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Anne Marie Helmenstine, Ph.D.

Flammable Versus Inflammable - What Is the Difference?

By January 8, 2011

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Answer: Flammable and inflammable mean exactly the same thing... burns easily.

Why are there two different words? According to Merriam-Webster's Dictionary of English Usage, back in the 1920s the National Fire Protection Association urged people to start using the word 'flammable' instead of 'inflammable' (which is the original word) because they were concerned some people might think inflammable meant not-flammable. Actually, the in- in inflammable was derived from the Latin preposition meaning en- (like enflamed), not the Latin prefix meaning -un. It's not like everyone knew the derivation of the word, so the change probably made sense. However, confusion persists today regarding which word to use.

Flammable is the modern term for a material that catches fire readily. Inflammable means the same thing. If a material won't burn easily, you could say it is not flammable or nonflammable. I don't think unflammable is a word (and really anything can burn if you try hard enough, right?).

Handheld Fireballs Video | How to Breathe Fire


February 24, 2011 at 1:14 pm
(1) Lanthanum says:

Can carbon tetrafluoride burn (react with a chemical which oxidizes it and releases energy in the process)?

April 23, 2011 at 6:33 pm
(2) atdouble@earthlink.net says:

All Inflammables are Flammable, but not all Flammables are Inflammable.

Real world example:Take a sheet of paper and a small can of Gasoline. Take a candle to both and they both ignite. That is Flammable.

But if the candle is 5 feet away, it cannot ignite the paper. It is possible however for gasoline vapor to migrate to the candle and ignite both fumes and the gas can. That is Inflammable. Opposite of both is NON flamable. But many inflamables are labeled Flammable to avoid confusing the public.

But depending what chemicals and Material Safety Data Sheets you deal with in a job, it is a difference you may need to know.

If it helps, think of the invisible man and the visible man. They are both there, but the more dangerous one is . . .IN visible.

August 31, 2011 at 10:59 am
(3) Rub says:


April 24, 2011 at 2:34 am
(4) Emerson says:

If they mean the same thing then why have two differently spelled words. Quite confusing esp. when teaching Technical English i.e. inoperable/operable, inability/ability, inactive/active mean entirely different things.

September 16, 2011 at 4:16 am
(5) Lurkio says:

Quite so. The National Fire Protection Agency, in an attempt to avoid confusion, simply added to it by making up a new word.

October 13, 2011 at 1:40 am
(6) Dos says:

I always imagined they meant the same way as famous and infamous. Infamous is being famous for negative reasons. (eg: Madonna is famous, Hitler is infamous)

In the same way you could describe natural gas as flammable, as we purposely use it to generate heat by burning it. However, on the side of a can of deodorant, it says “Danger – Highly Inflammable”, meaning it can catch fire, but thats generally not what you want to happen :-)

Im not saying im right, I always thought that made more sense though.

Summary: (I think) Inflammable refers to something being flammable in a bad way, similar to Infamous referring to someone being famous in a bad way

March 19, 2012 at 3:17 pm
(7) assegai says:

If both flammable and inflammable are the same.,then the inflammable has been forced to be an English word.I think it’s better idea to use the latin word (enflame) as it is.what I think is inflammable is different from flammable therefore inflammable means nothing

June 2, 2012 at 10:29 pm
(8) Purists says:

This is a good illustration of what happens when you try to accommodate the dumb masses instead of teaching them proper English. The trend continues with the appeasement of ghetto talk e.g. ‘that’s bad!’ to mean ‘that’s good’ or ignoring the obvious multiple negatives e.g. ‘I ain’t not doing nothing brother’

September 27, 2012 at 10:32 pm
(9) Francesco Zhu says:

No mean of ham, Joking kindly:
-”and really anything can burn if you try hard enough, right?).”
-How about water? can it burn :) ?

February 22, 2013 at 9:32 am
(10) treehood says:

Francesco Zhu says:
-How about water? can it burn
Let us think about this. Can H2O burn? I separate my water into two hydrogen atoms and one oxygen atom, now can i burn it? I think i can.

June 4, 2013 at 1:39 pm
(11) Matthew says:

treehood says:

Francesco Zhu says:
-How about water? can it burn
Let us think about this. Can H2O burn? I separate my water into two hydrogen atoms and one oxygen atom, now can i burn it? I think i can.

If you separate hydrogen atoms and one oxygen atom, it’s no longer H2O is half a cup of hydrogen and half of oxygen

June 5, 2013 at 8:35 am
(12) pie says:

what the flip! it’s wrong!

August 24, 2013 at 7:44 pm
(13) daniel says:

Matthew – to you point if you separate water into hydrogen and oxygen you no longer have water, so you’re correct.

However, if you want to use “cups” (a measurement of volume really)as a molecular measurement, when you separate water into hydrogen and oxygen you will actually have “a cup” of hydrogen and “half a cup” of oxygen.

Of course this is ignoring the obvious disparities between the molecular ‘volume’ of a hydrogen atom vs. an oxygen atom. I’m just sayin.

I’m 4 beers into my night and this seems obvious even to me

December 12, 2013 at 10:00 am
(14) john says:

To guys who think water can not burn.
Throw a chunk of sodium into water. You can not only see flames you may also explosions!

January 10, 2014 at 12:47 pm
(15) Big Tent GHuy says:

Madonna=Famous? More like infamous!

January 14, 2014 at 9:58 am
(16) superman says:

After just speaking to the fire brigade we have been imformed they are both the same.

May 10, 2014 at 7:35 am
(17) thanks says:

good explanation

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