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As far as I know, most flammable liquids are volatile. Are there flammable liquids that are non-volatile?

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The element cesium melts at 28.4°C which is slightly above "room temperature" but below human body temperature, so I think we can consider it a liquid in "normal" conditions. It is so flammable it readily self-ignites in the air, but if you put it in inert atmosphere you will see that it isn't particularly volatile.

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Flammability and volatility of a liquid are related.

According to the Globally Harmonized System of Classification and Labelling of Chemicals (GHS), the term “flammable liquid” is defined as follows:

Flammable liquid means a liquid having a flash point of not more than 60 °C.

flame (GHS02)

The European Agreement concerning the International Carriage of Dangerous Goods by Road (ADR) uses a very similar definition.

(…) have a flash-point of not more than 60 °C (…).

Class 3 – Flammable liquids

(Note that the definitions in some older national regulations and standards may refer to different temperatures.)

The flash point is the lowest temperature of the liquid at which application of an ignition source causes the vapour of the substance to ignite. (The flash point is an experimental value and not a constant physical-chemical property of the liquid. The exact definition and the resulting value depend on the used experimental method.) Thus, actually the vapour above the liquid (i.e. the mixture of vapour and air) and not the liquid itself is ignited. Therefore, for the liquid to be considered flammable, there must be a significant concentration of vapour in the air above the liquid at the given temperature.

If the volatility of the liquid is too low, it cannot be a flammable liquid. For example, biodiesel (flash point: 180 °C) and typical vegetable oils are not flammable liquids although these liquids can be burned.

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  • $\begingroup$ This addresses the technical definition of the word flammable but not the question which but its very nature is not using the technical definition. $\endgroup$
    – matt_black
    Commented Mar 21, 2020 at 16:22
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Most flammable liquids are flammable precisely because they are volatile (and combustible at that), so that they easily form vapors which easily catch fire. That being said, various oils are flammable (albeit less so than gasoline) and at the same time not very volatile.

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    $\begingroup$ for example vegetable cooking oil is pretty non-volatile and burns with a flame ok, although it hard to get it to ignite (at least on my gas cooker). $\endgroup$
    – porphyrin
    Commented Apr 22, 2017 at 9:20
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    $\begingroup$ But there are plenty of volatile liquids that are not flammable, for example dichloromethane which is a volatile as diethyl ether but won't burn at all. Combustibility (which is what the question seems to be asking about rather than the the more technical "flammability") has little relationship to volatility. $\endgroup$
    – matt_black
    Commented Mar 21, 2020 at 16:27
  • $\begingroup$ Methylene chloride will burn and explode upper explosive limit23% lower limit 13%. Even trichloroethylene will explode $\endgroup$
    – jimchmst
    Commented Sep 5, 2022 at 2:33
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combustibility and volatility are unrelated

Whether things burn or not (i.e. whether they are flammable) is unrelated to whether they are volatile. Volatility only determines whether things are easy to set alight.

Consider coal, for example. This is a non volatile solid but it is flammable though hard to set on fire. Long chain extracts from crude oil (tars and bitumen) are (technically) liquids but not at all volatile. They burn, though not easily (which is why some motorway accidents involving fires take so much time to repair). A range of other hydrocarbon fractions from crude oil are more liquid but not very volatile as are many vegetable oils (used in cooking because they are not volatile even at 200 °C but clearly flammable as you can see if splashed into a flame).

And there are plenty more examples. The confusion arises because many very volatile liquids are volatile enough that their vapours are flammable at room temperature. There is a good reason why you don't use bunsen burners anywhere near ether (bp ~40 °C): the vapour will ignite and flash back to the vessel even if the flame is far away. But many non-volatile things will also burn.

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    $\begingroup$ This answer is in direct contradiction to Loong's answer. I agree with Loong's definition of flammable as it is used this way in the scientific and industrial communities. What you are talking about is combustible. A substance can be "combustible" without being "flammable." It is unclear whether the OP's understanding of the word "flammable" is closer to yours or Loong's definition. This may explain why you have downvotes (I have abstained from voting either way.) $\endgroup$
    – Level River St
    Commented Apr 22, 2017 at 20:21
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    $\begingroup$ @LevelRiverSt You are right if the definition of flammable requested was the narrow technical one. But, if that is what was wanted, the question is tautological. So, in context, I addressed the informal version which creates a better grasp of the the key concepts. $\endgroup$
    – matt_black
    Commented Apr 22, 2017 at 22:50
  • $\begingroup$ Every answer that equates volatility with flammability is wrong, this one is correct. $\endgroup$
    – ThisGuyCantEven
    Commented Sep 4, 2022 at 16:35
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To tell the truth, "Flammable" means substance with easy ignitable vapors. But topicstater asked about "easy ignitable"- wider set of substances. Among weakly volatile ones I can add: 1)potassium-sodium eutectic alloy,liquid at ambient temperature.

2)white phosphorus - melts at ~40C,selfignites in the air.

3)thermally unstable chemicals like peroxides/nitrocompounds/some metal organic substances. Di-tert butyl peroxide (CH3)3COOC(CH3)3.

tert butyl hydroperoxide (CH3)3COOH ( https://pubchem.ncbi.nlm.nih.gov/compound/tert-butyl_hydroperoxide#section=Computed-Properties )

They easily react with oxygen of air (with or without heating) with subsequent selfheating to ignition. Or violently decompose, selfheat and finally burn.

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Cooking oil is flammable, but doesn't evaporate or evaporates very slowly over months or years. http://www.oliveoilsource.com/asktheexpert/does-cooking-oil-evaporate It's flammable because if you heat it up enough, it will start to burn. Once it starts to burn, the heat will increase causing it to burn faster.

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I am sorry to have entered this discussion so late. Flammable means how easy it is to set on fire. Volatile means how quickly it evaporates. It is easy to think of liquids that are both flammable and volatile: ethyl ether, pentane, gasoline, etc. Some liquids are volatile but NOT flammable. They include tetrachloroethylene, chloroform, hexafluoroisopropanol and water.

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    $\begingroup$ The question was whether there were liquids that are flammable and non-volatile. $\endgroup$
    – jezzo
    Commented Mar 20, 2020 at 23:28

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