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Every one knows that liquid oxygen is flammable, but why this tank labeled like this:

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so is it really liquid oxygen is non flammable?

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  • $\begingroup$ Liquid oxygen is non-flammable, that's why. See this for instance, or this. $\endgroup$ – Todd Minehardt Sep 7 '15 at 2:44
  • $\begingroup$ Because "flammable" is not a synonym to "increases the risk of devastating fire", though "everyone" (by your definition) thinks it is, and this question just keeps popping up every now and then. Come to think of it, would you call the flame itself flammable? $\endgroup$ – Ivan Neretin Sep 7 '15 at 6:07
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    $\begingroup$ To quote one of my professors: "Liquid oxygen is, by itself, not all that dangerous. Of course, if you accidentally left a little bit of oil on one of the surfaces you pour it onto, it'll do it's best impression of the Challenger and take your head off." $\endgroup$ – chipbuster Sep 7 '15 at 7:03
  • $\begingroup$ It is flammable in hydrogene atmosphere :-) $\endgroup$ – peterh - Reinstate Monica Sep 7 '15 at 19:47
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Oxygen is not flammable, as it does not burn, it supports burning. For burning to happen, a strong oxidizer (for example, oxygen) and a strong reducer (for example, carbon) must be present.

No, the problem with oxygen is, that while not being flammable, it is much more efficient in supporting burning. In air oxygen is mixed with nitrogen, meaning that for the same amount of reducer a quadruple amount of oxidizer is required and a lot more heat is lost with inert gases (nitrogen). For example, iron wire can burn in oxygen, but not in air. It is also a lot easier to lit things up in oxygen. A classic experiment is to move a smoldering splinter into a vial with pure oxygen. It immediately starts to burn with a bright flame

Now, liquid oxygen is an entirely new level of crazy. In addition to constantly releasing gaseous oxygen... If an organic material (for example, sawdust) is mixed with liquid oxygen, it becomes an explosive.

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Technically, Oxygen is almost never flammable. It oxidizes other materials quite easily and many materials will burn in the presence of oxygen. But oxygen will never actually burn itself except in the presence of fluorine.

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As many comments point out, liquid oxygen is not (in)flammable. But you might see the label "Oxidizer". That means it strongly supports or could set off combustion of things that are flammable.

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