Combustible material

Flammable materials are those which ignite more easily than other materials, whereas those which are less easily ignited or which burn less vigorously are combustible.

The degree of flammability or combustibility depends largely upon the chemical composition of the subject material, as well as the ratio of mass versus surface area. As an example, paper is made from wood. A piece of paper catches on fire quite easily, whereas a heavy oak desk is much harder to ignite, although the wood fibre is the same in each substance, be it a piece of paper or a wooden board. Also, Antoine Lavoisier's law of conservation of mass, states that matter can be neither created nor destroyed, only altered. Therefore, the combustion or burning of a substance causes a chemical change, but does not decrease the mass of the original matter. The mass of the remains (ash, water, carbon dioxide, and other gases) is the same as it was prior to the burning of the matter. Whatever is not left behind in ashes and remains, literally went up in smoke, but it all went somewhere and the atoms of which the substance consisted before the fire still exist after the fire, even though they may be present in other phases and molecules.

Historically, flammable, inflammable and combustible meant capable of burning. The word "inflammable" came through French from the Latin inflammāre = "to set fire to," where the Latin preposition "in-" means "in" as in "indoctrinate", rather than "not" as in "invisible" and "ineligible".

The word "inflammable" may be erroneously thought to mean "non-flammable". The erroneous usage of the word "inflammable" is a significant safety hazard. Therefore, since the 1950s, efforts to put forward the use of "flammable" in place of "inflammable" were accepted by linguists, and it is now the accepted standard in American English and British English. Antonyms of "flammable/inflammable" include: non-flammable, non-inflammable, incombustible, non-combustible, ininflammable,not flammable, and fireproof.

Flammable is used for materials which ignite more easily than other materials thus are more dangerous and more highly regulated. Less easily ignited or which burn less vigorously are combustible. For example, in the United States flammable liquids by definition have a flash point below 100 °F (38 °C) where combustible liquids have a flash point above 100 °F (38 °C). "Flammable solids are solids that are readily combustible, or may cause or contribute to fire through friction. Readily combustible solids are powdered, granular, or pasty substances which are dangerous if they can be easily ignited by brief contact with an ignition source, such as a burning match, and if the flame spreads rapidly." The technical definitions vary between countries so the United Nations created the Globally Harmonized System of Classification and Labelling of Chemicals which defines the flash point temperature of flammable liquids to be between 0 and 140 °F (60 °C) and combustible liquids between 140 °F (60 °C) and 200 °F (93 °C).

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