Flammable, Inflammable, and Nonflammable: How to Choose the Right Word

The adjectives flammable and inflammable mean exactly the same thing: easily set on fire and capable of burning quickly. Metaphorically speaking, inflammable also can mean easily angered or excited. Of the two terms, the older word for something capable of burning is inflammable, but early in the 20th century the word flammable was coined as a synonym for inflammable. The adjective nonflammable means not easily set on fire.

How to Use 'Inflammable'

Despite beginning with "in-," inflammable does mean burnable, and it has since at least 1605, according to the Oxford English Dictionary The prefix "in-" can make a word negative, as in incapable, inflexible, and incompetent, but it also can add emphasis, as in invaluable, inflame, and intense. The prefix also can mean within, as in incoming, inbreeding, and infighting.

The "in-" of inflammable, called an intensive or an intensifier, is of the emphatic type. But people came to believe that the prefix was confusing, which could be dangerous in emergency signage, so inflammable is falling out of use.

How to Use 'Flammable'

Flammable, the new kid on the block, didn't appear in print until more than 300 years later. In the 1920s, the National Fire Protection Association began using flammable instead of inflammable, which it thought was confusing because of the negative-sounding beginning of the word. Insurance companies and fire-safety advocates soon agreed.

In 1959, the British Standards Institution announced that, to avoid ambiguity, its policy was to encourage use of the terms flammable and nonflammable instead of inflammable and nonflammable.

So which word should a careful writer use? According to "Origins of the Specious: Myths and Misconceptions of the English Language," by Patricia T. O'Conner and Stewart Kellerman:

"History may be on the side of 'inflammable,' but common sense wins here. If you want to be sure you're understood—say, the next time you see a smoker about to light up near a gas pump—go with 'flammable.'"

But inflammable hasn't disappeared. Merriam-Webster's Dictionary of English Usage reports that, though both forms still are used, flammable seems to be less common in British English than in American English and inflammable is more common. In figurative uses, inflammable still serves a purpose.

How to Use 'Nonflammable'

For a time, a substance that couldn't easily catch fire was referred to as being noninflammable. Nonflammable began to replace that term as flammable become more prominent for the sake of clarity. So nonflammable is the word of choice for careful writers, especially those working in a public safety capacity.

Examples

Here are some sample sentences illustrating the differences among the three words, incorporating the demise of the word inflammable except for figurative purposes:

• Flammable or combustible liquids should not be stored in stairways or in areas used for exits. Here flammable means the same thing as combustible.
• The Douglas fir and the giant sequoia of western North America have developed thick, nonflammable bark to insulate the living tissue from the heat of the flames. In this example nonflammable means resistant to burning.
• Since Bill was fired, he has become inflammable about workers' rights and loses control in arguments on the topic. In this case, inflammable doesn't mean burnable; it means easily excited or angered. To most experts, it's the only remaining appropriate use for inflammable.

How to Remember the Difference

Flammable should now be the obvious choice for burnable. The first syllable looks like flame, and that's what it means: Capable of going up in flames. One way to remember to use it instead of inflammable is that it's a simpler word, and simpler often is best. Inflammable isn't incorrect, but it's imprecise, and that could be dangerous.

Nonflammable also should be the obvious choice: non (not) plus flammable, meaning it won't burn.

Sources

• "Flammable vs. Inflammable." https://www.merriam-webster.com/words-at-play/flammable-or-inflammable.
• O'Conner, Patricia T., and Kellerman, Stewart. "Origins of the Specious: Myths and Misconceptions of the English Language." Random House, 2010.