23/th... [2]: https://blogs.sciencemag.org/pipeline/archives/category/things-i-wont-work-with https://blogs.sciencemag.org/pipeline/archives/category/thin...

littlestymaar 7y ago

It's not that extreme. Things don't catch fire spontaneously even when the atmosphere is 100% oxygen (you still need an activation energy) but a fire that starts in this conditions is incredibility fast: some things even becomes explosive because of that. See the Apollo 1 accident [1]. [1] https://en.m.wikipedia.org/wiki/Apollo_1 https://en.m.wikipedia.org/wiki/Apollo_1