What is The Difference Between Flammable And Inflammable?

What is The Difference Between Flammable And Inflammable?

Both inflammable and flammable have the same meaning: easily ignitable, easy to catch, easy to burn. However, the word inflammable has had its use decreased over the last decades, the main reason for that is to avoid misinterpretation of its meaning.

Contrary to what it may seem inflammable is not an antonym of flammable, the correct antonym of flammable is nonflammable (or non-flammable) which is an adjective that indicates something does not easily catch on fire when it is subjected to an ignition source while in contact with air.

The word inflammable has its origins in the Latin language. The Latin prefix “in”  (translates to “to cause to”) and the Latin verb flammare (translates to “to catch fire”). So inflammare would mean ‘’to cause to catch fire”.

The inflammable was introduced to English in the start of the XVII century. Later on, in the early XIX century, the word flammable was coined from the Latin word flammare. And so from this point on there were two words with pretty much the same meaning.

French (1600) had the word inflammable with the translation being “able to be set a lit”. Medieval Latin had the word inflammabilis.

By the 1980s using the word inflammable started to be discouraged for the possibility that it could be interpreted as meaning the opposite of flammable, particularly in warning signs and in cases with possible hazards..

What Is The Meaning Of Prefix In-

The prefix in- most commonly indicates the opposite of the base of the word. Examples include inaccurate, incorrect, indecisive, indirect, incapable, incoherent. The prefix un- serves the same proposite.

In- can also indicate a sense of increment as in intonation, inland, include, insert. That is the case for the word inflammable, which as mentioned above has its origins in the Latin word ‘’in’’ which can be translated to ‘to cause to’’.

Is Flammable The Same As Combustible?

No, these words don’t have the exact same meaning even though they are very closely related. The word combustible often has at least two different but similar meanings.

Something being a combustible may simply mean that something can catch on fire or be ignited under the specified conditions of temperature, pressure, and the presence of other substances. By this definition anything that is flammable is necessarily also combustible.

But not every combustible material is necessarily flammable.

In other cases, however, the word combustible has a different meaning. For instance in the field of automobile and aircraft fuels, a fuel which has a flashpoint of up to 38 ºC (100 ºF) is considered a flammable while a fuel with a flash point between 38 and 93 ºC is considered a combustible fuel.

Also, there are materials that don’t have a measured flash point but are considered flammable nonetheless. For example hydrogen gas or metallic potassium.

Examples of Flammable Liquids

Technical definitions of flammable vary depending on the local relating agency. It is possible for some materials to be considered flammable in some locals while nonflammable in others.

For instance, according to the GHS a flammable liquid is one with a flash point equal to or above 93 ºC (194 ºF). But other agencies consider a flammable liquid one with a flash point of up to 37.8 ºC to be flammable (100 ºF).

Below is a list of examples of flammable liquids (according the the GHS) along with their flash point.

LiquidWhere Is It Present?Flash point
OctaneAutomobile fuels13 °C (55 °F)
DieselFuel> 52 °C (> 126 °F)
Kerosene Used in jet fuel38 ºC to 72 °C (100 to 162 °F)
EthanolHousehold alcohol, automobile fuel17 °C (62 °F)
Iso-propanolSanitizers12 ºC (53 ºF)
Acetic acid Vinegar39 ºC (103 ºF)

Examples of Flammable Gases

A flammable gas may be considered material which is a gas at a temperature of 20°C (68°F) or less and at a pressure of 101.3 kPa (1 atm) which can be ignited when in a mixture with the air in a proportion of at the most 13% (in volume).

Examples of flammable gases include:

  • Hydrogen gas (H2)
  • Methane (CH4)
  • Ethane (H3CCH3)
  • Ethene (H2CCH2)
  • Butane (C4H10)

Examples of Flammable Solids

Most solid materials naturally release vapors and therefore they have a vapor pressure and a flash point. Additionally, some solids can undergo a transition from solid phase to gas phase (this process is called sublimation).

An example of a flammable solid is camphor (C10H16O) which has a flash point of around 66 ºC (151 ºF). Moth balls which are made of para-dichlorobenzene (Cl2C6H4) are also flammable and have about the sme flash point of camphor.

Flammable Solids That Are Dangerous When Wet

Other examples of flammable solids include certain metallic hydrides such as sodium hydride (NaH), metallic sodium (Naº) and potassium (Kº). 

All these substances are different from the examples mentioned so far in the sense that the reason they catch on fire is that they react violently with water.

When sodium hydride, metallic sodium or potassium are in contact with enough water (humidity from the air may be enough) they quickly undergo a chemical reaction that generates a lot of heat and also hydrogen gas (H2).

Hydrogen gas is a highly flammable gas (in the past some called hydrogen gas inflammable gas).

Chemically, the reason hydrogen gas is so flammable is that when in a certain concentration a ignition source will cause it to react with the oxygen in the air. The product of such a reaction is water which is a very stable substance.

This indicates its formation from unstable substances such as hydrogen and oxygen releases a lot of energy. Energy that was previously in the chemical bonds of hydrogen and oxygen gases, As a side note, flames from burning hydrogen are almost invisible.

Flammable In Languages Other Than English

As a curiosity, in other languages with their roots in Latin such as spanish, french, italian and portuguese the word for flammable has retained the in at the start:

LanguageWord for ‘’flammable’’


In this article the answer to the question: what is the difference between flammable and inflammable was answered.

It is considered that the usage of the word inflammable in the English language should be discouraged given its potential to be confused with meaning the opposite of flammable when in reality the word flammable is derived from the word inflammable.

Additionally, some examples of flammable liquids, gases and solids were presented, as well as a brief discussion regarding the relevant definitions.

Frequently Asked Questions (FAQ): What is The Difference Between Flammable And Inflammable?

What does Unflammable mean?

This word may mean the same as nonflammable or non-flammable. Unflammable is not a word that is used in technical terms.

What gas is nonflammable?

All the gases in the air are nonflammable. The gases that compose the air are nitrogen (N2), oxygen (O2), argon, (Ar), carbon dioxide (CO2), water in the gas phase, neon (Ne), these gases are all nonflammable. There are other gases in the atmosphere in very low proportions, one of these gases is methane, which is flammable when in a proportion range between 5 and 17%. In 2021 the average concentration of methane on the atmosphere was at 0.0000018 % in volume.

What is the meaning of inflammable gas?

The meaning of inflammable gas is the same as flammable gas. The use of the word inflammable is not recommended to avoid confusion. In the past the term “inflammable gas” has been used to refer to the hydrogen gas (hydrogen is a flammable gas).

Is non inflammable a word?

No, the recommended word for something that is not flammable is: nonflammable or non-flamable.

What do you mean by non combustible?

Something that can not undergo a combustion reaction. Examples of materials that are non combustible are: water, helium (He), sand, concrete and oxygen (O2).

What is non corrosive?

Something that is non corrosive is something that does not cause corrosion to any other material.

Is glass flammable?

Common glasses are not flammable, but they can melt and/or break if enough heat is aplied to them.

What is the most flammable gas?

With the significantly high number of gases that are continuously being synthesized in chemistry laboratories worldwide it is pretty much impossible to determine the most flammable gas between all of them. Since, in order to determine that it would be necessary to perform cohesive tests across every single gas that has ever been synthesized. That being said, among the well studied gases, chlorine trifluoride (ClF3) is possibly the one with the highest flammability capacity.


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