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This question should perhaps go in Chemistry, to which I am committed, but since the Chemistry Stack Exchange forum is not yet in beta, I am wondering if you can help me from a physics perspective.

I am wondering about the definitions of the terms flammable, inflammable, and non-flammable. Wikipedia says that flammable and inflammable are synonyms, meaning "capable of burning". In contrast, non-flammable means "not capable of burning". To avoid confusion, it is recommended that use of the term inflammable be avoided, since the prefix in- here does not mean "not".

This generally makes sense and sounds like good advice, but as I was reading a journal paper today, I came across a paragraph using these terms. I am wondering if you can help me by telling me your interpretation of the intent of this paragraph:

During the last decade room temperature ionic liquids (RTIL), being salts of low temperature melting points, have been studied extensively. They may be used as solvents for many processes and as electrolytes in electrochemical devices. Batteries filled with such a type of electrolytes do not contain any volatile components and therefore, they are not flammable. Room temperature ionic liquids, being usually quaternary ammonium salts, are characterized by negligible vapor pressure, which makes them inflammable. In addition, they show a broad electrochemical stability window, generally >4 V, which is necessary for the application in lithium-ion batteries with high-energy cathodes.

This is from page 602 in "Ionic liquids as electrolytes for Li-ion batteries--An overview of electrochemical studies", Lewandowski, A.; Swidereska-Mocek, A. Journal of Power Sources 2009, 194, 601-609, which is available to subscribers here.

The first part, "...do not contain any volatile components and therefore, they are not flammable", seems to make sense; room temperature ionic liquids are promising in part because they do not ignite or burn easily, so they can potentially improve the safety of batteries.

However, the next mention seems to say just the opposite: "...are characterized by negligible vapor pressure, which makes them inflammable".

So, my question is, does it seem to you that the term inflammable has been used incorrectly in this paragraph? Does negligible vapor pressure imply that a substance is likely to burn readily or not burn readily? Thank you very much.

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Negligible vapour pressure usually makes things less likely to burn. Things burn by reacting with oxygen. If it is sitting as a blob of liquid, there isn't much oxygen around to react with. If it is a vapour and mixed in air, there's more oxygen readily available. See flash point. – Willie Wong Aug 22 '11 at 22:39
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Actually, this is probably one for english.SE. – David Zaslavsky♦ Aug 23 '11 at 1:15
Yep - see Difference between "inflammable" and "flammable". Note that they consider this sort of thing "general reference" on English.SE, plus it's a duplicate, so don't actually ask it there - just see a dictionary. – David Zaslavsky♦ Aug 23 '11 at 1:22
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...and on the third reading, I see that the essence of your question is "Does negligible vapor pressure imply that a substance is likely to burn readily or not burn readily?" If you ask that, it would probably fit under the physical-chemistry tag here. Just make it clear that you're not actually asking about the terminology. (You can edit this question if you like, rather than starting a new one) – David Zaslavsky♦ Aug 23 '11 at 1:27

closed as off topic by David Zaslavsky♦ Aug 23 '11 at 1:21

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1 Answer

up vote 1 down vote accepted

Flammable and inflammable are from separate French and Latin words (although ultimately from the same latin root)

You are correct - low vapour pressure makes things difficult to burn. Or at least difficult to start a fire with if you don't have a way of dispersing them in air. I suspect the author got confused or was a victim of spell checker auto-complete

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